Effect of 4-META on microtensile bond strength of cements to ceramics.

Background: This study assessed the effect of different concentrations of 4-methacryloyloxyethy trimellitate anhydride (4-META) added to silane on microtensile bond strength (µTBS) of light-cure and dual-cure resin cement to hybrid and zirconia-reinforced lithium silicate ceramics. Materials and Methods: This in vitro, experimental study was conducted on 32 Celtra Duo and 32 VITA Enamic ceramics bonded to Allcem Veneer light-cure and Allcem dual-cure resin cements using silane impregnated with 4-META in 0%, 2.5%, 5%, and 10 wt% concentrations in 16 groups (n = 4). The µTBS of specimens was measured by a universal testing machine and analyzed by the Kruskal-Wallis and Mann-Whitney tests, and the mode of failure was determined under a stereomicroscope and analyzed by the Chi-square test (alpha = 0.05). Results: The lowest mean µTBS was recorded in the Enamic ceramic group with 4-META (0%) bonded to dual-cure cement (14.26 MPa), and the highest mean µTBS was recorded in Enamic ceramic with 4-META (10%) bonded to light-cure cement (18.59 MPa) (P < 0.001). The µTBS of Celtra Duo was significantly higher than that of Enamic in bonding to light-cure cement using 4-META (2.5%) (P = 0.003). All failures (100%) were adhesive in most groups. The frequency of adhesive failure was the lowest (90%) in Celtra Duo bonded to dual-cure cement with 4-META (5%). Conclusion: According to the results of this pilot study, the addition of 4-META (10%) to silane caused a significant improvement in µTBS to light-cure cement. The addition of 4-META in all concentrations significantly improved the µTBS to Enamic ceramic in the use of dual-cure cement; however, it had no significant effect on µTBS of Celtra Duo. Nonetheless, the results should be interpreted with caution due to the relatively small sample size.

Antimicrobial effect of different physical and chemical compounds of zinc oxide and graphene oxide added to composite resins.

Background: Graphene oxide (GO), a product of graphite, is a candidate for nano-reinforcing cement-based materials due to its good water dispersibility and excellent mechanical properties. On the other hand, zinc oxide (ZnO) is well-known for its antibacterial characteristics as well. Therefore, we aimed to evaluate the impacts of adding ZnO and GO nanoparticles on the antibacterial properties of flowable composites. Materials and Methods: In this, in vitro experimental study was designated into five groups containing: (1) no nanoparticles as control group, (2) 1 wt.% ZnO nanoparticle, (3) 1 wt.% GO, (4) 1 wt.% physical compound of ZnO and GO, and (5) 1 wt.% chemical compound of ZnO and GO. The antibacterial properties of composite resin discs were evaluated by direct contact test. Data were analyzed using a one-way analysis of variance, followed by Tukey' post hoc tests (P = 0.05). Results: Streptococcus mutans colony counting in the first 24 h showed the least growth rate in the chemical compound group (2.2 × 10[5]). However, in 7 days, the least colony number was observed in the GO group (2 × 10[3]). Moreover, the physical compound showed the least bacterial adhesion. Conclusion: Adding GO alone to composites, compared to adding ZnO or physical and chemical compounds of GO-ZnO, was more helpful to increase the antimicrobial characteristics.

Oral mucosa and Streptococcus mutans count in the saliva. Does graphene oxide nanoparticle mouthwash have a good effect?

BACKGROUND: This study aimed to assess the effect of graphene oxide (GO) nanoparticles mouthwash on oral mucosa, Streptococcus mutans (S. mutans) count in the saliva of rats, and human enamel surface microhardness, in comparison with fluoride mouthwash. METHODS: This study was conducted in two phases namely an animal study, and an in vitro experimental study. GO mouthwash (0.005%), sodium fluoride (NaF) mouthwash (0.05%), and a combination of both (0.05% NaF-0.005% GO) were prepared. The oral cavity of 36 rats was inoculated with S. mutans, and they were randomly divided into 4 groups according to the type of mouthwash. The control group received saline mouthwash. Fourteen days after using the mouthwashes, all rats were sacrificed, and the salivary S. mutans count was measured. The buccal and tongue mucosa were also histologically examined for the type and severity of inflammation, number of blood vessels, epithelial thickness, and epithelial keratinization. For microhardness testing, 40 sound extracted human premolars were randomly assigned to four groups (n=10) of culture medium with S. mutans and different mouthwashes. The enamel microhardness was measured at 7 and 14 days, and compared with the baseline value. RESULTS: The mean S. mutans count in the saliva of rats in GO and NaF-GO groups was significantly lower than that in other groups (p<0.001). Enamel microhardness in NaF and NaF-GO groups significantly increased at 7 and 14 days, compared with baseline. CONCLUSION: Addition of GO nanoparticles improved the antibacterial properties without causing adverse mucosal effects such as ulceration, acute inflammation or atrophy of the epithelium of the oral mucosa, but had no effect on surface hardness of the enamel.

Effect of Hydrofluoric Acid Surface Treatments on Surface Roughness and Three-Point Flexural Strength of Suprinity Ceramic.

OBJECTIVES: This study aimed to evaluate the effects of hydrofluoric acid (HF) concentration and etching time on the surface roughness (SR) and three-point flexural strength of Suprinity and to analyze the surface elements before and after etching. MATERIALS AND METHODS: To measure the SR, 70 specimens of Suprinity (2×4×5mm3) were assigned to seven groups (n=10). Six groups were etched for 20, 60, and 120 seconds with 5% and 10% HF and 7th group was the control group. Specimens were evaluated using atomic force microscopy (AFM). One specimen from each group was used to analyze the surface elements using scanning electron microscopy (SEM). For measuring the three-point flexural strength, 60 specimens were divided into six groups (n=10) and etched as previously described. The flexural strength was measured using a universal testing machine. T-test, one-way analysis of variance (ANOVA), and two-way ANOVA were used for statistical analyses (P<0.05). RESULTS: The 10% concentration of HF caused higher SR compared to the 5% HF. The effect of HF concentration on the flexural strength was significantly different in the 20- and 60-second etching groups. Different etching times had no significantly different effect on the SR. With 5% HF, the flexural strength was significantly higher for 20-second etching time than for the etching times of 60 and 120 seconds. With 10% HF, there was a significant difference in flexural strength between etching times of 20 and 120 seconds. The atomic percentage (at%) of silica was enhanced by increasing the etching time. CONCLUSION: The best surface etching protocol comprises 10% HF used for 20 seconds.

The effect of office bleaching on the color and bond strength of resin restorations.

BACKGROUND: Bleaching may affect the bond strength of existing composite fillings and may weaken it. Hence, the aim of this study was to find the best method of in-office bleaching with the least effect on microshear bond strength (MSBS) of existing composite resin fillings to tooth structure. MATERIALS AND METHODS: In this in vitro study, Class V cavities were prepared on buccal surface of 50 extracted third human sound molars. The cavities in 25 teeth had enamel axial walls, Group E, which were divided into five subgroups of E1 through E5 and in 25 teeth had dentin axial walls, Group D, which were divided into five subgroups of D1 through D5. Cavities were treated with Single Bond 2 adhesive system and restored with composite resin (Z250). The corresponding subgroups received similar bleaching methods and materials; 1 - not bleached, 2 - hydrogen peroxide (HP) 25%, 3 - HP + ultraviolet light, 4 - HP + light-emitting diode-curing device, and 5 - HP + diode laser. Teeth colors were monitored before and after bleaching, and MSBS test and failure modes were examined. Results were analyzed with one-way ANOVA and Kruskal-Wallis tests. P < 0.05 was considered significant. RESULTS: One-way ANOVA did not show differences in MSBS of enamel subgroups but showed significant differences in dentin subgroups (P < 0.00). Adhesive fracture in all of the subgroups was the most frequent mode of failure. Kruskal-Wallis test showed that laser was the most effective instrument to change ΔE. CONCLUSION: Diode laser was the best method for tooth bleaching because lowering the shear bond strength between composite resin and enamel was minimum and also had the most ΔE in tooth bleaching.

Light transmittance of CAD/CAM ceramics with different shades and thicknesses and microhardness of the underlying light-cured resin cement.

OBJECTIVES: The aim of this in vitro study was to evaluate the effects of the thickness and shade of 3 types of computer-aided design/computer-aided manufacturing (CAD/CAM) materials. MATERIALS AND METHODS: A total of 120 specimens of 2 shades (A1 and A3) and 2 thicknesses (1 and 2 mm) were fabricated using VITA Mark II (VM; VITA Zahnfabrik), IPS e.max CAD (IE; IvoclarVivadent), and VITA Suprinity (VS; VITA Zahnfabrik) (n = 10 per subgroup). The amount of light transmission through the ceramic specimens was measured by a radiometer (Optilux, Kerr). Light-cured resin cement samples (Choice 2, Bisco) were fabricated in a Teflon mold and activated through the various ceramics with different shades and thicknesses using an LED unit (Bluephase, IvoclarVivadent). In the control group, the resin cement sample was directly light-cured without any ceramic. Vickers microhardness indentations were made on the resin surfaces (KoopaPazhoohesh) after 24 hours of dark storage in a 37°C incubator. Data were analyzed using analysis of variance followed by the Tukey post hoc test (α = 0.05). RESULTS: Ceramic thickness and shade had significant effects on light transmission and the microhardness of all specimens (p < 0.05). The mean values of light transmittance and microhardness of the resin cement in the VM group were significantly higher than those observed in the IE and VS groups. The lowest microhardness was observed in the VS group, due to the lowest level of light transmission (p < 0.05). CONCLUSION: Greater thickness and darker shades of the 3 types of CAD/CAM ceramics significantly decreased the microhardness of the underlying resin cement.

Effect of hydrofluoric acid surface treatments on micro-shear bond strength of CAD/CAM ceramics.

INTRODUCTION: Dental ceramics are appreciated as highly esthetic restorative materials that can simulate the appearance of natural dentition better than other materials. The aim of this study was to evaluate the effect of hydrofluoric acid concentration and etching time on micro-shear bond strength (µSBS) to IPS e.max CAD and Vita Mark II of a dual cured resin cement (Panavia F2.0). METHODS: This study was an experimental in vitro study, performed in the dental material research center of Babol University of Medical Sciences in 2016. Two hydrofluoric acid concentrations (5% and 10%) and three different etching times (20, 60 and 120 seconds) were used to etch the specimens respectively. A silane coupling agent (Clearfil porcelain activator) and priming and bonding agent (Clearfil SE bond) were used on the etched surfaces in accordance to the manufacturer's instructions of use. Then resin cement was applied on the prepared ceramic surfaces and light cured. µSBS between resin cement and the porcelains were measured with a universal testing machine. Mode of failure was observed with 40× magnification by means of a Stereo microscope. Data were analyzed with ANOVA and independent-samples t-test and Chi-square tests. RESULTS: In both e.max and Vita Mark II groups, µSBS were not significantly different when different etching times (one-way ANOVA) and HF acid concentrations (Independent-samples t-test) were used (p>0.05), but the highest µSBS was shown in e.max specimens etched 60 s with 5% HF and Vita Mark II specimens etched 20 s with 10% HF. µSBS of e.max was significantly higher than Vita Mark II (p=0.00). CONCLUSION: Best surface treatment for e.max and Vita Mark II ceramics is 20 s etch using 5 % hydrofluoric acid.

An In Vitro Comparison of the Bond Strength of Composite to Superficial and Deep Dentin, Treated With Er:YAG Laser Irradiation or Acid-Etching.

Introduction: The aim of this study was to compare the micro-shear bond strength of composite resin on superficial and deep dentin after conditioning with phosphoric acid and Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser. Methods: Thirty human molars were selected, roots were removed and crowns were bisected to provide a total of 60 half-crowns. Specimens were ground to expose superficial and deep dentin. Samples were assigned to six groups: (1) AS (acid etching of superficial dentin); (2) AD (acid etching of deep dentin); (3) LS (Er:YAG laser irradiation on superficial dentin); (4) LD (Er:YAG laser irradiation on deep dentin); (5) LAS (Er:YAG laser irradiation on superficial dentin followed by acid etching); (6) LAD (Er:YAG laser irradiation on deep dentin followed by acid etching) The adhesive protocol was performed. Samples were thermocycled and micro-shear bond strength was tested to failure. The data were submitted to statistical analysis with one-way analysis of variance (ANOVA) and Tukey post hoc test. Results: The AS group, demonstrated the greatest amount of micro-shear bond strength. Statistical analysis showed a decrease in bond strength in laser-treated groups which was more significant for deep dentin. Conclusion: Preparation of dentin with laser did not improve bonding to superficial and deep dentin.

Effect of different surface treatments on microtensile bond strength of two resin cements to aged simulated composite core materials.

OBJECTIVE: Roughening of the aged composite resin core (CRC) surface seems essential for durable adhesion. The aim of this study was to investigate the influence of various surface treatments and different resin cements on microtensile bond strength (µ TBS) between two aged core build-up composites (CBCs) and feldspathic ceramic. MATERIALS AND METHODS: A total of 16 composite blocks made of two CBCs, Core.it and Build-it were randomly assigned to four surface treatment groups after water storage and thermocycling (2 weeks and 500 cycles). Experimental groups included surface roughening with air abrasion (AA), hydrofluoric acid, pumice, and laser and then were bonded to computer-aided design/computer-aided manufacturing feldspathic ceramic blocks using two resin cements, Panavia F2 (PF), and Duo-link (DL). The µ TBS was tested, and the fracture mode was assessed. The data were analyzed with multiple analysis of variance to estimate the contribution of different surface treatments, resin cements, and two aged CRCs on µ TBS. Statistical significance level was set at α < 0.05. RESULTS: Surface treatment and cement type significantly affected bond strength (P < 0.001) but the type of CRC did not (P = 0.468). Between roughening methods, the highest and the lowest values of µ TBS were sequentially obtained in AA and Er.YAG laser groups. The highest bond strength was in AA group cemented with PF (31.83 MPa). The most common failure mode was cohesive fracture in the cement. CONCLUSION: Different surface treatments had different effects on µ TBS of aged CRCs to feldspathic ceramics. PF was significantly better than DL.

Experimental study of iron and multivitamin drops on enamel microhardness of primary tooth.

OBJECTIVES: Iron and multivitamin drops are being frequently prescribed in children less than 2 years of age. Due to their low pH levels, these drops may lead to the softening of enamel and accelerate the destructive process. The aim of the present study was to investigate the enamel microhardness of primary teeth after exposing them to iron and multivitamin drops. MATERIALS AND METHODS: Forty healthy anterior teeth were randomly divided into four groups of 10 samples each. Samples were exposed to two iron drops of Kharazmi (Iran) and Ironorm (UK) and two multivitamin drops of Shahdarou (Iran) and Eurovit (Germany) for 5 min. The surface microhardness was measured before and after exposure and data processing was done using statistical paired t-test and analysis of variance (ANOVA) test. The surface structure of the teeth was examined by scanning electron microscope (SEM). RESULTS: In all groups, microhardness was decreased, but it was not significant in Eurovit multivitamin group (P = 0.088). The reduction rate in Kharazmi iron group was significant compared to that in other groups (P < 0.005). Hardness reduction percent for Kharazmi iron drop was 28/12 ± 47/43. In SEM analysis, irregular granular appearance was observed in the enamel exposed to Kharazmi iron drop. CONCLUSION: The results showed that all the studied drugs have the potential to cause erosion; this potential is the most in Kharazmi iron drop and the least in Eurovit multivitamin drops. Therefore, after using these kinds of drops, preventive measures should be used in children.

Effect of fluoride-free and fluoridated carbamide peroxide gels on the hardness and surface roughness of aesthetic restorative materials.

BACKGROUND: Bleaching products may show some side effects on soft and hard tissues and restorative materials in the oral cavity. This study evaluated the effect of carbamide peroxide gel with and without fluoride ions on the microhardness and surface roughness of tooth-colored restorative materials. MATERIALS AND METHODS: In this in-vitro study, 76 cubic specimens (4 mm3 × 4 mm3 × 3 mm3) were fabricated from 4 aesthetic A3-shade restorative materials. These materials consisted of two composite resins and two glass ionomers. The specimens made from each material were treated with the following surface treatments: 1. CONTROL GROUP: The specimens were not bleached and were stored in normal saline. Group 2. Fluoridated 20% carbamide peroxide gel, treated 3 h a day for 4 weeks. Group 3. Treated 1 h a day with fluoride-less 22% carbamide peroxide for two weeks. From each group, three other specimens were selected to be evaluated in terms of changes in surface roughness, under scanning electron microscopy (SEM). RESULTS: In this study, fluoridated 20% carbamide peroxide gel increased the microhardness of the four aesthetic restorative materials. The fluoride-free carbamide peroxide 22% reduced the microhardness of the four used materials, which this change was significant for Vitremer and Amelogen. SEM analyses showed changes in surface roughness of glass ionomer specimens. CONCLUSION: The effect of bleaching on the microhardness of restorative materials is material dependent. Before the application of bleaching systems on the glass ionomer materials, the application of a protective barrier should be considered.