Objectives: The aim of the present study was to examine the role of genetic and environmental factors in the phenotypic variance of bruxism in a large population-based cohort of young adult twins in Finland.

Methods: The material of the present study derives from the FinnTwin16 cohort study consisting of five birth cohorts of twin pairs born in 1975–1979 who completed a questionnaire (at mean age 24, range 23–27 years) with data on frequency of sleep-related bruxism in 2000–2002. We used quantitative genetic modeling, based on the genetic similarity of monozygotic and dizygotic twins, to estimate the most probable genetic model for bruxism, based on decomposition of phenotypic variance into components: additive genetic effects (A), dominant genetic effects (D), and non-shared environmental effects (E).

Results: On average, 8.7% experienced bruxism weekly, 23.4% rarely, and 67.9% never, with no significant gender difference (p = .052). The best fitting genetic model for bruxism was the AE-model. Additive genetic effects accounted for 52% (95% CI 0.41–0.62) of the total phenotypic variance. Sex-limitation model revealed no gender differences.

Conclusions: Genetic factors account for a substantial proportion of the phenotypic variation of the liability to sleep-related bruxism, with no gender difference in its genetic architecture.

Dentists often use occlusal splints in the management of occlusodontic problems. Because they are considered to provide non-invasive and reversible treatment they are therapeutic devices that conform well to the current philosophy governing protocols for therapy of the masticatory system. Proper design and placement of occlusal splints requires that they respond to precise indications and that practitioners fabricate and maintain them with scrupulous care to assure that patients benefit from them. Splints help practitioners adjust the relationship between the jaws either by suppressing blockage of teeth to relax muscles or by repositioning the condyles in the articular fossas to recapture discs or to reduce painful excess intra-articular pressure derived from degenerative diseases.

Occlusal splints are also suitable as diagnostic tools to validate and evaluate contributions of behavioral, postural, and psychosocial factors to the multifactorial etiology of malfunctions of the masticatory apparatus. The simple introduction into a patient’s mouth of an appliance whose benefits have been well described to that patient will serve as a forward step in the psychological management of a TMD problem, especially if bruxism is one of its components.

Without realizing it, orthodontists may find themselves treating patients suffering from cranio-mandibular disorders, who may be adults, but not necessarily. Both young children and adolescents can also have these problems. Orthodontists often fall into the trap of not recognizing these disorders especially when the clinical signs are discreet or even non-existent. In order to save orthodontists from encountering unpleasant post-treatment surprises, we present in this paper a review of some of the indications of the etiology of craniomandibular dysfunction, how to diagnose it, and the importance of its major clinical signs that can be a great help to them in achieving a keener state of vigilance in this regard throughout orthodontic therapy.