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The aim of the study was to see whether the length of the enamel secretion zone in unimpeded rat incisors, measured precisely, is in agreement with the observed decrease in enamel thickness. Unimpeded eruption of mandibular incisors of five experimental and two control rats was induced by cutting off the erupted part of the incisors three times per week for 5 weeks. The length of the zone of enamel secretion in unimpeded and impeded control incisors was measured on longitudinal and serial transverse histological sections of fixed, demineralised and embedded hemimandibles. Impeded contralateral incisors were also included in the study. The length of the zone of enamel secretion in unimpeded incisors showed an increase to 8,398 ± 558 µm, that is 161% of the length in control incisors (5,213 ± 95 µm). The contralateral incisor showed a reduction in eruption rate, in length of the secretion zone, and the whole tooth was shifted somewhat apically. The measured length of the secretion zone is in agreement with the observed thickness of enamel (98 µm) in unimpeded incisors. The reduced eruption rate and the apical shift of the contralateral incisor are probably due to an increased occlusal load. [ABSTRACT FROM AUTHOR]

A major component of tooth innervation is made of capsaicin-sensitive primary afferents (CSPA). These fibers play a key role in tooth pain and inflammation; little is known, however, about the role of CSPA in tooth eruption. The aim of this study was to examine the role of the capsaicin-sensitive afferents in the process of eruption of intact rat incisors. CSPA fibers in several rat groups, were subjected to one of the following experimental procedures: systemic chemical ablation, systemic ablation followed by chemical sympathectomy and localized activation. The observed effects on incisor eruption were compared to those made on controls. The total amount of eruption in control/naïve rats, measured over a total period of 144 h, was 3.18 ± 0.07 mm and decreased to 2.43 ± 0.08 mm (n = 7; p < 0.001) following systemic ablation of CSPA. Further decrease to 2.24 ± 0.08 mm (n = 7; p < 0.001) was noticed when chemical sympathectomy was added to CSPA ablation. The average rate of eruption was 1.7 ± 0.25 mm following CSPA activation, compared to an average of 0.8 ± 0.07 mm for controls (n = 7; p < 0.001). Capsaicin sensitive fibers play an important role in tooth homeostasis, and intact neural supply is required for tooth growth under normal conditions. [ABSTRACT FROM AUTHOR]

Background and Objective This study investigated the effect of occlusal contact loss (induced by tooth shortening), on matrix metalloproteinase ( MMP)-2, membrane type 1-MMP ( MT1- MMP) and tissue inhibitor of the MMP-2 ( TIMP-2) expressions in the periodontal ligament of the rat incisor, as well as eruption rate, resistance and collagen organization. Material and Methods Male Wistar rats were distributed into a control group, denominated normofunctional group, whose lower teeth underwent a normal eruption process; and a hypofunctional group, whose lower left incisor teeth were shortened every 2 days during 14 days. Parameters were evaluated on the first, seventh and 14th days and the eruption rate was determined according to the size of the incisor during the eruption process. MMP-2 activity was determined by zymography and the expressions of the MT1- MMP and TIMP-2 proteins were quantitated by western blot. Collagen protein organization, as indicated by the birefringence of the periodontal ligament, was analyzed under polarized light and the periodontal ligament's resistance was determined from the load necessary to inject the incisor into its alveolar space, before extraction. Results Loss of occlusal contact, in rats submitted to hypofunctional eruption, increased MMP-2 activity and eruption rate, but decreased MT1- MMP and TIMP-2 expression and disrupted collagen organization in the periodontal ligament, consequently reducing periodontal ligament resistance. Conclusion We conclude that, after incisor eruption, occlusal contact may be an important factor for regulating the remodeling and the physiological resistance of the periodontal ligament against the continuous eruption process observed in rat incisors. [ABSTRACT FROM AUTHOR]

Objective To re-examine the morphology and potential functions of odontoblasts in intact rat incisors and after cavity preparation into dentine. Design Intact incisors were fixed, decalcified, snap frozen and sectioned (10 μm), before staining with rhodamine phalloidin or antibodies for cyto-skeletal proteins: vimentin and actin, ion transporter: NaK-ATPase, and dendritic cell marker: OX6. Samples with cavity were processed similarly and stained for actin and vimentin before comparing the lengths of odontoblast processes (OP) at baseline, 3 h and 24 h (n = 5 for each group). Results Actin was expressed through the full length of OP, while vimentin immunoreactivity was not uniform, with 4 distinct regions. OP showed morphological complexity with fine branches emanating within different regions of dentine. Novel actin-positive tree-like OP were identified within predentine which reduced in intensity and length toward the incisal portion of the tooth. Specimens with cavities showed time-dependant pulpal retraction of OP. Conclusions Differences in structural antibody expression suggest functional variations in OP within different regions of dentine. The role of actin positive OP in predentine is not known, but could be related to dentine deposition, cellular stability or sensing mechanisms. Cavity preparation into dentine was followed by programmed retraction of OP which could be controlled either mechanically by the spatial limitation of the OP within dentinal tubules or structurally by the presence of vimentin, in addition to actin, in the mid-dentine. [ABSTRACT FROM AUTHOR]

The present work aims to test the effect of gamma radiation on the rate of eruption of rat incisors. One hundred and five adult male albino rats were used and irradiated at different gamma doses. The effects of irradiation were investigated by numerical measurements of eruption rate, histological investigation using light microscope and spectral analysis using Fourier Transform Infra-Red (FTIR). No detectable changes were observed in the groups with smaller radiation doses. There was a significant decrease in the eruption rate starting from the 4 Gy radiation dose. The observation of histological sections revealed disturbance in cellular elements responsible for eruption as well as periodontal disturbance in the samples irradiated with 4 and 6 Gy. FTIR Spectroscopy of control group and the group irradiated by 0.5 Gy showed similar absorption bands with minor differences. However, samples irradiated by 1 Gy showed significant changes in both molecular structure and conformation related to carbonates and hydroxyl groups. From the previous results, it could be concluded that gamma irradiation negatively affects the eruption rate of the rat incisors especially with higher doses. [ABSTRACT FROM PUBLISHER]

Abstract: The aim of this study was to investigate the behavior of rat incisor tissues during the inhibition of tooth eruption. Twenty Sprague-Dawley rats were used in this study, and incisor eruption was inhibited by a screw pin. Animals were sacrificed 1, 3, 7 and 14 days after the start of the experiment. Cross-sections at the mesial point of the mandibular first molar and sagittal sections of the mandibular tooth germ area were examined using immunohistochemical and immunofluorescence methods. For morphometric analysis, numbers of TRAP-positive cells were calculated against the total number of cells. In cross-sections from the experimental group, dentin was thickened and pulp tissue was constricted day by day. On days 1, 3 and 7, nestin-positive cells were observed in all odontoblast cell bodies and processes, while on day 14 fewer nestin-positive cells were seen than in the control group. On day 14, the mesial area of the periodontal ligament was constricted and the number of TRAP-positive cells in the mesial area was significantly higher than in the control group. In sagittal sections, enamel formation was found to be increased on days 7 and 14. Furthermore, in the enamel matrix amelogenin was expressed more strongly than in the control group. PCNA-positive cells were significantly increased in cells of the tooth germ compared with the control group. These results suggest that inhibition of tooth eruption accelerates the apical elongation with resorption of the mesial area of the alveolar bone and stimulates cell proliferation with thickened enamel towards the apical end. [Copyright &y& Elsevier]

The effect of exposure to amoxicillin on tooth development remains to be elucidated. The purpose of this study was to investigate the effect of amoxicillin on rat incisor odontogenesis. Male Wistar rats weighing approximately 100 g were given a single intraperitoneal injection of 3.0 g/kg body weight amoxicillin. One week after injection, the rats were fixed, and the lower incisors were demineralized and prepared into paraffin sections for light microscopy (LM) and immunohistochemistry. Undemineralized samples were embedded in resin and ground for processing for contact microradiography (CMR) and scanning electron microscopy (SEM). Serum calcium, phosphate, and magnesium concentrations were measured. At 1 week after amoxicillin administration, LM, CMR, and SEM revealed a clear increase in the area of interglobular dentin, representing disruption of mineralization by odontoblasts. Immunohistochemistry demonstrated moderate levels of the small integrin-binding ligand N-linked glycoprotein family dentin matrix protein 1 in large areas of interglobular dentin. On the other hand, no morphological alteration or hypomineralization was observed in the enamel. Serum calcium values showed no significant differences between the control and experimental rats during the experimental period although both serum phosphate and magnesium levels increased at day 1 after amoxicillin injection. The results suggest that a single dose of amoxicillin specifically affects normal tooth dentin mineralization, but not enamel mineralization in rat incisor odontogenesis. The present results further our understanding of the clinical association between dentin abnormality and amoxicillin exposure during tooth development. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Our aim was to test the hypothesis that co-exposure to lead and fluoride alter the severity of enamel fluorosis. Materials and methods: Wistar rats were allocated in four groups: control, and 3 groups that received water containing 100ppm of fluoride (F), 30ppm of lead (Pb), or 100ppm of F and 30ppm of Pb (F+Pb) from the beginning of gestation. Enamel analysis and F and Pb determinations in enamel, dentine, and bone were performed in 81-day-old animals. Fluorosis was quantified using a new fluorosis index based on the identification of incisor enamel defects (white bands and white islets, representing hypomineralization, and cavities) weighted according to their severity and quantity. Hypomineralization was validated histopathologically by polarizing microscopy and microradiography. Scores were given by two blinded calibrated examiners (intra and interexaminer kappa values were 0.8 and 0.86, respectively). Results: The control and the Pb groups presented normal enamel. The F+Pb group presented more severe enamel defects compared with the F group (P <0.0001). Conclusions: This study shows that lead exacerbates dental fluorosis in rodents, suggesting that co-exposure to lead may affect the degree of fluorosis. [Copyright &y& Elsevier]

Mature enamel consists of densely packed and highly organized large hydroxyapatite crystals. The molecular machinery responsible for the formation of fully matured enamel is poorly described but appears to involve oscillative pH changes at the enamel surface. We conducted an immunohistochemical investigation of selected transporters and related proteins in the multilayered rat incisor enamel organ. Con- nexin 43 (Cx-43) is found in papillary cells and ameloblasts, whereas Na+-K+-ATPase is heavily expressed during maturation in the pap- illary cell layer only. Given the distribution of Cx-43 channels and Na+-K+-ATPase, we suggest that ameloblasts and the papillary cell layer act as a functional syncytium. During enamel maturation amelo- blasts undergo repetitive cycles of modulation between ruffle-ended (RA) and smooth-ended (SA) ameloblast morphologies. Carbonic anhydrase 11 and vacuolar H+-ATPase are expressed simultaneously at the beginning of the maturation stage in RA cells. The proton pumps are present in the ruffled border of RA and appear to be internalized during the SA stage. Both papillary cells and ameloblasts express plasma membrane acid/base transporters (AE2, NBC, and NHEI). AE2 and NHEI change position relative to the enamel surface as localization of the tight junctions changes during ameloblast modulation cycles. We suggest that the concerted action of the papillary cell layer and the modulating ameloblasts regulates the enamel microenvironment, resulting in oscillating pH fluctuations. The pH fluctuations at the enamel surface may be required to keep intercrystalline spaces open in the surface layers of the enamel, enabling degraded enamel matrix proteins to be removed while hydroxyapatite crystals grow as a result of influx of calcium and phosphate ions. [ABSTRACT FROM AUTHOR]

Abstract: The enamel-related periodontium (ERP) in rat incisors is related to bone resorption. In these teeth the face of the socket related to the enamel is continuously removed at the inner side and newly formed at the outer side. CSF-1, RANKL and OPG are regulatory molecules essential for osteoclastogenesis. To verify the effects of impeded eruption on bone remodeling, the tooth eruption was prevented by immobilization of lower rat incisor and CSF-1, RANKL and OPG distribution in the ERP was analyzed after 18 days of immobilization and in normal eruption. The region of the alveolar crest of the rat incisor was used. Immunohistochemistry and tartrate-resistant acid phosphatase (TRAP) were performed. The immunostaining of the dental follicle was quantified using Leica QWin software. Positive-TRAP osteoclasts were counted, and both groups were compared. In the normal incisor, the number of osteoclasts was significantly greater than in the immobilized tooth. In the dental follicle, there was no significant difference in the immunostaining intensity for CSF-1 and OPG between the groups (p >0.05), but for RANKL the immobilized incisor group showed immunostaining intensity smaller than the normal incisor group (p <0.01). These findings suggest that changes in the ERP, in the immobilized incisor, modify the RANKL/OPG ratio, in the presence of CSF-1, altering the metabolism of cells that participate in the bone remodeling. [Copyright &y& Elsevier]

While dental pulp appears to be able to form mineralized matrices that do not always resemble dentin, the precise characteristics of the hard tissue and the mechanism of its induction remain unknown. Therefore, we evaluated hard tissue induced by transplantation of pulp into subcutaneous tissue. Seven days after transplantation, initial hard tissue was formed at the inner periphery of the pulp. After 14 days, this hard tissue expanded inwardly. Mineralized matrix was immunopositive for osteocalcin, osteopontin, and bone sialoprotein, but negative for dentin sialoprotein. Transplantation of GFP-labeled pulp into wild-type rats showed these formative cells to have been derived from the transplant. TEM observation revealed apatite crystals within necrotic cells and matrix vesicles at the initial stage of calcification. These results indicate that pulp cells possess the ability to form a bone- or cementum-like matrix. Calcification of the matrix may occur in necrotic cells and matrix vesicles, followed by collagenous calcification. [ABSTRACT FROM AUTHOR]

Since a considerable amount of the world population is exposed to high doses of fluoride, it is of special concern to investigate its action mechanisms during dental enamel development. In this study, the toxicity of fluoride in ameloblasts during enamel development was evaluated by means of ultrastructural morphometric analysis. A total of 18 male Wistar rats were distributed into three groups. In Group I, the animals received deionized drinking water ad libitum (negative control) and in Groups II and III, they received sodium fluorided (NaF) drinking water at doses of 7 and 100 ppm ad libitum, respectively, for 6 weeks. Morphometric data were expressed as volume density of the most significant organelles present in the secretory and maturation phases of amelogenesis such as RER, granules, lysosomes, phagic vacuoles, microfilaments and mitochondria. The results showed that the volume density of mitochondria in the 100 ppm experimental group was 29% ( P < 0.05) higher than the control group in secretory ameloblasts. No remarkable differences were found in maturation ameloblasts for all organelles evaluated. Taken together, these data indicate that NaF at high doses is able to induce cellular damage in secretory ameloblasts, whereas no noxious effect was observed during maturation stage of amelogenesis as depicted by ultrastructural analysis. [ABSTRACT FROM AUTHOR]

Summary: Objective:: This study investigated the effect of age on tooth and periodontium morphology and on tooth eruption in the lower incisors of 28 female rats, initial age 10 weeks. Design:: Morphometric data of the incisors in three young mature rats (weight 199±2.4g) were compared to that of three 18-week-old (weight 260±5g) animals. The rate of eruption was monitored during 12 months in 11 rats with all teeth in occlusion and in 11 rats with one lower incisor kept constantly out of occlusion. Results:: The incisors continued to enlarge after the animals reached maturity with the size of the teeth increasing both longitudinally and circumferentially. Tooth volume increased by 21%, while that of the periodontal ligament was enlarged by only 12%. The rate of impeded eruption declined steadily from a mean value of 542±49μm/day during the first experimental month to a mean value of 443±25μm/day during the concluding month (p &#60;0.05). The eruption rate of the teeth exceeded that of attrition rate by 2.4%. The unimpeded eruption proceeded steadily throughout the experimental year, at a mean rate of 811±12. Conclusions:: Apparently in mature rats age has no effect on the genetic potential as expressed by the unimpeded eruption. In the impeded teeth age does affect the phenotypic expression of the eruptive function governed by occlusal forces as well as by the form and size ratio of the tooth and its PDL. [Copyright &y& Elsevier]

We investigated the effects of pulsed neodymium:yttrium-aluminium-garnet (Nd:YAG) laser irradiation time on the eruption of 56 mandibular incisors in 28 rats. Clinically, some incisors erupted and the others did not. The incisors were irradiated at 2 W, 20 pulses/s for the period of 3 s, 5 s, 7 s, and 10 s, and the regeneration process was monitored at 20 days after laser treatment. Incisors irradiated for 3-5 s continued their eruption; five incisors irradiated for 7 s and all incisors irradiated for 10 s did not erupt. In the incisors that continued to erupt, the inner epithelial cells differentiated into ameloblast and a part of the pulp cavity was occupied by osteodentin. In the teeth in which eruption had ceased, the inner epithelium cells did not differentiate into ameloblast, and most of the pulp cavity was occupied by osteodentin. The results indicate that a relatively short time duration of pulsed Nd:YAG laser irradiation in the pulp induced the reparative process without disturbing the eruption. [ABSTRACT FROM AUTHOR]

Shinohara J, Shibata T, Shimada A, Komatsu K. The biomechanical properties of the healing periodontium of replanted rat mandibular incisors. Dent Traumatol 2004; 20: 212–221. © Blackwell Munksgaard, 2004. One of the most important aspects in tooth replantation seems to be restoration of the tooth support function of the healing periodontal ligament (PDL). We examined the support function, as measured by the mechanical properties, of the healing PDL at 7, 14, and 21 days after replantation of the left mandibular incisor in rats. From each dissected left mandible, a transverse section(650 µm in thickness) of the incisor was cut through an axis near the labial alveolar crest. Each section was intrusively loaded at a rate of 5 mm min−1, and the shear stress–strain curve for the PDL was analyzed. Mechanical measures of the healing PDL showed gradual improvement after replantation. By 21 days, the mechanical strength returned to 53% of the control value; the extensibility, to 85%; the stiffness, to 61%; and the toughness, to 52%. The healing PDL exhibited reattachment of fibers in the middle region of the PDL, and the birefringent collagen fibers appeared to have regained the functional orientation by 14 days. The ratios occupied by the birefringent collagen fibers in the tooth-related, middle, and bone-related areas of the healing PDL gradually improved and returned to 78, 51, and 48% of the respective control values by 21 days. These results suggest that the support function of the healing PDL is gradually restored and that the biomechanical restoration is closely related to the reorganization and reorientation of collagen fiber bundles in replanted rat incisors. [ABSTRACT FROM AUTHOR]

Previous work has indicated that the enamel-related periodontium (ERP) has a role in the eruptive process of the rat lower incisor. By combining partial damage of this tissue with resection of the odontogenic organ, we examined the effect of the damage on subsequent incisor eruption. The connective tissue of the enamel-related periodontium was regenerated in less than 2 weeks, showing morphology close to normal. The injured part of the enamel organ was neither regenerated nor repaired, and a cement-like tissue, continuous with the true acellular cement, was formed on the denuded enamel. Before tooth exfoliation, the operated teeth erupted at a slower rate compared with root-resected and sham-operated incisors, probably because of the absence of a substantial part of the enamel organ due to surgical damage. As with the coronal dental follicle and the enamel organ in rat molars, the enamel-related periodontium and the enamel organ of rat incisors may have some control on their eruptive process. [Copyright &y& Elsevier]

Dental epithelial progenitor cells differentiate into various cell types during development of tooth germs. To study this mechanism, we produced immortalized dental epithelial progenitor cells derived from the cervical-loop epithelium of a rat lower incisor. The expression patterns of cytokeratin 14, nerve growth factor receptor p75, amelogenin, Notch2, and alkaline phosphatase were examined by immnohistochemistry in both lower and higher cell densities. The patterns of each were compared in the dental epithelium of rat lower incisors. The results demonstrated that these cells could produce ameloblast lineage cells, stratum intermedium cells, stellate reticulum, and outer enamel epithelium. Furthermore, fibroblast growth factor 10 stimulated proliferation of dental progenitor cells and subsequently increased the number of cells expressing alkaline phosphatase. These results suggest that fibroblast growth factor 10 plays a role in coupling mitogenesis of the cervical-loop cells and the production of stratum intermedium cells in rat incisors. [ABSTRACT FROM AUTHOR]

The effects of endogenous vasoactive substances were evaluated in anaesthetized rats using a laser Doppler flowmeter to monitor changes in pulpal blood flow, as well as directly in isolated pulpal arteriole preparations utilising a microperfusion and monitoring system to observe changes in vessel diameter. In anaesthetized rats, while systemic arterial blood pressure remained relatively stable, intra-arterial delivery of adrenaline (epinephrine) (A), noradrenaline (norepinephrine) (NA), phenylephrine (PHE), dopamine (DOPA), 5-hydroxytryptamine (5-HT), or endothelin-1 (ET-1) produced a dose-dependent reduction in pulpal blood flow (order of potency: ET-1≫A=NA>PHE=DOPA=5-HT); acetylcholine induced a dose-dependent increase in pulpal blood flow; histamine, isoproterenol and adenosine produced no significant changes. In isolated arteriole preparations, intraluminal delivery of A, NA, PHE, DOPA or 5-HT produced dose-dependent vasoconstriction (A=NA>PHE=DOPA=5-HT). Acetylcholine relaxed NA-precontracted vessels dose-dependently. Histamine and isoproterenol produced a small vasodilatation. Intraluminal ET-1 produced a small vasoconstriction at 10−8 M, whereas extraluminal ET-1 produced a dose-dependent vasoconstriction from 10−10 M and above. Intraluminal adenosine failed to dilate vessels precontracted with ET-1, whereas extraluminal adenosine caused a complete relaxation. These combined in vivo and in vitro data suggest that, in the rat incisor, the pulpal microcirculation is capable of functional regulation and that pulpal blood flow may be modulated by endothelium-related factors, metabolic (tissue-related) factors, as well as humoral (blood-borne) factors. [Copyright &y& Elsevier]

The most frequent results of trauma to tooth germs are enamel hypoplasia and enamel hypocalcification. These differing results may be due to the stage of amelogenesis at which trauma occurs. The cellular and biomolecullar events involved in the genesis of these defects are poorly understood. We hypothesized that one factor involved is the possibility that relatively high levels of serum albumin enter the enamel matrix through the damaged enamel organ, and impair mineralization of the matrix. The present study was undertaken to immunohistochemically and autoradiographically localize serum albumin in the enamel organs of rat incisors after trauma was inflicted to the mandibular incisor region of 4-day-old rats. Hemorrhage was seen surrounding the enamel organ and between the detached secretory-stage ameloblasts. One day after trauma, the most intense immunohistochemical (IHC) staining for albumin was localized in the outer layer of the enamel matrix adjacent to the detached secretory-stage ameloblasts. Albumin was also detected autoradiographically in the secretory-stage ameloblasts layer and enamel matrix. These findings indicate that serum albumin can leak between the detached ameloblasts and penetrate the enamel matrix after trauma. Leaked albumin was still present in the matrix during the maturation stage. Leaked albumin in the developing enamel could inhibit crystal growth and result in hypocalcification. [ABSTRACT FROM AUTHOR]

Dioxins are ubiquitous environmental pollutants that afflict developing teeth. To find out if the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the continuously erupting rat incisor is associated with the sensitivity to TCDD acute lethality and to see the histological basis for any macroscopic findings, we exposed 25 resistant Han/Wistar (Kuopio; H/W) and 20 sensitive Long-Evans (Turku/AB; L-E) female rats to total doses of 0.17, 1.7, 17, and 170 (only H/W rats) μg/kg TCDD. Each dose group comprised five animals. The treatment was started when the rats were 10 weeks old and continued for 20 weeks. The exposure time covered two life cycles of the incisor. Stereomicroscopic examination of the dissected mandibles showed color defects and pulpal perforation of the lower incisors at 17 and 170 μg/kg TCDD. Tissue sections revealed odontoblastic and pulpal cell death and the consequent arrest of dentin formation at the incisal tooth end at the same doses. H/W rat incisors were affected closer to the germinative tooth end at 170 than at 17 μg/kg TCDD, resulting in a larger perforation. In accordance with the enamel discoloration, the postsecretory enamel organ underwent, albeit inconsistently, precocious squamous metaplasia with pronounced proliferation. Thus, both the mesenchymal and, to a lesser extent, epithelial elements of the forming tooth were affected dose-dependently at relatively high doses of TCDD. Similar responses in both strains implied that the impaired formation of the incisor tooth, at least of its mesenchymal elements, is not associated with the differential resistance of H/W and L-E rats to TCDD acute lethality. [ABSTRACT FROM PUBLISHER]

The incisors of 21 Wistar rats were transected, pulp tissue was extirpated for 10 mm from the level of the gingival margin and each canal was prepared with files. The fibre tip of a pulsed neodymium:yttrium–aluminium–garnet laser was inserted into the root canal for 10 mm and laser irradiation delivered at 2 W and 20 pulses/s for 10 s. After 6 weeks the mandibles were removed and sectioned. Sections were stained either with haematoxylin and eosin or immunohistochemically using polyclonal antibodies against keratin/cytokeratin, amelogenin and type I collagen. The inner epithelial cells on the labial side differentiated into ameloblasts in animals where eruption had recovered. The pulp cells differentiated into odontoblast-like cells and staining for type I collagen was evident in pulp cells, odontoblast-like cells and inside dentinal tubules. In animals where eruption had ceased, the inner epithelial cells on the labial side did not differentiate into ameloblasts. Staining for type I collagen was observed in the mineralized nodules and tubules of dentine-like hard tissues in the pulp cavity. These results suggest that differentiation of epithelial cells on the labial side into ameloblasts is involved in the re-eruption process. [Copyright &y& Elsevier]

The impeded/unimpeded eruption rates of the rat incisor have been much studied. The most commonly used optical microscopic method, which has inherent weaknesses, was compared here with an image-analysis method to measure the eruption rate of the mandibular incisor. The study also evaluated the incisal edge as a reference point for the measurement of the unimpeded eruption rate, and the frequency of shortening the mandibular incisor. The image-analysis method was found to be a simple and reliable technique that could replace the optical method. There was no significant difference between the data from the two methods; their κ coefficients were similar at the 0.99 level. It was concluded that shortening the incisor in the measurement of the unimpeded eruption rate should be done at least every 48 h, and that the incisal edge of the shortened incisor can be used as the reference point for that measurement. [Copyright &y& Elsevier]

The aim was to determine the oxygen tension (PO2) and rate of oxygen consumption in the pulp. Twelve rats were anaesthetised and artificially ventilated. Under an operating microscope, a recessed oxygen-sensitive microelectrode was inserted into the pulp through a small saline-covered cavity on the labial surface of the lower incisor. PO2 was measured as a function of the transverse distance from the saline medium through to the middle of the pulp. Oxygen profiles were characterised by a decline of oxygen tension outside the pulp in the saline medium and a steeper gradient across the interface, before a localised oxygen consuming region corresponding to the odontoblasts. A plateau with some localised fluctuations was then followed by an increase in oxygen tension in the middle of the pulp. The average oxygen tension in the plateau region was 23.2 mmHg±2.1 mmHg (n=12). A mathematical model was used to extract oxygen consumption data from PO2 profiles recorded from non-perfused pulp (created by reducing systemic blood pressure). The analysis revealed that there was a distinct oxygen consumption zone in the outer pulp, which anatomically corresponded to the odontoblast layer. The average oxygen consumption rate of the odontoblasts was 3.2±0.2 ml O2/min per 100 g pulp tissue. The zone of high oxygen consumption was 68.7 μm±6.9 μm (n=24) thick. It is concluded that pulpal oxygen distribution is heterogeneous and that the odontoblast could be a major oxygen consumer within the rat incisor pulp. [Copyright &y& Elsevier]

Remodelling of the socket surrounding the continuously growing and erupting rat incisor was examined in teeth under normo, hyper and hypofunctional conditions. Cross-sections of the mandible were observed under fluorescence microscopy, where minocycline labelling evidenced bone remodelling. Animals had received minocycline (10 mg/day) during the experimental period. Control animals (from all three groups) received vehicle alone and samples from these animals were not fluorescent. Minocycline did not interfere with the eruption rates in any of the functional conditions studied. Normofunctional (impeded) incisors showed constant osteogenic activity in the alveolar bone facing the periodontal ligament in all regions of the incisor. Under hypofunctional (unimpeded) and hyperfunctional (impeded) conditions, osteogenesis in the region close to the alveolar crest was markedly increased in the mesial wall of the socket. The labial alveolar bone, facing the enamel-related periodontium, was almost entirely formed during the experimental period in all the groups, but in hyper and hypofunctional teeth the newly formed bone was thicker and contained a substantial amount formed before the experimental period. In the more apical regions of the socket no marked differences between the three functional conditions were found. The similar bone remodelling shown in hypo and hyperfunctional teeth might indicate that there are common factors causing this pattern. Consideration of possible factors appear to rule out the eruption rate, which is very different under these two functional conditions. [Copyright &y& Elsevier]

0.7 mg/kg VCR was administered intravenously to nine rats in three experimental groups. One hour after VCR injection the animals were injected with ³H-proline. The animals were sacrificed 1.5, 5 and 24 h after the VCR administration, and by comparison with nine control animals similarly injected with sodium chloride solution and ³H-proline, it was shown that VCR causes an early, intracellular retention of labeled proline in the odontoblasts, an abnormal intracellular retention of labeled material and a generally decreased secretion of dentinal matrix from the odontoblasts in the maxillary incisors. The severity of the effects were shown to vary in different parts of the incisors. [ABSTRACT FROM AUTHOR]

0.7 mg/kg VCR was given to nine rats in three experimental groups. Twenty-three hours after VCR injection the animals were injected with ³H-thymidine. The animals were sacrificed 24, 48 and 72 h after the VCR injection, and by comparison with nine control animals similarly injected with sodium chloride solution and nucleotide, it was shown that VCR causes a delayed migration of pulp cells from the proliferative pool and a small but distinct inhibition of the incisal growth of the incisors. The growth inhibition corresponded to the normal growth over a 24-h. period in non-VCR-injected animals. [ABSTRACT FROM AUTHOR]

The appearance of the junction between predentin and dentin of rat incisors was investigated after chemical fixation (aldehyde), physical fixation (high pressure freezing and freeze substitution) and by histochemistry. Physical fixation revealed a 1-2 μm wide intermediary zone, in which only the collagen fibers were mineralized. In dentin, which looked denser and more homogeneous, both collagen fibers and intercollagenous spaces were mineralized. The intermediary layer could not be seen after aldehyde fixation. When cationic dyes were used during fixation in order to retain proteoglycans, a 0.5-5 μm border zone located at the junction between predentin and dentin was densely stained on the dentin side, whereas in dentin only the intergiobular network displayed electron density. The periodic acid-thiocarbohydrazide-silver proteinase reaction, visualizing glycoproteins, and the phosphotungstic acid/chromic acid mixture, which reveals glycoproteins and phosphorylated proteins, produced extensive staining of the transitional zone located at the dentin edge, whereas staining was weaker in dentin. These morphological and histochemical investigations support the existence of an intermediary zone in which mineralization occurs. This transitional zone between predentin and dentin has specific properties: therefore we propose it be termed metadentin. [ABSTRACT FROM AUTHOR]

Fusobacterium nucleatum-derived components were studied for their effect on the ability of accessory pulpal cells to induce T-lymphocyte proliferation. In initial experiments, spleen cells were used to establish concentration ranges at which testing of the effect of the bacterial components would be suitable. At low concentrations, bacterial substances induced a stimulatory effect on the proliferation rate of spleen cells, but not when purified T-lymphocytes were incubated in the presence of concanavalin A and pulpal accessory cells. At increasing concentrations, a dose-dependent reduction was observed. Pretreatment with the bacterial products for 4 h gave a stimulatory effect in the absence of concanavalin A for both spleen cells and T-lymphocytes. Removal of low-molecular-weight components (<3.5 kDa) did not influence the inhibitory effect, whereas preheating the bacterial substances to 100°C eliminated the observed inhibition. Findings show that heat-sensitive, high-molecular-weight components of F. nucleatum can evoke a concentration-dependent stimulatory or suppressive effect on the proliferation rate of T-lymphocytes in the presence of accessory cells derived from the dental pulp. [ABSTRACT FROM AUTHOR]

Post-secretory, maturation-phase ameloblasts were studied by scanning electron microscopy of freeze-fractured or dry-dissected rat incisors. These cells are in contact with the enamel which they secreted at an earlier time and which undergoes a process of continuing mineralization. The lateral intercellular compartment between maturation ameloblasts is sometimes continuous with the intercellular space of the papillary layer of the enamel organ, but often closed by basal ring contacts which correspond to terminal bars seen in transmission electron microscopy. The distal poles of the cells sometimes possess striated borders. Lateral cell surfaces may show longitudinal gutter-like depressions between ridges from which numerous intercellular connections arise; or a maze of lateral folds and ridges; or they may have mostly microvillous surface projections bordering a minimal intercellular space compartment. Preliminary correlations of groupings of basal, lateral and distal cell features indicate that 'basal-closed plus distal striated border' cells may show every type of lateral surface. Cells without a striated border, whether open or closed basally, have ridge or maze lateral surfaces bordering a wide intercellular compartment. 'Basal-open plus striated border' cells have microvillous or maze-like surfaces. These combinations of features are encountered a few times along the length of the maturation zone of individual incisors and suggest the existence of cyclical changes in the type of activity of maturation ameloblasts. [ABSTRACT FROM AUTHOR]

Immunocompetent cells in the enamel organ of rat incisors were examined immunohistochemically using 0X6, EDI, and ED2 monoclonal antibodies known to recognize the Class II MHC molecules, a monocyte-macrophage lineage, and residential macrophages, respectively. The 0X6 immunopositive cells (MHC cells) were located exclusively in the enamel maturation zone. MHC cells increased in number in the incisal direction and occasionally extended cytoplasmic processes deep into the ameloblast layer. Migration of MHC cells in the ameloblast layer were also encountered. MHC cells lacked phagolysosomes and could be distinguished from typical macrophages. ED2 immunopositive cells were not seen in the enamel organ. EDI positive cells displayed identical localization to MHC cells except that some appeared in the transitional zone. MHC cells could not be seen in the enamel organ of rat molar tooth germs. Our data confirmed the presence of a large population of "dendritic" immunocompetent cells in the enamel organ of rat incisors and characterized the ultrastructural features of these cells. Biological significance of the immunocompetent cells in the enamel organ during amelogenesis needs to be clarified. [ABSTRACT FROM AUTHOR]

The effect of accelerated eruption of the rat lower incisor on enamel was studied in a series of segments obtained when the incisor was cut repeatedly out of occlusion over a five-week period. The segments were ground, cleaned, acid-etched, observed with SEM, and analyzed with EDX. Pigmentation was lost within 11 days. Pigmented superficial enamel was more acid-resistant than the rest of the enamel, but this quality decreased with decreasing iron content. Hypomineralized enamel first appeared in a restricted area at the mesio-labial angle of the tooth in the 6th-7th segment obtained after 11-14 days. Later, hypomineralization became more generalized. All enamel zones were retained throughout the experiment. The geometry of the prism pattern was affected. The angle between prism rows and the enamel-dentin junction increased from 44° to 48°, while the angle of decussation increased from 60° to 70°. The angle between the enamel surface and prisms in the outer enamel was more difficult to assess, but tended to increase from about 25° to 29°. However, the prisms retained their incisal direction. The connection between enamel and dentin was partly disrupted from about the 9th segment onward. The depth of the mesial concavity of the enamel-dentin junction decreased from about the 10th segment onward. Accelerated eruption affects all stages of enamel formation and is a suitable and predictable model for studying regulatory mechanisms in amelogenesis. [ABSTRACT FROM AUTHOR]

Conceptually, there should be a brief interval in time when newly secreted proteins "pile up" at secretory sites just outside the membrane of ameloblasts. Indeed, previous cytochemical studies have suggested that glycosylated and/or sulfated glycoproteins accumulate at enamel growth sites. Colloidal gold lectin cytochemistry and immunocytochemistry with antibodies to enamel proteins and phosphoserine, combined with cycloheximide and brefeldin A to inhibit protein synthesis and secretion, were applied to characterize the distribution of newly formed proteins at enamel interrod and rod growth sites. Although enamel growth sites show a "rarefied" appearance, the results indicate that one or more subclasses of enamel proteins accumulate near the cell surface at sites where elongation of enamel crystallites contributes to thickening of the enamel layer. These proteins are glycosylated and/or phosphorylated and, at least in the case of the glycosylated ones, are rapidly processed after they are released extracellularly. In contrast, immunolabeling for amelogenins is generally weaker near the cell surface and more intense at a short distance away from the site where crystallites elongate. The data suggest that the enamel proteins accumulating at growth sites likely belong to the non-amelogenin category and play a transient role in promoting the lengthening of crystallites. It is concluded that areas near the ameloblast membrane where certain enamel proteins accumulate in fact constitute the equivalent of a mineralization front. [ABSTRACT FROM AUTHOR]

A single, high dose of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) results in three different types of lesions along the enamel surface of the rat incisor, one of which is seen as a "bright band" crossing the final enamel surface in the scanning electron microscope (SEM). The present study presents the structural surface features of final enamel formation and its subsequent maturation in normal and HEBP-exposed rats. The position of the bright band is examined in relation to where the Tomes processes pits disappear (DTPP), where the boundary between "light" and "dark" enamel (LDB) as seen by SEM is located, and in particular, where the so-called opaque boundary (OB) is positioned. Groups of rats were given a subcutaneous dose of 0, 5, or 10 mg P/kg body wt of HEBP and killed at intervals of either 12 hours or 2 or 9 days. The mandibular incisors were processed for SEM after enzymatic digestion of enamel organ remains. Enamel surface nodules, 100-300 nm in diameter and composed of smaller units, were evident at the start of final enamel formation which was defined as the area from DTPP to LDB. With increasing maturation, the nodules merged to form a smooth surface. In HEBP-treated animals, growth and merging of these surface nodules became arrested at the time of injection resulting in an irreversible "porous" stage corresponding to that part of the surface enamel. This area--the bright band--developed corresponding to the start of the area of final enamel formation and was subsequently carried incisally during the eruption of the incisor.(ABSTRACT TRUNCATED AT 250 WORDS) [ABSTRACT FROM AUTHOR]

The effects of Vitamin D and 1,25(OH)D intoxication on growth and dentinogenesis were studied in impeded and unimpeded rat incisors. Animals were intoxicated either with Vitamin D (2 mg/kg/day) or 1,25(OH)D (400 ng/kg/day) for 19 days. Undecalcified transverse sections were obtained from all lower incisors. The outlines of all dental tissues were traced and fed into a computer which depicted the changes in all variables measured (circumference and cross-sectional area of tooth, pulp and dentin, width of dentin, CEJ [cemento-enamel junction] diameter and maximal labiolingual diameter). Eruption rates, which had been recorded previously every 48 h, were used to compute the physiological age of each tooth site, so that only areas of similar age be compared. Growth. External dimensions of all intoxicated teeth decreased as the experiment progressed in contrast with control incisors which continued to increase in size. This effect was more pronounced in unimpeded incisors and may be due to the inhibitory influence of 1,25(OH)D on cellular proliferation at the apical progenitor end. Dentinogenesis. 1,25(OH)D intoxication had no significant effect on the rate of eruption and dentin formation in both impeded and unimpeded incisors. The same was true for impeded incisors intoxicated with Vitamin D but, both eruption and dentin production rates were impaired in Vitamin D unimpeded incisors. [ABSTRACT FROM AUTHOR]

Effects of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) on the dentinogenesis of the rat maxillary incisor were microradiographically examined 96 hours after a single subcutaneous injection. HEBP produced hypomineralized incremental bands in the enamel (HPOe) and in the dentine (outer HPO1 and inner HPO2) in a dose-dependent manner. In the labial dentine, both HPO1 and HPO2 did not extend apically beyond the apical limit of the HPOe and were thus located in the circumpulpal dentine. The two lesions in the labial dentine fully developed with a dosage of 10 mg/ P/kg or larger, and with 15 mg P/kg or larger, gross hypoplastic lesions developed. Therefore, histological analysis at shorter postinjection intervals was carried out on the labial dentine with 10 mg P/kg of HEBP. The HPO1 appeared along the dentine-predentine junction by 24 hours and was characterized by reduced numbers of inorganic crystals and 10 nm particles which invested the collagen fibrils. Therefore, the HPO1 was judged to be produced by the disturbance of transformation of the predentine to dentine. The precursor lesion of HPO2 appeared in the proximal predentine by 4 hours, and was characterized by reduced number of collagen fibrils and unusually coarse interfibrillar stippled material. This lesion migrated to the dentine by 96 hours and became the HPO2, which was characterized by reduced number of collagen fibrils. Individual collagen fibrils in the HPO2 were invested by as many inorganic crystals and 10 nm particles as in the normal dentine. The HPO2 is considered to be produced by the disturbance of organic matrix formation. [ABSTRACT FROM AUTHOR]

Young male Wistar rats weighing 100 g were injected intravenously with 0.2 mg of vinblastine sulfate (VBL). At 24, 27, and 36 hours and 2, 4, and 6 days after introduction of the drug, the rats were fixed by means of perfusion and the upper incisors were removed for electron microscopy. Many secretion granules had accumulated in the young odontoblasts 24 hours after VBL administration. Newly formed predentin located between odontoblasts contained small amounts of an unusual collagen aggregate characterized by a fine, symmetrically striated structure, and paired, dense bands, which were present at both ends. After 27 hours, following the disappearance of the secretion granules in the odontoblasts, unusual collagen aggregates had increased in amount. Two days after administration, the predentin layer, which was close to the odontoblasts, was composed largely of unusual collagen aggregates. During dentinogenesis, the layer of unusual collagen aggregates gradually shifted into the dentin, where, 4 days after VBL administration, it was, to a large degree, located. Mineralization of the unusual collagen aggregates began with the deposition of fine, filamentous crystals that later grew into needle-shaped crystals 40 A thick. These findings suggest that unusual collagen aggregates are produced as a result of the secreting function of odontoblasts and are mineralized, as are normal collagen fibrils in dentin. [ABSTRACT FROM AUTHOR]

In the continuously growing upper incisor of 100 g rats about 25 arterioles arise from an artery outside the tooth and pass through the apical foramen to run parallel to one another in the central part of the pulp, each supplying a well-defined sector of the migrating odontoblast layer. The arterioles pass through a cycle of proliferation, growth, remodeling, regression and decay, phase displaced in relation to each other. Proliferative and degenerative processes occur in the arteriole wall throughout the cycle, but vary considerably in intensity at different phases. Proliferation takes place by mitosis in the endothelium and the innermost smooth muscle cells. The degenerative process consists of reduction in size of smooth muscle cells by partial autodigestion and by cell death. When the odontoblasts reach the incisal extremity of the tooth, they die, and the associated regressed arteriole disappears. The system of pulpal arterioles has remarkable spatio-temporal features and each of its vessels appears to be in a state of sensitive structural equilibrium. [ABSTRACT FROM AUTHOR]

The localization of amelogenin, an enamel matrix protein, was examined by ultrastructural immunocytochemistry using unembedded ultrathin frozen sections of undecalcified rat incisor ameloblasts. Antibody against bovine amelogenin labeled Golgi complexes, secretory granules, and lysosomal structures in the preameloblasts and inner enamel-secretory ameloblasts as well as the enamel. The antibody also labeled dentin matrix facing preameloblasts. These results support the findings in previous reports using conventional epon embedded specimens. However, rough-surfaced endoplasmic reticulum failed to be labeled by this antibody. [ABSTRACT FROM PUBLISHER]

Normal and colchlclne-injected rats were perfusion-fixed at 0 to 20 min after washing out the blood. Secretory ameloblasts and underlying enamel were examined ultrastructurally. In the normal rats, there was practically no accumulation of stippled material when the perfusion fixation was started immediately after washing out the blood. Various amounts of stippled material accumulated along the plasma membrane of Tomes' process and between the rod and interred enamel when the perfusion fixation was delayed. However, the ultrastructure of ameloblasts was still well preserved. Following colchicine injection, the amount of stippled material decreased greatly. From these results, it is suggested that accumulation of a large amount of stippled material is an artifact of fixation. However, it is also suggested that the secretory activity of the ameloblast plays an important role in the formation of stippled material [ABSTRACT FROM PUBLISHER]

Reparative dentinogenesis after administration of a large dose of colchicine was studied in rat incisors. Odontoblasts and the adjacent pulp tissue were destroyed soon after colchicine administration. At 6 days, spindle-shaped cells surrounded by a fibrous matrix appeared at the interface between the necrotic matrix and the normal pulp. Between 8–10 days, short columnar odontoblast-like cells had differentiated adjacent to a newly developing pre-dentin-like matrix. By 10–12 days, new tubular dentin-like structures had been formed in contact with the non-mineralized collagenous matrix. Various kinds of membrane-bounded extracellular vesicles were distributed between the collagen fibrils in the predentinal matrix produced by the new odontoblasts. Their morphological characteristics corresponded with true matrix vesicles. From these observations, it is suggested that the initial calcification process in reparative dentinogenesis after colchicine administration is essentially similar to the initial calcification process of normal dentin, namely by matrix vesicular calcification. [ABSTRACT FROM PUBLISHER]

Young male Wistar rats were given intravenous administrations of 2 mg/kg body weight of vinblastine sulfate (VBL). After the passage of 3, 6, 24, and 48 hr cytological changes in smooth-ended and ruffle-ended ameloblasts (SAs and RAs) were observed. Characteristic changes occurring 3 hr after VBL administration included reduction in numbers of microtubules, disturbed cell polarity caused by movement of organelles and nuclei, and shortening of microvillous projections in the RA ruffled border. Unusual accumulation of secretion granules and disruption of the rough-ER occurred 6 hr after administration. After 24 hr, deteriorative changes occurred in the mitochondria. But these kinds of cellular damage had all recovered 48 hr after administration. The SAs were more sensitive to VBL than the RAs and seemed to have disappeared as a result of vacuolization 6 hr after administration. SAs observed 24 hr after administration were presumed originally having been RAs that were morphologically modified during the recovery process. [ABSTRACT FROM PUBLISHER]

The relation of microtubules to the cell membrane in the secretory ameloblast of a rat incisor was morphologically investigated by using electron microscopy. Some of the microtubules were located along the cell membrane, where a filamentous structure was found between the microtubule and the cell membrane. This filamentous structure was the same in shape and size as each of the separated filaments or conjoined filaments forming a sheet, which are interposed in the microtubule bundle. Some of these membrane-associated microtubules were found at the junctional area, probably of a gap junction. [ABSTRACT FROM PUBLISHER]