Effect of preparation design on the fracture resistance and fracture patterns of 3D printed one-piece endodontic crowns.

STATEMENT OF PROBLEM: The impact of various preparation designs on the fracture resistance and fracture type of mandibular premolars restored with 3 dimensionally (3D) printed, 1-piece endodontic crowns remains unclear. PURPOSE: The purpose of this study was to investigate the effect of different preparation designs on the fracture resistance and fracture patterns of mandibular premolars restored with 3D printed 1-piece endodontic crowns after thermal aging. MATERIAL AND METHODS: Forty-five freshly extracted mandibular premolars received 3 different preparation designs: with at least 2 intact cuspal walls (2CW), with only 1 intact cuspal wall (1CW), and no cuspal wall present (NoCW). One-piece endodontic crowns were designed by using a computer-aided design (CAD) software program, 3D printed, cemented to the prepared teeth with self-adhesive resin cement, and thermocycled between 5 °C and 55 °C in artificial saliva. Subsequently, all specimens were subjected to a fracture test. The results were statistically analyzed using 1-way ANOVA (α=.05), and fracture types of all specimens were examined using a light microscope. RESULTS: The analysis of fracture resistance values across separate designs revealed no statistically significant differences (P>.05). Mean fracture resistance values were 724.5 N in 2CW, 713 N in 1CW, and 861 N in NoCW. In 2CW and 1CW, the 1-piece endodontic crowns mostly displayed Type III fractures, whereas those in NoCW exhibited a combination of Type II and Type III fractures. CONCLUSIONS: The mandibular premolar 1-piece endodontic crowns tested in this study exhibited similar fracture resistance and type of fracture with different preparation designs.

The comparison of the repair bond strength of the composite resin to direct and indirect composite restorations with different surface preparations.

Background: Indirect restorations have been employed in restorative dentistry to solve some of the drawbacks of direct restorations. The aim of this study was to evaluate the effect of different modes of a universal adhesive resin on the repair capacity of two indirect resin composites and a direct resin composite. Methods: Indirect composite resins (Ceramage and Gradia Plus) and a direct composite resin (Filtek Z250) were prepared in a plastic mold with a height and diameter of 2-mm and 6-mm, respectively. Composite blocks were thermocycled (5000 cycles, 5°C-55°C). Then, according to their surface treatments, composite blocks were categorized into six-groups: Group 1: ER (etch&rinse), Group 2: SE (self-etch), Group 3: Bur+ER (bur+etch&rinse), Group 4: Bur+SE (bur+self-etch), Group 5: Bur+Silane+ER (bur+silane+etch&rinse), Group 6: Bur+Silane+SE (bur+silane+self-etch), respectively. After surface treatments and adhesive application for bonding with a direct resin composite, all groups were then thermocycled before performing shear-bond-strength-test. Failure modes were evaluated using a stereomicroscope. Data were analyzed by two-way-ANOVA and Bonferroni-test (P<0.05). Results: The highest bond-strength values were obtained for Bur+Silane+SE groups, while the lowest values were obtained for the Bur+Silane+ER groups for all materials. Statistically significant differences were observed between the Bur+Silane+ER group and ER, Bur+ER and Bur+Silane+SE groups in Gradia Plus (P<0.05). Conclusion: The self-etch-mode of the universal-adhesive and silane applications led to the increase in the repair-strength of the adhesive in the Filtek Z250 and Ceramage. The self-etch-mode of the universal-adhesive might be used to reduce adhesive-application-steps in the clinical repair procedures.

Effect of microabrasion on the staining susceptibility of enamel: An in vitro study.

Background. Enamel microabrasion can eliminate enamel irregularities and discoloration. This study evaluated the staining susceptibility of enamel after microabrasion using different clinical protocols. Methods. A total of 210 extracted bovine incisors were used in this study. The teeth were randomly divided into five groups of 42 teeth each (n=42), including group 1: control (no treatment), group 2: microabrasion, group 3: microabrasion + fluoride polishing, group 4: macroabrasion (fine-grit diamond bur) + microabrasion, and group 5: macroabrasion (finegrit diamond bur) + microabrasion + fluoride polishing. The groups were then randomly divided into two subgroups for discoloration procedures: coffee and distilled water (n=21). A spectrophotometric evaluation was carried out at baseline and on the 1st, 7th, 14th, and 28th days of the staining period. Statistical analyses were performed using repeated-measures ANOVA and the post hoc Bonferroni test at a significance level of 0.05. Results. The greatest color change was observed in group 2 specimens, which were immersed in coffee solutions. The color change values for groups 3, 4, and 5 specimens, which were immersed in distilled water, were higher than those in group 1 specimens (P<0.05). The fluoride polishing + enamel microabrasion treatment groups (groups 3 and 5) exhibited greater resistance to color changes than the matched non-fluoride-polished groups (groups 2 and 4) (P<0.05). Conclusions. The teeth that underwent enamel microabrasion treatment and were polished with fluoride gel became more resistant to color changes. Our findings confirm that enamel microabrasion treatment is a conservative method for localized discoloration.

Effect of laser-assisted retrograde cavity preparation on push-out-bond-strength of mineral trioxide aggregate and calcium-enriched-mixture-cement / Efeito de preparo cavitário retrógrado assistido por laser na força de união de cimento de agregado trióxido mineral e cimento enriquecido com cálcio

Objective: This study aimed to determine the push-out-bond-strength(PBS) of mineral trioxide aggregate (BIOMTA+) and calcium-enriched-mixture-cement (CEM) in retrograde cavities prepared using Er: YAG laser and stainless-steel bur. Material and Methods: The root canals of 60 extracted single-rooted human teeth were prepared, filled and their apical portion of 3-mm were resected using a diamond bur and randomly divided into four groups according to technique of retrograde preparation and filling material as follows(n=15): Group1: bur/ BIOMTA+ ,Group2: bur/ CEM, Group3: Er:YAG laser/ BIOMTA+, Group4: Er:YAG laser/ CEM. PBS test were performed to specimens and failure modes were evaluated. The data were statistically analyzed with ANOVA, Post-Hoc Tukey and t tests (p< 0.05). Results: CEM was exhibited higher than bond strength compared to BIOMTA+ in retrograde cavity prepared using laser (p= 0.021) and BIOMTA+ in retrograde cavity prepared using bur was exhibited higher than bond strength compared to in retrograde cavities prepared using laser (p= 0.024). Failure modes were dominantly cohesive in all groups tested and one representative specimen each failure mode was examined in SEM and the general characteristics of the failure modes were confirmed. Conclusion: With in the limitations of the present study, when used CEM, Er: YAG laser-assisted retrograde cavity preparation positively affected the bond strength values compared to BIO MTA+. Considering its optimal adhesion, the calcium-enriched-mixture-cement (CEM) might be a good option as a filling material in retrograde cavities in clinical use. (AU)

Objetivo: O objetivo deste estudo foi determinar a força de união (PBS) de cimento de agregado trióxido mineral (BIO MTA+) e cimento enriquecido com cálcio (CEM) em preparos cavitários retrógrados realizados com: Laser Er-YAG e brocas de aço inoxidável. Material e Métodos: Canais radiculares de 60 dentes unirradiculares extraídos foram preparados, preenchidos e 3 mm de suas porções apicais foram ressecadas usando uma broca diamantada e divididos randomicamente em quatro grupos de acordo com a técnica de preparação retrógrada e o material de preenchimento (n=15): Grupo 1: Broca/BIO MTA+, Grupo 2: Broca/CEM, Grupo 3: Laser Er-YAG/BIO MTA+, Grupo 4: Laser Er-YAG/CEM. O teste de PBS foi realizado para as amostras e os modelos de falha foram avaliados. Os dados foram analisados estatisticamente pelos testes de ANOVA, Post-Hoc Tukey e testes t (p< 0.05). Resultados: CEM apresentou maior força de união que BIO MTA+ em cavidades retrógradas preparadas com laser (p= 0.021) e BIO MTA+ em cavidades retrógradas preparadas com brocas apresentou maior força de união quando comparado à cavidades retrógradas preparadas com laser (p= 0.024). Os modelos de falha foram predominantemente coesos em todos os grupos testados e um espécime representativo de cada modelo de falha foi examinado em MEV e as características gerais dos modelos de falha foram confirmadas. Conclusão: Com as limitações do presente estudo, quando usou-se CEM, o preparo de cavidades retrógradas através de Laser Er-YAG afetou positivamente os valores da força de união quando comparados com BIO MTA+. Considerando sua ótima adesão, o cimento enriquecido com cálcio (CEM) pode ser uma boa opção como um material de preenchimento em cavidades retrógradas no uso clínico.

Evaluation of the repair capacities and color stabilities of a resin nanoceramic and hybrid CAD/CAM blocks.

PURPOSE: This study evaluated the color stabilities of two computer-aided design and computer-aided manufacturing (CAD/CAM) blocks and a nanofill composite resin and the microtensile bond strength (µTBS) between the materials. MATERIALS AND METHODS: Twelve specimens of 4 mm height were prepared for both Lava Ultimate (L) and Vita Enamic (E) CAD/CAM blocks. Half of the specimens were thermocycled (10,000 cycle, 5° to 55℃) for each material. Both thermocycled and non-thermocycled specimens were surface treated with one of the three different methods (Er,Cr:YSGG laser, bur, or control). For each surface treatment group, one of the thermocycled and one of non-thermocycled specimens were restored using silane (Ceramic Primer II), universal adhesive (Single Bond Universal), and nanofill composite resin of 4-mm height (Filtek Ultimate). The other specimens were restored with the same procedure without using silane. For each group, 1 × 1 × 8 mm bar specimens were prepared using a microcutting device. Bar specimens were thermocycled (10,000 cycle, 5° to 55℃) and microtensile tests were performed. Staining of the materials in coffee solution was also compared using a spectrophotometer. Data were analyzed using one-way ANOVA, t-test and post-hoc Scheffe tests. RESULTS: µTBS were found similar between the thermocycled and non-thermocycled groups (P>.05). The highest µTBS (20.818 MPa) was found in the non-thermocycled, bur-ground, silane-applied E group. Silane increased µTBS at some E groups (P<.05). Composite resin specimens showed more staining than CAD/CAM blocks (P<.05). CONCLUSION: CAD/CAM blocks can be repaired with composite resins after proper surface treatments. Using silane is recommended in repair process. Color differences may be shown between CAD/CAM blocks and the nanofill composite after a certain time period.