Most surgical and restorative dental treatments require an effective and long-lasting local anesthesia protocol. The purpose of this short paper is to understand the pathophysiological basis of dental pain and to provide clinical insights into its management. In particular, some conditions characterized by above normal complexity linked to the pathology, the length of the procedure, or the patient’s requests will be addressed.
Irreversible pulpitis: pathophysiology and management
The dental pulp is a richly innervated and vascularized tissue. The neural component is made up of afferent nerve fibers of trigeminal origin, responsible for nociceptive transmission. These are associated with some orthosympathetic efferent fibers in charge of controlling the local blood flow. There is no agreement among scholars on the role of the parasympathetic component present.
Both nerves and vessels play a role in the nociception phenomenon and, upstream of the latter, the pulp inflammation (pulpitis) phenomenon encompasses microcirculation and nerve activity as components.
Reduced caliber and slow transmission fibers are normally used for nociception. In this case, the A-delta fibers, the smallest among myelinated fibers, do not have a relevant role or, more precisely, they apparently have a better response to stimulation at the level of the central tubules rather than of the pulp. The activation of the unmyelinated C fibers, caused by chemical or thermal stimuli, on the other hand, appears to cause, mainly through the mediation of the substance P, a vasomotor phenomenon of an inflammatory nature, then further amplified by the degranulation of histamine by the mast cells. Macrophages, in turn sensitive to substance P, release other mediators of PGE2 and thromboxane, and the pro-inflammatory cytokines IL-1, IL-6 and TNF. A further complicated vicious circle is therefore established, in which it is important to highlight the central role of the substance P.
As mentioned, a stimulus, such as the thermal stimulus, becomes the basis of the phenomenon, which becomes pathological only in the presence of pathological hypersensitivity conditions, observable in an inflammatory microenvironment.
In a more clinical sense, the most advanced stage of inflammation, defined as irreversible pulpitis, results in a problematic approach in obtaining an adequate local anesthesia regimen.
Such an acid and hyperemic pulp environment, has a negative effect on the pharmacokinetics of anesthetic molecules, both hindering concentration and promoting early removal.
There are many strategies proposed in order to contain the pain stimulus during irreversible pulpitis, with differences related to the target site.
Two of them will be considered below, one based on a variation in the administration of the local anesthetic, the other involving the use of additional drugs.
An intraligamentary injection has been suggested as a supplementary method to the conventional anesthesia but, more recently, it has established itself as a valid alternative to the latter. The main critical issue lies in the potential risks dictated by failure to control the release pressure of the liquid. In this regard, technologies, such as CCLAD (computer-controlled local anesthetic delivery), have been created that are able to remedy this issue and, indeed, exploit it to increase the effectiveness of local anesthesia.
Among the drugs that can be used for prophylactic purposes, NSAIDs (non-steroidal anti-inflammatory drugs) represent the class most used by dentists. Their usefulness is linked to the double action that is central but also peripheral. The risks, in this case, are mainly linked to some contraindications and to possible overdose. Thus the selected overall pharmacological protocols should be carefully evaluated.
The closed-mouth Vazirani-Akinosi technique: trismus and other clinical uses
Trismus is a severe problem of primary dental interest. It results in a condition of pathological reduction of the degree of opening of the mouth on a neuromuscular basis and must, therefore, be distinguished from ankylosis conditions linked to joint problems.
Trismus is classically one of the early symptoms of tetanus, fortunately under control thanks to the spread of the vaccine and the methods of sanitation and sterilization. In any case, infectious diseases are still probably the main cause of trismus. Among these, local pathologies are to be considered, that is odontogenic infections: pulpitis, abscesses, and pericoronites, particularly in the area of the lower third molar.
Further on this subject, trismus also constitutes a possible complication within the context of different dental procedures. Firstly, surgical extractions, starting from the previously indicated site, or in any case in the lower molar region. It also constitutes an anesthesiology complication, in particular the mandibular alveolar nerve (IA) block technique. In this case, the problem will be determined by incorrect positioning of the needle and will tend to occur even after 2-5 days from the injection.
Lastly, trismus can be related to major musculoskeletal traumas, as well as other serious but even rarer pathologies.
From an anesthesiological point of view, the lower alveolar nerve block Vazirani-Akinosi technique, otherwise called (not by accident) “Closed Mouth Technique” is a very valid option, if not mandatory in the most serious cases.
The effectiveness of the technique is linked to the anatomy of the upper part of the pterygomandibular space, where, in addition to the lower alveolar nerve, the lingual and buccal nerves also run, in a position therefore suitable for simultaneous anesthesia. It can be a great advantage over the traditional alveolar block technique. Such a procedure requires a great deal of effort from the patient in opening wide. The Vazirani-Akinosi technique, conducted with the patient’s mouth closed and at rest, therefore is also advantageous based on the level of cooperation needed.
The target site lies close to the cheek, approximately at the level of the mucogingival line of the second molar. The procedure involves palpation of the anterior and posterior margins of the mandibular nerve branch, in order to determine the midpoint.
The syringe is inserted parallel to the occlusal plane, with the needle slightly bent laterally. The liquid is deposited at the soft tissue level, on the medial side of the nerve branch.
The procedure has a positive aspiration rate of less than 10% (a minimum threshold for the inferior alveolar nerve block). The anesthetic effect appears within 40 seconds; it takes a total of 90 seconds to reach the level of surgical anesthesia. The success rate is up to 97%.
Beyond the clinical management of trismus, several authors have evaluated the Vazirani-Akinosi technique as a real alternative in all procedures conducted in the mandibule, especially in patients with a history of conventional technique failures.
Local anesthesia in professional oral hygiene sessions
The third and final part of the treatment focuses on a different form of complicated anesthesia, that is, the one in which the anesthesiology regimen is imposed by the patient’s needs. A practical example is the patient’s request for the use of local anesthesia in anticipation of a professional oral hygiene procedure.
Is local anesthesia necessary in oral hygiene procedures? In principle, the answer is no. Firstly, because, particularly with the spread of piezoelectric instruments, oral hygiene can be considered a relatively low pain impact treatment. It should be kept in mind that this is an intervention involving the entire dentition and, therefore, the anesthesia, while maintaining the definition of “local”, will be distributed on multiple nerve branches from both arches of the oral cavity. In this specific intervention, it is therefore, indicated for those patients with a verified (or previously known) low pain threshold. In reality, in addition to the latter, various patients, including adults, with special needs can be included. Above all in these cases, in addition to the anesthesiology technique itself, it is important to explore the options available in order to minimize the related anxiety.
The choice further imposes implications from a medical-legal point of view. Based on the country (or state, in the case of the United States), dental hygienists may be able to freely administer local anesthesia, administer it under the supervision of the dentist, or will not be able to administer it at all and, therefore, will have to refer the patient to a doctor.
According to what Moody Smith found in 2019, it is interesting, however, how patients, although generally unaware of the necessary theoretical-practical background, tend to be in favor of more permissive legislative developments for hygienists.
Regardless of who the actual professional administering anesthesia may be, the latter is required to find out the patient’s history in depth, because of the contraindications dictated by the type of molecule or by the use of the vasoconstrictor, and in order to predetermine the correct dosage of the drug to be administered. Beyond the strictly patient-related aspect, it is important to consider the depth and duration required for anesthesia. For example, it may be indicated to perform a milder anesthesia, but proceeding by arches: the AMSA technique (anterior middle superior alveolar nerve block) may be the right answer for the upper arch.
Ultimately, it is important to keep in mind new and highly effective hygiene procedures, such as full-mouth disinfection, which is more easily scheduled on two appointments within 24 hours. For this reason, it also becomes important to consider the overall severity of the periodontal framework, in order to direct the patient to the most suitable treatment. The more invasive the treatment, the more likely that it will be necessary to resort to local anesthesia.