First we must determine the number of implants, implant positioning, and final prosthesis design are determined. We must anticipate the end result before we begin the treatment. Treatment planing phase can never be completed without a mounted diagnostic cast, from which we constructed a surgical guide for our implant placement. A well mounted diagnostic cast also provides the interarch maxillo-mandibular relationship to determine our occlusion and also the interarch width from which to choose our retention mechanism (cast metal bar or locator/resilient attachment). The smile line should be registered as the wax trial denture setup performed. Radiographic included a panoramic x-ray. Tomogram or bone sounding should be performed in the implant site where adequate bone width is questionable. In the mandible, the good number of implants is four. I prefer one extra implant in the central incisor area as to provide better support during biting in the anterior area. Four implant allowed for maximal implant support, increased retention, increased stability due to shorter cantelever distance. The cantelever distance is the distance from the most posterior functioning tooth to the closest adjacent implant, also referred to as the length of the occlusal surface from the most distal abutment to the distalmost contact. The maximum cantelever distance (cantilever limitation) is calculated by measuring the distance from the most anterior implant to the most distal implant, then multiply by 1.5 or 2. Finally, implant positioning is governed by the patient maxillo-mandibular relation(normal, overbite, or underbite). Implant should be positioned such that to maximize the bone support during function.
Next is the implant surgical stage. I always graft the ridge width simultaneously using bone graft and membrane barrier if the ridge is inadequate. Remember the more bone supported under the prosthesis, the better for longevity of the prosthesis function. This is especially true for the mandible because there is no palatal coverage or support. All implants should be placed as parallel as much as possible. This will provide stability and better force distribution to the implant site. Moreover, the use of locator only allowed 15 degree of play in the path of draw. The path of draw of the prosthesis should be parallel to the angulation of the implant in the jaw.
After 6-8 months in the mandible from the date of surgical implant placement(to ensure osseointegration of the implant), we uncover the implant and attach the transmucosal component which emerges through the gum tissue. We then proceed to begin fabrication of the implant bar and the overdenture prosthesis after 28 days of soft tissue healing. The occlusal gingival height of the bar should be 6-8mm or the bar will flex especially at the cantelever portion. Flexing of the bar will put lateral stress to the implant abutment, cause inflammation to the surrounding tissue, and lead to implant failure. The fabrication of denture involves preliminary impression, final impression, wax try-in, bar try-in, and insertion of denture (at least 5 appointments, 1-2 weeks apart). In the mandible, careful consideration of the most distal occlusion should be made based on the number of implant and the cantelever distance. In the maxillary, complete palatal coverage is recommended unless patient have five or more implants placed. Another trick to add strength to the reduced palatal coverage prosthesis is to insert a metal framework into the acrylic(similar to that of the partial). My experience have shown that a definitive implant overdenture should have a palatal finish line or be reinforced with a metal framework. For more information on fabrication of maxillary implant supported overdenture please refer to Implant Support Overdenture, Maxillary Bar under services menu. Adjustment(s) are made for several appointments after insertion of denture. Once all the adjustment have been made, patient will report better function, speech, stronger bite force, and better retention.