Ornnicha Thanatvarakorn

Light transmission characteristics of dentine and resin composites with different thickness

OBJECTIVE The purpose of this study was to evaluate the light transmission characteristics of dentine and resin composites with different thickness. METHODS Disks of bovine dentine and three resin composites (Estelite Σ, Beautifil II and Clearfil Majesty) of OA2 shade were prepared with various thicknesses (0.5, 1.0 and 2.0mm). Using a goniophotometer, the distribution graphs of the light transmission intensity of each specimen were obtained, and diffusion factor (DF) as an indicator for a diffuse transmission property and peak-gain (G0) for a straight-line transmission property were calculated. Their colors were measured on black and white backings using a reflection spectrophotometer to calculate translucency parameter (TP). The data of each value (G0, DF and TP) were analyzed by two-way ANOVA and Dunnetts T3 for post hoc test (p=0.05). Regression analyses were used to determine the correlation between G0, DF, TP values and the thickness. RESULTS Regardless of the thickness, dentine had lower TP values than the resin composites. 0.5 mm-thick specimens of dentine and resin composite produced various G0 and DF values, with dentine exhibiting significantly lower G0 and higher DF than the resin composites (p<0.05), whereas with the 1.0 and 2.0mm-thick specimens, they were closely aligned. For dentine, G0 and DF increased in inverse proportion to the thickness (G0: R(2)=0.962, p<0.001; DF: R(2)=0.891, p<0.001). CONCLUSIONS Dentine had different light transmission characteristics from resin composite, depending on the thickness. CLINICAL SIGNIFICANCE Dentine has different light transmission characteristics (straight-line and diffusion) from resin composite, depending on thickness. Resin composite restoration might be different to accurately reproduce light transmission characteristics of dentine substrate.

In vitro evaluation of dentinal hydraulic conductance and tubule sealing by a novel calcium–phosphate desensitizer†

In the current trend of materials used for dentin hypersensitivity treatment, calcium-phosphate-containing desensitizers are expected to have advantages in oral environment. A newly formulated desensitizer containing tetracalcium phosphate and dicalcium phosphate anhydrous (CPD-100) was evaluated in comparison to oxalate containing desensitizer (SS) regarding permeability reduction (PR%) by measuring hydraulic conductance on the etched dentin discs in vitro. CPD-100 exhibited mean PR% of 91%, which significantly increased to 98% after immersion in artificial saliva (AS) for 4 weeks (p < 0.001), while SS showed a significant decrease from 99% to 93% (p < 0.01). SEM observation showed newly formed crystallites on CPD-100 treated dentin, which did not exist in SS treated dentin after AS immersion, suggesting that calcium oxalate inhibited formation of new calcium-phosphate minerals. Five-minute acid challenge did not significantly affect PR% of dentin treated by any of the desensitizers. The energy dispersive X-ray spectroscopy (EDS) analysis indicated that the formed layer of CPD-100 were minerals with similar Ca/P ratio to hydroxyapatite. In conclusion, the newly developed calcium-phosphate desensitizer has the potential to exhibit long-term stability in the oral environment, owing to its chemical properties that promote the crystal growth in salivary fluid.

Effect of smear layer deproteinizing on resin–dentine interface with self-etch adhesive

OBJECTIVES This study aimed to investigate deproteinizing effect of sodium-hypochlorite (NaOCl) and mild acidic hypochlorous-acid (HOCl) pretreatment on smear layer-covered dentine and to evaluate their effects on morphological characteristics of resin-dentine interface with self-etch adhesive. METHODS Human coronal-dentine discs with standardized smear layer were pretreated with 6% NaOCl or 50ppm HOCl for 15s or 30s. Their deproteinizing effects at the treated smear layer-covered dentine surfaces were determined by the measurement of amide:phosphate ratio using ATR-FTIR analysis. In addition, using TEM, micromorphological alterations of hybridized complex and nanoleakage expression were evaluated at the interface of a self-etch adhesive (Clearfil SE Bond) to the pretreated dentine surface with or without subsequent application of a reducing agent (p-Toluenesulfinic acid salt; Accel(®)). RESULTS Both pretreatments of NaOCl and HOCl significantly reduced the amide:phosphate ratio as compared with the no-pretreated group (p<0.05), coincident with the elimination of the hybridized smear layer on their bonded interfaces. Nanoleakage within the hybrid layer was found in the no-pretreated and NaOCl-pretreated groups, whereas the subsequent reducing agent application changed the reticular nanoleakage to spotted type. HOCl-pretreated groups showed less nanoleakage expression in a spotted pattern, regardless of reducing agent application. CONCLUSIONS NaOCl and HOCl solutions could remove the organic component on the smear layer-covered dentine, which could eliminate the hybridized smear layer created by self-etch adhesive, leading to the reduction of nanoleakage expression within hybrid layer. CLINICAL SIGNIFICANCE Smear layer deproteinizing could modify dentine surface, giving an appropriate substrate for bonding to self-etch adhesive system.

Effect of Scrubbing Technique with Mild Self-etching Adhesives on Dentin Bond Strengths and Nanoleakage Expression.

PURPOSE To evaluate the effect of a scrubbing technique with one-step self-etching adhesives on bond strengths and nanoleakage expression at the resin/dentin interface. MATERIALS AND METHODS Flat human dentin surfaces bonded with one of two mild self-etching adhesives, SE One (SE) or Scotchbond Universal (SU) applied either with scrubbing or without scrubbing technique, were prepared (n = 5). The microtensile bond strengths (μTBS), SE micrographs of morphological changes on treated dentin surfaces, and expression of nanoleakage along the bonded dentin interfaces as shown with TEM were evaluated. μTBS data were analyzed using two-way ANOVA and the post-hoc t-test at the significance level of 0.05. RESULTS The scrubbing technique had a significant positive effect on the μTBS of SU (p < 0.05), while it produced no significant difference for SE (p > 0.05). Morphological evaluation of the treated dentin surfaces demonstrated that SU with scrubbing showed the highest etching ability, followed by scrubbing SE > nonscrubbing SE > nonscrubbing SU. In the nonscrubbing groups, nanoleakage formation using SU exhibited a reticular pattern throughout the hybridized complex, whereas with SE, water-tree nanoleakage was only found in the adhesive layer at dentinal tubule orifices. The scrubbing groups of both adhesives did not exhibit any nanoleakage expression. CONCLUSION Using a scrubbing technique when applying mild self-etching adhesives could improve resin monomer infiltration into dentin, chase water on adhesive surfaces, and facilitate smear layer removal.

Smear layer-deproteinizing improves bonding of one-step self-etch adhesives to dentin

OBJECTIVES Smear layer deproteinizing was proved to reduce the organic phase of smear layer covered on dentin surface. It was shown to eliminate hybridized smear layer and nanoleakage expression in resin-dentin bonding interface of two-step self-etch adhesive. This study aimed to investigate those effects on various one-step self-etch adhesives. METHODS Four different one-step self-etch adhesives were used in this study; SE One (SE), Scotchbond™ Universal (SU), BeautiBond Multi (BB), and Bond Force (BF). Flat human dentin surfaces with standardized smear layer were prepared. Smear layer deproteinizing was carried out by the application of 50ppm hypochlorous acid (HOCl) on dentin surface for 15s followed by Accel® (p-toluenesulfinic acid salt) for 5s prior to adhesive application. No surface pretreatment was used as control. Microtensile bond strength (μTBS) and nanoleakage under TEM observation were investigated. The data were analyzed by two-way ANOVA and Tukeys post-hoc test and t-test at the significant level of 0.05. RESULTS Smear layer deproteinizing significantly improved μTBS of SE, SU, and BB (p<0.001). Hybridized smear layer observed in control groups of SE, BB, and BF, and reticular nanoleakage presented throughout the hybridized complex in control groups of BB and BF were eliminated upon the smear layer deproteinizing. SIGNIFICANCE Smear layer deproteinizing by HOCl and Accel® application could enhance the quality of dentin for bonding to one-step self-etch adhesives, resulting in the improving μTBS, eliminating hybridized smear layer and preventing reticular nanoleakage formation in resin-dentin bonding interface.

The strategies used for curing universal adhesives affect the micro-bond strength of resin cement used to lute indirect resin composites to human dentin

We evaluated the effect of different curing strategies for universal adhesives on micro-tensile bond strength (μTBS) between resin cement and dentin and/or between resin cement and indirect resin composite. Flat coronal dentin surfaces and composite resin disks were pretreated with silane-containing universal adhesives, with or without light-curing on the dentin-side and/or composite resin disk-side. Resin disks were luted onto the pretreated dentin surfaces with the corresponding dual-cure adhesive resin cements and light-cured, and cut into beams after 24-h water storage. After 0 or 10,000 thermocycles (5ºC/55ºC) in a water bath, the μTBS of the composite resin disk-dentin beam was tested. The μTBS was highest when universal adhesives were applied to both the dentin- and the indirect composite resin disk-side, followed by light-curing. Thermocycling decreased μTBS in all but the Scotchbond Universaltreated group, with light-curing on both sides. The effect of curing strategies is dependent upon the materials.

Smear Layer-Deproteinization: Improving the Adhesion of Self-Etch Adhesive Systems to Caries-Affected Dentin

Purpose of reviewThis paper reviews a new method of dentin surface modification, smear layer-deproteinization for self-etch adhesive systems, particularly in relation to improving the adhesion to caries-affected dentin.Recent FindingsRemnants of smear debris, which forms hybridized smear layer with self-etch adhesives, can prevent monomer infiltration and interfere with the chemical interaction of adhesive monomers and the underlying dentin. The hybridized smear layer weakens the physical and chemical properties of the resin-dentin hybridized complex both immediately and over time. Smear layer-deproteinization with NaOCl and HOCl solutions can improve the quality of resin-dentin interface of self-etch adhesives through elimination of the hybridized smear layer, development of monomer infiltration, and enhancement of the chemical interaction of adhesive monomers with hydroxyapatite due to an increase in the mineral/organic ratio on the dentin surface. These positive effects are influenced by the types of oxidizing solution and their application time and also depend upon the adhesive materials used because compromising effects of residual oxidized-byproducts at the dentin surface on the polymerization behavior of the adhesives are different between the materials. However, applying antioxidant/reducing agents can eliminate this problem.SummarySmear layer-deproteinization is more effective for improving the bonding efficacy of self-etch adhesives to caries-affected dentin than normal dentin because caries-affected dentin produces a thicker organic-rich smear layer. Smear layer-deproteinization with HOCl solution, which has a rapid and broad-spectrum antimicrobial activity with less irritating and sensitizing properties, along with the subsequent application of antioxidant/reducing agents could enhance the longevity of composite restoration with self-etch adhesives.