The Journal of Adhesive Dentistry, 03/2004

The aim of the present study was to evaluate the deproteination potential of 5% aqueous NaOCl solution applied by rubbing action on the molecular composition and morphology of smear-layer covered and acid-etched human coronal dentin surfaces. Paired specimens (n = 4 x 2 per group) of acid-etched (Group A) and smear-layer covered (Group B) human coronal dentin surfaces were sequentially treated with the NaOCl solution for time intervals ranging from 5 s to 120 s and analyzed by reflectance FTIR microspectroscopy and tapping mode atomic force microscopy. The changes in the mineral (v4 P-O stretching vibrations) to matrix (C = O stretching vibrations of amide I) peak area ratios and in the Ra roughness parameter were used to quantify the effect of treatment. Two-way ANOVA and Dunn's tests were used to assess the differences within each group and between groups (a = 0.05). In both groups, NaOCl treatment reduced organic matrix (amide I, II, III peaks), but did not affect carbonates and phosphates. In group A, the rate of deproteination was slow, and reached a peak value after 120 s. Tubule orifices became visible after 40 s of treatment; after 120 s, excessive porosity was detected, with Ra values presenting no statistically significant difference from group B. In group B after 10 s, the extent of deproteination was enhanced, reaching a plateau between 30 s and 60 s, and attaining a maximum after 120 s. Tubule diameter, intertubular porosity, and Ra were increased; intertubular dentin area was reduced. For both groups after 40 s of treatment, the mineral to matrix ratio recorded was similar to smear-layer-free sectioned dentin. The results of the present study imply that deproteination of mineralized or acid-etched dentin surfaces within a clinically relevant time frame may provide methods for bonding to dentin alternative to conventional technique-sensitive dentin hybridization. Keywords: dentin, sodium hypochlorite, FTIR, AFM, deproteination

To observe the ultrastructure of the dentin-adhesive interface after in vitro sequential challenge by acidic and basic chemicals around adhesive restorations. Box-shaped cavities were prepared in bovine root dentin and restored as follows: Reactmer Bond and Reactmer Paste (RB/RP), Clearfil SE Bond and Clearfil AP-X (SE/APX), ABF (experimental) and APX (ABF/APX), Single Bond and APX (SB/APX). After the specimens were stored in water for 1 week, the integrity of the bonds tested by sequential immersion were placed in an artificial demineralizing solution (pH 4.5) for 20 min and in 5% NaOCl for 20 min. The specimens were sectioned, polished, then argon-ion etched for 7 min, and gold sputter coated for SEM examination of the dentin-adhesive interface. The morphological results indicated tight bonding between the cavity wall dentin and the adhesive. For the fluoride-releasing restoration, RB/RP, a thick acid-resistant zone was clearly observed adjacent to the restoration; however, the bonding resin, RB, was partially degraded by the acid-base challenge. For SE/APX, ABF/APX and SB/APX, the bonding resins were resistant to the acid-base challenge. With the self-etching adhesive systems, SE and ABF, a thin band of acid-base resistant dentin less than 1 µm thick was observed beneath the hybrid layer. With the wet bonding system, SB, the hybrid layer was partially degraded by the acid-base challenge. SEM observation is useful for observing the reactions of adhesives to acid-base challenge. Prevention of secondary caries around a restoration may be influenced by the physical properties of the restorative and adhesive materials, quality of the hybrid layer, and fluoride-release. Keywords: hybrid layer, secondary caries, dentin bonding, SEM

The purpose of this study was to evaluate the effect of mechanical load cycling and tubule orientation on the ultimate tensile strength of crown and root dentin. Twenty bovine teeth were cleaned and their incisal surfaces reduced, resulting in a flat surface 4 mm above the cementoenamel junction. The teeth were divided into 4 groups: G1 = control (no mechanical load cycling); G2 = 1,000,000 load cycles at 50 N; G3 = 1,000,000 load cycles at 100 N; G4 = 1,000,000 load cycles at 200 N. Sections of 0.5 ± 0.1 mm thick were cut mesiodistally and the slabs further trimmed to 0.5 ± 0.1 mm in an hourglass shape, according to the tubule orientation (parallel and/or perpendicular to the long axis of the tooth) in the root and crown, with a fine diamond bur to produce a cross-sectional surface area of 0.25 mm2. All specimens were then subjected to ultimate tensile strength testing at a crosshead speed of 1 mm/min. Means and standard deviations were expressed in MPa. The bond strength data were analyzed with three-way ANOVA and Fisher's PLSD test (p 0.05). Ultimate tensile strength values did not differ statistically significantly between the loaded group and the control. However, statistical differences existed between root and coronal dentin (p 0.001) and between parallel and perpendicular orientation of tubules (p 0.001), where root and sections parallel to the tubules presented higher values than coronal and perpendicular, respectively. These differences were not related to mechanical loading. There was no effect of in vitro load cycling on ultimate tensile strength of dentin. Differences presented between ultimate tensile strength of crown vs root dentin and parallel vs perpendicular to the tubule orientation can be influenced by differences in the amount of organic and inorganic content as well as composition of the dentin matrix. It is important to consider these aspects when predicting the quality and durability of restorations according to the types of dentin and tubule orientation to be restored. Keywords: dentin, tubule orientation, mechanical load cycling, ultimate tensile strength

To compare the microtensile bond strength (µTBS) of five adhesives to human dentin prepared with 600-grit SiC abrasive paper (SiC), a diamond rotary instrument, or a carbide bur. The null hypothesis was that different cavity preparation instruments do not affect adhesion of resin adhesives. Human molars (n = 45) were randomly divided into three groups according to surface treatment. Each group was bonded using a total-etch adhesive (Single Bond, 3M ESPE), one of three self-etching primer systems (Clearfil SE Bond or ABF, Kuraray; Imperva Fluorobond, Shofu), or a self-etching adhesive (One-Up Bond F, Tokuyama). A 4-mm composite crown was built over the bonded surface. Specimens were stored in water for 24 h at 37°C. They were sectioned into 0.7-mm-thick slabs, trimmed to a cross-sectional area of 1 mm2, and loaded to failure at a crosshead speed of 1 mm/min using a tabletop tester (EZ-Test, Shimadzu). Microtensile bond strength data were analyzed using analysis of variance and Fisher's PLSD test. Surface preparation using a carbide bur generally yielded higher bond strengths than preparation using either a diamond rotary instrument or SiC abrasive paper. SE Bond had the highest mean µTBS of the five adhesives tested. Resin-dentin bond strengths can be affected by the type of instrument used to prepare the tooth. Specifically, higher bond strengths might be achieved by using carbide burs rather than diamond cutting instruments. Keywords: adhesion, dentin bonding, burs, self-etching primers, smear layer

To evaluate the effect of nonvital bleaching on the shear bond strength of composite resin using three adhesive systems. Two hundred seventy bovine teeth were assigned to 3 groups (n = 90): SP, paste of sodium perborate and water; CP, 37% carbamide peroxide; CO, control group (no treatment). After the bleaching treatment, the teeth in each group were cut into enamel (E) and dentin (D) sections. The teeth were embedded in polyester resin and polished in order to obtain a flat E or D surface. Each group was divided into 6 subgroups (n = 15) according to substrate (E and D) and adhesive system: SB, Single Bond (solvent: water/alcohol); PB, Prime & Bond NT (solvent: acetone); CLF, Clearfil SE Bond (solvent: water). The adhesive system was applied on each flat surface according to the manufacturer's instructions and a cylinder of composite resin Z-250 was overlaid. The specimens were stored in distilled water for 7 days at 37°C. The SBS test was performed in a universal testing machine with crosshead speed of 0.5 mm/min. The data obtained (in MPa) were statistically analyzed with two-way ANOVA and Tukey's test (p = 0.05). The bleaching treatment influenced the SBS, regardless of the adhesive system used. On enamel, the SP and CP bleaching treatments reduced the SBS values. On dentin, the SP bleaching agent reduced the SBS values, but the CP bleaching did not. Nonvital bleaching treatment with sodium perborate may adversely affect shear bond strength of composite resin for both enamel and dentin. Similar effects can be expected from 37% carbamide peroxide bleaching agent on enamel but not dentin bonding strength. The use of water/alcohol and acetone-based adhesive systems cannot reverse the effects of bleaching treatments on bond strengths. Keywords: bleaching agent, bond strength, adhesive system

To evaluate the effects of 1) wall grinding status, 2) thermal stress, and 3) time of polishing on sealing performance of two one-step bonding systems in cervical cavities. Semicircular cavities with dimensions of 3 x 3 x 1.5 mm were prepared along the CEJ of extracted human premolars. In experiment 1, the cavity walls were additionally ground with round steel diamond burs (regularly ground) or finished with superfine diamond burs. The cavities were treated with AQ Bond (AQ) or One-up Bond F (OB) and filled with a resin composite. Then thermocycling (5°C to 55°C, 1000 x) was performed. In experiment 2, the regularly ground cavities were used. After restoration, the teeth were subjected to thermocycling (1,000 to 5,000 x). In experiment 3, the restorations in the regularly ground cavities were polished immediately or 24 h after filling. No thermocycling was carried out in this group. All specimens were immersed in a dye solution for 2 h. Microleakage at coronal and apical walls was evaluated on the longitudinal sections of the restorations. For OB, the cavities finished with superfine burs exhibited more microleakage at the coronal wall than the regularly ground cavity (p 0.05). The leakage at the coronal walls increased with the number of thermal cycles for both systems (p 0.05). The delayed polishing generated better adaptation at the apical wall of AQ and at the coronal wall of OB (p 0.05). Grinding status, thermocycling, and time of polishing had influences on the sealing performance of the two one-step adhesive systems. Keywords: microleakage, one-step adhesives, cavity adaptation

To evaluate the effect of thermal and mechanical cycling on the degree and pattern of nanoleakage on cervical margins of Class II restorations. Forty box-type Class II cavities were prepared on bovine incisors. The cavities were restored with Single Bond and Z-250 composite resin (3M-ESPE) according to manufacturer's instructions. The teeth were randomly assigned to 4 groups: G1, control; G2, thermal cycling (2000 cycles, 5 to 55°C); G3, mechanical load cycling (100,000 cycles, 50 N); G4, thermal and mechanical load cycling group (2000 cycles 5 to 5°C/100,000 cycles, 50 N). The specimens were then sealed leaving a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for 24 h, and exposed to a photodeveloping solution for 8 h. Specimens were sectioned longitudinally, embedded in epoxy resin, polished and mounted on stubs, gold sputter coated, and examined under SEM using backscattered electron mode. Silver particle penetration length was measured directly on the SEM monitor and calculated as the percentage of the total length of cut dentin surface that was penetrated by silver nitrate. The data were analyzed with ANOVA and Fisher's PLSD test (p 0.05). The degree of nanoleakage significantly increased when thermal and mechanical cycling was performed on the same specimens, as compared to the other groups (p 0.05). No differences were observed between the control, thermal cycling, and mechanical cycling groups. No difference in nanoleakage pattern was observed between the groups. Thermal and mechanical cycling combined adversely affected nanoleakage values. Simulation of the oral condition might be crucial to better evaluate and understand the performance of adhesive materials. Keywords: thermal cycling, mechanical load cycling, nanoleakage, dentin, Class II restoration

To analyze the influence of two placement techniques and two adhesive systems on the marginal microleakage of Class II resin-based composite restorations using different resin composite materials. Two hundred standardized Class II cavities (5 mm x 3 mm x 1.5 mm) were cut in human premolars and restored using five resin composite materials (A.L.E.R.T.-AL, Solitaire-SO, SureFil-SU, Filtek A110-A, and Z100-Z), two adhesive systems (Bond 1-B1 and Etch & Prime 3.0-EP), and two placement techniques (incremental or bulk). Specimens were thermocycled (700 cycles, 5° - 55°C, 1 min dwell time), immersed in 0.5% methylene blue solution for 4 h, and sectioned longitudinally to evaluate the extent of microleakage. Data were submitted to statistical analysis using the Kruskal-Wallis test. It was observed that both adhesive systems presented similar results (p > 0.05), and neither achieved complete marginal sealing. The bulk placement technique led to greater microleakage than the incremental technique (p 0.001). Restorations prepared using SO resin composite showed greater microleakage than those performed using Z or AL materials. However, SO obtained similar values of microleakage when compared to SU and A materials. The use of incremental placement technique resulted in less microleakage for Class II resin-based composite restorations. No difference was observed among adhesive systems regarding prevention of marginal dye penetration. Furthermore, the type of resin composite material employed for restoration may have an influence on the extent of microleakage. Keywords: dental materials, resin composite, adhesives, microleakage

To evaluate the influence of the light intensity, irradiation time, and thickness of the indirect restoration composite on the bond strength of dual-cured resin cement immediately after cementation, applying the resin coating technique. Three hundred forty composite blocks as an adhesive surface and four thicknesses of indirect restoration composite disks were prepared. The surface of the composite blocks was coated with low-viscosity resin composite and immersed in water for 24 h. After immersion, dual-cured resin cement was applied to the resin-coated surface and the indirect restoration composite disks were placed on it. Light irradiation was performed through four thicknesses of indirect restoration composite disks with conventional halogen (40 s) and high intensity (10, 20, 40 s) light units. The specimens were stored in water at 37°C for 10 min or 24 h, and the tensile bond test was performed. For the 1-mm composite thickness, there were no significant differences in the bond strengths between 10 min and 24 h after cementation with the four light curing methods. For the composite thicknesses of 3 or 4 mm, the bond strength 24 h after cementation was significantly higher than that at 10 min after cementation with conventional halogen (40 s) and high-intensity light units at 10 s and 20 s, but there was no significant difference with the high-intensity light unit applied for 40 s. The bond strength of dual-cured resin cement immediately after cementation could be greatly influenced by the irradiation time and the light intensity penetrating the indirect restoration composite. Keywords: light intensity, resin cement, tensile bond test, resin coating

Using extended, standardized MOD preparations, it was the aim of this in vitro study to examine the performance of CAD/CAM ceramic inlays in comparison to composite inlays after mechanical and thermal fatigue loading in terms of marginal quality and stabilization of the remaining tooth structure. Standardized cavities with different wall thicknesses were prepared in 90 extracted premolars; 10 additional premolars remained untreated. Composite inlays (Tetric) and CAD/CAM restorations (Cerec II; Vita Mark II) were adhesively placed in the cavities. After loading in a chewing simulator, quantitative and qualitative marginal gap examinations were conducted and fracture resistance determined. The results show that ceramic inlays provide significantly greater stabilization and better marginal quality than do composite inlays. Chairside-fabricated ceramic inlays inserted using adhesive technology are able to stabilize weakened cusps. In the case of very thin remaining walls (about 1.3 mm), however, the marginal quality and the cusp-stabilizing effect are also reduced. Keywords: CAD/CAM, ceramic, composite, fracture resistance

The quality of fillings consisting of a hybrid composite was compared with fillings consisting of two different microfilled composites in a clinical examination. Within the design of a clinically controlled two-year study conducted under practice-relevant conditions, the composites C-Fill MH (Megadenta), Helio Progress (Vivadent), and Visio-Dispers (ESPE) were examined in anterior-tooth cavities in 134 patients by means of the split-mouth technique. The clinical examinations were performed based on modified Ryge criteria (marginal integrity, anatomical form, secondary caries, color, marginal discoloration, surface roughness) after 12 and 24 months. Immediately following filling application, all evaluation criteria except color were assessed as level A. After 12 and 24 months, C-Fill MH was found to be significantly superior to the other materials with regard to marginal integrity, color, and marginal discoloration. The hybrid composite C-Fill MH seems to be superior to the microfilled composites and should therefore be preferred as a restorative filling material. Keywords: Ryge criterion, clinical investigation, microfilled composite, hybrid composite, longitudinal study