title: Association between estrogen levels and temporomandibular disorders: a systematic literature review.
abstract: BACKGROUND
  To evaluate whether the hypothesis that estrogen levels are associated with temporomandibular disorders (TMD) in humans can be confirmed or contradicted by available literature.
  
  
  METHODS
  A systematic review based on the content of PubMed, Scopus, and Cochrane Library databases was performed. Studies were identified using a combination of key words 'temporomandibular disorder' and 'estrogen'. Nine studies were included into our review.
  
  
  RESULTS
  The relationship between estrogen levels and TMD was found in seven out of nine reviewed papers. Results from two papers suggest that a high estrogen level is associated with an increased prevalence of TMD. Five additional papers found a relationship between a low estrogen level and an increase in TMD pain. In considering the value of evidence and inconsistencies of results in the reviewed publications, we state that there is weak evidence to support the hypothesis that estrogen levels are associated with TMD.
  
  
  CONCLUSIONS
  Results of reviewed studies were divergent and sometimes contradictory. One possible explanation is that estrogen influences TMD pain processing differently than temporomandibular joints (TMJ) structures, as shown in many animal studies. Estrogen may influence TMD pain processing differently than TMJ structures. We suggest consideration of the dual action of estrogen when planning future studies on its association with TMD.
authors: Department of Functional Masticatory Disorders, Medical University of Lublin, Lublin, Poland.
authors: Marcin
authors: M
authors: Berger
authors: Department of Prosthetic Dentistry, Medical University of Lublin, Lublin, Poland.
authors: Leszek
authors: L
authors: Szalewski
authors: Department of Functional Masticatory Disorders, Medical University of Lublin, Lublin, Poland.
authors: Magdalena
authors: M
authors: Bakalczuk
authors: Department of Obstetrics, Gynaecology and Obstetrical-Gynaecological Nursing, Medical University of Lublin, Lublin, Poland.
authors: Grzegorz
authors: G
authors: Bakalczuk
authors: Non-Public Health Care Unit 'Ovum Reproduction and Andrology', Lublin, Poland.
authors: Szymon
authors: S
authors: Bakalczuk
authors: Department of Functional Masticatory Disorders, Medical University of Lublin, Lublin, Poland.
authors: Jacek
authors: J
authors: Szkutnik
keywords: estrogen level; hormone replacement therapy; menopause; temporomandibular disorders