Introduction

Phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO), another name for which is Irgacure 819, is a potential photoinitiator (Figure 1). BAPO is similar to diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO); it is a derivative of phosphine oxide and it does not require a co-initiator. The absorption range is 365–416 nm, and the absorbance maximum is 400 nm, which another source reports as 371 nm. This absorption range requires the use of dental lamps which have a wider spectrum of light; this is a significant disadvantage of using this photoinitiator. Phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide is solid and has a symmetric chemical structure and poor solubility in a variety of monomers. BAPO is a type-I photoinitiator that absorbs high levels of energy from violet light and undergoes cleavage of carbon-phosphorus bonds. This process is called alpha-cleavage, whereby the compound of BAPO breaks into radicals. Phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide produces more free radicals than TPO because it has two carbonyl groups in its structure. Four reactive radicals can be generated from one molecule of BAPO. Derivates of BAPO are used in the ink industry but have not been used in dentistry.[1]

Comparative Study of Applications

Study 1：Evaluation of the Selected Mechanical and Aesthetic Properties of Experimental Resin Dental Composites Containing 1-phenyl-1,2 Propanedione or Phenylbis (2,4,6-trimethylbenzoyl) -phosphine Oxide as a Photoinitiator

The goal of this study was to compare the mechanical properties of experimental resindental composites containing a conventional photoinitiating system (camphorquinone CQ and2-(dimethylami-no)ethyl methacrylate (DMAEMA)) to a photoinitiator system containing 1-phenyl1,2 propanedione (PPD) with 2-(dimethylami-no)ethyl methacrylate) or acting alone phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO). The manually produced composites consisted of an organic matrix: bis-GMA (60 wt. %), TEGDMA (40 wt. %), and silanized silica filler (45 wt. %). The composites contained 0.4/0.8 wt. %, 0.8/1.6 wt. %, and 1/2 wt. % of PPD/DMAEMA and another group included 0.25, 0.5, or 1 wt. % of BAPO. Vickers hardness, microhardness (in the nanoindentationtest), diametral tensile strength, and flexural strength were assessed, and CIE L* a* b* color imetric analysis was conducted for each composite produced. The highest average Vickers hardness values were obtained for the composite containing 1 wt. % BAPO (43.73 ± 3.52 HV). There was no statistical difference in the results of diametral tensile strength for the experimental composites tested. The results of 3-point bending tests were the highest for composites containing CQ (77.3 ± 8.84 MPa).Despite the higher hardness of experimental composites including PPD or BAPO, compared with composites with CQ, the overall results indicate that the composite with CQ still represents a better solution when used as a photoinitiator system. Moreover, the composites containing PPD and DMAEMA are not promising in terms of color or mechanical properties, especially as they require significantly longer irradiation times.[1]

Study 2:BAPO as an alternative photoinitiator for the radical polymerization of dental resins

Objectives. This study evaluated the performance of phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO) as an alternative photoinitiator in the polymerization kinetics (PK),flexural strength (σ) and elastic modulus (E) of a model dental resin. Methods. A monomer mixture based on Bis-GMA and TEGDMA was used as model dental resin. Initially a screening was performed to evaluate henylbis(2,4,6-trimethylbenzoyl)-phosphine Oxide concentrations (0.125,0.25, 0.50, 1, 2, and 4mol%). Photoinitiator systems were formed with the combination of camphorquinone (CQ), ethyl-dimethylamino benzoate (EDAB), diphenyliodonium hexafluorophosphate (DPIHFP), and BAPO. Groups with unitary photoinitiator systems (BAPO and CQ), binary (BAPO + EDAB, BAPO + DPIHFP and CQ + EDAB), ternary(BAPO +CQ + EDAB, BAPO +CQ + DPIHFP, BAPO + EDAB + DPIHFP and CQ + EDAB + DPIHFP) and quaternary (BAPO +CQ + EDAB + DPIHFP) were formulated for evaluation. Real-time Fourier transform infrared spectroscopy was used to investigate the PK and test mini-bending to evaluate σ and E. Results. When only CQ was used, a slow polymerization reaction was observed and a lower monomer conversion. When only BAPO was used as photoinitiator an increase in the polymerization rate was observed and conversion was higher than CQ + EDAB. The ternary system (BAPO + EDAB + DPIHFP) showed the highest polymerization and conversion rate, in short photo-activation time. Significance. Phenylbis(2,4,6-trimethylbenzoyl)-phosphine Oxide is a potential photoinitiator for the photopolymerization of dental materials.[2]

Study 3: Influence of Photoinitiator System on Physical-Chemical Properties of Experimental Self-Adhesive Composites

The aim of this study was to determine the influence of photoinitiator systems onphysical-chemical properties of flowable composites. Conventional (CFC), composed by bisphenol-glycidyl dimethacrylate (BisGMA)+triethyleneglycol dimethacrylate (TEGDMA), and self-adhesive (SAFC), composed by BisGMA+TEDGMA+bis[2-(methacryloyloxy) ethyl]phosphate (2MP), flowable composites were developed. Five photoinitiator systems were tested: camphorquinone (CQ), ethyl-4-dimethylaminobenzoate (EDMAB), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), phenylbis (2,4,6-trimethylbenzoyl)phosphine oxide(BAPO), CQ+EDMAB+TPO and CQ+EDMAB+BAPO. A two-peak LED was used; degree of conversion (DC) and the maximum polymerization rate (RPmax) were determined by near infrared spectroscopy. For the yellowing degree a spectrophotometer was used. Water sorption(Wsp) was obtained after 30 days of water storage (n=5). Data were submitted to two-way analysis of variance and Tukey’s test (α=0.05).Phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide presented the highest DC and RPmax values for both series. SAFCs presented lower DC and RPmax for CQ+EDMAB-based materials.Greater yellowing was observed for SAFCs compared with CFCs, except for phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide. Greater Wsp was observed for SAFCs compared with CFCs. The photoinitiator did not influence Wsp for CFCs, but TPO and phenylbis (2,4,6-trimethylbenzoyl)phosphine oxide presented the highest Wsp in SAFCs. The photoinitiatorsystem affected differently the physical-chemical properties of CFCs and SAFCs.[3]

Conclusion

Therefore, the aim of these studies was to evaluate the performance of the phenylbis (2,4,6-trimethylbenzoyl) -phosphine oxide (BAPO) as a radical photoinitiator, solely or associated with other initiators, as an alternative to the traditional CQ-based systems in a model dental resin through the polymerization kinetics and mechanical properties of the polymer. The hypotheses tested where that; (1) the photoinitiator BAPO is able to promote satisfactory polymerization and (2) the combination of BAPO and co-initiators may improve the polymerization efficiency of a model dental resins.

References

[1] Kowalska-Kuczyńska A, Soko?owski J, Szynkowska-Jó?wik MI, et al. Evaluation of the Selected Mechanical and Aesthetic Properties of Experimental Resin Dental Composites Containing 1-phenyl-1,2 Propanedione or Phenylbis(2,4,6-trimethylbenzoyl)-phosphine Oxide as a Photoinitiator. Int J Mol Sci. 2023;24(6):5573. Published 2023 Mar 14. doi:10.3390/ijms24065573

[2] Meereis CT, Leal FB, Lima GS, de Carvalho RV, Piva E, Ogliari FA. BAPO as an alternative photoinitiator for the radical polymerization of dental resins. Dent Mater. 2014;30(9):945-953. doi:10.1016/j.dental.2014.05.020

[3] Bertolo M V L ,Moraes, Rita de Cássia Martins, Pfeifer C ,et al.Influence of Photoinitiator System on Physical-Chemical Properties of Experimental Self-Adhesive Composites[J].Brazilian Dental Journal, 2017, 28(1):35.DOI:10.1590/0103-6440201700841.