AFM observation of collapse and expansion of phosphoric acid-demineralized dentin

In vitro mechanical stimulation facilitates stress dissipation and sealing ability at the conventional glass ionomer cement-dentin interface

OBJECTIVE

The aim of this study was to evaluate the induced changes in the chemical and mechanical performance at the glass-ionomer cement-dentin interface after mechanical load application.

METHODS

A conventional glass-ionomer cement (GIC) (Ketac Bond), and a resin-modified glass-ionomer cement (RMGIC) (Vitrebond Plus) were used. Bonded interfaces were stored in simulated body fluid, and then tested or submitted to the mechanical loading challenge. Different loading waveforms were applied: No cycling, 24 h cycled in sine or loaded in sustained hold waveforms. The cement-dentin interface was evaluated using a nano-dynamic mechanical analysis, estimating the complex modulus and tan δ. Atomic Force Microscopy (AFM) imaging, Raman analysis and dye assisted confocal microscopy evaluation (CLSM) were also performed.

RESULTS

The complex modulus was lower and tan delta was higher at interfaces promoted with the GIC if compared to the RMGIC unloaded. The conventional GIC attained evident reduction of nanoleakage. Mechanical loading favored remineralization and promoted higher complex modulus and lower tan delta values at interfaces with RMGIC, where porosity, micropermeability and nanoleakage were more abundant.

CONCLUSIONS

Mechanical stimuli diminished the resistance to deformation and increased the stored energy at the GIC-dentin interface. The conventional GIC induced less porosity and nanoleakage than RMGIC. The RMGIC increased nanoleakage at the porous interface, and dye sorption appeared within the cement. Both cements created amorphous and crystalline apatites at the interface depending on the type of mechanical loading.

CLINICAL SIGNIFICANCE

Remineralization, lower stress concentration and resistance to deformation after mechanical loading improved the sealing of the GIC-dentin interface. In vitro oral function will favor high levels of accumulated energy and permits micropermeability at the RMGIC-dentin interface which will become remineralized.

Molecular and morphological surface analysis: effect of filling pastes and cleaning agents on root dentin

The quality of the dentin root is the most important factor for restoration resin sealing and drives the outcome of endodontic treatment.

Direct Tensile Strength and Characteristics of Dentin Restored with All-Ceramic, Resin-Composite, and Cast Metal Prostheses Cemented with Resin Adhesives

A dentin-cement-prosthesis complex restored with either all-porcelain, cured resin-composite, or cast base metal alloy and cemented with either of the different resin cements was trimmed into a mini-dumbbell shape for tensile testing. The fractured surfaces and characterization of the dentin-cement interface of bonded specimens were investigated using a Scanning Electron Microscope. A significantly higher tensile strength of all-porcelain (12.5 ± 2.2 MPa) than that of cast metal (9.2 ± 3.5 MPa) restorations was revealed with cohesive failure in the cement and failure at the prosthesis-cement interface in Super-Bond C&B group. No significant difference in tensile strength was found among the types of restorations using the other three cements with adhesive failure on the dentin side and cohesive failure in the cured resin. SEM micrographs demonstrated the consistent hybridized dentin in Super-Bond C&B specimens that could resist degradation when immersed in hydrochloric acid followed by NaOCl solutions whereas a detached and degraded interfacial layer was found for the other cements. The results suggest that when complete hybridization of resin into dentin occurs tensile strength at the dentin-cement is higher than at the cement-prosthesis interfaces. The impermeable hybridized dentin can protect the underlying dentin and pulp from acid demineralization, even if detachment of the prosthesis has occurred.

Variations in collagen fibrils network structure and surface dehydration of acid demineralized intertubular dentin: effect of dentin depth and air-exposure time

OBJECTIVE

The aim was to characterize the variations in the structure and surface dehydration of acid demineralized intertubular dentin collagen network with the variations in dentin depth and time of air-exposure (3, 6, 9 and 12 min). In addition, to study the effect of these variations on the tensile bond strength (TBS) to dentin.

METHODS

Phosphoric acid demineralized superficial and deep dentin specimens were prepared. The structure of the dentin collagen network was characterized by AFM. The surface dehydration was characterized by probing the nano-scale adhesion force (F(ad)) between AFM tip and intertubular dentin surface as a new experimental approach. The TBS to dentin was evaluated using an alcohol-based dentin self-priming adhesive.

RESULTS

AFM images revealed a demineralized open collagen network structure in both of superficial and deep dentin at 3 and 6 min of air-exposure. However, at 9 min, superficial dentin showed more collapsed network structure compared to deep dentin that partially preserved the open network structure. Total collapsed structure was found at 12 min for both of superficial and deep dentin. The value of the F(ad) is decreased with increasing the time of air-exposure and is increased with dentin depth at the same time of air-exposure. The TBS was higher for superficial dentin at 3 and 6 min, however, no difference was found at 9 and 12 min.

SIGNIFICANCE

The ability of the demineralized dentin collagen network to resist air-dehydration and to preserve the integrity of open network structure with the increase in air-exposure time is increased with dentin depth. Although superficial dentin achieves higher bond strength values, the difference in the bond strength is decreased by increasing the time of air-exposure. The AFM probed F(ad) showed to be sensitive approach to characterize surface dehydration, however, further researches are recommended regarding the validity of such approach.

The effect of a peroxidase primer on bond strength of three luting systems to dentin

The purpose of the present study was to investigate the effect of an experimental primer containing a microperoxidase (MP-11) with 2-hydroxyethyl methacrylate on adhesive bonding of three different luting systems and dentin. The luting systems prepared were three etch-and-rinse systems (10-3/Super-Bond, 10-0/Super-Bond, 65PA/Super-Bond), a self-etching system (PanaviaF2.0), and a self-adhesive system (SA-Luting). These luting systems were used in conjunction with the MP-11 primer, and were designated as 10-3/MP-11/Super-Bond, 10-0/MP-11/Super-Bond, 65PA/MP-11/Super-Bond, MP-11/PanaviaF2.0, MP-11/SA-Luting, respectively. The dentin surfaces of human premolar teeth were treated, and then bonded with acrylic rods. Shear bond strengths were determined after 24 h of storage in water. The maximum mean bond strength was obtained with 10-0/MP-11/Super-Bond (48.7 +/- 6.6 MPa), followed by 10-3/MP-11/Super-Bond (36.3 +/- 10.2 MPa), 65PA/MP-11/Super-Bond (32.9 +/- 9.2 MPa), 10-3/Super-Bond (26.6 +/- 6.7 MPa), MP-11/PanaviaF2.0 (21.4 +/- 5.6 MPa), MP-11/SA-Luting (17.2 +/- 3.5 MPa), PanaviaF2.0 (16.9 +/- 5.7 MPa), 65PA/Super-Bond (12.8 +/- 2.0 MPa), SA-Luting (11.2 +/- 5.4 MPa), and 10-0/Super-Bond (9.6 +/- 3.9 MPa). The additional use of MP-11 primer significantly improved the bond strengths in the etch-and-rinse systems with 4-META/MMA-TBB resin. It is suggested that the peroxidase has a potential to improve dentin adhesion in the etch-and rinse, self-etching, and self-adhesive systems.

Removal of noncollagenous components affects dentin bonding

The structural integrity of fibrillar type I collagen is critical for effective dentin bonding. Since most noncollagenous matrix components in dentin are closely associated with collagen, we hypothesized that they may also contribute to dentin bonding. To test this hypothesis, bovine dentin was acid-etched, treated with chondroitinase ABC (C-ABC), endo-beta-galactosidase (Endo-beta), or trypsin. Controls were prepared in the same manner but without the enzymes. All control and experimental specimens were then bonded with One-Step. Bond strength data were analyzed by one-way ANOVA and Fisher's PLSD test (p < 0.05). When dentin was treated with C-ABC or trypsin, bond strengths significantly decreased for the rewetted groups (p < 0.05). The treatment with Endo-beta showed no effects on bond strengths (p > 0.05). When the treated dentin surfaces were observed under SEM, the C-ABC and trypsin treated groups revealed significant loss of collagen fibril architecture. The results indicate that chondroitin sulfate glycosaminoglycans and trypsin-digestible noncollagenous proteins play roles in maintaining the open dimensions of the collagen fibril scaffold, which is essential for optimal dentin bonding.

Microperoxidase primer promotes adhesion of butylborane-polymerized resin to dentin

The purpose of this study was to investigate the effect of dentin primers containing microperoxidase (MP-11) with 2-hydroxyethyl methacrylate (HEMA) on the bond strength between a tri-n-butylborane-initiated self-polymerizing resin and dentin. Bovine dentin surfaces were etched with 10 wt % phosphoric acid, primed, and then bonded with stainless steel rods. Tensile bond strength after 24 h of storage in water was significantly influenced by both MP-11 and HEMA. Groups with no MP-11 showed the lowest values. Without HEMA, the bond strengths of groups using 0.01, 0.1, and 1.0 micromol/g MP-11 were statistically identical, and also greater than that of the no MP-11 control. In the presence of HEMA, the bond strength was significantly enhanced with an increasing concentration of MP-11. The highest bond strength of 29.0 MPa was obtained with aqueous HEMA primer, containing 1.0 micromol/g MP-11. Microscopic observation showed the formation of a hybrid layer at the bonded interface. Polymerization of the resin was significantly accelerated with the MP-11 primer. In conclusion, MP-11 has a potential for adhesive bonding promoter between the resin and the demineralized dentin surface.

Ultrasound Effects after Post Space Preparation: An SEM Study

The aim of this study was to evaluate the effect of ultrasonic treatment on occlusion of dentine tubules in root canal walls after post space preparation in endodontically treated teeth. Twenty-four premolars were instrumented and filled using warm vertical condensation; after post space preparation, they were divided into two groups. The control group was treated using the etching procedure. The experiment samples were treated with EDTA irrigation and ultrasound activation for 30 s before the etching procedure. The roots were divided and the canal walls were examined under SEM at 1000x magnification. The debris and open tubule marks were observed at 2, 6, and 10 mm levels using a three-step scale and the differences in marks among the groups were tested for statistical significance. The following were observed: (a) A decrease in debris and open tubule marks in the samples treated with ultrasounds and the control group (p < 0.05), (b) no significant differences between the three levels of post space in debris and open tubule marks in the experiment samples, and (c) significant differences between the apical and coronal levels in debris and open tubule marks in the control group.

Nanoleakage within the hybrid layer: A correlative FEISEM/TEM investigation

The aim of this study was to compare the nanoleakage patterns of the resin-dentin interfaces of three dentin bonding systems at both TEM and field emission in lens SEM (FEI-SEM) levels. A standardized smear layer was created with 180-grit silicon carbide paper (SiC) on dentin disks obtained from 18 noncarious human third molars. Specimens were randomly divided into three groups and bonded with a two-step total etching adhesive (Single Bond, SB), a two-step, self-etching adhesive (Clearfil SE BOND, SEB), and a one-step, self-etching adhesive (XENO III, XEIII). Nanoleakage was evaluated by using an ammoniacal silver-nitrate solution. Specimens were processed for TEM and FEI-SEM observation. The TEM of SB revealed silver deposits in adhesive and hybrid layers (HL). High-magnification FEI-SEM micrographs clearly identified these deposits as spherical clusters mainly associated with nonembedded collagen fibrils. TEM and FEI-SEM examination of SEB revealed some clusters of silver deposits within porosities and small channels of the HL. Additional silver deposits were observed between the peritubular dentin walls and the resin tags. XEIII revealed very fine and diffuse silver grains throughout the entire HL. SEM visualization of nanoleakage at a high level of resolution has not been previously described. FEI-SEM technology supported the TEM visualization with three-dimensional morphological data of the relations between the HL constituents and nanoleakage. The results of the present study confirm the hypothesis that both total- and self-etch adhesives are not able to fully infiltrate the dentin substrate.

Importance of mini-dumbbell specimen to access tensile strength of restored dentine: historical background and the future perspective in dentistry

OBJECTIVES

The development of adhesive resins to dentine enables resin restorations to be more durable. Several bond strength measurement techniques for measuring adhesion have been proposed. A standardised method is needed which produced higher and more consistent bond strength values which allow bond stability and the bonding mechanism to be studied. Our aim was to investigate mainly the adhesives and not the substrate.

DATA SOURCES

This review is based on the literature on an adhesive, 4-META/MMA-TBB resin and conditioners to modify dentine substrates. The latter is a very important topic for developing our understanding of the bonding to dentine. The objective of the review is to explain the efficacy of the mini-dumbbell specimen in measuring the tensile strength of resin to dentine and to analyze the resin to dentine interface. Both the adhesive and the substrate control the quality of hybridized dentine.

CONCLUSIONS

By creating an impermeable acid resistant barrier to both biological and chemical stimuli between the exposed dentine and the restored tooth surface we are able to protect exposed dentine from caries (infection) at the same time as protecting the pulp and preventing toothache. This barrier also helps maintain tooth vitality and for the purposes of this article is termed 'artificial enamel'. Microleakage free restorations are possible through the introduction of this 'impermeable artificial enamel' barrier.