Retrospective Study of Pterygoid Implants in the Atrophic Posterior Maxilla: Implant and Prosthesis Survival Rates Up to 3 Years Marcos Martins Curi, DDS, MSc, PhD1/Camila Lopes Cardoso, DDS, MSc, PhD2/ Karina de Cássia Braga Ribeiro, DDS, PhD3 Purpose: Few reports have evaluated cumulative survival rates of implants placed in the pterygoid region in the medium term. The objective of this study was to evaluate success rates of pterygoid implants and prostheses in patients treated in the atrophic posterior maxilla. Materials and Methods: A retrospective study was performed of patients with an atrophic posterior maxilla rehabilitated with pterygoid implants between 1999 and 2010 and followed for at least 36 months after implant loading. Two outcome variables were considered: implant success and prosthesis success. The following predictor variables were recorded: sex, age, implant placement angulation, number and size of implants, prosthetic rehabilitation, bone loss, date of prosthesis delivery, and date of last follow-up. A statistical model was used to estimate the survival rates and associated confidence intervals. Data were analyzed using the Kaplan-Meier method and log-rank test to compare survival curves. Results: A total of 238 titanium implants (172 anterior and 66 pterygoid) were placed in 56 patients. The 3-year overall pterygoid implant survival rate was 99%. The 3-year overall prosthesis survival rate was 97.7%. The mean bone loss around pterygoid implants after 3 years of loading was 1.21 mm (range, 0.31 to 1.75). All patients were wearing the prostheses at the most recent follow-up examination. Conclusion: Placement of implants in the pterygoid region is a viable alternative treatment modality for rehabilitation of patients with an atrophic posterior maxilla. Int J Oral Maxillofac Implants 2015;30:378–383. doi: 10.11607/jomi.3665 Key words: atrophic maxilla, pterygoid, pterygoid implants, pterygomaxillary implants
I
mplants have been used successfully for the treatment of edentulous jaws since the introduction of the osseointegration concept by Brånemark et al.1 Osseointegrated implants have been used routinely to treat patients with partial and complete edentulism.2 The posterior maxilla represents a difficult and challenging intraoral area for rehabilitation with osseointegrated implants2,3 for many reasons, such as anatomy and presence of the maxillary sinus, insufficient bone volume, poor bone quality, and difficulties in accessing
1Chairman,
Department of Stomatology, Hospital Santa Catarina, São Paulo, Brazil; Assistant Professor, University Sagrado Coração, Bauru, SP, Brazil. 2 Assistant Professor, Department of Stomatology, Hospital Santa Catarina, São Paulo, Brazil; Assistant Professor, University Sagrado Coração, Bauru, SP, Brazil. 3Adjunct Professor, Department of Social Medicine, Faculdade de Ciências Médicas da Santa Casa de São Paulo, Brazil. Correspondence to: Dr Marcos Martins Curi, Department of Stomatology – Oncology, Hospital Santa Catarina, Av. Paulista 200, Bela Vista, São Paulo – Brasil. Fax: +55-11-983452225. Email: [email protected] ©2015 by Quintessence Publishing Co Inc.
the area. Other anatomical factors, such as large fatty marrow spaces and the rare presence of cortical bone covering the alveolus, have also made the posterior maxilla area less than ideally suited for implant placement.4 Biomechanical factors, ie, intense chewing forces generated during mastication, add to the difficulty in this area, as occlusal forces are higher in the premolar and molar regions than in the anterior maxilla. To compensate for these anatomical difficulties and to support occlusal forces in the posterior maxilla, various treatment modalities have been recommended.5 Bone graft surgical procedures, such as sinus elevation and onlay grafts, have been indicated to address some of these problems; however, these surgical techniques necessitate long healing periods, and there is a risk of morbidity at the donor site.6 Other surgical techniques, such as the use of more implants or wider-diameter implants, have been proposed to obtain greater surface area.7,8 Prosthetic techniques, such as longer posterior cantilevers, may result in complications, including screw and prosthesis fracture, marginal bone loss, and loss of implant osseointegration. To avoid these limitations, the pillar of bone composed of the maxillary tuberosity, the pyramidal process of the palatine bone, and the pterygoid process
378 Volume 30, Number 2, 2015 © 2015 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Curi et al
of the sphenoid bone has been recommended by some authors for implant placement to rehabilitate the posterior maxilla.9–22 In 1989, Tulasne20 introduced the idea of placing implants in the pterygoid region to solve problems related to rehabilitation of the atrophic posterior maxilla. If implants are engaged in this pillar of compact bone and successfully osseointegrated, they can provide support and stability for a bone-anchored prosthesis without bone grafting and without posterior prosthesis cantilevers. Implants placed in the pterygoid region have been reported in the literature as pterygomaxillary implants, pterygoid implants, and tuberosity implants.9–22 However, significant differences exist between pterygoid and tuberosity implants. Pterygoid implants are generally placed through the maxillary tuberosity—the pyramidal process of the palatine bone—and then engaged in the pterygoid process of the sphenoid bone.23 These implants are placed with an angulation of 30 to 60 degrees relative to the maxillary plane. In contrast, tuberosity implants are inserted almost entirely at the most distal portion of the maxillary alveolar process (tuberosity region), which is mainly composed of type 3 or 4 cancellous bone,3 and rarely with an angulation above 10 degrees. Survival outcomes between these two implants may be quite different because of differences in the quality of bone and the biomechanical effects of off-axis loading. It was hypothesized that implants placed in the pterygoid process will allow for the rehabilitation of patients with a severely atrophied posterior maxilla by means of partial or complete bone-anchored fixed prostheses. The aim of this study was to report the survival rates of pterygoid implants and the prostheses supported by them. The specific aim of this study was to correlate important clinical variables with the survival rates of pterygoid implants and prostheses used to rehabilitate the posterior maxilla.
MATERIALS AND METHODS Study Design
The researchers designed and implemented a retrospective study of all patients treated with fixed pterygoid implant–retained prostheses between 1999 and 2010. Patients underwent the same surgical, prosthetic, and follow-up protocol. Approval for this study was granted by the institutional review board.
Study Variables
Outcome Variables Two outcome variables were considered in the study: implant success and prosthetic success. The criteria for success of any pterygoid implant was based on the clinical and radiographic criteria proposed by
Albrektsson et al: absence of clinical implant mobility; absence of pain, discomfort, bleeding, or exudates; absence of peri-implant radiolucencies; and absence of bone loss greater than 0.2 mm annually after the first year of function.3 Total survival time for each implant was defined as the time from the date of implantation to the date of implant removal or the date of last follow-up visit for patients with surviving implants. Patients who received implants but did not complete prosthetic rehabilitation were excluded from the study to eliminate this condition as a confounding variable. The criteria for prosthesis success included overall stability, comfort, function, and patient acceptance. Total survival time for each prosthesis was defined as the time from the actual date of delivery to the date of prosthesis removal or the date of the last follow-up visit for patients wearing the prosthesis. Predictor Variables. The following predictor variables were addressed in this study: sex, age, implant angulation, number and dimensions of implants, type of prosthetic rehabilitation, bone loss, date of prosthesis delivery, and date of last follow-up. However, implant angulation and size, type of prosthetic rehabilitation, number of associated anterior implants, and bone loss were specifically selected for evaluation based on previous reports in the literature.
Pterygoid Rehabilitation Protocol
Patient Selection. All patients were treated following the same protocol, which included panoramic radiography prior to implant placement to assess the quantity of the remaining bone in the pterygomaxillary area. Included patients had to be in good general health and able to tolerate a minor oral surgical procedure. Patients were excluded from this study if there were general contraindications to oral surgery or a lack of bone in the pterygomaxillary region. Patients were also excluded if the implant was placed in the maxillary tuberosity and not engaged in the pillar bone (maxillary tuberosity, pyramidal process of palatine bone, and pterygoid process of sphenoid bone). All patients had a minimum follow-up period of at least 1 year after prosthesis insertion. Pterygoid Implant Surgical Protocol. All surgery was performed under local anesthesia with articaine with 1:100,000 adrenalin. The pterygoid surgical technique consisted of exposure of the maxillary tuberosity through a crestal incision over the alveolar bone. The implant bed was prepared by drilling with a straight handpiece in a posterior and upward direction (45 degrees) and oblique to the palate (15 degrees) to establish the direction of the implant axis. If a less angulated implant was desired in relation to the mesiodistal axis, a contra-angle handpiece was used to place the implant in a more vertical position. The International Journal of Oral & Maxillofacial Implants 379
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Curi et al
Drilling began with a 1.5- × 20-mm twist drill over the crest of the maxillary tuberosity and penetrated through the cancellous bone toward the tubero-palato-pterygoid column until resistance was felt from this high-density bone. At this point, the pressure over the handpiece was increased and drilling was controlled at a low speed until the pterygoid process was reached. Use of this tactile sensation during drilling helps reduce the potential surgical risks, especially the risk of hemorrhage. Preparation continued with a 2- × 20-mm twist drill in the same manner to increase the implant site diameter. At this point, it was possible to verify the accuracy of the implant angulation and limit the site length (implants were usually between 16 and 20 mm). After this, a 3- × 20-mm twist drill was used to widen the implant site. However, the site was not drilled to its full extent; at least 4 mm of the final implant site were left undrilled to improve the primary stability of the implant. After all drilling was completed, a Brånemark System implant (Nobel Biocare) was placed under low-speed rotation using mechanical techniques. The implant selection was based on bone quantity and quality, with the intention to maximize the initial primary stability of each implant. A variety of implant types was used in the pterygoid region; most were 18 or 20 mm long and 3.75 mm in diameter. The healing period before implants were loaded was approximately 3 to 4 months. During stage-two surgery, the surgeon determined whether angulated (17-degree) or standard abutments were necessary for prosthesis fabrication. The lengths of the abutments varied between 3 and 5 mm because of generally thicker mucosa in this area. After a healing period, the definitive partial or complete fixed prosthesis was fabricated in metal-ceramic or metal-acrylic resin. Marginal Bone Loss Evaluation. Marginal bone loss around pterygoid implants was evaluated with panoramic radiographs immediately after loading, 1 year after prosthesis insertion, and at the last follow-up visit. Distortion of panoramic radiographs was corrected using the known implant dimensions. For measurement purposes, the distance from the implant/prosthetic restoration junction to the bone crest on the mesial and distal sides of each pterygoid implant was recorded. To determine bone loss, a line was traced from the implant/restoration junction to the bone crest. The difference between the values recorded on each radiograph was used to calculate bone loss on each side of the implant. The higher value was considered to represent the bone loss for the implant in question.
Data Collection and Analysis
All data were recorded at each patient visit during the study period. One investigator collected all the data and transferred it into statistical analysis software (SPSS for Windows, version 15.0).
Statistical modeling was performed to estimate survival rates and associated confidence intervals. Implant and prosthesis success rates were calculated by KaplanMeier analysis. The log-rank test was used to assess the association between predictor variables and implant and prosthesis success. Results were considered statistically significant at P < .05. Descriptive analyses were performed using the t test for predictor variables and the Fischer exact test for categorical variables.
RESULTS This study comprised 56 patients with a severely resorbed edentulous posterior maxilla (40 women and 16 men; mean age, 60.9 years; range, 41 to 77 years). Sixty-six implants were placed in the pterygoid region and 172 implants were placed in the anterior maxilla. Of the 66 pterygoid implants placed into function, 62 implants survived during the cumulative follow-up period of 36 months. The overall 3-year success rates were 99% for pterygoid implants and 97.6% for all other implants placed in the anterior maxilla. All the pterygoid implants were Brånemark System Mk III (Nobel Biocare). Different implant sizes were used in this study; 43 implants were 3.75 mm wide and 23 implants were 4 mm wide, and 38 implants were 18 mm long and 28 implants were 20 mm long. Pterygoid implants were positioned at several different angles: 6 implants were positioned at 15 degrees, 14 implants were placed at 30 degrees, 12 implants were placed at 60 degrees, and the remaining 34 implants were positioned at 45 degrees (Table 1). The mean bone loss around the pterygoid implants at 36 months after loading was 1.21 mm (1.31 mm mesially and 1.01 mm distally). All the implants analyzed in this study had bone loss of less than 1.9 mm during the study period. Bone quality was evaluated for each of the 66 pterygoid implants. All implants were placed in type 3 or 4 bone, and tapping was not required in any case during implant placement. Sixteen implants were placed in type 3 bone and only one of these failed to osseointegrate. The remaining 50 implants were placed in type 4 bone, and three of these did not osseointegrate. All pterygoid implant failures occurred before loading, from a lack of osseointegration; there was no evidence of infection or associated symptomatology. Of the 56 prostheses, 34 were fixed partial prostheses and 22 were fixed full-arch (complete) prostheses. Forty were metal-ceramic and 16 were acrylic resin. All prostheses remained stable, comfortable, and in function at the last follow-up examination. The 3-year overall prosthesis survival rate was 100% for fixed partial dentures and 97.7% for full-arch dentures (P = .478) (Table 1).
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Curi et al
Postoperatively, no complications such as infection, bleeding, edema, or wound dehiscence were observed.
DISCUSSION The placement of implants in the pterygomaxillary region provides bone anchorage in the posterior maxilla without sinus augmentation or supplemental grafting procedures.12,24 Pterygoid implants can also eliminate the detrimental effects of cantilever-induced loading forces when only anterior implants are used to support a complete fixed prosthesis.12,24 From a surgical point of view, the placement of pterygoid implants requires operative skill.24 Attention to tactile sensation, ie, to the feeling of the compact bone when the pterygoid plate is reached, is an important step in stabilizing the implant and engaging the cortical bone at the implant’s apex. A straight handpiece may facilitate access for implant placement and angulation during drilling.21,24 Pterygoid implants should be long enough to pass through the maxillary tuberosity and the pyramidal process of the palatine bone, and then to engage the pterygoid process of sphenoid bone; the length of these implants ranges between 15 and 20 mm. Long implants can enhance primary stability and long-term success.12,24 The success rate for implants placed in the pterygomaxillary region has ranged from 80% to 99% (Table 2).9–12,14–19,21,22,24 In the present study, the survival of each implant was evaluated at the time of abutment connection surgery by means of a mobility test, and after insertion of the prosthesis, survival was evaluated by means of marginal bone maintenance, as observed on panoramic radiographs, and by the absence of pain or infection. The 3-year cumulative implant survival rate of the pterygoid implants in this study was 99%. The cumulative success rate of the anterior maxillary implants was 97.6%. In 2011, Bidra and Huynh-Ba12 published a systematic review of short- and long-term survival of pterygoid implants in the English language literature.12 The authors summarized that there is a lack of studies with adequate follow-up data and description of tuberosity implants and pterygoid implants. The authors suggested the adoption of the definition provided by the Glossary of Oral and Maxillofacial Implants for pterygoid implants as “implant placement through the maxillary tuberosity and into the pterygoid plate.”25 Among the nine articles included in that systematic review, the first-year survival rate of pterygoid implants was 92%, but the 1-year survival rate was unknown, because the minimum follow-up period of several implants was less than 1 year. Most implant failures (70/79) occurred before loading.
Table 1 Differences in Three-Year Overall Survival (OS) of Pterygoid Implants According to Demographic and Clinical Variables Variable/Category
3-year OS
95% CI OS
P
100.0 97.4
–
.003
100.0 92.7
– 73.9–98.1
.173
100.0 97.0 100.0
–
.215
100.0 100.0 100.0 88.9
– – –
.195
100.0 95.5
–
.478
100.0 97.5
–
.322
Sex Male Female Age (y) ≤ 50 > 50 Implant length (mm) 16 18 20
–
Angle of placement (deg) 15 30 45 60 Prosthesis material Metal-ceramic Acrylic resin Bone type 3 4 CI = confidence interval.
Table 2 Data from Studies of Pterygoid Implants Study
Year
Tulasne20
1992
No. of pterygoid Success Follow-up implants rate (%) (mo) 52
80
–
72
93
12–37
64
89
Bahat 25
1992
Graves15
1994
Balshi et al27
1995
51
86.3
Balshi et al11
1999
356
88.2
54
Krekmanov16
2000
14
85.8
12–123
Vrielinck et al22 2003
18
71
6–24
al10
– 1 – 63
2005
164
96.3
6–54
Valerón and Valerón21
2007
152
94.7
120
Peñarrocha et al18
2009
68
97.1
12–69
Current study
2013
66
99
Balshi et
36
– = Not stated.
In 2012, Peñarrocha et al24 published a literature review of patients with atrophic posterior maxillae treated with pterygoid implants. Thirteen studies were included in this review, which covered the years 1992 to 2009. Patients were rehabilitated with pterygoid implants and fixed prostheses, with 12 months’ minimum The International Journal of Oral & Maxillofacial Implants 381
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Curi et al
follow-up. A total of 1,053 pterygoid implants in 676 patients were included, and the weighted average success rate of pterygoid implants was 90.7%. Pterygoid implants had no remarkable complications compared with conventional implants, and the level of patient satisfaction with the prosthesis was high. From a biomechanical point of view, pterygoid implants should not be restored with distal cantilevers to avoid the risks inherent to cantilevers.11,26 The occlusal forces in the premolar and molar region are known to be very high.11,26 Inclination of the implants should be avoided to minimize potentially injurious occlusal forces. The longest possible implants should be used to achieve optimum primary stabilization and to engage the upper cortical plate with the apex of the implant. In patients in whom primary stabilization is not achievable, a longer healing period should be allowed. Bone loss was assessed in some studies.18,24,27 These studies have assessed bone loss in panoramic radiographs 1 year after loading, with an average marginal bone loss of 0.71 mm.18,24,27 Balshi et al27 assessed marginal bone loss after 1 year of loading and observed a mean bone loss of 1.3 mm mesially and 1.1 mm distally using panoramic radiographs; as in the present study, distortion was calculated using the known dimensions of the implants. In the current study, the mean bone loss around pterygoid implants at 36 months after loading was 1.21 mm (1.31 mm mesially and 1.01 mm distally), which is in accordance with previously published studies. 27 The clinical postoperative course for patients treated with implants placed in the pterygoid region is not remarkable.16,18,24 Few complications related to the surgical procedure were seen and included slight venous bleeding and edema.16,18,24 Bleeding in this region is related to the veins of the pterygoid muscles, and it can be easily stopped when the pterygoid implant is placed in the final position.21 Although the placement of pterygoid implants requires surgical experience and skills, this is a safe surgical procedure because there are no vital structures in the implant insertion region, as the internal maxillary artery crosses 1 cm above the pterygopalatine suture.16,18,21 Discomfort and pain were not reported during any postoperative reevaluations. No major complications related to the surgical procedure were reported. Bleeding was observed only in two cases, which was easily stopped after implant placement. Patient acceptance of distally positioned prosthetic components was excellent, as previously reported.10,11,16,24 Patients reported a high level of satisfaction with the fixed prostheses placed over pterygoid implants and reported no problems related to speaking ability or hygiene maintenance. There was no loss of pterygoid implants as a result of plaque
accumulation, tissue hyperplasia, or mucosal inflammation. Highly polished prostheses can be fabricated for optimal plaque control and oral hygiene.
CONCLUSION Pterygoid implants in the pterygoid region are an alternative treatment modality for rehabilitation of the atrophic posterior maxilla. These implants provide excellent stabilization for bone-anchored prostheses in partially and completely edentulous patients.
ACKNOWLEDGMENTS The authors reported no conflicts of interest related to this study.
REFERENCES 1. Brånemark P-I, Breine U, Adell R, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses I: Experimental studies. Scand J Plast Reconstr Surg 1969;3:81–100. 2. Adell R, Lekholm U, Rockler B, Brånemark P-I. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10:387–416. 3. Albrektsson T, Zarb GA, Worthington P, Eriksson A. The long-term efficacy of currently used dental implants: A review and proposed criteria of success. Int J Oral Maxillofac Implants 1986;1:11–26. 4. Jaffin RA, Berman CL. The excessive loss of Brånemark fixtures in type IV bone: A 5-year analysis. J Periodontol 1991;61:2–4. 5. Adell R, Eriksson B, Lekholm U, Brånemark P-I, Jemt T. A long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxillofac Implants 1990;5:347–359. 6. Wood RM, Moore DL. Grafting of the maxillary sinus with intraorally harvested autogenous bone prior to implant placement. Int J Oral Maxillofac Implants 1988;3:209–214. 7. Reiger MR, Loading considerations for implants. Oral Maxillofac Clin North Am 1991;3:795–804. 8. Langer B, Langer L, Herrman I, Jorneous L. The wide fixture: A solution for special bone situations and a rescue for the compromised implant. Int J Oral Maxillofac Implants 1993;8:400–408. 9. Bahat O. Osseointegrated implants in the maxillary tuberosity: Report on 45 consecutive patients. Int J Oral Maxillofac Implants 1992;7:459–467. 10. Balshi SF, Wolfinger GJ, Balshi TJ. Analysis of 164 titanium oxidesurface implants in completely edentulous arches for fixed prosthesis anchorage using the pterygomaxillary region. Int J Oral Maxillofac Implants 2005;20:946–952. 11. Balshi TJ, Wolfinger G, Balshi S. Analysis of 356 pterygomaxillary implants in edentulous arches for fixed prosthesis anchorage. Int J Oral Maxillofac Implants 1999;14:398–406. 12. Bidra AS, Huynh-Ba G. Implants in the pterygoid region: A systematic review of the literature. Int J Oral Maxillofac Surg 2011;40: 773–781. 13. Bidra AS, May GW, Tharp GE, Chambers MS. Pterygoid implants for maxillofacial rehabilitation of a patient with a bilateral maxillectomy defect. J Oral Implantol 2013;39:91–97. 14. Candel E, Peñarrocha D, Peñarrocha M. Rehabilitation of the atrophic posterior maxilla with pterygoid implants: A review. J Oral Implantol 2012;38:461–466. 15. Graves SL. The pterygoid plate implant: A solution for restoring the posterior maxilla. Int J Periodontics Restorative Dent 1994;14: 512–523.
382 Volume 30, Number 2, 2015 © 2015 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
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16. Krekmanov L. Placement of posterior mandibular and maxillary implants in patients with severe bone deficiency: A clinical report of procedure. Int J Oral Maxillofac Implants 2000;15:722–730. 17. Linkow LI. Maxillary pterygoid extension implants: The state of the art. Dent Clin North Am 1980;24:535–551. 18. Peñarrocha M, Carrillo C, Boronat A, Peñarrocha M. Retrospective study of 68 implants placed in the pterygomaxillary region using drills and osteotomes. Int J Oral Maxillofac Implants 2009;24: 720–726. 19. Ridell A, Grondahl K, Sennerby L. Placement of Brånemark implants in the maxillary tuber region: Anatomical considerations, surgical technique and long-term results. Clin Oral Implants Res 2009;20:94–98. 20. Tulasne JF. Osseointegrated fixtures in the pterygoid region. In: Worthington P, Brånemark PI (eds). Advanced Osseointegration Surgery. Applications in the Maxillofacial Region. Chicago: Quintessence, 1992:182–188. 21. Valerón JF, Valerón PF. Long-term results in placement of screwtype implants in the pterygomaxillary-pyramidal region. Int J Oral Maxillofac Implants 2007;22:195–200.
22. Vrielinck L, Politis C, Schepers S, Pauwels M, Naert I. Image-based planning and clinical validation of zygoma and pterygoid implant placement in patients with severe bone atrophy using customized drill guides. Preliminary results from a prospective clinical followup study. Int J Oral Maxillofac Surg 2003;32:7–14. 23. Lee SP, Paik KS, Kim MK. Anatomical study of the pyramidal process of the palatine bone in relation to implant placement in the posterior maxilla. J Oral Rehabil 2001;28:125–132. 24. Peñarrocha M, Peñarrocha D, Candel E. Rehabilitation of the atrophic posterior maxilla with pterygoid implants: A review. J Oral Implantol 2012;38:461–466. 25. Laney WR (ed). Glossary of Oral and Maxillofacial Implants. Hanover Park, IL: Quintessence, 2007. 26. Bahat O. Brånemark system implants in the posterior maxilla: Clinical study of 660 implants followed for 5 to 12 years. Int J Oral Maxillofac Implants 2000;15:646–653. 27. Balshi TJ, Lee Y, Hernandez RE. The use of pterygoid implants in the partially edentulous patient: A preliminary report. Int J Oral Maxillofac Surg 1995;10:89–98.
The International Journal of Oral & Maxillofacial Implants 383 © 2015 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
I
mplants have been used successfully for the treatment of edentulous jaws since the introduction of the osseointegration concept by Brånemark et al.1 Osseointegrated implants have been used routinely to treat patients with partial and complete edentulism.2 The posterior maxilla represents a difficult and challenging intraoral area for rehabilitation with osseointegrated implants2,3 for many reasons, such as anatomy and presence of the maxillary sinus, insufficient bone volume, poor bone quality, and difficulties in accessing
1Chairman,
Department of Stomatology, Hospital Santa Catarina, São Paulo, Brazil; Assistant Professor, University Sagrado Coração, Bauru, SP, Brazil. 2 Assistant Professor, Department of Stomatology, Hospital Santa Catarina, São Paulo, Brazil; Assistant Professor, University Sagrado Coração, Bauru, SP, Brazil. 3Adjunct Professor, Department of Social Medicine, Faculdade de Ciências Médicas da Santa Casa de São Paulo, Brazil. Correspondence to: Dr Marcos Martins Curi, Department of Stomatology – Oncology, Hospital Santa Catarina, Av. Paulista 200, Bela Vista, São Paulo – Brasil. Fax: +55-11-983452225. Email: [email protected] ©2015 by Quintessence Publishing Co Inc.
the area. Other anatomical factors, such as large fatty marrow spaces and the rare presence of cortical bone covering the alveolus, have also made the posterior maxilla area less than ideally suited for implant placement.4 Biomechanical factors, ie, intense chewing forces generated during mastication, add to the difficulty in this area, as occlusal forces are higher in the premolar and molar regions than in the anterior maxilla. To compensate for these anatomical difficulties and to support occlusal forces in the posterior maxilla, various treatment modalities have been recommended.5 Bone graft surgical procedures, such as sinus elevation and onlay grafts, have been indicated to address some of these problems; however, these surgical techniques necessitate long healing periods, and there is a risk of morbidity at the donor site.6 Other surgical techniques, such as the use of more implants or wider-diameter implants, have been proposed to obtain greater surface area.7,8 Prosthetic techniques, such as longer posterior cantilevers, may result in complications, including screw and prosthesis fracture, marginal bone loss, and loss of implant osseointegration. To avoid these limitations, the pillar of bone composed of the maxillary tuberosity, the pyramidal process of the palatine bone, and the pterygoid process
378 Volume 30, Number 2, 2015 © 2015 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
Curi et al
of the sphenoid bone has been recommended by some authors for implant placement to rehabilitate the posterior maxilla.9–22 In 1989, Tulasne20 introduced the idea of placing implants in the pterygoid region to solve problems related to rehabilitation of the atrophic posterior maxilla. If implants are engaged in this pillar of compact bone and successfully osseointegrated, they can provide support and stability for a bone-anchored prosthesis without bone grafting and without posterior prosthesis cantilevers. Implants placed in the pterygoid region have been reported in the literature as pterygomaxillary implants, pterygoid implants, and tuberosity implants.9–22 However, significant differences exist between pterygoid and tuberosity implants. Pterygoid implants are generally placed through the maxillary tuberosity—the pyramidal process of the palatine bone—and then engaged in the pterygoid process of the sphenoid bone.23 These implants are placed with an angulation of 30 to 60 degrees relative to the maxillary plane. In contrast, tuberosity implants are inserted almost entirely at the most distal portion of the maxillary alveolar process (tuberosity region), which is mainly composed of type 3 or 4 cancellous bone,3 and rarely with an angulation above 10 degrees. Survival outcomes between these two implants may be quite different because of differences in the quality of bone and the biomechanical effects of off-axis loading. It was hypothesized that implants placed in the pterygoid process will allow for the rehabilitation of patients with a severely atrophied posterior maxilla by means of partial or complete bone-anchored fixed prostheses. The aim of this study was to report the survival rates of pterygoid implants and the prostheses supported by them. The specific aim of this study was to correlate important clinical variables with the survival rates of pterygoid implants and prostheses used to rehabilitate the posterior maxilla.
MATERIALS AND METHODS Study Design
The researchers designed and implemented a retrospective study of all patients treated with fixed pterygoid implant–retained prostheses between 1999 and 2010. Patients underwent the same surgical, prosthetic, and follow-up protocol. Approval for this study was granted by the institutional review board.
Study Variables
Outcome Variables Two outcome variables were considered in the study: implant success and prosthetic success. The criteria for success of any pterygoid implant was based on the clinical and radiographic criteria proposed by
Albrektsson et al: absence of clinical implant mobility; absence of pain, discomfort, bleeding, or exudates; absence of peri-implant radiolucencies; and absence of bone loss greater than 0.2 mm annually after the first year of function.3 Total survival time for each implant was defined as the time from the date of implantation to the date of implant removal or the date of last follow-up visit for patients with surviving implants. Patients who received implants but did not complete prosthetic rehabilitation were excluded from the study to eliminate this condition as a confounding variable. The criteria for prosthesis success included overall stability, comfort, function, and patient acceptance. Total survival time for each prosthesis was defined as the time from the actual date of delivery to the date of prosthesis removal or the date of the last follow-up visit for patients wearing the prosthesis. Predictor Variables. The following predictor variables were addressed in this study: sex, age, implant angulation, number and dimensions of implants, type of prosthetic rehabilitation, bone loss, date of prosthesis delivery, and date of last follow-up. However, implant angulation and size, type of prosthetic rehabilitation, number of associated anterior implants, and bone loss were specifically selected for evaluation based on previous reports in the literature.
Pterygoid Rehabilitation Protocol
Patient Selection. All patients were treated following the same protocol, which included panoramic radiography prior to implant placement to assess the quantity of the remaining bone in the pterygomaxillary area. Included patients had to be in good general health and able to tolerate a minor oral surgical procedure. Patients were excluded from this study if there were general contraindications to oral surgery or a lack of bone in the pterygomaxillary region. Patients were also excluded if the implant was placed in the maxillary tuberosity and not engaged in the pillar bone (maxillary tuberosity, pyramidal process of palatine bone, and pterygoid process of sphenoid bone). All patients had a minimum follow-up period of at least 1 year after prosthesis insertion. Pterygoid Implant Surgical Protocol. All surgery was performed under local anesthesia with articaine with 1:100,000 adrenalin. The pterygoid surgical technique consisted of exposure of the maxillary tuberosity through a crestal incision over the alveolar bone. The implant bed was prepared by drilling with a straight handpiece in a posterior and upward direction (45 degrees) and oblique to the palate (15 degrees) to establish the direction of the implant axis. If a less angulated implant was desired in relation to the mesiodistal axis, a contra-angle handpiece was used to place the implant in a more vertical position. The International Journal of Oral & Maxillofacial Implants 379
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Curi et al
Drilling began with a 1.5- × 20-mm twist drill over the crest of the maxillary tuberosity and penetrated through the cancellous bone toward the tubero-palato-pterygoid column until resistance was felt from this high-density bone. At this point, the pressure over the handpiece was increased and drilling was controlled at a low speed until the pterygoid process was reached. Use of this tactile sensation during drilling helps reduce the potential surgical risks, especially the risk of hemorrhage. Preparation continued with a 2- × 20-mm twist drill in the same manner to increase the implant site diameter. At this point, it was possible to verify the accuracy of the implant angulation and limit the site length (implants were usually between 16 and 20 mm). After this, a 3- × 20-mm twist drill was used to widen the implant site. However, the site was not drilled to its full extent; at least 4 mm of the final implant site were left undrilled to improve the primary stability of the implant. After all drilling was completed, a Brånemark System implant (Nobel Biocare) was placed under low-speed rotation using mechanical techniques. The implant selection was based on bone quantity and quality, with the intention to maximize the initial primary stability of each implant. A variety of implant types was used in the pterygoid region; most were 18 or 20 mm long and 3.75 mm in diameter. The healing period before implants were loaded was approximately 3 to 4 months. During stage-two surgery, the surgeon determined whether angulated (17-degree) or standard abutments were necessary for prosthesis fabrication. The lengths of the abutments varied between 3 and 5 mm because of generally thicker mucosa in this area. After a healing period, the definitive partial or complete fixed prosthesis was fabricated in metal-ceramic or metal-acrylic resin. Marginal Bone Loss Evaluation. Marginal bone loss around pterygoid implants was evaluated with panoramic radiographs immediately after loading, 1 year after prosthesis insertion, and at the last follow-up visit. Distortion of panoramic radiographs was corrected using the known implant dimensions. For measurement purposes, the distance from the implant/prosthetic restoration junction to the bone crest on the mesial and distal sides of each pterygoid implant was recorded. To determine bone loss, a line was traced from the implant/restoration junction to the bone crest. The difference between the values recorded on each radiograph was used to calculate bone loss on each side of the implant. The higher value was considered to represent the bone loss for the implant in question.
Data Collection and Analysis
All data were recorded at each patient visit during the study period. One investigator collected all the data and transferred it into statistical analysis software (SPSS for Windows, version 15.0).
Statistical modeling was performed to estimate survival rates and associated confidence intervals. Implant and prosthesis success rates were calculated by KaplanMeier analysis. The log-rank test was used to assess the association between predictor variables and implant and prosthesis success. Results were considered statistically significant at P < .05. Descriptive analyses were performed using the t test for predictor variables and the Fischer exact test for categorical variables.
RESULTS This study comprised 56 patients with a severely resorbed edentulous posterior maxilla (40 women and 16 men; mean age, 60.9 years; range, 41 to 77 years). Sixty-six implants were placed in the pterygoid region and 172 implants were placed in the anterior maxilla. Of the 66 pterygoid implants placed into function, 62 implants survived during the cumulative follow-up period of 36 months. The overall 3-year success rates were 99% for pterygoid implants and 97.6% for all other implants placed in the anterior maxilla. All the pterygoid implants were Brånemark System Mk III (Nobel Biocare). Different implant sizes were used in this study; 43 implants were 3.75 mm wide and 23 implants were 4 mm wide, and 38 implants were 18 mm long and 28 implants were 20 mm long. Pterygoid implants were positioned at several different angles: 6 implants were positioned at 15 degrees, 14 implants were placed at 30 degrees, 12 implants were placed at 60 degrees, and the remaining 34 implants were positioned at 45 degrees (Table 1). The mean bone loss around the pterygoid implants at 36 months after loading was 1.21 mm (1.31 mm mesially and 1.01 mm distally). All the implants analyzed in this study had bone loss of less than 1.9 mm during the study period. Bone quality was evaluated for each of the 66 pterygoid implants. All implants were placed in type 3 or 4 bone, and tapping was not required in any case during implant placement. Sixteen implants were placed in type 3 bone and only one of these failed to osseointegrate. The remaining 50 implants were placed in type 4 bone, and three of these did not osseointegrate. All pterygoid implant failures occurred before loading, from a lack of osseointegration; there was no evidence of infection or associated symptomatology. Of the 56 prostheses, 34 were fixed partial prostheses and 22 were fixed full-arch (complete) prostheses. Forty were metal-ceramic and 16 were acrylic resin. All prostheses remained stable, comfortable, and in function at the last follow-up examination. The 3-year overall prosthesis survival rate was 100% for fixed partial dentures and 97.7% for full-arch dentures (P = .478) (Table 1).
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Postoperatively, no complications such as infection, bleeding, edema, or wound dehiscence were observed.
DISCUSSION The placement of implants in the pterygomaxillary region provides bone anchorage in the posterior maxilla without sinus augmentation or supplemental grafting procedures.12,24 Pterygoid implants can also eliminate the detrimental effects of cantilever-induced loading forces when only anterior implants are used to support a complete fixed prosthesis.12,24 From a surgical point of view, the placement of pterygoid implants requires operative skill.24 Attention to tactile sensation, ie, to the feeling of the compact bone when the pterygoid plate is reached, is an important step in stabilizing the implant and engaging the cortical bone at the implant’s apex. A straight handpiece may facilitate access for implant placement and angulation during drilling.21,24 Pterygoid implants should be long enough to pass through the maxillary tuberosity and the pyramidal process of the palatine bone, and then to engage the pterygoid process of sphenoid bone; the length of these implants ranges between 15 and 20 mm. Long implants can enhance primary stability and long-term success.12,24 The success rate for implants placed in the pterygomaxillary region has ranged from 80% to 99% (Table 2).9–12,14–19,21,22,24 In the present study, the survival of each implant was evaluated at the time of abutment connection surgery by means of a mobility test, and after insertion of the prosthesis, survival was evaluated by means of marginal bone maintenance, as observed on panoramic radiographs, and by the absence of pain or infection. The 3-year cumulative implant survival rate of the pterygoid implants in this study was 99%. The cumulative success rate of the anterior maxillary implants was 97.6%. In 2011, Bidra and Huynh-Ba12 published a systematic review of short- and long-term survival of pterygoid implants in the English language literature.12 The authors summarized that there is a lack of studies with adequate follow-up data and description of tuberosity implants and pterygoid implants. The authors suggested the adoption of the definition provided by the Glossary of Oral and Maxillofacial Implants for pterygoid implants as “implant placement through the maxillary tuberosity and into the pterygoid plate.”25 Among the nine articles included in that systematic review, the first-year survival rate of pterygoid implants was 92%, but the 1-year survival rate was unknown, because the minimum follow-up period of several implants was less than 1 year. Most implant failures (70/79) occurred before loading.
Table 1 Differences in Three-Year Overall Survival (OS) of Pterygoid Implants According to Demographic and Clinical Variables Variable/Category
3-year OS
95% CI OS
P
100.0 97.4
–
.003
100.0 92.7
– 73.9–98.1
.173
100.0 97.0 100.0
–
.215
100.0 100.0 100.0 88.9
– – –
.195
100.0 95.5
–
.478
100.0 97.5
–
.322
Sex Male Female Age (y) ≤ 50 > 50 Implant length (mm) 16 18 20
–
Angle of placement (deg) 15 30 45 60 Prosthesis material Metal-ceramic Acrylic resin Bone type 3 4 CI = confidence interval.
Table 2 Data from Studies of Pterygoid Implants Study
Year
Tulasne20
1992
No. of pterygoid Success Follow-up implants rate (%) (mo) 52
80
–
72
93
12–37
64
89
Bahat 25
1992
Graves15
1994
Balshi et al27
1995
51
86.3
Balshi et al11
1999
356
88.2
54
Krekmanov16
2000
14
85.8
12–123
Vrielinck et al22 2003
18
71
6–24
al10
– 1 – 63
2005
164
96.3
6–54
Valerón and Valerón21
2007
152
94.7
120
Peñarrocha et al18
2009
68
97.1
12–69
Current study
2013
66
99
Balshi et
36
– = Not stated.
In 2012, Peñarrocha et al24 published a literature review of patients with atrophic posterior maxillae treated with pterygoid implants. Thirteen studies were included in this review, which covered the years 1992 to 2009. Patients were rehabilitated with pterygoid implants and fixed prostheses, with 12 months’ minimum The International Journal of Oral & Maxillofacial Implants 381
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follow-up. A total of 1,053 pterygoid implants in 676 patients were included, and the weighted average success rate of pterygoid implants was 90.7%. Pterygoid implants had no remarkable complications compared with conventional implants, and the level of patient satisfaction with the prosthesis was high. From a biomechanical point of view, pterygoid implants should not be restored with distal cantilevers to avoid the risks inherent to cantilevers.11,26 The occlusal forces in the premolar and molar region are known to be very high.11,26 Inclination of the implants should be avoided to minimize potentially injurious occlusal forces. The longest possible implants should be used to achieve optimum primary stabilization and to engage the upper cortical plate with the apex of the implant. In patients in whom primary stabilization is not achievable, a longer healing period should be allowed. Bone loss was assessed in some studies.18,24,27 These studies have assessed bone loss in panoramic radiographs 1 year after loading, with an average marginal bone loss of 0.71 mm.18,24,27 Balshi et al27 assessed marginal bone loss after 1 year of loading and observed a mean bone loss of 1.3 mm mesially and 1.1 mm distally using panoramic radiographs; as in the present study, distortion was calculated using the known dimensions of the implants. In the current study, the mean bone loss around pterygoid implants at 36 months after loading was 1.21 mm (1.31 mm mesially and 1.01 mm distally), which is in accordance with previously published studies. 27 The clinical postoperative course for patients treated with implants placed in the pterygoid region is not remarkable.16,18,24 Few complications related to the surgical procedure were seen and included slight venous bleeding and edema.16,18,24 Bleeding in this region is related to the veins of the pterygoid muscles, and it can be easily stopped when the pterygoid implant is placed in the final position.21 Although the placement of pterygoid implants requires surgical experience and skills, this is a safe surgical procedure because there are no vital structures in the implant insertion region, as the internal maxillary artery crosses 1 cm above the pterygopalatine suture.16,18,21 Discomfort and pain were not reported during any postoperative reevaluations. No major complications related to the surgical procedure were reported. Bleeding was observed only in two cases, which was easily stopped after implant placement. Patient acceptance of distally positioned prosthetic components was excellent, as previously reported.10,11,16,24 Patients reported a high level of satisfaction with the fixed prostheses placed over pterygoid implants and reported no problems related to speaking ability or hygiene maintenance. There was no loss of pterygoid implants as a result of plaque
accumulation, tissue hyperplasia, or mucosal inflammation. Highly polished prostheses can be fabricated for optimal plaque control and oral hygiene.
CONCLUSION Pterygoid implants in the pterygoid region are an alternative treatment modality for rehabilitation of the atrophic posterior maxilla. These implants provide excellent stabilization for bone-anchored prostheses in partially and completely edentulous patients.
ACKNOWLEDGMENTS The authors reported no conflicts of interest related to this study.
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16. Krekmanov L. Placement of posterior mandibular and maxillary implants in patients with severe bone deficiency: A clinical report of procedure. Int J Oral Maxillofac Implants 2000;15:722–730. 17. Linkow LI. Maxillary pterygoid extension implants: The state of the art. Dent Clin North Am 1980;24:535–551. 18. Peñarrocha M, Carrillo C, Boronat A, Peñarrocha M. Retrospective study of 68 implants placed in the pterygomaxillary region using drills and osteotomes. Int J Oral Maxillofac Implants 2009;24: 720–726. 19. Ridell A, Grondahl K, Sennerby L. Placement of Brånemark implants in the maxillary tuber region: Anatomical considerations, surgical technique and long-term results. Clin Oral Implants Res 2009;20:94–98. 20. Tulasne JF. Osseointegrated fixtures in the pterygoid region. In: Worthington P, Brånemark PI (eds). Advanced Osseointegration Surgery. Applications in the Maxillofacial Region. Chicago: Quintessence, 1992:182–188. 21. Valerón JF, Valerón PF. Long-term results in placement of screwtype implants in the pterygomaxillary-pyramidal region. Int J Oral Maxillofac Implants 2007;22:195–200.
22. Vrielinck L, Politis C, Schepers S, Pauwels M, Naert I. Image-based planning and clinical validation of zygoma and pterygoid implant placement in patients with severe bone atrophy using customized drill guides. Preliminary results from a prospective clinical followup study. Int J Oral Maxillofac Surg 2003;32:7–14. 23. Lee SP, Paik KS, Kim MK. Anatomical study of the pyramidal process of the palatine bone in relation to implant placement in the posterior maxilla. J Oral Rehabil 2001;28:125–132. 24. Peñarrocha M, Peñarrocha D, Candel E. Rehabilitation of the atrophic posterior maxilla with pterygoid implants: A review. J Oral Implantol 2012;38:461–466. 25. Laney WR (ed). Glossary of Oral and Maxillofacial Implants. Hanover Park, IL: Quintessence, 2007. 26. Bahat O. Brånemark system implants in the posterior maxilla: Clinical study of 660 implants followed for 5 to 12 years. Int J Oral Maxillofac Implants 2000;15:646–653. 27. Balshi TJ, Lee Y, Hernandez RE. The use of pterygoid implants in the partially edentulous patient: A preliminary report. Int J Oral Maxillofac Surg 1995;10:89–98.
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