Bond strength of prefabricated and CAD-CAM milled glass fiber post-and-cores luted with conventional, universal, and self-adhesive composite resin cement.

STATEMENT OF PROBLEM: Little is known about the effect of different composite resin cements on the bond strength of prefabricated and milled glass fiber post-and-cores. PURPOSE: The purpose of this in vitro study was to compare the push-out bond strengths of root dentin and standard, relined, or computer-aided design and computer-aided manufacturing (CAD-CAM) glass fiber post-and-cores luted with conventional, universal, or self-adhesive composite resin cement. MATERIAL AND METHODS: Post spaces were prepared in 90 premolars. Standard and relined prefabricated and CAD-CAM-milled glass fiber post-and-cores were luted with conventional (RelyX ARC; 3M ESPE), universal (RelyX Ultimate; 3M ESPE), and self-adhesive (RelyX U200; 3M ESPE) composite resin cement (n=10). All specimens were thermally aged (5000 cycles at 5°C and 55°C with a 20-second dwell time) and mechanical fatigue (1 000 000 cycles at 2 Hz, 50-N load). The specimens were sectioned perpendicularly to the root long axis into 1-mm-thick sections (apical, middle, and cervical root thirds), the push-out bond strength was determined, and the mode of failure recorded. Data were submitted to the Kruskal-Wallis test followed by the Bonferroni-Dunn multiple comparison test (α=.05). RESULTS: Push-out bond strength values did not differ (P>.05) among posts at the same root thirds. Standard posts showed higher bond strength than CAD-CAM at the apical third for data grouped by composite resin cements (P<.001). The cervical root thirds had higher bond strength than the apical thirds (P<.05). The cervical, middle, and apical root thirds showed decreasing bond strength values for each type of post for data grouped by composite resin cement (P<.001). Adhesive failures at the dentin-cement interface were predominant. CONCLUSIONS: The type of posts and cements did not affect the bond strength of glass fiber posts. The cervical root thirds had better bonding performance than the apical thirds.

Multidisciplinary Treatment: Follow-Up of Dental Autotransplantation for 10 Years.

The objective is to present a clinical case of dental autotransplantation managed with surgery, orthodontics, endodontics, periodontics, and aesthetic rehabilitation. A 10-year-old boy sought treatment after avulsion of the maxillary left central incisor, which was not reimplanted. Based on anamnesis, clinical examination, and complementary examinations, agenesis of the maxillary and mandibular second premolars except the mandibular right second premolar was observed. After a multidisciplinary planning, the space in the maxillary left central incisor region was opened to receive the transplanted mandibular right second premolar. The receptor site was created in a single surgical procedure. Pulp necrosis was noted in the transplanted tooth, which was treated endodontically, and the agenesis spaces were closed using fixed orthodontic appliances. After removing the appliance, gingivectomy with osteotomy was performed in the maxillary right central incisor and the transplanted tooth regions to harmonize the height and shape of the gingival contour. Next, aesthetic readjustment was performed with tooth whitening, using office and home techniques, followed by microabrasion of the vestibular surface of the maxillary right central incisor. Direct composite resin restorations were placed in the maxillary incisors, and the teeth were rehabilitated using incisal and palatal guides. A multidisciplinary approach is essential for reestablishing the function and aesthetics of complex cases involving dental autotransplantation.

Effect of whitening dentifrices on color, surface roughness and microhardness of dental enamel in vitro.

PURPOSE: To evaluate the color, surface roughness and microhardness of human dental enamel subjected to brushing with whitening dentifrices. METHODS: The enamel samples (4 x 4 x 2 mm) were darkened using 0.2% chlorhexidine and black tea, and were randomly divided into seven groups (n= 15) for brushing cycles with only water; control; conventional dentifrice (Colgate Maximum Anticaries Protection); dentifrice containing 2% hydrogen peroxide (Colgate Luminous White Advanced); dentifrice containing sodium tripolyphosphate (Sensodyne True White); dentifrice containing activated charcoal (Black is White); and dentifrice containing blue covarine (Close Up White Now). The samples were submitted to 1,000 and 30,000 brushing cycles. The color values (CIE L*a*b*), surface roughness (Ra) and microhardness (Knoop) were recorded at four time points: baseline, after staining, after 1,000 and after 30,000 brushing cycles. The data were submitted to statistical analyses using paired t-test, ANOVA and Tukey. RESULTS: The color analysis, roughness and microhardness results showed interaction between the effect of the dentifrices and the time point (P< 0.001). The bleaching dentifrices brought about color changes (ΔE) significantly greater than those obtained with conventional dentifrices and the control; however, there were no significant color changes among the bleaching dentifrices. When the color coordinates were evaluated individually, the L* values increased and the a* and b* values decreased throughout the experiment. The conventional toothpaste and the toothpastes containing blue covarine, activated charcoal or hydrogen peroxide promoted a statistically significant increase in the surface roughness of the samples after the last brushing cycle. The sodium tripolyphosphate dentifrice caused a progressive reduction in roughness. The microhardness increased statistically after 30,000 cycles for the conventional toothpaste, blue covarine and hydrogen peroxide. It was concluded that the whitening dentifrices lightened the samples, which evidenced greater luminosity and reduction in reddish and yellow tones. Moreover, they did not have deleterious effects on microhardness, and caused acceptable changes in surface roughness. CLINICAL SIGNIFICANCE: Dentifrices with different whitening strategies changed the color of the samples, resulting in samples with greater luminosity and reduced reddish and yellowish tones. They also caused changes in surface roughness within the acceptable clinical limit and did not have a deleterious effect on the microhardness of dental enamel.

Reliability and correlation between microshear and microtensile bond strength tests of composite repairs.

The aim of this study was to evaluate the reliability of microshear (µSBS) and microtensile (µTBS) bond strength tests on composite repairs using universal adhesives with or without the application of additional silane. Cylindrical (µSBS) and block-shaped (µTBS) specimens were fabricated using nanofilled (F-Filtek One Bulk Fill) and nanohybrid (T-Tetric EvoCeram Bulk Fill) bulk-fill composites. The specimens were aged by thermocycling (5,000 cycles, 5-55 °C), sandblasted, and then divided into three groups (n = 30) as follows: non-repaired (FC and TC), repaired with universal adhesives (FA, Scotchbond Universal; and TA, Adhese Universal), and with the previous application of silane (FS and TS). After 48 h, the specimens were repaired using the same composite. The µSBS and µTBS specimens exhibited bonded areas of 1 mm2 and were subjected to shear stress and tension until failure, at a crosshead speed of 0.5 mm/min in a universal testing machine. Weibull analyses and Pearson correlation (α = 0.05) were applied to the data. At characteristic strength, FC, FA, and FS exhibited significantly higher µSBS when compared with TA and TS (p < 0.05). However when tested by µTBS at the same parameter, FA presented significantly lower bond strength when compared to FC, FS, and TA (p < 0.05). The correlation between Weibull modulus was strongly negative and not significant (p > 0.05). Both bond strength tests exhibited a material-dependent behavior. The microtensile bond strength test demonstrated more reliability than the microshear test for composite repair evaluation.

Effect of organic solvents compared to sandblasting on the repair bond strength of nanohybrid and nanofilled composite resins.

BACKGROUND: This study evaluated the effect of different surface treatments on the repair bond strength of nanohybrid (Empress Direct) and nanofilled (Filtek Z350 XT) composite resins. MATERIALS AND METHODS: A total of 120 specimens of each material (7.5 x 4.5 x 3 mm) were prepared and polished with SiC paper. Half of the specimens were kept in water for seven days and the other half for six months; they were then divided into six groups according to the type of surface treatment: negative control (no treatment), Al2O3sandblasted, liquid acetone, acetone gel, liquid alcohol and alcohol gel. Following application of the silane coupling agent and the adhesive system, composite resin cylinders were fabricated on the specimens and light cured (20 seconds). The same composite resins were used for the repair. Additionally, ten intact specimens of each composite resin (without repair) were prepared (positive control). The specimens were then loaded to failure in the microshear mode. Three additional specimens were fabricated in each group, and the surface treatments were analyzed by atomic force microscopy, energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). RESULTS: The nanofilled composite resin showed higher cohesive strength and repair bond strength than the nanohybrid composite resin. The aging process affected the repair bond strength of the nanofilled composite resin. Al2O3sandblasting was more efficient for the nanofilled composite resin and promoted greater surface roughness in both materials. The solvents demonstrated higher efficacy for the nanohybrid composite resin. CONCLUSION: The strengths resulting from the solvents were material dependent, and Al2O3sandblasting resulted in superior repair bond strength in both materials.

The effect of at-home bleaching and toothbrushing on removal of coffee and cigarette smoke stains and color stability of enamel.

BACKGROUND: The authors conducted a study to evaluate the stain removal ability of tooth bleaching and simulated toothbrushing after coffee and cigarette smoke staining and to determine the enamel susceptibility to restaining. METHODS: The authors used a colorimeter to determine the baseline color of 40 bovine labial enamel surfaces according to the Commission Internationale de l'Eclairage L*a*b* coordinates. They immersed one-half of the specimens in coffee and exposed one-half to cigarette smoke in a smoking machine. They took color measurements again and determined the color change from baseline (ΔE1) for each group. The authors divided each group into two subgroups and subjected the specimens to at-home bleaching (one hour per day for 21 days) or simulated toothbrushing (120 cycles per day for 21 days), followed by another color measurement (ΔE2). The authors repeated both staining procedures (that is, cigarette smoke and coffee) and followed them with a third color measurement (ΔE3). They analyzed the data by using a two-way analysis of variance and the Tukey test (α = 5 percent). RESULTS: Both staining procedures resulted in similar values for ΔE1. The specimens stained with coffee and cigarette smoke exhibited a significant reduction in color change after bleaching (P < .05). However, toothbrushing resulted in a significantly reduced color change only for cigarette smoke-stained specimens (P < .001). The discoloration in coffee-stained specimens increased after restaining, irrespective of the stain removal method (P < .05). CONCLUSIONS: The study results show that at-home bleaching removed both coffee and cigarette smoke staining. The restaining potential was greater for specimens stained with coffee than for those stained with cigarette smoke, regardless of the removal method used. CLINICAL IMPLICATIONS: Six percent hydrogen peroxide at-home bleaching was effective in removing stains caused by coffee or cigarette smoke. However, continued frequent consumption of coffee can increase the staining susceptibility of enamel.

Dynamic and static strength of an implant-supported overdenture model reinforced with metal and nonmetal strengtheners.

STATEMENT OF PROBLEM: Fractures of overdentures occur in the denture base through the abutments. PURPOSE: The purpose of this study was to evaluate the effect of reinforcements and the space available for their placement on the dynamic and static loading capacity of a simulated implant-supported overdenture model. MATERIAL AND METHODS: Rhomboidal (6 × 6 × 25 mm) test specimens (n=8), made with an acrylic resin and containing 2 metal O-ring capsules, were reinforced with braided stainless steel bar (BS), stainless steel mesh (SM), unidirectional E-glass fiber (GF), E-glass mesh (GM), woven polyethylene braids (PE), or polyaramid fibers (PA). Two distinct spaces for reinforcement placement were investigated: a 2.5 mm and a 1 mm space. Control groups consisted of nonreinforced specimens. Specimens were thermocycled (5°C and 55°C, 5,000 cycles) and then subjected to a 100,000 cyclic load regime. Unbroken specimens were then loaded until failure. The number of failures under fatigue (f) and static load (s) were compared with the Chi-Square test, while static load means were compared with the Kruskal-Wallis test (α=.05). RESULTS: The number of failures (f:s) of GF (0:16), PE (0:16), and PA (0:16) differed significantly from the control group (8:8) and SM (4:12) (P=.037 and P=.025, respectively). For the 2.5 mm space group, these same reinforcements also exhibited higher static load means than the control (P=.016, P=.003, and P=.003, respectively); under static load, no significant differences were detected between the reinforced groups and the control for the 1.0 mm space group (P=1.0). CONCLUSIONS: E-glass fibers, woven polyethylene braids, and polyaramid fibers withstood the fatigue regime and increased the flexural strength of the implant-supported overdenture model. The spaces available for reinforcement did not affect the dynamic strength or the static loading capacity of the implant-supported overdenture model.

Effect of cigarette smoke and whiskey on the color stability of dental composites.

PURPOSE: To evaluate the effect of cigarette smoke and whiskey on the color stability of resin composites. METHODS: Disk-shaped specimens (8 mm x 1 mm) were prepared with five composites in two different shades (n=10). After light-curing, the specimens were stored in dark containers with artificial saliva at 37 degrees C for 24 hours. Baseline color was measured by CIEL*a*b* using a colorimeter (Easy-Shade, VITA). Half of the specimens were subjected to a discoloration process in a cigarette smoking machine (SM) and the other half to an immersion in whiskey (WH) for 24 hours. Another color measurement was performed for discolored specimens. The samples subjected to smoking were immersed in whiskey (SM/WH) and those subjected to whiskey immersion were subjected to cigarette smoking (WH/SM) followed by another color measurement. Color changes (delta E*) were calculated and submitted to repeated measures 4-way ANOVA and Tukey tests (P<0.05). RESULTS: The most significant color change was observed after WH/SM (delta E*= 22.8-31.5) discoloration process, followed by SM (delta E*= 7.0-18.0), SM/WH (delta E*= 4.9-16.5) and WH (delta E*= 2.0 to 9.5). Translucent shades were more susceptible to discoloration than enamel shades. All the groups, with the exception of two, showed a significantly high perceptible color change (delta E*>3.3). Based on the results, the color stability of dental composites was affected by the discoloration process and was material and shade dependent.

Effect of storage temperature on pH of in-office and at-home dental bleaching agents.

The aim of this study was to determine the pH of several commercially available in-office and at-home dental bleaching products stored at room temperature and refrigerated. The products were divided into in-office (n=09) and at-home (n=12) bleaching gels and submitted to two different temperatures, namely, room temperature (23 degrees C +/- 1 degree C) and refrigeration temperature (4 degrees C +/- 1 degree C). The pH was measured using a portable pH meter with a direct electrode, which was calibrated with standard buffer solutions at pH 4.0 and 7.0 and recalibrated for each new product. The pH of the dental bleaching products tested ranged from 2.39 +/- 0.10 to 6.52 +/- 0.09, and was found to vary significantly both with temperature and between bleaching agents. Most of the bleaching gels were found to be acidic, especially the in-office bleaching products, and the refrigerated at-home gels had the highest pH values. Thus, we conclude that the storage temperature affected the pH of the products tested.

Effect of pre- and postpolymerization on flexural strength and elastic modulus of impregnated, fiber-reinforced denture base acrylic resins.

STATEMENT OF PROBLEM: Impregnated fibers require light polymerization; however, little information exists about how different protocols might affect the mechanical properties of reinforced denture base materials. PURPOSE: The purpose of this study was to compare the effects of pre- or postpolymerization of preimpregnated fibers on the flexural strength and elastic modulus of a reinforced autopolymerized and a heat-polymerized acrylic resin. MATERIAL AND METHODS: Seventy-two specimens were divided into 12 treatment groups (n=6), according to type of acrylic resin (autopolymerized or heat polymerized), type of reinforcement, and its pre- or postpolymerization. Impregnated glass fibers (Fibrex-Lab), unimpregnated glass fibers (Fibrante), and ribs made from a restorative composite resin (Z250) were used as reinforcements. The reinforcements were light polymerized either before or after incorporation and processing of the acrylic resins. Specimens were tested in 3-point load and the data were analyzed using 2-way ANOVA and Tukey post hoc test (alpha=.05). Specimens were further examined using light microscopy, atomic force microscopy, and scanning electron microscopy. RESULTS: Elastic modulus was significantly higher for heat-polymerized acrylic resins than for autopolymerized acrylic resins (P<.001). Prepolymerized fibers increased both flexural strength and elastic modulus of autopolymerized acrylic resins significantly more than postpolymerized fibers (P<.001); however, postpolymerized fibers yielded a higher elastic modulus than prepolymerized fibers for the heat-polymerized material (P<.001). CONCLUSIONS: Prepolymerized fibers improved the overall mechanical properties of reinforced autopolymerized acrylic resins more than postpolymerized fibers. However, postpolymerization of fibers yielded higher elastic modulus for reinforced heat-polymerized acrylics.

Fluorescence intensity of resin composites and dental tissues before and after accelerated aging: a comparative study.

This study quantitatively evaluated the fluorescence intensity of resin composites with different opacities and translucencies and determined changes in fluorescence after accelerated aging, using human enamel and dentin as controls. Six microhybrid and nanofilled composites, each in three different shades, were tested. Ten sound human incisors were used to obtain enamel and dentin specimens separately. Fluorescence measurements were obtained with a fluorescence spectrophotometer before (baseline) and after accelerated aging at 150 kJ energy for 120 hours. One-way analysis of variance (ANOVA) and Games-Howell multiple comparison tests were performed at a significance level of 0.05. Student's t-test was also used for comparison before and after aging. At baseline, there was no statistically significant difference (p>0.05) between the fluorescence intensity of dentin and any of the shades of Charisma or Opallis, Esthet-X dentin shade or Vit-l-escence enamel, or the translucent shades. After accelerated aging, all shades of the 4 Seasons, enamel and the translucent shades of Esthet-X had fluorescence intensities statistically similar to that of aged dentin (p>0.05). A significant reduction in fluorescence after aging (p<0.05) was observed for all the materials, except for human enamel and translucent Filtek Supreme XT. Accelerated aging reduced fluorescence in most of the composites evaluated.

Clinical evaluation of the ART technique using high density and resin-modified glass lonomer cements.

PURPOSE: The aim of this study was to evaluate the performance of two different glass ionomer cements using the Atraumatic Restorative Treatment (ART) technique in permanent teeth. MATERIALS AND METHODS: A total of 473 ART restorations were placed in 208 schoolchildren (7-12 years of age) by two previously trained operators, using high density and resin-modified glass ionomer cements. All the restorations were photographed at baseline and the patients were asked about postoperative sensitivity. After a period of 8 months, 193 patients were present after recall and 428 restorations were evaluated and photographed. Two independent examiners carried out the evaluation. RESULTS: The results showed a success rate of 86.2% for occlusal restorations with Fuji IX and 88.4% for those restored with Fuji Plus. A total of 86.7% of the approximal restorations with Fuji Plus were also judged to be successful after 8 months. No association was found between the materials and the clinical performance of the ART restorations in class I cavities. CONCLUSION: The type of restorative material did not influence the success or failure rates in class I cavities within this period. Fuji IX showed promising performance for occlusal ART restorations and Fuji Plus is also a promising material for occlusal and approximal ART restorations.