Evaluation of physical properties of a nanocomposite after aging, bleaching and staining.

PURPOSE: The objective of the in vitro study was to assess the effect accelerated artificial aging, bleaching agents and coffee staining on the color, gloss, roughness and microhardness of a nanocomposite. MATERIALS AND METHODS: 120 (7 × 2 mm) were prepared and randomly divided into 2 groups (n = 60) depending on the aging. Each group was further subdivided into 6 subgroups (n = 10) according to the bleaching and staining as follows: 10% carbamide peroxide (10% CP), 10% CP + staining, 35% hydrogen peroxide (35% HP), 35% HP + staining, without bleaching treatment (WB) and WB + staining. Scanning electron microscopy was performed for qualitative analysis of the resin surface. Data were submitted to 3-way analysis of variance (ANOVA) and Tukey's test for multiple comparisons. As for ∆E, multiple comparisons were performed by using Tukey's and Dunnett's tests (α = 0.05). RESULTS: The bleaching reduced significantly the microhardness of the nanocomposite in without aging groups. All physical properties were found to be negatively changed after the aging process, with bleaching treatment with 10% CP increasing significantly the roughness and loss of gloss compared to the 35% HP. Staining reduced microhardness of both with and without aging nanocomposite as well as the color of the former (E>25), a significantly different result compared to controls. CONCLUSIONS: The bleaching reduced the microhardness of the nanocomposite, whereas the aging process changed all the properties studied. The bleaching favored extrinsic staining of the with aging nanocomposite.

Efficacy of tooth bleaching with the prior application of a desensitizing agent.

AIM: In the present study, we evaluated the efficacy of bleaching on enamel and opposite dentin surfaces using 35% hydrogen peroxide (HP) with the prior application of a desensitizing agent. METHODS: Thirty bovine dental fragments, with thicknesses of 1 mm enamel and 1.75 mm dentin, were stained in a solution of black tea. The fragments were randomly divided into three groups (n = 10) according to the following protocols: (a) 2% neutral fluoride + bleaching; (b) desensitizing agent + bleaching; and (c) without desensitizer + bleaching. The bleaching efficacy was evaluated four times: after staining with tea (baseline) and after each of the 3 weeks of bleaching, by means of the CIE Lab method using a reflectance spectrophotometer. The data coordinate L* was evaluated by an analysis of repeated measures with PROC MIXED and Tukey-Kramer's test. The ΔE values were subjected to anova and Tukey's test (α = 0.05). RESULTS: The 35% HP treatment showed greater efficacy on deep dentin after removal of the enamel stains, with increasing means during all times in all treatments. CONCLUSION: The use of a desensitizing agent prior to the bleaching session did not affect the mechanism of action of 35% HP with regard to tooth depth.

Influence of remaining coronal structure and of the marginal design on the fracture strength of roots restored with cast post and core.

OBJECTIVE: The purpose of this study was to evaluate the fracture strength of roots that were prosthetically restored with cast post and core with or without any remaining coronal structure and with different finish lines. MATERIALS AND METHODS: Sixty bovine incisors were sectioned below the cementoenamel junction, endodontically treated and randomly divided into six experimental groups (n = 10) containing teeth with or without any remaining coronal structure and with a beveled shoulder, a chanfered or a shoulder finish line design. The cast post and core were luted with dual-cured resin cement. The metal crowns were cemented with zinc phosphate cement. The specimens were subjected to a tangential compressive load (135° angle) at a crosshead speed of 0.5 mm/min until failure, using a universal testing machine. The fracture strength data were analyzed using the ANOVA and LSMeans (least square means) tests (α = 0.05). RESULTS: The data indicated that the teeth with 2 mm of remaining coronal structure showed the highest fracture strength values when compared with the teeth without any remaining structure (p < 0.05). As to the different finish line designs, the highest fracture strength values were obtained for the beveled shoulder, followed by the chanfered and then by the shoulder designs (p < 0.05). CONCLUSIONS: It may be concluded that, to increase fracture strength, a beveled shoulder and 2 mm of remaining coronal structure are the ideal conditions.

Direct restorative treatment of anterior weared teeth after re-establishment of occlusal vertical dimension: a case report.

OBJECTIVE: The loss of posterior teeth resulting in a lack of stability may lead to excessive mandibular load on some points of occlusion of the remaining teeth, causing wear. The rehabilitation of these cases must be carefully planned and the treatment requires a period of adaptation with a new vertical dimension. BACKGROUND: This case report describes the treatment of a patient with a loss of almost all posterior inferior teeth and a consequential loss of occlusal vertical dimension and accentuated wear of anterior elements. MATERIALS AND METHODS: Provisional removable partial dentures were manufactured and the patient used them for a period of adaptation prior to restoration of the anterior teeth. After the patient's adaptation with the new occlusal dimension, anterior restorations were made using a mycrohibrid resin composite with different color aspects for an optimal stratification. RESULTS: The restorations achieved an aesthetic configuration with ideal function as the final result and the occlusion showed a satisfactory stability for a provisional removable partial dentures. CONCLUSION: This article presents an anterior direct rehabilitation approach not only as an alternative option, but also as viable and less expensive treatment option with an optimally aesthetic and functional result.

Impact of extended radiant exposure time on polymerization depth of fluoride-containing fissure sealer materials.

Physical properties such as surface hardness of dental materials are directly linked to their clinical behavior. The aim of this study was to investigate the influence of extended curing time on the polymerization depth offluoride-containing materials used as pit and fissure sealants. Conventional and extended exposure times (20 and 60 seconds) were used to photoactivate a gold-standard pit and fissure sealant (Fluroshield, Dentsply) and a flowable composite (PermaFlo, Ultradent). Twenty square-shaped samples (n=5) were prepared using a LED device (Bluephase 16i, Ivoclar). The Knoop Hardness Number (KHN) was calculated for the top and bottom surface of each sample 24 hours after polymerization. Bottom/top hardness ratio (B/T KHN) was than calculated. Averages were analyzed by two-way ANOVA and Tukey test (alpha=0.05). The flowable composite had higher KHN than conventional pit and fissure sealant for all experimental conditions (p<0.05). The 60-second photoactivation time increased KHN at the bottom surface and B/T KHN only of composite specimens. The flowable composite had better physical properties than the pit and fissure sealant, and they were improved by extended curing time.

Bond strength to high-crystalline content zirconia after different surface treatments.

The aim of this study was to evaluate the effect of primers, luting systems and aging on bond strength to zirconium oxide substrates. Eighteen zirconia discs (19.5 x 4 mm) were polished and treated (n = 3) either with a MDP primer (Md) or with a MDP and VBATDT primer (MV). In the control group (n = 3) no surface chemical treatment was performed. Zirconia specimens were cemented to prepolymerized composite discs utilizing resin cements - RelyX Unicem or Panavia 21 (RU and Pa, respectively). After 24 h, samples were sectioned for microtensile testing and returned to water at 37 degrees C for two different periods before being tested: 72 h or 60 days + thermocycling (5-55 degrees C/5000 cycles). Bond strength testing was performed at 1 mm/min. Values in MPa were analyzed through ANOVA and Tukey's Studentized Range (HSD) (p > 0.05). The application of MV primer resulted in the highest bond strength (22.77 MPa), statistically superior to Md primer (12.78 MPa), and control groups presented the lowest values (9.17 MPa). When luting systems were compared, RU promoted the highest bond strength (16.07 MPa) in comparison with Pa (13.75 MPa). The average bond strength decrease after aging (9.35 MPa) when compared with initial values (20.46 MPa). The results presented by this in vitro study suggest that a chemical surface treatment based on the MDP and VBATDT combination may improve bond strength between zirconia and luting system, without any previous mechanical treatment, depending on the luting system used. This chemical treatment may result in a reliable alternative to achieve adequate and durable bond strength.

Effect of endodontic sealer and resin luting strategies on pull-out bond strength of glass fiber posts to dentin.

The aim of this study was to evaluate the influence of eugenol-containing endodontic sealers and luting strategy on the pull-out bond strength of glass fiber posts to dentin. Sixty-four bovine incisors were randomly assigned into two groups of 32 specimens each for obturation procedure with gutta-percha only, or with Pulp Canal Sealer EWT Subsequently, the roots were prepared for the fiber post Reforpost and all specimens of each endodontic sealing procedure were allocated to four groups (n = 8), according to the strategies for post cementation: A) Single Bond 2 and RelyX ARC; B) All Bond 2 and C&B cement; C) All Bond 2 and RelyX ARC; D) Single Bond 2 and C&B Cement. The posts were cemented immediately after the endodontic treatment. The pull-out test was performed at a cross-head speed of 0.5 mm/min in a universal testing machine (EMIC). Data (Kgf) were submitted to a two-way ANOVA and Tukey test (p < or = 0.05). The eugenol-based sealer did not influence the pull-out bond strength of fiber posts regardless of the luting strategy. RelyX ARC showed higher bond strength than C&B Cement when used with Single Bond 2 adhesive system, when the eugenol-based sealer was present. All Bond 2, when associated to all cements studied, promoted similar bond strength, regardless of the eugenol-containing endodontic sealer In conclusion, eugenol-containing sealer did not influence the pull-out bond strength values of the resin luting systems for glass fiber post cementation. The bond system and resin cement association from the same manufacturer had similar bond strength values for dentin.