Anxiety is developed when patients face stressful conditions, such as medical interventions [14, 15]. Our results showed that the anxiety due to tooth extractions or receiving local anesthesia was higher than that of other procedures. This is in accordance with other studies [8,16]. The American Psychiatric Association (APA) classified dental anxiety under the blood-injection-injury phobia type which also supports our observation [17, 18]. This could be due to fear of gaging, chocking, action of injection, inability to see what is going on inside the mouth, or the strong aversion to the sight or thought of blood which is also reported by others [16, 19]. As a general, there is no difference between the study’s results and the findings of other studies [20- 24]. Where the overall results of the study showed that the pleasant olfaction provides a significant reduction in dental anxiety and the intensity of pain. The olfactory aromatherapy properly controls pain perception and minimizes emotional changes that are associated with dental visits. This corresponds to Paradopo et al., [14].
At the end of the second phase of the study, the power of the olfactory aromatherapy in reducing the MDAS and STAI was 3.4 and 4.2 times more than the control group, respectively. Regarding the pain intensity, its power is 2.4 times greater than that of the unstimulated olfaction. At the end of the study’s third phase, the power of the olfactory aromatherapy was 1.2, 2.2, and 1.4 times more than the control group regarding the MDAS, STAI, and pain intensity, respectively. This indicates that the olfactory aromatherapy has a significant effect on both intensity of pain and level of the anxiety, but it is more powerful in reducing the level of the anxiety more than its effect on the intensity of pain. And its greatest effect occurs in the phase of the waiting room before starting the dental treatment.
The study’s results are not in accordance with Muzzarelli et al., [25] who reported that the olfactory aromatherapy has no significant effect on the level of anxiety. Kritsidima et al., [26] also mentioned that although the olfactory aromatherapy reduced the level of the anxiety, it only affects the state anxiety, and it does not affect its cognitive aspect. Nevertheless, Kritsidima et al., [26] agreed with our results in certain points, where they concluded that the pleasant olfaction is used as on-the-spot reduction of the anxiety, not as an option for its treatment. As we know, the state anxiety measures how the patients feel at the moment during which the questions are answered, whereas the cognitive aspect of the anxiety is related to the bad thoughts about dental visits. In dental clinics, the control of the state anxiety is much more important than controlling the cognitive anxiety. This is because the control of the patients’ behavior and emotional changes enables the dentists to perform dental procedures.
Regarding the greatest effect of the aromatherapy on the anxiety, the study’s finding could be explained by the fact which states that the olfaction produces emotional changes, either positive or negative, in the body via three ways as follow: first, its effect on the limbic system of the brain [27]. The anxiety is induced by the negative impact of the stimuli on the amygdala in the limbic system. Amygdala controls emotional changes in humans, and its stimulation occurs mainly through the activation of the brain sensory system, especially olfactory, auditory, and visual cortices. It was proven that the olfactory bulb is intimately and directly linked to amygdala [28, 29]. So, odors are significantly affecting the emotional states in humans more than other sensations. If the stimulus is anxious, the stimulation of amygdala activates the hypothalamus which stimulates the pituitary gland to activate the adrenal gland which secrets stress hormones (adrenaline, noradrenaline, catecholamines, and corticosteroids). Those hormones elect reactions lead to negative behavioral and emotional responses in term of anxiety [28, 30]. Cortisol also increases anxiety through inhibition of serotonin secretions [28, 31]. The pleasant scent leads to positive stimulation of the amygdala which results in improved mood and increased sedation that overcome the anxiety by inhibiting secretion of the stress hormones. Second, Bombail [29] reported that pleasant odors produce its anxiolytic effect by altering the gamma-aminobutyric acid receptors in the brain akin to benzodiazepines which is considered anxiolytic substances. Third, some authors mentioned that the olfaction produces relaxation via modulating and reducing the cycle of the adenosine monophosphate which is responsible for sedation and relaxation [32]. All the above-mentioned ways indicate that the olfaction has tribble effect on the anxiety production system in the brain, but its effect on the intensity of pain is indirectly occurred via controlling the anxiety as it will be discussed later. On the other hand, our explanation is not in agreement with the findings of other authors who stated that there is no documentation that pleasant odors have inhibitory effect on the anxiety, and its effect is still unknown [26, 33].
Regarding the results of pain perception, the study’s results also showed that the olfaction aromatherapy significantly reduces the intensity of pain and omits the need for postoperative analgesics which was also reported by Moss et al., [34]. This could be due to the ability of the pleasant sent in regulating the cognition, mood, and behavior of the patients. As a result of controlling those emotional changes and anxiety, the pain threshold is elevated which reduces the pain perception. Many authors have documented that the mental stresses have an impact on the physiological frameworks of the body by increasing the cortisol production in the blood. Cortisol makes the patients more alert to the surrounding environment which increases pain perception in the brain and vice versa [20, 29, 35]. On the other hand, other authors mentioned that the effect of the pleasant olfaction is only limited to anxiety level with no significant impact on pain perception. This is because it only provides relaxation, not analgesia [36]. Despite that, the authors believe that the control of the anxiety is indirectly controlling pain perception. The APA supported our point of view, where it stated that the stress-anxiety system in the body is closely linked to the nervous system. So, the stresses and anxiety influences pain perception, and they produce hyperalgesia that exaggerates pain.
Regarding hemodynamic changes, the inhalation of the olfactory aromatherapy was significantly improving all the vital signs, except DBP. The same finding was also reported by Stanley et al., [15]. On the other hand, other authors found that its effect is only limited to SBP [37]. This controversy could be due to the difference between studies regarding the type of the inhaled oil, its concentration, and inhalation period. This authors’ explanation is in agreement with the opinion of Ebrahimi et al., [20].
The source of a patient’s anxiety might be in relation to fear of gagging or choking, fear of injec-tion, or a strong aversion to the sight or thought of blood The source of a patient’s anxiety might be in relation to fear of gagging or choking, fear of injec-tion, or a strong aversion to the sight or thought of blood The importance of the current study is that it provides novelty in predicting to what extent the olfactory aromatherapy affects the pain perception and anxiety in dental settings. However, the study has some limitations, such as a limited sample size, the patients were treated by many dentists who have different approaches regarding their behavior and attitude toward their patients. Also, there are many factors that influence patients’ satisfactions and honesty in answering questions. Nevertheless, our study has many strength points, such as its design avoided the age, gender, and time lapse as confounders that affect the results. Additionally, its preferred randomly control trial design and being a single institutional study are considered strength points.