The Journal of Adhesive Dentistry, 03/2015

Purpose: To determine if sealing dentin caries with a resin-modified glass ionomer (RMGI) decreases the number of viable microorganisms and demineralization depth, using an experimental dentin caries model of biofilms of Streptococcus mutans (S. mutans). Materials and Methods: Dentin caries lesions were created over a 15-day period on bovine dentin slabs with biofilms of S. mutans UA159. Once lesions were formed, biofilms were removed and the slabs were randomly allocated to one of the treatment groups: group A, surface sealed with a RMGI; or group B, unsealed slabs (control). At 5, 10, and 15 days, slabs were longitudinally sectioned to analyze the number of infiltrating viable bacteria by culturing on agar plates and demineralization depth by cross-sectional Knoop microhardness. Results: Dentin lesions sealed with RMGI decreased bacterial counts from the infected dentin, both with respect to baseline counts and also relative to the unsealed control (p 0.05). Consistently, demineralization depth was lower for sealed lesions when compared with unsealed slabs (p 0.05) at all analyzed timepoints. Conclusions: Sealing dentin lesions with RMGI appears to halt lesion progression in this experimental model by reducing bacterial viability. Keywords: tooth demineralization, dental caries, microbial viability, glass-ionomer cements, resin-modified glass ionomer, Streptococcus mutans, root caries, aging

Purpose: To study the biomechanical behavior of extensively restored premolars by determining the effect of the composite type, presence of cusp weakening, and compressive loading on the cusp deformation (CD), marginal integrity (MI), and fracture resistance (FR) of directly restored premolars. Materials and Methods: Forty premolars received Class II mesio-occlusal-distal (MOD) cavities and were divided into 4 groups (n = 10) in accordance with the two study variables: composite type (conventional: Filtek Z250 XT [Z250], 3M ESPE; low shrinkage: Venus Diamond [VD], Heraeus-Kulzer) and the presence of cusp weakening (with/without). Cusp deformation upon restoration was assessed using strain gauges during the restorative procedure and thereafter when the restorations were subjected to an occlusal load of 100 N. The samples were subjected to thermal and mechanical cycling. Epoxy resin replicas of the proximal tooth/restoration interfaces were made to analyze the marginal integrity (MI) using scanning electron microscopy. To determine the fracture resistance (FR), the teeth were loaded at a crosshead speed of 0.5 mm/min until fracture. Results: The conventional composite Z250 had higher CD, lower MI, and lower FR than the low-shrinkage composite VD. Cusp weakening had no influence on CD, but MI and FR decreased. Conclusion: The low-shrinkage composite VD performed better in restoring extensively destroyed premolars than did Z250. Keywords: composite, premolar, shrinkage stress, cusp deformation, marginal integrity, fracture resistance

Purpose: This study compared the dentin collagen cross-linking potential of carbodiimide (EDC) prepared in three most commonly used solvents in dental adhesive systems: water, ethanol, and acetone. Materials and Methods: Thirty-eight extracted caries-free human permanent molars were used in this study. Demineralized dentin beams were prepared and cross linked by 0.3 M EDC in water, acetone, or ethanol. The modulus of elasticity of demineralized dentin, the resistance of dentin matrix to enzymatic degradation, the swelling ratio, and the mass change of demineralized dentin matrix were examined to compare the cross-linking efficacy of EDC in their respective solvents. Results: The modulus of elasticity of demineralized dentin cross linked by EDC in acetone was significantly higher (p 0.05) than demineralized dentin cross linked by EDC in ethanol and EDC in water. Furthermore, the ultimate tensile strength of demineralized dentin cross linked by EDC in water and ethanol dropped significantly following enzymatic degradation, while the ultimate tensile strength of demineralized dentin cross linked by EDC in acetone was preserved. The swelling ratio of demineralized dentin cross linked by EDC in acetone and ethanol was significantly lower (p 0.05) than that of demineralized dentin cross linked by EDC in water. Conversely, the mass change of demineralized dentin cross linked by EDC in acetone was significantly higher (p 0.05) than demineralized dentin cross linked by EDC in water and EDC in ethanol. Conclusion: The dentin collagen cross-linking potential of EDC could be enhanced by using acetone as a solvent. Keywords: carbodiimide, cross linking, collagen, dentin, solvents

Purpose: To determine the influence of atmospheric pressure plasma (APP) treatment on the microtensile dentin bond strength of two self-etching adhesive systems after one year of water storage as well as observe the contact angle changes of dentin treated with plasma and the micromorphology of resin/dentin interfaces using SEM. Materials and Methods: For contact angle measurements, 6 human molars were sectioned to remove the occlusal enamel surface, embedded in PMMA resin, and ground to expose a flat dentin surface. Teeth were divided into two groups: 1) argon APP treatment for 30 s, and 2) blown air (control). For the microtensile test, 28 human third molars were used and prepared similarly to contact angle measurements. Teeth were randomly divided into 4 groups (n = 7) according to two self-etching adhesives and APP treatment (with/without). After making the composite resin buildup, teeth were sectioned perpendicular to the bonded interface to obtain beam specimens. The specimens were tested after 24 h and one year of water storage until failure. Bond strength data were analyzed by three-way ANOVA and Tukey's post-hoc test (α = 0.05%). Three beam specimens per group that were not used in the bond strength test were prepared for interfacial SEM analysis. Results: APP application decreased the contact angle, but increased the bond strength only for one adhesive tested. SEM evaluation found signs of degradation within interfacial structures following 1-year aging in water. APP increased the dentin surface energy, but the effects of APP and 1-year water storage on dentin bond strength were product dependent. Conclusion: APP increased the dentin surface energy. It also increased the bond strength for Scotchbond Universal, but storage for one year negated the positive effect of APP treatment. Keywords: plasma, microtensile, dentin adhesion

Purpose: To evaluate the effect of different mechanical pre-treatments on the bond durability to dental zirconia. Materials and Methods: Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were randomly assigned to one of 4 groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al2O3 (Danville), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) and (4) SilJet (Danville). The zirconia specimens were additionally pre-treated chemically using a 10-MDP/silane ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake). Two identically pre-treated zirconia blocks were bonded together using resin-composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass shape and stored in distilled water (7 days, 37°C), after which they were randomly tested as is or subjected to additional mechanical aging involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the microtensile bond strength was determined and SEM fractographic analysis performed. Results: Weibull analysis revealed the highest Weibull scale and shape parameters when zirconia was tribochemically silica sandblasted using either CoJet or SilJet. The Weibull shape parameter of Al2O3-sandblasted zirconia was significantly reduced upon mechanical aging, but not when zirconia was tribochemically silica sandblasted. Conclusion: The mechanical surface pre-treatment of zirconia using tribochemical silica sandblasting (CoJet, SilJet) resulted in the most favorable bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging. Keywords: zirconia, bond strength, tribochemical silica sandblasting, silane, composite cement, aging

Purpose: To evaluate the hardness of a dual-curing self-adhesive resin cement (RelyX U200) and a conventional dual-curing resin cement (RelyX ARC) cured with different light curing units of different wavelengths (Elipar Freelight 2 LED [430 to 480 nm, conventional], Bluephase LED [380 to 515 nm, polywave], AccuCure 3000 Laser [488 nm]) by means of the nanoindentation test. Materials and Methods: Bovine incisors were cleaned and then sectioned at the cementoenamel junction to remove the crown. After embedding in acrylic, dentin surfaces of the specimens were exposed and ground flat to standardize the surfaces. To simulate clinically placing indirect restorations, ceramic (IPS e.maxPress/Ivoclar Vivadent) or indirect composite resin (SR Adoro/Ivoclar Vivadent) slabs were cemented on dentin surfaces. The specimens were sectioned longitudinally at low speed under constant irrigation and then polished. In the positive control group, the cement was light cured without the interposition of indirect restorative material; in the negative control group, after the indirect restorative material was cemented, no light curing was performed, allowing only chemical polymerization of the cement. All specimens were stored in distilled water at 37°C for 7 days. Nanoindentadion hardness of the cement layer was measured under a 100-mN load. Data were statistically analyzed using ANOVA and Tukey's test (p 0.05). Results: Although the self-adhesive cement is technically simple, conventional cement showed the best polymerization performance. The polywave LED technology did not differ significantly from other light-curing units. The hardness of the resin cements evaluated was negatively influenced by the interposition of an indirect restorative material; only the LEDs were able to maintain the same degree of cement polymerization when an indirect restorative material was used. Conclusion: The photoactivation step is required during the cementation of indirect restorations to ensure adequate polymerization of dual-curing resin cements. Keywords: self-adhesive resin cement, hardness, nanoindentation, polymerization

Purpose: To investigate the influence of relative humidity and application time on bond strength to dentin of different classes of adhesive systems. Materials and Methods: A total of 360 extracted human molars were ground to mid-coronal dentin. The dentin specimens were treated with one of six adhesive systems (Syntac Classic, OptiBond FL, Clearfil SE Bond, AdheSE, Xeno Select, or Scotchbond Universal), and resin composite (Filtek Z250) was applied to the treated dentin surface under four experimental conditions (45% relative humidity/application time according to manufacturers' instructions; 45% relative humidity/reduced application time; 85% relative humidity/application time according to manufacturers' instructions; 85% relative humidity/reduced application time). After storage (37°C, 100% humidity, 24 h), shear bond strength (SBS) was measured and data analyzed with nonparametric ANOVA followed by Kruskal-Wallis tests and Mann-Whitney U-tests with Bonferroni-Holm correction for multiple testing (level of significance: α = 0.05). Results: Increased relative humidity and reduced application time had no effect on SBS for Clearfil SE Bond and Scotchbond Universal (p = 1.00). For Syntac Classic, OptiBond FL, AdheSE, and Xeno Select there was no effect on SBS of reduced application time of the adhesive system (p ≥ 0.403). However, increased relative humidity significantly reduced SBS for Syntac Classic, OptiBond FL, and Xeno Select irrespective of application time (p ≤ 0.003), whereas for AdheSE, increased relative humidity significantly reduced SBS at recommended application time only (p = 0.002). Conclusion: Generally, increased relative humidity had a detrimental effect on SBS to dentin, but reduced application time had no effect. Keywords: adhesion, adhesive treatment, dentin bonding, working time, moisture

Purpose: This study investigated the effect of diamond bur grit size on the repair bond strength of fresh and aged resin composites. Materials and Methods: Blocks of microhybrid composite (Opallis, FGM) were stored in distilled water at 37°C for 24 h (fresh composite) or subjected to 5000 thermal cycles (aged composite). The surfaces were roughened using diamond-coated, flame-shaped carbide burs with medium grit (#3168), fine grit (#3168F), or extra-fine grit (#3168FF). The control group underwent no surface treatment. Surface roughness, water contact angle, and surface topography by scanning electron microscopy (SEM) were evaluated (n = 3). Samples were restored with resin composite and sectioned into beam-shaped specimens, which were subjected to microtensile bond testing. Failure modes were classified using a stereomicroscope. Data were statistically analyzed using the Student- Newman-Keuls test and two-way ANOVA, with significance set at p 0.05. Results: Higher surface roughness was observed for groups treated with the medium- and fine-grit burs; aged composites were rougher than fresh composites. The water contact angle formed on the aged composite was lower than that on the fresh composite. The highest repair bond strength was observed for the fine-grit bur group, and the lowest was recorded for control. Interfacial failures were more predominant. SEM images showed that the surfaces treated with fine- and extra-fine-grit burs had a more irregular topography. Conclusion: Surface roughening of fresh or aged resin composites with diamond burs improved retention of the repair material. Fine-grit burs generally performed better than medium- and extra-fine-grit burs. Keywords: bonding, resin-based restoratives, SEM, surface roughness, surface treatments, wettability

Purpose: To assess the influence of simulated pulpal pressure (SPP) on the microtensile bond strength (μTBS) of four simplified luting strategies to indirect composite restorations. Materials and Methods: Dentin disks from 40 human molars were prepared and treated with 4 different techniques: (1) SB+ARC: two-step etch-and-rinse adhesive + conventional dual-curing resin cement (Adper Single Bond 2 + RelyX ARC, 3M ESPE); (2) ED+PAN: self-etching primer + conventional dual-curing resin cement (ED Primer + Panavia F2.0, Kuraray Medical); (3) S3+PAN: one-step self-etching adhesive (Clearfil S3, Kuraray) + Panavia F2.0; (4) U200: self-adhesive resin cement (RelyX U200, 3M ESPE). Pre-made indirect composite restorations (Filtek Z100, 3M ESPE) were luted onto the specimens. The luted specimens were cut into resin-dentin beams and the μTBS was tested after two different aging regimes: water storage at 37°C for one week (control) or three months under 20 cm H2O simulated pulpal pressure (SPP). The μTBS data was analyzed with two-way ANOVA and Tukey's test (p 0.05). Results: SB+ARC showed significantly higher μTBS after both aging regimes (p 0.001). The statistically significantly lowest μTBS was measured for control S3+PAN and U200 after 3 months SPP (p 0.001). S3+PAN was the only group not negatively affected by SPP (p = 0.699). Conclusions: Two-step etch-and-rinse adhesives associated with dual-curing conventional resin cements may achieve the highest μTBS, even after 3 months of SPP. The one-step self-etching adhesive along with the dualcuring conventional resin cement was able to maintain bond stability. Keywords: luting cements, simulated pulpal pressure, microtensile bond strength

Purpose: This study evaluated the long-term shear bond strength between an indirect composite material and a zirconia framework coated with silica-based ceramics, taking the effect of different primers into account. Materials and Methods: A total of 165 airborne-particle abraded zirconia disks were subjected to one of three pretreatments: no pretreatment (ZR-AB), airborne-particle abrasion of zirconia coated with feldspathic porcelain (ZR-PO-AB), and 9.5% hydrofluoric acid etching of zirconia coated with feldspathic porcelain (ZR-PO-HF). An indirect composite material (Estenia C&B) was then bonded to the zirconia disks after they were treated with one of the following primers: Clearfil Photo Bond (CPB), Clearfil Photo Bond with Clearfil Porcelain Bond Activator (CPB + Activator), Estenia Opaque Primer (EOP), Porcelain Liner M Liquid B (PLB), or no priming (CON, control group). Shear bond strength was tested after 100,000 thermocycles, and the data were analyzed using the Steel-Dwass U-test (α = 0.05). Results: For ZR-PO-AB and ZR-PO-HF specimens, bond strength was highest in the CPB+Activator group (25.8 MPa and 22.4 MPa, respectively). Bond strengths were significantly lower for ZR-AB specimens in the CON and PLB groups and for ZR-PO-AB specimens in the CON, CPB, and EOP groups. Conclusion: Combined application of a hydrophobic phosphate monomer (MDP) and silane coupling agent enhanced the long-term bond strength of indirect composite material to a zirconia coated with silica-based ceramics. Keywords: bond strength, coating, indirect composite, priming agent, zirconia

Purpose: In the present case series, the authors report on seven cases of erosively worn dentitions (98 posterior teeth) which were treated with direct resin composite. Materials and Methods: In all cases, both arches were restored by using the so-called stamp technique. All patients were treated with standardized materials and protocols. Prior to treatment, a waxup was made on die-cast models to build up the loss of occlusion as well as ensure the optimal future anatomy and function of the eroded teeth to be restored. During treatment, teeth were restored by using templates of silicone (ie, two "stamps," one on the vestibular, one on the oral aspect of each tooth), which were filled with resin composite in order to transfer the planned, future restoration (ie, in the shape of the waxup) from the extra- to the intraoral situation. Baseline examinations were performed in all patients after treatment, and photographs as well as radiographs were taken. To evaluate the outcome, the modified United States Public Health Service criteria (USPHS) were used. Results: The patients were re-assessed after a mean observation time of 40 months (40.8 ± 7.2 months). The overall outcome of the restorations was good, and almost exclusively "Alpha" scores were given. Only the marginal integrity and the anatomical form received a "Charlie" score (10.2%) in two cases. Conclusion: Direct resin composite restorations made with the stamp technique are a valuable treatment option for restoring erosively worn dentitions. Keywords: noninvasive technique, restoration, erosion, abrasion, annual failure rate, direct resin composite