Glass fiber posts relining: can composite opacity influence retention to root canal dentin?

This study aimed at evaluating the influence of glass-fiber post (GFP) relining with composites of different opacities on resin cement layer thickness (CLT), bond strength (BS) to root dentin, and resin cement degree of conversion (DC%). Standardized roots of 52 bovine incisors had their canals prepared and were distributed into 4 groups (n = 10 for CLT and BS; n = 3 for DC%) according to the post used: WP3 (Control)-Whitepost DC3; groups DE, EN and TR-Whitepost DC0.5 relined, respectively, with dentin, enamel, and translucent shade composites. After cementation, specimens were sectioned into six 1.0 mm-thick discs that were submitted to push-out BS test. CLT and failure pattern were evaluated using a stereomicroscope and DC% by micro-Raman spectroscopy. Data were analyzed by two-way ANOVA and Tukey test (α = 0.05). The control group showed greater CLT than all relined groups (p < 0.05), which did not differ from each other (p > 0.05). Groups relined with low opacity composites (TR; EN) showed the highest BS and DC% means (p < 0.05). BS was not different among root thirds (p > 0.05), while DC% decreased from cervical to apical third (p < 0.05). Adhesive failures between cement and dentin were predominant, except for group DE with frequent mixed failures. It could be concluded that composite opacity did not influence CLT, which was thinner when GFP were relined and that relining GFP with lower opacity composites led to higher BS and DC%.

Can the Use of a Warm-Air Stream for Solvent Evaporation Lead to a Dangerous Temperature Increase During Dentin Hybridization?

PURPOSE: To analyze the effect of a warm-air stream for solvent evaporation on the temperature rise in the pulp chamber during dentin hybridization. MATERIALS AND METHODS: Dentin disks with thicknesses of 0.5, 1.0 and 1.5 mm were obtained from extracted human molars. A model tooth was set up with the dentin disks between a molar with an exposed pulp chamber and a crown with an occlusal preparation. A K-type thermocouple connected to a digital thermometer was placed in the molar root until it entered the pulp chamber and made contact with the dentin disks. After 10 s of adhesive application, solvent evaporation was performed for 10, 20, 30, and 40 s and the increase in temperature was monitored for 200 s after the warm-air stream began. RESULTS: The temperature increase was significantly influenced by the thickness of the dentin disks (0.5 mm = 1.0 mm > 1.5 mm). With respect to the duration of the warm-air stream, the temperature increase was as follows: 10 s < 20 s < 30 s < 40 s (p < 0.05). The highest temperature was found after 40 s with dentin disks that were 0.5 mm (16.6°C) and 1.0 mm (15.8°C) thick, whereas the lowest temperature increase occurred after 10 s with a dentin disk that was 1.5 mm thick (4.1°C) (p < 0.05). CONCLUSION: The temperature in the pulp chamber was strongly influenced by the dentin thickness and the duration of the warm-air stream. Thinner dentin and a longer duration of the warm-air stream both lead to a greater temperature increase in the pulp chamber.

Can cement film thickness influence bond strength and fracture resistance of fiber reinforced composite posts?

OBJECTIVES: This study compared the influence of cement film thickness (CFT) on bond strength (BS) and fracture resistance (FR) of fiber-reinforced composite (FRC) posts to root canal. MATERIALS AND METHODS: One hundred bovine incisors were used for BS and FR analysis (n = 10) and distributed into five experimental groups according to FRC post diameters (WhitePost DC no. 0.5, no. 1, no. 2, no. 3, no. 4), leading to five different CFTs. The canals were prepared using drill no. 4 provided by the post manufacturer and irrigated with 2.5% NaOCl. After conditioning (24% H2O2/5 min) and silanization, posts were cemented with resin cement. BS was evaluated using push-out test and FR using the compression test at 45°. A stereomicroscope was used to measure CFT and to analyze failure pattern. BS data were subjected to two-way ANOVA and Scheffé test for contrast (α = 0.05); FR data were subjected to one-way ANOVA. RESULTS: BS was significantly affected by CFT, as the most well-adapted post achieved the highest values (p < 0.05). BS was similar for all root thirds. CFT did not affect fracture resistance. No root fractures were observed. CONCLUSIONS: A FRC post well adapted to the root canal results in higher BS values. Different CFTs did not influence the FR of teeth restored with FRC posts. CLINICAL RELEVANCE: The results indicate that post retention is improved when a well-adapted post is used, although this has not been critical to fracture resistance.

Evaluation of Recementation Protocols for Dislodged Glass Fiber Posts.

PURPOSE: To evaluate different protocols for recementation of dislodged glass fiber posts (GFPs). MATERIALS AND METHODS: The root canals of 50 bovine incisors were prepared to receive GFPs that were conditioned with 24% hydrogen peroxide, silanized, and cemented with a self-adhesive resin cement. After light curing, the specimens were submitted to a pullout test. The dislodged GPFs were distributed into five experimental groups (n = 10) for the recementation surface treatment: NT = no treatment; SI = silane; ET = 92.8% ethanol/silane; HP = 24% hydrogen peroxide/silane; and AL = airborne-particle abrasion (50 µm alumina)/silane. The GFPs were recemented with the same self-adhesive resin cement, and specimens were submiLed to a second pullout test. Data were analyzed with Student t test and one-way ANOVA (α = .05). RESULTS: For all groups, the recementation bond strength was higher than the strength obtained after the first cementa4on (P < .05). There were no statistical differences among the experimental recementation protocols (P = .096). CONCLUSIONS: All recementation protocols might be reliably applied because they led to higher bond strength than the first cementation. Int J Prosthodont 2023;36:e74-e87.

Development and characterization of biological bovine dentin posts.

This study aimed at evaluating the use of biological dentin post (BDP), achieved by milling bovine root, through the analyses of mechanical and optical properties. BDPs were compared to a glass fiber post (GFP) in the following tests (n = 10): a) elastic modulus (E) and flexural resistance (σ) by three point bending test; b) fracture resistance (FR) by compressive load at 45° and failure pattern; c) light transmitting (LT) ability and their influence on the resin cement's degree of conversion (DC%); d) bond strength (BS) by push-out test and failure pattern. Bovine teeth were decoronated and root length was standardized at 14 mm. The canals were prepared and irrigated with 2.5% NaOCl. GFP's surface was conditioned by 1 min immersion in 24% H2O2 solution before silanization. After root embedment, the root canal walls and the BDP's surface were hybridized (H3PO4 37% + self-cured adhesive) for FR and DC% analyses. Posts were fixed into the root canals using a conventional dual resin cement. For BS test, both posts were luted using the conventional and the self-adhesive cementation. A universal testing machine (EMIC DL2000; 1 mm/min) was employed for the mechanical tests (E, σ, FR and BS). For the LT analysis, opaque polyethylene discs were transfixed by the posts, leaving 10 mm of the posts' apical section for measurements. Posts' cervical portion was irradiated (800 mW/cm2) and a spectrometer recorded the number of photons transmitted to previously chosen lateral post regions and at the apical tip. The resin cement DC% was evaluated in several sites of the cement film. After normal distribution were checked (Shapiro-Wilk test), data were submitted to ANOVA (5%) and Scheffe post-hoc test (5%). Results showed that: a) E: BDP > GFP; b) σ: BDP < GFP; c) RF: BDP < GFP; d) LT could not be observed for BDP. For GFPs, the greatest number of photons was observed at the post apical tip. An exponential decay was observed from the cervical to the apical post region; e) resin cement DC% was statistically similar at all points of measurements for both posts; and, f) BS: BDP = GFP, regardless the adhesive protocol used. It was concluded that: a) teeth restored with BDP exhibited lower fracture resistance than those restored with GFP; b) resin cement DC% was not influenced by the light transmitting ability of the post; c) the retention provided by the BDP was similar to the one provided by GFP, independently of the luting protocol.

Influence of the degree of dentine mineralization on pulp chamber temperature increase during resin-based composite (RBC) light-activation.

OBJECTIVES: To analyse the influence of the degree of dentine mineralization on the pulp chamber temperature increase during composite light-activation. METHODS: Dentine discs (2mm thick) obtained from recently extracted teeth or those with extensive dentine sclerosis were analysed by FT-IR spectrometry in order to choose the two discs with the greatest difference in the degree of mineralization. A model tooth was set up with the dentine discs between a molar with the pulp chamber exposed and a crown with a standardized class II cavity. A K-type thermocouple was introduced into the molar root until it came into contact with the dentine discs and the cavity was filled with P60 resin composite. The temperature rise was measured for 120s after light-activation began: Standard (S) 600 mW/cm(2)/40s; Ramp (R) 0-->800 mW/cm(2)/10s+800 mW/cm(2)/10s; Boost (B) 85 0mW/cm(2)/10s and LED (L) 1.300 mW/cm(2)/40s (n=10). The same protocol was repeated after grinding the dentine discs to 1.0 and 0.5mm thickness. RESULTS: The temperature increase was significantly higher in dentine with high degree of mineralization (p<0.05). With respect to the dentine thickness, the following result was found: 2mm<1mm<0.5mm (p<0.05). The light-activation mode also presented significant difference as follows: S>R=L>B (p<0.05). CONCLUSIONS: The higher the degree of dentine mineralization the greater the increase in pulp chamber temperature. The temperature increase was influenced by the light-polymerization mode and dentine thickness.

Avaliação de hipersensibilidade dentinária em função do procedimento clareador: revisão de literatura / Literature review: evaluation of dentin hypersensitivity after tooth bleaching procedures

O clareamento dental como tratamento estético em Odontologia tem sido amplamente empregado nos últimos anos e, visando o melhoramento deste, técnicas e produtos passaram por modificações. Todavia, ainda são encontrados alguns problemas que devem ser contornados. A sensibilidade pós-clareamento afeta mais da metade dos pacientes em diferentes graus. O presente estudo objetiva revisar os principais métodos empregados atualmente para reduzir essa incidência e/ou intensidade, podendo ser utilizados alguns protocolos nas fases pré, trans e pós-operatórias. Entre eles, destacam-se a escolha da técnica e da concentração do gel, uso de dessensibilizantes, aplicação tópica de flúor e administração de analgésicos e anti-inflamatórios.

Tooth bleaching procedures have been largely used. Techniques and products were improved along the years. However, some problems are still present and must be surpassed. Dentin hypersensitivity after tooth bleaching affects over fifty percent of pacients, in different levels. The present study aimed to review the current literature on the methods available to prevent and reduce the incidence and the intensity of hypersensitivity, using clinical protocols before, during and after the bleaching procedure. Among them, we highlight the choice of the technique and gel concentration, use of desensitizing agents and fluoride application, and administration of analgesics and anti-inflammatory.