[Condylar positioning during clenching related to loss of posterior occlusal support]

In the last two decades, the Shortened Dental Arch (SDA) concept has been introduced as a treatment strategy for posterior edentulous patients. This study investigated whether the SDA concept applies to all posterior edentulous patients.

In the first study, objective evaluations for the temporomandibular joint (radiographic evaluation and measurement of condylar positioning during maximal voluntary contraction) were performed in patients with unilaterally posterior missing teeth. Abnormal condylar appearances were observed in 73% of subjects by radiographic evaluation and these phenomena coincided with edentulous-side in 55% of them. Condylar positioning during clenching was significantly larger on the edentulous-side compared to that in the dentulous-side. In the second study, we investigated the mandibular positioning during maximal voluntary contraction related to simulated loss of posterior occlusal supports in volunteers with natural dentitions. A greater bilateral loss of posterior occlusal support was associated with increased distances of positioning of both condyles. Moreover, subjects could be divided into two groups depending on the condylar mobility following reduced occlusal support. In the first group, the distance of condylar positioning significantly increased by cutting the splint sequentially from the posterior toward the anterior side. On the other hand, in the second group, no significant difference was observed between the distances measured under all the experimental occlusal conditions. In the supplemental study, a significant negative correlation was observed between the sagittal condylar guide inclination and the distance of ipsilateral condylar positioning. This result suggests that the steepness of the articular eminence is an important factor in condylar positioning during clenching.

We propose that clinical guidelines should be developed for determining whether to adopt a "Wait and See" approach for SDA patients without any proactive treatment, or to start prosthetic intervention immediately.