Implant Treatment Planning: A Time to Remember your Physics

When treatment planning for implant treatment is imperative
that we not only assess the dental condition that requires treatment...

: The difference between a tooth and implant.
The first requirement for successful osseointegration is primary stability. At the time of placement this is determined by the final seating torque, or more accurately, through RFA with an Osstell or Penguin device (Figure 2 & 3). By having enough stability to resist 150 microns of movement, integration will occur [2]. When comparing the accuracy of stability measurements [3], even though seating torque is a great predictor of stability and is backed up both anecdotal and research evidence, RFA is considered more accurate in the literature consensus.   By dispersing the masticatory forces over multiple implants, the individual load on each implant can be reduced. This happens in situations where multiple implants are tied together by a single restoration such as a bridge or a full arch restoration. In this type of situation, each implant shares the total load and forces generated to the hard tissue is minimized. In both multi and single unit cases, the forces to the per-implant bone can also be decreased by a larger surface area of bone-to-implant contact. Pressure caused by the implant laterally loading the bone around it will cause bone to resorb. If we look at the formula for pressure; P=Force/area, we can see that if we increase the area of implant to bone contact, the overall pressure will be decreased to any particular area. This increase in surface area can be achieved by either increasing the length of the implant or increasing the diameter or both (Figure 4 & 5).
The next important part of the equation is the patient-As patients age, their masticatory forces decrease. The forces females produce are generally lower than those produced by men and tend to decrease earlier in life than those of their male counterparts. Women tend to have a decrease after 25 years of age, while males decrease after 45 years [4]. The more dolichofacial they are, the lower the force generated. Brachyfacial individuals have shorter and thicker masseters which produce high forces with a more efficient lever system ( Figure 6). The position of the restoration plays a role in the potential forces generated along with the type of opposing dentition. The closer the restoration is to the TMJ, the higher the forces (Figure 7). This is like the force vs position when placing a nut in a nutcrackerthe closer to the hinge, the easier it is to break the nut. Evaluating what type of opposing dentition contributed greatly to the amount of force an implant and its restoration will receive. Natural dentitions can produce 250psi or greater while a full denture produce as low as 25psi. On top of these factors, those patients who suffer from bruxism can have masseter strength 6x's that of a non-bruxer [5].
Another important factor to consider when placing implants is the direction of the force to be exerted on it. Both implant components and peri-implant tissues accept axial loading much better than off-axis forces. In the posterior, axial loading should always be the goal unless it is part of a multi-unit system. In the anterior, off-axis loading is many times unavoidable, but the forces are lower than the posterior and therefore not as much of an issue.
A cantilevering force can be produced when there is a large amount of restoration that extends from the implant body to the adjacent tooth. The larger this cantilever, the more psi is exerted on the restoration and implant components (Figure 8). A vertical cantilevering force can be produced when an implant restoration becomes excessively "tall". In general, the restoration-to-implant length ration should not exceed 2.5: 1.

Figure 8: How cantilevers increase loads.
The final component to success is the quality of bone the implant is placed in. As we know bone is classified from D1, made up mostly of cortical bone to D4 which is very soft and is primarily trabecular in make-up ( Figure 9). As clinicians this is an important factor to consider when choosing implant diameter and length. ISQ values for implant placement in D1 bone were significantly higher than those for implants placed in D3 bone. In D1 bone, the implant length does not make any significant difference in primary stability and in D3 bone, the primary stability of the implant increased when longer implants were utilized [6].
Restoring the human dentition is a complicated task due to the varied factors that contribute to success or failure in both the shortand long-term treatment. By assessing the whole patient and not just focusing on whether a tooth is missing or not, we can provide the very best treatment for our patients.