Effects of varying density patterns and passes on depth of penetration in facial skin utilizing the carbon dioxide laser with automated scanner.

Histologic data describing the depth of penetration that occurs with the CO2 laser using variations in delivered energy, number of passes, and density settings have been limited. Most of the initial studies used a 3-mm collimated handpiece; few studies used the computerized pattern generator, which is now standard in treatment. This study examined histologic depth of thermal damage with varying density settings and number of passes using the computerized pattern generator. The Coherent UltraPulse 5000 CO2 laser with a computerized pattern generator was used. Preauricular (sun-exposed) and postauricular (sun-protected) facial skin samples were used from seven rhytidectomy patients aged 37 to 68 years. Preoperative skin treatment regimen included Retin-A and hydroquinone application for 3 weeks before the procedure. Three adjacent sites from the preauricular and postauricular regions were chosen from each ear (12 sites per patient). A density setting of 5 (30 percent overlap) was chosen for the right ear, and a density setting of 9 (60 percent overlap) was used for the left ear. Each region was subjected to one, two, and three passes. The laser delivers approximately 7.5 J/cm2 of fluence at a spot size of 2.25 mm and 300 mJ. Excisional biopsies were performed at the time of cervicofacial flap redraping. All specimens were evaluated for depth of thermal damage by a dermatopathologist who was blinded to the treatment parameters for each test site. Histologic examination of the treated test sites consistently demonstrated that one pass at these settings obliterated most or all of the epidermis, with minimal invasion into the papillary dermis. Test sites treated with two or three passes resulted in increased cumulative depth of penetration and thermal injury into the papillary dermis. Only one sample site showed any thermal injury extending into the reticular dermis. Depth of penetration was greater at the postauricular sites. Additionally, depth of penetration was greater with a density of 9 (60 percent overlap) than one of 5 (30 percent overlap) in both the preauricular and postauricular sites. Our study supported previous observations that the cumulative depth of penetration is greater with increasing levels of energy and additional passes. Additionally, we saw a greater average depth of penetration as density overlap increased, as one would predict. However, at these settings, fewer passes at a higher density setting did not achieve the same depth of penetration as more passes at a lower density setting. Furthermore, we found that the margin of safety using these settings is high: only 1 of 84 sites extended into the reticular dermis.