Tip Area (tip + area)

Distribution by Scientific Domains


Selected Abstracts


Irradiance Uniformity and Distribution from Dental Light Curing Units

JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 2 2010
FDS RCS (Edin), FRCD(c), RICHARD B. T. PRICE BDS
ABSTRACT Problem:, The irradiance from dental light-curing units (LCUs) is commonly reported as a single number, but this number does not properly describe the light output. Purpose:, This study examined the irradiance uniformity and distribution from a variety of LCUs as well as the effect of different light guides. Materials and Methods:, Five LCUs representing quartz-tungsten-halogen, plasma arc, and light emitting diode units were evaluated. One LCU was evaluated using two different light guides (Standard or Turbo style). The total power emitted from each LCU was measured and the irradiance calculated using conventional methods (ICM). In addition, a beam profiler was used to determine the optically active emitting area, the mean irradiance (IBP), the irradiance distribution, and the Top Hat Factor (THF). Five replications were performed for each test and compared using analysis of variance with Fisher's PLSD tests at a pre-set alpha of 0.05. Results:, The spatial distribution of the irradiance from LCUs was neither universally symmetrical nor was it uniformly distributed across the tip end. Significant differences in both the emitted power and THF were found among the LCUs. The THF values ranged from a high of 0.74 ± 0.01 to a low of 0.32 ± 0.01. Changing from a standard to a turbo light guide increased the irradiance, but significantly reduced beam homogeneity, reduced the total emitted power, and reduced the optical tip area by 60%. Conclusions:, Using different light guides on the same LCU significantly affected the power output, irradiance values, and beam homogeneity. For all LCUs, irradiance values calculated using conventional methods (ICM) did not represent the irradiance distribution across the tip end of the LCU. CLINICAL SIGNIFICANCE Irradiance values calculated using conventional methods assume power uniformity within the beam and do not validly characterize the distribution of the irradiance delivered from dental light curing units. (J Esthet Restor Dent 22:86,103, 2010) [source]


In vitro differences of stress concentrations for internal and external hex implant,abutment connections: a short communication

JOURNAL OF ORAL REHABILITATION, Issue 1 2006
Y. MAEDA
summary, The aim of this study was to clarify the difference in the stress distribution patterns between implants with external-hex or internal-hex connection systems using in vitro models. Three 13 mm fixtures with external-hex and internal-hex connections were installed into an acrylic bone analogue. One piece abutments of 7 mm height was connected. Strain gauges were attached to the abutment surface, and the cervical and fixture tip areas of the bone analogue surface. Vertical and horizontal load applied was 30 N. Data were normalized for each model by obtaining values relative to the sum of the three values. Almost the same force distribution pattern was found under vertical load in both systems. Fixtures with external-hex showed an increase in strain at the cervical area under horizontal load, while in internal-hex fixtures the strain was at the fixture tip area. Within limitations of our model study, it was suggested that fixtures with internal-hex showed widely spread force distribution down to the fixture tip compared with external hex ones. [source]


The Role of Filler Networking in Fatigue Crack Propagation of Elastomers under High-Severity Conditions

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2009
Manfred Klüppel
Abstract Structural parameters of the filler network have been evaluated by fitting quasi-static stress/strain cycles to the dynamic flocculation model. It is found that the size of filler clusters as well as the strength of filler,filler bonds increase with filler loading and carbon black activity (specific surface). This correlates with the behavior of the tear resistance obtained for pulsed loading under high-severity conditions, implying that the characteristics of the filler network govern the fracture properties of filled elastomers. The behavior of the power law exponent of fatigue crack propagation versus tearing energy can be explained by flash temperature effects in the crack tip area. [source]


In vitro differences of stress concentrations for internal and external hex implant,abutment connections: a short communication

JOURNAL OF ORAL REHABILITATION, Issue 1 2006
Y. MAEDA
summary, The aim of this study was to clarify the difference in the stress distribution patterns between implants with external-hex or internal-hex connection systems using in vitro models. Three 13 mm fixtures with external-hex and internal-hex connections were installed into an acrylic bone analogue. One piece abutments of 7 mm height was connected. Strain gauges were attached to the abutment surface, and the cervical and fixture tip areas of the bone analogue surface. Vertical and horizontal load applied was 30 N. Data were normalized for each model by obtaining values relative to the sum of the three values. Almost the same force distribution pattern was found under vertical load in both systems. Fixtures with external-hex showed an increase in strain at the cervical area under horizontal load, while in internal-hex fixtures the strain was at the fixture tip area. Within limitations of our model study, it was suggested that fixtures with internal-hex showed widely spread force distribution down to the fixture tip compared with external hex ones. [source]