Dentin Slabs Research Articles

Tubular occlusion of simulated hypersensitive dentin by the combined use of ozone and desensitizing agents

Objective. Ozone was suggested for treatment of hypersensitive dentin. The purpose of this study was to investigate the effect of ozone, with or without the use of desensitizing agents, on patency and occlusion of simulated hypersensitive dentin. Materials and methods. Sixty standardized dentin slabs were randomly divided into six groups: distilled water (Control), ozone treatment, fluoride desensitizer (ALLSolutions, Dentsply), oxalate desensitizer (D/Sense Crystal, Centrix), combined use of ozone/fluoride and combined use of ozone/oxalate. Ozone gas was delivered from OzonyTronX (Mymed). Specimens were evaluated using a scanning electron microscope and digital image analysis before and after treatment. Results. Statistical analysis using ANOVA and Mann-Whitney U-tests revealed significantly lower percentage of tubular occlusion with ozone treatment than distilled water at p ≤ 0.05. Scanning electron microscope photomicrographs of oxalate desensitizer specimens revealed a thick homogenous precipitate with significantly higher percentage of tubular occlusion than fluoride desensitizer and distilled water. Combined use of ozone/fluoride resulted in a significantly higher percentage of tubular occlusion than fluoride desensitizer alone. However, no significant difference was found between oxalate desensitizer and combined use of ozone/oxalate. Conclusions. The use of ozone gas is a viable adjunct to fluoride-containing desensitizers in enhancing tubular occlusion, but is not effective with oxalate desensitizers.

Dentine caries inhibition through CO2 laser (10.6 μm) irradiation and fluoride application, in vitro

ObjectiveThe purpose of the study was to investigate whether dentine irradiation with a pulsed CO2 laser (10.6μm) emitting pulses of 10ms is capable of reducing dentine calcium and phosphorus losses in an artificial caries model. DesignThe 90 dentine slabs obtained from bovine teeth were randomly divided into six groups (n=15): negative control group (GC); positive control group, treated with fluoride 1.23% (GF); and laser groups irradiated with 8J/cm2 (L8); irradiated as in L8+fluoride 1.23% (L8F); irradiated with 11J/cm2 (L11); irradiated as in L11+fluoride 1.23% (L11F). After laser irradiation the samples were submitted to a pH-cycling model for 9 days. The calcium and phosphorous contents in the de- and remineralization solutions were measured by means of inductively coupled plasma optical emission spectrometer – ICP-OES. Additionally intrapulpal temperature measurements were performed. The obtained data were analysed by means of ANOVA and Tukey's test (α=0.05). ResultsIn the demineralization solutions the groups L11F and GF presented significantly lower means of calcium and phosphorous losses than the control group; and in L11F means were significantly lower than in the fluoride group. Both irradiation parameters tested caused intrapulpal temperature increase below 2°C. ConclusionIt can be concluded that under the conditions of this study, CO2 laser irradiation (10.6μm) with 11J/cm2 (540mJ and 10Hz) of fluoride treated dentine surfaces decreases the loss of calcium and phosphorous in the demineralization process and does not cause excessive temperature increase inside the pulp chamber.

Fatigue and tensile properties of radicular dentin substrate

The purpose of this study was to compare the fatigue and tensile strengths of radicular dentin. Forty bovine lower central incisors were used, twenty teeth for the fatigue test and twenty teeth for the tensile test. Bovine teeth were each sectioned into coronal and radicular portions. Dentin slabs of 1mm thickness were prepared along the radicular tooth using a low-speed cutting machine and trimmed into dumbbell-shaped specimens. A dentin slab was harvested from each tooth. Subsequently, fatigue and tensile tests were performed in Hank's balanced saline solution at 37°C. The staircase method was employed to determine fatigue strength and its standard deviation. Fracture surfaces were observed by scanning electron microscopy. Mean fatigue strength and tensile strength were 44.3±5.0 and 84.4±8.3MPa, respectively. The fatigue strength of radicular dentin was significantly lower than the tensile strength. The fatigue strength of radicular dentin was only approximately one half of the tensile strength.

Effects of Concentrations and Exposure Times of Sodium Hypochlorite on Dentin Deproteination: Attenuated Total Reflection Fourier Transform Infrared Spectroscopy Study

Introduction The purpose of this study was to quantitatively analyze the effects of different concentrations and exposure times of sodium hypochlorite (NaOCl) on dentin deproteination and to determine the suitable concentrations and exposure times to minimize the effects of deproteination on dentin. Methods Intact human dentin slabs were treated with 0.5%, 1%, or 2.25% NaOCl for 1, 5, or 10 minutes. A 0.9% NaCl solution served as the control. To investigate the effect of NaOCl on the surface chemical changes to human dentin, the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy technique was used to analyze the amide:phosphate ratio and carbonate:phosphate ratio. Results The amide:phosphate ratio decreased significantly after NaOCl treatment as compared with the control group ( p < 0.05). In the 0.5% NaOCl treatment group, the amide:phosphate ratio was significantly higher than that in the 1% and the 2.25% NaOCl treatment groups ( p < 0.05). The different exposure times (1, 5, or 10 minutes) of NaOCl within the same concentration did not influence the amide:phosphate ratio ( p > 0.05). NaOCl treatment did not affect the carbonate:phosphate ratio ( p > 0.05). Conclusions NaOCl, 0.5%, is recommended as the predominant concentration for routine use during root canal therapy to minimize any NaOCl-induced dentin deproteination. It is suggested that a prolonged exposure to low concentrations of NaOCl is less damaging to dentin in attempting to achieve antisepsis during instrumentation of root canal therapy.

APF and Dentifrice Effect on Root Dentin Demineralization and Biofilm

Because dentin is more caries-susceptible than enamel, its demineralization may be more influenced by additional fluoride (F). We hypothesized that a combination of professional F, applied as acidulated phosphate F (APF), and use of 1100-ppm-F dentifrice would provide additional protection for dentin compared with 1100-ppm-F alone. Twelve adult volunteers wore palatal appliances containing root dentin slabs, which were subjected, during 4 experimental phases of 7 days each, to biofilm accumulation and sucrose exposure 8x/day. The volunteers were randomly assigned to the following treatments: placebo dentifrice (PD), 1100-ppm-F dentifrice (FD), APF + PD, and APF+FD. APF gel (1.23% F) was applied to the slabs once at the beginning of the experimental phase, and the dentifrices were used 3x/day. APF and FD increased F concentration in biofilm fluid and reduced root dentin demineralization, presenting an additive effect. Analysis of the data suggests that the combination of APF gel application and daily regular use of 1100-ppm-F dentifrice may provide additional protection against root caries compared with the dentifrice alone.

Diffusion of peroxides through dentine in vitro with and without prior use of a desensitizing varnish

Different bleaching regimens are used in dentistry possibly penetrating the dentine and affecting the pulp. The aim of the present study was to investigate peroxide diffusion through dentine pre-treated with a desensitizing varnish (Vivasens®) in a standardized in vitro setup during application of different bleaching materials. The penetration was tested using 1.3-mm-thick bovine dentine slabs. The following bleaching materials were tested with and without prior application of the desensitizing varnish on the external side of the dentine slabs: Vivastyle, Whitestrips, Simply White, Opalescence (external bleaching), and sodium perborate (internal bleaching, only tested without varnish; n = 8 samples per subgroup). The penetration of peroxides was measured photometrically using 4-aminoantipyrin as a substrate, the penetration of peroxides was monitored over 240 min. All bleaching agents yielded a diffusion of peroxides through the dentine, the kinetics of penetration were approximately linear for all materials tested. The significantly highest diffusion of peroxides was observed with Opalescence, the lowest with sodium perborate. The adoption of the desensitizing varnish reduced the diffusion of peroxides significantly for all external bleaching materials. Peroxides penetrated the dentine during application of bleaching materials; the penetration of peroxides can be reduced by application of a desensitizing agent.

Mechanical characterization of proanthocyanidin–dentin matrix interaction

Objectives To characterize the properties of dentin matrix treated with two proanthocyanidin rich cross-linking agents and their effect on dentin bonded interfaces. Methods Sound human molars were cut into 0.5 mm thick dentin slabs, demineralized and either treated with one of two cross-linking agents (grape seed—GSE and cocoa seed—COE extracts) or left untreated. The modulus of elasticity of demineralized dentin was assessed after 10 or 60 min and the swelling ratio after 60 min treatment. Bacterial collagenase was also used to assess resistance to enzymatic degradation of samples subjected to ultimate tensile strength. The effect of GSE or COE on the resin–dentin bond strength was evaluated after 10 or 60 min of exposure time. Data were statistically analyzed at a 95% confidence interval. Results Both cross-linkers increased the elastic modulus of demineralized dentin as exposure time increased. Swelling ratio was lower for treated samples when compared to control groups. No statistically significant changes to the UTS indicate that collagenase had no effect on dentin matrix treated with either GSE or COE. Resin–dentin bonds significantly increased following treatment with GSE regardless of the application time or adhesive system used. Significance Increased mechanical properties and stability of dentin matrix can be achieved by the use of PA-rich collagen cross-linkers most likely due to the formation of a PA–collagen complex. The short term resin–dentin bonds can be improved after 10 min dentin treatment.

Effect of fluoride and of calcium sodium phosphosilicate toothpastes on pre-softened dentin demineralization and remineralization in vitro

Objectives The purpose of this in vitro study was to evaluate the effect of toothpastes containing sodium fluoride in different concentrations or a calcium sodium phosphosilicate system on pre-softened dentin demineralization and remineralization. Methods During a ten day pH-cycling protocol, pre-softened bovine root dentin slabs were immersed twice daily, after the demineralization periods, for 2 min, in the following toothpaste slurries: (a) non-fluoridated (control), (b) 7.5% calcium sodium phosphosilicate, (c) 1450 ppm F, (d) 2800 ppm F and (e) 5000 ppm F. Subsequently, the specimens were subjected to a 15-h acid resistance test. Surface microhardness was assessed initially and during the pH-cycling and the acid resistance test period. Repeated measurements in each group were analyzed through appropriate regression models for longitudinal data. Results All fluoride groups, during pH cycling, showed significantly less microhardness loss ( p ≤ 0.010, p ≤ 0.002, p ≤ 0.002) and subsequently exhibited increased acid resistance ( p ≤ 0.010, p ≤ 0.001, p ≤ 0.001) compared to the control. The 5000 ppm and 2800 ppm F toothpastes, inhibited demineralization significantly more effectively than the 1450 ppm F ( p ≤ 0.001, p ≤ 0.030) and the calcium sodium phosphosilicate toothpaste ( p ≤ 0.001), while no significant differences were found between the two high fluoride groups ( p = 0.130). The calcium sodium phosphosilicate toothpaste, during pH cycling showed a difference that approached statistical significance compared to control ( p = 0.079), but its acid resistance behavior was similar to control ( p = 0.610). Conclusions Under these experimental conditions, the high fluoride toothpastes promoted remineralization and inhibited demineralization more effectively, than the 1450 ppm F, the non-fluoridated (control) and the calcium sodium phosphosilicate toothpastes.

In vitro photodynamic antimicrobial chemotherapy in dentine contaminated by cariogenic bacteria

The development of a method to ensure bacterial-free substrates without extensive cavity preparation would be highly useful to dentistry, since there is no currently available effective method for killing residual bacteria in dentinal tissue. This randomized in vitro study determined parameters for using toluidine blue O (TBO) with a light-emitting diode (LED) for dentine caries disinfection and monitored intrapulpal/periodontal temperatures during irradiation. Occlusal human dentine slabs were immersed in Streptococcus mutans culture for demineralization induction. Slabs were allocated to 10 groups (n = 15), which were treated with 0.1 mg ml−1 TBO with 5 min of incubation time or 0.9% NaCl solution for 5, 10 or 15 min, and submitted or not to irradiation for 5, 10 or 15 min (47, 94, and 144 J/cm2). Before and after treatments, dentine samples were analyzed with regard to S. mutans counts. In whole teeth, temperature in pulp and periodontium was measured by thermocouples during irradiation. Kruskal-Wallis/Student-Newman-Keuls, and ANOVA/Tukey test were respectively utilized to compare log reductions and temperature rises between groups. Bacterial reduction was observed when dentine was exposed to both TBO and LED at all irradiation times, as well as to LED alone for 10 and 15 min. Temperature increases lower than 2°C were observed for either pulp or periodontium. Concluding, LED combined with TBO is a safe and effective approach for dentine caries disinfection. Nevertheless, additional studies should be conducted to determine the influence of the irradiation in S. mutans viability in dentinal surface/tubules.

Effect of two restorative materials on root dentine erosion

This study sought to evaluate the microhardness of root dentine adjacent to glass-ionomer and composite resin restorations after erosive challenge. A crossover study was performed in two phases of 4 consecutive days each. One hundred twelve bovine root dentine slabs were obtained, and standardized box-shaped cavities were prepared at center of each specimen. The prepared cavities were randomly restored with glass-ionomer cement or composite resin. The slabs were randomly assigned among 14 volunteers, which wore intraoral palatal device containing four restored root dentin slabs. Starting on the second day, half of the palatal acrylic devices were immersed extraorally in a lemonade-like carbonated soft drink for 90 s, four times daily for 3 days. After 3-day wash-out, dentine slabs restored with the alternative material were placed into palatal appliance and the volunteers started the second phase of this study. After erosive challenges, microhardness measurements were performed. Regardless of the restorative material employed, eroded specimens demonstrated lower microhardness value (p < 0.0001). At eroded condition examined in this study, dentine restored with glass-ionomer cement showed higher microhardness values (p < 0.0001). It may be concluded that the glass-ionomer cement decreases the progression of root dentine erosion at restoration margin.

Effect of 16% Carbamide Peroxide Bleaching Gel on Enamel and Dentin Surface Micromorphology and Roughness of Uremic Patients: An Atomic Force Microscopic Study

To investigate the effect of 16% carbamide peroxide bleaching gel on surface micromorphology and roughness of enamel and root dentin of uremic patients receiving hemodialysis using atomic force microscopy (AFM). A total of 20 sound molars were collected from healthy individuals (n=10) and uremic patients (n=10). The roots were separated from their crowns at the cemento-enamel junction. Dental slabs (3 mm x 2 mm x 2 mm) were obtained from the buccal surface for enamel slabs and the cervical third of the root surface for dentin slabs. Dental slabs were then flattened and serially polished up to #2500-grit roughness using silicon carbide abrasive papers. Half of the slabs obtained from healthy individuals and uremic patients were stored in artificial saliva and left without bleaching for control and comparison. The remaining half was subjected to a bleaching treatment using 16% carbamide peroxide gel (Polanight, SDI Limited) 8 h/day for 14 days and stored in artificial saliva until AFM analysis was performed. Statistical analysis of the roughness average (Ra) results was performed using one-way ANOVA and Bonferroni post hoc multiple comparisons test. The micromorphological observation of bleached, healthy enamel showed exaggerated prism irregularities more than non-bleached specimens, and this observation was less pronounced in bleached uremic enamel specimens with the lowest Ra. Bleached healthy dentin specimens showed protruded peritubular dentin and eroded intertubular dentin with the highest Ra compared to bleached uremic dentin. The negative effects of the bleaching gel on uremic tooth substrates are less dramatic and non-destructive compared to healthy substrates because uremia confers different micromorphological surface changes.

Visualization of initial bacterial colonization on dentine and enamel in situ

Bacterial colonization of dentine is of high relevance in cariology, endodontology and periodontology. The aim of the present in situ study was to establish recent methods for visualization and quantification of initial bacterial adherence to dentine in comparison to enamel. For this purpose, bovine enamel and dentine slabs were fixed on buccal sites of individual upper jaw splints worn by 6 subjects for 30 min, 120 min and 360 min, respectively. Adherent bacteria on the slabs were visualized and quantified with DAPI-staining (4′,6-diamidino-2-phenylindole) and fluorescence in situ hybridization (FISH) of streptococci and eubacteria using the CLSM (confocal laser scanning microscopy) as well as an epifluorescence microscope. In addition, the number of colony forming units was quantified after desorption. Representative samples were processed for SEM (scanning electron microscopy) and TEM (transmission electron microscopy). All methods clearly indicated that a significantly higher number of bacteria adhered to dentine than to enamel. Furthermore, the amount of bacteria on the dentine increased with increasing oral exposure time, but remained rather constant on the enamel. The CLSM allowed visualization of bacteria in the dentinal tubules. Bacteria were found preferentially at the openings of the dentine tubules, but were distributed randomly on the enamel. In conclusion, the adopted methods are suitable for visualization and quantification of bacterial adhesion to dentine. Even the initial bacterial colonization of dentine is much more pronounced than bacterial adherence to the enamel.

Effects of laser and acid etching and air abrasion on mineral content of dentin

The aim of this study was to evaluate the mineral content of dentin prepared using an Er,Cr:YSGG laser at four different power settings, acid etching, and air abrasion. The study teeth comprised 35 molars which were randomly divided into seven equal groups. The occlusal third of the crowns were cut with a slow-speed diamond saw. The groups were as follows: group A, control group; group B, dentin etched with 35% buffered phosphoric acid for 30 s; group C, dentin abraded at 60 psi with 50-µm aluminium oxide for 1 s; groups D-G, dentin irradiated with the Er,Cr:YSGG laser at 1.50 W (group D), 2.25 W (group E), 3.00 W (group F), and 3.50 W (group G). The levels of Mg, P, Ca, K and Na in each dentin slab were measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Data were analysed by one way analysis of variance and Tukey HSD tests. There were no significant differences between the groups in the levels of Ca, P and Na, and the Ca/P ratio (p>0.05); however, there were significant differences in the levels of K (p<0.001) and Mg (p=0.13). In addition, the levels of Mg in the air abrasion group were higher than in the other groups (p<0.01). Etching with the Er,Cr:YSGG laser system, air abrasion and acid etching did not affect the levels of Ca, P and Na, or the Ca/P ratio, in the dentin surface.

Strength of the bond as a predictor of marginal performance: An in vitro evaluation of contemporary adhesives

Objective The aim of this study was to elucidate whether marginal performance (in terms of % of continuous margins) can, or not, be predicted from μTBS values. A relationship was attempted between μTBS and % of continuous margins (% CM) before and after loading of class V restorations made with five restorative systems from both etch & rinse and self-etch approach. Methods Resin–dentin slabs and as well as class V cavities with cervical margins in dentin were prepared and restored using five adhesive systems (Scotchbond Multipurpose Plus (SMPP), James 2, Experimental Bond, Xeno III and iBond) with their corresponding restorative composites. Bond strength and percentages of continuous margins were calculated before and after thermal and mechanical loading. Statistical correlation was calculated between bond strength/marginal adaptation before loading and bond strength/marginal adaptation after loading of the same adhesives. Results Ranking of materials according to their performance was test method dependent. A low weak correlation was found between bond strength and percentages of marginal adaptation. Significance No correlation could be established between strength of the bond and percentages of continuous margins. A direct comparison of bond strength with marginal adaptation data may be misleading.

Recent Advancements in Preventing Teeth Health Hazard: The Daily Use of Hydroxyapatite Instead of Fluoride

Hydroxyapatite (HA) is commonly considered the most promising synthetic biomaterial for biomedical applications in orthopaedic, dental and maxillofacial surgery for its biocompatibility, bioresorption and bioactivity. Only recently a chemical-physical experimental approach has been utilized to investigate the capability of synthetic carbonated hydroxyapatite nanocrystals (CHA) to produce in vivo biomimetic mineral deposition on enamel and dentine surface through a daily use. Demineralised enamel and dentine slabs have been treated in vitro with synthetic biomimetic hydroxyapatite nanocrystals for a few minutes. This induced a surface remineralisation, forming a biomimetic apatite coating on enamel and dentine surface. In fact, enamel remineralisation quickly occurs thanks to the specific chemicalphysical characteristics of innovative nanostructured hydroxyapatite particles which closely resemble mineral enamel constituents. Therefore the experimental results suggest the possibility to perform teeth wear-deterioration prevention. Carbonated hydroxyapatite nanocrystals synthesized with tailored biomimetic characteristics for composition, structure, size and morphology can chemically bind themselves on the surfaces of teeth hard tissues, filling the scratches, producing a bound biomimetic apatitic coating, protecting the enamel surface structure. Over the past few decades many products for dental damage prevention (toothpastes, rinses and gels) have been commercialized and patented expressly for the fluoride remineralisation effect. Only recently the numerous applications of hydroxyapatite as bone filler biomaterial for implantation surgery have evidenced innovative and important opportunities for decay prevention through a daily use of oral care products containing hydroxyapatite. The aim of this paper is to review these recent patents and classify them according to their actual possibilities to safeguard teeth health. Keywords: Hydroxyapatite, biomimetism, nanocrystals, enamel, dentine, teeth remineralization, fluoride

Evaluation of the antimicrobial effect of photodynamic antimicrobial therapy in an in situ model of dentine caries

Photodynamic antimicrobial therapy (PACT) promotes bacterial death as a result of the photosensitization of microbial components. This study evaluated the effect of PACT on dentine caries produced in situ. Over the course of 14 d, 20 volunteers wore intra-oral devices containing human dentine slabs that were treated 10 times daily with a 40% sucrose solution. Afterwards, the antimicrobial effect of toluidine blue O, associated with 47 or 94 J cm(-2) of a light-emitting diode, was evaluated. Before and after the treatments, dentine samples were analysed with regard to the total number of microorganisms, total streptococci, mutans streptococci, and lactobacilli. Significant reductions in the bacterial count were observed for PACT with both energy densities tested, with the following values observed for 47 and 94 J cm(-2) of irradiation: for total streptococci, 3.45 and 5.18; for mutans streptococci, 3.08 and 4.16; for lactobacilli, 3.24 and 4.66; and for total microorganisms, 4.29 and 5.43, respectively. The control, treated with 94 J cm(-2) of irradiation alone, was also effective against all bacteria. To conclude, PACT was effective in killing oral microorganisms present in dentine caries produced in situ and may be a useful technique for eliminating bacteria from dentine carious lesions before restoration.

Assessment of bioactive and bio‐adhesive therapies to enhance stem cell attachment to root surface dentine

To compare bioactive and bio-adhesive therapies to enhance stem cell attachment to the root dentine of human teeth. Dentine slabs (n = 72) were cut from the lower 3 mm of the roots of extracted human permanent teeth. The root dentine slabs were untreated, or coated with bio-adhesive, or human recombinant transforming growth factor-beta1 (hrTGF-B1), or human recombinant bone morphogenic protein-2 (hrBMP-2). The dentine slabs were placed with the root surface in contact with confluent periodontal stem cell (PSC) cultures using aseptic techniques. The cells and dentine slabs were submerged in culture media for 4, 24 and 72 h. The specimens were fixed in formalin, dehydrated and processed for scanning electron microscopy (SEM). SEM micrographs at x2000 magnification revealed PSC extensive adherence to root dentine for all of the bio-adhesive and bioactive treatments. The addition of bioactive molecules did not improve PSC attachment. Few cells attached to the negative control treatments. Bio-adhesive and bioactive growth factors were not needed to promote PSC attachment to the root dentine of human teeth, because it already appears to have good natural properties to promote PSC attachment. This suggests PSC can be used for the clinical replantation of avulsed teeth without the need for bio-adhesive and bioactive treatments.

An Evaluation of the Effect of Non-Setting Calcium Hydroxide on Human Dentine: A pilot Study

To evaluate the effect of non-setting calcium hydroxide (NSCH) on the hardness and elastic modulus of dentine from extracted permanent premolar human teeth. 30 freshly extracted single rooted human premolar teeth were decoronated and the roots then sectioned longitudinally into equal halves. In the experimental group a thin layer of NSCH was applied whilst the control group had no medicament. After 1, 3 and 6 months, nanoindentation was used to assess dentine hardness and the modulus of elasticity. Scanning Electron Microscopy (SEM) was used to visualize the depth of penetration of NSCH into the dentinal tubules. SEM images showed that there were no structural changes in the dentine slabs that had NSCH application after 1, 3 or even 6 months. However, penetration of NSCH into the dentine tubules was seen at both 3 and 6 months with a significant reduction in the hardness of dentine observed at 3 (p<0.02) and 6 months (p<0.01). The modulus of elasticity was significantly lower (p<0.01) at 6 months. It appears that there is a significant reduction in the hardness of dentine with increasing periods of calcium hydroxide application. Prolonged application of NSCH could have a detrimental effect on dentine, making the dentine more prone to fracture.

Effect of a 10% carbamide peroxide on wear resistance of enamel and dentine: In situ study

Objectives This triple-blind, 2 × 2 crossover in situ study, was undertaken to verify whether the wear resistance of enamel and root dentine would be affected by bleaching with a 10% carbamide peroxide agent and a placebo agent. Methods Thirty slabs of each substrate (2 mm × 3 mm × 2 mm) were selected for each phase, after flattening and polishing procedures and microhardness test. After a 7-day lead-in period, one specimen of each substrate was randomly bonded on the facial surface of each one of 30 subject's upper second premolars. The volunteers received instructions on how to perform toothbrushing and application of gel in the tray. Fifteen volunteers bleached their maxillary arch with a 10% carbamide peroxide bleaching agent for a 2-week period, while the remainders used a placebo agent. After a 1-week washout period, a new set of enamel and root dentine slabs were bonded to the premolars and volunteers were crossed over to the alternate agent for 14 days. The resistance of enamel and root dentine to wear following bleaching, toothbrushing and intraoral exposure was measured with a profilometer, using reference areas. Results For enamel, ANOVA did not demonstrate significant difference between wear provided by placebo and bleaching agent ( p = 0.3713), but higher wear depth was observed for bleached root dentine ( p = 0.0346). Conclusions While overnight bleaching caused no alteration in wear resistance of enamel, root dentine showed increased tissue loss.

Changes in elastic modulus of adhesive and adhesive-infiltrated dentin during storage in water

The purpose of this study was to determine the elastic modulus of components at the resin-dentin interface with the use of an ultrasound device. Dentin slabs were obtained from freshly extracted bovine incisors shaped into a rectangular form. After demineralization, the dentin specimens were immersed in adhesives and polymerized. Adhesives were also polymerized and trimmed into the same shape as the dentin slabs. The specimens were then immersed in distilled water at 37 degrees C for up to one year. The ultrasound equipment employed in this study was a Pulser-Receiver, transducers and an oscilloscope. By measuring the longitudinal and shear wave sound velocities, the elastic modulus was determined. When the elastic modulus of adhesive resin-infiltrated demineralized dentin was compared with that of adhesives, slightly but significantly lower values were found for adhesives used in a self-etching primer system. On the other hand, a higher elastic modulus was observed for resin-infiltrated dentin than for an adhesive used in an etch and rinse system. The elastic modulus of the resin-infiltrated dentin prepared with the etch and rinse system was affected by long-term storage in distilled water.