Degree of Conversion with LED Curing Lights

Depth of cure measurements are commonly reported using the ratio of top/bottom hardness or a scraping test (ISO 4049).

Objective: Here, the depth of cure was followed by measuring the degree of conversion (DC) as a function of depth from the surface of a composite resin polymerized by LED curing lights or a tungsten halogen light.

Method: Near infrared spectroscopy (NIR) was used to measure DC of Heliomolar (A1) immediately after curing for 40 s. The DC was measured (0.5, 2.0, and 3.5) mm from the top of the sample. Seven LED lights and a tungsten halogen (Optilux 400, control) were tested. The Barcol hardness was measured at the top and bottom of 2 mm thick composite disks.

Results: DC at the top of the sample was independent of the light used, with the LED and tungsten halogen lights giving the same DC (one way ANOVA, p>0.05). However, at 2.0 mm the DC for several LED lights was significantly lower than the tungsten halogen light (p<0.05). DC at 2.0 mm was strongly correlated to the lights' power density (ISO 10650; R²=0.826, Pearson Correlation, p<0.05). The bottom to top ratio for Barcol hardness measurements for all but one LED light was greater than 0.80. In contrast, the DC ratio at 2.0 mm fell to a fraction of less than 0.55 for half of the lights, while the 3.5 mm ratios ranged from 0.19-0.61.

Conclusions: Compared to a tungsten halogen light, LED lights gave similar DC at the top of a composite sample, but may not cure as deeply. Moreover, Barcol hardness measurements at the bottom of a 2 mm specimen may not adequately represent the much lower DC at such depth, which could lead to greater than anticipated leachability of uncured monomers. Supported by ADAF and NIST.

*0414 Degree of Conversion with LED Curing Lights*
C.J.E. FLOYD¹, K. ARAVAMUDHAN², S.H. DICKENS¹, F.C. EICHMILLER¹, P.L. FAN², and D. RAKOWSKI², ¹American Dental Association Foundation, Paffenbarger Research Center, Gaithersburg, MD, USA, ²American Dental Association, Research Institute, Chicago, IL, USA Depth of cure measurements are commonly reported using the ratio of top/bottom hardness or a scraping test (ISO 4049). Objective: Here, the depth of cure was followed by measuring the degree of conversion (DC) as a function of depth from the surface of a composite resin polymerized by LED curing lights or a tungsten halogen light. Method: Near infrared spectroscopy (NIR) was used to measure DC of Heliomolar (A1) immediately after curing for 40 s. The DC was measured (0.5, 2.0, and 3.5) mm from the top of the sample. Seven LED lights and a tungsten halogen (Optilux 400, control) were tested. The Barcol hardness was measured at the top and bottom of 2 mm thick composite disks. Results: DC at the top of the sample was independent of the light used, with the LED and tungsten halogen lights giving the same DC (one way ANOVA, p>0.05). However, at 2.0 mm the DC for several LED lights was significantly lower than the tungsten halogen light (p<0.05). DC at 2.0 mm was strongly correlated to the lights' power density (ISO 10650; R²=0.826, Pearson Correlation, p<0.05). The bottom to top ratio for Barcol hardness measurements for all but one LED light was greater than 0.80. In contrast, the DC ratio at 2.0 mm fell to a fraction of less than 0.55 for half of the lights, while the 3.5 mm ratios ranged from 0.19-0.61. Conclusions: Compared to a tungsten halogen light, LED lights gave similar DC at the top of a composite sample, but may not cure as deeply. Moreover, Barcol hardness measurements at the bottom of a 2 mm specimen may not adequately represent the much lower DC at such depth, which could lead to greater than anticipated leachability of uncured monomers. Supported by ADAF and NIST.
Seq #67 - Ceramics and FRC in Fixed Prosthodontics 10:15 AM-11:30 AM, Thursday, 11 March 2004 Hawaii Convention Center Exhibit Hall 1-2
Back to the Prosthodontics Research Program Back to the IADR/AADR/CADR 82nd General Session (March 10-13, 2004)
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