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The Evidence for Immediate Loading of Implants
FEATURE ARTICLE
The Evidence for Immediate Loading of Implants David L. Cochran, DDS, PhD From the Departments of Periodontics, The University of Texas Health Science Center San Antonio, San Antonio, TX INTRODUCTION Many clinicians today recommend implant therapy for patients requiring tooth replacement. This therapy can provide a highly successful restoration of both function and esthetics. As such, more and more dentists are providing restorations and patients are demanding these restorations. Along with such an increase in procedures comes a desire to simplify the experience in regard to many aspects including the time involved from starting the restoration to finishing the procedure. The shortest amount of time involved would be to place the restoration on the implant immediately after the surgical placement of the implant, a procedure called immediate restoration and/or loading. While immediate loading has been discussed in the literature and papers report on this technique, this procedure has not gained widespread acceptance. To understand the possibilities of immediate loading, one must take a careful look at the implant procedure from a historical perspective, from a biological perspective, and from a prospective of the available literature on the topic. This is the focus of this report. One confounding area when discussing immediate loading or any loading protocols is how various terms are defined. Different investigators define certain terms different ways and this can change the interpretation of the results of studies. An example is how Bimmediate loading[ is defined or even the term Bloaded.[ Some investigators suggest that placing an implant into bone and submerging it below the soft tissues results in loading of the implant. The rationale is that flexture of the jawbone upon opening and closing and during chewing exerts forces on the implant and thus Bloading[ the implant. Others would suggest that an implant is loaded when it becomes visible in the oral cavity. This would occur when a nonsubmerged implant is used or when a submerged implant’s closure screw becomes exposed through the soft tissue. The rationale here is that tongue movements, cheek pressure, and food could impact the top of the implant therefore placing a Bload[ onto the implant. Other individuals would suggest that the implant is not Bloaded[ until a temporary restoration or implant component of some shape is placed onto the implant Presented at the 2nd Evidence-Based Dentistry Conference November 6, 2005 Chicago, Illinois J Evid Base Dent Pract 2006;6:155<63 1532-3382/$35.00 Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jebdp.2006.04.018
and is in the oral cavity but is not in occlusion with the opposing dentition. Again the rationale in these cases would be tongue and cheek movements and food that would contact the temporary restoration and the opposing dentition. Last, other investigators and authors define Bloading[ as when the implant restoration is in direct contact with the opposing dentition. This is usually confirmed in centric occlusion with colored occlusal marking paper or shim stock. This is a more objective measure of loading and the term that will be used in this report for the loading of an implant restoration.
HISTORICAL PERSPECTIVE To understand the loading of implants, it is necessary to appreciate how loading protocols were established. Loading protocols were arrived at originally by Branemark and associates1 while working out clinical protocols for placing implants. These investigators described 3 distinct phases of development in the technique, which resulted in improved success rates after each stage of trial and error. The initial stage of development lasted from the mid 1960s until 1968. A development phase followed from 1968 until 1971 and then a routine stage for the technique followed from 1971 until 1975. During the early and development stages, one aspect that was investigated was loading protocols. Various healing times were evaluated and it was determined that shorter healing times resulted in failure of the implants. These findings suggested that a healing time of 3 months was required in the mandible and 6 months of healing was required for the maxilla. These healing times were used by clinicians and in many studies and, as such, 3 months in the mandible and 6 months in the maxilla became recognized as conventional healing times. The clinical experience that suggested a 3- and 6-month healing time in the mandible and maxilla respectively did not suggest a biological rationale for such a recommendation. Szmukler-Moncler et al2 speculate on 4 possible biological events that could account for the required healing times clinically established by Branemark et al.1 The first possibility was that early loading would result in fibrous encapsulation of the implant and no osseointegration. A second possibility was that the overheated bone tissue, which undergoes necrosis from the osteotomy preparation, needs to be replaced and during this time the tissue is not capable of supporting the implant. A third possibility suggested was that the necrotic bone created during osteotomy preparation is rapidly remodeled and turned over and that during the remodeling, the strength of the bone to implant contact is compromised. Last, it was speculated that the 3- to 6-month healing period
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was required in order to remodel bone adjacent to the boneimplant interface. This adjacent bone remodeling could compromise the ability to support the implant. Thus, several scenarios were envisioned that could explain why an extended healing period was required prior to loading of the implant. The findings regarding healing times established by Branemark et al1 were reinforced by work performed by Roberts.3 These latter findings suggested that the same healing periods were required prior to loading the implant. Without such a healing time prior to loading, the bone to implant interface was thought to be damaged by loading. Such reports led to the establishment of the conventional healing periods. These healing times were also reinforced by work during the 1970s in the orthopedic field.4<8 These studies all supported the finding that micromotion resulted in fibrous tissue encapsulation reinforcing the findings of Brannemark et al1 and Roberts.3 Thus, the predominance of research at that time supported a relatively long undisturbed healing period. As time passed, the observation was made that some implants could be loaded after shorter healing times and in some cases, the implants could even be loaded immediately after implant placement prior to any healing period. These conflicting reports raised the question as to why, under some conditions, implants become fibrous encapsulated while under other conditions, the implants became osseointegrated. Further investigation revealed that multiple factors played a role in how micromotion influenced the healing process around the implant. These factors were found to include the magnitude of the load that was being applied to the implant such that 50 to 150 microns of loading appeared to be tolerated (the implant became osseointegrated) under certain conditions and higher loads could not be tolerated (the implants were encapsulated by fibrous tissues). The duration, ie, the time and the frequency of the loading as well as the direction of the loading, were found to be important factors. Finally, the quality, quantity, and location of the surrounding bone also was found to influence the amount of micromotion that could be tolerated prior to changing the healing outcome. As a consequence of this last factor, research on the endosseous implant surface characteristics suggested that relatively rough implant surfaces, particularly those without porosity, were found to encourage more bone apposition to the implant surface at earlier time periods. As such, research on implant surface characteristics has significantly altered the ability to load the dental implant.9 Another more recent observation is that under some conditions, investigators have reported that the success rates on immediately loaded implants can be as high as success rates on conventionally loaded implants.10 These findings reinforce a visionary statement made by Ledermann11 in 1979. He suggested that the crucial factor for successful osseointegration was the stability of the implant during the healing phase such that any motion at the bone-to-implant interface was below a certain threshold. Other studies also suggest that for osseointegration to occur, the mobility of the implant must be maintained below a certain critical amount. Thus, 156
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the issue is not really the timing of the loading (immediate loading or not) rather, it is the ability to minimize the motion (less than 150 microns), during the healing process. If one considers ways to clinically minimize motion during the healing process, several ways are possible and have been used currently and in the past. These include (1) submerging the implant into the bone tissue below the soft tissues; (2) placing the implant into cortical bone coronally and apically, a process called bicortical stabilization; (3) rigid splinting of the implants orally; (4) accelerating the rate of healing around the implant; (5) providing cross-arch stabilization especially in cortical bone; (6) keeping the implant restoration out of occlusion and/or opposing a denture rather than a tooth or fixed partial denture; and (7) placing the implant with a large amount of primary contact and/or including Bpress fitting[ the implant in the cortical bone created by flaring the top of the implant. This last technique is performed by using drills with slightly less diameters than the implant diameter or preparing osteotomy sites smaller than recommended such as not using the final bur in the preparation of the osteotomy (Bunder drilling[) or using osteotomes to a diameter less than the implant diameter. All of these clinical procedures can minimize motion of the implant during the healing process and have been used in clinical practice. In retrospect, the evolution of implantology can be viewed as falling into 3 phases or periods (Fig. 1). In the Development Period, relatively long healing times were recommended and primary stability (stability at the time of implant placement) was considered to be very important. This period occurred roughly in the 1960s and 1970s. A second phase was an Exploration Period that followed in the 1980s and 1990s. During this period, many technological and procedural advances took place. These advances included changes in implant surface characteristics, surgical procedural changes such as Bunder drilling,[ and changes in the restorative procedures such as Bprogressive loading[ and tissue shaping using the temporary restorations. Maybe most importantly, however, was the realization that stability during the healing
Figure 1. Three periods of developments in implant dentistry and examples of concepts during the period. June 2006
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process was critical. In the final third phase, the Refinement Period, shortened healing protocols have been investigated and immediate loading protocols have been examined under defined conditions. This Refinement Period has been occurring in the last 5 to 6 years since 2000. These evolutionary periods have translated to patient care such that in the Development Period, techniques were developed to replace teeth in edentulous patients. During the Exploratory Period, these techniques were extended to provide tooth replacement in partially edentulous patients, and in the Refinement Period all these techniques are being optimized (Fig. 2). Features of the evolutionary periods in implantology include the following. In the Development Period, the techniques were begun in edentulous patients, the techniques were developed so that they became predictable, biocompatible materials were used, many implants were placed in each patient, the implants had long undisturbed healing times of 3 to 9 months, implants were placed in high-quality (predominantly cortical dense) bone, cross-arch stabilization was used, the opposing dentition was a denture, and, most significantly, there was minimal heating of the bone tissue during implant surgery. The outcome of the Development Period was help for the denture patient. During the Exploration Period, the implant technique began to be applied to partially edentulous patients. The same principles that had been learned in edentulous patients were assumed to be valid for partially edentulous patients; however, various aspects of the techniques were examined for their necessity since different clinical indications were being used. Some questions that were raised and that have been explored include the following: could the material the implants were made from change (eg, alloys of titanium rather than pure titanium), could you oppose teeth or fixed partial dentures rather than dentures with the implant restoration, was cross-arch stabilization required, could the implants be placed in lower quality bone, was bicortical stabilization necessary, could fewer implants be used including just a single implant, did you need to cover (submerge) the implant under the soft tissues in order to achieve osseointegration (although
Figure 2. Decades listed for the 3 development periods also listing the predominant patients treated. Volume 6, Number 2
Andre Schroeder had been using nonsubmerged implants since the 1970s12 ), could you load the implant prior to the 3- to 9-month healing time, and could you place the implant into extraction sites? The answers to these questions helped to define the implant technique in partially edentulous patients and thus benefited those patients missing 1 or more teeth. By the time of the Refinement Period, dental implant placement became a routine successful tooth replacement therapy for both edentulous and partially edentulous patients. Research during this time focused on optimizing surface characteristics of the implant including both morphology and chemistry and exploring ways to further shorten the healing times of the implant prior to restoration and loading, with the ultimate goal of loading the implant immediately, meaning at the time of implant placement. Also during the Refinement Period, tissue-engineering techniques were introduced to enhance the rate of healing and the quantity and quality of bone tissue around the implant (eg, the bone-to-implant contact). The outcome of these improvements during the Refinement Period led to the use of implant therapy to replace missing teeth in more indications and thus more patients.
BIOLOGICAL CONSIDERATIONS Loading protocols for endosseous dental implants can best be interpreted on the biologic basis of how the tissues respond to implant placement. In fact, few appear to realize that osseointegration occurs instantaneously on implant placement. Osseointegration was first defined as bone-to-implant contact at the light microscopic level and then later defined as a direct structural and functional connection between ordered living bone and the surface of a load-carrying implant.1 Cochran et al,13 in a study of the bone response to implants with 2 different surface characteristics, stated that when an implant is placed clinically into an osteotomy preparation, that the bone directly contacts the implant surface. This results in immediate osseointegration of the implant as defined by direct bone-to-implant contact if analyzed at the light microscopic level. In fact, when an osteotomy site is prepared, bone tissue is cut to a dimension of the implant drill. This leaves edges of the bone surrounding the hole left by the drill. More dense bone is found in the cortical areas while less dense bone, in the form of interrupted trabeculae, are found in areas of cancellous bone. When an implant is then placed into the preparation, especially if the implant has a slightly larger diameter than the implant drill, the implant is Bpress-fit[ along the cut bone edges and the implant contacts the bone, ie, is osseointegrated (bone-to-implant contact at the light microscopic level). These areas of bone contact with the implant surface are referred to as Bprimary bone contact.[13 Histologic analysis of such bone reveals intimate contact of the bone with the implant surface (osseointegration) including lamellar plastic deformation, elongated Haversion systems, and micro-fractures in the bone (Fig. 3). Because bone tissue is dynamic and remodels over time, these areas of bone contact are remodeled and are replaced by new bone. This Cochran
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new bone contact is termed Bsecondary bone formation.[ At the same time, new bone is also formed on the implant surface (especially if the surface is osteoconductive) in areas between the areas of primary bone contact. This new bone is also termed Bsecondary bone formation.[ Thus, at early time points there is a lot of primary bone contact along the implant surface (dependent on the existing quantity and quality of bone at the implant site) and very little secondary bone formation. At later time points, however, the ratio reverses such that primary bone contact decreases and secondary bone contact increases. This can be viewed diagrammatically as is shown in Fig. 4. Histological analyses of large numbers of implants in patients is not possible, so clinical alternatives have been used to determine if an implant is osseointegrated. One such sur-
Figure 3. Primary contact of implant with cortical bone. Original magnification: X25. Compression of the cortical bone can be observed. Reprinted with permission from Cochran DL, Schenk RK, Lussi A, Higginbottom FL, Buser D. Bone response to unloaded and loaded titanium implants with a sandblasted and acid-etched surface: a histometric study in the canine mandible. J Biomed Mater Res. 1998 Apr;40(1):1-11.13 158
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Figure 4. Schematic of bone contact against an implant surface and what happens to the bone over time.
rogate for osseointegration is to determine if the implant is stable in the jaw. Several methods are available to evaluate stability and one more recent way is to use resonance frequency analyses. Barewal et al14 have followed the stability of implants over early healing times with resonance frequency measurements. Their findings indicated that implants placed in areas of high bone quality are relatively stable over the early healing periods. However, as the quality of bone decreases, the stability of the implant decreases over the first 3 to 4 weeks with the least stability found for those implants in the lowest bone quality (Fig. 5). These findings suggest that implants placed in high-quality bone are surrounded by enough primary bone contact that stability of the implant is maintained by the primary contact while the remodeling and formation of new bone can occur to such a degree as to further maintain the stability as measured by resonance frequency analyses (Fig. 6 and Fig. 7). However, when the implant is placed into a site with poor bone quality, very little primary contact exists around the implant (Fig. 8 and Fig. 9). As remodeling occurs, the implant becomes less stable because (1) the remodeling process in this case takes place in a relatively high percentage of the bone surrounding the implant (little bone-to-implant contact initially because of poor bone quality; therefore, as remodeling occurs, this represents a large proportion of that small amount of bone), and (2) there has not been sufficient time for new bone to form (secondary bone formation). Thus, stability of the implant as measured by resonance frequency analyses reveals a significant decrease in stability between the time of primary bone contact remodeling and the formation of new bone or secondary bone contact. Therefore, the clinical stability of implants in bone, as measured by resonance frequency analyses, reflects the biological processes that are ongoing at the bone-to-implant interface. These events further emphasize that Bosseointegration[ is not a static event but rather represents a Bdynamic equilibrium[ at the site of boneto-implant contact. Thus, given this understanding, a new June 2006
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Figure 5. Stability of implants in different qualities of bone as detected by resonance frequency analyses over time. ISQ is the implant stability quotient. Reprinted with permission from Barewal RM, Oates TW, Meredith N, Cochran DL. Resonance frequency measurement of implant stability in vivo on implants with a sandblasted and acid-etched surface. Int J Oral Maxillofac Implants. 2003 Sep-Oct; 18(5):641-51.14
definition of osseointegration could be Bstability of an implant in bone that represents a dynamic equilibrium between existing native bone (primary bone contact) and remodeling and new bone formation (secondary bone contact), and its maintenance, at the bone-implant interface[ (Fig. 10).
LITERATURE EXAMPLES Understanding the biological consequences of implant integration allows an appreciation of what is possible in regard to the loading of implants. These events are then reflected by the literature on loading protocols. For instance, understanding that implants placed in excellent bone quality will Volume 6, Number 2
be stable over the early healing periods and remain stable (osseointegrated as defined above), suggests that multiple implants placed in the anterior mandible and are rigidly fixed orally can be successfully loaded. Thus, publications by Babbush et al,15 Schnitman et al,16 Tarnow et al,17 and Chiapasco et al18 are not surprising. Loading protocols in other indications are certainly possible but the implant sites must be carefully chosen as to reflect sites that can have high bone quality, the implant restoration can be stabilized by adjacent tooth structure etc, where implant stability can be maintained in the transition from primary bone contact to secondary bone contact. This is reflected in papers published and in reviews of literature on this topic as noted below. Cochran
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Figure 6. The change in primary bone contact when an implant placed in a site with a large proportion of dense bone such as cortical bone.
Figure 8. The change in primary bone contact when an implant is placed in a site with a large proportion of less dense bone such as cancellous bone.
An example of a recent study evaluating implant loading protocols examined various healing periods prior to loading including no healing period, 10 days, 21 days, and 3 months of loading.19 Teeth were extracted bilaterally in the canine mandible and after 5 months, implants were placed at different time points such that each animal received 3 implants at each of the 4 healing times. All gold, screw-retained crowns were placed on all the implants the same day and radiographs taken at monthly intervals until the study animals were killed at 3 months post-loading. Block sections were obtained from each implant site and histological analyses were performed in addition to the monthly radiographic analyses (Fig. 11 and Fig. 12). No implants were lost in spite of the varying loading times and occlusal wear on the gold crowns.
The conclusions demonstrated that no significant differences were found between the implants loaded after different healing times as evaluated clinically, radiographically, and histologically. Thus, both immediate and early loading of the implants did not have adverse effects on the survival or success of the implants. A meta-analysis was performed on more than 1000 implants in patients and compared loading times as evaluated by implant survival.20 This article analyzed 13 prospective clinical trials, 6 of which were randomized. Overall, no significant differences were detected between loading protocols. Furthermore, although a higher actual number of failures occurred in the early loading protocols (2 to 6 weeks of healing prior to loading) relative to the conventional loading
Figure 7. The stability of an implant placed in high quality bone is large (represented by a small gray area).
Figure 9. The lack of stability of an implant placed in low quality bone (represented by large gray area).
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Figure 10. New definition of osseointegration reflecting the dynamic biological processes that occur around an implant placed in bone.
protocol, there was no significant difference in the implant failure rate between loading protocols. It should be noted that conventional loading was defined as 3 to 6 months and immediate loading from 1 to 2 days; however, early loading included studies with a range of healing times (less than 14 days, within the first 35 days, and within the first 6 weeks). The authors noted a number of limitations of their study including only 6 randomized studies out of a total 13 studies, only 1266 implants evaluated, all the trials being underpowered, and the clinical heterogeneity of the studies.
An implant consensus conference was held in Gstaad, Switzerland, in 2003 by the International Team for Oral Implantology. One group at the consensus meeting evaluated immediate and early loading restoration and loading protocols for dental implants.21 Three papers were submitted that evaluated loading protocols in the literature related to edentulous patients,22 partially edentulous patients,23 and clinical techniques.24 After careful analyses and evaluation of the literature reviews, an international group of 17 clinicians made recommendations on loading protocols based on the literature and the collective experience of the group. This group determined that the volume of literature on loading protocols was moderate and the evidence was limited at best for the procedures considered. The predominant literature was case reports. Loading was defined as contact with the opposing dentition as opposed to restoration without contact. Conventional healing was defined as 3 months postYimplant placement until restoration, whereas immediate restoration was defined as restoration within 48 hours of implant placement but not in occlusion with the opposing dentition. This definition was based on the capacity to perform the restorative clinical procedures within a limited time frame from surgery (such as the surgical placement occurring in one office one day and the restorative procedures performed in
Figure 11. Histologic cross-sections of implants from a) Group A: 3 months, b) Group B: 21 days, c) Group C: 10 days, d) Group D: 2 days after 3 months of loading. Reprinted with permission from Quinlan P, Nummikoski P, Schenk R, Cagna D, Mellonig J, Higginbottom F, Lang K, Buser D, Cochran D. Immediate and early loading of SLA ITI single-tooth implants: an in vivo study. Int J Oral Maxillofac Implants. 2005 May-June;20(3):360-70.19 Volume 6, Number 2
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Figure 12. Tissue-to-implant contact between tissue and primary and secondary bone, bone marrow, and connective tissue for Groups A (3 months), B (21 days), C (10 days), and D (2 days). Bars indicate SE. Reprinted with permission from Quinlan P, Nummikoski P, Schenk R. Immediate and early loading of SLA ITI single-tooth implants: an in vivo study. Int J Oral Maxillofac Implants. 2005 May-June;20(3):360-70.19
another office the next day). Early restoration was defined as the placement of the restoration at least 48 hours subsequent to implant placement but not later than 3 months. Immediate loading was therefore defined as restoration within 48 hours of implant placement and occlusal contact with the opposing dentition. Early loading was therefore restoration at least 48 hours subsequent to implant placement but not later than 3 months and the restoration in contact with the opposing dentition. The consensus group noted that the results of the studies were obtained from conditions that were considered favorable in that the inclusion and exclusion criteria used in many of the studies limited their evaluation to a selected population. The consensus conference concluded that in the edentulous mandible, immediate loading (up to 48 hours) in patients with both overdentures and fixed prostheses was well documented in the literature (Fig. 13). Early loading was separated into 2 periods based on studies in the literature. One early loading period was between 48 hours and 6 weeks and the second period from 6 weeks to 3 months. In the edentulous mandible in the period of early loading from 48 hours to 6 weeks, the procedure for overdentures and fixed prostheses was not well documented. In the period from 6 weeks to 3 months, no overdenture literature was available but the literature on fixed prostheses was well documented. In regard to the edentulous maxilla, no literature was available on overdentures that involved immediate or early loading (Fig. 14). In regard to fixed prosthesis in the edentulous maxilla, literature was available on both immediate and early loading; however, the group determined that this procedure was not well documented in the literature. In regard to the partially dentate maxilla and mandible, overdentures were not 162
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Figure 13. Loading documentation in the literature for edentulous mandible. Reprinted with permission from Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants. 2004;19 Suppl:109-13.21
applicable (Fig. 15). Fixed prostheses used in immediate restoration or loading indications in the partially dentate patient were not well documented. In regard to early restoration or loading in the partially dentate patient, the procedure was well documented only after 6 to 8 weeks and then when an implant was used with a roughened titanium surface.
CONCLUSION A summary of loading protocols, based on historical development, biological considerations, and the literature indicate that shortened loading protocols are dependent on (1) the quantity and quality of bone at the implant site and, as a consequence, the amount of primary bone contact, and (2) the rapidity of the bone formation and remodeling of the
Figure 14. Loading documentation in the literature for edentulous maxilla. Reprinted with permission from Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants. 2004;19 Suppl:109-13.21 June 2006
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3. 4. 5. 6. 7.
8. 9.
Figure 15. Loading documentation in the literature for partially dentate maxilla and mandible. Reprinted with permission from Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants. 2004;19 Suppl: 109-13.21
10.
11.
12.
13.
bone surrounding the implant with resultant secondary bone contact. These conditions result in 2 clinical scenarios for supporting reduced healing times. If the implant site has high quality and quantity of existing bone, immediate loading protocols are possible. If the implant site has low quality and quantity of native bone and bone remodeling and bone formation are required, immediate loading is more contraindicated and early loading protocols are possible. However, many factors can be important such as the characteristics of the implant surface, the location of high-quality bone in the implant site, the ability to protect the implant restoration with adjacent tooth structure, the use of proteins (growth factors or stimulants) or materials and matrices used around the implant, and so forth. These factors are related to either (1) stimulating new bone-to-implant contact or (2) minimizing micromotion of the implant. In all situations, it is important to remember that the goal is improved patient care. Procedures that put the implant restoration at high risk in the patient are unacceptable. Understanding the historical development of implant healing times, the biological events that result in osseointegration as defined above, and knowing the literature on shortened healing times on implants, allows the clinician to appreciate options for various loading protocols and to improve the patient care they deliver.
REFERENCES 1. Branemark PI, Hansson BO, Adell R, Breine U, Lindstrom J, Hallen O, et al. Osseointegrated implants in the treatment of the edentulous jaw. Experience from a 10-year period. Scand J Plast Reconstr Surg Suppl 1977;16:1-132. 2. Szmukler-Moncler S, Piattelli A, Favero GA, Dubruille JH. Considerations
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preliminary to the application of early and immediate loading protocols in dental implantology. Clin Oral Implants Res 2000;11(1):12-25. Roberts WE. Bone tissue interface. J Dent Educ 1988;52(12):804-9. Schatzker J, Horne JG, Sumner-Smith G. The effect of movement on the holding power of screws in bone. Clin Orthop 1975;111:257-62. Cameron H, Macnab I, Pilliar R. Porous surfaced Vitallium staples. S Afr J Surg 1972;10(2):63-70. Cameron HU, Pilliar RM, MacNab I. The effect of movement on the bonding of porous metal to bone. J Biomed Mater Res 1973;7(4):301-11. Ducheyne P, De Meester P, Aernoudt E. Influence of a functional dynamic loading on bone ingrowth into surface pores of orthopedic implants. J Biomed Mater Res 1977;11(6):811-38. Unthoff HK, Germain JP. The reversal of tissue differentiation around screws. Clin Orthop 1975;123:248-52. Cochran DL, Buser D, ten Bruggenkate CM, Weingart D, Taylor TD, Bernard J-P, et al. The use of reduced healing times on ITI(R) implants with a sandblasted and acid-etched (SLA) surface. Clin Oral Impl Res 2002;13(2):144-53. Chiapasco M, Abati S, Romeo E, Vogel G. Implant-retained mandibular overdentures with Branemark System MKII implants: a prospective comparative study between delayed and immediate loading. Int J Oral Maxillofac Implants 2001;16(4):537-46. Ledermann P. [Complete denture support in edentulous problem mandibles with help from 4 titanium plasma-coated PDL screw implants]. SSO Schweiz Monatsschr Zahnheilkd 1979;89(11):1137-8. (German) Schroeder A, van der Zypen E, Stich H, Sutter F. The reactions of bone, connective tissue, and epithelium to endosteal implants with titaniumsprayed surfaces. J Maxillofac Surg 1981;9(1):15-25. Cochran DL, Schenk RK, Lussi A, Higginbottom FL, Buser D. Bone response to unloaded and loaded titanium implants with a sandblasted and acid-etched surface: a histometric study in the canine mandible. J Biomed Mater Res 1998;40(1):1-11. Barewal RM, Oates TW, Meredith N, Cochran DL. Resonance frequency measurement of implant stability in vivo on implants with a sandblasted and acid-etched (SLA) surface. Int J Oral and Maxillofac Implants 2003;18(5):641-51. Babbush CA, Kent JN, Misiek DJ. Titanium plasma-sprayed (TPS) screw implants for the reconstruction of the edentulous mandible. J Oral Maxillofac Surg 1986;44(4):274-82. Schnitman PA, Wohrle PS, Rubenstein JE. Immediate fixed interim prostheses supported by two-stage threaded implants: methodology and results. J Oral Implantology 1990;16(2):96-105. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implants 1997;12(3):319-24. Chiapasco M, Gatti C, Rossi E, Haefliger W, Markwalder TH. Implant-retained mandibular overdentures with immediate loading. A retrospective multicenter study on 226 consecutive cases. Clin Oral Implants Res 1997;8(1):48-57. Quinlan P, Nummikoski P, Schenk R, Cagna D, Mellonig J, Higginbottom F, et al. Immediate and early loading of ITI SLA single tooth implants: an in vivo study. Int J Oral Maxillofac Implants 2005; 20:360-70. Ioannidou E, Doufexi A. Does loading time affect implant survival? A meta-analysis of 1,266 implants. J Periodontol 2005;76(8):1252-8. Cochran DL, Morton D, Weber H-P. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants 2004;19(Suppl):109-13. Chiapasco M. Early and immediate restoration and loading of implants in completely edentulous patients. Int J Oral Maxillofac Implants 2004; 19(Suppl):76-91. Ganeles J, Wismeijer D. Early and immediately restored and loaded dental implants for single-tooth and partial-arch applications. Int J Oral Maxillofac Implants Suppl., 2004;19:92-102. Morton D, Jaffin R, Weber H-P. Immediate restoration and loading of dental implants: clinical considerations and protocols. Int J Oral Maxillofac Implants 2004;19(Suppl):103-8.
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The Evidence for Immediate Loading of Implants David L. Cochran, DDS, PhD From the Departments of Periodontics, The University of Texas Health Science Center San Antonio, San Antonio, TX INTRODUCTION Many clinicians today recommend implant therapy for patients requiring tooth replacement. This therapy can provide a highly successful restoration of both function and esthetics. As such, more and more dentists are providing restorations and patients are demanding these restorations. Along with such an increase in procedures comes a desire to simplify the experience in regard to many aspects including the time involved from starting the restoration to finishing the procedure. The shortest amount of time involved would be to place the restoration on the implant immediately after the surgical placement of the implant, a procedure called immediate restoration and/or loading. While immediate loading has been discussed in the literature and papers report on this technique, this procedure has not gained widespread acceptance. To understand the possibilities of immediate loading, one must take a careful look at the implant procedure from a historical perspective, from a biological perspective, and from a prospective of the available literature on the topic. This is the focus of this report. One confounding area when discussing immediate loading or any loading protocols is how various terms are defined. Different investigators define certain terms different ways and this can change the interpretation of the results of studies. An example is how Bimmediate loading[ is defined or even the term Bloaded.[ Some investigators suggest that placing an implant into bone and submerging it below the soft tissues results in loading of the implant. The rationale is that flexture of the jawbone upon opening and closing and during chewing exerts forces on the implant and thus Bloading[ the implant. Others would suggest that an implant is loaded when it becomes visible in the oral cavity. This would occur when a nonsubmerged implant is used or when a submerged implant’s closure screw becomes exposed through the soft tissue. The rationale here is that tongue movements, cheek pressure, and food could impact the top of the implant therefore placing a Bload[ onto the implant. Other individuals would suggest that the implant is not Bloaded[ until a temporary restoration or implant component of some shape is placed onto the implant Presented at the 2nd Evidence-Based Dentistry Conference November 6, 2005 Chicago, Illinois J Evid Base Dent Pract 2006;6:155<63 1532-3382/$35.00 Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jebdp.2006.04.018
and is in the oral cavity but is not in occlusion with the opposing dentition. Again the rationale in these cases would be tongue and cheek movements and food that would contact the temporary restoration and the opposing dentition. Last, other investigators and authors define Bloading[ as when the implant restoration is in direct contact with the opposing dentition. This is usually confirmed in centric occlusion with colored occlusal marking paper or shim stock. This is a more objective measure of loading and the term that will be used in this report for the loading of an implant restoration.
HISTORICAL PERSPECTIVE To understand the loading of implants, it is necessary to appreciate how loading protocols were established. Loading protocols were arrived at originally by Branemark and associates1 while working out clinical protocols for placing implants. These investigators described 3 distinct phases of development in the technique, which resulted in improved success rates after each stage of trial and error. The initial stage of development lasted from the mid 1960s until 1968. A development phase followed from 1968 until 1971 and then a routine stage for the technique followed from 1971 until 1975. During the early and development stages, one aspect that was investigated was loading protocols. Various healing times were evaluated and it was determined that shorter healing times resulted in failure of the implants. These findings suggested that a healing time of 3 months was required in the mandible and 6 months of healing was required for the maxilla. These healing times were used by clinicians and in many studies and, as such, 3 months in the mandible and 6 months in the maxilla became recognized as conventional healing times. The clinical experience that suggested a 3- and 6-month healing time in the mandible and maxilla respectively did not suggest a biological rationale for such a recommendation. Szmukler-Moncler et al2 speculate on 4 possible biological events that could account for the required healing times clinically established by Branemark et al.1 The first possibility was that early loading would result in fibrous encapsulation of the implant and no osseointegration. A second possibility was that the overheated bone tissue, which undergoes necrosis from the osteotomy preparation, needs to be replaced and during this time the tissue is not capable of supporting the implant. A third possibility suggested was that the necrotic bone created during osteotomy preparation is rapidly remodeled and turned over and that during the remodeling, the strength of the bone to implant contact is compromised. Last, it was speculated that the 3- to 6-month healing period
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was required in order to remodel bone adjacent to the boneimplant interface. This adjacent bone remodeling could compromise the ability to support the implant. Thus, several scenarios were envisioned that could explain why an extended healing period was required prior to loading of the implant. The findings regarding healing times established by Branemark et al1 were reinforced by work performed by Roberts.3 These latter findings suggested that the same healing periods were required prior to loading the implant. Without such a healing time prior to loading, the bone to implant interface was thought to be damaged by loading. Such reports led to the establishment of the conventional healing periods. These healing times were also reinforced by work during the 1970s in the orthopedic field.4<8 These studies all supported the finding that micromotion resulted in fibrous tissue encapsulation reinforcing the findings of Brannemark et al1 and Roberts.3 Thus, the predominance of research at that time supported a relatively long undisturbed healing period. As time passed, the observation was made that some implants could be loaded after shorter healing times and in some cases, the implants could even be loaded immediately after implant placement prior to any healing period. These conflicting reports raised the question as to why, under some conditions, implants become fibrous encapsulated while under other conditions, the implants became osseointegrated. Further investigation revealed that multiple factors played a role in how micromotion influenced the healing process around the implant. These factors were found to include the magnitude of the load that was being applied to the implant such that 50 to 150 microns of loading appeared to be tolerated (the implant became osseointegrated) under certain conditions and higher loads could not be tolerated (the implants were encapsulated by fibrous tissues). The duration, ie, the time and the frequency of the loading as well as the direction of the loading, were found to be important factors. Finally, the quality, quantity, and location of the surrounding bone also was found to influence the amount of micromotion that could be tolerated prior to changing the healing outcome. As a consequence of this last factor, research on the endosseous implant surface characteristics suggested that relatively rough implant surfaces, particularly those without porosity, were found to encourage more bone apposition to the implant surface at earlier time periods. As such, research on implant surface characteristics has significantly altered the ability to load the dental implant.9 Another more recent observation is that under some conditions, investigators have reported that the success rates on immediately loaded implants can be as high as success rates on conventionally loaded implants.10 These findings reinforce a visionary statement made by Ledermann11 in 1979. He suggested that the crucial factor for successful osseointegration was the stability of the implant during the healing phase such that any motion at the bone-to-implant interface was below a certain threshold. Other studies also suggest that for osseointegration to occur, the mobility of the implant must be maintained below a certain critical amount. Thus, 156
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the issue is not really the timing of the loading (immediate loading or not) rather, it is the ability to minimize the motion (less than 150 microns), during the healing process. If one considers ways to clinically minimize motion during the healing process, several ways are possible and have been used currently and in the past. These include (1) submerging the implant into the bone tissue below the soft tissues; (2) placing the implant into cortical bone coronally and apically, a process called bicortical stabilization; (3) rigid splinting of the implants orally; (4) accelerating the rate of healing around the implant; (5) providing cross-arch stabilization especially in cortical bone; (6) keeping the implant restoration out of occlusion and/or opposing a denture rather than a tooth or fixed partial denture; and (7) placing the implant with a large amount of primary contact and/or including Bpress fitting[ the implant in the cortical bone created by flaring the top of the implant. This last technique is performed by using drills with slightly less diameters than the implant diameter or preparing osteotomy sites smaller than recommended such as not using the final bur in the preparation of the osteotomy (Bunder drilling[) or using osteotomes to a diameter less than the implant diameter. All of these clinical procedures can minimize motion of the implant during the healing process and have been used in clinical practice. In retrospect, the evolution of implantology can be viewed as falling into 3 phases or periods (Fig. 1). In the Development Period, relatively long healing times were recommended and primary stability (stability at the time of implant placement) was considered to be very important. This period occurred roughly in the 1960s and 1970s. A second phase was an Exploration Period that followed in the 1980s and 1990s. During this period, many technological and procedural advances took place. These advances included changes in implant surface characteristics, surgical procedural changes such as Bunder drilling,[ and changes in the restorative procedures such as Bprogressive loading[ and tissue shaping using the temporary restorations. Maybe most importantly, however, was the realization that stability during the healing
Figure 1. Three periods of developments in implant dentistry and examples of concepts during the period. June 2006
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process was critical. In the final third phase, the Refinement Period, shortened healing protocols have been investigated and immediate loading protocols have been examined under defined conditions. This Refinement Period has been occurring in the last 5 to 6 years since 2000. These evolutionary periods have translated to patient care such that in the Development Period, techniques were developed to replace teeth in edentulous patients. During the Exploratory Period, these techniques were extended to provide tooth replacement in partially edentulous patients, and in the Refinement Period all these techniques are being optimized (Fig. 2). Features of the evolutionary periods in implantology include the following. In the Development Period, the techniques were begun in edentulous patients, the techniques were developed so that they became predictable, biocompatible materials were used, many implants were placed in each patient, the implants had long undisturbed healing times of 3 to 9 months, implants were placed in high-quality (predominantly cortical dense) bone, cross-arch stabilization was used, the opposing dentition was a denture, and, most significantly, there was minimal heating of the bone tissue during implant surgery. The outcome of the Development Period was help for the denture patient. During the Exploration Period, the implant technique began to be applied to partially edentulous patients. The same principles that had been learned in edentulous patients were assumed to be valid for partially edentulous patients; however, various aspects of the techniques were examined for their necessity since different clinical indications were being used. Some questions that were raised and that have been explored include the following: could the material the implants were made from change (eg, alloys of titanium rather than pure titanium), could you oppose teeth or fixed partial dentures rather than dentures with the implant restoration, was cross-arch stabilization required, could the implants be placed in lower quality bone, was bicortical stabilization necessary, could fewer implants be used including just a single implant, did you need to cover (submerge) the implant under the soft tissues in order to achieve osseointegration (although
Figure 2. Decades listed for the 3 development periods also listing the predominant patients treated. Volume 6, Number 2
Andre Schroeder had been using nonsubmerged implants since the 1970s12 ), could you load the implant prior to the 3- to 9-month healing time, and could you place the implant into extraction sites? The answers to these questions helped to define the implant technique in partially edentulous patients and thus benefited those patients missing 1 or more teeth. By the time of the Refinement Period, dental implant placement became a routine successful tooth replacement therapy for both edentulous and partially edentulous patients. Research during this time focused on optimizing surface characteristics of the implant including both morphology and chemistry and exploring ways to further shorten the healing times of the implant prior to restoration and loading, with the ultimate goal of loading the implant immediately, meaning at the time of implant placement. Also during the Refinement Period, tissue-engineering techniques were introduced to enhance the rate of healing and the quantity and quality of bone tissue around the implant (eg, the bone-to-implant contact). The outcome of these improvements during the Refinement Period led to the use of implant therapy to replace missing teeth in more indications and thus more patients.
BIOLOGICAL CONSIDERATIONS Loading protocols for endosseous dental implants can best be interpreted on the biologic basis of how the tissues respond to implant placement. In fact, few appear to realize that osseointegration occurs instantaneously on implant placement. Osseointegration was first defined as bone-to-implant contact at the light microscopic level and then later defined as a direct structural and functional connection between ordered living bone and the surface of a load-carrying implant.1 Cochran et al,13 in a study of the bone response to implants with 2 different surface characteristics, stated that when an implant is placed clinically into an osteotomy preparation, that the bone directly contacts the implant surface. This results in immediate osseointegration of the implant as defined by direct bone-to-implant contact if analyzed at the light microscopic level. In fact, when an osteotomy site is prepared, bone tissue is cut to a dimension of the implant drill. This leaves edges of the bone surrounding the hole left by the drill. More dense bone is found in the cortical areas while less dense bone, in the form of interrupted trabeculae, are found in areas of cancellous bone. When an implant is then placed into the preparation, especially if the implant has a slightly larger diameter than the implant drill, the implant is Bpress-fit[ along the cut bone edges and the implant contacts the bone, ie, is osseointegrated (bone-to-implant contact at the light microscopic level). These areas of bone contact with the implant surface are referred to as Bprimary bone contact.[13 Histologic analysis of such bone reveals intimate contact of the bone with the implant surface (osseointegration) including lamellar plastic deformation, elongated Haversion systems, and micro-fractures in the bone (Fig. 3). Because bone tissue is dynamic and remodels over time, these areas of bone contact are remodeled and are replaced by new bone. This Cochran
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new bone contact is termed Bsecondary bone formation.[ At the same time, new bone is also formed on the implant surface (especially if the surface is osteoconductive) in areas between the areas of primary bone contact. This new bone is also termed Bsecondary bone formation.[ Thus, at early time points there is a lot of primary bone contact along the implant surface (dependent on the existing quantity and quality of bone at the implant site) and very little secondary bone formation. At later time points, however, the ratio reverses such that primary bone contact decreases and secondary bone contact increases. This can be viewed diagrammatically as is shown in Fig. 4. Histological analyses of large numbers of implants in patients is not possible, so clinical alternatives have been used to determine if an implant is osseointegrated. One such sur-
Figure 3. Primary contact of implant with cortical bone. Original magnification: X25. Compression of the cortical bone can be observed. Reprinted with permission from Cochran DL, Schenk RK, Lussi A, Higginbottom FL, Buser D. Bone response to unloaded and loaded titanium implants with a sandblasted and acid-etched surface: a histometric study in the canine mandible. J Biomed Mater Res. 1998 Apr;40(1):1-11.13 158
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Figure 4. Schematic of bone contact against an implant surface and what happens to the bone over time.
rogate for osseointegration is to determine if the implant is stable in the jaw. Several methods are available to evaluate stability and one more recent way is to use resonance frequency analyses. Barewal et al14 have followed the stability of implants over early healing times with resonance frequency measurements. Their findings indicated that implants placed in areas of high bone quality are relatively stable over the early healing periods. However, as the quality of bone decreases, the stability of the implant decreases over the first 3 to 4 weeks with the least stability found for those implants in the lowest bone quality (Fig. 5). These findings suggest that implants placed in high-quality bone are surrounded by enough primary bone contact that stability of the implant is maintained by the primary contact while the remodeling and formation of new bone can occur to such a degree as to further maintain the stability as measured by resonance frequency analyses (Fig. 6 and Fig. 7). However, when the implant is placed into a site with poor bone quality, very little primary contact exists around the implant (Fig. 8 and Fig. 9). As remodeling occurs, the implant becomes less stable because (1) the remodeling process in this case takes place in a relatively high percentage of the bone surrounding the implant (little bone-to-implant contact initially because of poor bone quality; therefore, as remodeling occurs, this represents a large proportion of that small amount of bone), and (2) there has not been sufficient time for new bone to form (secondary bone formation). Thus, stability of the implant as measured by resonance frequency analyses reveals a significant decrease in stability between the time of primary bone contact remodeling and the formation of new bone or secondary bone contact. Therefore, the clinical stability of implants in bone, as measured by resonance frequency analyses, reflects the biological processes that are ongoing at the bone-to-implant interface. These events further emphasize that Bosseointegration[ is not a static event but rather represents a Bdynamic equilibrium[ at the site of boneto-implant contact. Thus, given this understanding, a new June 2006
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Figure 5. Stability of implants in different qualities of bone as detected by resonance frequency analyses over time. ISQ is the implant stability quotient. Reprinted with permission from Barewal RM, Oates TW, Meredith N, Cochran DL. Resonance frequency measurement of implant stability in vivo on implants with a sandblasted and acid-etched surface. Int J Oral Maxillofac Implants. 2003 Sep-Oct; 18(5):641-51.14
definition of osseointegration could be Bstability of an implant in bone that represents a dynamic equilibrium between existing native bone (primary bone contact) and remodeling and new bone formation (secondary bone contact), and its maintenance, at the bone-implant interface[ (Fig. 10).
LITERATURE EXAMPLES Understanding the biological consequences of implant integration allows an appreciation of what is possible in regard to the loading of implants. These events are then reflected by the literature on loading protocols. For instance, understanding that implants placed in excellent bone quality will Volume 6, Number 2
be stable over the early healing periods and remain stable (osseointegrated as defined above), suggests that multiple implants placed in the anterior mandible and are rigidly fixed orally can be successfully loaded. Thus, publications by Babbush et al,15 Schnitman et al,16 Tarnow et al,17 and Chiapasco et al18 are not surprising. Loading protocols in other indications are certainly possible but the implant sites must be carefully chosen as to reflect sites that can have high bone quality, the implant restoration can be stabilized by adjacent tooth structure etc, where implant stability can be maintained in the transition from primary bone contact to secondary bone contact. This is reflected in papers published and in reviews of literature on this topic as noted below. Cochran
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Figure 6. The change in primary bone contact when an implant placed in a site with a large proportion of dense bone such as cortical bone.
Figure 8. The change in primary bone contact when an implant is placed in a site with a large proportion of less dense bone such as cancellous bone.
An example of a recent study evaluating implant loading protocols examined various healing periods prior to loading including no healing period, 10 days, 21 days, and 3 months of loading.19 Teeth were extracted bilaterally in the canine mandible and after 5 months, implants were placed at different time points such that each animal received 3 implants at each of the 4 healing times. All gold, screw-retained crowns were placed on all the implants the same day and radiographs taken at monthly intervals until the study animals were killed at 3 months post-loading. Block sections were obtained from each implant site and histological analyses were performed in addition to the monthly radiographic analyses (Fig. 11 and Fig. 12). No implants were lost in spite of the varying loading times and occlusal wear on the gold crowns.
The conclusions demonstrated that no significant differences were found between the implants loaded after different healing times as evaluated clinically, radiographically, and histologically. Thus, both immediate and early loading of the implants did not have adverse effects on the survival or success of the implants. A meta-analysis was performed on more than 1000 implants in patients and compared loading times as evaluated by implant survival.20 This article analyzed 13 prospective clinical trials, 6 of which were randomized. Overall, no significant differences were detected between loading protocols. Furthermore, although a higher actual number of failures occurred in the early loading protocols (2 to 6 weeks of healing prior to loading) relative to the conventional loading
Figure 7. The stability of an implant placed in high quality bone is large (represented by a small gray area).
Figure 9. The lack of stability of an implant placed in low quality bone (represented by large gray area).
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Figure 10. New definition of osseointegration reflecting the dynamic biological processes that occur around an implant placed in bone.
protocol, there was no significant difference in the implant failure rate between loading protocols. It should be noted that conventional loading was defined as 3 to 6 months and immediate loading from 1 to 2 days; however, early loading included studies with a range of healing times (less than 14 days, within the first 35 days, and within the first 6 weeks). The authors noted a number of limitations of their study including only 6 randomized studies out of a total 13 studies, only 1266 implants evaluated, all the trials being underpowered, and the clinical heterogeneity of the studies.
An implant consensus conference was held in Gstaad, Switzerland, in 2003 by the International Team for Oral Implantology. One group at the consensus meeting evaluated immediate and early loading restoration and loading protocols for dental implants.21 Three papers were submitted that evaluated loading protocols in the literature related to edentulous patients,22 partially edentulous patients,23 and clinical techniques.24 After careful analyses and evaluation of the literature reviews, an international group of 17 clinicians made recommendations on loading protocols based on the literature and the collective experience of the group. This group determined that the volume of literature on loading protocols was moderate and the evidence was limited at best for the procedures considered. The predominant literature was case reports. Loading was defined as contact with the opposing dentition as opposed to restoration without contact. Conventional healing was defined as 3 months postYimplant placement until restoration, whereas immediate restoration was defined as restoration within 48 hours of implant placement but not in occlusion with the opposing dentition. This definition was based on the capacity to perform the restorative clinical procedures within a limited time frame from surgery (such as the surgical placement occurring in one office one day and the restorative procedures performed in
Figure 11. Histologic cross-sections of implants from a) Group A: 3 months, b) Group B: 21 days, c) Group C: 10 days, d) Group D: 2 days after 3 months of loading. Reprinted with permission from Quinlan P, Nummikoski P, Schenk R, Cagna D, Mellonig J, Higginbottom F, Lang K, Buser D, Cochran D. Immediate and early loading of SLA ITI single-tooth implants: an in vivo study. Int J Oral Maxillofac Implants. 2005 May-June;20(3):360-70.19 Volume 6, Number 2
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Figure 12. Tissue-to-implant contact between tissue and primary and secondary bone, bone marrow, and connective tissue for Groups A (3 months), B (21 days), C (10 days), and D (2 days). Bars indicate SE. Reprinted with permission from Quinlan P, Nummikoski P, Schenk R. Immediate and early loading of SLA ITI single-tooth implants: an in vivo study. Int J Oral Maxillofac Implants. 2005 May-June;20(3):360-70.19
another office the next day). Early restoration was defined as the placement of the restoration at least 48 hours subsequent to implant placement but not later than 3 months. Immediate loading was therefore defined as restoration within 48 hours of implant placement and occlusal contact with the opposing dentition. Early loading was therefore restoration at least 48 hours subsequent to implant placement but not later than 3 months and the restoration in contact with the opposing dentition. The consensus group noted that the results of the studies were obtained from conditions that were considered favorable in that the inclusion and exclusion criteria used in many of the studies limited their evaluation to a selected population. The consensus conference concluded that in the edentulous mandible, immediate loading (up to 48 hours) in patients with both overdentures and fixed prostheses was well documented in the literature (Fig. 13). Early loading was separated into 2 periods based on studies in the literature. One early loading period was between 48 hours and 6 weeks and the second period from 6 weeks to 3 months. In the edentulous mandible in the period of early loading from 48 hours to 6 weeks, the procedure for overdentures and fixed prostheses was not well documented. In the period from 6 weeks to 3 months, no overdenture literature was available but the literature on fixed prostheses was well documented. In regard to the edentulous maxilla, no literature was available on overdentures that involved immediate or early loading (Fig. 14). In regard to fixed prosthesis in the edentulous maxilla, literature was available on both immediate and early loading; however, the group determined that this procedure was not well documented in the literature. In regard to the partially dentate maxilla and mandible, overdentures were not 162
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Figure 13. Loading documentation in the literature for edentulous mandible. Reprinted with permission from Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants. 2004;19 Suppl:109-13.21
applicable (Fig. 15). Fixed prostheses used in immediate restoration or loading indications in the partially dentate patient were not well documented. In regard to early restoration or loading in the partially dentate patient, the procedure was well documented only after 6 to 8 weeks and then when an implant was used with a roughened titanium surface.
CONCLUSION A summary of loading protocols, based on historical development, biological considerations, and the literature indicate that shortened loading protocols are dependent on (1) the quantity and quality of bone at the implant site and, as a consequence, the amount of primary bone contact, and (2) the rapidity of the bone formation and remodeling of the
Figure 14. Loading documentation in the literature for edentulous maxilla. Reprinted with permission from Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants. 2004;19 Suppl:109-13.21 June 2006
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3. 4. 5. 6. 7.
8. 9.
Figure 15. Loading documentation in the literature for partially dentate maxilla and mandible. Reprinted with permission from Cochran DL, Morton D, Weber HP. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants. 2004;19 Suppl: 109-13.21
10.
11.
12.
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bone surrounding the implant with resultant secondary bone contact. These conditions result in 2 clinical scenarios for supporting reduced healing times. If the implant site has high quality and quantity of existing bone, immediate loading protocols are possible. If the implant site has low quality and quantity of native bone and bone remodeling and bone formation are required, immediate loading is more contraindicated and early loading protocols are possible. However, many factors can be important such as the characteristics of the implant surface, the location of high-quality bone in the implant site, the ability to protect the implant restoration with adjacent tooth structure, the use of proteins (growth factors or stimulants) or materials and matrices used around the implant, and so forth. These factors are related to either (1) stimulating new bone-to-implant contact or (2) minimizing micromotion of the implant. In all situations, it is important to remember that the goal is improved patient care. Procedures that put the implant restoration at high risk in the patient are unacceptable. Understanding the historical development of implant healing times, the biological events that result in osseointegration as defined above, and knowing the literature on shortened healing times on implants, allows the clinician to appreciate options for various loading protocols and to improve the patient care they deliver.
REFERENCES 1. Branemark PI, Hansson BO, Adell R, Breine U, Lindstrom J, Hallen O, et al. Osseointegrated implants in the treatment of the edentulous jaw. Experience from a 10-year period. Scand J Plast Reconstr Surg Suppl 1977;16:1-132. 2. Szmukler-Moncler S, Piattelli A, Favero GA, Dubruille JH. Considerations
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preliminary to the application of early and immediate loading protocols in dental implantology. Clin Oral Implants Res 2000;11(1):12-25. Roberts WE. Bone tissue interface. J Dent Educ 1988;52(12):804-9. Schatzker J, Horne JG, Sumner-Smith G. The effect of movement on the holding power of screws in bone. Clin Orthop 1975;111:257-62. Cameron H, Macnab I, Pilliar R. Porous surfaced Vitallium staples. S Afr J Surg 1972;10(2):63-70. Cameron HU, Pilliar RM, MacNab I. The effect of movement on the bonding of porous metal to bone. J Biomed Mater Res 1973;7(4):301-11. Ducheyne P, De Meester P, Aernoudt E. Influence of a functional dynamic loading on bone ingrowth into surface pores of orthopedic implants. J Biomed Mater Res 1977;11(6):811-38. Unthoff HK, Germain JP. The reversal of tissue differentiation around screws. Clin Orthop 1975;123:248-52. Cochran DL, Buser D, ten Bruggenkate CM, Weingart D, Taylor TD, Bernard J-P, et al. The use of reduced healing times on ITI(R) implants with a sandblasted and acid-etched (SLA) surface. Clin Oral Impl Res 2002;13(2):144-53. Chiapasco M, Abati S, Romeo E, Vogel G. Implant-retained mandibular overdentures with Branemark System MKII implants: a prospective comparative study between delayed and immediate loading. Int J Oral Maxillofac Implants 2001;16(4):537-46. Ledermann P. [Complete denture support in edentulous problem mandibles with help from 4 titanium plasma-coated PDL screw implants]. SSO Schweiz Monatsschr Zahnheilkd 1979;89(11):1137-8. (German) Schroeder A, van der Zypen E, Stich H, Sutter F. The reactions of bone, connective tissue, and epithelium to endosteal implants with titaniumsprayed surfaces. J Maxillofac Surg 1981;9(1):15-25. Cochran DL, Schenk RK, Lussi A, Higginbottom FL, Buser D. Bone response to unloaded and loaded titanium implants with a sandblasted and acid-etched surface: a histometric study in the canine mandible. J Biomed Mater Res 1998;40(1):1-11. Barewal RM, Oates TW, Meredith N, Cochran DL. Resonance frequency measurement of implant stability in vivo on implants with a sandblasted and acid-etched (SLA) surface. Int J Oral and Maxillofac Implants 2003;18(5):641-51. Babbush CA, Kent JN, Misiek DJ. Titanium plasma-sprayed (TPS) screw implants for the reconstruction of the edentulous mandible. J Oral Maxillofac Surg 1986;44(4):274-82. Schnitman PA, Wohrle PS, Rubenstein JE. Immediate fixed interim prostheses supported by two-stage threaded implants: methodology and results. J Oral Implantology 1990;16(2):96-105. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implants 1997;12(3):319-24. Chiapasco M, Gatti C, Rossi E, Haefliger W, Markwalder TH. Implant-retained mandibular overdentures with immediate loading. A retrospective multicenter study on 226 consecutive cases. Clin Oral Implants Res 1997;8(1):48-57. Quinlan P, Nummikoski P, Schenk R, Cagna D, Mellonig J, Higginbottom F, et al. Immediate and early loading of ITI SLA single tooth implants: an in vivo study. Int J Oral Maxillofac Implants 2005; 20:360-70. Ioannidou E, Doufexi A. Does loading time affect implant survival? A meta-analysis of 1,266 implants. J Periodontol 2005;76(8):1252-8. Cochran DL, Morton D, Weber H-P. Consensus statements and recommended clinical procedures regarding loading protocols for endosseous dental implants. Int J Oral Maxillofac Implants 2004;19(Suppl):109-13. Chiapasco M. Early and immediate restoration and loading of implants in completely edentulous patients. Int J Oral Maxillofac Implants 2004; 19(Suppl):76-91. Ganeles J, Wismeijer D. Early and immediately restored and loaded dental implants for single-tooth and partial-arch applications. Int J Oral Maxillofac Implants Suppl., 2004;19:92-102. Morton D, Jaffin R, Weber H-P. Immediate restoration and loading of dental implants: clinical considerations and protocols. Int J Oral Maxillofac Implants 2004;19(Suppl):103-8.
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