06 June 2021

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Effect of curing light on gingival cell proliferation

Lara Figini

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Light-emitting diode (LED) curing lamps and quartz-tungsten (QTH) halogen lamps are commonly used in dentistry for aesthetic restorations, whose involves photopolymerization. Both LED and QTH halogen lights have been shown to affect wound healing, proliferation and apoptosis of fibroblasts, skin and retinal pigment epithelial cells. However, no research has been conducted to evaluate the effect of these lights on the proliferation of human oral epithelial cells. 

Materials and methods
In an in vitro study, published on JADA, April 2021, the authors evaluated the effect of curing light, commonly used in the dental field for composite fillings, on the proliferation of human gingival epithelial cells. Smulow-Glickman (SG) cells were exposed to the light of a VALO (Ultradent) LED curing light and to the light of a XL3000 QTH (3MESPE) halogen curing light at a distance of 1mm or 6mm by 18, 39, 60 and 120 seconds. Untreated cells and cells treated with Triton X-100 (non-ionic surfactant) were considered into the control group. At 24, 48 and 72 hours after exposure to light, cell proliferation was assessed via 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide assay. The authors also measured the temperature by means of shining the light directly at an EX430 True RMS Multimeter Thermocouple (Extech Instruments) at the maximum power for 20 seconds. 

Results
The authors first evaluated the performances of these 2 lights. Both LED and QTH lights generated heat. The LED light generated less heat than the QTH light and could save approximately two-thirds of the curing time. When used for 18 seconds at a 6 mm distance, the LED light did not inhibit the proliferation of S-G cells. However, if the exposure time was longer (for example, 39, 60, or 120 seconds), the LED light inhibited cell proliferation. The inhibitory effect increased when the exposure time was increased to 39, 60, or 120 seconds. The QTH light did not inhibit S-G cell proliferation if the exposure time was less than 120 seconds. 

Conclusions
From the data of this study, which must be confirmed in other similar studies, it can be concluded that prolonged exposure to a curing light (both LED and QTH) inhibits the proliferation of gingival epithelial cells and can cause damage to oral soft tissues. 

Clinical implications
In the dental field, it is necessary to find the right balance in terms of curing light that allows the most polymerization possible of the composites, avoiding unnecessary prolonged exposure that could damage the gingival tissues. Is fundamental, in cases of prolonged curing light, the positioning of the dental dam, that acts as a barrier between light and gingiva.