A comparative study on inherited tooth morphology characters, in particular the incidence of Carabelli tubercles in the maxillary dentition, was conducted on standardized stone casts obtained from 240 Japanese (124 males (male) and 116 females (females)) and 160 Chinese (74 male, 86 female) young adults. The following results were obtained: 1) No significant differences in the incidence of Carabelli tubercles according to sex or body height were found between the two groups. 2) However, significant differences in the incidence of Carabelli tubercles according to sex were found in both groups. The tubercles occurred more frequently in males. 3) Significant differences between the bilateral and unilateral occurrence of Carabelli tubercles were observed in both the Japanese (p < 0.05) and Chinese (p < 0.01) groups; Carabelli tubercles on upper first molars were always bilateral. 4) The highest incidence of Carabelli tubercles was found in individuals with a body height of 166 approximately 175 cm in both groups, and a significant difference (p < 0.05) between the 156 approximately 165 cm and 166 approximately 175 cm groups was particularly evident in the Japanese adults. The authors postulate that bilateral occurrence of Carabelli tubercles was originally an inherited character in the molar region, but that the character was inhibited during the process of evolution of the masticatory system and regression of the molar dentition.

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Abstract:Elastic system fibers (ESFs) of the mandibular condyle were studied by histochemical methods, light and electron microscopy and quantitative techniques . Three different types of fibers were observed : oxytalan, elaunin and elastic fibers. The fine oxytalan fibers appeared at 16 days insemination age and completed their distribution at 18 days insemination age, then the elaunin fibers appeared. However, the elastic fibers were not observed until 1 day after birth. The fibers formed a fibrillar network at the lateral aspect of the mandibular disc , and became continuous with the epimysium of the external pterygoid muscle medially. Quantitatively the elastic fibers of the disc increased markedly in the lactation, and after the weaning period the fibers decreased. Furthermore , distribution of the elastic fibers changed with that of collagen fibers by the time mice reached physiological maturity.

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Summary: Elastic system fibers (ESFs), i.e., microfibrils (putative oxytalan fibers), elaunin and elastic (true elastin) fibers, in the rat mandibular joint were studied mainly using scanning electron microscopy (SEM) and light microscopy (LM) with the aid of image processing. The present quantitative analysis using LM showed that the articular disc and capsule, which are the sites that receive physical compressive force during mastication, contained more ESFs than the articular cartilage of the mandibular joint. In addition, oxytalan fibers were the principal ESFs in all the articular components (capsule, articular disc, supraosseous layer of articular surfaces and articular cartilage). Subsequently, ESFs in the articular disc, which contained more thick ESFs, were closely examined by SEM using both collagen-and elastin-digestion methods. SEM showed networks of microfibrils beneath the articular surfaces (superior and inferior layers) in the thin central portion of the articular disc; the principal microfibrils ran at nearly right angles to the collagen fibers. The microfibrils were cemented with amorphous elastin, thickened and shifted towards interconnecting oblique fibers and many main ESF trunks, which were oriented in the direction of the layered wavy collagen fibers and parallel to the direction of applied force, to sustain the mechanical force. From the superior and inferior layers, the main ESFs shisfted towards the middle portion of the disc, transitional zone (synovial osteochondral junction) and the other articular components, showing no specific directivity. Transmission mission electron microscopy revealed that the thick main ESFs in the elastic network were elaunin fibers. The present study indicated that ESFs unite, branch and therefore construct an extensive and complicated protective stretchable network, which is interposed with the less tensible collagen network in the mandibular articular disc.Elastin system fibers (ESFs), which are usually differentiated as microfibrils (oxytalan fibers), elaunin and elastic fibers based on their staining properties and the distribution of the microfibrils and amorphous cementing elastin, play a particularly important role in the elasticity of connective tissue (CottaPereira,