Influence of radiotherapy on the dentin properties and bond strength

The objective of this study was to evaluate the biomechanical properties of dentin and the microtensile bond strength (μTBS) performed before or after radiotherapy (RT).

Dentin chemical composition (infrared spectroscopy-FTIR), SEM images, and mechanical properties (Vickers microhardness-VHN and elastic modulus-E) were evaluated comparing no irradiated and irradiate dentin (n = 5). RT was defined by application of 72 Gy (1.8 Gy daily, 5 days per week, during 8 weeks) with sample immersed in distilled water. μTBS evaluated three groups (n = 10): NI-no irradiated; IB-irradiation before restoration; and IA-irradiation after restoration. Resin-dentin sticks (1.0 mm²) were obtained and submitted to μTBS. Analysis of the bonding interface was made by confocal microscopy.

After RT, percentage ratio of FTIR analysis showed increased absorption for all bands. SEM image showed a disorganized dentin structure. Two-way ANOVA showed increased VHN (p = 0.005) and decreased E (p < 0.001). For μTBS, one-way ANOVA and Duncan test showed significant differences among groups (p = 0.018). IB group presented the lowest bond strength values.

RT alters the absorption bands and SEM images showed a disorganization of the dentin structure. Mechanical properties were changed with increased VHN and decreased E. μTBS was affected by the radiotherapy and restoration period (before or after).

RT causes changes that contribute to increased risk of tooth decay. Restorative treatments can be performed using adhesive procedures, but it is preferable to be performed before of the irradiation protocol, to guarantee better adhesive properties to restoration.