Canine sexual dimorphism in Egyptian Eocene anthropoid primates: Catopithecus and Proteopithecus.
Two very small late Eocene anthropoid primates, Catopithecus browni and Proteopithecus sylviae, from Fayum, Egypt show evidence of substantial sexual dimorphism in canine teeth. The degree of dimorphism suggests that these early anthropoids lived in social groups with a polygynous mating system and intense male-male competition. Catopithecus and Proteopithecus are smaller in estimated body size than any living primates showing canine dimorphism. The origin of canine dimorphism and polygyny in anthropoids was not associated with the evolution of large body size. (+info)
A modern human pattern of dental development in lower pleistocene hominids from Atapuerca-TD6 (Spain).
The study of life history evolution in hominids is crucial for the discernment of when and why humans have acquired our unique maturational pattern. Because the development of dentition is critically integrated into the life cycle in mammals, the determination of the time and pattern of dental development represents an appropriate method to infer changes in life history variables that occurred during hominid evolution. Here we present evidence derived from Lower Pleistocene human fossil remains recovered from the TD6 level (Aurora stratum) of the Gran Dolina site in the Sierra de Atapuerca, northern Spain. These hominids present a pattern of development similar to that of Homo sapiens, although some aspects (e.g., delayed M3 calcification) are not as derived as that of European populations and people of European origin. This evidence, taken together with the present knowledge of cranial capacity of these and other late Early Pleistocene hominids, supports the view that as early as 0.8 Ma at least one Homo species shared with modern humans a prolonged pattern of maturation. (+info)
Comparison of cephalometric analysis using a non-radiographic sonic digitizer (DigiGraph Workstation) with conventional radiography.
Cephalometric analysis conventionally requires radiographic exposure which may not be compatible with the growing concern over radiation hazards. Recently, the Dolphin Workstation Imaging System introduced to the dental profession a non-radiographic system, called the DigiGraph Workstation which may be an alternative to cephalometric radiography. The aims of this study were to compare the validity and reproducibility of cephalometric measurements obtained from the DigiGraph Workstation with conventional cephalometric radiographs. The sample consisted of 30 human dry skulls. Two replicated sets of lateral cephalograms were obtained with steel ball markers placed at the majority of the cephalometric landmarks. Duplicate tracings prepared from each radiograph were digitized to obtain cephalometric measurements using the computer software, Dentofacial Planner. For the DigiGraph Workstation, double sonic digitizations were repeated twice for each skull, on two occasions. Fifteen angular and one linear measurements were obtained from both methods and these findings compared using ANOVA, paired t-tests and F-tests. All, except one, cephalometric measurement showed significant differences between the two methods (P < 0.0001). The DigiGraph Workstation consistently produced higher values in 11 measurements (mean differences +0.5 to +15.7 degrees or mm) and lower values in four measurements (mean differences -0.2 to -3.5 degrees). The standard deviations of the differences between readings of both methods were large (0.4-5.8 degrees or mm). The reproducibility of the DigiGraph Workstation measurements was lower than that of the radiographic measurements. The method error of the DigiGraph Workstation ranged from 7 to 70 per cent, while that of radiographic tracings was less than 2 per cent. It was concluded that measurements obtained with the DigiGraph Workstation should be interpreted with caution. (+info)
Morphological changes in periodontal mechanoreceptors of mouse maxillary incisors after the experimental induction of anterior crossbite: a light and electron microscopic observation using immunohistochemistry for PGP 9.5.
Ruffini nerve endings (mechanoreceptors) in the periodontal ligament (PDL) of mouse incisors were examined to elucidate whether experimentally-induced crossbites cause any changes or abnormalities in their morphology and distribution. Anterior guiding planes were attached to the mandibular incisors of 3-week-old C3H/HeSlc mice. At 3 days and 1, 2, 4, 6, and 8 weeks post-attachment of the appliance, the mice were sacrificed by perfusion fixation. Frozen sagittal cryostat sections of the decalcified maxillary incisors were processed for immunohistochemistry of protein gene product 9.5, followed by histochemical determination of tartrate-resistant acid phosphatase activity to reveal sites of alveolar bone resorption. Despite the absence of bone resorption within the lingual PDL of control mice, distinct resorption sites were seen in the respective regions of the experimental animals. Unlike the controls, many Ruffini endings showing vague and swollen contours, with unusually long and pedunculated micro-projections were observed in the affected lingual PDL of the incisors in the experimental animals with short-term anterior crossbite induction. Club-shaped nerve terminations with few, if any, micro-projections were observed in the lingual PDL of experimental animals with long-term induction, as well as in aged control mouse incisors. Differences in the distribution of Ruffini endings were also observed. These results indicate that changing the direction of the force applied to the PDL results in rapid and prolonged changes in the morphology of Ruffini-like mechanoreceptors. (+info)
Ectopic eruption of the maxillary canine quantified in three dimensions on cephalometric radiographs between the ages of 5 and 15 years.
The eruption paths of 20 ectopic maxillary canine teeth (10 right, 10 left) were measured in three dimensions on annual lateral and depressed postero-anterior cephalometric radiographs of 15 patients between the ages of 5 and 15 years and compared with the eruption of normal canines. It was found that between the ages of 8 and 12 years ectopic canines on the left side moved more anteriorly than the normally erupting canines and the same was true of the right canines between the ages of 7 and 12 years. While the ectopic canines moved occlusally, their vertical movement was less than normal which accounts for the clinical finding that canines are impacted in the palate at a high level. The average palatally ectopic canine always moves palatally, and never shares in the buccal movement shown by normally erupting canines between the ages of 10 and 12 years. It was interesting to find that the differences between growth of normal and ectopic canines in the lateral plane of space are present as early as 5-6 years. (+info)
The length and eruption rates of incisor teeth in rats after one or more of them had been unimpeded.
The eruption rate and length of all four incisor teeth in rats were measured under ether anaesthesia by recording the position of marks on their labial surfaces at 2-day intervals, using calibrated graticules in microscope eyepieces. The rats were divided into four groups and either a lower, an upper, both a lower and an upper, or no incisors were unimpeded. This paper describes the changes when the unimpeded incisors returned to the occlusion. Neither the unimpeded nor the impeded incisors simply returned to control values immediately the period of unimpeded eruption ended, but showed transient changes in their lengths and eruption rates. The results confirm that eruption rates are determined by the sum of the lengths of the lower and upper incisors, rather than by their own lengths, with longer teeth erupting more slowly. Specifically, restoring the bevel to the incisors did not slow their eruption below normal impeded rates. The slowing of the eruption of the longer of two adjacent incisors was related to the length differences of the incisors in the same jaw, not to the sum of the differences in both jaws. Contact with the contralateral incisor in the opposite jaw slowed the eruption of an incisor more than contact with the ipsilateral incisor. (+info)
Expression of chick Barx-1 and its differential regulation by FGF-8 and BMP signaling in the maxillary primordia.
The vertebrate face develops from a series of primordia surrounding the primitive mouth and is thought to be patterned by the differential expression of homeobox-containing genes. Here we describe the isolation of the chick homologue of the homeobox-containing gene, Barx-1, and show its expression in the developing facial primordia, stomach, and appendicular skeleton. In the maxillary primordia, mesenchymal expression of Barx-1 is complementary to that of Msx-1, which correlate with overlying epithelial expression of Fgf-8 and Bmp-4, respectively. We show that epithelial signals are required to maintain Barx-1 expression and that FGF-8 can substitute for the epithelium. By contrast, BMPs reduce Barx-1 expression and can antagonize FGF-8 signaling. This suggests that in vivo, FGF-8/BMP signaling may regulate Barx-1 gene expression. This provides evidence that the differential expression of FGF-8 and BMPs may determine homeobox-containing gene expression and hence patterning of the facial primordia. (+info)
Jaw reflexes evoked by mechanical stimulation of teeth in humans.
Jaw reflexes evoked by mechanical stimulation of teeth in humans. The reflex response of jaw muscles to mechanical stimulation of an upper incisor tooth was investigated using the surface electromyogram (SEMG) of the masseter muscle and the bite force. With a slowly rising stimulus, the reflex response obtained on the masseter SEMG showed three different patterns of reflex responses; sole excitation, sole inhibition, and inhibition followed by excitation. Simultaneously recorded bite force, however, exhibited mainly one reflex response pattern, a decrease followed by an increase in the net closing force. A rapidly rising stimulus also induced several different patterns of reflex responses in the masseter SEMG. When the simultaneously recorded bite force was analyzed, however, there was only one reflex response pattern, a decrease in the net closing force. Therefore, the reflex change in the masseter muscle is not a good representative of the net reflex response of all jaw muscles to mechanical tooth stimulation. The net response is best expressed by the averaged bite force. The averaged bite force records showed that when the stimulus force was developing rapidly, the periodontal reflex could reduce the bite force and hence protect the teeth and supporting tissues from damaging forces. It also can increase the bite force; this might help keep food between the teeth if the change in force rate is slow, especially when the initial bite force is low. (+info)