The Journal of Adhesive Dentistry, 05/2007

Purpose: To correlate the microtensile bond strength (µTBS) of dentin bonding agents to dentin for different hourglass designs with the stress distribution across the adhesive interface utilizing finite element stress analysis (FEA). Materials and Methods: Adper Scotchbond Multipurpose Plus dentin bonding agent was bonded to flat dentin surfaces in three experimental groups. A 5- to 6-mm layer of resin composite (Filtek Supreme, 3M ESPE) was built up incrementally. After 24 h water storage at 37°C, the bonded teeth were sectioned into hourglass designs of circular, parabolic, and spline shape, with a ca 1 mm2 cross-sectional area at the bonded interface (n = 30). The specimens were subjected to µTBS testing at a crosshead speed of 0.5 mm/min. The fracture surfaces were examined under SEM to determine the modes of failure. FEA models were constructed using the TOMECH program. A load of 100 N was applied and the stresses at the bonded interfaces were viewed using the FEMSYS visualization software. Results: One-way ANOVA, Tukey's and Kaplan-Meier tests revealed significant differences in the µTBS for the three designs: 36.7 ± 8.4, 21.4 ± 7.9 and 13.8 ± 4.3 MPa, for the circular, parabolic, and spline hourglass, respectively (p 0.05). FEA stress distribution data in the adhesive layer showed significant differences among the three designs, which is consistent with the bond strength values. The spline hourglass design showed a three-fold increase in the local stress concentration at its narrowest cross section. Conclusion: The specimen geometry greatly influences the measurement of the µTBS. The results are consistent with the FEA predictions. Keywords: microtensile bond strength, hourglass design, FEA, dentin bonding agents

Purpose: To evaluate the microtensile bond strength (µTBS) of two all-in-one self-etching adhesive systems and two selfetching adhesives with and without simulated hydrostatic pulpal pressure (PP). Materials and Methods: Flat coronal dentin surfaces of extracted human molars were prepared. Two all-in-one self-etching adhesive systems, One-Up Bond F (OBF; Tokuyama) and Clearfil S3 Bond (Tri-S, Kuraray Medical) and two self-etching primer adhesives, Clearfil Protect Bond (PB; Kuraray) and Clearfil SE Bond (SE; Kuraray) were applied to the dentin surfaces according to manufacturers' instructions under either a pulpal pressure (PP) of zero or 15 cm H2O. A hybrid resin composite (Clearfil AP-X, Kuraray) was used for the coronal buildup. Specimens bonded under PP were stored in water at 37°C under 15 cm H2O for 24 h. Specimens not bonded under PP were stored under a PP of zero. After storage, the bonded specimens were sectioned into slabs that were trimmed to hourglass-shaped specimens, and were subjected to microtensile bond testing (µTBS). The bond strength data were statistically analyzed using two-way ANOVA and the Holm-Sidak method for multiple comparison tests (α = 0.05). The surface area percentage of different failure modes for each material was also statistically analyzed with three one-way ANOVAs and Tukey's multiple comparison tests. Results: The µTBS of OBF and Tri-S fell significantly under PP. However, in the PB and SE bonded specimens under PP, there were no significant differences compared with the control groups without PP. Conclusions: The µTBS of the two all-in-one adhesive systems decreased when PP was applied. However, the µTBS of both self-etching primer adhesives did not decrease under PP. Keywords: dentin, pulpal pressure, all-in-one adhesives, microtensile bond strength

Purpose: This study evaluated the effect of surface conditioning methods and thermocycling on the bond strength between a resin composite and an indirect composite system in order to test the repair bond strength. Materials and Methods: Eighteen blocks (5 x 5 x 4 mm) of indirect resin composite (Sinfony) were fabricated according to the manufacturer's instructions. The specimens were randomly assigned to one of the following two treatment conditions (9 blocks per treatment): (1) 10% hydrofluoric acid (HF) for 90 s (Dentsply) + silanization, (2) silica coating with 30- Ìm SiOx particles (CoJet) + silanization. After surface conditioning, the bonding agent was applied (Adper Single Bond) and light polymerized. The composite resin (W3D Master) was condensed and polymerized incrementally to form a block. Following storage in distilled water at 37°C for 24 h, the indirect composite/resin blocks were sectioned in two axes (x and y) with a diamond disk under coolant irrigation to obtain nontrimmed specimens (sticks) with approximately 0.6 mm2 of bonding area. Twelve specimens were obtained per block (N = 216, n = 108 sticks). The specimens from each repaired block were again randomly divided into 2 groups and tested either after storage in water for 24 h or thermocycling (6000 cycles, 5°C to 55°C). The microtensile bond strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). The mean bond strengths of the specimens of each block were statistically analyzed using two-way ANOVA (α = 0.05). Results: Both surface conditioning (p = 0.0001) and storage conditions (p = 0.0001) had a significant effect on the results. After 24 h water storage, silica coating and silanization (method 2) showed significantly higher bond strength results (46.4 ± 13.8 MPa) than that of hydrofluoric acid etching and silanization (method 1) (35.8 ± 9.7 MPa) (p 0.001). After thermocycling, no significant difference was found between the mean bond strengths obtained with method 1 (34.1 ± 8.9 MPa) and method 2 (31.9 ± 7.9 MPa) (p > 0.05). Conclusion: Although after 24 h of testing, silica coating and silanization performed significantly better in resin-resin repair bond strength, both HF acid gel and silica coating followed by silanization revealed comparable bond strength results after thermocycling for 6000 times. Keywords: hydrofluoric acid, indirect composite, repair, silica coating, microtensile test

Purpose: The aim of the study was to examine the influence of dental ceramic translucency under different exposure conditions upon the polymerization rate of a dual-curing composite resin by measuring the depth of cure (DOC) and the Vickers microhardness (VHN). Materials and Methods: Three hundred twenty ceramic specimens (160 Empress 2, Ivoclar Vivadent, color 300, and 160 ProCAD, Ivoclar Vivadent, 300, Ι14; diameter 4 mm, height 1 mm or 2 mm) were inserted into steel molds and overlayed using a composite resin (Variolink II, Ivoclar Vivadent) with and without a self-curing catalyst. Specimens were cured either in contact with or at a 5-mm distance from a conventional halogen curing light (Elipar TriLight, 3M ESPE, exposure duration 40 s, standard mode) and a light-emitting diode (LED: Bluephase 16i, Ivoclar-Vivadent, exposure duration 20 s, high-power mode). DOC under the ceramic specimen was measured following ISO 4049:2000. The VHN of the resin composite was determined at 0.5 mm and 1.0 mm distance from the ceramic using a Vickers hardness tester. Statistical analysis was performed using the Mann-Whitney U-test (α = 0.05) and the error-rates method (ERM). Results: Higher translucency of the ceramic restoration resulted in higher DOC and VHN values, which were statistically significant for the halogen light source and in most cases for the LED groups. The use of a self-curing catalyst generally produced an increase in DOC and VHN data, with the exception of DOC data for the highly translucent ceramic and direct contact of the tip of the light source with the ceramic. No significant differences between VHN data of the highly translucent ceramic without catalyst and the opaque ceramic with catalyst were observed in 3 out of 4 pairwise comparisons and according to the ERM. Thus, there are indications that for a highly translucent ceramic with the LED unit tested the catalyst may be waived for a ceramic thickness up to 2 mm. Conclusions: There are indications that for a highly translucent ceramic with the LED unit tested, the catalyst may be omitted with a ceramic thickness up to 2 mm. High ceramic translucency improves polymerization of luting composite. Keywords: light curing, LED, ceramic, translucency, depth of cure, Vickers microhardness

Purpose: To evaluate in vitro the bond strength at the adhesive interface between a quartz fiber post, different adhesive systems, and different composite cements. Materials and Methods: Thirty extracted single-rooted teeth were endodontically treated and divided into three groups (n = 10). Quartz fiber posts (DT Light-Post) were cemented with the following materials: group I: Prime & Bond NT + Self Cure Activator, and Calibra as luting cement; group II: Prime & Bond NT + Self Cure Activator, and UniFil Core; group III: UniFil Bond in combination with Unifil Core. The specimens were processed for the push-out test to evaluate bond strength at the root dentin-cement-post interface. They were sectioned along the long axis of the post into 1-mm-thick slices. A total of 60 sections was obtained from group I. Group II provided 67 slices, while group III provided 69. Loading was performed at a crosshead speed of 0.5 mm/min until the post segment was dislodged from the root section. Results: There was no statistically significant difference between the three experimental groups. The mean bond strength obtained for group I was 9.81 ± 5.40 MPa. For group II it was 12.06 ± 6.25 MPa, and 9.80 ± 5.01 MPa for group III. Conclusion: All the materials tested were similar in terms of providing satisfactory bond strength when used for luting fiber posts. However, Unifil Core may be advantageous since it can also be used as a core buildup material, which simplifies the clinical procedures. Keywords: dental adhesives, resin cements, fiber posts, bond strength, push-out test

Purpose: To investigate longevity and reasons for failure of Class II posterior composite restorations (PCRs) placed with or without a lining of glass-ionomer cement. Materials and Methods: Four hundred fifty-eight Class II PCR placed in 248 patients (110 male, 138 female, age 18 to 80) by two dentists in a general practice between 1988 and 1997 were retrospectively examined from the patient files. The restorations were placed either with a total-etch technique or with a resin-modified glass-ionomer lining placed on the dentin. Items recorded were date of placement, date of last check-up visit, tooth number, and restored surfaces. Date of replacement and reason for failure of the PCR was recorded. A restoration was clinically acceptable when still in function and acceptable at the last check-up visit. Additionally, the caries risk for each patient was estimated by the treating clinician. Life tables and Kaplan-Meier curves were used to express survival rates. A Cox regression was applied to assess the influence of variables on survival. Results: Three hundred seventy-six total-etch PCRs and 82 PCRs with a lining were investigated. After 9 years, survival percentages of 88.1% for total-etch restorations and 70.5% for restorations with a resin-modified glass-ionomer lining were found. The most important reasons for failure were fracture and caries. Predominantly, failures started occurring after 3 to 4 years of clinical service. Results of the Cox regression show that the presence of a lining and high risk for caries significantly increased the failure rate of the restorations. Conclusion: PCRs placed with a resin-modified glass-ionomer lining clinically showed more frequent fractures than PCRs placed with a total-etch technique. Keywords: composite, glass ionomer, lining, longevity, clinical, Class II, restrospective, failure, sandwich

Purpose: The aim of this study was to compare postoperative sensitivity following placement of posterior composite restorations using the fast- or step-curing modes of an LED curing light. Materials and Methods: Thirty patients participated, with each having two homologous contralateral posterior teeth with Class II carious lesions. One restoration was cured using the fast-curing mode of the LED curing light (Mini LED), and the contralateral restoration cured using the step mode of the same curing light. The patients were contacted after 2 and 7 days postoperatively and asked about the presence or absence of sensitivity on a scale from 0 to 3. 0: no sensitivity, 1: slight sensitivity, 2: moderate sensitivity, and 3: severe sensitivity. If the patient experienced sensitivity at 7 days postoperatively, he/she was contacted again after 30 and 90 days. Results: There was a statistically significant difference in postoperative sensitivity between the two curing modes at days 2 and 7 postoperatively (p 0.05) but not at days 30 and 90 (p > 0.05). The intensity of sensitivity was also different between the two curing modes at days 2 and 7 postoperatively (p 0.05) but not at days 30 and 90 (p > 0.05). Conclusion: The step mode of the LED curing light reduced the incidence and severity of postoperative sensitivity following placement of posterior composite restorations compared to the fast mode of the same curing light. Keywords: clinical trial, resin composites, LED curing lights