The effect of argon laser polymerization on the degree of conversion, depth of cure, mechanical properties, and microleakage of light-cured dental composite resins
Shata, Abeer Bakri
MetadataShow full item record
0bjectives: In dentistry, resin-based tooth-colored restorative materials are typically applied using a visible light source to initiate polymerization. Recently, it has been hypothesized that because of the high intensity of argon laser and narrow spectral distribution (corresponding to the absorption peak for the photoinitiator in the dental resins), argon laser could be used as an alternative means of curing visible light-activated composite resins. This study compared the effect of argon laser and conventional visible light irradiation on the degree of conversion, depth of cure, and on mechanical properties such as hardness, diametral tensile and compressive strength. Additionally, an in-vitro test was carried out to compare the extent of microleakage in class V composite resin restorations cured by each method. Methods: Samples from different brands of composite resin, Herculite XRV, TPH Spectrum, and Z100 were made for each set of parameter tested. Two light sources, a conventional visible light with power density of 400 mw/cm2 and an argon laser of 100 and 250 mw power, were used to polymerize the composite resins. Samples for the degree of conversion and hardness test, 4 mm in length, were cured from one side only to determine the depth of cure. Degree of conversion was quantitatively analyzed by using a non-destructive Raman spectroscopy method. Hardness was measured with a Vickers microhardness test. Diametral tensile and compressive strength samples were tested on an Instron testing machine and the mean diametral tensile strength and compressive strength (MPa) values were calculated for each group. One way ANOVA tests were performed for all the above tests, followed by Scheffe test. For the in-vitro study, the extent of microleakage in v-Shaped class V composite resin restorations cured by each method was assessed, using 90 extracted premolar teeth, by dye penetration and thermocycling. Non-parametric Chi-square test followed by Mann Whitney “U” test were performed. All the results were obtained with 10 seconds argon laser curing versus 40 and/or 60 seconds visible light curing. Results: Three was no significant difference at the p[less than]0.01 level between the curing method, regarding the degree of conversion and Vickers microhardness numbers at the surface, as well as the diametral tensile and compressive strength values. However, there was a significantly higher degree of conversion percent in composite resins cured by argon laser at a depth of 2-4 mm and significantly higher Vickers values at a depth of 4 mm (p[less than]0.01). There was also a statistically higher degree of marginal leakage at p[less than]0.05 level in restorations cured by the argon laser. Conclusion: In this study, the effect of light sources on the bulk and the surface properties of dental composite materials were evaluated. In all composites tested, argon laser caused a higher degree of conversion at a depth of 2-4 mm (2 mm being the maximum conversion) and at 4 mm depth. This was evident both in Raman spectroscopy analysis (except for TPH with 60 seconds visible light irradiation) and in the Vickers hardness test, respectively. However, there was no statistical difference at the surface between the two curing methods regarding the degree of conversion analysis, hardness test, or the diametral tensile and compressive strength test. Also, argon laser caused a significantly higher degree of microleakage at the restoration-tooth interface, in class V cavities. In short, argon laser, as an alternative source for the curing of visible light-activated material, performed better in some tests and equally well in others (in a shorter amount of time). In one test, microleakage, argon laser performed poorly, a finding which warrants further exploration.
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact email@example.com.Thesis (DScD) --Boston University, Goldman School of Dental Medicine, 1999 (Department of Pediatric Dentistry).Includes bibliographic references: leaves 144-167.
RightsThis work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.