Abstract

SOSTENA, Michela M. D. S.; NOGUEIRA, Renata A.; GRANDINI, Carlos R.  and  MORAES, João Carlos Silos. Glass transition and degree of conversion of a light-cured orthodontic composite. J. Appl. Oral Sci. [online]. 2009, vol.17, n.6, pp. 570-573. ISSN 1678-7757.  http://dx.doi.org/10.1590/S1678-77572009000600006.

OBJECTIVE: This study evaluated the glass transition temperature (T_g) and degree of conversion (DC) of a light-cured (Fill Magic) versus a chemically cured (Concise) orthodontic composite. MATERIAL AND METHODS: Anelastic relaxation spectroscopy was used for the first time to determine the T_g of a dental composite, while the DC was evaluated by infrared spectroscopy. The light-cured composite specimens were irradiated with a commercial LED light-curing unit using different exposure times (40, 90 and 120 s). RESULTS: Fill Magic presented lower T_g than Concise (35-84ºC versus 135ºC), but reached a higher DC. CONCLUSIONS: The results of this study suggest that Fill Magic has lower T_g than Concise due to its higher organic phase content, and that when this light-cured composite is used to bond orthodontic brackets, a minimum energy density of 7.8 J/cm² is necessary to reach adequate conversion level and obtain satisfactory adhesion.

Keywords : Orthodontic composite; Glass transition temperature; Degree of conversion; Mechanical spectroscopy; Infra-red spectroscopy.