الفهرس 
• Introduction and Aim of the Work
Skin agingOnly 14 pages are availabe for public view
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Abstract
Skin aging is an inevitable process that occurs due to both extrinsic (photo-aging) and intrinsic factors (chronological aging). Photoaging is a cumulative process, that depends mainly on the degree of sun exposure, while chronological aging depends solely on the passage of time.
Skin aging is associated with many clinical manifestations (such as; wrinkles, dyspigmentation, atrophy, telangiectases, premalignant lesions, laxity, leathery appearance and precancerous and malignant lesions) and histopathological changes (such as; solar elastosis, decreased collagen fibers and fibroblasts, thinning of the epidermis with flattening of the DEJ, disorganized keratinocytes, decreased number of melanocytes and decreased skin appendages).
Many theories try to explain the process of skin aging, however 2 main theories exist; apoptosis and cumulative environmental damage. The most important factor is sun exposure because UVR can induce DNA damage to the skin and is a predisposing factor for malignant transformation.
Management of skin aging includes both prevention by sun screens and antioxidants and treatment using topical remedies, microdermabrasion, chemical peeling, BTX injection, dermal fillers, ablative procedures either mechanical (dermabrasion and dermasanding) or thermal (ablative lasers), non ablative rejuvenation either light based (non ablative lasers) or radiofrequency, fractional lasers, cosmetic surgery, skin needling and mesotherapy.
Laser resurfacing is a cornerstone in facial rejuvenation that may be ablative or non ablative. Ablative lasers (CO2 and Er:YAG lasers) remove the epidermis and reach the dermis causing a wound healing response. Prolonged time of healing with increased risk of side effects such as pigmentary changes, infection, scarring, keloid formation and herpes simplex viral infection are the main drawbacks. Non ablative lasers preserve the epidermis and target specific chromophores in the dermis with short downtime and decreased risk of side effects, but with claimed lower efficacy.
Er:YAG laser was the second ablative laser developed for skin resurfacing (after CO2 laser) and its wavelength is 2940 nm. Because the wavelength closely approximates the absorption peak of water (3000 nm) nearly all of the energy is absorbed in the epidermis and papillary dermis, yielding superficial ablation and less underlying thermal damage.
The new concept of fractional photothermolysis is developed to overcome the high risk of side effects caused by traditional lasers, to shorten the downtime after laser treatment and to give better results than non-ablative procedures. It depends on fractionation of the laser beam to induce microscopic treatment zones (MTZs) of controlled width, depth, and densities. These MTZs show thermal heating and tissue damage and are surrounded by spared areas of viable epidermis and dermis that allow for rapid repair. The fractional laser can be non ablative (preserve the epidermis) or ablative (cause MTZs of damaged epidermis and dermis).
The aim of the present work is to evaluate the effectiveness of ablative (one session) versus fractional (4 sessions) Er:YAG lasers in facial rejuvenation clinically, histopathologically and immunohistochemically.