Comparison of microleakage in Class II cavities restored with silorane-based and methacrylate-based composite resins using different restorative techniques over time.

BACKGROUND: Despite the growing tendency toward tooth-colored restorations in dentistry, polymerization shrinkage and subsequent marginal microleakage remains a problem. The aim of this in vitro study was to compare microleakage between silorane-based and methacrylate-based composite resins at different time intervals and with different restorative techniques. MATERIALS AND METHODS: In this in vitro study, 108 sound extracted human molar teeth were used. Mesial and distal proximal class II boxes with dimensions of 1.5 mm depth and 4 mm width were prepared. The gingival margins of all cavities were 1 mm below the cement enamel junction. The teeth were randomly divided into three groups based on test materials. In the first group, the teeth were restored by a nanocomposite (Filtek Z350XT, 3MESPE) and SE Bond adhesive (Kuraray, Japan), in the second group, the teeth were restored with a silorane-based (Filtek P90, 3MESPE) and Filtek P90 Adhesive (3M ESPE, USA) and in the third group, the teeth were restored with a microhybrid posterior composite resin (Filtek P60, 3MESPE) and SE Bond adhesive (Kuraray, Japan). Half of the proximal cavities in each of these three groups were restored in two horizontal layers and the other half in four horizontal layers. After a period of aging (24-h, 3-month and 6-month) in water and then application of 500 thermal cycles, the teeth were immersed for 24-h in 0.5% fuchsin and evaluated under a stereomicroscope at ×36 magnification to evaluate leakage in gingival margin. Data was statistically analyzed using Kruskal-Wallis and Mann-Whitney U-tests. P ≤ 0.05 was considered as significant. RESULTS: In Z350XT statistically significant differences were observed in microleakage in comparison of 24-h and 6-month intervals (P = 0.01) that was higher in 6-month. Comparison of microleakage in P90 and P60 composite resins was also statistically significant and was less in P90. Microleakage was not significantly different between P90 and Z350XT at 24-h. However, this difference was significant at 3-month and 6-month intervals. Differences in microleakage of P60 and Z-350XT composite resins were not statistically significant in all intervals (P = 0.38). P90 showed the lowest microleakage during storage in water. Z350XT had microleakage similar to P90 within 24-h, but after 6-month of storage in water, it showed the highest microleakage among all the groups. The number of layers (2 layers vs. 4 layers) did not result in any differences in microleakage scores of the composite resins (P = 0.42). CONCLUSION: Water storage times did not result in any significant effect on microleakage of P90 and P60.

Effect of fluoride dentifrices on the microhardness of deciduous enamel surfaces.

PURPOSE: To evaluate the changes in the enamel surface microhardness following the application of various suspensions of Crest and Pooneh toothpastes with and without fluoride. MATERIALS AND METHODS: Fifty-six enamel blocks of primary incisors were exposed to a pH-cycling regime consisting of demineralisation and remineralisation solution, then suspensions of the dentifrices Crest 1100, Crest 500, Pooneh 500, Pooneh without fluoride. Changes of the enamel surface microhardness in pre-demineralisation (initial), post-demineralisation (demineralised) and post-remineralisation (final) stages were measured for four groups and were analysed using the Student t test and one-way ANOVA. RESULTS: The percentages of changes in surface microhardness for Crest 1100, Crest 500, Pooneh 500 and Pooneh without fluoride were 45.4, 35.4, 28.6 and 23.7, respectively. CONCLUSION: Average changes of surface microhardness for Crest 1100 were significantly higher than Crest 500, Pooneh 500 and Pooneh without fluoride.

Effect of MTAD on the shear bond strength of self-etch adhesives to dentin.

BACKGROUND: As the use of different irrigants to eliminate residual debris and smear layer in the field of endodontic is unavoidable, by considering the effect of irrigants on the bond strength of resin composite restorations, this study was designed to evaluate the effect of a mixture of a tetracycline isomer, an acid, and a detergent (MTAD) on the shear bond strength of two self-etch adhesives, Clearfil SE Bond and Adper Prompt L- Pop to dentin. MATERIALS AND METHODS: The crowns of 80 extracted premolars were transversally sectioned to expose dentin. Flat dentin surfaces were wet abraded with 320-grit abrasive paper and randomly assigned to eight groups according to two self-etch adhesive and four dentin surface treatments: direct application over smear layer (no treatment), etching with 35% phosphoric acid for 15s, 1 min 5.25% NaOCl/1 min MTAD and 20min 1.3% NaOCl/5min MTAD. Shear bond strength was tested 24 h after storage in distilled water at 37°C in incubator. Data were analyzed using one-way ANOVA followed by duncan post-hoc (α=0.05). RESULTS: Phosphoric acid etching prior to SE Bond application significantly decreased the shear bond strength to dentin (P<0.05). Application of MTAD clinical protocol (20min 1.3% NaOCl/5min MTAD) did not significantly decrease the shear bond strength of self-etch adhesives to dentin (P=0.745) CONCLUSIONS: Based on the results of present investigation, it seems that the use of clinical protocol of 1.3% NaOCl as a root canal irrigant and a 5-min application of MTAD as a final rinse to remove the smear layer has no adverse effect on the shear bond strength of self-etch adhesives to dentin.

Poly(acrylic acid) grafted montmorillonite as novel fillers for dental adhesives: synthesis, characterization and properties of the adhesive.

OBJECTIVE: This work investigates the graft polymerization of acrylic acid onto nanoclay platelets to be utilized as reinforcing fillers in an experimental dental adhesive. Physical and mechanical properties of the adhesive and its shear bond strength to dentin are studied. The effect of the modification on the stability of the nanoparticle dispersion in the dilute adhesive is also investigated. MATERIALS AND METHODS: Poly(acrylic acid) (PAA) was grafted onto the pristine Na-MMT nanoclay (Cloisite(®) Na(+)) through the free radical polymerization of acylic acid in an aqueous media. The resulting PAA-g-nanoclay was characterized using FTIR, TGA and X-ray diffraction (XRD). The modified nanoclays were added to an experimental dental adhesive in different concentrations and the morphology of the nanoclay layers in the photocured adhesive matrix was studied using TEM and XRD. Shear bond strength of the adhesives containing different filler contents was tested on the human premolar teeth. The stability of nanoclay dispersion in the dilute adhesive was also studied using a separation analyzer. The results were then statistically analyzed and compared. RESULTS: The results confirmed the grafting reaction and revealed a partially exfoliated structure for the PAA-g-nanoclay. Incorporation of 0.2 wt.% of the modified nanoclay into the experimental adhesive provided higher shear bond strength. The dispersion stability of the modified nanoparticles in the dilute adhesive was also enhanced more than 25 times. SIGNIFICANCE: Incorporation of the modified particles as reinforcing fillers into the adhesive resulted in higher mechanical properties. The nanofiller containing bonding agent also showed higher shear bond strength due to the probable interaction of the carboxylic acid functional groups on the surface of the modified particles with hydroxyapatite of dentin.

Effect of fluoridated dentifrices on surface microhardness of the enamel of deciduous teeth.

BACKGROUND: Surface microhardness is a physical property which access the effect of chemical and physical agents on hard tissues of teeth, and a useful way to examine the resistance of fluoride treated enamel against caries. The purpose of this study was to evaluate microhardness of enamel following pH-cycling through demineralization and remineralization using suspensions of dentifrices with different fluoride contents. METHODS: In this in vitro study 56 enamel blocks of primary incisors were soaked in demineralizing solution and four dentifrices suspensions including: Crest 1100 ppm F (NaF), Crest 500 ppm F (NaF), Pooneh 500 ppm F (NaF,) and Pooneh without fluoride. The means and percentage changes of surface microhardness in pre-demineralization, after demineralization and remineralization stages in four groups were measured. The findings of four groups in three stages were compared by, ANOVA, Tukey and paired t-tests. (α=0.05) RESULTS: Average surface microhardness changes of Crest 1100 ppm F, was higher than Crest 500 ppm F, Pooneh 500 ppm F, and Pooneh without fluoride. The percentages of surface microhardness recovery for Crest 1100 ppm F, Crest 500 ppm F, Pooneh 500 ppm F, and Pooneh without fluoride were 45.4, 35.4, 28.6, and 23.7 respectively. Demineralization treatment decreased the surface microhardness of enamel (P<0.05) and the surface microhardness recovery in all groups were significant (P<0.0001). CONCLUSION: Surface microhardness of enamel after remineralization by Crest 1100 ppm F was higher than Crest 500 ppm F, Pooneh 500 ppm F, and Pooneh without fluoride.

Effect of phosphoric acid etching of enamel margins on the microleakage of a simplified all-in-one and a self-etch adhesive system.

Sixty buccal Class V cavities with beveled enamel margins were made at the cemento-enamel junction of extracted human premolars and randomly divided into five groups of 12 specimens. Clearfil SE bond was applied to Group 1; Group 2 had 35% phosphoric acid etching of the enamel margins plus Clearfil SE Bond; Group 3 was administered iBond; Group 4 had 35% phosphoric acid etching of the enamel margins plus iBond and Scotchbond Multi-Purpose was used on Group 5. All the groups were restored with a resin composite. After 24 hours of storage in 100% humidity, the samples were thermocycled, immersed in a dye solution and sectioned buccolingually and microleakage of the enamel margins was evaluated on a scale of 0 to 2. Differences among Groups 3 and 4 and Groups 3 and 5 were significant (p < 0.05); however, no statistically significant differences were found between the other groups (p > 0.05). The current study shows that simplified all-in-one adhesive systems need pre-etching of the enamel margins with phosphoric acid for an effective seal.