Fine motor control of the jaw following alteration of orofacial afferent inputs

Abstract

Objective: The study was designed to investigate if alteration of different orofacial afferent inputs would have different effects on oral fine motor control and to test the hypothesis that reduced afferent inputs will increase the variability of bite force values and jaw muscle activity, and repeated training with splitting of food morsel in conditions with reduced afferent inputs would decrease the variability and lead to optimization of bite force values and jaw muscle activity.

Material methods: Forty-five healthy volunteers participated in a single experimental session and were equally divided into incisal, mucosal, and block anesthesia groups. The participants performed six series (with ten trials) of a standardized hold and split task after the intervention with local anesthesia was made in the respective groups. The hold and split forces along with the corresponding jaw muscle activity were recorded and compared to a reference group.

Results: The hold force and the electromyographic (EMG) activity of the masseter muscles during the hold phase were significantly higher in the incisal and block anesthesia group, as compared to the reference group (P < 0.001). However, there was no significant effect of groups on the split force (P = 0.975) but a significant decrease in the EMG activity of right masseter in mucosal anesthesia group as compared to the reference group (P = 0.006). The results also revealed that there was no significant effect of local anesthesia on the variability of the hold and split force (P < 0.677). However, there was a significant decrease in the variability of EMG activity of the jaw closing muscles in the block anesthesia group as compared to the reference group (P < 0.041), during the hold phase and a significant increase in the variability of EMG activity of right masseter in the mucosal anesthesia group (P = 0.021) along with a significant increase in the EMG activity of anterior temporalis muscle in the incisal anesthesia group, compared to the reference group (P = 0.018), during the split phase.

Conclusions: The results of the present study indicated that altering different orofacial afferent inputs may have different effects on some aspects of oral fine motor control. Further, inhibition of afferent inputs from the orofacial or periodontal mechanoreceptors did not increase the variability of bite force values and jaw muscle activity; indicating that the relative precision of the oral fine motor task was not compromised inspite of the anesthesia. The results also suggest the propensity of optimization of bite force values and jaw muscle activity due to repeated splitting of the food morsels, inspite of alteration of sensory inputs.

Clinical relevance: Skill acquisition following a change in oral sensory environment is crucial for understanding how humans learn and re-learn oral motor behaviors and the kind of adaptation that takes place after successful oral rehabilitation procedures.

Keywords: Bite force; Local anesthesia; Optimization; Periodontal mechanoreceptors; Variability.

Fig. 1

Example of a force profile obtained from a single “hold and split” task. X-axis represents the force (N) and Y-axis represents time (s). The specific points of interest are A initial contact with the test food, B 0.2 s after the initial contact with the test food, C onset of the split defined as the point at which the force rate exceeded 5 N/s, D split force defined the peak force prior to the moment the test food split, indicated by a rapid decrease in the force. Ds duration of split defined as the time taken from the onset of the split (C) to the actual split (D). The hold force was defined as the mean of force exerted from points B to C and split force was defined as the absolute force at D

Fig. 2

Mean ± standard error of mean hold force (a), split force (b), and duration of split (c) during six series of the behavioral task in the mucosal anesthesia, incisal anesthesia, block anesthesia, and the reference group. The asterisk denote significant difference in the mucosal anesthesia (white) and the block anesthesia (black) compared to the reference group (P < 0.05). Mean ± standard error of mean of the Z scores for hold force (d), split force (e), and duration of split (f) during six series of the behavioral task in the mucosal, incisal, and block anesthesia group. The gray shades denote 90 % confidence interval (−1.64 to 1.64)

Fig. 3

Mean ± standard error of mean of variability (expressed as co efficient of variation) in hold force (a), split force (b), and duration of split (c) during six series of the behavioral task in the mucosal anesthesia, incisal anesthesia, block anesthesia, and the reference group. Mean ± standard error of mean of variability of the Z scores for hold force (d), split force (e), and duration of split (f) during six series of the behavioral task in the mucosal, incisal, and block anesthesia group. The gray shades denote 90 % confidence interval (−1.64 to 1.64)

Fig. 4

Mean ± standard error of mean of electromyographic activity (a, b) for right and left masseter (MAL and MAR); anterior temporalis (TAL) and suprahyoid (SHD) muscle in the mucosal anesthesia, incisal anesthesia, block anesthesia and the reference group during the hold phase (a) and split phase (b). The asterisk denote significant difference in the incisal anesthesia (white) and block anesthesia (black) compared to the reference group (P < 0.05). Mean ± standard error of mean of Z scores of electromyographic activity of right and left masseter (MAL and MAR); anterior temporalis (TAL) and suprahyoid (SHD) muscle in the mucosal anesthesia, incisal anesthesia, and block anesthesia during the hold phase (c) and split phase (d). The gray shades denote 90 % confidence interval (−1.64 to 1.64)

Fig. 5

Mean ± standard error of mean of variability of electromyographic activity for right and left masseter (MAL and MAR); anterior temporalis (TAL), and suprahyoid (SHD) muscle in the mucosal anesthesia, incisal anesthesia, block anesthesia, and the reference group during the hold phase (a) and split phase (b). The asterisk denote significant difference in the mucosal anesthesia (white), incisal anesthesia (gray), and block anesthesia (black) compared to the reference group (P < 0.05). Mean ± standard error of mean of Z scores of electromyographic activity for right and left masseter (MAL and MAR); anterior temporalis (TAL) and suprahyoid (SHD) muscle in the mucosal anesthesia, incisal anesthesia, and block anesthesia during the hold phase (c) and split phase (d). The gray shades denote 90 % confidence interval (−1.64 to 1.64)