Comparison of chin and jaw movements during gum chewing

Jaw tracking integration to the virtual patient: A 4D dynamic approach

This dental technique describes a novel cost-effective workflow for integrating mandible kinematics into a static virtual patient. Computed tomography data are segmented and merged with intraoral surface scans and a target tracking video reproducing the mandible movements. A 4-dimensional dynamic virtual patient is created by using an open-source software program, and all patient-specific parameters can be exported for individualization of a virtual or analog articulator.

Individuality of masticatory performance and of masticatory muscle temporal parameters

OBJECTIVE

Mammalian mastication serves to improve intra-oral food reduction. Insufficient food reduction creates potential swallowing problems, whereas over-reduction may accelerate tooth wear and increase feeding time. Either extreme has consequences. The study's objectives were: (1) to study the relationship between food reduction, number of chews in a sequence, and chewing rate, (2) to study how controlling the number of chews and chewing rate variability affects food reduction, and (3) to assess how dentoskeletal morphological and electromyographical (EMG) characteristics impact food reduction.

DESIGN

Twenty-three healthy, fully-dentate adults chewed a standardized test food under three conditions: (1) no control, (2) number of chews controlled, and (3) number of chews and chewing rate controlled. EMG activity was sampled from masseter and temporalis muscles bilaterally. Demographic, occlusal contact area in maximum intercuspation, and cephalometric data were obtained.

RESULTS

In uncontrolled conditions, food reduction and bout duration varied more than expected across subjects. Subjects with poor reduction under controlled conditions were those with poor reduction under uncontrolled conditions. Only occlusal contact area correlated with chewing performance under uncontrolled conditions. Chewing cycle duration, EMG burst duration, and EMG peak onset latency increased when the number of chews was restricted. EMG amplitude, a surrogate for bite force, increased in tasks controlling the number of chews and chewing rate. Chewing rate variability was difficult to diminish below individual-specific levels.

CONCLUSIONS

Results: provided evidence that bite force, chewing rate, chewing performance and chewing bout duration reflected individual preferences. Future work will determine whether similar findings occur among other mammals.

Changes in mandibular border movements in adult patients after correction of functional anterior crossbite

Background/purpose

An effective approach for assessing masticatory function is necessary. The goal of this study was to establish an efficient method for evaluating mandibular border movements in patients after functional anterior crossbite was corrected.

Materials and methods

Five patients with functional anterior crossbite were included in this study. They were treated with edgewise appliance and improved super-elastic nickel–titanium archwire. The digital images were collected before and after anterior crossbite was corrected. The trajectory paths of mandibular border movement were evaluated on both the frontal and sagittal planes.

Results

When the mandibular border movement paths were analyzed on the frontal plane for the vertical displacement, significant increases in the maximum left- and right-lateral movements were observed. For the horizontal displacement, although decreasing trends were observed in the maximum mouth opening and protrusive movements, no significant difference was detected. However, horizontal displacements were generally greater in men than in women. When the mandibular border movement paths were analyzed on the sagittal plane, significant increases in all the vertical and horizontal displacements were observed at all border movements, except the maximum mouth opening. However, if the data were compared between men and women, significant difference was shown only in the horizontal displacement of the maximum protrusion.

Conclusion

On both the frontal and sagittal planes, after correction of the anterior crossbite there are increases in vertical and horizontal displacements at all kinds of mandibular border movements except for the horizontal displacements at the maximum mouth opening and the maximum protrusion.

Quantitative Analysis of the Variability of Unilateral Chewing Movements in Young Adults

Kinesiography can be used as a diagnostic tool in a dental clinic context. In the current study, a kinesiograph was used to detect and record the three-dimensional motion of the mandibular mid-incisor point during unilateral chewing as a function of time. The aim of the study was to quantify the within-subject short-term reproducibility of the kinesiographic recordings in normal, healthy subjects. Ten seconds of unilateral (right and left) gum chewing were recorded in 20 control subjects using computerized kinesiography. Each subject performed 18 chewing sequences (three repetitions x three sessions x two sides). Chewing cycle duration, volume, standardized depth and width, and the number of reversed cycles were calculated. Intraclass correlation coefficients (two-way random effects analysis of variance with interactions) and paired t-tests were used to compare sessions. For each subject and side, chewing variability was expressed as the coefficient of variation (percentage ratio of standard deviation to mean) of each variable. Mean left and right side mastications were computed over all sessions and subjects. For all the analyzed variables, larger variations between subjects (analysis of variance, p < 0.001) than between sessions were found, with intraclass correlation coefficients ranging between 0.432 (left side cycle duration) and 0.989 (right side standardized width). No systematic errors between the three measurement sessions were found for cycle volume and shape (paired t, p > 0.05). The highest between subjects/ between sessions variance ratios (up to 223.28) were found for cycle duration and shape. In all subjects, chewing cycle volume was very variable, with mean coefficients of variation up to 47% (left side in females). Cycle duration and standardized depth and width were more reproducible, with mean coefficients of variation up to 10% (duration), 14% (standardized width), and 18% (standardized depth). The spatial characteristics of gum chewing cycles had a large within-subject variability. The temporal and size-standardized (shape) characteristics were more consistent within subject. The results should allow selection of a set of relatively more consistent variables for the definition of normality and the comparison of patients.

Analysis of temporal variation in human masticatory cycles during gum chewing

OBJECTIVE

The study investigated modulation of fast and slow opening (FO, SO) and closing (FC, SC) chewing cycle phases using gum-chewing sequences in humans.

DESIGN

Twenty-two healthy adult subjects participated by chewing gum for at least 20s on the right side and at least 20s on the left side while jaw movements were tracked with a 3D motion analysis system. Jaw movement data were digitized, and chewing cycle phases were identified and analysed for all chewing cycles in a complete sequence.

RESULTS

All four chewing cycle phase durations were more variant than total cycle durations, a result found in other non-human primates. Significant negative correlations existed between the opening phases, SO and FO, and between the closing phases, SC and FC; however, there was less consistency in terms of which phases were negatively correlated both between subjects, and between chewing sides within subjects, compared with results reported in other species.

CONCLUSIONS

The coordination of intra-cycle phases appears to be flexible and to follow complex rules during gum-chewing in humans. Alternatively, the observed intra-cycle phase relationships could simply reflect: (1) variation in jaw kinematics due to variation in how gum was handled by the tongue on a chew-by-chew basis in our experimental design or (2) by variation due to data sampling noise and/or how phases were defined and identified.

Measurement of jaw motion: the proposal of a simple and accurate method

The analysis of jaw movements has long been used as a measure for clinical diagnosis and assessment. A number of strategies are available for monitoring the trajectory; however most of these strategies make use of expensive tools, which are often not available to many clinics in the world. In this context, this research proposes the development of a new tool capable of quantifying the movements of opening/closing, protrusion and laterotrusion of the mandible. These movements are important for the clinical evaluation of both the temporomandibular function and muscles involved in mastication. The proposed system, unlike current commercial systems, employs a low-cost video camera and a computer program, which is used for reconstructing the trajectory of a reflective marker that is fixed on the jaw. In order to illustrate the application of the devised tool a clinical trial was carried out, investigating jaw movements of 10 subjects. The results obtained in this study were compatible with those found in the literature with the advantage of using a low-cost, simple, non-invasive and flexible solution customized for the practical needs of clinics. The average error of the system was less than 1.0%.

Current diagnosis of temporomandibular pathologies

The current scientific knowledge of TMJ pathologies points to the importance of etiological research and the need for differential diagnosis using the most modem technological resources. Those include MRI, computed tomography, serologic studies, genetic mapping, and bioelectronic instruments which allow clinicians to study, understand, and measure respectively, the structural changes of soft and hard tissues, infections, genetic susceptibility for autoimmune diseases, and stomatognathic function. The purpose of this article is an overview of the current knowledge and related tools for the diagnosis of TMJ pathologies.

A computational method for recording and analysis of mandibular movements

This study proposed the development of a new clinical tool capable of quantifying the movements of opening-closing, protrusion and laterotrusion of the mandible. These movements are important for the clinical evaluation of the temporomandibular function and muscles involved in mastication. Unlike current commercial systems, the proposed system employs a low-cost video camera and a computer program that is used for reconstructing the trajectory of a reflective marker that is fixed on the mandible. In order to illustrate the clinical application of this tool, a clinical experiment consisting on the evaluation of the mandibular movements of 12 subjects was conducted. The results of this study were compatible with those found in the literature with the advantage of using a low cost, simple, non-invasive, and flexible tool customized for the needs of the practical clinic.

Chewing-side determination of three food textures

Food texture affects chewing movement but it is not known if it also affects the chewing-side pattern. This study determined the chewing sides of three test foods with different textures during habitual chewing. Twenty healthy dental students (aged 20-24 years) chewed pieces of pork jerky, fresh asparagus and almonds on two separate sessions (1 week apart). In each session, each subject chewed 30 food specimens, 10 of the same food type, until swallowing while a video camera recorded the displacement of the chin with respect to the other two reference points vertically marked along the facial midline. A slow-speed video playback was used to identify the chewing side of each cycle. The chewing-side pattern (right preference, left preference, no preference) in each individual was determined statistically. The results showed that overall, 11 subjects did not have any side preference whereas six and three subjects preferred to chew on right or left sides respectively. The chewing-side pattern remained unchanged between three food types in about half of the subjects. When the same food was compared between 2 days, the chewing-side pattern of almonds was shown to be most reproducible (18 subjects). Unidentified cycles with little or no lateral displacement, labelled as bilateral, were observed more frequently near the end of the chewing sequence with more occurrences in almonds and jerky than asparagus (P < 0.01). It was suggested that chewing-side preference is not a fixed characteristic. Food texture seemed to influence the side preference and also the occurrence of bilateral cycles.

Predicting masticatory jaw movements from chin movements using multivariate linear methods

Previously, we have used bivariate correlations of maximum and minimum displacement, velocity and acceleration variables to compare masticatory chin and jaw movements (J. Prosthet. Dent. 81 (1999) 179). This previous study represented a first step in exploring the hypothesis that the chin contained useful information regarding jaw kinematics. The current study extends our understanding of the relationship between masticatory chin and jaw movements by: (1) reconstructing and evaluating a more continuous trajectory of chin and jaw movements, and (2) performing multivariate correlations comparing chin and jaw movements at discrete points along the trajectory in order to gain insight into the coupling of chin and jaw movements during a chewing cycle. Results indicated that chin and jaw movement trajectories were visually similar in the lateral, vertical, and anteroposterior axes. The adjusted R(2) results in the lateral, vertical, and anteroposterior dimensions averaged 0.74, 0.78, and 0.89, respectively. Within chewing cycles, the lowest correlations between chin and jaw movements in the lateral and vertical dimensions occurred when the jaw was relatively closed, whereas the lowest correlations between chin and jaw movements in the anteroposterior dimension occurred while the jaw was opening from a closed position. The results indicated that jaw and chin movements were qualitatively similar and that at least 74% of the variation in jaw movements could be accounted for by multivariate linear models of chin movement.

Quantification of translational and gliding components in human temporomandibular joint during mouth opening

OBJECTIVE

In humans, the opening movement of the mouth requires a complex combination of rotation in the lower temporomandibular joint compartment and of translation in the upper compartment. The aim of the current study was to quantitatively assess the percentage contribution of rotation and translation movements of the mandible at maximum mouth opening in normal, healthy individuals.

DESIGN

Free, habitual movements of mouth opening were recorded in 12 men and 15 women aged 19-30 years using an optoelectronic three-dimensional motion analyser. All subjects had a sound, complete, permanent dentitions with Angle Class I jaw relationships, without cast restorations or cuspal coverage, TMJ or craniocervical disorders. For each subject, the mandibular movements at the interincisor point (occlusal plane) were reconstructed, and, using suitable mathematical algorithms, divided into their rotation and gliding components. The relative contribution of the two components to the total movement was calculated for each frame of motion. In particular, the situation at maximum opening was assessed.

RESULTS

At maximum mouth opening, on average, men had significantly larger displacement of the mandibular interincisor point (56 mm versus 46 mm) and angle of rotation (34 degrees versus 32 degrees), than women. The percentage of mandibular movement explained by rotation at maximum mouth opening (77%) was not influenced by sex. The degree of rotation was significantly related to the displacement of the interincisor point: in women r2 = 87%, in men, r2 = 45%.

CONCLUSIONS

Overall, in normal subjects with a healthy stomatognathic apparatus, mouth opening was more determined by mandibular rotation than by translation.

A simple and inexpensive system for monitoring jaw movements in ambulatory humans

A simple and inexpensive method for recording vertical movements of the human mandible relative to the maxilla is presented. Measurements are made from accelerometers and a Hall-effect device temporarily glued to the upper and lower anterior teeth. The accelerometer signals are integrated once to give velocity and a second time to give position. Movements of the mandible relative to the maxilla are obtained by integrating the difference between the two accelerometer signals. The (relative) velocity and position records derived in this way are linear, but subject to drift when the jaw is stationary. Steady mandibular position is obtained from the Hall-effect system, but this signal must be corrected for its inherent non-linearity. This device can record rapid movements of the mandible even when the head is unrestrained, and interferes minimally with normal jaw movements.