Is a calcium hydroxide liner necessary in the treatment of deep caries lesions? A systematic review and meta-analysis.

The aim of this systematic review and meta-analysis was to evaluate whether the use of calcium hydroxide (CH) liner improves the clinical success in the treatment of deep caries lesions of primary and permanent teeth. The review was reported in accordance with the PRISMA Statement. Only studies that evaluated deep carious lesions treated with and without a CH liner were included. The required outcomes had to be obtained by clinical, radiographic or laboratory evaluations. Statistical analyses were performed with the RevMan 5.2 program (The Cochrane Collaboration, Copenhagen, Denmark) for randomized clinical trials with at least 12 months of follow-up, using fixed-effect models at a significance level of P < 0.05. The literature search was performed in eight databases: PubMed (MEDLINE), Lilacs, IBECS, BBO, Web of Science, Scopus, SciELO and The Cochrane Library. A total of 17 studies were included (15 in primary teeth, two in permanent teeth). The overall risk difference for CH versus adhesive system in primary teeth was 0.06 [95% CI -0.01 to 0.13], and the overall risk difference for CH versus GIC was 0.10 [95% CI -0.01 to 0.22], with no significant differences between materials. CH liner did not influence the clinical success of treatment for deep caries lesions of primary or permanent teeth. Although the present analysis demonstrated that use of CH liner in deep caries lesions was unnecessary, the evidence was of moderate to very low quality; thus, further well-designed, randomized and controlled clinical trials are necessary to provide stronger recommendations.

Bone tissue response to an MTA-based endodontic sealer, and the effect of the addition of calcium aluminate and silver particles.

AIM: To evaluate bone tissue reactions in rats to an MTA-based endodontic sealer with and without the addition of various concentrations of C3A or C3A + Ag. METHODOLOGY: Bone tissue reactions were evaluated in 45 Wistar rats after 7, 30 and 90 days (n = 5 per period). Three surgical cavities were prepared on the right femur and filled with 0.2 mL MTA Fillapex, MTA Fillapex + C3A and C3A + Ag at various concentrations: AH Plus (Dentsply DeTrey GmbH, Konstanz, Germany), EndoSequence BC (Brasseler USA, Savannah, GA, USA) or no sealer (negative control). By the end of each experimental period, animals were randomly euthanized. The samples were histologically processed and analysed using a light microscope. The presence of inflammatory cells, fibres and hard tissue barrier formation was evaluated. Data were analysed statistically using nonparametric tests to compare the differences between groups. Multiple groups were compared using the Kruskal-Wallis and Mann-Whitney U-tests with a Bonferroni correction at P = 0.05. RESULTS: The inflammatory response significantly decreased from 30 to 90 days (P < 0.05). Fibre condensation was similar amongst the groups at 07 and 30 days after intervention (P > 0.05). At 90 days, however, fibres were absent in most specimens of EndoSequence BC Sealer, AH Plus, MTA Fillapex and the control group, whilst they were still observed in samples of the modified sealers (P < 0.05). At 90 days, all specimens of AH Plus, EndoSequence BC Sealer and control group had complete formation of hard tissue barrier. In the MTA Fillapex group, as well as in the modified sealers groups, partial deposition of mineralized tissue was noticed. CONCLUSION: The hypothesis tested that the incorporation of C3A and C3A + Ag particles to MTA Fillapex would improve bone tissue repair was partially accepted, since modified MTA Fillapex did not have the same repair potential as the commercial bioceramic material.

Effect of thermally deposited siloxane-methacrylate coating on bonding to glass fibre posts.

AIM: To evaluate the alterations promoted by a thermally deposited siloxane-methacrylate coating on the surface of glass fibre posts and their effect on the bond strength of resin-core materials to the posts. METHODOLOGY: Fibre post surfaces were treated with experimental thermally deposited siloxane-methacrylate coatings or clinically available treatments (i.e. hydrogen peroxide and methylene chloride); nontreated posts were used as controls. The contact angles formed between the post surface and the water/adhesive were measured with a tensiometer. Scanning electron microscopy and electron dispersive spectroscopy were used to examine the topographies and chemical changes in the post surfaces following treatment. Surface roughness was evaluated with laser interferometry. Core resin was bonded to the fibre posts, and microtensile bond strength testing was subsequently performed. The data were individually submitted to anova and Tukey's tests (α = 0.05). RESULTS: The water contact angle was reduced significantly (P < 0.05) by the thermally deposited siloxane-methacrylate coating. All treatments significantly increased the adhesive contact angle (P ≤ 0.016) compared to the control as well as the surface roughness (P ≤ 0.006) and the amount of Si on post surfaces. Greater percentages of Si were observed for the thermally deposited coating. The bond strength to the posts was significantly improved by the thermally deposited coating (P < 0.05), whereas the other treatments did not differ from the control. CONCLUSION: Treating the surface of glass fibre posts with a thermally deposited siloxane-methacrylate coating improved the bond strength to resin-based materials. The coating could be performed by manufacturers of glass fibre posts in order to reduce the number of clinical steps required for luting posts into root canals.

NaOCl Application after Acid Etching and Retention of Cervical Restorations: A 3-Year Randomized Clinical Trial.

This study evaluated the retention of composite resin restorations in noncarious cervical lesions (NCCLs) performed with or without pretreatment with 10% NaOCl solution (deproteinization). A randomized, controlled, split-mouth, double-blinded trial was carried out. Thirty patients with at least two NCCLs were included in the study. The NCCLs were randomly allocated into two treatment groups: control (acid etching with 37% phosphoric acid + placebo solution + Adper Single Bond 2/3M Oral Care + Filtek Z350/3M Oral Care) or experimental group (acid etching with 37% phosphoric acid + 10% NaOCl solution + Adper Single Bond 2 + Filtek Z350). A calibrated examiner evaluated the restorations at baseline (1 week) and recalls (6, 12, 24, and 36 months) using the FDI criteria. The primary outcome evaluated was retention of the restorations. Data were analyzed by the Kaplan-Meier method and the log-rank test (α=0.05). After 3 years, 64 restorations were evaluated in 23 patients. The annual failure rate was 9% for the control group and 17.8% for the experimental group (deproteinization technique). Considering the failures and their distribution among the characteristics of the patients and NCCLs, no statistically significant differences were observed for the control and experimental treatment groups (p=0.077) or the number of teeth in the mouth (p=0.320). Restorations in the mandible (p=0.039) and premolars (p=0.013) showed significantly lower clinical survival rates. The deproteinization pretreatment with a 10% NaOCl solution did not promote additional retention of restorations in NCCLs. (clinicaltrials. gov: NCT03086720).

Characterization of Contemporary Conventional, Bulk-fill, and Self-adhesive Resin Composite Materials.

OBJECTIVE: To evaluate the physical and biological properties of different types of flowable resin composites and their bonding ability to dentin, comparing the performance of self-adhesive and bulk-fill materials with a conventional control. METHODS AND MATERIALS: Four flowable resin composites were tested: two self-adhesive (Y-flow [SA_YF]; and Dyad Flow [SA_DF]); one bulk-fill (Filtek Bulk Fill Flow [BF]); and one conventional composite (Opallis Flow [OF]). The microshear bond strength (µSBS) to dentin (bovine samples) was investigated at 24 hours and 6 months of storage. The materials were also characterized by degree of conversion, cross-link density, water contact angle, color stability, and cell viability (ISO 10993-5/2009) analyses. Data were analyzed using Analysis of Variance and Tukey tests (α=0.05). RESULTS: The µSBS values were higher for control specimens at 24 hours, whereas the resin-dentin bonds were similarly distributed among the groups after aging. Adhesive failure was the most frequent pattern observed at both time intervals. SA_YF was the only material that increased the bond strength over time. Degree of conversion increased in the following order: SA_YF (28.6±1.4%) < BF (49.7±0.8%) < OF (60.0±2.0%) = SA_DF (63.6±2.3%). Cross-link density was similar among all materials. The self-adhesive composites were more hydrophilic than the other types, with BF showing the lowest water contact angle and the greatest color alteration. All resin composites had a biocompatible behavior. CONCLUSION: Chemical composition appeared to be an influential factor affecting the physico-mechanical and biological behavior of the materials tested.

Bonding self-adhesive resin cements to glass fibre posts: to silanate or not silanate?

AIM: To evaluate the bond strength of self-adhesive resin cements (SARCs) to glass fibre posts with or without a silane coupling agent. METHODOLOGY: The SARCs tested were: Maxcem Elite (MXE; Kerr), RelyX Unicem clicker (UNI; 3M ESPE), seT capsule (SET; SDI), and SmartCem 2 (SC2; Dentsply Caulk). The conventional cement RelyX ARC (ARC; 3M ESPE) was evaluated as a reference. Rectangular-shaped flat posts were obtained (Angelus). After silanizing or not the posts, resin cement cylinders were built on the post surfaces. The cylinders were tested in shear after 24 h. Bond strength data were submitted to two-way anova and Student-Newman-Keuls' test (5%). Failure modes were classified under magnification as adhesive failure, mixed failure involving the cement or mixed failure involving the post. RESULTS: For ARC, MXE and SET, the silanated groups had higher bond strengths. For SC2 the silane had no influence, while for UNI silanization decreased the bond strength. The conventional ARC had the lowest bond strength when the posts were not silanated; UNI showed the highest values. When the posts were silanated, SET had the highest values, followed by MXE, ARC and SC2; UNI had the lowest values. A predominance of adhesive failures was detected for all groups, with higher number of mixed failures when the posts were silanated. CONCLUSION: As the silane impaired or generally had no effect on the bond strength of SARCs to the glass fibre posts, and also as the bond strength of all SARCs was higher than the conventional cement when the posts were not silanated, it seems that silanization of glass fibre posts is not necessary when SARCs are used.

Dual and self-curing potential of self-adhesive resin cements as thin films.

In this study, the dual- and self-curing potential of self-adhesive resin cements (SARCs) as thin, clinically-relevant cement films was investigated. The SARCs tested were: BisCem (BSC; Bisco), Maxcem Elite (MXE; Kerr), RelyX Unicem clicker (UNI; 3M ESPE), seT capsule (SET; SDI), and SmartCem 2 (SC2; Dentsply Caulk). The conventional cement RelyX ARC (3M ESPE) was tested as a reference. The degree of conversion (DC) as a function of time was evaluated by real-time Fourier transform infrared spectroscopy with an attenuated total reflectance (ATR) device. The cements were either photoactivated for 40 seconds (dual-cure mode) or not photoactivated (self-cure mode). The cement film thickness was 50 ± 10 µm. The DC (%) was evaluated 1, 5, 10, 15, 20, 25, and 30 minutes after placing the cement on the ATR cell. Data for DC as a function of time were analyzed by two-way repeated measures analysis of variance (ANOVA). DC values at 30 minutes for the self- and dual-cure modes were submitted to one-way ANOVA. Post hoc comparisons were performed using the Student-Newman-Keuls test (p<0.05). The rate and the extent of conversion were lower for the SARCs compared with the conventional cement. Means ± standard deviations (SD) for the dual-cure mode at 30 minutes were: 75 ± 5 (ARC)a, 73 ± 8 (SET)a, 61 ± 4 (MXE)b, 51 ± 9 (BSC)c, 51 ± 4 (UNI)c, and 48 ± 3 (SC2)c, while in the self-cure mode means and SD were 62 ± 6 (ARC)a, 54 ± 3 (MXE)b, 40 ± 6 (SC2)c, 35 ± 2 (UNI)c, 35 ± 3 (SET)c, and 11 ± 3 (BSC)d. The DC for the dual-cure mode was generally higher than the self-cure, irrespective of the time. Discrepancies in DC between the dual- and self-cure modes from 11% to 79% were observed. In conclusion, SARCs may present slower rate of polymerization and lower final DC than conventional resin cements, in either the dual- or self-cure mode.

Effect of LED Light-Curing Spectral Emission Profile on Light-Cured Resin Cement Degree of Conversion.

CLINICAL RELEVANCE: The use of multipeak LED light-curing guarantees efficiency on light activation of Ivocerin-containing light-cured resin cement.

Airborne-particle Abrasion and Dentin Bonding: Systematic Review and Meta-analysis.

CLINICAL RELEVANCE: The literature reviewed suggests that airborne particle abrasion has no negative effects on the bond strength of resin-based materials to dentin and that a positive influence on dentin bond strength was only achieved in specific air-abrasion conditions. SUMMARY: In this systematic review the authors investigated how airborne-particle abrasion (APA) using aluminum oxide affects the bond strength of resin-based materials to dentin. The search was performed in three databases. In vitro studies (Type of study) comparing the bond strength of resin-based materials (Outcome) to air-abraded (Intervention) compared with non-air-abraded (Comparison) human dentin (Population) were included (the PICOT elements are given parenthetically). From 5437 unique articles, 65 were read in full, 33 were included in the qualitative synthesis, and 32 were included in the meta-analysis. Methodologic quality and risk of bias were assessed. Comparisons were performed between air-abraded and control dentin groups by adopting a random-effects model (α=0.05). Additional analyses were carried out for the different parameters used in APA: type of surface treatment in the control group, particle size, air pressure, and APA duration. The bond strength to air-abraded dentin was favored only when the control surface was treated with a hand excavator. For particle size, APA was favored when the particle size was >30 µm and the controls were no treatment or hand excavator or when the particle size was ≤30 µm and the control was bur. In addition, the results favored air-abraded groups only when the pressure was > 5 bar and bur was used in the control group. No significant differences were observed for duration of APA. No comparison on bond strength considering the presence of aging conditions was possible in the included studies due to the low number of studies that aged the specimens. In conclusion, APA had no negative effects on the bond strength of resin-based materials to dentin and was able to improve the dentin bond strength only when the particle size was > 30 µm and air pressure was > 5 bar. PROSPERO registration protocol: CRD42018096128.

Small-scale gold mining and the COVID-19 pandemic: Conflict and cooperation in the Brazilian Amazon.

The COVID-19 pandemic exposes both conflict and cooperation in artisanal and small-scale gold mining in the Brazilian Amazon. Reporting on the experiences of artisanal and small-scale gold miners (garimpeiros, in Brazilian Portuguese), we show how, on the one hand, the pandemic challenges an already precarious working system that could lead garimpeiros, often invisible to public policies, to positions of further vulnerability; and, on the other hand, highlights the capacity of garimpeiros to self-organize and navigate the difficulties by finding alternative solutions to cope with the crisis. This leads us to argue that emerging strategies of cooperation, related to self-organization and communication channels have the potential to provide experiences useful for processes of conflict transformation in the post-crisis. We acknowledge that much depends on the severity of the crisis and its manifestations in the region; nevertheless, the potential for constructive outcomes from the crisis should not be disregarded.

Sealing ability, water sorption, solubility and toothbrushing abrasion resistance of temporary filling materials.

AIM: To evaluate marginal seal, water sorption, solubility and loss of mass after brushing of several temporary filling materials. METHODOLOGY: For marginal seal, Class I cavities, including endodontic access preparations, were made in human molar teeth and restored using one or other of several temporary filling materials (n = 10): zinc oxide/calcium sulphate-based cement (Cavit, 3M,ESPE, St. Paul, MN, USA), zinc oxide/eugenol cement (IRM, Dentsply Caulk, Milford, DE, USA), glass ionomer cement (Vidrion R, SSWhite, Rio de Janeiro, RJ, Brazil) or a dimethacrylate-based filling (Bioplic, Biodinâmica, Londrina, PR, Brazil). Dye penetration was assessed after thermocycling and immersion in 0.5% basic fuchsine solution. For water sorption, solubility and loss of mass analyses, disc-shaped specimens were made. Water sorption and solubility were evaluated by mass alteration after storage in distilled water for 7 days (n = 7). Loss of mass was calculated based on the difference of mass after abrasion with a toothbrush (n = 5), and surfaces were analysed by SEM. Data of water sorption, solubility and loss of mass were submitted to anova and Tukey's test, and marginal sealing data to Kruskal-Wallis test (P < 0.05). RESULTS: Statistically significant differences were observed for marginal sealing (P < 0.0001), water sorption (P < 0.01), solubility (P < 0.01) and loss of mass (P < 0.05). Bioplic had the best marginal seal. Cavit had the greatest water sorption and solubility. Vidrion R and Bioplic had the lowest solubility. Loss of mass after brushing was higher for Cavit, followed by Bioplic, IRM and Vidrion R. Cavit and Vidrion R were worn aggressively by brushing. CONCLUSIONS: The resin-based temporary filling Bioplic produced the best marginal seal, and was associated with the lowest water sorption, solubility and loss of mass.

Optical Stability of High-translucency Resin-based Composites.

This study investigated the stability of the optical properties of high-translucent shades of dental resin-based composites. Four commercial materials (Filtek Z350 XT, Opallis, Amelogen Plus, and IPS Empress Direct) and 14 non-Vita shades were tested. Disc-shaped specimens for each resin-based composite-shade combination (n=6) were evaluated at T0 (baseline), T1 (after 30 days of storage in water), and T2 (after 30 days of storage each in water and a coffee solution). Color measurements were performed according to the L'C'h' color system. Translucency Parameter (TP) and CIEDE2000 color difference (ΔE00) were calculated. Data were statistically analyzed at α = 0.05. Baseline TP values varied from 43 ± 1 to 55 ± 1. Changes in TP at T1 varied from -3.0% (Opallis T-Neutral) to 4.2% (Amelogen Plus Trans Orange), with no major differences from T0. At T2, most resin-based composites showed significantly increased opacity, with changes varying between -15.0% (Empress Direct Trans 20) and -2.7% (Z350 XT Blue). However, the TP values were ≥40 throughout the study. Storage in water caused negligible color differences, with ΔE00 values at T1 ≤ 0.9 ± 0.6. At T2, all materials tested showed significant color difference, and ΔE00 ≥ 3.2 ± 0.2. The orange shades from Opallis and Amelogen Plus showed lower color variation than did the other shades. The most significant optical changes upon storage were detected in the hue and particularly the chroma color coordinate. In conclusion, the high-translucent resin-based composites showed large variability in the stability of their optical properties among the tested brands and different shades of the same material. Regardless of the storage condition, the tested resin-based composites retained their high-translucency character over time.

12 Years of Repair of Amalgam and Composite Resins: A Clinical Study.

OBJECTIVE: The objective of this study was to clinically evaluate repaired posterior amalgam and composite restorations over a 12 year period, investigate the influence of repair in the survival of restorations, and compare their behavior with respect to controls. METHODS: Thirty-four patients, 18 to 80 years of age with 167 restorations, 67 composite resin (RC), and 100 amalgam (AM) restorations, participated. Restorations with localized, marginal, anatomical deficiencies and/or secondary caries, and "clinically judged" suitable for repair or replacement according to US Public Health Service (USPHS) criteria, were randomly assigned to four groups: repair (n=35, 20 AM, 15 RC), replacement (n=43, 21 AM, 22 RC), positive control (n=71, 49 AM, 22 RC), or negative control (n=18, 10 AM, 8 RC). The quality of the restorations was blind scored according to the modified USPHS criteria. Two examiners scored them at initial status (κ=0.74) and after one to five, 10, and 12 years (κ=0.88). Wilcoxon and Mann-Whitney tests provided for comparisons within the same group and between years, respectively. RESULTS: After 12 years, all groups behaved similarly in marginal adaptation, marginal stain, teeth sensitivity, anatomic form, and luster ( p≥0.05). Better behavior in roughness was observed in replaced RC ( p=0.049). CONCLUSIONS: Given that most clinical parameters investigated were similar between all groups during the follow-up, the repair of RC and AM restorations is a good clinical option because it is minimally invasive and can consistently increase the longevity of restorations.

Effect of different surface treatment techniques on the repair strength of indirect composites.

OBJECTIVES: Composite resin restorations present high survival rates and when a failure occurs repair is often possible. The aim of this study was to assess the effect of various repair techniques on indirect restorations. METHODS: LAVA Ultimate (3M), and Clearfil Estenia blocks (Kuraray) were repaired with our without surface roughness treatments, silane application and artificial ageing. Micro-shear bond stress tests were performed, while cohesive strength served as positive control. ANOVA was used for cohesive strength and effect of ageing, and linear mixed models to evaluate the effect of treatment variables on repair strength. RESULTS: Both materials reacted differently on surface treatments. Untreated (no treatment, no silane) repair strength was 16.3±6.3MPa for LAVA Ultimate and 19.0±4.3MPa for Estenia. Thermal cycling resulted in a 14-58% reduction of cohesive strength. Without cycling, all treatments resulted in a significant increase of bond strength in LAVA Ultimate (p<0.003). After cycling use of air-abrasion showed a positive trend for both substrates, significantly effective for LAVA Ultimate (p<0.04), and silane and CoJet for Estenia (p<0.024). The positive effect of HF treatment disappeared after cycling. CONCLUSION: It may be concluded that (1) the effect of surface treatment procedures on the repair bond strength of indirect composites is depended on the substrate and ageing. (2) Silane did not have a clear overall positive effect on bond strength and (3) artificial ageing had a strong negative influence on the stability of the adhesive interface and on the cohesive strength of one indirect composite resin material, but not the other.

Masking Colored Substrates Using Monolithic and Bilayer CAD-CAM Ceramic Structures.

OBJECTIVE: To evaluate the masking ability and translucency of monolithic and bilayer CAD-CAM ceramic structures. METHODS: Discs of high translucency (HT) and low translucency (LT) lithium disilicate-based ceramic (IPS e.max CAD) with different thicknesses (0.7, 1, 1.5, and 2 mm) were evaluated as a monolithic structure or combined (bilayer) with a 0.5-mm-thick zirconia framework (IPS e.max ZirCAD). The masking ability and translucency were calculated based on CIE L*a*b* color coordinates measured with a spectrophotometer (SP60, X-Rite). The translucency parameter (TP) was calculated using color coordinates measured over standard white-and-black backgrounds. The masking ability was calculated by CIEDE2000 color difference metric (ΔE00) for each specimen measured over a tooth-colored substrate (shade A2) compared to three darker backgrounds (shade C4 and two metal substrates). Confidence intervals (CI) for the means (95% CI) were calculated for TP and ΔE00. The Pearson correlation between ΔE00 and TP was investigated for monolithic and bilayer structures over all backgrounds. RESULTS: The thinner the lithium disilicate layer, the greater the translucency and the higher the ΔE00 values. The effect of ceramic thickness on both translucency and masking ability was more pronounced for the monolithic structures. In addition, monolayers always presented a greater color variation than their bilayer counterparts. The metallic background produced greater ΔE00 than the C4-shaded substrate. CONCLUSION: Monolithic veneers were able to mask C4-shaded background but did not mask metallic backgrounds. Bilayer structures showed greater shade masking ability than monolithic structures.

Longevity of Bonding of Self-adhesive Resin Cement to Dentin.

OBJECTIVE: To evaluate the effect of root dentin treatment on the bonding of self-adhesive resin cement after 24 hours and after 6 months. METHODS: A total of 48 single-rooted premolars were endodontically treated and divided into four groups (n=12): Adper Scotchbond Multi-Purpose + RelyX ARC (ARC); RelyX U200 (U200); EDTA + RelyX U200 (EU200); and phosphoric acid (H3PO4) + RelyX U200 (HU200). After filling the roots, an Exacto No. 2 fiber post was cleaned, treated with silane (60 seconds), positioned, and light cured (LED; 60 seconds at 1200 mW/cm(2)). After storage (37°C/24 h), the roots were cut to obtain two discs (1 mm) of each third. They were stored in distilled water (24 hours at 37°C); one disc of each root-third was subjected to the push-out test (0.5 mm/min) at 24 hours and the other disc after six months of water storage (37°C). The data on the root-thirds were averaged for statistical purposes. The average values of bond strength (MPa) were analyzed by two-way analysis of variance and post hoc Student-Newman-Keuls (5%). RESULTS: There were statistical differences for the treatment of dentin (p<0.001), for time (p=0.003), and the interaction of treatment and time (p=0.017). After 24 hours, we observed lower bond strength in the HU200 group when compared with other groups (ARC, U200, and EU200). After six months, HU200 showed the lowest bond strength. Higher strengths were observed for EU200 and U200 similarly, which were higher than ARC. CONCLUSION: The bonding of the self-adhesive resin cement varied over time in the tested groups.

Reliability and failure behavior of CAD-on fixed partial dentures.

OBJECTIVES: To estimate the reliability and failure behavior of fixed partial dentures (FPDs) fabricated using the CAD-on technique. METHODS: FPDs (n=25) were fabricated using a CAD/CAM system: IPS e.max ZirCAD - Crystall./Connect and IPS e.max CAD (Ivoclar). The restoration type ("three-unit bridge") and design method ("multilayer") based on Biogenerics were used. Framework and porcelain structures were united using a fusion ceramic (Crystall./Connect, Ivoclar). Mechanical fatigue was tested in a servohydraulic load frame machine at a cyclic loading (frequency: 2Hz; load ratio: 0.1). Based on previous data from specimens tested in fast fracture, three different stress profiles were used. The lifetime data were analyzed using an inverse power law-Weibull cumulative damage model (ALTA PRO, Reliasoft). All failed specimens were examined under a field emission scanning electron microscope. RESULTS: Porcelain chipping was the predominant (60%) mode of failure for FPDs tested in fast fracture and connector failure was predominant (67%) under fatigue. For fast fracture data, the Weibull modulus (ß) of FPDs was 7.8 combining the two failure modes. When chipping and connector fracture data were analyzed separately, ß values were 7.9 and 2.9. For the step stress fatigue test, ß values were lower than estimated using fast fracture, being 1.6 for connector fracture and 1.3 for porcelain chipping. SIGNIFICANCE: The test method (fast fracture or fatigue) significantly influenced the reliability of FPDs fabricated using the CAD-on technique, but it did not influence their failure behavior.

Strengthening of Porcelain Provided by Resin Cements and Flowable Composites.

This study evaluated the effect of mechanical properties of resin-based luting agents on the strength of resin-coated porcelain. The luting agents tested were two flowable resin composites (Filtek Z350 Flow and Tetric-N Flow), a light-cured resin cement (Variolink Veneer [VV]), and a dual-cured resin cement (Variolink II) in either light-cured (base paste) or dual-cured (base + catalyst pastes [VD]) mode. Flexural strength (σf) and modulus of elasticity (Ef) of the luting agents were measured in three-point bending mode (n=5). Porcelain discs (Vita VM7) were tested either untreated (control) or acid etched, silanized, and coated with the luting agents. Biaxial flexural strength (σbf) of the porcelain discs was tested using a ball-on-ring setup (n=30). The σbf of the resin-coated specimens was calculated at z-axial positions for multilayer specimens in the ball-on-ring test: position z = 0 (ceramic surface at the bonded interface) and position z = -t2 (luting agent surface above ring). The σf and Ef data were subjected to analysis of variance and the Student-Newman-Keuls test (α=0.05). A Weibull analysis was performed for σbf data. Weibull modulus (m) and characteristic strength (σ0) were calculated. Linear regression analyses investigated the relationship between mechanical properties of the luting agents and the strengthening of porcelain. VD had higher and VV had lower mechanical strength than the other materials. At z = 0, all resin-coated groups had higher σbf than the control group. No significant differences between the luting agents were observed for σbf and σ0. At z = -t2, VD had the highest σbf and σ0, whereas VV had the poorest results. No significant differences in m were observed across groups. A linear increase in flexural strength of the porcelain was associated with increased σf and Ef of the luting agents at position z = -t2. In conclusion, resin coating and use of luting agents with better physical properties generally improved the mechanical performance of porcelain.

Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials.

This study was designed to develop and characterize a silica-coating method for crystalline nonsilicate ceramic nanoparticles (Al2O3, TiO2, and ZrO2). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetraethyl orthosilicate as a silica precursor, followed by heat treatment. The chemical and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before preparation of hybrid composites, which contained glass microparticles in addition to the nanoparticles. The composites were mechanically tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chemical and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were observed depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of crystalline nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.

Flexural strength and reliability of monolithic and trilayer ceramic structures obtained by the CAD-on technique.

OBJECTIVE: To evaluate the flexural strength, Weibull modulus, fracture toughness, and failure behavior of ceramic structures obtained by the CAD-on technique, testing the null hypothesis that trilayer structures show similar properties to monolithic structures. METHODS: Bar-shaped (1.8mm×4mm×16mm) monolithic specimens of zirconia (IPS e.max ZirCAD - Ivoclar Vivadent) and trilayer specimens of zirconia/fusion ceramic/lithium dissilicate (IPS e.max ZirCAD/IPS e.max CAD Crystall./Connect/IPS e.max CAD, Ivoclar Vivadent) were fabricated (n=30). Specimens were tested in flexure in 37°C deionized water using a universal testing machine at a crosshead speed of 0.5mm/min. Failure loads were recorded, and the flexural strength values were calculated. Fractography principles were used to examine the fracture surfaces under optical and scanning electron microscopy. Data were statistically analyzed using Student's t-test and Weibull statistics (α=0.05). RESULTS: Monolithic and trilayer specimens showed similar mean flexural strengths, characteristic strengths, and Weibull moduli. Trilayer structures showed greater mean critical flaw and fracture toughness values than monolithic specimens (p<0.001). Most critical flaws in the trilayer groups were located on the Y-TZP surface subjected to tension and propagated catastrophically. Trilayer structures showed no flaw deflection at the interface. SIGNIFICANCE: Considering the CAD-on technique, the trilayer structures showed greater fracture toughness than the monolithic zirconia specimens.