Myositis ossificans traumatica(MOT) in head and neck area is a rare non-neoplastic, heterotopic bone formation within a muscle, arising after trauma or surgery. Although the several case reports have described the occurrence of MOT in other muscles of oro-facial musculature, MOT has never been reported in mentalis muscle. We demonstrate a case of MOT occurred in mentalis muscle of a 64 years old male. He recently complained of a movable mass with no pain. He had experienced a hitting trauma on his right anterior mandible about 25 years ago. Since then, the trauma area has been asymptomatic. The lesion showed severe muscular degeneration, resulted in a pseudocystic change without epithelial lining. The ectopic ossification was closely associated with the fibrous fascia of adjacent muscles. The lesion contained a lot of basophilic materials admixed with atrophying cells, which were supposed to be derived from muscle parenchyma injured previously. It was presumed that the basophilic materials induced callus-like ossification in the fibro-muscular lesion, also recruited macrophages and fibroblasts. However, the ossification processes in MOT were predominantly characterized by dystrophic calcification without osteoblastic differentiation of mesenchymal cells. Even more, there appeared some skeletal muscle bundles which were calcified dystrophically. Therefore, we suggest the present case of MOT might be initiated by dystrophic calcification in the degenerating muscle tissue

Ⅰ. INTRODUCTION
 Ⅱ. CASE REPORT
 Ⅲ. DISCUSSION
 Ⅳ. REFERENCES

• 김연숙(Department of Dental Hygiene Cheongju University) | Yeon Sook Kim
• 박종철(Department of Oral Pathology College of Dentistry, Gangneung-Wonju National University) | Jong Cheol Park
• 이석근(Department of Oral Pathology College of Dentistry, Gangneung-Wonju National University) | Suk Keun Lee correspondence