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PubMed2006

Quantitative analysis of human mandibular shape using three-dimensional geometric morphometrics.

Human mandibular morphology is often thought to reflect mainly function, and to be of lesser value in studies of population history. Previous descriptions of human mandibles showed variation in ramal height and breadth to be the strongest difference among recent human groups. Several mandibular traits that differentiate Neanderthals from modern humans include greater robusticity, a receding symphysis, a large retromolar space, a rounder gonial area, an asymmetric mandibular notch, and a posteriorly positioned mental foramen in Neanderthals. Nevertheless, the degree to which these differences are part of modern human variation and/or are related to size and function remains unclear. The aim of this study was to document geographic and functional patterning in the mandibular shape of recent humans, to assess the effects of allometry on mandibular form, and to quantitatively evaluate proposed "Neanderthal" mandibular traits through comparison with samples of geographically diverse recent humans. Data were collected in the form of three-dimensional coordinates of 28 landmarks. Unlike previous studies, this analysis found that modern human mandibular shape exhibits considerable geographic patterning, with some aspects of mandibular morphology reflecting a climatic gradient, and others, a functional specialization. Population history is also reflected in mandibular form, albeit relatively weakly. Proposed "Neanderthal" traits were found to separate Neanderthal from modern human mandibles successfully in the statistical analysis. Of these, the retromolar gap was found to be related to increased mandibular size in modern humans. The status of this trait as a Neanderthal autapomorphy should therefore be treated with caution.

Anatomy, Comparative↗
PubMed1993

Developmental differences in the ossification process of the human corpus and ramus mandibulae.

A correlation was sought between the organization of the dental crest and the ossification of the corpus mandibulae in 14 human embryos and 13 human fetuses. The different types of ossification between the corpus and the ramus mandibulae suggest that the cartilago mandibularis (meckeliensis) guides the formation of the mandibula, while the dental crest acts as a coorganizer. In the area of the foramen mentale, the lamina dentalis begins to invaginate (to give rise to the dental crest), and at this level intramembranous ossification of the corpus mandibulae commences. These findings, together with the presence of the cartilago mandibularis before the appearance of the dental crest, and the fact that the former is seen along the entire length of the mandibula (from the symphysis mandibulae to the capsula otica), support the hypothesis that the dental crest, rather than the cartilago mandibularis, acts as the coorganizer in the corpus mandibulae.

Cartilage↗
PubMed1994

Meckel's cartilage in the human embryo and fetus.

This work studied the development of the ventral part of Meckel's cartilage in a series of human embryos (classified in stages) and fetuses. These stages appeared particularly important: stage 16, appearance of Meckel's cartilage; stage 20, beginning of membranous ossification of mandible; and stage 23, end of the embryonic period (8th week). The primitive bony nodule which develops from the embryonic mesenchyme appears as a double bony layer forming a groove containing the neurovascular bundle, into which the dental lamina is also invaginated. It was concluded that during the fetal period, the cartilage participates in the formation of the body of the mandible in an area close to the mental foramen via endochondral ossification. The cartilage disappears in parallel with the development of ossification by the sixth month.

Cartilage↗
PubMed2004

Geometric morphometric analysis of allometric variation in the mandibular morphology of the hominids of Atapuerca, Sima de los Huesos site.

Allometry is an important factor of morphological integration that contributes to the organization of the phenotype and its variation. Variation in the allometric shape of the mandible is particularly important in hominid evolution because the mandible carries important taxonomic traits. Some of these traits are known to covary with size, particularly the retromolar space, symphyseal curvature, and position of the mental foramen. The mandible is a well studied system in the context of the evolutionary development of complex morphological structures because it is composed of different developmental units that are integrated within a single bone. In the present study, we investigated the allometric variation of two important developmental units that are separated by the inferior nerve (a branch of CN V3). We tested the null hypothesis that there would be no difference in allometric variation between the two components. Procrustes-based geometric morphometrics of 20 two-dimensional (2D) landmarks were analyzed by multivariate regressions of shape on size in samples from 121 humans, 48 chimpanzees, and 50 gorillas (all recent specimens), eight fossil hominids from Atapuerca, Sima de los Huesos (AT-SH), and 17 Neandertals. The findings show that in all of the examined species, there was significantly greater allometric variation in the supra-nerve unit than in the infra-nerve unit. The formation of the retromolar space exhibited an allometric relationship with the supra-nerve unit in all of the species studied. The formation of the chin-like morphology is an "apodynamic" feature of the infra-nerve unit in the AT-SH hominids. The results of this study support the hypothesis that allometry contributes to the organization of variation in complex morphological structures.

Animals↗
PubMed2006

Radiological trace of mandibular primary growth center in postnatal human mandibles.

The mandibular primary growth center (MdPGC) of human fetus was conspicuously defined in the soft X-ray view of fetal mandibles. As the peripheral adaptive growth of mandible advances during the postnatal period, the MdPGC image became overshadowed by condensed cortical bones in soft X-ray view. In this study, we traced a sclerotic sequela of MdPGC during the postnatal period. Panoramic radiograms of 200 adults and soft X-ray views of 30 dried adult mandibles were analyzed by statistical methods. The former clearly showed an MdPGC below the middle portion of apices of canine and first premolar, which was distinguishable from mental foramen, and the latter also showed the MdPGC at the same area as a radiating and condensed radiopaque image, measuring 0.5-1.0 cm in diameter. This MdPGC position was seldom changed in the elderly people, even in the edentulous mandibles. Additionally, in the radiological examination, the benign tumors including odontogenic cysts hardly involved the MdPGC, while the malignant tumors of both primary and metastatic cancer frequently destroyed the MdPGC.

Adolescent↗
PubMedDate not supplied

Mandibular osteotomy in the surgical approach to the oral cavity.

The improved stability that results from the combination of K-wire transfixion of a mandibular osteotomy with direct wiring has made it possible to use a straight, as opposed to a stepped, bone cut and to avoid the invariable need for dental extractions. It has also made possible an alternative osteotomy site, immediately anterior to the mental foramen. The use of this site allows mandibular swing to take place after division only of mucous membrane and mylohyoid. It is best combined with a modified lip-splitting incision which has been found to improve ultimate cosmesis.

Humans↗
PubMed1983

Assessment of adult skeletons to detect prenatal exposure to acetazolamide in mice.

A skeletal variant assay system (SVAS) consisting of a group of 88 spontaneously occurring qualitative variations of the adult mouse skeleton was applied to CD-1 animals that had been exposed in utero to 0, 200, or 1,000 mg/kg/day of the sodium salt of acetazolamide dissolved in distilled water, presented by SC injection of the dam during day 8 or days 9-11 of gestation. Two separate series of experiments were performed, and skeletons were examined at postnatal 62 +/- 2 days. Variation occurred in 62 and 67 characters in the two series. Frequencies of occurrence differed from untreated (UNTD) and vehicle-treated (VEH) values of substantial numbers of variants in a dose related manner for both series in both treatment regimes as did the number of variants which showed significantly different frequencies (P less than .01) in comparisons of experimental with either UNTD or VEH. At the high doses 12 and 16 variants occurred with significantly different frequencies from UNTD in day 8 treatments in the two series, and 15 and 19 variants differed in the days 9-11 treated group. Contrasting high-dose animals with appropriate vehicle controls revealed differences in 13 and 12 variants in day 8 treatment groups and in 18 and 15 variants in days 9-11 groups. Agreement between the two series was good, especially in the D9-11 treatments. Several variants differed significantly from both UNTD and VEH in both series of experiments. Among these were a number which appeared more or less specific to acetazolamide exposure. They include: day 8 treatments--accessory parietal, frontal extension, and 27 presacral vertebrae; day 9-11 treatments--sacral fusions in dorsal processes and vertebral bodies, and caudal fusions and malformations; both sets of treatments--lumbar fusions, and fusions of the transverse processes of the sacral vertebrae. Other importantly affected variants, also seen in exposure to other compounds include: day 8 treatments--abnormal metoptic roots; day 9-11 treatments--accessory mental foramen, foramina transversaria imperfecta of the atlas, arch foramen of the fifth cervical (C) vertebra, malformed sternebrae, fossa olecrani perforata, and fewer than 30 caudal vertebrae; both treatment regimes--parted frontals, accessory transverse foramina in C3-C6, reduced articular processes on the thoracic vertebrae, and 14 ribs. By all criteria applied, the SVAS is able to detect prenatal exposure to acetazolamide in adult skeletons even in the absence of any gross morphological abnormalities.

Acetazolamide↗
PubMedDate not supplied

A gradient of size and shape for the Atapuerca sample and Middle Pleistocene hominid variability.

The Atapuerca sample reveals that differential development of morphology of distinct areas of the mandible gives rise to a spectrum of morphology which virtually encompasses the entire range of variability detected in European Middle Pleistocene samples. Two new mandibles collected at Atapuerca SH site (Spain) give new insight into this matter. Specimen AT-950 demonstrates that there is a continuum between the peculiar morphology of Mauer and other Middle Pleistocene specimens. Specimen AT-888 increases the size range, and also sheds light on the significance of traits such as the retromolar space and the position of the mental foramen.

Animals↗
PubMed2002

Middle Pleistocene human remains from the Bau de l'Aubesier.

Excavations in later Middle Pleistocene levels at the Bau de l'Aubesier, Vaucluse, France yielded a maxillary molar (M(1) or M(2); Aubesier 10) and a partial mandible from the left C(1) alveolus to the right condylar base lacking the coronoid process (Aubesier 11). Dentally they are similar to other later Middle Pleistocene Europeans in dental dimensions and variable taurodontism (Aubesier 10 but not Aubesier 11). The small Aubesier 11 mandible exhibits a retreating symphyseal profile with a minimal tuber symphyseos, an anterior marginal tubercle at P(4)/M(1), the mental foramen at P(4)/M(1)-M(1), a modest retromolar space, no lingular bridging of the mandibular foramen, an enlarged superior medial pterygoid tubercle, a modest lateral condylar tubercle, and a mandibular notch crest that intersects the middle third of the condylar margin. All of these features fall within the ranges of variation of later Middle Pleistocene Neandertal lineage humans, and some are characteristic of Middle Pleistocene human mandibles in general. In addition, Aubesier 11 exhibits pervasive ante mortem alveolar resorption with apical abscesses, alveolar bone destruction, universal labial/buccal bone loss, ante mortem tooth loss (for > or =81.8% of preserved alveoli), a lingual alveolar fenestration, and two broken root apices with masticatory attrition. These lesions indicate significantly impaired masticatory function, the oldest specimen currently known with such a reduced degree of dental function but one of several Middle Pleistocene human remains with indications of serious abnormalities.

Alveolar Bone Loss↗
PubMed1994

Anterior buccal mandibular depression (ABMD). Anatomic and histologic features.

The anterior buccal mandibular depression (ABMD) is a bilateral symmetrical depression located anterior to the mental foramen and extends under the alveoli of the first premolar to the central incisor. The prevalence, dimensions and contents of the ABMD in cadavers of fetuses and adult modern humans were evaluated. ABMD was found in all fetuses and in 31.8% of adults. The average dimensions of the ABMD in adults were depth 2.36 mm, width 5.44 mm and length 12.43 mm. The present study contributes to a better evaluation of the differential diagnosis and treatment planning in the anterior region of the mandible. A possible etiology for the development of ABMD is suggested.

Aged↗
PubMed1994

[Morphometric studies on the fetal development of the human mandible].

Serial sections of eleven human mandibles of embryos and fetuses ranging in size from 18 mm CRL to 66 mm CRL were computer-graphically reconstructed. The extension of the Meckel cartilage and the mandibular bony structures were morphometrically studied. In emphasis the study encompassed measurements portraying length, width, dorsal opening angle, and the position of the mental foramen. In addition five mandibles of human embryos and fetuses with a size range between 30 and 50 mm CRL were radiographically examined. Results showed that in the younger specimens between 21 and 29 CRL size development of the structures of the mandible and the development of overall fetal body size take place independently from each other. During further development a change in the form of the mandible from a wide V over an acute V to a more rounded U form was observed.

Cartilage↗
PubMed2004

Number of teeth and residual alveolar ridge height in subjects with a history of self-reported osteoporotic fractures.

The purpose of this case-control study was to determine if elderly subjects with a history of osteoporotic fractures have fewer teeth and greater residual ridge resorption than subjects without such fractures. Patients older than 60 with a panoramic radiograph were invited to a phone interview. Information was obtained regarding fracture history, smoking, and hormone replacement therapy (HRT). The number of teeth was obtained from the panoramic radiograph. The residual ridge height of the edentulous mandible was measured at the site of the mental foramen. Multiple regression models were used to assess the association between fracture status and number of teeth or residual ridge height (controlling for age, gender, HRT, smoking, height and weight). Cases (n=93) were individuals reporting osteoporotic fractures (fractures occurring after minor impact). Controls (n=394) were individuals reporting traumatic fractures (n=105) or no fractures (n=289). Fracture status in this population affect neither the number of teeth nor the residual ridge height. In the regression model, the variables that had a statistically-significant effect on the number of teeth were age (p<0.0001) and smoking (p<0.0001). There was a dose-effect of smoking on the number of teeth. In the regression model, the variables that had a significantly-significant on residual ridge height (n=95 edentulous subjects) were age and gender. Our conclusion was that in elderly dental-school patients the number of teeth and residual ridge height were not influenced by fracture status. Age and smoking had the most influence; there was no effect from HRT. The clinical implication is that a history of osteoporotic fractures is not an important cause for tooth loss and residual ridge resorption in an elderly dental-school population.

Age Factors↗
PubMed1999

Mineralization density and apparent density of bone in cranial and postcranial sites in the aging human.

This study addressed the question whether bone density of the mandible reflects bone density at other sites. Samples of cranial bone (mandible and parietal bone) and postcranial bone (fourth lumbar vertebral body, iliac crest and femoral neck) from 14 individuals aged 69-96 years were compared. One slice from each bone was used for apparent density determination by weighing it and dividing by a volume calculated as the product of section thickness and the mean area of the two sides of the section. Another slice was embedded in poly(methylmethacrylate) and micromilled to study the mineralization density by quantitative backscattered electron (QBSE) analysis in a scanning electron microscope, rescaling image histograms to the signal range from a monobrominated (0) to a monoiodinated (255) dimethacrylate resin standard. Mandibular QBSE values (e.g., at the mental foramen region 178.0) were much higher (p < 0.0001, paired t-test) than at other sites (parietal, 170.1; fourth lumbar vertebra (L4), 155.4; iliac crest (IC), 155.2; femoral neck (FN), 160.7 units), and correlated only with parietal bone (r = 0.70). Mean QBSE values for the postcranial sites were correlated (L4 with IC, r = 0.63; L4 with FN, r = 0.88; IC with FN, r = 0.59) as were the apparent density values (L4 with IC, r = 0.87; L4 with FN, r = 0.75; IC with FN, r = 0.80). Neither the apparent density nor the mineralization density of the mandible showed a correlation with values for the postcranial sites. The condition of bone in the elderly mandible should not be used to infer status at postcranial sites.

Aged↗
PubMed2006

Anatomic research on the perioral muscles, functional matrix of the maxillary and mandibular bones.

The aim of this research was to study, on the basis of anatomic specimen, the insertion of and the existing correlation between the orbicularis oris, the perioral and the buccinator muscles. Dissections were performed on 40 embalmed caucasian specimens. The skin and the subcutaneous stratum were removed from the perioral zone starting from the base of the nose and the zygomatic arch down to the hyoid bone. The orbicularis oris and the facial muscles were isolated in the successive planes. In the more superficial layer, the following muscles were displayed: the orbicularis oris around the oral opening, the mentalis in the lower part, the transversus menti, the depressor anguli oris and the depressor labii inferioris, the risorius, and the zygomaticus major and minor positioned on the area of the labial commissure. The buccinator muscle was situated under this superficial stratum. In 85% of the specimens we found a fourth inferior band of the buccinator muscle that runs continuously from one side to the other of the mandible. This bundle always ran cranially to the foramen mentale. The findings have been compared with magnetic resonance images obtained from ten patients. One of the main findings was that the majority of these muscles were so densely interrelated that they could be considered parts of two functional units. A deep unit is composed of the buccinator muscle and the inner ring of the orbicularis oris and a superficial unit is built up by the depressor anguli oris, the zygomaticus, the risorius and the outer ring of the orbicularis oris. MR imaging confirmed these findings.

Cadaver↗
PubMed2003

Prenatal development of the human mandible. 3D reconstructions, morphometry and bone remodelling pattern, sizes 12-117 mm CRL.

Human embryos and fetuses ( n=25) ranging from 12 to 117 mm CRL (crown-rump-length) were serially sectioned and the mandibles were reconstructed in 3D. In addition, characteristic areas of apposition, resorption and resting zones were projected onto the surface of the mandibular reconstructions after histological evaluation of the remodeling processes. Furthermore, morphometric data were taken to describe growth processes in horizontal views. In this way the changing outlines as seen in 3D could be correlated with the remodeling patterns and with the changes in growth. In these stages the mandible showed a general appositional growth, but resorption areas were found at the posterior margins of the mental foramen and at the lateral and medial posterior bony planes at concave surfaces. The bulging of bone underneath and over Meckel's cartilage could be recognized as active appositional growth areas. Meckel's cartilage itself lay in a trough which could be characterized by less apposition and even resorption. Questions were raised in how much the gap between our present knowledge of genetic expression of signaling molecules and the precise morphologic description of the mandibles can be bridged.

Bone Remodeling↗
PubMed1988

A study of the height of intact alveolar bone on panoramic radiographs of adult patients.

This study describes a method of estimating alveolar bone height on panoramic radiographs by using constant anatomic landmarks as reference points and calculating ratios of given distances between certain of these landmarks in dentate patients with no radiographic evidence of horizontal bone loss. Measurements were performed on four different types of panoramic radiographs. Results determined for the maxillae and mandible were constant between the different types of panoramic films. Because of differences in the measurements obtained on the right and left sides on Panorex films that have been trimmed and spliced to remove anatomic overlap in the midline areas, this type of projection may not be suitable for analysis of the maxillary alveolar bone as described in this study. The use of the mental foramen as a constant anatomic landmark for analysis of mandibular alveolar bone on panoramic radiographs may not be feasible since it appears that it may not be possible to consistently determine the exact location of the foramen. The results of the present study suggest a difference of as much as 25% among patients in the same ratio in the maxillae and as much as 12% in the same ratio in the mandible. Therefore, the results may not be of significant value as "baseline" data to estimate alveolar bone loss at a given time after tooth loss. However, this method could prove valuable in serial studies where alveolar bone height for a single patient is compared at different times before and after tooth loss.

Adolescent↗
PubMed1992

Sonographic measurement versus mapping for determination of residual ridge width.

To achieve long-term success of dental implants, evaluation of the dimensions of the resorbing alveolar process must be accurate because an implant should be surrounded by at least 1 mm of bone. Estimating the thickness of bone is more difficult because the mucosal contour can mask the actual dimension of the residual ridge. With ultrasound, it is possible to analyze and visualize the diameter of maxillary or mandibular residual ridges. Data obtained from ultrasound measurement of residual ridges were compared with the data from ridge mapping with the Wilson bone caliper and the Spoerlein caliper. The ultrasound measurement produced nearly the same data at all measurement points as ridge mapping. Ultrasound also provides exact information about the location of the mental foramen and the maxillary sinus. By using all three methods the initial stage of implant treatment can be planned.

Aged↗
PubMed1993

Osteoporosis and reduction of residual ridge in edentulous patients.

The relationship between the height of the mandibular residual ridge and the severity of osteoporosis in elderly edentulous patients was investigated. The height of the mandibular residual ridge was measured by use of the mental foramen on panoramic radiographs. The severity of osteoporosis was determined by examining frontal and lateral radiographs of the vertebrae. All of the patients received a blood analysis. The correlation coefficient between age and the height of residual ridge was -0.38, which was statistically significant (p < 0.01). The residual ridge in women was lower than that of men, showing a statistical significance (p < 0.01). The correlation coefficient was -0.42 between degree of severity of osteoporosis and the height of the residual ridge, which was significant (p < 0.01). The parathyroid hormone level was high in the patients with a low residual ridge, and the calcitonin (CT) level was low. This study indicates that osteoporosis strongly affects reduction of the residual ridge in edentulous patients.

Age Factors↗