​The importance of occlusal force measurement in orthognathic surgery - A pilot study

Purpose: This pilot investigation was designed to apply several, newly developed and more sophisticated methods of measuring muscle structure and function in a situation where adaptation of muscle is pivotal to the success of a therapeutic approach. Materials and Methods: Patients attending the combined orthodontic/orthognathic surgery clinic at the Clitrofa – Centro Médico, Dentário e Cirúrgico, in Trofa - Portugal were tested according to the protocol of Bite force and occlusal contact area were simultaneously measured with Bite Training Machine and Occlusal Force Diagnostic System. An Experimental design used for the measurement of occlusal force. The study involved the contribution of two independent examiners that measured the bite pressure (psi) in five different FSS sensors at three different time moments. A combination of different parametric tests has been used to compare the different experimental variables. Results: Neither the variation of examiner, nor the variations of time have shown to influence the bite pressure (psi). In contrast, the occlusal force measurement system developed has shown a high level of sensitivity due to the distribution of the five FSS sensors in the horseshoe-shaped form. A three-pressure region model fits the experimental data shown in this study, comprising a low-pressure region located in the anterior part of the dental arch, a medium-pressure region in the medial part of the dental arch and an high-pressure region located in the posterior part of the dental arch. Conclusions: The piezoelectric sensors used in the present study have shown high reproducibility of measurement. Due to the recent miniaturization of FSS sensors, the authors are developing new occlusal force measurement systems comprising a higher number of piezoelectric sensors, with the objective of attaining even higher sensitivity of measurement throughout the different region of the dental arches.

Effects of bruxism on the maximum bite force

Background/Aim. Bruxism is a parafunctional activity of the masticatory system, which is characterized by clenching or grinding of teeth. The purpose of this study was to determine whether the presence of bruxism has impact on maximum bite force, with particular reference to the potential impact of gender on bite force values. Methods. This study included two groups of subjects: without and with bruxism. The presence of bruxism in the subjects was registered using a specific clinical questionnaire on bruxism and physical examination. The subjects from both groups were submitted to the procedure of measuring the maximum bite pressure and occlusal contact area using a single-sheet pressure-sensitive films (Fuji Prescale MS and HS Film). Maximal bite force was obtained by multiplying maximal bite pressure and occlusal contact area values. Results. The average values of maximal bite force were significantly higher in the subjects with bruxism compared to those without bruxism (p < 0.001). Occlusal contact area was significantly higher in the subjects suffering from bruxism (p < 0.001), while the maximal bite pressure values did not show a significant difference between the studied groups (p > 0.01). Maximal bite force was significantly higher in the males compared to the females in all segments of the research. Conclusion. The presence of bruxism influences the increase in the maximum bite force as shown in this study. Gender is a significant determinant of bite force. Registration of maximum bite force can be used in diagnosing and analysing pathophysiological events during bruxism.

Illusion caused by vibration of muscle spindles reveals an involvement of muscle spindle inputs in regulating isometric contraction of masseter muscles

Spindle Ia afferents may be differentially involved in voluntary isometric contraction, depending on the pattern of synaptic connections in spindle reflex pathways. We investigated how isometric contraction of masseter muscles is regulated through the activity of their muscle spindles that contain the largest number of intrafusal fibers among skeletal muscle spindles by examining the effects of vibration of muscle spindles on the voluntary isometric contraction. Subjects were instructed to hold the jaw at resting position by counteracting ramp loads applied on lower molar teeth. In response to the increasing-ramp load, the root mean square (RMS) of masseter EMG activity almost linearly increased under no vibration, while displaying a steep linear increase followed by a slower increase under vibration. The regression line of the relationship between the load and RMS was significantly steeper under vibration than under no vibration, suggesting that the subjects overestimated the ramp load and excessively counteracted it as reflected in the emergence of bite pressure. In response to the decreasing-ramp load applied following the increasing one, the RMS hardly decreased under vibration unlike under no vibration, leading to a generation of bite pressure even after the offset of the negative-ramp load until the vibration was ceased. Thus the subjects overestimated the increasing rate of the load while underestimating the decreasing rate of the load, due to the vibration-induced illusion of jaw opening. These observations suggest that spindle Ia/II inputs play crucial roles both in estimating the load and in controlling the isometric contraction of masseter muscles in the jaw-closed position.

Changes in occlusal contact area and average bite pressure during treatment of anterior crossbite in primary dentition

The purpose of this study was to examine changes in functional parameters of patients with anterior crossbite in primary dentition during orthodontic treatment. Occlusal contact area (OCA), average bite pressure (ABP) and integrated occlusal load (IOL) were measured. Data obtained before the start of treatment (period A), data obtained when crossbite had improved (period B) and data obtained when the appliance had been removed (period C) were compared. OCA showed the lowest value in period B, and then gradually increased. ABP increased until period B and then declined or became constant. OCA and IOL showed significant differences in periods A and B and periods B and C (p&lt;0.05). The results suggest that about 6 months is required for stability of the occlusion and acquisition of function in the new occlusion after improvement of crossbite.