The Journal of Adhesive Dentistry, 01/2008

Purpose: To evaluate how six different test parameters (TP) of the microtensile bond strength (µTBS) methodology influence the test outcome. Materials and Methods: The microtensile bond strength of adhesives bonded to dentin was measured, and the resultant failure patterns and stress-time graphs were analyzed, varying the µTBS specimen-fixation mode (TP1), the microspecimen geometry (TP2), the microspecimen bond surface area (TP3), the remaining dentin thickness of the microspecimens (TP4), the procedure employed to glue the microspecimen to the µTBS jig (TP5), and the µTBS crosshead speed (TP6). Results: The orientation of the microspecimens to the actual interface primarily influenced the resultant µTBS value and the eventual failure pattern. A notched jig consistently yielded significantly higher µTBS values than samples fixed onto a flat jig or following a "top-bottom" design (TP1). A higher bond strength, a lower standard deviation/coefficient of variation, a failure closer to the interface, and a more representative number of specimens per tooth were obtained for nontrimmed, square microspecimens (TP2). The most reproducible results were obtained using square specimens of 1 mm2 (TP3), which could also be most easily prepared. The remaining dentin thickness (TP4) was an influential factor as well, whereas the microspecimen gluing protocol (TP5) and the crosshead speed (TP6) appeared less influential. Conclusion: As several test parameters significantly influenced the µTBS outcome, sufficient attention should be paid to these methodology variables with regard to the µTBS-test reliability and reproducibility. Keywords: microtensile bond strength, test methodology, test parameters, bonding, dentin

Purpose: To evaluate the bond strength on different cavity walls of Class II preparations. Different bonding systems and the effect of thermomechanical cycling were investigated. Materials and Methods: Human third molars received MOD preparations with dentin margins. Teeth were randomly assigned to 18 groups (n = 5) according to the combination of cavity wall (axial, occlusal, and gingival), bonding system (Single Bond Plus, Clearfil SE Bond, and Adper Prompt) and the occurrence of thermomechanical cycling. Restorations were concluded with Filtek Z250 composite. Specimens were sectioned according to the respective cavity wall (4 slabs/restoration), and the adhesive interface was trimmed to an hourglass shape (1 mm2). Slabs were tested under tension, and failure mode was observed. Bond strength data were analyzed with three-way ANOVA/Tukey's test. Results: Single Bond Plus and Clearfil SE Bond performed similarly under most experimental conditions. Single Bond Plus presented similar bond strength on the three cavity walls, regardless of the aging condition. Clearfil SE Bond exhibited significant differences among cavity walls: the occlusal wall showed higher means in both aging conditions. Non-aged gingival walls and aged axial and gingival walls yielded lower means. Non-aged Adper Prompt produced similar bond strengths on the three cavity walls. After thermomechanical cycling, the gingival wall showed lower means. Conclusion: The effect of cavity walls was dependent on the bonding system and thermomechanical cycling. Adper Prompt demonstrated bond strengths lower than Single Bond Plus or Clearfil SE Bond under most experimental conditions. Keywords: dental adhesion, class II restoration, fatigue, thermal cycling, bond strength testing

Purpose: In light of the concept of minimally invasive dentistry, erbium lasers have been considered as an alternative technique to the use of diamond burs for cavity preparation. The purpose of this study was to assess the bonding effectiveness of adhesives to Er,Cr:YSGG laser-irradiated dentin using irradiation settings specific for cavity preparation. Materials and Methods: Fifty-four midcoronal dentin surfaces, obtained from sound human molars, were irradiated with an Er,Cr:YSGG laser or prepared with a diamond bur using a high-speed turbine. One etch-and-rinse (Optibond FL/Kerr) and three self-etching adhesives (Adper Prompt L-Pop/3M ESPE, Clearfil SE Bond/Kuraray, and Clearfil S3 Bond/Kuraray) were used to bond the composite to dentin. The microtensile bond strength (µTBS) was determined after 24 h of storage in water at 37°C. The Kruskal-Wallis test was used to determine pairwise statistical differences (p 0.05). Prepared dentin surfaces, adhesive interfaces, and failure patterns were analyzed using a stereomicroscope and Field-emission gun Scanning Electron Microscopy (Feg-SEM). Results: Significantly lower µTBS was observed to laser-irradiated than to bur-cut dentin (p 0.05), irrespective of the adhesive employed. Feg-SEM photomicrographs of lased dentin revealed an imbricate patterned substrate and the presence of microcracks at the dentin surface. Conclusion: Morphological alterations produced by Er,Cr:YSGG laser-irradiation adversely influence the bonding effectiveness of adhesives to dentin. Keywords: dentin, adhesion, adhesives, laser, Er, Cr:YSGG

Purpose: To investigate whether and to what extent the bonding capacity of one-step, self-etching adhesives is influenced by the degree to which solvent is evaporated. Materials and Methods: Seven one-step, self-etching adhesives were tested (Adper Prompt L-Pop, Clearfil S3 Bond, Futurabond NR, G-Bond, Hybrid Bond, iBond, Xeno III). The variation in degree of evaporation was obtained by varying the duration of the air-blowing step. The duration required to immobilize the adhesive layer, as established in a pilot study, was used as control. Two experimental air-blowing durations, shorter (half the control duration) and longer (double the control duration) than the control duration, were chosen. The resin composite Herculite XRV was bonded to flat human dentin surfaces treated with one of the adhesives following manufacturer's instructions, except for the air-blowing duration after application. After being stored in water at 37°C for 1 week, the bonded specimens were broken in shear. Failure modes were evaluated under stereomicroscope. Results: Air-blowing duration and brand of adhesive both had an effect on shear bond strength. An interaction was found between adhesive and air-blowing duration. Some adhesives were insensitive to variations in air-drying duration, but in general, air-blowing durations shorter than the control duration produced lower shear bond strengths. Significant effects of adhesive and air-blowing duration were also detected in relation to failure mode. More adhesive failures were observed with shorter air-blowing durations. A significant negative correlation between number of adhesive failures and bond strength was found. Conclusion: On the basis of this in vitro study, it may be concluded that the one-step, self-etching adhesives evaluated were sensitive to degree of evaporation of the solvents. Keywords: bond strength, composite resins, dental bonding, dentin-bonding agents, volatilization

Purpose: To evaluate preparation designs of compromised cusps and whether or not they influence masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial-coverage restorations (PCRs) luted on mandibular molars. Materials and Methods: Sixty-four caries-free molars were equally divided into four groups. Control group NP received no preparation (NP). Group B-IN received a basic inlay (IN) preparation with buccal (B) cusp conservation and occlusal reduction of both lingual cusps. Group B-ON was prepared in the same way, except buccal cusps were prepared with an angle of 45 degrees to the occlusal plane (buccal onlay). Group B-OV preparation was similar to group B-ON, but buccal cusps received a further shoulder preparation on the buccal aspect (buccal overlap). Forty-eight all-ceramic IPS e.max Press PCRs were fabricated and luted adhesively. Specimens underwent mouth-motion fatigue (1.2 million cycles, 1.6 Hz, 49 N) and 5500 thermal cycles (5°C/55°C). Fracture patterns were observed. Surviving specimens were loaded until fracture. Marginal discrepancies were examined. Results: Only one specimen of group B-ON fractured during fatigue. Median fracture loads (N) [IQR=x.25-x.75]: group NP = 1604 N [1182-1851 N], group B-IN = 1307 N [1262-1587N], group B-ON = 1396 N [817-1750N], group B-OV = 1205 N [1096-1542N]. No significant differences in fracture resistance were found between restored molars and unprepared teeth (p >= 0.18). Different preparation designs showed no significant influence on PCR fracture resistance. Mouth-motion fatigue caused a significanty decrease of marginal accuracy in groups B-IN (p = 0.009) and B-ON (p = 0.008). Marginal discrepancy values of groups B-IN and B-OV were significantly different after fatigue (p = 0.045). Conclusion: Ceramic coverage of compromised cusps did not demonstrate an increase of fracture resistance after fatigue when compared to less invasive partial-coverage restorations. However, enhanced exposure of restoration margins to occlusal wear could result in more extensive marginal discrepancies. Keywords: fracture resistance, marginal discrepancy, partial coverage restoration, ceramic, fatigue

Purpose: New methods are available for the rapid generation of 3-D finite element models of dental structures and restorations. Validation of these methods are required. The aim of the present study is to utilize stereolithography and surface-driven automatic meshing to generate models of specific restorative conditions, and to examine these models under loading. The data generated are compared to existing experimental data in an attempt to validate the model. Materials and Methods: An intact maxillary central incisor was digitized with a micro-CT scanner. Surface contours of enamel and dentin were fitted following tooth segmentation based on pixel density using an interactive medical image control system. Stereolithography (STL) files of enamel and dentin surfaces were then remeshed to reduce mesh density and imported in a rapid prototyping software, where Boolean operations were used to assure the interfacial mesh congruence (dentinoenamel junction) and simulate different tooth preparations (endodontic access, veneer, proximal, and Class III preparations) and restorations (Class III composites). The different parts were then imported in a finite element software package to create 3D solid models. A 50-N point load perpendicular to the tooth's long axis and centered on the incisal edge was applied either on the buccal or palatal surface. The surface strain was obtained from selected nodes corresponding to the location of the strain gauges in the validation experiments. Results: The increase in crown flexure (compared to the unaltered tooth) ranged from near zero values (conservative endodontic access, removal of proximal enamel) to ca 10% (aggressive endodontic access, conservative Class III preparations), 23% and 34% (moderate and aggressive Class III preparations, respectively), and 91% (veneer preparation). Placement of Class III composite resin restorations resulted in 85% recovery of the original crown stiffness. 3D FEA data correlated well with existing experimental data. In two situations, smaller FEA strains were recorded compared to the experimental strains, perhaps due to enamel cracking under the strain gauges. This artefact was not simulated by the FEA models. Conclusion: Experimental data validated the FEA models. The described method can generate detailed three-dimensional finite element models of a maxillary central incisor with different cavities and restorative materials. This method is rapid and can readily be used for other medical (and dental) applications. Keywords: finite element analysis, anterior tooth, flexure, resin composite restoration, stiffness, veneer

Purpose: To evaluate the influence of surface treatments on microtensile bond strength of luting resin cements to fiber posts. Materials and Methods: Forty-two quartz fiber posts (Light Post, RTD) were divided into 7 groups (n = 6) according to the surface treatment. I and II: experimental patented industrial treatment consisting of zirconium oxide coating and silanization (RTD); III: industrial treatment followed by adhesive application (XPBond, Dentsply Caulk); IV: adhesive (XPBond); V: adhesive (Prime&Bond NT, Dentsply Caulk); VI: silane (Calibra Silane, Dentsply Caulk); VII: no treatment. Adhesives were used in the self-curing mode. Two cements (Sealbond, RTD - group I, and Calibra, Dentsply Caulk - groups II to VII) were applied on the posts to produce cylindrical specimens. Post/cement interfaces were evaluated under SEM. The surface of the industrially coated posts was examined using energy dispersive analysis by x-ray. Cylinders were cut to obtain microtensile sticks that were loaded in tension at a crosshead speed of 0.5 mm/min until failure. Statistical analysis was performed using Kruskal-Wallis analysis of variance followed by Dunn's multiple range test for post-hoc comparisons (p 0.05). Weibull analysis was also performed. Results: The post/cement bond strength was significantly higher on fiber posts treated industrially (I: 23.14 ± 8.05 MPa; II: 21.56 ± 7.07 MPa; III: 22.37 ± 7.00 MPa) or treated with XPBond adhesive (IV: 21.03 ± 5.34 MPa) when compared to Prime&Bond NT application (V: 14.05 ± 5.06 MPa), silanization (VI: 6.31 ± 4.60 MPa) or no treatment (VII: 4.62 ± 4.31) of conventional fiber posts (p 0.001). Conclusion: The experimental industrial surface treatment and the adhesive application enhanced fiber post to resin cement interfacial strength. Industrial pretreatment may simplify the clinical luting procedure. Keywords: fiber posts, resin cement, microtensile bond strength, surface treatment, zirconium oxide coating

Rehabilitation of masticatory ability in patients with reduced periodontal tissue support is a multiple challenge in dentistry. It has been shown that tooth mobility is reduced by a splint in place. Splints may be constructed of various materials. Development of fiber-reinforced composite materials offers a new and conservative approach for tooth replacement and stabilization. This case report describes the rehabilitation and 2-year follow-up of a patient with advanced periodontal problems by using a glass fiber-reinforced composite resin material. Keywords: mobility, periodontal problem, fiber-reinforced composite resin splints