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At least 865 records · Page 48Linked to original sources
PubMed1994

Integrin regulatory switching in development: oscillation of beta 5 integrin mRNA expression during epithelial-mesenchymal interactions in tooth development.

Integrin receptors for extracellular matrix molecules are thought to play important roles in morphogenesis since they mediate aspects of embryonic cell adhesion and migration. Using in situ hybridization, the mRNA expression pattern of the beta 5 integrin receptor subunit was examined during murine tooth development, a classical system for studying morphogenesis. In developing tooth, high-level expression of beta 5 integrin mRNA alternates from epithelium to mesenchyme and back to epithelium. Each switch in localization occurs within one day. These results demonstrate that an integrin mRNA can be precisely and rapidly up- and down-regulated over unexpectedly short time spans, and that expression can oscillate between adjacent, interacting epithelial and mesenchymal tissues during morphogenesis. This rapid modulation of mRNA expression suggests a potential regulatory role for the beta 5 integrin receptor in morphogenesis.

Animals↗
PubMed1991

Periodontal tissue reactions to orthodontic extrusion. An experimental study in the dog.

Orthodontic tooth extrusion is used at crown lengthening procedures or in conjunction with periodontal therapy aimed at eliminating or reducing angular bone defects. A technique for orthodontic extrusion combined with resection of the supracrestal attachment fibers (fiberotomy) was recently proposed as an adjunct to certain restorative procedures. The aim of the present investigation was to analyze reactions of the periodontal tissues to orthodontic extrusion when combined with fiberotomy. In 5 beagle dogs, the mesial roots of the 2nd, 3rd and 4th hemisected mandibular premolar were used as target roots while the distal roots served as reference units. After a baseline examination, an orthodontic extrusion device (stent) was installed and reactivated at 2-week intervals during an 8-week period of active tooth movement. Immediately following the installation of the stent and once every 2nd week, the target roots were exposed to fiberotomy. After the active period, the teeth were retained in their new position for a period of 8 weeks. Clinical, radiographical and histological measurements were performed. The results from the investigation demonstrated that orthodontic extrusion combined with supracrestal fiberotomy resulted in a coronal displacement of the tooth and was associated with pronounced recession of the gingival margin and extensive loss of connective tissue attachment. The degree of gingival recession and the amount of loss of connective tissue attachment were, however, less extensive than the amount of tooth extrusion. Thus, repeated fiberotomy obviously failed to entirely prevent coronal migration of the attachment apparatus. It was also observed that undesired attachment loss had occurred at the reference roots.

Animals↗
PubMed1995

Periosteal migration in the growing mandible: an animal model.

Migration of mandibular periosteum and attached musculature was tracked along the inferior border of the ramus in growing and nongrowing guinea pigs (Cavia porcellus) over a 6-week period. Particulate metallic growth-tracing implants were placed through the bony mandible and adjacent musculature at two anteroposterior locations and two bony reference markers were placed anteriorly. Quantification from weekly radiographs of growing animals showed marked posterior migration of the periosteum, whereas in nongrowing animals there was negligible periosteum movement. Significantly greater migration occurred in posterior (6.37 +/- 0.76 mm) implants relative to the anterior implants (3.45 +/- 0.86 mm, p < 0.001). The neutral zone, where little periosteal migration occurs, was calculated to be approximately at the anteroposterior center of the molar tooth row. Analysis of the orientation of the medial pterygoid muscle relative to the mandible showed that muscle fibers on average become more horizontal. Thus, the study found differential anteroposterior migration of the mandibular periosteum in growing animals and correlative changes in orientation of the medial pterygoid muscle.

Animals↗
PubMed2003

Dental caries in South Pacific populations: a review.

Dental caries (tooth decay) was uncommon in Pacific Island communities before European trading and migration expanded into the Region. The etiology of this oral microbial disease is a consequence of changed diets, food preparation and lifestyle. In particular, the easy availability of a high level of frequent dietary supplementation with refined sucrose (sugar) and carbohydrates is the key factor in the etiology of tooth decay. While tooth decay initially developed as a health problem in the more accessible Pacific islands over a century ago, it has spread increasingly as trading, travel and cash economies have developed to include even the more geographically remote communities. In this review selected epidemiological data are presented to show the magnitude, variation and secular changes in the prevalence of tooth decay in different communities. Tooth decay in conjunction with the historically endemic adult gum diseases poses a major public health problem in terms of pain, premature loss of teeth and the need for oral rehabilitation. Implementation and monitoring of caries control programs is a priority need in most communities. It is impractical to consider a return to indigenous diets and lifestyles as a strategy for caries prevention. Instead promotion of proven modern community preventive programmes, notably appropriate use of fluorides, 'fissure sealants' together with control of excessive consumption of diets rich in refined sugar is required if a significant increase in the levels of tooth decay is to be avoided.

Cooking↗
PubMed1987

Bacterial endotoxin inhibits migration, attachment, and orientation of human gingival fibroblasts in vitro and delays collagen gel contraction.

The purpose of this study was to assess the effect of endotoxin adsorbed to dental surfaces and to collagen type I on the migration, attachment, and orientation of human gingival fibroblasts (HGF). Transversely cut porcine tooth root slices (RS), 200 micron thick, were prepared. Half of the RS obtained were partially demineralized in EDTA. Half of the demineralized and non-demineralized RS were incubated with 400 micrograms/mL of endotoxin for 24 hr, whereas the other half were maintained in PBS and served as controls. Experimental and control RS were placed on confluent layers of HFG and cultured for six days. Cell migration toward and cell attachment to the periphery of the RS and the formation of oriented cell sheets were assessed by means of photographic techniques. Additionally, six-day-old cultures were fixed and processed for SEM observation. In separate experiments, the effect of endotoxin on cell attachment to collagen type I and on contraction of three-dimensional collagen gels was assessed. It was found that: (i) bacterial endotoxin inhibited migration and attachment of HGF to both demineralized and non-demineralized cementum and interfered with the development of oriented cellular structure: (ii) the inhibitory effect was significantly more pronounced for non-demineralized than for demineralized cementum: (iii) the morphology of HGF attached to endotoxin-treated dental surfaces was altered compared with that of their controls: and (iv) bacterial endotoxin inhibited cell attachment to collagen type I and delayed the contraction of collagen gel.

Animals↗
PubMed1980

Immunohistochemical evidence for the intracellular formation of basement membrane collagen (type IV) in developing tissues.

Antibodies to type IV collagen obtained from the basement membrane of the mouse EHS tumor were incubated with sections of rat incisor teeth and other tissues for immunostaining by direct or indirect methods. In all locations, the immunostaining was pronounced in basement membranes in which it was restricted to the "basal lamina" layer, from which "bridges" often extended to nearby basal laminae. Usually no immunostaining was detectable in the cells associated with the basement membranes. However, examination of the capillaries at the posterior extremity of the rat incisor tooth, where tissues are at an early stage of development, showed immunostaining not only of the basement membrane, but also of the endothelial cells. The staining was localized in rough endoplasmic reticulum cisternae, some Golgi saccules and their peripheral distensions, and structures believed to be secretory granules. These findings suggest that the synthesis of type IV collagen proceeds along the classical secretory pathways through rough endoplasmic reticulum and Golgi apparatus. At the same time, immunostaining was usually lacking in the cells of the capillaries that had migrated about 2 mm away from the posterior end of the incisor tooth and also in the cells of most other tissues examined, even though the associated basal laminae were reactive. It is, therefore, presumed that the production of type IV collagen may be high in cells at an early stage of development and that any later production and turnover of basement membrane collagen can only be minimal.

Animals↗
PubMed1996

A critical evaluation of methods for root coverage.

Gingival recession is the exposure of root surfaces due to apical migration of the gingival tissue margins. Although it seldom results in tooth loss, marginal tissue recession is associated with thermal and tactile sensitivity, esthetic complaints, and a tendency toward root caries. This article reviews the current surgical procedures for the coverage of exposed root surfaces, including their advantages and disadvantages. Today, the outcome of root coverage procedures is predictable, aesthetically acceptable, and, together with the use of guided tissue regeneration, at the forefront of regenerative procedures.

Citrates↗
PubMed1981

Fibroblast cell population kinetics in the mouse molar periodontal ligament and tooth eruption.

Fibroblast cell population kinetics in the developing molar periodontal ligament was investigated in 10, 12, 16 and 20 days old mice by autoradiography after the administration of [3H]thymidine. Labelled mitoses, in number per unit area, were counted over the apical zones of the sections and percentage labelled mitoses (PLM) curves were drawn. Median values for some phases durations were read off at the 0.5 level of mitotic labelling. In determining other kinetic parameters the periodontal fibroblast population was considered separately as (1) a steady state system, (2) an exponentially growing system. An attempt was made to estimate mean values for these parameters using the Gilbert Computer programme. The programme generated the original data points and the fitted curve in graphical and numerical form together with the mean values and standard errors. The fact that the Gilbert programme assumes a stationary population in its theoretical PLM curve analysis was used to establish the kinetic type of the periodontal fibroblast population. The present study has demonstrated that in the growing periodontal ligament where cell specialisation and migration occurs steady state system is the kinetic model applicable. Failure of the computed PLM curves to fit the data adequately confirmed the fibroblast migration (apico-occlusal migration) from the apical zone to other zones. A definite cytokinetic basis for the periodontal ligament fibroblast proliferation and migration was established. Accordingly, fibroblast proliferation and migration takes place by a reduction in the DNA synthesis time (T8), cell generation tie (Tc) and possibly by a similar reduction in other parameters. Maximum reduction in these parameters is associated with the peak proliferative and migratory activity in the 12 days old group which is also the time that tooth eruption takes place in the mouse. Thus fibroblast proliferation and migration are major causative factors responsible for tooth eruption. Based on these results, a mechanism for tooth eruption is proposed.

Aging↗
PubMed2006

CMT-3 inhibits orthodontic tooth displacement in the rat.

OBJECTIVE: Orthodontic tooth movement requires extensive remodeling of the periodontal ligament (PDL) and the alveolar bone. Osteoclasts resorb bone, allowing teeth to migrate in the direction of the force. Matrix metalloproteinases (MMPs) are able to degrade the extracellular matrix of the periodontal tissues. Chemically modified tetracyclines (CMTs) can inhibit MMPs, but lack antimicrobial activity. We hypothesize that CMT-3 will decrease the rate of orthodontic tooth movement in the rat. DESIGN: Eighteen Wistar rats received a standardized orthodontic appliance at one side of the maxilla. During 14 days, three groups of six rats received a daily dose of 0, 6 or 30mg/kg CMT-3, and tooth displacement was measured. Thereafter, osteoclasts were counted on histological sections using an ED-1 staining. Multi- and mononuclear ED-1-positive cells in the PDL were also counted. In addition, sections were stained for MMP-9. RESULTS: CMT-3 significantly inhibited tooth movement (p=0.03) and also decreased the number of osteoclasts at the compression sides in the 30mg/kg group (p<0.05). Significantly more mono- than multinuclear ED-1-positive cells were present in the PDL, but no significant differences were found between the dosage groups. Osteoclasts in the 30mg/kg group seemed to contain less MMP-9 than in the control. CONCLUSIONS: CMT-3 inhibits tooth movement in the rat, probably by reducing the number of osteoclasts at the compression side. This might be due to induction of apoptosis in activated osteoclasts or reduced osteoclast migration. Reduced MMP activity by CMT-3 might also directly inhibit degradation of the organic bone matrix.

Alveolar Process↗
PubMed1978

Homologies of the toothcomb.

A recently described juvenile specimen of Avahi was supposed to show that indriines have an unreplaced deciduous canine and that the indriine toothcomb was composed only of incisors. To the contrary, this specimen demonstrates quite dramatically a growth phenomenon earlier discussed: in indriines, the anteriormost of the four deciduous lower teeth posterior to the toothcomb migrates mesially toward the toothcomb (Schwartz, '74). In this particular Avahi, this tooth has even become associated with the toothcomb. The alignment of this tooth with the toothcomb is a strictly impermanent situation and cannot be taken into consideration when determining homologies of the teeth of the toothcomb. Morphologically and developmentally the lateral teeth of both indriine and lemur and loris toothcombs are similar to each other and distinct from the central set of teeth. Thus, if the lateral teeth of the lemur/loris toothcomb are canines, then the lateral teeth of the indriine toothcomb are canines as well.

Animals↗
PubMed1992

Brief communication: interproximal tooth wear: a new observation.

Microscopic observations were made of wear on the proximal surfaces of tooth crowns of Australian Aboriginals and whites. Typical wear facets displayed well-defined borders within which vertical or near vertical furrows, ranging from about 0.1 to 0.5 mm in width, were noted. Furrows on the interproximal surface of one tooth seemed to "interdigitate" with those on the proximal surface of the adjacent tooth. These observations are not consistent with the commonly-held view that interproximal tooth wear results from a buccolingual movement of adjacent teeth that maintain contact through mesial migration. Vertical or near vertical movement of teeth, possibly including a tipping action, must be an important factor, although the precise nature of the movement requires further investigation.

Humans↗
PubMed1993

Early cellular events in an actinomycin D-created dentin niche in the rat incisor.

Administration of actinomycin D at a dose level of 0.375 microgram/g resulted in the selective disruption of developing odontoblasts at a critical stage of morphogenesis. A dentin niche was formed which was later repaired by cellular reparative dentin. The cellular changes which resulted in dentin niche formation were studied histologically and ultrastructurally in serial longitudinal and transverse sections from tissues obtained 10 h to 80 h following injection of the drug. Five stages were identified: initial destruction (10-20 h), rapid destruction (30-40 h), debris removal (50-60 h), proliferation (60-80 h) and matrix deposition (post 80 h). The cellular changes found in the dental papilla were considerably different from those found in inflammation, resolution and repair of fibrous connective tissue. These early stages were dominated by apoptosis and heterophagy, and after 80 h by disordered dentin matrix formation. The three-dimensional morphology of the defect was reconstructed from serial sections. The shape of the niche was the result of interference by actinomycin D in the patterns of proliferation and migration of the cells in the apical region of the rat incisor tooth.

Acid Phosphatase↗