Avoiding Osseous Grafting in the Atrophic Posterior Mandible for Implant-Supported Fixed Partial Dentures: A Report of 2 Cases
Bone atrophy occurs after tooth extraction in the posterior mandible, placing the mandibular canal and its neural, arterial, and venous contents closer to the osseous facial aspect and the coronal crest. This proximity places the structure in danger of damage when dental implants are surgically placed to support fixed or removable prostheses. Several options are available to treat these areas for implant-supported fixed and removable complete or partial dentures. Osseous grafting and ridge expansion are surgical options that enable acceptance of standard sized dental implants but have serious morbidities. Additionally, vertical osseous augmentation is not predictable at this time. Narrow diameter dental implants can be placed to avoid the mandibular canal, but some bone volume situations preclude this. Very wide and very short (6.5 × 5 mm) dental implants may be placed at an angle in atrophic sites to successfully support fixed partial dentures. An anterior guidance occlusal scheme may be used in maxillary dentate patients or group function in maxillary complete denture patients. A 100 micron occlusal relief in fixed partial dentures in dentate patients may be required to account for natural tooth intrusion and to prevent occlusal overload of the implant-supported partial denture.
Figure 1. As demonstrated in this schematic drawing, edentulism results in osseous atrophy (1) that proceeds mainly from the facial and crestal aspects, resulting in a narrow ridge at the crest and making implant placement problematic in avoiding the mandibular canal (2). Figure 2. Stock abutments are prepared for parallelism and standard crown and bridge impressions and laboratory procedures. Figure 3. The final fixed partial denture in place. Figure 4. Radiographically, short wide implants can appear spherical when placed at an angle. Standard diameter implants were used in the more anterior sites.
Figure 5. When an atrophic ridge presents with little bone volume, a short (5 mm) and wide (6.5 mm) implant may be placed at an angle to avoid the mandibular canal. A 2 mm radiographic margin should be observed at the crest and at the inferior aspect. The abutment has a wide diameter and can be prepared for parallelism for a fixed partial denture. Figure 6. The short wide implant was placed at a severe angle toward the facial. Abutment #28 was replaced with a 15 degree stock abutment placed angled toward the facial. Each abutment was then prepared for parallelism and subsequent impression. Figure 7. After the abutments were prepared and impressed, a free gingival graft was performed and the site covered with a bis-acryl stent, applied free-hand. No sutures were placed. The stent was removed after 1 week of healing.
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