Biomechanical Factors Affecting Long-Term Implant Success
Bone resorption around dental implants can be caused by premature loading or repeated overloading. Vertical orangular bone loss is usually characteristic of bone
tion caused by occlusal trauma. When pressure from traumatic occlusion is concentrated, bone resorption occurs by osteoclastic activity. In the natural dentition, bone reposition would typically occur once jhe severe stress concentnit ion is reduced or eliminated. However, in theosseointegrated implant system, after bone resorbs, it willnot usually reform. Because dental implants can resist forces directed primarily in the long axis of the implantmore effectively than they-can resist lateral forces, lateral forces on implants should be minimized. Lateral forces in
the.posterior part of the mouth have higher impact and are more ,destructive than lateral forces in the anterio rpart of the mouth. When lateral forces cannot be cornpletely’eliminated from the implant prosthesis, efforts should be made to equally distribute the lateral ‘forcesover as many teeth and irnplants as possible. Divergent implant placement can also increase the momentum through which force ‘is transferred to thebone-to-implant interface. Such force could potentially exceed the threshold for bone resorption. Inadequate .implant distribution, which leads to excessive cantilevers, can also potentially overload individual fixtures (Fig.14-8).Connecting a single osseointegrated implant to onenatural tooth with a fixed partial denture may effectively create an excessive cantilever situation, as well.Because of the relative immobility of the osseointegrated
implant compared with the functional mobility of anatural tooth, when loads are applied to the bridge, the tooth can move within the limits of its periodontal ligament.This can create stresses at the neck’ of theimplant up to 2 times the applied load on the prosthesis (Fig. 14-9). Potential problems with this type of restoration are described in Box 14-2. Therefore reestandingimplant restorations should be planned wheneverpossible.
Additionally pathogenetic forces can be placed on implants by non passively fitting frameworks. If screws are tightened to close gaps between the abutment and the nonpassive framework, compressive force is placed on the interfacial bone. Excessive force of this nature can lead to
implant failure (Fig. 14-10).
BOX 14-2 ‘
Potential Problems with Tooth and hand plant-Supported Fixed Partial Denture.
1. Breakdown of osseointegration
2. Cement failure on natural abutments I
3. Screw or abutment loosening
4. Failure of implant prosthetic component
Advantages of Two-Stage Osseointegrated Cylinder Implants
A. Surgical .
1. Documented success rate
2. In-office procedure
3. Adaptable to multiple intraoral locations
4. Precise implant site preparation
5. Reversibility in the event of implant failure
1. Multiple restorative options
2. Versatility of second-stage components
a. Angle correction
b. Esthetics ‘
c. Crown contours
d. Screw- or cement-retained restorations
3. RetrievabiJity in the event of prosthodontic failure