A scanning electron microscope and microradiographic study of closure of human coronal dentinal tubules related to occlusal attrition and caries

Comparative analysis of sclerotic dentinal changes in attrited and carious teeth around pulp chamber for age determination

AIM

The aim of this study was to estimate age by comparing sclerotic dentin thickness around coronal pulp chamber in carious and attrited teeth.

METHODOLOGY

Inclusion criteria for teeth selection was eruption age around six to seven years (incisors and first molars). 100 teeth (50 carious + 50 attrited) were ground up to their pulp chamber, observed and photographed under an Olympus stereomicroscope. Image J 1.38 NIH software was employed to analyze dentinal thickness.

STATISTICAL ANALYSIS

Regression formula was employed for evaluating age and compared with clinical age obtained at time of extraction.

RESULTS

No matching values were found between calculated age and actual clinical age.

CONCLUSION

Sclerotic dentin thickness values cannot be used as an indicator for the purpose of age estimation.

Morphological characterization and permeability of attrited human dentine

OBJECTIVE

Dentine is a vital tissue that can be changed by physiological and pathological condition. The purpose of this study was to clarify the morphology and permeability of dentine that changed by wearing process.

METHODS

Twenty extracted human molars with enamel attrition and dentine was exposed and 20 intact human extracted third molars that had not reached occlusion were used. Ten teeth per each group were observed under light microscope (LM) and transmission electron microscope (TEM). Remaining 10 teeth per each group were subjected for evaluation of dentine permeability.

RESULTS

Under LM, the transparent dentine and reactionary dentine were found in the attrition group but were not found in the group unaffected by attrition. When the transparent dentine were examined under the TEM, it was found that dentinal tubules were partially or completely occluded by growth of peritubular dentine or by precipitation of needle-like or rhombohedral crystals in transparent dentine. In reactionary dentine, tubular dentine structures that were comparable to those in secondary physiologic dentine were observed whereas atubular dentine demonstrated occlusion of tubules by high mineral substances or by peritubular dentine under the TEM. Permeability of dentine from worn teeth was less than those from unoccluded teeth significantly.

CONCLUSION

Change in dentine by wear resulted in the formation of reactionary dentine and transparent dentine that illustrated various types and degrees of tubular occlusion. These decrease the dentine permeability.

Age-related changes in ac-impedance spectroscopy studies of normal human dentine

Non-destructive methods, such as the ac-impedance technique, have recently been applied to early caries detection and to identify micro-leakage between tooth structure and filling materials. However, in vitro impedance measurements are affected by a number of external factors. The purpose of present study was to investigate the effect of the age of teeth on impedance measurements of human dentine by employing electrical impedance spectroscopy (EIS). Fully hydrated dentine samples were prepared from extracted third molars of 20 and 50 year old patients. Ac-impedance measurements were carried out over a wide frequency range. Impedance measurements showed that there were differences in impedance between young and older dentine. In their circuit models, both resistance and capacitance were found to be significantly different (p < 0.05) for the two age groups. One of the age-related changes in dentine is the formation of peritubular dentine on the inner walls of dentinal tubules and we propose that this is responsible for the differences in impedance. Sample or patient age therefore must be considered when making impedance measurements on any tooth.

Age-related changes in hardness and modulus of elasticity of dentine

OBJECTIVES

Little knowledge has been clarified about the relationship between the morphological and physical changes of dentine during aging. The purpose of this study was to clarify the modulus of elasticity and hardness related to the morphological changes of dentine by aging using a transmitted light microscope (TLM) and a nano-hardness tester (NHT).

METHODS

Aged human molars and young third molars were used. The dentine morphology was observed under a TLM. The hardness and Young's modulus of elasticity related to the morphologic study were evaluated with an NHT.

RESULTS

The thickness of mantle dentine and globular dentine of aged teeth were less than that of young teeth. Transparent dentine was observed only underneath the attrition of young teeth. Reactionary tertiary dentine formed and a "dark zone" was found at the junction between physiologic secondary and reactionary dentine only in aged teeth. At the mantle dentine, hardness and modulus of elasticity of aged dentine were higher than those of young dentine. The reactionary dentine in aged teeth and newly developed secondary dentine in young teeth demonstrated lower modulus of elasticity and hardness than those of other circumpulpal dentine. Relatively low modulus of elasticity and hardness were observed at the zone between secondary and reactionary dentine.

CONCLUSIONS

Changes in dentine due to aging resulted in transformation of morphological features causing changes to their hardness and modulus of elasticity at the explicit areas such as the increase of hardness and modulus of elasticity at mantle dentin and the reduction of these properties at the "dark zone" that found in aged teeth.

Dynamics of the pulpo-dentin complex

Dentin has a relatively high water content due to its tubular structure. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid shifts across dentin are thought to cause sufficient shear forces on odontoblasts, nerve endings, nearby fibroblasts, and blood vessels to cause significant mechanical irritation, disruption, or damage, depending on the magnitude of the fluid shift. Even in the absence of fluid shifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic stimuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external irritants. However, pulpal tissues react to these challenges by increasing the activity of nerves, blood vessels, the immune system, and interstitial fluid turnover, to make the exposed dentin less permeable either physiologically, via increased outward fluid flow, or microscopically, by lining tubules with proteins, mineral deposits, or tertiary dentin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dentin and pulp, both in the initiation of the processes and in their resolution. These responses of the dental pulp to irritation of dentin demonstrate the dynamic nature of the pulpo-dentin complex.

Restorative therapy for erosive lesions

More needs to be learned about the etiology of erosion lesions before they can be accurately diagnosed, confidently treated and, more importantly, prevented. The treatment is dependent on the location and the degree of erosion. The decision to treat an erosion lesion should be based on careful consideration of the etiology and progression of the condition. Reasons for restoring noncarious enamel/dentin lesions are discussed and various therapeutic measures are provided. Preventive and restorative therapeutic measures for noncarious abrasive/ erosive lesions are proposed such as: a change of dietary or behavior patterns; application of desensitization products; intensive fluoride therapy with or without iontophoresis; brushing with desensitizing dentifrices; adhesive penetration with dentin bonding agents; glass ionomers and compomers; resin composites; composite or porcelain veneers; crown and bridge work; occlusal adjustments and nightguard fabrication if the abfraction factor coincides. The clinical durability of restorative therapy and important clinical factors related to the restoration of multifactorial defects are discussed.

Progressive changes in the pulpo-dentinal complex and their clinical consequences

With changes in the age structure and oral health in the population, changes in the pulpo-dentinal complex are becoming more relevant clinically. Age-related changes in the structure of dentine and pulp are reviewed. The influence of these changes on restorative dentistry are considered with particular emphasis on endodontics and the use of adhesive restorative materials.

Relationship between age and deposit of peritubular dentine

Peritubular dentine is a mineralised deposit formed centripetally in the dentine tubules with advancing age, so that the tubular diameter is smaller in teeth from older persons. The aim of the present study was to investigate the relationship between age in humans and the amount of peritubular dentine and the extent of the consequent obliteration of the tubules, and to find out whether this relationship was strong enough to be used as a parameter for age estimation. Fifty mandibular central and lateral human incisors were ground on the lingual aspect of the root and examined in a scanning electron microscope (SEM). The number of open tubules was counted and the diameter of the tubules measured both before and after etching with 35% orthophosphoric acid. The difference in the number of tubules in unetched and etched specimens was taken to be the number of occluded tubules, and the difference in radii before and after etching to be the thickness of peritubular dentine. The results did not demonstrate a significant relationship between age and the reduction in the number of tubules. One explanation might be that a certain age has to be reached before obliterated dentine tubules can be observed. The correlation between age and the thickness of peritubular dentine was not significant in teeth extracted because of periodontal disease, so these teeth were excluded from the regression analysis with age as the dependent variable.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro bond strengths and SEM evaluation of dentin bonding systems to different dentin substrates

In comparison to enamel, bonding to normal dentin is a greater challenge because of its organic constituents, fluid-filed tubules, and variations in intrinsic composition. Bonding to sclerotic dentin is even more difficult. To evaluate the shear bond strengths of four adhesive systems to dentin substrates with different levels of mineralization, 120 extracted human teeth were randomly assigned to three groups (n = 40). After mid-coronal dentin was exposed, groups of specimens were artificially hypermineralized by immersion in a remineralizing solution, demineralized by means of an acetic acid demineralizing solution, or stored in distilled water to model sclerotic, carious, and normal dentin, respectively. Resin composite was bonded to dentin by use of commercial adhesive systems. After the specimens were thermocycled, shear bond strengths were determined in an Instron universal testing machine. Dentin substrates and resin/dentin interfaces were examined by SEM. For each adhesive system, the mean shear bond strength to normal dentin was significantly higher than that to either of the other substrates. Shear bond strengths to hypermineralized dentin were significantly higher than those to demineralized dentin with all adhesives except Prisma Universal Bond 3.

Measurement of dentin permeability and wetness by use of the Periotron device

The ability of the Periotron device to measure changes in dentin permeability and wetness was evaluated by use of extracted human teeth in vitro. Pulpal pressures were varied from zero to 40 cm H2O for simulation of different pulpal tissue pressures. Non-physiologic pulpal pressures of 703 cm H2O were used for comparison of dentin permeability measurements made with the Periotron device with those made using micropipettes. Measurements made with the Periotron device correlated well with methods used previously for measurement of dentin permeability. The shear bond strength of Scotchbond 2/Silux was measured 24 h after being bonded to dentin held at zero pulpal pressure. There was an inverse correlation between the shear bond strengths of Scotchbond 2/Silux and Periotron values, suggesting that increased wetness decreases the bond strength of that system. The Periotron device offers a new, simple, convenient measure of dentin surface wetness which may be useful in dentin bonding studies.

Class II antigen expressing cells in experimentally induced pulpitis

This study reports on the occurrence of class II antigen expressing cells in inflammatory lesions experimentally induced in the rat incisor pulp. Concanavalin A and lipopolysaccharide of Bacteroides gingivalis were applied to the exposed pulp following a preparation through alveolar bone and dental tissues in the midpart of the root. In a set of control teeth, pulpal exposures were capped with Cavit without the placement of antigenic material. Animals were killed after 3, 12, 24, 48 or 96 hours. Pulp tissue specimens were subjected to immunohistochemical analysis utilizing a monoclonal mouse anti-rat class II antigen antibody. Semi-quantitative assessment of positively stained cells was carried out under the light microscope. Significantly more class II antigen expressing cells were identified in the challenged pulps than in the controls at all experimental periods. The increase in cells peaked at 48 hours to taper off at the subsequent 96-hour observation. The rapid and intense influx of class II antigen expressing cells suggests that these cells are associated with the initial defence of the dental pulp.

Scanning electron microscopic characterization of sensitive vs. insensitive human radicular dentin

Our aim was to investigate the structural changes of dentinal tubules in specimens obtained from both hypersensitive and naturally desensitized areas in wedge-shaped defects on the same exposed cervical dentin surface of a hypersensitive tooth. A new biopsy technique that makes use of a hollow, cylindrical diamond bur was designed so that specimens from exposed root dentin of vital teeth could be obtained. Twenty-two dentin biopsy pairs were divided into two groups; one was prepared for scanning electron microscopy (SEM) and the other for microradiography (MR). Small hypersensitive areas were identified by a scratch test on exposed human dentin in vivo. SEM observation of the dentin biopsies showed that the orifices of many dentinal tubules in hypersensitive areas were open and that membranous structures appeared on the walls of dentinal tubules. In naturally desensitized areas on the same dentin surface, most of the dentinal tubules were obturated with rhombohedral crystals of all sizes; membranous structures were not observed in these tubules. These results showed that hypersensitivity occurred on the exposed dentin when most of the tubular orifices were open.

Quantitative histological analysis of the human coronal dentine in dentinogenesis imperfecta types I and II

The coronal dentine of 3 teeth from dentinogenesis imperfecta (DI) type I, 9 teeth from DI type II and 4 controls were examined by a quantitative histological technique. In each case, two representative demineralized sections, one stained in H + E and the other in Schmorl's picrothionin were used. The relative amount of dentinal tubule, atubular dentine and canals/clefts were assessed using the point-counting method. Three basic patterns of distribution of tubules were observed. Pattern 1 formed the largest group and showed a gradual decrease in tubule count from enamel-dentine junction (EDJ) pulpwards, pattern 2 was characterized by a drop in tubule count approximately midway between EDJ and pulpal border, and pattern 3 exhibited a gradual increase in tubule score as the pulp was approached. At the 5 per cent level, both patterns 1 and 2 were found to be statistically significant. Pattern 3 was statistically insignificant for the test specimens and highly significant for the controls. The variation in the distribution of the tubules in coronal dentine in this study indirectly supports the concept of abnormal dentinogenesis in DI attributable to a diminution or lack of normal functional odontoblasts.

The dentin-predentin complex and its permeability: anatomical overview

This paper provides an anatomical overview of the dentin-predentin complex and its permeability. An unique anatomical feature of this complex is the presence of dentinal tubules which extend peripherally from the odontoblast-predentin junction throughout the thickness of the tissue. The permeability of dentin is a consequence of the presence of these tubules. Thus, this review concentrates on the anatomy of dentinal tubules and, in particular, on those studies which in the last decade have increased our knowledge of this anatomy. The structure, size, and number of dentinal tubules and the relationship of these features to the permeability of the tissue are discussed. This is followed by a description of the contents of dentinal tubules, with particular emphasis being paid to the literature concerning the extent of the odontoblast process.

Dentin-predentin complex and its permeability: pathology and treatment overview

This review paper focuses attention on tissue changes which may take place in dentin and on localized alterations in tissue formation in the predentin area. A number of reaction patterns has been described in dentin affecting both the inorganic and organic components. Dentinal tubules may become partly or completely obturated by growth of the peritubular dentin. Precipitation of mineral salts within the tubules, which may be a reprecipitation of minerals from adjacent demineralized dentin, represents a fundamentally different mode of obturation of dentinal tubules. Initially, demineralization selectively affects the peritubular dentin. If dentin is exposed to the oral environment, the surface layer may become hypermineralized. The surface layer of dentin, exposed by grinding, becomes covered by a smear layer. Displacement of the contents of the tubules or of the odontoblasts is a characteristic change in the organic components. Odontoblast destruction or degeneration will lead to a lack of, or reduced, predentin formation. Changes in the protein components which lead to alterations in dentin permeability have also been reported. The structure of the interface between dentin and localized formations of irregular secondary dentin varies considerably. If there is no tubular communication between primary and secondary dentin, the interface will act as an impermeable barrier. Changes in dentin, including irregular secondary dentin formation, affect the permeability of the tissue. Such changes are clinically important for the outcome of all types of restorative work performed on vital teeth.

Microradiographic and electron microscopic observations of the enamel-covered dentine in rat molars

The enamel-covered primary and secondary coronal dentine in the molars of 90-day-old and 360-day-old rats was examined using microradiography. Some preparations were subsequently examined by transmission and scanning electron microscopy (SEM). Fractured dentine surfaces and methacrylate casts of the tubular system in the primary dentine were also examined with SEM. No microradiographic evidence of a hypermineralized peritubular matrix, such as that seen in man and other species, was seen in either young or old rats. Transmission and SEM confirmed the microradiographic findings. The tubule obliteration and extensive intra-luminal mineral deposits which have been reported in the enamel-free coronal dentine of the rat molar were not seen in the enamel-covered coronal dentine but some evidence of tubule obliteration was seen in the secondary dentine.

Electron microscopy of dentinal tubule sclerosis in the enamel-free region of the rat molar

Ultrastructural changes in dentinal tubule contents were followed for periods up to 6 weeks following tooth eruption into the mouth. Characteristic odontoblast processes were observed in some tubules throughout the enamel-free dentine. Many dentinal tubules contained shrunken odontoblast processes, large collagen fibres and/or accumulations of mineral in various forms. The mineralization patterns suggest mechanisms of tubule occlusion other than simple formation of peritubular dentine. Both the degenerating odontoblast processes and collagen fibres appear to provide an organic framework for deposition of mineral. This region of rat molar dentine is recommended as useful for study of naturally-occurring tubular sclerosis.

The histology of sclerotic human root dentine

Studies by optical microscopy, microradiography and SEM suggested that sclerosis is the result of occlusion of the dentinal tubules by a mineral substance with a refractive index similar to that of the rest of the dentine. Translucence appeared before the majority of the tubules were completely occluded. The deposition of the occluding mineral took place initially in individual tubules or in groups of tubules. The occluding material and the peritubular dentine were almost indistinguishable under SEM. Both were smooth and densely mineralized. The process of deposition of occluding mineral appeared to be more like that of in-vitro mineralization and thus different from that of peritubular dentine.

Microscopy of the dentine of enamel-free areas of rat molar teeth

Dentine of the enamel-free areas (EFA) of first mandibular molar teeth of rats aged between 20-150 days was examined by scanning electron microscopy. Demineralized sections were stained with Gram-Twort's stain and examined for dental caries. In newly erupted teeth, a few dentinal tubules opened on the EFA surface. As teeth became worn down, extensive areas of EFA showed numerous patent tubules. In primary dentine, no occlusion or partial occlusion of tubules was apparent at any age except at the occlusal surface. It is postulated that this surface narrowing was caused either by dentine debris or salivary deposits. The only other covering of tubule openings appeared to be a thin salivary pellicle which in older animals was plaque-like. Patent tubules in primary dentine contained odontoblast processes which even in worn teeth extended to EFA surfaces. Processes in adjacent enamel-covered dentine also extended to the enamel-dentine junction. Only a few examples of bacterial invasion of EFA dentine were seen: in younger animals bacteria occupied cracks in the EFA surface, but in older animals they also occupied tubules. The EFA dentine does not appear to respond to attrition by infilling of the tubules; the persistence of vital odontoblast processes in worn teeth suggests that dead tract formation is not extensive. Continuous occlusal wear may restrict the progress of caries in EFA but odontoblasts in the rat may be also physiologically and immunologically involved in restricting the ingress of bacteria into otherwise poorly protected EFA.

Progressive decrease in dentine permeability following cavity preparation

Dentine permeability determinations were made longitudinally in cavities prepared in dog teeth in vivo, using two different techniques: isotope clearance and fluid filtration. Measurements made with both techniques indicate that there is a large reduction in dentine-permeability within the first week following cavity preparation. The phenomenon requires an intact pulp and is not the result of microleakage of temporary restorations.

The effects of plasma and salivary constituents on dentin permeability

The experiments described in this report were designed to determine the possible influence of plasma and salivary constituents on dentin permeability, in vitro. The results indicate that plasma, serum, and whole (mixed) saliva are all capable of causing immediate reductions in dentin permeability. Individual plasma protein fractions and several different types of bacteria were also effective in reducing the ease with which fluid can move across dentin. These observations may provide a mechanism for the "spontaneous" reductions in dentin sensitivity seen by clinicians following periodontal therapy.

Morphologic findings in dens evaginatus

10 specimens of dens evaginatus were partly examined by light microscopy, and by scanning electron microscopy. The morphological findings were consistent with the diagnosis of dens evaginatus although they indicated that the morphology of the evagination appears more complex than is seen in decalficied material alone. In two cases SEM revealed the existence of dental hard material within the evagination which in the other cases was filled out by necrotic pulpal material. This probable attempt of repair of the evagination is shortly discussed.

Dentin hydraulic conductance: changes produced by red blood cells

Red blood cells were forced into dentinal tubules in vitro under known hydrostatic pressures. This resulted in a 1 7-fold fall in the hydraulic conductance of dentin. The histologic appearance of red blood cells forced into dentin in vitro was very similar to that found in dog pulps following full crown preparations without adequate cooling in vivo.