Comparison of epidermal/dermal damage between the long-pulsed 1064 nm Nd:YAG and 755 nm alexandrite lasers under relatively high fluence conditions: quantitative and histological assessments

Abstract

Objective: The purpose of this study was to compare degrees of epidermal/dermal tissue damage quantitatively and histologically after laser irradiation, to find ideal treatment conditions with relatively high fluence for skin rejuvenation.

Background data: A number of recent studies have evaluated the clinical efficacy and safety of therapeutic lasers under relatively low fluence conditions.

Methods: We transmitted the long-pulsed 1064 nm Nd:YAG and 755 nm Alexandrite lasers into pig skin according to different fluences and spot diameters, and estimated epidermal/dermal temperatures. Pig skin specimens were stained with hematoxylin and eosin for histological assessments. The fluence conditions comprised 26, 30, and 36 J/cm2, and the spot diameter conditions were 5, 8, and 10 mm. Pulse duration was 30 ms for all experiments.

Results: Both lasers produced reliable thermal damage on the dermis without any serious epidermal injuries, under relatively high fluence conditions. The 1064 nm laser provided more active fibrous formations than the 755 nm laser, while higher risks for tissue damages simultaneously occurred.

Conclusions: The ideal treatment conditions for skin rejuvenation were 8 mm diameter with 30 J/cm2 and 10 mm diameter with 26 J/cm2 for the 1064 nm laser, and 8 mm diameter with 36 J/cm2 and 10 mm diameter with 26 J/cm2 for the 755 nm laser.

FIG. 1.

Experimental setup for estimating epidermal and dermal temperatures using the 1064 nm Nd:YAG and 755 nm Alexandrite lasers.

FIG. 2.

Comparison of the maximum dermal temperatures at a depth of 2.5 mm between the 1064 nm Nd:YAG and 755 nm Alexandrite lasers according to the different fluence and spot diameter conditions. (A) Spot diameter of 5 mm. (B) Spot diameter of 8 mm. (C) Spot diameter of 10 mm.

FIG. 3.

Comparison of the maximum epidermal temperatures between the 1064 nm Nd:YAG and 755 nm Alexandrite lasers for the different fluence and spot diameter conditions. (A) Spot diameter of 5 mm. (B) Spot diameter of 8 mm. (C) Spot diameter of 10 mm.

FIG. 4.

Representative hematoxylin and eosin stain (H&E) of pig skin specimens after the two laser irradiation modalities. (A) Control specimen. (B and C) The most active stimulation of fibroblast activity and collagen reformation. (D and E) Irreversible tissue damages on the epidermal and dermal layers, respectively (×100). a, formation of fibrous tissue; b, epidermolysis; c, cornification; d, epidermal necrosis; e, collapse of basal layer. Scale bar=100 μm.

FIG. 4.

Representative hematoxylin and eosin stain (H&E) of pig skin specimens after the two laser irradiation modalities. (A) Control specimen. (B and C) The most active stimulation of fibroblast activity and collagen reformation. (D and E) Irreversible tissue damages on the epidermal and dermal layers, respectively (×100). a, formation of fibrous tissue; b, epidermolysis; c, cornification; d, epidermal necrosis; e, collapse of basal layer. Scale bar=100 μm.