- Email: [email protected]
Management of overbite with the Invisalign appliance
ORIGINAL ARTICLE
Management of overbite with the Invisalign appliance Roozbeh Khosravi,a Bobby Cohanim,a Philippe Hujoel,b Sam Daher,c Michelle Neal,d Weitao Liu,a and Greg Huanga Seattle and Kirkland, Wash, and Vancouver, British Columbia, Canada
Introduction: Most of the published literature on the management of overbite with the Invisalign appliance (Align Technology, Santa Clara, Calif) consists of case reports and case series. Methods: In this retrospective study of 120 patients, we sought to assess the nature of overbite changes with the Invisalign appliance. Records were collected from 3 practitioners, all experienced with the Invisalign technique. The patients were consecutively treated adults (.18 years old) who underwent orthodontic treatment only with the Invisalign appliance. Patients with major transverse or anteroposterior changes or extraction treatment plans were excluded. The study sample included 68 patients with normal overbites, 40 with deepbites, and 12 with open bites. Their median age was 33 years, and 70% of the patients were women. Results: Cephalometric analyses indicated that the deepbite patients had a median overbite opening of 1.5 mm, whereas the open bite patients had a median deepening of 1.5 mm. The median change for the normal overbite patients was 0.3 mm. Changes in incisor position were responsible for most of the improvements in the deepbite and open bite groups. Minimal changes in molar vertical position and mandibular plane angle were noted. Conclusions: The Invisalign appliance appears to manage the vertical dimension relatively well, and the primary mechanism is via incisor movements. (Am J Orthod Dentofacial Orthop 2017;151:691-9)
T
he Invisalign appliance (Align Technology, Santa Clara, Calif) consists of a series of computerdesigned clear plastic shells that fit closely over the teeth and incrementally move the teeth to their correct position.1,2 Orthodontic treatment with the Invisalign appliance may be more esthetically appealing to some patients when compared with conventional fixed appliances; this partly explains the increasing demand for this treatment method.3 The Invisalign technique was initially proposed to treat mild orthodontic cases.2,4-6 Nonetheless, there are reports of complex orthodontic cases treated with the Invisalign appliance in the literature.7-9 For example, a recent study demonstrated the successful closure of a
a Department of Orthodontics, School of Dentistry, University of Washington, Seattle, Wash. b Department of Oral Health Sciences, School of Dentistry, University of Washington, Seattle, Wash. c Private practice, Vancouver, British Columbia, Canada. d Private practice, Kirkland, Wash. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Funded by the University of Washington Orthodontic Alumni Association. Address correspondence to: Roozbeh Khosravi, University of Washington, Department of Orthodontics, Box 357446, Room location: HSB-D5691959, NE Pacific St., Seattle, WA 98195; e-mail, [email protected]. Submitted, May 2016; revised and accepted, September 2016. 0889-5406/$36.00 http://dx.doi.org/10.1016/j.ajodo.2016.09.022
4-mm anterior open bite by extrusion of the anterior teeth using a series of 35 Invisalign aligners.9 Soon after the introduction of the Invisalign system in the late 1990s, practitioners noticed that the appliance commonly induced deepening of the overbite.10 It was suggested that aligners covering all posterior teeth could function as a bite-block, thereby intruding the posterior teeth. This would result in a reduction of the posterior vertical dimension and consequent deepening of the overbite.11 The Invisalign system has evolved over the last 16 years, and various strategies have been developed to better manage the vertical dimension. For example, an early strategy to prevent bite deepening was the removal of occlusal coverage on the second molars. Align Technology recently developed new treatment options including specially designed attachments and virtual bite ramps. Attachments are composite buttons attached to the labial surfaces of the teeth, and they come in various shapes to assist with tooth movement. Specifically, these attachments increase retention, transmit desirable force to the teeth, and support auxiliary functions such as placement of elastics.12 Virtual bite ramps function similar to bite plates or bite turbos. These bite ramps, incorporated into the maxillary aligner, contact the mandibular incisors to disocclude the posterior teeth when patients bring their teeth together. 691
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Despite these advancements in the Invisalign appliance, evidence supporting the effectiveness of these treatment modalities is limited to case reports and case series. Studies with larger samples and better designs are required to understand the mechanism by which the Invisalign appliance manages the vertical dimension. In this retrospective study, we sought to investigate the vertical dimension changes in patients with various pretreatment overbite relationships treated only with the Invisalign appliance. Moreover, we aimed to identify the dental and skeletal changes associated with bite closing or opening. See Supplemental Materials for a short video presentation about this study. MATERIAL AND METHODS
This study was approved by the institutional review board of the University of Washington. The study sample consisted of adult patients consecutively treated with the Invisalign appliance in 3 private orthodontic offices. Two practices were located in the greater Seattle area, Wash and one Vancouver, British Columbia. A total of 313 patient records were screened; records of 193 patients (62%) were excluded. The most common reason for exclusion was lack of final lateral cephalometric radiographs. The second most common reason was that the posterior teeth were out of occlusion when the radiograph was taken. The study sample was stratified into groups of normal overbite, deepbite, and open bite based on the pretreatment overbite measured on cephalometric radiographs. Normal overbite was defined as pretreatment overbite ranging from 0 mm to less than 4 mm. Patients with 4 mm or greater pretreatment overbite were classified in the deepbite group.13 The open bite group included patients with negative pretreatment overbite. Inclusion criteria were (1) the patient was 18 years or older at the beginning of treatment, (2) the treatment was completed between January 1, 2010, and January 1, 2014, (3) 11 to 40 aligners were used for each arch, (4) a maximum of 3 revision sets of aligners was used, (5) the treatment plan was nonextraction, (6) the molar anteroposterior occlusal relationship was not changed (eg, no Class II to Class I occlusion change), (7) posterior-transverse relationships were not changed significantly (eg, no correction of posterior crossbite), (8) fixed appliances were not used, and (9) the patient had good-quality pretreatment and posttreatment cephalometric radiographs. Two investigators (R.K. and W.L.) screened consecutively treated patients at each orthodontic office. Each subject eligible for the study was then assigned an anonymous identification number, and the records were deidentified with these numbers.
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The collected records included (1) pretreatment and posttreatment lateral cephalometric radiographs, (2) the Invisalign Treatment Overview form with information regarding number and location of attachments as well as potential interproximal reduction plans, (3) patient's age at the start of the treatment, (4) patient's sex, and (5) questionnaires filled out by the clinicians regarding their treatment strategies. Deidentified lateral cephalometric radiographs were imported into software (Dolphin Imaging, Chatsworth, Calif) to perform cephalometric analyses. Seventeen landmarks were marked on the initial and final lateral cephalometric radiographs. We opted to mark the landmarks for the pretreatment and posttreatment radiographs of each patient sequentially to reduce potential landmark identification error. The software then calculated the linear and angular measurements, which were used in our statistical analyses. To assess the changes during treatment, 9 linear and 3 angular measurements were measured (Fig 1). Palatal, occlusal, and mandibular planes were used as the reference lines. The palatal plane was defined as a straight line passing through the anterior and posterior nasal spine points.14 The occlusal plane was defined as a straight line drawn through the bisection of the mesiobuccal cusp tips of the first molars and the bisection of the incisal edge of the most anterior central incisors.15 The mandibular plane was defined as a straight line connecting menton to constructed gonion.16 To assess the changes in the anterior vertical dimensions, we made these measurements. The linear measurements were overbite, defined as the shortest vertical distance between the tip of the maxillary incisor and the tip of the mandibular incisor perpendicular to the occlusal plane, and the vertical position of the incisors, defined as the shortest distance between the maxillary and mandibular incisors to the palatal and mandibular planes, respectively (reference lines).17 Additionally, the anterior facial linear height was measured: defined as the shortest distance between defined as the shortest distance between anterior nasal spine and menton was measured.18 The angular measurements were the angle between the maxillary incisor's long axis and the nasion-A point line and the angle between the mandibular incisor's long axis and the nasion-B point line.19 To assess the changes in the posterior vertical dimension, several linear and angular measurements were measured. The vertical dimension changes of the maxillary and mandibular molars were determined using linear measurements. The shortest distances between the palatal plane and the maxillary first and second molars' mesiobuccal cusp tips were measured.
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Fig 1. Linear and angular cephalometric measurements used to assess the anterior and posterior vertical dimension changes in patients who underwent orthodontic treatment with the Invisalign appliance. A, Linear measurements: 1, overbite; 2, maxillary incisor tooth tip to palatal plane; 3, mandibular incisor tooth tip to mandibular plane; 4, anterior facial height; 5, maxillary molar mesial cusp tip to palatal plane; 6, mandibular molar mesial cusp tip to mandibular plane; 7, posterior facial height. B, Angular measurements: 8, maxillary incisor axis to nasion-A-point; 9, mandibular incisor axis to nasion-B-point; 10, mandibular plane angle.
Similarly, the shortest distances between the mandibular first and second molars' mesiobuccal cusp tips to the mandibular plane were measured.17 The posterior facial height was measured as the shortest distance between constructed gonion and articulare.18 The angle between the mandibular plane and the sella-nasion reference line was measured.20 Approximately 2 weeks after the initial measurements we, 10 cephalometric radiographs were randomly selected by the R statistical package (version 2.11.1; RStudio, Boston, Mass) through RStudio (version 0.99.491) for the measurement error analysis. Landmarks on these lateral cephalometric radiographs were reidentified, and the measurements were recalculated using the Dolphin Imaging software. The measurement error was reported as the mean difference between the initial and retraced cephalometric values.21 Statistical analysis
Statistical analyses were conducted in 2 phases. Initially, descriptive analyses were performed to examine the cephalometric measurements of the pretreatment and posttreatment radiographs in all 3 groups. Detailed descriptive analyses are presented in the Appendix. To examine the difference between cephalometric measurements before and after treatment, we used
Table I. Intra-rater reliability for the cephalometric analysis (n 5 10) Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
Mean
SD
0.03 0.35 0.14 0.13
0.08 0.73 1.16 1.24
1.12 0.94
2.19 2.03
0 0.56 0.2 0.18 0.43
0.54 0.96 0.83 0.74 1.28
0.31
1.16
U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar.
the nonparametric Wilcoxon signed rank test at the P 5 0.05 level of significance. We opted to use this analysis because the majority of our variables were not normally distributed. Additionally, KruskalWallis analysis at the P 5 0.05 level of significance was used to investigate overbite changes in the 3 groups.
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Table II. Pretreatment patient characteristics Normal overbite (n 5 68) Demographics Age (y) Incisor position (mm) Overbite Overjet U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
Deepbite (n 5 40)
Median 32
Mean 34
SD 12
2.3 3.3 27.7 41.3 65.9
2.3 3.3 27.9 41.0 65.4
19.1 25.4
Open bite (n 5 12)
Median 38
Mean 40
SD 14
Median 30
Mean 34
SD 11
1.1 1.1 2.8 3.3 5.0
5.1 3.9 29.5 40.6 64.2
5.3 4.0 29.0 41.1 65.0
1.0 1.2 3.4 4.3 6.9
0.8 2.3 28.9 43.5 69.8
1.1 2.8 29.6 43.2 72.1
0.9 2.2 3.6 4.1 7.3
19.9 25.9
5.9 5.9
12.7 20.1
12.8 21.7
6.2 8.8
25.2 27.6
23.0 30.4
8.2 6.2
22.4 32.5 19.9 30.3 87.6
22.3 32.4 19.7 29.9 86.9
2.3 2.8 2.7 2.9 7.2
21.8 31.5 17.9 28.8 85.1
21.9 32.3 18.0 29.3 86.6
3.2 3.3 3.9 3.1 8.1
22.9 31.8 19.6 29.2 84.8
23.7 33.3 19.9 30.3 85.6
3.7 3.8 3.8 3.7 9.0
29.2
29.6
7.1
29.9
28.9
7.1
34.3
35.6
8.7
U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar.
The statistical analyses were conducted using the R statistical package (RStudio). RESULTS
A total of 120 patients (normal overbite group, 68; deepbite group, 40; open-bite group, 12) were included in this study. Their median age was 33 years (interquartile range 5 17), and 70% of the patients were women. Specifically, 46 (67%) patients in the normal overbite group, 28 (70%) patients in the deepbite group, and 8 (66%) patients in the open-bite group were women. The intraexaminer error analysis indicated a measurement error of 0.03 6 0.08 mm for overbite, which was the primary outcome in this study. Other linear measurement errors were less than 1 mm. The error in the angular measurements assessing the incisor position was about 1 . The measurement error for the mandibular plane angle was 0.3 6 1.2 . The details of the intraexaminer analysis are reported in Table I. Table II summarizes the pretreatment cephalometric measurements. A detailed summary of cephalometric values is presented in the Appendix (Tables I-III). The Invisalign appliance maintained overbite in patients with normal pretreatment overbite. The anterior vertical dimension in patients with normal pretreatment overbite showed minimal change (Fig 2). The median overbite change was 0.3 mm in
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this group. Moreover, our results suggested minor proclinations of the maxillary and mandibular incisors that were only statistically significant for the maxillary incisors (DU1-NA 5 0.7 and DL1-NB 5 0.6 ). The anterior facial height increased by 0.7 mm, which was a statistically significant change. However, this change was within the range of measurement error. The posterior vertical dimension, similar to the anterior vertical dimension, was largely maintained in the normal overbite group. The median mandibular plane angle change was 0.4 , within the range of measurement error. The Invisalign appliance reduced the overbite in patients with pretreatment deepbite. We observed a 1.5-mm median opening of the overbite in the deepbite patients. The primary mechanism responsible for reducing overbite in this group seemed to be proclination of the mandibular incisors and intrusion of the maxillary incisors (Fig 3). Our results suggested that the mandibular first and second molars were extruded by 0.5 mm on average, within the range of measurement error. Similar changes were detected in the mandibular plane angle (Appendix Table II). Taken together, it appears that overbite improves in patients with pretreatment deepbite. Proclination of the mandibular incisors was the main mechanism of bite opening. The Invisalign appliance deepened the overbite in patients with pretreatment open bite.
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Fig 2. Vertical dimension changes in normal overbite patients treated with the Invisalign appliance (n 5 68). Lateral cephalometric radiographs of adults with pretreatment normal overbite were analyzed. The box plots represent changes between the initial and final cephalometric measurements, which examined anterior and posterior vertical dimension changes. Details of these measurements are presented in the Appendix. The Invisalign appliance appeared to minimally affect the anterior and posterior vertical dimensions.
Overbite improved in all patients with pretreatment open bite (Fig 4), with a median deepening of 1.5 mm (Appendix Table III). Overbite correction in these patients was primarily accomplished by extrusion of the maxillary and mandibular incisors (DU1-PP 5 0.9 mm, DL1-MP 5 0.8 mm).
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Fig 3. Vertical dimension changes in deepbite patients treated with the Invisalign appliance (n 5 40). Lateral cephalometric radiographs of adults with pretreatment deepbite were analyzed. Changes in initial and final cephalometric measurements, which examined anterior and posterior vertical dimension, are shown in the box plots. Details of cephalometric measurements are presented in the Appendix. The Invisalign appliance appeared to normalize the overbite primarily through proclination of the mandibular incisors and intrusion of the maxillary incisors. Mandibular molars were also slightly extruded.
No significant changes were detected in linear measurements of the posterior vertical dimension in patients with pretreatment open bite (Appendix Table III). Moreover, the mandibular plane angle changes were insignificant (DSN-MP 5 0.3 ).
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maintain the overbite in patients with normal pretreatment overbite were cutting off the terminal portion of the aligners distal to the first molars and maintaining the curve of Spee. To correct the deepbite, the study orthodontists used overbite overcorrection, leveling the curve of Spee, and virtual bite ramps. Using attachments to extrude incisors was a common strategy among the 3 orthodontists to manage anterior open bite. DISCUSSION
Fig 4. Vertical dimension changes in open-bite patients treated with the Invisalign appliance (n 5 12). Lateral cephalometric radiographs of 12 adults with pretreatment open bite were analyzed. To examine changes in the anterior and posterior vertical dimension, differences between initial and final cephalometric measurements were analyzed and are presented in the box plots. Details of cephalometric measurements are reported in the Appendix. The Invisalign appliance reduced anterior overbite by extrusion of the maxillary and mandibular incisors.
Similar treatment strategies were reported to manage overbite with the Invisalign appliance. A summary of the responses from the questionnaires filled out by the 3 practitioners is presented in Table III. Two common approaches that these clinicians used to
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The idea to incrementally move teeth with removable clear appliances was introduced in the 1970s.22 In 1999, Align Technology introduced the Invisalign technique, which used virtual digital technology to sequentially reposition the teeth to their correct locations.1 Plastic shells were then manufactured based on the sequential models. The Invisalign appliance has been greatly improved over the last 16 years. Nonetheless, our understanding of the appliance is largely limited to marketing claims from Align Technology and some case reports in the orthodontic literature.23 A recent systematic review on the efficiency of clear aligners in controlling orthodontic tooth movement identified 11 publications from 2000 to 2014.23 Six of these studies had a moderate risk of bias, whereas the risk of bias in the other studies was unclear. Therefore, one could reason that studies with large sample sizes and stringent research designs are required to better understand how the Invisalign appliance corrects malocclusions. To this end, we report on management of overbite with the Invisalign appliance using the records of consecutively treated patients from 3 private practices. The first aim of this study was to investigate the control of overbite with the Invisalign appliance in patients with normal pretreatment overbite. Our results suggest that the Invisalign appliance is typically successful in maintaining the anterior and posterior vertical dimension in these patients (Fig 5). This finding contradicts the common notion among clinicians that the Invisalign appliance deepens the bite. The assumption that the Invisalign appliance deepens the overbite is often supported anecdotally by a practitioner's daily experience, as well as by an early study that suggested that the Invisalign appliance intrudes the posterior teeth during treatment, thereby increasing the overbite.10 Our results indicate a trend of minor extrusion of posterior teeth in patients with normal overbite. Improvements in the Invisalign technique, such as virtual bite ramps, could be partly
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Table III. Treatment strategies to manage overbite Normal overbite Practitioner Virtual bite ramp A Cut off terminal molars or premolars Cut distal to the canine in treatmentinduced postopen bite, sometimes along with vertical elastics
Deepbite Virtual bite ramp Vertical posterior elastics No contacts on incisors Overcorrection of overbite Level curve of Spee
Open bite Attachments for extrusion of anterior teeth Attachments for intrusion of posterior teeth
Practitioner Trim distal aspect of second molars Do not use virtual bite ramps B
Virtual bite ramps Sometime no contacts on incisors Overcorrection of overbite Use overcorrecting aligners
Attachment for extrusion of incisors Extra thickness of plastics covering the posterior teeth Overcorrection of overbite Clenching exercise to intrude posterior teeth
Practitioner Maintain curve of Spee C Maintain positive occlusal contacts on posterior teeth
Level curve of Spee by extruding mandibular premolars and intruding mandibular incisors Level curve of Wilson
Fig 5. Overbite changes in patients with normal pretreatment deepbites and open bites (n 5 120). Cephalometric analyses were used to determine the overbite changes in patients treated with the Invisalign appliance. The box plot represents overbite changes among patients with normal overbite, deepbite, and open bite. The KruskalWallis analysis indicated that overbite changes in the 3 group were statistically significant (P 5 0.0001).
responsible for maintaining posterior vertical dimension, despite the potential bite-block effect of this appliance. An alternative explanation could be the
Attachment for extrusion of incisors (1-1.5 mm maximum) Intrusion of posterior maxillary and mandibular teeth
use of treatment strategies by orthodontists to prevent deepening of the overbite. The second aim of this study was to determine the effectiveness of the Invisalign appliance in correcting deepbites and open bites. Our findings from deepbite patients indicate that the anterior vertical dimension was improved in the majority of these patients (Fig 5). To our knowledge, this is the first report of a large consecutively treated sample of patients providing evidence that the Invisalign appliance is effective for correcting overbite in patients with deepbite. Nonetheless, some of the more severe deepbites in our study were not corrected to normal overbite values. Moreover, our subjects were all treated before the introduction of Invisalign's G5 technology specifically designed to treat patients with deepbite.1 Our cephalometric analyses to determine the mechanism by which the Invisalign appliance corrects deepbites suggests that proclination of mandibular incisors, along with intrusion of maxillary incisors and extrusion of mandibular molars, is the primary source of deepbite correction with the Invisalign appliance. These findings contradict the recommendation by a recent systematic review suggesting that the Invisalign appliance can only be used to treat mild deepbites.23 Part of the second aim of this study concentrated on patients with pretreatment open bites. We found that the Invisalign appliance appears to be successful in improving the overbite in patients with moderate anterior open bite (Fig 5). Additionally, these corrections were mainly linked to extrusion of the incisors. A systematic review has suggested that the Invisalign appliance cannot be relied on to correct open bites,23 based on a
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Fig 6. Scatterplot showing posttreatment overbite as a function of pretreatment overbite (n 5 120). Overbites measured in pretreatment and posttreatment cephalometric radiographs were plotted to examine the posttreatment overbite association with pretreatment overbite. This plot shows that patients with normal overbite (green dots) stay in the normal overbite range (gray zone). Additionally, our results indicate that overbite improved in all patients with deepbites (blue dots) and open bites (red dots), and that most of these patients achieved an overbite between 0 and 4 mm, which could be considered to be within the range of normal overbite.
study that reported only partial success in extrusion of anterior teeth with the Invisalign appliance.24 Our study is somewhat consistent with this finding, since our open-bite patients had only mild to moderate open bites, and they did not all achieve a positive overbite at the end of treatment. The results of our second aim indicated that overbite was corrected to normal values in most patients (Fig 6). Overbite in most patients with normal pretreatment overbite remained in the normal range (Fig 6). The third aim of the study was to identify the effectiveness of treatment strategies often used to maintain or correct overbite with the Invisalign appliance. We could not collect complete patient-specific information used to correct or control overbite in our studied sample. We learned that the practitioners have routine strategies, which are often not documented completely in the patient records. Nonetheless, it would seem that these strategies (Table III) are usually effective in maintaining or achieving normal anterior vertical dimensions. A recent systematic review on the effectiveness of the Invisalign appliance recommended that
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randomized clinical trials with a rigorous methodology should be conducted to determine its effectiveness.23 Although we agree with the authors, 1 essential barrier to conducting randomized clinical trials to evaluate the effectiveness of the Invisalign appliance is the lack of available funding. Therefore, at this time, well-designed retrospective studies might improve our knowledge until randomized trials can be performed. Our results suggested that about 1.5 mm of overbite improvement can be expected when the Invisalign appliance is used in deepbite patients. A previous systematic review on the stability of deepbite correction reported an average of 3 mm overbite correction with fixed appliances.13 Our result of a 1.5-mm median correction in open-bite patients is half of the reported average open-bite correction with a nonsurgical fixed appliance approach.25 These comparisons may indicate that aligners can usually improve deepbites and open bites, but they might not accomplish as much correction as fixed appliances. Challenges in lateral cephalometric analysis were the primary limitation of this study.26 Inconsistent head positioning, movement during exposure, inconsistent exposures, magnification error, and landmark identification are all potential challenges in studies with lateral cephalometric radiographs. To reduce potential measurement error and bias, we opted to use Dolphin Imaging software for our cephalometric analyses. This allowed us to reduce the potential error to only landmark identification, since the software automatically calculates the linear and angular measurements.21 All pretreatment and posttreatment cephalometric radiographs were taken using the same cephalometric x-ray machines in each of the 3 practices; this helped to further reduce measurement error. Additionally, landmark identifications on pretreatment and posttreatment radiographs for each patient were sequentially performed to minimize landmark identification error. The second limitation of this study was that almost 50% of screened patients were not included because of the absence of posttreatment cephalometric radiographs. It is unknown whether this might have introduced selection bias to this study. The small sample size for the open-bite group is the third limitation of this study. Most of the screened openbite patients had surgical treatment plans, which eliminated them from our study. Further studies with larger samples of open-bite patients are needed to verify our findings. Finally, all 3 practitioners have considerable experience with the Invisalign appliance. This is not necessarily a limitation, but it is possible that the results in their
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patients may be better than those achieved by less experienced clinicians. CONCLUSIONS
Our findings indicate that the Invisalign appliance is relatively successful in managing overbite. It maintains the overbite in patients with normal overbite. Additionally, these results did not support the idea that posterior teeth intrude during treatment with the Invisalign appliance. This study also suggests that the Invisalign appliance improves deepbites primarily by proclination of the mandibular incisors. Our results indicate that the Invisalign appliance corrects mild to moderate anterior open bites, primarily through incisor extrusion. ACKNOWLEDGMENTS
We thank the team members of the private orthodontic practices that provided the sample for this study and the patients whose records allowed us to conduct this study. SUPPLEMENTARY DATA
Supplementary data related to this article can be found online at http://dx.doi.org/10.1016/j.ajodo. 2016.09.022. REFERENCES 1. System for incrementally moving teeth. Santa Clara, Calif: Align Technology; 1998. 2. Joffe L. Invisalign: early experiences. J Orthod 2003;30:348-52. 3. Lingenbrink JC, King G, Bollen AM, Hujoel P, Huang G, OrsiniAlcalde G. Quality of life comparison between clear removable and conventional orthodontics. J Dent Res 2002;81(suppl)434. 4. Bollen AM, Huang G, King G, Hujoel P, Ma T. Activation time and material stiffness of sequential removable orthodontic appliances. Part 1: ability to complete treatment. Am J Orthod Dentofacial Orthop 2003;124:496-501. 5. Phan X, Ling PH. Clinical limitations of Invisalign. J Can Dent Assoc 2007;73:263-6. 6. Vlaskalic V, Boyd R. Orthodontic treatment of a mildly crowded malocclusion using the Invisalign system. Aust Orthod J 2001; 17:41-6. 7. Boyd RL. Complex orthodontic treatment using a new protocol for the Invisalign appliance. J Clin Orthod 2007;41:525-47.
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8. Castroflorio T, Garino F, Lazzaro A, Debernardi C. Upper-incisor root control with Invisalign appliances. J Clin Orthod 2013;47: 346-51. 9. Guarneri MP, Oliverio T, Silvestre I, Lombardo L, Siciliani G. Open bite treatment using clear aligners. Angle Orthod 2013; 83:913-9. 10. Boyd RL, Miller RJ, Vlaskalic V. The Invisalign system in adult orthodontics: mild crowding and space closure cases. J Clin Orthod 2000;34:203-12. 11. Kuster R, Ingervall B. The effect of treatment of skeletal open bite with two types of bite-blocks. Eur J Orthod 1992;14: 489-99. 12. Tuncay OC. The Invisalign system. Chicago: Quintessence; 2006. 13. Huang GJ, Bates SB, Ehlert AA, Whiting DP, Chen SS, Bollen AM. Stability of deep-bite correction: a systematic review. J World Fed Orthod 2012;1:e89-96. 14. Jacobson A, Jacobson RL. Radiographic cephalometry. Chicago: Quintessence; 2006. 15. Downs WB. Analysis of the dentofacial profile. Angle Orthod 1956; 26:191-212. 16. American Board of Orthodontics. Construction of the mandibular plane. Available at: https://www.americanboardortho.com. Accessed February 15, 2016. 17. Burke M, Jacobson A. Vertical changes in high-angle Class II, division 1 patients treated with cervical or occipital pull headgear. Am J Orthod Dentofacial Orthop 1992;102:501-8. 18. Bishara SE, Peterson LC, Bishara EC. Changes in facial dimensions and relationships between the ages of 5 and 25 years. Am J Orthod 1984;85:238-52. 19. Steiner CC. Cephalometrics for you and me. Am J Orthod 1953;39: 729-55. 20. McNamara JA. A method of cephalometric evaluation. Am J Orthod 1984;86:449-69. 21. Erkan M, Gurel HG, Nur M, Demirel B. Reliability of four different computerized cephalometric analysis programs. Eur J Orthod 2012;34:318-21. 22. Ponitz RJ. Invisible retainers. Am J Orthod 1971;59:266-72. 23. Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL. Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod 2015;85:881-9. 24. Kravitz ND, Kusnoto B, BeGole E, Obrez A, Agran B. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. Am J Orthod Dentofacial Orthop 2009;135:27-35. 25. Greenlee GM, Huang GJ, Chen SS, Chen J, Koepsell T, Hujoel P. Stability of treatment for anterior open-bite malocclusion: a meta-analysis. Am J Orthod Dentofacial Orthop 2011;139:154-69. 26. Houston WJ, Maher RE, McElroy D, Sherriff M. Sources of error in measurements from cephalometric radiographs. Eur J Orthod 1986;8:149-51.
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Appendix Table I. Cephalometric analysis of patients with pretreatment normal overbite treated with the Invisalign
appliance (n 5 68)
Mean Measurements Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
T0
T1
2.3 27.9 41.0 65.4
1.9 28.0 41.1 66.1
19.9 25.9
Median D
SD
Minimum
D
T0
T1
D
T0
T1
1.7 27.8 41.1 66.1
0.3 0.0 0.1 0.7
1.1 2.8 3.3 5.0
1.0 2.9 3.3 5.3
1.0 1.1 1.0 1.8
0.2 20.3 34.0 51.4
0.2 20.9 34.2 53.2
19.1 25.4
18.8 25.7
0.7 0.6
5.9 5.9
5.3 4.6
5.4 4.8
5.9 11.4
0.2 0.3 0.1 0.2 0.3
22.4 32.5 19.9 30.3 87.6
22.1 32.3 19.6 29.9 88.0
0.2 0.4 0.1 0.4 0.3
2.3 2.8 2.7 2.9 7.2
2.4 2.9 2.8 2.9 7.0
0.9 1.0 0.8 1.2 1.6
0.3
29.2
29.5
0.4
7.1
7.0
1.6
T0
T1
0.4 0.1 0.1 0.7
2.3 27.7 41.3 65.9
18.2 26.0
1.7 0.1
22.3 32.4 19.7 29.9 86.9
22.5 32.7 19.7 30.1 87.2
29.6
29.9
Wilcoxon signed rank
Maximum D
T0
T1
D
P value
2.6 2.2 2.3 3.5
3.9 34.5 49.0 75.6
4.0 35.0 49.2 76.9
3.1 3.1 2.4 5.0
0.0012* 0.4824 0.6554 0.0032*
2.7 8.7
17.7 15.1
35.6 51.6
30.4 42.3
8.0 9.3
0.0454* 0.5311
15.8 25.7 13.2 23.1 72.4
16.5 26.8 11.6 22.8 70.5
2.2 2.1 2.4 4.0 3.8
30.4 38.2 29.5 36.4 103.3
30.4 38.4 29.4 36.6 102.1
3.3 2.1 1.6 2.3 3.3
0.0651 0.0228* 0.3552 0.0406* 0.1228
13.2
15.4
4.1
53.1
50.4
4.4
0.0935
Summary of linear and angular cephalometric measurements for patients with normal overbite. P values and 95% confidence intervals were calculated using the Wilcoxon signed rank test at P 5 0.05. T0, Pretreatment; T1, posttreatment; D, pretreatment to posttreatment changes. U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar. *Statistically significant at the P 5 0.05.
Appendix Table II. Cephalometric analysis of patients with pre-treatment deepbite treated with the Invisalign appli-
ance (n 5 40)
Mean Measurements Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
T0
T1
Median D
T0
T1
SD
Minimum
D
T0
T1
D
T0
1.0 3.4 4.3 6.9
0.9 3.3 4.4 6.8
0.9 1.1 1.3 1.7
4.0 0.9 22.4 22.7 32.9 33.7 53.5 55.3
5.3 3.7 29.0 28.6 41.1 41.2 65.0 66.0
1.6 0.4 0.0 1.0
5.1 3.6 29.5 28.4 40.6 41.4 64.2 64.9
1.5 0.5 0.0 0.9
12.8 13.3 21.7 24.2
0.4 2.5
12.7 12.9 20.1 23.4
0.5 6.2 1.6 8.8
7.4 5.5 7.9 5.8
21.9 32.3 18.0 29.3 86.6
21.8 32.7 18.4 29.7 87.2
0.1 0.4 0.4 0.4 0.7
21.8 31.5 17.9 28.8 85.1
0.1 0.5 0.2 0.5 0.7
3.2 3.3 3.3 3.1 8.5
28.9 29.4
0.5
29.9 30.6
21.3 32.6 17.9 29.1 86.2
3.2 3.3 3.9 3.1 8.1
0.4 7.1
0.9 1.0 1.4 1.3 1.5
7.0 1.0
T1
Wilcoxon Signed rank
Maximum D
T0
T1
D
P value
3.1 2.1 3.9 2.6
8.0 35.6 53.4 81.0
6.2 37.9 53.0 80.9
0.1 3.2 3.1 4.7
0.0001* 0.0259 0.8718 0.0009*
30.1 42.8
28.1 42.3
18.1 17.7
0.8350 0.0201*
29.1 29.1 39.2 39.5 26.0 26.6 36.3 37.6 107.4 108.9
1.5 2.3 4.8 4.0 4.2
0.9458 0.0164* 0.2136 0.0489* 0.0652
3.2
0.0104*
0.1 4.6
0.3 7.3
8.6 7.7
15.6 26.5 7.7 24.1 74.1
16.3 26.9 11.8 24.5 74.1
2.3 1.2 1.8 2.3 3.2
10.7 12.2
1.3
44.7
44.6
Summary of linear and angular cephalometric measurements for patients with deepbite. P values and 95% confidence intervals were calculated using the Wilcoxon signed rank test at P 5 0.05. T0, Pretreatment; T1, posttreatment; D, pretreatment to posttreatment changes. U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar. *Statistically significant at the P 5 0.05.
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Appendix Table III. Cephalometric analysis of patients with pretreatment open bite treated with the Invisalign appli-
ance (n 5 12)
Mean Measurements Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
Median D
T0
1.1 0.2 29.6 30.3 42.8 43.5 71.6 71.6
1.3 0.7 0.8 0.0
22.3 20.9 30.2 30.1 23.5 33.1 19.9 30.0 84.2
SD
Minimum
Wilcoxon signed rank
Maximum
D
T0
T1
D
T0
T1
D
T0
T1
D
P value
0.5 0.1 28.9 28.7 43.5 43.5 69.8 69.4
1.5 0.9 0.8 0.0
1.0 3.7 3.6 6.9
0.9 3.8 4.1 7.4
0.6 1.2 1.0 1.5
2.4 24.9 38.0 61.8
1.5 25.4 37.3 61.1
0.0 1.5 0.7 2.2
0.1 35.9 49.4 82.1
1.4 36.5 52.4 82.8
2.2 2.7 3.0 2.8
0.005* 0.129 0.029* 0.878
1.4 0.1
25.1 22.7 27.6 30.0
2.3 1.2
7.6 6.6 4.7 6.0 5.7 2.9
11.0 22.7
6.5 20.2
9.2 6.0
34.3 37.4
30.2 6.4 37.6 3.6
23.6 33.3 19.9 30.2 84.2
0.1 0.2 0.0 0.2 0.1
22.9 33.6 19.6 29.8 84.8
22.8 32.8 19.6 29.6 84.2
0.1 0.1 0.2 0.3 0.0
3.4 2.9 3.5 2.8 7.2
1.0 1.1 0.8 1.4 1.6
19.2 29.4 15.7 27.0 75.6
18.4 29.2 15.4 25.3 75.0
1.7 28.8 29.0 1.1 40.0 42.6 0.9 25.8 25.6 1.7 37.4 40.4 3.2 101.8 102.1
36.5 36.9
0.4
36.1 36.2
0.3
8.0 7.0 1.7
25.7
26.6
2.1
T0
T1
T1
3.6 3.7 3.6 3.9 7.5
51.5
0.248 1
1.6 2.6 1.4 3.0 2.1
0.799 0.929 0.790 0.965 0.799
51.5 3.5
0.445
Summary of linear and angular cephalometric measurements for patients with openbite. P values and 95% confidence intervals were calculated using the Wilcoxon signed rank test at P 5 0.05. T0, Pretreatment; T1, posttreatment; D, pretreatment to posttreatment changes. U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar. *Statistically significant at the P 5 0.05.
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Management of overbite with the Invisalign appliance Roozbeh Khosravi,a Bobby Cohanim,a Philippe Hujoel,b Sam Daher,c Michelle Neal,d Weitao Liu,a and Greg Huanga Seattle and Kirkland, Wash, and Vancouver, British Columbia, Canada
Introduction: Most of the published literature on the management of overbite with the Invisalign appliance (Align Technology, Santa Clara, Calif) consists of case reports and case series. Methods: In this retrospective study of 120 patients, we sought to assess the nature of overbite changes with the Invisalign appliance. Records were collected from 3 practitioners, all experienced with the Invisalign technique. The patients were consecutively treated adults (.18 years old) who underwent orthodontic treatment only with the Invisalign appliance. Patients with major transverse or anteroposterior changes or extraction treatment plans were excluded. The study sample included 68 patients with normal overbites, 40 with deepbites, and 12 with open bites. Their median age was 33 years, and 70% of the patients were women. Results: Cephalometric analyses indicated that the deepbite patients had a median overbite opening of 1.5 mm, whereas the open bite patients had a median deepening of 1.5 mm. The median change for the normal overbite patients was 0.3 mm. Changes in incisor position were responsible for most of the improvements in the deepbite and open bite groups. Minimal changes in molar vertical position and mandibular plane angle were noted. Conclusions: The Invisalign appliance appears to manage the vertical dimension relatively well, and the primary mechanism is via incisor movements. (Am J Orthod Dentofacial Orthop 2017;151:691-9)
T
he Invisalign appliance (Align Technology, Santa Clara, Calif) consists of a series of computerdesigned clear plastic shells that fit closely over the teeth and incrementally move the teeth to their correct position.1,2 Orthodontic treatment with the Invisalign appliance may be more esthetically appealing to some patients when compared with conventional fixed appliances; this partly explains the increasing demand for this treatment method.3 The Invisalign technique was initially proposed to treat mild orthodontic cases.2,4-6 Nonetheless, there are reports of complex orthodontic cases treated with the Invisalign appliance in the literature.7-9 For example, a recent study demonstrated the successful closure of a
a Department of Orthodontics, School of Dentistry, University of Washington, Seattle, Wash. b Department of Oral Health Sciences, School of Dentistry, University of Washington, Seattle, Wash. c Private practice, Vancouver, British Columbia, Canada. d Private practice, Kirkland, Wash. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Funded by the University of Washington Orthodontic Alumni Association. Address correspondence to: Roozbeh Khosravi, University of Washington, Department of Orthodontics, Box 357446, Room location: HSB-D5691959, NE Pacific St., Seattle, WA 98195; e-mail, [email protected]. Submitted, May 2016; revised and accepted, September 2016. 0889-5406/$36.00 http://dx.doi.org/10.1016/j.ajodo.2016.09.022
4-mm anterior open bite by extrusion of the anterior teeth using a series of 35 Invisalign aligners.9 Soon after the introduction of the Invisalign system in the late 1990s, practitioners noticed that the appliance commonly induced deepening of the overbite.10 It was suggested that aligners covering all posterior teeth could function as a bite-block, thereby intruding the posterior teeth. This would result in a reduction of the posterior vertical dimension and consequent deepening of the overbite.11 The Invisalign system has evolved over the last 16 years, and various strategies have been developed to better manage the vertical dimension. For example, an early strategy to prevent bite deepening was the removal of occlusal coverage on the second molars. Align Technology recently developed new treatment options including specially designed attachments and virtual bite ramps. Attachments are composite buttons attached to the labial surfaces of the teeth, and they come in various shapes to assist with tooth movement. Specifically, these attachments increase retention, transmit desirable force to the teeth, and support auxiliary functions such as placement of elastics.12 Virtual bite ramps function similar to bite plates or bite turbos. These bite ramps, incorporated into the maxillary aligner, contact the mandibular incisors to disocclude the posterior teeth when patients bring their teeth together. 691
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Despite these advancements in the Invisalign appliance, evidence supporting the effectiveness of these treatment modalities is limited to case reports and case series. Studies with larger samples and better designs are required to understand the mechanism by which the Invisalign appliance manages the vertical dimension. In this retrospective study, we sought to investigate the vertical dimension changes in patients with various pretreatment overbite relationships treated only with the Invisalign appliance. Moreover, we aimed to identify the dental and skeletal changes associated with bite closing or opening. See Supplemental Materials for a short video presentation about this study. MATERIAL AND METHODS
This study was approved by the institutional review board of the University of Washington. The study sample consisted of adult patients consecutively treated with the Invisalign appliance in 3 private orthodontic offices. Two practices were located in the greater Seattle area, Wash and one Vancouver, British Columbia. A total of 313 patient records were screened; records of 193 patients (62%) were excluded. The most common reason for exclusion was lack of final lateral cephalometric radiographs. The second most common reason was that the posterior teeth were out of occlusion when the radiograph was taken. The study sample was stratified into groups of normal overbite, deepbite, and open bite based on the pretreatment overbite measured on cephalometric radiographs. Normal overbite was defined as pretreatment overbite ranging from 0 mm to less than 4 mm. Patients with 4 mm or greater pretreatment overbite were classified in the deepbite group.13 The open bite group included patients with negative pretreatment overbite. Inclusion criteria were (1) the patient was 18 years or older at the beginning of treatment, (2) the treatment was completed between January 1, 2010, and January 1, 2014, (3) 11 to 40 aligners were used for each arch, (4) a maximum of 3 revision sets of aligners was used, (5) the treatment plan was nonextraction, (6) the molar anteroposterior occlusal relationship was not changed (eg, no Class II to Class I occlusion change), (7) posterior-transverse relationships were not changed significantly (eg, no correction of posterior crossbite), (8) fixed appliances were not used, and (9) the patient had good-quality pretreatment and posttreatment cephalometric radiographs. Two investigators (R.K. and W.L.) screened consecutively treated patients at each orthodontic office. Each subject eligible for the study was then assigned an anonymous identification number, and the records were deidentified with these numbers.
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The collected records included (1) pretreatment and posttreatment lateral cephalometric radiographs, (2) the Invisalign Treatment Overview form with information regarding number and location of attachments as well as potential interproximal reduction plans, (3) patient's age at the start of the treatment, (4) patient's sex, and (5) questionnaires filled out by the clinicians regarding their treatment strategies. Deidentified lateral cephalometric radiographs were imported into software (Dolphin Imaging, Chatsworth, Calif) to perform cephalometric analyses. Seventeen landmarks were marked on the initial and final lateral cephalometric radiographs. We opted to mark the landmarks for the pretreatment and posttreatment radiographs of each patient sequentially to reduce potential landmark identification error. The software then calculated the linear and angular measurements, which were used in our statistical analyses. To assess the changes during treatment, 9 linear and 3 angular measurements were measured (Fig 1). Palatal, occlusal, and mandibular planes were used as the reference lines. The palatal plane was defined as a straight line passing through the anterior and posterior nasal spine points.14 The occlusal plane was defined as a straight line drawn through the bisection of the mesiobuccal cusp tips of the first molars and the bisection of the incisal edge of the most anterior central incisors.15 The mandibular plane was defined as a straight line connecting menton to constructed gonion.16 To assess the changes in the anterior vertical dimensions, we made these measurements. The linear measurements were overbite, defined as the shortest vertical distance between the tip of the maxillary incisor and the tip of the mandibular incisor perpendicular to the occlusal plane, and the vertical position of the incisors, defined as the shortest distance between the maxillary and mandibular incisors to the palatal and mandibular planes, respectively (reference lines).17 Additionally, the anterior facial linear height was measured: defined as the shortest distance between defined as the shortest distance between anterior nasal spine and menton was measured.18 The angular measurements were the angle between the maxillary incisor's long axis and the nasion-A point line and the angle between the mandibular incisor's long axis and the nasion-B point line.19 To assess the changes in the posterior vertical dimension, several linear and angular measurements were measured. The vertical dimension changes of the maxillary and mandibular molars were determined using linear measurements. The shortest distances between the palatal plane and the maxillary first and second molars' mesiobuccal cusp tips were measured.
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Fig 1. Linear and angular cephalometric measurements used to assess the anterior and posterior vertical dimension changes in patients who underwent orthodontic treatment with the Invisalign appliance. A, Linear measurements: 1, overbite; 2, maxillary incisor tooth tip to palatal plane; 3, mandibular incisor tooth tip to mandibular plane; 4, anterior facial height; 5, maxillary molar mesial cusp tip to palatal plane; 6, mandibular molar mesial cusp tip to mandibular plane; 7, posterior facial height. B, Angular measurements: 8, maxillary incisor axis to nasion-A-point; 9, mandibular incisor axis to nasion-B-point; 10, mandibular plane angle.
Similarly, the shortest distances between the mandibular first and second molars' mesiobuccal cusp tips to the mandibular plane were measured.17 The posterior facial height was measured as the shortest distance between constructed gonion and articulare.18 The angle between the mandibular plane and the sella-nasion reference line was measured.20 Approximately 2 weeks after the initial measurements we, 10 cephalometric radiographs were randomly selected by the R statistical package (version 2.11.1; RStudio, Boston, Mass) through RStudio (version 0.99.491) for the measurement error analysis. Landmarks on these lateral cephalometric radiographs were reidentified, and the measurements were recalculated using the Dolphin Imaging software. The measurement error was reported as the mean difference between the initial and retraced cephalometric values.21 Statistical analysis
Statistical analyses were conducted in 2 phases. Initially, descriptive analyses were performed to examine the cephalometric measurements of the pretreatment and posttreatment radiographs in all 3 groups. Detailed descriptive analyses are presented in the Appendix. To examine the difference between cephalometric measurements before and after treatment, we used
Table I. Intra-rater reliability for the cephalometric analysis (n 5 10) Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
Mean
SD
0.03 0.35 0.14 0.13
0.08 0.73 1.16 1.24
1.12 0.94
2.19 2.03
0 0.56 0.2 0.18 0.43
0.54 0.96 0.83 0.74 1.28
0.31
1.16
U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar.
the nonparametric Wilcoxon signed rank test at the P 5 0.05 level of significance. We opted to use this analysis because the majority of our variables were not normally distributed. Additionally, KruskalWallis analysis at the P 5 0.05 level of significance was used to investigate overbite changes in the 3 groups.
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Table II. Pretreatment patient characteristics Normal overbite (n 5 68) Demographics Age (y) Incisor position (mm) Overbite Overjet U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
Deepbite (n 5 40)
Median 32
Mean 34
SD 12
2.3 3.3 27.7 41.3 65.9
2.3 3.3 27.9 41.0 65.4
19.1 25.4
Open bite (n 5 12)
Median 38
Mean 40
SD 14
Median 30
Mean 34
SD 11
1.1 1.1 2.8 3.3 5.0
5.1 3.9 29.5 40.6 64.2
5.3 4.0 29.0 41.1 65.0
1.0 1.2 3.4 4.3 6.9
0.8 2.3 28.9 43.5 69.8
1.1 2.8 29.6 43.2 72.1
0.9 2.2 3.6 4.1 7.3
19.9 25.9
5.9 5.9
12.7 20.1
12.8 21.7
6.2 8.8
25.2 27.6
23.0 30.4
8.2 6.2
22.4 32.5 19.9 30.3 87.6
22.3 32.4 19.7 29.9 86.9
2.3 2.8 2.7 2.9 7.2
21.8 31.5 17.9 28.8 85.1
21.9 32.3 18.0 29.3 86.6
3.2 3.3 3.9 3.1 8.1
22.9 31.8 19.6 29.2 84.8
23.7 33.3 19.9 30.3 85.6
3.7 3.8 3.8 3.7 9.0
29.2
29.6
7.1
29.9
28.9
7.1
34.3
35.6
8.7
U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar.
The statistical analyses were conducted using the R statistical package (RStudio). RESULTS
A total of 120 patients (normal overbite group, 68; deepbite group, 40; open-bite group, 12) were included in this study. Their median age was 33 years (interquartile range 5 17), and 70% of the patients were women. Specifically, 46 (67%) patients in the normal overbite group, 28 (70%) patients in the deepbite group, and 8 (66%) patients in the open-bite group were women. The intraexaminer error analysis indicated a measurement error of 0.03 6 0.08 mm for overbite, which was the primary outcome in this study. Other linear measurement errors were less than 1 mm. The error in the angular measurements assessing the incisor position was about 1 . The measurement error for the mandibular plane angle was 0.3 6 1.2 . The details of the intraexaminer analysis are reported in Table I. Table II summarizes the pretreatment cephalometric measurements. A detailed summary of cephalometric values is presented in the Appendix (Tables I-III). The Invisalign appliance maintained overbite in patients with normal pretreatment overbite. The anterior vertical dimension in patients with normal pretreatment overbite showed minimal change (Fig 2). The median overbite change was 0.3 mm in
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this group. Moreover, our results suggested minor proclinations of the maxillary and mandibular incisors that were only statistically significant for the maxillary incisors (DU1-NA 5 0.7 and DL1-NB 5 0.6 ). The anterior facial height increased by 0.7 mm, which was a statistically significant change. However, this change was within the range of measurement error. The posterior vertical dimension, similar to the anterior vertical dimension, was largely maintained in the normal overbite group. The median mandibular plane angle change was 0.4 , within the range of measurement error. The Invisalign appliance reduced the overbite in patients with pretreatment deepbite. We observed a 1.5-mm median opening of the overbite in the deepbite patients. The primary mechanism responsible for reducing overbite in this group seemed to be proclination of the mandibular incisors and intrusion of the maxillary incisors (Fig 3). Our results suggested that the mandibular first and second molars were extruded by 0.5 mm on average, within the range of measurement error. Similar changes were detected in the mandibular plane angle (Appendix Table II). Taken together, it appears that overbite improves in patients with pretreatment deepbite. Proclination of the mandibular incisors was the main mechanism of bite opening. The Invisalign appliance deepened the overbite in patients with pretreatment open bite.
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Fig 2. Vertical dimension changes in normal overbite patients treated with the Invisalign appliance (n 5 68). Lateral cephalometric radiographs of adults with pretreatment normal overbite were analyzed. The box plots represent changes between the initial and final cephalometric measurements, which examined anterior and posterior vertical dimension changes. Details of these measurements are presented in the Appendix. The Invisalign appliance appeared to minimally affect the anterior and posterior vertical dimensions.
Overbite improved in all patients with pretreatment open bite (Fig 4), with a median deepening of 1.5 mm (Appendix Table III). Overbite correction in these patients was primarily accomplished by extrusion of the maxillary and mandibular incisors (DU1-PP 5 0.9 mm, DL1-MP 5 0.8 mm).
695
Fig 3. Vertical dimension changes in deepbite patients treated with the Invisalign appliance (n 5 40). Lateral cephalometric radiographs of adults with pretreatment deepbite were analyzed. Changes in initial and final cephalometric measurements, which examined anterior and posterior vertical dimension, are shown in the box plots. Details of cephalometric measurements are presented in the Appendix. The Invisalign appliance appeared to normalize the overbite primarily through proclination of the mandibular incisors and intrusion of the maxillary incisors. Mandibular molars were also slightly extruded.
No significant changes were detected in linear measurements of the posterior vertical dimension in patients with pretreatment open bite (Appendix Table III). Moreover, the mandibular plane angle changes were insignificant (DSN-MP 5 0.3 ).
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maintain the overbite in patients with normal pretreatment overbite were cutting off the terminal portion of the aligners distal to the first molars and maintaining the curve of Spee. To correct the deepbite, the study orthodontists used overbite overcorrection, leveling the curve of Spee, and virtual bite ramps. Using attachments to extrude incisors was a common strategy among the 3 orthodontists to manage anterior open bite. DISCUSSION
Fig 4. Vertical dimension changes in open-bite patients treated with the Invisalign appliance (n 5 12). Lateral cephalometric radiographs of 12 adults with pretreatment open bite were analyzed. To examine changes in the anterior and posterior vertical dimension, differences between initial and final cephalometric measurements were analyzed and are presented in the box plots. Details of cephalometric measurements are reported in the Appendix. The Invisalign appliance reduced anterior overbite by extrusion of the maxillary and mandibular incisors.
Similar treatment strategies were reported to manage overbite with the Invisalign appliance. A summary of the responses from the questionnaires filled out by the 3 practitioners is presented in Table III. Two common approaches that these clinicians used to
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The idea to incrementally move teeth with removable clear appliances was introduced in the 1970s.22 In 1999, Align Technology introduced the Invisalign technique, which used virtual digital technology to sequentially reposition the teeth to their correct locations.1 Plastic shells were then manufactured based on the sequential models. The Invisalign appliance has been greatly improved over the last 16 years. Nonetheless, our understanding of the appliance is largely limited to marketing claims from Align Technology and some case reports in the orthodontic literature.23 A recent systematic review on the efficiency of clear aligners in controlling orthodontic tooth movement identified 11 publications from 2000 to 2014.23 Six of these studies had a moderate risk of bias, whereas the risk of bias in the other studies was unclear. Therefore, one could reason that studies with large sample sizes and stringent research designs are required to better understand how the Invisalign appliance corrects malocclusions. To this end, we report on management of overbite with the Invisalign appliance using the records of consecutively treated patients from 3 private practices. The first aim of this study was to investigate the control of overbite with the Invisalign appliance in patients with normal pretreatment overbite. Our results suggest that the Invisalign appliance is typically successful in maintaining the anterior and posterior vertical dimension in these patients (Fig 5). This finding contradicts the common notion among clinicians that the Invisalign appliance deepens the bite. The assumption that the Invisalign appliance deepens the overbite is often supported anecdotally by a practitioner's daily experience, as well as by an early study that suggested that the Invisalign appliance intrudes the posterior teeth during treatment, thereby increasing the overbite.10 Our results indicate a trend of minor extrusion of posterior teeth in patients with normal overbite. Improvements in the Invisalign technique, such as virtual bite ramps, could be partly
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Table III. Treatment strategies to manage overbite Normal overbite Practitioner Virtual bite ramp A Cut off terminal molars or premolars Cut distal to the canine in treatmentinduced postopen bite, sometimes along with vertical elastics
Deepbite Virtual bite ramp Vertical posterior elastics No contacts on incisors Overcorrection of overbite Level curve of Spee
Open bite Attachments for extrusion of anterior teeth Attachments for intrusion of posterior teeth
Practitioner Trim distal aspect of second molars Do not use virtual bite ramps B
Virtual bite ramps Sometime no contacts on incisors Overcorrection of overbite Use overcorrecting aligners
Attachment for extrusion of incisors Extra thickness of plastics covering the posterior teeth Overcorrection of overbite Clenching exercise to intrude posterior teeth
Practitioner Maintain curve of Spee C Maintain positive occlusal contacts on posterior teeth
Level curve of Spee by extruding mandibular premolars and intruding mandibular incisors Level curve of Wilson
Fig 5. Overbite changes in patients with normal pretreatment deepbites and open bites (n 5 120). Cephalometric analyses were used to determine the overbite changes in patients treated with the Invisalign appliance. The box plot represents overbite changes among patients with normal overbite, deepbite, and open bite. The KruskalWallis analysis indicated that overbite changes in the 3 group were statistically significant (P 5 0.0001).
responsible for maintaining posterior vertical dimension, despite the potential bite-block effect of this appliance. An alternative explanation could be the
Attachment for extrusion of incisors (1-1.5 mm maximum) Intrusion of posterior maxillary and mandibular teeth
use of treatment strategies by orthodontists to prevent deepening of the overbite. The second aim of this study was to determine the effectiveness of the Invisalign appliance in correcting deepbites and open bites. Our findings from deepbite patients indicate that the anterior vertical dimension was improved in the majority of these patients (Fig 5). To our knowledge, this is the first report of a large consecutively treated sample of patients providing evidence that the Invisalign appliance is effective for correcting overbite in patients with deepbite. Nonetheless, some of the more severe deepbites in our study were not corrected to normal overbite values. Moreover, our subjects were all treated before the introduction of Invisalign's G5 technology specifically designed to treat patients with deepbite.1 Our cephalometric analyses to determine the mechanism by which the Invisalign appliance corrects deepbites suggests that proclination of mandibular incisors, along with intrusion of maxillary incisors and extrusion of mandibular molars, is the primary source of deepbite correction with the Invisalign appliance. These findings contradict the recommendation by a recent systematic review suggesting that the Invisalign appliance can only be used to treat mild deepbites.23 Part of the second aim of this study concentrated on patients with pretreatment open bites. We found that the Invisalign appliance appears to be successful in improving the overbite in patients with moderate anterior open bite (Fig 5). Additionally, these corrections were mainly linked to extrusion of the incisors. A systematic review has suggested that the Invisalign appliance cannot be relied on to correct open bites,23 based on a
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Fig 6. Scatterplot showing posttreatment overbite as a function of pretreatment overbite (n 5 120). Overbites measured in pretreatment and posttreatment cephalometric radiographs were plotted to examine the posttreatment overbite association with pretreatment overbite. This plot shows that patients with normal overbite (green dots) stay in the normal overbite range (gray zone). Additionally, our results indicate that overbite improved in all patients with deepbites (blue dots) and open bites (red dots), and that most of these patients achieved an overbite between 0 and 4 mm, which could be considered to be within the range of normal overbite.
study that reported only partial success in extrusion of anterior teeth with the Invisalign appliance.24 Our study is somewhat consistent with this finding, since our open-bite patients had only mild to moderate open bites, and they did not all achieve a positive overbite at the end of treatment. The results of our second aim indicated that overbite was corrected to normal values in most patients (Fig 6). Overbite in most patients with normal pretreatment overbite remained in the normal range (Fig 6). The third aim of the study was to identify the effectiveness of treatment strategies often used to maintain or correct overbite with the Invisalign appliance. We could not collect complete patient-specific information used to correct or control overbite in our studied sample. We learned that the practitioners have routine strategies, which are often not documented completely in the patient records. Nonetheless, it would seem that these strategies (Table III) are usually effective in maintaining or achieving normal anterior vertical dimensions. A recent systematic review on the effectiveness of the Invisalign appliance recommended that
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randomized clinical trials with a rigorous methodology should be conducted to determine its effectiveness.23 Although we agree with the authors, 1 essential barrier to conducting randomized clinical trials to evaluate the effectiveness of the Invisalign appliance is the lack of available funding. Therefore, at this time, well-designed retrospective studies might improve our knowledge until randomized trials can be performed. Our results suggested that about 1.5 mm of overbite improvement can be expected when the Invisalign appliance is used in deepbite patients. A previous systematic review on the stability of deepbite correction reported an average of 3 mm overbite correction with fixed appliances.13 Our result of a 1.5-mm median correction in open-bite patients is half of the reported average open-bite correction with a nonsurgical fixed appliance approach.25 These comparisons may indicate that aligners can usually improve deepbites and open bites, but they might not accomplish as much correction as fixed appliances. Challenges in lateral cephalometric analysis were the primary limitation of this study.26 Inconsistent head positioning, movement during exposure, inconsistent exposures, magnification error, and landmark identification are all potential challenges in studies with lateral cephalometric radiographs. To reduce potential measurement error and bias, we opted to use Dolphin Imaging software for our cephalometric analyses. This allowed us to reduce the potential error to only landmark identification, since the software automatically calculates the linear and angular measurements.21 All pretreatment and posttreatment cephalometric radiographs were taken using the same cephalometric x-ray machines in each of the 3 practices; this helped to further reduce measurement error. Additionally, landmark identifications on pretreatment and posttreatment radiographs for each patient were sequentially performed to minimize landmark identification error. The second limitation of this study was that almost 50% of screened patients were not included because of the absence of posttreatment cephalometric radiographs. It is unknown whether this might have introduced selection bias to this study. The small sample size for the open-bite group is the third limitation of this study. Most of the screened openbite patients had surgical treatment plans, which eliminated them from our study. Further studies with larger samples of open-bite patients are needed to verify our findings. Finally, all 3 practitioners have considerable experience with the Invisalign appliance. This is not necessarily a limitation, but it is possible that the results in their
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patients may be better than those achieved by less experienced clinicians. CONCLUSIONS
Our findings indicate that the Invisalign appliance is relatively successful in managing overbite. It maintains the overbite in patients with normal overbite. Additionally, these results did not support the idea that posterior teeth intrude during treatment with the Invisalign appliance. This study also suggests that the Invisalign appliance improves deepbites primarily by proclination of the mandibular incisors. Our results indicate that the Invisalign appliance corrects mild to moderate anterior open bites, primarily through incisor extrusion. ACKNOWLEDGMENTS
We thank the team members of the private orthodontic practices that provided the sample for this study and the patients whose records allowed us to conduct this study. SUPPLEMENTARY DATA
Supplementary data related to this article can be found online at http://dx.doi.org/10.1016/j.ajodo. 2016.09.022. REFERENCES 1. System for incrementally moving teeth. Santa Clara, Calif: Align Technology; 1998. 2. Joffe L. Invisalign: early experiences. J Orthod 2003;30:348-52. 3. Lingenbrink JC, King G, Bollen AM, Hujoel P, Huang G, OrsiniAlcalde G. Quality of life comparison between clear removable and conventional orthodontics. J Dent Res 2002;81(suppl)434. 4. Bollen AM, Huang G, King G, Hujoel P, Ma T. Activation time and material stiffness of sequential removable orthodontic appliances. Part 1: ability to complete treatment. Am J Orthod Dentofacial Orthop 2003;124:496-501. 5. Phan X, Ling PH. Clinical limitations of Invisalign. J Can Dent Assoc 2007;73:263-6. 6. Vlaskalic V, Boyd R. Orthodontic treatment of a mildly crowded malocclusion using the Invisalign system. Aust Orthod J 2001; 17:41-6. 7. Boyd RL. Complex orthodontic treatment using a new protocol for the Invisalign appliance. J Clin Orthod 2007;41:525-47.
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8. Castroflorio T, Garino F, Lazzaro A, Debernardi C. Upper-incisor root control with Invisalign appliances. J Clin Orthod 2013;47: 346-51. 9. Guarneri MP, Oliverio T, Silvestre I, Lombardo L, Siciliani G. Open bite treatment using clear aligners. Angle Orthod 2013; 83:913-9. 10. Boyd RL, Miller RJ, Vlaskalic V. The Invisalign system in adult orthodontics: mild crowding and space closure cases. J Clin Orthod 2000;34:203-12. 11. Kuster R, Ingervall B. The effect of treatment of skeletal open bite with two types of bite-blocks. Eur J Orthod 1992;14: 489-99. 12. Tuncay OC. The Invisalign system. Chicago: Quintessence; 2006. 13. Huang GJ, Bates SB, Ehlert AA, Whiting DP, Chen SS, Bollen AM. Stability of deep-bite correction: a systematic review. J World Fed Orthod 2012;1:e89-96. 14. Jacobson A, Jacobson RL. Radiographic cephalometry. Chicago: Quintessence; 2006. 15. Downs WB. Analysis of the dentofacial profile. Angle Orthod 1956; 26:191-212. 16. American Board of Orthodontics. Construction of the mandibular plane. Available at: https://www.americanboardortho.com. Accessed February 15, 2016. 17. Burke M, Jacobson A. Vertical changes in high-angle Class II, division 1 patients treated with cervical or occipital pull headgear. Am J Orthod Dentofacial Orthop 1992;102:501-8. 18. Bishara SE, Peterson LC, Bishara EC. Changes in facial dimensions and relationships between the ages of 5 and 25 years. Am J Orthod 1984;85:238-52. 19. Steiner CC. Cephalometrics for you and me. Am J Orthod 1953;39: 729-55. 20. McNamara JA. A method of cephalometric evaluation. Am J Orthod 1984;86:449-69. 21. Erkan M, Gurel HG, Nur M, Demirel B. Reliability of four different computerized cephalometric analysis programs. Eur J Orthod 2012;34:318-21. 22. Ponitz RJ. Invisible retainers. Am J Orthod 1971;59:266-72. 23. Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL. Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod 2015;85:881-9. 24. Kravitz ND, Kusnoto B, BeGole E, Obrez A, Agran B. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. Am J Orthod Dentofacial Orthop 2009;135:27-35. 25. Greenlee GM, Huang GJ, Chen SS, Chen J, Koepsell T, Hujoel P. Stability of treatment for anterior open-bite malocclusion: a meta-analysis. Am J Orthod Dentofacial Orthop 2011;139:154-69. 26. Houston WJ, Maher RE, McElroy D, Sherriff M. Sources of error in measurements from cephalometric radiographs. Eur J Orthod 1986;8:149-51.
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Appendix Table I. Cephalometric analysis of patients with pretreatment normal overbite treated with the Invisalign
appliance (n 5 68)
Mean Measurements Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
T0
T1
2.3 27.9 41.0 65.4
1.9 28.0 41.1 66.1
19.9 25.9
Median D
SD
Minimum
D
T0
T1
D
T0
T1
1.7 27.8 41.1 66.1
0.3 0.0 0.1 0.7
1.1 2.8 3.3 5.0
1.0 2.9 3.3 5.3
1.0 1.1 1.0 1.8
0.2 20.3 34.0 51.4
0.2 20.9 34.2 53.2
19.1 25.4
18.8 25.7
0.7 0.6
5.9 5.9
5.3 4.6
5.4 4.8
5.9 11.4
0.2 0.3 0.1 0.2 0.3
22.4 32.5 19.9 30.3 87.6
22.1 32.3 19.6 29.9 88.0
0.2 0.4 0.1 0.4 0.3
2.3 2.8 2.7 2.9 7.2
2.4 2.9 2.8 2.9 7.0
0.9 1.0 0.8 1.2 1.6
0.3
29.2
29.5
0.4
7.1
7.0
1.6
T0
T1
0.4 0.1 0.1 0.7
2.3 27.7 41.3 65.9
18.2 26.0
1.7 0.1
22.3 32.4 19.7 29.9 86.9
22.5 32.7 19.7 30.1 87.2
29.6
29.9
Wilcoxon signed rank
Maximum D
T0
T1
D
P value
2.6 2.2 2.3 3.5
3.9 34.5 49.0 75.6
4.0 35.0 49.2 76.9
3.1 3.1 2.4 5.0
0.0012* 0.4824 0.6554 0.0032*
2.7 8.7
17.7 15.1
35.6 51.6
30.4 42.3
8.0 9.3
0.0454* 0.5311
15.8 25.7 13.2 23.1 72.4
16.5 26.8 11.6 22.8 70.5
2.2 2.1 2.4 4.0 3.8
30.4 38.2 29.5 36.4 103.3
30.4 38.4 29.4 36.6 102.1
3.3 2.1 1.6 2.3 3.3
0.0651 0.0228* 0.3552 0.0406* 0.1228
13.2
15.4
4.1
53.1
50.4
4.4
0.0935
Summary of linear and angular cephalometric measurements for patients with normal overbite. P values and 95% confidence intervals were calculated using the Wilcoxon signed rank test at P 5 0.05. T0, Pretreatment; T1, posttreatment; D, pretreatment to posttreatment changes. U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar. *Statistically significant at the P 5 0.05.
Appendix Table II. Cephalometric analysis of patients with pre-treatment deepbite treated with the Invisalign appli-
ance (n 5 40)
Mean Measurements Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
T0
T1
Median D
T0
T1
SD
Minimum
D
T0
T1
D
T0
1.0 3.4 4.3 6.9
0.9 3.3 4.4 6.8
0.9 1.1 1.3 1.7
4.0 0.9 22.4 22.7 32.9 33.7 53.5 55.3
5.3 3.7 29.0 28.6 41.1 41.2 65.0 66.0
1.6 0.4 0.0 1.0
5.1 3.6 29.5 28.4 40.6 41.4 64.2 64.9
1.5 0.5 0.0 0.9
12.8 13.3 21.7 24.2
0.4 2.5
12.7 12.9 20.1 23.4
0.5 6.2 1.6 8.8
7.4 5.5 7.9 5.8
21.9 32.3 18.0 29.3 86.6
21.8 32.7 18.4 29.7 87.2
0.1 0.4 0.4 0.4 0.7
21.8 31.5 17.9 28.8 85.1
0.1 0.5 0.2 0.5 0.7
3.2 3.3 3.3 3.1 8.5
28.9 29.4
0.5
29.9 30.6
21.3 32.6 17.9 29.1 86.2
3.2 3.3 3.9 3.1 8.1
0.4 7.1
0.9 1.0 1.4 1.3 1.5
7.0 1.0
T1
Wilcoxon Signed rank
Maximum D
T0
T1
D
P value
3.1 2.1 3.9 2.6
8.0 35.6 53.4 81.0
6.2 37.9 53.0 80.9
0.1 3.2 3.1 4.7
0.0001* 0.0259 0.8718 0.0009*
30.1 42.8
28.1 42.3
18.1 17.7
0.8350 0.0201*
29.1 29.1 39.2 39.5 26.0 26.6 36.3 37.6 107.4 108.9
1.5 2.3 4.8 4.0 4.2
0.9458 0.0164* 0.2136 0.0489* 0.0652
3.2
0.0104*
0.1 4.6
0.3 7.3
8.6 7.7
15.6 26.5 7.7 24.1 74.1
16.3 26.9 11.8 24.5 74.1
2.3 1.2 1.8 2.3 3.2
10.7 12.2
1.3
44.7
44.6
Summary of linear and angular cephalometric measurements for patients with deepbite. P values and 95% confidence intervals were calculated using the Wilcoxon signed rank test at P 5 0.05. T0, Pretreatment; T1, posttreatment; D, pretreatment to posttreatment changes. U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar. *Statistically significant at the P 5 0.05.
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Appendix Table III. Cephalometric analysis of patients with pretreatment open bite treated with the Invisalign appli-
ance (n 5 12)
Mean Measurements Incisor position (mm) Overbite U1 to palatal plane L1 to mandibular plane Anterior facial height Incisor position ( ) U1-nasion-A-point L1-nasion-B-point Molar position (mm) U6 to palatal plane L6 to mandibular plane U7 to palatal plane L7 to mandibular plane Posterior facial height Mandibular plane ( ) SN-mandibular plane
Median D
T0
1.1 0.2 29.6 30.3 42.8 43.5 71.6 71.6
1.3 0.7 0.8 0.0
22.3 20.9 30.2 30.1 23.5 33.1 19.9 30.0 84.2
SD
Minimum
Wilcoxon signed rank
Maximum
D
T0
T1
D
T0
T1
D
T0
T1
D
P value
0.5 0.1 28.9 28.7 43.5 43.5 69.8 69.4
1.5 0.9 0.8 0.0
1.0 3.7 3.6 6.9
0.9 3.8 4.1 7.4
0.6 1.2 1.0 1.5
2.4 24.9 38.0 61.8
1.5 25.4 37.3 61.1
0.0 1.5 0.7 2.2
0.1 35.9 49.4 82.1
1.4 36.5 52.4 82.8
2.2 2.7 3.0 2.8
0.005* 0.129 0.029* 0.878
1.4 0.1
25.1 22.7 27.6 30.0
2.3 1.2
7.6 6.6 4.7 6.0 5.7 2.9
11.0 22.7
6.5 20.2
9.2 6.0
34.3 37.4
30.2 6.4 37.6 3.6
23.6 33.3 19.9 30.2 84.2
0.1 0.2 0.0 0.2 0.1
22.9 33.6 19.6 29.8 84.8
22.8 32.8 19.6 29.6 84.2
0.1 0.1 0.2 0.3 0.0
3.4 2.9 3.5 2.8 7.2
1.0 1.1 0.8 1.4 1.6
19.2 29.4 15.7 27.0 75.6
18.4 29.2 15.4 25.3 75.0
1.7 28.8 29.0 1.1 40.0 42.6 0.9 25.8 25.6 1.7 37.4 40.4 3.2 101.8 102.1
36.5 36.9
0.4
36.1 36.2
0.3
8.0 7.0 1.7
25.7
26.6
2.1
T0
T1
T1
3.6 3.7 3.6 3.9 7.5
51.5
0.248 1
1.6 2.6 1.4 3.0 2.1
0.799 0.929 0.790 0.965 0.799
51.5 3.5
0.445
Summary of linear and angular cephalometric measurements for patients with openbite. P values and 95% confidence intervals were calculated using the Wilcoxon signed rank test at P 5 0.05. T0, Pretreatment; T1, posttreatment; D, pretreatment to posttreatment changes. U1, Maxillary incisor; L1, mandibular incisor; U6, maxillary first molar; L6, mandibular first molar; U7, maxillary second molar; L7, mandibular second molar. *Statistically significant at the P 5 0.05.
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