Guilherme Brião Camacho

Effect of polishing techniques and time on surface roughness, hardness and microleakage of resin composite restorations.

This study evaluated the effects of immediate and delayed polishing on the surface roughness, microhardness and microleakage of a microfilled (Filtek A110) and a hybrid (Filtek Z250) resin composite. Standardized preparations were made on the buccal surfaces of 256 bovine teeth; half were restored with each composite (128 teeth per composite). Immediately after curing, gross finishing was carried out with #280 sandpaper. The specimens restored with each composite were divided into two subgroups. The first group (IM) was polished immediately after gross finishing, using three different systems (n=16): Sequence A, Sof-Lex; Sequence B, Flexicups and Sequence C, Flexicups + Jiffy Polishing Brush + Flexibuffs. The specimens were then stored for three weeks in saline 37 degrees C. The second group (DE) was stored for two weeks, then polished with the same systems and stored for one additional week. The controls (n=16) were analyzed without polishing. Five readings per specimen were taken for surface roughness and hardness. After immersion in basic fuchsin, microleakage was evaluated (40x) using standardized scores. The data were analyzed at a significance level of 0.05, with analysis of variance and an SNK test (surface roughness and microhardness) or with Kruskal-Wallis (microleakage). In both composites, only for the sequential technique was there an influence of delay in polishing on roughness (Ra). Flexicups exhibited the highest Ra of the three systems. The IM and Filtek Z-250 groups showed higher hardness than the DE and Filtek A-110 groups, respectively. Dentin margins showed more leakage than enamel margins; the sequential technique produced more leakage than the other techniques in dentin (p<0.05) and delay of polishing was not significant in the majority of situations. In conclusion, several conditions--composite, time and polishing technique--had a significant influence on surface roughness, hardness and microleakage. Generally, immediate polishing produced no detrimental effect compared to delayed polishing.

Fracture resistance and gap formation of MOD restorations: influence of restorative technique, bevel preparation and water storage.

This in vitro study evaluated the effect of technique, use of a bevel and thermal cycling on the fracture resistance and gap formation of resin composite MOD restorations. Fracture resistance was measured on standard MOD cavities prepared in 100 upper premolars that were stored for 24 hours and 6 months with 1000 thermal cycles. Subgroups (n=10) were: beveled or non-beveled preparations and direct restorations (Adper Single Bond/Filtek Z250) and indirect restorations (prepolymerized Filtek Z250 cemented with Rely XARC). Ten sound teeth and 10 specimens with MOD preparations without restorations served as the positive and negative controls, respectively. The specimens were subjected to axial compression in a universal testing machine at a crosshead speed of 0.5 mm/minute. Failure patterns were analyzed by stereomicroscopy (40x). To evaluate gap presence or absence, proximal box cavities were prepared in 24 human third molars that were restored as described above. The specimens were evaluated under SEM examination after 24 hours and six months. Data were statistically analyzed by ANOVA and multiple comparison tests at the 0.05 level of significance. After 24 hours, the beveled restorations exhibited higher fracture strength values than the non-beveled restorations, and all groups showed resistance similar or superior to sound teeth. After six months, the highest fracture resistance was obtained for beveled inlays and the lowest values were observed for direct restorations with butt joints. Thermal cycling decreased fracture resistance in the majority of the groups. The main fracture pattern observed was cohesive failure in the material, but adhesive failures increased over time, especially in the non-beveled restorations. Under SEM examination, no difference was observed among the groups after 24 hours. However, after six months, the beveled restorations exhibited no gap formation. It was concluded that storage with thermal cycling decreased fracture resistance, bevels improved fracture resistance and, in general, indirect restorations were not superior to direct restorations.

Fracture resistance of thermal cycled and endodontically treated premolars with adhesive restorations

STATEMENT OF PROBLEM Cavity preparations have routinely been associated with decreased fracture strength of restored teeth. PURPOSE The purpose of this study was to evaluate the influence of endodontic treatment and thermal cycling on the fracture resistance of teeth restored with ceramic or composite resin inlay restorations. MATERIAL AND METHODS One hundred sound, maxillary premolars were selected. Twenty intact teeth served as a control group. Eighty teeth were prepared with MOD cavity preparations; half of them were also endodontically treated. Inlay restorations were prepared with composite resin (Filtek Z250) or feldspathic ceramic (Vitadur Alpha). Half of the specimens for each group were submitted to thermal cycling (500 cycles, between 5 and 55 degrees C, dwell time of 30 seconds). The specimens were subjected to compressive axial loading using a steel ball. Data were analyzed using 3-way ANOVA and post hoc Tukeys test (alpha=.05). RESULTS Except for those teeth restored with ceramic without endodontic treatment and thermal cycling, no other group achieved fracture strength similar to sound teeth. Ceramic and composite resin restorations provided similar resistance to fracture. There was a significant interaction between endodontic therapy and thermal cycling (P<.001). In the nonthermal cycled groups, endodontically treated teeth showed significantly lower fracture resistance (P<.001). All experimental groups had similar fracture strength when submitted to thermal cycling. CONCLUSIONS Both restorative techniques provided similar fracture resistance. Endodontic treatment decreased the fracture resistance of nonthermal cycled specimens, while thermal cycling decreased the fracture resistance of nonendodontically treated specimens.

Fracture resistance of premolars restored with inlay and onlay ceramic restorations and luted with two different agents

PURPOSE The purpose of this study was to evaluate the fracture resistance of human maxillary premolars restored with 2 ceramic systems (Vitadur Alpha and In Ceram) comparing 3 preparation designs and 2 luting agents. METHODS Seventy sound teeth were prepared to receive ceramic restorations (Vitadur Alpha; n=14) as follows: (1) control, sound premolars, with no preparation, (2) inlays, (3) partial onlays (palatal cuspid coverage), (4) total onlays (both cuspids coverage), and (5) total onlays with an In Ceram core. The ceramic restorations were cemented using Enforce or RelyX ARC (half restorations with each cement), placed into the cavity and held under pressure, except for the control group. The teeth were subjected to compressive axial loading at 0.5 mm min⁻¹ using a 9 mm steel ball until fracture. Data were analyzed by 3-way ANOVA and post hoc Tukeys test (α=.05). RESULTS There was a significant difference between cements and among preparation designs (P<.05). All restorations cemented with Enforce exhibited significantly higher fracture resistance (P<.05). Inlay restorations showed similar fracture resistance when compared to control group (P>.05). Partial and total onlays did not statistically differ and showed the weakest performance. The use of an In Ceram core did not produce higher fracture resistance. CONCLUSIONS Within the limitations of this study, the cements tested had different mechanical properties, while cuspid coverage did not result in improved fracture resistance of the restored teeth.

Antibacterial Efficacy and Effect of Chlorhexidine Mixed with Irreversible Hydrocolloid for Dental Impressions: A Randomized Controlled Trial

This study aimed to evaluate whether chlorhexidine mixed with irreversible hydrocolloid powder decreases microbial contamination during impression taking without affecting the resulting casts. Twenty volunteers were randomly divided into two groups (n = 10) according to the liquid used for impression taking in conjunction with irreversible hydrocolloid: 0.12% chlorhexidine or water. Surface roughness and dimensional stability of the casts were evaluated. Chlorhexidine mixed with irreversible hydrocolloid decreased the percentage of microorganisms when compared with water (P < .001) but did not affect the surface quality or dimensional stability of the casts. Mixing chlorhexidine with irreversible hydrocolloid powder is an alternative method to prevent contamination without sacrificing impression quality.