Does Curing Tip Cover Influence Mechanical Properties of Composites?

Objectives: The aim of this research was evaluate the influence of polymer curing tip: cover and uncover. Used in a light cure device with LED light and the causing effect over the degree of conversion and Knoop hardness of composites.
Methods: A curing light device with polymer tips (600 mW / Ultrablue IS – DMC) was used in this research, 40 specimens of each material were made using a stainless steel matrix with the dimensions: 4 mm of diameter and 2 mm thickness (ISO 4049). Two layers of 1 mm thickness were add inside the matrix, and each layer was cured for 40 seconds. Two composite resin were used, Filtek Z250XT (3M ESPE) and Filtek Z350XT (3M ESPE). They were divided in 20 specimens of each material evaluated by degree of conversion and 20 specimens for Knoop hardness. Knoop hardness was measured at the bottom and the top of the specimens. G1 – Z250XT tip covered; G2 – Z350XT tip covered; G3 – Z250XT tip uncovered; G4 – Z350XT tip uncovered. Statistical analysis was carry out for all groups and conditions using two-way ANOVA (p<0.05).
Results: Degree of conversion results was not statistically significant difference among all groups. They are provided in ascending positions G2 (36,15±8,87) < G4 (39,66±12,20) < G1 (54,27±17,78) < G3 (55,59±12,97). However, specimens’ top and bottom measurements of Knoop hardness, all groups presented statistically significant difference. The top Knoop hardness measurements are disclose in ascending positions G2 (34,96±1,24) < G4 (37,33±1,28) < G1 (39,94±1,50) < G3 (42,48±0,57), followed by the bottom measurements G2 (15,46±1,53) < G4 (17,78±3,10) < G1 (31,02±3,75) < G3 (36,51±2,03).
Conclusions: Degree of conversion was not influenced either by composite or tip covering. Despite that the Knoop hardness altered when more LED light is directed properly towards the material, furthermore the composites within this research have different Knoop hardness.