Craniomaxillofacial Reconstructive and Corrective Bone Surgery - part 3 docx

140 H P. Weber, D.A. Buser, and D. Weingart sink depth. They are press-fit implants, which achieve the re- quired primary stability with the preparation of a precise, con- gruent implant bed. The instruments necessary for bone prepa- ration are in part the same as for the HS implant (Figure 15.5): three round burs of increasing diameters, predrill, trephine mill, and a color-coded depth gauge. However, tap, ratchet, and guidance key are not necessary. To insert the implant, the insertion device is attached to the implant top in the sterile ampoule. The implant is then removed from the ampoule and placed into the bone cavity until a slight resistance is de- tectable. Subsequently, the inserting device is removed, and the implant is tapped to its final position using a special tap- ping instrument and a mallet. The gentle press-fit after inser- tion allows for good primary stability in recipient sites with a firm bone structure. ITI Implant Material and Tissue Reactions ITI implants are endosseous implants that are anchored in the bone and penetrate the soft tissue cover. Therefore, the im- plant surface is not only in contact with the bone but also with the mucosa. Since their inception 20 years ago, ITI implants have been made of commercially pure titanium with a TPS surface in the bone-anchoring section. This coating procedure, first described by Hahn and Palich, 11 was introduced in implant dentistry for the first time with ITI implants in 1974. It creates a rough and microporous implant surface, with a porosity between 30 and 50 ␮ m (Figure 15.6). The oxide film responsible for the bio- compatibility of titanium forms on this sprayed layer. There- fore, the biocompatibility of the TPS surface is equivalent to a solid titanium body. Technical details of this procedure and the TPS surface were described by Steinemann. 12 Bone Direct bone apposition onto TPS surfaces was clearly shown at the beginning of the research project in animal experiments, and results were reported by Schroeder and coworkers in 1976 and 1978 using a new histologic technique with nondecalci- fied sections. 13,14 This phenomenon of direct bone-implant contact is often termed osseointegration, 15 or functional anky- losis. 16 Light-microscopic images demonstrate the anchorage of titanium implants with osseointegration (Figure 15.7). The FIGURE 15.5 Instruments for hollow cylinder site preparation. FIGURE 15.6 Titanium-plasma-sprayed surface (TPS) in a close-up view. FIGURE 15.7 Micrograph demonstrating direct bone-to-implant con- tact (osseointegration) to TPS surface (experimental sample from primate). 15. The ITI Dental Implant System 141 higher magnification reveals the direct apposition of newly formed bone onto the surface of titanium implants with a TPS surface without an intervening layer of connective tissue. The vitality of the bone is demonstrated by the presence of os- teocytes and blood vessels close to the implant surface (Fig- ure 15.8). Osseointegration was also confirmed on a few hu- man implants, which had to be removed (e.g., due to recurrent peri-implant infections in the crestal area; see Figure 15.9). Furthermore, direct bone-implant contact was also demon- strated in scanning electron-microscopic analyses, as well as in a transmission electron-microscopic study by Listgarten et al. 17 using titanium evaporated epoxy resin implants (Figure 15.10). Osseointegration is generally not observed to have 100% bone contact along a given implant surface. The extent of bone-implant interface depends mainly on three factors: (1) the implant and surface material used; (2) the roughness of the implant surface; and (3) the density of the surrounding bone. As mentioned earlier, ITI implants have been coated with a TPS surface since their inception in 1974 as this porous tita- nium surface offers several advantages from a clinical point of view. An animal study in rats demonstrates that the TPS surface accelerates bone apposition during early wound heal- ing. 18 TPS implants revealed the first visible bone-implant contact after 7 days of healing, whereas smooth titanium im- plants demonstrated the first contacts after 21 days. In a study of miniature pigs, titanium implants with TPS coatings demon- FIGURE 15.9 Osseointegration in apical section of hollow-cylinder implant, cross-sectional view (human explant). FIGURE 15.10 Direct bone apposition to TPS surface in electron mi- croscopic view (magnification 16,000, sample from canine experi- ment with TPS coated epoxy implants). FIGURE 15.8 Direct bone-implant contact without interpositioning of soft tissue. Blood vessels in contact with implant surface (experi- mental sample from canine model). 142 H P. Weber, D.A. Buser, and D. Weingart strated a significantly higher percentage of direct bone-implant contact in cancellous bone when compared to smooth- or fine- structured titanium surfaces. 19 And finally, a study in sheep revealed significantly higher removal torques for TPS implants when compared with smooth- or fine-structured titanium im- plants. 20 Summarizing these studies, it can be concluded that titanium implants with TPS surfaces achieve significantly faster and better bone anchorage when compared with titanium implants with smooth- or fine-structured surfaces. To achieve osseointegration of ITI implants, four prereq- uisites need to be fulfilled: (1) biocompatible material; (2) atraumatic surgical technique using a slow drilling technique to prevent overheating of the bone; (3) primary implant sta- bility; and (4) a healing period of 3 to 4 months without di- rect loading. 7 As already mentioned, ITI implants were de- signed as nonsubmerged implants. If placed as such, they are not covered by the oral mucosa during healing and pen- etrate the crestal mucosa from the time of implant place- ment. In contrast to the frequently stated requirement for a submerged implant placement, 15 nonsubmerged ITI im- plants achieve osseointegration with high predictability if the aforementioned prerequisites are followed. 7,21–25 This clinical fact observed over more than 20 years has been con- firmed in the recent past by several experimental stud- ies. 13,14,16,17,19,26–30 Supracrestal Connective Tissue and Epithelium Dental implants are not covered by a closed integument. The fact that they penetrate the mucosa and are consequently ex- posed to the environment of the oral cavity with all its pos- sible contaminants creates a delicate problem. Thus the components of the soft tissue cover (i.e., the supracrestal con- nective tissue as well as the epithelium) have to act as an im- portant barrier between the internal and external environment if long-term function is to be expected. 26 As demonstrated above, bone as mineralized connective tis- sue adheres to the rough TPS surface. Therefore, it could be expected that a similar reaction would occur when the non- mineralized supracrestal connective tissue directly contacted the TPS surface, and when the implant post is located in ker- atinized attached mucosa. Light-microscopic experiments on TPS-coated implants placed in monkeys 16 or beagle dogs 28 demonstrated a fiber orientation perpendicular to the implant surface (Figure 15.11). However, studies in beagle dogs eval- uating titanium implants with smooth or sandblasted sur- faces 17,29 revealed no evidence of perpendicular fiber attach- FIGURE 15.11 Supracrestal connective tissue fibers in perpendicular orientation to TPS coated implant surface (cross-sectional view). FIGURE 15.12 Absence of perpendicular fibers close to the implant surface. Collagen fibers with a parallel orientation distant from the implant surface. Blood vessel and cell-free zone in contact with im- plant surface. 15. The ITI Dental Implant System 143 ment to the tested nonporous titanium surfaces. The connec- tive tissue in direct contact with the implant post was mainly dominated by circularly oriented collagen fibers. This inner zone of connective tissue was free of blood vessels and re- sembled most likely an inflammation-free scar-tissue forma- tion (Figure 15.12). The obvious difference to the aforemen- tioned studies with perpendicular fiber attachment can probably be explained by the difference in the surface char- acteristics. Based on biological considerations for successful mainte- nance of healthy peri-implant soft tissues, ITI implants have a smoothly machined titanium surface in the transmucosal section to reduce the risk of plaque accumulation. Thus it has to be expected that a similar arrangement of circularly ori- ented connective tissue fibers is predominantly present around ITI implants in patients due to the smooth surface in the supracrestal area (Figure 15.13). Different light-microscopic studies using nonsubmerged ti- tanium implants in different animal models 16,28–30 demon- strated no evidence of an epithelial downgrowth to the bone- crest level. The micrographs revealed the formation of a peri-implant sulcus, with the most apical epithelial cells be- ing located approximately 1 mm above the bone-crest level (Figure 15.14). The epithelial structures around titanium im- plants are similar to those found around teeth (i.e., sulcular epithelium-like and, more apically, junctional epithelium-like cell layers along the implant surface; see Figure 15.15). Prosthodontic Concept Abutments Various abutments are available for the two-part ITI implants. They consist of a number of conical abutments for screw- retained and/or cemented restorations including an angled abutment (Figure 15.16), an octagonal abutment for screw- retained restorations only, and the retentive anchor used for implant treatments with overdentures. The abutments all have the same apical portion fitting to the inner top portion of the implant with an M2 (2-mm) screw and an 8° cone (Figure 15.17). This cone-to-screw interface serves as a nonrotational friction fit or mechanical lock on the basis of the Morse ta- per principle. It has shown to be three to four times as strong as a conventional, flat-coupling screw connection. 31 To se- cure the abutments into this nonrotational fit, they are inserted with a torque of 35 Ncm using a special torque instrument (Figure 15.18). FIGURE 15.13 Circular fibers around implant post in cross-sectional view (canine experiment). FIGURE 15.14 Microradiograph demonstrating peri-implant soft tis- sue morphology. At the top apical extension of peri-implant epithe- lium. At the bottom is the crestal bone height. Connective tissue con- tact height extends from the crestal bone height to the epithelium. F IGURE 15.19 Solid conical abutments (4-mm, 5.5-mm, and 7-mm height) for cemented restorations. 144 H P. Weber, D.A. Buser, and D. Weingart FIGURE 15.15 Peri-implant epithelium resembling sulcular and junc- tional epithelium at natural teeth. FIGURE 15.16 ITI abutments. From left to right: Solid abutments, angled abutment retentive anchor, and octa-abutment. FIGURE 15.17 Cone-to-screw design (Morse taper principle) for ro- tation safe anchorage of abutment in implant. FIGURE 15.18 Torque instrument for abutment insertion (35 Ncm) and tightening of occlusal screws (20 Ncm). FIGURE 15.20 Schematic overview of restorative steps for cemented restorations. 15. The ITI Dental Implant System 145 Conical Abutments The conical abutments come as solid abutments without in- ternal screw threads in heights of 4, 5.5, and 7 mm, for ce- mentation of restorations (Figure 15.19). They are especially easy to use and, therefore, save time and reduce costs. After placement of the conical abutment, an impression is made, a stone cast is poured, and the crowns or fixed partial dentures are waxed directly to the stone model and then completed as conventional crown-bridge work (Figure 15.20). Octa-abutment for Screw-Retained Restorations For screw-retained prostheses, the Octa-system with different prefabricated parts for accurate transfer and laboratory proce- dures has been added to the ITI armamentarium in the more recent past. 31 The top of the Octa-abutment has eight sides and is 1.5 mm high (Figure 15.21), with an M2 screw hole in its top to retain the restoration. This 2-mm occlusal screw limits the occurrences of screw loosening or fractures commonly re- ported for implant restorations. The Octa-abutment is anchored in the implant with the same cone-to-screw interface as the con- ical abutments described earlier, and they provide a nonrota- tional friction fit. Transfer copings are used for impressions. Once an impression is made, one-piece analogs are secured into the transfer copings and die stone poured. After the stone has set, the transfer copings are removed. Prefabricated gold cop- ings made from nonoxidizing, high gold-content alloys with a high melting range are placed on the analogs. Long wax-up or guide screws are used to secure the copings on the analogs and to create the space for the future occlusal screw access canal. The frame of the future restoration is then waxed and cast to the copings. In case of porcelain-fused-to-gold restorations, the porcelain is added thereafter. It is important that for such restorations, a layer of gold compatible with the ceramic ma- terial to be used is cast onto the copings. Gold copings with an octagonal inside are chosen for single-tooth cases, whereas gold copings with rounded insides are used for fixed partial dentures. The step-by-step procedure for screw-retained restorations is summarized in Figure 15.22a,b. The prefabricated gold copings have an outstanding precision, which can be documented in SEM images (Figure 15.23). The resistance of the implant- abutment-superstructure complex to lateral forces is superior due to the precise component fit and even enhanced by the 45° inclination of the implant shoulder. Angled abutments and a transversal screw retention concept have been added to the prosthodontic concept more recently. For instructions on their use, the reader is referred to the respective, detailed system lit- erature. They assist the restorative dentist in overcoming im- FIGURE 15.22 (a,b) Schematic overview of procedural steps for screw-retained restorations with the octa-abutment concept and its prefabricated components. a b Cemented Restorative Technique FIGURE 15.21 Octa-abutment for screw-retained restoration in close- up view. Non-Repositionable Transfer Technique 146 H P. Weber, D.A. Buser, and D. Weingart FIGURE 15.23 Precise fit of gold coping to 45° implant shoulder. FIGURE 15.24 Angled abutments to correct angulation problems in fixed partial denture cases. FIGURE 15.25 Transverse screw coping for single-tooth restorations. F IGURE 15.26 Octa-abutments on four implants for bar-retained over- denture. plant angulation and/or divergence problems (Figures 15.24 and 15.25). Overdentures on Bars In cases in which support for dentures is needed, two to four implants can be placed and restored with a gold bar and an overdenture after completion of implant healing. 9,10 Prefabri- cated gold copings, gold bars with round or oval profile, and gold clips or bar sleeves are the available components. Note that these gold copings are different from the ones used for cast restorations. The bar-retaining copings are only to be used to affix prefabricated bar segments via soldering procedure, in that they are fit tightly onto the bars and fitted into the denture as retentive elements (Figures 15.26–15.28). Overdenture on Retentive Anchors When moderate additional retention is required for a mandibu- lar or maxillary denture, two implants can be placed, and round (retentive) anchors are inserted in the implants after the 3- to 4-month healing period. 32 Because no reopening surgery is necessary, the restorative phase begins at the end of this healing period. Female matrices are processed into the den- ture to fit tightly to the retentive anchors with a simple im- pression and pick-up method (Figures 15.29–15.31). Case Reports Figures 15.32 to 15.37 show illustrative examples from case reports. 15. The ITI Dental Implant System 147 FIGURE 15.27 Gold bar in place. Bar segments are soldered to gold copings different from the ones used for cast restorations. FIGURE 15.28 Finished overdenture demonstrating bar clips in situ. A metal lingual plate for strength and minimizing interference with tongue function is recommended as shown. FIGURE 15.29 Retentive anchor in close-up view. FIGURE 15.30 Schematic illustration of function of gold matrix on retentive anchor. The presence of the polyethylene sleeve around the matrix is important for proper retentive function of the matrix. FIGURE 15.31 Tissue side of overdenture with retentive matrices in place. 148 H P. Weber, D.A. Buser, and D. Weingart FIGURE 15.32 (a) Master cast with dies of conical abutments for ce- mented crowns. (b) Finished restorations on dies. (c) Lingual view of cemented restorations. (d) Buccal view of cemented resotrations. (e) Radiographic control 3 years after implant placement. a b c d e 15. The ITI Dental Implant System 149 FIGURE 15.33 (a) Custom-angled abutment in case with maxil- lary alveolar protrusion in right canine area. Note the placement of the implant below tissue level for aesthetic crown emergence. (b) View of custom angled abutment on an HS implant. The cus- tom angled abutment was waxed and cast on an octogonal gold coping and then custom milled. (c) Procelain-fused-to-metal crown in place. (d) Radiographic control at 3 years after crown insertion. a b c d [...]... Aspekte Schweiz Monatsschr Zahnmed 1991;101: 132 1– 133 1 Fugazzotto P Ridge augmentation with titanium screws and guided tissue regeneration: Technique and report of a case Int J Periodont Rest Dent 19 93; 13: 335 33 9 Becker W, Becker BE, McGuire MK Localized ridge augmentation using absorbable pins and e-PTFE barrier membranes: a 1 63 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 new surgical technique Case reports... strength between implants and bone Adv Biomater 1990;9 :30 9 21 Buser D, Weber HP, Lang NP Tissue integration of non-submerged implants Clin Oral Implants Res 1990;1 :33 22 Buser D, Weber HP, Brägger U, Balsiger C Tissue integration of one-stage ITI implants: 3- year results of a longitudinal study with hollow-cylinder and hollow-screw implants Int J Oral Maxillofac Implants 1991;6:405 23 Buser D, Sutter F,... Implants 1992;7: 233 –241 Schenk RK, Buser D, Hardwick WR, Dahlin C Healing pattern of bone regeneration in membrane-protected defects A histologic study in the canine mandible Int J Oral Maxillofac Implants 1994;9: 13 29 Gotfredsen K, Warrer K, Hjøerting-Hansen E, et al Effect of 16 Localized Ridge Augmentation 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 membranes and hydroxyapatite on healing in bone defects... procedures Membrane-supporting devices such as mini-screws21– 23 or pins29 ,30 have been used The surgical results were improved, but partial membrane collapse lateral to the support posts still posed a problem It became obvious that an appropriate filling material was needed in non–space-making defects Autogenous bone is still considered the material of first choice for bone defect grafting .32 ,33 Consequently,... plate and simultaneous bone grafting with autogenous iliac bone (f) Radiological control 6 months after fracture treatment and augmentation on the left side of the mandible (g) Augmentation on the anterior and right region of the mandible: the implants are inserted through the corticocancellous bone graft into the mandible (see Figure 17.6) Good interfragmentary compression be- tween the natural bone. .. materials, which consisted of autogenous symphysis bone (44.4% bone) , hydroxyapatite (20 .3% bone) , hydroxyapatite and demineralized bone, 7:1 (4.6% bone) , and hydroxyapatite and autogenous symphysis bone, 1:1 (59.4% bone) .11 Treatment Planning A multitude of prosthetic and surgical alternatives exist for treatment of the partially or completely edentulous posterior maxilla It must first be determined if... Surrounding bone is perforated with a small round bur to promote bleeding and a source for cells with bone- forming po- tential (c) Autologous bone particles obtained from implant bed preparation (bone core) placed in area of dehiscence Small closure screw placed in implant (d) GTAM membrane adapted as “poncho” over implant and secured with two Memfix screws (e) Primary wound closure (f) Postoperative follow-up... membranes and hydroxylapatite J Periodontol 1990;61;157–165 Becker W, Becker B, Handlesman M, et al Bone formation at dehisced dental implant sites treated with implant augmentation material: a pilot study in dogs Int J Periodont Rest Dent 1990; 10: 93 101 Lazarra RJ Immediate implant placement into extraction sites: Surgical and restorative advantages Int J Periodont Rest Dent 1989;9 :33 3 34 3 Nyman S,... new concept of ITI hollow-cylinder and hollow-screw implants: Part 2, Clinical aspects, indications, and early clinical results Int J Oral Maxillofac Implants 1988 ;3: 1 73 5 Sutter F, Schroeder A, Buser D Das neue ITI-Implantatkonzept Technische Aspekte und Methodik Quintessenz 1988 ;39 : (Teil 1)1875–XX; (Teil 2)2057 6 Sutter F, Krekeler G, Schwammberger AE, Sutter FJ Das ITIBonefitimplantatsystem: Implantatbettgestaltung... procedures and results Clark’s Clin Dentistry 1992;5:1–22 24 Mericske-Stern R Clinical evaluation of overdenture restorations supported by osseointegrated implants: a retrospective study Int J Oral Maxillofac Implants 1990;5 :37 5 H.-P Weber, D.A Buser, and D Weingart 25 Mericske-Stern R, Steinlin-Schaffner T, Marti P, Geering AH Peri-implant mucosal aspects of ITI implants supporting overdentures A five-year . with normal healing capacity and an alveo- lar bone (defect) site rendering the opportunity for vasculariza- tion and colonization with bone- forming cells is a good candi- date for GBR procedure new concept of ITI hollow-cylinder and hollow-screw implants: Part 2, Clinical aspects, indications, and early clinical results. Int J Oral Max- illofac Implants. 1988 ;3: 1 73. 5. Sutter F, Schroeder. Res. 1990;1 :33 . 22. Buser D, Weber HP, Brägger U, Balsiger C. Tissue integration of one-stage ITI implants: 3- year results of a longitudinal study with hollow-cylinder and hollow-screw implants.