Three-dimensional reconstruction of soft palate modeling from subject-specific magnetic resonance imaging data.

PURPOSE: The objectives of this study were to extract a computational three-dimensional (3D) soft palate model from a set of magnetic resonance imaging (MRI) data and to identify an approach that generates a patient-specific model in a computerized visual platform. METHODS: Multiple MRI slices of the head and neck region of a young, non-overweight Caucasian male volunteer were taken in the supine position with a passive oral appliance in place. The DICOM (Digital Imaging and Communications) MRI slices were registered into a high-resolution volumetric data set for manually segmentation to generate a surface mesh and, with additional editing, a volume mesh. For biomechanical dynamic simulation and for physical simulation of the anatomical structures, the volume mesh format and multiple landmarks of each muscle were imported into ArtiSynth, a 3D biomechanical modeling toolkit. RESULTS: The segmented soft palate complex consisted of five groups of muscles: levator veli palatini, tensor veli palatini, palatoglossus, palatopharyngeous and musculus uvulae. The palatine tonsil between the pharyngopalatine and glossopalatine arches was included in the segmentation. CONCLUSIONS: The same procedure was used to build up a generic reference model of the dentition, tongue, mandible and airway from a mixture of medical records (CT and dental casts) of the same subject. This manual segmentation method eliminated the common errors that occur from an automatic segmentation although it was more time-consuming. It remains a fundamental process for analyzing the dynamic interaction between anatomical components in the oral, pharyngeal, and laryngeal areas.

Three-dimensional computer-assisted study model analysis of long-term oral-appliance wear. Part 1: Methodology.

INTRODUCTION: The aim of this study was to test a 3-dimensional (3D) computer-assisted dental model analysis system that uses selected landmarks to describe tooth movement during treatment with an oral appliance. METHODS: Dental casts of 70 patients diagnosed with obstructive sleep apnea and treated with oral appliances for a mean time of 7 years 4 months were evaluated with a 3D digitizer (MicroScribe-3DX, Immersion, San Jose, Calif) compatible with the Rhinoceros modeling program (version 3.0 SR3c, Robert McNeel & Associates, Seattle, Wash). A total of 86 landmarks on each model were digitized, and 156 variables were calculated as either the linear distance between points or the distance from points to reference planes. Four study models for each patient (maxillary baseline, mandibular baseline, maxillary follow-up, and mandibular follow-up) were superimposed on 2 sets of reference points: 3 points on the palatal rugae for maxillary model superimposition, and 3 occlusal contact points for the same set of maxillary and mandibular model superimpositions. The patients were divided into 3 evaluation groups by 5 orthodontists based on the changes between baseline and follow-up study models. RESULTS: Digital dental measurements could be analyzed, including arch width, arch length, curve of Spee, overbite, overjet, and the anteroposterior relationship between the maxillary and mandibular arches. A method error within 0.23 mm in 14 selected variables was found for the 3D system. The statistical differences in the 3 evaluation groups verified the division criteria determined by the orthodontists. CONCLUSIONS: The system provides a method to record 3D measurements of study models that permits computer visualization of tooth position and movement from various perspectives.

Three-dimensional computer-assisted study model analysis of long-term oral-appliance wear. Part 2. Side effects of oral appliances in obstructive sleep apnea patients.

INTRODUCTION: Oral appliances (OAs) are widely prescribed for the treatment of obstructive sleep apnea (OSA). The occlusal changes that occur after long term OA treatment have not been well described based on detailed computerized three-dimensional (3D) assessment. METHODS: Seventy patients with OSA (mean age, 50.0 years) who had been treated with an OA were identified for this study. A MicroScribe-3DX dental study model analysis system was used to make 3D measurements on baseline and follow-up (88.4 +/- 26.7 months) study models. RESULTS: The following dental measurements showed significant changes (P <0.05) with long-term use of an OA: mandibular arch width increased more than maxillary arch width, crowding decreased in both arches, the curve of Spee became flat in the premolar area, the mandibular canine to second molar segment moved forward in relation to the maxillary arch, the bite opened and the overjet decreased except in some molar areas. CONCLUSIONS: A variety of occlusal changes occur with long-term OA treatment for OSA. The changes could be regarded as either adverse or beneficial depending upon the baseline characteristics.

Dental changes evaluated with a 3D computer-assisted model analysis after long-term tongue retaining device wear in OSA patients.

Oral appliances (OAs) have been used to treat obstructive sleep apnea (OSA) patients for decades. However, detailed dental side effects in long-term OA cases analyzed with an accurate three-dimensional (3D) measurement tool have seldom been reported. The purpose of this study is to evaluate dental side effects in five OSA patients, who had used a tongue retaining device (TRD) (with occasional other OA wear) for an average of 6 years and 4 months. The baseline and follow-up orthodontic study models were measured with a newly developed MicroScribe-3DX analysis system. High compliance of TRD wear was confirmed in all cases and different patterns and amounts of dental changes were observed. The most common appliance-induced dental changes included anterior and/or unilateral posterior open-bites and reduced anterior overjets. It was hypothesized that there might be two possible mechanisms for the TRD side effects--one is the forward pressure of the tongue upon the anterior dental arch and the other is the lateral pressure of the tongue upon the posterior arch. Considerations to correct the TRD dental side effects should be guided by these different mechanisms of the tongue on the dental arch. Possible solutions to minimize occlusal changes and maximize the benefits for OSA patients are also discussed.