The Ruffini ending as the primary mechanoreceptor in the periodontal ligament: its morphology, cytochemical features, regeneration, and development.
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The periodontal ligament receives a rich sensory nerve supply and contains many nociceptors and mechanoreceptors. Although its various kinds of mechanoreceptors have been reported in the past, only recently have studies revealed that the Ruffini endings--categorized as low-threshold, slowly adapting, type II mechanoreceptors--are the primary mechanoreceptors in the periodontal ligament. The periodontal Ruffini endings display dendritic ramifications with expanded terminal buttons and, furthermore, are ultrastructurally characterized by expanded axon terminals filled with many mitochondria and by an association with terminal or lamellar Schwann cells. The axon terminals of the periodontal Ruffini endings have finger-like projections called axonal spines or microspikes, which extend into the surrounding tissue to detect the deformation of collagen fibers. The functional basis of the periodontal Ruffini endings has been analyzed by histochemical techniques. Histochemically, the axon terminals are reactive for cytochrome oxidase activity, and the terminal Schwann cells have both non-specific cholinesterase and acid phosphatase activity. On the other hand, many investigations have suggested that the Ruffini endings have a high potential for neuroplasticity. For example, immunoreactivity for p75-NGFR (low-affinity nerve growth factor receptor) and GAP-43 (growth-associated protein-43), both of which play important roles in nerve regeneration/development processes, have been reported in the periodontal Ruffini endings, even in adult animals (though these proteins are usually repressed or down-regulated in mature neurons). Furthermore, in experimental studies on nerve injury to the inferior alveolar nerve, the degeneration of Ruffini endings takes place immediately after nerve injury, with regeneration beginning from 3 to 5 days later, and the distribution and terminal morphology returning to almost normal at around 14 days. During regeneration, some regenerating Ruffini endings expressed neuropeptide Y, which is rarely observed in normal animals. On the other hand, the periodontal Ruffini endings show stage-specific configurations which are closely related to tooth eruption and the addition of occlusal forces to the tooth during postnatal development, suggesting that mechanical stimuli due to tooth eruption and occlusion are a prerequisite for the differentiation and maturation of the periodontal Ruffini endings. Further investigations are needed to clarify the involvement of growth factors in the molecular mechanisms of the development and regeneration processes of the Ruffini endings. (+info)
Natural history of Streptococcus sanguinis in the oral cavity of infants: evidence for a discrete window of infectivity.
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The heterogeneous group of oral bacteria within the sanguinis (sanguis) streptococci comprise members of the indigenous biota of the human oral cavity. While the association of Streptococcus sanguinis with bacterial endocarditis is well described in the literature, S. sanguinis is thought to play a benign, if not a beneficial, role in the oral cavity. Little is known, however, about the natural history of S. sanguinis and its specific relationship with other oral bacteria. As part of a longitudinal study concerning the transmission and acquisition of oral bacteria within mother-infant pairs, we examined the initial acquisition of S. sanguinis and described its colonization relative to tooth emergence and its proportions in plaque and saliva as a function of other biological events, including subsequent colonization with mutans streptococci. A second cohort of infants was recruited to define the taxonomic affiliation of S. sanguinis. We found that the colonization of the S. sanguinis occurs during a discrete "window of infectivity" at a median age of 9 months in the infants. Its colonization is tooth dependent and correlated to the time of tooth emergence; its proportions in saliva increase as new teeth emerge. In addition, early colonization of S. sanguinis and its elevated levels in the oral cavity were correlated to a significant delay in the colonization of mutans streptococci. Underpinning this apparent antagonism between S. sanguinis and mutans streptococci is the observation that after mutans streptococci colonize the infant, the levels of S. sanguinis decrease. Children who do not harbor detectable levels of mutans streptococci have significantly higher levels of S. sanguinis in their saliva than do children colonized with mutans streptococci. Collectively, these findings suggest that the colonization of S. sanguinis may influence the subsequent colonization of mutans streptococci, and this in turn may suggest several ecological approaches toward controlling dental caries. (+info)
Dental follicle cell-conditioned medium enhances the formation of osteoclast-like multinucleated cells.
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An influx of mononuclear cells and the subsequent increase of osteoclasts around tooth germs suggests that the dental follicle (DF) regulates or influences bone resorption required for tooth eruption. In order to study the effects of DF cell products on osteoclast formation during tooth eruption, a conditioned medium (CM) was created in which DF cells were added to mouse bone marrow cultures. Tartrate-resistant acid phosphatase (TRAP)-positive osteoclast-like multinucleated cells were formed in the presence of 10 nM 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The CM, dose-dependently, stimulated the formation of TRAP-positive cells in the presence of 1,25(OH)2D3 for 14 days culture. The number of these cells decreased due to degradation in the control culture. A semi-solid methylcellulose assay in the presence of CM showed little expression of colony-stimulating activity. These results suggest that the DF cells of a developing tooth produce factor(s) that enhance osteoclast formation and bone resorption necessary for tooth eruption. (+info)
It's only teething...a report of the myths and modern approaches to teething.
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Paediatric dentistry is not my usual field of work. I am now based almost entirely in restorative dentistry and it is five years since I worked in the dental department of a children's hospital. An essay on teething would appear to be an unusual choice of topic. With the current professional climate of 'general professional education' and 'lifelong learning' I can easily justify my time and effort studying a subject somewhat removed from my regular work. However, to be completely honest, I have reached that age when many of my friends, relatives and colleagues are enjoying the sleepless nights that accompany expanding families. Add to this the fact that I have recently married into a family of midwives, health visitors, nurses and new mothers. I was not sure that I was giving the best, most up to date advice when asked about teething. So some reading around was required. If only it were that simple. I now feel equipped to give a little more help than simply saying, "It's only teething..." (+info)
Dental enamel formation and its impact on clinical dentistry.
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The nature of tooth enamel is of inherent interest to dental professionals. The current-day clinical practice of dentistry involves the prevention of enamel demineralization, the promotion of enamel remineralization, the restoration of cavitated enamel where demineralization has become irreversible, the vital bleaching of dental enamel that has become discolored, and the diagnosis and treatment of developmental enamel malformations, which can be caused by environmental or genetic factors. On a daily basis, dental health providers make diagnostic and treatment decisions that are influenced by their understanding of tooth formation. A systemic condition during tooth development, such as high fever, can produce a pattern of enamel defects in the dentition. Knowing the timing of tooth development permits estimates about the timing of the disturbance. The process of enamel maturation continues following tooth eruption, so that erupted teeth can become less susceptible to decay over time. Mutations in the genes encoding enamel proteins lead to amelogenesis imperfecta, a collection of inherited diseases having enamel malformations as the predominant phenotype. Defects in the amelogenin gene cause X-linked amelogenesis imperfecta, and genes encoding other enamel proteins are candidates for autosomal forms. Here we review our current understanding of dental enamel formation, and relate this information to clinical circumstances where this understanding may be particularly relevant. (+info)
Origin of the tooth-replacement pattern in therian mammals: evidence from a 110 Myr old fossil.
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Living placental and marsupial mammals (therians) use distinctive tooth-replacement patterns that have not yet been traced back fully to their time of divergence in the Early Cretaceous (>100 Myr ago). Slaughteria eruptens, a small 110 Myr old fossil mammal from Texas, USA, is near the base of that divergence. Using ultra-high-resolution X-ray CT analysis we demonstrate that Slaughteria preserves an unrecognized pattern of tooth replacement with simple posterior premolars replacing molariform precursors. Differing from both placentals that have a more complex posterior adult premolar, and from marsupials, in which only one premolar is replaced, Slaughteria provides the first direct evidence of a tooth-replacement pattern that is plausible for the common ancestor of all therians. By our interpretation Slaughteria has only one adult molar in place and contains two mental foramina in the jaw, thus changing characters that are critical to reconstruction of mammalian relationships and to species discrimination and interpretations of diversity for Early Cretaceous mammals. (+info)
Dental development after successful treatment of infantile osteopetrosis with bone marrow transplantation.
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A 3-week-old boy was diagnosed with congenital osteopetrosis. He underwent a bone marrow transplant at 6 weeks of age. At 3 years of age the primary teeth had all erupted, but the canines and the first molars totally lacked root development. The teeth were smaller in size and had evidence of both enamel hypomineralization and hypoplasia. In the permanent dentition, multiple missing teeth were found. The incisors were conical and the mandibular laterals were extremely small. All permanent teeth had normal eruption. This case shows that dental development and eruption of teeth can be reconstituted in a child with congenital osteopetrosis. Bone marrow transplantation induces normalization of osteoclast function, which is a prerequisite for normal dental development and eruption of teeth. (+info)
Unilateral distalization of a maxillary molar with sliding mechanics: a case report.
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INTRODUCTION: A unilateral Class II relationship could arise due to early loss of an upper second deciduous molar on one side during the mixed dentition period. This would allow the mesial drift of the molars, which may block the eruption of the second premolar. METHODS AND RESULTS: A 15-year 8-month-old male patient presented with a Class II molar relationship on the right, and Class I canine and molar relationship on the left side. His E was extracted when he was 5 years old. The 54 were impacted and the 3 was ectopically positioned due to the space loss from the mesial migration of the 76. In addition 21 1 were in cross-bite. Skeletally he had Class III tendency with low MMPA. He presented with a straight profile and retruded upper lip. For maxillary molar distalization, a newly developed 'Keles Slider' was used. The appliance was composed of one premolar and two molar bands, and the anchorage unit was composed of a wide Nance button. 46 were connected to the Nance button and, therefore, included into the anchorage unit. The point of distal force application was close to the centre of resistance of the 6 and parallel to the occlusal plane. Ni-Ti coil springs were used and 200 g of distal force was applied. Seven months later the space required for eruption of the permanent premolars and canine was regained, and the anterior cross-bite corrected. The appliance was removed and final alignment of the teeth was achieved with fixed appliances. CONCLUSION: At the end of the second phase treatment Class I molar and canine relationship was achieved on the both sides, the anterior cross-bite was corrected, inter-incisal angle was improved, and ideal overbite and overjet relationship was achieved. The active treatment time was 27 months. (+info)