Waiting Time for Coronal Preparation and the Influence of Different Cements on Tensile Strength of Metal Posts

This study aimed to assess the effect of post-cementation waiting time for core preparation of cemented cast posts and cores had on retention in the root canal, using two different luting materials. Sixty extracted human canines were sectioned 16 mm from the root apex. After cast nickel-chromium metal posts and cores were fabricated and luted with zinc phosphate (ZP) cement or resin cement (RC), the specimens were divided into 3 groups (n = 10) according to the waiting time for core preparation: no preparation (control), 15 minutes, or 1 week after the core cementation. At the appropriate time, the specimens were subjected to a tensile load test (0.5 mm/min) until failure. Two-way ANOVA (time versus cement) and the Tukey tests (P < 0.05) showed significantly higher (P < 0.05) tensile strength values for the ZP cement groups than for the RC groups. Core preparation and post-cementation waiting time for core recontouring did not influence the retention strength. ZP was the best material for intraradicular metal post cementation

Influência da aplicação do laser de ND: yag na durabilidade de adesão de um sistema adesivo universal à dentina humana

Pesquisas sobre pré-tratamento da dentina têm sido desenvolvidas a fim de minimizar os efeitos da degradação da interface adesiva e aumentar a longevidade da adesão. A irradiação com laser Neodmiyum: ítrio-aliminum granada (Nd:YAG) promove alterações morfológicas e estruturais na dentina que podem favorecer a estabilidade da resistência de união ao longo do tempo. Este trabalho visou avaliar, in vitro, o efeito do uso do laser de Nd:YAG na resistência de união (RU), imediata e em longo prazo, bem como modo de falha (MF), de um sistema adesivo universal (SAU) à dentina humana, aplicado no método convencional e autocondicionante. Trinta e dois terceiros molares humanos hígidos tiveram suas porções oclusais removidas para exposição da dentina e foram aleatoriamente divididos em 4 grupos (n=8), de acordo com modo de aplicação do SAU (Single Bond Universal, 3M ESPE), autocondicionante ou convencional, e da irradiação da superfície com laser de Nd:YAG (100mJ/10Hz) ou não (controle). As superfícies de dentina foram restauradas com resina composta (FiltekTM Z350 XT, 3M ESPE). Após 24 hs, os blocos dentina-resina foram seccionados em amostras em forma de “palitos” (1mm2 de área adesiva), os quais foram aleatoriamente divididos conforme o tempo de armazenamento em água (AA) após restauração: 24 horas e seis meses. Os palitos foram submetidos ao teste de microtração em máquina universal de ensaio com velocidade de 0.5mm/min. A análise do MF foi realizada por meio de um esteromicroscópio (30x). Os resultados de RU (MPa) foram submetidos ao teste de ANOVA a três critérios (a= 0,05) e os dados de MF a estatística descritiva (%). Não houve interação tripla significativa entre os fatores em estudo (p = 0,603). A irradiação com Nd:YAG resultou em valores significativamente maiores de RU (p = 0,031), independente do modo de aplicação de SAU ou tempo de AA. RU foi estatisticamente semelhante quando SAU foi empregado no modo convencional ou autocondicionante (p &lt; 0,001), tenha sido irradiada ou não a dentina, tanto no tempo 24 horas quanto após 6 meses de AA. A RU foi significativamente reduzida após 6 meses de armazenamento (p = 0,007), independentemente se a dentina foi ou não irradiada e da forma pela qual o sistema adesivo universal foi aplicado. Houve predomínio de falhas adesivas em todos os grupos. Conclui-se que o laser de Nd:YAG afetou positivamente a resistência de união do sistema adesivo universal, independente de seu modo de aplicação, à dentina. No entanto, sua aplicação à dentina não promoveu estabilidade da união ao longo dos 6 meses de armazenamento em água

Effect of green tea extract on bonding durability of an etch-and-rinse adhesive system to caries-affected dentin

Objective Green tea extract has been advocated as a matrix metalloproteinase (MMP) inhibitor; however, its effect on bond durability to caries-affected dentin has never been reported. Thus, the aim of this in vitro study was to evaluate the effect of two MMP inhibitors (2% chlorhexidine and 2% green tea extract), applied after acid etching, on bond durability of an etch-and-rinse adhesive system to caries-affected dentin. Material and Methods Occlusal enamel was removed from third molars to expose the dentin surface, and the molars were submitted to a caries induction protocol for 15 days. After removal of infected dentin, specimens were conditioned with 37% phosphoric acid (15 seconds) and randomly divided into three groups, according to the type of dentin pretreatment (n=10): NT: no treatment; GT: 2% green tea extract; CLX: 2% chlorhexidine. The etch-and-rinse adhesive system (Adper™ Single Bond 2, 3M ESPE, St. Paul, MN, USA) was applied according to the manufacturer's instructions, and composite resin restorations were built on the dentin. After 24 hours, at 37°C, the resin-tooth blocks were sectioned perpendicularly to the adhesive interface in the form of sticks (0.8 mm2 of adhesive area) and randomly subdivided into two groups according to when they were to be submitted to microtensile bond strength (μTBS) testing: immediately or 6 months after storage in distilled water. Data were reported in MPa and submitted to two-way ANOVA for completely randomized blocks, followed by Tukey’s test (α=0.05). Results After 24 hours, there was no significant difference in the μTBS of the groups. After 6 months, the GT group had significantly higher μTBS values. Conclusion It was concluded that the application of 2% green tea extract was able to increase bond durability of the etch-and-rinse system to dentin. Neither the application of chlorhexidine nor non-treatment (NT - control) had any effect on bond strength after water storage

Implant insertion angle and depth : peri-implant bone stress analysis by the finite element method

The study aimed to assess the influence of different implant insertion angles and depths on the stresses produced on the surface of peri-implant bone tissue under axial and oblique loading. The entire study followed the recommendations of the Checklist

Titanium dioxide nanotubes incorporated into bleaching agents: physicochemical characterization and enamel color change

Titanium dioxide nanotubes are nanostructures that can accelerate the oxidation reaction of bleaching procedures and promote a more effective whitening effect. Objective: This study evaluated physicochemical properties of bleaching agents incorporated with titanium dioxide (TiO2) nanotubes, and the effects on tooth color change at different periods. Methodology: 40 premolars were treated according to the following groups (n=10): CP - 10% carbamide peroxide (1 hour daily/21 days); CPN - CP incorporated into TiO2; HP - 40% hydrogen peroxide (three 40-minute sessions/7 days apart); HPN - HP incorporated into TiO2. Color shade was evaluated at five different periods (baseline, after 7, 14 and 21 days of bleaching, and 7 days after end of treatment) according to Vita Classical, CIELab and CIEDE2000 scales. Mean particle size (P), polydispersity (PO) and zeta potential (ZP) were evaluated using dynamic light scattering. Data on the different variables were analyzed by mixed model tests for measures repeated in time (ZP e L*), generalized linear models for measures repeated in time (P, PO, Vita Classical and b*), and Friedman and Mann-Whitney tests (a* and color change/ΔE and ΔE00). Results: CP and CPN presented higher P, higher PO and lower ZP than HP and HPN (p≤0.05). All groups showed a significant decrease in Vita Classical color scores after 7 days of bleaching (p&lt;0.05), and HPN presented a greater significant reduction than the other groups. L* increased in TiO2 presence, in all groups, without any differences (p&gt;0.05) in bleaching time. A significant reduction occurred in the a* and b* values for all the groups, and HPN presented lower a* and b* values (p&lt;0.05) than CPN. ΔE was clinically noticeable after 7 days, in all groups, and all groups resulted in a perceptible color change according to ΔE00. Conclusion:TiO2 did not influence physicochemical properties of the bleaching agents. HPN presented more effective tooth bleaching than CP

Application of polyetheretherketone (PEEK) posts: evaluation of fracture resistance and stress distribution in the root: in vitro and finite element analyses

Abstract To evaluate the feasibility of using a milled polyetheretherketone (PEEK) post and core in endodontically treated teeth with or without a ferrule. Sixty bovine tooth roots were endodontically treated followed by cementation of intraradicular retainers (IR), according to each experimental group: a) non-ferrule glass fiber post (f0FP); b) 2-mm-ferrule glass fiber post (f2FP); c) non-ferrule resized glass fiber post (f0PR); d) 2-mm-ferrule resized glass fiber post (f2PR); e) non-ferrule PEEK post and core (f0PPC); and f) 2-mm-ferrule PEEK post and core (f2PPC). Metal crowns were made and cemented. A periodontal ligament was simulated using polyether. A force was applied to the palatine portion of each sample at 45°, until fracture. Fracture resistance data were submitted to two-way ANOVA and Tukey’s test (α = 0.05). Three-dimensional digital models were developed to calculate the tensions formed in the root using finite element analysis. Models of glass fiber posts and PEEK posts and cores were evaluated with or without a ferrule. The results were analyzed by the Mohr-Coulomb criterion. The type of IR was not influenced by fracture strength (p = 0.243). There were significant statistical differences among the remaining factors. Ferrule groups had greater fracture resistance, and the failure mode of teeth with a ferrule was more catastrophic than the non-ferrule group. A ferrule increases fracture resistance and influences failure mode; the PEEK post and core did not modify the biomechanics of endodontically treated teeth, and resembled the glass fiber post results. The crack initiation point differed between the ferrule and non-ferrule groups

Micro-shear bond strength and surface micromorphology of a feldspathic ceramic treated with different cleaning methods after hydrofluoric acid etching

OBJECTIVE: The aim of this study was to evaluate the effect of feldspathic ceramic surface cleaning on micro-shear bond strength and ceramic surface morphology. MATERIAL AND METHODS: Forty discs of feldspathic ceramic were prepared and etched with 10% hydrofluoric acid for 2 minutes. The discs were randomly distributed into five groups (n=8): C: no treatment, S: water spray + air drying for 1 minute, US: immersion in ultrasonic bath for 5 minutes, F: etching with 37% phosphoric acid for 1 minute, followed by 1-minute rinse, F+US: etching with 37% phosphoric acid for 1 minute, 1-minute rinse and ultrasonic bath for 5 minutes. Composite cylinders were bonded to the discs following application of silane and hydrophobic adhesive for micro-shear bond strength testing in a universal testing machine at 0.5 mm/min crosshead speed until failure. Stereomicroscopy was used to classify failure type. Surface micromorphology of each treatment type was evaluated by scanning electron microscopy at 500 and 2,500 times magnification. RESULTS: One-way ANOVA test showed no significant difference between treatments (p=0.3197) and the most common failure types were cohesive resin cohesion followed by adhesive failure. Micro-shear bond strength of the feldspathic ceramic substrate to the adhesive system was not influenced by the different surface cleaning techniques. Absence of or less residue was observed after etching with hydrofluoric acid for the groups US and F+US. CONCLUSIONS: Combining ceramic cleaning techniques with hydrofluoric acid etching did not affect ceramic bond strength, whereas, when cleaning was associated with ultrasound, less residue was observed

Fracture resistance of abutment screws made of titanium, polyetheretherketone, and carbon fiber-reinforced polyetheretherketone

Fractured abutment screws may be replaced; however, sometimes, the screw cannot be removed and the entire implant must be surgically removed and replaced. The aim of this study was to compare the fracture resistance of abutment retention screws made of titanium, polyetheretherketone (PEEK) and 30% carbon fiber-reinforced PEEK, using an external hexagonal implant/UCLA-type abutment interface assembly. UCLA-type abutments were fixed to implants using titanium screws (Group 1), polyetheretherketone (PEEK) screws (Group 2), and 30% carbon fiber-reinforced PEEK screws (Group 3). The assemblies were placed on a stainless steel holding apparatus to allow for loading at 45o off-axis, in a universal testing machine. A 200 N load (static load) was applied at the central point of the abutment extremity, at a crosshead speed of 5 mm/minute, until failure. Data was analyzed by ANOVA and Tukey&#8217;s range test. The titanium screws had higher fracture resistance, compared with PEEK and 30% carbon fiber-reinforced PEEK screws (p < 0.05). In contrast, no statistically significant difference was observed between the fracture resistance of the PEEK and the 30% carbon fiber-reinforced PEEK screws (p> 0.05). Finally, visual analysis of the fractions revealed that 100% of them occurred at the neck of the abutment screw, suggesting that this is the weakest point of this unit. PEEK abutment screws have lower fracture resistance, in comparison with titanium abutment screws

Small cross-sectional survey of composite restoration attributes associated with choices for replacement

The aim of this work was to present a small cross-sectional survey of composite restoration clinical attributes associated with choices for replacement. Ninety-four composite fillings selected to be replaced were included in this study. A questionnaire was filled out after each procedure in order to assess the clinical conditions that indicated the restoration replacement (marginal staining, unsatisfactory restoration anatomy, marginal fracture, fractured restoration body, painful symptoms, dental fracture, composite discoloration and/or restoration displacement). These conditions could be combined. The chi-square and Exact Fisher tests were performed to analyze the different variables (p < 0.05). The results showed that composite shade discoloration was the main cause of restoration replacement (63.8%). Marginal staining (50%), unsatisfactory restoration anatomy (50%), marginal fracture (14.9%), painful symptoms (8.5%), fractured restoration body (4.3%), dental fracture (1.1%) and total displacement of the restoration (1.1%) were conditions that could be associated. The main cause of dental composite restoration replacement was material shade mismatch with the dental structure (anterior teeth) or marginal staining and unsatisfactory restoration shape (posterior teeth). Marginal staining and composite shade discoloration contrasting with dental structure were related to the presence of caries