The combined effect of light-illuminating direction and enamel rod orientation on color adjustment at the enamel borders of composite restorations.

OBJECTIVES: To investigate the effect of light-illuminating direction (from composite or enamel side) on color adjustment at the coronal and cervical enamel borders in composite restorations. MATERIALS AND METHODS: Forty cylindrical holes (3.0-mm diameters) were prepared in bovine enamel disks (1.0-mm thickness). After application of a one-step self-etch adhesive, one of four resin composites (Estelite Asteria, EA; Estelite Pro, EP; Kalore, KA; Clearfil Majesty ES-2 Premium, MJ) was restored in the holes. After 24-h storage, the colors (L*, C*, or h* values) at the restored enamel disks over a black background were measured in a black box using a CIE XYZ camera, spotted with D65 standard illuminant either from coronal or cervical side at 45°/0° geometry. The color shifting rate was calculated at the coronal and cervical enamel borders of the composite restorations, and analyzed by three-way ANOVA with Dunnett's T3 and t test for post hoc analysis (p < 0.05). RESULTS: The light-illuminating directions significantly affected the L* shifting rate at the cervical enamel border in EP and MJ (p < 0.05), and the C* shifting rate at the coronal enamel border in EA, EP, and MJ (p < 0.05). CONCLUSIONS: The color appearance at the border of the composite restoration was influenced by the light-illuminating direction in conjunction with the enamel rod orientation in the coronal or cervical enamel border. CLINICAL RELEVANCE: The line-of-vision angle would affect the perception of color adaptation at the enamel borders in the composite restorations.

Adhesive sealing of dentin surfaces in vitro: A review.

PURPOSE: This review describes the evolution of the use of dental adhesives to form a tight seal of freshly prepared dentin to protect the pulp from bacterial products, during the time between crown preparation and final cementation of full crowns. The evolution of these "immediate dentin sealants" follows the evolution of dental adhesives, in general. That is, they began with multiple-step, etch-and-rinse adhesives, and then switched to the use of simplified adhesives. METHODS: Literature was reviewed for evidence that bacteria or bacterial products diffusing across dentin can irritate pulpal tissues before and after smear layer removal. Smear layers can be solubilized by plaque organisms within 7-10 days if they are directly exposed to oral fluids. It is likely that smear layers covered by temporary restorations may last more than 1 month. As long as smear layers remain in place, they can partially seal dentin. Thus, many in vitro studies evaluating the sealing ability of adhesive resins use smear layer-covered dentin as a reference condition. Surprisingly, many adhesives do not seal dentin as well as do smear layers. RESULTS: Both in vitro and in vivo studies show that resin- covered dentin allows dentin fluid to cross polymerized resins. The use of simplified single bottle adhesives to seal dentin was a step backwards. Currently, most authorities use either 3-step adhesives such as Scotchbond Multi-Purpose or OptiBond FL or two-step self-etching primer adhesives, such as Clearfil SE, Unifil Bond or AdheSE.

Application of ethanol improves the resin-dentin bond strength of a two-bottle, self-etching primer-adhesive.

PURPOSE: To investigate whether the application of ethanol to a two-step self-etching adhesive can improve its resin-dentin bond performance. METHODS: Four different ethanol concentrations were added to the adhesive of Clearfil SE Bond to create four ethanol primers (40, 60, 80 or 100% ethanol). 24 extracted third molars were divided into four groups. Each group corresponded to one of the four hydrophobic ethanol primer concentrations. The teeth in the control group were bonded with Clearfil SE Bond according to the manufacturer's instructions. The primed teeth in the experimental groups were treated with the ethanol primer prior to application of the solvent-free adhesive. Microtensile bond strengths (mTBS) were tested 24 hours after specimen preparation. Another 14 teeth were bonded using the same methods to evaluate mTBS after 1 year. Nanoleakage was evaluated under field-emission scanning electron microscopy before and after aging. RESULTS: In the 24-hour group, the mTBS in the 60% ethanol/40% adhesive primer group increased significantly (21.6%, P < 0.05) over the no ethanol control. After 12-month water storage, the bond strength of that experimental group was still higher than that of the control group (19.5%, P < 0.05). Before aging, the nanoleakage was clearly seen in the control group but hardly any was seen in the experimental group. After aging, the nanoleakage increase in the experimental group was much less than that in the control group.

Influence of central and peripheral dentin on micro-tensile bond strength estimated using a competing risk model.

The bonding performance of dental adhesives is most frequently evaluated using the micro-tensile bond strength (µTBS) test. Despite lacking evidence, peripheral specimens are often discarded to avoid regional variability. This study, therefore, examined whether µTBS to central and peripheral dentin differed. Dentin surfaces of extracted human molars were bonded with various self-etch adhesives, built up with a resin composite, cut into beams, and stressed in tension. Failure mode was classified as adhesive, cohesive in dentin, or other using scanning electron microscopy. Since cohesive failures in dentin were frequent and could confound µTBS results, the data from central/peripheral dentin were analyzed using a Weibull competing risk (CR) model distinguishing failure modes, and its outcomes were compared to a conventional failure mode non-distinguishing Weibull model. Based on the strength data of cohesively failed specimens, the CR model also estimated the strength of dentin. For comparison, the ultimate tensile strength (UTS) of dentin was measured in both regions. The conventional model suggested that peripheral µTBS was higher than central µTBS. Conversely, the CR model disclosed no significant difference in µTBS between the regions but indicated a higher strength of peripheral dentin. This finding was confirmed by UTS measurements, and further supported by the significantly higher incidence of cohesive failures in central dentin. Therefore, peripheral specimens can be used in the µTBS test as well as central ones, but a CR model should be used for statistical analysis if cohesive failures in dentin are frequent, as the strength of peripheral dentin is higher.

Degree of conversion and dentin bond strength of light-cured multi-mode adhesives pretreated or mixed with sulfinate agents.

The influence of sulfinate agents applied as a dentin pretreatment or a mixture with multi-mode one-step self-etch adhesives (1-SEAs) on the degree of conversion (DC) and micro-tensile bond strength (µTBS) of light-cured 1-SEAs was investigated. 1-SEAs Clearfil Universal Bond Quick (UBQ) or Scotchbond Universal Adhesive (SBU) were applied to dentin in etch&rinse or self-etch mode using various application strategies: 1) no pretreatment, 2) pretreatment with 90 wt% ethanol, 3) pretreatment with a sulfinate agent Clearfil DC Activator (UDC) or Scotchbond Universal DCA (SDC), or 4) a mixture of UBQ+UDC or SBU+SDC. µTBS was measured after 24 h. Additionally, DC was measured using attenuated total reflectance Fourier-transform infrared spectroscopy. Pretreatment with sulfinate agents resulted in the highest µTBS and DC, significantly improving them especially in etch&rinse mode. The mixture of sulfinate agents with 1-SEAs was less effective. Pretreatment with ethanol significantly improved µTBS in etch&rinse mode but compromised µTBS in self-etch mode.

Stress distribution in tooth resin core build-ups with different post-end positions in alveolar bone level under two kinds of load directions.

This study aimed to evaluate influence of different post-end positions in alveolar bone level on stress distributions in resin-core build-up tooth under different load directions. Three-dimensional mathematical models of a root-filled mandibular premolar tooth were constructed. Resin post and core were built-up with six post lengths: 0, 1, 2, 3, 4, and 6 mm. Finite element analysis calculated stress distributions with oblique load of 400 N to buccal cusp 45 degree from buccal side or from lingual side. The 3 mm-post length (post-end position equal to cancellous bone level) caused highest equivalent stress of post-end compared with the shorter or longer post length. When change of load direction, the direction of maximum shear stress became completely opposite at mesiodistal cervical edge of core-part without a change of the magnitude. Changing shear stress direction would increase risk of debonding at mesiodistal cervical edge.

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.

The influence of elastic moduli of core materials on shear stress distributions at the adhesive interface in resin built-up teeth.

This study aimed to investigate shear stress distributions in resin built-up teeth using resin composites of varying elastic moduli (E), with or without fiber posts. Three-dimensional mathematical models of a root-filled mandibular premolar tooth were constructed. Resin post and cores were built-up with resin composites of three different E: 12,000, 18,000 and 24,000 MPa, with or without fiber posts. Finite element linear analysis was performed to calculate shear stress distributions at bonding interface between resin core and dentin. Regardless of fiber post insertion, the shear stress on the cervical surface of resin core decreased as the E of resin composites increased. Insertion of fiber posts increased the shear stress on the post surface of resin core, with increases in the E of resin composites. In conclusion, using resin core materials with higher E decreased the shear stress at cervical interface between resin core and dentin regardless of fiber post insertion.

Is chlorhexidine-methacrylate as effective as chlorhexidine digluconate in preserving resin dentin interfaces?

OBJECTIVES: The aim of the current study was to evaluate the effect of 2% CHX and 2% CHX-methacrylate compared to the resin-dentin bonds created by a two-step etch-and-rinse adhesive system after 24h, 6min and 12min. METHODS: Microtensile bond strengths and interfacial nanoleakage within resin-dentin interfaces created by Adper Single Bond 2, with or without CHX or CHX-methacrylate pre-treatment for 30s on acid-etched dentin surfaces, were evaluated after 24h, 6min and 12min of storage in distilled water at 37°C. RESULTS: Twelve months of storage resulted in a significant decrease in microtensile bond strength in the control group, and significant increases in silver nanoleakage. In contrast, Single Bond 2+CHX, and to a greater extent CHX-methacrylate, significantly reduced the rate of deterioration of resin-dentin interfaces over the 12min water storage period, in terms of bond strength. CONCLUSIONS: Similar to Single Bond 2+CHX, Single Bond+CHX-methacrylates reduced the degradation of resin-bonded interfaces over a 12 month storage period. Thus it can be concluded that Single Bond 2+CHX-methacrylate may be important to improve durability of bonded interfaces and therefore, prolong the life span of adhesive restorations. CLINICAL SIGNIFICANCE: Although CHX primers have been shown to enhance the durability of etch-and-rinse adhesives, that protection is lost after 2h. The use of CHX-methacrylate should last much longer since it may copolymerize with adhesive monomers, unlike CHX.

Effects of a Dicalcium and Tetracalcium Phosphate-Based Desensitizer on In Vitro Dentin Permeability.

The present study evaluated the effectiveness of a dicalcium and tetracalcium phosphate-based desensitizer in reducing dentin permeability in vitro. Dentin fluid flow was measured before and after treatment of dentin with patent dentinal tubules using 1 or 3 applications of the dicalcium and tetracalcium phosphate containing agent TeethmateTM (TM) and comparing the results with two sodium fluoride varnishes VellaTM (VLA) and VanishTM (VAN), after storage in artificial saliva for 24 h, 48 h and 7 days. Significant differences were observed among the 4 methods employed for reducing dentin permeability (p < 0.001) and the 3 post-treatment times (p < 0.001). VLA and VAN never achieved 50% permeability reductions consistently in any of the 3 time periods. Only the calcium phosphate-based desensitizer applied for 3 times consistently reduced dentin permeability by 50% after 24 h. When applied once, the permeability reduction of TM increased progressively over the 3 time periods. After 7 days, only one and three applications of the calcium phosphate-based desensitizer consistently reduced dentin permeability by more than 50%. Permeability reductions corresponded well with scanning electron microscopy examination of dentinal tubule orifice occlusion in dentin specimens treated with the agents. Overall, the dicalcium and tetracalcium phosphate-based desensitizer is effective in reducing dentin permeability via a tubule occlusion mechanism. The ability of the agent to reduce dentin permeability renders it to be potentially useful as a clinical dentin desensitizing agent, which has to be confirmed in future clinical studies. By contrast, the two sodium fluoride varnishes are not effective in dentin permeability reduction and should be considered as topical fluoride delivering agents rather than tubular orifice-blocking agents.

Cross-linked dry bonding: A new etch-and-rinse technique.

OBJECTIVE: To determine if acid-etched, cross-linked dentin can be dehydrated without lowering bond strength below that of cross-linked wet-bonded dentin in vitro. METHODS: Using extracted human third molars, control acid-etched dentin was bonded with Single Bond Plus, using either the wet- or dry-bonding technique. Experimental acid-etched dentin was treated with 5mass% grape seed extract (GSE) in different solvents for 1min before undergoing wet vs dry resin-dentin bonding with Single Bond Plus. Completely demineralized dentin beams were treated with 5% GSE for 0, 1 or 10min, before measuring stiffness by 3-point flexure. Other completely demineralized beams were treated similarly and then incubated in buffer for 1 week to measure the collagen solubilization by endogenous dentin proteases. RESULTS: 24h microtensile bond strengths (µTBS) in wet and dry controls were 53.5±3.6 and 9.4±1.8MPa, respectively (p<0.05). 5% GSE in water gave µTBS of 53.7±3.4 and 39.1±9.7MPa (p<0.05), respectively, while 5% GSE in ethanol gave µTBS of 51.2±2.3 and 35.3±2.0MPa (p<0.05). 5% GSE in 5% EtOH/95% water gave wet and dry µTBS of 53.0±2.3 and 55.7±5.1MPa (p>0.05). Cross-linking demineralized dentin with 5% GSE increased stiffness of dentin and decreased collagen degradation (p<0.05). SIGNIFICANCE: 5% GSE pretreatment of acid-etched dentin for 1min permits the dentin to be completely air-dried without lowering bond strength.