Does long-term use of unstable dentures weaken jaw muscles?

Although it is well known that conventional denture wearers have lower maximum bite forces than dentate subjects, no previous studies have compared the strength of the jaw muscles between these two groups. This study compared maximum bite forces, electromyographic (EMG) activity and estimated jaw muscle strength among three groups: (i) 17 edentulous subjects using newly acquired implant-retained overdentures (seven men, 10 women; mean age 60.3 +/- 13.0 years); (ii) 10 age-matched, fully dentate subjects (five men, five women; mean age 57.9 +/- 11.0 years); and (iii) 39 young, fully dentate subjects (19 men, 20 women; mean age 24.4 +/- 3.5 years). Electromyographic activity was recorded from subjects' bilateral superficial masseter and anterior temporalis muscles while they generated maximum voluntary bite forces at the right central incisor, right first premolar and right first molar positions. Jaw muscle strength was estimated as the ratio of average EMG activity for all four muscles to the maximum bite force. At all three bite positions, edentulous subjects produced maximum bite forces that were less than half that of dentate subjects. Edentulous subjects also produced significantly less EMG activity and had significantly lower estimated jaw muscle strength. Our results suggest that weakened jaw muscles are one factor contributing to lower maximum bite forces among users of conventional dentures.