Investigation on the use of triphenyl bismuth as radiopacifier for (di)methacrylate dental adhesives

In this study the suitability of using the organometallic compound triphenyl bismuth (TPB) as a radiopacifier for dental adhesive resins was investigated. A model photocurable (di)methacrylate co-monomer was loaded with 0 (control), 5%, 10%, 15%, 20%, or 30% mass fraction of TPB. Viscosity of the monomer was assessed using an oscillatory viscometer. Polymer radiopacity was investigated using a phosphor plate digital system. Other fundamental polymer properties evaluated were: translucency parameter by spectrophotometry, degree of C=C conversion by infrared spectroscopy, flexural strength/modulus and work-of-fracture in 3-point bending mode, water/ethanol sorption and solubility, and shear bond strength to dentin. Data were analyzed using one-way ANOVA (homoscedastic data) or ANOVA on Ranks (heteroscedastic data) followed by Student-Newman–Keulsʹ test (5%). The phenyl rings of TPB were identified by peaks in the 700–800-cm−1 infrared area. Incorporation of ≥20% of TPB affected the co-monomer viscosity. Linear increase in radiopacity was associated with the increase in TPB concentration, although no significant differences were detected between 20% and 30%. Addition of TPB did not affect monomer conversion or dentin bond strength. Flexural properties were generally lower for materials with ≥10% of TPB. Polymer translucency was affected by TPB incorporation above 10%. Ethanol/water sorption was lower in TPB-containing materials, while solubility was higher. TPB may be a suitable agent to render dental adhesives radiopaque, although methods to improve the polymer strength might be necessary.