ABSTRACT
OBJECTIVE: The aim of this study was to evaluate the flexure strength of unidirectional fiber-reinforced resins under static and cyclic loading with and without thermal cycling. METHODS: The fiber-reinforced resin materials chosen for this project were commercially available endodontic posts and commercially procured bar samples. For all materials, controls for flexure strength were tested in air and in water using three-point loading. Specimens were thermal cycled between 7 and 63 degrees C for 6000 cycles. A staircase approach was used to determine the flexure fatigue limit and scanning microscopy was used to examine the microstructure. RESULTS: The carbon/graphite fiber-reinforced resin posts and the glass FiberKor posts were significantly stronger than the ceramic (zirconia) and the other glass-reinforced resin materials. Thermal cycling caused a significant lowering (11-24%) of the flexure strength for each resin based post system. The ceramic post system decreased only by 2%. Further, for standard size glass fiber-reinforced resin bars, no significant differences between testing in air and water was observed, but a significant difference between static and cyclic loading was noted. SIGNIFICANCE: The decreases in the strength property due to thermal cycling and the cyclic loading of these materials indicates that their utilization in the oral environment enhances their degradation, and potentially shortens their clinical life.
Subject(s)
Composite Resins/chemistry , Dental Materials/chemistry , Air , Bisphenol A-Glycidyl Methacrylate/chemistry , Carbon/chemistry , Carbon Fiber , Glass/chemistry , Humans , Materials Testing , Methacrylates/chemistry , Microscopy, Electron, Scanning , Pliability , Polycarboxylate Cement/chemistry , Post and Core Technique/instrumentation , Stress, Mechanical , Surface Properties , Thermodynamics , Water , Zirconium/chemistryABSTRACT
The purpose of this study was to examine the effect of cyclic loading on the flexural strength and fracture toughness of a conventional glass ionomer cement (GIC), a metal containing GIC, hybrid GICs, and, for comparison, a composite. Two sets of specimens were evaluated: a set of controls (at 37 degrees C and 95% humidity) and a set aged for 9 months at 37 degrees C in water. The specimens were tested in static loading in air and water, and cyclic loaded in water. Cyclic loading and aging decreased the flexure strength of all materials significantly. However, wet static fracture toughness did not change on aging, and occasionally increased. Cyclic fracture toughness was lower with all materials except a hybrid glass ionomer without aging. Deterioration in properties was related to relative amount of glass ionomer vs. the resin component. Both flexural strength and fracture toughness of these materials were significantly affected by testing environment, aging and cyclic loading. The lower the resin component of the material, the lower the mechanical properties. The influence of these parameters should be given importance in considering their clinically durability in the oral environment.
Subject(s)
Glass Ionomer Cements , Analysis of Variance , Bisphenol A-Glycidyl Methacrylate , Composite Resins/chemistry , Dental Stress Analysis , Drug Storage , Glass Ionomer Cements/chemistry , Hardness , Materials Testing , Pliability , Resins, Synthetic , Silanes , Silicon Dioxide , Statistics, Nonparametric , Time FactorsABSTRACT
It is generally viewed that with advancing age, humans and other animals including mice experience a gradual decline in the rate of bone formation. This, in part, may be due to the rise in oxygen-derived free radical formation. Vitamin E, a strong antioxidant, functions as a free radical scavenger that potentially can suppress bone resorption while stimulating bone formation. Although the effects of vitamin E on immune functions are well documented, there is a paucity of information on its effect on skeletal health in vivo. The purpose of this study was to explore the influence of vitamin E supplementation on bone in young adult and old mice. Six and twenty-four month-old male C57BL/6NIA mice each were divided into two groups and fed a diet containing either adequate (30 mg/kg diet) or high (500 mg/kg diet) levels of vitamin E. Thirty days later, mice were killed and bones were removed for analyses including biomechanical testing using three-point bending and mRNA expressions of insulin-like growth factor-I (IGF-I), osteocalcin, and type 1alpha-collagen using Northern blot. In old but not the young adult mice, high-dose vitamin E enhanced bone quality as evident by improved material and structural bone properties in comparison with adequate. This improved quality was accompanied by increases in bone dry weight, protein, and mRNA transcripts for osteocalcin, type Ialpha-collagen, and IGF-I. These data demonstrate that high-dose vitamin E has pronounced effects on bone quality as well as matrix protein in old mice by augmenting bone matrix protein without reducing bone mineralization as evidenced by unaltered bone density.
