Supplemental pulpal anesthesia for mandibular teeth.

Clinical pulpal anesthesia is dependent on the interaction of three major factors. (1) the dentist (2) the patient and (3) local anesthesia. Many patients fear endodontic treatment due to a concern about pain. Although pain treatment is well managed in many endodontic patients, there exists a group of patients who do not receive adequate local anesthesia. The purpose of this review article is to discuss the possible reasons for pulpal anesthetic failures and also to focus on the measures for developing effective approaches for the same.

Achieving adequate pulpal anesthesia in the mandible can often be a challenge to the clinician. In most cases after the conventional Inferior alveolar nerve block (IANB) injection the onset of pulpal anesthesia usually occurs within 10-15 min.[1-6] Teeth with irreversible pulpitis demonstrate an eight fold higher rate of local anesthetic failure compared to control teeth with normal vital dental pulp.

Supplemental injections with different techniques and/or types of anesthesia are frequently required in patients with irreversible pulpitis, primarily because pulpal anesthesia resulting from an initial injection is often inadequate for the completion of endodontic procedure.[7-9]

The purpose of this article is to focus on the failures of pulpal anesthesia and the measurement for achieving adequate anesthesia in endodontic.

Reasons for Low Success Rate of Inferior Alveolar Mandibular Block

Accessory innervation

Mylohyoid nerve is the accessory nerve most often cited as a cause for failure with mandibular anesthesia. When the IANB is compared to a combination injection of IANB plus the mylohyoid nerve block, the mylohyoid injection did not significantly enhance the pulp anesthesia of IANB.[10]

Cross innervation

Cross innervation from the contra-lateral inferior alveolar nerve has been implicated in failure to achieve anesthesia in anterior teeth after IANB. Experimentally, cross innervations occurs in incisors but play a very small role in failure with IANB.[1112]

Needle deflection

Needle deflection has also be theorized as a cause for failure with IANB.[1314] In asymptomatic subjects it was found that the orientation of needle bevel, for an IANB did not affect anesthetic success or failure.

Inaccurate IANB: It has been theorized that the lack of accurate IANB causes failure. Studies using ultrasound[15] and radiographs[1617] to accurately locate the inferior alveolar neurovascular bundle or mandibular foramen revealed accurate needle location did not guarantee successful pulpal anesthesia.

Reasons for Pulpal Anesthetic Failure after IANB

The central core theory

This theory states that the nerve on the outside of the nerve bundle supply molar teeth while the nerve and the inner supply the anterior teeth.[18]

The anesthetic solution may not diffuse into the nerve trunk to reach all the nerves to produce an adequate block even if deposited at the correct site. This theory may explain the higher experimental failure rates in the anterior teeth with IANB but not posterior teeth.[1-6]

Hot tooth

The term hot tooth generally refers to a pulp that has been diagnosed with irreversible pulpitis. Pre-operative pain is a risk factor for incomplete local anesthesia observed in patients with irreversible pulpitis. Although the mechanism mediating this clinical problem is incompletely understood several hypothesis have been advanced.

Ion trapping

trapping of local anesthetics is due to the low pH. The lowered pH of inflamed tissue reduces the amount of the base form of anesthetic to penetrate the nerve membrane. Consequently there is less of the ionized form within the nerve to achieve anesthesia. However this is only possible for infiltration injections, block injections are not likely to involve acidotic tissues.

Altered membrane excitability of peripheral nociceptors

from inflamed tissue have altered resting potential and decreased excitability threshold. Wallace et al. demonstrated that the local anesthetic agents are not sufficient to prevent impulse transmission as a result of these lower excitability thresholds.[1920]

Tetrodotoxin resistant channels

has been shown that Tetrodotoxin resistant channels (TTXr) class of sodium channels are resistant to the action of local anesthesia. A related factor is the increased expression of sodium channels in pulp diagnosed with irreversible pulpitis.[21] TTXr channels represent a logical mechanism for local anesthetic failures. These channels are relatively resistant to lidocaine, they are expressed on nociceptors and their activity with Prostoglandin E2 (PG E2).

Central sensitization

Increased sensitization may amplify incoming signals from sensory nerves. Under conditions of central sensitization, there is an exaggerated response to peripheral stimuli and under these conditions the IANB may permit for sufficient signaling to occur to lead to the perception of pain. Thus the central sensitization may contribute to local anesthetic failures.

Psychological factors

Patient anxiety may contribute to local anesthetic failure. Experienced clinicians understand that apprehensive patient have a reduced pain threshold and are more likely to report an unpleasant dental experience.[7]

Methods to Improve Pulpal Anesthesia in Endodontics

Supplemental injections

Intraligamentary (periodontal ligament) anesthesia

to the injection it is recommended that the site of penetration is swabbed with an antiseptic solution. The needle is inserted at 30° to the long axis of the tooth at the mesio-buccal aspect of the roots. The needle is forced to maximum penetration until it is wedged between the tooth and the crestal bone.[22] Success is independent of needle gauge.[23] Some authors recommend that the needle bevel should face the alveolar wall,[24] as this reduces the chances of blockage and increases the efficacy of the injection.[25] Once the needle is correctly positioned, the solution is injected under back-pressure. The amount of solution injected into the periodontal ligament (PDL) is little. It is recommended that 0.2 ml solution is deposited into the periodontium of each root. When using the specialized syringes, it is important to maintain the needle in position for about 5-10 s following depression of the lever to allow escape of solution from the cartridge. Removing the needle from the PDL too soon will result in loss of solution from the cartridge. The most critical factor governing success of the technique is that the injection is performed against resistance.[26] Rapid onset of anesthesia is a striking feature of intraligamentary anesthesia. Anesthesia is achieved within 30 s and can be immediate.[23242627]

Duration of Intraligamentary Anesthesia

Duration of intraligamentary anesthesia is variable. The duration of pulpal anesthesia to be around 15 min for single rooted teeth and rather less for lower molar.[28]

Factors influencing efficiency

The anesthetic solution: The presence of vasoconstrictor significantly increases efficacy. Lidocaine with adrenaline was effective in 91.6% of PDL injection whereas without the vasoconstrictor the success rate was only 42%.[29]

The operative procedure: The greatest success is achieved prior to exodontia and the least for endodontic procedures.[273031]

The type of tooth: Cowan (1986) found significant differences in the efficacy of intraligamentary anesthesia between the jaws, recording 55% success in the mandible and 83.3% in the maxilla.[28] On the other hand, white et al.(1988) reported no difference in the incidence of pulpal anesthesia between maxillary and mandibular teeth.[32] They also reported the least success for pulpal anesthesia with mandibular lateral incisors (18.2% success). The low success rate for pulpal anesthesia with lateral incisors may be owing to the paucity of perforations within the mandibular incisor sockets and the limited cancellous space.

Advantages

Smaller doses are required (0.2 ml/root).

Overcomes failed conventional anesthesia.[33]

Limited soft tissue anesthesia.

Mandibular anesthesia in patients with bleeding disorders.[34]

Disadvantages

Produce bacteremia (endocarditis).[35]

There is rapid entry into circulation (cardio vascular effects).[36]

Pre- and post-injection discomfort.[37]

May damage periodontal tissues and pulp.[25]

Injection equipment may be damaged.[242930]

Advanced armamentarium for intraligamentary injection

Computer controlled local anesthesia delivery system

Milestone scientific introduced the first Computer controlled local anesthesia delivery (C-CLAD) system in the United States in 1997. Originally known as the Wand, subsequent versions were sequentially renamed the Wand Plus and then CompuDent, the current designation.

The CompuDent system has three components: A base unit, a foot pedal, and a disposable hand piece assembly. The base unit contains a microprocessor and connects to both the foot pedal and the end of the hand piece assembly that accepts the local anesthetic cartridge. The microprocessor controls a piston that expresses local anesthetic by pushing the local anesthetic plunger up into the cartridge. The anesthetic solution is then forced into the tissue. Pressing lightly on the foot pedal activates a slow injection rate (0.005 ml/s) appropriate for needle insertion, PDL injection, and palatal administration. Heavier pressure on the pedal increases injection speed to deliver the entire content of the cartridge in 1 min (i.e., 0.03 ml/s) which is normally used for buccal infiltration.

In 2007, Milestone Scientific added the single tooth anesthesia (STA) system to its product line. The STA unit adds dynamic pressure sensing technology, which provides continuous feedback to the user about pressure at the needle tip to help identify ideal needle placement for PDL injections.

The comfort control syringe differs from the Milestone products in that there is no foot pedal. It has two main components: A base unit and a syringe. Several functions of the unit most importantly injection and aspiration - can be controlled directly from the syringe, possibly making its use easier to master for practitioners accustomed to the traditional manual syringe.

The comfort control syringe has five different basic injection rate settings designed for specific injections: Blocks, infiltrations, PDL, intra-osseous and palatal. Each rate is selected by the push of a button. A comparison between the traditional dental syringe and the comfort control syringe revealed no meaningful differences in ease of administration, injection pain and efficacy and acceptance by patients.[38]

Three features of C-CLAD support the assertion that there may be less pain on injection.

First is the ability to administer small amounts of local anesthetics continuously during needle insertion.

Second is the steady infusion of the anesthetic may reduce discomfort.

Third is the reduced force for needle insertion has improved comfort.

Various investigators[39-41] have reported no differences in injection pain with Milestone products.

Intra-osseous anesthesia

The use of intra-osseous anesthesia was described by Lilienthal[42] and this author notes the reluctance at that time of operators to use the method. Since that time, specialized delivery systems have been introduced and this may increase the acceptance of the technique.[43]

Technique - This method is as follows

The point of perforation is infiltrated with 0.2 ml local anesthetic and 50-60 s. allowed to pass to ensure gingival anesthesia.[43] This point should lie in attached gingiva and is determined by imagining two lines running at right angles to one another. The horizontal line runs along the buccal gingival margins of the teeth and the vertical line bisects the distal interdental papilla of the tooth of interest. The point of penetration is 2 mm apical to the intersection of these lines. If this point lies within the reflected mucosa, an area of attached gingiva coronal to this is chosen. While using the specialized equipment, the perforator (attached to a slow-speed hand piece) is advanced through the anaesthetized gingiva and bone until a characteristic ’give’ indicating penetration through to the cancellous bone is experienced. At this stage, the perforator is removed, the short (8 mm) 27 gauge needle is inserted through the perforation into the cancellous space and around 1.0 ml solution is delivered slowly (over a 2 min period).This technique anaesthetizes the tooth of interest and will also anaesthetize the teeth mesial and distal to that tooth in the majority of cases.[44]

Duration of anesthesia

The onset of intra-osseous anesthesia is rapid.[43-45] The onset of anesthesia ranged from 10 s to 120 s. The success falls of rapidly over one hour.

Factors governing success;

Anesthetic solution: The efficacy of intra-osseous injections is poor in the absence of vasoconstrictor. Repogle et al. (1997) reported less than 50% success in mandibular first molars when a plain 3% mepivacaine solution was injected compared to 74% success with lidocaine and adrenaline.[44]

Type of tooth: The efficacy of the intra-osseous technique varies between teeth. Coggins et al. (1996) reported a 75% success rate with mandibular first molars compared to 93% success with maxillary first molars.[45]

Advantages of intra-osseous anesthesia

Smaller doses are used.

The amount of soft tissue anesthesia produced is less.[43]

Overcome failure after conventional techniques.

Disadvantages of intra-osseous anesthesia

Technically more difficult.

Specialized equipment may be required.

Rapid entry of local anesthetic and vasoconstrictor into the circulation.

Post-injection discomfort.

Devices for Intra-osseous Anesthesia

Three systems are available in the United States: Stabident, X-tip and Intra Flow.

Stabident

The stabident system for intra-osseous anesthesia includes a solid 27-guage perforator needle with a simple beveled tip and a plastic base designed to fit a latch-type-slow speed contra-angle hand-piece. The operator uses the perforator to create a small tunnel through the attached gingiva, periosteum, and alveolar bone. The typicinsertion point is on the attached gingiva, 2 mm below the facial gingival margin, and midway between the tooth of interest and an immediately adjacent (preferably distal) tooth. Local anesthesia should be administered to anesthetize the local gingival tissue, if it is not already numb from a previous injection.

Penetration is made using short bursts with light pressure to deposit anesthetic solution into the cancellous.

X-tip

The X-tip anesthesia delivery system was designed to solve the primary technical difficulty encountered with stabident system - finding the hole and inserting the needle. The X-tip system comprises three parts: The driller (perforator), a 25-guage guide sleeve that fits over the 27-guage drill, and an ultra-short needle of the same diameter. The drill leads the guide sleeve through the cortical plate into the cancellous bone. The drill portion is then removed, leaving the guide sleeve in place. The guide sleeve is then used to direct the needle into the cancellous bone to deposit the anesthetic solution. The primary difference in using the X-tips are:

The penetration need not be performed through the attached gingiva,

The guide sleeve must be carefully removed with a hemostat after the after the injection is performed.

Intra Flow

The Intra Flow HTP anesthesia delivery system is designed as an all-in-one system that allows the user to perforate the bone and deposit anesthetic solution in a single intra oral step. The Intra Flow device is essentially a dental hand piece equipped with an injection system build into the body. A 24-guage hollow perforator is used to penetrate the bone and infuse the local anesthetic solution. Anesthetic from the dental cartridge is routed to the perforator by a disposable transfuser that also serves to cover the switch used to select between perforator rotation and anesthetise infusion modes.

Clinical uses

Anesthesia of single tooth.

Primary method of pain control or as a supplementary technique.

In mandibular molars with irreversible pulpitis, patients requiring endodontic treatment in whom conventional local anesthetic injection fail to provide adequate pain relief for assessing the pulp.[46-48] A supplement intra-osseous injection of 2% lidocaine with 1:100,000 provided complete anesthesia in 82-89% of these subjects. This method may be helpful in treating children and adolescents.

Side effects and complications

The most common effect is tachycardia from the injected vasoconstrictor. The heart rate accelerates within seconds after injection and remains elevated for several minutes thereafter.[49] The injection of the solution containing epinephrine should be limited in patient with cardiac disease.

Separation of the perforator or drill needle. Post injection, hyperocclusion is relatively common.

Moderate post injection pain.

Dentinal tooth damage and osteonecrosis of bone.[50]

Intrapulpal anesthesia

In about 5-10% of mandibular posterior teeth with irreversible pulpitis, supplement injections even when repeated do not produce profound anesthesia. Pain persist when pulp is entered. This is an indication for an intrapulpal injection.

Technique

This method relies on deposition of solution directly into the pulp chamber. It will normally be administered following the injection of an anesthetic 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. The important point is that the injection must be administered under pressure.

The amount of solution injected is around 0.2 ml. The only way to ensure no back flow is to introduce the needle through a small pulpal opening.[51]

Factors influencing efficacy

Although some authors claim that efficacy is dependent upon the anesthetic solution,[52] a recent double-blind study has shown that intrapulpal anesthesia may be obtained just as effectively by injecting saline compared to a local anesthetic solution.[53]

Advantages of intrapulpal anesthesia

As mentioned above the method does not require a local anesthetic.

The method provides a useful means of overcoming failure in teeth where conventional techniques have been unsuccessful.

Although theoretically this technique uniquely could provide single-tooth anesthesia, the fact that it is normally administered after failure of another method precludes this possibility in most cases.

The systemic effects of intrapulpal anesthesia appear to be negligible.

Disadvantages of intrapulpal anesthesia

The injection may be painful.

Limited application as it involves pulpal exposure.

Not indicated as a primary method.

Mandibular buccal infiltration with articaine

An infiltration of articaine after an IANB if the patient has pain after a clinically successful IANB (lip numbness), helped in providing profound pulpal anesthesia.

Strategies to improve success of the IANB injection

Use of fast acting anti-inflammatory drugs has an adjunct to the provision of local anesthesia to teeth with inflamed pulp and peri-radicular tissue.

Reducing pulpal level of inflammatory mediator PGE2 would be beneficial in two ways, firstly, decreasing pulpal nociceptors, sensitization would mitigate an increase in resistance to local anesthetics.[54] Secondly, it may diminish a prostonoid induced stimulation of TTXr sodium channel activity. This channel also displaces relative resistance to lidocaine. Reduction of PGE2 could be accomplished with either Non steroidal anti inflammatory drugs (NSAIDS) or steroids.

Double blind clinical trial have showed that the injectable NSAID ketorolac, when injected intraorally or intra muscularly produce significant analgesia in patient with severe odontogenic pain.[5556]

Intra-osseous injection of 40 mg methylprednisolone in patients with irreversible pulpitis resulted in less pain.[57] Finally reducing anxiety by sublingual triazolam[58] or nitrous oxide, and a caring chair side manner, increases the likelihood of effective local anesthesia in endodontic pain patients.

Conclusion

Mandibular anesthesia remains a challenge in dentistry and especially an endodontics. Knowledge of the various methods is useful as these techniques might be required to provide pain control for teeth that prove difficult to anaesthetize by the operator′s normal route.