This method relies on deposition of solution directly into the pulp chamber. It will normally be administered following the injection of an anaesthetic solution by another route. It is important that the solution is injected into the pulp under pressure. An opening into the pulp should be made with a small round bur to allow the snug fit of the needle. If a large opening is present in the pulp chamber, then the needle should be advanced into the canal until the fit is tight (Fig. 4). The important point is that the injection must be administered under pressure. The amount of solution injected is around 0.2 mL (Malamed1998).A number of methods such as obliterating a large pulpal opening with gutta-percha (Bircheld & Rosenberg 1975) or a cotton pledged (Van Gheluwe & Walton 1997) have been suggested to aid in the buildup of pressure. However, Smith & Smith (1983) claim the only way to ensure no back flow is to introduce the needle through a small pulpal opening.
It has been suggested that an alternative method of obtaining anaesthesia via the pulp is to allow local anaesthetic solution to bathe an exposed pulp for a period of 30 s (Malamed 1998). In addition, anecdotal accounts of the use of topical anaesthetics applied to the pulp have been reported (DeNunzio1998). However, published studies (see below) indicate that the method described above is preferred.
Spread of intrapulpal anaesthesia Smith & Smith (1983) in a study in dogs showed that material injected intrapulpally reached the apex of 62% of (injected) roots and only 15% of adjacent roots in multirooted teeth. Therefore, these authors recommend injecting each root in multirooted teeth.
Figure 4. Delivery of intrapulpal anaesthesia by inserting the needle into the pulp canal until a tight fit is obtained (illustration reproduced by kind permission of Oxford University Press).Factors influencing efficacy.
Although some authors claim that efficacy is dependent upon the anaesthetic solution (Gurney 1967, Malamed 1998) a recent double-blind study has shown that intrapulpal anaesthesia may be obtained just as effectively by injecting saline compared to a local anaesthetic solution (VanGheluwe & Walton 1997). These authors reported successful anaesthesia in 33 of 35 teeth injected intrapulpally with either 2% lidocaine with 1:100 000 adrenaline or saline. That study confirmed the results of Bircheld & Rosenberg (1975) who achieved similar success with saline or lidocaine with 1: 50 000 adrenaline after intrapulpal injection. In the latter, failure was owing to leakage of solution and all the failed teeth were successfully anaesthetized when the leak was plugged with gutta percha and the pulps reinjected. Advantages of intrapulpal anaesthesia.
Disadvantages of intrapulpal anaesthesia.
- As mentioned above the method does not require a local anaesthetic.
- The method provides a useful means of overcoming failure in teeth where conventional techniques have been unsuccessful. Bircheld & Rosenberg (1975) reported success in 53 out of 56 teeth which had failed anaesthesia after conventional approaches.
- Although theoretically this technique uniquely could provide single-tooth anaesthesia, the fact that it is normally administered after failure of another method precludes this possibility in most cases.
- The systemic effects of intrapulpal anaesthesia appear to be negligible. Pashley (1986) demonstrated in dogs that the injection of 0.3 mL local anaesthetics containing 1:100 000 adrenaline produced no cardiovascular response unlike the events after an injection of the same amount via the periodontal ligament (see above).
- The injection may be painful (Malamed1998).
- The technique has limited application as it involves pulpal exposure. Interestingly, however, one study on the use of intrapulpal anaesthesia for pulpotomy suggested that the injection did not affect healing of pulpotomized teeth, although no histological examination was performed (Teixeira et al.1999).
- This method is not indicated as a primary method of anaesthesia as it can be uncomfortable and is only employed after an initial anaesthetic failure.