2005 Volume 9 Issue 2 Pages 228-233
【Objectives】The “Jaw Opening” procedure described in Daniels and Worthingham's Muscle Testing (DMT) is a simple technique for the clinical evaluation of mouth opening movement．However，the evaluation is subjective，and it is difficult to distinguish between functional (F) and weakly functional (WF) mouth opening．We have previously confirmed the usefulness in healthy adults of the manual resistance movement described in DMT and an indirect cervical traction device that simply and objectively evaluates mouth opening movement in the quantitative evaluation of the force (maximum mouth opening force) required to maintain maximum mouth open position against resistance in the mouth closing direction．
It is not uncommon for the mouth opening muscles to be resected in surgical oral cancer patients；however，to date，there is no mention of the quantitative evaluation of pre/postoperative changes in maximum mouth opening force in the literature．In the present study，we clinically applied a method for measuring mouth opening force using an indirect cervical traction device before and after surgery in tongue cancer patients．
【Subjects and Methods】The subjects were 6 patients (mean age，62 years) admitted for radical treatment of tongue cancer．The surgical procedure involved hemigrossectomy and unilateral resection of the suprahyoid muscles in 4 patients and subtotal glossectomy and extensive resection of the suprahyoid muscles in 2 patients． Evaluation were performed twice，once each before and after surgery．Measurement of maximum mouth opening force：Subjects were seated with the head and neck in the neutral position．The researcher placed one hand on top of the subject's head to restrain head movement，while instructing the subject to maintain maximum mouth opening．A belt was placed under the mandible，and traction was applied in an approximately perpendicular direction relative to the axis of the trunk，and the maximum value (kg) was confirmed． Measurement of maximum mouth opening (distance)：Subjects were asked to open their mouths as wide as possible，and bimaxillary central incisor distance was measured in mm using calipers．
【Results and discussion】The maximum mouth opening force (mean ± standard error) was 18.7 ± 2.0kg before surgery and 16.7 ± 1.3kg after surgery，representing a non-significant decrease postoperatively．The maximum mouth opening (mean ± standard error) was 49.5 ± 2.4mm before surgery and 34.8 ± 2.8mm after surgery， representing a significant decrease postoperatively．These findings indicate that，with respect to mouth opening movement after tongtie cancer surgery in which the suprahyoid muscles were resected and the infrahyoid muscles were compensated，maximum mouth opening force was preserved，notwithstanding a reduction in maximum mouth opening．It is therefore possible that the infrahyoid muscles play a more important role than the suprahyoid muscles in maximum mouth opening force．
