- Email: [email protected]
Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics
Accepted Manuscript
Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics Christopher Riolo DDS MS PhD , Samuel A. Finkleman DDS , Cali Kaltschmidt PII: DOI: Reference:
S1073-8746(18)30050-1 https://doi.org/10.1053/j.sodo.2018.08.001 YSODO 538
To appear in:
Seminars in Orthodontics
Please cite this article as: Christopher Riolo DDS MS PhD , Samuel A. Finkleman DDS , Cali Kaltschmidt , Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics , Seminars in Orthodontics (2018), doi: https://doi.org/10.1053/j.sodo.2018.08.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
CR IP T
Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics
Authors: Christopher Riolo DDS MS PhDab Samuel A. Finkleman DDSa
AN US
Cali Kaltschmidtb
University of Washington, School of Dentistry, Dept. of Orthodontics, Seattle, WA.
b
Private Practice in Seattle WA.
M
a
ED
Corresponding Author:
Christopher Riolo DDS MS PhD
PT
509 Olive Way, Suite 824 Seattle WA. 98101
CE
[email protected]
AC
(206) 467.4441
1
ACCEPTED MANUSCRIPT
Abstract Clear aligners disrupted the orthodontic marketplace almost twenty years ago.1 The result of this disruption has been a significant increase in the demand for adult esthetic orthodontic treatment.2,3 Today, we are in the midst of another disruption in orthodontics; direct to patient orthodontic care. Direct to patient care is a result of the
CR IP T
evolution of digital orthodontics, which has led to the development of custom orthodontic appliances. Besides the disruption of the orthodontic marketplace, custom appliances also offer an opportunity to add value to the care that we offer our patients through the development of appliances systems that are superior in esthetics and in certain
circumstances offer biomechanical advantages4 In this paper, we will present issues
AN US
related successful lingual mechanics, one of the custom appliance opportunities
available to us that add value to the care we offer our patients. We will consider the problem associated with lingual mechanics and the solutions offered by custom lingual appliance systems.
M
Introduction
Lingual orthodontics has traditionally been considered difficult for practitioners and
ED
patients, alike.5-7 This is a result of experience gained using stock lingual systems, without using a treatment setup to accurately “build in” or “customize” the system of brackets and wires. An orthodontist, who bonds stock brackets to the lingual surface of
PT
teeth to conventionally treat a patient, will quickly acquire an appreciation for the issues associated with lingual orthodontics. A “stock” lingual appliance is not practical for the
CE
correction of any, but the most basic orthodontic problems. The key to success with lingual orthodontics is to understand why lingual mechanics are difficult and how these
AC
challenges can be overcome with modern custom appliance systems.8,9 In this paper, we will first present why lingual orthodontics is challenging. Then, we will discuss how modern, custom lingual systems are designed to overcome these difficulties. Modern, lingual appliance systems are an example of how orthodontics is changing today.
Section 1: Why is lingual orthodontics difficult? 2
ACCEPTED MANUSCRIPT
The reasons why lingual orthodontics is difficult can be broadly organized into four categories: 1) Biomechanical issues; 2) Bracket design choices/constraints; 3) Lingual anatomy and 4) Logistical issues. As I mentioned above, the biomechanical difficulties associated with lingual mechanics arise from either anatomical issues or constraints imposed by bracket design choices; all these choices involve tradeoffs. Understanding
CR IP T
these choices and their consequences is the key to understanding the strengths and weaknesses of the various lingual systems you have chosen and, thereby, being on the “road of evidence based clinical experience” to your destination “clinical expertise” with lingual mechanics.
We will categorize the biomechanical issues that are imposed by the lingual anatomy of
AN US
the teeth into five categories: 1st order problems, 2nd order problems, 3rd order
problems, problems involving the point of force application vs. the center of resistance, and problems related to inter-bracket distance. Let us begin with 1st order problems. If you consider the anatomy of the buccal surfaces of the teeth, there are similarities from tooth-to-tooth (see Figure 1); all the teeth have convex surfaces. Thus, if we apply a
M
zero Rx bracket, in a reasonable position, to the buccal surface of teeth and insert a
ED
generic arch formed wire, the teeth will generally align (see figure 2).
This is not the case for the lingual appliances. The lingual surfaces of the teeth are
PT
concave, convex, and frequently both concave and convex. Furthermore, the teeth are highly variable in terms of their buccal lingual dimension. As we are trying to align the
CE
buccal surfaces of these teeth not the lingual surfaces, an “offset” (see figure 1) is needed when working from the lingual. This buccal offset can be place in the bracket,
AC
the wire, or both.
Dr. Fujita published the first description of an attempt to compensate for this 1st order discrepancy using “straight wire mechanics”.13 Small compensations were placed in the base of the bracket with composite, allowing the use of a mushroom-shaped wire on the lingual. This mushroom-shaped arch form is still available today from wire vendors. 3
ACCEPTED MANUSCRIPT
Other systems, such as the “lingual liberty” system, use similar composite bases to achieve a “straight wire” lingual appliance (see figure 3). The required buccal-lingual offsets are affected by the choice of the wire plane. For
CR IP T
example, when the wire plane is placed more cervical, the required “canine offset” can frequently be minimized. The choice of the wire plane is also dictated by the occlusion and the amount of crown available due to crown anatomy, altered passive eruption, and/or hyperplastic gingiva. In general, bracket placement that minimizes buccal-lingual compensations also results in a wire plane in which the amount of occlusal
interferences with the brackets is minimized. When bracket placement choices are
AN US
made, considerations of the trade-offs between 1st order discrepancies, 2nd order discrepancies, and occlusal interferences with brackets must be considered. In addition, robotic wire bending limitations must be considered (see Figure 4).
M
The 2nd and 3rd order lingual problems are related.14 This relationship is due to differences in both the anatomy of the lingual and buccal surfaces of the teeth and the
ED
topology of the lingual surfaces of neighboring teeth (consider the lingual surface topology of the canines relative to that of the first premolars, see figure 1a). Following a
PT
particular wire plane from tooth-to-tooth the lingual surfaces may change from concave to convex (see figure 1). This variation in lingual topology may cause the slot
CE
orientation to be quite different from one tooth to the next. These extreme differences in slot orientation due to individual lingual surface anatomy is complicated further if you allow the wire plane to vary in the inciso-gingival dimension (See figure 5). As
AC
displayed in figure 5, if the wire plane is varied by 1mm with a buccal appliance, you may experience a difference in slot orientation of perhaps 5 degrees. This is well within the amount of slot play normally present when using a 19x25SS and the most precise buccal, fixed appliance.15 In other words, it is extremely rare to notice these differences in slot orientation when working on the buccal surface, even when a 4
ACCEPTED MANUSCRIPT
more incisal oriented wire plane is used versus a more gingivally oriented wire plane. A common illustration of this issue on the buccal involves canine torque; most of us have experienced adverse canine torque due to extreme incisal or gingival bracket placement when using a buccal fixed appliance. This is because of the relatively extreme convexity of the buccal surface of the canine, at least compared to the incisors, and the amount of
CR IP T
slot play that is invariably present in our buccal appliances.15 To understand why adverse anatomical torque is not usually expressed when using a buccal fixed
appliance16, consider the mathematics of the slot-wire interface shown in figure 6 and the resulting values shown in Table 1. This equation is a simplified mathematical
representation of the wire-bracket interface. This simplified equation assumes ideal wire and bracket slot geometry. These assumptions are unrealistic for all bracket
AN US
systems.17-21 In figure 6, θ represents the engagement angle of the wire with the slot of the bracket.
As the size and shape of the wire varies, the engagement angle, θ varies. Cash et al.
M
showed us that bracket geometry varies considerably.17 Only 27% of brackets that they examined had parallel slot walls, thus brackets with parallel slot wall are the exception
ED
not the norm. Brackets slots are invariably oversized by as much as 24%; the best brackets were 5% oversized. If we do the math assuming that 1) our wires have perfect
PT
geometry and our brackets are among the 27% that have decent slot geometry and 2) the wire slots of our brackets are only 5% oversized, the engagement angle or amount
CE
of slot play is, at best, 10 degrees (see table 1). In reality, under the best of circumstances, the engagement angle is, at least, 15 degrees due to wire geometry variation.15 Therefore, a 5 degree change in the orientation of the bracket slot due to
AC
anatomical variation or a change in the incisal-gingival wire plane is rarely expressed with buccal appliances. However, consider a 20-degree change in slot orientation, which is not uncommon when using a stock lingual fixed appliance due to either variation in topology of the lingual surfaces of neighboring teeth or changes in the vertical position of the wire plane (see figure 7). 5
ACCEPTED MANUSCRIPT
The clinical implications of these facts are clear. A standard prescription can work for our patients using stock buccal fixed appliances but trying to use a stock lingual fixed appliance will invariably results in an unmanageable problem involving anatomical torque. Once the first rectangular wire is placed in a stock lingual fixed appliance system, the adverse anatomic torque will begin to express. In addition to the adverse
CR IP T
anatomic torque, other complicating factors, such as decreased interbracket distance, further increases the difficulty of using stock lingual brackets, bending the wires by hand, and engaging said wire!
So far, we have considered what I refer to as “anatomical torque”, but there is another type of torque problem that needs to be managed when treating patients with a lingual
AN US
appliance system. I will refer to this as the “bio-mechanical torque” problem (See Figure 8). Unfortunately, with a stock lingual system these two types of torque problems can only be addressed by mutually exclusive solutions.
With a stock system, the more you “fill” the bracket slot (minimize the engagement angle), the more problems you will have with anatomical torque and the more
M
complicated the wire bending requirements become. At the same time, due to the decreased interbracket distance, it is very difficult to engage these full size rectangular
ED
wires with numerous 1st, 2nd and 3rd order bends. One may be tempted to think that smaller, less slot filling wires will make a stock lingual system more manageable from a
PT
wire bending and engaging perspective. This is true and is exactly why, when a stock lingual system is used for limited treatment (say alignment relapsed lower anterior
CE
teeth), it is best to stay in round wire. The use of round wire will facilitate alignment of relapsed lower anterior teeth, the wires are simple to bend and engage, and there is no chance of expressing adverse anatomical torque. The problem with this solution, in
AC
general, is there is no torque control. As we are about to see, excellent torque control is especially important in lingual mechanics. The “biomechanical torque problem” is related to the point of force application in lingual mechanic compared to the center of resistance of the teeth (see figure 8). This relationship results in an increased tendency for extrusion and lingual “dumping” when either retracting anterior teeth in extraction treatments or using heavy Cl II mechanics 6
ACCEPTED MANUSCRIPT
with a lingual fixed appliances system. This biomechanical issue is well documented in the literature; these papers can be categorized into two types; Mathematical modeling papers22 and finite element analysis (computer modeling) papers23,24. The literature is replete with papers examining the difference in biomechanics between lingual and buccal appliance systems and there is no disagreement on this issue; when using a
CR IP T
lingual fixed appliance system, there is a significantly increased tendency for both extrusion of the anterior teeth and torque loss during space closure and during the use of Cl II mechanics.
This means that we must pay special attention to the expression of torque in these
AN US
types of treatments. The most obvious means to maintain excellent torque control is the use of full-sized wires that fill the brackets slots, but as we have seen this will aggravate the anatomical torque problem! So here we are with two types of torque issues, one that ideally requires slot filling wires and one that certainly does not! Early lingual practitioners dealt with this contradiction when using stock systems, which is exactly
M
why lingual orthodontics has a reputation for being difficult. The solution to reconcile these two torque issues is customization of the lingual appliance to each individual
ED
patient, thereby eliminating the anatomical torque problem (not to mention, at the same time, deal with the first order issue presented earlier) and allowing the orthodontist to
PT
use a slot filling wire for biomechanical torque control. Decreased interbracket distance is a major issue when working from the lingual
CE
surfaces of the teeth. The difference between buccal and lingual interbracket distance was outlined by Moran, in 1987.25 Moran measured the lingual interbracket distance to
AC
be 35.4% less than the buccal interbracket distance in the maxilla and 27.7% less in the mandible. This decreased interbracket distance significantly effects how the wires behave. Specifically, the decreased interbracket distance results in a 3-fold increase in the stiffness of the wire for 1st and 2nd order displacements and a 40% increase in the stiffness of the wire for 3rd order displacements. The biomechanical difficulties of lingual mechanics in five categories: 1st order problems, 2nd order problems, 3rd order problems, problems involving the point of force 7
ACCEPTED MANUSCRIPT
application vs. the center of resistance, and problems related to inter-bracket distance. Let us begin with 1st order problems. The first three categories of problems result in the need for additional 1st, 2nd, and 3rd order bends to compensate for the anatomical issues outlined above. At the same time, extra torque is required to compensate for the increased tendency for lingual crown tipping due to the point of force application vs.
CR IP T
center of resistance issue. On top of these difficulties, the wires that behave as if they are extra stiff because of the reduce interbracket distance. All these factors combined make it almost impossible to use stock brackets bonded directly to the lingual surfaces of the teeth and hand bend wires to treat patients. The solution is to customize the appliance by building as much correction into the brackets and wires as possible. This is
AN US
exactly what modern lingual appliance systems do so well. These systems employ custom brackets, custom composite bases for the stock brackets, and/or custom
robotically bend wires.9 Each system has its own strengths and weaknesses, which we must understand.
I will briefly outline some of the logistical issues but will not consider them in depth in
M
this paper. Logistical issues include but are not limited to: training both staff and orthodontist, scheduling difficulties, cost issues, and patient management issues. The
ED
learning curve for lingual orthodontics can be steep for both orthodontists and staff. Staff training is critical because for most busy orthodontic practices the orthodontist
PT
cannot afford to be randomly tied up for 30 to 40 minutes to deal with a lingual appliance emergency. It is critical that there is staff trained to implement solutions with
CE
indirect supervision by the orthodontist. Training in lingual mechanic for the orthodontist is a problem. Most residencies do not have either the resources or the time to comprehensively prepare residents in lingual
AC
mechanics. There are four university based post-doctoral lingual orthodontic programs in Europe and one in North America. All of the European programs admit qualified orthodontists for training using with lingual appliances.10 The European programs are the master’s degree program (MAS) in lingual orthodontics at the University of Basel, Switzerland, the program offered by Hanover Medical School, Lingual Post-Graduate Course, Paris V. University, Paris, and the Master of Lingual Orthodontics post doc 8
ACCEPTED MANUSCRIPT
program at the Universitat de València, Spain. In North America, the University of Texas at San Antonio, School of Dentistry offers an 18-month post doc fellowship in lingual orthodontics. Each year, there are several international meetings each year dedicated to lingual orthodontics.11,12 The European Society of Lingual Orthodontics (ESLO) and the World
CR IP T
Society of Lingual Orthodontics (WSLO) hold their biennial meetings. In North America, lingual meetings tend to be corporate sponsored (for example, annual Incognito users meetings and SureSmile user meetings). These meetings frequently offer hands on sessions for orthodontists and staff, covering common techniques employed for the specific lingual system involved.10
AN US
Scheduling can also be difficult for established practices. Lingual procedures tend to run longer than buccal those involving traditional, buccal fixed appliance procedures and broken lingual appliances most often result in an emergency appointment due to tissue irritation. Of course, if you choose to only train your most talented assistants in lingual orthodontics, then your emergency lingual appointments will tie up either you or
M
your most talented assistants. The solution… is to train all your assistants to be at least minimally competent with your lingual appliance of choice. That means, all your
ED
assistants in your office should be able to do a basic lingual retie and deal with basic lingual emergencies to get the patient comfortable. Most of the lingual orthodontic
PT
practices, with which I am familiar, train all their staff in lingual orthodontic procedures just like any other common procedure employed in their office. As in with all change,
CE
this training will take some effort, but it will pay off in the long run allowing your practice to thrive.
AC
The cost of providing orthodontic treatment with a custom, lingual orthodontic system is significantly higher than a buccal stock system. The lab cost of the custom appliance is just the beginning; Unlike a stock buccal fixed appliance system, there is a significant amount of work involved in the setup and planning of treatment with a custom lingual appliance. Lingual orthodontic appointments tend to be longer than buccal appointment, depending on the lingual system. Furthermore, you and your team should be compensated for the skills that you so diligently worked to obtain with lingual 9
ACCEPTED MANUSCRIPT
systems. Do not hesitate to charge a premium for your services using lingual fixed appliances. Not only do these patients expect to pay, but they also will often demand the highest level of customer service and they can be difficult patients to manage. For example, we rarely extract first premolars in the maxillary arch without a plan to deliver provisional pontics that will be reduced as the space is closed; lingual patients will
CR IP T
demand that these spaces be managed with pontics. Patients choose a lingual appliance because of their esthetic concerns and they will demand the highest level of esthetic treatment. Patients that demand the highest level of esthetic orthodontic
treatment will consume a disproportionate percentage of your time and the time of your staff. Do not resent this! On the contrary, enjoy providing the best possible clinical care
AN US
and highest level of service using the most esthetically appliances available. Providing esthetic orthodontic treatment is one aspect of functioning at the highest level of our profession.
M
Section 2: Implicit and explicit design choices in lingual orthodontic appliance systems.
ED
Custom orthodontics is changing the way orthodontists provide and think about treatment.4 The resurgence of lingual orthodontics using custom lingual appliances is
PT
an example of how custom appliances are changing the profession.8 The most common custom appliances in orthodontics are clear aligners. However, clear aligners such as Invisalign and their storefronts, Smile Direct Club and Candid Co, are disrupting
CE
the orthodontic profession. It is “digital orthodontics” that has made possible mass production of custom orthodontic appliances. I am going to define Digital Orthodontics
AC
as “the planning and execution of orthodontic treatment using digital orthodontic records”. Digital orthodontics only requires that we are using digital radiography, photography and intraoral scanning when collecting records on our patients. It is only a matter of time before 100% of orthodontists are completely “digital”. Although digital orthodontics can be as simple as taking digital records, it can be as involved as using these records to digitally “setup” a patient’s treatment, manufacturing a custom appliance, and 3D printing the final intraoral scans to fabricate Essix type retainers. I 10
ACCEPTED MANUSCRIPT
have referenced “custom appliances” throughout this paper; what are custom appliances and what is custom orthodontics? I am going to define Custom Orthodontics as “the use of a pre-programmed, orthodontic appliance to treat a patient to a precisely predetermined occlusal outcome”. The preprogrammed orthodontic appliance referred to in the previous definition is a “Custom Appliance System”.
CR IP T
All custom appliances are fabricated using a treatment setup. This is true of clear
aligner systems such as Invisalign and Clear Correct, buccal systems like SureSmile and Insignia, and lingual systems like Incognito and Lingual Liberty. The treatment setup is used to fabricate the custom appliance, incorporating individualized correction either in the brackets, wires, or both. In lingual orthodontic system this customization is
AN US
used to compensate for issues such as the “anatomical torque” problem. Using a
treatment setup has other benefits for the patient and the practitioner. The treatment objectives are implicitly described by the setup itself. The treatment setup also serves to describe essential detail of the planned treatment, such as IPR (amount and surfaces), expansion, tooth inclinations, torque requirements, space appropriation
M
issues, and anchorage requirements. In many instances, the process of developing the treatment setup allows the orthodontist to consider the plausibility of the proposed
ED
correction as well as examine treatment alternatives. With interdisciplinary treatment, a treatment setup is an essential tool to effectively collaborate with the other providers
PT
and communicate with patients.26 Digital orthodontics has made custom orthodontics possible and custom orthodontics is driving the paradigm shift from “Reactive Treatment Planning” to “Proactive Treatment Planning”. Proactive treatment
Implicitly codifying the treatment objectives
AC
CE
planning involves a treatment setup. This treatment setup has many benefits, including:
Communication with patients
Communication with other care providers/ Interdisciplinary treatment
Facilitating an understanding of the mechanics/ anchorage requirements of the proposed treatment
11
ACCEPTED MANUSCRIPT
Reactive treatment planning does not involve a “treatment setup”. It involves a general treatment plan, perhaps specifying extraction vs. non-extraction, IPR, and Cl II or Cl III mechanics. Decisions are made step by step throughout treatment; each decision tends to reduce the degrees of freedom that the orthodontist has with respect to the remaining treatment. For example, if lower incisor proclination occurs as a result of Cl II
CR IP T
mechanics during treatment, the orthodontist may decide to compromise the overjet or perform additional IPR. These types of decisions are made at each appointment,
usually with minimum of consideration. Reactive treatment planning is employed by default and, in general, it works well when treating children and adolescents. However, reactive treatment planning does not tend to produce optimal results when treating
AN US
patients with debilitated, severely worn or highly restored dentitions or the instance of complex orthodontic treatment, such as interdisciplinary treatment. Digital orthodontics has allowed the development of custom orthodontics and it is custom orthodontics that has made lingual orthodontics possible for the average orthodontist. Digital orthodontics has driven the resurgence of lingual orthodontics as
M
well as custom, clear aligner systems.1 It was Invisalign that first disrupted the orthodontic profession in the early 2000’s by marketing of their clear aligner system to
ED
patients and general dentist. At that time, orthodontists did not realize that Invisalign was creating the esthetic, adult orthodontic market. Through its national and
PT
international marketing efforts, Invisalign has been driving the demand for esthetic, adult orthodontic treatment options. These efforts raise awareness of esthetic orthodontic treatment options and drive patients desiring these types of treatments into our
CE
orthodontic practices.3 One of the obvious treatment options for a patient who desires an esthetic appliance, but is not a candidate for clear aligner therapy, is treatment with a
AC
lingual appliance system. It is useful to discuss the various custom lingual systems in context of the choices that are universal with the systems. These choices remain as appliances system change; there is no perfect appliance system for all patients and there never will be. However, these systems will continue to improve, and the day is coming in which the treatment setup will be used to design custom treatment for every patient. Orthodontists that 12
ACCEPTED MANUSCRIPT
ignore lingual orthodontics will be giving up a powerful tool that differentiates us from the generalist by adding value to what we offer patients. In the previous section, we reviewed why lingual orthodontics is difficult. Modern lingual systems have evolved to deal with these challenges through “customization”. The reasons why lingual orthodontics therapy is difficult to accomplish with stock appliances
CR IP T
are invariant, whereas these custom appliance systems are not. In the future, lingual systems will change. They will improve both with respect to the physical technology, such as the brackets and the wires, but also with respect to the software that is used to design these appliances. In the last section of this paper, we will review the choices that are made when selecting and designing a custom lingual appliances system. We will
AN US
discuss the implication of using a treatment setup to design these appliances and
discuss the how these setup force us to start planning proactively, rather than reactively when implementing orthodontic treatment.
In the literature, people have tried to present indications and contraindications for the use of lingual orthodontics.27,28 Virtually all patients can be treated with a custom lingual
M
appliance system. The limiting factor is the knowledge of the practitioner regarding the strengths and weaknesses of the particular system employed, not the system itself. In
ED
other words, excellent clinical results29 can be obtained with all the modern custom systems. There are numerus systems that have been developed around the world.
PT
Some systems are more popular in Europe and Asia, such as Win, Alias, eBraces and the Lingual Liberty systems. We compare two of the more popular systems in North
CE
America, SureSmile by Orametrix and Incognito (3M Unitek) in table 2. Each system has its advantages and disadvantages (see table 2); when selecting a lingual system, both implicit and explicit design choices will be made. For example, with Incognito, you
AC
are implicitly choosing to use a ribbon arch wire and vertical slots in the anterior, rather than the traditional edgewise wire/slot interface seen most commonly in lingual brackets. There are implications to this choice; for example, it may be easier to engage a full-sized wire for biomechanical torque control in a system with anterior vertical slots. However, it is more difficult to control angulation and place bends by hand in ribbon arch wires with vertically oriented slots. There are also explicit choices that must be made 13
ACCEPTED MANUSCRIPT
when using these lingual systems. For example, with Incognito, do you want a hook or no hook on a particular first or second molar? Do you want a tube or a bracket on a particular tooth? Do you want to cover the lingual surface of the tooth with the custom base or do you want half occlusal, or even full occlusal, coverage of the tooth by the custom base? With the SureSmile system, you will need to choose a stock bracket
CR IP T
system; this bracket system may be self-ligating or not. You can choose combinations of stock systems on a single case. You may decide to use a self-ligating bicuspid
bracket on the second molar due to the lingual anatomy of a particular tooth. Again, there are consequences to these explicit choices. A self-ligation bracket may have a larger mesio-distal dimension and, thereby, reduce the interbracket distance. While the
AN US
non-self ligating bracket may be problematic for an office where the staff has limited experience with lingual ligation techniques.
All major, fixed lingual systems have custom features in one or more of three essential components of the system: 1) Brackets, 2) Wires and 3) Software. This variation makes each system unique with respected to one another. In Table 1, we compare two popular
M
North American systems with respect to brackets, wire, and software.
ED
Brackets: There are significant differences between the brackets used by SureSmile and Incognito. SureSmile employs stock brackets. There are a myriad of stock lingual
PT
brackets in their library from which to choose, including multiple examples of both selfligating and conventional ligating brackets. If, by chance, your brackets or prescription
CE
is not currently available in their library, it can be added. Almost any stock lingual bracket that you choose to employ with SureSmile will be manufactured using metal
AC
injection molding (MIM). SureSmile has concentrated its innovation into their wires and software; currently, their technology in these areas is unsurpassed. SureSmile puts 100% of the customization into the wires. Therefore, each bracket will have a small compensating bend to the mesial and distal of the bracket. While custom brackets allow the use of straight wire mechanics; they rarely result in treatment that does not require some compensations in the wire. This is especially true in the correction of gingival balance issue (see figure 9a). 14
ACCEPTED MANUSCRIPT
A unique strength of the SureSmile system is the fact that 1st, 2nd, and 3rd order bends can be placed in NiTi wires, in addition to stainless steel, TMA, and elgaloy. The software allows the orthodontist to easily make changes to the wires and the overall plan. This may be the ideal system when finishing details cannot easily be estimated
CR IP T
before treatment is initiated. One of the disadvantages of the SureSmile system is the fact that you are forced to employ stock brackets. It can be difficult or impossible to bond to non-enamel surfaces with stock orthodontic brackets. Therefore, a patient with a heavily restored or debilitated dentition may not be an ideal candidate for this system. Alternatively, the Incognito system employs custom brackets with custom bracket bases.
AN US
This allows bonding to virtually any surface including gold, amalgam, non-precious
metal, composite, ceramic, as well as a combination of materials. Properly designed brackets minimize the frequency of debonded brackets on even the most difficult surfaces. The custom bases can be extended to maximize surface area on the lingual and occlusal surfaces. The bases can even extend to the buccal surfaces of the
M
posterior teeth. While all lingual appliance systems employ a 018 slot size, the brackets of the Incognito system are different than most lingual systems with respect the their
ED
slot orientation. Incognito uses a ribbon arch wire and vertically oriented slots in the anterior and horizontal slots in the posterior. There are similar systems to Incognito,
PT
such as eBrace and Winn, that employ an anterior vertical slot. The lower anterior Incognito brackets do have a quasi-self-ligating feature that allows 012NiTi and 014NiTi
CE
wires to be inserted behind the bracket wings of the six lower anterior teeth. Selfligating brackets are a huge advantage for busy practices without staff trained in the various ligation techniques employed with horizontal and vertical slot lingual bracket
AC
systems.30 Most self ligating lingual brackets are made using Metal Injection Molding, MIM and we have discussed the limitation of these brackets with respect to the accuracy of the slot and its effect on the engagement angle of the wire.17,19,21 Therefore, if extra biomechanical torque is required, it must be added by hand. The Incognito brackets are not MIM’ed. Instead, Incognito 3D prints the patterns, casts the brackets using a lost material technique, then finishes the slot of the anterior brackets using an 15
ACCEPTED MANUSCRIPT
Electronic Discharge Machining (EDM). These anterior brackets tend to have tight tolerances (low engagement angles) at the bracket/wire interface. In theory, this should translate into more predictable torque expression15 and, in turn, less need to place post hoc torque into the maxillary stainless steel wires during space closure and when using heavy Cl II mechanics.
CR IP T
Wires: The SureSmile system does 100% of the custom compensations in the wires, using stock lingual brackets. Currently, there is only company that has the ability to place 1st, 2nd and 3rd order bends in NiTi wires. The ability to place 3rd order bends in NiTi wire allows SureSmile to compensate for the anatomical torque problem, facilitating the transition from round to rectangular NiTi wires using stock lingual brackets. The
AN US
SureSmile wire robots can also place all three orders of bends in stainless steel, TMA, and elgaloy wires. Alternatively, Incognito compensates for anatomical torque discrepancies using their custom brackets. Other approaches are employed by other systems. With Lingual Liberty, the anatomical torque (see figure 6) issue is addressed through a custom composite “pad” between a stock lingual bracket and the tooth
M
surface. In fact, Lingual Liberty also uses this custom composite pad to make first order compensations, which allows the use of a “universal” arch wire. This “straight wire”
ED
technique allows the orthodontist to operate in a familiar way in unfamiliar territory, the lingual surfaces of the teeth. On the other hand, Incognito employs a ribbon arch wire. It
PT
can be very difficult to place post hoc torque in the 16x24SS ribbon arch wire due to existing robotically bend compensations in the wires in addition to the tight fit between the anterior custom bracket slots and the full size ribbon arch wires. Due to these
CE
difficulties, when using a 16x24SS ribbon arch wire to retract anterior teeth, it is recommended to request that extra torque is placed robotically. Incognito wires are
AC
charged ala cart and not all wires have the same bends. The initial round and rectangular NiTi wire will have 1st order bends, while 2nd and 3rd order bends are not placed until stainless steel and TMA wires. The choice of a particular lingual system for a patient should also depend on the treatment objective and the required tooth movements. For example, if a treatment objective is to correct a ≥4mm midline discrepancy in the upper arch, a system that employs a horizontal slot rather than a vertical slot in the anterior may be advantageous. Let’s again consider the smile in 16
ACCEPTED MANUSCRIPT
figure 9a, we have a significant disturbance in the gingival balance due to extrusion of the upper anterior teeth and probably also altered passive eruption. It is not possible to know exactly how much intrusion will be required, until after crown lengthening. Additionally, the apical migration of the gingiva is not 1:1 with intrusion of the crown; intrusion of 1mm may result in .8mm of gingival migration. Therefore, it is not possible
CR IP T
to fabricate a custom appliance system that will achieve an optimal treatment result without modification of the original treatment setup. In situations like this, a lingual appliance system that allows flexibility should be selected to be able to make the
required modifications easily and inexpensively. For a treatment involving correction of gingival imbalance, a system with a horizontal slot, the ability to modify wires either
AN US
digitally or by hand, and excellent software to interface between the setup and the lab is desired.
Software: The third component of a custom lingual appliance system is the software. At first, the importance of the software associated with a custom appliance system is easy to overlook. However, the software is as important as any of the other components of
M
the system. As the sophistication of these programs improve, we will be able to integrate buccal fixed appliances and clear aligners with lingual fixed appliance into a
ED
custom system to optimize orthodontic treatment for our patients. Elemetrix, the software system employed by SureSmile, can be used to integrate these three
PT
treatment modalities, today. 3M claims that their Clarity Aligners will be integrated with their fixed lingual system, Incognito, very soon. Software is used to communicate with the lab to produce the treatment setup, which, in turn, is used to fabricate the custom
CE
appliance system. The communication with the lab is critical. It is not possible to create a custom appliance without excellent communication and control over the treatment
AC
setup. The treatment setup can also be used as a platform to communicate with other dental professional for interdisciplinary case. Finally, the treatment setup can be used to communicate with patient regarding the treatment objectives. The quality of the software experience varies tremendously from one appliance system to another. The treatment setup can also be used to simulate various treatment options. For example, various extraction patterns can be explored, as opposed to interproximal 17
ACCEPTED MANUSCRIPT
reduction (IPR), or in conjunction with IPR. When treating adult patients with varying degrees of tooth attrition and complex restorative histories, determining the best occlusal outcome without a treatment setup is, at best, a guess. Interdisciplinary treatment requires collaboration between two or more dental professionals and a treatment setup is a necessary component of interdisciplinary treatment planning. 26
CR IP T
These treatment setups not only serve to clarify the details of the orthodontic treatment, but are also used to plan the restorative phase of treatment. In this case, the software performs a crucial function in communication with both other dental professionals as well as the patient. Each of the lingual appliance systems employs software to develop and present the treatment setup. SureSmile uses Elementrix, whereas Incognito uses
AN US
TMP. Conclusions:
While all lingual systems have strengths and weaknesses, the choice of a particular system is secondary to having a proper understanding of the system used; as well as, the proper armentarium and clinical experience to implement the treatment plan. In this
M
paper, we have outlined the basic knowledge required to evaluate and select a lingual system that best fits the patient, orthodontist and his or her team. With the current
ED
disruption in the orthodontic marketplace it is important that orthodontic specialists employ the benefits that digital orthodontics and custom orthodontic appliance system
PT
offer in order provide the best possible care in the competitive environment in which most of us practice today. Lingual mechanics provides added value for our patients that
CE
truly differentiates the orthodontic specialist from the generalist as well as direct to
AC
patient modalities.
1.
Kuo E, Miller RJ. Automated custom-manufacturing technology in orthodontics. Am J Orthod Dentofacial Orthop. 2003;123(5):578-581. 18
ACCEPTED MANUSCRIPT
9.
10. 11. 12. 13. 14. 15. 16. 17. 18.
AC
19.
CR IP T
8.
AN US
7.
M
6.
ED
5.
PT
3. 4.
Rosvall MD, Fields HW, Ziuchkovski J, Rosenstiel SF, Johnston WM. Attractiveness, acceptability, and value of orthodontic appliances. Am J Orthod Dentofacial Orthop. 2009;135(3):276.e271212; discussion 276-277. McCrostie HS. Lingual Orthodontics: The Future. Seminars in Orthodontics. 2006;12(3):211-214. Jheon AH, Oberoi S, Solem RC, Kapila S. Moving towards precision orthodontics: An evolving paradigm shift in the planning and delivery of customized orthodontic therapy. Orthod Craniofac Res. 2017;20 Suppl 1:106-113. Ling PH. Lingual orthodontics: history, misconceptions and clarification. J Can Dent Assoc. 2005;71(2):99-102. Ata-Ali F, Ata-Ali J, Ferrer-Molina M, Cobo T, De Carlos F, Cobo J. Adverse effects of lingual and buccal orthodontic techniques: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop. 2016;149(6):820-829. Wu A, McGrath C, Wong RW, Wiechmann D, Rabie AB. Comparison of oral impacts experienced by patients treated with labial or customized lingual fixed orthodontic appliances. Am J Orthod Dentofacial Orthop. 2011;139(6):784-790. George RD, Hirani S. Fully-customized lingual appliances: how lingual orthodontics became a viable treatment option. J Orthod. 2013;40 Suppl 1:S8-13. Wiechmann D, Rummel V, Thalheim A, Simon JS, Wiechmann L. Customized brackets and archwires for lingual orthodontic treatment. Am J Orthod Dentofacial Orthop. 2003;124(5):593599. Das S, Labh S, Barik A. Lingual orthodontic education: An insight. APOS Trends in Orthodontics. 2016;6(4):185-190. Chatoo A. A view from behind: a history of lingual orthodontics. J Orthod. 2013;40 Suppl 1:S2-7. Echarri P. Revisiting the History of Lingual Orthodontics: A Basis for the Future. Seminars in Orthodontics. 2006;12(3):153-159. Fujita K. New orthodontic treatment with lingual bracket mushroom arch wire appliance. Am J Orthod. 1979;76(6):657-675. Stamm T, Wiechmann D, Heinecken A, Ehmer U. Relation between second and third order problems in lingual orthodontic treatment. Vol 32000. Archambault A, Lacoursiere R, Badawi H, Major PW, Carey J, Flores-Mir C. Torque expression in stainless steel orthodontic brackets. A systematic review. Angle Orthod. 2010;80(1):201-210. Sifakakis I, Pandis N, Makou M, Eliades T, Katsaros C, Bourauel C. A comparative assessment of torque generated by lingual and conventional brackets. Eur J Orthod. 2013;35(3):375-380. Cash AC, Good SA, Curtis RV, McDonald F. An evaluation of slot size in orthodontic brackets--are standards as expected? Angle Orthod. 2004;74(4):450-453. Sebanc J, Brantley WA, Pincsak JJ, Conover JP. Variability of effective root torque as a function of edge bevel on orthodontic arch wires. Am J Orthod. 1984;86(1):43-51. Gioka C, Eliades T. Materials-induced variation in the torque expression of preadjusted appliances. Am J Orthod Dentofacial Orthop. 2004;125(3):323-328. Meling TR, Odegaard J. The effect of cross-sectional dimensional variations of square and rectangular chrome-cobalt archwires on torsion. Angle Orthod. 1998;68(3):239-248. Siatkowski RE. Loss of anterior torque control due to variations in bracket slot and archwire dimensions. J Clin Orthod. 1999;33(9):508-510. Geron S, Romano R, Brosh T. Vertical forces in labial and lingual orthodontics applied on maxillary incisors--a theoretical approach. Angle Orthod. 2004;74(2):195-201. Liang W, Rong Q, Lin J, Xu B. Torque control of the maxillary incisors in lingual and labial orthodontics: a 3-dimensional finite element analysis. Am J Orthod Dentofacial Orthop. 2009;135(3):316-322.
CE
2.
20. 21. 22. 23.
19
ACCEPTED MANUSCRIPT
25. 26. 27. 28. 29.
AC
CE
PT
ED
M
AN US
30.
Lombardo L, Scuzzo G, Arreghini A, Gorgun O, Ortan YO, Siciliani G. 3D FEM comparison of lingual and labial orthodontics in en masse retraction. Prog Orthod. 2014;15(1):38. Moran KI. Relative wire stiffness due to lingual versus labial interbracket distance. Am J Orthod Dentofacial Orthop. 1987;92(1):24-32. Kokich VG, Spear FM. Guidelines for managing the orthodontic-restorative patient. Semin Orthod. 1997;3(1):3-20. Echarri P. Lingual Orthodontics: Patient Selection and Diagnostic Considerations. Seminars in Orthodontics. 2006;12(3):160-166. Romano R. Concepts on Control of the Anterior Teeth Using the Lingual Appliance. Seminars in Orthodontics. 2006;12(3):178-185. Grauer D, Proffit WR. Accuracy in tooth positioning with a fully customized lingual orthodontic appliance. Am J Orthod Dentofacial Orthop. 2011;140(3):433-443. Dalessandri D, Lazzaroni E, Migliorati M, Piancino MG, Tonni I, Bonetti S. Self-ligating fully customized lingual appliance and chair-time reduction: a typodont study followed by a randomized clinical trial. Eur J Orthod. 2013;35(6):758-765.
CR IP T
24.
20
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
M
AN US
CR IP T
Manuscript Legends
Figure 1 Illustrates the similarity of the buccal anatomy of teeth. The differences in the buccallingual dimension of teeth requires a buccal lingual “offset” to align the buccal surfaces of the teeth. 21
CR IP T
ACCEPTED MANUSCRIPT
PT
ED
M
AN US
Figure 2 demonstrates the alignment of the dental arches possible by using stock brackets on the buccal surface of the teeth with a natural arch formed stock wire. This is not possible using stock bracket on the lingual surface of the teeth without a buccal-lingual “offset” to align the buccal surfaces of the teeth.
AC
CE
Figure 3 shows the three common lingual arch wire configurations: Completely customized with a unique bend between each tooth, the Fujita “mushroom archform, and a straight wire. Each of these arch wire configurations has biomechanical implications.
22
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
Figure 4 shows a completely customized wire; the heighted areas indicate portions of the wire that are “Unbendable” by the wire bending robots. These wires bending limitations effect bracket placement, frequently bracket position choices must be considered in the context of wire bending limitations when using a lingual system with completely customized wires.
23
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
M
Figure 5 shows the difference in bracket slot orientation (torque expression) with a small change position in an inciso-gingival direction. On the buccal surface a small change in position may result in up to a 5 degree change the orientation of the bracket slot while on the lingual this same change in position can result is a slot orientation change of 20 degrees.
24
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
Figure 6 illustrates the geometry associated “slot play”. The equation shown here describes the relation ship between the engagement angle, θ and wire size ( a and b) for a given slot size, c.
25
ACCEPTED MANUSCRIPT
ED
M
AN US
CR IP T
Figure 7 illustrate the “anatomical torque” problem. Along a fixed wire plane on the lingual, difference in the lingual surface anatomy from tooth to neighboring tooth result in large differences in slot orientation and therefore torque expression when using a stock lingual brackets.
AC
CE
PT
Figure 8 shows the different force vectors associated with incisor intrusion and retraction using lingual and buccal mechanics. There is a well-documented22,33,24 increased tendency for “torque loss” through lingual tipping and extrusion when implementing lingual mechanics versus conventional mechanics.
26
PT
ED
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
Figure 9a shows an altered gingival balance due to extrusion of the maxillary anterior teeth. Figure 9b is a image of a corrected gingival balance.
Table 1
Best Case Theoretical Engagement Angle With 5% and 15% Oversized Slots (Assuming Ideal Geometry) WIRE SLOT SIZE 5% 10% 27
ACCEPTED MANUSCRIPT
.018 .018 .022
8° 4° 10°
Table 2
Brackets
Wires
Stock brackets used. Stock bracket choices unlimited. Any bracket can be used on any tooth. All customization is placed in the wires.
Unlimited included with case 1st, 2nd,3rd order bends in Niti, TMA and elgiloy Each wire can be completely customized
Software
Charged per wire 1st order bends in Niti 1st, 2nd and 3rd order bends in TMA and SS Wires can vary in terms of customizing the wire bends
AC
CE
PT
ED
Custom cast base, SL on in lower anterior for 012N and 014N Vertical slot in anterior, Horizontal slot in Posterior, 25x18
M
Incognito
Digital indirect bracket placement, Indirect transfer tray printing Overlay and sophisticated metric and analysis available Control over individual tooth movement Export STL files, No specialized communication features Integration of roots and Alveolar bone from CBCT data in treatment setups Coordinate Buccal, Lingual and Clear Aligners TMP Software for digital case submission/ ordering Basic overlay and 3D model manipulation Dental metrics available with analysis Some communication features/ export STL files Only setup lingual fixed appliances at this time, no ability to integrate Clear Aligners or Buccal fixed appliances
AN US
SureSmile
13° 9° 16°
CR IP T
16x22 17x25 19x25
28
Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics Christopher Riolo DDS MS PhD , Samuel A. Finkleman DDS , Cali Kaltschmidt PII: DOI: Reference:
S1073-8746(18)30050-1 https://doi.org/10.1053/j.sodo.2018.08.001 YSODO 538
To appear in:
Seminars in Orthodontics
Please cite this article as: Christopher Riolo DDS MS PhD , Samuel A. Finkleman DDS , Cali Kaltschmidt , Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics , Seminars in Orthodontics (2018), doi: https://doi.org/10.1053/j.sodo.2018.08.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
CR IP T
Lingual orthodontics: Understanding the issues is the key to success with lingual mechanics
Authors: Christopher Riolo DDS MS PhDab Samuel A. Finkleman DDSa
AN US
Cali Kaltschmidtb
University of Washington, School of Dentistry, Dept. of Orthodontics, Seattle, WA.
b
Private Practice in Seattle WA.
M
a
ED
Corresponding Author:
Christopher Riolo DDS MS PhD
PT
509 Olive Way, Suite 824 Seattle WA. 98101
CE
[email protected]
AC
(206) 467.4441
1
ACCEPTED MANUSCRIPT
Abstract Clear aligners disrupted the orthodontic marketplace almost twenty years ago.1 The result of this disruption has been a significant increase in the demand for adult esthetic orthodontic treatment.2,3 Today, we are in the midst of another disruption in orthodontics; direct to patient orthodontic care. Direct to patient care is a result of the
CR IP T
evolution of digital orthodontics, which has led to the development of custom orthodontic appliances. Besides the disruption of the orthodontic marketplace, custom appliances also offer an opportunity to add value to the care that we offer our patients through the development of appliances systems that are superior in esthetics and in certain
circumstances offer biomechanical advantages4 In this paper, we will present issues
AN US
related successful lingual mechanics, one of the custom appliance opportunities
available to us that add value to the care we offer our patients. We will consider the problem associated with lingual mechanics and the solutions offered by custom lingual appliance systems.
M
Introduction
Lingual orthodontics has traditionally been considered difficult for practitioners and
ED
patients, alike.5-7 This is a result of experience gained using stock lingual systems, without using a treatment setup to accurately “build in” or “customize” the system of brackets and wires. An orthodontist, who bonds stock brackets to the lingual surface of
PT
teeth to conventionally treat a patient, will quickly acquire an appreciation for the issues associated with lingual orthodontics. A “stock” lingual appliance is not practical for the
CE
correction of any, but the most basic orthodontic problems. The key to success with lingual orthodontics is to understand why lingual mechanics are difficult and how these
AC
challenges can be overcome with modern custom appliance systems.8,9 In this paper, we will first present why lingual orthodontics is challenging. Then, we will discuss how modern, custom lingual systems are designed to overcome these difficulties. Modern, lingual appliance systems are an example of how orthodontics is changing today.
Section 1: Why is lingual orthodontics difficult? 2
ACCEPTED MANUSCRIPT
The reasons why lingual orthodontics is difficult can be broadly organized into four categories: 1) Biomechanical issues; 2) Bracket design choices/constraints; 3) Lingual anatomy and 4) Logistical issues. As I mentioned above, the biomechanical difficulties associated with lingual mechanics arise from either anatomical issues or constraints imposed by bracket design choices; all these choices involve tradeoffs. Understanding
CR IP T
these choices and their consequences is the key to understanding the strengths and weaknesses of the various lingual systems you have chosen and, thereby, being on the “road of evidence based clinical experience” to your destination “clinical expertise” with lingual mechanics.
We will categorize the biomechanical issues that are imposed by the lingual anatomy of
AN US
the teeth into five categories: 1st order problems, 2nd order problems, 3rd order
problems, problems involving the point of force application vs. the center of resistance, and problems related to inter-bracket distance. Let us begin with 1st order problems. If you consider the anatomy of the buccal surfaces of the teeth, there are similarities from tooth-to-tooth (see Figure 1); all the teeth have convex surfaces. Thus, if we apply a
M
zero Rx bracket, in a reasonable position, to the buccal surface of teeth and insert a
ED
generic arch formed wire, the teeth will generally align (see figure 2).
This is not the case for the lingual appliances. The lingual surfaces of the teeth are
PT
concave, convex, and frequently both concave and convex. Furthermore, the teeth are highly variable in terms of their buccal lingual dimension. As we are trying to align the
CE
buccal surfaces of these teeth not the lingual surfaces, an “offset” (see figure 1) is needed when working from the lingual. This buccal offset can be place in the bracket,
AC
the wire, or both.
Dr. Fujita published the first description of an attempt to compensate for this 1st order discrepancy using “straight wire mechanics”.13 Small compensations were placed in the base of the bracket with composite, allowing the use of a mushroom-shaped wire on the lingual. This mushroom-shaped arch form is still available today from wire vendors. 3
ACCEPTED MANUSCRIPT
Other systems, such as the “lingual liberty” system, use similar composite bases to achieve a “straight wire” lingual appliance (see figure 3).
CR IP T
example, when the wire plane is placed more cervical, the required “canine offset” can frequently be minimized. The choice of the wire plane is also dictated by the occlusion and the amount of crown available due to crown anatomy, altered passive eruption, and/or hyperplastic gingiva. In general, bracket placement that minimizes buccal-lingual compensations also results in a wire plane in which the amount of occlusal
interferences with the brackets is minimized. When bracket placement choices are
AN US
made, considerations of the trade-offs between 1st order discrepancies, 2nd order discrepancies, and occlusal interferences with brackets must be considered. In addition, robotic wire bending limitations must be considered (see Figure 4).
M
The 2nd and 3rd order lingual problems are related.14 This relationship is due to differences in both the anatomy of the lingual and buccal surfaces of the teeth and the
ED
topology of the lingual surfaces of neighboring teeth (consider the lingual surface topology of the canines relative to that of the first premolars, see figure 1a). Following a
PT
particular wire plane from tooth-to-tooth the lingual surfaces may change from concave to convex (see figure 1). This variation in lingual topology may cause the slot
CE
orientation to be quite different from one tooth to the next. These extreme differences in slot orientation due to individual lingual surface anatomy is complicated further if you allow the wire plane to vary in the inciso-gingival dimension (See figure 5). As
AC
displayed in figure 5, if the wire plane is varied by 1mm with a buccal appliance, you may experience a difference in slot orientation of perhaps 5 degrees.
ACCEPTED MANUSCRIPT
more incisal oriented wire plane is used versus a more gingivally oriented wire plane. A common illustration of this issue on the buccal involves canine torque; most of us have experienced adverse canine torque due to extreme incisal or gingival bracket placement when using a buccal fixed appliance. This is because of the relatively extreme convexity of the buccal surface of the canine, at least compared to the incisors, and the amount of
CR IP T
slot play that is invariably present in our buccal appliances.15 To understand why adverse anatomical torque is not usually expressed when using a buccal fixed
appliance16, consider the mathematics of the slot-wire interface shown in figure 6 and the resulting values shown in Table 1. This equation is a simplified mathematical
representation of the wire-bracket interface. This simplified equation assumes ideal wire and bracket slot geometry. These assumptions are unrealistic for all bracket
AN US
systems.17-21 In figure 6, θ represents the engagement angle of the wire with the slot of the bracket.
As the size and shape of the wire varies, the engagement angle, θ varies. Cash et al.
M
showed us that bracket geometry varies considerably.17 Only 27% of brackets that they examined had parallel slot walls, thus brackets with parallel slot wall are the exception
ED
not the norm. Brackets slots are invariably oversized by as much as 24%; the best brackets were 5% oversized. If we do the math assuming that 1) our wires have perfect
PT
geometry and our brackets are among the 27% that have decent slot geometry and 2) the wire slots of our brackets are only 5% oversized, the engagement angle or amount
CE
of slot play is, at best, 10 degrees (see table 1). In reality, under the best of circumstances, the engagement angle is, at least, 15 degrees due to wire geometry variation.15 Therefore, a 5 degree change in the orientation of the bracket slot due to
AC
anatomical variation or a change in the incisal-gingival wire plane is rarely expressed with buccal appliances. However, consider a 20-degree change in slot orientation, which is not uncommon when using a stock lingual fixed appliance due to either variation in topology of the lingual surfaces of neighboring teeth or changes in the vertical position of the wire plane (see figure 7).
ACCEPTED MANUSCRIPT
The clinical implications of these facts are clear. A standard prescription can work for our patients using stock buccal fixed appliances but trying to use a stock lingual fixed appliance will invariably results in an unmanageable problem involving anatomical torque. Once the first rectangular wire is placed in a stock lingual fixed appliance system, the adverse anatomic torque will begin to express. In addition to the adverse
CR IP T
anatomic torque, other complicating factors, such as decreased interbracket distance, further increases the difficulty of using stock lingual brackets, bending the wires by hand, and engaging said wire!
So far, we have considered what I refer to as “anatomical torque”, but there is another type of torque problem that needs to be managed when treating patients with a lingual
AN US
appliance system. I will refer to this as the “bio-mechanical torque” problem (See Figure 8). Unfortunately, with a stock lingual system these two types of torque problems can only be addressed by mutually exclusive solutions.
With a stock system, the more you “fill” the bracket slot (minimize the engagement angle), the more problems you will have with anatomical torque and the more
M
complicated the wire bending requirements become. At the same time, due to the decreased interbracket distance, it is very difficult to engage these full size rectangular
ED
wires with numerous 1st, 2nd and 3rd order bends. One may be tempted to think that smaller, less slot filling wires will make a stock lingual system more manageable from a
PT
wire bending and engaging perspective. This is true and is exactly why, when a stock lingual system is used for limited treatment (say alignment relapsed lower anterior
CE
teeth), it is best to stay in round wire. The use of round wire will facilitate alignment of relapsed lower anterior teeth, the wires are simple to bend and engage, and there is no chance of expressing adverse anatomical torque. The problem with this solution, in
AC
general, is there is no torque control. As we are about to see, excellent torque control is especially important in lingual mechanics. The “biomechanical torque problem” is related to the point of force application in lingual mechanic compared to the center of resistance of the teeth (see figure 8). This relationship results in an increased tendency for extrusion and lingual “dumping” when either retracting anterior teeth in extraction treatments or using heavy Cl II mechanics 6
ACCEPTED MANUSCRIPT
with a lingual fixed appliances system. This biomechanical issue is well documented in the literature; these papers can be categorized into two types; Mathematical modeling papers22 and finite element analysis (computer modeling) papers23,24. The literature is replete with papers examining the difference in biomechanics between lingual and buccal appliance systems and there is no disagreement on this issue; when using a
CR IP T
lingual fixed appliance system, there is a significantly increased tendency for both extrusion of the anterior teeth and torque loss during space closure and during the use of Cl II mechanics.
This means that we must pay special attention to the expression of torque in these
AN US
types of treatments. The most obvious means to maintain excellent torque control is the use of full-sized wires that fill the brackets slots, but as we have seen this will aggravate the anatomical torque problem! So here we are with two types of torque issues, one that ideally requires slot filling wires and one that certainly does not! Early lingual practitioners dealt with this contradiction when using stock systems, which is exactly
M
why lingual orthodontics has a reputation for being difficult. The solution to reconcile these two torque issues is customization of the lingual appliance to each individual
ED
patient, thereby eliminating the anatomical torque problem (not to mention, at the same time, deal with the first order issue presented earlier) and allowing the orthodontist to
PT
use a slot filling wire for biomechanical torque control. Decreased interbracket distance is a major issue when working from the lingual
CE
surfaces of the teeth. The difference between buccal and lingual interbracket distance was outlined by Moran, in 1987.25 Moran measured the lingual interbracket distance to
AC
be 35.4% less than the buccal interbracket distance in the maxilla and 27.7% less in the mandible. This decreased interbracket distance significantly effects how the wires behave. Specifically, the decreased interbracket distance results in a 3-fold increase in the stiffness of the wire for 1st and 2nd order displacements and a 40% increase in the stiffness of the wire for 3rd order displacements. The biomechanical difficulties of lingual mechanics in five categories: 1st order problems, 2nd order problems, 3rd order problems, problems involving the point of force 7
ACCEPTED MANUSCRIPT
application vs. the center of resistance, and problems related to inter-bracket distance. Let us begin with 1st order problems. The first three categories of problems result in the need for additional 1st, 2nd, and 3rd order bends to compensate for the anatomical issues outlined above. At the same time, extra torque is required to compensate for the increased tendency for lingual crown tipping due to the point of force application vs.
CR IP T
center of resistance issue. On top of these difficulties, the wires that behave as if they are extra stiff because of the reduce interbracket distance. All these factors combined make it almost impossible to use stock brackets bonded directly to the lingual surfaces of the teeth and hand bend wires to treat patients. The solution is to customize the appliance by building as much correction into the brackets and wires as possible. This is
AN US
exactly what modern lingual appliance systems do so well. These systems employ custom brackets, custom composite bases for the stock brackets, and/or custom
robotically bend wires.9 Each system has its own strengths and weaknesses, which we must understand.
I will briefly outline some of the logistical issues but will not consider them in depth in
M
this paper. Logistical issues include but are not limited to: training both staff and orthodontist, scheduling difficulties, cost issues, and patient management issues. The
ED
learning curve for lingual orthodontics can be steep for both orthodontists and staff. Staff training is critical because for most busy orthodontic practices the orthodontist
PT
cannot afford to be randomly tied up for 30 to 40 minutes to deal with a lingual appliance emergency. It is critical that there is staff trained to implement solutions with
CE
indirect supervision by the orthodontist. Training in lingual mechanic for the orthodontist is a problem. Most residencies do not have either the resources or the time to comprehensively prepare residents in lingual
AC
mechanics. There are four university based post-doctoral lingual orthodontic programs in Europe and one in North America. All of the European programs admit qualified orthodontists for training using with lingual appliances.10 The European programs are the master’s degree program (MAS) in lingual orthodontics at the University of Basel, Switzerland, the program offered by Hanover Medical School, Lingual Post-Graduate Course, Paris V. University, Paris, and the Master of Lingual Orthodontics post doc 8
ACCEPTED MANUSCRIPT
program at the Universitat de València, Spain. In North America, the University of Texas at San Antonio, School of Dentistry offers an 18-month post doc fellowship in lingual orthodontics. Each year, there are several international meetings each year dedicated to lingual orthodontics.11,12 The European Society of Lingual Orthodontics (ESLO) and the World
CR IP T
Society of Lingual Orthodontics (WSLO) hold their biennial meetings. In North America, lingual meetings tend to be corporate sponsored (for example, annual Incognito users meetings and SureSmile user meetings). These meetings frequently offer hands on sessions for orthodontists and staff, covering common techniques employed for the specific lingual system involved.10
AN US
Scheduling can also be difficult for established practices. Lingual procedures tend to run longer than buccal those involving traditional, buccal fixed appliance procedures and broken lingual appliances most often result in an emergency appointment due to tissue irritation. Of course, if you choose to only train your most talented assistants in lingual orthodontics, then your emergency lingual appointments will tie up either you or
M
your most talented assistants. The solution… is to train all your assistants to be at least minimally competent with your lingual appliance of choice. That means, all your
ED
assistants in your office should be able to do a basic lingual retie and deal with basic lingual emergencies to get the patient comfortable. Most of the lingual orthodontic
PT
practices, with which I am familiar, train all their staff in lingual orthodontic procedures just like any other common procedure employed in their office. As in with all change,
CE
this training will take some effort, but it will pay off in the long run allowing your practice to thrive.
AC
The cost of providing orthodontic treatment with a custom, lingual orthodontic system is significantly higher than a buccal stock system. The lab cost of the custom appliance is just the beginning; Unlike a stock buccal fixed appliance system, there is a significant amount of work involved in the setup and planning of treatment with a custom lingual appliance. Lingual orthodontic appointments tend to be longer than buccal appointment, depending on the lingual system. Furthermore, you and your team should be compensated for the skills that you so diligently worked to obtain with lingual 9
ACCEPTED MANUSCRIPT
systems. Do not hesitate to charge a premium for your services using lingual fixed appliances. Not only do these patients expect to pay, but they also will often demand the highest level of customer service and they can be difficult patients to manage. For example, we rarely extract first premolars in the maxillary arch without a plan to deliver provisional pontics that will be reduced as the space is closed; lingual patients will
CR IP T
demand that these spaces be managed with pontics. Patients choose a lingual appliance because of their esthetic concerns and they will demand the highest level of esthetic treatment. Patients that demand the highest level of esthetic orthodontic
treatment will consume a disproportionate percentage of your time and the time of your staff. Do not resent this! On the contrary, enjoy providing the best possible clinical care
AN US
and highest level of service using the most esthetically appliances available. Providing esthetic orthodontic treatment is one aspect of functioning at the highest level of our profession.
M
Section 2: Implicit and explicit design choices in lingual orthodontic appliance systems.
ED
Custom orthodontics is changing the way orthodontists provide and think about treatment.4 The resurgence of lingual orthodontics using custom lingual appliances is
PT
an example of how custom appliances are changing the profession.8 The most common custom appliances in orthodontics are clear aligners. However, clear aligners such as Invisalign and their storefronts, Smile Direct Club and Candid Co, are disrupting
CE
the orthodontic profession. It is “digital orthodontics” that has made possible mass production of custom orthodontic appliances. I am going to define Digital Orthodontics
AC
as “the planning and execution of orthodontic treatment using digital orthodontic records”. Digital orthodontics only requires that we are using digital radiography, photography and intraoral scanning when collecting records on our patients. It is only a matter of time before 100% of orthodontists are completely “digital”. Although digital orthodontics can be as simple as taking digital records, it can be as involved as using these records to digitally “setup” a patient’s treatment, manufacturing a custom appliance, and 3D printing the final intraoral scans to fabricate Essix type retainers. I 10
ACCEPTED MANUSCRIPT
have referenced “custom appliances” throughout this paper; what are custom appliances and what is custom orthodontics? I am going to define Custom Orthodontics as “the use of a pre-programmed, orthodontic appliance to treat a patient to a precisely predetermined occlusal outcome”. The preprogrammed orthodontic appliance referred to in the previous definition is a “Custom Appliance System”.
CR IP T
All custom appliances are fabricated using a treatment setup. This is true of clear
aligner systems such as Invisalign and Clear Correct, buccal systems like SureSmile and Insignia, and lingual systems like Incognito and Lingual Liberty. The treatment setup is used to fabricate the custom appliance, incorporating individualized correction either in the brackets, wires, or both. In lingual orthodontic system this customization is
AN US
used to compensate for issues such as the “anatomical torque” problem. Using a
treatment setup has other benefits for the patient and the practitioner. The treatment objectives are implicitly described by the setup itself. The treatment setup also serves to describe essential detail of the planned treatment, such as IPR (amount and surfaces), expansion, tooth inclinations, torque requirements, space appropriation
M
issues, and anchorage requirements. In many instances, the process of developing the treatment setup allows the orthodontist to consider the plausibility of the proposed
ED
correction as well as examine treatment alternatives. With interdisciplinary treatment, a treatment setup is an essential tool to effectively collaborate with the other providers
PT
and communicate with patients.26 Digital orthodontics has made custom orthodontics possible and custom orthodontics is driving the paradigm shift from “Reactive Treatment Planning” to “Proactive Treatment Planning”. Proactive treatment
Implicitly codifying the treatment objectives
AC
CE
planning involves a treatment setup. This treatment setup has many benefits, including:
Communication with patients
Communication with other care providers/ Interdisciplinary treatment
Facilitating an understanding of the mechanics/ anchorage requirements of the proposed treatment
11
ACCEPTED MANUSCRIPT
Reactive treatment planning does not involve a “treatment setup”. It involves a general treatment plan, perhaps specifying extraction vs. non-extraction, IPR, and Cl II or Cl III mechanics. Decisions are made step by step throughout treatment; each decision tends to reduce the degrees of freedom that the orthodontist has with respect to the remaining treatment. For example, if lower incisor proclination occurs as a result of Cl II
CR IP T
mechanics during treatment, the orthodontist may decide to compromise the overjet or perform additional IPR. These types of decisions are made at each appointment,
usually with minimum of consideration. Reactive treatment planning is employed by default and, in general, it works well when treating children and adolescents. However, reactive treatment planning does not tend to produce optimal results when treating
AN US
patients with debilitated, severely worn or highly restored dentitions or the instance of complex orthodontic treatment, such as interdisciplinary treatment. Digital orthodontics has allowed the development of custom orthodontics and it is custom orthodontics that has made lingual orthodontics possible for the average orthodontist. Digital orthodontics has driven the resurgence of lingual orthodontics as
M
well as custom, clear aligner systems.1 It was Invisalign that first disrupted the orthodontic profession in the early 2000’s by marketing of their clear aligner system to
ED
patients and general dentist. At that time, orthodontists did not realize that Invisalign was creating the esthetic, adult orthodontic market. Through its national and
PT
international marketing efforts, Invisalign has been driving the demand for esthetic, adult orthodontic treatment options. These efforts raise awareness of esthetic orthodontic treatment options and drive patients desiring these types of treatments into our
CE
orthodontic practices.3 One of the obvious treatment options for a patient who desires an esthetic appliance, but is not a candidate for clear aligner therapy, is treatment with a
AC
lingual appliance system. It is useful to discuss the various custom lingual systems in context of the choices that are universal with the systems. These choices remain as appliances system change; there is no perfect appliance system for all patients and there never will be. However, these systems will continue to improve, and the day is coming in which the treatment setup will be used to design custom treatment for every patient. Orthodontists that 12
ACCEPTED MANUSCRIPT
ignore lingual orthodontics will be giving up a powerful tool that differentiates us from the generalist by adding value to what we offer patients. In the previous section, we reviewed why lingual orthodontics is difficult. Modern lingual systems have evolved to deal with these challenges through “customization”. The reasons why lingual orthodontics therapy is difficult to accomplish with stock appliances
CR IP T
are invariant, whereas these custom appliance systems are not. In the future, lingual systems will change. They will improve both with respect to the physical technology, such as the brackets and the wires, but also with respect to the software that is used to design these appliances. In the last section of this paper, we will review the choices that are made when selecting and designing a custom lingual appliances system. We will
AN US
discuss the implication of using a treatment setup to design these appliances and
discuss the how these setup force us to start planning proactively, rather than reactively when implementing orthodontic treatment.
In the literature, people have tried to present indications and contraindications for the use of lingual orthodontics.27,28 Virtually all patients can be treated with a custom lingual
M
appliance system. The limiting factor is the knowledge of the practitioner regarding the strengths and weaknesses of the particular system employed, not the system itself. In
ED
other words, excellent clinical results29 can be obtained with all the modern custom systems. There are numerus systems that have been developed around the world.
PT
Some systems are more popular in Europe and Asia, such as Win, Alias, eBraces and the Lingual Liberty systems. We compare two of the more popular systems in North
CE
America, SureSmile by Orametrix and Incognito (3M Unitek) in table 2. Each system has its advantages and disadvantages (see table 2); when selecting a lingual system, both implicit and explicit design choices will be made. For example, with Incognito, you
AC
are implicitly choosing to use a ribbon arch wire and vertical slots in the anterior, rather than the traditional edgewise wire/slot interface seen most commonly in lingual brackets. There are implications to this choice; for example, it may be easier to engage a full-sized wire for biomechanical torque control in a system with anterior vertical slots. However, it is more difficult to control angulation and place bends by hand in ribbon arch wires with vertically oriented slots. There are also explicit choices that must be made 13
ACCEPTED MANUSCRIPT
when using these lingual systems. For example, with Incognito, do you want a hook or no hook on a particular first or second molar? Do you want a tube or a bracket on a particular tooth? Do you want to cover the lingual surface of the tooth with the custom base or do you want half occlusal, or even full occlusal, coverage of the tooth by the custom base? With the SureSmile system, you will need to choose a stock bracket
CR IP T
system; this bracket system may be self-ligating or not. You can choose combinations of stock systems on a single case. You may decide to use a self-ligating bicuspid
bracket on the second molar due to the lingual anatomy of a particular tooth. Again, there are consequences to these explicit choices. A self-ligation bracket may have a larger mesio-distal dimension and, thereby, reduce the interbracket distance. While the
AN US
non-self ligating bracket may be problematic for an office where the staff has limited experience with lingual ligation techniques.
All major, fixed lingual systems have custom features in one or more of three essential components of the system: 1) Brackets, 2) Wires and 3) Software. This variation makes each system unique with respected to one another. In Table 1, we compare two popular
M
North American systems with respect to brackets, wire, and software.
ED
Brackets: There are significant differences between the brackets used by SureSmile and Incognito. SureSmile employs stock brackets. There are a myriad of stock lingual
PT
brackets in their library from which to choose, including multiple examples of both selfligating and conventional ligating brackets. If, by chance, your brackets or prescription
CE
is not currently available in their library, it can be added. Almost any stock lingual bracket that you choose to employ with SureSmile will be manufactured using metal
AC
injection molding (MIM). SureSmile has concentrated its innovation into their wires and software; currently, their technology in these areas is unsurpassed. SureSmile puts 100% of the customization into the wires. Therefore, each bracket will have a small compensating bend to the mesial and distal of the bracket. While custom brackets allow the use of straight wire mechanics; they rarely result in treatment that does not require some compensations in the wire. This is especially true in the correction of gingival balance issue (see figure 9a). 14
ACCEPTED MANUSCRIPT
CR IP T
before treatment is initiated. One of the disadvantages of the SureSmile system is the fact that you are forced to employ stock brackets. It can be difficult or impossible to bond to non-enamel surfaces with stock orthodontic brackets. Therefore, a patient with a heavily restored or debilitated dentition may not be an ideal candidate for this system. Alternatively, the Incognito system employs custom brackets with custom bracket bases.
AN US
This allows bonding to virtually any surface including gold, amalgam, non-precious
metal, composite, ceramic, as well as a combination of materials. Properly designed brackets minimize the frequency of debonded brackets on even the most difficult surfaces. The custom bases can be extended to maximize surface area on the lingual and occlusal surfaces. The bases can even extend to the buccal surfaces of the
M
posterior teeth. While all lingual appliance systems employ a 018 slot size, the brackets of the Incognito system are different than most lingual systems with respect the their
ED
slot orientation. Incognito uses a ribbon arch wire and vertically oriented slots in the anterior and horizontal slots in the posterior. There are similar systems to Incognito,
PT
such as eBrace and Winn, that employ an anterior vertical slot. The lower anterior Incognito brackets do have a quasi-self-ligating feature that allows 012NiTi and 014NiTi
CE
wires to be inserted behind the bracket wings of the six lower anterior teeth. Selfligating brackets are a huge advantage for busy practices without staff trained in the various ligation techniques employed with horizontal and vertical slot lingual bracket
AC
systems.30 Most self ligating lingual brackets are made using Metal Injection Molding, MIM and we have discussed the limitation of these brackets with respect to the accuracy of the slot and its effect on the engagement angle of the wire.17,19,21 Therefore, if extra biomechanical torque is required, it must be added by hand. The Incognito brackets are not MIM’ed. Instead, Incognito 3D prints the patterns, casts the brackets using a lost material technique, then finishes the slot of the anterior brackets using an 15
ACCEPTED MANUSCRIPT
Electronic Discharge Machining (EDM). These anterior brackets tend to have tight tolerances (low engagement angles) at the bracket/wire interface. In theory, this should translate into more predictable torque expression15 and, in turn, less need to place post hoc torque into the maxillary stainless steel wires during space closure and when using heavy Cl II mechanics.
CR IP T
Wires: The SureSmile system does 100% of the custom compensations in the wires, using stock lingual brackets. Currently, there is only company that has the ability to place 1st, 2nd and 3rd order bends in NiTi wires. The ability to place 3rd order bends in NiTi wire allows SureSmile to compensate for the anatomical torque problem, facilitating the transition from round to rectangular NiTi wires using stock lingual brackets. The
AN US
SureSmile wire robots can also place all three orders of bends in stainless steel, TMA, and elgaloy wires. Alternatively, Incognito compensates for anatomical torque discrepancies using their custom brackets. Other approaches are employed by other systems. With Lingual Liberty, the anatomical torque (see figure 6) issue is addressed through a custom composite “pad” between a stock lingual bracket and the tooth
M
surface. In fact, Lingual Liberty also uses this custom composite pad to make first order compensations, which allows the use of a “universal” arch wire. This “straight wire”
ED
technique allows the orthodontist to operate in a familiar way in unfamiliar territory, the lingual surfaces of the teeth. On the other hand, Incognito employs a ribbon arch wire. It
PT
can be very difficult to place post hoc torque in the 16x24SS ribbon arch wire due to existing robotically bend compensations in the wires in addition to the tight fit between the anterior custom bracket slots and the full size ribbon arch wires. Due to these
CE
difficulties, when using a 16x24SS ribbon arch wire to retract anterior teeth, it is recommended to request that extra torque is placed robotically. Incognito wires are
AC
charged ala cart and not all wires have the same bends. The initial round and rectangular NiTi wire will have 1st order bends, while 2nd and 3rd order bends are not placed until stainless steel and TMA wires. The choice of a particular lingual system for a patient should also depend on the treatment objective and the required tooth movements. For example, if a treatment objective is to correct a ≥4mm midline discrepancy in the upper arch, a system that employs a horizontal slot rather than a vertical slot in the anterior may be advantageous. Let’s again consider the smile in 16
ACCEPTED MANUSCRIPT
figure 9a, we have a significant disturbance in the gingival balance due to extrusion of the upper anterior teeth and probably also altered passive eruption. It is not possible to know exactly how much intrusion will be required, until after crown lengthening. Additionally, the apical migration of the gingiva is not 1:1 with intrusion of the crown; intrusion of 1mm may result in .8mm of gingival migration. Therefore, it is not possible
CR IP T
to fabricate a custom appliance system that will achieve an optimal treatment result without modification of the original treatment setup. In situations like this, a lingual appliance system that allows flexibility should be selected to be able to make the
required modifications easily and inexpensively. For a treatment involving correction of gingival imbalance, a system with a horizontal slot, the ability to modify wires either
AN US
digitally or by hand, and excellent software to interface between the setup and the lab is desired.
Software: The third component of a custom lingual appliance system is the software. At first, the importance of the software associated with a custom appliance system is easy to overlook. However, the software is as important as any of the other components of
M
the system. As the sophistication of these programs improve, we will be able to integrate buccal fixed appliances and clear aligners with lingual fixed appliance into a
ED
custom system to optimize orthodontic treatment for our patients. Elemetrix, the software system employed by SureSmile, can be used to integrate these three
PT
treatment modalities, today. 3M claims that their Clarity Aligners will be integrated with their fixed lingual system, Incognito, very soon. Software is used to communicate with the lab to produce the treatment setup, which, in turn, is used to fabricate the custom
CE
appliance system. The communication with the lab is critical. It is not possible to create a custom appliance without excellent communication and control over the treatment
AC
setup. The treatment setup can also be used as a platform to communicate with other dental professional for interdisciplinary case. Finally, the treatment setup can be used to communicate with patient regarding the treatment objectives. The quality of the software experience varies tremendously from one appliance system to another. The treatment setup can also be used to simulate various treatment options. For example, various extraction patterns can be explored, as opposed to interproximal 17
ACCEPTED MANUSCRIPT
reduction (IPR), or in conjunction with IPR. When treating adult patients with varying degrees of tooth attrition and complex restorative histories, determining the best occlusal outcome without a treatment setup is, at best, a guess. Interdisciplinary treatment requires collaboration between two or more dental professionals and a treatment setup is a necessary component of interdisciplinary treatment planning. 26
CR IP T
These treatment setups not only serve to clarify the details of the orthodontic treatment, but are also used to plan the restorative phase of treatment. In this case, the software performs a crucial function in communication with both other dental professionals as well as the patient. Each of the lingual appliance systems employs software to develop and present the treatment setup. SureSmile uses Elementrix, whereas Incognito uses
AN US
TMP. Conclusions:
While all lingual systems have strengths and weaknesses, the choice of a particular system is secondary to having a proper understanding of the system used; as well as, the proper armentarium and clinical experience to implement the treatment plan. In this
M
paper, we have outlined the basic knowledge required to evaluate and select a lingual system that best fits the patient, orthodontist and his or her team. With the current
ED
disruption in the orthodontic marketplace it is important that orthodontic specialists employ the benefits that digital orthodontics and custom orthodontic appliance system
PT
offer in order provide the best possible care in the competitive environment in which most of us practice today. Lingual mechanics provides added value for our patients that
CE
truly differentiates the orthodontic specialist from the generalist as well as direct to
AC
patient modalities.
1.
Kuo E, Miller RJ. Automated custom-manufacturing technology in orthodontics. Am J Orthod Dentofacial Orthop. 2003;123(5):578-581. 18
ACCEPTED MANUSCRIPT
9.
10. 11. 12. 13. 14. 15. 16. 17. 18.
AC
19.
CR IP T
8.
AN US
7.
M
6.
ED
5.
PT
3. 4.
Rosvall MD, Fields HW, Ziuchkovski J, Rosenstiel SF, Johnston WM. Attractiveness, acceptability, and value of orthodontic appliances. Am J Orthod Dentofacial Orthop. 2009;135(3):276.e271212; discussion 276-277. McCrostie HS. Lingual Orthodontics: The Future. Seminars in Orthodontics. 2006;12(3):211-214. Jheon AH, Oberoi S, Solem RC, Kapila S. Moving towards precision orthodontics: An evolving paradigm shift in the planning and delivery of customized orthodontic therapy. Orthod Craniofac Res. 2017;20 Suppl 1:106-113. Ling PH. Lingual orthodontics: history, misconceptions and clarification. J Can Dent Assoc. 2005;71(2):99-102. Ata-Ali F, Ata-Ali J, Ferrer-Molina M, Cobo T, De Carlos F, Cobo J. Adverse effects of lingual and buccal orthodontic techniques: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop. 2016;149(6):820-829. Wu A, McGrath C, Wong RW, Wiechmann D, Rabie AB. Comparison of oral impacts experienced by patients treated with labial or customized lingual fixed orthodontic appliances. Am J Orthod Dentofacial Orthop. 2011;139(6):784-790. George RD, Hirani S. Fully-customized lingual appliances: how lingual orthodontics became a viable treatment option. J Orthod. 2013;40 Suppl 1:S8-13. Wiechmann D, Rummel V, Thalheim A, Simon JS, Wiechmann L. Customized brackets and archwires for lingual orthodontic treatment. Am J Orthod Dentofacial Orthop. 2003;124(5):593599. Das S, Labh S, Barik A. Lingual orthodontic education: An insight. APOS Trends in Orthodontics. 2016;6(4):185-190. Chatoo A. A view from behind: a history of lingual orthodontics. J Orthod. 2013;40 Suppl 1:S2-7. Echarri P. Revisiting the History of Lingual Orthodontics: A Basis for the Future. Seminars in Orthodontics. 2006;12(3):153-159. Fujita K. New orthodontic treatment with lingual bracket mushroom arch wire appliance. Am J Orthod. 1979;76(6):657-675. Stamm T, Wiechmann D, Heinecken A, Ehmer U. Relation between second and third order problems in lingual orthodontic treatment. Vol 32000. Archambault A, Lacoursiere R, Badawi H, Major PW, Carey J, Flores-Mir C. Torque expression in stainless steel orthodontic brackets. A systematic review. Angle Orthod. 2010;80(1):201-210. Sifakakis I, Pandis N, Makou M, Eliades T, Katsaros C, Bourauel C. A comparative assessment of torque generated by lingual and conventional brackets. Eur J Orthod. 2013;35(3):375-380. Cash AC, Good SA, Curtis RV, McDonald F. An evaluation of slot size in orthodontic brackets--are standards as expected? Angle Orthod. 2004;74(4):450-453. Sebanc J, Brantley WA, Pincsak JJ, Conover JP. Variability of effective root torque as a function of edge bevel on orthodontic arch wires. Am J Orthod. 1984;86(1):43-51. Gioka C, Eliades T. Materials-induced variation in the torque expression of preadjusted appliances. Am J Orthod Dentofacial Orthop. 2004;125(3):323-328. Meling TR, Odegaard J. The effect of cross-sectional dimensional variations of square and rectangular chrome-cobalt archwires on torsion. Angle Orthod. 1998;68(3):239-248. Siatkowski RE. Loss of anterior torque control due to variations in bracket slot and archwire dimensions. J Clin Orthod. 1999;33(9):508-510. Geron S, Romano R, Brosh T. Vertical forces in labial and lingual orthodontics applied on maxillary incisors--a theoretical approach. Angle Orthod. 2004;74(2):195-201. Liang W, Rong Q, Lin J, Xu B. Torque control of the maxillary incisors in lingual and labial orthodontics: a 3-dimensional finite element analysis. Am J Orthod Dentofacial Orthop. 2009;135(3):316-322.
CE
2.
20. 21. 22. 23.
19
ACCEPTED MANUSCRIPT
25. 26. 27. 28. 29.
AC
CE
PT
ED
M
AN US
30.
Lombardo L, Scuzzo G, Arreghini A, Gorgun O, Ortan YO, Siciliani G. 3D FEM comparison of lingual and labial orthodontics in en masse retraction. Prog Orthod. 2014;15(1):38. Moran KI. Relative wire stiffness due to lingual versus labial interbracket distance. Am J Orthod Dentofacial Orthop. 1987;92(1):24-32. Kokich VG, Spear FM. Guidelines for managing the orthodontic-restorative patient. Semin Orthod. 1997;3(1):3-20. Echarri P. Lingual Orthodontics: Patient Selection and Diagnostic Considerations. Seminars in Orthodontics. 2006;12(3):160-166. Romano R. Concepts on Control of the Anterior Teeth Using the Lingual Appliance. Seminars in Orthodontics. 2006;12(3):178-185. Grauer D, Proffit WR. Accuracy in tooth positioning with a fully customized lingual orthodontic appliance. Am J Orthod Dentofacial Orthop. 2011;140(3):433-443. Dalessandri D, Lazzaroni E, Migliorati M, Piancino MG, Tonni I, Bonetti S. Self-ligating fully customized lingual appliance and chair-time reduction: a typodont study followed by a randomized clinical trial. Eur J Orthod. 2013;35(6):758-765.
CR IP T
24.
20
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
M
AN US
CR IP T
Manuscript Legends
Figure 1 Illustrates the similarity of the buccal anatomy of teeth. The differences in the buccallingual dimension of teeth requires a buccal lingual “offset” to align the buccal surfaces of the teeth. 21
CR IP T
ACCEPTED MANUSCRIPT
PT
ED
M
AN US
Figure 2 demonstrates the alignment of the dental arches possible by using stock brackets on the buccal surface of the teeth with a natural arch formed stock wire. This is not possible using stock bracket on the lingual surface of the teeth without a buccal-lingual “offset” to align the buccal surfaces of the teeth.
AC
CE
Figure 3 shows the three common lingual arch wire configurations: Completely customized with a unique bend between each tooth, the Fujita “mushroom archform, and a straight wire. Each of these arch wire configurations has biomechanical implications.
22
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
Figure 4 shows a completely customized wire; the heighted areas indicate portions of the wire that are “Unbendable” by the wire bending robots. These wires bending limitations effect bracket placement, frequently bracket position choices must be considered in the context of wire bending limitations when using a lingual system with completely customized wires.
23
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
M
Figure 5 shows the difference in bracket slot orientation (torque expression) with a small change position in an inciso-gingival direction. On the buccal surface a small change in position may result in up to a 5 degree change the orientation of the bracket slot while on the lingual this same change in position can result is a slot orientation change of 20 degrees.
24
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
PT
ED
Figure 6 illustrates the geometry associated “slot play”. The equation shown here describes the relation ship between the engagement angle, θ and wire size ( a and b) for a given slot size, c.
25
ACCEPTED MANUSCRIPT
ED
M
AN US
CR IP T
Figure 7 illustrate the “anatomical torque” problem. Along a fixed wire plane on the lingual, difference in the lingual surface anatomy from tooth to neighboring tooth result in large differences in slot orientation and therefore torque expression when using a stock lingual brackets.
AC
CE
PT
Figure 8 shows the different force vectors associated with incisor intrusion and retraction using lingual and buccal mechanics. There is a well-documented22,33,24 increased tendency for “torque loss” through lingual tipping and extrusion when implementing lingual mechanics versus conventional mechanics.
26
PT
ED
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
AC
CE
Figure 9a shows an altered gingival balance due to extrusion of the maxillary anterior teeth. Figure 9b is a image of a corrected gingival balance.
Table 1
Best Case Theoretical Engagement Angle With 5% and 15% Oversized Slots (Assuming Ideal Geometry) WIRE SLOT SIZE 5% 10% 27
ACCEPTED MANUSCRIPT
.018 .018 .022
8° 4° 10°
Table 2
Brackets
Wires
Stock brackets used. Stock bracket choices unlimited. Any bracket can be used on any tooth. All customization is placed in the wires.
Unlimited included with case 1st, 2nd,3rd order bends in Niti, TMA and elgiloy Each wire can be completely customized
Software
Charged per wire 1st order bends in Niti 1st, 2nd and 3rd order bends in TMA and SS Wires can vary in terms of customizing the wire bends
AC
CE
PT
ED
Custom cast base, SL on in lower anterior for 012N and 014N Vertical slot in anterior, Horizontal slot in Posterior, 25x18
M
Incognito
Digital indirect bracket placement, Indirect transfer tray printing Overlay and sophisticated metric and analysis available Control over individual tooth movement Export STL files, No specialized communication features Integration of roots and Alveolar bone from CBCT data in treatment setups Coordinate Buccal, Lingual and Clear Aligners TMP Software for digital case submission/ ordering Basic overlay and 3D model manipulation Dental metrics available with analysis Some communication features/ export STL files Only setup lingual fixed appliances at this time, no ability to integrate Clear Aligners or Buccal fixed appliances
AN US
SureSmile
13° 9° 16°
CR IP T
16x22 17x25 19x25
28