ABSTRACT
The most popular oligomer currently used in dentistry for dental composite preparation based on a combination of a highly viscous bifunctional monomer Bisphenol A-Glycidyl methacrylate (Bis-GMA) mixed with low viscosity dimethacrylates like triethylene glycol dimethacrylate (TEGDMA). The resin is the binder for the filler and it is the continuous phase. From a clinical perspective, the dentist prefers visible light cure composites due to the convenience of visible light activation for polymerization. Dentistry has an ever expanding variety of restorative materials that require curing by photoinitiation. The most commonly used photoinitiator is (-) camphor quinone (CQ) which is a diketone with a λmax at 473 nm along with a suitable amine as electron donor. The CQ has a yellowish color that makes harder to match the shades. The CQ forms a slow polymerization trajectory with only 50-75% initial conversion on light exposure [1] which improves slowly to reasonable levels. Also CQ needs an
amine which functions as an electron donor. Presence of amine results to change in shade, loss of activity during storage and toxicity of the resultant restorative. Moreover, CQ has an unbleachable chromophore group and a limitation in its use remains discoloration of the set material. Exceeding a critical concentration limit, whereby unreacted molecules are not able to react with the co-initiator and return to the ground state results in yellow discoloration [2-5] which may result in an aesthetically undesirable restoration. In order to formulate bright white or translucent shades of resin based composites, some manufacturers use less CQ and/or alternative photoreactive species such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (Lucirin-TPO) and 1-phenyl-1,2-propanedione (PPD), which has a maximum absorbance spectral peak in lower wavelength ranges (390 and 410 nm peak respectively) have been used in combination with CQ to lessen the yellowing effect and ultimately improve the curing efficiency of the polymerization system [6, 7] The high efficiency of the reaction coupled with the strong absorption and its stability toward hydrolysis has made TPO [8] as a commercial photoinitiator for curing polymer resins. The objective of the present study was to evaluate the photosensitization efficiency of TPO on a new organically modified ceramic resin and compare it with Bis-GMA in terms of properties such as depth of cure (DP), compressive strength (CS), diametral tensile strength (DTS), flexural strength (FS), flexural modulus (FM) and Vickers hardness number (VHN) of cured composite.
