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The pharmacological basis of pain and anxiety control

Morton Rosenberg and Michael Thompson

INTRODUCTION

Despite their ability to reduce fear, anxiety, and apprehension, behavioral techniques may be inadequate for some patients, and pharmacological interventions may be necessary in addition to and/or in combination with behavioral strategies. The use of sedation and even general anesthesia may be necessary to access dental care for some severely phobic patients. Local anesthesia continues to be the foundation of clinical dentistry, and, unfortunately, is related to many of the dental phobic’s fears. This chapter is intended to present an overview of the use of sedation in dentistry and not intended as one directed at teaching technique.

Studies continue to affirm a significant percentage of the population is very anxious or even terrified of the dental environment.¹ Despite the advances in understanding of these issues, the incidence of dental anxiety has remained basically unchanged for the last 50 years.^2,3

Many of the causative factors surrounding the development of dental phobia and avoidance of care center upon pain. These factors include if the patient has had painful dental experiences in the past, or if the patient believes that painful treatment is inevitable.^4–6 Fear of dental pain and avoidance of care has even been linked with genetic variations associated with red hair color. Subjects with red hair color caused by variants of the MC1R gene are less sensitive to subcutaneous local anesthetics,⁷ and report more anxiety and fear of dental pain than participants lacking the MC1R gene variations.⁸

LOCAL ANESTHESIA

The administration of local anesthesia is one of the most stressful and difficult procedures for the dental phobic. Many of the psychogenic medical emergencies encountered in dentistry occur in the period prior, during, or immediately after the injection.⁹ Unfortunately, intraoral injections are administered into a region of the body that is richly innervated, in addition to having deep psychological implications. For many dental patients, it is the local anesthetic injection procedure that often represents the most fear provoking portion of the dental experience. When patients are asked to judge their dentists, the most important criteria is “a dentist who gives a painless injection.”¹⁰

Nondrug techniques such as behavior modification, hypnosis, distraction, and other methods of reducing the anxiety and fear surrounding the dental injection can be useful. The attention to the patient’s fears and apprehension by a concerned dentist makes the greatest difference in the injection period, which many feel is the most stressful part of the dental appointment. For example, the use of a topical anesthetic prior to injection will provide a degree of anesthesia to nonkeratanized tissues to a depth of 2–3 mm, which reduces the pain of needle insertion and has become a patient expectation. Benzocaine 20% and lidocaine 5% are the most popular topical anestheteics and gels, ointments, and sprays for this purpose are available. Additionally, eutectic mixtures of local anesthetics (prilocaine and lidocaine) are available in a vehicle (Oraqix^®, Dentsply International, Philadelphia, PA) that is expressed as a liquid and becomes an adherent gel at body temperature when deposited in the periodontal space. Using this technique, full quadrant periodontal curettage can be accomplished without the use of multiple local anesthetic injections. ¹¹ The compound can also be used as pre-injection topical anesthetic.¹² More recently, it has been reported that using a refrigerant (1,1,1,3,3-pentafluoropropane/1,1,1,2-tetrafluoroethane) as a preinjection anesthetic was more effective than a topical anesthetic gel of 20% benzocaine in reducing the pain of posterior palatal injection.¹³

Alternative anesthetic techniques and equipment have also been introduced to make the administration of local anesthesia less stressful, more dependable and easier for many patients.

The attempt to modify the medical technique of transcutaneous electrical nerve stimulation (TENS) to dentistry with the use of intraoral electrodes was termed electronic dental anesthesia (EDA). Although initially thought to have great promise, its lack of consistency in providing reliable pulpal anesthesia and equipment issues has decreased its popularity and utility in dentistry.¹⁴

Techniques or devices that create pressure or vibration have been shown to inhibit painful sensations prior to or at the same time as a painful stimuli is applied. A battery-powered attachment to the regular dental syringe, Vibraject^® (VibraJect LLC, Irvine, CA), produces a series of fine vibrations that has been reported to reduce pain during needle insertion.¹⁵

Computer-controlled local anesthetic delivery systems (CCLDS), beginning with the Wand ™, enable the dentist to accurately control needle placement with fingertip accuracy. The system replaces the classical dental syringe with a lightweight handpiece, and the dentist delivers the local anesthetic by a foot activated control.¹⁶ Flow rate of the local anesthetic solution is computerized and thus very consistent. Randomized clinical studies confirm a significant reduction in pain perception with the use of CCLDS as opposed to the use of standard equipment.¹⁷

The ability to anesthetize a single tooth rather than an entire quadrant is very important for some phobic patients. In addition to simple infiltration techniques, the periodontal ligament injection (PDL) or intraligamentary injection (ILI) and intraosseus anesthesia, provide pulpal anesthesia to a single tooth with only localized soft tissue anesthesia surrounding that tooth developing. The success rate for the PDL injection is high although it can be painful.¹⁸ The introduction of a new iteration of the CCLAD, Single Tooth Anesthesia (STA^™, Milestone Scientific, Piscataway, NJ) incorporates dynamic pressuring sensing technology that continually measures the exit pressure of the local anesthetic solution during a PDL injection. By strictly regulating pressure of the local anesthetic being infused into the periodontal ligament space, most patients experience less discomfort than with traditional syringes.¹⁹

Intraosseous anesthesia is the technique of injecting local anesthesia directly into the cancellous bone spaces adjacent to the target tooth and results in rapid onset of local anesthesia. It allows for profound single tooth anesthesia and has a high degree of success in teeth unable to be anesthetized by standard injection techniques.^20,21

There are patients who do fear the prolonged lingering soft tissue numbness following routine dental local anesthesia. While pulpal anesthesia from local anesthetics containing vasconstrictors may last approximately 45–60 min, the soft tissue anesthesia and associated functional deficits may last 3–5 h. Phentolamine mesylate (OraVerse^™) is FDA approved to reduce the time necessary to return of normal nerve function following the administration of local anesthesia. OraVerse™ acts by dilating the blood vessels constricted by the vasoconstrictor in the local anesthetic, increasing the blood flow to carry away the local anesthetic, and is thus not a true reversal agent or antagonist to the local anesthetic itself. It does the decrease the duration of mandibular inferior alveolar block anesthesia 121% faster than control and maxillary infiltration 166% faster than control.^22,23

Sedation

Despite the advances in local anesthesia administration and the application of behavioral technique, there are many phobic patients who will need sedation and anesthesia to access dental care. The need of sedative services has been documented, but unfortunately there are not enough qualified dentists to provide sedative services for the population especially for patients requiring more than minimal sedation. Need and demand studies indicate 23 million more Americans would access dental care on a routine basis if sedation services were available.²⁴ Among dentists using sedation on their patients, a majority use minimal sedation (82.3%), with fewer utilizing moderate sedation via the enteral route (28.3%), moderate sedation via the parenteral route (12.4%), and less than one in 10 are trained to competency in deep sedation.²⁵ The perceived invasiveness or stress of the dental procedure dramatically increases the need for sedation/anesthesia with patient preference rising from 2% for a dental cleaning to 47% for an extraction, to 55% for an endodontic procedure to 68% for periodontal surgery.²

Dentistry and medicine sedative/anesthesia providers have come to consensus and are unified as to the fact that sedation/anesthesia is a continuum and therefore it is not always possible to predict how an individual will respond to a central nervous system depressant. It is imperative to practice with one’s educational qualifiers and state permitting. The most important concept of this continuum is that ability to rescue (diagnose and manage) patients who enter a deeper level of sedation (e.g., from moderate to deep sedation) than initially intended. For all levels of sedation, the practitioner must have the training, skills, and equipment to identify and manage such an occurrence until either assistance arrives (emergency medical service) or the patient returns to the intended level of sedation without airway or cardiovascular complication.

The American Dental Association has always recognized the right of and privilege of educationally qualified dentists to deliver sedation/ anesthesia to their dental patients (Box 5.1).

The levels of the continuum are:

(1) Minimal sedation—a minimally depressed level of consciousness, produced by a pharmacological method, that retains the patient’s ability to independently and continuously maintain an airway and respond normally to tactile stimulation and verbal command. Although cognitive function and coordination may be modestly impaired, ventilatory and cardiovascular functions are unaffected.

(2) Moderate sedation—a drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate. Cardiovascular function is usually maintained.

(3) Deep sedation—a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.