Morphological and chemical comparative analysis of the human and bovine dentin-adhesive layer

Transdentinal cytotoxicity of resin luting cements using the bovine and human dentin barrier

STATEMENT OF PROBLEM

Based upon ethical questions and because of the difficulty of obtaining intact human teeth, researchers have used bovine teeth to assess the physical and mechanical properties of different dental materials. However, data from transdentinal cytotoxicity tests showing that the bovine dentin barrier is similar to the human dentin barrier is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate whether the bovine dentin barrier produces similar results to those obtained when the human dentin barrier is used to assess the transdentinal cytotoxicity of resin luting cements.

MATERIAL AND METHODS

The number and diameter of dentinal tubules present in the human dentin barrier and bovine dentin barrier were evaluated and assessed with a t test (α=.05). After inserting the standardized dentin barriers into artificial pulp chambers, murine dental papilla-derived cells (MDPC-23) were seeded on the pulpal surface of the specimens, and the luting cements were applied to their occlusal surfaces. Then, the following groups were established for both human and bovine dentin barriers: no treatment (negative control); Single Bond Universal; RelyX Luting 2; RelyX U200; and RelyX Ultimate. After 24 hours, the viability (alamarBlue) and morphology (scanning electron microscopy) of the cells were evaluated with a 2-way analysis of variance and the Tukey honest significance test (α=.05).

RESULTS

Dentinal tubules with larger diameters were observed in bovine dentin (P<.05), but the number of tubules was similar (P>.05). A reduction in viability and notable changes in the morphology of MDPC-23 cells occurred in the Single Bond Universal and RelyX Luting 2 groups in comparison with the negative control (P<.05). The RelyX U200 and RelyX Ultimate groups were statistically similar to the negative control (P>.05). No difference was found in cytotoxicity when the same luting cement was applied on human or bovine dentin barriers (P>.05).

CONCLUSIONS

For transdentinal cytotoxicity tests of resin luting cements, the bovine dentin barrier proved similar results to the human dentin barrier.

Effect of 0.2% Chitosan Associated with Different Final Irrigant Protocols on the Fiber Post Bond Strength to Root Canal Dentin of Bovine Teeth: An In-vitro Study

Objective:

This in-vitro study investigated the effect of 0.2% Chitosan associated with different final irrigant protocols on the bond strength of fiber posts (FP) to root canal dentin.

Methods:

Fifty bovine incisors roots were prepared using the ProTaper Universal system, irrigated with 2.5% sodium hypochlorite, and divided into one control group (n=10) with no final irrigant protocol and four experimental groups (n=10), which were defined according to the combination of chelating solution (17% EDTA and 0.2% Chitosan) and irrigant activation/delivery method [conventional irrigation (CI), and passive ultrasonic irrigation (PUI)]. Post spaces were prepared to a depth of 12 mm using #1-5 Largo drills, and the FP were cemented using self-adhesive resin cement. Two slices of 2 mm in thickness from each third were obtained and submitted to the micropush-out test. After testing the push-out strength, the slices were analyzed under a stereomicroscope at 40× magnification for bond failure patterns determination. Statistical analysis was performed using three-way ANOVA followed by Tukey’s test (α = 0.05).

Results:

The control and 17% EDTA + CI groups exhibited significantly lower bond strength than 0.2% Chitosan + CI, 17% EDTA + PUI, and 0.2% Chitosan + PUI groups in the cervical third (P = 0.00). The cervical third had higher values than the middle and apical thirds in control (P = 0.00), 17% EDTA + PUI (P = 0.00), and 0.2% Chitosan + PUI groups (P = 0.00). Adhesive cement-dentin failure type was predominant in all groups.

Conclusion:

The use of 0.2% chitosan did not affect the bond strength of FP to root dentin. Passive ultrasonic activation of chelating solutions resulted in an improvement in bonding strength.

Microtensile bond strength to sealer-contaminated dentin after using different cleaning protocols

Background/purpose

Sealer residues on dentin may affect bonding to restorative materials. This study aimed to evaluate the bond strength to sealer-contaminated dentin after using different cleaning protocols.

Materials and methods

Freshly extracted bovine incisors were prepared and exposed the buccal pulp chamber dentin, obtaining segments measuring 5 mm × 5 mm with a height of 3 mm. The segments were randomly distributed into 4 groups (n = 7) according to different protocols. Control group: no contamination was performed. In the three experimental groups, the segments were contaminated with epoxy resin-based sealer for 5 min, and different cleaning protocols were performed. Acetone group: acetone-saturated cotton pellets were used to wipe the sealer. Ultrasound group: ultrasonic ET-20D tip cleaning. Acetone combined with ultrasound group: cleaning with acetone-saturated cotton pellets and ultrasonic tip. All segments were bonded using a self-etch adhesive. Two samples in each group were scanned by swept-source optical coherence tomography (SS-OCT) to evaluate sealer residues. A microtensile test was performed on the remaining 5 samples, which were built up with composite resin.

Results

Sealer residues were observed in 3 of 14 (21.4%) sections of acetone group by SS-OCT. Compared to the control, ultrasound alone or in combination with acetone preserved the bond strength (P > .05). The ultrasound group exhibited the highest bond strength (39.38 MPa), which differed from that of the acetone group, which provided the lowest bond strength (32.88 MPa) (P < .05).

Conclusion

Cleaning epoxy resin-based sealer-contaminated dentin surfaces using ultrasound or combined with acetone could preserve the bond strength.

Influence of de-remineralization process on chemical, microstructural, and mechanical properties of human and bovine dentin

OBJECTIVES

This study compared the chemical composition, microstructural, and mechanical properties of human and bovine dentin subjected to a demineralization/remineralization process.

MATERIALS AND METHODS

Human and bovine incisors were sectioned to obtain 120 coronal dentin beams (6 × 1 × 1 mm³) that were randomly allocated into 4 subgroups (n = 15) according to the time of treatment (sound, pH-cycling for 3, 7, and 14 days). Three-point bending mechanical test, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), thermogravimetric (TG), and X-ray diffraction (XRD) techniques were employed to characterize the dentin samples.

RESULTS

Regarding chemical composition at the molecular level, bovine sound dentin showed significantly lower values in organic and inorganic content (collagen cross-linking, CO₃/amide I, and CO₃/PO₄; p = 0.002, p = 0.026, and p = 0.002, respectively) compared to humans. Employing XRD analyses, a higher mineral crystallinity in human dentin than in bovines at 7 and 14 days (p = 0.003 and p = 0.009, respectively) was observed. At the end of the pH-cycling, CI (ATR-FTIR) and CO₃/PO₄ ratios (ATR-FTIR) increased, while CO₃/amide I (ATR-FTIR), PO₄/amide I (ATR-FTIR), and %mineral (TG) ratios decreased. The extension by compression values increased over exposure time with significant differences between dentin types (p < 0.001, in all cases), reaching higher values in bovine dentin. However, flexural strength (MPa) did not show differences between groups. We also observed the correlation between compositional variables (i.e., PO₄/amide I, CI, and %mineral) and the extension by compression.

CONCLUSIONS

Human and bovine dentin are different in terms of microstructure, chemical composition, mechanical strength, and in their response to the demineralization/remineralization process by pH-cycling.

CLINICAL RELEVANCE

These dissimilarities may constitute a potential limitation when replacing human teeth with bovines in in vitro studies.

Effect of different surface treatments of human occlusal sclerotic dentin on micro-tensile bond strength to resin composite core material

The objectives of this study were to evaluate the micro-tensile bond strength (μTBS) of composite bonded to human occlusal sclerotic dentin following different surface treatments to determine the sclerotic dentin morphology. Human molars without (normal dentin; group 1) or with occlusal wear (sclerotic dentin; groups 2-5) were divided and subjected to different surface treatments, including the normal protocol for the Contax self-etch bonding system (group 1 and 2); doubled etch-prime time (group 3); pre-conditioning with 37% phosphoric acid before normal protocol (group 4); or pre-conditioning with 37% phosphoric acid before doubling the self-etching time (group 5). All teeth were restored with composite (Luxacore Z dual), sectioned into stick specimens and stored for 24 h in water before specimens were subjected to the μTBS test (n = 50 per group). The μTBS of normal dentin was not statistically significantly different from that of the sclerotic dentin groups, except for the doubled etch-prime time group which showed lower μTBS. Sclerotic dentin pre-treated with phosphoric acid resulted in less sclerotic casts and wider dentinal tubules, while doubled etch-prime time did not alter the morphology, as shown by scanning electron microscopy. In conclusion, the use of 37% phosphoric acid before applying self-etch bonding resulted in more tubule openings and a significantly higher μTBS when compared with the doubled etch-prime time group.

Surface characteristics of a modified acidulated phosphate fluoride gel with nano-hydroxyapatite coating applied on bovine enamel subjected to an erosive environment

This study evaluated the antierosive effect applying a modified acidulated phosphate fluoride (APF) gel containing nano-hydroxyapatite (nHAp) on the enamel surface before erosion. After polishing, the exposed flat enamel surfaces (n = 7/group) from bovine incisors were treated with artificial saliva (S - negative control), orange juice (ERO), APF gel (positive control) and APF_nHAp gel. All samples were subjected to six cycles of demineralization (orange juice, pH ~ 3.5, 10 min) followed by remineralization (saliva, 37°C, 1 hr). The enamel surface morphology, topography, and inorganic composition were analyzed using scanning electron microscopy, roughness testing, and micro energy-dispersive X-ray fluorescence spectrometry, respectively. The mean (standard deviation) roughness values (Ra, μm) were S, 0.13 (0.05); ERO, 0.25 (0.07); APF, 0.22 (0.08); and APF_nHAp, 0.17 (0.04). Ra values were significantly higher after ERO (p < .01) and APF (p < .05) treatments than after S. The enamel surface morphology was altered by the treatments, except for the S specimens. The mineral content of the enamel showed a clear trend with Ca and P reduction in the order of APF < S < APF_nHAp < ERO and APF < S < ERO < APF_nHAp, respectively. We can conclude that APF gel increased mineral concentration on the enamel. Moreover, the APF_nHAp material modified the composition and morphology of the enamel surface.

Degradation of Multimode Adhesive System Bond Strength to Artificial Caries-Affected Dentin Due to Water Storage

The purpose of this study was to evaluate the influence of water storage on bond strength of multimode adhesive systems to artificially induced caries-affected dentin. One hundred twelve sound bovine incisors were randomly assigned to 16 groups (n=7) according to the dentin condition (sound; SND, artificially induced caries-affected dentin; CAD, cariogenic challenge by pH cycling for 14 days); the adhesive system (SU, Scotchbond Universal Adhesive; AB, All-Bond Universal; PB, Prime & Bond Elect; SB, Adper Single Bond 2; and CS, Clearfil SE Bond), and the etching strategy (etch-and-rinse and self-etch). All adhesive systems were applied under manufacturer's instructions to flat dentin surfaces, and a composite block was built up on each dentin surface. After 24 hours of water storage, the specimens were sectioned into stick-shaped specimens (0.8 mm2) and submitted to a microtensile test immediately (24 hours) or after six months of water storage. Bond strength data (MPa) were analyzed using three-way repeated-measures analysis of variance and post hoc Tukey test (α=5%), considering each substrate separately (SND and CAD). The etching strategy did not influence the bond strength of multimode adhesives, irrespective of the dentin condition. Water storage only reduced significantly the bond strength to CAD. The degradation of bond strength due to water storage was more pronounced in CAD, regardless of the etching strategy.