Periodontal-Masseteric Reflexes Decrease with Tooth Pre-load

Abstract

The responses of incisal periodontal mechanoreceptors to increasing mechanical stimulation are known to follow a hyperbolic-saturating course. The implications of these properties for the reflexive control of bite-force have not been examined directly. In line with the above mentioned receptor characteristics, we hypothesized that the periodontal-masseteric reflex will reduce as a function of increasing incisal pre-load. In 10 participants, a central incisor was repeatedly tapped (0.4 N). We measured the modulation by pre-load (0.2-2.0 N) of the reflex frequency-response at and between 3 and 20 Hz. The entrainment of the reflex increased with frequency up to 20 Hz and diminished with increasing pre-load. Importantly, the hyperbolic relationship shown here between the periodontal-masseteric reflex and tooth pre-load agreed with the load/response relationships predicted by single-receptor and tooth movement studies. This study demonstrated that periodontal mechano-receptors are able to contribute to the ongoing control of only small bite-forces.

Comparison of the Physiological Properties of Human Periodontal-Masseteric Reflex Evoked by Incisor and Canine Stimulation

“…When axial pressure stimulation was applied to the maxillary molar, an inhibitory reflex occurred in the masseter muscle when the occlusal force was large, while an excitatory reflex was easily evoked when the occlusal force was small (Yamamura et al, 1993). Sowman and Türker (2008) found that the RR of incisor-driven PMR is negatively correlated with the amount of pre-load applied to the incisor. Our finding that there was a significant negative correlation between RR and BGA for the canine as well as the central incisor is consistent with their findings.…”

“…The force-encoding properties of periodontal afferents that supply anterior teeth have been described in several animal species (Hannam, 1982; Linden, 1990). While some studies have also been performed in humans, they only targeted the incisors (Türker et al, 1994, 1997; Trulsson and Johansson, 1996; Yang and Türker, 2001; Brinkworth et al, 2003; Sowman et al, 2007, 2010; Sowman and Türker, 2008; Naser-ud-Din et al, 2010). …”

“…Indeed, among the anterior teeth, the incisors, and canines play different roles in mastication in humans. The periodontal-masseteric reflex (PMR) has historically been used to understand the role of intra-oral mechanoreceptors in masticatory function, and the central incisor-driven PMR has been studied exclusively (Sessle and Schmitt, 1972; Louca et al, 1994; Türker et al, 1994; Türker and Jenkins, 2000; Sowman and Türker, 2008), while involvement of the canines has not been studied. Moreover, the mechanism that underlies the bilateral cooperation of the PMR remains unclear, although the PMR is evoked bilaterally even under unilateral stimulation.…”

“…Moreover, the mechanism that underlies the bilateral cooperation of the PMR remains unclear, although the PMR is evoked bilaterally even under unilateral stimulation. Another potential shortcoming in previous studies that used electromyographic (EMG) recording to study the PMR is the use of mass EMG potentials (Türker et al, 1997; Brinkworth et al, 2003; Sowman and Türker, 2008; Naser-ud-Din et al, 2010). Although an analysis of mass EMG potentials can provide ample information regarding the global tendency of muscle activity, small changes at the functional level of motor units (MU) may not be detected (Türker et al, 1994).…”

Mouse incising central pattern generator: Characteristics and modulation by pain

“…The effects of low threshold afferents on the CPG for mastication, such as mucosal and skin receptor afferents in the inferior alveolar nerve activated by low levels of electrical stimulation, have been studied at the segmental level and multiple studies demonstrate the phasic modulation of motoneuron excitability [22–24]. Low threshold inputs such as those from periodontal afferents can have a mixed effect on motoneuron excitability, with low tooth force levels causing excitation, while high tooth forces elicit inhibition [25–29]. The influence of sensory afferents on rhythm generation and motoneuron activation in the home cage environment has not been examined.…”