Implant Prosthodontics 10.pdf

274 O. M. Muller and T. J. Salinas n Learning Aims impression posts used to transfer this information. The 1. Implants placed into a partially dentate site behave various types of osseointegrated implants wer...

274 O. M. Muller and T. J. Salinas n Learning Aims impression posts used to transfer this information. The 1. Implants placed into a partially dentate site behave various types of osseointegrated implants were dis- somewhat differently than do natural teeth. cussed previously. 2. Although predictable, osseointegrated dental Abutments are simply transmucosal extensions for implants have certain biologic requirements to the attachment of prostheses. Abutments can be used to maintain healthy peri-implant tissues. provide a restorative connection above soft tissues and 3. When using dental implants to replace teeth, the to provide for the biologic width. Abutments can be distribution of the edentulous span is one of the used for attachment of screw-retained or cemented con- most critical predictors of biomechanical success. nections and can be made of metal or ceramic. The most 4. The use of immediate load prostheses is beneficial commonly used abutment material is machined tita- to stabilizing the implants and stabilizing the occlu- nium, which has been shown to be strong and resistant sal plane and assists in making patients comfort- to plaque retention and to react favorably to soft tissues. able through their time of osseointegration and Titanium abutments have been used historically for the healing. attachment of screw-retained connections. Two of these 5. The use of osseointegrated implants in microvas- types of abutments are shown in. Fig. 10.1. Titanium cular osseous flaps assists well with occlusal reha- abutments are also used in many cases in which a bilitation of patients afflicted with orofacial defects cemented prosthetic connection is desired. With thin from tumor ablative surgery. gingiva, the gray hue of these abutments can be prob- lematic in aesthetic areas. Cast gold has been used for abutment connections owing to its blend with translu- 10.1 Introduction cent gingival tissues. Other alternatives are to anodize the abutment with a variety of anodization colors such 10 z Implant Components as gold or pink, making this less conspicuous through A wide array of dental implant components is available thin tissues. Although no hemidesmosomal attach- for impression procedures, laboratory fabrication, and ment is found with cast alloys or dental porcelain , direct restorative dentistry. A new array of digital com- yellow gold creates a warm appearance in aesthetically ponents allows transferring information to the labora- critical areas. In aesthetic areas, ceramic abutments have tory virtually. Scan bodies are the digital version of also been used in cemented designs for single- and a b. Fig. 10.1 a, Premachined abutment for screw-retained restorations. b, abutment for cement-retained restorations Implant Prosthodontics 275 10 a b. Fig. 10.2 a and b, Aluminum oxide cemented abutment with an all-ceramic crown. (a and b, prostheses prepared in collaboration with Avishai Sadan, DMD) a b. Fig. 10.3 a, Abutment transfer impression using closed-tray technique. b, abutment transfer impression using open-tray technique multiple-unit crowns (. Fig. 10.2). Similar to titanium, a portion of the implant; therefore, the prosthesis may these abutments manifest a biologic attachment. The be connected directly to the implant, bypassing the need material used in these products has been mainly alumi- for an abutment. If the restorative dentist is unsure of num oxide and zirconium oxide. Generally, when soft which abutment to use, a fixture-level impression can be tissues are less than 2 mm in thickness in the aesthetic recorded and the selection process completed as a con- zone, the use of ceramic abutments are indicated. sideration in the laboratory. The decision to use an abutment for screw-retained Impression procedures used for dental implants are restorations can be made based on the depth of tissue. based on transferring either the abutment position or Generally, 3 mm or more of tissue depth necessitates the the implant position to the laboratory. If abutments are use of an abutment. As with any restorative procedure, to be used for a screw-retained restoration, an impres- biologic width is the driving force between the alveolar sion coping is placed on the abutment, and either a bone and the prosthetic margin. If the tissue depth is closed- or an open-tray technique can be used less than 3 mm, biologic width is probably created from (. Fig. 10.3). The open-tray technique is considerably  276 O. M. Muller and T. J. Salinas a b. Fig. 10.4 a, Implant-level transfer impression using open-tray technique. b, implant-level transfer impression using closed-tray technique 10 more accurate and is indicated for multiple splinted 10.2 Biomechanical Considerations units. At this point, an abutment analogue or replica is attached in the impression, and a cast is poured in the z Peri-Implant Biology laboratory to simulate the oral situation. Considerations for tooth replacement with osseointe- If no abutment is to be used or if a cemented design grated dental implants include the biologic principles of is to be employed, a fixture-level impression with an soft and hard tissues of adjacent teeth to the implant impression post can be made in a similar open- or site. The placement of an implant between two peri- closed-tray technique. Subsequently, an implant ana- odontally healthy teeth is a unique situation, whereby logue or replica is attached to the impression post in the the bone and soft tissue are maintained in part by the impression, and simulated gingival material is placed; teeth. Original studies by Waerhaug and Gargiulo then, a cast is poured to create a soft tissue master model and colleagues showed the width of the dentogingival (. Fig. 10.4). The simulated gingival material allows complex surrounding natural teeth approaching 3 mm. the dentist or technician to select an appropriate abut- Although the peri-implant tissues are fundamentally ment and/or design the prosthesis while preserving the different, a study by Cochran and coworkers assimi- actual position of the gingiva. lated the peri-implant tissues to a similar dimension. Impressions captured digitally have also been shown Based on these principles, the suggested depth of place- to be quite helpful as specific impression posts (also ment of an implant below the free margin of soft tissue known as scan bodies) are used. This “impression” is is approximately 3–4 mm (. Fig. 10.6). This distance actually a three-dimensional file created by a scanning provides room for biologic width, proper emergence of device captured by confocal photography and assembled restoration, and aesthetics and also should allow for into a three-dimensional file called STL (Standard remodeling of the soft tissue and bone, which occurs Tessellation Language). From this file, creation of resto- between 6 months and 1 year. It has been postulated ration, abutment connection, and even models can be by some that the type of periodontium influences how produced from digital workflows by selected predesig- extensive this remodeling process is. In other words, nated dental laboratories. The production of single-unit thin, scalloped gingiva recedes more extensively than restorations has been demonstrated to be proficient does thick, nonscalloped gingiva [8, 9]. Restorative (. Fig. 10.5). Some difficulties remain with fabrication interfaces with metal should be kept below the free mar- of multiple-unit restorations as the fidelity of data for gin of tissues in anticipation of this remodeling. Tarnow these cases attenuates with increasing numbers of and associates have shown that there is a relation- implants. Some of this difficulty is related to producing ship of the underlying bone to soft tissue in the inter- accurate models which can be either milled or printed. dental spaces between natural teeth. A relationship from Implant Prosthodontics 277 10. Fig. 10.5 Single implant scanned with a digital impression and transfered to laboratory for fabrication of abutment and crown. Fig. 10.6 Osseointegrated implant placed at a depth of 3–4 mm for biologic width and emergence profile. Fig. 10.7 Suggested minimum distances of implant to natural tooth and implant to implant both implant to natural tooth and implant to implant has been demonstrated. Therefore, the distance sug- then stabilizes—one criterion of success as outlined by gested from the side of the implant to the adjacent tooth Albrektsson and coworkers. Whereas this pattern of should be about 2 mm to avoid horizontal bone loss bone loss is typically followed by Branemark-type affecting the adjacent tooth. Similarly, Tarnow and col- implants, other types of implant systems demonstrate a leagues showed the critical distance between implant different pattern of bone loss that can emulate one of surfaces approached about 3 mm before the mutually four different patterns. These four patterns include destructive process of lateral bone resorption acceler- Albrektsson’s previously described low-rate marginal ated each other’s processes (. Fig. 10.7). Typically, each bone loss over the years, low-rate marginal bone loss in implant loses peri-implant bone within the first year and the first few years followed by rapid bone loss after  278 O. M. Muller and T. J. Salinas abutment connection, high-rate marginal bone loss in the long-term success of dental implants [15–17]. In one the first few years followed by almost no bone loss, and study, failure rates of implants placed in type 4 bone continuous high-rate bone loss followed by complete approached 35% in smokers; placement of implants into loss of bone support. types 1, 2, and 3 bone of smokers resulted in a failure rate approaching 3%. It is important to note, how- z Patient Factors ever, that these older publications had cited these effects Soft tissue evaluation before implant placement is criti- specifically to turned surface implants. Even though cal for long-term success and maintenance. A sufficient smoking detracts from the long-term success of osseoin- volume of keratinized and fixed tissue is needed to prop- tegration with micro-roughened surfaced implants, erly maintain hygiene around an implant, just as it is recent publications on surveying the success of moder- needed around a natural tooth. Occasionally, it may be ately roughened surfaces disclose a more favorable out- necessary to incorporate subepithelial connective tissue come in smokers and also in type 4 bone. or full-thickness soft tissue grafts to prospective implant Although osteoporosis can be a negating factor to sites. When restoring single missing teeth, the interprox- bone density, this disease seems to affect the hip and imal bone between the remaining teeth is a good prog- spine of those afflicted. No clear correlation can be nostic indicator of the likelihood of creating and demonstrated that osteoporosis is a contraindication to preserving interdental papilla. Generally, the distance the placement of dental implants. from the residual alveolar bone to the contact area of Periodontal disease is a local factor that should be the restoration can be assessed on a periapical film. The under control to avoid adverse effects of a unique popu- likelihood of having a papilla is depicted in. Table 10.1. lation of microbiota affecting these diseased sites. Patients treated over a 10-year course with implants that Bone volume is best assessed by radiographic techniques, were severely periodontally compromised seem to 10 although a rudimentary estimate can be made clinically require advanced surgical intervention with antibiotics by palpation and inspection. Assessing a patient for and suggest that regular follow-up care is needed to pre- mandibular implant reconstruction may include intra- vent the need for advanced care. oral/extraoral palpation as well as panoramic, occlusal, Bruxism is another local factor that can compromise lateral cephalometric, and cone beam radiographs. long-term success. Generally, bruxism promotes micro- Single-tooth replacement in the aesthetic zone also can movement of the implant bone interface. In bone types be assessed by comparison of the bony topography of 3 and 4, bruxism may have a more pronounced effect on the adjacent teeth as well as periapical/panoramic radio- the long-term osseointegration. Off-axis and lateral graphs. Even these sites can be best topographically ana- loading of dental implants by bruxism or other para- lyzed by cone beam CT radiographs. Bone is a functional forces can be deleterious in the long term scaffold for soft tissue, and it is typical for bone loss to with respect to accelerated bone loss and prosthetic fail- occur on a scale of 0.2 mm/yr after stabilization of initial ure. Self-awareness and occlusal splint therapy may pro- bone loss pattern. Therefore, it is not unusual that soft vide appropriate protection. If these factors cannot be tissue recession occurs in this period of time. This reces- controlled preoperatively, alternative treatment should sion should be anticipated, especially when considering be considered. placing implants in the aesthetic zone and elsewhere. Radiation to the head and neck in excess of 50 Gy is It is well documented that local and systemic factors, considered a relative contraindication to dental implant such as cigarette smoking, have a deleterious effect on placement in most cases. There are instances in which the radiation has created a significant degree of xero- stomia, which is incompatible with retaining natural. Table 10.1 Potential of creating/preserving papilla teeth or stabilizing maxillofacial prostheses. Given the risks of osteoradionecrosis, hyperbaric oxygen should Distance from bone to Chance of creating papilla (%) be considered if placement of implants would signifi- contact area (mm) cantly improve the oral health and quality of life in these individuals [22–24]. However, several studies 4.0 100 refute the benefit of hyperbaric oxygen to the long- 5.0 100 term survival of dental implants [25, 26]. Standard pro- 6.0 56 tocol suggested by Marx and Ames is 20 preoperative dives and 10 postoperative dives. Osseous 7.0 27 healing from extractions/alveolar remodeling and the Adapted from Tarnow et al. cascade of osseointegration events are probably differ- ent physiologic processes. Implant Prosthodontics 279 10 The survival rate of implants placed within radiated tissues approaches 60–70th percentile. In tissues where dosages exceed 6500 cGy, there is substantial risk in performing implant placement. Reflection of periosteal tissues in these cases can lead to a chronic wound healing problem and poses a risk also from osteora- dionecrosis. Systemic factors such as diabetes, connective tissue diseases, autoimmune diseases, and human immunode- ficiency virus (HIV) are considered relative contraindi- cations to treatment with osseointegrated implants. Patients afflicted with dermal manifestations of rheu- matoid arthritis and lupus seem to have advanced peri- implant bone loss over time. If these disease processes are well controlled, it may be advisable to treat the patient to improve the overall quality of life. Chemotherapy given to patients during osseointegra- tion critical times has not been shown to be subtractive in success [30–33]. 10.3 Radiographic Evaluation Periapical radiographs are an excellent way to evaluate. Fig. 10.8 Presurgical planning for placement of an implant into single missing teeth because they depict a minimally site no. 10. Minimal magnification is noted from the periapical magnified amount of bone and root topography. radiograph Adjacent root angulation, pulp chamber size, periodon- tal defects, interproximal bone, and residual pathology are some of the factors critical to the treatment planning of single-tooth implant restorations (. Fig. 10.8). Occlusal radiographs for mandibular arch assess- ment also can give an appreciation of the size of the buccal and lingual cortices as well as the position of the mental foramina (. Fig. 10.9). It may be also feasible to incorporate a radiographic marker on the patient’s den- ture to give a perspective of the relationship of the men- tal foramina to the overlying prosthesis. This can be done with either lead foil from a film packet adhered to the underside of the patient’s denture or a stainless steel wire attached to the buccal or occlusal portion of the mandibular denture. Panoramic radiographs are excellent screening examinations that give a broad perspective on the infe- rior alveolar canal, maxillary sinuses, mental foramina,. Fig. 10.9 Occlusal radiograph gives the relative position of men- and nasal floor; they are used for treatment planning of tal foramina and the taper of mandible single and multiple missing teeth. The panoramic film generally has a magnification factor of about 25%, periapical radiograph is preferable because the incident which should be anticipated on the workup to gain a beam of the tube is more likely to be perpendicular to better appreciation of the actual position of vital struc- the long axis of the implant. Also, many edentulous tures and the size of implant to be selected. This varies patients have a shallow floor of mouth and flat palatal from patient to patient, by location, and also with the vault owing to resorption. It is far easier to obtain a per- machine used. Panoramic radiographs are also useful pendicular view of the implant platform in these circum- for verifying complete seating of impression and restor- stances, which is critical to the accurate performance in ative components. The use of this film over a standard the treatment stages.  280 O. M. Muller and T. J. Salinas. Fig. 10.10 Lateral cephalograms may assist in the workup for determining maxillomandibular relationships and occlusal schemes Lateral cephalometric radiographs assess the maxil- lomandibular relationship as well as that of the maxilla and mandible to the cranial base. A lateral cephalogram. Fig. 10.11 Cone beam imaging technique to show hard tissue may give an appreciation of the concavity of the lingual deficit related to proposed positions of teeth 10 surface of the anterior mandible vitally important to surgical consideration of implants in the anterior man- A radiographic or imaging stent can be used when dibular area. Development of anticipated implant there is a need to join the prosthetic information to occlusion is well assessed with lateral radiographic ceph- the bony topographic information. In creating these alography, which becomes especially useful when recre- stents, acrylic resin can be mixed with 30% or less bar- ating anterior guidance and posterior occlusal schemes ium sulfate as a radiographic marker to create the (. Fig. 10.10). contour of the intended restoration. Some denture Cone beam computed tomography (CBCT) is a more teeth are true to anatomic form and create a radi- contemporary technique that gives a reasonable three- opaque appearance when included in the stent. As an dimensional perspective to the interpretation of the alternative, access channels can be filled with gutta- adjacent anatomy of a proposed implant site. This tech- percha as a radiographic marker. If verified radio- nique may be indicated in an implant placement sce- graphically, this imaging stent may double as a surgical nario, in which the volume of bone is compromised or stent. diminished, such as an extensively resorbed jaw or Additionally, CT scans can also be of benefit where prominent maxillary sinus or inferior alveolar canal the use of osseous flaps is planned for reconstruction of (. Fig. 10.11). The advantage of using the cone beam maxillofacial defects along with simultaneous implant technique is a markedly reduced radiation dose, planning. Because of the complex nature of reconstruc- increased survey volume, and a reduced scan time in tion, the use of computerized planning is essential to comparison with conventional single-plane properly manage these demanding operations where CT. Additional factors that acquire a better perspective bone spatial location and implant placement are critical of osseous pathology can be appreciated by three-. Imaging of the donor site also becomes imperative dimensional films more so than two-dimensional radi- to assess vascular supply and bony anatomy ography. characteristics. CT can be helpful when considering maxillary reha- bilitation with a full complement of implants or when other craniofacial landmarks are planned for use. CT 10.4 Implant Surgical Guides may be used in conjunction with computerized technol- ogy to aid implant placement. These images may be Fabrication of surgical guides for implant placement reformatted to construct a three-dimensional image of should be part of every case because the placement is the selected part of the craniofacial skeleton. CT scans permanent and irrevocable after integration. Planning are useful in assessing the health of the maxillary sinus of each case includes the collection of all diagnostic before augmentive procedures. data, as previously mentioned. Once this data has helped Implant Prosthodontics 281 10. Fig. 10.12 Guide used to place the implants within the confines of the occlusal table. Fig. 10.13 Surgical guide showing proposed gingival margin and incisal/occlusal plane. (Surgery performed by Michael S. Block, DMD) create a thorough treatment plan, fabrication of a surgi- Fixed-implant-supported complete dentures man- cal guide can begin from the diagnostic models and date the use of a surgical stent because the occlusal other information from the workup. access channels are desired to be through the posterior Construction of prostheses begins with a confirma- teeth and the lingual aspects of the anterior teeth. In tion of occlusal relationships and the need to direct these situations, a slot can be created through these occlusal forces over the long axes of the implants. This areas to provide the surgeon with latitude in site selec- becomes exceptionally critical when a fixed restoration is tion. A clear processed duplicate of the patient’s den- to be used. On this basis, a site is selected and a guide ture may be the best technique in surgical guide design. made to assist the surgeon at placement (. Fig. 10.12). If immediate loading protocols are to be used, the This information may also be translated from radio- patient’s complete denture can be used for this purpose graphic findings to a surgical guide in the position of the and modified to fit to the placed implants for immediate mental foramina (previously described). This informa- load use. tion can be used to place implants far away enough from Implant surgical guide design for fixed prostheses is the foramina and each other to be mechanically advanta- mandated, in which selection of a specific prosthetic geous. Again, parallelism is of paramount importance if design may be entirely dependent on implant position a stud-retained overdenture is used. This guide can be as and orientation. In the aesthetic zone, the cemented simple as a vacuum-adapted thermoplastic sheet over an design may be the preferred method of prosthesis, and edentulous cast or a clear processed duplicated denture. placement of an implant in an orientation just palatal Implant-supported overdenture construction may through the incisal edge is optimal. Also, the implant incorporate the use of the surgical guide to keep the platform should be approximately 3–4 mm below the implant fixtures away from the peripheral confines of free edge of the gingival margin. Two vital pieces of the prosthesis. This may be beneficial to avoid encroach- information contained on a surgical guide are the ing on the peripheral seal in either aesthetic or func- occlusal/incisal plane and gingival margin of the pro- tional areas. Also, occlusal forces may be better directed posed restoration (. Fig. 10.13). To obtain this infor- over the long axes of the implants. The device can be mation, a wax-up is performed in the desired occlusal either a duplicate of a diagnostic wax-up in clear resin position. Once completed, this model should be dupli- or simply a duplicate of the patient’s denture, if accept- cated into another cast. A vacuum-adapted guide can able. A guide may be critical in this situation because it be made on this duplicate cast. The matrix can be will be supported with a splinted structure in which can- trimmed with a hot knife and rotary instrument. Guide tilevering may be used. More sophisticated guide design channels can be created with previous surgical drills or can incorporate the use of the cone beam CT planning laboratory burs. The constant access diameter of these to positionally coordinate implant placement within the stents is based on the concentric enlargement of each anatomic confines of the jaw. These stents contain a succeeding drill diameter. These guides are usually eas- series of placement guides that telescope to the final ily made, are cost effective, are self-retaining, and do placement drill guide, making precision placement not require pre-fitting. Because they usually fit well, it attainable in compromised host sites. is only necessary to extend the guide two to three teeth  282 O. M. Muller and T. J. Salinas on either side of the edentulous spaces for partially dentate cases. Printed implant surgical guides are considerably more accurate and allow proper execution of implant position and orientation. They require scanned models and access to CBCT data that can be manipulated in a software program that allows printing of an STL file that contains the surgical guide sleeves specific to that implant system. Additionally small windows can be built into the guide to insure that it is completely seated, adding to the accuracy of placement. 10.5 Implant Site Selection The use of implants in each jaw can be best approached by evaluation of the three-dimensional volume of bone and proximity to adjacent teeth. If the remaining teeth are salvageable, it is then determined if the existing verti- cal dimension and occlusal scheme will be made confor- mative or reorganized. In other words, does the existing occlusal vertical dimension work at this level, or 10 will the natural teeth and new implant prostheses be built to new requirements? Based on the proposed pros- thesis support, the number and distribution of implants relative to the proposed occlusal table is attributed to the best long-term result of the implant prosthesis survival. Fig. 10.14 Ideal crown-to-implant ratio occurs when X ≤ Y. It is through this plan where oral and maxillofacial surgery and prosthodontic first dialogue are most criti- cal. Each discipline has the understanding of the other, vorable crown-to-implant ratios. If the restoration par- whereby the final result is based upon mutual agreement ticipates in anterior guidance, it should be splinted to to meet the expectations of the patient. other implants. If the restoration participates in poste- rior occlusion, it should be protected by natural canine teeth to limit lateral loads in excursions. If it is placed in > Dialogue Between Surgeon and Restorative conjunction with other implants in the posterior, it may Dentist be splinted for mutual support. Although this is often 5 Collaborative dialogue between surgeon and assimilated as with natural teeth, osseointegrated restorative dentist to plan treatment with prosthe- implant restorations need not necessarily follow this sis design based on surgical planning should be construct since many decade-old restorations have been undertaken. quite successful without compromise. This is merely 5 Patient understands and agrees to treatment and is meant as a guideline to approaching biomechanical dis- understanding of approach used with simultane- tribution as well as prosthesis design. ous understanding of timing. 5 Advanced understanding of complication manage- ment between disciplines. 10.7 Occlusion > Several Axioms in Implant Dentistry Relate to the 10.6 Crown-to-Implant Ratio Development of Occlusal Scheme 5 Efforts should be made to match implant distribu- Ideally, a crown-to-implant ratio of 1:1 or less is desired tion to the extent of the occlusal table. (. Fig. 10.14). For this reason, the minimum length 5 When restoring occlusion of maxillary and man- needed approaches 10–12 mm because the clinical crown dibular arches, favor the weaker of the two arches in length frequently approaches this measurement. Often, occlusal design. (In other words, an implant-borne replacement of teeth in a compromised site gives rise to restoration opposing a complete denture should be single- or multi-unit restorations that have poor or unfa- restored with bilateral balanced occlusion.) Implant Prosthodontics 283 10 5 Avoid fixed maxillary reconstructions against par- 10.8 Full-Arch Restorations tial or complete mucosal-borne mandibular pros- theses. Although generally recommended, complete arch recon- 5 Lateral component forces can be destructive and structions of the maxilla has been based on placement should be avoided, if possible. In other words, steep of 6–10 implants splinted for cross-arch stability [41, anterior guidance placed upon single implants 42]. Reasonable length implants (>10 mm) should be should be avoided. If disclusion is needed, it should considered, especially in the posterior maxilla, because be shared with natural teeth. shorter implants into this relatively soft bone have been shown to do poorly in the long term. Again, the lit- One additional consideration is that, unlike natural erature from years past that incorporate the use of teeth, implants have no proprioception. In fact, many turned surface implants is quite different in outcome patients restored with dental implants have a signifi- than textured surface implants. The maxillary sinuses cantly increased bite force within the first year [38–40]. may preclude placement of a desired distribution of In partially dentate cases, the implant restoration should implants, and sinus augmentation or perhaps the use of have equal or slightly less occlusal loading than the nat- extended-length implants into the zygomatic bones ural tooth (. Fig. 10.15). Also, the occlusal contacts bilaterally may allow an optimum force distribution for should preferably be placed within the platform of the full-arch prostheses (. Fig. 10.16). Additional publica- implant to minimize the possibility of screw loosening. tions have explored the use of four implants placed ante- Although this often may not be possible, it should be rior to the maxillary sinuses by incorporating a tilt to the striven for to minimize complications. posterior implants, thereby increasing the anteroposte- rior spread [43, 44]. This technique has been further augmented by the use of immediate load and splinting with a provisional prosthesis. The use of cortical stabili- zation of all implants, the use of implants greater than 13 mm in length, and risk profiling to avoid smokers, bruxers, and those with poor bone quality seemed to be favorable with initial success. Full-arch reconstruction of the mandible can involve different considerations because the mandible is a dynamic bone that flexes and rebounds as it opens and closes. In addition, treating edentulous patients by the use of the approach of four to six implants between the mental foramina with a minimal cantilever to the poste- rior was used in the pilot studies of osseointegration [45, 46]. The greater the anteroposterior spread or distribu-. Fig. 10.15 Contact of the implant occlusion should be over the tion, the greater the amount of cantilever possible. The platform of the implant and slightly less intense than that of natural use of cantilevered restorations is not necessarily met teeth with a high risk for complications and is a plausible a b. Fig. 10.16 a and b: Well-distributed maxillary and mandibular implants supporting a fixed prosthesis  284 O. M. Muller and T. J. Salinas a b. Fig. 10.17 a and b: Implant platform supported prosthesis with average cantilever extension prosthesis design. On average, a 16-mm distal canti- lever is permitted (. Fig. 10.17). Although successful for edentulous patients, this model is not universally applicable to all configurations of an edentulous man- dible and may be limited by the amount of anteroposte- rior spread of the implants. To avoid using a cantilever, it may be necessary to place implants distal to the men- tal foramen if supra-canal height permits placement. In such a case, division of the prosthesis into two compo- 10 nents prevents unfavorable stress transfer. Another option is to use the distal fixtures for vertical support and not engage the abutment-implant junction with an abutment-coping screw. This allows some flexure of the mandible without transferring stress to the prosthesis and/or implants. 10.9 Implant Selection Historically, osseointegrated dental implants were intro- duced in their original configuration as a machined parallel-walled screw. The implant possessed a platform. Fig. 10.18 Standard externally hexed implant with a 4.1-mm diameter, an external hex implant plat- form (originally used to drive the implant into position), the use of replacements for single and multiple teeth and and a 3.75-mm-diameter body; this has been the most with immediate loading, an increased need for secure common implant type placed worldwide (. Fig. 10.18) abutment connections, aesthetic versatility, and and has been successfully duplicated in a variety of improved surgical stability in trabecular bone became world populations [48–51]. The original applications more apparent. Significant mechanical improvement in were piloted for the edentulous patient, and limited abutment and screw-retained components occurred in restorative options were available in the first years of its the early 1990s and markedly decreased complications introduction. In later years, the use of surface-textured. Since the early 2000s, industrial trends are toward press-fit-type implants also became popular because the use of tapered macroretentive implant configura- their surgical installation was simplistic and achieved tions, based on the fact that tapered screw-type implants earlier integration (because of hydroxylapatite coating) have increased surgical stability in soft bone. An exam- into softer types of bone (. Fig. 10.19). At this time, ple of these types of implants is shown in. Fig. 10.20. the connection of abutments or prostheses to the sur- Implant surfaces have also changed in the early 2000s to face of the implant was characterized as a butt-joint incorporate the use of moderately rough implant sur- connection. Abutment stability with single- and multi- faces. The roughness values are often denoted by two ple-tooth replacement using standard externally hexed variables: the first is a three-dimensional measurement implants has a history of cyclic fatigue with abutment of the peak-to-valley arithmetic mean (Sa value); the screw loosening. As extended applications developed for second is a measure of the randomness of surface rough- Implant Prosthodontics 285 10 element of interest in the fact that several studies have shown that there may be some difference in bone levels around restorations that have a smaller abutment or direct to implant connection in comparison to those that are matched circumference [54, 55]. This term is known as platform switching and has been variably interpreted outcomes in patient-specific circumstances. From a soft tissue coverage, this seems to allow a more coronal position of soft tissues, making a favorable impression in aesthetically critical areas. Platform switching is a concept of using a dental implant abutment of smaller diameter than the dental implant; longitudinal radiographic observation has demonstrated decreased vertical bone resorption. Implants that possess a flat surfaced platform to where. Fig. 10.19 Press-fit cylinder-type implant abutment and prosthesis components are affixed clearly have an advantage to resist deformation over time when a preload for screw torque is applied. Although the trend may be changing, certain implant platforms appear to be more favorable choices than others where off-centered loading, cantilevering, or angle correction is employed. When these connections are compared, there is loss of the preload originally applied after cycling to 100,000 repetitions. In fact, residual torque value is significantly higher in externally hexed implants in comparison to internally connected implants. If the goal of prosthesis design is to make screw retained direct to implant connection, making analogue impressions of flat-surface implant platforms is more simplistic than that of multiple internal connections. If multiple internally connected implants are used in these cases, the use of abutments often becomes necessary to make this mechanically feasible. The Morse taper, a cone within a cone attachment mechanism, is a feature of some implant systems that allow the abutment-prosthetic connection to facilitate installation and to maintain stability (. Fig. 10.21). This taper creates a seating effect of the connection to the internal aspects of the implant; therefore, fewer lat- eral stresses are transferred to the abutment screw,. Fig. 10.20 Tapered-wall screw implant resulting in a less frequent incidence of screw loosening and fracture. Morse tapers are measured in percentage ness called “isotropism.” In animal studies, it has been units that reflect the shaft length relative to the radius of demonstrated that isotropic (regularly irregular) sur- the shaft. Thus, if for every centimeter of shaft the faces with Sa values of 1–2 μm elicit the more robust radius increases 0.01 cm, this would by definition be a bone response. 1% Morse taper. Most Morse tapers are anywhere from Certain factors that exist in choosing implants also 1% to 7%, and dentistry most commonly employs the allow favorable biologic responses by the host. For 4–7% series. The use of specific implants resistant to the instance, the use of platform switching has had some problems of abutment screw loosening and immediate  286 O. M. Muller and T. J. Salinas ture. A 2-mm amount of coronal tooth structure has been shown to improve long-term structural resistance to failure [59–61]; in total, biologic width plus a 2-mm ferruled tooth structure necessitates about 4–5 mm of suprabony tooth structure. If this is not available, it may be created by either orthodontic extrusion or crown elongation, which may sometimes create unfavorable crown-to-root ratios or furcation exposure. In this sce- nario, it may be prudent to consider extraction and either replacement with a fixed partial denture (FPD) or a single-tooth implant-supported restoration. Much of the literature indicates standard FPD survival to be in the high 80th percentile at 10 years and the 60th percen- tile at 15 years. However, typical complications occurring at different time points are related to end- odontics, recurrent caries, periodontal factors, and fail- ures in retention. Single-tooth implant studies reveal complications as well. However, in comparison with. Fig. 10.21 Morse taper internal connection other implant restorations, the single crown implant is the most successful. If sufficient bone, soft tissue, and stability is probably more critical in cases of single miss- restorative dimension exist, replacement with an ing teeth or in which a cemented implant crown and implant-supported single-tooth restoration is consid- 10 bridge are planned. The traditional parallel-walled ered the standard of care and should be offered to the screw continues to enjoy success in the general popula- patient [64, 65]. tion of edentulous patients restored with implants. The vast majority of prospective and retrospective studies > The decision to remove a tooth based on restorability have concluded that this specific implant is highly suc- and additional procedures needed may better direct cessful for restorations in edentulous patients. Long- resources so that implant replacement is a more pre- term development has resulted in an increased number dictable outcome. of components for edentulous and partially dentate applications. It is advisable for the surgeon to become familiar with the restorative components available when z The Aesthetic Zone treatment planning for implant cases. Aesthetic considerations encompass additional complex concerns, such as gingival display, proportion of teeth in the aesthetic zone, and bone density support. The aes- 10.10 Single-Tooth Replacement thetic zone is generally considered to be the maxillary anterior area. When considering replacement of a single z The Non-Restorable Tooth tooth in the aesthetic zone, the adjacent dentition should Replacement of a single missing tooth should start with also be evaluated for proportionality and position. From an evaluation of the periodontium and structural sup- a frontal plane, the lateral incisor should be about two- port. Periodontal defects, periapical pathology, bone thirds the width of the central incisor. Likewise, the loss, mobility, and pain are indications for periodontal/ width of the canine when viewed from the same vantage endodontic treatment or extraction. Other factors that point should be about two-thirds the width of the lateral require assessment before consideration for either resto- incisor and so on. The width-to-length ratio of aestheti- ration or extraction are the remaining coronal tooth cally pleasing central incisors should be approximately structure, root fracture, and restorative space. The deci- 66–80%. The axioms are ranges found in nature and mated tooth may have only one wall of the coronal are considered pleasing to the human eye. If these pro- structure remaining. Structural deficits of this type can portions are not present, they may be augmented by sur- be restored by using intracoronal anchorage methods gical periodontics, restorative dentistry, orthodontics, (i.e., elective endodontics or post and core). However, and, if appropriate, osseointegrated implants. vertical deficits that encroach upon the biologic width Occasionally, replacement of maxillary or mandibu- may necessitate crown elongation to provide enough lar canines may present a compromise in either occlu- tooth structure necessary for a ferrule or external bevel, sion or aesthetics for the functional goal of eliminating which provides encasement of remaining tooth struc- lateral forces on the restoration/implant. Aesthetic and/ Implant Prosthodontics 287 10 or functional correction may dictate the need for pre- z Cemented Single Units treatment orthodontics, endodontics, periodontics, and Cemented prostheses may be preferable to screw- concurrent restorative dentistry. A complete examina- retained designs for single-unit crowns in the anterior tion that includes diagnostic models, radiographs, and areas. They tend to provide minimized bulk of the resto- clinical photographs can be invaluable. ration. Overcontoured bulky restorations are not Aesthetic considerations for removable prosthodon- hygienic and are detrimental to the maintenance of peri- tics may be a concern for maxillary edentulous arches implant tissues. The axis of implant placement should when restoring the facial contours typically lost when be aimed through the incisal edge for standard-diameter missing teeth. The demarcation between the residual implants (. Fig. 10.22). This results in predictable aes- alveolar ridge and the use of a flange may be necessary thetics and manageable soft tissues. If a comparably to eliminate the interface usually apparent in these cases. wider implant is placed (4.3, 5.0, or 6.0 mm) in an aes- Occasionally, surgical reduction of bone further is thetic site, the long axis should traverse just palatal needed to make this less conspicuous. The use of a through the incisal edge. Errors in placement to the flange in the edentulous maxillary arch may be benefi- facial of the incisal edge produce not only difficulties cial to restore upper lip support as well as the aesthetic with angulation correction but also a soft tissue problem integrity so critical to this area. A functional lingual because the bone support in this area is lost owing to the maxillary alveolar seal is essential for correct labioden- osteotomy (. Fig. 10.23). Errors in placement too far tal consonant production; in cases of advanced resorp- palatally create ridge-lapping and hygiene difficulties. tion of the maxilla, an overdenture may be the The superior/inferior placement of the implant platform appropriate treatment. should be 3–4 mm below the anticipated free gingival margin. The use of a surgical guide in placement aids in creating an optimal site for implant restoration. The choice of cemented restorations for a posterior tooth is plausible and becomes especially useful when angula- tion in placement is less than ideal. Most posterior res- torations are feasibly designed as screw retained to better permit retrieval and servicing. The resistance and retention form of an abutment should be sufficient to resist dislodgment. The choice of specific abutments can be planned in advance if place- ment is based on an ideal scenario. Anatomy should not dictate placement of the implant position, but rather the placement should be based on restorative parameters. This information can be obtained by the use of surgical stents, which may provide critical information about where to develop the occlusion and where to recreate the. Fig. 10.22 Long axis of implant placement through the incisal edge of the stent for cement-retained prostheses. (Surgery performed emergent path as the restoration exits the gingival sul- by Michael S. Block, DMD) cus. It is critical to ensure removal of all luting cement a b. Fig. 10.23 a and b, Implant placed too far facially resulting in compromised peri-implant soft tissues  288 O. M. Muller and T. J. Salinas. Table 10.2 Screw retention versus cement retention Advantages Disadvantages Screw retention Cement retention Screw retention Cement retention Retrievability Aesthetic Implant placement critical Cement removal subgingivally Porcelain Angle correction possible Screw access channel visible Abutment selection critical in anterior emergence Cost-effective Less bulk of restoration in anterior Deep channels should be Provisional restoration needed in areas sealed anterior Elimination of Built-in load indicator by two Cost factor with abutment/restoration cement interfaces retrieval Problematic retrievability a b 10. Fig. 10.24 a and b, Screw-retained restoration supported by implant permitting angle correction. Screw permitting angled drive by the use of retraction cord, vent holes, and radio- cemented prostheses. However, using screw-retained graphic verification because this can lead to soft tissue prostheses requires strict attention to placement and con- recession/irritation and bone loss. fines the axis of the implant through the desired area of emergence within the restoration. Some newer implant z Screw-Retained Single Units designs permit screw retention for the angulation differ- The treatment plan for replacement of a single tooth with ence so inherent to this area. Up to 25-degree angulation screw retention may be the professional preference of the differences can be accommodated when using this type of restorative dentist. There are advantages and disadvan- implant (. Fig. 10.24). This can be especially useful in tages to using this design for single and multiple missing the anterior maxilla where trajectory of bone frequently teeth (. Table 10.2). Screw-retained prostheses are sim- is different than long axes of teeth. Screw-retained pros- plistic to retrieve, are easy to trial fit, and can be shaped to theses are especially useful in the anterior dentition the desired emergence with either porcelain, ceramics, or because retrievability is much easier than with the metal. This design also eliminates the uncertainties of cemented prosthetic design and a controlled degree of loosening and incomplete debris removal associated with retention is afforded as well (. Fig. 10.25). Implant Prosthodontics 289 10 a b c. Fig. 10.25 a, Incisal view of screw-retained central incisors. b, facial representation of restorations placed. c, occlusal view of a screw- retained restoration for a posterior single unit 10.11 Restorations for the Partially implant position accurately is critical especially when Edentulous Patient: Fixed Partial several implants are being connected together. The use of a verification index has been shown to reliably Dentures (FPDs) transfer this information to the laboratory (. Fig. 10.26). FPDs require the first assessment of site planning as with other types of restorations. It is of prime impor- z FPDs in the Aesthetic Zone tance to understand that the implant bridge should be supported entirely by dental implants. Combining the > Placement of multi-unit restorations in the anterior support with natural teeth has been shown to involve maxilla should bring to mind several anatomic con- prosthetic complications and intrusion of the abut- siderations for surgical planning: ment teeth for a number of reasons. Although these 5 Adequate depth of the residual alveolar ridge to studies may use the specific scenario of a three-unit the nasal floor FPD supported by a natural tooth and implant, other 5 Buccolingual width of the bony ridge to provide studies have advocated strategic teeth in combination for implant placement with implants for full-arch prostheses. For the use in 5 Assessment of the lip when relaxed and upon acti- short-span FPDs, it is prudent to keep the restoration vation of a smile supported entirely by dental implants to avoid prob- 5 Participation of the restoration in anterior guid- lems concerning abutment fracture, screw loosening, ance in conjunction with the adjacent teeth tooth intrusion, malocclusion, and other complica- tions. Designing the FPD to be screw-retained as opposed to cement-retained is largely based on per- Anterior FPDs or any restoration in the aesthetic zone sonal preference but may be tailored to what can be should first begin with a diagnostic wax-up or template serviced and maintained most easily. Acquiring (. Fig. 10.27). This should be tried in place to assess  290 O. M. Muller and T. J. Salinas a b. Fig. 10.26 A and B: Verification index fabrication for multiple implants in conjunction with a custom tray. Radiographic verification of complete seating also insures quality check a b 10. Fig. 10.27 a and b, Diagnostic cast and wax-up of missing maxillary anterior teeth the dynamics of the patient’s lips in relaxed and smiling more predictable in these circumstances. If the surgical actions. workup determines implant placement will be done con- This will give an idea as to the incisal edge position comitantly with or without a bone graft, the diagnostic as well as the available restorative dimension and should wax-up should be used to fabricate a surgical guide or be verified in the patient’s mouth to correspond with stent for implant placement. If a bone graft is necessary, facial landmarks, such as the center of the face and the surgical guide references the incisal edge and gingi- interpupillary line. Also, a proportional relationship val aspect of the future restoration to aid in establishing should exist from the central incisor to the canine from the proper amount and positioning of the bone graft an anterior perspective. This proportionality becomes (. Fig. 10.28). Superior/inferior positioning of implants critical in aesthetically prominent areas. The wax-up is virtually the same as for single units, described previ- may also indicate how much tissue has been lost as a ously. However, the mesiodistal assessment of restor- result of the missing teeth, soft tissue, and associated ative space should be done first to determine the alveolar process. In these cases, it may be necessary to appropriate implant number and dimension to be consider horizontal or vertical bone augmentive proce- placed. Using a 2-mm rule from each adjacent tooth and dures as a first phase, followed by placement of implants a 3-mm rule from implant to implant, the appropriate in a second phase. In some cases, it may not be feasible implant number and dimension can be calculated. If the to perform bone grafting owing to local or systemic fac- available space does not allow an appropriate number of tors. Making precision detachable bridgework that implants or encroachment upon the implant-implant replaces teeth, soft tissues, and alveolar bone may be proximity, either restorative dentistry or orthodontics Implant Prosthodontics 291 10. Fig. 10.29 Placement of two implants in strategic locations to permit hygiene access and force distribution abutments. Conversely, it occasionally becomes neces- sary to perform angle correction because there is fre- quent disparity between the long axes of tooth and the long axis of bone available in the anterior maxilla. An intimate fit of FPDs is far easier to achieve with a cemented prosthetic design than with a screw-retained restoration. The subtle inaccuracies of impression- making, alloy casting, and porcelain application make the simultaneous and coincident fit of screw-retained FPDs difficult; thus, a cemented prosthetic design is a more appropriate choice. Creation of a surgical guide is critical for accurate placement and aesthetic success of the implant restoration. After placing and uncovering the implants, it is prudent to create provisional restora- tions to develop soft tissues. As with other techniques in restorative dentistry, the provisional restoration allows creation of an occlusal. Fig. 10.28 Computerized navigation reveals the amount of soft/ scheme, verifies accurate occlusal position, is available hard tissue loss for a backup during repair sessions needed for the defin- itive restoration, and serves to assess speech and esthet- may be indicated. Occasionally, the use of a cantilever ics. Only in this way can an acceptable aesthetic outcome bridge design can be advantageous, where space con- become predictable in the aesthetic zone. straints or insufficient bone prohibits placement. If it becomes necessary to cantilever the FPD either mesially z FPDs in the Anterior Mandible or distally, a screw-retained design permits a framework Placement of multiple-unit restorations in the anterior that better withstands the cyclic loading of occlusion mandible requires similar forethought as with the ante- and subsequent problems of dislodgement. Screw- rior maxilla. Placement of multiple implants in the ante- retained prostheses require an accurate transfer of rior mandibular area presents a unique challenge in that implant or abutment positioning. This is best done by one-to-one replacement of teeth with implants can cre- the use of verification indices made from splinting the ate implant to implant or implant to tooth proximity impression components with rigid material prior to concerns (. Fig. 10.29). Tarnow and colleagues removing from the mouth with open-tray impression. have outlined the pattern of bone loss to be about 3 mm This assembly can also be used later as a base for mak- from the edge of the implant to an adjacent implant. ing a provisional restoration described below. Therefore, placement of implants closer than 3 mm to It is considerably more difficult to create a properly each other can create accelerated bone loss patterns in fitting screw-retained framework than a cemented these areas. This pattern seems to be somewhat less framework that has intimate fit with the supporting (~2 mm) when the implant abuts a natural tooth.  292 O. M. Muller and T. J. Salinas a b. Fig. 10.30 a and b, Screw-retained prosthesis permits hygiene access Because the anterior mandible is mostly composed of dense compact bone, an implant-to-tooth replacement ratio of 1:2 may be acceptable as long as the crown-to- implant length ratio is 1:1. Gingival prosthetic seal/ adaptation in the anterior mandible is not as critical as 10 it is in the anterior maxilla because consonant produc- tion is primarily made in relation to the maxilla. Screw- retained designs for FPDs in the anterior mandible seem to work well (. Fig. 10.30). Implant proximity should also be assessed before placement for hygiene proce- dures because the placement of even an appropriate number of small-diameter implants in this area can cre- ate hygiene difficulties. z FPDs in the Posterior Maxilla Placement of implants in the posterior maxilla requires. Fig. 10.31 Alveolar bone loss resulting in the need for an onlay sufficient bone buccally and lingually as well as inferior bone graft before implant placement to the maxillary sinus. Although short implant lengths have been used, 12 mm of bone in actual height is the minimum required for a macroretentive screw-type implant to adequately support occlusal forces. After the loss of a tooth in the posterior maxilla, this required dimension might not be available (. Fig. 10.31). Progressive enlargement of the maxillary sinus as well as residual ridge resorption is often seen after tooth loss. Diagnosis of either of these problems helps one deter- mine the appropriate treatment. If pneumatization has taken place, sinus augmentation procedures can be indi- cated with either concomitant or delayed implant place- ment. Residual ridge resorption or traumatic destruction of alveolar bone by trauma or periodontal disease may also have taken place. In these cases, onlay bone grafting may be a more appropriate treatment (. Fig. 10.32).. Fig. 10.32 Cranial onlay bone graft in the posterior maxilla. The decision to replace a posterior maxillary quadrant (Image courtesy of Leon F. Davis, DMD, MD) Implant Prosthodontics 293 10. Fig. 10.33 Individual fixed units protected from canine rise in lateral excursions. Fig. 10.34 Placement of two implants in the posterior mandible after inferior alveolar nerve transpositioning with individual crowns versus fewer splinted implants acting as an FPD may be related to the length of implant or the presence of natural canine teeth with canine- protected occlusion (. Fig. 10.33). Other strategies place the implants in a slightly staggered configuration from buccal to lingual and then splint them together. Screw-retained designs seem to allow retrievability and offer advantages for modifying hygiene and performing reparative metal ceramic procedures. z FPDs in the Posterior Mandible As with the posterior maxilla, tooth loss for an extended time can result in residual ridge resorption. In such cases, onlay bone grafting may provide an appropriate bone volume for implant installation. A limiting factor for implant placement in the posterior mandible is not only residual ridge resorption but also relative position of the inferior alveolar canal. Panoramic radiographs may give a full appreciation of the position of the inferior alveo- lar canal. In some patients, this may assume a relatively high position, making placement of implants of reason-. Fig. 10.35 Anterior cantilever fixed partial denture able length impossible. In these cases, lateral reposition- ing of the inferior alveolar nerve with implant placement may be the only option for treatment other than a remov- be especially useful when there is an insufficient amount able partial denture. Nerve repositioning is an effective of bone or when significant site morbidity may result. adjunct in implant placement, but the technique can Posterior cantilevering probably is a more common sce- have significant adverse nerve injury (. Fig. 10.34). nario, typically owing to a greater availability of bone in There is also some risk of mandibular fracture by the use the anterior area of the jaws. Anterior cantilevering may of this technique. In some cases, it may be preferable to be used in areas where posterior anchorage is superior sacrifice teeth anterior to the edentulous area to permit to anterior anchorage (. Fig. 10.35). Cantilevering placement of sufficient length implants anterior to the requires that a framework be connected at a maximum mental foramen with extension to the posterior. clamp force; such stability is best achieved with screw- retained frameworks. A further strategy is to use direct z Cantilevered FPDs to implant connections owing to a comparably robust Cantilevered FPDs may be used in implant dentistry screw joint connection. Occlusal contact created on the provided there is adequate length to the supporting pontic should be very light to coincident as with adjacent implants and limited distance to the cantilever. This may teeth.  294 O. M. Muller and T. J. Salinas 10.12 Restorations for the Edentulous Patient z The Edentulous Arch The success of removable prostheses relies on the com- bination of retention, support, and stability, which can be deficient. A conventional mandibular prosthesis should be evaluated for retention, support, and stability. Difficulty with speech, swallowing, and mastication should be considered when evaluating prostheses. Patient acceptance of conventional prostheses may be contingent on stability and comfort when masticating. A patient’s chief complaint should be closely scrutinized and correlated with the clinical examination to help for- mulate the proper treatment; the complaint is the foun-. Fig. 10.36 Stud-retained overdenture using O-ring attachments dation for a wide array of considerations that determine avenues possible for a candidate considering treatment dible. Although the use of stud attachments connected with osseointegrated implants. Patient factors of pros- to the implants can be a cost-effective measure to thetic satisfaction can be quantified and evaluated before improve retention, stability, and support (. Fig. 10.36), proposing initiation of further treatment. Many of there is an increasing need for aftercare and servicing for these considerations help to determine which imaging these patients. If a stud-retained denture is planned, the studies, preparatory treatment, and number of ancillary implants should be as parallel as possible to avoid pre- 10 procedures are needed, if the treatment goals are feasi- mature wear of the attachment mechanism. Alternative ble, and what time and cost commitment is involved. cylindrical attachment mechanisms have been intro- Treatment should be targeted at specific goals to achieve duced to allow for an easier rate of servicing in the after- a predictable outcome that addresses the patient’s func- care period (. Fig. 10.37). The vertical height of the tional and/or aesthetic problem. The treatment may attachment should be considered because some edentu- encompass several different routes paying attention to lous mandibular arches do not provide more than 4 mm time, cost, longevity, and levels of invasiveness. of restorative dimension for the mandibular denture. The amount of keratinized/fixed tissue, vestibular Preoperative planning calls for the evaluation of the depth, available bone, and opposing occlusion are all patient’s present difficulty. Reasonable aesthetics, occlu- important factors to consider before implant treatment sion, and extension should be evaluated first. If these (i.e., natural dentition, edentulous arch, and implant- factors seem to be appropriate, panoramic radiographs borne occlusion). It may be appropriate to recommend and possibly an occlusal radiograph are helpful in deter- only an implant-retained overdenture for a favorable mining the position of the mental foramina. A prime mandibular arch. However, mandibular arches with lim- objective is to place at least two implants as far apart as ited support, vestibular extension, and extensive bone possible within this area. The anterior loop of the infe- resorption may require an implant-borne prosthesis. rior alveolar nerve can extend as far forward as 7 mm before exiting the mental foramen; thus, consideration z Implant-Retained Overdentures should be given to proper site selection. A radio- Patients older than 65 years are said to represent a sig- graphic marker such as a standardized stainless steel nificant proportion of the US population, and the aver- shot can be secured to the patient’s denture and placed in age life expectancy has risen by 30 years since 1900. A the mouth before panoramic and/or occlusal radiogra- sizable portion of this group is edentulous or partially phy. This will give an indication of the correct site selec- dentate in at least one arch. Many in this age group tion for implants in the anterior mandible. After the site have difficulty wearing mandibular complete dentures has been selected, an open channel can be created in the owing to poor support and retention precipitated by stent to allow surgical latitude. Either duplication of the advanced bone resorption, xerostomia, loss of attached patient’s denture or a wax trial tooth arrangement subse- keratinized tissue, and neuromuscular degeneration. The quently processed in clear acrylic resin can be helpful in use of implants for these edentulous patients has been determining the position. In general, tapered arch forms shown to actually preserve existing bone as opposed to with extensive resorption may direct placement of results with conventional dentures. Increased sup- implants in close proximity to each other. In other words, port and anchorage can be improved with the use of at implants placed less than 20 mm apart may not be least two osseointegrated implants in the anterior man- mechanically advantageous for use independently as Implant Prosthodontics 295 10 a b. Fig. 10.37 a and b, Cylindrical attachments intraorally with corresponding placement of matrix in overdenture base stud attachments. In these cases, it may be desirable to connect the implants with a bar attachment to create a wider base of anchorage. There are several reasons to plan the implant-retained denture for a bar attachment. First, short (≤10 mm) implants or implants placed in cancellous bone or types 3 and 4 bone, not typically seen in the anterior mandibular area, may be better sup- ported by the splinting effect of a bar attachment. Second, nonparallel implants create different paths of insertion, which subsequently serve to wear and disable the stud attachment prematurely. In these cases, the bar attachment can correct this problem by providing a sin- gle path of insertion. Third, implants placed in close proximity to each other may provide better anchorage to the overdenture if a bar attachment is incorporated that places the attachment mechanism at a wider base than the interimplant distance. The fourth reason is to pro- vide indirect retention of the denture base where mal- related arches would tend to tip the denture base. There are some spatial considerations of using a bar attachment that should be evaluated before treatment planning. The vertical height needed for a bar attach-. Fig. 10.38 Minimum clearances needed for a bar-attached over- ment can approach 11 mm. This measurement is taken denture from the occlusal plane to the highest point of the alveo- lar process. This distance will provide for the height of implant-retained or implant-supported overdentures. the bar (2–4 mm), 1–2 mm under the bar for mainte- Depending on the implant site distribution, it may be nance of hygiene, and at least 7–8 mm of restorative prudent to also incorporate full palatal coverage to material in the overdenture (usually acrylic resin) assist with some residual load transfer to the hard pal- (. Fig. 10.38). Some early evidence points to the added ate. The prosthetic treatment of these implant cases is benefit of using metal reinforcing frameworks in man- assimilated to the Kennedy class I partially edentulous dibular overdentures to decrease the risk of fracture of arch in that stress-breaking attachments and stress dis- these restorations. tribution to the soft tissue support posteriorly are Implant-retained overdentures for the maxilla can important considerations. Also shown to be successful is incorporate the use of bar attachments. A minimum of the use of abutment retention for maxillary overden- four implants in the anterior maxilla splinted with a bar tures. Discretion should be made for distribution of the seems to be appropriate treatment. Whenever possible, abutment relative to rotational force requirements as cross-arch stabilization is preferred for maxillary many abutment systems are resilient.  296 O. M. Muller and T. J. Salinas z Implant-Supported Overdentures Implant-supported overdentures may be indicated when a patient has significant difficulty in all factors of sup- port, retention, and stability. Anatomically, there may be cause to suspect that extensive resorption has taken place that has resulted in the loss of alveolar structure. Consequently, implant anchorage can be used to aid in the support and retention of overdenture prostheses. Historically, most of the literature available on implant-supported restorations in the mandible has been planned for four to six implants intraforaminally. More contemporary literature suggests the use of four widely spaced implants in this region opposing an eden- tulous arch with equally successful rates [74–76]. The strategy for using implants in the anterior mandibular. Fig. 10.39 Bar attachment milled to a 2-degree taper for implant- area allows segments to be cantilevered posteriorly in supported overdenture accordance with the anteroposterior spread of the implants. On average, this equates to 10–20 mm or the area of the lower first molar. The decision to extend the cantilever can be based on the arch form of the fixtures, fixture length, anterior cantilevering, natural maxillary dentition, and parafunctional habits. Favorable factors 10 for extension of the cantilever are a tapered arch with long fixtures, no anterior cantilevering, edentulous max- illary arch, and no parafunctional activity. The most posterior implant supports a load typically of compres- sion in comparison with the anterior implants, which are placed under tension. Also, the mandible may be viewed as a dynamic bony structure undergoing flexure. This can approximate 2 mm at the mandibular angle upon maximum opening. For this reason, implants placed distal to the foramen should not be rigidly con- nected to the contralateral side. Planning for implant support of a prosthesis in the edentulous maxilla has traditionally involved at least. Fig. 10.40 Precision detachable overdenture with attachments eight fixtures. This may require the use of sinus augmen- for engaging the bar. (Prostheses courtesy of Northshore Dental Laboratory, Lynn, MA) tation, or for consideration of fewer implants, extended- length implants into the zygomatic process have been successfully used. The use of zygoma implants has been bar attachment (. Fig. 10.40). Usually, this restoration favorable, approaching a success rate that surpasses contains either plunger or swivel attachments that lock those conventional implants to which they are attached the overdenture as it comes to complete placement over [77, 78]. Additional approaches can be placement of the bar attachment. This technique is very effective but four zygoma implants to allow sufficient anchorage into over time can allow a small degree of micromovement. craniofacial bone. This has also shown success in recent An additional method of electrical discharge years. machining, also known as “spark erosion,” can be used Attachment mechanisms for implant-supported in these cases; it results in a precise fit between the super- overdentures can range from the simple to the structure and the bar. This technology, which results in sophisticated. Bar-clip attachments are a cost-effective an essentially detachable fixed bridgework, may be sig- and predictable means of connecting implants. More nificant in costs and still require some long-term mainte- sophisticated milled bar and plunger attachments can be nance. precision methods in telescopic placement of a remov- able prosthesis. The milled bar can be machined to a z Fixed Detachable Prostheses 2-degree taper, allowing a precise path of placement One alternative treatment method for an edentulous (. Fig. 10.39). The underside of this overdenture has a mandible is the use of an implant-supported fixed com- cast metallic housing that acts as a guide over the milled plete denture also known as a fixed/removable restora- Implant Prosthodontics 297 10 tion (hybrid denture). This restoration contains a retained prostheses offer stable occlusal support while screw-retained metal framework with a veneer of acrylic allowing some degree of posterior cantilevering. resin and denture teeth, thus coining the term hybrid. Treating patients with an edentulous maxilla is Such restorations are fixed and are not removable by the dependent upon a number of factors. The primary deter- patient; however, they do allow adequate room for oral mining factor is one of available space. Generally, the hygiene procedures (. Fig. 10.41). As might be more space available (13+ mm vertically), the more indi- expected, no denture flange is present, and a minimum cation there is for an overdenture prosthesis. Incipient vertical restorative space of 12–15 mm is necessary for resorption or minimal space availability (9–12 mm verti- structural integrity and hygiene access. Placement of cally) may indicate the use of a metal ceramic design implants for a hybrid denture should incorporate the use (. Fig. 10.42). Implant-supported maxillary overden- of a surgical stent because the exit sites for the access tures are frequently used in cases of moderate to severe channels are critical. The surgeon may be cautioned on resorption because they replace not only missing masti- careful implant placement in those patients with a skel- cation and aesthetics but also facilitate phonetic physiol- etal class III or severe class II relationship as revealed by ogy as well. Speech production may rely heavily on cephalometric radiography. Recently, application of this adaptation of the prosthesis to the palatal gingiva. If immediate load technique has become popular. there is ample space, this is best accomplished with an Of course, a full-arch metal ceramic design could overdenture prosthesis to seal this linguo-alveolar area also be used in these circumstances in which a minimal phonetically while allowing for daily hygiene procedures. restorative dimension exists. In this circumstance, screw- Attachment mechanisms for the maxillary implant- supported overdenture are the same for the mandibular overdenture with the exception of plunger or locking attachments placed palatally (. Fig. 10.43). 10.13 Contemporary Techniques z Immediate Placement Immediate placement of implants into extraction sock- ets has been considered for some time. Although it has been performed successfully, inflammation and infec- tion should be eradicated for predictable osseointegra- tion to occur. Considerations for using immediate placement capitalize on the osteogenic potential of a