Douglas Schoon Schoon Scientific and Regulatory Consulting, Dana Point, CA, USA The natural nail plate can be cosmetically elongated and enhanced to beautify the hands, but cosmetics made for this purpose are also used to effectively address discolored, thin, and weak or malformed fingernails. When used properly, these cosmetic products and services provide great value and enhance self‐esteem. Artificial nails not only add thickness and strength to the nail plate, but they also extend its length, typically 0.25–0.75 inches beyond the fingertip. A skilled nail technician can closely mimic the length and shape of the final product to create natural‐looking artificial nails. Certain techniques utilizing custom blending of colored products allow the appearance of the nail bed to be extended beyond its natural boundary, which can dramatically lengthen the appearance of the fingers (Figure 30.1). Different types of artificial nail coatings are applied to provide a range of benefits, as well as numerous decorative colors and designs, collectively known as “nail art.” A typical nail salon client wears artificial nail products to correct problems they are having with their own natural nails such as discoloration, splitting, breaking, unattractive or deformed nails (i.e. median canal dystrophy or splinter hemorrhages). There are several basic types from which to choose: nail wraps and nail dips, liquid and powder, powder gels, ultraviolet (UV) gels, or UV gel polish/manicures. An overview of each type is given in Table 30.1. Liquid and powder systems (aka acrylic nails) were the original artificial nail enhancements designed to extend the length of the natural nail plate. These systems were similar to certain dental products made from methacrylate monomers and polymers. Methacrylates are structurally different from acrylates, have different safety profiles, and should not be confused with one another. The literature frequently confuses methacrylates with acrylates and/or incorrectly suggests they are a single category (i.e. [meth] acrylate). The first structure shown in Figure 30.2 has a branching methyl group (–CH3) attached to the double bond of ethyl methacrylate (EMA). The branching changes both the size (10% larger) and shape of the methacrylate molecule, which reduces the potential for skin penetration. This helps explain why methacrylate monomers are less likely to cause adverse skin reactions than homologous acrylate monomers (i.e. ethyl acrylate and EMA). It is also one important reason why artificial nails containing acrylates are more likely to cause adverse skin reactions than those based solely on methacrylate monomers [1]. The polymer powders are polymerized to very high molecular weights and therefore unlikely to cause adverse skin reactions. Methacrylate monomer liquid systems have been among the most widely used type of artificial nail enhancement in the world but have lost popularity in recent years primarily due to the advent of alternative nail coating systems. The “liquid” is actually a complex mixture of EMA (60–95%) and other di‐ or tri‐functional methacrylate monomers (3–5%) that provide cross‐linking and improved durability, inhibitors such as hydroquinone (HQ) or methyl ether hydroquinone (MEHQ) (100–200 p.p.m.), UV stabilizers, catalysts such as dimethyl tolyamine (0.75–1.25%), flexibiizing plasticizers, and other additives. The “powder” component is made from poly methyl and/or EMA polymer beads (approximately 50–80 μm), coated with 1–2% benzoyl peroxide (BPO) as the polymerization initiator, colorants, opacifiers such as titanium dioxide, and other additives. Table 30.1 The three main types of artificial nail enhancements. Figure 30.1 The use of custom‐blended colored powders with methacrylate monomers to “illusion sculpt” and extend the apparent length of a short nail bed while also correcting a habitually splitting nail plate. (Source: CND, Inc., Vista, CA, USA. Reproduced with permission.) Liquid and powder systems are applied by dipping a brush into the monomer liquid, wiping off the excess on the inside lip of a low volume container (3–5 mL) called a dappen dish. The excess monomer is removed by wiping the brush on the edge of the dappen dish. The tip of the brush is drawn through the polymer powder, also in a dappen dish, and a small bead or slurry forms at the end of the brush. Three to six beads are normally applied and smoothed into shape with the brush. Pink powders are applied over the nail bed and white powders are used to simulate the free edge of the nail plate. The slurry immediately begins to polymerize and hardens on the nail within 2–3 minutes. If the proper ratio of liquid and powder are used, over 95% of the polymerization occurs in the first 5–10 minutes, but complete polymerization can take 24–48 hours [2]. After hardening, the nail is then shaped either by hand filing or with an electric file to achieve the desired length and shape. The finished nail can be buffed to a high shine or nail color applied. Figure 30.2 Chemical structure differences between methacrylates and acrylates. Length is added to the nail plate in one of two ways: Proper preparation of the natural nail’s surface is the key to ensuring good adhesion. Before the service begins, natural nails should be thoroughly scrubbed with a clean, disinfected, soft‐bristled brush to remove contaminants from the service of the nail plate as well as underneath the free edge (Figure 30.3). This removes surface oil and debris that can block adhesion. The nail is then lightly filed with a low grit abrasive file (180–240 grit) to increase surface area for better adhesion. Nail surface dehydrators containing drying agents such as isopropyl alcohol are applied to remove surface moisture and residual oils. Adhesion promoting “primers” may then applied to increase surface compatibility between the natural nail and artificial nail product. These adhesion promoters contain proprietary mixtures of hydroxylated monomers or oligomers, carboxylic acids, etc. In the past, methacrylic acid was frequently used but has fallen out of favor because of its potential as a skin and eye corrosive [3]. Figure 30.3 Equipment used to create liquid and powder artificial nails. 1, Nail scrub brush; 2, Dappen dishes containing liquid and powder; 3, Mylar nail form; 4, Abrasive files; 5, Nail enhancement application brush; 6, ABS preformed nail tips; 7, Plastic‐backed cotton pad; 8, Nitrile gloves; 9, N‐95 dust mask. (Source: Paul Rollins Photography, Inc. Geyserville, CA, USA.) As the natural nail grows, the artificial nail advances leaving a small space of uncoated nail plate. Every 2–4 weeks the nail technician will file the artificial nail down to one‐third its thickness, reapply fresh product, and reshape the artificial nail, thereby covering the area of new growth. This process is called “rebalancing” and is essential to maintaining the durability and appearance of the artificial nail. Rebalancing is done primarily with services designed to be long lasing, e.g. liquid and powder nails and UV gels. Other types of nail coatings and some UV gels typically are removed completely and replaced. Products that cure under low‐intensity UVA lights, typically with major spectral outputs from 410–350 nm. These are used to create artificial nails called “UV gels or UV polish”. Far UVA (below 350 nm), UVB, and UVC are not used to create UV gel nails [4]. Traditionally, UVA fluorescent style lamps have been largely replaced by newer types of UV nail lamps utilize instead LED (light‐emitting diodes) technology to produce the UVA needed to polymerize UV curable nail coatings of any type. LED produce a much narrower emission bandwidths centered at either 405 or 395 nm. This allows for faster and more efficient curing. Due to significant differences in curing times, artificial nail coatings are formulated to properly cure with a specific type of UV nail lamp, either LED or fluorescent style (Figures 30.4 and 30.5). Curing them under an improper nail lamp can lead to a wide range of problems, including under or over curing. Unlike traditional two‐part liquid and powder systems, UV gels are not mixed with another substance to initiate the curing process. Historically, UV gels have been blends of polymerization photoinitiators (1–5%), urethane or epoxy acrylate oligomers, and durability improving, cross‐linking monomers (approximately 75–95%), and catalysts such as dimethyl tolyamine (0.75–1.25%). Newer formulations using urethane methacrylate oligomers and monomers with lower the potential for adverse skin reactions. Rate of cure can be a hindrance for UV‐curable artificial nails. Slow cure rates allow atmospheric oxygen to block curing of the uppermost layers of UV gel products. This sticky upper layer can also be observed with certain types of liquid monomers, e.g. lower odor or “odorless” products that utilize hydroxyethyl or hydroxypropyl methacrylate as the main reactive monomer. This residual sticky surface layer is called the “oxygen inhibition layer” [5]. Skin contact with this layer should be avoided since it contains unreacted monomers, of in the case of UV curing products, unreacted monomers, or oligomers. Figure 30.4 Traditional fluorescent‐style UV nail lamp (Source: Paul Rollins Photography, Inc. Geyserville, CA, USA.) Figure 30.5 Newer LED‐style UV nail lamp (Source: Paul Rollins Photography, Inc. Geyserville, CA, USA.) UV gels can be clear, tinted, or heavily colored. The natural nail is cleaned, filed, the surface dehydrated, and coated with adhesion promoters. The UV gel is then applied to the nail, shaped, and finished in the same fashion as two‐part liquid and powder systems and produces very similar looking results. In most cases, the same equipment used to create other types of artificial nails is used (Table 30.2). Some UV gels cure when placed under a UVA fluorescent‐style lamp for 2–3 minutes per applied layer, while others are designed to cure in about 10–30 seconds per layer by LED‐style nail lamps. Because UVA does not efficiently penetrate more than a few millimeters into the UV gel, these products are best applied and cured in several successive layers to ensure proper cure. UV gels are also applied over ABS nail tips or nonstick nail forms to lengthen the appearance of the natural nail. Table 30.2 Specialized equipment used to create artificial nail enhancements.
CHAPTER 30
Cosmetic Prostheses as Artificial Nail Enhancements
Introduction
Liquid and powder
Type
Chemistry
Also known as
Hardener
Nail wraps
Cyanoacrylate monomers
Fiberglass wraps, resin wraps, no‐light gels, silk, or paper wraps
Spray, drops, powder, or fabric treated with a tertiary aromatic amine moisture cure
Nail dips
Cyanoacrylate monomers
Glue and powder
Methacrylate powder, moisture cure
Liquid and powder
Methacrylate monomers and polymers – two parts
Acrylic, porcelain nails, solar nails
Polymer powder treated with benzoyl peroxide; monomer liquid contains tertiary aromatic amine
UV gels
Urethane acrylate or urethane methacrylate oligomers/monomer, expoxidized methacrylate, or acrylates.
Gel nails
UV gels
Soak‐off gels
Low‐power UVA lamp to activate the photoinitiator and tertiary aromatic amine catalyst
Polymer gels
Methacrylate monomers and polymers – one part
Polygel nails
Low‐power UVA lamp to activate the photoinitiator and tertiary aromatic amine catalyst
UV gel polish/manicure
Urethane acrylate or urethane methacrylate oligomers/monomer, expoxidized methacrylate or acrylate, solvents, e.g. acetone, ethyl acetate
Permanent polish
UV polish
Low‐power UVA lamp to activate the photoinitiator and tertiary aromatic amine catalyst 
Rebalancing
UV gels
Item
Description
Brush
Natural or synthetic hair brush for application, spreading, and shaping of monomer and oligomers products on the nail plate
Dappen dish
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