Journal of
Oral Rehabilitation
Journal of Oral Rehabilitation 2014
Review
Bruxism and genetics: a review of the literature F. LOBBEZOO*, C. M. VISSCHER*, J. AHLBERG† & D. MANFREDINI‡
*Department of
Oral Kinesiology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, MOVE Research Institute Amsterdam, Amsterdam, The Netherlands, †Department of Stomatognathic Physiology and Prosthetic Dentistry, Institute of Dentistry, University of Helsinki, Helsinki, Finland and ‡Department of Maxillofacial Surgery, TMD Clinic, University of Padova, Padova, Italy
SUMMARY People who suffer from bruxism (teethgrinding) often ask their dentists whether their condition is hereditary. The purpose of this study is to enable dentists to provide an ‘evidence-based’ answer to this question. The biomedical literature was searched using PubMed, and 32 publications were identified, of which nine proved relevant to the research question. The references cited by the publications identified yielded one further publication, bringing the total number of publications included in the analysis to 10. Four publications related to family studies, five related
Introduction Sleeping near to someone who grinds their teeth can be difficult. The noise is penetrating and, although the ‘perpetrator’ usually sleeps well, the person subjected to the noise (the ‘victim’) often experiences sleep disturbance. Not surprisingly, therefore, patients – urged by their loved ones – frequently turn to their dentists for help. In such cases, reference is often made to the fact that other members of the family grind their teeth as well. The anecdotal evidence encountered in dental practice points strongly to the conclusion that teethgrinding is hereditary. Most people who talk to their dentists about teeth-grinding problems say that one or more family members grind their teeth as well. This information is often given spontaneously, without the dentist asking; the possibility that the condition may run in the family is clearly something that people wonder about. Nevertheless, in © 2014 John Wiley & Sons Ltd
to twin studies and one related to a DNA analysis. With the exception of one of the twin studies, all the included studies concluded that bruxism appears to be (in part) genetically determined. Dentists whose patients ask them about bruxism can therefore tell them that teeth-grinding does indeed ‘run in families’. KEYWORDS: bruxism, heredity, systematic review Accepted for publication 3 April 2014
the practice of modern evidence-based dentistry, the question arises: is there sound scientific data to support the anecdotal evidence? Hence, the study described in this article sought to establish whether teeth-grinding – bruxism (1) – is indeed hereditary. The study’s findings can be used to give authoritative answers to the many patients who raise the question.
Methods In December 2013, PubMed (US National Library of Medicine) was searched using the following query: ‘Bruxism’[Mesh] AND (genetic* OR heredit*). The search was restricted to English language literature. It yielded 32 publications, from the period 1966 to 2012. The titles and (where available) the abstracts of the publications were examined to establish whether the publications could shed light on the research question. doi: 10.1111/joor.12177
2
F . L O B B E Z O O et al. Twenty-three of the 32 publications were judged to be unusable on the basis of their title and abstract. The reasons for excluding the studies in question were as follows: 1 Literature reviews: n = 4 2 Case reports: n = 3 3 Letters to the editor: n = 1 4 Bruxism as comorbidity associated with a hereditary condition: n = 8
5 6 7 8 9
a Prader–Willi syndrome: n = 1 b Down’s syndrome: n = 2 c Nocturnal frontal lobe epilepsy: n = 1 d Rett syndrome: n = 1 e Huntington’s disease: n = 2 f Cerebral paresis: n = 1 Indirect evidence of bruxism (torus palatinus): n=3 Oral health without focus on bruxism: n = 1 Association between bruxism and nicotine use: n=1 Personality characteristics associated with bruxism: n=1 Epidemiological characteristics of bruxism: n = 1
Five of the 32 publications were immediately identified as usable, and a further four publications appeared to be usable from their titles, but lacked abstracts. The latter four publications were therefore read in full, after which all were found to support the
research objective. Finally, the references cited by the nine publications were examined, revealing one more usable publication, from 1963. Thus, the total number of publications ultimately identified as usable for analysis was 10.
Results The 10 publications dealing with the heredity of bruxism are summarised in Tables 1–3. Table 1 details the study type, study design, diagnosis and diagnostic approach. Table 2 provides information about the characteristics of the study subjects. Table 3 summarises the results and the authors’ conclusions, as well as containing a number of explanatory notes. Four of the 10 publications concerned family studies (2–5). The studies in question investigated whether the reported prevalence of bruxism was higher in the families of bruxists than in families of non-bruxists. Reding et al. (2), Abe and Shimakawa (3) and Olkinuora (4) all used a case–control study design, while Lavigne et al. (5) reported the results of a previously unpublished cohort study in the context of a literature survey. Hence, the characteristics of the subjects of the latter study are not available (Table 2). The study considered only the presence or absence of sleep bruxism, as determined by sleep registration (polysomnography – the golden standard technique for the definite diagnosis (1) of sleep bruxism). The
Table 1. Studies into the heredity of bruxism: study type, study design, diagnosis and basis of diagnosis Author(s)
Year
Study type
Study design
Diagnosis
Diagnostic approach
Horowitz (6) Reding et al. (2) Abe and Shimakawa (3) Olkinuora (4) Lindqvist (7) Hublin et al. (8) Michalowicz et al. (9) Lavigne et al. (5)
1963 1966 1966
Twin study Family study Family study
Concordance study Case–control study Case–control study
Teeth-grinding Sleep bruxism Sleep bruxism
Attrition (study casts) Questionnaire Questionnaire (see note, Table 3)
1972 1974 1998 2000
Family study Twin study Twin study Twin study
Case–control study Concordance study Concordance study Concordance study
2008
Family study
Cohort study
Oral history and/or attrition (clinical) Attrition (clinical and study casts) Questionnaire Questionnaire and clinical examination Polysomnography
Abe et al. (11)
2012
Case–control study (DNA analysis)
Rintakoski et al. (10)
2012
Population study (patients and staff at a university clinic) Twin study
Teeth-grinding Teeth-grinding Sleep bruxism Teeth-grinding/ clenching Sleep bruxism (teeth-grinding) Sleep bruxism
Sleep bruxism
Questionnaire
Concordance study
Clinical examination and electromyography (BiteStrip)
© 2014 John Wiley & Sons Ltd
© 2014 John Wiley & Sons Ltd
2012
1141 pairs of twins (MZ = 333%)
SB, Sleep bruxism; Co, controls; MZ, monozygotic; DZ, dizygotic; W, women.
Rintakoski et al. (10)
2008 2012
117 pairs of twins (MZ = 239%) 3717 pairs of same-sex twins (MZ = 349%) 494 pairs of twins (MZ or DZ known for 242 pairs; MZ = 603%) Unknown SB = 66; Co = 48
1972
1974 1998 2000
Bruxists with stress problems = 34; without stress problems = 35
1966
Abe and Shimakawa (3) Olkinuora (4)
Lindqvist (7) Hublin et al. (8) Michalowicz et al. (9) Lavigne et al. (5) Abe et al. (11)
Unknown Children with SB = 175; Young adults with Co = 982 SB = 117; Co = 2173 Children SB = 39; Co = 297
1963 1966
Horowitz (6) Reding et al. (2)
Number
Year
Author(s)
Table 2. Studies into the heredity of bruxism: characteristics of the subjects
Young adults: 16–36 years
Unknown SB = 305 83 years; Co = 330 114 years Young adults: 24; 23–27 years
With stress problems = 351 106 years; without stress problems = 367 147 years 121 (108–141) years Adults: 44 78; 33–60 years 464 123 (16–80) years
3 years
Unknown Children: 3–17 years
Age
Young adults (SB): W = 385%
Roughly 50%–50%
Unknown SB: W = 485%; Co: W = 521%
Roughly 50%–50% Roughly 50%–50% W = 64%
With stress problems: W = 824%; without stress problems: W = 857%
Unknown Children (SB): W = 40% Unknown
Gender
BRUXISM AND GENETICS: REVIEW 3
1972
1974
1998
2000
2008
Olkinuora (4)
Lindqvist (7)
Hublin et al. (8)
Michalowicz et al. (9)
Lavigne et al. (5)
Similar attrition patterns are more common in MZ twins (393%) than in DZ twins (112%) The (retrospectively recorded) variance in youth SB is 49% genetically determined in men and 64% genetically determined in women. The (cross-sectional) figures for adult SB are 39% and 53%, respectively. The correlation between youth SB and adult SB is 095 in men and 089 in women No difference found in the incidence of teeth-grinding and/ or clenching in MZ and DZ twins. Whether a pair of twins grow up together or separately does not influence the incidence of teeth-grinding and/or clenching 37% of the teeth-grinding SB patients have at least one bruxist family member; 15% have two or more bruxist family members The C allele of the variant (‘single nucleotide polymorphism’; SNP) rs6323 of the HTR24 gene on chromosome 13 is associated with a 425-fold increase in the risk of SB. The gene in question codes for 5-HT 2A (serotonin) receptors Genetic factors determine 52% of the variance in SB, both in men and in women
Bruxists with stress problems are less likely to have a positive family history of teeth-grinding (298%) than bruxists without stress problems (643%)
A few MZ pairs of twins exhibited similar attrition patterns. The only DZ pair of twins who had suffered attrition exhibited different attrition patterns (serious attrition vs. very little attrition) There is significant association between SB and having a family member with SB, both amongst children and young adults, with no difference between the sexes Children with at least one parent with (a history of) SB exhibit more SB (513%) than children without a bruxist parent (306%)
Results
SB, Sleep bruxism; MZ, monozygotic; DZ, dizygotic.
2012
1966
Abe and Shimakawa (3)
Rintakoski et al. (10)
1966
Reding et al. (2)
2012
1963
Horowitz (6)
Abe et al. (11)
Year
Author(s)
Table 3. Studies into the heredity of bruxism: results, conclusion and notes
Report is based on the author’s personal interest in the role of genetic and environmental factors in various dental conditions The study was intended primarily to determine the incidence of bruxism (as evidenced by attrition) in children and young adults It is unclear whether – in addition to the questionnaire study – the parents of subjects were interviewed and/or clinical research was undertaken to establish whether the subjects suffered from SB It is unclear to what extent additional clinical observations (jaw muscle pain/fatigue; limited mouth opening) were involved in the diagnosis of bruxism The presence of attrition was interpreted as indicative of bruxism Data were analysed by means of structural equation modelling to determine the relative contribution of genetic and environmental factors to the variance in SB
Attrition may be genetically determined, at least in part
Sleep bruxism may be genetically determined, at least in part
Genetic factors determine the variance in sleep bruxism to a substantial degree
Data were analysed by means of quantitative genetic modelling
Data were subjected to multivariate stepwise logistic regression analysis (multiple psychological, behavioural and genetic variables included in the analysis)
Data are unpublished (attributed to S. Khoury et al.) and form part of a review
Sleep bruxism/teeth-grinding appears to be partly genetically determined Genetic factors may contribute to the aetiology of sleep bruxism
Data were analysed using generalised estimating equations (GEEs)
Genetic factors do not play a role in teeth-grinding and/or clenching, nor do environmental factors
Genetic factors play a role in the incidence and patterns of attrition Sleep bruxism is a persistent condition, determined to a significant extent by genetic factors
Genetic factors play a role, mainly in bruxists without stress problems
Sleep bruxism may be genetically determined, at least in part
Notes
Conclusion
4
F . L O B B E Z O O et al.
© 2014 John Wiley & Sons Ltd
BRUXISM AND GENETICS: REVIEW four family studies all led to the conclusion that bruxism appears to be partly genetically determined. Five of the 10 publications described the findings of twin studies, all of which used a concordance study design (6–10). Concordance is the extent to which both of a pair of twins share a given condition. A concordance study involves the analysis of concordance data to establish whether a given condition (in this case bruxism) is more prevalent in monozygotic twins than in dizygotic twins. If the concordance of the condition of interest is significantly higher in monozygotic twins as compared to dizygotic twins, heredity plays a role in the development or perpetuation of that condition. The basis for that conclusion being that monozygotic twins are genetically identical, while dizygotic twins share only about 50% of their genetic material. Like the family studies, most of the twin studies led to the conclusion that bruxism is at least partly determined by genetic factors; according to Hublin et al. (8) and Rintakoski et al. (10), the genetic contribution is substantial. Only Michalowicz et al. (9) concluded that neither genetic nor environmental factors play a role in bruxism. One publication described a DNA analysis (11). The reported study was concerned with the identification of genetic markers for sleep bruxism. A case–control study design was used with the focus on genetic factors connected with the metabolism of serotonin – a neurotransmitter believed to play a role in the aetiology of bruxism (12). Abe et al. (11) found that a particular variant of the HTR24 gene on chromosome 13, which codes for certain serotonin receptors, is associated with a 425-fold increase in the risk of sleep bruxism. Accordingly, the authors concluded that genetic factors could contribute to the aetiology of sleep bruxism.
Discussion This article describes the first systematic literature study into the heredity of bruxism. Although there is considerable variety among the publications included, both in terms of the research methods used and the characteristics of the research subjects, most of the findings indicate that bruxism has a genetic component. That observation confirms the findings of Hublin and Kaprio (13), who – on the basis of a traditional (non-systematic) literature study – concluded that genetic factors play a significant role in the © 2014 John Wiley & Sons Ltd
incidence of bruxism. Hublin and Kaprio acknowledged that the precise genetic mechanisms involved and the manner of transmission were unknown. Lavigne et al. (5) were a little more cautious, concluding on the basis of a non-systematic analysis of the literature then available that it was unclear whether bruxism was genetically determined. The authors emphasised that future research should make use of valid quantitative techniques to establish the presence or absence of bruxism. However, our systematic analysis of the literature indicates that it is probable that bruxism does indeed have a significant genetic cause, although this may not be the sole cause. It is not clear why Michalowicz et al. (9) were unable to identify any role for genetic factors in the causation of bruxism. Half of the publications included related to twin studies. The concordance analyses that twin studies involve provide strong evidence as to whether a condition is at least partly hereditary. That is not the case with family studies – the category into which four of the ten included studies fall. Although a family study can indicate whether bruxism is hereditary, it cannot provide conclusive evidence, because it is possible that the reported bruxism is a manifestation of learned behaviour. Neither twin studies nor family studies can shed light on the physiological mechanisms involved in bruxism. That requires DNA analysis – the study method used in only one of the included studies (11). That study is, however, limited to a single set of gene variants associated with serotonin metabolism. Additionally, genome-wide research would be required to establish the overall genetic contribution to bruxism. A great deal has been written and said about the diagnosis of bruxism. Recently, international consensus has been reached as to how the presence of sleep bruxism and/or awake bruxism may be determined with reasonable certainty (1). The importance of such a consensus is underlined by the fact that bruxism was diagnosed in a variety of different ways for the studies included in our systematic analysis. Many of the studies made use of questionnaires, while the presence of attrition was also regularly used as a basis for diagnosis. Questionnaires have the disadvantage that the quality of the findings depends on the extent to which the subject is aware of his or her teethgrinding. The use of attrition as a basis for diagnosis has the drawback that attrition is an irreversible process, meaning that evidence of attrition does not
5
6
F . L O B B E Z O O et al. necessarily indicate a current bruxism problem. Furthermore, attrition cannot always be distinguished from other forms of dental wear, such as erosion and abrasion. Hence, the only way of establishing with reasonable certainty whether a person suffers from bruxism is to use a more complex technique, such as polysomnography (5) or electromyography (11). Polysomnography is expensive, however, and unavailable in many cases. Electromyography has a drawback in the context of sleep bruxism diagnosis, insofar as the subject’s consciousness cannot be taken into account. Abe et al. (11) used a ‘BiteStrip’: a surface electrode, which is attached to the skin over a jaw muscle while the subject sleeps, and which displays the number of bruxism instances per hour of sleep, which is then recorded when the patient awakes. However, the validity of this simple electromyographic device has not been demonstrated. The reader should therefore be cautious about interpreting the findings of Abe et al. (11).
Concluding observations Relatively few studies have been performed with a view to establishing whether bruxism is hereditary. A structured search of biomedical literature identified 10 publications. Systematic analysis of those studies suggests that bruxism is partly genetically determined. Therefore, when asked by a patient whether teethgrinding runs in families, a dentist may answer with a cautious ‘Yes’.
Acknowledgments This paper is a translated version of the Dutch article ‘Ook tandenknarsen is erfelijk’ by F. Lobbezoo et al., published in ACTA Quality Practice, 2014, with permission from Prelum Publishers, Houten, The Netherlands.
Ethical considerations Not applicable.
Conflicts of interest No conflict of interests declared.
References 1. Lobbezoo F, Ahlberg J, Glaros AG, Kato T, Koyano K, Lavigne GJ et al. Bruxism defined and graded: an international consensus. J Oral Rehabil. 2013;40:2–4. 2. Reding GR, Rubright WC, Zimmerman SO. Incidence of bruxism. J Dent Res. 1966;45:1198–1204. 3. Abe K, Shimakawa M. Genetic and developmental aspects of sleeptalking and teeth-grinding. Acta Paedopsychiatr. 1966;33:339–344. 4. Olkinuora M. A psychosomatic study of bruxism with emphasis on mental strain and familiar predisposition factors. Proc Finn Dent Soc. 1972;68:110–123. 5. Lavigne GJ, Khoury S, Abe S, Yamaguchi T, Raphael K. Bruxism physiology and pathology: an overview for clinicians. J Oral Rehabil. 2008;35:476–494. 6. Horowitz SL. Clinical aspects of genetic research in dentistry. J Dent Res. 1963;42(Suppl):1330–1343. 7. Lindqvist B. Bruxism in twins. Acta Odontol Scand. 1974;32:177–187. 8. Hublin C, Kaprio J, Partinen M, Koskenvuo M. Sleep bruxism based on self-report in a nationwide twin cohort. J Sleep Res. 1998;7:61–67. 9. Michalowicz BS, Pihlstrom BL, Hodges JS, Bouchard TJ Jr. No heritability of temporomandibular joint signs and symptoms. J Dent Res. 2000;79:1573–1578. 10. Rintakoski K, Hublin C, Lobbezoo F, Rose RJ, Kaprio J. Genetic factors account for half of the phenotypic variance in liability to sleep-related bruxism in young adults: a nationwide Finnish twin cohort study. Twin Res Hum Genet. 2012;15:714–719. 11. Abe Y, Suganuma T, Ishii M, Yamamoto G, Gunji T, Clark GT et al. Association of genetic, psychological and behavioral factors with sleep bruxism in a Japanese population. J Sleep Res. 2012;21:289–296. 12. Winocur E, Gavish A, Voikovitch M, Emodi-Perlman A, Eli I. Drugs and bruxism: a critical review. J Orofac Pain. 2003;17:99–111. 13. Hublin C, Kaprio J. Genetic aspects and genetic epidemiology of parasomnias. Sleep Med Rev. 2003;7:413–421. Correspondence: Frank Lobbezoo, Department of Oral Kinesiology, Academic Centre for Dentistry Amsterdam (ACTA), Gustav Mahlerlaan 3004, 1081 LA Amsterdam, The Netherlands. E-mail: [email protected]
Funding This research was carried out without funding.
© 2014 John Wiley & Sons Ltd
Oral Rehabilitation
Journal of Oral Rehabilitation 2014
Review
Bruxism and genetics: a review of the literature F. LOBBEZOO*, C. M. VISSCHER*, J. AHLBERG† & D. MANFREDINI‡
*Department of
Oral Kinesiology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, MOVE Research Institute Amsterdam, Amsterdam, The Netherlands, †Department of Stomatognathic Physiology and Prosthetic Dentistry, Institute of Dentistry, University of Helsinki, Helsinki, Finland and ‡Department of Maxillofacial Surgery, TMD Clinic, University of Padova, Padova, Italy
SUMMARY People who suffer from bruxism (teethgrinding) often ask their dentists whether their condition is hereditary. The purpose of this study is to enable dentists to provide an ‘evidence-based’ answer to this question. The biomedical literature was searched using PubMed, and 32 publications were identified, of which nine proved relevant to the research question. The references cited by the publications identified yielded one further publication, bringing the total number of publications included in the analysis to 10. Four publications related to family studies, five related
Introduction Sleeping near to someone who grinds their teeth can be difficult. The noise is penetrating and, although the ‘perpetrator’ usually sleeps well, the person subjected to the noise (the ‘victim’) often experiences sleep disturbance. Not surprisingly, therefore, patients – urged by their loved ones – frequently turn to their dentists for help. In such cases, reference is often made to the fact that other members of the family grind their teeth as well. The anecdotal evidence encountered in dental practice points strongly to the conclusion that teethgrinding is hereditary. Most people who talk to their dentists about teeth-grinding problems say that one or more family members grind their teeth as well. This information is often given spontaneously, without the dentist asking; the possibility that the condition may run in the family is clearly something that people wonder about. Nevertheless, in © 2014 John Wiley & Sons Ltd
to twin studies and one related to a DNA analysis. With the exception of one of the twin studies, all the included studies concluded that bruxism appears to be (in part) genetically determined. Dentists whose patients ask them about bruxism can therefore tell them that teeth-grinding does indeed ‘run in families’. KEYWORDS: bruxism, heredity, systematic review Accepted for publication 3 April 2014
the practice of modern evidence-based dentistry, the question arises: is there sound scientific data to support the anecdotal evidence? Hence, the study described in this article sought to establish whether teeth-grinding – bruxism (1) – is indeed hereditary. The study’s findings can be used to give authoritative answers to the many patients who raise the question.
Methods In December 2013, PubMed (US National Library of Medicine) was searched using the following query: ‘Bruxism’[Mesh] AND (genetic* OR heredit*). The search was restricted to English language literature. It yielded 32 publications, from the period 1966 to 2012. The titles and (where available) the abstracts of the publications were examined to establish whether the publications could shed light on the research question. doi: 10.1111/joor.12177
2
F . L O B B E Z O O et al. Twenty-three of the 32 publications were judged to be unusable on the basis of their title and abstract. The reasons for excluding the studies in question were as follows: 1 Literature reviews: n = 4 2 Case reports: n = 3 3 Letters to the editor: n = 1 4 Bruxism as comorbidity associated with a hereditary condition: n = 8
5 6 7 8 9
a Prader–Willi syndrome: n = 1 b Down’s syndrome: n = 2 c Nocturnal frontal lobe epilepsy: n = 1 d Rett syndrome: n = 1 e Huntington’s disease: n = 2 f Cerebral paresis: n = 1 Indirect evidence of bruxism (torus palatinus): n=3 Oral health without focus on bruxism: n = 1 Association between bruxism and nicotine use: n=1 Personality characteristics associated with bruxism: n=1 Epidemiological characteristics of bruxism: n = 1
Five of the 32 publications were immediately identified as usable, and a further four publications appeared to be usable from their titles, but lacked abstracts. The latter four publications were therefore read in full, after which all were found to support the
research objective. Finally, the references cited by the nine publications were examined, revealing one more usable publication, from 1963. Thus, the total number of publications ultimately identified as usable for analysis was 10.
Results The 10 publications dealing with the heredity of bruxism are summarised in Tables 1–3. Table 1 details the study type, study design, diagnosis and diagnostic approach. Table 2 provides information about the characteristics of the study subjects. Table 3 summarises the results and the authors’ conclusions, as well as containing a number of explanatory notes. Four of the 10 publications concerned family studies (2–5). The studies in question investigated whether the reported prevalence of bruxism was higher in the families of bruxists than in families of non-bruxists. Reding et al. (2), Abe and Shimakawa (3) and Olkinuora (4) all used a case–control study design, while Lavigne et al. (5) reported the results of a previously unpublished cohort study in the context of a literature survey. Hence, the characteristics of the subjects of the latter study are not available (Table 2). The study considered only the presence or absence of sleep bruxism, as determined by sleep registration (polysomnography – the golden standard technique for the definite diagnosis (1) of sleep bruxism). The
Table 1. Studies into the heredity of bruxism: study type, study design, diagnosis and basis of diagnosis Author(s)
Year
Study type
Study design
Diagnosis
Diagnostic approach
Horowitz (6) Reding et al. (2) Abe and Shimakawa (3) Olkinuora (4) Lindqvist (7) Hublin et al. (8) Michalowicz et al. (9) Lavigne et al. (5)
1963 1966 1966
Twin study Family study Family study
Concordance study Case–control study Case–control study
Teeth-grinding Sleep bruxism Sleep bruxism
Attrition (study casts) Questionnaire Questionnaire (see note, Table 3)
1972 1974 1998 2000
Family study Twin study Twin study Twin study
Case–control study Concordance study Concordance study Concordance study
2008
Family study
Cohort study
Oral history and/or attrition (clinical) Attrition (clinical and study casts) Questionnaire Questionnaire and clinical examination Polysomnography
Abe et al. (11)
2012
Case–control study (DNA analysis)
Rintakoski et al. (10)
2012
Population study (patients and staff at a university clinic) Twin study
Teeth-grinding Teeth-grinding Sleep bruxism Teeth-grinding/ clenching Sleep bruxism (teeth-grinding) Sleep bruxism
Sleep bruxism
Questionnaire
Concordance study
Clinical examination and electromyography (BiteStrip)
© 2014 John Wiley & Sons Ltd
© 2014 John Wiley & Sons Ltd
2012
1141 pairs of twins (MZ = 333%)
SB, Sleep bruxism; Co, controls; MZ, monozygotic; DZ, dizygotic; W, women.
Rintakoski et al. (10)
2008 2012
117 pairs of twins (MZ = 239%) 3717 pairs of same-sex twins (MZ = 349%) 494 pairs of twins (MZ or DZ known for 242 pairs; MZ = 603%) Unknown SB = 66; Co = 48
1972
1974 1998 2000
Bruxists with stress problems = 34; without stress problems = 35
1966
Abe and Shimakawa (3) Olkinuora (4)
Lindqvist (7) Hublin et al. (8) Michalowicz et al. (9) Lavigne et al. (5) Abe et al. (11)
Unknown Children with SB = 175; Young adults with Co = 982 SB = 117; Co = 2173 Children SB = 39; Co = 297
1963 1966
Horowitz (6) Reding et al. (2)
Number
Year
Author(s)
Table 2. Studies into the heredity of bruxism: characteristics of the subjects
Young adults: 16–36 years
Unknown SB = 305 83 years; Co = 330 114 years Young adults: 24; 23–27 years
With stress problems = 351 106 years; without stress problems = 367 147 years 121 (108–141) years Adults: 44 78; 33–60 years 464 123 (16–80) years
3 years
Unknown Children: 3–17 years
Age
Young adults (SB): W = 385%
Roughly 50%–50%
Unknown SB: W = 485%; Co: W = 521%
Roughly 50%–50% Roughly 50%–50% W = 64%
With stress problems: W = 824%; without stress problems: W = 857%
Unknown Children (SB): W = 40% Unknown
Gender
BRUXISM AND GENETICS: REVIEW 3
1972
1974
1998
2000
2008
Olkinuora (4)
Lindqvist (7)
Hublin et al. (8)
Michalowicz et al. (9)
Lavigne et al. (5)
Similar attrition patterns are more common in MZ twins (393%) than in DZ twins (112%) The (retrospectively recorded) variance in youth SB is 49% genetically determined in men and 64% genetically determined in women. The (cross-sectional) figures for adult SB are 39% and 53%, respectively. The correlation between youth SB and adult SB is 095 in men and 089 in women No difference found in the incidence of teeth-grinding and/ or clenching in MZ and DZ twins. Whether a pair of twins grow up together or separately does not influence the incidence of teeth-grinding and/or clenching 37% of the teeth-grinding SB patients have at least one bruxist family member; 15% have two or more bruxist family members The C allele of the variant (‘single nucleotide polymorphism’; SNP) rs6323 of the HTR24 gene on chromosome 13 is associated with a 425-fold increase in the risk of SB. The gene in question codes for 5-HT 2A (serotonin) receptors Genetic factors determine 52% of the variance in SB, both in men and in women
Bruxists with stress problems are less likely to have a positive family history of teeth-grinding (298%) than bruxists without stress problems (643%)
A few MZ pairs of twins exhibited similar attrition patterns. The only DZ pair of twins who had suffered attrition exhibited different attrition patterns (serious attrition vs. very little attrition) There is significant association between SB and having a family member with SB, both amongst children and young adults, with no difference between the sexes Children with at least one parent with (a history of) SB exhibit more SB (513%) than children without a bruxist parent (306%)
Results
SB, Sleep bruxism; MZ, monozygotic; DZ, dizygotic.
2012
1966
Abe and Shimakawa (3)
Rintakoski et al. (10)
1966
Reding et al. (2)
2012
1963
Horowitz (6)
Abe et al. (11)
Year
Author(s)
Table 3. Studies into the heredity of bruxism: results, conclusion and notes
Report is based on the author’s personal interest in the role of genetic and environmental factors in various dental conditions The study was intended primarily to determine the incidence of bruxism (as evidenced by attrition) in children and young adults It is unclear whether – in addition to the questionnaire study – the parents of subjects were interviewed and/or clinical research was undertaken to establish whether the subjects suffered from SB It is unclear to what extent additional clinical observations (jaw muscle pain/fatigue; limited mouth opening) were involved in the diagnosis of bruxism The presence of attrition was interpreted as indicative of bruxism Data were analysed by means of structural equation modelling to determine the relative contribution of genetic and environmental factors to the variance in SB
Attrition may be genetically determined, at least in part
Sleep bruxism may be genetically determined, at least in part
Genetic factors determine the variance in sleep bruxism to a substantial degree
Data were analysed by means of quantitative genetic modelling
Data were subjected to multivariate stepwise logistic regression analysis (multiple psychological, behavioural and genetic variables included in the analysis)
Data are unpublished (attributed to S. Khoury et al.) and form part of a review
Sleep bruxism/teeth-grinding appears to be partly genetically determined Genetic factors may contribute to the aetiology of sleep bruxism
Data were analysed using generalised estimating equations (GEEs)
Genetic factors do not play a role in teeth-grinding and/or clenching, nor do environmental factors
Genetic factors play a role in the incidence and patterns of attrition Sleep bruxism is a persistent condition, determined to a significant extent by genetic factors
Genetic factors play a role, mainly in bruxists without stress problems
Sleep bruxism may be genetically determined, at least in part
Notes
Conclusion
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F . L O B B E Z O O et al.
© 2014 John Wiley & Sons Ltd
BRUXISM AND GENETICS: REVIEW four family studies all led to the conclusion that bruxism appears to be partly genetically determined. Five of the 10 publications described the findings of twin studies, all of which used a concordance study design (6–10). Concordance is the extent to which both of a pair of twins share a given condition. A concordance study involves the analysis of concordance data to establish whether a given condition (in this case bruxism) is more prevalent in monozygotic twins than in dizygotic twins. If the concordance of the condition of interest is significantly higher in monozygotic twins as compared to dizygotic twins, heredity plays a role in the development or perpetuation of that condition. The basis for that conclusion being that monozygotic twins are genetically identical, while dizygotic twins share only about 50% of their genetic material. Like the family studies, most of the twin studies led to the conclusion that bruxism is at least partly determined by genetic factors; according to Hublin et al. (8) and Rintakoski et al. (10), the genetic contribution is substantial. Only Michalowicz et al. (9) concluded that neither genetic nor environmental factors play a role in bruxism. One publication described a DNA analysis (11). The reported study was concerned with the identification of genetic markers for sleep bruxism. A case–control study design was used with the focus on genetic factors connected with the metabolism of serotonin – a neurotransmitter believed to play a role in the aetiology of bruxism (12). Abe et al. (11) found that a particular variant of the HTR24 gene on chromosome 13, which codes for certain serotonin receptors, is associated with a 425-fold increase in the risk of sleep bruxism. Accordingly, the authors concluded that genetic factors could contribute to the aetiology of sleep bruxism.
Discussion This article describes the first systematic literature study into the heredity of bruxism. Although there is considerable variety among the publications included, both in terms of the research methods used and the characteristics of the research subjects, most of the findings indicate that bruxism has a genetic component. That observation confirms the findings of Hublin and Kaprio (13), who – on the basis of a traditional (non-systematic) literature study – concluded that genetic factors play a significant role in the © 2014 John Wiley & Sons Ltd
incidence of bruxism. Hublin and Kaprio acknowledged that the precise genetic mechanisms involved and the manner of transmission were unknown. Lavigne et al. (5) were a little more cautious, concluding on the basis of a non-systematic analysis of the literature then available that it was unclear whether bruxism was genetically determined. The authors emphasised that future research should make use of valid quantitative techniques to establish the presence or absence of bruxism. However, our systematic analysis of the literature indicates that it is probable that bruxism does indeed have a significant genetic cause, although this may not be the sole cause. It is not clear why Michalowicz et al. (9) were unable to identify any role for genetic factors in the causation of bruxism. Half of the publications included related to twin studies. The concordance analyses that twin studies involve provide strong evidence as to whether a condition is at least partly hereditary. That is not the case with family studies – the category into which four of the ten included studies fall. Although a family study can indicate whether bruxism is hereditary, it cannot provide conclusive evidence, because it is possible that the reported bruxism is a manifestation of learned behaviour. Neither twin studies nor family studies can shed light on the physiological mechanisms involved in bruxism. That requires DNA analysis – the study method used in only one of the included studies (11). That study is, however, limited to a single set of gene variants associated with serotonin metabolism. Additionally, genome-wide research would be required to establish the overall genetic contribution to bruxism. A great deal has been written and said about the diagnosis of bruxism. Recently, international consensus has been reached as to how the presence of sleep bruxism and/or awake bruxism may be determined with reasonable certainty (1). The importance of such a consensus is underlined by the fact that bruxism was diagnosed in a variety of different ways for the studies included in our systematic analysis. Many of the studies made use of questionnaires, while the presence of attrition was also regularly used as a basis for diagnosis. Questionnaires have the disadvantage that the quality of the findings depends on the extent to which the subject is aware of his or her teethgrinding. The use of attrition as a basis for diagnosis has the drawback that attrition is an irreversible process, meaning that evidence of attrition does not
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F . L O B B E Z O O et al. necessarily indicate a current bruxism problem. Furthermore, attrition cannot always be distinguished from other forms of dental wear, such as erosion and abrasion. Hence, the only way of establishing with reasonable certainty whether a person suffers from bruxism is to use a more complex technique, such as polysomnography (5) or electromyography (11). Polysomnography is expensive, however, and unavailable in many cases. Electromyography has a drawback in the context of sleep bruxism diagnosis, insofar as the subject’s consciousness cannot be taken into account. Abe et al. (11) used a ‘BiteStrip’: a surface electrode, which is attached to the skin over a jaw muscle while the subject sleeps, and which displays the number of bruxism instances per hour of sleep, which is then recorded when the patient awakes. However, the validity of this simple electromyographic device has not been demonstrated. The reader should therefore be cautious about interpreting the findings of Abe et al. (11).
Concluding observations Relatively few studies have been performed with a view to establishing whether bruxism is hereditary. A structured search of biomedical literature identified 10 publications. Systematic analysis of those studies suggests that bruxism is partly genetically determined. Therefore, when asked by a patient whether teethgrinding runs in families, a dentist may answer with a cautious ‘Yes’.
Acknowledgments This paper is a translated version of the Dutch article ‘Ook tandenknarsen is erfelijk’ by F. Lobbezoo et al., published in ACTA Quality Practice, 2014, with permission from Prelum Publishers, Houten, The Netherlands.
Ethical considerations Not applicable.
Conflicts of interest No conflict of interests declared.
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Funding This research was carried out without funding.
© 2014 John Wiley & Sons Ltd
