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PubMed2005

In vitro radiographic analysis of Nd:YAG-laser-irradiated dentin.

The aim of this study was to evaluate the effects of Nd:YAG laser irradiation on the dentin radiographic image. Previous studies have shown that Nd:YAG laser irradiation is capable of promoting morphological and chemical changes of the dentin surface, indicating the possibility of an alteration of its radiographic image. Dentin of 2-mm-thick mid-coronal sections from 68 extracted posterior teeth was irradiated for 30 s by a Nd:YAG laser (lambda=1,064 nm) on one half of its surface area. The other half was left as a control. The irradiation parameters were: 80 mJ/pulse, 0.8 W, 10 Hz, with a 320-mum flexible quartz optic fiber in contact mode. The 68 samples were radiographed with a 70-kV X-ray setup. The focus-film distance was established as 30 cm and there was no distance between the object and the film. The X-ray exposure time was set as 0.16 s and the radiographic film used was an F-speed dental film. The obtained radiographic images were submitted to a densitometric analysis. The images analyzed showed that there were statistically significant differences between the density of the irradiated dentin images and the non-irradiated dentin images. The image density data showed that the irradiated dentin radiographic images were 6.36% more radiopaque than the non-irradiated dentin images. The Nd:YAG laser irradiation of dentin is able to alter its radiographic image, producing more radiopaque images of the irradiated dentin.

Absorptiometry, Photon↗

PubMed1983

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.

Age Factors↗

PubMed1989

The permeability of dentine from bovine incisors in vitro.

The permeability of coronal dentine was investigated by measuring the hydraulic conductance of dentine discs. Reductions in dentine thickness from the enamel side of disc resulted in a greater increase in permeability than reductions from the pulpal side. Scanning electron microscopy revealed fewer dentinal tubules with smaller diameters in superficial dentine than in deep dentine. The permeability of coronal incisor bovine dentine is six to eight times less than that of unerupted coronal human third molar dentine but similar to that of human root dentine.

Animals↗

PubMed1994

Degradation of insoluble bovine collagen and human dentine collagen pretreated in vitro with lactic acid, pH 4.0 and 5.5.

The purpose of the study was to test the hypothesis that both insoluble pure type I collagen from bovine Achilles tendon and dentine collagen in root dentine powder from human teeth required acid pretreatment for subsequent degradation by trypsin, a non-specific protease. Pure type I collagen or dentine powder was treated with lactic acid, at pH 4 or 5.5, or distilled, deionized water (pH 7) as a negative control. After incubation at 37 degrees C for 24 h, extracts of pure type I collagen solutions were analysed for soluble collagen with the hydroxyproline assay. Extracts of dentine powder solution were analysed for Ca2+, total protein, final pH, and hydroxyproline. Residual, undegraded pellets were washed and then treated with trypsin or collagenase. After 24 h of incubation, the soluble fractions from the enzyme-treated pure type I collagen and dentine powder solutions were analysed for hydroxyproline. Results showed that almost no pure type I collagen was degraded during acid pretreatment. Trypsin degraded significantly more pure type I collagen in the pH 4-treated group than in the other groups. Collagenase degraded about 70% of the pure type I collagen irrespective of acid pretreatment. While acid pretreatment at pH 4 did not degrade dentine collagen, data from Ca2+ analyses and collagen breakdown by trypsin suggested that pretreatment at pH 4 demineralized and denatured dentine collagen so that the collagen could be subsequently degraded by enzymes. After pretreatment at pH 4, about 27 and 57% of the dentine collagen was degraded by trypsin and collagenase, respectively, in contrast to minimal degradation of non-acid-treated dentine collagen by the same enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Achilles Tendon↗

PubMed1996

Hardness and Young's modulus of human peritubular and intertubular dentine.

A specially modified atomic-force microscope was used to measure the hardness of fully hydrated peritubular and intertubular dentine at two locations within unerupted human third molars: within 1 mm of the dentine enamel junction and within 1 mm of the pulp. The hardness of fully hydrated peritubular dentine was independent of location, and ranged from 2.23 to 2.54 GPa. The hardness of fully hydrated intertubular dentine did depend upon location, and was significantly greater near the dentine enamel junction (values ranged from 0.49 to 0.52 GPa) than near the pulp (0.12-0.18 GPa). A Nanoindenter was used to estimate the Young's modulus of dehydrated peritubular and intertubular dentine from the unloading portion of the load displacement curve. The modulus values averaged 29.8 GPa for the peritubular dentine (considered to be a lower limit), and ranged from 17.7 to 21.1 GPa for the intertubular dentine, with the lower values obtained for dentine near the pulp.

Analysis of Variance↗

PubMed2004

Partial biochemical characterisation of collagen in carious dentin of human primary teeth.

The process of dentin caries is a complex event involving demineralisation and matrix degradation. The objective of this study was to biochemically characterise collagen, the major dentin matrix component, by amino acid and cross-link analyses in two distinct carious dentin regions of human primary teeth. Twenty-seven carious primary teeth were obtained from 3 to 11-year-old patients and three layers of dentin, i.e. outer, inner carious dentin and normal dentin, were identified by a 1% acid red solution and dissected from each tooth. The samples were pulverised, the respective layers obtained from three to five teeth were pooled and six samples per layer were analysed. Aliquots of the dried dentin powder were hydrolysed with 6N HCl at 110 degrees C for 24h and subjected to amino acid analyses. Other aliquots were demineralised, reduced with standardised NaB3H4, hydrolysed and subjected to quantitative collagen cross-link analyses. The results demonstrated that in the outer carious layer the collagen-associated amino acids were significantly lower and the reducible cross-links were markedly diminished when compared to the other two groups. There was no significant difference in these parameters between the inner carious and the normal layers. The data indicate that while the collagen in the outer carious dentin is significantly altered and degraded, the one in the inner carious dentin is relatively unaffected in primary teeth.

Amino Acids↗

PubMed2004

Effect of hydrogen peroxide on intertubular dentine.

OBJECTIVES: To evaluate the effect of 30% hydrogen peroxide on the surface changes and nanomechanical properties of intertubular dentine. METHODS: Five freshly extracted human premolars were sectioned and two specimens were obtained from each tooth. Atomic force microscopy (AFM) images of dentine were taken. Baseline hardness and Young's modulus of intertubular dentine were determined using nanoindentation testing and recorded. The specimens were then treated with either 0.5 ml of Hank's balanced salt solution (control group) or 30% hydrogen peroxide at 24 degrees C for 24 h. AFM imaging and determination of hardness and Young's modulus of intertubular dentine were then repeated. The images were compared and statistical analyses of hardness and Young's modulus were carried out using paired sample t-tests. RESULTS: The AFM images showed recession of the intertubular dentine surface post-bleaching. For the control group, there was no significant change in hardness (p=0.124) and Young's modulus (p=0.438) of intertubular dentine. However, a significant decrease in hardness (p=0.002) and Young's modulus (p=0.001) of intertubular dentine was observed for the experimental group. CONCLUSIONS: Exposure to 30% hydrogen peroxide for 24 h caused surface changes to intertubular dentine and significantly decreased the hardness and Young's modulus of intertubular dentine.

Dentin↗

PubMed2005

Induction of cyclooxygenase-2 expression in human pulp cells stimulated by dentin bonding agents.

OBJECTIVES: Histological investigations have demonstrated that dentin bonding agents can induce pulpal inflammation. However, there is little information on the precise mechanisms about dentin bonding agent-induced pulpal inflammation. Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at the site of inflammation. The aim of this study was to investigate the effects of dentin bonding agents on the expression of COX-2 in human pulp cells. STUDY DESIGN: Human pulp cells were cultured from extracted impacted third molars using an explant technique. Patients gave informed consent. The reverse-transcriptase polymerase chain reaction and Western blot assays were used to investigate the effects of cultured human pulp cells exposed to dentin bonding agents. In addition, NS-398 (a selective COX-2 inhibitor) was added to test how it modulated the cytotoxic effects of dentin bonding agents. RESULTS: The exposure of quiescent human pulp cells to dentin bonding agents resulted in the induction of COX-2 mRNA and protein expression. The expression of COX-2 signals depended on the materials tested. In addition, NS-398 at noncytotoxic dose was not able to prevent dentin bonding agent-induced cytotoxicity (P > .05). CONCLUSION: The activation of COX-2 expression may be one of the pathogenesis of dentin bonding agent-induced pulpal inflammation. In addition, dentin bonding agent-induced cytotoxicity is not directly via the induction of COX-2 expression.

Acetone↗

PubMed2005

Dentin enhances the effectiveness of bioactive glass S53P4 against a strain of Enterococcus faecalis.

OBJECTIVE: The aim of the current study was to test the impact of dentin powder on the antimicrobial efficacy of bioactive glass S53P4 (BAG). STUDY DESIGN: BAG was suspended (preincubated) in saline at 37 degrees C for different time periods with or without human dentin powder, hydroxylapatite, or decalcified dentin. Subsequently, Enterococcus faecalis ATCC 29212 cells were added to these suspensions and bacterial recovery measured with and without the use of gentle sonication. Furthermore, survival of bacteria in test and control suspensions was assessed over time. Supernatants of suspensions were analyzed for their element contents using atomic absorption spectrophotometry. The effects of pH, silica, and osmolarity on E faecalis viability were assessed using specifically prepared solutions. RESULTS: BAG preincubated with dentin powder caused a significant (P < .05) decrease in viability compared to pure BAG suspensions. This was not based on adherence of bacteria to solid particles or agglutination of the cells, because sonication did not increase bacterial yields. Hydroxylapatite and decalcified dentin did not increase BAG killing efficacy. The additive effect of BAG + dentin powder was dose dependent, occurred only with solids in suspension, and increased with suspension time. An augmented dissolution of glass components, especially silicon, was measured in BAG + dentin powder compared to pure BAG suspensions or counterparts containing hydroxylapatite or decalcified dentin. High osmolarity per se did not affect E faecalis viability, whereas high pH and silica levels did. CONCLUSION: The observed phenomenon was related to an increased BAG dissolution triggered by dentin powder, causing elevated local pH and silica levels.

Anti-Infective Agents, Local↗

PubMed2004

Calbindin D-28k distribution in odontoblasts underneath tertiary dentine in human carious teeth.

OBJECTIVE: The aim of this study was to examine the calbindin D-28k immunoreactivity in carious teeth to know whether this protein may have a function in tertiary dentine formation. METHODS: Human extracted teeth with or without carious lesions were immersion-fixed with Zamboni fixative, demineralized in 4.13% EDTA solution (pH 7.4), frozen-sectioned, and processed for calbindin immunoreactivity and hematoxylin-eosin stain. The intensity of the immunostaining was evaluated by quantitative densitometry. RESULTS: In intact teeth, numerous odontoblasts were aligned underneath the secondary dentine and their cell bodies showed the immunoreactivity. In carious teeth, tertiary dentine had poor- or rich tubular patterns under the carious lesion. Underneath the tubule-poor tertiary dentine, distinct odontoblasts could not be seen at the central site. However, some cells with a flat appearance were located at this site and were immunonegative for calbindin D-28k. On the other hand, columnar odontoblasts were seen at the peripheral site, and their cell bodies and processes showed strong immunoreactivity. Underneath the tubule-rich tertiary dentine, columnar odontoblasts were abundantly distributed, and the strong immunoreactivity was observed in their cell bodies and processes. The immunoreactivity in odontoblasts underneath the tertiary dentine with poor or rich tubular pattern was more intense than that for the secondary dentine in intact teeth (P<0.05). On the other hand, the intensity of the immunoreactivity in odontoblasts was similar underneath the secondary dentine in intact and carious teeth. CONCLUSIONS: The present study demonstrated that calbidin D-28k was actively synthesised by odontoblasts under the carious lesion. These findings may suggest that this protein plays an important role in the tertiary dentine formation.

Adult↗

PubMed1991

Proton NMR spin grouping and exchange in dentin.

The nuclear magnetic resonance spin-grouping technique has been applied to dentin from human donors of different ages. The apparent T2, T1, and T1 rho have been determined for natural dentin, for dentin which has been dried in vacuum, and for dried dentin which has been rehydrated in an atmosphere with 75% relative humidity. All apparent spin relaxation has been analyzed for exchange between the spin groups in which the dentin protons exist; the analyses incorporate the results of selective inversion recovery T1 measurements which better probe the effects of exchange. The exchange analyses of the high fields and rotating frame spin-lattice relaxation have also been correlated to determine uniquely the inherent relaxation parameters of the proton spin groups constituting the dentin magnetization. The natural dentin contains protons on water, protein, and hydroxy apatite; these spins contribute 50%, 45%, and 5% to the total dentin proton magnetization, respectively. The water exists in three distinct environments, the dynamics of each environment has been modeled. In the natural dentin 30% of the water undergoes uni-axial reorientation. 52% of the water has similar relaxation characteristics to bound water hydrating a large molecule, and the majority of the remaining water acts as bulk water undergoing isotropic reorientation. The results are independent of the age of the donor.

Adult↗

PubMed1993

The effects of dehydration and rehydration on some mechanical properties of human dentine.

This study was designed to investigate the effect of dehydration and rehydration on the brittleness and toughness of human dentine. Tensile and three-point bend tests were carried out on hydrated, dehydrated and rehydrated dentine bars, sectioned from sound extracted, human third molar teeth. The stress, strain and fracture energy (toughness) were calculated and the results were analysed using ANOVA and Duncan's multiple range test at p = 0.01. Stress at fracture did not differ significantly between hydrated, dehydrated or rehydrated dentine in bending or tensile tests. Strain at fracture and fracture energy were significantly greater for hydrated and rehydrated than for dehydrated dentine. In bending, the elastic energy (resilience) of dehydrated dentine was significantly greater than that of hydrated or rehydrated dentine, but dehydrated dentine showed no plastic energy (deformation) in contrast with the high values for hydrated and rehydrated dentine. Dehydration of human dentine resulted in decreased strain at fracture and demonstrated a brittle behaviour. The absence of plastic energy of deformation and the significantly reduced energy required to induce fracture were indicative of decreased toughness by dehydration. These changes were abolished after rehydration.

Body Water↗

PubMed1998

Effect of enamel and dentin surface wetness on shear bond strength of composites.

PURPOSE: This study investigated the effect of the wetness of human enamel and dentin surfaces on the shear bond strength of composites. MATERIAL AND METHODS: Seven dentin bonding systems were used. Three methods of preparing the enamel or dentin surface before applying primer or bonding agent were adopted as test conditions: wet (blot dried), semidry (3-second air blast), and dry (15-second air drying). Shear bond strength was measured with a universal testing machine. Mean bond strengths were analyzed with analysis of variance and Scheffe's F-test. Enamel and dentin surfaces were observed by a dissecting microscope after shear bond testing. RESULTS: Enamel specimens tested by all systems and dentin tested by two systems did not reveal significant differences in shear bond strengths (p > 0.05). Among dentin specimens tested by two systems with water-based primers, the shear bond strength values of the dry technique group were higher than those of the other two groups (p < 0.05). However, among dentin specimens tested by systems having acetone-based primers or bonding agents, bond strength values of the wet or semidry technique groups were higher than those of the dry technique group (p < 0.05). CONCLUSION: It was concluded that some water might be needed by dentin surfaces or for primers to obtain high bond strength on the dentin surface, but that drying methods did not affect bonding strength to enamel surfaces either before priming or after conditioning.

Analysis of Variance↗

PubMed1988

Quantitative assessment of collagen crosslinks in dissected predentin and dentin.

Dentinogenesis offers a unique system for the study of changes in collagen structure occurring simultaneously with mineralization. Bovine dentin was found to contain about one reducible crosslink per collagen molecule; rat dentin contained twice this amount. In contrast, bovine dentin contained twice as much pyridinium crosslink as did rat dentin collagen. These results indicate that the collagen in rat teeth is less mature and again emphasize the difference in composition between the organic matrices of rat and bovine dentin. In dissected bovine predentin, the unmineralized precursor of dentin, the content of reducible crosslinks was almost double that of dentin. Only minute amounts of non-reducible crosslinks were found in predentin, whereas both pyridinoline and deoxy-pyridinoline were present in collagen from mineralized dentin. The observed differences in crosslinking between predentin and dentin of the same teeth may indicate some alterations within the area of mineralization.

Animals↗

PubMed2003

Micro-mechanical characterisation of the properties of primary tooth dentine.

OBJECTIVES: Understanding the mechanical properties of dentine is of importance as adhesive restorative materials mainly achieve their bonding to the tooth structure through dentine. The current study measures the hardness and modulus of elasticity of primary molar dentine using an Ultra-Micro-Indentation System (UMIS), which allows the dentine to remain hydrated and thus is assumed to be closer to the in vivo conditions. METHODS: Eight sound primary molar teeth were axially sectioned, embedded in resin and fine polished. Two linear arrays of indentations were done on coronal dentine, from the pulp wall to dentino-enamel junction (DEJ) parallel to the tubule direction under a force load of 25mN. RESULTS: The mean hardness and elastic modulus of the dentine nearest the pulp wall was 0.52+/-0.24 and 11.59+/-3.95GPa, respectively, which was significantly lower than those of dentine in the middle area, which was 0.85+/-0.19 and 17.06+/-3.09GPa, respectively, and the dentine nearest DEJ, which was 0.91+/-0.15 and 16.33+/-3.83GPa, respectively. There is a statistically significant linear correlation between the hardness and modulus of elasticity. CONCLUSIONS: The hardness and modulus of elasticity of dentine decreases with decreasing distance from the pulp. This is of importance to clinicians because an extension of cavity preparation towards the pulp may lead to less mechanical support for a restoration.

Biomechanical Phenomena↗

PubMed1999

Effect of endodontic irrigation solutions on microhardness of root canal dentine.

OBJECTIVES: This study was undertaken to evaluate the effect of several endodontic irrigation solutions on the microhardness of root canal dentine. METHODS: Eighteen freshly extracted maxillary incisors were used in this experiment. The crowns of teeth were sectioned at the cemento-enamel junction. The root canals were instrumented to an apical size #50 file, and irrigated with saline solution. The prepared roots were divided equally into two groups each of nine roots. Each root was sectioned transversely into cervical, middle and apical segments. The three sections of each root were separately mounted in a metal chuck with acrylic resin. The coronal dentine surfaces of the root segments were polished. The microhardness of the dentine was measured for the purposes of control data at 500 microns and 1 mm from the pulpo-dentinal interface. The canal portions in the root segments included in the first group were irrigated with 3% H2O2 and 5% NaOCl solutions used alternatively, while 17% EDTA solution was the irrigation used in the second group. One millilitre of each solution/segment was applied for 60 s exposure time. After irrigation, dentine microhardness was re-assessed and compared with the control values obtained before the irrigation treatment. Data were statistically analysed using ANOVA and Scheffe's test. RESULTS: The results showed that, irrigation with either H2O2/NaOCl or EDTA decreased the microhardness value of root dentine. Irrigation with EDTA gave more reduction of dentine hardness compared to H2O2/NaOCl irrigation. The reduction of KHN of dentine following the irrigation treatment was statistically significant (p < 0.05) at both levels of hardness measurement. CONCLUSIONS: Both H2O2/NaOCl and EDTA irrigating solutions significantly reduced the microhardness of root canal dentine.

Adult↗

PubMed2003

Investigation of erosion and abrasion on enamel and dentine: a model in situ using toothpastes of different abrasivity.

BACKGROUND: Studies in vitro suggest that abrasion and erosion may act synergistically to produce wear of enamel and dentine. Methods in situ are recently available to study separately erosion and abrasion of dental tissues. The aim of this study was to combine two in situ protocols to study the interplay between erosion and abrasion of enamel and dentine. METHOD: The study was a single-blind, randomised, five-treatment cross-over design involving 15 healthy volunteers. During each 10-day study period, subjects wore from 0900 to 1700 h an upper removable acrylic appliance holding one polished enamel and one polished dentine specimen. The specimen treatment regimens were: 1. Drinking water and brushing with toothpaste A. 2. Drinking water and brushing with toothpaste B. 3. Drinking orange juice. 4. Drinking orange juice and brushing with toothpaste A. 5. Drinking orange juice and brushing with toothpaste B. Drinking and brushing times were around 0900, 1100, 1300 and 1500 h. Drinks were consumed as 250 ml over 10 min and brushing ex vivo for 1 min to each specimen. Measurement of tissue loss was made on days 5 and 10 of each period using a profilometer. RESULTS: All treatments produced increasing tissue loss over time, which was considerably greater for dentine than enamel. For enamel, the data at days 5 and 10 showed a significant effect for erosion (i.e. orange juice was significantly more erosive than water), but no significant effect for abrasion (i.e. no significant difference between the two toothpaste treatments). The combined orange juice and toothpaste effects were directional for synergy but did not reach significance. For dentine at day 10, many specimens exceeded the 50 microm set limit of the profilometer and only day 5 data were considered. There were significant effects for erosion (orange juice produced significantly more erosion than water) and for abrasion (paste A was significantly more abrasive to dentine than paste B). The synergy effect could not be examined for dentine due to the truncation effect as the set limit of the profilometer was exceeded. CONCLUSIONS: Erosion increases the susceptibility of enamel to toothpaste abrasion. Dentine is considerably more susceptible than enamel to erosion and abrasion alone or combined. Dentine loss appears to correlate with toothpaste abrasivity (RDA value).

Adolescent↗

PubMed2000

Immunohistochemical and ultrastructural evaluation of the effects of phosphoric acid etching on dentin proteoglycans.

It has been reported that phosphoric acid (PA) produces structural and molecular alterations in dentin collagen fibrils; however, no relevant information exists on the influence of etching with PA on dentin non-collagenous macromolecules. The present study investigated, by immunohistochemistry and ultrastructural histochemistry, the behavior of dentin proteoglycans (PG) after etching human dentin samples with 35% PA gel (thickened with colloidal silica) or with a 35% PA liquid for 15, 30 and 120 s. Immunolabeling with a mouse monoclonal anti-chondroitin sulfate antibody demonstrated that glycosaminoglycans (GAG) were preserved within dentinal tubules opened to the surface after etching with PA gel. In addition, the cationic tracer polyethyleneimine, used for the ultramicroscopic localization of PG anionic sites, revealed that treatment of dentin samples with PA gel preserved the polyanionic peritubular PG in the etched area. On the other hand, etching with the PA liquid produced loss of peritubular GAG and PG anionic sites in the etched dentin surface. The results obtained indicated that similar concentrations of PA in gel or liquid formulations differently affect the organization of dentin PG. The clinical significance of these in vitro findings and the structural and molecular interactions of dentin PG with adhesive systems are still unknown.

Acid Etching, Dental↗