- Email: [email protected]
Immediate loading of dental implants in the edentulous mandible
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dental implants in the edentulous mandible. We performed a literature search using PUBMED and Ovid databases. For this review, we considered 31 articles in English from 1969 to 2003 pertaining to immediate loading of the anterior mandible. We have developed a technique to provide the patient with an immediately loaded implant in the edentulous mandible that incorporates a bar (that splints the im-
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he use of dental implants in the completely or partially edentulous jaw has become a common treatment modality in restorative dentistry.1-4 It has become particularly common in the edentulous mandible where the use of implants for improved retention of prostheses is a successful and well-documented treatment option.5-8 Traditional techniques for treating edentulous patients have been discussed in the early osseointegration literature. They involve a two-stage surgical approach with a healing time for implant integration and a transitional The literature period during which the patient wears a review temporary, removable prosthesis.2,9-11 2 demonstrated Brånemark and colleagues recomthat immediate mended a stress-free unloaded healing period to ensure osseointegration of loading of endosseous implants. High success rates anterior for the two-stage implant protocol have mandibular been documented.3,7,12,13 Likewise, sevimplants is an eral authors have used immediate acceptable loading in the anterior mandible and with difmethod, with reported high success rates ferent restorative options.14-20 predictable In this article, we review the literaresults. ture regarding immediate loading of
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PAULINO CASTELLON, D.D.S.; MARKUS B. BLATZ, D.M.D., Dr.Med.Dent.; MICHAEL S. BLOCK, D.M.D.; ISRAEL M. FINGER, D.D.S., M.S.; BILL ROGERS, C.D.T.
Background. The authors review the literature regarding immediate A D A implant loading in the J anterior edentulous ✷ ✷ mandible, demonstrate the technique they curN rently use, review prelimiC U A ING EDU 1 nary results and present RT ICLE an illustrative case. Materials and Methods. The authors conducted a literature search using PUBMED and Ovid databases. They considered for review 31 articles in English from 1969 to 2003 that pertained to immediate loading of the anterior mandible. The authors developed a technique to provide a bar-supported prosthesis on the day of surgery. They treated five patients and followed them up for at least six months. The preliminary results are presented. Results. This literature review demonstrated that immediate loading of anterior mandibular implants is an acceptable method, with predictable results. This case series demonstrates the potential for delivering a final bar on the day of surgery, based on the current evidence and clinical application. Conclusions and Practice Implications. The method described provides patients with immediate prosthetic restorations and a decreased treatment time compared with that for the traditional two-stage implant approach. CON
Immediate loading of dental implants in the edentulous mandible
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plants together) placed on the day of implant surgery. Our definition of an immediately loaded implant is one that is restored in occlusion on the day of implant placement. We also present a case to illustrate this technique. LITERATURE REVIEW
Immediate loading with provisional restorations. Schnitman and colleagues21 placed 46 smooth, machined, titanium-threaded implants (Nobel Biocare, Göteborg, Sweden) in the anterior mandible, with 26 submerged for four months and 20—used as extra implants not essential for the final prosthesis—
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immediately loaded to support an interim fixed Horiuchi and colleagues26 reported that 140 prosthesis. The implants were placed into healed smooth, machined-threaded titanium implants in sites or fresh extraction sockets. None of the 12 mandibles and five maxillae were loaded immediately loaded implants was placed into immediately with a heat-polymerizing resinfresh extraction sockets. The authors concluded based provisional prosthesis. After 24 months, that relatively smooth, machined, titanium136 implants osseointegrated, for a 97.2 percent threaded implants placed into the mandibles of success rate. edentulous or partially edentulous patients can In 2001, Ganeles and colleagues16 placed 186 be used to support interim, fixed, full-arch implants in 27 patients. One hundred sixty-one of restorations. these implants were loaded immediately with a In 1997, Schnitman and colleagues22 reported fixed provisional restoration. The authors that they had refined their technique. They reported that 99 percent of the implants inteplaced 28 implants into immediate function at the grated and were radiographically successful over time of implant placement by loading them with a mean period of 25 months. They concluded that provisional restorations. They used an interim, immediate loading with fixed provisional restorafixed partial denture to eliminate the need for a tions accompanied by appropriate surgical and removable denture. These implants functioned restorative techniques can be a predictable prosuccessfully during a three-month cedure, with a high success rate. healing period. Immediate loading with a Of the 28 implants placed into final prosthesis. Brånemark and The concept of 17 immediate function, four failed, colleagues developed a concept for primary stability is three before six months and one at patients to receive endosseous of paramount 18 months. All of the implants that implants and a final mandibular importance for the failed were distal to the incisor prosthesis on the day of implant survival of region. The authors explained that placement. This shortened the these failures were the result of healing period and eliminated the immediately loaded inadequate implant length (7 milneed for a second surgical appointimplants. limeters for posterior implants) and ment, as well as provided the poor bone quality in the posterior patient with a comfortable and mandible. stable prosthesis. This protocol17 23 In 1991, Krump and Barnett reported involves the use of prefabricated components and treating 11 patients with 41 implants that were surgical guides, which eliminates the need for a loaded immediately with a removable overdenfinal impression and provides the patient with a ture; the survival rate was 93 percent after 19 to final prosthesis. 48 months. One hundred fifty implants (Novum, Nobel In a study of 21 patients, Gatti and colleagues24 Biocare) were placed in 50 patients, who were folreported placing 84 ITI screw-type implants lowed up for six months to three years.17 The (Straumann, Waldenburg, Switzerland) in the overall implant survival rate was 98 percent. The interforaminal area; four rough-surfaced, authors concluded that a precise surgical and threaded implants in each jaw immediately prosthetic protocol allows for successful prosthetic received mandibular overdentures. The authors rehabilitation of patients with mandibular edenreported that the success rate for immediately tulism, and that the final mandibular reconstrucloaded mandibular implants was similar to that tion can be performed on the day of implant for implants with delayed loading. surgery. Tarnow and colleagues25 placed a total of 107 Their concept was confirmed by Chow and colimplants in edentulous patients, restoring six leagues27 (who used a fixed provisional prosthesis mandibles and four maxillae. Sixty-nine implants rather than a final prosthesis); they installed 123 were loaded with cemented or screw-retained proimplants and regularly followed them up for three visional prostheses. Sixty-seven of the immedito 30 months. Two implants failed, resulting in an ately loaded implants integrated into bone. The overall implant survival rate of 98.3 percent. authors concluded that immediate loading of mulImportance of primary stability of tiple, rigidly splinted implants in an edentulous immediately loaded implants. The concept of arch can be a viable treatment modality. primary stability is of paramount importance for 1544
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TABLE
KEY FACTORS TO BE CONSIDERED FOR IMPLANT SUCCESS. FACTOR
RATIONALE
Primary Stability of Implants
Minimizing micromotion and bicortical engagement of the implant increases the likelihood of successful integration17,28-30
Implants at Least 10 Millimeters in Length
Literature indicates that long implants have been successful; data are not available regarding short implants with immediate loading17,22
Bilateral Splinting of Implants
Mechanical analysis indicates that less nonaxial loading on implants results with cross-arch stabilization16,17,25,26
Bone Quantity and Quality
Literature implies that denser bone results in greater success because of higher torque required at implant placement17,22
Passive-Fitting Provisional Restoration With a Metal or Acrylic Framework
Literature implies that passive frameworks are critical to success17,25,26,30
the survival of immediately loaded implants. Cameron and colleagues28 attempted to define the conditions, with respect to movement of the implants, under which porous metal will bond to bone. Pilliar and colleagues29 demonstrated that micromovement above 150 micrometers should be considered excessive and, therefore, deleterious for osseointegration. In a more recent study, Brunski30 stated that “micromotion can be deleterious at the boneimplant interface, especially if it occurs soon after implantation.” According to Brunski, micromotion of more than 100 µm should be avoided. Motion greater than 100 µm will cause the wound to undergo fibrous repair rather than osseous apposition. Primary stability can be achieved by splinting multiple fixtures with a suprastructure. The table lists the key factors to be considered with regard to implant success based on our review of the literature. CURRENT PROTOCOL FOR IMMEDIATELY LOADED MANDIBULAR IMPLANTS
Preoperative laboratory procedures. We evaluated a completely edentulous patient (Figure 1) for this protocol. One of us (P.C.) fabricated maxillary and mandibular complete dentures for the patient. He evaluated the mandibular arch for implant placement. The preoperative work-up—based on the denture setup and the mandibular master cast—results in a working model of the planned implant placement from which the surgical guide stent will be made and a segmented bar will be cast (Figures 2 and 3). The practitioner fabricates a surgical stent on the mandibular cast. He or she then flasks the
mandibular denture using polysiloxane impression material and duplicates it in clear acrylic. To determine the position of the implants, the clinician uses radiographs to evaluate the height of the alveolar ridge and the amount of bone available for implant placement. He or she determines the angulation of the lingual and facial cortical bone from the radiographs and the physical examination of the patient. The surgeon or restorative dentist then places implant analogs in the cast. A slow-speed dental handpiece or mandrel is attached to a surveyor. Using conventional surgical drills, the dentist cuts a hole through the surgical stent, such as the duplicated denture in clear acrylic, to place the implant analogs in the mandibular cast. Drills are chosen to match the size of the implant analogs. The surgeon places metal tubes in the stent to provide him or her with an accurate prescription to guide the angulation of the implants, which minimizes the margin of error when transferring the implants from the cast to the patient (Figure 4, page 1547). The internal diameter of the metal tubes is slightly larger than the implant system’s pilot drill. After securing the implant analogs in the cast, the clinician constructs a gold bar. He or she places waxing sleeves onto the implant analogs and makes the milled bar in four sections. The two distal extension segments consist of a 2degree plastic premilled, or PPM, bar with a 1.5-mm hole drilled through the bar to receive a retentive attachment. The PPM bars should be placed over the crest of the mandibular ridge with no more than a 15-mm cantilever. The two middle sections have extensions facing toward the distal abutment. These extensions are used to position
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Figure 1. Preoperative view of the mandibular edentulous arch.
Figure 2. Four implant analogs and abutments are placed on the master cast, taking into consideration the location of the teeth from the denture setup and the radiograph.
Figure 3. A bar is made into four sections. Two distal extension segments consist of a 2-degree plastic premilled bar with a 1.5-millimeter hole drilled through the bar to receive the distal attachment. The two middle sections have extensions facing toward the distal abutment. The four sections of the bar are cast with type IV gold.
the bar intraorally and allow for the sections to be luted together with pattern resin after the implants have been placed and the incisions closed with sutures (Figure 3). The clinician should cast the bar with type IV gold, and seat each of the four sections individually on the master cast with the analogs in place. 1546
When the bar is finished, a gap of approximately 1 mm is left between sections to allow for correction of angulation discrepancy when the implant is placed, as well as to provide adequate space for soldering. After the four sections have been cast, the clinician fabricates two metal sleeves that will house the retentive attachments. The sleeves provide support for the denture and help position the attachments at delivery. The clinician positions the retentive attachment inside the wax sleeve pattern next to the bar. He or she then adds acrylic beads to the wax pattern for retention. The sleeves are cast in nonprecious metal (patent pending). After casting the sleeve, the clinician attaches the retentive attachment to the sleeve via laser welding or cold curing, to make it easier to pick up the attachments intraorally after the bar has been soldered (typically several hours after implant placement or after the patient has recovered from the surgery within a few days or weeks). To provide anterior stability, the clinician fits another attachment to the anterior segment after the sleeves have been completed. After completing the bar and sleeves, the dentist blocks out the bar to accept the final denture. Because the bar is not in its final position, minor rotational and height differences between the bar position on the cast and the bar position in the patient’s mouth may exist after the implants have been placed. The dentist must leave enough space for the attachments to be picked up intraorally on delivery. The model is duplicated in stone for processing. Once the denture is processed and finished, the dentist seats it back onto the original cast with the bar. At this point, the preoperative work-up is completed and the patient is ready to undergo surgery. Surgical treatment protocol. The surgeon administers local anesthetic to the anterior mandible. When a satisfactory plane of anesthesia has been reached, he or she makes a crestal incision that bisects the keratinized gingivae on the alveolar crest. If necessary, vertical releasing incisions are made posterior to the mental foramen, and a full-thickness mucoperiosteal flap is elevated from the labial and lingual bone. The surgeon locates the mental foramen and identifies the slope of the lingual cortex. The surgeon smooths the sharp-edged crestal bone and places the surgical guide stent. He or she uses the surgical guide stent to accurately
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place the implants in the predetermined position (Figure 4). The surgeon places guide pins in all four sites to confirm the ideal location of the implants, as planned in the presurgical work-up. He or she places the implants with the vertical position such that the abutments, once placed, will extend 2 to 4 mm above the gingivae. After placing the implants, the surgeon places the abutments and sutures the gingivae with resorbable suture (Figure 5). Depending on the restorative and surgical team, the restorative dentist may be at the surgeon’s clinic or waiting at his or her office for the next stage of the protocol. The patient may need to be transported by escort to the restorative dentist’s office after the incisions have been closed and prescriptions for antibiotics and pain medication given to the patient. Indexing the bar. Once the implants have been placed, the dentist lutes the sections of the bar together with light-cured resin material or autopolymerizing resin (Figure 6). To retain the resin for the index, the dentist should leave the surface of the bar in a rough, unpolished condition. After luting the bar segments together, the dentist removes the retaining screws. He or she removes the bar from the patient’s mouth and brings it to the laboratory. If the bar is to be placed the next day, the dentist relines the denture with soft liner. The laboratory technician fabricates a soldering investment burnout cast and solders or laser-welds the bar. The technician then polishes the bar and prepares it for delivery. Within 24 hours, the restorative dentist places the bar into the patient’s mouth and confirms the passive fit of the bar. He or she then secures the bar to the four implants with screws (Figure 7). The denture is relined with soft liner in occlusion. The dentist then adjusts the inner aspect of the denture as necessary. Depending on the preference of the dental team, the attachments can be placed into the prosthesis on the same day as implant placement, or after the local anesthetic has worn off or the soft-tissue swelling has resolved. The dentist fits the attachments over the bar, and tries in the denture, verifying occlusion. Using self-curing resin material, the dentist then picks up the attachments. He or she verifies that the teeth are in occlusion. The denture is taken to the laboratory for a final polishing. The laboratory technician or dentist places the anterior stabilizing attachment (Figures 7 and 8). When completed,
Figure 4. Guide pins are placed into the four implant sites to confirm the ideal location of the implants, as planned in the presurgical work-up.
Figure 5. The implants are placed with the vertical position such that the abutments, once placed, will extend 2 to 4 millimeters above the gingivae. After the implants are placed, the abutments are placed and the gingivae are sutured with resorbable suture.
Figure 6. The surface of the bar should be left in a rough, unpolished condition. After the bar segments are luted together, the retaining screws are removed and the bar is removed from the patient’s mouth. It is then soldered in the laboratory.
the bar and denture are delivered to the patient. Figure 9 shows the panoramic radiograph of the completed bar at the one-year follow-up visit. CASE REPORT
In 2002, a 58-year-old man visited the Department of Prosthodontics, Louisiana State Univer-
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Figure 7. The anterior stabilizing attachment is added to the bar. In this patient, a Dalla-Bona system was used. After the bar is polished, it is returned for delivery to the patient. The denture then is relined with soft material in occlusion.
Figure 8. The denture is completed in the laboratory. Note the bilateral distal attachments and the anterior stabilizing attachment.
Figure 9. Panoramic radiograph of the completed bar at the one-year follow-up visit.
sity School of Dentistry, New Orleans. His medical history was unremarkable. One of us (P.C.) performed an oral examination, which revealed an edentulous mandible and maxilla, with 15 mm of height in the anterior mandible. The patient had maxillary and mandibular complete dentures. He complained of a loose and poorly fitting mandibular denture. 1548
We scheduled preoperative visits for preliminary impressions of the maxilla and mandible. On the preliminary cast, occlusal rims were made to standard dimensions. The mandibular occlusal rim was made so that a four-implant–retained bar could be made to fit within the teeth and acrylic of the prosthesis. The dentist obtained maxillomandibular relationships and selected tooth sites. After completing the initial denture try-in and verifying the centric occlusion and vertical dimension of occlusion, the dentist prepared the mandibular cast to receive the implant analogs. We followed the protocol described above and as depicted in Figures 1 through 9. Within one week of implant placement and receipt of the final prosthesis, the patient received the retentive attachments. He was satisfied that his treatment time had been reduced dramatically from that for the standard two-stage technique or an immediate provisional protocol. A one-year follow-up examination revealed crestal bone maintenance and excellent gingival health with minimal hygiene problems. Results of preliminary case series of patients. In 2002, one of us (P.C.) placed 20 implants (16 SwissPlus, Zimmer Dental, Carlsbad, Calif., and four Osseotite IC, Implant Innovations, Palm Beach Gardens, Fla.) in five patients. All 20 implants integrated into bone. The dentist positioned the attachments in all patients after the local anesthetic had worn off and the preliminary soft-tissue swelling had resolved. After one year of follow-up, crestal bone levels were maintained at the level of the first thread of the implants. Gingival health has been maintained, with no evidence of exudate or gingival hyperplasia. To date, all five patients are eating a normal textured diet without pain. Postoperative satisfaction questionnaires indicate that all patients were satisfied with the procedure, would undergo it again and would recommend the procedure to their friends. CONCLUSIONS
After reviewing the available literature, we conclude that there is sufficient evidence to show that, when placed into adequate bone, threaded implants can be loaded immediately when they are splinted together by a rigid bar; when they are positioned properly in a parallel fashion; when the attachments are positioned in final
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Dr. Castellon is an assistant professor, Department of Prosthodontics, Louisiana State University School of Dentistry, 1100 Florida Ave., New Orleans, La. 70119, e-mail “[email protected]”. Address reprint requests to Dr. Castellon.
Dr. Block is a professor, Department of Oral and Maxillofacial Surgery, Louisiana State University School of Dentistry, New Orleans.
occlusion and the dynamics of mandibular function have returned after the anesthetic has worn off; and when a functioning prosthesis has been fabricated. ■
Dr. Blatz is an associate professor, Department of Prosthodontics, Louisiana State University School of Dentistry, New Orleans.
Dr. Finger is a former professor and former director of the graduate program in prosthodontics, Louisiana State University School of Dentistry, New Orleans. He now is retired. Mr. Rogers is a former professor, Department of Prosthodontics, Louisiana State University School of Dentistry, New Orleans. He now is in private practice as a dental technician. 1. Becker W, Becker BE, Alsuwyed A, Al-Mubarak S. Long-term evaluation of 282 implants in maxillary and mandibular molar positions: a prospective study. J Periodontol 1999;70:896-901. 2. Brånemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses, I: experimental studies. Scand J Plast Reconstr Surg 1969;3(2):81-100. 3. Eckert SE, Wollan PC. Retrospective review of 1170 endosseous implants placed in partially edentulous jaws. J Prosthet Dent 1998;79:415-21. 4. Jaffin RA, Kumar A, Berman CL. Immediate loading of implants in partially and fully edentulous jaws: a series of 27 case reports. J Periodontol 2000;71:833-8. 5. Jemt T, Stalblad P-A, Haraldson T. Functional evaluation of patients treated with overdentures in the mandible supported by osseointegrated fixtures: A one-year follow-up study. In: van Steenberghe D, Albrektson T, Brånemark PI, Henry PJ, Holt R, Liden G, eds. Proceedings of International Congress on Tissue Integration in Oral and Maxillofacial Reconstruction, Brussels, May 1985. Amsterdam: Excerpta Medica; 1986. 6. Meijer HJ, Raghoebar GM, Van’t Hof MA, Geertman ME, Van Oort RP. Implant-retained mandibular overdentures compared with complete dentures: a 5 years’ follow-up study of clinical aspects and patient satisfaction. Clin Oral Implants Res 1999;10:238-44. 7. von Wowern N, Harder F, Hjorting-hansen E, Gotfredsen K. ITI implants with overdentures: a prevention of bone loss in edentulous mandibles? Int J Oral Maxillofac Implants 1990;5(2):135-9. 8. Zitzmann NU, Marinello CP. Treatment outcomes of fixed or removable implant-supported prostheses in the edentulous maxilla, part I: patients’ assessments. J Prosthet Dent 2000;83:424-33. 9. Johansson C, Albrektsson T. Integration of screw implants in the rabbit: a 1-year follow-up of removal torque of titanium implants. Int J Oral Maxillofac Implants 1987;2(2):69-75. 10. Schwartz-Arad D, Gulayev N, Chaushu G. Immediate versus nonimmediate implantation for full-arch fixed reconstruction following extraction of all residual teeth: a retrospective comparative study. J Periodontol 2000;71:923-8.
11. Roynesdal AK, Ambjornsen E, Haanaes HR. A comparison of 3 different endosseous nonsubmerged implants in edentulous mandibles: a clinical report. Int J Oral Maxillofac Implants 1999;14:543-8. 12. Albrektsson T, Zarb G, Worthington P, Eriksson AR. The longterm efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants 1986;1(1):11-25. 13. Naert I, Quirynen M, Theuniers G, van Steenberghe D. Prosthetic aspects of osseointegrated fixtures supporting overdentures: a 4-year report. J Prosthet Dent 1991;65:671-80. 14. De Bruyn H, Kisch J, Collaert B, Linden U, Nilner K, Dvarsater L. Fixed mandibular restorations on three early-loaded regular platform Brånemark implants. Clin Implant Dent Relat Res 2001;3(4): 176-84. 15. Chiapasco M, Abati S, Romeo E, Vogel G. Implant-retained mandibular overdentures with Brånemark System MKII implants: a prospective comparative study between delayed and immediate loading. Int J Oral Maxillofac Implants 2001;16:537-46. 16. Ganeles J, Rosenberg MM, Holt RL, Reichman LH. Immediate loading of implants with fixed restorations in the completely edentulous mandible: report of 27 patients from a private practice. Int J Oral Maxillofac Implants 2001;16:418-26. 17. Brånemark PI, Engstrand P, Ohrnell LO, et al. Brånemark Novum: a new treatment concept for rehabilitation of the edentulous mandible—preliminary results from a prospective clinical follow-up study. Clin Implant Dent Relat Res 1999;1(1):2-16. 18. Ericsson I, Randow K, Nilner K, Peterson A. Early functional loading of Brånemark dental implants: 5-year clinical follow-up study. Clin Implant Dent Relat Res 2000;2(2):70-7. 19. Colomina LE. Immediate loading of implant-fixed mandibular prostheses: a prospective 18-month follow-up clinical study—preliminary report. Implant Dent 2001;10(1):23-9. 20. Randow K, Ericsson I, Nilner K, Petersson A, Glantz PO. Immediate functional loading of Brånemark dental implants: an 18-month clinical follow-up study. Clin Oral Implants Res 1999;10(1):8-15. 21. Schnitman PA, Wohrle PS, Rubenstein JE. Immediate fixed interim prostheses supported by two-stage threaded implants: methodology and results. J Oral Implantol 1990;16(2):96-105. 22. Schnitman PA, Wohrle PS, Rubenstein JE, DaSilva JD, Wang NH. Ten-year results for Brånemark implants immediately loaded with fixed prostheses at implant placement. Int J Oral Maxillofac Implants 1997;12:495-503. 23. Krump JL, Barnett BG. The immediate implant: a treatment alternative. Int J Oral Maxillofac Implants 1991;6(1):19-23. 24. Gatti C, Haefliger W, Chiapasco M. Implant-retained mandibular overdentures with immediate loading: a prospective study of ITI implants. Int J Oral Maxillofac Implants 2000;15(3):383-8. 25. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implants 1997;12:319-24. 26. Horiuchi K, Uchida H, Yamamoto K, Sugimura M. Immediate loading of Brånemark system implants following placement in edentulous patients: a clinical report. Int J Oral Maxillofac Implants 2000;15:824-30. 27. Chow J, Hui E, Liu J, et al. The Hong Kong Bridge Protocol: immediate loading of mandibular Brånemark fixtures using a fixed provisional prosthesis—preliminary results. Clin Implant Dent Relat Res 2001;3(3):166-74. 28. Cameron HU, Pilliar RM, MacNab I. The effect of movement on the bonding of porous metal to bone. J Biomed Mater Res 1973;7:30111. 29. Pilliar RM, Lee JM, Maniatopoulos C. Observations on the effect of movement on bone ingrowth into porous-surfaced implants. Clin Orthop 1986;208:108-13. 30. Brunski JB. Biomechanical factors affecting the bone-dental implant interface. Clin Mater 1992;10(3):153-201.
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dental implants in the edentulous mandible. We performed a literature search using PUBMED and Ovid databases. For this review, we considered 31 articles in English from 1969 to 2003 pertaining to immediate loading of the anterior mandible. We have developed a technique to provide the patient with an immediately loaded implant in the edentulous mandible that incorporates a bar (that splints the im-
I
he use of dental implants in the completely or partially edentulous jaw has become a common treatment modality in restorative dentistry.1-4 It has become particularly common in the edentulous mandible where the use of implants for improved retention of prostheses is a successful and well-documented treatment option.5-8 Traditional techniques for treating edentulous patients have been discussed in the early osseointegration literature. They involve a two-stage surgical approach with a healing time for implant integration and a transitional The literature period during which the patient wears a review temporary, removable prosthesis.2,9-11 2 demonstrated Brånemark and colleagues recomthat immediate mended a stress-free unloaded healing period to ensure osseointegration of loading of endosseous implants. High success rates anterior for the two-stage implant protocol have mandibular been documented.3,7,12,13 Likewise, sevimplants is an eral authors have used immediate acceptable loading in the anterior mandible and with difmethod, with reported high success rates ferent restorative options.14-20 predictable In this article, we review the literaresults. ture regarding immediate loading of
T
PAULINO CASTELLON, D.D.S.; MARKUS B. BLATZ, D.M.D., Dr.Med.Dent.; MICHAEL S. BLOCK, D.M.D.; ISRAEL M. FINGER, D.D.S., M.S.; BILL ROGERS, C.D.T.
Background. The authors review the literature regarding immediate A D A implant loading in the J anterior edentulous ✷ ✷ mandible, demonstrate the technique they curN rently use, review prelimiC U A ING EDU 1 nary results and present RT ICLE an illustrative case. Materials and Methods. The authors conducted a literature search using PUBMED and Ovid databases. They considered for review 31 articles in English from 1969 to 2003 that pertained to immediate loading of the anterior mandible. The authors developed a technique to provide a bar-supported prosthesis on the day of surgery. They treated five patients and followed them up for at least six months. The preliminary results are presented. Results. This literature review demonstrated that immediate loading of anterior mandibular implants is an acceptable method, with predictable results. This case series demonstrates the potential for delivering a final bar on the day of surgery, based on the current evidence and clinical application. Conclusions and Practice Implications. The method described provides patients with immediate prosthetic restorations and a decreased treatment time compared with that for the traditional two-stage implant approach. CON
Immediate loading of dental implants in the edentulous mandible
ABSTRACT
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plants together) placed on the day of implant surgery. Our definition of an immediately loaded implant is one that is restored in occlusion on the day of implant placement. We also present a case to illustrate this technique. LITERATURE REVIEW
Immediate loading with provisional restorations. Schnitman and colleagues21 placed 46 smooth, machined, titanium-threaded implants (Nobel Biocare, Göteborg, Sweden) in the anterior mandible, with 26 submerged for four months and 20—used as extra implants not essential for the final prosthesis—
JADA, Vol. 135, November 2004 Copyright ©2004 American Dental Association. All rights reserved.
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immediately loaded to support an interim fixed Horiuchi and colleagues26 reported that 140 prosthesis. The implants were placed into healed smooth, machined-threaded titanium implants in sites or fresh extraction sockets. None of the 12 mandibles and five maxillae were loaded immediately loaded implants was placed into immediately with a heat-polymerizing resinfresh extraction sockets. The authors concluded based provisional prosthesis. After 24 months, that relatively smooth, machined, titanium136 implants osseointegrated, for a 97.2 percent threaded implants placed into the mandibles of success rate. edentulous or partially edentulous patients can In 2001, Ganeles and colleagues16 placed 186 be used to support interim, fixed, full-arch implants in 27 patients. One hundred sixty-one of restorations. these implants were loaded immediately with a In 1997, Schnitman and colleagues22 reported fixed provisional restoration. The authors that they had refined their technique. They reported that 99 percent of the implants inteplaced 28 implants into immediate function at the grated and were radiographically successful over time of implant placement by loading them with a mean period of 25 months. They concluded that provisional restorations. They used an interim, immediate loading with fixed provisional restorafixed partial denture to eliminate the need for a tions accompanied by appropriate surgical and removable denture. These implants functioned restorative techniques can be a predictable prosuccessfully during a three-month cedure, with a high success rate. healing period. Immediate loading with a Of the 28 implants placed into final prosthesis. Brånemark and The concept of 17 immediate function, four failed, colleagues developed a concept for primary stability is three before six months and one at patients to receive endosseous of paramount 18 months. All of the implants that implants and a final mandibular importance for the failed were distal to the incisor prosthesis on the day of implant survival of region. The authors explained that placement. This shortened the these failures were the result of healing period and eliminated the immediately loaded inadequate implant length (7 milneed for a second surgical appointimplants. limeters for posterior implants) and ment, as well as provided the poor bone quality in the posterior patient with a comfortable and mandible. stable prosthesis. This protocol17 23 In 1991, Krump and Barnett reported involves the use of prefabricated components and treating 11 patients with 41 implants that were surgical guides, which eliminates the need for a loaded immediately with a removable overdenfinal impression and provides the patient with a ture; the survival rate was 93 percent after 19 to final prosthesis. 48 months. One hundred fifty implants (Novum, Nobel In a study of 21 patients, Gatti and colleagues24 Biocare) were placed in 50 patients, who were folreported placing 84 ITI screw-type implants lowed up for six months to three years.17 The (Straumann, Waldenburg, Switzerland) in the overall implant survival rate was 98 percent. The interforaminal area; four rough-surfaced, authors concluded that a precise surgical and threaded implants in each jaw immediately prosthetic protocol allows for successful prosthetic received mandibular overdentures. The authors rehabilitation of patients with mandibular edenreported that the success rate for immediately tulism, and that the final mandibular reconstrucloaded mandibular implants was similar to that tion can be performed on the day of implant for implants with delayed loading. surgery. Tarnow and colleagues25 placed a total of 107 Their concept was confirmed by Chow and colimplants in edentulous patients, restoring six leagues27 (who used a fixed provisional prosthesis mandibles and four maxillae. Sixty-nine implants rather than a final prosthesis); they installed 123 were loaded with cemented or screw-retained proimplants and regularly followed them up for three visional prostheses. Sixty-seven of the immedito 30 months. Two implants failed, resulting in an ately loaded implants integrated into bone. The overall implant survival rate of 98.3 percent. authors concluded that immediate loading of mulImportance of primary stability of tiple, rigidly splinted implants in an edentulous immediately loaded implants. The concept of arch can be a viable treatment modality. primary stability is of paramount importance for 1544
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TABLE
KEY FACTORS TO BE CONSIDERED FOR IMPLANT SUCCESS. FACTOR
RATIONALE
Primary Stability of Implants
Minimizing micromotion and bicortical engagement of the implant increases the likelihood of successful integration17,28-30
Implants at Least 10 Millimeters in Length
Literature indicates that long implants have been successful; data are not available regarding short implants with immediate loading17,22
Bilateral Splinting of Implants
Mechanical analysis indicates that less nonaxial loading on implants results with cross-arch stabilization16,17,25,26
Bone Quantity and Quality
Literature implies that denser bone results in greater success because of higher torque required at implant placement17,22
Passive-Fitting Provisional Restoration With a Metal or Acrylic Framework
Literature implies that passive frameworks are critical to success17,25,26,30
the survival of immediately loaded implants. Cameron and colleagues28 attempted to define the conditions, with respect to movement of the implants, under which porous metal will bond to bone. Pilliar and colleagues29 demonstrated that micromovement above 150 micrometers should be considered excessive and, therefore, deleterious for osseointegration. In a more recent study, Brunski30 stated that “micromotion can be deleterious at the boneimplant interface, especially if it occurs soon after implantation.” According to Brunski, micromotion of more than 100 µm should be avoided. Motion greater than 100 µm will cause the wound to undergo fibrous repair rather than osseous apposition. Primary stability can be achieved by splinting multiple fixtures with a suprastructure. The table lists the key factors to be considered with regard to implant success based on our review of the literature. CURRENT PROTOCOL FOR IMMEDIATELY LOADED MANDIBULAR IMPLANTS
Preoperative laboratory procedures. We evaluated a completely edentulous patient (Figure 1) for this protocol. One of us (P.C.) fabricated maxillary and mandibular complete dentures for the patient. He evaluated the mandibular arch for implant placement. The preoperative work-up—based on the denture setup and the mandibular master cast—results in a working model of the planned implant placement from which the surgical guide stent will be made and a segmented bar will be cast (Figures 2 and 3). The practitioner fabricates a surgical stent on the mandibular cast. He or she then flasks the
mandibular denture using polysiloxane impression material and duplicates it in clear acrylic. To determine the position of the implants, the clinician uses radiographs to evaluate the height of the alveolar ridge and the amount of bone available for implant placement. He or she determines the angulation of the lingual and facial cortical bone from the radiographs and the physical examination of the patient. The surgeon or restorative dentist then places implant analogs in the cast. A slow-speed dental handpiece or mandrel is attached to a surveyor. Using conventional surgical drills, the dentist cuts a hole through the surgical stent, such as the duplicated denture in clear acrylic, to place the implant analogs in the mandibular cast. Drills are chosen to match the size of the implant analogs. The surgeon places metal tubes in the stent to provide him or her with an accurate prescription to guide the angulation of the implants, which minimizes the margin of error when transferring the implants from the cast to the patient (Figure 4, page 1547). The internal diameter of the metal tubes is slightly larger than the implant system’s pilot drill. After securing the implant analogs in the cast, the clinician constructs a gold bar. He or she places waxing sleeves onto the implant analogs and makes the milled bar in four sections. The two distal extension segments consist of a 2degree plastic premilled, or PPM, bar with a 1.5-mm hole drilled through the bar to receive a retentive attachment. The PPM bars should be placed over the crest of the mandibular ridge with no more than a 15-mm cantilever. The two middle sections have extensions facing toward the distal abutment. These extensions are used to position
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Figure 1. Preoperative view of the mandibular edentulous arch.
Figure 2. Four implant analogs and abutments are placed on the master cast, taking into consideration the location of the teeth from the denture setup and the radiograph.
Figure 3. A bar is made into four sections. Two distal extension segments consist of a 2-degree plastic premilled bar with a 1.5-millimeter hole drilled through the bar to receive the distal attachment. The two middle sections have extensions facing toward the distal abutment. The four sections of the bar are cast with type IV gold.
the bar intraorally and allow for the sections to be luted together with pattern resin after the implants have been placed and the incisions closed with sutures (Figure 3). The clinician should cast the bar with type IV gold, and seat each of the four sections individually on the master cast with the analogs in place. 1546
When the bar is finished, a gap of approximately 1 mm is left between sections to allow for correction of angulation discrepancy when the implant is placed, as well as to provide adequate space for soldering. After the four sections have been cast, the clinician fabricates two metal sleeves that will house the retentive attachments. The sleeves provide support for the denture and help position the attachments at delivery. The clinician positions the retentive attachment inside the wax sleeve pattern next to the bar. He or she then adds acrylic beads to the wax pattern for retention. The sleeves are cast in nonprecious metal (patent pending). After casting the sleeve, the clinician attaches the retentive attachment to the sleeve via laser welding or cold curing, to make it easier to pick up the attachments intraorally after the bar has been soldered (typically several hours after implant placement or after the patient has recovered from the surgery within a few days or weeks). To provide anterior stability, the clinician fits another attachment to the anterior segment after the sleeves have been completed. After completing the bar and sleeves, the dentist blocks out the bar to accept the final denture. Because the bar is not in its final position, minor rotational and height differences between the bar position on the cast and the bar position in the patient’s mouth may exist after the implants have been placed. The dentist must leave enough space for the attachments to be picked up intraorally on delivery. The model is duplicated in stone for processing. Once the denture is processed and finished, the dentist seats it back onto the original cast with the bar. At this point, the preoperative work-up is completed and the patient is ready to undergo surgery. Surgical treatment protocol. The surgeon administers local anesthetic to the anterior mandible. When a satisfactory plane of anesthesia has been reached, he or she makes a crestal incision that bisects the keratinized gingivae on the alveolar crest. If necessary, vertical releasing incisions are made posterior to the mental foramen, and a full-thickness mucoperiosteal flap is elevated from the labial and lingual bone. The surgeon locates the mental foramen and identifies the slope of the lingual cortex. The surgeon smooths the sharp-edged crestal bone and places the surgical guide stent. He or she uses the surgical guide stent to accurately
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place the implants in the predetermined position (Figure 4). The surgeon places guide pins in all four sites to confirm the ideal location of the implants, as planned in the presurgical work-up. He or she places the implants with the vertical position such that the abutments, once placed, will extend 2 to 4 mm above the gingivae. After placing the implants, the surgeon places the abutments and sutures the gingivae with resorbable suture (Figure 5). Depending on the restorative and surgical team, the restorative dentist may be at the surgeon’s clinic or waiting at his or her office for the next stage of the protocol. The patient may need to be transported by escort to the restorative dentist’s office after the incisions have been closed and prescriptions for antibiotics and pain medication given to the patient. Indexing the bar. Once the implants have been placed, the dentist lutes the sections of the bar together with light-cured resin material or autopolymerizing resin (Figure 6). To retain the resin for the index, the dentist should leave the surface of the bar in a rough, unpolished condition. After luting the bar segments together, the dentist removes the retaining screws. He or she removes the bar from the patient’s mouth and brings it to the laboratory. If the bar is to be placed the next day, the dentist relines the denture with soft liner. The laboratory technician fabricates a soldering investment burnout cast and solders or laser-welds the bar. The technician then polishes the bar and prepares it for delivery. Within 24 hours, the restorative dentist places the bar into the patient’s mouth and confirms the passive fit of the bar. He or she then secures the bar to the four implants with screws (Figure 7). The denture is relined with soft liner in occlusion. The dentist then adjusts the inner aspect of the denture as necessary. Depending on the preference of the dental team, the attachments can be placed into the prosthesis on the same day as implant placement, or after the local anesthetic has worn off or the soft-tissue swelling has resolved. The dentist fits the attachments over the bar, and tries in the denture, verifying occlusion. Using self-curing resin material, the dentist then picks up the attachments. He or she verifies that the teeth are in occlusion. The denture is taken to the laboratory for a final polishing. The laboratory technician or dentist places the anterior stabilizing attachment (Figures 7 and 8). When completed,
Figure 4. Guide pins are placed into the four implant sites to confirm the ideal location of the implants, as planned in the presurgical work-up.
Figure 5. The implants are placed with the vertical position such that the abutments, once placed, will extend 2 to 4 millimeters above the gingivae. After the implants are placed, the abutments are placed and the gingivae are sutured with resorbable suture.
Figure 6. The surface of the bar should be left in a rough, unpolished condition. After the bar segments are luted together, the retaining screws are removed and the bar is removed from the patient’s mouth. It is then soldered in the laboratory.
the bar and denture are delivered to the patient. Figure 9 shows the panoramic radiograph of the completed bar at the one-year follow-up visit. CASE REPORT
In 2002, a 58-year-old man visited the Department of Prosthodontics, Louisiana State Univer-
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Figure 7. The anterior stabilizing attachment is added to the bar. In this patient, a Dalla-Bona system was used. After the bar is polished, it is returned for delivery to the patient. The denture then is relined with soft material in occlusion.
Figure 8. The denture is completed in the laboratory. Note the bilateral distal attachments and the anterior stabilizing attachment.
Figure 9. Panoramic radiograph of the completed bar at the one-year follow-up visit.
sity School of Dentistry, New Orleans. His medical history was unremarkable. One of us (P.C.) performed an oral examination, which revealed an edentulous mandible and maxilla, with 15 mm of height in the anterior mandible. The patient had maxillary and mandibular complete dentures. He complained of a loose and poorly fitting mandibular denture. 1548
We scheduled preoperative visits for preliminary impressions of the maxilla and mandible. On the preliminary cast, occlusal rims were made to standard dimensions. The mandibular occlusal rim was made so that a four-implant–retained bar could be made to fit within the teeth and acrylic of the prosthesis. The dentist obtained maxillomandibular relationships and selected tooth sites. After completing the initial denture try-in and verifying the centric occlusion and vertical dimension of occlusion, the dentist prepared the mandibular cast to receive the implant analogs. We followed the protocol described above and as depicted in Figures 1 through 9. Within one week of implant placement and receipt of the final prosthesis, the patient received the retentive attachments. He was satisfied that his treatment time had been reduced dramatically from that for the standard two-stage technique or an immediate provisional protocol. A one-year follow-up examination revealed crestal bone maintenance and excellent gingival health with minimal hygiene problems. Results of preliminary case series of patients. In 2002, one of us (P.C.) placed 20 implants (16 SwissPlus, Zimmer Dental, Carlsbad, Calif., and four Osseotite IC, Implant Innovations, Palm Beach Gardens, Fla.) in five patients. All 20 implants integrated into bone. The dentist positioned the attachments in all patients after the local anesthetic had worn off and the preliminary soft-tissue swelling had resolved. After one year of follow-up, crestal bone levels were maintained at the level of the first thread of the implants. Gingival health has been maintained, with no evidence of exudate or gingival hyperplasia. To date, all five patients are eating a normal textured diet without pain. Postoperative satisfaction questionnaires indicate that all patients were satisfied with the procedure, would undergo it again and would recommend the procedure to their friends. CONCLUSIONS
After reviewing the available literature, we conclude that there is sufficient evidence to show that, when placed into adequate bone, threaded implants can be loaded immediately when they are splinted together by a rigid bar; when they are positioned properly in a parallel fashion; when the attachments are positioned in final
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Dr. Castellon is an assistant professor, Department of Prosthodontics, Louisiana State University School of Dentistry, 1100 Florida Ave., New Orleans, La. 70119, e-mail “[email protected]”. Address reprint requests to Dr. Castellon.
Dr. Block is a professor, Department of Oral and Maxillofacial Surgery, Louisiana State University School of Dentistry, New Orleans.
occlusion and the dynamics of mandibular function have returned after the anesthetic has worn off; and when a functioning prosthesis has been fabricated. ■
Dr. Blatz is an associate professor, Department of Prosthodontics, Louisiana State University School of Dentistry, New Orleans.
Dr. Finger is a former professor and former director of the graduate program in prosthodontics, Louisiana State University School of Dentistry, New Orleans. He now is retired. Mr. Rogers is a former professor, Department of Prosthodontics, Louisiana State University School of Dentistry, New Orleans. He now is in private practice as a dental technician. 1. Becker W, Becker BE, Alsuwyed A, Al-Mubarak S. Long-term evaluation of 282 implants in maxillary and mandibular molar positions: a prospective study. J Periodontol 1999;70:896-901. 2. Brånemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses, I: experimental studies. Scand J Plast Reconstr Surg 1969;3(2):81-100. 3. Eckert SE, Wollan PC. Retrospective review of 1170 endosseous implants placed in partially edentulous jaws. J Prosthet Dent 1998;79:415-21. 4. Jaffin RA, Kumar A, Berman CL. Immediate loading of implants in partially and fully edentulous jaws: a series of 27 case reports. J Periodontol 2000;71:833-8. 5. Jemt T, Stalblad P-A, Haraldson T. Functional evaluation of patients treated with overdentures in the mandible supported by osseointegrated fixtures: A one-year follow-up study. In: van Steenberghe D, Albrektson T, Brånemark PI, Henry PJ, Holt R, Liden G, eds. Proceedings of International Congress on Tissue Integration in Oral and Maxillofacial Reconstruction, Brussels, May 1985. Amsterdam: Excerpta Medica; 1986. 6. Meijer HJ, Raghoebar GM, Van’t Hof MA, Geertman ME, Van Oort RP. Implant-retained mandibular overdentures compared with complete dentures: a 5 years’ follow-up study of clinical aspects and patient satisfaction. Clin Oral Implants Res 1999;10:238-44. 7. von Wowern N, Harder F, Hjorting-hansen E, Gotfredsen K. ITI implants with overdentures: a prevention of bone loss in edentulous mandibles? Int J Oral Maxillofac Implants 1990;5(2):135-9. 8. Zitzmann NU, Marinello CP. Treatment outcomes of fixed or removable implant-supported prostheses in the edentulous maxilla, part I: patients’ assessments. J Prosthet Dent 2000;83:424-33. 9. Johansson C, Albrektsson T. Integration of screw implants in the rabbit: a 1-year follow-up of removal torque of titanium implants. Int J Oral Maxillofac Implants 1987;2(2):69-75. 10. Schwartz-Arad D, Gulayev N, Chaushu G. Immediate versus nonimmediate implantation for full-arch fixed reconstruction following extraction of all residual teeth: a retrospective comparative study. J Periodontol 2000;71:923-8.
11. Roynesdal AK, Ambjornsen E, Haanaes HR. A comparison of 3 different endosseous nonsubmerged implants in edentulous mandibles: a clinical report. Int J Oral Maxillofac Implants 1999;14:543-8. 12. Albrektsson T, Zarb G, Worthington P, Eriksson AR. The longterm efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants 1986;1(1):11-25. 13. Naert I, Quirynen M, Theuniers G, van Steenberghe D. Prosthetic aspects of osseointegrated fixtures supporting overdentures: a 4-year report. J Prosthet Dent 1991;65:671-80. 14. De Bruyn H, Kisch J, Collaert B, Linden U, Nilner K, Dvarsater L. Fixed mandibular restorations on three early-loaded regular platform Brånemark implants. Clin Implant Dent Relat Res 2001;3(4): 176-84. 15. Chiapasco M, Abati S, Romeo E, Vogel G. Implant-retained mandibular overdentures with Brånemark System MKII implants: a prospective comparative study between delayed and immediate loading. Int J Oral Maxillofac Implants 2001;16:537-46. 16. Ganeles J, Rosenberg MM, Holt RL, Reichman LH. Immediate loading of implants with fixed restorations in the completely edentulous mandible: report of 27 patients from a private practice. Int J Oral Maxillofac Implants 2001;16:418-26. 17. Brånemark PI, Engstrand P, Ohrnell LO, et al. Brånemark Novum: a new treatment concept for rehabilitation of the edentulous mandible—preliminary results from a prospective clinical follow-up study. Clin Implant Dent Relat Res 1999;1(1):2-16. 18. Ericsson I, Randow K, Nilner K, Peterson A. Early functional loading of Brånemark dental implants: 5-year clinical follow-up study. Clin Implant Dent Relat Res 2000;2(2):70-7. 19. Colomina LE. Immediate loading of implant-fixed mandibular prostheses: a prospective 18-month follow-up clinical study—preliminary report. Implant Dent 2001;10(1):23-9. 20. Randow K, Ericsson I, Nilner K, Petersson A, Glantz PO. Immediate functional loading of Brånemark dental implants: an 18-month clinical follow-up study. Clin Oral Implants Res 1999;10(1):8-15. 21. Schnitman PA, Wohrle PS, Rubenstein JE. Immediate fixed interim prostheses supported by two-stage threaded implants: methodology and results. J Oral Implantol 1990;16(2):96-105. 22. Schnitman PA, Wohrle PS, Rubenstein JE, DaSilva JD, Wang NH. Ten-year results for Brånemark implants immediately loaded with fixed prostheses at implant placement. Int J Oral Maxillofac Implants 1997;12:495-503. 23. Krump JL, Barnett BG. The immediate implant: a treatment alternative. Int J Oral Maxillofac Implants 1991;6(1):19-23. 24. Gatti C, Haefliger W, Chiapasco M. Implant-retained mandibular overdentures with immediate loading: a prospective study of ITI implants. Int J Oral Maxillofac Implants 2000;15(3):383-8. 25. Tarnow DP, Emtiaz S, Classi A. Immediate loading of threaded implants at stage 1 surgery in edentulous arches: ten consecutive case reports with 1- to 5-year data. Int J Oral Maxillofac Implants 1997;12:319-24. 26. Horiuchi K, Uchida H, Yamamoto K, Sugimura M. Immediate loading of Brånemark system implants following placement in edentulous patients: a clinical report. Int J Oral Maxillofac Implants 2000;15:824-30. 27. Chow J, Hui E, Liu J, et al. The Hong Kong Bridge Protocol: immediate loading of mandibular Brånemark fixtures using a fixed provisional prosthesis—preliminary results. Clin Implant Dent Relat Res 2001;3(3):166-74. 28. Cameron HU, Pilliar RM, MacNab I. The effect of movement on the bonding of porous metal to bone. J Biomed Mater Res 1973;7:30111. 29. Pilliar RM, Lee JM, Maniatopoulos C. Observations on the effect of movement on bone ingrowth into porous-surfaced implants. Clin Orthop 1986;208:108-13. 30. Brunski JB. Biomechanical factors affecting the bone-dental implant interface. Clin Mater 1992;10(3):153-201.
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