Dentin Depth Research Articles

Bond Strength of High-Viscosity Glass Ionomer Cements is Affected by Tubular Density and Location in Dentin?

This study evaluated the influence of tubular density of different dentin depths and location on the bond strength of high-viscosity glass ionomer cements (GIC). A total of 20 molars were selected and assigned into six experimental groups, considering two different high-viscosity GICs-Fuji IX (FIX) or Ketac Molar (KM), and dentin location-proximal, occlusal superficial, or occlusal deep dentin (n=10). Teeth were cut and a topographical analysis of four sections per group was performed to obtain data about the tubular density of each different dentin location and depths by laser scanning confocal microscopy (100×). Polyethylene tubes were placed over the pretreated surfaces and filled with one of the GICs. Microshear bond strength (µSBS) test was performed after storage in distilled water (24 h at 37°C). Failure modes were evaluated using a stereomicroscope (400×). Multilevel regression analysis was performed to compare the results at a significance level set at 5%. The tubule density was inversely proportional to the bond strength for both GICs (p<0.05). Adhesive/mixed failure prevailed in all experimental groups. Proximal (30036.5±3433.3) and occlusal superficial 29665.3±1434.04 dentin shows lower tubule density, resulting in a better GIC bonding performance (proximal: FIX-3.61±1.05; KM-3.40±1.62; occlusal superficial: FIX-4.70±1.85; KM-4.97±1.25). Thus, we can concluded that the lowest tubule density in proximal and occlusal superficial dentin results in a better GIC bond strength performance.

Effect of 2% chlorhexidine digluconate application and water storage on the bond strength to superficial and deep dentin

The aim of the present in vitro study was to evaluate the effect of chlorhexidine, applied before a self-etching adhesive system (Clearfil SE Bond) on microtensile bond strength to superficial and deep dentin (DD), immediately and after six months of water storage (WS). Forty dentin specimens were divided into two groups according to dentin depth: superficial and deep. The specimens were then divided according to the solution to be applied (n = 10): CLX: 2% chlorhexidine (passively applied for 60 s) and NT (no treatment). A self-etching adhesive system was applied according to the manufactures instructions, with composite restorative placed on the dentin surface. After 24 h, dentin–resin blocks were sectioned into beam-shaped specimens that were submitted to microtensile bond strength testing either immediately or after six months of WS. Data were submitted to three-way ANOVA (α = 0.05). Bond strength values for the deep dentin group were significantly lower than those observed for superficial dentin (SD) (p = 0.002), whether chlorhexidine solution had been applied or not. There was no statistical difference in bond strength for specimens tested after 24 h and 6 months of WS. The application of chlorhexidine did not affect immediate and long-term bond strength to dentin. Bond strength in deep dentin was lower than in SD.

Antimicrobial Activity of Nanoparticle Calcium Hydroxide against Enterococcus Faecalis: An In Vitro Study.

Enterococcus faecalis (E. faecalis) has the ability to invade the dentinal tubules and resist high pH levels. As a result, calcium hydroxide (CH) is not much effective on this bacterium. In theory, nanoparticle calcium hydroxide (NCH) has smaller size and high surface area that enables it to penetrate into the deeper layers of dentin and be more effective on E. faecalis. This in vitro study was designed to compare the antimicrobial activity of NCH and CH against E. faecalis. The antimicrobial activity of NCH against E. faecalis was evaluated by two independent tests: the minimum inhibitory concentration (MIC) of intracanal medicament and agar diffusion test (ADT). The efficiency of the medicament in dentinal tubules was evaluated on 23 human tooth blocks that were inoculated with E. faecalis. The tooth blocks were assigned to one control group (saline irrigation) and two experimental groups receiving CH and NCH as intracanal medication. The optical density in each group was assessed with spectrophotometer after collecting samples from dentin depths of 0, 200 and 400 µm. Data were analyzed by SPSS software ANOVA, Kruskal-Wallis and Dunnett's test. The MIC for NCH was 1/4 of the MIC for CH. NCH with distilled water (DW) produced the greatest inhibition zone in agar diffusion test. NCH had greater antimicrobial activity in dentin samples from depths of 200 and 400 µm compared to CH. The antimicrobial activity of NCH was superior to CH in culture medium. In dentinal tubules the efficacy of NCH was again better than CH on the 200- and 400-µm samples.

A photochemical method for in vitro evaluation of fluid flow in human dentine

ObjectiveTo evaluate the flow dynamics of dentine fluid using a chemiluminescence method in vitro. Materials and methodsHorizontally sliced coronal dentine specimens with thicknesses of 1.4, 1.6, 1.8, and 2.0mm (n=10 each) were prepared from extracted human third molars. After cleaning with EDTA, a mounted specimen was clamped between 2 acrylic chambers attached to both the occlusal and pulpal sides. The occlusal chamber, which was closed with a glass coverslip, was filled with a chemiluminescent solution (0.02% luminol and 1% sodium hydroxide in water). A trigger solution of 1% hydrogen peroxide and 1% potassium ferricyanide was injected into the pulpal chamber at a constant pressure of 2.5kPa, and allowed to immediately flow into the patent dentinal tubules. Four consecutive measurements (T1–T4) were performed on each sample by recording the emission of chemiluminescence with a photodetector. The relationship between the crossing time of the liquid through the slice and dentine thickness was examined. ResultsAn apparent time delay was detected between the starting points of the trigger solution run and photochemical emission at T1. Dt (Dt, s) values of each thickness group were 13.6±4.25 for 1.4mm, 18.1±2.38 for 1.6mm, 28.0±2.46 for 1.8mm, and 39.2±8.61 for 2.0mm, respectively. Dt significantly decreased as dentine became thinner towards the pulp chamber (P<0.001). ConclusionsThe velocity of fluid flow increased both with increasing dentine depth or reduction of remaining dentine thickness.

Stability of bonds made to superficial vs. deep dentin, before and after thermocycling

ObjectivesBonding stability of resinous adhesives to dentin is still problematic and may involve regional variations in dentin composition. This study is to evaluate the effect of dentin depth on the stability of resin-dentin bonds under thermocycling challenge. MethodsDentin slabs with two flat surfaces parallel to the tooth axis were obtained from extracted human third molars. The slabs were randomized into eight groups according to the location of dentin [deep dentin (DD) or superficial dentin (SD)], the adhesive treatment (Single Bond 2 or Clearfil S3 Bond), and the storage treatment (thermocycling for 5000 times vs. no). After the adhesive treatment and composite buildup on the dentin slabs, the micro-shear bond strength (μSBS) of each group was detected. The concentrations of cross-linked carboxyterminal telopeptide of type I collagen (ICTP) were also evaluated using an immunoassay to detect the degree of collagen degradation in each group. ResultsDentin depth, adhesive treatment and storage treatment all showed significant effects on both the μSBSs and the ICTP values (P<0.05). Regardless of the adhesive type, thermocycling decreased the μSBSs and increased the ICTP values (P<0.05). The DD groups showed significantly lower μSBSs and higher ICTP values than SD groups after thermocycling aging (P<0.05). The treatment with Single Bond 2 significantly increased the ICTP values (P<0.05), whereas Clearfil S3 Bond showed no effect on the ICTP values (P>0.05). SignificanceDeep dentin showed significantly more bond degradation after thermocycling than did superficial dentin.

Antibacterial activity of various root canal sealers and root-end filling materials in dentin blocks infected ex vivo with Enterococcus faecalis

Objective. The aim was to investigate the antibacterial activity of the root-end filling materials MTA and IRM, different endodontic sealers and calcium hydroxide [Ca(OH)2] in experimentally infected dentinal tubules. Materials and methods. Ninety-four human root segments were prepared and the root canals were enlarged to ISO size 90. After smear removal, the specimens were infected with Enterococcus faecalis for 3 weeks. The roots were divided into eight groups and filled either with MTA, IRM, Ca(OH)2, gutta-percha and EndoRez (ER)/GuttaFlow (GF)/AH Plus (AH+) or with Resilon and Epiphany (EpRe). One group of specimens was left unfilled for control. Half of the specimens were treated for 1 day and the other half for 7 days in humid conditions at 37°C. Dentin samples from each canal were collected by enlarging the canals to ISO size 150; thus a dentinal depth of 300 µm was sampled. The number of cultivable bacteria was determined for each specimen. Statistical significance was set to 5%. Results. After 1-day or 7-days of treatment, compared to control, all materials (except ER and GF at day 7) significantly reduced the number of bacteria. At day 1 and day 7, no significant difference was found between ER and GF and between Ca(OH)2, AH+, EpRe, IRM and MTA. However, a significant difference was found between these two groups of materials (except between GF and EpRe at day 7). Significantly more bacteria were cultured in the ER, GF, EpRe and IRM groups at day 7 compared to day 1. Conclusions. All materials exerted varying degrees of antibacterial activity which generally tended to decrease with time. The most stable antibacterial effect throughout the 7-day period was for Ca(OH)2, AH+ and MTA.

Quantitative detection of matrix metalloproteinase-2 in normal coronal dentine of young people

To compare the distribution and concentration of matrix metalloproteinases-2 (MMP-2) in different dentin depth of premolar and molar of young people. Freshly extracted human premolars and molars (aged between 20-30) were sectioned to 1.5 mm thick slices along the longitudinal axis of the tooth separately. Enamel and pulp of each slice was removed, and then the premolar and molar slices were respectively divided into two subgroups according to superficial or deep dentin and pulverized to fine powder. After dentin protein was extracted, the concentrations of MMP-2 in different tooth were detected using fluorescent microsphere immunoassay. The content of MMP-2 in superficial layer dentin of premolar was (0.022 ± 0.006) ng/mg. The content of MMP-2 in deep layer dentin of premolar was (2.087 ± 0.090) ng/mg. The content of MMP-2 in superficial layer dentin of molar was (0.336 ± 0.037) ng/mg. The content of MMP-2 in deep layer dentin of molar was (3.312 ± 0.308) ng/mg. MMP-2 exists in human coronal dentin. In the same type of teeth of young people, the concentration of MMP-2 in deep dentin was significant higher than those in superficial dentin. In the same dentin depth, the concentration of MMP-2 in molar was significant higher than those in premolar.

Nanoindentation hardness of intertubular dentin in sound, demineralized and natural caries-affected dentin

The purpose of this study was to investigate the mechanical properties of intertubular dentin in sound, natural caries-affected (NCAD) and artificial caries-affected dentin (ACAD) using nanoindentation. Materials and methodsNon-caries molars and caries molars with International Caries Detection and Assessment System (ICDAS II) score 5 at the occlusal site were used and caries was excavated using a spoon excavator, a round bur at low speed without water and a dye solution as guidance to detect the infected tissue. Specimens with remaining dentin thickness (RDT) >2mm were selected. ACAD teeth were created from sound teeth over 7 days in a demineralizing solution. Specimens were embedded into plastic rings with acrylic resin and then sagittal mesial–distal sectioned from crown to the long axis of the root under cooling water using a low-speed diamond blade. The surface of interest was fine polished sequentially. Hardness measurement was performed within an axial depth of 1000μm with at least of 320 indentations on each sample. Mann–Whitney U Test was used to compare the hardness as the variable among different dentin types (SOUND, NCAD and ACAD) at each dentin depth level. ResultsThere was no significant difference in nanohardness between NCAD and ACAD up to a depth of 130μm (p>0.05). NCAD consistently showed lower hardness. ACAD showed no significant difference in hardness with SOUND dentin beyond 190μm (p<0.05). The lesion front in ACAD was considered to be located around the depth of 180μm. ConclusionNatural and artificial caries-affected dentin tissues were superficially comparable in intertubular nanohardness. There is a certain layer within the natural caries-affected dentin with higher hardness; however the long-term effects of caries beneath the lesion extend deeply through intertubular dentin. Sound dentin at deep areas (close to the pulp chamber) is considered to be soft.

Tubule Density and Diameter in Coronal Dentin from Primary and Permanent Human Teeth

This study compared dentinal tubule density and diameter of human primary and permanent teeth at different depths of the coronal dentin. Crowns of eight primary second molars and eight permanent third molars were serially sectioned into three disks of ~0.5 mm thickness (superficial, middle, and deep layers), perpendicular to the long axis. Tubule density and diameter were evaluated in 2,000× and 3,000× magnifications by scanning electron microscopy. Data obtained were subjected to two-way repeated measures ANOVA and Tukey's post hoc test (α = 0.05). Tubule density was greater in primary teeth compared with permanent ones, regardless of depth (primary: 124,329 ± 43,594 mm2; permanent: 45,972 ± 21,098 mm2). In general, the tubule density increased as the dentin depth increased, except to the superficial and middle layers from permanent teeth. Tubule diameter was larger in the dentin layer close to the pulp chamber (superficial: 2.4 ± 0.07 μm; middle: 3.70 ± 0.06 μm; deep: 4.28 ± 0.04 μm). No difference was observed between primary (3.48 ± 0.81 μm) and permanent teeth (3.47 ± 0.73 μm). The tubule diameter increases as the dentin depth increases for primary and permanent teeth; however, the tubule density is higher in primary teeth.

Newly developed hardness testing system, “Cariotester”: Measurement principles and development of a program for measuring Knoop hardness of carious dentin

We previously discovered that when a cone-shaped indenter coated with paint was pressed into an object, the paint disappeared in accordance with the depth of the indentation. Based on this fact, we developed the Cariotester, a portable system for measuring the Knoop hardness (KHN) of carious dentin. The Cariotester is composed of a handpiece with an indenter, a microscope, and a computer. In this system, the painted indenter is forced into the material with a 150-gf load, and the indentation depth (CT depth) is obtained from the paint disappearance. The CT depth by the Cariotester and the KHN by a microhardness tester were determined at 14 dentin regions. From the data, a program was created to convert the CT depth of the carious dentin into the KHN. As a result, if the CT depth is measured with this system, the KHN of carious dentin can be displayed in real time.

Pulpar temperature changes during mechanical reduction of equine cheek teeth: Comparison of different motorised dental instruments, duration of treatments and use of water cooling

Although equine motorised dental instruments are widely used, there is limited information on their thermal effect on teeth. The recently described variation in subocclusal secondary dentine depth overlying individual pulp horns may affect heat transmission to the underlying pulps. This study compared the effect of 3 different equine motorised dental instruments on the pulpar temperature of equine cheek teeth with and without the use of water cooling. It also evaluated the effect of subocclusal secondary dentine thickness on pulpar temperature changes. A thermocouple probe was inserted into the pulp horns of 188 transversely sectioned maxillary cheek teeth with its tip lying subocclusally. Pulpar temperature changes were recorded during and following the continuous use of 3 different equine motorised dental instruments (A, B and C) for sequential time periods, with and without the use of water cooling. Using motorised dental instrument B compared with either A or C increased the likelihood that the critical temperature was reached in pulps by 8.6 times. Compared with rasping for 30 s, rasping for 45, 60 and 90 s increased the likelihood that the critical temperature would be reached in pulps by 7.3, 8.9 and 24.7 times, respectively. Thicker subocclusal secondary dentine (odds ratio [OR] = 0.75/mm) and water cooling (OR = 0.14) were both protective against the likelihood of the pulp reaching the critical temperature. Prolonged rasping with motorised dental instruments increased the likelihood that a pulp would be heated above the critical temperature. Increased dentinal thickness and water cooling had protective roles in reducing pulpar heating. Motorised dental instruments have the potential to seriously damage equine pulp if used inappropriately. Higher speed motorised dental instruments should be used for less time and teeth should be water cooled during or immediately after instrument use to reduce the risk of thermal pulpar damage.

Effect of the regional variability of dentinal substrate and modes of application of adhesive systems on the mechanical properties of the adhesive layer

Aim:This study assessed the effect of the dentin depth and the application mode on the hardness and elastic modulus of the adhesive layer.Materials and Methods:Occlusal surfaces of 48 caries-free human third molars were removed, at two levels: Superficial and deep dentin. For each type of surface, the test specimens were randomly divided into groups which underwent the application: A conventional two-step adhesive system (Adper™ Single Bond [SB]) and self-etch adhesives system (Adper™ SE Plus [SE] and AdheSE® [AD]). The adhesives applied were active or passive. Composite build-ups were constructed incrementally. The teeth were sectioned, embedded, and polished. The nanoindentation test was performed in the adhesive layer. The results were analyzed by ANOVA and Tukey tests.Results:In the adhesive layer, the higher hardness (0.307 ± 0.006 GPa) and elastic modulus (4.796 ± 0.165 GPa) of SE were obtained in superficial dentin in passive application. The elastic modulus of SE (4.115 ± 0.098 GPa) was lowest in active application in superficial dentin. The active application significantly increased the hardness of the SB in the deep dentin (0.011 ± 0.314 GPa) compared the superficial dentin (0.280 ± 0.010 GPa). For the AD, only the mode of application was statistically significant (P=0.0041) for the hardness, active application (0.289 ± 0.015 GPa) being higher than passive application (0.261 ± 0.013 GPa) (P=0.0042) in deep dentin.Conclusion:The experimental results reveal that the mechanical properties were influenced for the application mode of adhesive systems and dentin depth.

Bonding of adhesives to Er:YAG laser-treated dentin

The shear bond strength of adhesives applied to dentin was investigated after irradiation with an erbium-doped yttrium aluminum garnet (Er:YAG) laser. Superficial and deep dentin specimens from human molars were treated either with carbide bur or an Er:YAG laser. Two etch and rinse adhesives (Single Bond and XP Bond) and two self-etch adhesives (Prompt L-Pop and Xeno III) were employed to bond the composite. Shear bond strength (SBS) was determined after storage in water for 24 h using a universal testing machine with a crosshead speed of 0.5 mm/min. Failure patterns and modes were analyzed and evaluated using a stereomicroscope. In addition, samples were processed for Scanning Electron Microscopy SEM evaluation. A linear mixed model was used, and pairwise comparisons were made using the Bonferroni test. Results showed significant differences between the levels of dentin treatment (p=.01) in carbide bur-cut dentin and lased dentin, as well as significant interaction effects due to the depth of dentin and the bonding system used. The etch and rinse adhesives bonded less effectively with lased dentin than with carbide bur-cut dentin, while self-etch adhesives bonded equally well with lased and bur-cut superficial dentin but much less effectively with lased deep dentin than with bur-cut deep dentin. SEM revealed a predominantly adhesive failure mode in laser-ablated fractured specimens, while a mixed failure mode was apparent in the bur-cut fractured specimens. Cavities prepared by laser seem less receptive to adhesive procedures than conventional bur-cut cavities.

Measurement of Histological and Radiographic Depth and Width of Occlusal Caries Lesions: A Methodological Study

Aim: To develop a measurement method to quantify the depth and width of occlusal caries lesions. Material and Methods: One hundred and ten extracted permanent molars with occlusal caries lesions were selected, then visually scored by ICDAS scoring system and then sectioned mesiodistally, resulting in a facial and a lingual fraction. Digital photos and radiographs were taken from each section. By randomization, one of the sections was chosen for further examinations. First digital photos were taken. Depth and width of the lesions were marked with arrows on the images both before (H_un-col) and after coloring (H_col) the sections. The same types of measurements were done on the radiographs (R). The relative dentinal depth and width of the lesions were measured in the same order. Results: Weighted intra- and interexaminer kappa value for ICDAS scorings varied between 0.85 and 0.90. Intraexaminer kappa for dentinal depth in 36 randomized selected teeth was calculated to 0.75 (H_un-col), 0.91 (H_col), 0.79 (R) and for dentinal width to 0.84 (H_un-col), 0.96 (H_col), 0.84 (R). Significant correlations were found between ICDAS scorings and the measurements of depth and width of lesions in H_un-col, H_col, and R (p < 0.000). The lowest difference was measured between H_un-col and H_col in both relative depth and width of the lesion with maximum differences up to 45% (H_un-col–H_col) and 73% (H_col–R). Conclusion: It is possible to measure depth and width of occlusal caries lesions by means of histological and radiographic technique with acceptably high reproducibility using this method.

Adhesion of conventional and simplified resin-based luting cements to superficial and deep dentin

This study evaluated the bond strengths of conventional (chemically and dual-polymerized) and simplified resin-based luting cements with their corresponding adhesives to superficial dentin (SD) and deep dentin (DD). Recently extracted third molars (N = 70, n = 10 per group) were obtained and prepared for testing procedures. After using their corresponding etchants, primers, and/or adhesive systems, the conventional and simplified cements (Variolink II [group A, conventional], Bifix QM [group B, conventional], Panavia F2.0 [group C, conventional], Multilink Automix [group D, simplified], Superbond C&B [group E, conventional], Clearfil Esthetic Cement [group F, simplified], Ketac-Fil [group G, conventional]) were adhered incrementally onto the dentin surfaces using polyethylene molds (inner diameter 3.5 mm, height 5 mm) and polymerized accordingly. Resin-modified glass-ionomer cement (RMGIC) acted as the control material. Shear bond strengths (1 mm/min) were determined after 500 times of thermocycling. Kruskal-Wallis and Mann-Whitney tests were used to analyze the data (α = 0.05). Bond strength (MPa) results were significantly affected by the cement types and their corresponding adhesive systems (p ≤ 0.05). The shear bond strengths (MPa ± SD) for groups A-G were 14.6 ± 3.8, 18.9 ± 3.9, 5.5 ± 4.5, 3.1 ± 3.6, 1.1 ± 2.5, 15.5 ± 2.6, 7 ± 4.3 and 7.1 ± 5.8, 15.1 ± 7.8, 8.4 ± 7.3, 7.5 ± 7.3, 4.9 ± 5.1, 12.5 ± 2.1, 6 ± 2.6 for SD and DD, respectively. The level of dentin depth did not decrease the bond strength significantly (p > 0.05) for all cements, except for Variolink II (p < 0.05). On the SD, bond strength of resin cements with "etch-and-rinse" adhesive systems (Variolink II, Bifix QM, Super-Bond C&B) showed similar results being higher than those of the simplified ones. Simplified cements and RMGIC as control material showed inferior adhesion to superficial and deep dentin compared to conventional resin cements tested.

Nano- and micromechanical properties of dentine: Investigation of differences with tooth side

The soft zone in dentine beneath the dentino-enamel junction is thought to play an important role in tooth function, strain distribution and fracture resistance during mastication. Recently reported asymmetry in mechanical properties with tooth side may point at a basic property of tooth function. The aim of our study was to test if this asymmetry was reflected in the nano- and micromechanical properties of dentine.We investigated the mechanical properties of dentine on the buccal and lingual side of nine extracted human teeth using nano- and microindentation. Properties were analysed on the natural log scale, using maximum likelihood to estimate the parameters. Two-sided 0.05-level likelihood ratio tests were used to assess the influences of surface (buccal versus lingual) and dentine depth, measured from the DEJ in crown dentine and from the CDJ in root dentine.Results showed the well known gradual increase in mechanical properties with increasing distance from the DEJ. Coronal dentine showed higher elastic modulus and hardness on the lingual side of teeth for all measurements, while root dentine was harder on the buccal side. Due to the subtlety of these effects and the small number of teeth studied, results failed to reach statistical significance. Results suggest that dentine nano- and micromechanical properties vary with tooth side in agreement with recent literature using macroscopic methods. They also reveal that buccal–lingual ratios of hardness are in opposite directions in crown and root dentine, suggesting compensatory functions.

Shear bond strength of self-etch and total-etch bonding systems at different dentin depths

The purpose of this study was to evaluate the dentin shear bond strength of four adhesive systems (Adper Single Bond 2, Adper Prompt L-Pop, Magic Bond DE and Self Etch Bond) in regards to buccal and lingual surfaces and dentin depth. Forty extracted third molars had roots removed and crowns bisected in the mesiodistal direction. The buccal and lingual surfaces were fixed in a PVC/acrylic resin ring and were divided into buccal and lingual groups assigned to each selected adhesive. The same specimens prepared for the evaluation of superficial dentin shear resistance were used to evaluate the different depths of dentin. The specimens were identified and abraded at depths of 0.5, 1.0, 1.5 and 2.0 mm. Each depth was evaluated by ISO TR 11405 using an EMIC-2000 machine regulated at 0.5 mm/min with a 200 Kgf load cell. We performed statistical analyses on the results (ANOVA, Tukey and Scheffé tests). Data revealed statistical differences (p < 0.01) in the adhesive and depth variation as well as adhesive/depth interactions. The Adper Single Bond 2 demonstrated the highest mean values of shear bond strength. The Prompt L-Pop product, a self-etching adhesive, revealed higher mean values compared with Magic Bond DE and Self Etch Bond adhesives, a total and self-etching adhesive respectively. It may be concluded that the shear bond strength of dentin is dependent on material (adhesive system), substrate depth and adhesive/depth interaction.

Effect of Different Bonding Strategies on Adhesion to Deep and Superficial Permanent Dentin

To evaluate the effect of different bonding strategies on the microtensile bond strength to deep and superficial permanent dentin. Forty-eight teeth were randomly flattened according to the dentin depth: superficial dentin (SD) and deep dentin (DD). Subsequently, three adhesive systems were applied (n=8): an etch-and-rinse (Adper Single Bond 2 - SB), a "mild" two-step self-etching (Clearfil SE Bond - SE) and a one-step self-etching adhesive system (Futurabond - FB). Each specimen was restored with a composite resin and sectioned into 1.0-mm(2) thick slabs. After 24 hours, resin-dentin sticks were submitted to tensile stress in a universal testing machine (0.5 mm/min). Data were submitted to two-way ANOVA and Tukey's test at a level of 0.05%. Superficial dentin showed the highest microtensile bond strength values, which differed statistically from those obtained in the deep dentin, irrespective of the adhesive system used. FB yielded the highest bond strength values, which were statistically similar to the bond strength values of SE, but statistically different from those obtained when the SB adhesive was used. Bond strength obtained in superficial dentin was significantly higher than in deep dentin, for all adhesive systems tested. Adhesion was affected by the different bonding strategies: the one-step, low pH, acetone-based self-etching adhesive promoted the higher bond strength values, which were statistically similar to those obtained with the two-step, water-based self-etching adhesive.

A study of the thickness of cheek teeth subocclusal secondary dentine in horses of different ages

There is limited knowledge on the thickness of subocclusal secondary dentine in equine cheek teeth (CT). Subocclusal secondary dentine is of consistent thickness above different pulp horns in individual horses and its thickness increases with age. 408 permanent CT were extracted post mortem from 17 horses aged 4-30 years, with no history of dental disease. The CT were sectioned longitudinally in the medio-lateral (bucco-palatal/lingual) plane through each pulp horn, and the thickness of the secondary dentine overlying each pulp horn was measured directly. The subocclusal thickness of secondary dentine above the pulp horns of CT varied from a mean thickness (above all pulp horns) of 12.8 mm (range 5-33 mm) in a 4-year-old to 7.5 mm (range 2-24 mm) in a 16-year-old horse. There was wide variation in the depth of subocclusal secondary dentine above different pulp horns, even within the same CT. In contrast to expectations, occlusal secondary dentine thickness did not increase with age. There were no significant differences in occlusal secondary dentine thickness between rostral and caudal, or medial and lateral aspects of the CT, or between contralateral CT. Mandibular CT had significantly thicker subocclusal secondary dentine than maxillary CT. Pink coloured secondary dentine was sometimes found 1-3 mm occlusal to the pulp horn in sectioned CT and this was likely caused by artefactual blood staining from the underlying pulp during sectioning. The thickness of subocclusal secondary dentine varies greatly between individual pulp horns, teeth and individual horses and can be as low as 2 mm over individual pulp horns. Due to the great variation in the thickness of subocclusal secondary dentine between horses, and even between pulp horns in individual CT, there is a risk of exposure or thermal damage to pulp and thus of apical infection, even with modest therapeutic reductions of CT occlusal overgrowths. In the light of these findings, great care should be taken when reducing equine CT overgrowths and larger dental overgrowths should be reduced in stages.

3D variations in human crown dentin tubule orientation: A phase-contrast microtomography study

Tubules dominate the microstructure of dentin, and in crowns of human teeth they are surrounded by thick mineralized peritubular cuffs of high stiffness. Here we examine the three-dimensional (3D) arrangement of tubules in relation to enamel on the buccal and lingual aspects of intact premolars and molars. Specifically we investigate the angular orientation of tubules relative to the plane of the junction of dentin with enamel (DEJ) by means of wet, non-destructive and high-resolution phase-contrast (coherent) tomography. Enamel capped dentin samples (n=16), cut from the buccal and lingual surfaces of upper and lower premolar and molar teeth, were imaged in water by high-resolution synchrotron-based phase-contrast X-ray radiography. Reconstructed 3D virtual images were co-aligned with respect to the DEJ plane. The average tubule orientation was determined at increasing distances from the DEJ, based on integrated projections onto orthogonal virtual planes. The angle and curl of the tubules were determined every 100 microm to a depth of 1.4mm beneath the DEJ. Most tubules do not extend at right angles from the DEJ. Even when they do, tubules always change their orientations substantially within the first half-millimeter zone beneath the DEJ, both on the buccal and lingual aspects of premolar and molar teeth. Tubules also tend to curl and twist within this zone. Student t-tests indicate that lower teeth seem to have greater tilts in the tubule orientations relative to the DEJ normal with an average angle of 42 degrees (+/-2.0 degrees), whereas upper teeth exhibit a smaller change of orientation, with an average of 32 degrees (+/-2.1 degrees). Tubules are a central characteristic of dentin, with important implications on how it is arranged and what the properties are. Knowing about the path that tubules follow is important for various reasons, ranging form improving control over restorative procedures to understanding or simulating the mechanical properties of teeth. At increasing depths of dentin beneath enamel, tubules are significantly tilted relative to the DEJ norm, which may be important to understand clinical challenges such as sensitivity, effectiveness of bonding techniques or prediction of possible paths for bacterial invasion. Our data show dissimilar average tubule angles of upper versus lower teeth with respect to the DEJ which presumably contributes to different shear responses of the tissue under function. The degree to which this may warrant improved restoratives or new adhesive techniques to enhance adhesive restorations merits further investigation.