The evaluation prior to injection helps to determine the type of anesthetic procedure to be used as well as the need for any analgesic after the treatment. Simple procedures rarely require the use of adjunctive agents, except for very anxious patients. Be aware that a medical history must be taken and a physical examination performed prior to the use of any medication (Snow 1982). Preexisting medical conditions such as hypertension and heart diseases may influence the use of anesthetics in combination with epinephrine. A history of alcohol consumption, use of sedatives, and problems with anesthetics during dental procedures may indicate that extra care should be taken with these patients. It is important to ask the patients if they have had any undesirable experience with topical, infiltrative, or blocking procedures. Patients should also be asked about the use of any illegal drugs before the administration of any anesthetic medication.

Local anesthetics decrease or completely block sensory, autonomic, and motor functions. They act by blocking sodium channels at the cell membrane and interrupting the excitation-conduction process (Carvalho and Mathias 1997). The systemic absorption of local anesthetics depends upon the vascular flow at the injection site, the chemical and physical characteristics of the agents, and the adjunctive use of vasoconstrictors such as epinephrine. Vasoconstrictors will decrease the absorption and enhance the availability of the local anesthetic to the nerve cells, thus prolonging the duration of action and decreasing possible systemic effects. Care should be taken not to inject local anesthetics with epinephrine into areas of terminal circulation, due to an increased risk of necrosis.

In most cases, the level of anesthesia achieved with a topical anesthetic will be sufficient to alleviate discomfort during the injection of dermal fillers. There are basically two groups of topical agents: the ester group (cocaine, tetracaine, and benzocaine) and the amide group (lidocaine and prilocaine).

The stratum corneum is a strong barrier to the absorption of drugs through the skin. The skin should be cleaned with antiseptics before applying the topical anesthetic cream, as this will allow better permeation of the topical agents. The effect may also be enhanced by rubbing dry gauze onto the surface to remove dead cells and grease. The vasodilatation that results from this rubbing of the skin may also increase the permeation of the drug.

One of the most common topical anesthetics is a eutectic mixture of 2.5 % lidocaine and 2.5 % prilocaine, which is marketed as EMLA cream. It is a nontoxic mixture which use results in very low plasma levels. The usual dose is 1 g for each 10 cm² of intact epidermis. The cream should be in contact with the skin for approximately 45 min to 1 h with occlusive dressing (Hallen and Uppfeldt 1982). There is a new lidocaine and tetracaine mixture on the market which is marketed in Europe as Pliaglis. So far (Summer 2013) the experience with this product, which is quite different from EMLA (more a paste than a cream), is limited (Cohen 2013).

Cryoanesthesia is another method of inducing topical anesthesia. The simple application of ice bags may enhance the anesthetic effect. In fact, for some patients, the use of ice bags alone will provide enough anesthesia. Other topical freezing agents include ethyl chloride or dichlorotetrafluoroethane sprays, but these are unlikely to be used when the treatment involves dermal fillers.

Direct inhibition of nerve ending excitation may be achieved by infiltrative anesthesia. The drug of choice is generally 1 % lidocaine, which is injected intradermally or subcutaneously. Intradermal injection results in a rapid onset and longer duration of anesthesia, but it has the disadvantage of being painful and causing tissue distortion. Subcutaneous injection is less painful but has a shorter-lasting effect (Arndt et al. 1983

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