Long-term follow-up of posterior implant restorations showing under-occlusion: a superimposition analysis of dentition change.

Under-occlusion ('infraocclusion' as defined in the natural teeth) after implant restoration in the posterior area is commonly encountered in clinical practice; however, it has rarely been reported. Most importantly, the under-occlusion change mechanism remains unknown. The purpose of this case report was to analyze how the dentition of both arches changed in a patient, including teeth tilting, elongation and occlusal plane change with under-occlusion of the posterior implant restoration after long-term function. Based on this, we hypothesized a mechanism of under-occlusion of the posterior implant restoration. Among patients showing the under-occlusion phenomenon, three patients who had a long-term follow-up and had a model produced at the time of restoration were enrolled. The dentition changes were analyzed via digital scanning and superimposition of the model at the time of restoration, with the current model showing under-occlusion. Based on the result of superimposition, tooth elongation occurs mainly in the maxilla, and two types of positional changes occur in the mandible, specifically in the anterior-superior and posterior-inferior direction. The mechanism of under-occlusion of the posterior implant could be the result of tooth elongation and the relative positional change of the mandible.