Optimization of jaw muscle activity and fine motor control during repeated biting tasks Abhishek Kumar a,d, * , Krister G. Svensson b,d , Lene Baad-Hansen a,d , Mats Trulsson b,d , Flemming Isidor c , Peter Svensson a,d a Section of Clinical Oral Physiology, Department of Dentistry, Aarhus University, Denmark b Section for Oral Rehabilitation, Department of Dental Medicine, Karolinska Institute, Sweden c Section of Prosthetic Dentistry, Department of Dentistry, Aarhus University, Denmark d Scandinavian Center for Orofacial Neuroscience (SCON) 1. Introduction Mastication is a complex process which can be divided into the preparation phase, the reduction phase, the pre-swallowing phase and the swallowing phase. 1,2 Holding the food morsel between the teeth and applying the optimum force required to split the food morsel may be considered as the first step in mastication. This process is assisted by the tongue, jaw and facial muscles which act in coordination with each other to position the food morsel appropriately. 3 The jaw muscles control and move the mandible and in that way regulate the a r c h i v e s o f o r a l b i o l o g y 5 9 ( 2 0 1 4 ) 1 3 4 2 – 1 3 5 1 a r t i c l e i n f o Article history: Accepted 17 August 2014 Keywords: Behavioural learning Periodontal mechanoreceptors Neuroplasticity a b s t r a c t Objective: To investigate if repeated holding and splitting of food morsel change the vari- ability of force and jaw muscle activity in participants with natural dentition. Methods: Twenty healthy volunteers (mean age = 26.2 Æ 3.9 years) participated in a single session divided into six series. Each series consisted of ten trials of a standardized beha- vioural task (total 60 trials) involving holding and splitting a flat-faced tablet (8 mm, 180 mg) placed on a bite force transducer with the anterior teeth. The hold and split forces along with the electromyographic (EMG) activity of the left and right masseter (MAL and MAR), left anterior temporalis (TAL) and digastric (DIG) muscles were recorded. A series (ten trials) of natural biting tasks was also performed before and after the six series of the behavioural task. Results: The mean hold force (P < 0.001) but not the mean split force (P = 0.590) showed significant effect of number of series. No significant effect of series was seen on the variability of hold and split force and the EMG activity except for the variability of EMG activity for MAL during the hold phase (P = 0.021) and DIG during the split phase (P < 0.001). The behavioural task had no effect on the EMG activity of the natural biting task. Conclusion: There was no evident optimization of jaw motor function in terms of reduction in the variability of bite force values and muscle activity, when this simple task was repeated up to sixty times in participants with normal intact periodontium. # 2014 Elsevier Ltd. All rights reserved. * Corresponding author at: Section of Clinical Oral Physiology, Department of Dentistry, Vennelyst Boulevard 9, Aarhus University, Aarhus 8000, Denmark. Tel.: +45 8716 7407; fax: +45 8619 5665. E-mail addresses: a.kumar@odont.au.dk, dockumarabhishek@gmail.com (A. Kumar). Available online at www.sciencedirect.com ScienceDirect journal homepage: http://www.elsevier.com/locate/aob http://dx.doi.org/10.1016/j.archoralbio.2014.08.009 0003–9969/# 2014 Elsevier Ltd. All rights reserved.