Causes and mechanisms of tooth eruption. A literature review.
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Alveolar Process↗
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Cell-matrix interrelation and cell-to-cell connection in the secretory ameloblast layer of kitten teeth.
To investigate the cell-matrix interrelation and the structure and permeability of the junctional complexes of secretory ameloblasts, molar tooth germs from kittens were examined by means of scanning electron microscopy, routine thin sections and freeze-fracture replication. Scanning electron microscopy showed remarkably dissolved growth fronts of enamel in materials that had been fixed with glutaraldehyde and then subjected to EDTA perfusion for 10 min. By the action of EDTA, intercrystallite spaces in rod and interrod enamel were prominently widened, and their longitudinal ends of crystallites displayed irregular and extremely sparse structures. In enamel rods surrounded entirely by interrod enamel, and in enamel rods of the typical key hole shape with successive interrod enamel participation, the most striking dissolution of crystallites occurred at the boundaries between rod and interrod enamel, where broad expanses of rod-sheath spaces were observed. In thin sections, the Tomes processes of secretory ameloblasts occupying the above rods were rectangular or variations of a rectangular shape, respectively; and interameloblast spaces opened to the enamel growth fronts, which corresponded to the junction between rod and interrod enamel. In enamel rods standing in regular rows and showing the typical arcade shape, the centers of the rods were drastically dissolved and exhibited single and deep slits, whereas the boundaries between rod and interrod enamel showed no wide furrows. The Tomes processes occupying such arcade-shaped rods were typically triangular, and the interameloblast space always joined the type-1 face of process, which is responsible for enamel rod formation. Secretory ameloblast possessed two sets of junctional complexes at the proximal and distal ends of the cell body. The distal one was situated proximally to the Tomes process. Freeze-fracture replication demonstrated the functional structures of these junctions: the proximal junction was fascia occludens, and the distal one incomplete zonula occludens with many free-ending tight junctional strands and interstrand spaces or a less developed irregular junction.
Ameloblasts↗
Effect of smear layer removal on the diffusion permeability of human roots.
Ten human maxillary incisors, extracted because of periodontal disease or nonrestorable caries, were obtained and instrumented to a size #70 K-Flex file at the working length using a standard stepback technique. Tritiated water (3H2O) was placed in the root canals and allowed to diffuse to the external surface of the roots until it reached a constant rate. The smear layer in each of the experimental roots was then removed using 0.5 M EDTA followed by 5.25% sodium hypochlorite (NaOCI). The constant rate diffusion of 3H2O was remeasured. The roots were then stored in deionized H2O for 2 months and the constant rate diffusion of 3H2O was remeasured. A statistically significant difference was noted between all three groups. A decrease in the diffusion permeability of the root to 3H2O was noted immediately after smear layer removal and the highest permeability was recorded after storage in the deionized water for 2 months.
Dentin↗
Resistance of cementum in Class II and V cavities to penetration by an adhesive system.
OBJECTIVES: As the cervical margin located in cementum-dentin is still the most unpredictable area of an adhesive resin restoration, the aim of this investigation was to evaluate the morphology of the cementum layer at the cervical margins of Class V and Class II cavities and the impregnability of this layer to resin bonding systems. METHODS: Three different types of in vitro investigations of the cervical margins were performed by scanning electron microscopy: 1) direct anatomical observation of conditioned cavities; 2) observation of resin replicas; and 3) observation of resin infiltration. During direct observation, the presence of opened tubules was evaluated; in the resin replicas, the presence of resin tags and their density were observed; in the observation of resin infiltration, the presence of an acid-resistant interdiffusion was investigated. RESULTS: From direct observation, cut tubules were seen 200 microns from the cervical margin. After treatment with a dentin bonding system, the outer layer was infiltrated by the resin. In the resin replica, the presence of resin tags was detectable 150-200 microns from the margin. In Class II samples, the presence of an outer layer at the cervical margin, which could not be identified as bulk dentin or cementum, was clearly detectable by both direct and indirect observation. In the Class V samples, the border between this layer and bulk dentin was less evident. SIGNIFICANCE: The presence of a cementum layer of approximately 150-200 microns at the cervical margins of cavities may pose a serious clinical problem for reliable bonding. Although in the present study the observation of a zone of resin-impregnated cementum may confirm the improvement obtained with the last generation of hybridizing dentin bonding systems, the effectiveness of the bond is still unclear.
Composite Resins↗
Collagen cross-linking and ultimate tensile strength in dentin.
Several studies have indicated differences in bond strength of dental materials to crown and root dentin. To investigate the potential differences in matrix properties between these locations, we analyzed upper root and crown dentin in human third molars for ultimate tensile strength and collagen biochemistry. In both locations, tensile strength tested perpendicular to the direction of dentinal tubules (undemineralized crown = 140.4 +/- 48.6/root = 95.9 +/- 26.1; demineralized crown = 16.6 +/- 6.3/root = 29.0 +/- 12.4) was greater than that tested parallel to the tubular direction (undemineralized crown = 73.1 +/- 21.2/root = 63.2 +/- 22.6; demineralized crown = 9.0 +/- 3.9/root = 16.2 +/- 8.0). The demineralized specimens showed significantly greater tensile strength in root than in crown. Although the collagen content was comparable in both locations, two major collagen cross-links, dehydrodihydroxylysinonorleucine/its ketoamine and pyridinoline, were significantly higher in the root (by ~ 30 and ~ 55%, respectively) when compared with those in the crown. These results indicate that the profile of collagen cross-linking varies as a function of anatomical location in dentin and that the difference may partly explain the site-specific tensile strength.
Adolescent↗
[A mathematical model of the development of dental caries].
A mathematical model is suggested, simulating the development of carious process in a tooth, based on an analytical approach. The process of hydrogen ions diffusion into enamel microspaces is described via transport equation. A simplified model explaining the formation of the involvement of the body of the tooth under the enamel surface at the initial stages of caries development is described in detail. Analysis has shown that the theoretical model is in good correlation with experimental data on the rate of chemical reaction of Ca radionuclide accumulation in the enamel surface and deeper layers.
Dental Caries↗
[Cervical wedge-shaped lacunae and dentin hypersensitivity--a histological and SEM study].
The purpose of this study was to establish a correlation between dentinal hypersensitivity and tissular modifications of the pulp-dentinal complex at the level of cervical abrasions. 65 freshly extracted human teeth (from patients aged 20 to 80 years) presenting cervical abrasions without carious lesions were prepared in order to be examined histologically (31 teeth) and by scanning electron microscopy (34 teeth). Open tubules were present on the abraded surfaces in 83.3% of the specimens with presence of cytoplasmic processes in 78.46% of the cases without any correlation with tooth age and depth of the abrasions. The sensitivity could be partially explained by the persistence of cervical dentinal permeability. This permeable dentin seems to be susceptible to mechanical, chemical and bacterial irritations, no matter how thick the reactional dentin is. In the absence of any reliable and biological product capable to seal efficiently the open tubules, only nonabrasive hygiene methods can preserve the integrity of cervical dental tissues.
Adult↗
[Biophsical study of dental tissues under the effect of a local strontium application].
Microradiographic and electronmicroscopic observations show that topical application of concentrated strontium chloride solution on an abraded dentinal surface caused the formation in the dentine of very compact superficial layer composed of fine granules and with a high degree of radiodensity. This layer not only forms a continuous deposit on the superficial zone, but also penetrates and fills the canclicules to a certain distance. A barrier is thus created, diminishing the permeability of the dentine, which would explain the desensitization of the tooth. Electron probe microanalysis and X-ray diffraction studies show that the fundamental mechanism of the formation of strontium deposits is an exchange with the calcium fo the dentinal tissue, and recrystallization in the form of strontium apatite.
Dental Enamel↗
In vitro penetration of the pulp chamber by three brands of carbamide peroxide.
PURPOSE: Vital tooth bleaching has become a popular procedure for whitening teeth. Most home bleaching products contain 10% carbamide peroxide. The purpose of this in vitro study was to measure the quantity of hydrogen peroxide that reaches the pulp chamber from three carbamide peroxide products: Opalescence, Sparkle, and Rembrandt. MATERIALS AND METHODS: Seventy roots of extracted premolars were amputated approximately 3 mm apical to the cementoenamel junction, and the pulp tissues were removed. They were divided into three experimental groups (n = 20) and a control group of 10 teeth. An acetate buffer solution was placed in the pulp chamber before the crown was exposed to the bleaching agent at 37 degrees C for 25 minutes. The buffer solution was removed and reacted with leukocrystal violet and horseradish peroxidase. The optical density of blue color that developed was measured at a wavelength of 596 nm and read from a standard curve for hydrogen peroxide quantity. RESULTS: The measured amounts of hydrogen peroxide were 3.605 +/- 1.405, 1.282 +/- 0.762, and 0.339 +/- 0.251 micrograms for the Opalescence, Sparkle, and Rembrandt groups, respectively. A statistically significant difference in the hydrogen peroxide levels was observed by analysis of variance (p < .05) among the three groups. It was concluded that the penetration of commercial bleaching products was different even though the products were labeled as having the same 10% carbamide peroxide. CLINICAL SIGNIFICANCE: Carbamide peroxide penetration to the pulp varies significantly for various commercial bleaching products. This may result in different levels of tooth sensitivity or bleaching efficacy.
Carbamide Peroxide↗
Ultrastructural study of developing rat molar tooth germ in vitro. 2. The influence of cultivation and culture medium on the penetration of lanthanum into the ameloblast layer.
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Ameloblasts↗
[An experimental study on healing process of replanted mature permanent teeth. Changes of periodontal vascular network].
This study was conducted to clarify both changes of periodontal vascular architecture and concomitant remodelling phenomena associated with hard tissues in the healing process of replanted teeth of first premolar. Utilizing both vascular corrosive resin casts method, scanning electron microscopy, and histological examinations, 45 matured mongrel dogs were used for this study. The results were as follows: 1. 4 days after operation: Newly formed vascular networks with a exceedingly irregular course were observed on lower two thirds of the alveolar wall. They derived from comparatively less damaged periodontal vascular components. No vascular networks were observed surrounding in the crevicular area of the replanted tooth where the periodontal membrane tissue was thoroughly damaged when tooth was extracted. 2. 1 week after operation: Newly formed periodontal vascular networks with a slightly irregular course were observed over the entire alveolar bone surface. 3. 2 weeks after operation: Formation of Sharpey's fibers occurred. The surrounding alveolar bone was remodelled and rearrangement of periodontal vascular architecture was observed. Also, several Howship's lacunae were observed on the root surface where characteristic capillary loops with glomerular-like appearance penetrated into these lacunae. 4. 3 weeks after operation: Root resorption was advanced and capillary loops with glomerular-like appearance were extensively distributed in association with each lacunae. On the other hand, the less space where periodontal membrane vasculature occupied, the more space was occupied by osteoid tissue. 5. 4 weeks after operation: Blood vessels within the periodontal space were reduced in number and the osteoid tissue showed bony fusion adjacent to the extensively resorbing surface of dentin. 6. 12 weeks after operation: Functional arrangement of Sharpey's fibers was completed. Restoration of Howship's lacunae on the root surface and two layered arrangements of vascular network within the periodontal space were observed. Newly formed periodontal vascular architecture showed a fine meshwork pattern, which was somewhat different from that of the control (noreplantation) group. 7. 20 weeks after operation: Increased number of capillary loops was observed with leakage of methacrylate resin through the weakened endothelial linings of capillaries in one case. It is supposed that this leakage through capillaries is correlated with the inflammatory root resorption that occurs clinically in marginal periodontitis. Also in some cases, periodontal capillary network showed secondary occlusal traumatic changes. Above results indicated that periodontal vascular architecture varied depending upon the reactions of periodontium following tooth replantation and the prognosis of replanted tooth was deeply associated with repair of periodontal vascular network.
Alveolar Process↗
Remineralization of caries lesions extending into dentin.
Remineralization is one aspect of the overall process of tooth decay. However, it is primarily studied in shallow lesions. The aim of this study was to explore whether caries lesions in enamel and extending into the dentin can be remineralized. A single-section model was developed for the longitudinal and non-destructive monitoring of changes in enamel and dentin. Lesions at least 200 microm into dentin were formed in undersaturated acetate buffers. Next, the lesions were divided into groups (three treatment and one control) and remineralized. The treatments were: weekly immersion in 1,000 ppm fluoride, single treatment with methanehydroxybisphosphonate, and a constant level of 1 ppm fluoride. De- and remineralization was assessed by transverse microradiography. Remineralization was observed in enamel, but also in dentin, indicating that, deep into dentin, the pores become supersaturated to apatite formation. Treatments affected remineralization only in the outer part of enamel. Both findings are explained by a relatively fast diffusion of mineral ions, with precipitation being rate-limiting. The results suggest that dentin remineralization, underneath enamel, can be achieved and could possibly be used in clinical treatment strategies.
Analysis of Variance↗
Enamel cracks. The role of enamel lamellae in caries initiation.
Lamellae or cracks are distributed throughout tooth enamel in both deciduous and permanent dentitions. While earlier authors postulated that lamellae may be pathways of entry for caries, no evidence was adduced and the theory appears to have been discounted. The present study seeks to show that, at least in some cases, lamellae are permeable to dyes, may be associated with caries initiated in the dentine, supporting the hypothesis of Hardwick and Manly of lamellae penetration by Streptococcus mutans and lactobacilli. The enamel lamellae are shown to be a permeable pathway allowing caries-producing bacteria access to the dentine-enamel junction. Caries can thus be established within the tooth without visible evidence at the surface.
Azo Compounds↗
Sterilization of teeth by gamma radiation.
Clinical simulations and restorative materials research and development conducted in vitro require the use of large numbers of extracted teeth. The simultaneous need for infection control procedures and minimal alterations of structure and properties of the tissue prompted this study of gamma irradiation as a method to eliminate microbes associated with extracted teeth and their storage solutions. Evaluations of potential change in structure of dentin were conducted in terms of permeability, Fourier transform infrared spectroscopy (FTIR), and optical properties. The dose required for sterilization by gamma irradiation was established by means of a tooth model inoculated with Bacillus subtilis (10(8) organisms/mL). Sterilization occurred at a dose above 173 krad with use of a Cesium (Cs137) radiation source. Gamma irradiation did not affect permeability of crown segments of dentin. A comparative evaluation of the effects of four sterilization methods on dentin disks was based on FTIR and ultraviolet-visible-near infrared (UV/VIS/NIR) spectra before and after sterilization by (1) gamma irradiation; (2) ethylene oxide; (3) dry heat; and (4) autoclaving. No detectable changes were found with gamma irradiation, but all other methods introduced some detectable change in the spectra. This suggests that common methods of sterilization alter the structure of the dentin, but gamma irradiation shows promise as a method which both is effective and introduces no detectable changes as measured by FTIR, UV/VIS/NIR, or permeability.
Bacteria↗
In vitro determination and quantification of 30% hydrogen peroxide penetration through dentin and cementum during bleaching.
Bleaching pulpless teeth with 30% hydrogen peroxide was reported to cause external cervical root resorption. It was hypothesized that H2O2 penetrated open dentin tubules to initiate an inflammatory response that could result in root resorption. No direct experimental evidence was provided to support this theory. An in vitro model for determination and quantification of H2O2 penetration during bleaching procedures is suggested. Artificial defects of the cementum covering the cementoenamel junction were performed in 22 extracted human premolars. After 15 minutes of thermocatalytic bleaching, H2O2 could be detected in the medium surrounding all the tested teeth. Cervical root permeability to 30% H2O2 could reach up to 82% of the total amount applied.
Dental Cementum↗
In vitro study of the penetration of three bacterial strains into root dentine.
The purpose of this study was to assess in vitro migration of the following three bacterial species into dentinal tubules: Streptococcus sanguis, Actinomyces naeslundii and Prevotella intermedia. Twenty-seven bovine incisors were randomly divided into three groups. Only the root dentin was used for the experiment. Within each group, the nine incisors were sectioned into 36 dentin blocks that were incubated with one of the tested bacterial suspensions. Twelve samples were taken after 10, 20, and 28 days. Half the samples were observed with scanning electron microscopy and the others with light microscopy after standard histologic procedures, and the depth of bacterial penetration was measured. Analysis of the examinations showed that whatever the technique used, only one strain on this experimental model migrated into dentinal tubules. S. sanguis was observed at a depth of 792 microns, but no migration was observed for either A.naeslundii or P.intermedia. The differences in migration of the bacteria tested appear to be related to their morphologic factors and cellular arrangement.
Actinomyces↗
Effect of cementum defects on radicular penetration of 30% H2O2 during intracoronal bleaching.
Bleaching pulpless teeth with 30% hydrogen peroxide has been reported to cause external cervical root resorption. It has been hypothesized that H2O2 penetrating through open dentin tubules can initiate an inflammatory reaction which could result in root resorption. Extracted human premolars were treated endodontically and bleached intracoronally using the thermocatalytic technique. The teeth were divided into three groups; one group with no cementum defects at the cementoenamel junction, one group with artificial cementum defects at the cementoenamel junction, and another group with artificial cementum defects at the middle third of the root. The radicular penetration of 30% hydrogen peroxide in the three groups was assessed directly and compared using an in vitro model. Radicular penetration of hydrogen peroxide was found in all of the groups tested. The penetration of hydrogen peroxide was significantly higher in teeth with cementum defects at the cementoenamel junction than in those without defects.
Dental Cementum↗
Adhesion of light-cured composite resin to bleached and unbleached bovine dentin.
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Acid Etching, Dental↗