Chewing Phase Research Articles

Modulation of reflex responses of the anterior and posterior bellies of the digastric muscle in freely moving rats.

Chewing and licking are primarily activated by central pattern generator (CPG) neuronal circuits in the brainstem and when activated trigger repetitive rhythmic orofacial movements such as chewing, licking and swallowing. These CPGs are reported to modulate orofacial reflex responses in functions such as chewing. This study explored the modulation of reflex responses in the anterior and posterior bellies (ant-Dig and post-Dig, respectively) of the digastric muscle evoked by low-intensity trigeminal stimulation in conscious rats. The ant-Dig and post-Dig reflexes were evoked by using low-intensity electrical stimulation applied to either the right or left inferior alveolar nerve. Peak-to-peak amplitudes and onset latencies were measured. No difference was observed between threshold and onset latency for evoking ant-Dig and post-Dig reflexes, suggesting that the latter was also evoked disynaptically. The peak-to-peak amplitude of both reflexes was significantly reduced during chewing, licking and swallowing as compared to resting period and was lowest during the jaw-closing phase of chewing and licking. Onset latency was significantly largest during the jaw-closing phase. Inhibitory level was similar between the ant-Dig and post-Dig reflex responses and between the ipsilateral and contralateral sides. These results suggest that both the ant-Dig and post-Dig reflex responses were significantly inhibited, probably due to CPG activation during feeding behaviours to maintain coordination of jaw and hyoid movements and hence ensure smooth feeding mechanics.

An Unexpected Thoracic Finding in a Patient With COVID-19

Question: A 75-year old woman presented to the emergency department with a history of epigastric discomfort and rapidly worsening thoracic pain. She had no fever or cough. On physical examination, she appeared overweight (102 kg, height 162 cm). Laboratory examination revealed normal cardiac troponin levels and slight increase in inflammatory markers (C-reactive protein and neutrophil-lymphocyte ratio). As a nasal screening swab was positive for coronavirus 2019 (COVID-19) infection, she was transferred to the COVID isolation ward. A subsequent computed tomography scan of the chest showed no interstitial lung disease. However, the presence of a monstrous esophageal dilatation with sigmoid shape and dislodgment of the surrounding structures was seen. The esophagus appeared full of solid content compatible with accumulated undigested food residues (Figure A–C). The patient was then referred to our gastroenterology unit. Upper endoscopy was performed under general anesthesia with endotracheal intubation. Endoscopic esophageal findings are shown in Figure D. What is the most likely diagnosis and how should it be managed? Look on page 1112 for the answer and see the Gastroenterology web site (www.gastrojournal.org) for more information on submitting your favorite image to Clinical Challenges and Images in GI. The patient was suffering from type II achalasia, which was refractory to previous endoscopic and surgical treatment. In detail, she had undergone three endoscopic pneumatic dilation sessions in 2005 and ultimately laparoscopic Heller-Dor myotomy in 2015. In 2018, an esophageal high-resolution manometry was unsuccessful, probably because the catheter did not reach the stomach in the sigmoid dilated esophagus. We treated our patient with prolonged fasting and nasoesophageal tube placement at 35 cm from the incisors teeth. Multiple daily irrigations with saline solution were performed without apparent benefit. Three endoscopic sessions were then performed to clean the entire esophagus from the huge amount of feces-like food residues. We believe that 2 reasons were behind this ominous presentation. First, the patient suffered from poorly controlled hypothyroidism for which she was taking levothyroxine per os. Laboratory examination revealed high levels of thyrotropin (103 μU/mL) and low levels of free thyroxine (<2.5 pg/mL) and free tri-iodothyronine (1.5 pg/mL). Her severe hypothyroidism was probably due to the inability of oral levothyroxine to reach the stomach, thus decreasing the subjective awareness of her own clinical condition. Second, she was edentulous and this affected the chewing phase, favoring episodes of food impaction and accumulation of food in the esophagus. Surprisingly, she did not experience weight loss and her general nutritional status was good. Achalasia is an uncommon esophageal motility disorder, usually characterized by dysphagia to solids and liquids, chest pain, regurgitation, and weight loss. High-resolution esophageal manometry is the gold standard test for the diagnosis. Diagnostic findings include distal esophageal aperistalsis and integrated relaxation pressure of >15 mm Hg. Achalasia is classified as type 1 classic, type 2 compartmentalized high pressure in esophageal body, and type 3 spastic.1Weusten B.L.A.M. Barret M. Bredenoord A.J. et al.Endoscopic management of gastrointestinal motility disorders - part 1: European Society of Gastrointestinal Endoscopy (ESGE) Guideline.Endoscopy. 2020; 52: 498-515Crossref PubMed Scopus (41) Google Scholar In the last few years, peroral endoscopic myotomy is the most frequent endoscopic intervention for achalasia leading to outcomes that are comparable with those of laparoscopic Heller myotomy. Additional interventions are represented by pneumatic dilation and botulinum toxin injection. Esophagectomy is the last option to manage end-stage achalasia.2Familiari P. Greco S. Volkanovska A. et al.Achalasia: current treatment options.Expert Rev Gastroenterol Hepatol. 2015; 9: 1101-1114Crossref PubMed Scopus (11) Google Scholar,3Hammad A. Lu V.F. Dahiya D.S. et al.Treatment challenges of sigmoid-shaped esophagus and severe achalasia.Ann Med Surg (Lond). 2020; 61: 30-34Crossref PubMed Scopus (5) Google Scholar Peroral endoscopic myotomy was not considered for our patient because of the patent cardia (Figure E), the lack of manometric data, and the poor expected outcome in sigmoid esophagus. She was referred to the endocrinologist for further therapeutic workup. Moreover, dental prosthesis implantation was recommended.

The reciprocal jaw-muscle reflexes elicited by anterior- and back-tooth-contacts\u2014a perspective to explain the control of the masticatory muscles

AimsTooth-contact sensations are considered essential to boost jaw adductor muscles during mastication. However, no previous studies have explained the importance of the inhibitory reflex of human anterior-tooth (ANT)-contacts in mastication. Here I present the “reciprocal reflex-control-hypothesis” of mammalian mastication.Subjects and setting of the studyI demonstrate the hypothesis with the live kinematics of free jaw-closures as inferred from T-Scan recordings of dental patients.ResultsThe jaw-closures started with negligible force, predominantly with ANT-contacts (the AF-bites). The first ANT-contact inhibited the first kinematic tilt of the mandible, whereas the bites starting from a back-tooth (BAT)-contact (the BF-bites) accelerated the first tilt. The second tilt established a low-force static tripod of the ANT- and bilateral BAT-contacts for a fixed mandible-maxilla relation. Thereafter, semi-static bite force increased rapidly, relatively more in the BAT-area.Discussion and ConclusionsIn the vertical-closure phase of chewing, the primate joint-fulcrum (class 3 lever) conflicts with the food-bolus-fulcrum in the BAT-area (class 1 lever). The resilient class 3 and 1 lever systems are superseded by an almost static mechanically more advantageous class 2 lever with a more rigid fulcrum at the most anterior ANT-contact. For humans, the class 2 levered delivery of force also enables forceful horizontal food grinding to be extended widely to the BAT-area.

Comparison of dynamic occlusal contacts during chewing between children with primary dentition and normal adult females

ObjectiveInvestigation of dynamic occlusal contacts when food particles are being pulverized during chewing is of interest for many researchers and clinicians. However, measurement of dynamic occlusal contacts during chewing is difficult, and differences between children and adults have not been established. The purpose of this study is to test the hypothesis that dynamic occlusal contacts of children differ from those of adult females. Subjectsand methods: Thirteen healthy children (4–6 years of age; mean age 5 years, 7 months) and thirteen adult females (18–26 years of age; mean age 20 years, 7 months) with normal occlusion participated in this study. Occlusal contact area (OCA) was estimated with a developed measurement system combining 3-D digitization of tooth shape with 3-D tracking of mandibular movements (1) during the closing stroke, (2) at the maximum closing position (MCP), and (3) during the opening stroke. OCA at static maximum intercuspation (ICP) was also estimated. ResultsAt the MCP, the children's OCA was less than 76.4% of the contact area seen at the ICP. The timing of maximum OCA in children was shifted more towards the opening stroke compared with adults, and the OCA remained greater during opening in children than adults. The occurrence of the MCP was less stable in children than in adults, both between subjects and within subjects. ConclusionsWe conclude that both the amount of OCA and the pattern of occlusal contacts during the occlusal phase of chewing completely differ between children and adult females.

Influence of Chewing Cycles on Flavor Recognition Time in Healthy Adults.

Flavor recognition times were measured in 23 young, healthy participants of both sexes using an electromyography-based system. The participants were instructed to chew a gummy candy, which was randomly selected among six commercially available types, and to press a button immediately on flavor recognition. A total of 107 normally distributed, flavor recognition times were analyzed, with an average time of 7.5 seconds (± 2.34 seconds, standard deviation). No significant differences were found among the six types of candies in terms of recognition time. Analysis of the association between flavor recognition and chewing phase showed that 70 (65%) of the analyzed 107 recognition signals occurred between 0.2 seconds before and 0.4 seconds after the end of jaw closing. Recognition signals occurring during the jaw-opening phase prolonged its duration by an average of 21%, whereas those occurring during the jaw-closing phase did not influence it.

Effect of Saliva and Mucin-Based Saliva Substitutes on Fretting Processes of 316 Austenitic Stainless Steel

The paper presents the results of research of the fretting process of 316 austenitic stainless steel in the environment of natural saliva and mucin-based saliva preparations. The aim of the work was the evaluation of synthetic saliva preparations on biomaterial wear during fretting and fretting-corrosion. The fretting process, in the oscillatory micro-movements conditions, occurs in the joints of removable dentures, especially during the chewing phase. Fretting usually leads to the intensification of fatigue damage processes of materials. Experimental research, through rheological, fretting, fretting-corrosion, and microscopic analysis were performed. Tests indicate that natural saliva and saliva preparations are similar in terms of viscoelastic properties. The statistically significant proposed saliva solutions reduced the material wear in comparison to dry sliding, which is important in the case of people with saliva secretion problem. The addition of xanthan gum to the artificial saliva composition improved rheological characteristics, but on the other hand, led to an increase of secondary wear. It was confirmed by the volumetric wear of the samples and evaluation of energy dissipated during friction. Fretting-corrosion processes were explained by a mechanism related to crevice corrosion supported by friction.

The three-axial gyroscope sensor detects the turning point between opening and closing phases of chewing.

Most devices measuring the kinematics of masticatory function are cumbersome to setup and not portable. Data collection would be facilitated, particularly in the elderly, if the device used for the objective measurement of mastication was easily transportable and simple to setup. Accelerometers and gyroscope sensors are lightweight and portable and may be useful alternatives. The definition of the turning point between the opening and closing phases of chewing is important for studies of associations between muscle activity and effects of perturbations. Measures of the mediolateral angle (specifically, the mandibular tilt from the lateral view) allow the detection of the turning point between the opening and closing phases. The aim was to determine whether a three‐axial gyroscope sensor can detect the turning point between opening and closing phases of chewing. Fourteen asymptomatic participants chewed gum while the output was recorded from a three‐axial gyroscope sensor (Seiko Epson, Japan) attached to the chin and a 6 degree‐of‐freedom electromagnetic jaw‐tracking device (Pollhemus, USA). Bland–Altman plots were used to assess the matching of the recordings made by the three‐axial gyroscope sensor and the jaw‐tracking device. The turning points between the opening and closing phases of chewing matched closely when recorded by a jaw‐tracking device and when using a three‐axial gyroscope sensor. A three‐axial gyroscope sensor can validly detect the turning point between the opening and closing phases during chewing of gum.

FEM Investigation of the Stress Distribution over Mandibular Bone Due to Screwed Overdenture Positioned on Dental Implants.

The objective of the present investigation was to evaluate how dental implant positioning can influence the masticatory stress distribution over screwed mandibular prosthodontics restoration and over the surrounding bone tissue. Moreover, the dental implant components and overdenture bar strengths under masticatory cycles have been investigated in order to evaluate possible screw and prosthesis breakage. A “virtual jaw” model and 3D dental implant were reproduced to realise finite element analysis in order to underline the parameters and the mechanical characteristics of the bone and of the dental implants connected to the overdenture bar. The distribution of a nonspecific chewing phase, analysing the overall load on the fixtures of the lower jaw, was performed. The study investigating frontal and horizontal planes and vertical directions of occlusal forces showed how position and perspective of fixtures strongly influenced the stress distribution and the consequent jawbone tissue remodelling. Prostheses elements such as cantilever, passing screws, and dental implants are strictly related to the correct selection of dental implant position. This study suggested a virtual method to guide the surgeon in the choice of implant number, position, diameter, and length, and cantilever length and shape, and to evaluate the prospective stress distribution of chewing strengths for a correct prosthesis rehabilitation.

The influence of food consistency on chewing rate and muscular work

Food properties influence the parameters of the masticatory process, such as jaw movement, muscle activity and chewing rate. Firm foods will require more muscle activity than softer foods. However, the influence of food hardness on chewing rate is ambiguous as both slower and higher chewing rates have been reported for harder foods. Rheological characteristics of the food, such as plasticity and elasticity, may help to explain differences in chewing rate. The aim of our study was to determine the influence of food properties on chewing rate and muscular work in five phases of a chewing sequence. Eighty-four participants chewed on five foods, which strongly differed in consistency. Chewing gum was used as a reference food. The phase in the chewing sequence had a large significant effect on cycle duration for the five foods. A significant decrease in cycle duration at the beginning of chewing was followed by an increase in later phases, leading to U-shaped curves. Food type had a small effect on the average cycle duration. However, large significant differences in cycle duration were observed between the foods at the beginning of a chewing sequence. In that phase, the firm foods were chewed much slower than the soft foods. Muscular work was significantly influenced by both chewing phase and food type.

Effects of chewing and swallowing behavior on jaw opening reflex responses in freely feeding rabbits

It has been reported that the jaw opening reflex (JOR) evoked by intra-oral innocuous stimulation was suppressed during a reflex swallow in anesthetized animals only. However, the mechanism of JOR inhibition during swallowing has not yet been elucidated. The aim of the present study was to investigate the effects of peripheral nerve stimulation on masticatory behaviors, as well as the modulation of low threshold afferent evoked JOR responses during chewing and swallowing in freely feeding animals. The JOR in the digastric muscle was evoked by low threshold electrical stimulation of the inferior alveolar nerve (IAN). Changes in the peak-to-peak amplitude of digastric electromyographic responses were compared among the phases of chewing and swallowing. IAN stimulation did not produce any differences in cycle duration, gape of the jaw in one cycle, or swallowing interval, suggesting a minimal effect on feeding behaviors. The JOR amplitude during the fast-closing, slow-closing, and slow-opening phases of chewing was significantly smaller than that of the control (recorded when the animal was at rest) and fast-opening phase. During swallowing, the JOR amplitude was significantly less than the control. Inhibition of the JOR during swallowing is assumed to prevent unnecessary opposing jaw opening motion.

Jaw‐movement smoothness during empty chewing and gum chewing

A major goal of motor coordination is the production of a smooth movement. Jerk-cost, which is an inverse measure of movement smoothness, has been evaluated during gum chewing in previous studies. However, the effect of the gum bolus is still unclear. The aims of this study were to compare the jerk-cost values of normal gum chewing with those of empty chewing. Thirteen subjects undertook, empty chewing, then chewing of gum, and then a second empty chewing. Jerk-cost was calculated from an accelerometer attached to the skin of the mentum. There was a significantly higher smoothness (i.e. lower jerk-cost, P < 0.05) during the opening and second-half closing phases in empty chewing compared with gum chewing. There were no significant differences in jerk-costs (i.e. opening or closing) between the first and the second empty-chewing sequences. These results suggest that the influence of the mechanical effects of tooth contact on jerk-cost is not restricted just to the occlusal phase of chewing, but rather the effect influences the entire opening and closing phases of chewing.

Reflection of induced and amplified food motivation in impulse activity of the masticatory muscles during electrostimulation of the “hunger center” in the lateral hypothalamus in rabbits

We studied reflection of artificially induced and amplified food motivation in impulse activity of the masticatory muscles during electrostimulation of "hunger center" of the lateral hypothalamus in the absence and presence of food. The threshold stimulation of the lateral hypothalamus in hungry and satiated animals in the absence of food induced incessant food-procuring behavior paralleled by regular generation of spike bursts in masticatory muscles with biomodal distributions of intervals between pulses. This reaction of masticatory muscles during stimulation of the lateral hypothalamus in the absence of food was an example of the anticipatory reaction reflecting characteristics of the action result acceptor. Higher level of hunger motivation during threshold stimulation of the lateral hypothalamus in hungry and satiated rabbits in the course of effective food-procuring behavior increased the incidence of spike burst generation during the food capture phase, but did not modify this parameter during the chewing phase. Impulse activity of the masticatory muscles reflected convergent interactions of food motivation and support excitation on neurons of the central generator of chewing pattern.

Analyses of the facilitatory effect of orexin on eating and masticatory muscle activity in rats

The orexins (orexin-A and orexin-B) are neuropeptides that are secreted from neurons in the lateral hypothalamus and that participate in the regulation of feeding behavior. It remains to be determined, however, how the orexins exert their effects on feeding behavior, including masticatory movements. To this end, we analyzed food intake behavior and masticatory muscle activity using video analysis and electromyography (EMG) recording methods. The results showed that the cumulative food intake over 4 h was larger in rats intraventricularly injected with either orexin-A or orexin-B than in saline-injected control rats. The latency to eating and the feeding time for a fixed amount of pellets were shortened by injections of orexins in a dose-dependent manner, with a more potent effect by orexin-A than orexin-B. The shorter feeding time corresponded to a decreased number of chewing cycles. EMG recordings from both the digastric and masseter muscles showed two distinct patterns of bursts corresponding to the gnawing and chewing phases. After the injection of orexin-A, the magnitude of the bursts became larger in both phases in the masseter muscle, the burst duration became longer in the chewing phase in the masseter muscle, and the interburst interval became shortened in the gnawing phase in both muscles. Consequently, the burst frequency in the chewing phase was increased in the digastric muscle and, conversely, reduced in the masseter muscle. These results suggest that the orexin-A-induced facilitatory feeding behavior is characterized by a dynamic jaw-opener activity that opens the mouth rapidly and a powerful jaw-closer activity for crushing the increased amount of food taken into the mouth. The possible involvement of orexin-A in binge eating disorder is discussed.

Modulation of spindle discharge from jaw-closing muscles during chewing foods of different hardness in awake rabbits

The relationships between jaw-closing muscle spindle unit discharge and the hardness of foods were evaluated during chewing in awake rabbits. Spindle unit discharges recorded from the left mesencephalic trigeminal nucleus were correlated with the simultaneous recording of jaw movements and electromyographic (EMG) activities of the left masseter (jaw-closing) muscle during chewing soft and hard foods. A chewing cycle was divided into the fast-closing (FC), slow-closing (SC) and opening (OP) phases according to jaw movements. The chewing was classified as ipsilateral and contralateral chewing according to ipsilateral and contralateral to the recording side of the neuron, respectively. Spindle unit discharge was significantly higher during the FC and SC phases of the hard food than the soft food during both ipsilateral and contralateral chewing. The discharge was observed to be higher when the masseter muscle activity was higher. A comparison between the chewing sides reveals that the discharge was significantly higher during the slow-closing phase of ipsilateral chewing than contralateral chewing. From the above findings, the relationship of the spindle unit discharge with the hardness of foods was observed. Moreover, this relationship exists even when an animal chews food on the contralateral side suggesting the significance of the muscle spindle information for smooth chewing. In addition, the phase dependent difference of the spindle unit discharge between chewing sides suggests the distinct roles of the spindle information on the chewing and non-chewing sides.

Measurement of jerk-cost using a triaxial piezoelectric accelerometer for the evaluation of jaw movement smoothness

Jerk-cost as a measure of jaw movement smoothness has been used to evaluate the masticatory function of patients with tooth loss and malocclusion. Jerk-cost measuring systems have thus far been unable to determine the jerk-cost of each chewing phase over time. The purposes of this study were (i) to develop a new method for measuring momentary jerk-cost of the jaw movement using a small triaxial piezoelectric accelerometer and (ii) to test the hypothesis that the lowest smoothness is seen during jaw-opening phase. The accelerometer was attached to the skin of the mentum of each subject. Vertical jaw displacement, acceleration, the jerk, and the time differential of jerk-cost during gum chewing were analysed as a function of time in five normal dentate subjects (n = 5). The system revealed intra-class correlation coefficients of intra-examiner, inter-examiner, and test-retest consistency of substantially high values (0.80-0.88). In all subjects, the highest jerk-cost was observed in the opening phase of each chewing cycle when the gum was parting from the teeth; the lowest jerk-cost was observed in the intercuspal phase throughout the chewing cycle, thus confirming the hypothesis. Significant differences were observed between the opening, closing, and intercuspal chewing phases (N = 5, P = 0.007). The smoothness measurement system used in this study evaluated the momentary smoothness of each chewing phase in the masticatory cycle. The system may serve as a diagnostic tool to evaluate the smoothness of the jaw movement in general dental practice.

The study of comminution behavior of food on buccal and lingual side during mastication.

In this study, we observed comminution behavior of food on buccal and lingual side by sieve method. Six dentate subjects participated in this study. Peanuts were used as the test food and chewed for 1-8, 10, 12, 14, 16, 18, 20, 22 and 24 strokes on their preferred chewing side. Peanuts were gathered separately from buccal and lingual sides after varying number of chewing strokes. The crushed peanuts were sieved through a stack of eight level sieves (0.85 to 5.6mm). The comminution of coarse particles above 4.75 mm was almost finished within 10 strokes. The dynamic change in the median particle size also disappeared about 10 strokes. This suggested that we should pay attention to the initial phase of the chewing when we observed about mastication. As a result, comminution behavior of lingual coarse particles better conformed to fluctuation of median particle sizes of whole mouth, expressing masticatory performance precisely, than that of buccal coarse particles.

In Vivo Aroma Release of Milk Gels of Different Hardnesses: Inter-individual Differences and Their Consequences on Aroma Perception

The effect of textural modifications of solid milk gels on in vivo aroma release and aroma perception was investigated with a panel of 14 subjects. Great inter-individual differences were observed on aroma-release data, and the consequences of these differences on aroma perception were studied. From a hierarchical cluster analysis performed with several parameters extracted from release curves, the subjects were gathered into two groups, and a specific aroma-release profile was identified for each one. Then, by using a sensory profile, we showed that the intensity of the aroma perception was dependent on the release profile presented by the panelist. Second, we observed that, during the chewing phase, the aroma was perceived as more intense for the firmer gel and for panelists for whom the aroma release begins during the chewing of the product.

Roles of intrinsic and extrinsic tongue muscles in feeding: Electromyographic study in pigs

The performance of tongue muscles in various feeding behaviours is not well defined. This study was undertaken to examine the role of the intrinsic and extrinsic tongue muscles during natural drinking, food ingestion and chewing. Ten 12-week-old Yucatan miniature pigs (5 in each gender) were used. Under anesthesia, fine-wire electrodes were inserted into three intrinsic (verticalis and transversus [V/T]; superior and inferior longitudinalis [SL and IL]) and two extrinsic (genioglossus [GG] and styloglossus [SG]) tongue muscles and two jaw muscles (masseter [MA] and anterior digastricus [DI]). Electromyogram (EMG) and jaw movement were recorded and synchronized when pigs were drinking water, ingesting and chewing food freely. Chewing frequency (CF), onset of activation, burst duration and integrated activity (IEMG) were assessed quantitatively, and EMG activities during drinking and ingestion were examined qualitatively. Results indicate that during chewing, the V/T and GG had one phase of activity starting at early jaw opening, and the V/T activity lasted through late of jaw closing. The SL, IL and SG had double phases with the first starting at jaw opening and the second at late jaw closing phases. The three intrinsic tongue muscles and the SG were active during 35–48% of the chewing cycle. IEMG values of the SL, IL and SG of both sides were significantly greater compared to the other muscles ( p < 0.05–0.01). Both the SL and the IL showed significantly higher activities in the contralateral than ipsilateral sides ( p < 0.05). The timing sequences of both extrinsic and intrinsic muscles were similar between ingestion and chewing, but amplitudes of the GG and IL were greatly enhanced and those of the MA and SL were reduced during ingestion. The simultaneous activation of the MA, GG and V/T were seen during drinking, along with major activity in the GG and V/T. These results suggested that the majority of activity in the intrinsic and extrinsic tongue muscles occurred during jaw opening and the occlusal phases of chewing. The activity of the GG and IL played a major role during ingestion, whereas simultaneous activation of jaw, extrinsic and intrinsic tongue muscles and major activity in the GG and V/T occurred during drinking.

Evaluation of transitional implant stabilized overdentures: a case series report

Transitional implants (TI) can immediately improve the stability and retention of existing unstable mandibular complete dentures. This study evaluated the improvement of mandibular complete denture stability and retention with the use of TI. Three TIs were placed in the intraforaminal region of the edentulous mandible of seven patients (three men, four women; mean age 69.7 years). The patients' existing mandibular complete dentures were immediately modified to TI-stabilized overdentures. Their masticatory movements (mandibular movements during mastication) were measured using a commercially available tracking device (BioPACK, Bioresearch, Japan), both before TI placement and about 1 month after delivery of the TI-stabilized overdentures. The mean time of each chewing phase (opening, closing, and occluding) and coefficients of variation were calculated. The patients also completed a questionnaire about the foods they could chew and indicated on a 100 mm Visual Analog Scale (VAS) their personal levels of comfort, ease of chewing, speech, and stability. For masticatory movements, there were no significant differences (P > 0.05) between the TI-stabilized overdentures and existing complete dentures. However, the number of foods that could be chewed increased, and the stability and comfort were reported as improved with the TI-stabilized overdentures. Using TIs, the stability and comfort of the existing mandibular complete dentures studied in this report could be immediately improved.

A device for investigating neuromuscular control in the human masticatory system

A new apparatus has been developed to study the control of mastication in humans. The subject places his/her teeth on fixed upper and mobile lower bite plates; the device then enables opening and closing movements of the lower jaw against a controlled resistance. It is also possible to vary the number of teeth in contact with the device during an experiment from the entire dental arcade to a single tooth. The specially designed lower bite plate is dynamic and allows for both rotation and translation of the lower jaw during movement, thus, permitting the natural curvilinear trajectory of the jaw. The lower bite plate can follow chewing initiated by the subject without resisting the movement (‘no force’ mode) via a dedicated microprocessor controlled compensation mechanism. Another function of the device is to inject a constant predetermined load onto the lower bite plate so that the subject ‘chews’ against a fixed resistance simulating rapidly yielding food bolus (‘fixed force’ mode). The device can be programmed to increase or decrease the force during the closing or opening phase of chewing by feeding the position information into the force compensation system so both position and force change in parallel, hence, simulating a bite onto a non-yielding, or sticky, food bolus (‘normal chewing’ mode). By use of a jaw position compensation mechanism, the device can actively move the lower jaw, following any imposed position pattern (‘position controlled’ mode). The chewing simulator also has a mode that holds the position at a fixed level and allows the force to change (‘position hold’ mode). Furthermore, the device can inject additional rapid or slow forces or displacements onto the lower bite plate in order to elicit reflexes so that the response of jaw muscles to such stimuli can be examined at various jaw positions, force levels, phases of motion and velocities. The different modes of the apparatus can be used to study the operation and feedback control of human mastication; in particular whether modulations in jaw muscle activity and reflexes are due to changes in force, velocity, position, chewing cycle phase or a combination of these factors.