Effect of Light Curing Unit Characteristics on Light Intensity Output, Depth of Cure and Surface Micro-Hardness of Dental Resin Composite

Background: Modern dental composite restorations are wholly dependent on the use of Visible Light Curing devices. The characteristics of these devices may influence the quality of composite resin restorations.Objective: To determine the characteristics of light curing units (LCUs) in dental clinics in Nairobi and their effect on light intensity output, depth of cure (DOC) and surface micro-hardness (SMH) of dental resin composite.Design: Laboratory based, cross-sectional analytical studySetting: Public and private dental clinics in Nairobi, Kenya.Subjects: Eighty three LCUs which were in use in private and public dental health facilities in Nairobi, Kenya and resin composite specimens.Results: Of the 83 LCUs studied, 43(51.8%) were Light Emitting Diodes (LEDs) and 39(47.0%) were Quartz-Tungsten-Halogen (QTH) and 1 (1.2%) was Plasma Arc Curing (PAC) light. Mean light intensity for QTH and LED lights was 526.59mW/cm2 and 493.67mW/cm2 respectively (p=0.574), while the mean DOC for QTH lights was 1.71mm and LED was 1.67mm (p=0.690). Mean Vickers Hardness Number (VHN) for LED was 57.44 and for QTH was 44.14 (p=0.713). Mean light intensity for LCUs . 5years was596.03mW/cm2 and 363.17mW/cm2 for units > 5years old (p=0.024). The mean DOC for the two age groups was 1.74mm and 1.57mm respectively (p=0.073). For SMH, the . 5years and >5years age groups gave a mean VHN of 58.81 and 51.46 respectively (p=0.1). On maintenance history, the frequency of routine inspection, duration since the last repair/replacement of a part or other maintenance activity and the nature of the last  maintenance activity were determined and were not found to have  influenced the light intensity, DOC and SMH.Conclusion:The LCU age has a statistically significant influence on its light intensity (p=0.024) while the type and maintenance history have no significant influence on its light intensity and composite DOC and SMH (p=0.574, p=0.690, p=0.713 respectively)

Effect of light intensity on the cure characteristics of photo-polymerised dental composites

Objective: To determine the light intensity emitted by light curing units (LCUs) and its effect on the cure characteristics of composites polymerised with it.Design: A laboratory based cross sectional study.Setting: Public and private dental clinics in Nairobi, Kenya.Results: Thirty five (42.17%) LCUs produced light of intensity  .300mWcm-2 while 43 (51.8%) LCUs had their intensities between 300 and 1200mWcm-2. Mean DOC and surface hardness for the 0-300mWcm-2 LCUs was 1.34mm and 46.60VHN respectively. The mean DOC increased steadily from the lowest intensity group (1.34mm) to the  1200-1500mWcm-2 group (2.32 mm) and then declined to 1.98mm for the 1500-1800mWcm-2 group. Statistical analysis showed significant differences in the mean DOC (p=0.000) and surface micro-hardness (p=0.002) for the different intensity groups.Conclusion: Light intensity output of LCUs has a significant influence on the cure characteristics of dental composites with both DOC and surface micro-hardness increasing with increase in light intensity up to  1500mWcm-2