Effect of exposure time and moving the curing light on the degree of conversion and Knoop microhardness of light-cured resin cements

• Published in: Dental materials Vol. 36; no. 11; pp. e340 - e351
• Main Authors: Bragança, Gabriel Felipe, Vianna, Arthur Silva, Neves, Flávio Domingues, Price, Richard Bengt, Soares, Carlos José
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-11-2020; Elsevier BV
• Subjects: Canine teeth; Ceramic veneer; Conversion; Curing; Degree of conversion; Dentistry; Emitters; Exposure; Exposure time; Glass ceramics; Irradiance; Light; Light exposure technique; Light-curing unit; Lithium; Microhardness; Photocuring; Polymers; Resin cement; Resins; Teeth; Variance analysis; Resin cement; Degree of conversion; Light exposure technique; Light-curing unit; Exposure time; Ceramic veneer; Microhardness
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2020.08.016

•A motorized device was developed to simulate movements of light curing unit.•Different cements, LCUs and exposure protocols can lead to different in vitro results.•Delivering intermittent light, the properties of the resin cements is decreased.•Increasing the exposure times increases the properties of the resin cements.•A single-peak LCU can activate a resin that uses Ivocerin™ as the photoinitiator.
To evaluate the effect of exposure time and moving the light-curing unit (LCU) on the degree of conversion (DC) and Knoop microhardness (KH) of two resin cements that were light-cured through ceramic.
Two resin cements: AllCem Veneer APS (FGM) and Variolink Esthetic LC (Ivoclar Vivadent) were placed into a 0.3 mm thick matrix in 6 locations representing the canine to canine. The resins were covered with 0.5 mm thick lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent). A motorized device moved the LCUs over the ceramic when the LCU was on. Two single-peak LCUs: Elipar DeepCure-L (3M Oral Care) and Emitter C (Schuster), and one multi-peak: Bluephase G2 (Ivoclar Vivadent) were used with 3 different exposure protocols: a localized exposure centered over each tooth for 10 or 40 s; moving the tip across the 6 teeth for a total exposure time of 10 or 40 s; and moving the tip across the 6 teeth resins for a total exposure time of 60 or 240 s. After 24 h, the DC and KH were measured on the top surfaces and the data was analyzed using three-way ANOVA and Tukey’s tests (α = 0.05).
Interposition of 0.5 mm of ceramic reduced the irradiance received by the resin by approximately 50%. The 40 s localized exposure over each tooth always produced significantly higher DC and KH values. Moving the LCUs with a total exposure time of 10 s resulted in the lowest DC and KH. There was no beneficial effect on the DC or KH when the multi-peak (violet-blue) LCU (Elipar DeepCure-L or Bluephase G2), but the lower light output from a small tip LCU reduced the DC and KH values (Emitter C).
Moving the LCUs when photo-curing light-cured resin cements is not recommended. This study showed that a single-peak LCU could activate a resin cement that uses Ivocerin™ as well as the multi-peak LCU.