1.Histological examination of the control group

The attachment site of the deep layer of the masseter muscle to the mandible was classified into three sites based on the morphology of the attachment to the bone5,6): the periosteal attachment site, transition site, and tendinous attachment site.

1)Periosteal attachment site (Fig.2)

At these sites, muscle fibers were attached to the bone via the periosteum. Sharpey's fibers had infiltrated between the periosteum and the bone, and a layer of membranous ossification was evident at the site of infiltration.

2)Transition site

t these sites, the morphology of attachment suggested a transition from periosteal to tendinous attachment sites.

3)Tendinous attachment site

At these sites, muscle fibers were attached to the tendon. The tendon was connected to the bone tissue.

2.Histological examination of the experimental groups

1)Three days after surgery (Fig.3)

The tendinous attachment site and the transition site were damaged and had lost its alignment. The muscle fibers of the periosteal attachment site were severed and had lost continuity. Similar findings were observed in the other specimens of this group. These findings made little difference compared to the ones observed in seven days after surgery.

2) Fourteen days after surgery (Fig.4)

The tendinous tissue ( the outer most layer of the masseter musle ) of the tendinous attachment site had been repaired and had regained its alignment. However, the periosteal attachment site and the transition site had not yet recovered. By this time, the rats were not only soft but also regular feed, suggesting that their masticating function had recovered to some degree. Similar findings were observed in the other specimens of this group.