Motor learning might contribute to a therapeutic anterior shift of the habitual mandibular position-An exploratory study.

BACKGROUND: Passive mandibular advancement with functional appliances is commonly used to treat juvenile patients with mandibular retrognathism. OBJECTIVE: The aim of this study was to investigate whether active repetitive training of the mandible into an anterior position would result in a shift of the habitual mandibular position (HMP). METHODS: Twenty adult healthy subjects were randomly assigned to one of two groups: a training group receiving six supervised functional training sessions of 10 min each and a control group without training. Bonded lateral biteplates disengaged occlusion among both groups throughout the 15-day experiment. Customised registration-training appliances consisted of a maxillary component with an anterior plane and a mandibular component with an attached metal sphere. Training sessions consisted of repeated mouth-opening/closing cycles (frequency: 30/min) to hit an anteriorly positioned hemispherical target notch with this metal sphere. The HMP was registered at defined times during the experiment. RESULTS: The HMP in the training group showed a statistically significant anterior shift of 1.6 mm (interquartile range [IQR]: 1.2 mm), compared with a significant posterior shift of -0.8 mm (IQR: 2.8 mm) in the control group (p < .05). Although the anterior shift among the training group showed a partial relapse 4 days after the first training block, it then advanced slightly in the 4-day interval after the second training block, which might indicate neuroplasticity of the masticatory motor system. CONCLUSIONS: Motor learning by repetitive training of the mandible into an anterior position might help to improve the results of functional appliance therapy among patients with mandibular retrognathism.

Effects of preventing intercuspation on the precision of jaw movements.

BACKGROUND: Closing movements are among the jaw's basic physiological motor actions. During functional movements, the jaw changes position continually, which requires appropriate proprioception. However, the significance of the various proprioceptive receptors involved and how they interact is not yet fully clear. OBJECTIVES: This study's main objective was to test whether preventing intercuspation (IC) for 1 week would affect the precision of jaw-closing movements into IC and the functional space of habitual chewing movements (HCM). A secondary objective was to compare precision of jaw-closing movements into IC with the precision of movements into a target position (TP) far from IC. METHODS: Fourteen participants' HCM and jaw-closing movements into IC were recorded on two sessions (T1 and T2) 1 week apart. Between sessions, participants wore posterior bite plates to prevent IC. They also received a 10-minute training session at T1 to guide their jaw-closing movements into TP. The precision of the closing movements into IC and TP was analysed. For HCM, the vertical amplitude, lateral width and area of chewing cycles were evaluated. RESULTS: The precision of jaw movements into IC increased as the jaw gap decreased, but precision did not differ significantly between T1 and T2. For HCM, the vertical amplitude and area of chewing cycles increased significantly between T1 and T2. The precision of the closing trajectory into TP increased significantly during the training session. CONCLUSION: Our results confirm the excellent adaptability of the craniomandibular system, controlled by stringent motor programmes that are supported by continuous peripheral sensory input.