Note: A portable laser induced breakdown spectroscopy instrument for rapid sampling and analysis of silicon-containing aerosols.

A portable instrument has been developed for measuring silicon-containing aerosols in near real-time using laser-induced breakdown spectroscopy (LIBS). The instrument uses a vacuum system to collect and deposit airborne particulate matter onto a translatable reel of filter tape. LIBS is used to analyze the deposited material, determining the amount of silicon-containing compounds present. In laboratory testing with pure silica (SiO2), the correlation between LIBS intensity for a characteristic silicon emission and the concentration of silica in a model aerosol was determined for a range of concentrations, demonstrating the instrument's plausibility for identifying hazardous levels of silicon-containing compounds.

A comparative study of Caucasian and Japanese mandibular clinical arch forms.

The purpose of this study was to clarify morphological differences between Caucasian and Japanese mandibular clinical arch forms in Class I, II, and III malocclusions. The study included 60 Class I, 50 Class II, and 50 Class III cases from each ethnic group. The most facial portion of 13 proximal contact areas was digitized from photocopied images of the mandibular dental arches. Clinical bracket points were calculated for each tooth based on mandibular tooth thickness data. Four linear and 2 proportional measurements were taken. The dental arches were classified into square, ovoid, and tapered forms to determine and compare the frequency distributions between the 2 ethnic groups. The Caucasian population had a statistically significant decreased arch width and increased arch depth compared with the Japanese population. When the subjects were regrouped by arch form, no statistically significant difference in arch dimension was observed between the 2 ethnic groups in any of the arch form samples. Our results suggest that there is no single arch form specific to any of the Angle classifications or ethnic groups. It appears to be the frequency of a particular arch form that varies among Angle classifications or ethnic groups.

The extraction-nonextraction dilemma as it relates to TMD.

Extraction has been a controversial subject for as long as the specialty of orthodontics has existed. Some authors believe that the extraction of premolars leads to temporomandibular disorders. This occurs, they say, because the vertical dimension collapses. Concomitantly, over-retraction and retroclination of the incisors cause the facial profile to flatten, bring about premature anterior contacts, and distally displace the mandible and mandibular condyle. Numerous correlation studies in the dental literature do not support this contention. There appears to be no higher incidence of temporomandibular disorders in patients treated with the extraction of premolars than in nontreated patients or those treated without extractions. Analysis of premolar extraction cases reveals that there is no collapse of the vertical dimension; on the contrary, the vertical dimension is either maintained or slightly opened. Similarly, there is no evidence that premolar extraction causes undesirable flattening of the facial profile. The facial profile established during treatment is primarily the result of diagnosis and treatment mechanics. Excessive anterior interferences resulting in possible posterior condyle displacement are the result of treatment mechanics. When arches are leveled properly and space closure and overjet reduction are adequately controlled, there is no reason that such interferences should occur.

Malocclusion and the temporomandibular joint--an historical perspective.

A review of changing attitudes and information on temporomandibular joint disorders, with a compilation of clinical conditions that can contribute to such problems.