Efficacy, spread and duration of anaesthesia are dependent upon the following factors: The anaesthetic solution.
The presence of a vasoconstrictor significantly increases efficacy. Gray et al. (1987) reported that lidocaine with adrenaline was effective in 91.6% of periodontal ligament injections whereas without the vasoconstrictor the success rate was only 42%. Meechan (1989) reported 55% success when plain 2% lidocaine was used whereas 2% lidocaine with 1 : 80 000 adrenaline was successful in 82% of extractions. Kim (1986) noted the concentration of adrenaline employed also affected the efficacy of 2% lidocaine during intraligamentary anaesthesia, recording 81% success when the vasoconstrictor was present as a 1 :100 000 solution compared to 88% success with a 1 : 50 000 concentration. Kaufman et al. (1984) claim that the duration of anaesthesia varies with the type of solution used, pulpal anaesthesia ranging from a mean of 1.05 min with 2% lidocaine to 27.05 min when 2% lidocaine containing 1: 50 000 adrenaline was employed. Studies comparing the efficacy of long-acting local anaesthetic agents such as etidocaine (Johnson et al.1985), mepivacaine (Schleder et al.1988) and bupivacaine (Kaufman et al.1984) to lidocaine for intraligamentary anaesthesia have concluded that success is more related to the concentration of vasoconstrictors employed than to the anaesthetic agent used. Schleder et al. (1988) found 3% mepivacaine more effective than 2% lidocaine (41.9 and 13.8% success, respectively) when injected into the periodontal ligament of human mandibular premolars, however, both solutions were significantly less effective than 2% lidocaine with 1 :100 000 adrenaline (86.7% success). Kaufman et al. (1994) noted no difference in success between different concentrations of lidocaine but confirmed the importance of adrenaline in relation to efficacy. The injection of1:100 000 adrenaline alone into the periodontal ligament does not produce dental anaesthesia (Schleder et al.1988). The operative procedure.
The greatest success is achieved prior to exodontia and the least for endodontic procedures (Malamed 1982, Kaufman et al. 1983, Miller 1983). Malamed (1982) reported a 60% success rate prior to endodontics compared to 100% when the technique was employed before extractions; in the study of Miller (1983), the equivalent success rates were 72 and 98.4%, respectively. The type of tooth.
Cowan (1986) found significant differences in the efficacy of intraligamentary anaesthesia between the jaws, recording 55% success in the mandible and 83.3% in the maxilla. On the other hand, White et al. (1988) reported no difference in the incidence of pulpal anaesthesia between maxillary and mandibular teeth.
Kaufman et al. (1983) reported the technique to be successful in anaesthetizing canines in 46% of cases compared to at least 85% success for other teeth. Similarly, Meechan (1989) claimed the poorest success with canines (78%) when intraligamental injections were used prior to dental extractions, incisors (94%) being the easiest to successfully anaesthetize. Grundy (1984) found significantly poorer success with lower third molars compared to lower first molars. White et al. (1988) reported least success for pulpal anaesthesia with mandibular lateral incisors (18.2%success).The low success rate for pulpal anaesthesia with lateral incisors may be owing to the paucity of perforations within the mandibular incisor sockets and the limited cancellous space in this region making it difficult for the anaesthetic solution to enter intraosseously (White et al.1988). Davidson& Craig (1987) noted that, in children receiving intraligamentary anaesthesia for restorative procedures, the efficacy was significantly greater for those teeth with both mesial and distal contact points.