Comparative evaluation of marginal adaptation and microleakage of low-shrinking composites after thermocycling and mechanical loading

AIMS

The aim of this study was to evaluate and correlate marginal adaptation and microleakage of different low-shrinking composites.

MATERIALS AND METHODS

Standardized class V cavities (n = 20/group) with occlusal margin in enamel and gingival margin in dentin were restored with low-shrinking silorane-based (Filtek Silorane) or methacrylate-based (Clearfil Majesty Posterior, Grandio, Reflexions XLS, Tetric EvoCeram, Premise, Ceram-X Duo, Aelite LS Posterior) composites and a conventional composite (Filtek Z250). All teeth were stored in water (24 h), thermocycled (5000×), and mechanically loaded (60,000×). Marginal adaptation of epoxy resin replicas was analyzed using scanning electron microscope. Microleakage of the restoration was assessed by dye penetration on sectioned specimens under stereomicroscopy. Data were statistically analyzed with Mann-Whitney U test, with a significance of P < 0.05. Pearson's correlation test was used to evaluate the correlation between results of margin analysis and microleakage.

RESULTS

No statistical difference in marginal gap formation was determined between Filtek Silorane and Z250. The lowest microleakage score at dentin margins was recorded for Filtek Silorane, which was not significantly different from that of all other groups. No similar ranking between the results of microleakage at enamel and dentin margins was observed for the materials tested. Marginal adaptation was not correlated to microleakage, except for Filtek Silorane, Grandio, and Filtek Z250.

CONCLUSIONS

Compared to the conventional composite Filtek Z250, Filtek Silorane demonstrated no improvements with reduced marginal gap formation. Low-shrinking properties of composites appear to have no ability of sealing restoration margins and preventing leakage.

Comparison of Er,Cr:YSGG Laser Handpieces for Class II Preparation and Microleakage of Silorane- or Methacrylate-Based Composite Restorations

OBJECTIVE

The aim of this study was to evaluate the influence of cavity preparation with different Er,Cr:YSGG laser handpieces on microleakage of different posterior composite restorations.

METHODS

Fifty-four extracted intact human premolars were randomly assigned to three groups according to cavity preparation method: Bur Group: high-speed diamond bur (Diatech), MD Group: Er,Cr:YSGG laser Waterlase MD handpiece (Biolase Millennium II), and Turbo Group: Er,Cr:YSGG laser Waterlase MD TURBO handpiece (Biolase Millennium II). One hundred eight Class II slot cavities were prepared on the mesial and distal proximal surfaces of each tooth, and the cavity preparation times required were determined. The groups were then subdivided according to the restorative systems used (n = 12): a conventional methacrylate-based microhybrid composite (Filtek P60+Adper Single Bond 2/3M); a silorane-based resin composite (Filtek Silorane+Silorane System Adhesive/3M); and a nanohybrid methacrylate-based composite (Kalore+G-Bond/GC). The restorative systems were applied according to the manufacturers' recommendations. Following thermocycling (X5000; 5°C-55°C), the teeth were coated with nail varnish except the restoration margins, immersed in 0.5% basic fuchsin dye solution, and sectioned in a mesiodistal direction. Dye penetration was evaluated under a light microscope for occlusal and cervical margins. Data were analyzed with one-way ANOVA and chi-square tests (p < 0.05).

RESULTS

The cavity preparation time (mean ± SD) required for Bur, MD, and Turbo group was 31.25 ± 3.82, 222.94 ± 15.85, and 92.5 ± 7.42 sec, respectively, and the differences among the groups were statistically significant (p < 0.05). Comparing the occlusal and cervical microleakage scores, no statistically significant differences were found among the groups and subgroups (p > 0.05).

CONCLUSIONS

Er;Cr:YSGG laser cavity preparation with the Turbo handpiece needed shorter time than the MD handpiece, although it needed longer time than the conventional diamond bur. The use of different handpieces of Er,Cr:YSGG laser did not differ from conventional preparation with diamond bur in terms of microleakage with the tested methacrylate- and silorane-based posterior composite restorative systems.

The effect of home bleaching carbamide peroxide concentration on the microhardness of dental composite resins

Bleaching is a conservative treatment for discolored teeth, but the effect of this treatment on newer, silorane-based composite resins is unclear. This study evaluated the effect of at-home bleaching on the microhardness of methacrylate- and silorane-based composites. Forty blocks each of a methacrylate-based composite and a silorane-based composite were prepared. The 80 specimens were tested in 8 groups (n = 10): 2 composites, each exposed to 3 different carbamide peroxide concentrations (10%, 16%, or 22%) as well as distilled water (control). The surface of the test specimens was covered daily with the bleaching gel at room temperature for the time period recommended by the manufacturer for each carbamide peroxide concentration. A Vickers hardness testing machine was used with a 100-g load for 20 seconds to register specimen microhardness prior to and after 2 weeks of bleaching. The load was applied at 3 points, and the mean microhardness was calculated. Repeated-measures analysis of variance, paired t test, and Tukey test were used to analyze the data. All bleaching concentrations significantly decreased the microhardness of the methacrylate-based composite resin groups, while microhardness was significantly increased in the silorane-based composite resin groups. There was no evident difference in effects among the different gel concentrations (P > 0.05).

Silorane-based Composite Resin Restorations Are Not Better than Conventional Composites - A Meta-Analysis of Clinical Studies

PURPOSE

To perform a systematic review of the clinical performance of a low polymerization shrinkage, siloranebased composite (SBC) compared with a methacrylate-based composite (MBC) in posterior restorations.

MATERIALS AND METHODS

Electronic databases were searched: PubMed, Scopus, Bireme, Science Direct, Web of Science, ClinicalTrials.gov and OpenGrey. The search strategy included MeSH terms, synonyms and keywords with no language or date restrictions. Reference lists of eligible studies were cross checked in an attempt to identify additional studies. Based on the PICOS strategy, only randomized clinical trials (RCTs) were included. The risk of bias in the included studies was assessed and classified through the Cochrane Collaboration common scheme for bias. Two meta-analyses were performed using RevMan software, one with all 11 studies and another that included only studies with over 24 months of follow-up, for the main parameters analyzed.

RESULTS

A total of 544 studies were identified. After removing duplicates and examinating titles and abstracts, 17 texts were selected and read in full. Six of them were excluded, so the final sample of this systematic review included 11 studies. Six of the 11 studies were classified as having a "low risk of bias" and five were "unclear". The heterogeneity (I²) in all parameters was not significant. The exclusion of studies with less than 24 months of follow- up did not change the final result of the meta-analysis: both SBC and MBC have satisfactory and statistically similar clinical performances.

CONCLUSION

Low polymerization shrinkage is not the principal factor that determines the superiority of a resin.

[Aging of silorane- and methacrylate-based composite resins: effects on color and translucency]

OBJECTIVE

To evaluate the color stability and translucency of silorane-based low shrinkage composite after in vitro aging procedures of thermal cycling and water storage respectively, and to compare with those of conventional methacrylate-based posterior composite.

METHODS

Three light-cured composite resins, dimethacrylate-based composite A (Filtek™ Z350), B (Filtek™ P60) and silorane-based composite C (Filtek™ P90), were tested in this study. Ten specimens (10 mm in diameter, 1 mm in height) of each composite were prepared. The ten specimens in each group were then divided into two subgroups (n = 5). One subgroup underwent thermal cycling [(5.0 ± 0.5)~(55.0 ± 1.0) °C, 10 000 cycles] and the other was stored in 37 C° distilled water for 180 days. With a spectrophotometer, the CIE L * a * b * parameters of the specimens were tested before and after artificial aging against white, medium grey and black backgrounds, respectively. △E, TP and △TP were calculated and data were analyzed using independent-samples t test and partial analysis (P < 0.05).

RESULTS

With regard to color stability, silorane-based composite showed color alteration above the clinically acceptable levels (△E > 3.3), and also showed higher △E with a statistically significant difference in comparison with the other composites (B and C) (P < 0.05) after artificial aging. With regard to translucency, composite C showed more alteration compared with composite B (P < 0.05) after thermal cycling.

CONCLUSIONS

It may be concluded that the silorane-based composite underwent greater alteration with regard to color stability and translucency.

Effect of Selective Etch on the Bond Strength of Composite to Enamel Using a Silorane Adhesive

An improvement in bond strength to enamel has been demonstrated with the use of phosphoric acid prior to bonding with self-etch methacrylate-based adhesive agents. No research has evaluated the effect of phosphoric-acid etching of enamel with a newer self-etch silorane adhesive. The purpose of this study was to evaluate the shear-bond strength of composite to enamel using the self-etch silorane adhesive compared to other self-etching methacrylate-based adhesives, with or without a separate application of phosphoric acid. Bovine incisors were sectioned using a diamond saw and mounted in plastic pipe. The bonding agents were applied to flattened enamel surfaces with or without the application of 35% phosphoric acid. The bonded tooth specimens were inserted beneath a mold, and composite was placed incrementally and light cured. The specimens were stored for 24 hours and six months in water and tested in shear. Data were analyzed with a three-way analysis of variance (ANOVA) to evaluate the effects of surface treatment, adhesive agent, or time on the bond strength of composite to bovine enamel (α=0.05). Significant differences were found between the groups based on surface treatment (p<0.01) or adhesive agent (p<0.01), but not on time (p=0.19), with no significant interactions (p>0.14). Phosphoric-acid etching of bovine enamel significantly increased the bond strength of the self-etch methacrylate and the silorane adhesives. The methacrylate-based adhesives had significantly greater bond strength to enamel than the silorane adhesive.

Bonding durability of silorane and methacrylate-based resins to enamel

AIM

Few studies compared the silorane and mechacrylate based resins bonded to enamel. The aim of this study was to evaluate the bonding durability of silorane and methacrylate-based resins to enamel.

METHODS

Twenty seven molars were divided into G1 Clearfil SE Bond/Filtek Z350; G2 Adper Easy One/Filtek Z350; and G3 P90 Adhesive System/Filtek P90 groups. Following application of adhesive systems, blocks of composites were built, samples were stored in water (24 hours/37 ºC), sectioned (0.8 mm²) and tested in tensile (24 hours and 6 months). Fractures were observed (40×). Bond strength (in MPa) was analysed by MANOVA General Linear Model and Tukey's post-hoc test at 5%. The power test was calculated. The etching pattern was observed.

RESULTS

There were differences for material (P=0.029), storage time (P=0.012) and their interaction (P=0.000). Similar bond strengths were found at 24 h for all. The bond strength of G1 decreased after 6 months. At 6 months, G2 showed higher bond strength than G1 and G3, that were similar. The power-test value was 0.87. Mixed fractures and enamel rods were observed.

CONCLUSION

Bond strength varied over time depending on the restorative system.

[Microtensile strength of composite-composite bonding: an in vitro study]

OBJECTIVE

To investigate the bonding strength of different resin composites.

METHODS

Methacrylate-based resin APX and silorane-based resin composite P90 were chosen in this study, with their corresponding adhesives Clearfil SE Bond (SE) and Filtek P90 System Adhesive (SA). The specimens were divided into three groups: (1) bulk group, filling each block with the same composite, then curing; (2) direct filling group, curing and polishing one composite, then filling a new composite directly; (3) bonding group, after curing and polishing one composite, conditioning the surface with adhesives, then filling a new composite. Cut each resin blocks into 1 mm×1 mm×14 mm each piece, detecting the microtensile strength, and analyzing by One-Way ANOVA and LSD.

RESULTS

(1) The microtensile strength of the bulk group was the highest. (2) In direct filling group, the microtensile strength of 4 subgroups showed no statistical significance with each other but lower than that of the bulk group. (3) In bonding group, the microtensile strength of repairing with APX was higher than that with P90. When repairing with same composite, the microtensile strength was higher if the resin type of substrates was same with restorations than that was different. The microtensile strength of adhesives SE was higher than that of SA. (4) The sorting of the microtensile strength: bulk>SE bonding APX>SA bonding APX>SE bonding P90=direct filling>SA bonding P90.

CONCLUSION

Retention force is higher when substrates are repaired with Methacrylate-based resins and corresponding adhesives. Retention force is lower when repaired with silorane-based composites and corresponding adhesives. Types of the substrate composites show no influence on the bonding strength.

Wear and surface roughness of silorane composites after pH cycling and toothbrushing abrasion

PURPOSE

To evaluate the effects of toothbrushing abrasion associated with pH cycling on the surface roughness and wear of methacrylate- and silorane-based resin composites.

METHODS

Microhybrid methacrylate-based (Filtek Z250), nanofilled methacrylate-based (Filtek Supreme Ultra) and microhybrid silorane-based (Filtek LS) composites were selected for this investigation. For each composite, two groups (n = 10) of rectangular specimens were made. The initial roughness (Ra) of all of the groups was evaluated based on the average of three random tracings with a profilometer, and each specimen had half of its surface protected with two layers of nail varnish to serve as controls. Half of the specimens of each resin were submitted to pH cycling, while the other half were stored in deionized water for 14 days. Subsequently, 100,000 strokes of simulated toothbrushing were performed. Final roughness and wear were measured with the same profilometer, and the values were submitted to ANOVA, Student's t-test and Tukey's test (P < 0.05).

RESULTS

The data revealed an increase in surface roughness for Filtek Z250 and Filtek Supreme Ultra after toothbrushing, while Filtek LS showed the opposite behavior. Methacrylate-based composites presented lower wear values [Z250 (4.19 ± 1.73 μm); Supreme Ultra (4.16 ± 0.95 μm)], while the silorane-based composite presented increased surface roughness (11.51 ± 5.69 μm), particularly when submitted to pH cycling (15.31 ± 5.41 μm). Despite the good properties of silorane-based composites, particularly its smooth surface roughness even after pH cycling and toothbrushing abrasion, this composite still presented increased wear, which is an important issue for the development of new resin compositions.

The effect of surface treatment and bonding procedures on the bond strength of silorane composite repairs

OBJECTIVE

The aim of this study was to evaluate the effect of surface treatments and adhesive protocols on the microtensile bond strength of a low-shrinkage composite repair.

MATERIALS AND METHODS

Ninety-six blocks of composite resin Filtek LS were prepared using a half-hourglass-shaped silicone matrix. The specimens were storage for 24 h in distilled water and were randomly divided into the experimental (6) and negative control (2) groups (n = 12) according to the surface treatment (diamond bur and aluminum oxide sandblasting) and adhesive protocol (none; Filtek LS adhesive; phosphoric acid + Filtek LS adhesive; and phosphoric acid + silane + Filtek LS adhesive). After the adhesive procedure, the specimens were fixed in an hourglass-shaped silicone matrix and the other half of the specimen was restored. Hourglass shaped specimens (n = 12) were used as positive control (cohesive strength of the resin). The microtensile bonding test was performed at a crosshead speed of 0.5 mm/min. The data were analyzed using ANOVA, Tukey's and Dunnett's tests (α = 0.05).

RESULTS

The bond strength values were similar for all experimental groups, except the groups without adhesive application. None of the experimental groups presented results similar to the positive control group.

CONCLUSIONS

The repair of silorane restorations is viable; nevertheless, the different bonding procedures tested were incapable to produce bond strengths similar to the cohesive strength of the material.

Microtensile bond strength of methacrylate and silorane resins to enamel and dentin

The aim of this study was to evaluate the microtensile bond strength (µTBS) of two substrates (enamel and dentin) considering two study factors: type of composite resin [methacrylate-based (Filtek Supreme) or silorane-based (Filtek LS)] and aging time (24 h or 3 months). Twenty human molars were selected and divided into 2 groups (n=10) considering two dental substrates, enamel or dentin. The enamel and dentin of each tooth was divided into two halves separated by a glass plate. Each tooth was restored using both tested composite resins following the manufacturer's instructions. The samples were sectioned, producing 4 sticks for each composite resin. Half of them were tested after 24 h and half after 3 months. µTBS testing was carried out at 0.05 mm/s. Data were analyzed by three-way ANOVA and Tukey's HSD tests at α=0.05. Significant differences between composite resins and substrates were found (p<0.05), but no statistically significant difference was found for aging time and interactions among study factors. The methacrylate-based resin showed higher µTBS than the silorane-based resin. The µTBS for enamel was significantly higher than for dentin, irrespective of the composite resin and storage time. Three months of storage was not sufficient time to cause degradation of the bonding interaction of either of the composite resins to enamel and dentin.

Effect of different bonding strategies on the marginal adaptation of class 1 silorane restorations

PURPOSE

To evaluate the quality of marginal and internal adaptation of Filtek Silorane composite in standardized class 1 cavities before and after thermo-mechanical loading using different application protocols of the Silorane System Adhesive (SSA).

METHODS

Five groups (n = 10) of class 1 cavities were restored with Filtek Silorane using different SSA applications. Total bonding (TB): Group A (SSA), Group B (SSA without primer polymerization), Group C (enamel etching + SSA), Group D (enamel etching + SSA without primer polymerization) and Selective bonding (SB): Group E. Marginal adaptation was assessed on replicas in the SEM at x200 magnification before and after thermomechanical loading (3,000 x 5-55 degrees C, 1.2.10(6) x 49N; 1.7Hz) under simulated dentin fluid. After loading, the samples were sectioned and the internal adaptation was evaluated as well.

RESULTS

The lowest scores of %CM (Continuous Margin) before/after thermo-mechanical loading being 80.8 (+/- 8.2) / 32.1 (+/- 8.3) were observed in the control group A. Enamel phosphoric acid etching prior to the application of the SSA resulted in significantly higher %CM before and after loading in comparison with the "non-etched" groups (P > 0.05). When enamel etching was performed before the application of the adhesive system, no statistically significant differences (P > 0.05) were observed regardless of how the SSA was applied (total vs. selective bonding). Internal adaptation was negatively influenced by omitting the SSA-primer polymerization (P > 0.05).

Shear bond strength of a novel silorane adhesive to orthodontic brackets and unprepared bovine enamel

PURPOSE

To evaluate the suitability of a novel epoxy-based resin, Filtek Silorane, for orthodontic bracket bonding on unprepared enamel.

MATERIALS AND METHODS

Shear forces to bovine enamel were measured for Filtek Silorane and Transbond XT in combination with steel, ceramic, and polymer brackets. For Filtek Silorane, etching was performed with the Silorane self-etching primer alone or an additional previous application of phosphoric acid. Transbond XT (conventional methacrylate) was used for the control group and the enamel was previously etched with 35% phosphoric acid. All samples were thermocycled (1000X, 5°to 55° C). Shear bond testing was done with an Instron 3344 at a crosshead speed of 1 mm/min. In addition, adhesive remnant index (ARI) scores were evaluated.

RESULTS

The shear forces showed a weak adhesion of Filtek Silorane to unprepared enamel both with the selfetching primer and conventional etching (0.87 to 4.28 MPa). The shear forces of the control group were significantly higher (7.6 to 16.5 MPa). The ARI scores showed a clear failure at the enamel/adhesive interface for all Filtek Silorane samples. For the combination of Transbond XT and different brackets, the failure was found at the adhesive/bracket interface.

CONCLUSION

The novel epoxy-based resin Filtek Silorane is not appropriate for bonding of brackets to unprepared enamel.

Effect of dentin pre-treatment with a casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) paste on dentin bond strength in tridimensional cavities

OBJECTIVE

This study aimed to evaluate the push-out bond strength of dimethacrylate (Clearfil SE Bond/Filtek Z250; and Adper SE Plus/Filtek Z250) and silorane-based (Filtek P90 adhesive system/Filtek P90 composite resin) restorative systems following selective dentin pre-treatment with a CPP-ACP-containing paste (MI Paste).

MATERIALS AND METHODS

Sixty bovine incisors were utilized. The buccal surface was wet-ground to obtain a flat dentin area. Standardized conical cavities were then prepared. Adhesive systems were applied according to manufacturers' directions and the composites were bulk-inserted into the cavity. The push-out bond strength test was performed at a universal testing machine (0.5 mm/min) until failure; failure modes were analyzed by scanning electron microscopy. Data were analyzed by two-way ANOVA and Tukey post-hoc test (p < 0.05).

RESULTS

For Clearfil SE Bond/Filtek Z250 and Filtek P90 adhesive system/Filtek P90 composite resin, the dentin pre-treatment did not influence bond strength means. For Adper SE Plus/Filtek Z250, dentin samples treated with MI Paste had statistically higher bond strength means than non-treated specimens. Adhesive failures were more frequent.

CONCLUSION

Dentin pre-treatment with the CPP-ACP containing paste did not negatively affect bond strength for Clearfil SE Bond/Filtek Z250 and Filtek P90 adhesive system/Filtek P90 composite resin restorative systems and improved bond strength for the Adper SE Plus/Filtek Z250 restorative system.

Supragingival relocation of subgingivally located margins for adhesive inlays/onlays with different materials

PURPOSE

This study evaluated the marginal adaptation of supragingivally relocated cervical margins. Newly developed and reference materials were compared.

MATERIALS AND METHODS

Eighty-eight extracted human teeth were divided into 11 groups. A standardized boxshaped cavity (4.0 mm mesiodistal width, 1.5 mm axial depth) was prepared on each tooth with the cervical margin 1.3 mm below the cementoenamel junction. Seven different restorative materials (Filtek Silorane [Sil], Clearfil AP-X [APX], Clearfil Majesty Posterior [CMP], Clearfil Majesty Flow [CMFlow], RelyX Unicem [RelyX], SDR [SDR], Vertise Flow [VertFlow]) were applied in a layer of 1.5 mm, combined with different adhesive systems (Filtek Silorane Primer + Bond [SilPB], Clearfil Profect Bond [ClePB], Filtek Silorane Bond [SilB]). No indirect restorations (ie, inlays/onlays) were placed on these restorations. SEM analysis was performed to evaluate marginal adaptation in enamel and dentin. The results were subjected to statistical analysis by Kruskal Wallis and Duncan post-hoc tests.

RESULTS

In both dentin and enamel, statistically significant differences were present between groups (p < 0.001). In enamel, the lowest percentage of continuous margin was observed for SilPB/CMP, SilPB/APX, and ClePB/SDR, while SilPB/Sil exhibited the highest percentage of continuous margin, although this was not statistically different from other groups except for SilPB/CMP, SilPB/APX, and ClePB/SDR. In dentin, a higher percentage of continuous margin was observed for all materials than in enamel (p < 0.002). Statistically significant differences were found between ClePB/SilB/Sil, ClePB/SDR, and RelyX, SilPB/APX, ClePB/APX, and ClePB/Sil. ClePB/Sil showed the lowest marginal adaptation. Considering the overall marginal length, the best marginal adaptation was exhibited by ClePB/SilB/Sil, followed by SilPB/Sil, ClePB/SDR, and ClePB/CMP.

CONCLUSION

Marginal adaptation of supragingivally relocated cervical margins is significantly influenced by the materials used.

Evaluation of sorption, solubility and staining of universal and silorane resin-based composites

Resin-based composite staining is a multifactoral phenomenon and can be caused by intrinsic and extrinsic factors. The purpose of this study was to compare staining, sorption and solubility of silorane resin-based and universal resin-based composites. Five different resin-based composites (4 Seasons, Charisma, Filtek Silorane, Filtek Supreme and Grandio) were tested. Twenty five specimens were prepared (10 mm diameter and 1.5 mm thick). To staining test, the specimens were divided into 3 groups (n = 5): distilled water (control), coffee and red wine. The specimens were immersed in one of the solutions at 37 degrees C for 7 days. Using the values of L*, a*, b*, color variation (CIEDE2000) was determined. For sorption and solubility test, the specimens were divided into 2 groups (n = 5): with previous desiccation (Group 1) and with no previous desiccation (Group 2). The methodology used for sorption and solubility test was based on ISO 4049:2000. The results presented no significant difference in staining between composites. In sorption and solubility test, Filtek Silorane presented the smallest values, followed by Grandio. Under tested experimental conditions, it is not possible to assert the dependence of staining in sorption that composites are undergone. There was no significant correlation between colour change and sorption values.

The influence of different placement techniques on the microtensile bond strength of low-shrink silorane composite bonded to Class I cavities

The aim of this in vitro study was to evaluate the microtensile bond strength (µTBS) of a low-shrink silorane-based composite (Filtek Silorane) and a methacrylate-based composite (Filtek Z250) to the bottom dentin of a Class I cavity using different placement techniques. Twelve third molars were used. Standard, box-type Class I cavities (6.0 x 4.0 x 2.5 mm) were prepared at the occlusal crown center, with the pulpal floor ending approximately at the midcoronal dentin. The teeth were then randomly divided into four groups, according to each placement technique: ZI--Filtek Z250 placed incrementally; ZB--Filtek Z250 placed in bulk; SI--Filtek Silorane placed incrementally; and SB--Filtek Silorane placed in bulk. Each restored third molar was subjected to microtensile bond testing after 24 hours of storage in distilled water at 37 degrees C. After storage, each molar was longitudinally sectioned in both axes to obtain rectangular sticks with an approximate 0.49 mm2 cross-sectional area. Data were analyzed by one-way ANOVA followed by a Tukey post hoc test (P = 0.05). After debonding, the failure modes were analyzed using a stereomicroscope. The ZI group (72.6 MPa) showed the highest µTBS, followed by the ZB group (60.2 MPa), while the SI (34.4 MPa) and SB (42.6 MPa) groups demonstrated statistically significant lower bond strengths. The type of placement technique did not influence the µTBS of silorane-based composites to the bottom dentin of Class I cavities. The methacrylate-based composite showed superior performance, regardless of the placement technique.

Surface roughness of one nanofill and one silorane composite after polishing

The aim of this study was to compare the roughness of the surface of one nanofill (Filtek Supreme XT 3M Espe, St. Paul, USA) and one silorane (Filtek Silorane, 3M Espe, St. Paul, USA) composite after polishing. Five specimens of each composite were polymerized under a polyester strip for 40 seconds. After curing four probes were polished with different Sof-Lex discs and one probe with Pogo for ten seconds. For the surface appointment a contact stylus profilometer was used. The profilometer made ten tracings for each sample at different locations. There was a significant difference in roughness between both composites. The Ra (average surface roughness) results for the silorane composite were almost always significantly higher than for the nanofill composite (T-test). For both composites Sof-Lex fine and superfine discs produced smoother final surfaces than Pogo. The nanofill composite used showed the smoothest surfaces after the polishing and finishing procedures.

Oxidative stress and cytotoxicity generated by dental composites in human pulp cells

Dental composites are a source of residual monomers that are released into the oral environment. Since monomers act on cultured cells through reactive oxygen species (ROS), we hypothesized that composites generate ROS associated with cytotoxicity. Human pulp-derived cells were exposed to extracts of methacrylate-based materials including triethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate-free composites (Tetric Ceram, Tetric EvoCeram, els, els flow, Solitaire 2) and a silorane-based composite (Hermes III). The materials were polymerized in the presence and absence of a polyester film and then extracted in culture medium. The generation of ROS was measured by flow cytometry, and cytotoxicity was determined as well. Methacrylate-based composites reduced cell survival but varied in efficiency. Undiluted extracts of Solitaire 2 specimens prepared in the absence of a polyester film reduced cell survival to 26% compared with untreated cultures. Cytotoxicity was reduced when specimens were covered with a polyester film during preparation. Cytotoxicity of the composites was ranked as follows: Solitaire 2 >> els flow > Tetric Ceram = Tetric EvoCeram = els > Hermes III. The generation of ROS followed the same pattern as detected with cytotoxic effects. A positive correlation was found between ROS production and cell survival caused by extracts made from materials not covered with a polyester film. These findings suggest that components released from composites affect cellular signaling networks through ROS formation. Regenerative and reparative capacities of the dentine-pulp complex may be impaired by biologically active resin monomers released from composite restorations.

Influence of ozone application on the repair strength of silorane-based and ormocer-based composites

PURPOSE

To evaluate the effect of gasiform ozone on the repair strength of ormocer-based and silorane-based composites.

METHODS

160 cavities were created in methacrylate cylinders. Half of the cavities were filled with a silorane-based composite, whereas the other half was filled with an ormocer-based composite. After storage (1 week, deionized water, 37 degrees C) the specimens of each restorative material were divided into two main experimental groups: in Group 1 the specimens were subjected to a 60-second ozone gas application; in Group 2 no pretreatment was performed (control). The corresponding adhesive of each restorative material was applied as the intermediate repair agent in both groups. Repair cylinders were then built up with the homologous material. Half of the specimens in each group were subjected to thermocycling (5,000 cycles, 5 degrees C-55 degrees C, dwell time 30 seconds, transfer time 5 seconds) prior to testing, whereas the other specimens were immediately tested. The repair strength was assessed with a shear test. The two-way ANOVA with pretreatment and thermocycling as the main factors was used to analyze the shear bond strength data within each restorative material.

RESULTS

The pretreatment, the thermocycling and their interaction did not significantly affect the repair strength of either tested materials (P > 0.05). The ozone treatment did not significantly affect the repair strength. The silorane-based composite showed lower repair strengths compared to those of the ormocer-based composite. The immediate repair strengths in the ozone-treated and control groups were respectively, 28.1 (13.8) MPa and 28.8 (8.8) MPa for the silorane-based composite and 31.5 (9.3) MPa and 35.6 (10.6) MPa for the ormocer-based composite. After thermocycling, the repair strengths in the ozone-treated and control groups were 27.7 (9.7) MPa and 29.5 (11.1 ) MPa for the silorane-based composite and 31.4 (6.0) MPa and 34.2 (4.5) MPa for the ormocer-based composite. Mixed failures occurred most frequently in all experimental groups. In conclusion, ozone did not affect the repair strength of the tested silorane-based and ormocer-based composites.

Selected mechanical and physical properties and clinical application of a new low-shrinkage composite restoration

Polymerization shrinkage is a major concern for bonded direct posterior restorations. Recently, a new low-shrinkage composite resin restorative material was developed. However, few data are available regarding clinical manipulation of this composite. Silorane-based composites represent an alternative to conventional methacrylate-based composites for direct posterior restorations. This article critically discusses the latest peer-reviewed reports related to polymerization, bonding, polishing, and color stability of silorane composite, focusing on its clinical application. Initial evaluation of this new category of composite material shows acceptable mechanical and physical properties.

Surface properties and in vitro Streptococcus mutans adhesion to self-etching adhesives

PURPOSE

The aim of this in vitro study was to investigate the surface properties and in vitro adhesion of Streptococcus mutans to dental self-etching two-step adhesives using an artificial mouth system.

MATERIALS AND METHODS

Carriers of a denture base resin supplemented with hydroxyapatite were manufactured, polished, and surface treated with various two-step self-etching dental adhesives (Clearfil Protect Bond, Silorane System Adhesive, Adper Scotchbond SE) according to the manufacturers' instructions. For each adhesive, 14 samples were inserted in an artificial mouth system and successively rinsed with mucin solutions (2 h) and Streptococcus mutans NCTC 10449 suspension (4 h). Surface free energy of the specimens was determined before and after mucin coating. The amount of adhered bacteria was quantified using a fluorescent dye (Resazurin/Alamar Blue) for viable cell quantification.

RESULTS

Before mucin coating, significant differences in surface free energies were found between the various adhesives, with total surface free energies ranging from 34.26 mJ/m(-2) to 42.30 mJ/m(-2). Mucin coating clearly levelled surface free energy differences. Significantly lower fluorescence intensities, indicating lower adhesion of Streptococcus mutans, were found for Silorane System Adhesive than for Clearfil Protect Bond and Adper Scotchbond SE, regardless of mucin coating.

DISCUSSION

The findings of this in vitro study indicate that the initial adhesion of Streptococcus mutans is lower to Silorane System Adhesive than to Clearfil Protect Bond or Adper Scotchbond SE. Our data correlated with the common thermodynamic approaches explaining streptococcal adherence to solid surfaces.