Rat Molar Tooth Research Articles

The effect of the loss of molar teeth on spatial memory and acetylcholine release from the parietal cortex in aged rats

It has been demonstrated that a loss of teeth is a troublesome problem among age-related pathological phenomena of the oral cavity, which influences the entire body, due to the impairment of mastication. The present studies investigated the abilities of learning and memory and acetylcholine (ACh) release in the parietal cortex in aged rats without molar teeth (hereafter referred to as 'teethless’). After the molar teeth of rats were extracted, the rats were fed with powdered food for 135 weeks. Although the performance in the radial arm maze was progressively acquired by daily training, an increase in the number of errors and a decrease in the initial correct responses were observed in the teethless aged rats compared to the control aged rats, indicating impaired acquisition of spatial memory in the teethless aged rats. The basal level of extracelluar ACh in the parietal cortex was not different between the teethless aged rats and the control aged rats. However, the extracellular ACh level of the teethless aged rats under high-concentration of K+ and atropine sulfate stimulation was significantly low compared to that of the control aged rats. These results suggest that the impairment of spatial memory in the teethless aged rats may be due to the functional deterioration of the cholinergic neuronal system induced by tooth loss and that there is a possibility that the loss of teeth may be one of the risk factors for senile dementia.

Parvalbumin-immunoreactive nerve endings in the periodontal ligaments of rat teeth

Parvalbumin-immunoreactive nerve fibres were most abundant in the lingual periodontal ligaments of incisor teeth. In the part of the ligament adjacent to the alveolar bone, thick and smooth parvalbumin-immunoreactive nerve fibres left main nerve bundles and passed towards the part of the ligament adjacent to the tooth. In the ligament, halfway between the bone and tooth surfaces, these nerve fibres repeatedly branched and extended one to four twigs to produce bush-like endings. Parvalbumin-immunoreactive fibres and terminals were infrequent in the periodontal ligaments of the molar teeth. It is possible that parvalbumin-immunoreactive endings are periodontal mechanoreceptors, but at present it is difficult to account for the different representations around rat molar and incisor teeth.

Dendritic cells: a novel cellular component of the rat incisor enamel organ appearing in the late stages of enamel maturation.

Immunocompetent cells in the enamel organ of rat incisors were examined immunohistochemically using OX6, ED1, and ED2 monoclonal antibodies known to recognize the Class II MHC molecules, a monocyte-macrophage lineage, and residential macrophages, respectively. The OX6 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. ED1 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.

Surface ultrastructure of rat molar teeth after experimentally induced erosion and attrition.

Young Osborne-Mendel rats were given different diets for 6 weeks. Effects of soft and rough food as well as acidic sport drink on the lingual surfaces of first mandibular molars were studied. In addition, the effect of fluoride on erosion was examined. A Jeol JSM-35 scanning electron microscope was used to visualize tooth surface ultrastructure. Intact surfaces were found in the rats given soft food and distilled water. Sport drink (pH 3.2) caused severe erosion with total loss of supragingival enamel and exposure of dentin. Attrition effects were seen on the cuspal parts of the surface when rough food was given. Tooth tissue loss was greatest in the rats given rough food and sport drink; signs of both erosion and attrition could be seen. When fluoride was added to the sport drink erosion lesions were less severe and if dentin was exposed, the dentinal tubules were partly occluded. These SEM observations support earlier studies which have suggested that erosion may alter tooth surface so that it is more susceptible to attrition; in those lesions, however, clinical diagnosis of the initial causes may be difficult.

TrkB-like immunoreactivity in trigeminal sensory nerve fibers of the rat molar tooth pulp: development and response to nerve injury.

The localization of TrkB, a signal transducing receptor for brain-derived neurotrophic factor and neurotrophin-4, was studied in the rat mandibular molar pulp during development and following nerve injury. Sections were incubated with rabbit polyclonal antiserum against the catalytic part of the TrkB receptor, thus only binding to full-length TrkB receptors, and examined by immunofluorescence microscopy and EM immunocytochemistry. At embryonic day 17, strongly TrkB-positive fibers were located in mandibular nerve trunks, in nerve fibers of deeper mesenchyme in close spatial relation to sites of future tooth development and in subepithelial nerve plexa. At postnatal days 1-12 intensely TrkB-positive nerve fibers surrounded and eventually invaded the developing dental papillae and pulps. In the normal adult pulp TrkB-immunoreactive axons were seen extending through the radicular pulp into the coronal areas. Double labelling demonstrated a considerable overlap between TrkB-like immunoreactivity and low affinity neurotrophin receptor-like immunoreactivity in the pulp, although some low affinity neurotrophin receptor-positive nerve fibers lacked TrkB-like immunoreactivity. Immunogold electron microscopy showed TrkB-like immunoreactivity in myelinated as well as in unmyelinated axons. One week following inferior alveolar nerve injury there was a dramatic decrease in the level of TrkB-like immunoreactivity labelling in the pulp, which paralleled an increase in the expression of Schwann cell low affinity neurotrophin receptor-like immunoreactivity. The first signs of regenerating TrkB-positive nerve fibers were found at 4 weeks post-operative, and at 9 weeks the distribution of pulpal TrkB-like immunoreactivity had returned to normal. These data indicate that brain-derived neurotrophic factor and/or neurotrophin-4 could be target-derived factors involved in sensory trigeminal tooth pulp nerve fiber development, differentiation or regeneration.

Responses of immunocompetent cells to cavity preparation in rat molars: an immunohistochemical study using OX6-monoclonal antibody.

Responses of immunocompetent cells, especially class II major histocompatibility complex (MHC) antigen-expressing cells, were investigated after cavity preparation in the erupted upper first molar teeth of rats, by immunohistochemistry using OX6-monoclonal antibody. In control teeth, OX6-immunopositive cells were predominantly located beneath the odontoblast layer in the dental pulp. Cavity preparation caused an acute edematous reaction between the injured odontoblasts and predentin, and most of OX6-immunopositive cells in the affected site shifted away from the pulp-dentin border. After 12-24 hours, many OX6-immunopositive cells accumulated along the pulp-dentin border and extended their cytoplasmic processes into the exposed dentinal tubules. After 72 hours, newly differentiated odontoblasts replaced the degenerated odontoblasts, and few OX6-immunopositive cells remained along the pulp-dentin border. Our data suggest that some of the class II MHC antigen-expressing cells in the dental pulp participate in the initial defense reaction and presumably serve as a biological sensor for the external stimuli arriving through the exposed dentinal tubules.

Growth hormone and insulin-like growth factor-I in odontogenesis.

This review documents recent insights into the roles of growth hormone and insulin-like growth factor-I during tooth formation. Hereditarily growth hormone-deficient Lewis dwarf rats and hypophysectomized rats have been used to document the influence of growth hormone on growth of the rat incisor and molar teeth in vivo. Cell population studies using bromodeoxyuridine labeling have shown that growth hormone administration to dwarf rats affects odontogenic cell proliferation in the incisor teeth. Immunohistochemistry, employing well-characterized monoclonal antibodies directed against the hormone, its binding protein/receptor, the growth factor and its receptor, has enabled the location of these proteins to be mapped in the ontogenic sequences of ameloblasts, odontoblasts and cementoblasts. This mapping is consistent with the concept that differentiating odontogenic cells are targets for the hormone and that insulin-like growth factor I is implicated as a secondary messenger in the same differentiating cell populations. The content of predentine and precementum matrices proteoglycans appears to be growth hormone-dependent. The proteoglycans implicated so far are rich in chondroitin sulphate and thus they may also be insulin-like growth factor I (sulphation factor)-dependent. Thus matrix synthesis may be what is principally affected by growth hormone in odontogenesis although no evidence of an effect on enamel matrix synthesis or proteoglycan content has yet been documented.

Streptococci and actinomyces inhibit regrowth of Streptococcus mutans on gnotobiotic rat molar teeth after chlorhexidine varnish treatment.

Clinical studies suggest that the long-term suppression of mutans streptococci on tooth surfaces after intensive chlorhexidine therapy is mainly due to bacterial interference. Other streptococci and also Actinomyces naeslundii are proposed to inhibit regrowth of mutans streptococci after suppression by the agent. We have tested this hypothesis in gnotobiotic rats associated with Streptococcus mutans alone, or associated with S. mutans and strains of Streptococcus oralis, Streptococcus sanguis, Streptococcus gordonii, Streptococcus mitis biovar I, and A. naeslundii. Left lower jaws in these rats were treated with concentrated chlorhexidine varnish, and the return of S. mutans on the treated jaws monitored. In mono-associated rats, S. mutans regained the level of the untreated right lower jaw in approximately 1 week. In contrast, S. mutans remained suppressed for several weeks in rats multi-associated with other streptococci and actinomyces strains. The suppression was more pronounced in the rats fed on basal diet with little free sugars than in rats fed on a sucrose-containing diet. Counts of other streptococci recovered quickly from the intensive chlorhexidine treatment, but A. naeslundii remained suppressed for at least 1 week. The findings demonstrate the crucial importance of the oral microflora in controlling regrowth of mutans streptococci after chemotherapy.

Relation between the trans-Golgi network and the Golgi stack on development of the Golgi apparatus of the ameloblast in developing rat molar tooth germs.

The problem of how the functional compartments of the Golgi apparatus organizes during cell differentiation to become a well-formed Golgi apparatus is as yet an unresolved issue. This study was designed to define the involvement of the trans-Golgi network (TGN) and the Golgi stack in organizing the Golgi apparatus. The distribution of the TGN marker enzyme was examined in the ameloblast of developing rat molar tooth germs using cytochemistry with Co-enzyme A phosphatase (CoA Pase) and cytidine monophosphatase (CMPase). Typically formed Golgi apparatus was observed in the secretory ameloblast but not in the presecretory ameloblast. Organization of the Golgi apparatus through the presecretory ameloblast was noted. In the presecretory ameloblast, Golgi stacks of different sizes and clusters of small vesicles were located in the cytoplasm lateral to the nucleus. The saccules with enzymes marked for TGN were also observed in the cytoplasm lateral to the nucleus. These saccules were adjacent to the cluster of small vesicles and/or the Golgi stack. Upon cell differentiation, Golgi stacks were seen in line along the long axis of the cell, and the file of the stacks in the cytoplasm lateral to the nucleus was formed. The positive saccule was seen in a parallel line equal to the length of the Golgi stacks. In organizing the Golgi apparatus, the development process of the TGN and the Golgi stack appear to be different, and new Golgi stacks seem to be formed through the accumulation of small vesicles near the pre-existing TGN.

Immunolocalization of connexin 43 in the tooth germ of the neonatal rat

Rabbit polyclonal antibodies to amino acids 346-360 of connexin 43, the 'heart' gap junction protein, were employed to immunolocalize connexin 43 gap junctions in the neonatal rat molar tooth germ. Connexin 43 appears early in the differentiation of both ectodermally derived and ectomesenchymally derived cells of the developing tooth. Connexin 43 immunoreactivity is present in the epithelial components of the enamel organ, including the area of the proximal and distal junctional complexes of the ameloblast layer, and the stratum intermedium, stellate reticulum and outer enamel epithelium. Secretory odontoblasts and developing alveolar bone also display a pattern of connexin 43 immunostaining. Both the epithelial and ectomesenchymally-derived components of the developing tooth acquire connexin 43 channels in a manner that correlates with cell differentiation. In addition, three regions can be defined by connexin 43 immunostaining: the epithelia of the enamel organ that are derived from the oral epithelium, the odontoblast layer derived from the ectomesenchyme, and the alveolar bone. The results suggest that connexin 43 may provide the mechanism for functional compartmentalization of the tissues associated with tooth formation. Compartmentalization suggested by connexin 43 expression could play important roles in the development and functions of these tissues.

Cholesterol in the distal portions of differentiating and fully differentiated rat odontoblasts observed by freeze-fracture

Freeze-fracture replicas of rat molar tooth germs in conjunction with the 3-β-hydroxysterol marker filipin were used to study the distribution of cholesterol in the distal portions of odontoblast plasma membrane. Filipin-sterol deformations (interactions) appeared as clusters interspersed with deformation-free regions on the distal plasma membrane of early differentiating odontoblasts. In fully differentiated odontoblasts, the whole distal membrane, including the process, was occupied by packed deformations with no free regions. It seems that early developing odontoblasts are poorer in cholesterol than the fully differentiated cells. As the content and/or distribution of 3-β-hydroxysterols (cholesterol) is known to influence membrane fluidity, the low cholesterol content of early differentiating odontoblasts might be related to the fluidity required for the budding off of matrix vesicles.

Development of an in vitro culture system for the study of osteoclast activity and function

Resorption is a difficult process to study in vivo because of the complex organization of mineralized tissue. The objective of this study was to develop an in vitro culture system for studying osteoclast attachment and activity. Transparent, microporous substrata were prepared using radio frequency-sputtering techniques to apply a thin layer of hydroxyapatite on polycarbonate filters previously coated with Type I collagen. Dentinoclasts isolated from the root surface of rat molar teeth undergoing inflammatory resorption and osteoclasts isolated from the endosteal surfaces of rat long bones were incubated on the experimental substrata. The culture system proved successful, supporting osteoclast viability and activity as demonstrated by cellular attachment and spreading seen by scanning electron microscopy. Activity was further demonstrated by monitoring acid production using a fluorescent probe, acridine orange. Isolated osteoclasts or dentinoclasts, when combined with synthetically prepared substrata, were observed to respond by mechanisms comparable to those that occur in vivo. Therefore, the system developed permits basic observations of osteoclasts in an in vitro system.

Ultrastructure of quick-frozen secretory ameloblasts of the rat molar tooth

Ameloblasts in molar tooth germs from 4 to 12-day-old neonatal rats were quick-frozen and then freeze-substituted in acetone-tannic acid and acetone-osmium tetroxide. Following quick freezing and freeze-substitution, the preservation of ameloblasts was principally the same as seen in conventionally-fixed ones. Several differences, however, became apparent between two methods. Concerning enamel formation, the quick-freezing procedure greatly improved the preservation including that of the extrusion of secretory granules into the extracellular space. This exocytosis is a type of merocrine secretion. The precursor stippled material was demonstrated at the front of Tomes' processes and in the intercellular space of the distal terminal junction. In the more advanced stage, the stippled material tended to decrease gradually in amount. Prior to the formation of the typical Tomes' process, large secretory granules fused directly with the distal plasma membrane, which plays a role in the formation of prismless enamel. After the typical Tomes' process had formed, secretory granules containing electron-dense material instead of the large secretory granules accumulated in the distal portion of the Tomes' process. These latter secretory granules had two different destinations; i.e. the granules discharged their contents into the infoldings of the distal part of Tomes' process and into the infoldings of the lateral cell membrane. These types of secretion seem to have a functional role in the rod or inter-rod enamel formation. The ultrastructure of the stippled material consisted of 3-dimensionally interconnected strands after quick freezing, which is different from the appearance of granules embedded in amorphous material after conventional fixation. The stippled material was seen in the intercrystal space among the newly formed crystals. Also, an extensive tubulo-vesicular structure was preserved in both the cell body and Tomes' process. The present data suggest that the membrane of this structure showed a smooth contour opening to the extracellular space, and also an intimate relationship with the secretory granules.

An immunohistochemical study examining the role of collagen type VI in the rodent periodontal ligament

The distribution of collagen types I and VI has been examined in the periodontal ligaments of rat incisor and molar teeth using cryosections and immunohistochemical staining procedures. The stain for collagen type I was uniform in all the ligaments examined. Uniform staining for collagen type VI was evident only in the ligament of the fully erupted molars, and the stain was absent from the mid-zone of the ligaments of the erupting molars and incisors. The staining pattern of the collagen type VI antibodies is consistent with previous reports which have suggested that the removal of collagen type VI precedes the degradation of major banded collagen fibrils in remodelling connective tissues. The removal of collagen type VI from the mid-zone of the incisor ligament may precede the remodelling events which facilitate tooth eruption.

Changes of lectin staining pattern of the Golgi stack during differentiation of the ameloblast in developing rat molar tooth germs

Changes of lectin staining patterns in the Golgi stack during cell differentiation were examined in the ameloblasts of developing rat molar tooth germs, using HRP-labeled lectins: Canavalia ensiformis (Con A), Griffonia simplicifolia I (GS-I), Glycine max (SBA), Ulex europeus I (UEA-I), Triticum vulgaris (WGA), and Arachis hypogaea (PNA). The Golgi stacks of the inner enamel epithelial cells and the presecretory ameloblasts were stained with the lectins, although the staining strength and pattern varied among the stacks with each lectin. In some cases, the reaction products for the lectins were observed in most or all saccules of the Golgi stack. In the secretory ameloblasts, however, discrete staining patterns of the Golgi stack were found for each lectin. The reaction products deposited in definite saccules of the Golgi stack of the secretory ameloblast, especially for UEA-I and PNA which stained only the trans Golgi saccules of the stack. The reaction-positive saccules distributed more extensively in the Golgi stack of the inner enamel epithelial cell and the presecretory ameloblast than in the secretory ameloblast. These findings suggest that the Golgi stack is not fully compartmentalized in the inner enamel epithelial cell and the presecretory ameloblast. It is proposed that, in the differentiating ameloblast, various glycosyltransferases may coexist in most saccules of the Golgi stack.

Dentin sialoprotein: biosynthesis and developmental appearance in rat tooth germs in comparison with amelogenins, osteocalcin and colagen type-I

A non-collagenous protein, extracted from rat incisor dentin, is a dentin sialoprotein (DSP). We examined immunohistochemically the developmental appearance and tissue distribution of DSP in 1 to 3-day-old rat molar and incisor tooth germs. The earliest staining for DSP was observed in newly differentiated odontoblasts. In more advanced stages, immunostaining for DSP gradually increased in pre-dentin, odontoblasts and dentin, and appeared in many cells of the dental papilla. In early stages of development before the breakdown of the dental basement membrane, pre-ameloblasts were also positive for DSP. This staining disappeared from the ameloblast cell body soon after deposition of the first layer of mineralized dentin. Radiolabelling of tooth matrix proteins with 14C-serine in vitro followed by immunoprecipitation and fluorography confirmed that DSP was synthesized by tooth-forming cells. The immunolocalization for DSP was different from that of either collagen type-I, osteocalcin or the amelogenins. Whereas collagen type-I and osteocalcin were restricted to the mesenchymal dental tissues, the amelogenins were detectable in both epithelial and mesenchymal dental cells and tissues at the epithelio-mesenchymal interface at early stages of development, prior to the onset of dentin mineralization. We conclude that DSP is expressed in and secreted by odontoblasts and some dental papilla cells from early stages of dentinogenesis onwards, i.e. later than type-I collagen, but before deposition of the first layer of mineralized dentin. In pre-mineralizing stages, some of the matrix proteins may be endocytosed from the pre-dentin by both cell types involved in the epithelio-mesenchymal interaction.

SÜT VE AYRANIN RAT DİŞLERİNDEKİ KALSİYUM MİKTARINA ETKİSİNİN ATOMİK ABSORBSİYON YÖNTEMİ İLE ARAŞTIRILMASI *-INVESTIGATION OF THE EFFECT OF MILK AND AYRAN ON THE AMOUNT OF CALCIUM IN RAT TEETH BY ATOMIC ABSORBTION TECHNIQUE

OZET Bu calismada; curuk yapici diyet ile birlikte sut, ayran ve bidistue deiyonize su verilen ratlarm. sol alt 1. 2. ve 3. molar dislerindeki kalsiyum miktari Atomik AbsorbsIyon yontemi ile arastirildi. Sonucta, bidistile deiyonize su icen gruptaki ratlann dislerindeki kalsiyum miktari, ayran icen gruba gore, sut icen grupta bulunan ratlann dislerindeki kalsiyum miktari ise her iki gruba gore Onemli oranda yuksek bulundu. Arastirmamizda kullanilan sut ve ayranin, gida analizi yapildi. Kalsiyum ve laktik asit miktarlari arastirildi. Sutun, ayrana gore daha fazla kalsiyum daha az oranda laktik asit icerdigi saptandi. Anahtar sozcukler: Sut, rat disleri, kalsiyum miktari. ABSTRACT In this study the calcium amount in mandibular first, second and third molar teeth of rats which were fed with cariogenic diet and milk, bidistilled deionizedwater has been measured with the method of Atomic Absorb-tion. Finally the amount of calcium in the teeth of rats which were fed with bidistilled deionized water was more than that of the group which was fed with ayran and the group which was given milk is found out to contain the most amount of calcium compared to the others. Milk and which are being used in our research have been analized and the amount of calcium, lactic acid have been determined. It has been obtained that milk contains more calcium but less lactic acid than those of ayran. Key words: Milk, ayran, rat teeth, calcium amount.

P-456 - In vitro measurement of tooth movements in molar teeth of rats given β-aminopropionitrile or hydrocortisone.

P-456 - In vitro measurement of tooth movements in molar teeth of rats given β-aminopropionitrile or hydrocortisone.

Seam Structures Observed along the Junctional Line of Hertwig’s Epithelial ‘Root’ Sheaths in Rat Incisors

Linear structures were occasionally found on the lingual surface of the cementum of infant rat incisors along the long axis of the incisors, which are teeth that grow continuously from a persistent odontogenic organ. The observations strongly suggest that these linear structures on the junctional line of Hertwig's epithelial 'root' sheaths correspond to the seams on the multirooted molar teeth of rats.

Erosion by soft drinks of rat molar teeth assessed by digital image analysis.

A digital imaging analysis (DIA) procedure for recording and assessing erosive changes on teeth was developed and evaluated against an older subjective method. Results after exposure of rats' teeth to various soft drinks showed that the DIA system was superior to the conventional method, with improved precision. The system provided a direct and highly sensitive means of quantifying the erosion of dental hard tissues by three different soft drinks, showing that it could be used to evaluate erosiveness and other dental damage. After 6 weeks' exposure to soft drinks in the diet, the area of intact enamel on the lingual surface of the first mandibular molar averaged 47% on apple juice, 27% on still orange and 6% on carbonated orange. The greatest exposure of dentine (36%) was on the still orange drink. Eroded enamel accounted for 72.5% of the tooth surface on the carbonated drink.