The challenge of ceramic restorations on dark substrate: a case report.

The use of dental ceramics on anterior teeth is associated with predictable and long-lasting esthetic results. However, treatment on darkened substrates is challenging. Various conservative options, including ceramic veneers, are available to change the shape and color of anterior teeth. The aim of this case report is to describe the esthetic rehabilitation of a darkened central incisor in a maxillary anterior region that had irregular gingival contours, multiple composite resin restorations, and unsatisfactory tooth shapes. Harmony was restored through periodontal recontouring surgery, placement of a lithium disilicate crown (consisting of a veneer cemented to a coping) on the darkened central incisor, and placement of lithium disilicate veneers on the other maxillary anterior teeth.

Influence of different endodontic sealers on bond strength of fiber posts to weakened roots after resin restoration.

OBJECTIVES: To assess the influence of different sealers used in root canal filling, in terms of bond strength (BS) to dentin, after restoration of weakened roots using resin composite (RC) and fiber posts. MATERIAL AND METHODS: Roots of 39 maxillary incisors were used. After root canal preparation, root dentin was flared to produce a space between fiber post and root canal walls. The root canals were randomly distributed into three groups (n = 13), according to the sealer used: Endofill, AH Plus, and Acroseal. After removing the filling material to a depth of 12 mm, the flared roots were adhesively restored using RC. Posts were cemented and, after 24 h, roots were sectioned transversely producing 1-mm-thick slices. The slices from 30 roots were used for push-out test, and failure modes were noted. The remaining slices were analyzed by scanning electron microscopy (SEM). RESULTS: Statistical analysis by 2-way ANOVA showed a significant difference among sealers (p = 0.001) and among root regions (p < 0.001). The BS mean of Endofill was lower and significantly different from the others. Overall, the coronal region presented higher BS mean values, followed by the middle and apical regions of the reinforced roots. The most frequent failure type was the adhesive failure between RC and dentin. SEM analysis showed the formation of a hybrid layer and many tags in the coronal and middle regions, while the apical region exhibited remnants of the endodontic sealers in all groups. CONCLUSIONS: AH Plus and Acroseal sealer groups presented similar results, and the Endofill sealer negatively affected the BS of fiber post to restored root dentin. CLINICAL RELEVANCE: Weakened dentin walls are often found in teeth undergoing endodontic treatment, so the sealer used must allow or at least not interfere the bonding between restorative materials and root dentin.

Different Strategies to Bond Bis-GMA-based Resin Cement to Zirconia.

PURPOSE: To evaluate the effect of different bonding strategies on short- and long-term bis-GMA-based resin cement bond strengths to zirconia. MATERIALS AND METHODS: One hundred twenty samples of fully-sintered zirconia (Prettau Zirconia) were sandblasted and randomly distributed into 5 groups (n = 24): UA: Scotchbond Universal Adhesive; SZP: Signum Zirconia Bond I + II; ZPP: Z-Prime Plus; EXP: MZ experimental primer; CO: no primer application (control). After performing these surface treatments, translucent tubes (0.8 mm diameter and 1.0 mm height) were placed on the zirconia specimens, and bis-GMA-based cement (Duo-Link) was injected into them and light cured. Specimens were tested for microshear bond strength either 24 h or 6 months (m) after water storage (37°C) and surfaces were characterized by SEM and EDX. Two-way ANOVA and Tukey's post-hoc test (p < 0.05) were used to evaluate bond strength results. RESULTS: The mean bond strengths (MPa ± SD) were: UA=14.6 ± 4.7a (24 h); 16.0 ± 4.8a (6 m); SZP = 14.0 ± 5.4ab (24 h); 11.9 ± 2.6ab (6 m); ZPP=8.0 ± 1.8b (24 h); 8.6 ± 3.3b (6 m); EXP = 1.2 ± 0.5c (24 h); 0.6 ± 0.7c (6 m); CO=1.0 ± 1.2c (24 h); 1.3 ± 1.2c (6 m). Bonding strategy significantly influenced bond strength (p = 0.0001), but storage time did not (p = 0.841). Groups UA and SZP showed a homogeneous layer covering the zirconia surface. In these groups, EDX demonstrated the presence of phosphorus. Group ZPP resulted in a nonhomogeneous layer, exposing the zirconia substrate underneath. EXP application resulted in an undetectable layer. CONCLUSION: Water storage did not affect resin cement bond strengths to zirconia irrespective of the surface treatment. Bis-GMA-based resin cement bond strengths to zirconia are affected by specific bonding strategies.

Enamel hypoplasia: challenges of esthetic restorative treatment.

Enamel defects, such as white or yellow-brown spots, usually cause problems that are more esthetic than functional. Enamel hypoplasia may be the result of hereditary, systemic, or local factors. Dental trauma is a local etiologic factor. It is relatively common in the primary dentition and can cause defects on the surface of permanent successors. Treatment for such defects can differ, depending on the depth of the spots. For deeper white-spot lesions, a composite resin restoration may be necessary. This is an excellent mode of treatment, due to both its low cost and its conservation of healthy tooth structure. The objective of this case report is to describe composite resin restoration of a maxillary central incisor affected by enamel hypoplasia.

One-year Clinical Evaluation of Resin Composite Restorations of Noncarious Cervical Lesions in Smokers.

PURPOSE: To evaluate the one-year clinical performance of composite restorations in noncarious cervical lesions placed in smoking and non-smokers using a multimode adhesive system with two adhesive strategies. MATERIALS AND METHODS: Among the selected cervical lesions, four experimental groups were formed based on the patients' smoking habit and bonding strategies with a multimode adhesive system (n = 38): G1: etchand- rinse in non-smokers; G2: selective enamel etching in non-smokers; G3: etch-and-rinse in smokers; G4: selective enamel etching in smokers. The restorations were paired, ie, each patient received at least two restorations. A nanofilled resin composite was applied and light cured incrementally in all groups by one operator. Two calibrated examiners evaluated the restorations at baseline, 6 and 12 months after placement. The modified USPHS criteria were used for evaluation. Data were analyzed using the chi-square (for associations between groups) and McNemar tests. RESULTS: No statistically significant difference was found between groups for the criteria of retention, marginal discoloration, color match, marginal integrity, or sensitivity after 6 and 12 months. The assessments over time showed a statistically significant difference only for marginal discoloration at 12 months for groups 1, 3, and 4 when compared to baseline (p = 0.031). There were no statistical differences for any criteria evaluated among smokers and non-smokers, except for color match, where a difference was found after the baseline evaluation. Regarding the adhesive strategy, etch-and-rinse resulted in a clinical performance similar to that of selective enamel etching over 12 months. CONCLUSION: Neither cigarette smoking habit nor adhesive strategy influenced the clinical performance of resin composite cervical restorations over the first year.

Two-year clinical performance of a two-step etch-and-rinse adhesive in non-carious cervical lesions: Influence of subject's age and dentin etching time.

AIM: The aim of this study was to evaluate the influence of the subject's age and dentin etching time on the clinical performance of a two-step etch-and-rinse adhesive in class V non-carious cervical lesions (NCCLs). MATERIALS AND METHODS: Forty patients with NCCLs (classified as degrees 2 and 3 of dentin sclerosis) were enrolled in this study. The lesions were selected and assigned into two groups (n = 70/group) according to the subject's age: (G1) between 21-35 years old and (G2) between 40-54 years old. Each group was randomly divided into two subgroups (n = 35/group) according to dentin etching time using recommended application time (15 s) and an extended application time (30 s). A total of 140 restorations with XP Bond (Dentsply DeTrey, Germany) were placed. The composite resin Esthet X (Dentsply) was placed incrementally. All restorations were evaluated using the modified USPHS criteria. Data was analyzed by the McNemar and chi-square tests (p < 0.05). RESULTS: At the end of 2 years, 132 restorations (94.2% recall rate) were evaluated. The 24-month retention rates (%) were 93.5 for G1(15), 97.1 for G1(30), 93.9 for G2(15), and 97.0 for G2(30). There were no statistical differences in the retention rates in each recall period among groups. CONCLUSION: For the selected age groups, neither the subject's age nor the etching time had any influence on the clinical performance of XP Bond adhesive in NCCLs over a 24-month period. CLINICAL RELEVANCE: The clinical effectiveness of the XP Bond was excellent after 2 years of clinical service. Long-term clinical evaluations are necessary to confirm this finding.

Bonding of Composite Cements Containing 10-MDP to Zirconia Ceramics Without Dedicated Ceramic Primer.

PURPOSE: To measure zirconia-to-zirconia microtensile bond strength (µTBS) using composite cements with and without primer. MATERIALS AND METHODS: Two Initial Zirconia UHT (GC) sticks (1.8x1.8x5.0 mm) were bonded using four cements with and without their respective manufacturer's primer/adhesive (G-CEM ONE [GOne] and G-Multi Primer, GC; Panavia V5 [Pv5]), and Panavia SA Cement Universal [PSAu], and Clearfil Ceramic Plus, Kuraray Noritake; RelyX Universal (RXu) and Scotchbond Universal Plus [SBUp], 3M Oral Care). Specimens were trimmed to an hour-glass shaped specimen whose isthmus is circular in cross-section. After 1-week water storage, the specimens were either tested immediately (1-week µTBS) or first subjected to 50,000 thermocycles (50kTC-aged µTBS). The fracture mode was categorized as either adhesive interfacial failure, cohesive failure in composite cement, or mixed failure, followed by SEM fracture analysis of selected specimens. Data were analyzed using linear mixed-effects statistics (α = 0.05; variables: composite cement, primer/adhesive application, aging). RESULTS: The statistical analysis revealed no significant differences with aging (p = 0.3662). No significant difference in µTBS with/without primer and aging was recorded for GOne and PSAu. A significantly higher µTBS was recorded for Pv5 and RXu when applied with their respective primer/adhesive. Comparing the four composite cements when they were applied in the manner that resulted in their best performance, a significant difference in 50kTC-aged µTBS was found for PSAu compared to Pv5 and RXu. A significant decrease in µTBS upon 50kTC aging was only recorded for RXu in combination with SBUp. CONCLUSION: Adequate bonding to zirconia requires the functional monomer 10-MDP either contained in the composite cement, in which case a separate 10-MDP primer is no longer needed, or in the separately applied primer/adhesive.

Semidirect Resin Composite Veneers in a Patient with Bruxism.

This case report details the esthetic rehabilitation of a 32-year-old male patient suffering from sleep bruxism, primarily manifesting as a fracture and significant loss of tooth structure in the anterior maxillary central incisors. To address these concerns, the patient underwent a restorative treatment involving the application of semidirect resin composite veneers on the maxillary incisors and direct resin composite restoration on the incisal regions of the maxillary canines. This approach not only restored the functional integrity of the teeth but also significantly enhanced the patient's esthetic appearance.

A Comparative Study of Shade-Matching Reproducibility Using an Intraoral Scanner and a Spectrophotometer.

BACKGROUND: We compared the repeatability of the shade determination of resin composite restorations and acrylic teeth in light and darker shades at baseline and after an aging process through two digital tooth color-matching methods: using a Trios 3Shape intraoral scanner and using a Vita Easyshade Compact spectrophotometer. MATERIAL AND METHODS: Forty upper central incisor acrylic teeth in the shade A1 (n = 10) and A3 (n = 10) were randomly assigned to be restored with Filtek Bulk Fill in the shade A1 (n = 10) or A3 (n = 10). Subsequently, 20 Class V cavities were prepared in a standardized manner (mesio-distal = 3.0 mm, cervical-occlusal = 2.0 mm, depth = 1.5 mm). Cavities were restored using an universal adhesive system and resin composite in two increments and were light-cured. The shade difference between the resin composite Class V restorations in acrylic teeth of the A1 and A3 shades was evaluated at baseline and after aging. Aging was simulated using ultraviolet light for 120 h. An Easyshade device and an intraoral scanner were used under D65 illumination. Measurements were taken five times, on top of the restoration and on the acrylic teeth, in a randomized manner. RESULTS: Data analysis was on the calculation of the arithmetic mean for the percentage of repeatability conducted by the Trios scanner and the Easyshade device. There was no statistically significant comparison between the shade measurement devices (p > 0.05). At baseline, the repeatability for both the Trios intraoral scanner and the Vita Easyshade Compact device for artificial teeth in the shades A1 and A3 was 100%. After aging, the trueness recorded by the intraoral scanner and the Easyshade device for artificial teeth in the shade A1 was 80%. For Class V restoration with shade A1, the intraoral scanner recorded 80% trueness and the Easyshade device recorded 60% trueness at baseline. For shade A3, the intraoral scanner recorded 60% trueness and the Easyshade device recorded 60% trueness. CONCLUSIONS: The intraoral scanner and Easyshade device are reliable for baseline shade selection, but their accuracy decreases after aging, particularly for darker shades.

Does operatory field isolation influence the performance of direct adhesive restorations?

PURPOSE: To evaluate the influence of different adhesive strategies (etch-and-rinse and self-etching adhesives) and type of field isolation (absolute or relative) on the clinical performance of restorations of noncervical carious lesions (NCCLs). MATERIALS AND METHODS: One hundred forty NCCLs were selected from 38 patients, according to previously established inclusion/exclusion criteria, and assigned to one of four groups (n = 35): etch-and-rinse/rubber-dam (ERR), etch-and-rinse/cotton roll (ERC), self-etching/rubber-dam (SER) and self-etching/cotton roll (SEC). The adhesive systems used were: Adper Single Bond 2 (3M ESPE) and Adper SE Plus (3M ESPE), with restorations made using a composite resin (Z350, 3M ESPE). Using the USPHS modified criteria, 140 restorations were evaluated by two calibrated examiners at 5 different times: immediately after placement, at 7 days, and 2, 6, and 12 months. In order to evaluate the presence of gingival recession after the use of the #212 rubber-dam clamp, the clinical crowns of the teeth from groups ERR and SER were measured at six different periods (baseline, immediately, and at 7 days, 2, 6, and 12 months). Data were subjected to McNemar's, chi-square, and Student's t-tests. RESULTS: Both adhesive strategies reduced tooth sensitivity beyond the second period of evaluation (7 days); tooth sensitivity disappeared after the third period of evaluation (2 months). There were no statistically significant differences between the adhesive techniques or isolation techniques, except for a Bravo score for marginal discoloration in group SEC at 6 months, which was significantly different from the other groups. The rubber-dam isolation technique was more uncomfortable for the patient and resulted in short-term gingival recession. CONCLUSION: No significant differences were found between the types of isolation or adhesive strategy in this clinical evaluation, with the exception of 2 restorations in group SEC that showed marginal discoloration, possibly due to inadequate enamel etching by the self-etching adhesive. Class V restorations perform equally well placed with or without rubber-dam.

Linear Accuracy of Intraoral Scanners for Full-Arch Impressions of Implant-Supported Prostheses: A Systematic Review and Meta-Analysis.

This article compares the accuracy of intraoral scanners (IOSs) used in the digital impression of full arches to fabricate implant-supported complete prostheses. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was registered in the Open Science Framework (DOI 10.17605/OSF.IO/CPM9K). Six electronic databases, gray literature databases, and a manual search were performed in April 2022. Studies that evaluated the accuracy of intraoral scan impressions compared with conventional impressions in full-arch impressions were included for complete implant-supported prostheses. In addition, an adapted checklist for reporting in vitro studies was used to assess the risk of bias. Meta-analysis was conducted using a random-effects Hunter- Schmidt model. Nine studies were included in the analysis. IOS impressions present higher accuracy (137.86 µm) than conventional impressions (182.51 µm) (p<0.001). The heterogeneity of the study's methodology was I2»18.34. However, impression accuracy varies significantly with scan body type, IOS type, scanning strategy, and modification technique. For most IOS systems, the acceptable clinical threshold of linear accuracy of 200 µm can be achieved, except for the True Definition Scanner in one of the studies. Based on the results of the included studies, digital impressions using IOS present similar or better linear accuracy than conventional impression techniques.

Clinical performance of cervical restorations with desensitizing agents: 18-month clinical trial.

PURPOSE: To evaluate the clinical performance and postoperative sensitivity of noncarious Class V restorations with and without the use of a potassium oxalate-based desensitizing agent over a period of 18 months. MATERIALS AND METHODS: One hundred forty cervical lesions (40 patients) were selected and randomly divided into four groups: group 1 (G1) - teeth restored with the application of a potassium oxalate-based desensitizing agent (BisBlock) after acid etching and before the application of the adhesive Adper Single Bond 2; group 2 (G2) - teeth restored using the same adhesive system used in G1, without the use of any desensitizing agent; group 3 (G3) - similar to G1, but using the adhesive One-Step; group 4 (G4) - similar to G3, but without the application of BisBlock. All restorations were evaluated (double blind) after 1 week and 2, 6, 12, and 18 months according to the modified USPHS criteria. The McNemar and chi-square tests were used to analyze the results (p ≤ 0.05). RESULTS: There were no statistical differences between groups restored with or without the use of a desensitizing agent for postoperative sensitvity. After 18 months, retention rates proved to be statistically significantly lower for One-Step than Adper Single Bond 2. CONCLUSION: The use of potassium oxalate-based desensitizing agent did not decrease postoperative sensitivity when it was used under composite resin restorations.

Color difference between the vita classical shade guide and composite veneers using the dual-layer technique.

Background: The purpose of this in vitro study was to evaluate the color difference between the Vita Classical Shade Guide and composite veneers using the dual-layer technique. Material and Methods: Thirty samples were fabricated using a custom-made mold (Easy Layering Shade Guide Kit, 3M) using two resin composites: Filtek Supreme Ultra (3M); and Estelite Omega (Tokuyama) (n=3). The composite veneers were made by layering the different enamel and body or dentin shades from each composite. The color measurements were taken using a spectrophotometer (Vita Easyshade V®, Vita Zahnfabrik). The ΔE00 between the Vita Classical Shade Guide (Vita Zahnfabrik) and the composite veneers were calculated using the CIEDE2000 formula. Results: For the composite veneers using Filtek Supreme Ultra, the best match for A1 Vita shade was achieved layering either EA1 with DA2 or DA3; EA2 with DA1 or DA2 (ΔE00= 1.53 ~ 1.96 ± 0.4). For A2 Vita shade the best match would be EA3 with DA3 or EA3 with DA2 (ΔE00= 1.40 ~ 1.85 ± 0.1); or for A3 Vita shade the best match would be EA3 with DA2 2.50±(0.6). For the composite veneers using Estelite Omega, the were no best match for neither A1, A2 or A3 Vita shade (ΔE00> 2.5). Conclusions: The combination of enamel and dentin shades from Filtek Supreme Ultra provided acceptable color match for A1, A2 and A3 shades from the Vita Shade Guide, while Estelite Omega did not provide acceptable color match for any of the Vita Shade Guide standard shades tested. Key words:Color, color matching, optical properties, resin composite, layering.

Effect of dentin age and acid etching time on dentin bonding.

PURPOSE: To compare the bond strengths of young and old dentin using a single-bottle etch-and-rinse adhesive system with two acid-etching times (15 s and 30 s), and to examine the correlation between dentin hardness and bond strength. MATERIALS AND METHODS: Twenty-four molars from 18- to 22- or 55- to 60-year-old patients were prepared to expose the occlusal dentin, cut into two equal parts, and assigned to four groups (G), varying the etching time (15 s and 30 s) and dentin age (young [Y]or old [O]): G15Y, G30Y, G15O and G30O. After etching, AdperSingleBond (3M ESPE) adhesive was applied and the tooth was built up with a composite (Filtek Z250). The specimens were prepared for the microtensile bond strength test (µTBS) at a crosshead speed of 0.5 mm/min and the interfaces were observed under SEM. Also, the Knoop hardness (KHN) of young vs old dentin was measured. RESULTS: The mean (± SD) µTBS (MPa) were: G15Y = 45.9 (± 10.7)a, G15O = 34.1 (± 9.4)b, G30Y = 48.6 (± 14.3)a and G30O = 47.7 (± 11.0)a. Two-way ANOVA showed no difference in µTBS between young and old dentin. Old dentin acid etched for 15 s (G15O) had a lower µTBS than when acid etched for 30 s (G30O). Dentin hardness was higher for old dentin (67.0 ± 4.8KHN) than young dentin (63.7 ± 2.9KHN) (p < 0.004). No correlation between µTBS and dentin hardness was observed. Resin tags were larger and more numerous for young dentin. The hybrid layer formed in intertubular old dentin (G15O) was very thin. CONCLUSION: Bonding to old dentin with 30 s of etching time resulted in higher bond strength and more homogeneous hybrid layer formation than dentin acid etched for 15 s.

Clinical performance of vital bleaching techniques.

This study compared the clinical outcome of bleaching techniques in vital teeth. After IRB approval and informed consent, 90 subjects were selected based on the shade of their anterior teeth (A2 or darker, Vita Classic shade guide). Subjects were assigned to three treatment groups in a split-mouth study design: Group I: HB (at-home bleaching with 10% carbamide peroxide for two weeks) vs OBL (in-office bleaching with 35% hydrogen peroxide, two sessions, two-week intervals, with light irradiation); Group II: OB (in-office bleaching without light irradiation) vs OBL; Group III: HB vs combination (one session plus HB). Color change and color rebound (deltaE) were measured for a 16-week period. Color measurements were carried out with both a spectrophotometer and a shade guide at baseline, 1, 2, 4, 8 and 16 weeks. Tooth sensitivity was evaluated using a VAS scale for 15 days. Both the Student's t-test and Tukey-Kramer test were used to analyze the results (p < 0.05). After one week, one session of OBL followed by HB resulted in lower color values, compared with the other bleaching methods. Group III resulted in the least shade values at one-week evaluation, when compared with the other bleaching methods. After two weeks, HE alone resulted in similar color changes as OB, OBL and OBL+HB. The use of light irradiation did not improve bleaching efficacy (OB = OBL). OBL and OB resulted in higher sensitivity rates than HB.

Effect of grape seed extract-containing phosphoric acid formulations on bonding to enamel and dentin.

The aim was to evaluate the effect of 2% grape seed extract (GSE) containing phosphoric acid (PhA) on the bond strength to enamel and dentin. The control group was 37% PhA. The following three PhA formulations with 2% GSE and 20% ethanol were obtained: GSE5 = 5% PhA; GSE10 = 10% PhA; and GSE20 = 20% PhA. The enamel and dentin surfaces of molars were etched with the acid solutions, followed by Scotchbond Multi-Purpose adhesive and composite resin application. The tensile bond strength (TBS) test evaluated the bond to enamel after 24 h, and the microtensile bond strength (µTBS) test evaluated the bond to dentin after 24 h and 12-month water storage. Etched enamel and dentin were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The TBS data were submitted to one-way ANOVA, while µTBS data were submitted to two-way ANOVA and Tukey's test (α = 0.05). The TBS (MPa) to enamel did not significantly differ among the control (48.1 ± 15.7), GSE5 (46.1 ± 9.6), GSE10 (49.8 ± 13.6) and GSE20 (44.1 ± 11.9) groups (p = 0.537). The µTBS (MPa) to dentin of the control (28.4 ± 14.4) and GSE20 (24.1 ± 8.1) groups were significantly higher than those of the GSE5 (16.8 ± 7.4) and GSE10 (17.5 ± 6.6) groups at 24 h (p < 0.006). After 12-month storage, only GSE5 (21.0 ± 7.8) and GSE10 (17.6 ± 8.0) did not show significantly decreased µTBS (p > 0.145). SEM micrographs showed a shallower enamel etching pattern for GSE5. AFM images showed the formation of collagenous globular structures for GSE5 and GSE10. The different acid solutions did not influence the TBS to enamel, and the µTBS to dentin was stable over time when dentin was etched with GSE5 and GSE10.

Adhesive procedures in daily practice: essential aspects.

Adhesive procedures are essential to most restorative protocols used in modern dentistry. Increasing demand and constant interest in new products have stimulated dental manufacturers to produce new adhesive systems and marketing campaigns that announce fast and easy bonding. However, laboratorial and clinical studies show that, usually, ease of application of an adhesive system does not relate to its competence in creating a quality, long-term adhesive interface. This article will present relevant data from the scientific literature to help clinicians understand quality adhesion and achieve excellent results with the current adhesion systems.

Fracture resistance of veneers in premolars.

OBJECTIVE: The purpose of the study was to compare the fracture resistance of ceramic veneers and composite resin veneers with and without dental preparation. MATERIALS AND METHODS: Forty freshly extracted mandibular premolars were selected and randomly assigned into four groups (n = 10): Group NPR = no dental preparation and direct veneer with 0.2 mm thick composite resin (Amelogen Plus, Ultradent); Group NPC = no dental preparation and 0.2 mm thick lithium disilicate ceramic veneer (IPS e.max Press, Ivoclar Vivadent); Group P2C = Tooth preparation of 0.2 mm and 0.2 mm thick ceramic veneer (IPS e.max Press); and Group P5C = Tooth preparation of 0.5 mm and 0.5 mm-thick ceramic veneer (IPS e.max Press). In all groups, the restorations covered 1 mm of the occlusal surface of the buccal cusp, and the thickness of this area was the same of the buccal area (0.2 mm or 0.5 mm). After the luting procedure, all groups were thermocycled (10,000 cycles, 5°C-55°C) and subjected to fracture resistance test under compression (Instron 4444 with a crosshead speed of 0.5 mm/min). The mode of failure analysis was performed under a ×10 magnification. Data were subjected to one-way ANOVA and Duncan's post hoc test (P < 0.05). RESULTS: The mean fracture resistance (men ± standard deviation) was NPR = 690.33 ± 233, NPC = 790.52 ± 408, P2C = 1131.34 ± 341, and P5C = 983.56 ± 202. There were significant differences of the fracture resistance values between all groups (P = 0.013). NPR and NPC groups showed mean values of fracture resistance significantly lower than P2C. However, P5C presented intermediate values without a significant difference from the other groups. The mode of failure for all groups was mixed (60%), cohesive failures (20%), root failures (15%), and adhesive failures (5%). CONCLUSION: Minimally invasive tooth preparation (0.2-mm) allowed to achieve higher fracture resistance in premolars restored with lithium disilicate ceramic veneers. Attention should be given to the 0.5 mm preparation since catastrophic fractures only happened when this preparation depth was performed.

Microtensile bond strength of a nanofilled composite resin to human dentin after nonvital tooth bleaching.

PURPOSE: The purpose of this in vitro study was to measure the microtensile bond strength of a nanofilled composite resin to human dentin after nonvital bleaching at different post-bleaching time intervals, and to analyze the fracture mode under SEM. MATERIALS AND METHODS: Thirty-six sound human maxillary premolars extracted for orthodontic reasons were prepared in a standardized manner, and randomly assigned to four groups (n = 9): non bleached (control) (NB); bleached with sodium perborate and 35% hydrogen peroxide (SP-HP); bleached with 35% hydrogen peroxide (HP); and bleached with 37% carbamide peroxide (CP). Each group was subdivided into 3 subgroups (n = 3): restored immediately (RO); restored after 7 days (R7); and restored after 14 days (R14). The teeth were stored in distilled water for 24 h, sectioned 4 mm below cementoenamel junction, and the crown was serially sectioned to obtain sticks (0.9 mm2 cross section) for microtensile bond strength testing. The microTBS samples were attached to a universal testing machine (Instron, model 4444), using a Geraldeli's device. The test was performed until the fracture of the specimens, and all specimens were analyzed under a scanning electron microscope (Philips XL-30). RESULTS: Two-way ANOVA (p = 0.05) revealed that there were no statistically significant differences of bond strength values for the bleaching agents used, or at different post-bleaching time intervals. CONCLUSION: It was concluded that the definitive restoration can be accomplished immediately after nonvital bleaching treatment.