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

This study assessed dentin-resin interface integration in Class I cavities restored with simplified adhesives by using a focused ion-beam milling (FIB) and transmission electron microscope (TEM). Class I cavities (1.5-mm depth with dentin thickness of ∼0.5 mm, 4-mm length, and 2-mm width) were prepared on freshly extracted, sound human molars. Two all-in-one adhesive systems (Scotchbond/Single Bond Universal [SUD] and Xeno-V(+) [X5D]) were used and compared with a two-step etch-and-rinse system (Prime&Bond NT [NTD]). The adhesives were applied according to the manufacturers' guidelines. A universal resin composite (Filtek Z350 XT Universal) was used to restore the cavities in one bulk filling and was irradiated at 550 mW/cm(2) for 40 seconds by a quartz-tungsten-halogen light (Optilux 501). After exposure to liquid nitrogen coolant, the specimens were milled to nanoscale thickness by FIB to view and then assess the area of dentin-resin interface by TEM. Unlike the unfilled X5D, a noticeably smooth transition zone at the dentin-resin interface was shown for the SUD and NTD adhesives. The SUD demonstrated an uneven hybrid layer with clearly demineralized collagen bundles. Ultramorphologically, dispersed needlelike apatite crystals were detected within the partially demineralized dentin or the hybrid layer of both compositionally different all-in-one simplified adhesives. Conversely, these crystals were entirely absent from the hybrid layer of the etch-and-rinse NTD adhesive. In the X5D group, a bright band was noted beneath the hybrid layer. The methacryloxydecyl dihydrogen phosphate monomer containing ultramild self-etch adhesive (SUD) was still validated in terms of its capability in dentin adhesion.

Influence of the LED curing source and selective enamel etching on dentin bond strength of self-etch adhesives in class I composite restorations

The aim of this study was to evaluate the influence of the LED curing unit and selective enamel etching on dentin microtensile bond strength (μTBS) for self-etch adhesives in class I composite restorations. On 96 human molars, box-shaped class I cavities were made maintaining enamel margins. Self-etch adhesives (Clearfil SE - CSE and Clearfil S(3) - S3) were used to bond a microhybrid composite. Before adhesive application, half of the teeth were enamel acid-etched and the other half was not. Adhesives and composites were cured with the following light curing units (LCUs): one polywave (UltraLume 5 - UL) and two single-peak (FlashLite 1401 - FL and Radii Cal - RD) LEDs. The specimens were then submitted to thermomechanical aging and longitudinally sectioned to obtain bonded sticks (0.9 mm(2)) to be tested in tension at 0.5 mm/min. The failure mode was then recorded. The μTBS data were submitted to a three-way ANOVA and Tukey's (α = 0.05). For S3, the selective enamel-etching provided lower μTBS values (20.7 ± 2.7) compared to the non-etched specimens (26.7 ± 2.2). UL yielded higher μTBS values (24.1 ± 3.2) in comparison to the photoactivation approach with FL (18.8 ±3.9) and RD (19.9 ±1.8) for CSE. The two-step CSE was not influenced by the enamel etching (p ≥ 0.05). Enamel acid etching in class I composite restorations affects the dentin μTBS of the one-step self-etch adhesive Clearfil S(3), with no alterations for Clearfil SE bond strength. The polywave LED promoted better bond strength for the two-step adhesive compared to the single-peak ones.

An in vitro comparison of adhesive techniques and rotary instrumentation on shear bond strength of nanocomposite with simulated pulpal pressure

Aim:

The aim of this study is to evaluate the shear bond strength of composite to tooth using different adhesive techniques and rotary instruments under simulated pulpal pressure.

Materials and Methods:

Sixty extracted human molars were randomly divided into two groups of 30 samples each (group I and II), according to the adhesive technique followed (i.e. total etch and self etch groups). Each group was further divided into two sub-groups (Sub-groups A and B) of 15 samples each according to the cutting instrument (diamond abrasive or carbide burs) used. Class II cavities were made with diamond abrasive or carbide burs, and restored with nano-composite under positive intra-pulpal pressure. Shear bond strength of the specimens were recorded simultaneously.

Results:

After statistical evaluation using two-way ANOVA and t-test, the mean shear bond strength values of the groups are as follows: Group IA- 4.69 MPa, Group IB-6.15 MPa, Group IIA-4.3 MPa, and Group IIB-6.24 MPa. It was seen that group IIB showed highest bond strength followed by group IB. Group II A showed the least bond strength.

Conclusions:

Within the limitations of the study, diamond abrasive gave better bond strength than carbide bur with both the adhesive techniques.

Effect of dentine smear layer on the performance of self-etching adhesive systems: A micro-tensile bond strength study

This study aimed to evaluate the effect of the smear layer on the micro-tensile bond strength when two self-etching adhesives were used with different techniques. Flat dentine surfaces were prepared using either medium grit diamond burs or tungsten carbide burs. Ten specimens from each prepared surfaces were subjected for smear layer evaluation under SEM. Forty specimens from each of the prepared surfaces were further divided into two groups, bonded with either Clearfil SE Bond (SE) or Clearfil S(3) Bond (S3) using one of four applications (as manufacturer's instructions, agitation, reapplication, and increased application time), restored with composites and subjected to a micro-tensile bond strength test. Smear layers created with diamond burs were thicker than those created with tungsten carbide burs. Surfaces prepared with tungsten carbide burs produced a higher bond strength than those prepared with diamond burs and the same type of adhesive resin. SE demonstrated a higher bond strength than S3 for all surfaces. S3 applied with the agitation technique demonstrated a higher bond strength to dentine prepared with tungsten carbide and diamond burs than that applied with other techniques. SE applied with increased time on dentine treated with carbide burs produced the highest bond strength. In conclusion, a thick smear layer decreased bond strength to dentine, and this might be improved by modification of application technique.