Biomechanical Assessment

The importance of biomechanics with dental implants was initially underestimated. Clinical experience and research over the years has shown the significant importance of biomechanics in the success and predictability of implants. When a prosthesis is installed immediately, for example 1 day to 2 weeks, occlusal overload must be avoided.^26-27,29 Sites such as maxillary posterior implants will likely undergo periods of less bone support in the early stages of bone apposition due to the initial stage of bone resorption. However, once osseointegration is achieved, dental implants will resist forces of occlusion.

The absence of a periodontal ligament around the dental implant reduces tactile sensitivity and the patient's reflex function, as well as the implant not being able to migrate to compensate for premature occlusal contacts like natural dentition with a periodontal ligament. Implants and their rigid-attached restoration do not move. Therefore, biomechanic assessment is crucial to implant success.^35,40

Bone response to mechanical occlusal overload, improper implant occlusal design, or parafunctional habits may cause microfractures in the bone leading to bone loss and fibrous inflammatory tissue around the implant. Excessive forces are destructive to osseintegration and long-term success. The load-bearing capacity of implants are influenced by several factors, including the size and number of implants, the arrangement and angulation of the implants, and the quality of the bone.^9,29

When excessive loads persist, bone loss will continue, leading to implant failure. The percentage of bone-to-implant ratio, called the bone appositional index, is an important factor to consider when evaluating the load-bearing capacity. Less bone density and a low bone-to-implant contact provide less support and resistance to occlusal loading. For example, with the posterior maxilla, the bone appositional index is significantly less than the anterior mandible (Figure 3). The trabecular bone in the anterior mandible is typically dense with a thick cortical bone layer. However, in the posterior maxilla, the trabecular bone is less dense and the cortical bone layer is thin. The bone appositional index for implants in the posterior maxilla will typically range from 30-60%, where the index for implants in the anterior mandible typically ranges from 65-90%.^30-42

Figure 3.

Figure 3.

Courtesy of Dr. Samuel L. Corey

Preventive treatment such as occlusal mouthguards and equilibration are considered depending on the individual patient. Other considerations in regards to anatomic location involving the posterior maxilla as the maxillary sinus, where it can limit the dental implant length. Sinus lift surgery is used in conjunction with posterior maxilla dental implant therapy with greater success. With mandibular implants, the inferior alveolar nerve limits the length of the implants used. Augmentation and graft procedures appear to be widely accepted producing improved implant predictability.³⁸