Efficiency of light curing units in dental clinics in Nairobi, Kenya

Abstract

Background: To achieve adequate cure, a resin composite restoration must be exposed for a specified duration of time to a light of sufficient intensity and the right wavelength. However, some commonly used light curing units (LCUs) may yield inadequately cured restorations due to their insufficient light intensity output. Furthermore, the efficiency of light curing units in dental clinics and the extent to which dentists practice the recommended maintenance techniques is largely unknown. Objective: To determine the efficiency of Light Curing Units (LCUs) in dental clinics in Nairobi, Kenya. Study design: A laboratory-based, cross-sectional analytical study. Study area: The study was set in private and public dental clinics in Nairobi, Kenya. A total of 83 light curing units selected through a convenient sampling procedure were used. Materials and methods: The light intensity output of light curing units in dental clinics was measured using a digital dental radiometer and the result entered in a data collection form. Each light curing unit was then used to polymerise two cylindrical resin composite specimens made using custom-made split brass moulds; one measuring 4mm in diameter and 6mm in thickness used to determine the depth of cure (DOC) and the other 8mm in diameter and 3mm in thickness used to determine the surface hardness by using a Vickers Hardness tester. Within 6-7 hours of fabrication, the depth of cure specimens were immersed in a capsule containing 99%- acetone solvent which was then vibrated in a mixing device. The DOC was calculated from the undissolved length of the specimen. The surface Vickers Hardness was evaluated by making three xv surface indentations with a diamond indenter using a load of 200g and a dwell time of 15-seconds. A conversion table was used to convert measurements from the diamond indentations into hardness numbers. The light intensity output and the depth of cure and surface micro-hardness numbers of the resin composite specimens were then used to assess the efficiency of each dental light curing unit. Three main components of the maintenance history of the light curing units, as well as the age and type of the light curing unit were also recorded. The data was entered into a computer using SPSS version 12. The independent sample t-test, one way analysis of variance (ANOVA) with Post Hoc test and Chi-square tests were used for data analysis. The results were summarized in tables and figures. Results: Of the 83 LCUs studied, 43(51.8%) were LED and 39(47.0%) were OTH and 1 (1.2%) was PAC light. LCU type and light intensity output, DOC and hardness: Mean light intensity for OTH and LED lights was 526.59mW/cm2 and 493.67mW/cm2 respectively (p=0.574), while the mean DOC for OTH lights was 1.71mm and LED was 1.67mm (p=0.690). Mean VHN for LED was 57.44 and for OTH was 44.14 (p=0.713). Light curing unit type had no statistically significant effect on DOC, surface hardness and the intensity of the light. Effect of age of LCU on light intensity output, hardness and DOC: Mean light intensity for LCUs ::;5years was 596.03mW/cm2 and 363.17mW/cm2 for units> 5years old. Age showed a significant effect on light intensity (p=O.024). The mean DOC for the two age groups was 1.74mm and 1.57mm respectively (p=O.073). For surface micro-hardness, the ::; 5years and > 5years age groups gave a mean VHN of 58.81 and 51.46 respectively (p=O.1) XVI Efficiency of the LCUs: when intensity was used to measure efficiency, 48 (57.8%) LCUs were efficient and 35 (42.2%) were inefficient. Only the LCU age significantly affected efficiency by light intensity output (p=O.008). Only 24 (28.9%) LCUs gave sufficient DOC as opposed to 59 (71.1%), which gave insufficient DOC. Of the units tested for surface micro-hardness, 15 (25.9%) had adequate surface micro-hardness while the rest (43 or 74.1%) had inadequate surface micro-hardness. The type of LCU and its age did not significantly influence efficiency as measured using depth of cure and surface micro-hardness of the resin restoration. On the whole, 11 (19%) of the LCUs which had all the three tests of efficiency done were satisfactory in all the 3 aspects. Conclusions: Eleven (19%) of the light curing units used in Nairobi dental clinics were efficient when subjected to a combined light intensity, and composite resin depth of cure and surface hardness evaluation, and that the type and maintenance history of a LCU had no significant influence on its efficiency. Age had a significant influence on the light intensity of the curing units - there was a decrease in light intensity output with increase in age of the units. There was a non-linear relationship between the light intensity output of a LCU and the depth of cure and surface micro-hardness of the cured composite.