Ultramorphological assessment of dentin-resin interface after use of simplified adhesives

Tooth-composite bond failure with a universal and an etch-and-rinse adhesive depending on mode and frequency of application

OBJECTIVES

To evaluate the effect of an additional layer of universal adhesive on the interfacial enamel/dentin-composite gap formation in relation to application mode and aging, via spectral domain optical coherence tomography (SD-OCT) and scanning electron microscopy (SEM).

METHODS

In vitro class V cavities in 114 caries-free premolars were restored by applying one or two layers of a universal adhesive (Scotchbond Universal, SBU) in self-etch (se) and etch-and-rinse (er) mode or the reference adhesive OptiBond FL (OFL-er). The restorations were imaged by SD-OCT (six groups, n = 8) and SEM (n = 3) directly after filling (t1), water storage (t2, 24 h), embedding (t3), and thermo-mechanical loading (t4, TCML). The interfacial gaps were quantified using 26 parameters and analyzed using principal component analysis and linear mixed effect models.

RESULTS

Gap formation at enamel and dentin was significantly influenced by the adhesive, the application mode and number of layers (p < 0.001). This was due to the influence of the SBU-er mode (p < 1e-05), which showed significantly more gap formation and a greater range of variation with double application when compared to SBU-se and OFL. The fewest interfacial gaps occurred with one or two applications of OFL-er and one layer of SBU-er.

SIGNIFICANCE

Adhesive application mode and the number of adhesive layers are relevant factors in the tooth-composite bond failure. Double application worsened the adaptation of SBU to freshly prepared dentin conditioned with phosphoric acid.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Optical changes of human dentin after non-vital bleaching and effect of Er,Cr:YSGG laser on micro-shear bond strength of a self-etch and an etch-and-rinse adhesive system

The aim was to evaluate the optical changes of bleached human dentin and the efficacy of Er,Cr:YSGG laser on micro-shear bond strength (μSBS) of two adhesive systems for immediate and delayed applications. Seventy-two human dentin specimens (1 mm) were obtained. Colour measurements of 30 specimens (control and bleaching groups) were made at baseline, after bleaching and a 7-day delay. Differences at colour (ΔE₀₀), translucency (ΔTP₀₀) and whiteness (ΔWI_D) were calculated by recorded data. Forty-two specimens were used to compare μSBS of a self-etch (Clearfil SE Bond [SE]) and an etch-and-rinse (Prime&Bond NT [PBNT]) adhesive to bleached dentin. Additional to a negative group, six groups were contemplated for each adhesive, considering the time of composite application (immediate, delayed) and whether additional surface treatment by laser (1 W, 2 W) or not. Colour and μSBS data were statistically analysed. For optical analysis, only ΔE₀₀ and ΔWI_D calculated for the difference between baseline and bleaching were found significantly different for control and bleaching groups. Whiteness of bleached specimens was remarkably decreased after a 7-day delay. Despite immediate applications of SE showing lower μSBS than negative control, delayed applications showed no significant differences except that of the 2 W laser etching. For PBNT, laser etching increased μSBS for both of the immediate and delayed applications, and no significant difference was observed from negative control. Related with the preferred adhesive system, Er,Cr:YSGG laser etching can be an alternative for optimal bond strength of immediate restorations, but the clinicians should always keep in mind that perceived colour and whiteness will change by the passing time which can affect the shade match.

Effect of Cariogenic Challenge on the Degradation of Adhesive-Dentin Interfaces

The aim was to evaluate, in vitro, the influence of pH cycling on microtensile bond strength (µTBS) and percentage of nanoleakage (%NL) in the dentin-adhesive interface. Flat dentin surfaces were obtained in 56 extracted third molars. The teeth were randomly divided into four groups (n=14): G1- Single Bond Universal (etch-and-rinse mode); G2- Single Bond Universal (self-etch mode); G3- Scotchbond Multi-Purpose; G4- Clearfil SE Bond. A block of composite was built on the adhesive area. Eight tooth/resin sets were cut parallel to the tooth's long axis to obtain 48 beams (0.8 mm2) for each group. Half of the beams were submitted to four cycles of pH cycling (demineralizing solution for 6 h and remineralizing solution for 18 h). The samples were submitted to µTBS test in a universal testing machine. Six tooth/resin sets were cut parallel to the tooth's long axis to obtain three slices of the central region (1.0 mm thickness). Half of the slices were submitted to pH cycling. The nanoleakage methodology was applied to obtain the %NL at the adhesive interfaces. According to two-way ANOVA, the interaction between factors (adhesive system x storage) was significant (p=0.0001) for µTBS and %NL. After pH cycling, there was a significant decrease in µTBS and a significant increase in %NL for all adhesives. The adhesives applied in the self-etch mode obtained lower %NL, differing significantly from the etch-and-rinse adhesives. It was concluded that the pH cycling negatively influenced the µTBS and %NL for all adhesives evaluated. However, self-etch adhesives allowed less %NL.

Effect of Pretreatment and Activation Mode on the Interfacial Adaptation of Nanoceramic Resin Inlay and Self-adhesive Resin Cement

OBJECTIVES

The first objective of this study was to determine if the luting material used for resin nanoceramic inlay affects interfacial adaptation. The second was to investigate whether pretreatment and the adhesive curing method before cementation affects interfacial adaptation. The final objective was to compare activation modes of luting material.

METHODS

Class I cavities were prepared on extracted human third molars. Resin nanoceramic inlays were fabricated using Lava Ultimate CAD/CAM block (3 M). For the control groups, inlays were cemented using Panavia V5 (Kuraray Noritake). For the experimental groups, teeth were randomly divided into five experimental groups with four subgroups using different self-adhesive cements (SACs). Cement in Group I was dual-cured without pretreatment. In Group II, the cement was dual-cured after polyacrylic acid treatment of the tooth cavity. In Groups III and IV, the cement was dual-cured after universal dentin adhesive treatment with pre-cure and co-cure methods. In Group V, the inlay was cemented in self-cure mode. After thermocycling, interfacial adaptation at the inlay-tooth interface was measured using swept-source optical coherence tomography (SS-OCT) imaging. Finally, polymerization shrinkage strain of the luting material was measured and compared.

RESULTS

Interfacial adaptation differed depending on the luting material. After application of a universal adhesive, some subgroups showed improved interfacial adaptation. Interfacial adaptation and polymerization shrinkage strain differed significantly depending on activation mode.

SIGNIFICANCE

Interfacial adaptation for a resin nanoceramic inlay can differ according to the type of SAC and activation mode. For some SACs, application of a universal adhesive before cementation improves interfacial adaptation.

Does previous application of silver diammine fluoride influence the bond strength of glass ionomer cement and adhesive systems to dentin? Systematic review and meta-analysis

BACKGROUND

Silver diammine fluoride (SDF) applied before a restoration may prevent recurrent caries; therefore, its effect on the bonding of restorative materials is contradictory.

AIM

To assess through a systematic review and meta-analysis the influence of SDF on the bonding performance of adhesive materials to dentine.

DESIGN

A systematic search was carried out in PubMed, Web of Science, LILACS, and Scopus. Studies comparing bond strength of adhesive systems or glass ionomer cement to SDF-treated and -untreated (control) dentine were included. Global analysis comparing the bond strength data was performed, separately for adhesive systems and glass ionomer cement, using RevMan5.1, with a random-effect model, at a 5% significance level.

RESULTS

Eleven studies were included in the review and ten in the meta-analyses. Overall pooled effect for glass ionomer cement has shown no significant difference between the groups (Z = 0.47; P = .64). SDF treatment significantly impairs the bonding of adhesive systems to dentine (Z = 2.11; P = .03); this effect can be eliminated by the rinsing step (Z = 0.85; P = .40).

CONCLUSIONS

The previous application of SDF does not influence the dentine bond strength of glass ionomer cement, but compromises the bonding of adhesive systems.

Uninfiltrated Collagen in Hybrid Layers produced after Reduced Acid-etching Time on Primary and Permanent Dentin

AIM

This study evaluated the influence of acid-etching time on collagen exposure in adhesive interfaces established on primary and permanent dentin.

MATERIALS AND METHODS

Flat dentin surfaces were produced on sound primary molars and premolars (n = 8). The surfaces were divided into mesial and distal halves, and each half was etched with phosphoric acid for 5 or 15 seconds. The teeth were randomly allocated into two groups according to the adhesive system applied: Prime & Bond NT or Prime & Bond 2.1. After the adhesive application, the specimens were processed for Goldner's trichrome staining. The thickness of the uninfiltrated collagen zone (UCZ) in the hybrid layer was measured under optical microscopy. Data were analyzed by analysis of variance and Tukey tests (α = 0.05).

RESULTS

The thickness of UCZ was adhesive dependent. Within the same substrate, the specimens treated with Prime & Bond 2.1 presented thicker UCZ when etched for 15 seconds. Collagen exposure was significantly higher for the primary teeth etched for 5 seconds and treated with Prime & Bond 2.1.

CONCLUSION

The thickness of UCZ in hybrid layers is directly affected by acid-etching time and by the adhesive system applied. Primary dentin seems to be more susceptible to collagen exposure than is permanent dentin.

CLINICAL SIGNIFICANCE

Both acid-etching time and adhesive system can influence the amount of exposed collagen interfering on resin-dentin bond quality, especially on primary dentin.

Ultrastructural features of dentinoenamel junction revealed by focused gallium ion beam milling

To take full advantage of focused ion beam (FIB) in preparation of ultrathin sections of biological tissues, we have used a cryo-milling process. In this study, extracted human teeth were scanned by optical coherence tomography to inspect the samples for intactness and to determine the area of interest. Then, the selected area of interest was cross-sectioned for examination under a confocal laser scanning microscope to determine the target location of the dentinoenamel junction (DEJ) that was later milled by cryo-FIB at preset parameters, followed by transmission electron microscope examination of the final sliced specimens for ultrastructural characterization. The proposed technique was able to outline the DEJ and to identify the different tooth layers in a single section, without artefacts or tissue damage. The DEJ was outlined as fine longitudinal projections intermingling between the solid electron-dense enamel and intricate electron-lucent hollow dentin. In conclusion, this study has shown the great potential of cryo-FIB in handling different biological tissues having different physical properties, with great precision and accuracy and minimum artefacts.