
As a person’s life style becomes more complicated, the occurrence of sleep disturbances is increasing [1]. The most common sleep disturbances comprise bruxism, snoring and insomnia. Bruxism includes both tooth clenching which is a continuously static position of maximum intercuspation and tooth grinding indicating a forceful movement of the jaw from side to side [2]. Snoring can be associated with obstructive sleep apnea characterized by intermittent collapse of the upper airway during sleep. The prevalence rate of snoring was reported 25.7% in young adults [3]. Insomnia usually shows the delay of sleep onset, difficulty staying asleep, or awakening too early, which may contribute to initiating or perpetuating orofacial pain [4].
There have been reports on the association of psychological status with sleep disturbances [5-7]. Kang et al. [1] showed the close relation between sleep quality and psychogenic condition using the Symptom Checklist-90-Revised (SCL-90-R) and Pittsburgh Sleep Quality Index. Manfredini et al. [8] supported an association between bruxism and certain psychopathological symptoms by means of self-report version of the Structured Clinical Interview for Panic-Agoraphobic Spectrum. Restrepo et al. [9] found a strong correlation among bruxism, the high anxiety level and the high tension personality trait using the Children’s Personality Questionnaire and the Conners’ Parents Rating Scales. Enright et al. [10] reported that observed apneas during sleep were associated with depression in elderly women through the modified Center for Epidemiologic Studies Depression. Buysse et al. [11] confirmed the increased risk of subsequent depression among individuals with insomnia by means of SCL-90-R.
The revised version of the Minnesota Multiphasic Personality Inventory (MMPI-2) is one of the most widely used psychometric instruments. Higher scores in MMPI-2 indicating maladaptive personality traits predicted incident chronic insomnia [12]. The psychological characteristics of the patients with bruxism were asessed by the Minnesota Multiphase Personality Inventory (MMPI) [13]. The associations between polysomnographic variables in obstructive sleep apnea and a variety of psychological responses including depressive symptoms were evaluated by MMPI [14]. Though these studies have been performed for various age groups, the study in young adults is rare. Hence, the aim of current study is to assess influences of psychological factors on sleep disturbances through MMPI-2 in young adults.
This study is approved by the Institutional Review Board of Shingu College (IRB-2019-101).
Data were collected from two hundred and ninety nine college students in Gyeonggi-do, including seventy six men and two hundred and twenty three women. Mean age of the subjects was 19.2±2.7 years (Table 1).
Data were obtained from October to December of 2019. Visiting a classroom, an examiner explained each item of the questionnaire (Appendix 1) related to sleep disturbances and asked the students to answer it by self-evaluation and retrieved the completed answers at their classroom. Moreover, a psychologist administered MMPI-2 to the students.
The MMPI-2 scales consist of the clinical scales, restructured clinical (RC) and personality psychopathology five (PSY-5) scales, the content scales, and supplementary scales. Every clinical scale concerns a particular psychological aspect:hypochondriasis (Hs), depression (D), hysteria (Hy), psychopathic deviation (Pd), masculinity-femininity (Mf), paranoia (Pa), psychasthenia (Pt), schizophrenia (Sc), hypomania (Ma), social introversion (Si). A set of RC scales are less intercorrelated and have greater discriminant validity than the original clinical scales:demoralization (RCd), somatic complaints (RC1), lowpositive emotions (RC2), cynicism (RC3), antisocial behavior (RC4), ideas of persecution (RC6), dysfunctional negative emotions (RC7), aberrant experiences (RC8), hypomanic activation (RC9). The PSY-5 scales were constructed to assess personality traits relevant to both normal functioning and clinical problems: aggressiveness (AGGR), psychoticism (PSYC), disconstraint (DISC), negative emotionality/neuroticism (NEGE), introversion/low positive emotionality (INTR). The content scales represent well the content dimensions of the original MMPI: anxiety (ANX), fears (FRS), obsessiveness (OBS), depression (DEP), health concerns (HEA), bizarre mentation (BIZ), anger (ANG), cynicism (CYN), antisocial practices (ASP), type A behavior (TPA), low self-esteem (LSE), social discomfort (SOD), family problems (FAM), work interference (WRK), negative treatment indicators (TRT). The supplementary scales are judged to be a very helpful supplementary source of information in interpreting the clinical scales: anxiety (A), repression (R), ego strength (Es), dominance (Do), social responsibility (Re), college maladjustment (Mt), post-traumatic stress disorder (PK), marital distress scale (MDS), hostility (Ho), overcontrolled-hostility (O-H), MacAndrew alcoholism-revised (MAC-R), addiction admission scale (AAS), addiction potential scale (APS), masculine gender role (GM), feminine gender role (GF) [15].
Collected response data were recorded in an Excel file. All the statistical analyses were performed by IBM SPSS Statistics for Windows, Version 25.0 (IBM Co., Armonk, NY, USA). Logistic regression analyses were conducted to evaluate impacts of MMPI-2 scales on sleep disturbances. The significance level was set to 5% (p<0.05).
The odds of tooth grinding increased significantly with the increase of T-score of Hy scale (β=0.095, p=0.016). The risk of insomnia increased significantly as T-score of Ma (β=0.047, p=0.008) and Si scale (β=0.034, p=0.045) increased (Table 2). The occurrence of insomnia increased significantly as T-score of RC1 (β=0.040, p=0.029) and PSYC scale (β=0.046, p=0.008) increased (Tables 3,4). The odds of tooth grinding increased significantly as T-score of ANX (β=0.049, p=0.046) and FAM scale (β=0.043, p=0.028) increased. The occurrence of insomnia decreased significantly with the increase of T-score of TPA scale (β=–0.047, p=0.046) (Table 5). The increase of T-score of Do scale significantly contributed to the risk of tooth clenching (β=0.046, p=0.041). The odds of tooth grinding decreased significantly as T-score of MAC-R scale (β=–0.071, p=0.003) increased, whereas it increased significantly as T-score of APS (β=0.045, p=0.020) increased (Table 6). No scale of MMPI-2 significantly affected the occurrence of snoring.
The importance of sleep in maintaining health is now becoming increasingly recognised in young adults, particularly due to our 24-hour culture of connectivity and media consumption [16,17]. The prevalence of bruxism depends on the development of civilization and the modern lifestyle [18]. The prevalence of bruxism, with either grinding or clenching was documented by 6% to 20% of adults according to epidemiologic surveys in USA student population [19]. In the current study 22.1% of subjects clenched teeth during sleep and 21.7% ground teeth during sleep. While about one third of the United Kingdom population aged 18 and above snored at night [20], 39.8% of subjects in the present study reported snoring. The prevalence rate of insomnia in this study was 49.5% which was higher than that noted in previous investigation in which insomnia was reported by 22.8% of the general Korean adult population [21].
There has been an increasing interest in the relationship between sleep problems and mental health. Bruxing behavior was observed in those with higher Hy scores of MMPI, indicating that there was a close relationship between Hy and bruxing behavior [22]. The mean anxiety scores of the Hospital Anxiety Depression Scales and the Hamilton Anxiety Rating Scale were statistically significant higher in patients with bruxism compared with those without bruxism. suggesting that there may be an association between bruxism and higher levels of anxiety [23]. Problems such as discord in the family are often revealed during taking the bruxer’s medical history [18]. Sleep bruxism was associated positively with alcohol, caffeine, and tobacco [24]. These studies support the current result that the odds of tooth grinding increased significantly with the increase of T-score of Hy, ANX, FAM, and APS scale on MMPI-2. The present result that odds of tooth grinding decreased significantly with the increase of T-score of MAC-R scale was contrary to my expectation. This result reflects the fact that high scores on MAC-R scale may indicate persons who are socially extroverted less vulnerable to stress although high scores of MAC-R scale suggest the possibility of alcohol or other substance abuse problems [15]. While high scorers on Do scale appear stronger in face-to-face personal situations and self-confident, high scorers on Si scale are insecure in social situations and lack self-confidence [15]. The current result that the risk of tooth clenching increased significantly with the increase of T-score of Do scale seems contradictory to the previous study [13] that the group of clenching type had higher score on Si scale.
Certain personality traits may constitute important predisposing and perpetuating factors for insomnia [25]. Mendelson et al. [26] revealed that insomniacs had higher scores on Si scale of MMPI than control subjects. Schneider-Helmert [27] concluded that patients with insomnia were somatizing and more introverted when compared to normal sleepers. Insomniacs had significantly higher MMPI scores than did normal sleepers on Hy and Sc scales, appearing to be more neurotic, anxious, and worried than their normal counterparts [28]. Shealy et al. [29] found that insomniacs who failed in treatment generally had higher scores on Ma and Sc scales of MMPI. These findings explain the present result that the odds of insomnia increased significantly with the increase of T-score of Ma, Si, RC1, and PSYC scale on MMPI-2. Against the expectation, the odds of insomnia decreased significantly with the increase of T-score of TPA scale in the current result, since high scorers on TPA scale are hard-driving, frequently hostile, irritable and easily annoyed [15]. Lee JS et al. suggested that there was no significant difference in T-score of TPA scale on MMPI-2 between the elderly insomniacs and noninsomniacs [30].
This study was subject to limitations comprising subjects of narrow age range, simple items of the questionnaire, and no use of polysomnography. However, It investigated all scales on MMPI-2 in contrast to previous studies focusing on clinical scales.
Conclusively, T-scores of Hy, ANX, FAM, Do, MAC-R, and APS scales on MMPI-2 affected the risk of bruxism. T-scores of Ma, Si, RC1, PSYC, and TPA scales on MMPI-2 influenced the occurrence of insomnia. The psychometric instrument such as MMPI-2 is helpful in understanding and managing bruxism and insomnia.
No potential conflict of interest relevant to this article was reported.
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