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PubMed2001

Sonic hedgehog regulates epithelial proliferation and cell survival in the developing tooth germ.

Shh expression is highly restricted to the future sites of tooth development during the initiation of odontogenesis. This suggests a role for Shh as a proliferative factor, as localized epithelial thickenings invaginate to form a tooth bud. We have investigated this role by blocking Shh signaling between E10.5 and E12.5 in murine mandibular processes using a 5E1 blocking antibody and the PKA activator Forskolin. This results in down-regulation of Ptc, a principle target of Shh signaling. The effects of inhibition varied with developmental time. At E10.5, tooth development was arrested as epithelial thickenings and the numbers of teeth developing were considerably reduced. Inhibition at E12.5 produced localized apoptosis in the epithelium at the tip of the tooth buds, although some teeth were able to develop. Thus, Shh has dual roles in early odontogenesis, first in bud formation by stimulating epithelial proliferation, and second in the development of cap-stage tooth germs by increasing epithelial cell survival.

Animals↗

PubMed2002

Identification of cis-DNA regions controlling Bmp4 expression during tooth morphogenesis in vivo.

Epithelial-mesenchymal interactions are required for tooth formation. Bone morphogenetic protein 4 (Bmp4) is a crucial signaling molecule during this process. For better understanding of the role of the Bmp4 gene during tooth development, we studied the mechanisms that control its temporal and spatial expression during development. Using a transgenic approach, we determined that the domains which controlled Bmp4 expression in epithelium-derived ameloblasts were located in the region between 0.26 kb and 1.1 kb of the murine Bmp4 promoter. In contrast, the domains controlling Bmp4 expression in mesenchyme-derived odontoblasts and pulp cells existed in other regions of the Bmp4 gene. We have also demonstrated that the domains controlling Bmp4 expression in primordial tooth cells differ from those controlling Bmp4 expression in mature tooth tissues. The determination of unique domains by controlling the expression of the Bmp4 gene suggests that different transcriptional factors regulate the Bmp4 level at different stages during tooth morphogenesis.

Ameloblasts↗

PubMed1984

Influence of serum on cultured murine tooth organ allotransplants.

Previous investigations indicated that in vitro culture of fetal tooth germs before allotransplantation prolonged graft survival. This study assessed the influence of different sources of serum in culture medium on post-transplant development of neonatal tooth organs. The results indicate that recipient-strain serum, but not donor-strain serum or calf serum, increased tooth survival compared with that of uncultured controls, which were rejected by the fourteenth post-transplant day. The survival curve for cultured tooth organs was shifted to the right by two days. No tooth transplant survived beyond three wk.

Animals↗

PubMed1990

Risk factors for tooth loss over a 28-year period.

Over 500 residents of Tecumseh, Michigan, were dentially examined in 1959 as part of a community-wide health study. In 1987, the dental examinations were repeated, with use of the same criteria as in 1959, for 167 dentate persons from the original group. Another 28 reported by telephone that they had become edentulous since 1959. This report uses a historical cohort analysis for exploration of the risk factors for tooth loss, both total and partial, over the 28-year period. Over that time, the edentulous lost an average of 18.0 teeth (95% confidence interval 15.5, 20.7), whereas the age-matched 90 dentate persons lost only 3.2 (2.2, 4.2) teeth each. Descriptive data showed the edentulous to have higher baseline scores for plaque, calculus, and gingivitis, and a higher proportion of them smoked, though only loss of periodontal attachment (LPA) of 4 mm or more, early loss of first molars, and educational attainment were significant risk factors in regression analysis. Odds ratios for these three variables were 4.0 (1.2, 12.8), 2.0 (1.3, 3.1), and 0.6 (0.4, 0.9), respectively. The strongest risk factors for partial tooth loss among 116 dentate persons were baseline gingivitis (which was correlated with LPA of 4 mm or more) and the baseline number of teeth present, with odds ratios of 2.4 (1.2, 5.2) and 0.8 (0.7, 1.0), respectively. While the analysis had to be carried out without caries data, it was concluded that total tooth loss is a social-behavioral issue as much as it is disease-related. Social-behavioral factors were less clearly related to partial tooth loss in dentate persons; oral disease characteristics were the most prominent risk factors for partial tooth loss.

Cohort Studies↗

PubMed1996

Interleukin (IL)-1 beta, IL-6, tumor necrosis factor-alpha, epidermal growth factor, and beta 2-microglobulin levels are elevated in gingival crevicular fluid during human orthodontic tooth movement.

Bone remodeling is a complex process regulated by several mediators. Recent work has revealed that cytokines and growth factors have significant effects on bone cell metabolism. However, little information is available concerning the production of cytokines during orthodontic tooth movement in human subjects, and there is no non-invasive model for determining the production of cytokines. Therefore, the purpose of this study was to identify and quantify the various cytokines in human gingival crevicular fluid (GCF), and to investigate the changes in their levels during orthodontic tooth movement. Twelve patients (mean age, 14.4 years) were used as subjects. An upper canine of each patient having one treatment for distal movement served as the experimental tooth, whereas the contralateral and antagonistic canines were used as controls. The GCF around the experimental and the two control teeth was taken from each subject immediately before activation, and at 1, 24, and 168 hr after the initiation of tooth movement. Cytokine levels were determined by ELISAs. The concentrations of interleukin (IL)-1 beta, IL-6, tumor necrosis factor-alpha, epidermal growth factor, and beta 2-microglobulin were significantly higher in the experimental group than in the controls at 24 hr after the experiment was initiated. All the cytokines remained at baseline levels throughout the experiment for the two control groups. In contrast to cytokine alteration, the amount of total protein in the GCF exhibited a gradual increase, but no significant difference was observed between the control and experimental groups. Since all cytokines in GCF play an important role in the bone remodeling processes in vitro, the present results indicate that the changes in cytokines in GCF are associated with orthodontic tooth movement.

Adolescent↗

PubMed1997

Reduced chlorhexidine tooth stain coverage by sequential administration of monoperoxyphthalic acid in the beagle dog.

Extrinsic tooth stain is sometimes a side-effect observed with the chronic use of chlorhexidine-containing oral care products. This chlorhexidine (CHX)-induced tooth staining is observed both in humans as well as in experimental animals. The present study tested the hypothesis that the sequential administration of monoperoxyphthalic acid (MPA) will reduce the development of chlorhexidine-induced tooth stain coverage in a beagle dog. For this study, dogs were treated with 30 mL of mouthrinse b.i.d. for 28 days. The following treatment groups ( = 12 dogs/group) were tested: water (negative control), 1.0% MPA rinse, 0.12% CHX rinse, and 1.0% MPA rinse followed by 0.12% CHX rinse. The sequential dosing of 1.0% MPA followed by 0.12+ CHX resulted in significantly (p < or = 0.05) less tooth stain than when dogs were dosed with 0.12% CHX alone. Additionally, the sequential dosing of MPA followed by chlorhexidine resulted in a 75% reduction in plaque formation in this model, which was significantly different (p < or = 0.05) from results with either treatment alone. A further study demonstrated that similar results could be obtained when MPA plus CHX treatment alone. A further study demonstrated that similar results could be obtained when MPA plus CHX treatments were separated by approximately a five-hour period in an AM and PM schedule. We conclude that the oxidizer, MPA, can significantly reduce tooth stain induced by CHX while enhancing its antiplaque and antigingivitis activity.

Animals↗

PubMed1997

Enamel subsurface damage due to tooth preparation with diamonds.

In clinical tooth preparation with diamond burs, sharp diamond particles indent and scratch the enamel, causing material removal. Such operations may produce subsurface damage in enamel. However, little information is available on the mechanisms and the extent of subsurface damage in enamel produced during clinical tooth preparation. The aim of this study, therefore, was to investigate the mechanisms of subsurface damage produced in enamel during tooth preparation by means of diamond burs, and to examine the dependence of such damage on enamel rod orientation, diamond particle size, and removal rate. Subsurface damage was evaluated by a bonded-interface technique. Tooth preparation was carried out on two enamel rod orientations, with four clinical diamond burs (coarse, medium, fine, and superfine) used in a dental handpiece. The results of this study showed that subsurface damage in enamel took the form of median-type cracks and distributed microcracks, extending preferentially along the boundaries between the enamel rods. Microcracks within individual enamel rods were also observed. The median-type cracks were significantly longer in the direction parallel to the enamel rods than perpendicular to the rods. Preparation with the coarse diamond bur produced cracks as deep as 84 +/- 30 microns in enamel. Finishing with fine diamond burs was effective in crack removal. The crack lengths in enamel were not significantly different when the removal rate was varied. Based on these results, it is concluded that subsurface damage in enamel induced by tooth preparation takes the form of median-type cracks as well as inter- and intra-rod microcracks, and that the lengths of these cracks are sensitive to diamond particle size and enamel rod orientation, but insensitive to removal rate.

Dental Enamel↗

PubMed1998

Inhibition of tooth eruption in the rat by a bisphosphonate.

Studies of osteopetrotic rodents suggest that localized alveolar bone resorption must occur if the tooth is to erupt. To test this hypothesis directly, we injected postnatal rats with pamidronate, a bisphosphonate that reduces bone resorption by osteoclasts. The results of these experiments demonstrate that this bisphosphonate inhibits the time of tooth eruption of both rat molars and incisors. Pamidronate does not inhibit the gene expression of the putative tooth eruption molecules, colony-stimulating factor-1 and c-fos, both of which are expressed in the dental follicle, the tissue that is required for eruption to occur. Pamidronate does increase the size of the osteoclasts, including an increase in the number of nuclei, suggesting that the precursor mononuclear cells can still fuse to form osteoclasts despite the reduced ability of the osteoclasts to resorb bone. Thus, we report the discovery of an agent that inhibits tooth eruption and also show that tooth eruption requires alveolar bone resorption.

Acid Phosphatase↗

PubMed1998

Alterations in ultrastructural localization of growth-associated protein-43 (GAP-43) in periodontal Ruffini endings of rat molars during experimental tooth movement.

It is known that orthodontic forces induce discomfort and/or abnormal sensation after application of an orthodontic appliance in patients, suggesting the adaptation of periodontal neural elements to environmental changes. However, no morphological data have been provided. The present study investigated, by immunoelectron microscopy, the localization of growth-associated protein-43 (GAP-43) in periodontal Ruffini endings in rat molars during experimental tooth movement. In the untreated control group, immunoelectron microscopy demonstrated that GAP-43-like immunoreactivity in the Ruffini endings was confined to the Schwann sheaths around the axon terminals, and was in neither the cell bodies of terminal Schwann cells nor the axon terminals themselves. Immunoelectron microscopic observation revealed alterations in the localization of GAP-43-like immunoreactivity in the periodontal Ruffini endings during experimental tooth movement. After 1 day of treatment, the cell bodies of the terminal Schwann cells associated with Ruffini endings appeared to contain immunoreaction products for GAP-43, and retained GAP-43-like immunoreactivity during tooth movement. From 5 to 7 days, a major population of the axoplasm of the periodontal Ruffini endings, which was immunonegative in control, filled the GAP-43 immunoreactions, showing a tendency to decrease in number later, and disappeared completely at 14 days. These findings suggest that orthodontic forces easily induce the remodeling of the mechanoreceptive Ruffini endings as well as the active tissue remodeling in a close relationship. Since the ultrastructural localization of GAP-43-like immunoreactivity was drastically changed in the Ruffini endings during tooth movement, GAP-43 functions as one of the key molecules in the remodeling of mechanoreceptive Ruffini endings during tooth movement.

Acid Phosphatase↗

PubMed1999

Endodontic disease of the mandibular first molar tooth secondary to caudal crossbite in a young Shetland sheepdog.

A six month-old intact female Shetland sheepdog was referred to the University of Illinois Veterinary Dental Clinic with a left-sided mandibular deviation and a thickened left ventral mandible in the region of the first molar tooth. On oral examination, left caudal crossbite was diagnosed. Dental radiographs revealed endodontic disease of the mandibular first molar tooth involved in the crossbite. Because of the difficulty of treating caudal crossbite and the potential of a pathological mandibular fracture, the endodontically affected tooth was extracted. Ten months following the extraction, mandibular deviation and alveolar bone lysis were resolved, but alveolar ridge resorption was present. The abnormal occlusal relationship caused by the caudal crossbite may have led to movement of the tooth, resorption of the tooth alveolus, and irreversible pulpal damage. Although not employed in this case, use of alveolar ridge preservation techniques can prevent mandibular bone loss after extractions.

Alveolar Bone Loss↗

PubMed2003

Increased preventive practices lead to greater tooth retention.

Prior research has rarely examined the impact of ADA-recommended preventive practices on tooth retention. We hypothesized that better oral hygiene leads to increased tooth retention. We examined the association of cross-sectional and long-term assessments of preventive practices, as well as various combinations of hygiene practices, with tooth retention. Among 736 male participants in the VA Dental Longitudinal Study, we utilized cross-sectional and longitudinal self-reports of toothbrushing, dental floss use, annual prophylaxis, and combinations of such behaviors, and examined their association with clinically assessed numbers of teeth. Baseline and long-term hygiene behaviors (except brushing) were associated with an increased baseline number of teeth and decreased subsequent tooth loss. Use of multiple hygiene behaviors was associated with greater tooth retention, cross-sectionally and longitudinally. Adherence to ADA recommendations for preventive care leads to better oral health, and consistently practicing preventive behaviors over the long term confers greater benefits than doing so over the short term.

Adult↗

PubMed2005

Organized tooth-specific cellular differentiation stimulated by BMP4.

Mammalian teeth develop on the oral surface of the first pharyngeal arch by a series of reciprocal interactions between epithelial and mesenchymal cells. The embryonic first pharyngeal arch oral epithelium is able to induce tooth formation when combined with mesenchymal cells from the second pharyngeal arch, a region devoid of tooth development. Second pharyngeal arch mesenchyme is thus competent to form teeth if provided with the correct signals. First-arch oral epithelium expresses several signaling molecules that could be potential inducers of tooth development, including BMP4. The addition of BMP4 to intact second-arch explants resulted in the development of organized structures containing layers of cells that express marker genes of tooth-specific cells, odontoblasts and ameloblasts. Thus, although overt tooth development did not occur, BMP4 has the ability to stimulate organized differentiation of epithelial- and mesenchymal-derived dental-specific cells from non-dental primordia.

Ameloblasts↗

PubMed2002

Cellular, molecular, and genetic determinants of tooth eruption.

Tooth eruption is a complex and tightly regulated process that involves cells of the tooth organ and the surrounding alveolus. Mononuclear cells (osteoclast precursors) must be recruited into the dental follicle prior to the onset of eruption. These cells, in turn, fuse to form osteoclasts that resorb alveolar bone, forming an eruption pathway for the tooth to exit its bony crypt. Some of the molecules possibly involved in the signaling cascades of eruption have been proposed in studies from null mice, osteopetrotic rodents, injections of putative eruption molecules, and cultured dental follicle cells. In particular, recruitment of the mononuclear cells to the follicle may require colony-stimulating factor-one (CSF-1) and/or monocyte chemotactic protein-1 (MCP-1). Osteoclastogenesis is needed for the bone resorption and may involve inhibition of osteoprotegerin transcription and synthesis in the follicle, as well as enhancement of receptor activator of NF kappa B ligand (RANKL), in the adjacent alveolar bone and/or in the follicle. Paracrine signaling by parathyroid-hormone-related protein and interleukin -1 alpha, produced in the stellate reticulum adjacent to the follicle, may also play a role in regulating eruption. Osteoblasts might also influence the process of eruption, the most important physiologic role likely being at the eruptive site, in the formation of osteoclasts through signaling via the RANKL/OPG pathway. Evidence thus far supports a role for an osteoblast-specific transcription factor, Cbfa1 (Runx2), in molecular events that regulate tooth eruption. Cbfa1 is also expressed at high levels by the dental follicle cells. This review concludes with a discussion of the several human conditions that result in a failure of or delay in tooth eruption.

Animals↗

PubMed1992

Aesthetic tooth modification for patients with cleft lip and palate.

Alongside orthodontic treatment, tooth shape modification may be indicated for teeth associated with clefts of the lip and alveolus, and in non-carious teeth, minimal tooth preparation techniques appear to be most appropriate. Two methods of tooth shape modification are described. In one, hybrid composite materials, bonded to tooth enamel using the acid-etch technique, may be considered to provide a permanent, low cost, aesthetically satisfactory result, often without tooth preparation and with minimal operating time. Alternatively, indirect veneers may be appropriate for treatment of more severely malformed teeth.

Anodontia↗

PubMed2004

Coordination of trigeminal axon navigation and patterning with tooth organ formation: epithelial-mesenchymal interactions, and epithelial Wnt4 and Tgfbeta1 regulate semaphorin 3a expression in the dental mesenchyme.

During development, trigeminal nerve fibers navigate and establish their axonal projections to the developing tooth in a highly spatiotemporally controlled manner. By analyzing Sema3a and its receptor Npn1 knockout mouse embryos, we found that Sema3a regulates dental trigeminal axon navigation and patterning, as well as the timing of the first mandibular molar innervation, and that the effects of Sema3a appear to be mediated by Npn1 present in the axons. By performing tissue recombinant experiments and analyzing the effects of signaling molecules, we found that early oral and dental epithelia, which instruct tooth formation, and epithelial Wnt4 induce Sema3a expression in the presumptive dental mesenchyme before the arrival of the first dental nerve fibers. Later, at the bud stage, epithelial Wnt4 and Tgfbeta1 regulate Sema3a expression in the dental mesenchyme. In addition, Wnt4 stimulates mesenchymal expression of Msx1 transcription factor, which is essential for tooth formation, and Tgfbeta1 proliferation of the dental mesenchymal cells. Thus, epithelial-mesenchymal interactions control Sema3a expression and may coordinate axon navigation and patterning with tooth formation. Moreover, our results suggest that the odontogenic epithelium possesses the instructive information to control the formation of tooth nerve supply.

Animals↗

PubMed1991

Associations between transforming growth factor beta 1 RNA expression and epithelial-mesenchymal interactions during tooth morphogenesis.

We have studied the expression of transforming growth factor beta-1 (TGF-beta 1) RNA during mouse tooth development, using in situ hybridization and experimental tissue recombinations. Analysis of the serial sections revealed the appearance of local expression of TGF-beta 1 RNA in the dental epithelium at bud-staged teeth (13-day embryos). Just before transition to the cap stage, TGF-beta 1 RNA expression rapidly increased in the epithelial bud, and it also extended to the condensed dental mesenchyme. At cap stage (14- and 15-day embryos), there was an intense expression of TGF-beta 1 RNA in the morphologically active cervical loops of the dental epithelium. During early bell stage (16- and 17-day embryos), TGF-beta 1 RNA expression was detected in the inner enamel epithelium where it subsequently almost disappeared (18-day embryos). After birth TGF-beta 1 transcripts transiently appeared in these cells when they were differentiating into ameloblasts (1-day mice). The transcripts were lost from the ameloblasts when they became secretory (4-day mice), but the expression continued in ameloblasts in enamel-free areas. Transient expression of TGF-beta 1 RNA was also detected in epithelial stratum intermedium cells at the time of ameloblast differentiation. In the mesenchyme, TGF-beta 1 RNA was not detected during bell stage until it appeared in differentiated odontoblasts (18-day embryos). The secretory odontoblasts continued to express TGF-beta 1 RNA at all stages studied including the odontoblasts of incisor roots. Analysis of the distribution of bromodeoxyuridine (BrdU) incorporation indicated apparent correlations between TGF-beta 1 RNA expression and cell proliferation at the bud and cap stages but not at later stages of tooth development. Tissue recombination experiments of bud-staged (13-day embryos) dental and non-dental tissues showed that tooth epithelium, when cultured together with tooth mesenchyme, expressed TGF-beta 1 RNA. When the tooth epithelium was combined with non-dental jaw mesenchyme, TGF-beta 1 transcripts were not expressed. However, TGF-beta 1 RNA expression was seen in oral epithelium cultured with dental mesenchyme, while no expression of TGF-beta 1 transcripts was seen in the oral epithelium during normal development. Thus, TGF-beta 1 RNA expression seems to be regulated by epithelial-mesenchymal interactions.

Animals↗

PubMed1995

A role for mesenchyme-derived tachykinins in tooth and mammary gland morphogenesis.

Tachykinin peptides such as substance P (SP) function as neurotransmitters and neuromodulators in the mammalian central and peripheral nervous systems. Here, we provide evidence that they may also play an important role in the morphogenesis of some nonneural organs where epithelial-mesenchymal interactions are involved. We show the following. (1) mRNA encoding tachykinin precursor proteins is expressed transiently in condensing mesenchyme during the development of mouse tooth germ, mammary gland, limb bud, external auditory meatus and genital tubercle. (2) In developing tooth germ and mammary gland; mRNA encoding the neutral endopeptidase (NEP) that degrades secreted tachykinins is spatially and temporally co-expressed with tachykinin precursor mRNA. (3) SP and the mRNA encoding SP receptors are also expressed in the developing tooth germ. (4) Tooth development in explant cultures is blocked both by tachykinin-precursor-specific antisense oligonucleotide and by an SP receptor antagonist: in both cases the block is relieved by exogenous SP. Together, these findings suggest a surprising new role for tachykinins in tooth and mammary gland morphogenesis, and possibly also in limb, ear and external genitalia morphogenesis.

Animals↗

PubMed1996

Hepatocyte growth factor is involved in the morphogenesis of tooth germ in murine molars.

The patterns of gene expression for hepatocyte growth factor (HGF) and its receptor, c-Met, were revealed in the tooth germ of rat mandibular molars using RT-PCR. In situ hybridization demonstrated that the HGF gene was expressed only in the cells of the dental papilla of the tooth germ in vivo. The characteristic temporospatial distribution of HGF and c-Met during germ development was revealed using immunohistochemical studies in vivo. In order to demonstrate the functional role played by HGF in tooth development, HGF translation arrest by antisense phosphorothioate oligodeoxynucleotide (ODN) was carried out in vitro. In the control experiment, explants of tooth germs from embryonic 14 day mice were cultured in a modification of Trowell's system under serum-free and chemically defined conditions for two weeks. Other explants were cultured with 15mer antisense or sense ODN targeted to the HGF mRNA. Both the control and the sense-treated explants showed normal histological structure, as observed in vivo. On the other hand, antisense-treated explants exhibited an abnormal structure in which the enamel organs were surrounded by a thin layer of dentin and dental papilla, appearing 'inside-out' compared to the control and sense-treated explants, although the cytodifferentiation of ameloblasts and odontoblasts was not inhibited. The explants treated with recombinant human HGF combined with antisense ODN showed normal development, indicating that exogenous HGF rescued the explants from the abnormal structure caused by antisense ODN. The findings of a BrdU incorporation experiment suggested that the imbalance between the proliferation activity of the inner enamel epithelium and that of the dental papilla caused by HGF translation arrest results in the abnormal structure of the tooth germ. These results indicate that HGF is involved in the morphogenesis of the murine molar.

Animals↗