The Association Between Dental Anxiety And Psychiatric Disorders And Symptoms: A Systematic Review

Background: A growing amount of evidence suggests that dental anxiety is associated with other psychiatric disorders and symptoms. A systematic review was conducted to critically evaluate the studies of comorbidity of dental anxiety with other specific phobias and other Axis I psychiatric disorders. Objective: The aim of the review was to explore how dental anxiety is associated with other psychiatric disorders and to estimate the level of comorbid symptoms in dental anxiety patients. Methods: The review was conducted and reported in accordance with the MOOSE statement. Data sources included PubMed, PsycInfo, Web of Science and Scopus. Results: The search produced 631 hits, of which 16 unique records fulfilled the inclusion criteria. The number of eligible papers was low. Study populations were heterogeneous including 6,486 participants, and a total of 25 tests and in few cases clinical interviews were used in the evaluation processes. The results enhanced the idea about the comorbidity between dental anxiety and other psychiatric disorders. The effect was found strong in several studies. Conclusion: Patients with a high level of dental anxiety are more prone to have a high level of comorbid phobias, depression, mood disorders and other psychiatric disorders and symptoms.


INTRODUCTION
Dental anxiety is a phenomenon that is seen almost every day in dental offices, and it can be a major challenge for both patient and a dental care provider. Between roughly one patient out of eight and one patient out of six reports, the Records thought to fulfill the inclusion criteria were labelled "yes" or "maybe" and full-text articles were obtained. A group of four unblind reviewers (authors) judged the material by using the 10-item checklist, scoring each from 0-1 points (see Appendix 1) modified from a checklist created for the assessment of randomised and non-randomised studies [22]. Disagreements on the exclusion/inclusion of the record were resolved by consensus. Reference lists of accepted articles were then hand-checked for additional studies fulfilling the inclusion criteria (see the flowchart in Fig. 1). Fig. (1). Flow chart.

Inclusion / Exclusion Criteria
The material was accepted for review if the original study included the examination of comorbidity of dental fear with other specific phobias or psychiatric disorders and symptoms.
The material was included if one or more of the following methods was used to evaluate dental anxiety: i) in general populations, the level of anxiety was measured by test or questionnaire, ii) if the study population consisted of (referred or self-referred) patients seeking treatment from a dental fear clinic, or iii) if the patients fulfilled the specific dental phobia criteria described in the ICD-10 [9] or DSM-III [23] / DSM-IV [10]. We decided to exclude material if dental anxiety was self-reported by single item or question, since narrative and subjective experiences can mean almost any level of fear, and there is no effort to objectively evaluate the level of dental fear.

Records screened (n=631)
Full-text articles excluded with reasons (n=53) Comorbidity not included, n=21 Child population, n=4 No original data, n=7 Case report, n=1 Not a dentally anxious population, n=2 Miscellaneous, inclusion criteria not included, n=18 Records excluded (n=562) Studies included in qualitative synthesis (n=16) Full-text articles assessed for eligibility (n=69) In the same manner, we accepted the material if comorbid phobias and disorders were studied i) using a test, ii) a self-report questionnaire(s) or iii) a psychiatric clinical interview according to ICD-10 or DSM-III/DSM-IV criteria.
We decided to include the material if the study populations consisted only of adult patients or other individuals. The age limit was set at 18 years.
Case reports and treatment considerations were excluded from the review. We also excluded all studies in an effort to explain the origin of dental anxiety if the comorbidity was not examined in the original study.
In order to reduce publication bias, no limits were set to publication language or year.

Procedure
If the original study included both cases and controls, the difference between comorbid diagnoses and /or the severity of symptoms was compared between the groups. If only cases were included, we then evaluated how dental anxiety was associated with other symptoms and also estimated the level of comorbid diagnoses. In population-based studies, the association of the dental anxiety/phobia with other psychiatric diagnoses and symptoms was estimated.
The effect size estimates (Cohen's d values, correlations or odds ratios) in each study were categorised as small (*), moderate (**) and large (***) effects, based on the cut-offs presented by Rosenthal [24]. For the cut-offs used, see Table 2.

Material
The search produced 631 hits, of which, 16 unique articles fulfilled the inclusion criteria and were reviewed (see the flowchart in Fig. 1). Finally, all of these were in English. The most common reasons for exclusion were that no tests/interviews were used or that the comorbidity was not examined in the article.
In the articles reviewed, five different structured tests (see Appendix 2) were used to measure dental anxiety; the Dental Anxiety Scale DAS [25], the Dental Beliefs Survey [26], the Dental Fear Survey [27], the Gatchel Fear Scale [28] and the Modified Dental Anxiety Scale MDAS [29]. A total of 20 tests were used to evaluate comorbid phobias and disorders. In three of the studies [12,31,33], clinical interviews were used.

Study Populations
The articles reviewed included a total of 6,486 adult patients, students, volunteers and other participants. Study populations were heterogeneous; patients were collected from birth cohort studies (two articles), dental fear clinics (eight articles), randomly selected volunteers (three articles) and three other populations; university students (one article), university employees population (one article) and patients scheduled for an appointment at university dental clinic (one article).

Dental Anxiety and Comorbid Phobias
Dental anxiety was significantly correlated with agoraphobia [2,3,11,30] and social phobia [2,3,13,31]. The association between dental anxiety and various specific (simple) phobias was found in seven studies of which the effect size was strong (***) in five: DeJongh [32] [13] 2015***. The results showed that the prevalence of co-existing simple phobia can be up to 45% [12]. The results were equal in patients of special dental fear clinics and with patients from birth cohort studies or selected randomly and then compared to the normative population.

Dental Anxiety and Comorbid Psychiatric Disorders and Symptoms
Results also had a similar degree of associations with comorbidity in different populations in studies of dental anxiety and comorbid psychiatric disorders Tables 1a and b. The authors concluded that, despite the cooccurrence of dental phobia and bloodinjection-injury phobia, dental anxiety should be considered a specific, independent phobia within DSM-IV. To study 1) the overlap between dental anxiety and BI (blood and injury) fears 2) the psychological characteristics of dentally anxious patients with and without BI fears 3) the contribution to BI fears make to dental anxiety Dental anxiety had a significant positive correlation to depression and mood disorders in four population-based studies [2,3,33,35] and in four studies of dentally fearful patients [12,30,36,37].

Author
The positive association between dental anxiety and (other) anxiety disorders was found in a total of nine studies, and, in five of them, the association was found to be strong (***): Aartman [30] Table 2. Five of these were studies of dentally fearful patients. The association between dental anxiety and generalised anxiety disorder was found in one study [31].

Main Findings
The comorbid diagnoses and psychiatric symptoms were found equally in population-based studies and in studies with patients of dental fear clinics Table 2.
Some main findings emerged, however. The most common comorbid finding with association with dental fear was anxiety-related disorders; a positive correlation was found in one birth cohort study, two randomly selected populations, one university student volunteer population, a total of four populations of special dental fear clinic patients and one population of patients seeking treatment at a university dental clinic. *somatization *cognitiveperformance difficulty **interpersonal sensitivity and paranoid ideation (Aartman et al. 1997) Cohen's d <0.5 or Pearson's r <0.3 or Odds Ratio <2.5 or Difference in percentage <18 ** Cohen's d<0.8 or Pearson's r <0.5 or Odds Ratio <4 or Difference in percentage <30 *** Cohen's d ≥0.8 or Pearson's r ≥0.5 or Odds Ratio ≥4 or Difference in percentage ≥30 (Rosenthal 1996) 1 Prevalence of comorbid diagnosis in dentally anxious participants.
The positive association of dental anxiety to depression and mood disorders was proven in eight different original studies (a total of three populations of a special dental fear clinic, one birth cohort study, two randomly selected populations, one university student volunteer population and one population of patients seeking treatment at a university dental clinic).
Agoraphobia and social phobia were found to be associated with dental anxiety in three original studies, and, other specific (simple) phobias in seven studies. Commonly, patients with dental anxiety had more than one additional specific phobia; most common simple phobias were blood-injection-injury-related phobias. In all phobia subtypes, the association was found both in population-based and dental fear clinic patients.
The gender difference was observed in seven articles. In all cases, women had more comorbidity between dental anxiety and general fears and phobias, depression and blood-injury fears than men [11, 30, 32, 34, 37 -39].
Even though the type of representation of the results was scattered in the original articles, these findings were coherent in all studies, thus enhancing the idea of similarity between dental fear and these factors.

Methodological Discussion
In only three different studies [12,31,33] were clinical interviews used, while the others were based only on the use of different questionnaires, which brings some criticism to the interpretation of the results. However, the main findings were quite similar between these two methods; except generalized anxiety disorder, which was only found in a clinical interview-based study [31], and agoraphobia, found in three questionnaire-based studies [2,3,11,30].
The tests used partly overlap: Some psychiatric and specific phobia questionnaires also include scales to measure dental fear. Most tests used in original papers are known to be commonly used in clinical practice.
The results also suggest that dental anxiety either increased or decreased in concert with the number of other fears [32], and, in a longitudinal study [33] during the follow-up drop-outs had a higher level of dental fear (Table 1a).
Some findings in the screening process and in clinical evaluation also support the results. For example, the personality trait neuroticism, understood as incapability to cope with psychological stress, is associated with dental anxiety and its maintenance over time [33,40,41]. Neuroticism is well known to be connected with (general) anxiety disorders, depression and substance use disorders. Some of the latest findings suggest that genetic factors play at least some role in the development of fear [42,43]. However, in order to limit the focus, we decided to exclude studies about personality traits, genetic factors and dental anxiety, since they best explain the origin, not comorbidity of dental fear.
The number of articles identified was relatively low when taking into account a large number of studies on dental anxiety (the term "dental anxiety" produced over 4,000 hits in PubMed). The idea of similarity with other fears and a patient's role in the acquisition of fear are quite new, and so is the psychological testing in the research work. In the evaluation process, many original articles were excluded because of the methodology, despite careful study design and patient selection.

Strengths and Limitations
As far as we know, no previous systematic reviews of the comorbidity of dental anxiety to other psychiatric disorders and symptoms exist. The search strategy was very representative and thorough, including Axis I categories of mood disorders, anxiety disorders, substance-related and psychotic disorders. Although the number of articles was only a small minority of all search hits (about 2.5 percent), we believe that we have located all the relevant studies on the topic.
The tests used in the original articles and even the aims of different studies were very heterogeneous. Because of this heterogeneity in methods, we decided not to pool the results for a meta-analysis, although this left us a body of descriptive data for a systematic and critically review the articles. However, when possible, we estimated the magnitude of the effects.
This heterogeneity was also a benefit; when the same result based on an ICD-10 or DSM-IV classification is made by multiple tests, it will increase the reliability of the results, thus lowering the bias. In the same manner, the heterogeneity of the study populations gave a representative and large sample of dentally anxious individuals.
The limitation to the interpretation of our results is the question of how diagnoses were made and symptoms were assessed in the original papers. The diagnosis of (specific) dental phobia, as well as any other phobia, depression, or other disorder, is always made by a psychiatrist. A test, for example, for anxiety or depression inventory, can be used for research purposes, but it is not a clinical diagnosis. Only in a few of the papers reviewed were clinical interviews used.
The prevalence of anxiety disorders in large national epidemiologic surveys [44 -46] can vary between 14.4 and 18.1%, while the prevalence of mood disorders can be up to 9.5% [45]. If a control group is used in the original study, as was the case in eight (half) of the reviewed articles, the level of this "natural" co-existing anxiety/mood disorders can be evaluated and distinguished from the disorders associated with dental fear. However, in the other half of the articles, the control group was not used in the study, so the results must be interpreted carefully.
Also, some of the original studies were cross-sectional and some had a longitudinal aspect, suggesting that there may be a trait (dental) anxiety and state (dental) anxiety involved. We were not able to study these separately from the articles included.
Although no limits were set to publication language or year, with only a few exceptions, all the records identified through database searching were in English. This may be due to language bias in the databases. The results were relatively robust across all the articles, but it is possible that there exists some publication bias. It is possible that studies have been conducted in which the association was not found to be significant, but such studies have not been published or made available anywhere.

CONCLUSION
A high level of dental anxiety (dental fear) has a strong positive correlation with a high level of other comorbid phobias, depression, mood disorders and other psychiatric disorders and symptoms. However, on the basis of the articles reviewed, it cannot be concluded whether patients with dental anxiety are more prone to have a high level of other psychiatric disorders, or whether other psychiatric conditions are the primary disorder predisposing a given individual to the development of dental anxiety. This brings a challenge to clinical work; how should a dentist manage a patient with dental anxiety, or should a patient be advised to consult a psychologist or a psychiatrist? Further examinations are needed.

CONSENT FOR PUBLICATION
Not Applicable.

CONFLICT OF INTEREST
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Professor Jouko Miettunen was supported by the Academy of Finland (#268336).

Internal Validity -Confounding (Selection Bias)
Were the patients in different intervention groups (trials and cohort studies) or were the cases and controls (case-1. control studies) recruited from the same population? Was there adequate adjustment for confounding in the analyses from which the main findings were drawn? 2.
Were losses of patients to follow-up taken into account? 3.

APPENDIX 2
Appendix Table. Description of the tests used to measure dental anxiety in reviewed articles. All tests are widely used in clinical and research practice.

Test
No. of Items Description of the Test Dental Anxiety Scale DAS [25] 4 Level of dental anxiety is measured from 4 (no fear) to 20 (extreme fear).
Dental Beliefs Survey DBS [26] 15 Explores patients' confidence in dentist-patient interaction on a scale from 15 (highly positive beliefs) to 75 (highly negative beliefs).
Dental Fear Survey DFS [27] 20 Test varies from 20 to 100 and assesses 3 different areas of fear reactions: avoidance, autonomic arousal and fear of specific objects or situations.
Gatchel Fear Scale GFS [28] Subjects are asked to rate their fear of dentist on a scale in which 1 means no fear, 5 moderate and 10 extreme fear.
Modified Dental Anxiety Scale MDAS [29] 5 Level of dental anxiety is measured from 5 (no fear) to 25 (extreme fear).