Operative tips 293

Local anesthesia

Local anesthesia is the procedure whereby only a certain operative area is desensitized to pain, with no loss of consciousness. The sensory, or afferent, nerves are blocked either at the operative field itself or at any point between the operative field and the brain. There are a number of methods for producing local anesthesia, and these generally fall into four categories. It is the first two categories, however, that are of greatest interest to the implantologist.

Infiltration anesthesia. In infiltration anesthesia, also called peripheral or terminal anesthesia, the peripheral nerves are anesthetized in a localized area by directly injecting the anesthetic solution into the area. Several sites may be used.

The anesthesia may be injected subperiosteally, that is, between the periosteum both buccally and lingually, to reach the bone. This approach is used in conjunction with block anesthesia when extensive surgery is anticipated.

For anesthetizing the soft tissues, as is necessary for retracting them to expose the bone, a supraperiosteal injection is recommended. This involves placing the solution beneath the mucous membrane and above the periosteum.

Intraosseous infiltration involves depositing the anesthetic between the buccal and lingual cortical plates of bone. To do this, the outer cortical plate of bone first must be penetrated with a bone bur. This is used at times for pinpoint localization of the anesthesia to avoid desensitizing the entire side of the jaw. The method is preferred for patients who do not like to have the entire face numb, and it is also used for the removal of root tips, cysts, and any other bone-clearing procedures necessary before implantation.

The anesthetic agent may also be injected periodontally, directly into the periodontal membrane. This method is particularly useful when block and infiltration methods fail to adequately anesthetize a tooth with a pericementitis. An intraseptal anesthetic agent is injected into the cancellous interdental septum. This is used mainly on older patients whose gingival tissues have receded, leaving the periodontal membrane deformed. As a result periodontal anesthesia is reduced in effect.

Conduction anesthesia. In conduction, or nerve block, anesthesia the anesthetic is injected into the nerve somewhere between the periphery of the nerve trunk and the brain. This eliminates sensation in the area distal to the injection point. This approach can be subdivided into mandibular, zygo-

matic or tuberosity, infraorbital, and second division injections.

Intraarterial anesthesia. Although not too important to the implantologist, intraarterial anesthesia is a useful means of producing local anesthesia by injecting the desensitizing agent into the arterial circulation supplying the area to be anesthetized.

Intravenous anesthesia. Occasionally the veins leading from the given operative field are injected, and the distal end of the area is bandaged to prevent the blood from circulating away. This method, how-ever, is rarely used during an implant intervention.

Pressure anesthesia. Although anesthetizing the pulp by pressure cannot be classified as an infiltration method, it is nevertheless a method of producing local anesthesia.

Tips for local anesthesia. A thorough knowledge of the nerve innervations of the maxilla and mandible is of utmost importance to anesthetize the patient skillfully with a minimal amount of the solution.

An edentulous area need not have as much anesthetic agent introduced as would be needed for a full crown preparation, because there is very little nerve innervation in osseous tissue.

There is some difference of opinion over the type of injection to be given in the lower jaw. The mandibular soft tissues are supplied by a particularly rich vascular system. If only infiltrating the mandible without giving a nerve block, the anesthetic must be sufficiently concentrated and strategically placed in order to be effective. A 2% solution of a good brand of local anesthetic is the most commonly used. There is no need to use stronger concentrations, as they could be more toxic to the patient. It is important to remember that intolerance to an anesthetic is increased in a square proportional to the increase in concentration.

When anesthetizing the lower jaw for an implant intervention, some operators (mostly European) eliminate the inferior alveolar block injection and just infiltrate the area to be worked on. In this manner the operator has the patient's sensitivity as an additional guide when he is approaching the mandibular canal. However, if this landmark is clearly visible in the radiographs, the operator can feel free to give a block injection.

When injecting the maxilla, it is usually necessary only to infiltrate the various implant sites. How-ever, the operator may also choose to give a posterior superior alveolar or anterior palatine injection.

When injecting either the maxilla or the man-