Universal Adhesive Application Modes Differentially Affect the Fracture Resistance of Resin Composite Restored Teeth.

This study evaluated the fracture resistance of teeth with mesio-occluso-distal (MOD) resin composite restorations using universal adhesive (Single Bond Universal; SBU) in three different manipulation modes compared with those using two-step self-etch (Clearfil SE bond; CSE) and 3-step etch-and-rinse (Scotchbond Multi-Purpose; SBMP) adhesives at 24 hours and after thermocycling. One hundred and sixty maxillary premolars were assigned into eight groups of 20 each. Intact teeth and nonrestored cavity-prepared teeth served as controls. For the remaining specimens, cavities were restored with resin composite using different adhesives-SBU in self-etch, etch-and-rinse, or selective enamel etching modes; CSE in self-etch or selective enamel etching; and SBMP. Specimens from each group were either stored in 37°C water for 24 hours or further submitted to thermocycling for 30,000 cycles (n=10), then subjected to axial compression stress until fracture. Fracture patterns were observed microscopically. Data were statistically analyzed at a 95% confidence level. Among the restored teeth, mean failure load of the group using SBMP was the highest at both short-term and long-term evaluation periods (p<0.05). Fracture strengths of the SBU groups where enamel was etched with phosphoric acid prior to the adhesive application were similar and were greater than in those specimens without pre-etching (p<0.05). After thermal aging, a significant decrease in fracture resistance value was detected only for the group using SBU in etch-and-rinse application mode (p<0.05). For the self-etch strategy, SBU demonstrated lower load to fracture than CSE following thermocycling; all specimens failed at and beneath the crestal level (p<0.05). Application of SBU universal adhesive in selective enamel etching mode provided higher and more stable fracture resistance of teeth with MOD resin composite restorations than in self-etch mode.

Bond strengths of resin cements to astringent-contaminated dentin.

The current study evaluated the micro-shear bond strength of two resin cements to astringent-contaminated dentin. Twelve occlusal dentin discs were prepared from extracted caries-free human molars and divided into two groups subjected to two types of resin cements, Panavia F (PF) and Variolink II (VL). Each disc was ground with 600 grit SiC paper and sectioned into two semi-disks, one for the normal dentin surface and the other for the contaminated dentin surface. For contaminated dentin, an astringent containing aluminum chloride was applied for two minutes and rinsed before the bonding procedures. A micro tygon tube was placed on the dentin surface following the bonding application and then filled with a resin cement. After the resin was polymerized, the specimen was kept in water for 24 hours before the micro-shear bond strengths evaluation. The micro morphology of the treated surfaces and resin-dentin interfaces were observed under a scanning electron microscope (SEM). Aluminum content under different dentin conditions was also examined. No significant differences were found between the dentin bond strengths to normal dentin and contaminated dentin surfaces in both the PF and VL groups (p>0.05). PF showed similar bond strengths to VL on normal and contaminated dentin (p>0.05). SEM observations of the VL groups revealed no differences in the treated dentin surfaces and the resin-dentin interfaces between normal and contaminated dentin. However, for the PF group, an inconsistent etching pattern of the self-etching primer and gap formation at the interface of resin cement to contaminated dentin were observed.

Changes in resin-infiltrated dentin stiffness after water storage.

Plasticization of polymers by water sorption lowers their mechanical properties in a manner that is predictable by the polarity of their component resins. This study tested the hypothesis that when adhesive resins were used to create resin-infiltrated dentin, the reductions in their flexural moduli after water storage would be lowered proportional to their hydrophilic characteristics. Three increasingly hydrophilic resin blends were used to fabricate polymer beams and macro-hybrid layer models of resin-infiltrated dentin for testing with a miniature three-point flexure device, before and after 1-4 weeks of water storage. Flexural modulus reductions in macro-hybrid layers were related to, and more extensive than, reductions in the corresponding polymer beams. Macro-hybrid layers that were more hydrophilic exhibited higher percent reductions in flexural modulus, with the rate of reduction proportional to the Hoy's solubility parameters for total intermolecular attraction forces (delta(t)) and polar forces (delta(p)) of the macro-hybrid layers.

Microtensile bond strengths of two adhesive resins to discolored dentin after amalgam removal.

Studies have reported the discoloration of dentin beneath amalgam restorations. The purpose of this study was to test the hypothesis that the bond strengths of adhesive resins to this discolored dentin are lower than those to normal dentin, and are related to the presence of metallic ions or corrosion products. Amalgam-filled extracted human teeth were used. After the removal of amalgam, the discolored dentin and surrounding normal dentin were bonded with Single Bond or Clearfil SE Bond and tested for microtensile bond strengths. The bond strengths of Single Bond and Clearfil SE Bond to normal dentin were greater than to discolored dentin. Clearfil SE Bond demonstrated higher bond strength to normal dentin than did Single Bond. However, no differences were found between the bond strengths to the discolored dentin of both adhesives. Elemental micro-analysis revealed various amounts of tin in all discolored dentin.

Effective bond strength of current adhesive systems on deciduous and permanent dentin.

PURPOSE: To evaluate the bond strength of a total-etching, self-priming system (Single Bond) and a self-etching system (Clearfil SE Bond) to deciduous and permanent human dentin. METHODS AND MATERIALS: Buccal dentin discs were prepared with a diamond disc from permanent first premolars, permanent third molars and deciduous second molars. The flat dentin surfaces were obtained by polishing with wet 600 grit silicon carbide papers. The specimens of each group were further divided into two groups for bonding to either Single Bond or Clearfil SE Bond. After 24 hours, the microshear bond strength testing was executed on a universal testing machine. Statistical analysis was performed at alpha = 0.05. RESULTS: No significant differences in bond strength were found between materials. However, deciduous dentin demonstrated significantly lower bond strengths than permanent premolar dentin when Single Bond was applied (p < 0.05). CONCLUSION: The difference in bonding substrate (permanent or deciduous dentin) had a significant effect on bond strength when the total-etching, self-priming system was applied.

Micro-tensile bond strengths of bonding agents to pulpal floor dentine.

AIM: The purpose of this study was to characterize the dentine surface of the pulpal floor and to determine the micro-tensile bond strengths of two dentine adhesive systems used in conjunction with a resin composite core material to pulpal floor dentine. METHODOLOGY: Thirty-six extracted human molars were cut horizontally with a slow-speed diamond saw to expose the pulp chamber and the pulp tissue was removed. Eight teeth were used to investigate characteristics of untreated and etched dentine surfaces of the pulpal floor using SEM. Twenty-eight teeth were randomly allocated to two groups, each of 14 teeth. In group 1, a 'one-bottle' system (Prime & Bond NT) was used as dentine bonding agent and in group 2, a self-etching-priming system (Clearfil SE Bond) was applied. Pulp chambers of both groups were then filled with resin composite core buildup (FluoroCore) and kept moist in tap water at 37 degrees C for 24 h. Samples were prepared for micro-tensile bond testing by sectioning each tooth vertically in the mid-pulpal floor region and shaped to an hour-glass form of 1 +/- 0.2 mm(2) area at the bonded interface. Micro-tensile bond strengths were determined using a universal testing machine at a crosshead speed of 1 mm min-1. Fractured surfaces were examined by SEM. RESULTS: The intact pulpal floor showed numerous calcospherites with variable tubule density and few accessory canals. Etching the pulpal floor with 34% phosphoric acid gel resulted in an irregular surface with patent dentinal tubules and the dome-shaped calcospherites mostly lost. With self-etching primer, the superficial dentine surface was less demineralized and little peritubular dentine matrix was removed. Mean bond strength for the self-etching-priming (Clearfil SE Bond) specimens was significantly greater than for 'one-bottle' (Prime & Bond NT) specimens (P< 0.05, Student's t-test). The fracture mode of Clearfil SE Bond specimens was mostly partial cohesive failure within dentine, whilst Prime & Bond NT specimens mostly showed partial cohesive failure in bonding resin/composite. CONCLUSIONS: Despite an irregular surface morphology and absence of a smear layer, bonding to pulpal floor dentine was weaker than previously reported for cut coronal dentine. The self-etching-priming system bonded more strongly than the 'one-bottle' system.

Adhesion of a glass-ionomer root canal sealer to the root canal wall.

Glass-ionomer root canal sealer is commonly used because of its chemical bonding and favorable physical characteristics when bonding to dentin. This study was designed to determine the tensile bond strength of a glass-ionomer sealer (Ketac Endo, Espe, Seefeld, Germany) on root canal walls after pretreatment with different conditioners. Flat inner surfaces of root canal specimens were prepared. The specimens were divided into five groups of 10 teeth, and the groups were conditioned with one of the following smear layer removal solutions: 15% EDTA/NaOCl, 10% polyacrylic acid, 35% phosphoric acid, 6% citric acid, and 5.25% NaOCl as a control. Then the exposed root canal areas were coated with Ketac-Endo. Tensile bonding was measured using a universal testing machine until ultimate failure was obtained. The groups that were treated with phosphoric acid and citric acid showed significantly higher bond strengths than the groups that were treated with 15% EDTA and polyacrylic acid (p < 0.05). Bonding to dentin without smear layer removal (NaOCl group) was too low to be measured in the testing apparatus. Scanning electron microscopy confirmed that phosphoric and citric acids were more effective in removing smear layer than EDTA or polyacrylic acid. The result supported the view that pretreatment with phosphoric acid or citric acid should be used in association with glass-ionomer root canal sealer to achieve the most effective removal of the smear layer and to provide better adhesion.

In vivo adhesive interface between resin and dentin.

V-shaped cervical cavities prepared in monkey teeth were restored with several dentin bonding systems, and the in vivo resin-dentin interfacial structures were observed under the scanning electron microscope using an argon-ion etching technique. The hybrid layer could be clearly observed; its depth was dependent on the conditioner/primer used and tended to be thinner at the deep part of the cavity. Resin tags were also clearly observed, and their structure at the inner part was noted to be rougher than that closer to the tubule orifices. When 37% phosphoric acid gel was used, the tags in the deeper parts of the cavity were much rougher. Hemispherical and spherical roughened structures were observed directly above the tubule orifices, which were thought to be a mixture of dentinal fluid and bonding resin that had flowed out from the tubules. The acidic primer containing maleic acid and HEMA could not remove the smear plugs, and undissolved smear particles were observed in the tubules.

Adhesive interface between resin and etched dentin of cervical erosion/abrasion lesions.

The interfacial structure between an adhesive composite resin and the dentinal walls of cervical erosion/abrasion lesions etched with 37% phosphoric acid gel for 60 seconds was investigated. Almost all dentinal tubules were occluded with rod-like structural depositions that remained undissolved even after acid conditioning. The hybrid layer between the adhesive resin and surface-demineralized dentin was found to be 0.3 to 3 microns, much thinner than that routinely found in either normal dentin or cariously affected dentin. The hybrid layer was thinnest at the occlusal walls of the cavity where the dentinal tubules run parallel to the cavity surface. The bond strength of adhesive resin to these areas may differ from that to intact normal dentin.

Interfacial structure between dentin and seven dentin bonding systems revealed using argon ion beam etching.

The interfacial structure of seven dentin adhesive systems was studied morphologically. Argon ion beam etching of an undecalcified section clearly revealed the resin-impregnated demineralized dentin at the adhesive interface of the seven systems when observed under the scanning electron microscope.

Interfacial morphology of an adhesive composite resin and etched caries-affected dentin.

The interfacial structure between an adhesive composite resin and dentin after caries removal and acid conditioning was investigated. The hybrid layer between the adhesive resin and surface-demineralized dentin was found to be wider in the area of empty tubules compared with that of the occluded tubules, and was found to be the thinnest at the lateral walls of the cavity where the dentinal tubules run parallel to the cavity surface. Thus, the extent of demineralization by acid conditioning as well as impregnation of resin into the intertubular dentin forming the hybrid layer is probably related to the degree of closure and direction of the dentinal tubules.

Pulpal responses to various dentin bonding systems in dentin cavities.

The purpose of this study was to investigate pulpal response and bacterial invasion associated with five dentin bonding systems placed in cavities without an enamel margin. Two hundred and twenty-four dentin margin cavities were created by removing the surrounding marginal enamel of class V cavities in monkey teeth. These cavities were restored with a resin composite using various current dentin bonding systems. All of the dentin bonding systems showed odontoblastic layer changes to varying degrees, and slight to moderate inflammation at the initial stage. With the lapse of time, the degree of inflammation tended to decrease markedly, except for those cases in which bacteria were present. The result of SA/Photo Bond corresponded to that of the glass ionomer cement (negative control). Accordingly, this study suggests that a good bond and adaptation between resin and dentin should be obtained for eliminating pulpal irritation, even in the dentin cavity.

Pulpal response to a new light-cured composite placed in etched glass-ionomer lined cavities.

This study evaluated the pulp biocompatability of a new light-cured composite resin which was placed in etched glass-ionomer-lined cavities of monkey teeth. The pulpal response to this material was less than that to zinc-oxide eugenol cement in each observation period. Therefore this material seems to meet acceptable biocompatability standards in nonhuman primates.

[Finishing and polishing of composite resins. The experimentally designed silicone cup hards and their polishing ability].

To establish the most efficient polishing technique for composite resins, four kinds of silicone cup hards were experimentally designed, and the surface texture of two semihybrid composite resins polished with these experimental polishing tools were examined using a surface roughness recorder and by SEM. The individual silicone cup hard consisted of a hard rubber and silicone carbide abrasive particles being sized into #180 (P0), #360 (P2), #600 (P3), and #2500 (P4), respectively. Combination polishing with both P3 and P4, as well as from P0 through P4 in this order, efficiently created the smoothest surfaces for the semihybrid composite resins, which are generally considered to be hard to polish in the routine clinic.

[Establishment of a composite resin inlay technique. Part 1. The effects of various curing modes on mechanical properties of composite resins].

The effects of the curing mode on mechanical properties of composite resins were examined. Four resins as inlay, and three chemically-cured and five visible light-cured restorative resins were employed. The resin specimens were prepared by three kinds of curing modes; regular setting (according to the manufacturer's instruction), subsequently added light and heat curing after regular setting, and subsequently added heat and pressure curing after regular setting. Knoop hardness, flexure strength, compressive strength, and diametral tensile strength were determined. All restorative composites were remarkably increased in knoop hardness number due to the subsequently added curing methods. Both subsequently added curing methods provided higher flexure strength to all restorative resins, and particularly in the chemically-cured resins the flexure strength provided by the subsequently added light and heat curing was higher than those by the subsequently added heat and pressure curing. Compressive strength and diametral tensile strength were slightly increased by the subsequently added curing methods with the restorative resins. No correlation was found between the filler distribution and the mechanical properties provided by the subsequently added curing methods. The subsequently added heat curing seems to be preferable for creating higher mechanical properties of resins. The IC-2 resin, experimentally designed for resin inlay, seems to be the most promising resin for inlay restoration, based on the mechanical properties, and further detailed laboratory and clinical researches are required.