An in vitro study of microleakage of occlusal composite restorations polymerized by a conventional curing light and a PAC curing light

J Stritikus, B Owens
Journal of Clinical Pediatric Dentistry 2000, 24 (3): 221-7
With the increase in usage of bonded dentistry procedures, so comes the development of advanced technology to polymerize it. The purpose of this in vitro study was to evaluate the microleakage of sealants and resin restorations utilizing two different curing lights. The conventional Ortholux curing light (OCL) and the Plasma Arc Curing (PAC) light attached to the KCP air abrasion unit of American Dental Technologies were utilized to polymerize sealants and resin restorations on extracted third molars and premolars. Forty-eight caries-free teeth were divided into 4 groups of 12 specimens. Occlusal sealants were polymerized on groups 1 and 3. Class I composite resin restorations were polymerized on groups 2 and 4. The PAC light polymerized group 2 and the OCL was used for groups 3 and 4. Therefore a comparison between the two light sources' polymerization could be measured by evaluating the microleakage of the two sets of specimens. The PAC light polymerized the Z100 adhesive for 5 seconds and the OCL polymerized it for 10 seconds. The Z100 A-1 composite placed in two 1 mm increments was polymerized with the PAC light for 10 seconds and the OCL for 40 seconds. The teeth were thermocycled 200 times between 5 degrees C and 55 degrees C. The teeth, coated with fingernail polish excluding the occlusal surface, were soaked in 5% methylene blue for 4 hours, removed, and rinsed with water. The teeth were invested in clear resin (Castin Craft) and sectioned longitudinally using an Isomet diamond saw. Microleakage was scored "0" if no leakage was present. Scored "1" if the leakage was present to 1/2 the preparation depth. Scored "2" if the leakage was present past the 1/2 way point but not to the pulpal floor of the preparation. A score of "3" was used if the leakage reached the pulpal floor. Unpaired t-Tests were used to statistically analyze the data. A significant difference (p < 0.05) was found between groups 1 and 3. The PAC light used to polymerize the sealants in group 1 produced no microleakage. A significant difference (p < .005) was found between groups 2 and 4. The OCL produced less microleakage (16 and 20 out of 24 sections) than the resin restorations polymerized with the PAC (only 8 of 24 sections with no microleakage. The 10-second cure by the PAC light appears to be insufficient in polymerizing a class I composite resin restoration. Possibly longer exposures with the PAC would produce less microleakage. Further research needs to be performed to evaluate if the PAC light, with an intensity of 1196 mW/cm2, may be producing high levels of strain within the setting composite. This strain may be responsible for the statistically significant increase in microleakage of the restorations polymerized with the PAC light.). It appears the PAC light would be best utilized to cure sealants and/or possibly polymerize orthodontic brackets. The conventional curing light appears to remain the best choice for polymerizing class I composite restorations.

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