04-Implant Single Crowns
Content
IMPLANT SINGLE CROWNS
RESD 854
Charles J. Goodacre, DDS, MSD Professor, Restorative Dentistry Loma Linda University Loma Linda, California
INTRODUCTION
Osseointegrated implants have been successfully used to replace single teeth, both anteriorly and posteriorly (figure 1A, 1B, 1C, 1D, 2A, 2B, 3A, 3B, 4A, 4B, 4C, 4D, 5A, 5B, 5C, 5D, 6A, 6B, 7A, 7B). While implant single crowns have been used for shorter time periods than other types of implant prostheses, considerable information has emerged regarding their design, clinical procedures, and success/failure/complications1-37. A list of the complications identified in clinical studies of implant single crowns is presented in table 1.
SUCCESS, FAILURE, COMPLICATIONS
Implant Loss Between 1991 and 2001, 27 clinical studies10-36 reported data regarding the number of implants placed and lost over a specified time. In the combined data from all the studies, 1870 implants were placed and they were observed for times between 1 and 10 years. A total of 51 implants were lost for a mean loss of 3%. This failure rate, shared with implants that support mandibular fixed complete dentures, is the lowest failure rate encountered in implant prosthodontics. Three studies24,34,36 provided data that permitted a comparison of maxillary and mandibular implant loss. Six studies10,15,17,18,24,36 provided data regarding the time (preprosthetic or postposthetic) when the implants were lost. Forty-seven percent of the implants were lost preprosthetically and 53% postprosthetically. Other Complications Other implant single crown complications identified in the studies included prosthesis screw loosening (26%)20,29; abutment screw loosening with early screw designs reported from 1991-1996 (25%)10,13,15,16,18,19,21; fistulas at implant-abutment level (8%)10,13,15,17,18,22;abutment screw loosening with newer screw designs reported from 1998-2000 (7%)25,26,30-33; esthetic problems (7%)10,15,19,25,30,37; implant dehiscence before stage two (4%)10,17,22,23; neurosensory disturbance after surgery (4%)10,22; and abutment screw fracture (2%)22,30.
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These incidences are specific to implant single crowns and therefore they differ from the data presented in the implant complications portion of this CD (which was calculated by combining the data from all types of prostheses).
DESIGN PRINCIPLES
Rangert, Jemt and Jörneus1 (reference 1) evaluated the forces and moments that occur on Brånemark implants. They proposed some general design guidelines for implants that included recommendations regarding how far the crown can extend lateral to the implant without creating a potential overload situation (the dimensions of the occlusal table compared to the implant diameter). In another article2, information regarding bending overload and implant fracture is presented (reference 2). Rangert et al3 also identified risk factors that increase the load applied to implants and several of these factors can be related to implant single crowns (reference 3). Anterior Biomechanics Given the previously cited guidelines of Rangert et al1, it appears reasonable to conclude that anterior implant single crowns can extend laterally beyond the implant a distance that is about 2 times the diameter of the implant (the maximum horizontal cantilever). As an example, if an anterior crown is being placed on a 4 millimeter diameter implant, the crown can safely extend mesial, distal, facial, or lingual to the implant a distance of 8 millimeters (2 times the implant diameter) before a biomechanical overload is developed. There are no anterior teeth where the mesiodistal or faciolingual dimensions would create an adverse lever arm since no anterior tooth even approaches such a mediodistal (figure 8, 9) or faciolingual dimension. However, in an incisocervical dimension, biomechanical overload of an anterior crown is more likely to occur since the distance from the top of the implant to the location of occlusal contact can be substantial especially when the implant is placed deep below the soft tissue for esthetic reasons (figure 10A, 10B). When there is the potential for implant overload due to the presence of risk factors, alterations in the incisal guidance and implant angulation in the bone may be helpful in decreasing the potential for overload4 (reference 4). Posterior Biomechanics In applying the previous recommendations about forces and moments1 to posterior single crowns being placed on implants, it appears the crown should not extend lateral to the implant more than one implant diameter. For a 4 millimeter diameter implant, the maximum lateral cantilever is 4 millimeters. Therefore, the crown can only extend mesially, distally, facially or lingually a distance of 4 millimeters beyond the implant (figure 11A, 11B). This relationship limits the total mesiodistal or faciolingual dimension of the crown to 12 millimeters. The dimensions of a typical premolar do not exceed these guidelines nor do average sized molars. However, there can be a potential biomechanical overload with
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molars due to the presence of heavy occlusal forces (figure 12A) or larger than normal mesiodistal/faciolingual dimensions. Figure 13 has been adapted from a figure in reference 2 and documents the relative number of fractures that occurred with implants located in first molar sites. Should a single molar implant be placed so it is not centered under the crown, biomechanical overload is much more likely to occur (figure 14A, 14B, 14C, 14D, 15A, 15B). The possibility of an overload also increases as the distance from the occlusal surface to the implant increases (figure 16A, 16B). Methods of compensating for potential overload of 4 millimeter diameter molar implants include narrowing the occlusal table or the use of 2 implants to support one molar crown (figure 17A, 17B, 17C, 17D, 18A, 18B, 19A, 19B). A common method of compensating for potential overload is to use a wider diameter implant (5 or 6 millimeters) (figure 7A, 7B, 12A, 12B, 12C). A clinical report5 has been published regarding the use of wide diameter implants and double implants. The report indicates good success is possible but the authors emphasize the importance of proper surgical execution (Bahat, 1996). A study6 of 47 patients compared the use of one implant with the use of 2 implants to replace a single molar. Of 72 implants placed, one was lost. There was much greater screw loosening (48%) in the one implant group compared with the two implant group (8%), demonstrating a biomechanical advantage of using 2 implants to replace one molar (Balshi, 1996). Implant Location/Alignment The location of the implant in the bone is an important aspect of biomechanical success and crown esthetics with using implant single crowns. The implant should be centered mesiodistally in the edentulous space for esthetic and biomechanical reasons (figure 1A, 1D, 4B, 4D, 20A, 20B). This position equalizes the lever arm developed by the mesial and distal portions of the crown which project laterally to the implant. When the implant is displaced to the mesial or distal of center and occlusal forces are applied, there is greater leverage exerted on the implant and other components than if the implant were centered (figure 21A, 21B). Centering the implant mesiodistally also facilitates the development of normal emergence profile and permits better morphologic replication of the contralateral tooth (figure 22A, 22B). When locating the implant in bone, care must be exercised to avoid approximating adjacent teeth which can lead to the need for endodontic treatment, damage to the roots, and/or loss of the implant (figure 23A, 23B).
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The faciolingual positioning of the implant is also important to biomechanical success. Centering an implant beneath a posterior crown helps reduce the potential for biomechanical overload, a factor particularly important for molars or premolars when heavy occlusal forces are present. In esthetically critical locations, a position slightly to the facial is preferred when existing bone dimensions permit (figure 1A, 24). Centering the implant faciolingually may produce a crown with deficient cervical contour (figure 6A) or a crown where porcelain must overlap the facial soft tissue to create the desired cervical crown morphology (figure 25A, 25B, 22B, 26A, 26B). The overlapping makes oral hygiene more difficult and could present an esthetic liability should the soft tissue position recede apically. When the implant is placed lingual to the faciolingual center of the adjacent teeth, there will either be a substantial amount of the crown overlapping (figure 27A, 27B, 27C) facial soft tissue (like occurs with certain fixed partial denture pontics) or the crown will assume a form with significant cervical deficiencies (figure 28A, 28B). Placing an implant too far facially creates substantial esthetic challenges that often cannot be overcome (figure 29A, 29B). It is possible that an implant could be so malaligned that it would have to be removed, bone fill allowed to occur, and another implant subsequently placed in a more favorable position. Aligning the implant so it will be perpendicular to the occlusal surface decreases the leverage that will be applied to the various metal components (figure 30A, 30B). The incisocervical/occlusocervical location of the implant is largely determined by the location of existing bone (figure 1C, 4B, 10B, 16B) and the esthetic need to transition from a smaller diameter round form to a larger diameter form with a different geometric perimeter. Typically, implants have been placed apical to the cementoenamel junction of adjacent teeth to permit the required changes in morphology to occur somewhat gradually (figure 31). One textbook7 recommended that implants located in the esthetic zone be placed 4 millimeters or more apical to the cementoenamel junctions of adjacent teeth (Parel, 1989). Soft Tissue/Interdental Papilla Form Achieving ideal soft tissue form and interdental papilla height can be a challenge when placing implants into highly visible edentulous areas (figure 1D, 2B, 3B, 4D, 5C, 5D). Interdental dark spaces may be present (figure 2B, 32A, 32B, 32C, 32D), the marginal tissue may be thicker than the gingival margin present around adjacent teeth (figure 32B, 33A, 33B, 33C, 33D), the apical location of the soft tissue margin may not be at the same height as adjacent or contralateral natural teeth (figure 3B, 22B), interdental papillae may not possess the most desirable form or height (figure 1D, 2B, 3B, 32B, 32C, 32D, 33C, 33D), or recession of the soft tissue may lead to crown length variations and/or exposed metal (figure 34A, 34B).
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Some of these deficits may not be noticeable to patients whereas others can produce substantial esthetic challenges. Fortunately, if bone is present at the proper height interproximally, the soft tissue can fill in small spaces over time (figure 4C, 4D). One study8 of 21 patients compared the use of a conventional surgical flap that included the interdental papilla with a design that did not sever the 2 interdental papillae when a single implant had been placed. The modified flap design preserved at least 1 millimeter of both papillae (adjacent to the natural teeth). A reduction in the crestal bone loss was noted which presumably would enhance the esthetic result achieved (Gomez-Roman, 2001). Gingival recession has been measured in a 1-year prospective study9. The authors indicate about 1 millimeter of recession can generally be expected following abutment connection surgery. Eighty percent of the buccal sites exhibited recession. Since most of the recession occurred within the first 3 months, the authors proposed waiting 3 months after abutment connection surgery before making the definitive impression (Small, 2000). The longer the area has been edentulous, the more likely there will be a soft tissue discrepancy due to bone resorption and concomitant changes in the soft tissue contour. When there will be a substantial esthetic deficiency as noted clinically or from a diagnostic wax pattern formed on a cast, bone and/or soft tissue grafting may be necessary (figure 35A, 35B, 35C). However, some esthetic deficiencies are not totally correctable through grafting procedures and therefore it is generally felt that emphasis should be placed on retaining soft tissue form rather than restoring lost tissue. Methods of retaining soft tissue form and location include immediate implant placement and immediate placement of a provisional restoration when these procedures are indicated.
SYNOPSIS OF DESIGN GUIDELINES
• • • • • • • • • Center the implant mesiodistally in the edentulous space. If possible, position the implant faciolingually so a normal emergence profile can be developed and the crown does not have to overlap the peri-implant mucosa on the facial surface to develop proper cervical contour. If facial overlapping of the soft tissue will be necessary, consider some type of bone augmentation procedure so the implant can be placed in a more facial location. Place the implant as perpendicular to the occlusal surface as possible. With posterior implant single crowns, avoid extending the occlusal surface lateral to the implant by a distance greater than the diameter of the implant. Use wider diameter implants when access, bone dimensions, and esthetics permit. Maintain light centric occlusal contact (shim stock just slides through) between the implant single crown and the opposing tooth during normal tapping occlusal contact. When the patient fully engages their musculature, the shim stock should only then be grasped by the crown with the same intensity as opposing natural teeth. Avoid eccentric occlusal contact on the implant single crown or develop group function if contact cannot be avoided.
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The presence of bruxism increases the magnitude of the force applied and its frequency. Avoid using short implants and have the patient wear an occlusal device (night guard).
CLINICAL PROCEDURES
Examination/Diagnosis and Treatment Planning A clinical examination, medical and dental history, periapical and bitewing radiographs, and diagnostic casts are required to plan treatment. There should be an evaluation of systemic factors that can compromise implant success. The clinical examination and radiographs should be used to evaluate bone health and quality, incisocervical/occlusocervical bone dimensions, the distance between adjacent roots, presence of any caries, the pulpal and periodontal health of adjacent teeth, and the quality/integrity of existing restorations in adjacent teeth. Any diseases in teeth approximating the edentulous area should be treated. Untreated diseases can cause implant loss. When examining patients who have single missing teeth and could potentially benefit from implant supported/retained single crowns, it is important to determine if the morphologic form of a crown would be esthetically appropriate when developed on the existing edentulous ridge with the implant contained in available bone (figure 36A, 36B, 36C, 36D). This decision requires that a diagnostic pattern of the crown be developed. Any esthetic deficiencies in crown dimensions or cervical contour due to bone resorption of the alveolar ridge will be identified by this diagnostic procedure. Radiographic Template Through either bone sounding or a linear tomogram, it is possible to determine available bone dimensions in the alveolar ridge. By using a radiographic template in conjunction with a linear tomogram (figure 37A, 37B, 37C, 37D), the diagnostic form/location of the crown can be related to available bone to determine if an implant can be positioned within available bone and lead to the development of a crown with appropriate form and dimensions. This data coupled with the clinical examination, diagnostic casts, and diagnostic pattern of the most desirable crown form will identify patients where bone augmentation will be necessary to achieve the best possible esthetic result and allow the patient to make decisions regarding their treatment.
Ridge Augmentation When ridge augmentation is needed, the ideal ridge form can be developed in wax on the diagnostic cast while simultaneously adapting a denture tooth to the wax ridge. This process is continued until the desired crown form is established (figure 38A). A provisional removable partial denture can then be fabricated over the form of the ideal ridge that was developed in wax.
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The provisional prosthesis serves to validate the desired esthetic crown form (figure 38B, 38C) and also can be used as a template during the ridge augmentation procedure. The flap is reflected (figure 38D), bone graft material packed against the ridge (figure 38E), the provisional prosthesis placed into the mouth for the purpose of evaluating whether the ridge has been sufficiently enhanced in size (figure 38F), and then a barrier membrane placed over the graft material (figure 38G). The flap is then closed and sutured (figure 38H). After healing, an assessment can be made as to whether the desired ridge form has been achieved. A less than optimal incisocervical result can be seen in figures 38I, 38J, 38K, 38L, and 38M. A better result can be observed in figures 35A, 35B, 35C, 39A, 39B, 39C, 39D, 39E. Surgical Template/Implant and Abutment Placement/Provisional Crown Based on a pattern of the most desirable crown form and location, a surgical template is fabricated to guide implant placement (figure 40A, 40B, 40C, 40D). The implant is placed and the soft tissue sutured. After the appropriate healing time, the implant is uncovered and either a healing abutment or a definitive abutment placed. In esthetic zones, placement of a definitive abutment and provisional crown allows the soft tissue form to be developed around the contours of the provisional crown which can be more natural in shape than healing abutment contours (figure 41A, 41B, 41C, 41D, 41E, 41F, 41G, 42A, 42B, 42C). Impression/Cast/Crown Fabrication When a definitive prefabricated abutment (supplied by a manufacturer) has been placed, an abutment level impression is made using an impression coping (figure 43A, 43B, 43C, 43D, 43E, 43F). An abutment analog is positioned into the impression coping and a cast poured (figures44A, 44B). More commonly, an implant level impression is made using an impression coping that attaches to the implant (figure 45A). There are two types of impression copings: tapered (allows the impression to be removed from the mouth while the impression coping remains attached to the implant); and geometrically shaped copings that possess undercuts (the impression cannot be removed from the mouth until the coping is unscrewed from the implant). Tapered impression copings are used when the long axis of the implant (and therefore the long axis of the coping) is sufficiently parallel to the natural teeth that the impression can be removed from the mouth after the impression material polymerizes (Video A). This type of impression has been termed a closed-tray impression because a conventional impression tray can be used (the impression tray does not have to have a hole in its surface to provide access to the impression coping after the impression material polymerizes).
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When the long axis of the implant is different from the remaining teeth, impression material locks around a tapered impression coping (due to its angulation being different from the teeth) and prevents removal of the polymerized impression from the patient's mouth. Under these circumstances, a geometrically shaped coping is used (Video B). The geometric form (that possesses undercuts) allows the coping to be grasped by the impression material and it is therefore retained in the impression material. A screw (in the form of a metal rod) is used to attach this form of coping to the implant. The metal rod (screw) is long enough to pass through the impression tray. The screw can then be loosened after the impression material polymerizes, allowing the impression to be removed while the coping is retained within the impression material. This type of impression has been termed an open-tray impression because the impression tray must contain a hole through which the screw can project, thereby permitting the screw to be loosened after the impression material hardens. An implant analog (machined replica of the implant) is attached to the coping and a cast poured (figure 45B). The resulting cast can then be used to determine the most appropriate size and type of prefabricated abutment to used (figure 46A, 46B, 46C, 46D, 46E, 47A, 47B, 47C, 47D, 47E, 47F) or a custom abutment can be fabricated (figure 48A, 48B). It is also possible to place a prefabricated abutment, prepare the metal in the same manner that a tooth would be prepared (figure 49A), place gingival retraction cord, make a conventional impression (figure 49B) that records the abutment finish line and shape of the prepared abutment, and then pour a die and cast (figure 49C). The definitive crown is fabricated on the working cast in a manner that it can be cemented over the abutment (figure 50A, 50B, 50C) or be retained by a screw (figure 51A, 51B, 51C, 51D).
TABLE
Table 1 Implant Single Crown Complications # Studies Providing Data 2 7 6 6 6 4 2 27 2 Total # Patients or Components Affected (%) 27 of 105 screws (26) 151 of 613 screws (25) 38 of 451 implants (8) 42 of 623 screws (7) 34 of 483 crowns (7) 11 of 270 implants (4) 5 of 141 patients (4) 51 of 1870 implants (3) 4 of 165 screws (2)
Prosthesis screw loosening Abutment screw loosening (1991-1996) Fistula at implant-abutment level Abutment screw loosening (1998-2000) Esthetic problems Implant dehiscence before stage two Neurosensory disturbance (after surgery) Implant loss Abutment screw fractures
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REFERENCES
1. Rangert B, Jemt T, Jörneus L. Forces and moments on Brånemark implants. Int J Oral Maxillofac Implants 1989;4:241-247. Based on theoretical considerations and clinical experience with Brånemark implants, this article presented quidelines for controlling the forces applied to implants. They recommended that the restoration not extend lateral to the implant more than approximately one implant diameter in the molar region and no more than two implant diameters in the incisor region. They indicated greater extensions may be acceptable if more than one implant is being subjected to the bending moment, such as with an implant fixed partial denture or an implant fixed complete denture. 2. Rangert B, Krogh PHJ, Langer B, Van Roekel, N. Bending overload and implant fracture: A retrospective clinical analysis. Int J Oral Maxillofac Implants 1995;10:326-334. Probable causes of 39 implant fractures were discussed as they related to 39 patients that had been treated by 3 of the authors. Eighteen implants fractured while supporting a posterior fixed partial denture, 9 while supporting a single crown, 7 while connected to a natural tooth, 4 while supporting a maxillary fixed complete denture, and 1 while supporting an overdenture. All 9 fractures of implants supporting single crowns occurred in the mandibular molar area (8 first molars and 1 second molar). Several factors were discussed that place adverse loads on implants and they included the following: a. excessive height of the occlusal surface above the implant; b. deviation of the long axis of the implant from a perpendicular relationship to the occlusal plane; c. substantial differences between the dimension of the occlusal surface and the diameter of the implant; and d. bruxism or heavy occlusal forces. 3. Rangert BR, Sullivan RM, Jemt TM. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-370. This article identified risk factors that increase the load applied to implants. Several of the factors can be related to implant single crowns: extension of the occluding surfaces lateral to the implant (creating leverage); increasing the distance from the occlusal contact to the implant; use of one implant to support a multi-rooted tooth; and bruxism or the presence of heavy occlusal forces as evidenced by wear/tooth structure fractures.
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When a molar is replaced by using a single implant, the authors emphasize the importance of controlling the occlusion so it is not in heavy centric occlusal contact. They suggest light centric occlusal contact. 4. Katona TR, Goodacre CJ, Brown DT, Robert WE. Force-moment systems on single maxillary anterior implants: effects of incisal guidance, fixture orientation, and loss of bone support. An engineering model was developed that compared the effects of incisal guidance steepness, implant angulation in the bone, and the level of bone support on the moment developed on the implant. Reducing the steepness of the incisal guidance reduced the moment and labial component of force. Implants that can be placed more vertically in the bone because of existing maxillary bone morphology will have reduced moments placed on the implant. Changes in the bone height (either due to bone loss or from more apical placement of the implant) increased the moment. Five millimeters of change in the bone height doubled the moment.
REFERENCE LIST
1. Rangert B, Jemt T, Jörneus L. Forces and moments on Brånemark implants. Int J Oral Maxillofac Implants 1989;4:241-247. 2. Rangert B, Krogh PHJ, Langer B, Van Roekel N. Bending overload and implant fracture: a retrospective clinical analysis. Int J Oral Maxillofac Implants 1995;10:326-334. 3. Rangert B, Sullivan RM, Jemt TM. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-370. 4. Katona TR, Goodacre CJ, Brown DT, Roberts WE. Force-moment systems on single maxillary anterior implants: effects of incisal guidance, fixture orientation, and loss of bone support. Int J Oral Maxillofac Implants 1993;8:512-522. 5. Bahat O, Handelsman M. Use of wide implants and double implants in the posterior jaw: a clinical report. Int J Oral Maxillofac Implants 1996;11:379-386. 6. Balshi TJ, Hernandez RE, Pryszlak MC, Rangert B. A comparative study of one implant versus two replacing a single molar. Int J Oral Maxillofac Implants 1996;11:372-378. 7. Parel SM, Sullivan DY. Esthetics and Osseointegration, Dallas, Osseointegration Seminars Incorporated, 1989, pp19-23. 8. Gomez-Roman G. Influence of flap design on peri-implant interproximal crestal bone loss around single-tooth implants. Int J Oral Maxillofac Implants 2001;16:6167. 9. Small PN, Tarnow DP. Gingival recession around implants: a 1-year longitudinal prospective study. Int J Oral Maxillofac Implants 2000;15:527-532. 10. Jemt T, Laney WR, Harris D, Henry PJ, Krogh PH Jr, Polizzi G, et al. Osseointegrated implants for single tooth replacement: a 1-year report from a multicenter prospective study. Int J Oral Maxillofac Implants 1991;6:29-36.
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11. Babbush CA, Shimura M. Five-year statistical and clinical observations with the IMZ two-stage osteointegrated implant system. Int J Oral Maxillofac Implants 1993;8:245-253. 12. Fugazzotto PA, Gulbransen JH, Wheeler SL, Lindsay IA. The use of IMZ osseointegrated implants in partially and completely edentulous patients: success and failure rates of 2,023 implants cylinders up to 60+ months in function. Int J Oral Maxillofac Implants 1993;8:617-621. 13. Jemt T, Pettersson P. A 3-year follow-up study on single implant treatment. J Dent 1993;21:203-208. 14. Schmitt A, Zarb GA. The longitudinal clinical effectiveness of osseointegrated dental implants for single-tooth replacement. Int J Prosthodont 1993;6(1):97-202. 15. Ekfeldt A, Carlsson GF, Borjesson G. Clinical evaluation of single-tooth restorations supported by osseointegrated implants: a retrospective study. Int J Oral Maxillofac Implants 1994;9(1):79-83. 16. Laney WR, Jemt T, Harris D, Henry PJ, Krogh PH, Polizzi G, et al. Osseointegrated implants for single-tooth replacement: progress report from a multicenter prospective study after 3 years. Int J Oral Maxillofac Implants 1994;9:49-54. 17. Cordioli G, Castagna S, Consolati F. Single-tooth implant rehabilitation: a retrospective study of 67 implants. Int J Prosthodont 1994;7:525-531. 18. Andersson B, Odman P, Lindvall AM, Lithner B. Single-tooth restorations supported by osseointegrated implants: results and experiences from a prospective study after 2 to 3 years. Int J Oral Maxillofac Implants 1995;10:702-711. 19. Haas R, Mensdorff-Pouilly N, Mailath G, Watzek G. Brånemark single tooth implants: a preliminary report of 76 implants. J Prosthet Dent 1995;73(2):74-79. 20. Becker W, Becker BE. Replacement of maxillary and mandibular molars with single endosseous implant restorations: a retrospective study. J Prosthet Dent 1995;74:5155. 21. Henry PJ, Laney WR, Jemt T, Harris D, Krogh PHJ, Polizzi G, Zarb GA, Herrmann I. Osseointegrated implants for single-tooth replacement: a prospective 5-year multicenter study. Int J Oral Maxillofac Implants 1996;11:450-455. 22. Avivi-Arber L, Zarb GA. Clinical effectiveness of implant-supported single tooth replacement: the Toronto study. Int J Oral Maxillofac Implants 1996;11:311-321. 23. Karlsson U, Gotfredsen K, Olsson C. Single-tooth replacement by osseointegrated Astra Tech dental implants: a 2-year report. Int J Prosthodont 1997;10:318-324. 24. Kemppainen P, Eskola S, Ylipaavalniemi P. A comparative prospective clinical study of two single-tooth implants: a preliminary report of 102 implants. J Prosthet Dent 1997;77(4):382-387. 25. Andersson B, Ödman P, Lindvall A-M, Brånemark P-I. Cemented single crowns on osseointegrated implants after 5 years: results from a prospective study on CeraOne. Int J Prosthodont 1998;11:212-218. 26. Scheller H, Urgell P, Kultje C, Klineberg I, Goldberg PV, Stevenson-Moore P, Alonso JMN, Schaller M,Corria RM, Engquist B, Toreskog S, Kastenbaum F, Smith CR. A 5-year multicenter study on implant-supported single crown restorations. Int J Oral Maxillofac Implants 1998;13:212-218.
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27. Wannfors K, Smedberg JI. A prospective clinical evaluation of different single-tooth restoration designs on osseointegrated implants. A 3-year follow-up of Brånemark implants. Clin Oral Implants Res 1999;10(6):453-458. 28. Watson CJ, Tinsley D, Ogden AR, Russell JL, Mulay S, Davison EM. A 3 to 4 year study of single tooth hydroxylapatite coated endosseous dental implants. Br Dent J 1999;187(2):90-94. 29. Levine RA, Clem DS 3rd, Wilson TG Jr, Higginbottm F, Solnit G. Multicenter retrospective analysis of the ITI implant system used for single-tooth replacements: results of loading for 2 or more years. Int J Oral Maxillofac Implants 1999;14(4):516-520. 30. Priest G. Single-tooth implants and their role in preserving remaining teeth: a 10year survival study. Int J Oral Maxillofac Implants 1999;14:181-188. 31. Schwartz-Arad D, Samet N, Samet N. Single tooth replacement of missing molars: a retrospective study of 78 implants. J Periodontol 1999;70:449-454. 32. Bianco G, Di Raimondo R, Luongo G, Paoleschi C, Piccoli P, Piccoli C, Rangert B. Osseointegrated implant for single-tooth replacement: a retrospective multicenter study on routine use in private practice. Clin Implant Dent Relat Res 2000;2:152158. 33. Palmer RM, Palmer PJ, Smith BJ. A 5-year prospective study of Astra single tooth implants. Clin Oral Implant Res 2000;11:179-182. 34. Polizzi G, Rangert B, Lekholm U, Gualini F, Lindstrom H. Brånemark System Wide Platform implants for single molar replacement: clinical evaluation of prospective and retrospective materials. Clin Implant Dent Relat Res 2000;2(2):61-69. 35. Chaushu G, Chaushu S, Tzohar A, Dayan D. Immediate loading of single-tooth implants: immediate versus non-immediate implantation. A clinical report. Int J Oral Maxillofac Implants 2001;16(2):267-272. 36. Cooper L, Felton DA, Kugelberg CF, Ellner S, Chaffee N, Molina AL, Moriarty JD, Paquette D, Palmqvist U. A multicenter 12-month evaluation of single-tooth implants restored 3 weeks after 1-stage surgery. Int J Oral Maxillofac Implants 2001;16(2):182-192. 37. Chang M, Ödman PA, Wennström JL, Andersson B. Esthetic outcome of implantsupported single-tooth replacements assessed by the patient and prosthodontists. Int J Prosthodont 1999;12:335-341.
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RESD 854
Charles J. Goodacre, DDS, MSD Professor, Restorative Dentistry Loma Linda University Loma Linda, California
INTRODUCTION
Osseointegrated implants have been successfully used to replace single teeth, both anteriorly and posteriorly (figure 1A, 1B, 1C, 1D, 2A, 2B, 3A, 3B, 4A, 4B, 4C, 4D, 5A, 5B, 5C, 5D, 6A, 6B, 7A, 7B). While implant single crowns have been used for shorter time periods than other types of implant prostheses, considerable information has emerged regarding their design, clinical procedures, and success/failure/complications1-37. A list of the complications identified in clinical studies of implant single crowns is presented in table 1.
SUCCESS, FAILURE, COMPLICATIONS
Implant Loss Between 1991 and 2001, 27 clinical studies10-36 reported data regarding the number of implants placed and lost over a specified time. In the combined data from all the studies, 1870 implants were placed and they were observed for times between 1 and 10 years. A total of 51 implants were lost for a mean loss of 3%. This failure rate, shared with implants that support mandibular fixed complete dentures, is the lowest failure rate encountered in implant prosthodontics. Three studies24,34,36 provided data that permitted a comparison of maxillary and mandibular implant loss. Six studies10,15,17,18,24,36 provided data regarding the time (preprosthetic or postposthetic) when the implants were lost. Forty-seven percent of the implants were lost preprosthetically and 53% postprosthetically. Other Complications Other implant single crown complications identified in the studies included prosthesis screw loosening (26%)20,29; abutment screw loosening with early screw designs reported from 1991-1996 (25%)10,13,15,16,18,19,21; fistulas at implant-abutment level (8%)10,13,15,17,18,22;abutment screw loosening with newer screw designs reported from 1998-2000 (7%)25,26,30-33; esthetic problems (7%)10,15,19,25,30,37; implant dehiscence before stage two (4%)10,17,22,23; neurosensory disturbance after surgery (4%)10,22; and abutment screw fracture (2%)22,30.
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These incidences are specific to implant single crowns and therefore they differ from the data presented in the implant complications portion of this CD (which was calculated by combining the data from all types of prostheses).
DESIGN PRINCIPLES
Rangert, Jemt and Jörneus1 (reference 1) evaluated the forces and moments that occur on Brånemark implants. They proposed some general design guidelines for implants that included recommendations regarding how far the crown can extend lateral to the implant without creating a potential overload situation (the dimensions of the occlusal table compared to the implant diameter). In another article2, information regarding bending overload and implant fracture is presented (reference 2). Rangert et al3 also identified risk factors that increase the load applied to implants and several of these factors can be related to implant single crowns (reference 3). Anterior Biomechanics Given the previously cited guidelines of Rangert et al1, it appears reasonable to conclude that anterior implant single crowns can extend laterally beyond the implant a distance that is about 2 times the diameter of the implant (the maximum horizontal cantilever). As an example, if an anterior crown is being placed on a 4 millimeter diameter implant, the crown can safely extend mesial, distal, facial, or lingual to the implant a distance of 8 millimeters (2 times the implant diameter) before a biomechanical overload is developed. There are no anterior teeth where the mesiodistal or faciolingual dimensions would create an adverse lever arm since no anterior tooth even approaches such a mediodistal (figure 8, 9) or faciolingual dimension. However, in an incisocervical dimension, biomechanical overload of an anterior crown is more likely to occur since the distance from the top of the implant to the location of occlusal contact can be substantial especially when the implant is placed deep below the soft tissue for esthetic reasons (figure 10A, 10B). When there is the potential for implant overload due to the presence of risk factors, alterations in the incisal guidance and implant angulation in the bone may be helpful in decreasing the potential for overload4 (reference 4). Posterior Biomechanics In applying the previous recommendations about forces and moments1 to posterior single crowns being placed on implants, it appears the crown should not extend lateral to the implant more than one implant diameter. For a 4 millimeter diameter implant, the maximum lateral cantilever is 4 millimeters. Therefore, the crown can only extend mesially, distally, facially or lingually a distance of 4 millimeters beyond the implant (figure 11A, 11B). This relationship limits the total mesiodistal or faciolingual dimension of the crown to 12 millimeters. The dimensions of a typical premolar do not exceed these guidelines nor do average sized molars. However, there can be a potential biomechanical overload with
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molars due to the presence of heavy occlusal forces (figure 12A) or larger than normal mesiodistal/faciolingual dimensions. Figure 13 has been adapted from a figure in reference 2 and documents the relative number of fractures that occurred with implants located in first molar sites. Should a single molar implant be placed so it is not centered under the crown, biomechanical overload is much more likely to occur (figure 14A, 14B, 14C, 14D, 15A, 15B). The possibility of an overload also increases as the distance from the occlusal surface to the implant increases (figure 16A, 16B). Methods of compensating for potential overload of 4 millimeter diameter molar implants include narrowing the occlusal table or the use of 2 implants to support one molar crown (figure 17A, 17B, 17C, 17D, 18A, 18B, 19A, 19B). A common method of compensating for potential overload is to use a wider diameter implant (5 or 6 millimeters) (figure 7A, 7B, 12A, 12B, 12C). A clinical report5 has been published regarding the use of wide diameter implants and double implants. The report indicates good success is possible but the authors emphasize the importance of proper surgical execution (Bahat, 1996). A study6 of 47 patients compared the use of one implant with the use of 2 implants to replace a single molar. Of 72 implants placed, one was lost. There was much greater screw loosening (48%) in the one implant group compared with the two implant group (8%), demonstrating a biomechanical advantage of using 2 implants to replace one molar (Balshi, 1996). Implant Location/Alignment The location of the implant in the bone is an important aspect of biomechanical success and crown esthetics with using implant single crowns. The implant should be centered mesiodistally in the edentulous space for esthetic and biomechanical reasons (figure 1A, 1D, 4B, 4D, 20A, 20B). This position equalizes the lever arm developed by the mesial and distal portions of the crown which project laterally to the implant. When the implant is displaced to the mesial or distal of center and occlusal forces are applied, there is greater leverage exerted on the implant and other components than if the implant were centered (figure 21A, 21B). Centering the implant mesiodistally also facilitates the development of normal emergence profile and permits better morphologic replication of the contralateral tooth (figure 22A, 22B). When locating the implant in bone, care must be exercised to avoid approximating adjacent teeth which can lead to the need for endodontic treatment, damage to the roots, and/or loss of the implant (figure 23A, 23B).
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The faciolingual positioning of the implant is also important to biomechanical success. Centering an implant beneath a posterior crown helps reduce the potential for biomechanical overload, a factor particularly important for molars or premolars when heavy occlusal forces are present. In esthetically critical locations, a position slightly to the facial is preferred when existing bone dimensions permit (figure 1A, 24). Centering the implant faciolingually may produce a crown with deficient cervical contour (figure 6A) or a crown where porcelain must overlap the facial soft tissue to create the desired cervical crown morphology (figure 25A, 25B, 22B, 26A, 26B). The overlapping makes oral hygiene more difficult and could present an esthetic liability should the soft tissue position recede apically. When the implant is placed lingual to the faciolingual center of the adjacent teeth, there will either be a substantial amount of the crown overlapping (figure 27A, 27B, 27C) facial soft tissue (like occurs with certain fixed partial denture pontics) or the crown will assume a form with significant cervical deficiencies (figure 28A, 28B). Placing an implant too far facially creates substantial esthetic challenges that often cannot be overcome (figure 29A, 29B). It is possible that an implant could be so malaligned that it would have to be removed, bone fill allowed to occur, and another implant subsequently placed in a more favorable position. Aligning the implant so it will be perpendicular to the occlusal surface decreases the leverage that will be applied to the various metal components (figure 30A, 30B). The incisocervical/occlusocervical location of the implant is largely determined by the location of existing bone (figure 1C, 4B, 10B, 16B) and the esthetic need to transition from a smaller diameter round form to a larger diameter form with a different geometric perimeter. Typically, implants have been placed apical to the cementoenamel junction of adjacent teeth to permit the required changes in morphology to occur somewhat gradually (figure 31). One textbook7 recommended that implants located in the esthetic zone be placed 4 millimeters or more apical to the cementoenamel junctions of adjacent teeth (Parel, 1989). Soft Tissue/Interdental Papilla Form Achieving ideal soft tissue form and interdental papilla height can be a challenge when placing implants into highly visible edentulous areas (figure 1D, 2B, 3B, 4D, 5C, 5D). Interdental dark spaces may be present (figure 2B, 32A, 32B, 32C, 32D), the marginal tissue may be thicker than the gingival margin present around adjacent teeth (figure 32B, 33A, 33B, 33C, 33D), the apical location of the soft tissue margin may not be at the same height as adjacent or contralateral natural teeth (figure 3B, 22B), interdental papillae may not possess the most desirable form or height (figure 1D, 2B, 3B, 32B, 32C, 32D, 33C, 33D), or recession of the soft tissue may lead to crown length variations and/or exposed metal (figure 34A, 34B).
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Some of these deficits may not be noticeable to patients whereas others can produce substantial esthetic challenges. Fortunately, if bone is present at the proper height interproximally, the soft tissue can fill in small spaces over time (figure 4C, 4D). One study8 of 21 patients compared the use of a conventional surgical flap that included the interdental papilla with a design that did not sever the 2 interdental papillae when a single implant had been placed. The modified flap design preserved at least 1 millimeter of both papillae (adjacent to the natural teeth). A reduction in the crestal bone loss was noted which presumably would enhance the esthetic result achieved (Gomez-Roman, 2001). Gingival recession has been measured in a 1-year prospective study9. The authors indicate about 1 millimeter of recession can generally be expected following abutment connection surgery. Eighty percent of the buccal sites exhibited recession. Since most of the recession occurred within the first 3 months, the authors proposed waiting 3 months after abutment connection surgery before making the definitive impression (Small, 2000). The longer the area has been edentulous, the more likely there will be a soft tissue discrepancy due to bone resorption and concomitant changes in the soft tissue contour. When there will be a substantial esthetic deficiency as noted clinically or from a diagnostic wax pattern formed on a cast, bone and/or soft tissue grafting may be necessary (figure 35A, 35B, 35C). However, some esthetic deficiencies are not totally correctable through grafting procedures and therefore it is generally felt that emphasis should be placed on retaining soft tissue form rather than restoring lost tissue. Methods of retaining soft tissue form and location include immediate implant placement and immediate placement of a provisional restoration when these procedures are indicated.
SYNOPSIS OF DESIGN GUIDELINES
• • • • • • • • • Center the implant mesiodistally in the edentulous space. If possible, position the implant faciolingually so a normal emergence profile can be developed and the crown does not have to overlap the peri-implant mucosa on the facial surface to develop proper cervical contour. If facial overlapping of the soft tissue will be necessary, consider some type of bone augmentation procedure so the implant can be placed in a more facial location. Place the implant as perpendicular to the occlusal surface as possible. With posterior implant single crowns, avoid extending the occlusal surface lateral to the implant by a distance greater than the diameter of the implant. Use wider diameter implants when access, bone dimensions, and esthetics permit. Maintain light centric occlusal contact (shim stock just slides through) between the implant single crown and the opposing tooth during normal tapping occlusal contact. When the patient fully engages their musculature, the shim stock should only then be grasped by the crown with the same intensity as opposing natural teeth. Avoid eccentric occlusal contact on the implant single crown or develop group function if contact cannot be avoided.
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The presence of bruxism increases the magnitude of the force applied and its frequency. Avoid using short implants and have the patient wear an occlusal device (night guard).
CLINICAL PROCEDURES
Examination/Diagnosis and Treatment Planning A clinical examination, medical and dental history, periapical and bitewing radiographs, and diagnostic casts are required to plan treatment. There should be an evaluation of systemic factors that can compromise implant success. The clinical examination and radiographs should be used to evaluate bone health and quality, incisocervical/occlusocervical bone dimensions, the distance between adjacent roots, presence of any caries, the pulpal and periodontal health of adjacent teeth, and the quality/integrity of existing restorations in adjacent teeth. Any diseases in teeth approximating the edentulous area should be treated. Untreated diseases can cause implant loss. When examining patients who have single missing teeth and could potentially benefit from implant supported/retained single crowns, it is important to determine if the morphologic form of a crown would be esthetically appropriate when developed on the existing edentulous ridge with the implant contained in available bone (figure 36A, 36B, 36C, 36D). This decision requires that a diagnostic pattern of the crown be developed. Any esthetic deficiencies in crown dimensions or cervical contour due to bone resorption of the alveolar ridge will be identified by this diagnostic procedure. Radiographic Template Through either bone sounding or a linear tomogram, it is possible to determine available bone dimensions in the alveolar ridge. By using a radiographic template in conjunction with a linear tomogram (figure 37A, 37B, 37C, 37D), the diagnostic form/location of the crown can be related to available bone to determine if an implant can be positioned within available bone and lead to the development of a crown with appropriate form and dimensions. This data coupled with the clinical examination, diagnostic casts, and diagnostic pattern of the most desirable crown form will identify patients where bone augmentation will be necessary to achieve the best possible esthetic result and allow the patient to make decisions regarding their treatment.
Ridge Augmentation When ridge augmentation is needed, the ideal ridge form can be developed in wax on the diagnostic cast while simultaneously adapting a denture tooth to the wax ridge. This process is continued until the desired crown form is established (figure 38A). A provisional removable partial denture can then be fabricated over the form of the ideal ridge that was developed in wax.
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The provisional prosthesis serves to validate the desired esthetic crown form (figure 38B, 38C) and also can be used as a template during the ridge augmentation procedure. The flap is reflected (figure 38D), bone graft material packed against the ridge (figure 38E), the provisional prosthesis placed into the mouth for the purpose of evaluating whether the ridge has been sufficiently enhanced in size (figure 38F), and then a barrier membrane placed over the graft material (figure 38G). The flap is then closed and sutured (figure 38H). After healing, an assessment can be made as to whether the desired ridge form has been achieved. A less than optimal incisocervical result can be seen in figures 38I, 38J, 38K, 38L, and 38M. A better result can be observed in figures 35A, 35B, 35C, 39A, 39B, 39C, 39D, 39E. Surgical Template/Implant and Abutment Placement/Provisional Crown Based on a pattern of the most desirable crown form and location, a surgical template is fabricated to guide implant placement (figure 40A, 40B, 40C, 40D). The implant is placed and the soft tissue sutured. After the appropriate healing time, the implant is uncovered and either a healing abutment or a definitive abutment placed. In esthetic zones, placement of a definitive abutment and provisional crown allows the soft tissue form to be developed around the contours of the provisional crown which can be more natural in shape than healing abutment contours (figure 41A, 41B, 41C, 41D, 41E, 41F, 41G, 42A, 42B, 42C). Impression/Cast/Crown Fabrication When a definitive prefabricated abutment (supplied by a manufacturer) has been placed, an abutment level impression is made using an impression coping (figure 43A, 43B, 43C, 43D, 43E, 43F). An abutment analog is positioned into the impression coping and a cast poured (figures44A, 44B). More commonly, an implant level impression is made using an impression coping that attaches to the implant (figure 45A). There are two types of impression copings: tapered (allows the impression to be removed from the mouth while the impression coping remains attached to the implant); and geometrically shaped copings that possess undercuts (the impression cannot be removed from the mouth until the coping is unscrewed from the implant). Tapered impression copings are used when the long axis of the implant (and therefore the long axis of the coping) is sufficiently parallel to the natural teeth that the impression can be removed from the mouth after the impression material polymerizes (Video A). This type of impression has been termed a closed-tray impression because a conventional impression tray can be used (the impression tray does not have to have a hole in its surface to provide access to the impression coping after the impression material polymerizes).
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When the long axis of the implant is different from the remaining teeth, impression material locks around a tapered impression coping (due to its angulation being different from the teeth) and prevents removal of the polymerized impression from the patient's mouth. Under these circumstances, a geometrically shaped coping is used (Video B). The geometric form (that possesses undercuts) allows the coping to be grasped by the impression material and it is therefore retained in the impression material. A screw (in the form of a metal rod) is used to attach this form of coping to the implant. The metal rod (screw) is long enough to pass through the impression tray. The screw can then be loosened after the impression material polymerizes, allowing the impression to be removed while the coping is retained within the impression material. This type of impression has been termed an open-tray impression because the impression tray must contain a hole through which the screw can project, thereby permitting the screw to be loosened after the impression material hardens. An implant analog (machined replica of the implant) is attached to the coping and a cast poured (figure 45B). The resulting cast can then be used to determine the most appropriate size and type of prefabricated abutment to used (figure 46A, 46B, 46C, 46D, 46E, 47A, 47B, 47C, 47D, 47E, 47F) or a custom abutment can be fabricated (figure 48A, 48B). It is also possible to place a prefabricated abutment, prepare the metal in the same manner that a tooth would be prepared (figure 49A), place gingival retraction cord, make a conventional impression (figure 49B) that records the abutment finish line and shape of the prepared abutment, and then pour a die and cast (figure 49C). The definitive crown is fabricated on the working cast in a manner that it can be cemented over the abutment (figure 50A, 50B, 50C) or be retained by a screw (figure 51A, 51B, 51C, 51D).
TABLE
Table 1 Implant Single Crown Complications # Studies Providing Data 2 7 6 6 6 4 2 27 2 Total # Patients or Components Affected (%) 27 of 105 screws (26) 151 of 613 screws (25) 38 of 451 implants (8) 42 of 623 screws (7) 34 of 483 crowns (7) 11 of 270 implants (4) 5 of 141 patients (4) 51 of 1870 implants (3) 4 of 165 screws (2)
Prosthesis screw loosening Abutment screw loosening (1991-1996) Fistula at implant-abutment level Abutment screw loosening (1998-2000) Esthetic problems Implant dehiscence before stage two Neurosensory disturbance (after surgery) Implant loss Abutment screw fractures
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REFERENCES
1. Rangert B, Jemt T, Jörneus L. Forces and moments on Brånemark implants. Int J Oral Maxillofac Implants 1989;4:241-247. Based on theoretical considerations and clinical experience with Brånemark implants, this article presented quidelines for controlling the forces applied to implants. They recommended that the restoration not extend lateral to the implant more than approximately one implant diameter in the molar region and no more than two implant diameters in the incisor region. They indicated greater extensions may be acceptable if more than one implant is being subjected to the bending moment, such as with an implant fixed partial denture or an implant fixed complete denture. 2. Rangert B, Krogh PHJ, Langer B, Van Roekel, N. Bending overload and implant fracture: A retrospective clinical analysis. Int J Oral Maxillofac Implants 1995;10:326-334. Probable causes of 39 implant fractures were discussed as they related to 39 patients that had been treated by 3 of the authors. Eighteen implants fractured while supporting a posterior fixed partial denture, 9 while supporting a single crown, 7 while connected to a natural tooth, 4 while supporting a maxillary fixed complete denture, and 1 while supporting an overdenture. All 9 fractures of implants supporting single crowns occurred in the mandibular molar area (8 first molars and 1 second molar). Several factors were discussed that place adverse loads on implants and they included the following: a. excessive height of the occlusal surface above the implant; b. deviation of the long axis of the implant from a perpendicular relationship to the occlusal plane; c. substantial differences between the dimension of the occlusal surface and the diameter of the implant; and d. bruxism or heavy occlusal forces. 3. Rangert BR, Sullivan RM, Jemt TM. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-370. This article identified risk factors that increase the load applied to implants. Several of the factors can be related to implant single crowns: extension of the occluding surfaces lateral to the implant (creating leverage); increasing the distance from the occlusal contact to the implant; use of one implant to support a multi-rooted tooth; and bruxism or the presence of heavy occlusal forces as evidenced by wear/tooth structure fractures.
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When a molar is replaced by using a single implant, the authors emphasize the importance of controlling the occlusion so it is not in heavy centric occlusal contact. They suggest light centric occlusal contact. 4. Katona TR, Goodacre CJ, Brown DT, Robert WE. Force-moment systems on single maxillary anterior implants: effects of incisal guidance, fixture orientation, and loss of bone support. An engineering model was developed that compared the effects of incisal guidance steepness, implant angulation in the bone, and the level of bone support on the moment developed on the implant. Reducing the steepness of the incisal guidance reduced the moment and labial component of force. Implants that can be placed more vertically in the bone because of existing maxillary bone morphology will have reduced moments placed on the implant. Changes in the bone height (either due to bone loss or from more apical placement of the implant) increased the moment. Five millimeters of change in the bone height doubled the moment.
REFERENCE LIST
1. Rangert B, Jemt T, Jörneus L. Forces and moments on Brånemark implants. Int J Oral Maxillofac Implants 1989;4:241-247. 2. Rangert B, Krogh PHJ, Langer B, Van Roekel N. Bending overload and implant fracture: a retrospective clinical analysis. Int J Oral Maxillofac Implants 1995;10:326-334. 3. Rangert B, Sullivan RM, Jemt TM. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-370. 4. Katona TR, Goodacre CJ, Brown DT, Roberts WE. Force-moment systems on single maxillary anterior implants: effects of incisal guidance, fixture orientation, and loss of bone support. Int J Oral Maxillofac Implants 1993;8:512-522. 5. Bahat O, Handelsman M. Use of wide implants and double implants in the posterior jaw: a clinical report. Int J Oral Maxillofac Implants 1996;11:379-386. 6. Balshi TJ, Hernandez RE, Pryszlak MC, Rangert B. A comparative study of one implant versus two replacing a single molar. Int J Oral Maxillofac Implants 1996;11:372-378. 7. Parel SM, Sullivan DY. Esthetics and Osseointegration, Dallas, Osseointegration Seminars Incorporated, 1989, pp19-23. 8. Gomez-Roman G. Influence of flap design on peri-implant interproximal crestal bone loss around single-tooth implants. Int J Oral Maxillofac Implants 2001;16:6167. 9. Small PN, Tarnow DP. Gingival recession around implants: a 1-year longitudinal prospective study. Int J Oral Maxillofac Implants 2000;15:527-532. 10. Jemt T, Laney WR, Harris D, Henry PJ, Krogh PH Jr, Polizzi G, et al. Osseointegrated implants for single tooth replacement: a 1-year report from a multicenter prospective study. Int J Oral Maxillofac Implants 1991;6:29-36.
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11. Babbush CA, Shimura M. Five-year statistical and clinical observations with the IMZ two-stage osteointegrated implant system. Int J Oral Maxillofac Implants 1993;8:245-253. 12. Fugazzotto PA, Gulbransen JH, Wheeler SL, Lindsay IA. The use of IMZ osseointegrated implants in partially and completely edentulous patients: success and failure rates of 2,023 implants cylinders up to 60+ months in function. Int J Oral Maxillofac Implants 1993;8:617-621. 13. Jemt T, Pettersson P. A 3-year follow-up study on single implant treatment. J Dent 1993;21:203-208. 14. Schmitt A, Zarb GA. The longitudinal clinical effectiveness of osseointegrated dental implants for single-tooth replacement. Int J Prosthodont 1993;6(1):97-202. 15. Ekfeldt A, Carlsson GF, Borjesson G. Clinical evaluation of single-tooth restorations supported by osseointegrated implants: a retrospective study. Int J Oral Maxillofac Implants 1994;9(1):79-83. 16. Laney WR, Jemt T, Harris D, Henry PJ, Krogh PH, Polizzi G, et al. Osseointegrated implants for single-tooth replacement: progress report from a multicenter prospective study after 3 years. Int J Oral Maxillofac Implants 1994;9:49-54. 17. Cordioli G, Castagna S, Consolati F. Single-tooth implant rehabilitation: a retrospective study of 67 implants. Int J Prosthodont 1994;7:525-531. 18. Andersson B, Odman P, Lindvall AM, Lithner B. Single-tooth restorations supported by osseointegrated implants: results and experiences from a prospective study after 2 to 3 years. Int J Oral Maxillofac Implants 1995;10:702-711. 19. Haas R, Mensdorff-Pouilly N, Mailath G, Watzek G. Brånemark single tooth implants: a preliminary report of 76 implants. J Prosthet Dent 1995;73(2):74-79. 20. Becker W, Becker BE. Replacement of maxillary and mandibular molars with single endosseous implant restorations: a retrospective study. J Prosthet Dent 1995;74:5155. 21. Henry PJ, Laney WR, Jemt T, Harris D, Krogh PHJ, Polizzi G, Zarb GA, Herrmann I. Osseointegrated implants for single-tooth replacement: a prospective 5-year multicenter study. Int J Oral Maxillofac Implants 1996;11:450-455. 22. Avivi-Arber L, Zarb GA. Clinical effectiveness of implant-supported single tooth replacement: the Toronto study. Int J Oral Maxillofac Implants 1996;11:311-321. 23. Karlsson U, Gotfredsen K, Olsson C. Single-tooth replacement by osseointegrated Astra Tech dental implants: a 2-year report. Int J Prosthodont 1997;10:318-324. 24. Kemppainen P, Eskola S, Ylipaavalniemi P. A comparative prospective clinical study of two single-tooth implants: a preliminary report of 102 implants. J Prosthet Dent 1997;77(4):382-387. 25. Andersson B, Ödman P, Lindvall A-M, Brånemark P-I. Cemented single crowns on osseointegrated implants after 5 years: results from a prospective study on CeraOne. Int J Prosthodont 1998;11:212-218. 26. Scheller H, Urgell P, Kultje C, Klineberg I, Goldberg PV, Stevenson-Moore P, Alonso JMN, Schaller M,Corria RM, Engquist B, Toreskog S, Kastenbaum F, Smith CR. A 5-year multicenter study on implant-supported single crown restorations. Int J Oral Maxillofac Implants 1998;13:212-218.
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27. Wannfors K, Smedberg JI. A prospective clinical evaluation of different single-tooth restoration designs on osseointegrated implants. A 3-year follow-up of Brånemark implants. Clin Oral Implants Res 1999;10(6):453-458. 28. Watson CJ, Tinsley D, Ogden AR, Russell JL, Mulay S, Davison EM. A 3 to 4 year study of single tooth hydroxylapatite coated endosseous dental implants. Br Dent J 1999;187(2):90-94. 29. Levine RA, Clem DS 3rd, Wilson TG Jr, Higginbottm F, Solnit G. Multicenter retrospective analysis of the ITI implant system used for single-tooth replacements: results of loading for 2 or more years. Int J Oral Maxillofac Implants 1999;14(4):516-520. 30. Priest G. Single-tooth implants and their role in preserving remaining teeth: a 10year survival study. Int J Oral Maxillofac Implants 1999;14:181-188. 31. Schwartz-Arad D, Samet N, Samet N. Single tooth replacement of missing molars: a retrospective study of 78 implants. J Periodontol 1999;70:449-454. 32. Bianco G, Di Raimondo R, Luongo G, Paoleschi C, Piccoli P, Piccoli C, Rangert B. Osseointegrated implant for single-tooth replacement: a retrospective multicenter study on routine use in private practice. Clin Implant Dent Relat Res 2000;2:152158. 33. Palmer RM, Palmer PJ, Smith BJ. A 5-year prospective study of Astra single tooth implants. Clin Oral Implant Res 2000;11:179-182. 34. Polizzi G, Rangert B, Lekholm U, Gualini F, Lindstrom H. Brånemark System Wide Platform implants for single molar replacement: clinical evaluation of prospective and retrospective materials. Clin Implant Dent Relat Res 2000;2(2):61-69. 35. Chaushu G, Chaushu S, Tzohar A, Dayan D. Immediate loading of single-tooth implants: immediate versus non-immediate implantation. A clinical report. Int J Oral Maxillofac Implants 2001;16(2):267-272. 36. Cooper L, Felton DA, Kugelberg CF, Ellner S, Chaffee N, Molina AL, Moriarty JD, Paquette D, Palmqvist U. A multicenter 12-month evaluation of single-tooth implants restored 3 weeks after 1-stage surgery. Int J Oral Maxillofac Implants 2001;16(2):182-192. 37. Chang M, Ödman PA, Wennström JL, Andersson B. Esthetic outcome of implantsupported single-tooth replacements assessed by the patient and prosthodontists. Int J Prosthodont 1999;12:335-341.
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