Temporomandibular joint morphology changes with mandibular advancement surgery and rigid internal fixation: a systematic literature review.

The purpose of this systematic review was to evaluate the effect of bilateral sagittal split mandibular osteotomy (BSSO) with rigid internal fixation (RIF) on temporomandibular joint (TMJ) morphology. Controlled trials of BSSO with RIF treatment of Class II patients using transcranial radiographs, submental vertex (SMV) radiographs, tomographic radiography, computed tomography (CT) scan, or magnetic resonance imaging (MRI) to assess TMJ morphology were identified by Medline (1966-2001) and PubMed. Case reports were excluded. On the basis of our search only six studies were included in this review. All studies used internal controls with pre- and posttreatment imaging. Two studies used SMV, one used transcranial radiographs, one used tomography, two used CT scan and one used MRI. Methodological deficiencies prevent major conclusions regarding osseous remodeling and disk status. There was a wide range of individual variability in condyle position change. The reviewed studies have highlighted the importance of further research. Prospective controlled studies using serial MRI and tomography or CT scan are required to establish effect of BSSO with RIF on TMJ morphology.

A comparison of dynamic and static testing of latex and nonlatex orthodontic elastics.

The purpose of this study was to determine the effects of repeated stretching (cyclic testing) and static testing on the force decay properties of two different types of orthodontic elastics from a single supplier. Samples of American Orthodontics' 0.25 inch, 4.5 oz (6.35 mm, 127.5 g) latex and nonlatex elastics were used and a sample size of 12 elastics per group was tested. Static testing involved stretching the elastics to three times marketed internal diameter (19.05 mm) and measuring force levels at intervals over 24 hours. Cyclic testing used the same initial extension but cycled the elastics an additional 24.7 mm to simulate extension with maximal opening in the mouth. Both types of elastic had similar initial forces that were statistically below the marketed force (122 and 118 g for latex and nonlatex elastics, respectively) at three times marketed internal diameter. Cyclic testing caused significantly more force loss and this difference occurred primarily within the first 30 minutes. For statically tested elastics the percentage of initial force remaining at 4, 8, and 24 hours was 87%, 85%, 83%, and 83%, 78%, 69% for latex and nonlatex elastics, respectively. For cyclically tested elastics the percentage of initial force remaining at 4, 8, and 24 hours was 77%, 76%, 75%, and 65%, 63%, 53% for latex and nonlatex elastics, respectively.

An in vitro comparison of 4 brands of nonlatex orthodontic elastics.

The purpose of this study was to compare 4 brands of nonlatex orthodontic elastics with respect to initial force produced and force decay over a 24-hour period. Sample sizes of 12 elastics from American Orthodontics (Sheboygan, Wis), Ortho Organizers (San Marcos, Calif), GAC International (Islandia, NY), and Masel (Bristol, Pa) were used. Equivalent or near-equivalent products were tested: the quarter-in (6.35 mm), 4 or 4.5 oz (113 or 128 g) elastics from each company. An apparatus that repeatedly cycled the elastics to simulate interarch usage with chewing was used to measure force decay over a 24-hour period. Results showed a wide range of initial forces between the brands at an extension of 3 times the marketed internal diameter. The elastics from American Orthodontics, Ortho Organizers, and Masel generated forces statistically below their marketed force levels at 3 times their marketed internal diameter extensions. GAC elastics generated significantly higher forces than marketed at 3 times internal diameter extension. All elastics generated forces below those marketed at 2 times internal diameter. Initial force production was significantly correlated with the measured cross-sectional area of the elastics (P <.01). The force decay patterns of all brands were very similar, but there were significant differences in their abilities to withstand testing. Grouped average percentages of initial force at 4, 8, and 24 hours were 68%, 61%, and 49%, respectively, for the elastics that did not break during testing.