ABSTRACT
The fracture of denture base resins is not uncommon due to different causes and always followed by repairing of fractured portions. The fluctuation of temperature in the oral cavity is an influencing factor on the properties of polymers
Purpose: This study aimed at investigating the mechanical response of thermocycled dentrure base resin; intact and repaired, when subjected to static and dynamic loading
Materials and Methods: Heat cured and chemically polymerized acrylic resins were used. Three metallic moulds were machined for the preparation of 40 samples; 20 intact and 20 repaired ones. All specimens were thermocycled between 5-55[degree sign] C for 400 cycles with dwell time 2 min. Each 20 specimens was assigned according to the applied load; 5 specimens were tested under static loading to determine flexural characteristic, 5 specimens were tested under dynamic sudden loading to measure impact strength and 10 specimens were tested under dynamic cyclic loading to assess fatigue strength. The repaired specimens were examined after each mode of loading to inspect site of failure and its type. Laser Raman spectroscopy was employed in order to calculate the degree of conversion [DC] for both heat cured and chemically polymerized acrylic resin
Results: The aged specimens recorded higher flexural characteristics, impact and fatigue strengths than published in the literature. This may be referred to the increased [DC] after thermo-cycling as indicated by Raman spectra. In this study, the mode of failure was cohesive in the repaired material under static loading while it was adhesive under dynamic loading. Generally, the reduction in the tested properties of the repaired specimens was in common trend by about 1/3 those of intact ones
ABSTRACT
Purpose: To investigate the influence of the fillers on the shear bond strength of hybrid and nan-ofilled resin based restorative materials bonded with unfilled and filled bonding agents to dentin substrate
Materials and Methods: Two types of resin based restorative materials; hybrid and nano-filled composites; and two types of bonding agent systems; unfilled and filled bonding agents; were used in this study. A total of twenty specimens for shear bond strength testing were prepared, ten for each restorative material. Five specimens of each group were bonded with unfilled bonding agent, whereas the other five were bonded with filled bonding agent. The specimens were then subjected to shear bond strength test and scanning electron micrograph characterization of the hybrid layer morphology
Results: When comparing the two types of resin based restorative materials; nanofilled composite showed always higher shear bond values than the corresponding hybrid ones. However, no significant difference was found. But when comparing the two types of the bonding agent systems the composites bonded with the unfilled bonding agent recorded higher values than the corresponding ones bonded with the filled bonding agents. This was significant only with the nanofilled composite [P < 0.05] scanning electron [SE] microscopic examination confirmed the obtained results
Conclusions: 1-The incorporating filler characteristics; loading and size distribution; in resin based restoration influence their shear bond strength. 2- The optimal adaptation of the unfilled bonding agent system to the dentin is a contributing factor in improving their shear bond strength. 3- The incorporating fillers in the bonding agent system has a negative effect on the of shear bond strength
ABSTRACT
This research was performed to evaluate some physico-mechanical properties of four different types of provisional restorative materials: water sorption, color stability, flexural strength and marginal fit. The tested materials included one type of heat-processed methyl methacrylate resin, one type of auto-polymerized methyl methacrylate resin and two types of auto-polymerized resin composite [hand-mixed and auto-mixed]. As regards the water sorption test, the corrected water sorption of the disc specimens of the four investigated materials [10 mm in diameter, 2 mm in thickness] was calculated up to six weeks immersion period in distilled water. Concerning the color stability test, the disc specimens of the four tested materials [10 mm in diameter, 2 mm in thickness] were immersed in distilled water for one month the color change [AE] was calculated after one week and one month. For flexural strength test, the bar specimens [25 x 5 x 2 mm] of the four tested materials were subjected to a three point loading using the Universal Testing Machine 24 hours after polymerization. As regards the marginal fit test, a die resembling a prepared molar was constructed and the marginal gap in millimeters was measured for the four tested materials using the Travelling Microscope. Based on the results of this study, it can be concluded that: [1] The method of activation of the tested provisional restorative materials, whether heat or chemical processing, plays the principal role in the improvement of the selected physico-mechanical properties. [2] The compositional pattern of the tested provisional restorative materials regarding the resin type and/or the incorporated filler type and loading affect dramatically their physico-mechanical behaviour. [3] The dispensing system [mixing technique] of the provisional restorative materials is a contributing factor in obtaining adequate physico-mechanical properties. [4] The water sorption process is usually associated with color change of the tested provisional restorative materials
ABSTRACT
Life usually gets simpler, but in the case of photocuring dental restorative materials just the opposite is true. Confusing and contradictory barrages of clinical claims have been made with the evergrowing variety of light curing sources, techniques and materials available today. This study was carried out to evaluate the marginal integrity of different elastic modulus resin composites polymerized using Light Emitting Diodes [LED] and Halogen light curing units [LCUs] in either standard or exponential curing mode. Sixty standardized box-shaped class V cavities were prepared in sound human premolars. The teeth were randomly divided into three equal groups according to the resin composite utilized. In the first group, cavities were restored with Teric Ceram, the second group, restored with Tetric Flow, and the third group, cavities were lined with Tetric Flow then restored with Tetric Ceram. Each group was further subdivided into two equal subgroups according to the LCU used; either LED or Halogen. In all teeth the buccal cavities were cured in standard full intensity mode [400 mW/cm[2] for 40 seconds], while the lingual cavities were cured in an exponential mode [0-400 mW/cm[2] for 12 seconds, plus 400 mW/cm[2] for 28 seconds] in case of LED, and [120- 400 mW/cm[2] for 15 seconds plus 400 mW/cm[2] for 25 seconds] in case of Halogen curing. The teeth were then sectioned buccolingually and observed under a binocular stereo microscope connected to an image analysis soft ware. For each specimen, the pore number, mean pore area, as well as the mean surface area of pores, [representing the total gap area at the tooth/restoration interface] were calculated. The results were statistically analyzed using unpaired two-way analysis of variance [Students' t-test]. The results revealed that all groups cured with Halogen LCU showed significantly less total gap area than those cured with LED LCU. The results also revealed that using exponential curing mode or using low modulus flowable resin composite showed superior marginal integrity of class V restoration cured with Halogen LCU, but no statistical significant difference was found in LED cured restorations. Therefore, it was concluded that in order to optimize clinical success, the polymerization protocol must be appropriate for a given light and composite system. Problems reto LED LCU may be corrected when more powerful LEDs are introduced and when LEDs with different spectral outputs are added to the LEDs currently used in dentistry. Clinical relevance. The use of initial low curing intensities and low-modulus composites as a liner or restorative material in class V cavities is strongly advocated when curing with Halogen LCU, but has no significant effect when curing with LED LCU
ABSTRACT
The penetration of visible light into dental materials is an essential factor in photoinitiation of setting reaction and in optical aspects of dental aesthetics. Recently, the indirect composite restoration is a versatile technique for aesthetic restoration of posterior teeth. This technique offers improvement in overcoming some of the problems associated with direct placement composites. However, the indirect procedure remains technique sensitive principally related to the luting agent used to bond the resin composite inlay to the tooth structure. The purpose of the present investigation was to analyse the optical transmission through different indirect resin composite restorations. The effect of the material, shade, thickness and surface finish on light energy transmission was investigated. The effect of transmitted light on resin cement polymerization was also in vestigated. Two commercially available visible light-cured resin composite materials, with two different shades each, were used in this study. A total of 160 resin composite specimens 10 mm in diameter with different thickness ranging from 1 to 4 mm were prepared and visible light-cured according to the manufacturer's instructions. Half of the specimens were prepared against Mylar strip, while the rest of the specimens were finished with silicon carbide paper. Specimens were dry stored at 37°C for 24 hours before testing. The amount of light energy transmitted through various thickness and shades of each light-cured resin composite was measured using spectrophotometer and its influence on degree of conversion of the resin composite luting cement was studied. Data were collected and statistically analysed. It was concluded that the improved light transmission through the indirect resin composite restorations and consequent adequate polymerization of the underlying resin cement couldn't be generalized for all condensable resin composites. The predominant influencing factor was the compositional pattern of the resin composite. Both thickness and shade of the resin composite inlays were the overwhelming factors affecting the light transmission and curing of the underlying luting resin cement. Lighter shades and lower thickness resin composite inlays would guarantee better light transmission and resin cement polymerization. Surface finish of the inlay was not an efficient factor in light transmission and curing of resin cement. If photoactivated resin cement has to be used for a resin-based restoration, the attenuation of the curing light through the restoration must be taken into consideration