A comparison of the position of the mental foramen in Chinese and British mandibles

The antero-posterior position of the mental foramen was studied in 68 Chinese and 44 British skulls of known or calculated age at death. All skulls showed low pre-mortem tooth loss and had a good occlusion. The position of the foramen was related to the body of the mandible as well as to the standing mandibular teeth using two previously published methods. There was no significant difference in the size of the Chinese and British mandibles. There was a significant difference between the two groups when measurements relating the foramen to the body of the mandible (symphysis menti) were considered, the foraminal position being more distal in the Chinese group. The modal position of the foramen in the Chinese sample was along the long axis of the second premolar, whereas in the British sample it lay between the apices of the first and second premolar. The foraminal position apparently moved distally in both groups with age and this was likely to be associated with mesial tooth drift and age-related attrition.     

A clinical and anatomical study of the location of the mental foramen in adult Chinese mandibles

One hundred mandibles of adult Chinese cadavers of both sexes without missing teeth, alveolar bone resorption and malposition of teeth were studied. The anatomical location of each mandibular mental foramen was measured by using a combination of three previous methods. Our results showed that the location of the mental foramen below the apex of the lower second premolar (relation IV: 58.98%) was the most common. On average, the distance between the most anterior portion of the anterior border of the mental foramen and the mandibular symphysis was 28.06 mm, between the most anterior portion of the anterior border of the mental foramen and the posterior border of the ramus 74.14 mm, between the inferior border of the mental foramen and the lower border of the mandibular body 14.70 mm, between the superior border of the mental foramen and the bottom of the lower second premolar socket 2.50 mm. The distance across the mental foramen between the alveolar crest and the lower border of the mandibular body was 30.29 mm. Our results were compared with those of other investigators. The significance of identifying the anatomical location of the mental foramen in dental practice is discussed.     

Relation of the mental foramen to teeth on the mandibles belonging to the Byzantium period

Fifty mandibles belonging to the Byzantium period were studied in order to determine to racial differences about of the localization of the mental foramen according to the mandibular teeth. Mandibles of adult males without missing teeth, proximal decay and proximal attrition were used. On the right side, the most common position of the mental foramen was between the first and second lower teeth (50%), whereas on the left side, the most common position was in line with the longitudinal axis of the lower second premolar tooth (46%). Because of materials including mostly Alpine's and a few of Mediterranean subraces, two different positions of the mental foramen were determined in high similar ratios.     

Tooth wear and the position of the mental foramen

Variation in the position of the mental foramen with respect to the teeth ("apparent" position) seems to be associated with race, but in the determination of this position, factors which affect the disposition of the teeth plainly have a bearing on the results. The apparent position was investigated in a sample of southern Chinese skulls of known age which were classified by the degree of tooth wear. Controlling for "true" position and size of the mandible, a highly significant correlation between wear and position was found, age and tooth size having no significant contribution as additional explanatory variables. The effect of tooth wear on the apparent position of the foramen may partly explain racial variation.     

Ontogenetic migration of the mental foramen in Neandertals and modern humans

Since the nineteenth century, researchers have noted that Neandertal and modern human adults differ in mental foramen position, although the ontogenetic changes in the position of this feature have only recently come under the scrutiny of paleoanthropologists. Research on mental foramen position has focused on whether this feature is inferior to a particular tooth. However, tooth position may not be a reliable indicator of mental foramen position because of variability in tooth size within and between taxa and during eruption events. As opposed to observing the mental foramen with respect to the postcanine teeth, we examined linear distances from the mental foramen to other mandibular landmarks. Modern human adults may appear truncated, or paedomorphic, in mental foramen position with respect to Neandertal adults. However, infants of the two taxa differ substantially in anterior mandibular form. The initial differences in the shape of the mental region may be related to the embryological position of the mental foramen in modern humans and its role in the development of the mental trigone. The shape changes that accrue thereafter, possibly from faster mandibular growth rates in Neandertals, further distinguish the adults from one another. Although mandibular shape differences exist from early infancy onwards, adults of the two taxa are broadly similar in bi-mental foramen breadth with respect to mandibular size. For this reason, qualitative assessments of mental foramen position may provide less taxonomic information than previously thought.     

Absence of foramen spinosum and abnormal middle meningeal artery in cranial series

In comparative and evolutionary aspects in humans, the middle meningeal artery enters the cranium through the foramen spinosum, whereas in great apes the middle meningeal artery can enter the cranium through foramen spinosum, through foramen ovale or through petrosphenoid fissure. Generally, in nonhuman primates the anterior meningeal system is associated with the ophthalmic branch of the internal carotid artery. The vessels joining the two systems pass through the additional channels: the superior orbital fissure or through the cranio-orbital foramen. In anatomically modern humans, the absence of foramen spinosum involves abnormal development and course of the middle meningeal artery and it is usually accompanied with replacement of the conventional middle meningeal artery with such, arising from the ophthalmic artery system. In these cases the middle meningeal artery most often enters the middle cranial fossa through the superior orbital fissure and rarely through the meningo-orbital foramen. All skulls, investigated in the present study, belonged to adult individuals of both sexes, conditionally grouped into three cranial series--contemporary male, medieval male, and medieval female series. The absence of foramen spinosum was established only among the medieval male and female series--in 1 (0.70%) male and in 1 (0.72%) female skull on the right side and in 3 (2.13%) female skulls on the left side. In 1 (0.72%) female skull, a small atypically located foramen spinosum was established on the right side. In all of the described cases, the intracranial meningeal grooves started from the lateral edge of the superior orbital fissure and probably reflect the ophthalmic origin of the middle meningeal artery.     

Influence of teeth, alveoli, and periodontal ligaments on torsional rigidity in human mandibles.

We investigated the influence of teeth, periodontal ligaments, and alveoli on the structural integrity of human mandibles loaded in torsion. Surface bone strain was recorded from the mandibular corpus below the first molar on each of four specimens. These specimens were loaded by an external force that caused primarily torsion about the long axis of the corpus, and bone strain was recorded under the following conditions: 1) all supporting structures intact, 2) all supporting structures intact and the M1 loaded by a simulated bite force, 3) M1 removed and 4) alveolar bone of the M1 removed. For comparative purposes, experiments were also designed to investigate the effects of intermittent holes on the torsional rigidity of a baboon femur. This permitted comparison of the mechanical behavior of the mandibles with that of a more homogeneous bony member. These experiments suggest that the presence of teeth within alveoli has a measurable role in the maintenance of torsional rigidity. The condition of the periodontal ligament also appears to influence these stress-bearing capabilities. Moreover, the alveolar bone supporting the teeth also provides structural support for countering torsional loads. For the specific case of corpus twisting, the mandible does not behave as a member with open or closed sections as predicted by theoretical models. The observed magnitudes of bone strain, however, conform more closely to the predictions generated by a closed-section model.     

Absence of tRNA-guanine transglycosylase in a human colon adenocarcinoma cell line.

Queuosine (Q), found exclusively in the first position of the anticodons of tRNA(Asp), tRNA(Asn), tRNA(His) and tRNA(Tyr), is synthesized in eucaryotes by a base-for-base exchange of queuine, the base of Q, for guanine at tRNA position 34. This reaction is catalyzed by the enzyme tRNA-guanine transglycosylase (EC 2.4.2.29). We measured the specific release of queuine from Q-5'-phosphate (queuine salvage) and the extent of tRNA Q modification in 6 human tumors carried as xenografts in immune-deprived mice. Q-deficient tRNA was found in 3 of the tumors but it did not correlate with diminished queuine salvage. The low tRNA Q content of one tumor, the HxGC3 colon adenocarcinoma, prompted us to examine a HxGC3-derived cell line, GC3/M. GC3/M completely lacks Q in its tRNA and measurable tRNA-guanine transglycosylase activity; the first example of a higher eucaryotic cell which lacks this enzyme. Exposure of GC3/M cells to 5-azacytidine induces the transient appearance of Q-positive tRNA. This result suggests that at least one allele of the transglycosylase gene in GC3/M cells may have been inactivated by DNA methylation. In clinical samples, we found Q-deficient tRNA in 10 of 46 solid tumors, including 2 of 13 colonic carcinomas.     

Calcite in the mandibles of a marine polychaete

Calcite forms a thick pad on the anterior-ventral surface of the mandibles of Eunice aphroditois (Pallas) (Annelida, Polychaeta, Eunicida, Eunicea). The calcite pads apparently serve as an abrasive in feeding; they are possibly renewed by continuous calcite deposition. Mandibular calcite pads are not usually recognized in the fossil record because they are destroyed during the leaching of limestones for the recovery of scolecodonts.     

A population study of the jugular foramen bridging of the human cranium

The author previously proposed a simple standard for diagnosing the jugular foramen bridging in man. The incidence of this bridging trait was investigated according to that standard in nine cranial series of East Indians, Micronesians, Japanese, Ainu, Mongols, Aleuts, Alaskan Eskimos, Canadian Eskimos, and Ontario Iroquois. No sex difference in incidence of the trait was recognized. Side difference in trait incidence was also slight but was statistically significant in the combined series of all the population samples examined. The bridging trait occurred more frequently on the right side than on the left side. Occurrences of the bridging trait were definitely associated between sides. Incidence of the trait was less in East Indians, Ontario Iroquois, and Micronesians, but greater in Alaskan Eskimos and Canadian Eskimos, the incidences in Japanese, Ainu, Aleuts, and Mongols being intermediate. The differences in trait incidence among the nine population samples were considered to reflect the differences in genetic compositions of these specific populations.