Background: The aging face loses the tensile strength of structural integrity. Cog threads have been used recently to tighten lax skin and soft tissue.
Objective: A comparative study of the effects of cog, monofilament, and multifilament threads under rat skin.
Methods: Each cog, monofilament, and multifilament thread was inserted under the facial skin of a cadaver and the panniculus carnosus of rat dorsal skin. The maximum holding strength (MHS) of the thread and the tearing strength of the skin around the thread were measured with a tensiometer. The thickness of the capsule around the thread and the myofibroblasts was observed histologically.
Results: In the cadaver, the MHS of the cog thread was 190.7 +/- 65.6 g. It was greater than that of the monofilament (22.4 +/- 7.7 g) or multifilament (40.4 +/- 19.7 g) thread. In the rat, the MHS of the cog thread was 95.1 +/- 18.8 g. It was greater than that of the monofilament (4.3 +/- 1.3 g) or multifilament (10.9 +/- 2.1 g) thread in the second week. The thickness of the capsule around the cog thread was 93.0 +/- 3.2 microm. It was thicker than the monofilament thread's capsule, 39.2 +/- 12.1 microm, in the fourth week. The number of myofibroblasts presented significantly more in the cog (96.0 +/- 72.4) than in the monofilament thread (4.3 +/- 4.4). The rumpled in-between skin suspended by each of the three different threads returned to its original state in 2 weeks.
Conclusion: The cog thread placed under the rat skin immediately pulled the skin and subcutaneous tissue. The myofibroblasts around the thread played a role in fibrous tissue contracture 4 weeks postinsertion of the thread. These findings could be the basis for clinical application.