art-Matej-Par

ORAL MEDICINE
PSYCHONEUROIMMUNOLOGY OF ORAL DISEASES – A REVIEW




                                                                                                                                                              Review Article
Matej Par1a*         , Zrinka Tarle1b*

1
    Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Zagreb, Croatia


DMD, PhD, Postdoctoral Researcher
a

DMD, PhD, Professor, Dean
b




    ABSTRACT                                    DOI: https://doi.org/10.25241/stomaeduj.2019.6(1).art.7
Background: Various oral stimuli that are perceived by the brain as stressful can trigger patterns
                                                                                                                                OPEN ACCESS This
of neurological activity which then directly influence immune and endocrine response.                                           is an Open Access article
Objective: To analyze the psycho-neuro-endocrine-immunological interactions involved in oral                                    under the CC BY-NC 4.0
                                                                                                                                license.
diseases and conditions.
Data sources: Web of Science, PubMed, Google Scholar were databases researched for peer                                         Peer-Reviewed
                                                                                                                                Article
review articles in indexed journals.
Study selection: A literature search limited to peer-reviewed articles in indexed journals published                        Citation: Par M, Tarle Z.
                                                                                                                            Psychoneuro-immunology of
before January 2019 was performed using specific keywords. 107 articles were selected.                                      oral diseases – a review.
Data extraction: The aspects related to psycho-neuro-immune interactions relevant for dental                                Stoma Edu J. 2019;6(1):55-65

practitioners were synthesized and presented in the form of narrative review. Oral diseases and                             Received: March 14, 2019
                                                                                                                            Revised: March 21, 2019
conditions in which psychological factors act through neurological, endocrine and immunological                             Accepted: March 27, 2019
mechanisms are discussed. The following clinical entities were included: periodontitis, oral lichen                         Published: March 28, 2019
planus, recurrent aphthous stomatitis, temporomandibular disorders, herpes labialis, burning                                *Corresponding author:
mouth syndrome, and atypical odontalgia. Additionally, the role of psycho-neuro-immunological                               Dr. Matej Par, DMD, PhD
                                                                                                                            Gunduliceva 5, Department of
factors on bacterial adherence and oral microbiome is briefly discussed.                                                    Endodontics and Restorative
Data synthesis: Various oral diseases and conditions of multifactorial etiology can be influenced                           Dentistry, School of Dental
                                                                                                                            Medicine, University of Zagreb,
by psycho-neuro-immunological interactions. In daily practice, clinicians should be aware of the                            Zagreb, Croatia
interplay between mental and general health and consider addressing psychological disturbances                              Tel.: +3851 480 2203, Fax:
                                                                                                                            +3851 4802 203, e-mail:
as a supplement for conventional treatment modalities. Recognizing these interactions should                                mpar@inet.hr
help to better understand the relationship between mental and physical health.                                              Copyright: © 2019 the
Keywords: Periodontitis; Lichen planus, oral; Stomatitis, aphthous; Temporomandibular joint                                 Editorial Council for the
disorders; Herpes labialis.                                                                                                 Stomatology Edu Journal.




1. Introduction                                                                   that stress-induced immunosuppression, stress-
Psychoneuroimmunology is an interdisciplinary field                               induced inflammation, and various subtle changes
which represents the convergence of psychology,                                   in the regulation of the endocrine and immune
neuroscience, endocrinology, and immunology.                                      system caused by psychological factors can modify
Various stimuli that are perceived by the brain as                                the course of different diseases. This review is
stressful can trigger patterns of neurological activity                           focused on the diseases affected by psycho-neuro-
which then directly influence immune and endocrine                                immunological factors which occur in the oral cavity.
response. Since many cells of the nervous, immune,
and endocrine systems share common signaling
pathways, these systems do not act as isolated                                    2. Methodology
functional units, but instead interact with each other                            A literature search limited to peer-reviewed articles
to yield an integrated response. By recognizing                                   in indexed journals published before January 2019
these interactions, psychoneuroimmunology helps                                   (1983-2018) which were identified by searching
to better understand the relationship between                                     the Web of Science, PubMed (Medline) and
mental and physical health. The idea of the interplay                             Google Scholar using the following keywords:
between psychological factors and physical health                                 (psychoneuroimmunology OR psychological OR
is not new – its origins can be traced back to Galen,                             psychiatric OR mental health OR stress OR depression
who in the year 200 presented the observation                                     OR cortisol OR hypothalamic-pituitary-adrenal) AND
that melancholic women are more susceptible to                                    (oral OR dental OR dentistry OR periodontitis OR
breast cancer than sanguine women [1]. Almost                                     oral lichen planus OR recurrent aphthous stomatitis
two millennia later, contemporary studies have                                    OR temporomandibular disorders OR herpes OR
collected a great deal of experimental data and                                   burning mouth syndrome OR atypical odontalgia
clinical evidence which support the hypothesis                                    OR eating disorders OR microbiome). The aspects



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                 PSYCHONEUROIMMUNOLOGY OF ORAL DISEASES
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Review Article    Table 1. Systematic division of the cited articles according to the
                 discussed topics.                                                        perpetuation [4]. The effect of periodontitis on
                                                                                          systemic health has been extensively studied and
                  Topic                                              Reference No.
                                                                                          many connections with illnesses of remote organs
                  Periodontitis                                            2-40           have been hypothesized [5, 6]. Many of these
                  Oral lichen planus                                       41-54          connections have also been supported by evidence,
                  Recurrent aphthous stomatitis                            55-62          although to varying extents. Rather compelling
                  Temporomandibular disorders                              63-82          evidence exists for the association of periodontitis
                                                                                          with cardiovascular disease [7] and diabetes mellitus
                  Herpes labialis                                          83-87
                                                                                          [8]. Obstetric complications, respiratory diseases,
                  Burning mouth syndrome                                  88, 89          chronic kidney disease, and cancer have also been
                  Atypical odontalgia                                        90           linked to periodontitis [9-12]. Two major mechanisms
                  Eating disorders                                         91-97          of systemic action involve (I) invasion of periodontal
                                                                                          pockets bacteria, leading to bacteremia and
                  Oral microbiome                                       4, 98-107
                                                                                          dissemination of living bacteria or products of their
                                                                                          decomposition; and (II) excessive production of
                 of psycho-neuro-immune interactions relevant for                         long-range pro-inflammatory cytokines, resulting in
                 dental practitioners were synthesized and presented                      their elevated systemic levels. The latter mechanism
                 in the form of a narrative review.                                       clearly represents an immuno-endocrine response,
                                                                                          while the former mechanism is also immunologically-
                                                                                          mediated since the presence of bacterial antigens in
                 3. Results                                                               the bloodstream causes a cross-reactive
                 Oral diseases and conditions in which psychological                      immunological response which then leads to the
                 factors act through neurological, endocrine                              destruction of host tissues [5]. The relationship
                 and immunological mechanisms are discussed.                              between periodontitis and systemic health is often
                 The following clinical entities were included:                           bidirectional: a complex immuno-endocrine
                 periodontitis, oral lichen planus, recurrent aphthous                    response initiated by the microbiome in periodontal
                 stomatitis, temporomandibular disorders, herpes                          pockets modulates various systemic conditions,
                 labialis, burning mouth syndrome, and atypical                           while the impaired systemic health, in turn, affects
                 odontalgia. Additionally, the role of psycho-neuro-                      the progress of periodontal disease. For example,
                 immunological factors on bacterial adherence and                         elevated levels of pro-inflammatory cytokines due to
                 oral microbiome is briefly discussed. The systematic                     periodontitis can increase insulin resistance, while
                 division of referenced articles regarding individual                     the resulting hyperglycemia and formation of
                 topics is presented in Table 1.                                          glycosylation end products enhance the destructive
                                                                                          potential of periodontitis [13]. Without going further
                 3.1. Periodontitis                                                       into detailed descriptions of the pathophysiology of
                 Periodontitis is an inflammatory disease which                           periodontitis and the related systemic conditions, it
                 progressively damages periodontal tissues,                               is evident that many of the interactions stem from
                 eventually leading to tooth loss. Although                               the underlying dysregulation of the immune system
                 periodontitis is clearly associated with the presence                    and can be affected by psycho-neurological factors.
                 of certain microbial species, it cannot be regarded as                   Although the psycho-neurological influence on the
                 a classical infective disease because the damage to                      complex interactions between periodontitis and
                 periodontal tissues results from an inappropriate                        systemic diseases currently remain unexplored, the
                 inflammatory reaction and not from the destructive                       psycho-neurological aspects of periodontitis itself
                 action of the microbes alone [2]. The pathophysiology                    have been well documented. Clinical observations
                 of periodontitis is thus related to a complex interplay                  and epidemiological studies have indicated that
                 between the microbial challenge and host immune                          stress [14], depression [15], and inadequate coping
                 response [3], while the differences in immunological                     behaviors [16] are related to the onset and
                 reactivity and susceptibility to periodontal                             progression of periodontitis. Psychological factors
                 destruction between individual persons are                               have long been known to present a risk factor for
                 determined genetically. These differences explain                        acute necrotizing ulcerative gingivitis and
                 why the presence of a certain microbial community                        periodontitis – these aggressive forms were the first
                 can cause an aggressive disease in some individuals,                     to be related to psychological factors about 50 years
                 whereas in others the same microbial species may                         ago [17-20]. A systematic review from the year 2013
                 not trigger any destructive reaction. Additionally, it                   analyzed 14 studies and showed that 8 studies
                 is still unclear whether the bacterial strains found in                  identified a positive relation between psychosocial
                 active periodontal pockets truly initiate the disease                    factors and periodontitis, 4 studies identified a
                 or these strains simply prefer the new environment                       positive relation between some characteristics of
                 created by pocket formation and active inflammation,                     psychological factors and periodontal disease,
                 without an active role in its initiation and                             whereas only 2 studies were unable to identify any



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                                                                PSYCHONEUROIMMUNOLOGY OF ORAL DISEASES
                                                                                            – A REVIEW




                                                                                                                        Review Article
relation [19]. Contrary to early beliefs that stress        In any case, a relation between psychological factors
response mediated through catecholamines and                and periodontal health has been repeatedly
cortisol is primarily immunosuppressive, the immune         observed. In studies on the relation between stress
system may be affected by psychological stress in           and periodontitis, it is generally difficult to
both directions. This happens because the individual        distinguish between the contribution of stress-
cell or tissue reaction to elevated levels of stress        related behavioral factors (poor oral hygiene, poor
hormones depends on the presence or absence of              nutrition, smoking, and generally neglected health)
particular receptors [21]. Short-term stress appears        from exclusively psychoneuroimmunological stress-
to suppress cellular immunity, whereas chronic              related factors which directly affect the progress of
stress leads to a more comprehensive dysregulation          the disease, without a behavioral intermediary [15].
of the immune system, affecting both cellular and           The psycho-neuro-immunological mechanism is
humoral immunity [15]. Psychological status was             evidenced by the role of cortisol and other stress-
found to correlate with salivary levels of cortisol and     related hormones. In an experimentally induced
β-endorphin, which were in turn identified as               periodontitis in rats which had genetically different
determinants for tooth loss due to periodontal              responsiveness of the hypothalamic-pituitary-
disease [22]. Depression has also been associated           adrenal axis, the high-responding rats developed
with increased risk and severity of periodontitis.          more severe periodontal disease. Additionally, they
Various psychometric factors, such as depression            showed elevated corticosterone blood levels due to
and anxiety scores, subjective well-being, somatic          a local inflammatory response induced by
complaints, quality of life, and introversion have          experimentally enhancing the accumulation of
been correlated with periodontitis [23]. Traumatic          subgingival microbiome, indicating a positive
life events such as the loss of a spouse, as well as the    feedback loop between the hypothalamic-pituitary-
personality trait of exercising extreme external            adrenal axis activation and local periodontal
control were shown to increase the risk for severe          inflammation [31]. In a rat model of depression
periodontitis [24]. Stress-related depression and           induced by olfactory bulbectomy, the role of psycho-
exhaustion have been associated with increased              neuro-endocrine factors has been demonstrated by
levels of cortisol and IL-6 in the gingival crevicular      a decreased expression of glucocorticoid receptors
fluid, as well as higher levels of gingival inflammation    in the hippocampus, different response to injected
and plaque accumulation [25]. Women on long-term            lipopolysaccharide and more extensive periodontal
sick leave for depression had more severe                   bone loss in depressive animals [32]. The association
periodontitis and elevated levels of IL-6 in gingival       between cortisol and periodontitis has also been
crevicular fluid compared to healthy controls [26].         observed in humans; patients undergoing stressful
Patients with rapidly progressing periodontitis             life events had higher cortisol levels and more severe
presented significantly higher depression and               periodontitis [33]. Other studies have confirmed that
loneliness scores compared to patients with chronic         hyperactivation of the hypothalamic-pituitary-
adult periodontitis and healthy controls [27].              adrenal axis and the resulting increase in cortisol
Depression was associated with a more extensive             level was positively related to the extent and severity
periodontal breakdown [28]. Psychosocial measures           of periodontitis [34]. Psychological stress, depression,
of stress and depression associated with financial          and salivary cortisol levels were found to be
strain were shown to be significant risk indicators for     positively correlated with the extent of periodontal
severity of periodontitis in adults [16].            The    destruction, independent of the level of oral hygiene
effectiveness of coping behavior has also been              [35]. In addition to cortisol, levels of another stress-
identified as a modulating factor for periodontitis in      related hormone whose secretion is regulated by
patients exposed to psychological stress. Adequate          corticotrophin, dehydroepiandrosterone, were also
coping behaviors, such as problem-based coping              related to the extent and severity of periodontitis,
were shown to reduce the stress-associated risk [16].       adding to the evidence for the role of hypothalamic-
Conversely, patients with inadequate coping                 pituitary-adrenal axis hyperactivation in the
techniques (passive coping) were shown to be at             pathogenesis of periodontitis [36]. The outcome of
greater risk for severe periodontitis [29]. Ineffective     periodontal treatment can be negatively affected by
coping was also associated with poorer responses to         stressful life events [37], occupational stress [38], and
nonsurgical periodontal treatment, whereas patients         clinical depression [39], indicating that psycho-
with active coping had less severe forms of disease         neuro-immunological factors play a role in wound
and better treatment outcomes [30]. Although                healing and recovery following an invasive
psychological factors have been identified as risk          treatment. From a clinical standpoint, these findings
factors for periodontitis in multiple studies, rigorous     indicate that routine periodontal treatments may
analyses highlight the issue of heterogeneity of            benefit from an adjunctive stress-management
study designs, methodology and assessment criteria,         therapy which would comprise the assessment of
thus claiming that it is not yet possible to regard         patient’s stress levels and their ability to cope with
psychological stress as a definitive risk factor [19,21].   stress, followed by implementation of stress-



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Review Article   reduction protocols [40]. Similarly, addressing             scores on anxiety and depression tests compared
                 depression in patients with periodontitis may help          to healthy controls [43]. Higher sensitivity to stress
                 to alleviate the course of periodontitis through            perception and reduced capability of coping with
                 immunologic and behavioral changes conducive of             stress was also observed [44]. A study evaluating
                 periodontal healing [35].                                   psychological personality profiles of patients with
                                                                             oral lichen planus found significantly higher scores
                 3.2. Oral lichen planus                                     for hypochondriasis, depression, and hysteria
                 Oral lichen planus is a chronic inflammatory disorder       compared with controls, whereas the scores at
                 which clinically manifests on the oral mucosa as            other clinical scales (psychopathic deviate, paranoia,
                 multiple bilateral papular, reticular, erythematous,        psychasthenia, schizophrenia, and hypomania)
                 and erosive lesions. Besides the significant negative       were not different from controls [47]. In that study, a
                 effect on the quality of life due to its chronic course,    two-fold increase in serum cortisol levels was found
                 oral lichen planus lesions have a potential for             between patients with erosive lesions and controls,
                 malignant transformation at an overall frequency            whereas patients with reticular lesions had similar
                 of 0.3-3 % [41]. Although the etiology of oral lichen       cortisol levels as controls. Elevated plasma cortisol
                 planus is unclear, the underlying pathophysiology           levels were also found to be associated with more
                 has been known to involve a dysregulated T-cell             aggressive erosive lesions in another study [48],
                 immune response to an induced antigenic change in           suggesting that cortisol levels may be predictive
                 the oral mucosa. The hypothesized etiologic factors         of the severity of the disease. Cortisol levels were
                 which have the potential to induce that antigenic           positively correlated with scores on clinical scales
                 change include dental amalgam, non-steroid anti-            for hysteria, hypochondriasis, and depression [47].
                 inflammatory drugs, and hepatitis C virus [41].             Conversely, a study on diurnal cortisol production
                 The association of oral lichen planus with                  reported that patients with oral lichen planus
                 psychological      stress     has    generally     been     had decreased salivary cortisol production in the
                 acknowledged and reported in multiple studies               morning hours compared with healthy controls
                 [42-45]; however, the causal relationship is less           [44]. Despite some inconsistencies in the studies of
                 clear since chronic discomfort due to persistent            cortisol levels, the findings indicate that oral lichen
                 lesions may itself act as a stressing factor [46]. An       planus may be related to the dysregulation of the
                 interesting approach for evaluating a possible              hypothalamic-pituitary-adrenal axis triggered by
                 etiological role of psychosocial stressors on oral          psychological factors. Considering the autoimmune
                 lichen planus was employed in a double-controlled           background of oral lichen planus, additional
                 study which involved healthy individuals as a               evidence for the role of neuro-immune crosstalk for
                 negative control and patients with burning mouth            the systemic immune response is the finding that
                 syndrome, atypical facial pain, and myofascial pain         bilateral transection of glossopharyngeal nerves
                 dysfunction syndrome as a positive control [45].            can attenuate the dose-dependent febrile response
                 That study found significantly higher stress, anxiety,      to injection of lipopolysaccharide or IL-1-b into
                 and depression levels in oral lichen planus patients        the soft palate of rats [49]. This demonstrates that
                 and positive control compared to the general                the communication between the central nervous
                 population, whereas no significant differences were         system and the immune system is not exclusively
                 found between the oral lichen planus patients and           mediated by cytokines and other humoral pathways,
                 the positive control group. These results have led          but instead requires a local neural route linked to
                 the investigators to hypothesize that psychological         the site at which the antigen was administered.
                 disturbances in susceptible persons may indeed play         The common treatment for oral lichen planus is
                 a causative role in the pathophysiology of oral lichen      symptomatic and involves topical, intralesional, and
                 planus, probably by acting as a starting point for the      systemic administration of corticosteroids, while
                 initiation of autoimmune reactions.                         other immunosuppressive agents (cyclosporine
                 In a study which assessed the psychiatric status of 56      and tacrolimus) or retinoids can also be used in
                 patients with clinically and histologically verified oral   more severe cases [46]. Although the disease can
                 lichen planus, 52% of patients were diagnosed with          be successfully controlled by these medications in
                 mental disturbances (12 patients with slight, 3 with        most cases, the effects of the treatment are usually
                 moderate, and 14 with severe disturbances); that            transient and the side effects of long-term treatment
                 percentage was significantly higher than in healthy         may outweigh the benefits. Addressing the psychical
                 participants in the control group and the general           health as a possible adjunctive therapy in treating
                 population [42]. In a study on anxiety, depression,         oral lichen planus has been suggested decades
                 and stress in patients with oral lichen planus, no          ago [42,47,50], however, no studies evaluating the
                 differences were found between the acute and                effectiveness of this approach have been published
                 remission stage, while patients diagnosed with              up to date. A multidisciplinary approach to the
                 oral lichen planus reported encountering stressful          treatment of oral lichen planus could be beneficial
                 life events more frequently and received higher             because the psychological well-being of patients



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                                                             PSYCHONEUROIMMUNOLOGY OF ORAL DISEASES
                                                                                         – A REVIEW




                                                                                                                   Review Article
with oral lichen planus can be severely affected by      the conventional treatment for RAS is symptomatic
the disease itself. Psychological support may help       and ineffective in the long-term, a supportive
in breaking the vicious circle formed by the disease     psychotherapy may be beneficial for alleviating the
that is both causing and being perpetuated by            discomfort that RAS patients experience [56].
impaired psychological status [51]. Oral microbiome
in patients with oral lichen planus has been shown       3.4. Temporomandibular disorders
to be altered in comparison to healthy controls [52].    Temporomandibular disorders (TMD) encompass
Also, different colonization patterns were observed      several clusters of symptoms involving chronic pain
at the sites of oral mucosa affected by lesions          in the temporomandibular joint and masticatory
compared to healthy control sites within the same        muscles, limitations in the range of mandibular
patient [53]. However, it has not yet been clarified     movement and sounds occurring during movements.
if the dysbiosis associated with oral lichen planus      Pain can be spontaneous or triggered by mandibular
has some causative role, for example by invading         movement or palpation of the masticatory muscles.
the epithelial barrier and modifying the immune          The etiology of TMD remains poorly understood
response [54]. Alternatively, the dysbiosis may          and involves psychological, behavioral and
simply be an epiphenomenon due to the changed            environmental factors. TMD usually presents no
oral environment, without having an active role in       observable organic pathology and shares many
the immunopathology of oral lichen planus.               features with other chronic pain conditions. TMD is
                                                         often comorbid with other chronic pain conditions,
3.3. Recurrent aphthous stomatitis                       such as fibromyalgia, headaches, spinal pain, and
Recurrent aphthous stomatitis (RAS) is a chronic         back pain [63]. Although it causes significant distress
disease of unclear etiopathogenesis, characterized       to affected patients, TMD is self-limiting and usually
by a recurrent onset of solitary or multiple painful     does not lead to a progressive structural or functional
ulcerations and erosions appearing predominantly         deterioration [64]. Being predominantly a functional
on unattached oral mucosa. Clinical characterization     rather than structural disorder, TMD appears more as
distinguishes three main types of oral lesions: minor,   a symptom than a disease.
major and herpetiform. The disease is considered to      The inseparable interplay between psychological
be caused by a hyper-reactive immune response,           stress and the experience of pain is biologically
which is influenced by genetic predisposition and        based on the fact that most of the molecules
modulated by a multitude of factors, some of which       which regulate the stress response are the same
include: viral and bacterial infections, nutritional     as those involved in pain modulation [65]. As
deficiencies, food allergies, psychological stress,      in other chronic pain conditions, psychological
mechanical trauma, and hormonal imbalance                factors are generally implicated in the occurrence
[55]. The exacerbation of RAS is often related to        of TMD, with the involvement of the hypothalamic-
psychological stress. Higher anxiety levels coupled      pituitary-adrenal axis, as well as the serotoninergic
with elevated cortisol levels in plasma and saliva       and opioid system [66]. In addition to the psycho-
have been associated with RAS [56]. Exposure             neuro-immunological dysregulation, the symptoms
to stressful situations and conditions appears           can be aggravated by hyperactivity of masticatory
to be more important for the onset of RAS than           muscles which often accompanies TMD. However,
personality profiles and stable psychological traits     the stress-induced parafunctional activities are not
[57]. However, some evidence exists that trait           necessarily related to muscle pain and [67] and
anxiety may be a predisposing factor for RAS [58].       thus cannot be regarded as the primary source
A study in which 160 RAS patients were followed by       of TMD symptoms. This is supported by a study
weekly phone surveys over 1 year found a significant     evaluating the association of masticatory muscle
association of stressful life events and exacerbations   pain and nocturnal electromyography activity with
of RAS, while a stronger association was found for       psychological factors demonstrating that muscle
psychological than physical stressors [59]. However,     pain is more related to psychological stress than to
no association of stressful life events with the         parafunctional activity [68].
duration of RAS episodes was identified in that study.   Studies have indicated that patients with TMD tend
There are also reports of no association of RAS with     to present higher levels of anxiety [69], depression
alterations in cortisol levels [60] and psychological    and somatization [70]. Stress and emotional
factors (stress and depression) [61], which is in line   distress have also been shown to be associated
with the complex and multifactorial etiology of          with TMD pain, as well as muscular tension and
RAS. Frequent exacerbations of painful RAS lesions       parafunctional habits which can independently
interfere with normal daily activities and negatively    contribute to the painful experience [71]. TMD
affect the quality of life [62]. The psychological       patients showed higher electromyographic activity
consequences may then influence the course of            during experimentally induced stress compared
disease thus forming a vicious circle in a similar       to patients with other chronic painful conditions
manner as mentioned for oral lichen planus. Since        (e.g. chronic back pain) and healthy controls [72].



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Review Article   Subjects with maladaptive coping were at greater           establishes a latent infection in ganglionic neurons
                 risk for TMD pain than the subjects with adaptive          which can be reactivated under conditions of
                 coping [73]. A prospective cohort study of 171             impaired immune surveillance, thus causing a
                 healthy female volunteers identified the first-onset       recurrent infection. The potential of psychological
                 TMD in 8.8% of the participants over the course of         stress to exacerbate the recurrence of herpes virus
                 3 years and demonstrated a high predictive value of        infection has been well documented and various
                 depression, perceived stress, and mood for the onset       factors such as short-term stress, stressful life events,
                 of TMD [74]. Some of the TMD patients showed               dysphoria, anxiety, anger, and negative mood were
                 cortisol hypersecretion in response to stress, which       associated with viral reactivation at both oral and
                 could be regarded as a biological predisposition to        genital sites [84]. Since cellular immunity plays
                 TMD [75]. However, the excessive cortisol secretion        an important role in maintaining the infection
                 may represent a response to a painful stimulus, as         in a latent stage, an exacerbation is considered
                 evidenced in a study which showed that cortisol            to occur when the cellular immune response is
                 hypersecretion occurred mostly while the subjects          impaired due to the stress-induced imbalance in
                 were awake, i.e. aware of pain [76].                       the secretion of catecholamines, glucocorticoids,
                 Sleep disorders may also be implicated in the              and pro-inflammatory cytokines (IL-1, IL-6, and
                 pathophysiology of TMD through increasing central          TNF) [85]. For example, it has been demonstrated
                 sensitivity to pain, but also by being associated with     that adrenaline and glucocorticoids can be used
                 muscular parafunctions leading to myofascial pain          to experimentally induce herpes simplex virus
                 [77]. The relation between sleep bruxism and TMD           reactivation in animal models [86]. A longitudinal
                 is unclear, as it has been shown that not all patients     study which evaluated daily mood states and weekly
                 with parafunctional habits develop myofascial pain         levels in neuroendocrine markers found that the
                 [78]. The cause and effect relation between sleep          number of natural killer cells and serum levels of
                 disorders and related parafunctions of masticatory         adrenaline were associated with herpes labialis
                 muscles are difficult to establish since sleep disorders   exacerbations [83]. Additionally, that study found
                 are commonly accompanied by depression and                 that adrenaline levels were positively correlated
                 other psychological disturbances which may                 to scores of affect intensity. Although the role of
                 independently influence TMD symptoms [79].                 psychoneuroimmunological interaction in the
                 The usual symptomatic treatment of TMD involves            recurrent herpes infections has been well confirmed,
                 the use of orthopedic appliances which are intended        it remains difficult to quantify psychological stress
                 to improve the biomechanics of temporomandibular           and its etiological significance for the onset of the
                 joint thus reducing muscle activity and joint              disease [87].
                 loading, while simultaneously increasing patient
                 awareness of parafunctional habits [80]. Due to            3.6. Burning mouth syndrome
                 multifactorial etiology of TMD, a multidisciplinary        Burning mouth syndrome is a chronic pain condition
                 treatment approach encompassing physiotherapy,             of unknown etiology, usually characterized by
                 biofeedback, and cognitive behavioral therapy              burning or stinging sensation coupled with a
                 seems reasonable [81]. Therapeutic modalities              subjective feeling of dryness and altered taste.
                 targeting psychological factors may be beneficial          Besides sensory disorders, clinically no oral lesions or
                 for reducing painful symptoms and functional               other objective signs can be identified. The condition
                 limitations; however, the level of evidence for their      is usually associated with a number of psychological
                 effectiveness is currently low [82]. In any case, it       factors, leading some authors to refer to it as psycho-
                 appears that combined treatment modalities can             stomatodynia [88]. Higher levels of neuroticism,
                 be more effective and yield longer-lasting results         anxiety, depression, exposure to stressful life events
                 than the conventional treatment which employs              have been associated with the syndrome and the
                 orthopedic appliances alone [81]. Also, as in other        involvement of some personality disorders as well as
                 chronic pain conditions, the TMD pain can in many          cortisol dysregulation have been hypothesized [89].
                 patients be mitigated by antidepressants regardless        The treatment should aim at identifying and treating
                 of their possible comorbidity with depressive              underlying psychological disturbances.
                 disorder [66].
                                                                            3.7. Atypical odontalgia
                 3.5. Herpes labialis                                       Atypical odontalgia is persistent idiopathic pain
                 Most individuals have been exposed to herpes               which mimics toothache but lacks any identifiable
                 simplex virus through their lifetime, as evidenced         organic cause. It may occur at a healed extraction
                 by the presence of antibodies in up to 90% of the          site or in a healthy, restored or endodontically
                 general population. About 75% of the general               treated tooth which presents with no evidence of
                 population is affected by clinically evident herpes        pathology on clinical or radiographic examination.
                 labialis at some time in life [83]. After a primary        Etiopathogenesis of atypical odontalgia is unclear
                 infection on skin or mucosa, herpes simplex virus          and the involvement of psychogenic and neuropathic



   60                                                          Stoma Edu J. 2019;6(1): 55-65          http://www.stomaeduj.com
                                                             PSYCHONEUROIMMUNOLOGY OF ORAL DISEASES
                                                                                         – A REVIEW




                                                                                                                      Review Article
factors has been proposed, although the primary          (e.g. ammonia-producing species which elevate oral
cause remains unclear and thus no causal treatment       pH values) and pathogenic (e.g. acidogenic species
exists [90].                                             which cause tooth caries through demineralization
The symptomatic treatment is generally difficult         of dental hard tissues).
and unsuccessful, usually leading to unnecessary         In fact, two most frequent diseases in the oral cavity,
extractions of multiple teeth due to patients’           i.e. caries and periodontitis, are caused by complex
persistent requests for treatment driven by              changes in the microbial community, rather than by
persistent pain. Thus psychological factors need to      infection with a specific pathogen [101]. Especially
be thoroughly considered in patients with atypical       in the case of periodontitis, well-known shifts of
odontalgia in order to avoid irreversible iatrogenic     microbial ecology in favor of specific bacterial
damage.                                                  species are associated with the destructiveness of the
                                                         disease. Healthy periodontal tissues express a low-
3.8. Eating disorders: anorexia and bulimia nervosa      grade controlled inflammation which represents the
Eating disorders which are characterized by              host response to periodontal microbiome, whereas
restricted food intake (anorexia nervosa) or purging     the transition towards destructive inflammation
behavior by means of induced vomiting or laxative        occurs in susceptible individuals when the microbial
use (bulimia nervosa) are psychiatric disorders          dysbiosis occurs [102].
of unclear etiology with probable involvement            The primary local beneficial effect of the commensal
of serotoninergic dysregulation in the brain [91].       microbiome is the inhibition of colonization of the
Frequent exposure of dental hard tissues to gastric      oral cavity by pathogenic species, the so-called
acid due to vomiting can lead to cumulative              colonization resistance [103]. Disbalances of the
demineralization and extensive erosions on enamel        commensal microbiome can lead to opportunistic
and dentin. The resulting defects usually require        infections by Candida spp. or Staphylococcus
comprehensive restorative or prosthodontic               aureus, which are commonly seen as a side-effect
treatment. Eating disorders are associated with          of antimicrobial therapy. Oral microbiome also has
elevated levels of pro-inflammatory cytokines            some systemic effects, as exemplified by its role in
such as TNF- α and IL-6, indicating a psycho-neuro-      the metabolism of nitrates. Nitrate is secreted into
immune interplay [92,93].                                the saliva (about 25% of the total ingested amount)
Also, eating disorders are related to psychological      and reduced by oral bacteria into nitrite which is then
stress and inadequate coping behaviors and are           absorbed through gastric mucosa and converted
often comorbid with other psychiatric disturbances       into nitric oxide. Nitric oxide has an important
such as anxiety and depression, with a probable          role in regulating vasodilatation and maintaining
bidirectional interaction [94]. The acute phase          blood pressure homeostasis. For example, orally
of anorexia nervosa has been associated with             ingested nitrates in the form of food supplements
increased levels of salivary cortisol, secretory         help to reduce blood pressure by exploiting this
immunoglobulin-A, and alpha-amylase, reflecting          mechanism [104]. It is clear that the oral microbiome
dysregulation of hypothalamic-pituitary-adrenal          plays a complex role in both local and systemic
axis [95]. Some patients with bulimia nervosa            health, whereas its imbalances reach beyond a
have shown changes in the enzymatic activity             straightforward infective disease caused by a single
of proteases, collagenase, and pepsin in resting         pathogen. However, the effects of psycho-neuro-
and simulated saliva, which contributes to the           immunological factors on the oral microbiome
progression of dental erosions [96]. Gut microbiome      and the consequences of that interaction on
can also play a role in the regulation of food intake.   systemic health have not been extensively studied.
For example, bacterial metabolic products such as        Considering the better-established links of
short-chain fatty acids exert a neuroactive effect       psycho-neuro-immunological factors with the gut
which affects the host appetite, possibly playing a      microbiome, it is plausible that a similar interplay may
role in the pathophysiology of eating disorders [97].    occur in the oral cavity. If the link is to be established
                                                         and mechanisms elucidated, the oral microbiome
3.9. The role of the oral microbiome                     could be altered by using probiotics in a manner
Besides the gut and the skin, as two sites of the        similar to what is now commonly accepted for gut
human body that are most heavily populated               microbiome [105]. In such a scenario, modifying the
by microbes, the oral cavity is also an important        oral microbiome could aid in mitigating the course
habitat for 500-1000 bacterial species [4, 98, 99].      of periodontal destruction through two major
The discrepancy in the number of species which is        mechanisms: (I) inhibition of microbial adhesion,
encountered in the literature stems from the fact that   colonization, growth, and biofilm formation; and
approximately half of the bacterial species found        (II) altering the destructive host response involving
in the mouth cannot be cultured under laboratory         inhibition of pro-inflammatory pathways and
conditions [100]. Most of the species present can be     inflammation-induced enzymes [106].
regarded as commensal, while some are symbiotic



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                                                                                                                               Matej PAR
                                                                                             DMD, PhD, Postdoctoral Researcher
                                                                            Department of Endodontics and Restorative Dentistry
                                                                                 School of Dental Medicine, University of Zagreb
                                                                                                                Zagreb, Croatia


                 CV
                 Mater Par, DMD, PhD is a postdoctoral researcher at the Department of Endodontics and Restorative Dentistry, School of Dental
                 Medicine in Zagreb, Croatia. He is a young researcher who authored 26 original research articles and contributed to 2 textbook
                 chapters. His primary areas of interest include dental biomaterials and the development of experimental remineralizing resin
                 composites.




   64                                                                         Stoma Edu J. 2019;6(1): 55-65                     http://www.stomaeduj.com
                                                           PSYCHONEUROIMMUNOLOGY OF ORAL DISEASES
                                                                                       – A REVIEW


Questions




                                                                                                               Review Article
1. Why should dental practitioners consider psycho-neuro-immune interactions
in their daily practice?
qa. Dental treatment may have a negative long-term effect on the psychological status in susceptible
patients;
qb. Certain oral diseases may be affected by psychological disturbances;
qc. Early signs of some psychiatric disorders can be recognized in the mouth;
qd. Major modifications of dental treatment are needed in patients with some personality disorders.


2. Which of the following is incorrect?
qa. Periodontitis can affect systemic health, and some systemic diseases can influence the course of
periodontitis;
qb. Severity of periodontitis can be affected by stress, depression, and coping behavior;
qc. Some forms of periodontitis can be successfully treated using psychotherapy, without the need for local
periodontal treatment;
qd. Despite considerable amount of evidence, psychological factors cannot be yet regarded as definitive risk
factors for the onset of periodontitis.


3. Which of the following conditions usually does not present with painful
symptoms?
qa. Periodontitis and tooth caries;
qb. Herpes labialis and recurrent aphthous stomatitis;
qc. Temporomandibular disorder;
qd. Burning mouth syndrome.


4. Choose the correct statement:
qa. Oral microbiome consists of 500-1000 bacterial species; diseases such as caries and periodontitis occur
in cases of imbalances in microbiome in which only one bacterial species becomes dominant over others;
qb. Exacerbations of periodontitis and oral lichen planus have been shown to correlate with certain
psychological states but no association of these diseases with stress-related hormones such as cortisol was
observed;
qc. Necrotizing ulcerative gingivitis and periodontitis are the only forms of periodontal disease which are
not associated with psychological factors;
qd. Burning mouth syndrome and atypical odontalgia usually present with no clinical or radiological signs of
organic pathology but the patients affected by these conditions often show some psychological disturbance.




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