Exercise training, creatine supplementation, and bone health in ovariectomized rats.

UNLABELLED: Evidence suggests that creatine may have some beneficial effects on bone. The study aimed to investigate the effects of exercise alone or combined with creatine on bone health in ovariectomized rats. Findings show that exercise, but not creatine, has an important role in improving bone health. INTRODUCTION: The aim of this study was to investigate the effects of exercise training alone or combined with creatine supplementation on bone health parameters in ovariectomized rats. METHODS: Wistar rats were randomly allocated into one of five groups: (i) sham-operated, (ii) ovariectomized non-trained placebo-supplemented, (iii) ovariectomized non-trained creatine-supplemented, (iv) ovariectomized exercise-trained placebo-supplemented, and (v) ovariectomized exercise-trained creatine-supplemented. Downhill running training and/or creatine supplementation (300 mg/kg body weight) were administered for 12 weeks. Bone mineral content (BMC), bone mineral density (BMD), and biomechanical and histomorphometric parameters were assessed. RESULTS: No interaction effects were observed for BMC and BMD at whole body, femur, and lumbar spine (p > 0.05). Importantly, a main effect of training was detected for whole body BMC and BMD (p = 0.003 and p < 0.001, respectively), femoral BMC and BMD (p = 0.005 and p < 0.001, respectively), and lumbar spine BMC and BMD (p < 0.001 and p < 0.001, respectively), suggesting that the trained animals had higher bone mass, irrespective of creatine supplementation. Main effects of training were also observed for maximal load (p < 0.001), stiffness (p < 0.001), and toughness (p = 0.046), indicating beneficial effects of exercise training on bone strength. Neither a main effect of supplementation nor an interaction effect was detected for biomechanical parameters (p > 0.05). No main or interaction effects were observed for any of the histomorphometric parameters evaluated (p > 0.05). CONCLUSIONS: Exercise training, but not creatine supplementation, attenuated ovariectomy-induced bone loss in this rat model.

Understanding contradictory data in contraction stress tests.

The literature shows contradictory results regarding the role of composite shrinkage and elastic modulus as determinants of polymerization stress. The present study aimed at a better understanding of the test mechanics that could explain such divergences among studies. The hypothesis was that the effects of composite shrinkage and elastic modulus on stress depend upon the compliance of the testing system. A commonly used test apparatus was simulated by finite element analysis, with different compliance levels defined by the bonding substrate (steel, glass, composite, or acrylic). Composites with moduli between 1 and 12 GPa and shrinkage values between 0.5% and 6% were modeled. Shrinkage was simulated by thermal analogy. The hypothesis was confirmed. When shrinkage and modulus increased simultaneously, stress increased regardless of the substrate. However, if shrinkage and modulus were inversely related, their magnitudes and interaction with rod material determined the stress response.

Can fiber posts increase root stresses and reduce fracture?

The clinical success of fiber posts has been attributed to their lower elastic modulus. The tested hypothesis was that fiber posts could lead to lower risk of post debonding and lower risk of root fracture, despite an increase in root stresses. Stress analyses were carried out with a 3D finite element model of a premolar restored with a metallic or a fiber post. Bonded and non-bonded post/cement interface conditions were simulated. We calculated risk-of-fracture indices by determining the highest principal stress values divided by the tensile strength. Shear stresses along the post/cement interface were analyzed for the bonded models. Compared with the premolar restored with a metallic post, the fiber post generated lower stresses along the interface and higher stresses in the root. However, with the fiber post, fracture was less likely to occur in the root, since its core and post fracture indices were higher.

Effect of the C-factor and dentin preparation method in the bond strength of a mild self-etch adhesive.

This study evaluated the effect of the C-factor and dentin preparation method (DPM) in the bond strength (BS) of a mild self-etch adhesive; the study also observed the SEM superficial aspects of the corresponding smear layer. For purposes of this study, 25 molars (n=5) were used in a bond strength test. The molars were divided into two parts (buccal and lingual): one part received a Class V cavity (C-factor=3) and the other received a flat surface (C-factor=0) with the same bur type (coarse diamond or carbide bur and fine diamond or carbide bur), both within the same dentin depth. Five teeth were prepared with wet 60-grit and 600-grit SiC papers. After restoration with Clearfil SE Bond, microtensile beans (0.8 mm2) were prepared and tested after 24 hours in a universal testing machine (0.5 mm/minute). An additional two teeth for each DPM were prepared for SEM evaluation of the smear layer superficial aspects. The BS values were submitted to one-way ANOVA, considering only the DPM (flat surfaces) and two-way ANOVA (C-Factor x DPM, considering only burs) with p=0.05. Although the DPM in the flat surfaces was not significant, the standard deviations of carbide bur-prepared specimens were markedly lower. The BS was significantly lower in cavities. The fine carbide bur presented the most favorable smear layer aspect. It was concluded that different dentin preparation methods could not prevent the adverse effect in bond strength of a high C-factor. A coarse cut carbide bur should be avoided prior to a mild self-etch adhesive, because it adversely affected bond strength. In contrast, a fine cut carbide bur provided the best combination: high bond strength with low variability, which suggests a more reliable bond strength performance.

[Dimensional changes of silver and gallium-based alloy]. / Alteração dimensional de amálgama de prata e liga à base de gálio.

Gallium-based dental alloys were created with the aim of solving the problem of toxicity of mercury. The material shows mechanical properties similar to those of dental amalgam, but researches point out two unfavorable characteristics: great corrosion and excessive post-setting expansion, and the latter is capable of cracking dental structures. The aim of this study was to evaluate, during 7 days, the in vitro dimensional alteration of a gallium dental alloy (Galloy, SDI, Australia), in comparison with a dental amalgam containing zinc (F400, SDI, Australia), as a function of the contact with saline solution (0.9% NaCl) during the setting period. The storage experimental conditions were: storage in dry environment, immersion in saline solution and contamination during condensation. Additionally, the effects of contamination during the trituration of dental amalgam and the effects of protecting the surface of the gallium alloy with a fluid resin were studied. Specimens were stored at 37 degrees C +/- 1 degree C, and measuring was carried out, sequentially, every 24 h during 7 days. When the gallium alloy was either contaminated or immersed, an expansion significantly greater than that observed in the other experimental conditions was noticed after 7 days. The application of a fluid resin to protect the surface of the cylinders was able to avoid the increase in expansion caused by superficial moisture. The amalgam alloy did not show significant dimensional alterations, except when it was contaminated during trituration.

Influence of time and adhesive system on the extrusion shear strength between feldspathic porcelain and bovine dentin.

OBJECTIVES: The behavior of dual-cure cements over time remains unclear. This study evaluated the extrusion shear strength of the bond between feldsphatic porcelain and bovine dentin at different time intervals, using three adhesive systems based on dual-cure cements and one based on a self-cure cement. METHODS: The adhesive systems evaluated included: C&B/One-Step, Enforce/Prime&Bond NT Dual-Cure, RelyX ARC/Single Bond and Variolink II/Syntac SC. Discs of bovine root dentin, 2.5 mm thick, had the root canal prepared with a standardized taper. Porcelain truncated cones etched with 4% hydrofluoric acid and silanized were bonded into the perforations. The extrusion shear test was performed after 15 min, 4 h, 12 h, 24 h, and 7 days. Data were analyzed using the Weibull distribution. The failure mode was accessed by stereomicroscope and SEM. RESULTS: Statistical differences were found between 15 min and 7 days for Variolink II/Syntac SC and RelyX ARC/Single Bond, and between 15 min and 24 h for Enforce/Prime&Bond NT Dual-Cure. For C&B/One-Step, difference was found between 15 min and 4 h. Between 24 h and 7 days, only the system RelyX ARC/Single Bond showed a significant increase in the characteristic strength. SEM analysis revealed that the failure involved the hybrid layer/dentin or the hybrid layer/adhesive interfaces, regardless of the time interval and adhesive system. SIGNIFICANCE: High characteristic strengths were observed after 15 min when dual-cure cements were used. In general, the values found at 24 h or 7 days were higher than at 15 min. However, there was always a considerable probability of bonding failure at low stress levels for all the systems tested.

Influence of different dentinal substrates on the tensile bond strength of three adhesive systems.

PURPOSE: To evaluate the influence of the method and duration of storage for different types of teeth prior to their use in dentin bonding tests with three adhesive systems. MATERIALS AND METHODS: Recently extracted sound human molars, bovine incisors, and human caries-free molars obtained from exhumed bones 5 years postmortem were used. The latter group of teeth was kept dry for 6 months, and then rehydrated in distilled water over a period of 30 days. The adhesive systems used were Prime&Bond 2.1. Single Bond, and Etch&Prime 3.0. Human teeth were embedded longitudinally in PVC cylinders; bovine incisors were embedded leaving the buccal surface exposed. Flat dentin surfaces were cut with a diamond disk and ground with up to 600-grit SiC paper. Adhesives were applied following manufacturers' instructions. A silicone mold with a cone-shaped perforation (4.5 mm high and 2 mm diameter at the smallest) was fixed on the dentin surface and filled with TPH composite resin. The specimens were stored in distilled water for two weeks before testing. RESULTS: ANOVA did not detect statistical differences either in the main factors (substrate and adhesive system) or in their interaction (p > 0.05). Tensile bond strength averages ranged from 11.6 to 14.2 MPa. The dentinal substrates showed similar performances, regardless of the adhesives tested. CONCLUSION: The differences among the three dentin substrates do not appear to be critical for the tensile bond strength test for the three adhesive systems. The adhesive systems presented similar bond strengths.

Pilot study on the early shear strength of porcelain-dentin bonding using dual-cure cements.

STATEMENT OF PROBLEM: One of the most critical steps of the porcelain restoration technique is cementation. Mechanical stress before the resin cement reaches a certain degree of polymerization can displace or even fracture the restoration. Dual-cure materials are intended to be more effective at early stages of polymerization because they contain both photoinitiator and components for chemically activated reaction. PURPOSE: This study evaluated the early shear strength of bonding between porcelain and dentin, using dual-cure cements. MATERIAL AND METHODS: Sixty nonrestored human molars and premolars were randomly divided in 12 groups. The dual-cure cements tested were Porcelite and Dual. A chemically activated cement was also tested (C&B luting composite). Ceramic pieces, 3 mm high, were etched with hydrofluoric acid, silane-coated, and then bonded to flat dentin surfaces with each of the cements, associated with Optibond adhesive system. Photoactivation was made by using a light unit with 450 mW/cm2. The specimens were stored in water at 37 degrees C. Testing times were 10, 30, 90 minutes, and 7 days (referred to as maximum strength). RESULTS: Both Porcelite and Dual dual-cure cements show statistically similar shear strength for the same time interval. The chemically activated material showed statistically lower values when compared with both dual-cure cements, regardless of the time interval. Results at 7 days were much higher than those obtained at 90 minutes for the 3 cements tested. CONCLUSIONS: Both dual-cure cements tested presented similar results. The bond strength of dual-cure cements to dentin was higher at all time intervals than that obtained for chemically activated material. The high values for the coefficient of variation confirmed the technique-sensitive nature of the porcelain/dentin bonding procedure. Although dual-cure cements reach higher bonding strength values faster than the chemically activated material, it is not recommended to stress the bonding until 90 minutes after cementation, because the strength at that time is much lower than the maximum.