A preliminary report on the effect of a mandibular advancement device on obstructive sleep apnea using magnetic resonance imaging and polysomnography.

This preliminary study investigated the effect of a mandibular advancement device on upper airway collapsibility in seven patients with obstructive sleep apnea. Overnight polysomnography and dynamic magnetic resonance imaging were performed at the retropalatal and retroglossal levels, and the apnea-hypopnea Index(AHI), anteroposterior and lateral distances, and airway volumes were recorded. The tests were repeated following a 3-month period of wearing a customized mandibular advancement device. A significant reduction in AHI (from 31 events per hour to 18.2 events per hour) and improvement in airway dimension at both the retropalatal and retroglossal levels were recorded, suggesting a baseline record for future studies with a larger patient sample.

Finite element analysis of stresses in fixed prosthesis and cement layer using a three-dimensional model.

CONTEXT: To understand the effect of masticatory and parafunctional forces on the integrity of the prosthesis and the underlying cement layer. AIMS: The purpose of this study was to evaluate the stress pattern in the cement layer and the fixed prosthesis, on subjecting a three-dimensional finite element model to simulated occlusal loading. MATERIALS AND METHODS: Three-dimensional finite element model was simulated to replace missing mandibular first molar with second premolar and second molar as abutments. The model was subjected to a range of occlusal loads (20, 30, 40 MPa) in two different directions - vertical and 30° to the vertical. The cements (zinc phosphate, polycarboxylate, glass ionomer, and composite) were modeled with two cement thicknesses - 25 and 100 µm. Stresses were determined in certain reference points in fixed prosthesis and the cement layer. STATISTICAL ANALYSIS USED: The stress values are mathematic calculations without variance; hence, statistical analysis is not routinely required. RESULTS: Stress levels were calculated according to Von Mises criteria for each node. Maximum stresses were recorded at the occlusal surface, axio-gingival corners, followed by axial wall. The stresses were greater with lateral load and with 100-µm cement thickness. Results revealed higher stresses for zinc phosphate cement, followed by composites. CONCLUSIONS: The thinner cement interfaces favor the success of the prosthesis. The stresses in the prosthesis suggest rounding of axio-gingival corners and a well-established finish line as important factors in maintaining the integrity of the prosthesis.

Effect of a palatal lift prosthesis in individuals with velopharyngeal incompetence.

PURPOSE: The aim of this study was to assess the effect of a palatal lift prosthesis (PLP) on the speech intelligibility of cleft palate patients treated with pharyngeal flap surgery, the minimum duration required for improvement in nasality, and the sustenance of speech improvement after removing the appliance. MATERIALS AND METHODS: Seven patients ranging between 16 and 26 years of age were recruited for this study. These subjects had velopharyngeal dysfunction secondary to a surgically corrected cleft palate, which failed to improve following pharyngeal flap surgery. A PLP was given to these patients and improvements in speech intelligibility were assessed using two speech examinations: perceptual analysis and nasometry. The nasal resonance, nasal air emission, and articulation were measured prior to the insertion of the prosthesis and at the end of every month for the next 3 months, following which the prosthesis was removed and the tests were repeated. RESULTS: There was a statistically significant decrease in nasalance percentage at the end of the 3 months, and it was found that this improvement in speech persisted even after the removal of the prosthesis. CONCLUSIONS: A PLP, when used for a minimum duration of 3 months, causes a significant decrease in nasal resonance, thereby improving speech intelligibility in patients who failed to see improvement following pharyngeal flap surgery for velopharyngeal incompetence.