The Efficacy of LED Light Polymerization Units in Private Dental Offices in Toronto, Canada

Light-emitting-diode (LED) light-polymerization units (LPUs) are currently routinely used for resin-based composites (RBC) photopolymerization. This study aimed to determine the effectiveness of LED-LPUs used in participating private dental practices in Toronto, Canada. One-hundred dental practices were recruited, and 113 LED-LPUs were examined. Part 1 evaluated radiant exposure (RE) of participants’ LED-LPUs. Majority of LPUs (n=87, 77%) passed the study-required criterion (delivering equivalent to 16 J/cm2 in 20s). A strong, negative correlation between LPUs' age, light-probe damage, and RE was found. Part 2 evaluated operator's technique to deliver 8 J/cm2 of RE in 10s to simulated restorations before and post-instructional. Before instructions, 73.6% of participants delivered required-energy to anterior restoration, and 32.2% of participants delivered required-energy to posterior restoration. Following instructions, 94.3% of participants delivered required-energy to anterior restoration, and 73.6% of participants delivered required-energy to posterior restoration. Part 3 examined relative-hardness (RH) of two RBCs polymerized at 1mm and 4mm, tip-to-target distance. Both RBCs polymerized at 1mm had average RH (ratio of mean lower/upper surface hardness) greater than 0.80, but not at 4mm tip-to-target distance. Part 4 evaluated the diametral tensile strength (DTS) of two RBCs polymerized with participating LED-LPUs. No significant difference between mean DTS values of two RBCs was observed. Mean DTS values were highly correlated among the LED-LPUs tested. In conclusion, 23% of LED-LPUs tested were deemed as incompetent for sufficient RBC polymerization. A high percentage of dental practitioners failed to deliver 8 J/cm2 in 10s exposure cycle, even after receiving specific instructions (5.7% to anterior restoration and 26.4% to posterior restoration). The outcome was due to a combination of LPUs performance and operator's technique. This finding is alarming as it relates well to early failure of Class-2 RBC restorations due to insufficient polymerization.Ph.D