Abstract:

Objective： To investigate the effect of occlusal interference on the energy metabolism of masticatory muscle by studying the changes of adenosine triphosphate (ATP), adenosine diphosphate (ADP), inosine monophosphate (IMP), phosphocreatine, creatine, lactate and pH level in masseter muscles of rats after occlusal interference. Methods: Fifty male Sprague-Dawley rats were randomly assigned into experimental group (n=40) and control group (n=10). In experimental group, 0.4 mm thick metal crown was cemented to the upper right first molar of the rat, and maintained for 3, 7, 10, 14 d separately (n=10 for each time point). No occlusal interference was applied for control group. Bilateral masseter muscles of all the rats were acquired under general anesthesia. The samples of 5 rats in each group were fully homogenized with 0.4 mol/L perchlorate (10 mL/g). The homogenates were centrifuged, filtered and analyzed for ATP, ADP, IMP, phosphocreatine, creatine and lactate content by high performance liquid chromatography. The other samples in each group were mixed with homogenates containing 5 mmol/L sodium iodoacetate (10 mL/g), then homogenized and measured for pH value by pH meter in thermostatic water bathunder 37 degrees centigrade. Results: Compared with control group, ATP content in bilateral masseter of the rats increased  3 d after occlusal interference ［right side：(5.36±0.13) μmol/g，left side：(5.77±0.25) μmol/g］ (P<0.05), and back to normal on 7, 10 and 14 d- There was an increase in IMP ［right side：(0.21±0.03) μmol/g，left side：(0.19±0.03) μmol/g］and creatine content ［right side：(24.76±2.94) μmol/g，left side：(27.75±2.23) μmol/g］in bilateral masseter of the rats  7 d after occlusal interference (P<0.05) and no difference was detected on 3, 10, and 14 . Phosphocreatine content in bilateral masseter started to decline  7 d after occlusal interference and maintained the low level on 10 and 14 d ［right side：(10.70±0.71) μmol/g, (11.57±0.52) μmol/g, (10.74±1.39) μmol/g, left side：(10.05±0.57) μmol/g, (10.75±1.12)μmol/g, (10.61±1.15) μmol/g］(P<0.05). No change of ADP, lactate or pH level in bilateral muscles of the rats after occlusal interference was observed (P>0.05).  Conclusion: Occlusal interference influences the content of energy metabolites in masticatory muscle of rats, which may be related to the pathological process of masticatory muscles induced by occlusal interference, such as muscle pain, dysfunction and altered fiber architecture.

Key words: Dental occlusion, traumatic, Massetermuscle, Purine nucleotides, Inosine monophosphate, Phosphocreatine