title: Inflammatory pain memory facilitates occlusal interference-induced masticatory muscle hyperalgesia in rats.
abstract: BACKGROUND
  Patients with an orofacial pain history appear to be more susceptible to occlusal interference pain in dental practice for unknown reasons. Pain memory has a critical function in subsequent pain perception. This study aims to explore whether orofacial pain memory could affect the masticatory muscle pain perception for occlusal interference.
  
  
  METHODS
  Cross-injection of 2% carrageenan into bilateral masseters in male rats was carried out to establish the inflammatory pain memory model. The effects of pain memory on masseter muscle nociception were tested by applying crowns with heights beyond the occlusal plane by 0.2 or 0.4 mm onto a maxillary molar 2 weeks after inflammation in the right masseter. The 0.4-mm crowns were removed on day 2 or day 4 after application to further confirm the effects of pain memory. Moreover, memory impairment was established using ibotenic acid (IBO) infusion into the bilateral hippocampus, followed by behaviour tests, including the Morris water maze test and the locomotor activity test. The relationship between pain memory and occlusal interference-induced masseter muscle pain perception was subsequently re-examined. The head withdrawal thresholds of masseters on both sides were measured to reflect the perception.
  
  
  RESULTS
  Inflammatory pain memory aggravated the 0.2-mm crown-induced mechanical hyperalgesia of the masseters, but not in the 0.4-mm crown group. However, the recovery of the 0.4-mm crown-induced mechanical hyperalgesia was postponed. The effects of pain memory were reversed in rats with impaired mnemonic function of the hippocampus.
  
  
  CONCLUSIONS
  Inflammatory pain memory facilitated occlusal interference-induced masseter muscle pain.
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: T-T
authors.initials: TT
authors.lastname: Ding
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: X-X
authors.initials: XX
authors.lastname: Xu
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: C-R
authors.initials: CR
authors.lastname: Liu
authors.affiliation: Central Laboratory and Center for TMD & Orofacial Pain, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Gan
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing, China.|Center for Oral Functional Diagnosis, Treatment and Research, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: Q-F
authors.initials: QF
authors.lastname: Xie
mesh_terms: D000818:Animals; D002351:Carrageenan; D005157:Facial Pain / Q000209:etiology* / Q000523:psychology*; D006930:Hyperalgesia / Q000209:etiology* / Q000523:psychology*; D007051:Ibotenic Acid; D007249:Inflammation / Q000150:complications* / Q000523:psychology*; D008297:Male; D008410:Masticatory Muscles / Q000503:physiopathology*; D018782:Maze Learning; D008568:Memory; D008569:Memory Disorders / Q000139:chemically induced / Q000523:psychology; D009043:Motor Activity; D059225:Nociception; D058748:Pain Perception; D017288:Pain Threshold; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007051:Ibotenic Acid; D002351:Carrageenan