CHEWING PATTERNS IN SINGLE IMPLANT MANDIBULAR RETAINED OVERDENTURE

AIM: Mastication is one of the most important functional activity of the stomatognathic system. It is a rhythmic movement characterized by a diversity of jaw patterns, established by the integration between the peripheral and cortical inputs and the pattern generator in the brainstem. It has been observed that mastication is involved in cognitive processes and the preservation of the physiological chewing pattern is important for the quality of life of elderly subjects. In edentulous patients, the loss of teeth, the loss of periodontal mechanoreceptors and the alveolar bone resorption without new bon formation, require an important adaptation of the neural motor control. Neverthless, the functional aspect of the single implant mandibular overdenture is still little known even though the balance of the masticatory function is important for avoiding damage to the stomatognathic system and for maximizing efficiency. Aim of this study was a within-subject comparison of chewing pattern kinematics in complete denture wearers with and without a single implant retention during an observation period of 5 years after the prosthetic connection. METHODS: The within subject trial has been conducted on edentulous elders at the Dental School of Turin. Treated in the same facility and wearing complete denture for at least 1 year, they have been invited to participate to the trial. Exclusion criteria were cranio-mandibular disorders, local and systemic contraindications to implant surgery, neurological degenerative progressive diseases, multiple sclerosis, lateral amyotrophic sclerosis. Single symphyseal implants were inserted in all patients. Delayed load protocol has benn followed and prosthetic connection realized after three months, with Locator attachments (Zest Anchors). Stability and precision were double checked and in case relinings performed. All patients underwent the recording of the chewing cycles with a kinesiograph K7 (K7-I; Myotronics, Tukwila, WA, USA), using a gelatinous semi-solid (20x20x20mm) bolus. The kinematic signals were analyzed using a custom-made software and were recorded three months after the anchorage of the lower denture to a single-tooth implant and at 5 year follow-up. RESULTS: 15 patients were included in the study, following exclusion and inclusion criteria. 10 patients completed at this time the 5 years follow up. The results showed a significant decrease of the anomalous percentage of the reverse-chewing patterns at 5 years follow-up (p<0.03) and a significant improvement of the parameters involved in the chewing efficiency: total number of chewing cycles (p<0.01) (closure angle p<0.03, pattern width p<0.01, height p<0.01, duration p<0.01, closure duration p<0.004). CONCLUSION: A denture anchored with a single implant is more retentive and for this reason patients subjectively feel more comfortable during mastication. This study showed that beyond the subjective sensation, significantly the anomalous pattern decreased and the chewing patterns objectively improved the parameters of efficiency; accordingly, the neural control of the masticatory function becomes more stable with positive influence on the maintenance of the cognitive activity of the elderly.