The frequency of accessory mental foramina in four ethnic groups.

The frequency of accessory mental foramina (AMF) was studied in four population groups: 20th century Asian Indians, African Americans and American Whites, and Pre-Columbian Nazca Indians. AMF were found less frequently in the American White and Asian Indian populations than in the other groups (American White, 1.4%; Asian Indian, 1.5%; African American, 5.7% and Nazca, 9.0%). The incidence of AMFs did not differ significantly between right- and left-hand sides. In certain ethnic groups, i.e., African American, AMF may occur more often in males. Additional studies with larger samples are needed to show whether AMFs are more common in males.

Styloid chain ossification: report of a case with articulations.

A bilateral ossified stylohyoid ligament was observed in a cadaver specimen. On the left side, the stylohyoid chain was markedly enlarged. The stylohyoid ligament was completely ossified into two segments separated by a diarthrodial-like joint. An articulation was also observed between the enlarged styloid process and the ossified ligament. On the right side, the styloid process had a normal appearance. The middle part of the stylohyoid ligament was ossified and it was attached to the styloid process and to the hyoid bone by a fibrous band. Proposed theories to account for the ossification of this ligament are discussed. Since the presence of an enlarged and ossified stylohyoid chain can cause much discomfort and pain, a greater understanding of the causative factors responsible for this anomaly is needed to provide for more effective diagnosis and treatment.

Dens evaginatus in a Chilean population.

A high rate of occurrence on dens evaginatus (DE) is reported in certain cultural groups in a Chilean population. Factors affecting the reported incidence of DE are discussed as are the clinical complications and treatment requirements related to this anomaly.

Retromolar foramen: a mandibular variant important to dentistry.

The retromolar foramen (RMF) was found to occur in eighteen of 234 adult human mandibles studied (7.7%). No statistically significant difference was found between left and right sides or between sexes. A statistical correlation was made between the occurrence of the RMF and accessory mandibular foramina, accessory mental foramina, mandibular third molars, and three-rooted mandibular first molars. Only the accessory mandibular foramen showed a significant positive correlation with RMF regarding same-side occurrence. Three-rooted first molars were not found in any of the mandibles studied. Due to the relatively frequent occurrence of RMF, it is important for the dental practitioner to be aware of this variant and the possible complications which may occur during the administration of anesthesia and surgical procedures in the region.

Mylohyoid and jugular foramen bridging in pre-Columbian Chileans.

The occurrence of mylohyoid groove bridging and jugular foramen bridging was determined in a population of adult Pre-Columbian Chileans. Two hundred forty-one crania (110 males, 131 females) were examined for jugular foramen bridging and 464 mandibles (252 males and 212 females) were observed for mylohyoid groove bridging. The overall incidence of jugular foramen bridging was 14.94%, with females showing a higher occurrence (18.32%) than males (10.91%); however, no statistical significance was found between the sexes. The right side showed a greater incidence than the left, but again no statistical difference was noted and the occurrence of this trait was found to be associated between the sides. This frequency of jugular foramen bridging is higher than that found in other studies and approaches that reported in North American Eskimo populations. In the case of mylohyoid groove bridging, the incidence was 4.09% with no difference found between the sexes. This frequency of occurrence is less than the values reported previously for the other American populations of Mongoloid ancestry including the Pre-Columbian Peruvian population. The importance of nonmetric skeletal traits for defining population groups and their usefulness as anthropological tools is discussed. It is concluded that hard tissue variations such as bony bridging may be reliable markers to aid in discretely identifying population groups, but their importance can be significantly enhanced by coupling as many traits as possible in future studies.

Jugular foramen and mylohyoid bridging in an Asian Indian population.

The incidence of jugular foramen and mylohyoid groove bridging was studied in a population of East Asian Indian skulls (125 males and 109 females). The criteria of Dodo (J. Anat. 144:153-165, 1986) was used in the identification of a jugular bridge. There was an overall incidence of 8.1% in jugular foramen bridging, with males showing a higher rate, though the difference did not reach statistical significance. The right side showed a statistically significant greater occurrence than the left, and the trait tended to be associated between sides. The overall incidence of mylohyoid bridging was found to be 2.6%, with no difference observed between the sexes. This frequency is less than the values reported for other Asian Indian studies. Studies concerned with the incidences of nonmetric traits such as bony bridging may be useful in population studies especially when utilized in combination, thereby enhancing the value of each trait as an anthropological tool.

Intercellular bridges in ovaries of the newborn gerbil.

This study describes intercellular bridges in the ovaries of neonatal gerbils. Electron microscopy has revealed the presence of true intercellular bridges, connecting oogonia or oocytes, in ovaries of newborn gerbils. The cytoplasm of the intercellular channels is similar to that of the connected cells, with mitochondria, smooth and rough endoplasmic reticulum, and free ribosomes present. Lysosomes are also occasionally present in the intercellular bridges and they may be involved in early waves of oocyte atresia. An electron-dense substance, 350-500 A thick, is located immediately beneath the unit membrane of the intercellular bridges. Accumulation of electron-dense material increases the thickness of the walls of the intercellular bridges, supporting and maintaining the patency of the channels. It is suggested that the intercellular channels probably allow the interchange of nutrients, organelles, and possibly regulatory materials as well.

Properties of an altered dihydrofolate reductase encoded by amplified genes in cultured mouse fibroblasts.

We have studied a line of 3T6 mouse embryo fibroblasts grown in progressively increasing concentrations of methotrexate. Resistance of cells to low concentrations of the inhibitor (less than 5 X 10(-5) M) is attributed to selective multiplication of the genes coding for dihydrofolate reductase and the resulting elevation of enzyme content. Cells isolated at a higher methotrexate concentration (4 X 10(-4) M) contain high levels of a dihydrofolate reductase with a reduced affinity for methotrexate. The altered dihydrofolate reductase exhibits a 270-fold reduction in binding affinity for methotrexate as measured by equilibrium dialysis (Kd = 5.4 X 10(-8) M versus 2 X 10(-10) M for the wild type enzyme). While binding to NADPH is unchanged, the Km for dihydrofolate is increased 3-fold over wild type enzyme and the turnover number for the reduction of dihydrofolate to tetrahydrofolate is decreased 20-fold. The altered dihydrofolate reductase shows a broader and more predominant acidic peak in its pH profile for this reaction. The molecular weights of the altered and wild type enzymes are identical as determined by sodium dodecyl sulfate-gel electrophoresis, but 2-dimensional electrophoresis reveals a significant basic shift in the migration of the altered enzyme. Studies with various folic acid analogs suggest that modifications involving the para-aminobenzoyl moiety of the inhibitor molecules are associated with the most dramatic differential binding between the altered and wild type dihydrofolate reductases.

The effect of a magnesium deficient diet and cortisone on the growth of the rat incisor.

Incisors of Mg-deficient rats showed a marked inhibition of eruption and a decrease in mitoses of apical tissues. Cortisone administration resulted in some increase in eruption rate and cell division though these remained below the values of Mg-supplemented controls. An improvement in gross condition and a less severe histopathology of incisor tissues were also observed in cortisone-treated rats.

Studies on the attachment of carbohydrate to ovalbumin nascent chains in hen oviduct.

We have examined the question, is the carbohydrate moiety of ovalbumin attached to nascent chains or to the completed protein after its release from polyribosomes. Ovalbumin nascent chains have been isolated from hen oviduct by immunoprecipitation of ovalbumin-synthesizing polysomes and subsequent isolation of peptidyl-tRNA by DEAE-cellulose chromatography. Our results indicate that both glucosamine and mannose are incorporated into ovalbumin nascent chains by hen oviduct fragments. Although the asparagine to which the carbohydrates are attached is 10 amino acid residues from the NH2 terminus, the majority of the carbohydrate, if not all, is attached only to those peptide chains that have been essentially completed.