Written by Bill Abbo, DDS, MS, and Michael E. Razzoog, DDS, MS, MPH Tuesday, 01 April 2008 00:00
The success of implant therapy begins with meticulous treatment planning and properly performed implant placement. Prosthetic complications may occur with misaligned implants, especially when multiple implants are involved.1 Gladly, most of the case reports that appear in the dental literature are of perfect and well-coordinated clinical cases. Yet experience tells us that at times there are situations where conditions are less than ideal. These conditions require all of our expertise to address the challenge of preserving function and aesthetics. Treatment circumstances at times necessitate the replacement of soft-tissue contours, or in some instances the placement of additional implants may not be an option and a fixed restoration not feasible. Unconventional techniques, such as a milled titanium implant bridge, may offer a solution for the practitioner.
The titanium framework is made through a computer-assisted milling process from a single block of titanium. Individual preparations may be designed to accommodate improved aesthetic restorations, using all-ceramic restorative materials.2,3 Fixed complete dentures may also be fabricated using this technique by adding heat-cured acrylic resin and artificial teeth instead of all-ceramic restorations. These implant-retained restorations may require cantilever sections that are attached to multiple units.4 It should be understood that the same complications that occur with fixed partial dentures on natural dentition may also occur with implant-retained or supported restorations. When using cantilevers in conjunction with dental implants, stress is biomechanically transferred to the implants, framework, and the bone.5-6 Several techniques are referred to in the literature to reduce the load on the cantilever area, involving the use of acrylic resin on the occlusal surfaces to absorb forces, relief of occlusal contacts, and avoiding the use of porcelain or gold.7,8
This case report describes the rationale and prosthodontic treatment of a partially edentulous patient who presented with 2 endosseous implants placed in an undesirable location and angulations. The rationale and prosthodontic reconstruction of these 2 implants composes the unique aspect of this patient treatment. While such implant placement is never planned, the reality is that it does occur in practice. When implants are not placed in the correct position, new approaches and techniques need to be set in action to solve the predicament and satisfy the patient’s dental needs.
|Figure 1. Misaligned implants with healing abutments.|
A 68-year-old male reported to the University of Michigan School of Dentistry, Department of Prosthodontics, with a chief complaint of wanting to restore 2 maxillary implants that had previously been placed. During the clinical evaluation it was found that the left lateral incisor was fractured at the level of the gingival margin, and the left second molar had recurrent caries. The 2 endosseous implants were positioned in the area of the left cuspid and the left first premolar in a less-than-desirable position and angulation (Figure 1). The patient was functioning with a mandibular removable partial denture that was deemed clinically acceptable, with proper fit and acceptable aesthetics. After a complete dental examination was performed by the treating dentist, as well as a review of the medical history, no findings contraindicated dental care, including implant surgery.
Several treatment options were offered to the patient. The first was root canal treatment—a cast post and core with an all-ceramic restoration for the left lateral incisor, an all-ceramic restoration on the second molar, removal of the endosseous implants, and eventual placement of new implants with the correct position and angulations to retain a 3-unit all-ceramic bridge. The second included the same treatment for the left lateral incisor and the left second molar, along with removal of the 2 endosseous implants and placement of a removable partial denture.
After careful study the patient expressed the desire not to undergo additional surgery procedures, and instead elected to restore the existing implants. The restorative dilemma was how to fabricate a fixed prosthesis that would provide function and aesthetics. The decision was to restore the implants with a short-span milled titanium bridge coupled with all-ceramic restorations to complete the occluding areas.
The initial phase of treatment consisted of endodontic retreatment of the left lateral incisor and fabrication of a cast post and core using acrylic resin pattern (GC Pattern Resin [GC America]) cast dowel and core. A cast post and core was fabricated using gold type 4 and cemented with a resin-modified glass ionomer cement (FujiCEM [GC America]). After cementation of the post and core, the tooth was circumferentially prepared with a moderate chamfer margin and a 2-mm ferrule. The previous restoration on the left second molar was removed, caries eliminated, and a new core build-up material placed (CompCore [Premier Products Company]). The left second molar was also circumferentially prepared with a moderate chamfer margin. Autopolymerizing acrylic resin (Lang Dental Manufacturing) was used to fabricate the provisional restorations.
The restorative phase of treatment consisted of the following:
|Figure 2. Master cast of implants and tooth preparation.||Figure 3. Titanium framework with pink porcelain applied.|
|Figure 4. Final restorations, intraoral view.||Figure 5. Final restorations, extraoral view.|
- Closed tray impression copings were placed on the implants and verified radiographically for adaptation to the implant platform.
- On the left lateral incisor and left second molar retraction cord “00” (Ultradent Products) impregnated with hemostatic solution (Hemodent [Premier Products Company]) was placed for gingival retraction.
- A closed tray implant-level impression was performed to relate the position of the implant platform to the other teeth as well as the soft-tissue contours. This technique consists of connecting the impression coping to the implant and utilizing a closed tray impression technique with vinyl polysiloxane impression material (Extrude Extra-Heavy and Light Bodied [Kerr]). During this impression process the left lateral incisor and the left second molar were also included and reproduced.
- The impression was poured (Figure 2) using a soft-tissue moulage with elastic, pink-colored vinyl polysiloxane (Gingitech [Ivoclar Vivadent]) and type V gypsum material (Jade Stone [Whip Mix]).
- An acrylic pattern (GC Pattern Resin) was designed to compensate for the angulations and position of the 2 implants. The pattern also provided the shape of the substructure on which the ceramic restorations would eventually be cemented. Nonengaging temporary abutments (Nobel Biocare) were used as the connectors of the acrylic resin pattern to the implant replicas. The acrylic resin pattern was contoured to receive 3 all-ceramic single-unit restorations, using a moderate chamfer margin. The master cast along with the resin pattern were then sent to the Procera production facility (Nobel Biocare) in Gothenburg, Sweden, for the manufacture of the one-piece milled titanium bridge that duplicated the provided acrylic resin pattern. Using CAD/CAM technology, the pattern is milled from a block of titanium, and the master cast is digitalized using a laser digitizer that records the position of the implant analogs.
- After the framework was returned it was tried in the patient’s mouth to verify the precision of fit by radiographic and visual means. Shade selection for the soft tissue as well as for the all-ceramic restorations was obtained at this appointment.
- In the laboratory an impression of the titanium framework’s tooth analog substructure using polysiloxane impression material (Extrude Extra-Heavy and Light Bodied) was taken and poured using type V gypsum material (Jade Stone). Dies were fabricated, trimmed, and digitalized using a touch probe scanner (Procera Piccolo [Nobel Biocare]) for the left second molar and left lateral incisor, as well as for the 3 preparations on the titanium bar. Zirconia copings were chosen due to the material’s high flexural strength8 and resistance to fracture.9 Once these copings had been returned, the veneering porcelain (Nobel-Rondo [Nobel Biocare]) was applied to complete the aesthetic portion of the crowns. Gingival shade porcelain (NobelRondo) was applied to the soft-tissue replacement portion of the titanium framework (Figure 3).
- The single crowns on the left lateral incisor and the left second molar were placed onto the tooth preparation and evaluated for marginal integrity, occlusal relationship, and aesthetics. The margins of the single restorations were evaluated radiographically, and a tactile assessment of marginal integrity was also conducted. The teeth were cleaned with fine pumice (Whip Mix) and treated with chlorhexidine, and the internal surface of the restorations was cleansed with alcohol. A thin coat of resin-modified glass ionomer cement (FujiCEM) was placed into the internal surface of the all-ceramic restorations and delivered with finger pressure. The delivery of the framework consisted of placing it onto the implants and applying a 35 Ncm torque to each of the retaining screws. Wax was placed in the 2 screw access holes, and pink Triad gel (DENTSPLY) was applied and light-cured to cover the access holes. The individual ceramic restorations were then placed onto the framework, and occlusal contacts and aesthetics were evaluated, and marginal integrity was verified visually and via tactile assessment. Cementation was completed by placing a thin coat of resin-modified glass ionomer cement onto the internal surface of the all-ceramic restorations and delivering with finger pressure (Figures 4 and 5).
The patient was recalled at 1 week and at 1 month; no occlusal adjustment was needed after the cementation appointment.
Many different approaches may be followed in restoring the partially and completely edentulous patient, but when the treatment of choice includes implants the planning needs to move ahead with caution. Planning should eventually include the fabrication of surgical guides to achieve the correct positioning of the implants. Once the implants are placed there exist numerous treatment procedures or modalities for the final restoration of the implants. The 1-piece milled titanium implant-retained fixed partial denture is one of these procedures that can help achieve functional and aesthetic results. These structures aid in compensating for missing soft and hard tissues, and also in some situations for the occasional misaligned implant.
The use of surgical guides for the placement of implants is imperative to achieve their correct positioning. In everyday practice we will have patients that have implants placed in areas that are not the most ideal, and it is in these situations that we must know about the different techniques that can help us achieve predictable, aesthetically pleasing, and functionally correct results. With the use of computer-aided technology we are able to solve many of the problems encountered with the malpositioning of implants, and are able to achieve aesthetic results.
- Akca K, Iplikcioglu H, Cehreli MC. A surgical guide for accurate mesiodistal paralleling of implants in the posterior edentulous mandible. J Prosthet Dent. 2002;87:233-235.
- Oden A, Andersson M, Krystek-Ondracek I, et al. Five-year clinical evaluation of Procera AllCeram crowns. J Prosthet Dent. 1998;80:450-456.
- Razzoog ME, Lang LA, McAndrew KS. AllCeram crowns for single replacement implant abutments. J Prosthet Dent. 1997;78:486-489.
- Himmel R, Pilo R, Assif D, et al. The cantilever fixed partial denture: a literature review. J Prosthet Dent. 1992;67:484-487.
- Brunski JB. Biomechanical factors affecting the bone-dental implant interface. Clin Mater. 1992;10:153-201.
- Tashkandi EA, Lang BR, Edge MJ. Analysis of strain at selected bone sites of a cantilevered implant-supported prosthesis. J Prosthet Dent. 1996;76:158-164.
- Cibirka RM, Razzoog ME, Lang BR, et al. Determining the force absorption quotient for restorative materials used in implant occlusal surfaces. J Prosthet Dent. 1992;67:361-364.
- White SN, Miklus VG, McLaren EA, et al. Flexural strength of a layered zirconia and porcelain dental all-ceramic system. J Prosthet Dent. 2005;94:125-131.
- Guazzato M, Albakry M, Ringer SP, et al. Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part II. Zirconia-based dental ceramics. Dent Mater. 2004;20:449-456.
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