Fear is an emotional reaction to real or imagined imminent danger or pain. A certain degree of fear provides a protective mechanism against environmental dangers, but some fears, such as those that pertain to dental care, are learned and exceed the level warranted by the actual threat [2]. The exact number of patients who are fearful of dental treatment is unknown, because research is complicated by the large and diverse patient population, lack of universal definitions, and reluctance of patients to admit to fears. Dental fear is generally considered to be a less severe reaction than clinical anxiety disorder and specific phobia, but it can vary from mild to severe.

Anxiety disorders are the most commonly diagnosed psychiatric disorders in the general population, and specific phobia is the most commonly identified anxiety disorder [5]. Specific phobia is characterized by persistent (longer than six months), marked anxiety about a specific object or situation (e.g., flying, spiders, blood, dentistry) to the extent that the trigger is avoided or endured with severe fear or anxiety [49]. Patients with specific phobia will go to extremes to avoid the situation or the object that is the basis of their phobia. In dentistry, needle phobia can make the administration of a local anesthetic virtually impossible unless the patient has received some level of sedation. Claustrophobia, or the fear of being enclosed in and unable to escape from small spaces, may be triggered by coverings or masks (e.g., rubber dams) on the face, being surrounded by dental professionals during procedures, and/or small dental treatment rooms. Some objects or situations that are the basis for a person's phobias can be avoided. For example, a person can opt to drive or take a train rather than fly. However, there is no substitute for routine dental care, and avoiding it will increase the risk for the development of periodontal disease and carious lesions. These conditions will become more expensive to treat and more symptomatic with the passage of time, which can exacerbate the phobia.

The dental profession relies on precise measurements as an important parameter in assessing clinical situations (e.g., the depth of periodontal pockets) to determine the appropriate course of treatment. For example, a crown with an open margin of as little as 0.1 mm will allow bacterial ingress in between the crown margin and the prepared tooth, with the subsequent development of recurrent caries and a consequent clinical failure. Such precision requires patient cooperation in addition to clinician skill, and apprehensive patients may be unable to comply to the level necessary to ensure optimal dental care. Dental professionals should understand that patients' dental apprehensions are real and subjective; they cannot be measured objectively. However, there are questionnaires to help assess dental anxiety and fear. The Corah Dental Anxiety Scale uses a series of four questions with answers ranging from "A," for the lowest level or absent anxiety, through "E," for the most severe anxiety reactions. The lowest cumulative point total (4) corresponds to a relaxed patient, while the highest cumulative point total (20) identifies a patient with severe dental apprehension [52].

Studies indicate that the majority of patients with dental phobia have onset in childhood or adolescence, with an average age at onset of 12 years [40,45]. Intense anxiety or unexpected panic responses in the presence of specific objects or situations can mark phobia onset but are not the sole causal route. Disgust, either alone or combined with fear, may trigger the onset and maintenance of blood-injection-injury phobias. Onset can even occur indirectly by observing others reacting fearfully. Some stimuli are more likely to induce phobias than others through evolutionary threat relevance.

The origin of dental apprehension can be generally categorized into two distinct groups: exogenous and endogenous. Patients with exogenous dental fear and/or anxiety have experienced a traumatic dental event (either personally or vicariously). Examples of personally traumatizing dental events include difficult and lengthy surgical procedures, an inability to achieve an appropriate level of local anesthesia during a dental procedure, and severe pain following a dental procedure. However, not all patients who experience these or similar events during dental treatment will become fearful, anxious, or phobic toward future dental treatment. Endogenous dental fear or anxiety has no known triggering experience and instead develops as a result of an individual's unique predisposition or vulnerability to anxiety [6]. These categories are not mutually exclusive, and many patients display characteristics of each. It is important to remember that patients with a psychiatric or psychological disorder (other than specific dental phobia) may not have fear, anxiety, or phobia and may undergo dental treatment without incident.

The fear of pain is one of the most common sources of dental apprehension and is usually associated with previous experiences of dental treatment-related pain [7]. The avoidance of pain is a basic survival instinct and can trigger the "fight-or-flight" response that provides a protective mechanism for humans [8]. A traumatic dental experience can stimulate this basic, yet essential response and cause the patient to approach future dental appointments with fear, anxiety, or even phobia. Dental pain may also cause a loss of trust. If a dental clinician promises a procedure will be pain-free and this is untrue, the patient may believe any procedure can result in pain.

Beyond the fear of pain, there are many other situations that can cause varying levels of dental apprehension. The fear of a loss of control or helplessness is another potential source of dental apprehension [9]. Most dental procedures are performed with the patient in a supine position, with the dentist and assistant in a position above them. These positions can make some patients feel that they have relinquished control and that they are defenseless to communicate any degree of pain or discomfort to the dental staff. The introduction of unfamiliar dental procedures or instruments, unanticipated problems with the actual procedure, and prolonged treatment times may exacerbate these fears. An inability to see and understand the specifics of the dental procedure and the dental terminology being used between the attending staff members can create a feeling of isolation between the patient and staff, amplifying the patient's perception of loss of control.

The use of medications adjunctive to dental treatment can also contribute to patients' perception that they are not in control of their immediate situation. Sedation can depress neuromuscular reflex activity and make patients feel that they are in a vulnerable position. Most local anesthetics contain a vasoconstrictor (e.g., epinephrine) to prolong the effect of the anesthetic and facilitate the coagulation process after oral or periodontal surgery. Epinephrine is a catecholamine with a stimulant effect on the sympathetic nervous system. If a local anesthetic with epinephrine is inadvertently injected directly into an artery or a venous plexus, this can cause untoward effects. An intravascular bolus of epinephrine can increase heart rate, respiratory rate, and blood pressure, with patients experiencing heart palpitations and tightness in the chest that can mimic or precipitate a panic attack. An intravascular injection of the local anesthetic itself can have adverse effects on cardiac tissue and cerebral tissue, inducing syncope and seizures. Patients who have experienced these incidents can develop fear, anxiety, or phobia of local anesthetic. It is important to note that the apprehension these patients develop is not generally related to a phobia of needles but is related to the potential adverse effects of the local anesthetic.

Another possible source of dental apprehension is excessive or aggressive criticism regarding patients' neglect of their oral health and presentation with advanced periodontal disease and widespread carious lesions. Fear of reprimand prevents some patients from seeking preventive dental care, creating a cycle of worsening oral health and increasing embarrassment and fear. Clinicians who strongly scold patients may increase patients' dental apprehension and construct another obstacle to needed dental treatment.

In the dental setting, needles (mainly used for the injection of local anesthetics) and high- or low-speed hand pieces are the instruments most likely to induce fear or anxiety. Injection of a local anesthetic is indispensable when providing painless dental care. Most patients have a certain degree of fear of the injection process but can tolerate the procedure without event. However, approximately 10% of the population has belonephobia, a phobia of needles and injections [17]. Clinically, needle phobia is grouped with phobias of blood, injections, and/or trauma in the blood-injection-injury phobia category. There is some evidence that this type of phobia is or may be partially inherited, with higher concordance rates among first-degree relatives [17].

Another common fear among dental patients is of uncontrollable gagging, which can lead to nausea, vomiting, choking, or swallowing dental materials or instruments. Gagging is a protective reflex that is meant to prevent the aspiration or ingestion of foreign bodies. The degree of stimulation required to initiate this response and the intensity of the response vary considerably among patients. In the oral cavity, the areas most likely to stimulate a gag response are the soft palate, the lateral surfaces of the posterior border of the tongue, and the dorsum of the tongue. However, even minimal stimulation of any intraoral surface can initiate a gag reflex in patients who are hypersensitive. Most commonly, a tactile sensation against susceptible intraoral tissues during dental treatment initiates the gag reflex, but visual, auditory, and/or olfactory stimuli can also induce this response [18]. For susceptible patients, obtaining impressions for fixed or removable prostheses may be difficult. Impression materials are viscous but can still flow toward the soft palate (in the case of maxillary impressions) or toward the posterior borders of the tongue (in the case of mandibular impressions). Patients may also fear that the flow of the impression material will extend into the pharynx and compromise their ability to breathe.

Patients who have experienced problems with the impression procedure in the past may begin to gag at the sight of the impression tray. Even the particular fragrance or taste of an impression material may trigger an excessive gag reflex. Numerous impression materials are available with varying complete polymerization times, and the option with the shortest set time should be selected for these patients. Vomiting or premature removal of the impression tray will ruin the impression and require that the process be repeated. Further, incompletely set impression materials can cling to teeth and soft tissues, and removing the residual materials can also stimulate a sensitive gag reflex.

While there are no universal solutions to eliminate the gag reflex and related problems, techniques have been developed to minimize a gagging response. Most dental procedures are accomplished with the patient in a supine position, but moving the patient to an upright position with his or her head tilted toward the floor will decrease the flow of impression material toward the posterior of the oral cavity. When possible, impressions may be taken with a quadrant tray rather than a full arch tray to minimize the amount of impression material introduced into the oral cavity.

Local anesthetic sprays may be applied to the mucosal tissues prior to taking an impression in an effort to decrease the gag reflex. However, these formulations should be used with caution, because if the spray is inadvertently directed into the pharynx, it can lead to laryngospasm.

Placement of salt on the tip of the tongue stimulates taste receptors whose ascending neural pathways lead to the hypothalamus, the part of the brain that also receives neural input for the gag reflex [19]. The presence of this competing stimulus can dampen the gag reflex. A similar diversion technique can be employed by having the patient lift his or her legs off the chair; the flexing of muscles can also provide enough of a distraction to reduce the intensity of the gag reflex. When these or similar techniques are not adequate, nitrous oxide sedation or anxiolytic medications may be required. When pharmacotherapy is used, a responsible adult driver should be present to transport the patient home.

Verbal signs of dental fear and anxiety include the actual words spoken, but also the manner and inflection of the speech. Speech cues that suggest underlying fear or anxiety include a trembling lip, variances in speech tone or inflection (e.g., vocal tremors), an atypically loud or silent demeanor, and a very rapid or very slow rate of speech [20]. Statements that reflect strong negative feelings about previous dental encounters may also be an indicator and include comments about hating dentists, hating to go to the dentist, fainting at the sight of a needle or after receiving an injection, having difficulty achieving local anesthesia, or being hurt during a previous dental encounter. Similarly, patients who speak with little or no eye contact may also have an undisclosed fear and/or anxiety of dental treatment.

Behavioral signs and body language may also be signals of a patient's dental apprehension. Being startled or jumping when a staff member enters the room, places an instrument or an x-ray film in the mouth, applies a topical anesthetic, or administers a local anesthetic are all potential signs of fear [21]. Strongly grasping the dental chair (e.g., "white knuckle") is a classic presentation of an apprehensive dental patient. Patients who sit with their arms and/or legs crossed tightly, fidget or are generally uncooperative, shut their eyes tightly, hold their breath, have pronounced tension and flexion of the facial musculature, or require excessive breaks during a dental procedure are likely expressing stress and anxiety. Again, this is not an exhaustive list, but it reflects some of the more common physical manifestations of dental fear and anxiety. The greater the degree of underlying fear and anxiety, the greater the tendency to display these verbal and nonverbal signs.

In guided imagery, the clinician walks the patient through visualization of him- or herself in a soothing place or having a pleasant experience. The purpose of guided imagery as a coping exercise is to provide the patient with a safe, healthy mental escape that he or she can access when needed. At first, the clinician's voice is the guide to take the patient to this place. If a clinician feels uncomfortable developing guided imagery scenarios, there are many good free scripts available online, including hundreds of variations on the standard calm, happy, or safe place [15]. Patients who can develop and maintain a strong and detailed visualization will have a higher degree of distraction from their dental treatment.

In recent years, the dental profession has advertised and marketed "sleep dentistry" as a means for patients with high levels of dental apprehension to receive dental treatment. In the United States, this is most commonly achieved by oral sedation [25]. Patients who receive oral sedation from a general dentist should only be titrated to levels of minimal-to-moderate sedation. Minimal sedation refers to a minimally depressed level of consciousness in which the patient can independently and continuously maintain a patent airway and can respond normally to tactile sensation and verbal commands [26]. Respiratory and cardiovascular functions remain normal, and there is no intent for the patient to lose consciousness. Moderate sedation is a deeper level of sedation in which the patient still responds purposefully to verbal commands but may need slight tactile stimulation to do so [27]. General dentists should not seek to place patients in a state of deep sedation, as the patient's ability to maintain a patent airway can be impaired.

Individual state regulations and requirements vary as to the level of training required for dentists and dental staff involved in caring for patients who are given oral sedation. Some states require the use of equipment to monitor vital signs for the duration of the sedation. Further, training in cardiopulmonary resuscitation may be required at the Advanced Cardiac Life Support level (rather than the Basic Life Support level) for dentists and the entire staff. Most states require that an automated external defibrillator be present in the dental office and that all staff members be trained in its use. Staff members should be aware of the location of the emergency kit, used if a medical emergency occurs. The use of a medication that is appropriate for the given medical emergency is the responsibility of the dentist. Periodic mock emergency drills in which staff members are assigned a specific role increase the chance of an appropriate staff response and survival of the patient.

Diazepam was invented in 1963 and was the successor to the first benzodiazepine, chlordiazepoxide [29]. Today, diazepam is approved for the treatment of anxiety disorders, acute alcohol withdrawal, and skeletal muscle spasms. When diazepam is used to manage dental fear and anxiety, the dosage and schedule will vary according to the medical history, of the patient's age and weight, the degree of sedation desired, and the concurrent use of any other medication. The usual adult dose is 2–10 mg the night before the appointment and 2–10 mg one hour before the appointment. Diazepam is a highly lipophilic molecule with 100% oral bioavailability. It has a rapid onset of action (20 to 40 minutes after administration), and plasma levels peak one to two hours after its administration [30]. These favorable pharmacokinetic properties are countered by a long half-life, or the time required for the blood-plasma concentration of the medication to be reduced by one-half. The half-life of diazepam can range from 20 to 100 hours due to its production of active major metabolites, such as desmethyldiazepam [31]. This extended half-life can make patients feel sleepy for a few days after its administration. Patients should not drive, operate machinery, or perform any task that requires intense concentration or decision making during this period. Diazepam is metabolized by the liver, so hepatic dysfunction and older age can decrease its metabolism and prolong plasma concentration [32]. At the anxiolytic doses used for dental treatment, diazepam is a moderate tranquilizer that causes drowsiness and some loss of anterograde (short-term) memory [33]. Because of this effect, the patient may remember little or nothing of the dental procedure.

Triazolam is a benzodiazepine frequently used for the treatment of short-term insomnia, but it has become a popular medication for the oral sedation of apprehensive dental patients. A sublingual formulation is available with very rapid onset of action (i.e., within 30 minutes of administration). The peak blood plasma concentration occurs approximately 75 minutes after the initial dose, with a bioavailability of 44% with conventional tablets or 53% with the sublingual formulation [34]. It is not available in intravenous or intramuscular formulations. Triazolam has muscle relaxant, hypnotic, sedative, and amnesic properties, which can reduce memories associated with the unpleasant aspects of dental treatment [35].

Some medications used in the treatment of oral infections can also have adverse interactions with triazolam. The azole antifungal agents ketoconazole and itraconazole, which are used to treat the intraoral candidiasis, can prolong the duration of the effect of triazolam. Macrolide antibiotics (e.g., erythromycin, clarithromycin) to treat odontogenic bacterial infections can increase the blood plasma levels of triazolam and amplify its effect [38]. Triazolam should not be used as an anxiolytic medication if the patient is utilizing these antifungal or antibiotic medications.

Lorazepam is an intermediate-acting benzodiazepine with a half-life of approximately 10 to 20 hours—longer than triazolam, but shorter than diazepam. This property makes lorazepam a good choice for patients who are undergoing longer dental procedures. The usual adult dose for oral sedation is 0.5–4 mg two hours before dental treatment; another dose may be taken the night before the appointment for those patients whose anxiety will interrupt their sleep [39].

Nitrous oxide/oxygen combination can be used as a single anxiolytic agent or may be combined with oral anxiolytic medications. The use of combined oral medications and nitrous oxide/oxygen is governed by various state regulations pertaining to mandatory training, emergency preparedness requirements, maximum doses, and the age of the patient.

Nitrous oxide/oxygen decreases pain, anxiety, and the memory of the dental treatment. It does not replace a local anesthetic, but it can relax a patient so he or she is more receptive to it. The onset of action can begin in as little as 30 seconds, with the peak effect occurring in about five minutes. Upon completion of the dental procedure, delivery of 100% oxygen for five minutes eliminates the nitrous oxide from the body. As opposed to oral anxiolytic medications, nitrous oxide/oxygen is not metabolized by the body [42]. Modern delivery units include a flowmeter that will stop the flow of nitrous oxide if the ratio of nitrous oxide to oxygen exceeds 70%/30% as a safeguard to prevent hypoxia [43]. The exact ratio can be customized to the needs of the patient, with the concentration of nitrous oxide usually ranging from 25% to 50%. There are relatively few side effects from nitrous oxide/oxygen sedation, with nausea and vomiting being the most common. Absolute contraindications for the use of nitrous oxide/oxygen include emphysema, pneumothorax, middle ear surgery, and an air embolus [44]. The use of nitrous oxide/oxygen in pregnant patients has been controversial. Short-term use at low concentrations may be appropriate if dental treatment cannot be delayed. There have been reports of infertility, congenital abnormalities, and spontaneous abortions following prolonged occupational exposure, which is more of an issue for dental staff members than patients [31]. The patient's obstetrician should be consulted before nitrous oxide/oxygen is used during pregnancy.

Nitrous oxide/oxygen decreases pain, anxiety, and the memory of the dental treatment. It does not replace a local anesthetic, but it can relax a patient so he or she is more receptive to it. The onset of action can begin in as little as 30 seconds, with the peak effect occurring in about five minutes. Upon completion of the dental procedure, delivery of 100% oxygen for five minutes eliminates the nitrous oxide from the body. As opposed to oral anxiolytic medications, nitrous oxide/oxygen is not metabolized by the body [42]. Modern delivery units include a flowmeter that will stop the flow of nitrous oxide if the ratio of nitrous oxide to oxygen exceeds 70%/30% as a safeguard to prevent hypoxia [43]. The exact ratio can be customized to the needs of the patient, with the concentration of nitrous oxide usually ranging from 25% to 50%. There are relatively few side effects from nitrous oxide/oxygen sedation, with nausea and vomiting being the most common. Absolute contraindications for the use of nitrous oxide/oxygen include emphysema, pneumothorax, middle ear surgery, and an air embolus [44]. The use of nitrous oxide/oxygen in pregnant patients has been controversial. Short-term use at low concentrations may be appropriate if dental treatment cannot be delayed. There have been reports of infertility, congenital abnormalities, and spontaneous abortions following prolonged occupational exposure, which is more of an issue for dental staff members than patients [31]. The patient's obstetrician should be consulted before nitrous oxide/oxygen is used during pregnancy.

Patients with known dental fear and/or anxiety should be scheduled for appointments as early in the morning as possible, as this will minimize their opportunity to dwell upon the source(s) of their apprehension. Upon arrival at the office, patients should be greeted warmly, escorted to the treatment area promptly, and made to feel welcome by the dental assistant and the dentist. It is important that patients are not left to wait by themselves for an extended period after they are seated, as this will also provide an opportunity to contemplate the situations and items that are a source of their dental fear, anxiety, or phobia. This can be amplified if they hear patients in the adjacent operatory complain of pain or discomfort during a dental procedure. Because some patients will feel vulnerable in a completely supine position, a semi-reclined position may be used for the procedure (or an upright position if impressions are required) to reduce feelings of vulnerability and helplessness. If a patient feels unable to communicate pain or discomfort with the dental staff during anesthesia, when a rubber dam is placed to isolate a tooth, or when dental instruments occupy much of the oral cavity, a prearranged hand signal can serve to communicate this need and ameliorate the patient's concerns.

The tell-show-do technique can also decrease patients' fears about unfamiliar dental procedures [46]. This involves telling the patient what will be done, showing a diagram or video of the actual procedure, and then finally doing the procedure. Any explanations should be given in terms the patient understands and at a pace that allows for absorption of the information.

Because the sight of dental instruments can be a source of apprehension, they should remain out of the patient's line of vision as much as possible. Placing instruments on a bracket stand behind the patient and delivering them to the clinician without being seen by the patient will help decrease these fears.

A patient's apprehension will increase if the he or she believes the clinician is having difficulty with a procedure. For example, a clinician with minimal experience with oral surgery should not attempt a difficult surgical procedure on any patient, especially those who are apprehensive about dental treatment. Clinicians should confront the limits of their clinical skills and should refer patients who require procedures that are beyond their expertise to another practitioner or to a specialist who can ensure the patient is treated appropriately and comfortably. A positive dental experience and outcome may give apprehensive patients the confidence to return for future treatment.

The demands of practicing dentistry are numerous, and this can take a toll on all members of the dental staff. The ability to successfully treat apprehensive dental patients is rewarding, but the cumulative stresses of addressing these patients' fear and anxiety can lead to compassion fatigue [47,48]. Compassion fatigue is comprised of two components: burnout and vicarious traumatic stress [51]. The first component consists of characteristic negative feelings such as frustration, anger, exhaustion, and depression. The second component, vicarious traumatic stress, may result when the professional is negatively affected through vicarious or indirect exposure to trauma through their work.

Compassion fatigue can be insidious in its development, taking months or years to develop. Each individual's susceptibility to compassion fatigue is different, with some clinicians exhibiting no or minimal levels while others suffer personal and professional repercussions that can compromise their professional abilities and impact their quality of life. The cumulative exposure to apprehensive dental patients, the emotional energy expended to maintain their comfort, pressure to complete the dental procedure quickly and effectively, and the need to maintain a reassuring and confident demeanor can lead to emotional exhaustion. General signs of compassion fatigue include feeling anxious or developing a sense of dread when treating dental patients or feeling unusually tired or exhausted after completing procedures that had not previously evoked this response. It is beyond the scope of this course to explore all of the emotional and psychological experiences of the dental staff as they provide treatment for patients, apprehensive or otherwise. However, dental staff members should be cognizant that these problems can arise and adversely affect all aspects of their lives, including their ability to provide dental care. Professional intervention should be sought to address and rectify these emotional or psychological problems if they are identified in a staff member.