Effect of exposure time on curing efficiency of polymerizing units equipped with light-emitting diodes. (57/99)

A study was conducted to evaluate the top and bottom hardness of two composites cured using polymerizing units equipped with light-emitting diodes [LED] (LEDemetron; Elipar FreeLight, Coltolux LED) and one quartz-tungsten halogen device [QTH] (Optilux 501) under different exposure times (20, 40 and 60 sec). A matrix mold 5 mm in diameter and 2 mm in depth was made to obtain five disc-shaped specimens for each experimental group. The specimens were cured by one of the light-curing units (LCUs) for 20, 40 or 60 sec, and the hardness was measured with a Vickers hardness-measuring instrument (50 g/30 sec). Data were subjected to three-way ANOVA and Tukey's test (alpha = 0.05). LED LCUs were as effective as the QTH device for curing both composites. A significant increase in the microhardness values were observed for all light LCUs when the exposure time was changed from 20 sec to 40 sec. The Z250 composite showed hardness values that were usually higher than those of the Charisma composite under similar experimental conditions. LED LCUs are as efficient for curing composites as the QTH device as long as an exposure time of 40 sec or higher is employed. An exposure time of 40 sec is required to provide composites with a uniform and high Knoop hardness when LED light-curing units are employed.  (+info)

Depth of cure and hardness of an indirect composite polymerized with three laboratory curing units. (58/99)

This study determined the hardness and curing depth of a light-activated indirect composite polymerized with three laboratory light-polymerizing units for the purpose of comparing the curing performance of the three units. A light-activated composite material for indirect application (Vita Zeta) was polymerized with three light-polymerizing units equipped with the following light sources: 1) one halogen lamp and two fluorescent lamps (alpha-Light II); 2) three halogen lamps (Twinkle HLG); and 3) one metal halide lamp (Twinkle LI). Knoop hardness and curing depth were determined for groups of five specimens using standardized testing methods. The results were compared using analysis of variance (ANOVA) and Scheffe's S intervals (alpha = 0.05). The Knoop hardness number (KHN) generated with the halogen-fluorescent unit (12.5 KHN) was significantly (P < 0.05) lower than those produced by the halogen unit (13.9 KHN) and the metal halide unit (14.2 KHN). Of the three units, the halogen-fluorescent unit exhibited the lowest depth of cure. Both the hardness and curing depth of the composite were influenced by the laboratory polymerizing units employed.  (+info)

Efficacy of new LED light-curing units in hardening of Class II composite restorations. (59/99)

PURPOSE: The aim of this study was to determine the efficacy of new light-emitting diode (LED) curing units in the hardening of Class II composite restorations. METHODS AND MATERIALS: Disk specimens 2 mm in diameter and 2.5 mm thick were prepared from 2 composites (Vit-l-escence, shade A3, Ultradent; Herculite XRV, shade A2, Kerr) in the following manner. An extracted permanent molar tooth was prepared to receive a Class II restoration with proximal slot only. The tooth was sectioned horizontally on a plane above the gingival floor level such that the remaining depth of the proximal box was 4 mm. A Tofflemire matrix band and retainer were secured around the tooth. Composite specimens were placed below the tooth to coincide with the location of the slot opening at the bottom of the gingival floor. The specimens were subjected to light polymerization with various combinations of curing cycle and light unit: 1 of 3 continuous curing cycles (20 seconds, 40 seconds or 60 seconds) and 1 of 2 LED units (Utralume-5, Ultradent; IQ Smartlite, Dentsply) or a control quartz-tungsten-halogen (QTH) unit (Optilux 501, Kerr). Specimens were stored at 37 degrees C for 24 hours. A hardness tester was used to obtain 4 measurements of Knoop hardness number (KHN) for each surface (upper and lower) of each specimen. Relative hardness (RH) was calculated as the KHN of the lower surface divided by the KHN of the upper surface. Data were analyzed with analysis of variance (ANOVA) and Tukey"s test. RESULTS: ANOVA indicated significant differences in mean RH among the groups (p < 0.001). RH increased with increasing curing time. For the 60-second cycle with Vit-l-escence composite, mean RH was 0.47, 0.25 and 0.39 for the Ultralume-5, IQ Smartlite and Optilux 501 curing units, respectively. For the 60-second cycle with Herculite XRV composite, mean RH was 0.71, 0.81 and 0.56 for the Ultralume-5, IQ Smartlite and Optilux 501 curing units, respectively. CONCLUSIONS: In general, the 2 LED units performed as well as the QTH unit; however, brand of composite and curing cycle had significant effects on RH values.  (+info)

Bacterial, fungal and yeast contamination in six brands of irreversible hydrocolloid impression materials. (60/99)

This study assessed the level of contamination of six commercially available irreversible hydrocolloids (two containing chlorhexidine) and identified the contamination present in the materials. Petri dishes containing selective and enriched culture media were inoculated with alginate powder (0.06 g), in triplicate. After incubation (37 degrees C/7 days), the colony-forming units (CFU) were counted and Gram stained. Biochemical identification of the different morphotypes was also performed. The contamination levels for the materials were: Jeltrate--389 CFU/g; Jeltrate Plus--516 CFU/g; Jeltrate Chromatic--135 CFU/g; Hydrogum--1,455 CFU/g; Kromopan--840 CFU/g; and Greengel--59 CFU/g. Gram staining revealed the presence of Gram-positive bacillus and Gram-positive cocci. The bacteria Staphylococcus epidermidis, Bacillus subtilis, Bacillus sp., Bacillus coagulans, Bacillus licheniformis, Bacillus cereus, Micrococcus luteus, and Nocardia sp.; the filamentous fungi Aspergillus niger, Aspergillus flavus, Rhizopus sp., Neurospora sp.; and the yeast Candida sp. were isolated. The contamination detected in the impression materials points out the need for adopting measures to improve the microbiological quality of these materials. The use of contaminated materials in the oral cavity goes against the basic principles for controlling cross-contamination and may represent a risk for debilitated or immunocompromised patients.  (+info)

Mechanical properties of light-curing composites polymerized with different laboratory photo-curing units. (61/99)

This study aimed to analyze the microhardness (KHN) and diametral tensile strength (DTS) of two hybrid resin composites (TPH Spectrum and Filtek Z250). To this end, the composites were polymerized with six laboratory photo-curing units (LPUs) and the results compared with an alternative polymerization method using conventional halogen light source in conjunction with additional polymerization in an autoclave (15 minutes/100 degrees C). LPUs were used following the manufacturers' instructions. Diametral tensile strength and Knoop hardness tests were conducted for all groups (n=5). Data were statistically compared using ANOVA and Tukey's test (alpha = 0.05). Among the LPUs, the one that provided light curing in conjunction with heat and nitrogen pressure resulted in a significant increase in KHN and DTS of resin composites. Between the resin composites, Filtek Z250 showed higher hardness values than TPH Spectrum. It was concluded that the use of alternative polymerization with conventional light polymerization and autoclave was feasible with a wide implication for the general public in terms of reduced dental treatment cost.  (+info)

Tweezer dexterity aptitude of dental students. (62/99)

The rationale for using the Perceptual Ability Test (PAT) as a component in admissions decisions for dental schools is that candidates vary in an underlying aptitude that is predictive of degree of success in technique course performance and perhaps in clinical performance. There have been periodic attempts to identify tests that more directly measure manual dexterity aptitude that would supplement the predictive power of admissions decisions. Previous research has demonstrated that a commercially available "speeded" tweezer dexterity test (Johnson O'Connor Test #32022) is not associated with performance in dental school or dental practice. Our research investigated both Test #32022 and Test #18 that measure both speed and accuracy as potential predictors of dental school performance in technical and clinical courses. This article reports the results of a longitudinal, comparative study of tweezer dexterity scores for students at the University of the Pacific School of Dentistry during their first and last quarters in school. The goals of the study were to 1) evaluate the correlation between beginning students' scores on two different types of tweezer dexterity tests; 2) compare dental students' scores to normative data for the general population; 3) determine the effect of a dental curriculum on students' performance on Test #18; and 4) evaluate the two tests as potential dental school admission screening instruments in comparison to the PAT. Fifty first-quarter students were tested from a class of 134. Forty-nine of these students were retested on Test #18 during their final quarter. The predictor value of the initial scores for the two dexterity tests was assessed for seven outcome measures reflecting student technique performance. Analysis showed a significant correlation (r=0.318, p<0.05) between the two dexterity tests. The difference between the norm mean (41.58) and the dental student mean for Test #18 (40.42) was not significant (p>0.05). The correlation between the first and final quarter administrations for Test #18 was r=0.517 (p<0.01). The predictive power of these tests for the seven educational outcomes measures was weak. Results suggest that dental student tweezer dexterity is no different from that of the general population and is not changed by completing a dental school curriculum. The ability for an applicant to perform successfully in dental school will not be reliably predicted by tweezer dexterity score.  (+info)

Lawsuit against a dentist related to serious ocular infection possibly linked to water from a dental handpiece. (63/99)

This case report highlights the risks that may be associated with amoebae in the water of a dental unit. A woman with contact lenses visited her dentist for replacement of a bridge. During the treatment, a stream of water was directed from the handpiece into her right eye. Because of subsequent pain in the eye, the patient consulted several ophthalmologists, who discovered abrasive lesions of the cornea and inflammation. Despite antibacterial and anti-inflammatory treatments, the patient"s visual acuity declined gradually over a period of several days. A microbiological examination nearly 2 months later revealed amoebae in corneal samples. A lawsuit against the dentist was initiated. Although a causal relation with the dental treatment was rejected by the judge in this case, high numbers of amoebae in the water of dental units can present a risk if a patient with pre-existing corneal lesions is splashed. According to the precautionary principle, complete evidence of risk does not have to exist to institute measures to protect individuals and society from that risk. This case reinforces the importance of having patients wear safety glasses during dental treatments and of dental personnel draining the waterlines of dental units, as recommended by the Canadian Dental Association.  (+info)

Legionella contamination in the water system of hospital dental settings. (64/99)

BACKGROUND AND AIM OF THE WORK: Among hospital facilities the dental unit is an environment that is at major risk of Legionella due to equipment such as the air/water syringe, the turbine, the micromotor and the scaler which generate potentially harmful aerosols that may to be a source of exposure to Legionella spp. particularly in immunodeficient patients, and those affected by chronic diseases, and also in dental personnel. Therefore, an examination of the extent of Legionella spp. contamination in the dental chairs waterlines and the incoming water supply of some public dental units is the subject of the present study. METHODS: From February 2002 to March 2004, a total of 208 water samples were collected: 160 samples from the water supply of 4 dental chair and 48 samples from the cold incoming tap water of 2 units. RESULTS: Legionella spp. was detected in 46 samples (22.1% ): 19 of them (41.3% of Legionella spp.; 9.1% of the total) were Legionella pneumophila; Pseudomonas aeruginosa was detected in 86 samples (41.4%) and both microorganisms were detected in 2 samples (0.96%). CONCLUSIONS: Our results show a microbiological condition in dental settings, that is not at all satisfactory due to the presence of Legionella in concentrations that are considered to be a health hazard (> or = 10(3)) in certain cases. Given the extent of the health risk in these surroundings, the difficulty in its assessment, and also considering the wide diffusion of general dental care, our investigation has confirmed the need to regularly monitor the microbiological condition of water in dental units.  (+info)