Comparison between a bulk-fill resin-based composite and three luting materials on the cementation of fiberglass-reinforced posts.

Objectives: This study verified the possibility of cementing fiberglass-reinforced posts using a flowable bulk-fill composite (BF), comparing its push-out bond strength and microhardness with these properties of 3 luting materials. Materials and Methods: Sixty endodontically treated bovine roots were used. Posts were cemented using conventional dual-cured cement (CC); self-adhesive cement (SA); dual-cured composite (RC); and BF. Push-out bond strength (n = 10) and microhardness (n = 5) tests were performed after 1 week and 4 months of storage. Two-way repeated measures analysis of variance (ANOVA), 1-way ANOVA, t-test, and Tukey post-hoc tests were applied for the push-out bond strength and microhardness results; and Pearson correlation test was applied to verify the correlation between push-out bond strength and microhardness results (α = 0.05). Results: BF presented higher push-out bond strength than CC and SA in the cervical third before aging (p < 0.01). No differences were found between push-out bond strength before and after aging for all the luting materials (p = 0.84). Regarding hardness, only SA presented higher values measured before than after aging (p < 0.01). RC and BF did not present 80% of the maximum hardness at the apical regions. A strong positive correlation was found between the luting materials' push-out bond strength and microhardness (p < 0.01, R2 = 0.7912). Conclusions: The BF presented comparable or higher push-out bond strength and microhardness than the luting materials, which indicates that it could be used for cementing resin posts in situations where adequate light curing is possible.

Interplay between different manual toothbrushes and brushing loads on erosive tooth wear.

OBJECTIVE: To investigate the effect of different types of manual toothbrushes and brushing loads on the progression of erosive tooth wear (ETW) on enamel. METHODS: Bovine enamel specimens (n = 10) were submitted to a 5-day erosive-abrasive cycling model (0.3 % citric acid for 5 min, artificial saliva for 60 min, 4x/day). Toothbrushing was carried out 2x/day for 15 s, according to the toothbrushes tested (ultra-soft (a): Curaprox 5460; ultra-soft (b): Sensodyne Repair & Protect; soft (a): Colgate Slim Soft; soft (b): Oral-B Indicator Plus; medium: Johnson's Professional; hard: Tek) and brushing loads (1.5 N, 3 N). Surface loss (SL, in µm) was assessed by optical profilometry on conclusion of the cycling. Some of the toothbrush characteristics were evaluated. Data were statistically analyzed (α = 0.05). RESULTS: For the 1.5 N load, the hard brush showed the highest SL value, with statistical significance. The other toothbrushes did not differ significantly, except that ultra-soft (a) caused significantly higher SL than ultra-soft (b). For the 3 N load, hard and soft (a) exhibited the highest SL. Soft (b) and medium had the lowest SL value, with statistical significance. Only soft (a) and ultra-soft (b) showed significant difference between loads, with lower SL for the load of 1.5 N. None of the toothbrush characteristics were significantly correlated with SL. CONCLUSIONS: Although different degrees of enamel surface loss were observed with use of the different toothbrushes, no association was found between the toothbrush characteristics and SL. Depending on the toothbrush, the force of brushing was capable of modulating the ETW of enamel. Based on the brushing loads usually applied by healthy individuals, hard brushes are not recommended for use by patients with ETW. CLINICAL SIGNIFICANCE: The use of hard bristle brushes is not recommended for use by individuals who exert healthy forces when brushing their teeth. The toothbrush characteristics are of secondary importance in terms of causing enamel loss in ETW.

Mechanical Properties of the Mandible in Postmenopausal Women Under Aledronate Treatment.

AIMS: This study evaluated the mechanical properties of mandibular bone tissue retrieved from postmenopausal women under alendronate treatment. METHODS: Twenty postmenopausal women were divided into two groups: healthy postmenopausal subjects (control group) and osteoporotic subjects treated with alendronate (alendronate group). Mandibular bone samples were retrieved with a trephine bur at the time of dental implant placement and fixed in 4% formalin. Samples were processed for hard tissue histology, and the bone surface was analyzed for nanohardness measurement. Nanohardness and elastic modulus were evaluated by using a Berkovich tip with elastic modulus of 1.016x106 MPa, Poisson coefficient of 0.3, and a load of 100 mN. Each cycle was configured with a load time of 18 seconds (speed of 1 mN/second), the discharge time of 18 seconds, and a rest time of 5 seconds during indentation at a depth of 10 µm. RESULTS: The control group presented the highest values for nanohardness and elastic modulus (p less than 0.05) in relation to the osteoporotic subjects. CONCLUSIONS: Within the limitations of the study, it can be concluded that treatment with alendronate negatively influenced the mechanical properties of mandibular bone in postmenopausal women by reducing bone nanohardness and elastic modulus.

Five second photoactivation? A microhardness and marginal adaptation in vitro study in composite resin restorations.

INTRODUCTION: Studies defining the characteristics of light curing units and photoactivation methods are necessary to allow the correct choices to be made in daily practice. This study aimed to determine whether different photoactivation protocols for composite resins [periodic level shifting (PLS) - 5 second and soft-start] are able to maintain or enhance the mechanical properties and marginal adaptation of restorations. METHODS: Restorations were placed in bovine teeth using the following photoactivation methods: continuous light for 20 seconds (control group); PLS technology (PLS - 5 second group); and continuous light and a light guide tip distance of 6 mm after which the tip was placed at the surface of the restoration (soft-start group). The teeth were transversely sectioned in the incisal-cervical direction. Thirty halves were randomly selected for Knoop microhardness testing (n = 10). The other 30 halves were subjected to scanning electron microscopy analysis. The images obtained were measured to identify the highest marginal gap, and statistical tests for variance analysis were conducted. RESULTS: Microhardness tests showed no statistically significant difference between the photoactivation methods analysed (P ≥ 0.01). The tests showed a difference among depths (P < 0.01), with the deeper layers being the hardest. In analysing marginal adaptation, no significant difference was identified between the higher marginal gap values in the continuous (mean = 10.36) and PLS - 5 second (mean = 10.62) groups, and the soft-start group (mean = 5.83) presented the lowest values (P < 0.01). CONCLUSIONS: The PLS - 5 second and soft-start protocols did not alter the hardness of the restorations. Moreover, the PLS - 5 second protocol did not alter the marginal adaptation, whereas the soft-start protocol improved marginal adaptation.

Influence of Curing Units and Indirect Restorative Materials on the Hardness of Two Dual-curing Resin Cements Evaluated by the Nanoindentation Test.

PURPOSE: To evaluate the hardness of a dual-curing self-adhesive resin cement (RelyX U200) and a conventional dual-curing resin cement (RelyX ARC) cured with different light curing units of different wavelengths (Elipar Freelight 2 LED [430 to 480 nm, conventional], Bluephase LED [380 to 515 nm, polywave], AccuCure 3000 Laser [488 nm]) by means of the nanoindentation test. MATERIALS AND METHODS: Bovine incisors were cleaned and then sectioned at the cementoenamel junction to remove the crown. After embedding in acrylic, dentin surfaces of the specimens were exposed and ground flat to standardize the surfaces. To simulate clinically placing indirect restorations, ceramic (IPS e.maxPress/Ivoclar Vivadent) or indirect composite resin (SR Adoro/Ivoclar Vivadent) slabs were cemented on dentin surfaces. The specimens were sectioned longitudinally at low speed under constant irrigation and then polished. In the positive control group, the cement was light cured without the interposition of indirect restorative material; in the negative control group, after the indirect restorative material was cemented, no light curing was performed, allowing only chemical polymerization of the cement. All specimens were stored in distilled water at 37°C for 7 days. Nanoindentadion hardness of the cement layer was measured under a 100-mN load. Data were statistically analyzed using ANOVA and Tukey's test (p < 0.05). RESULTS: Although the self-adhesive cement is technically simple, conventional cement showed the best polymerization performance. The polywave LED technology did not differ significantly from other light-curing units. The hardness of the resin cements evaluated was negatively influenced by the interposition of an indirect restorative material; only the LEDs were able to maintain the same degree of cement polymerization when an indirect restorative material was used. CONCLUSION: The photoactivation step is required during the cementation of indirect restorations to ensure adequate polymerization of dual-curing resin cements.

Influência do método de fotoativação na dureza de uma resina composta / Influence of the photoactivation method on the hardness of a composite resin

Objetivo: avaliar a dureza de uma resina composta fotoativada com dois métodos diferentes, contínuo e soft-start, por meio da variação da distância entre a ponta fotoativadora e a resina composta (7 mm e 0 mm). Materiais e métodos: Foram confeccionados 20 corpos-de-prova, nos quais a superfície irradiada e a oposta foram analisadas, totalizando 40 superfícies divididas em quatro grupos (n = 10): Grupo 1, método contínuo superfície irradiada; Grupo 2, método contínuo superfície oposta; Grupo 3, método soft-start superfície irradiada; Grupo 4, método soft-start superfície oposta. Os corpos-de-prova foram confeccionados com o auxílio de matrizes pretas de polipropileno, com 4 mm de diâmetro e 2 mm de espessura, utilizando a resina composta Z350 (3M ESPE) na cor AO3 e o fotoativador Elipar Freelight 2 (3M ESPE). Os corpos-de-prova foram submetidos ao teste de microdureza Vickers, no microdurômetro HMV- 2000 (Shimadzu). Foram realizados cinco entalhes por superfície, com carga de 50 gf por 45 segundos. Para a análise estatística, foram realizados os testes de ANOVA e Tukey. Resultados: Não foi encontrada diferença estatisticamente signifi cante entre os métodos avaliados nas superfícies irradiadas. Entretanto, nas superfícies opostas, houve diferença entre os protocolos, sendo que o soft-start obteve menores valores de dureza. Quando comparadas as diferentes profundidades, houve redução nos valores de dureza para ambos os métodos de fotoativação, de forma que a porcentagem de dureza máxima de 80% não foi atingida na superfície oposta à irradiada. Relevância: O cirurgião-dentista, em sua prátic clínica, deve atentar para o método de fotoativação de suas restaurações, visto que este pode prejudicar a qualidade da polimerização de resinas compostas, especialmente na profundidade de 2 mm em resinas opaca.

Objective: to evaluate the hardness of a composite resin polymerized with two different methods, continuous and soft-start, by varying the distance between the activator tip and the composite resin (7 mm and 0 mm). Materials and Methods: Twenty test specimens were fabricated, in which the irradiated and the opposite surfaces were analyzed, totaling 40 surfaces divided into 4 groups (n = 10): Group 1, continuous method + irradiated surface; Group 2, continuous method + opposite surface; Group 3, soft-start method + irradiated surface; Group 4, soft-start method + opposite surface. The test specimens were prepared using black polypropylene matrices, with a diameter of 4 mm and thickness of 2 mm, Z350 composite resin (3M ESPE), shade AO3, and the Elipar Freelight 2 curing unit (3M ESPE). The test specimens were subjected to nthe Vickers hardness test in an HMV-2000 microhardness tester (Shimadzu). Five indentations were made per surface with a load of 50 gf for 45 seconds. The ANOVA and Tukey tests were used for the statistical analysis. Results: No statistically signifi cant difference between the evaluated methods was found in the irradiated surfaces; however, in the opposite surfaces, there were differences between protocols, in that the soft-start protocol achieved the lowest hardness values. When comparing the different depths, there was a reduction in hardness values for both activation methods, so that the maximum hardness percentage of 80% was not achieved in the opposite surface. Relevance: The dentist should be knowledgeable of the photoactivation method applied to his/her restorations, since it may reduce the polymerization quality, especially in depths of 2 mm when using opaque resins.