The root surface in human teeth: a microradiographic study. (1/1126)

In an attempt to clarify the nature of the human cemento-dentinal junction, ground sections of incompletely formed and fully formed extracted teeth were prepared and their histology compared with their microradiographic appearances. The results showed that incompletely formed teeth possess distinctive surface layers outside the granular layer of Tomes. The evidence indicates that these layers are of dentinal origin; their presence during development supports previous explanations by the author of the hyaline layer of Hopewell-Smith and of so-called intermediate cementum. The results also indicate that the granular layer of Tomes does not represent the outer limit of root dentine. The relationship of these surface layers to the definitive cementum which is present in fully formed teeth was studied in both young and older patients. From the results it was concluded that cementum formation begins in the more apical region of the teeth at a time when root formation is well advanced, and that it spreads towards the crown rather than in the generally accepted reverse direction.  (+info)

Modified cuspal relationships of mandibular molar teeth in children with Down's syndrome. (2/1126)

A total of 50 permanent mandibular 1st molars of 26 children with Down's syndrome (DS) were examined from dental casts and 59 permanent mandibular 1st molars of normal children were examined from 33 individuals. The following measurements were performed on both right and left molars (teeth 46 and 36 respectively): (a) the intercusp distances (mb-db, mb-d, mb-dl, db-ml, db-d, db-dl, db-ml, d-dl, d-ml, dl-ml); (b) the db-mb-ml, mb-db-ml, mb-ml-db, d-mb-dl, mb-d-dl, mb-dl-d angles; (c) the area of the pentagon formed by connecting the cusp tips. All intercusp distances were significantly smaller in the DS group. Stepwise logistic regression, applied to all the intercusp distances, was used to design a multivariate probability model for DS and normals. A model based on 2 distances only, mb-dl and mb-db, proved sufficient to discriminate between the teeth of DS and the normal population. The model for tooth 36 for example was as follows: p(DS) = (e(30.6-5.6(mb-dl)+25(mb-db)))/(1 + e(30.6 5.6(mb-dl)+25(mb db))). A similar model for tooth 46 was also created, as well as a model which incorporated both teeth. With respect to the angles, significant differences between DS and normals were found in 3 out of the 6 angles which were measured: the d-mb-dl angle was smaller than in normals, the mb-d-dl angle was higher, and the mb-dl-d angle was smaller. The dl cusp was located closer to the centre of the tooth. The change in size occurs at an early stage, while the change in shape occurs in a later stage of tooth formation in the DS population.  (+info)

A modern human pattern of dental development in lower pleistocene hominids from Atapuerca-TD6 (Spain). (3/1126)

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)

An autoradiographical study of [3H]thymidine incorporation into subcutaneously transplanted mouse molar teeth. Cell proliferation and migration in transplanted teeth. (4/1126)

Mice bearing either allografts or isografts of 10 day old molar teeth were injected with [3H]thymidine to identify proliferating and migrating cells within the graft and surrounding tissues. In isografts proliferating cells were found successively in the area underlying the cervix, in the cervical pulp and the coronal pulp. However, cells did not migrate from the cervical host tissue into the pulp, and it was concluded that donor cells are responsible for reparative processes in tooth isografts. Very few labelled cells were identified at any time in tooth allografts, which were not repaired. It is suggested that allografts are not repaired because allogeneic inhibition prevents the residual donor tissue from proliferating and differentiating. Inhibition of proliferation of residual cells may also account for the absence of a cell-mediated immune response to tooth allografts.  (+info)

Arrested eruption of the permanent lower second molar. (5/1126)

The incidence of retention/impaction of the permanent lower second molar (M2inf) lies between 0.6/1000 and 3/1000. Therefore, the purpose of the present study was to investigate the craniofacial morphology, the frequency of dental anomalies and the inclination of the affected M2inf and the adjacent first molar in patients with arrested eruption of M2inf. The overall goal was to elucidate the aetiology of arrested tooth eruption and to present the characteristics of these patients in order to improve diagnosis and treatment planning. Radiographic material (profile radiographs and orthopantomograms) from 19 patients (nine females and 10 males; 13-19 years of age at the time of referral) were analysed. The ages of the patients when profile radiographs were taken for cephalometric analysis varied from 8 to 16 years. The study shows that this group of patients, compared with a reference group, had an increased sagittal jaw relationship (Class II). Specifically, the mandibular prognathism was less, the mandibular gonial angle smaller, the mandibular alveolar prognathism enlarged and the maxillary incisor inclination less than in the reference group. Furthermore, this group of patients had a more frequent occurrence of morphological tooth anomalies, such as root deflections, invaginations, and taurodontism. However, none of the patients with arrested eruption of M2inf had agenesis of the lower third molar. The study did not reveal an association between the degree of inclination of the M2inf and that of the first molar in the same region. The results of this investigation show that conditions such as the craniofacial morphology and deviations in the dentition are associated with arrested eruption of M2inf. Therefore, it is important to evaluate these conditions in future diagnosis and treatment planning of patients with arrested eruption of M2inf.  (+info)

Histological and histochemical quantification of root resorption incident to the application of intrusive force to rat molars. (6/1126)

This study was conducted to investigate the nature of root resorption resulting from intrusive forces applied to the rat lower molars, by means of histological and histochemical techniques with tartrate resistant acid phosphatase (TRAP). Thirty-eight 13-week-old Wistar strain male rats were used. Intrusive force was created by a fixed appliance which was adjusted to exert an initial force of 50 g for the duration of 1, 2, and 3 weeks. The degree of root resorption and distribution of TRAP positive cells were evaluated. On the root surface, the TRAP positive scores were low in the apical regions. Significant differences in the scores were found in the inter-radicular region of the roots between the experimental and control groups for the 2- and 3-week groups. More active resorption of bone occurred during the experimental period, as denoted by greater TRAP positive scores on the bone than on the root surface. Root resorption scores in the apical root region were larger in the 2- and 3-week groups than in the 1-week group. Significant differences in the root resorption scores were also found between the 1- and 3-week groups in the inter-radicular region, indicating that intrusive force application of a longer duration may lead to a higher frequency of root resorption. It is shown that, irrespective of the level of TRAP positive cells and root resorption scores, the degree of root resorption activity is higher in the apical root region than in the inter-radicular area. These results indicate that cellular cementum may be resorbed more easily because of its richer organic components and low mineralized structure.  (+info)

Histochemical studies of glycosaminoglycans in developing periodontal ligaments of ICR mice. (7/1126)

Although the periodontal ligament (PL) contains an abundance of glycosaminoglycans (GAGs), there are only a few histochemical studies describing GAGs in the developing PL. In the present study, the relationship between the formation of principal fibers and the molecular species of GAGs in the developing PL was examined by light microscopic histochemistry. Jcl:ICR mice were killed on day 0 to day 28 after birth. Paraffin-embedded tissue sections were routinely made and stained with hematoxylin-eosin (H&E), Azan, or the sensitized high iron diamine (S-HID) procedure combined with enzyme digestions. Before tooth eruption, thin threads of collagen fibers in the PL assembled and constructed principal fibers, which projected from both the side of the alveolar bone and the root of the tooth. After tooth eruption, the principal fibers from both sides were tightly entangled. In the developing PL, the molecular species of GAGs was mainly dermatan sulfate. Moreover, the relative amount of dermatan sulfate increased together with the maturation of the principal fibers, while the principal fibers adjacent to the alveolar bone and cementum contained chondroitin sulfate. These results suggest that dermatan sulfate contributes to collagen fiber assembly in the PL and that chondroitin sulfate relates to PL adhesion to the alveolar bone and to the cementum of the root.  (+info)

Collagen-phagocytosing ability of periodontal osteoblasts at the bone surface. (8/1126)

The collagen-phagocytosing activity of osteoblasts at the alveolar bone-ligament interface of rat mandibular first molars was investigated both histologically and histochemically. Alveolar bones of male Wistar rats (6 months old) were used in this study. Collagen-containing phagosomes appeared in cuboidal osteoblasts aligned on the bone surface. The 5.7% of the osteoblasts exhibiting alkaline phosphatase activity revealed collagen-containing phagosomes, and the collagen fibrils within the phagosomes were at various stages of degradation. In addition, acid phosphatase activity and the immunocytochemical distribution of cathepsin B were found in these collagen-containing phagosomes at similar locations. The presence of both enzymes in the phagosomes suggests that an intracellular degradation of collagen occurs. Therefore, in addition to the osteoblastic functions of synthesizing and secreting bone matrices, osteoblasts are also capable of phagocytosis and the intracellular disintegration of collagen. Our findings suggest that osteoblasts at the alveolar bone-periodontal ligament interface have a collagen-phagocytosing ability and play an important role in the physiological remodeling and metabolic breakdown of collagen fibrils of periodontal ligament without osteoclastic bone remodeling.  (+info)