Recently, extensive data suggest that intensity-modulated radiation therapy (IMRT) is safe and efficacious in the adjuvant setting for oral cavity cancer (OCC) (10-12). Hsiung et al. (13) and Chen et al. (14) confirmed that radiation induced trismus progressed over time and improved by IMRT. Hsiung et al. (13) found the averages of normalized maximal interincisal distance (MID) were 94% and 98.1% at 5 ms and 12 ms post-IMRT, respectively. In addition, only 0.2 mm the deterioration of radiation-induced trismus in the period from 12-18 months post-IMRT was noted. Moreover, Chen et al. (14) also confirmed that radiation induced trismus progressed over time and improved by IMRT. However, Kent et al. (15) examined the incidence of trismus in IMRT group compared to conventional radiotherapy group. There was no significant difference in the maximum vertical dimension between the IMRT and the conventional RT groups, (38.8 ± 9.0 vs 33.7 ± 10.1 mm, respectively, p = 0.11).