ABSTRACT
The purpose of this investigation was to evaluate the existence of third molar germs in orthodontic patients in Japan and to examine the relationship between the existence of third molars and sagittal maxillomandibular jaw relationships. The subjects comprised 306 patients from the orthodontic clinic of Hokkaido University Dental Hospital who were younger than 15 years. The subjects were divided into 2 groups: 1 group included 144 patients who were born between 1966 and 1969 (60s group), and the other group included 162 patients who were born between 1980 and 1987 (80s group). Assessments were made from panoramic radiographs and lateral cephalograms. The following results were obtained: (1) all 4 third molar germs were present in 77% of subjects, (2) mandibular third molars were present significantly more often than maxillary third molars, and (3) the percentage of skeletal Class III subjects who had all 4 third molars was lower than that of skeletal Class II subjects. The chi(2) test was used to determine statistical significance in differences.
Subject(s)
Malocclusion/classification , Molar, Third/anatomy & histology , Tooth Germ/anatomy & histology , Adolescent , Cephalometry , Chi-Square Distribution , Child , Female , Humans , Japan , Male , Malocclusion/diagnostic imaging , Malocclusion, Angle Class II/diagnostic imaging , Malocclusion, Angle Class II/pathology , Malocclusion, Angle Class III/diagnostic imaging , Malocclusion, Angle Class III/pathology , Mandible , Maxilla , Molar, Third/diagnostic imaging , Orthodontics, Corrective , Radiography, Panoramic , Tooth Eruption , Tooth Germ/diagnostic imaging , Tooth, Impacted/diagnostic imagingABSTRACT
A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), fibrous fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC).
