Testing the retention of attachments for implant overdentures - validation of an original force measurement system.

The aim of this study was to validate an original portable device to measure attachment retention of implant overdentures both in the lab and in clinical settings. The device was built with a digital force measurement gauge (Imada) secured to a vertical wheel stand associated with a customized support to hold and position the denture in adjustable angulations. Sixteen matrix and patrix cylindrical stud attachments (Locator) were randomly assigned as in vitro test specimens. Attachment abutments were secured in an implant analogue hung to the digital force gauge or to the load cell of a traction machine used as the gold standard (Instron Universal Testing Machine). Matrices were secured in a denture duplicate attached to the customized support, permitting reproducibility of their position on both pulling devices. Attachment retention in the axial direction was evaluated by measuring maximum dislodging force or peak load during five consecutive linear dislodgments of each attachment on both devices. After a wear simulation, retention was measured again at several time periods. The peak load measurements with the customized Imada device were similar to those obtained with the gold standard Instron machine. These findings suggest that the proposed portable device can provide accurate information on the retentive properties of attachment systems for removable dental prostheses.

Validation of video versus electromyography for chewing evaluation of the elderly wearing a complete denture.

Chewing efficiency may affect nutritional status in the elderly. Many elderly patients are complete denture wearers, and often present cognitive problems. Those two factors make evaluation of mastication difficult with experimental methods. Analysis of video recording may be a simple way to routinely assess chewing parameters. This study aimed at validating several parameters of video evaluation versus electromyography (EMG), which is considered the 'gold standard'. The design was a prospective randomized study, carried out at the Faculty of Dentistry, University of Auvergne, Clermont-Ferrand, France. Twelve complete denture wearers chewed four model foods differing in hardness. Sessions were videotaped and EMG recordings were registered. Mastication time, number of masticatory cycles and cleaning time were recorded simultaneously by video and EMG. Two investigators independently analyzed the videos twice, in random order. Evaluation of criterion validity: a positive video/EMG correlation was found for the parameters 'chewing time' (0.89, Pearson) and 'number of masticatory cycles' (0.94, Spearman), whereas no statistical difference was found between these two EMG and video variables (t-test). Inter and intra-rater reliability gave a positive intraclass coefficient (ICC) for duration of mastication (0.86-0.98), number of masticatory cycles (0.90-0.97) and cleaning time (0.90-0.98). Discriminatory ability was studied using anova (P = 0.01): variation was significant in masticatory duration (F = 10), number of masticatory cycles (F = 10) and cleaning time (F = 4). Video may be a useful assessment tool in prosthetic rehabilitation and can be applied to help choose the type of food (solid, semi-liquid or liquid) to administer to dependent persons, particularly those suffering from dementia.

Mastication of model products in complete denture wearers.

OBJECTIVE: The aim of this study was to define the characteristics of muscular activity in complete denture wearers and in dentate subjects during mastication of model foods differing in hardness but similar in terms of rheologically properties. MATERIAL AND METHODS: The foodstuffs used in this study were laboratory-developed gumdrops demonstrating viscoelastic properties. The test foods cover a range of four hardness levels. The group of complete denture wearers included 15 subjects, while the control group included 9 subjects with normal dentition. Electromyograph (EMG) recordings were taken from the masseter and temporal muscles during mastication of the test foods. The results were evaluated by one-way and two-way ANOVA followed by means comparisons using a Student-Newman-Keuls post hoc test (alpha=0.05). RESULTS: Preparing the same food bolus for swallowing required a greater number of masticatory cycles and a longer duration of mastication for complete denture wearers than for dentate subjects. In addition, complete denture wearers failed to increase EMG activity per cycle in response to hardness of the food. CONCLUSION: Denture wearers experienced difficulties during mastication, as indicated by a decreased masticatory rate and the observed failure to increase EMG activity per cycle in response to increased food hardness. The increases in number of cycle and masticatory duration appear to be a response to this impaired masticatory function.

Effects of increased hardness on jaw movement and muscle activity during chewing of visco-elastic model foods.

When food is chewed, sensory feedback adapts the motor program to the characteristics of the food. However, the relationship between the physical properties of different foods and the motor response is poorly understood. In this study, we developed edible and well-controlled model foods in order to describe some of the stimulus-response functions of the food-mastication loop. Four gelatine-based visco-elastic model foods identical in shape and size but differing in hardness were prepared. They displayed reproducible sensory and physical characteristics and were distributed on a wide hardness scale. Electromyographic activity of masseter and temporalis muscles and jaw movements in the frontal plane were simultaneously recorded during mastication in 15 young men with intact dentition and good oral status. Almost all EMG and jaw movement parameters were clearly affected by increasing hardness of model foods. However, it is possible to summarise the results by reducing the number of parameters to three: the number of chewing cycles, EMG activity of any one of the two temporal or the two masseter muscles and the amplitude of the opening mandibular movements. Indeed, these were the best transcriptors of the hardness range of the model foods used in this study. As inferred from these parameter recordings, the food hardness modifications were strongest during the first five strokes, began as early as the first stroke and lasted for the whole sequence.

Variability of the masticatory process during chewing of elastic model foods.

Many studies show a consistent individual chewing pattern; chewing being governed by a pattern generator and regulated by sensory feedback. The aim of this study was to determine the variation in chewing between sessions, replicates and subjects using elastic model foods. Fifteen young male subjects were selected to chew four food products differing in hardness. Four sessions were performed at 1-wk intervals for each subject and, within each session, the four model foods were presented 3 times each. Jaw movement was recorded simultaneously with masseter and anterior temporalis electromyographic activities. Several chewing characteristics increased progressively from one session to the next; the largest increase occurred from the 1st to the 2nd session, with little difference between the last two sessions. No differences were observed between the samples of the same food product within a session. As mastication progressed, the amplitude and speed of the cycles and the muscular work decreased progressively. The first cycle appeared to be very different from the subsequent for all parameters except for occlusal duration. Thus, under our experimental conditions, the origin and amount of variation in chewing patterns were identified and provide information to improve the accuracy and comparability of results in studies of mastication.