The effect of different thicknesses of some restorative materials, tooth structures and air on light intensity reduction: A laboratoary evaluation

Introduction:
The minimum acceptable light intensity for light cure systems is 233mW/Cm². This intensity is acceptable just for curing the surface of composite and is not acceptable for the deeper areas. Light intensity decrease after passing through different thicknesses of tooth structures and dental materials can affect the degree and depth of polymerization of light cure materials. The purpose of this study is evaluation of light intensity decrease after passing through different thicknesses of dental structures, light activated hybrid and microfilled composites, light activated glass ionomer, bioglass, dental porcelain and also air.
Materials and Methods:
Six groups each containing five samples including hybrid composite, microfilled composite, glass ionomer, dental porcelain, bioglass and dental structures in five thicknesses from 1 up to 5 millimeter were prepared. The intensity of curing light was measured by radiometer after passing through samples and the air.
Results:
Rate of light intensity reduction reduces dramatically after passing through different thicknesses of dental porcelain¸ tooth structures¸ microfilled composite¸ hybrid composite¸ bioglass¸ glass ionomer and air respectively .The reduction rates for dental porcelain¸ tooth structures¸ microfilled composite¸ hybrid composite¸ bioglass¸ glass ionomer and air with 1.0 mm thickness are 88,80,78,68,47,44 and 0.7 percent respectively.As thickness increases, reduction of light intensity increases. Higher light intensity reduction occures after passing through dental porcelain and the lower occures within air.
Conclusions:
1. Application of light cure material in less than 1.mm thickness could have better results due to polymerization.
2. for light cure glass ionomer it is acceptable to cure only for one millimeter thickness.
3. For bioglass as a light coducting insert and material, the acceptable curing depth is up to 3mm. So higher light curing intensity is suggested for different sizes and thickness of these inserts.
4. For other materials and tooth structures even after passing through 1mm thickness, the adequate intensity is not aquired. So units with the ability of producing higher intensity radiation patterns are suggested.
5. The reduction rate of light intensity due to different distances is considerably lower than when light is passed through different thicknesses of dental materials and tooth structures.