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The study aimed to evaluate the hypothesis that chewing is a mechanical and physiological contributor to swallowing, physiologic/pathologic processes of the gastrointestinal tract (GIT), and nutrition-related factors. A search strategy was applied to three different databases to investigate if chewing function in adults affects the swallowing, physiologic/pathologic processes of the GIT, and nutrition-related factors compared to controls with no exposure. The included studies were evaluated for methodological quality and risk of bias and certainty of evidence. The results showed 71 eligible studies. Overall, the results showed that 46 studies supported the hypothesis while 25 refuted it. However, the GRADE analysis showed low to very low certainty of the evidence to support the hypothesis that chewing is an important contributor in the swallowing process, and physiologic/pathologic processes in the GIT. The GRADE analysis also showed a moderate to very low certainty of the evidence to suggest that chewing function contributes to nutrition-related parameters. The overall results of the current study showed that a majority (64.7%) of the studies (46 out of 71) supported the hypothesis. However, robust studies with proper design, adequate sample size, and well-defined outcome parameters are needed to establish conclusive evidence.

Objective: To investigate the effect of short-term training on behavioral learning and skill acquisition during a natural yet novel biting task., Methods: Thirty (18 women) healthy volunteers in the age range of 18-32 years were divided into a naive (n = 17) and expert (n = 13) groups based on the self-reported familiarity to perform a complex behavioral biting task. The volunteers participated in a single experimental session divided into three sets with three series, each with ten trials of a standardized biting task. The task was to position, split and retrieve a sunflower seed from its shell without crushing the seed. The two consecutive sets were separated by fifteen minutes of short-term training. During the short-term training, the participants repeatedly performed the biting task for about fifteen minutes. A five-point grading system was devised to determine the performance and video registrations were made to determine the duration of the task., Results: There was a significant main effect of training on the task performance scores (P < .001). The performance scores of the naive group before training was significantly lower than all the sets of the expert group (P < .010). The performance scores of the naive group were also significantly better after training than before (P = .001). However, the expert group took significantly shorter time to complete the task than the naive group., Conclusion: The results of the present study show a significant effect of training on the performance of a complex behavioral biting task. Training resulted in improved performance scores and a subtle decrease in the duration of the task., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Mastication is a complex sensorimotor interaction between the central nervous system and the peripheral masticatory apparatus. To understand the effect of oro-facial abnormalities on mastication, it is important to first understand the normal development of jaw sensorimotor control and chewing in healthy children. Original studies which investigated four main objective parameters of chewing, i.e. maximum occlusal bite force, electromyography (EMG), jaw kinematics and chewing efficiency in children were systematically searched using three established databases. The targeted sample was healthy children below the age of 18-years. All studies that subjectively assessed mastication, studies of children with abnormalities, or non-English studies were excluded. A total of 6193 papers were identified, 53 met the final inclusion criteria. Results are presented according to the dentition stage. Children below 6-years (primary dentition) had lower biting forces and EMG activity, and the frontal jaw movement pattern was more laterally displaced and less stable than children older than 6-years. EMG activities and bite forces increased in children 6- to 10-year-old (early mixed dentition) with a reduction in lateral jaw displacement and an increase in vertical jaw displacement. Twelve-year-old children were able to chew food into smaller particles compared to 6-year-olds. Gender differences were visible in all parameters except EMG activity in late mixed dentition (10- to 12-years). After 12-years, there was a significant increase in bite forces and EMG activities, and the frontal jaw pattern became similar to adults. Studied chewing parameters gradually improve with the development of the oro-facial structures and were mainly influenced by dental eruption. A significant development of chewing parameters occurs after 12 years of age. A transition to the adult-type of masticatory behavior occurs between 10- to 14-years of age., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Previously we have reported a biphasic increase in excitatory drive of the masseter muscle during natural chewing in young adults. We now hypothesize that sensory inputs from the periodontal mechanoreceptors (PMRs) are responsible for the late increase in excitatory drive during this biphasic movement. 13 participants with implant-supported bridges in both jaws, and thus lacking PMRs, and 13 participants with natural dentition chewed and swallowed model food of different hardness. Electromyographic (EMG) activity of the masseter muscle was recorded, along with the position of the mandible, and the muscle activity and jaw kinematics during the different phases of the chewing cycle were analyzed. Throughout the entire masticatory sequence, the excitatory drive of the masseter muscle during the jaw closing increased in a biphasic manner for the dentate participants; whereas biphasic elevation was observed only during the middle and last segments in the implant participants. Dentate participants exhibited significantly greater boosting of the EMG activity during late jaw closing than the implant participants, irrespective of food hardness and segment of the masticatory sequence. Sensory information from PMRs are required for boosting the enhancement of masseter muscle activity during the late jaw closing, during tooth-food contact.

Tooth loss, decreased mass and strength of the masticatory muscles leading to difficulty in chewing have been suggested as important determinants of eating and nutrition in the elderly. To compensate for the loss of teeth, in particular, a majority of the elderly rely on dental prosthesis for chewing. Chewing function is indeed an important aspect of oral health, and therefore, oral rehabilitation procedures should aim to restore or maintain adequate function. However, even if the possibilities to anatomically restore lost teeth and occlusion have never been better; conventional rehabilitation procedures may still fail to optimally restore oral functions. Perhaps this is due to the lack of focus on the importance of the brain in the rehabilitation procedures. Therefore, the aim of this narrative review was to discuss the importance of maintaining or restoring optimum chewing function in the superageing population and to summarise the emerging studies on oral motor task performance and measures of cortical neuroplasticity induced by systematic training paradigms in healthy participants. Further, brain imaging studies in patients undergoing or undergone oral rehabilitation procedures will be discussed. Overall, this information is believed to enhance the understanding and develop better rehabilitative strategies to exploit training-induced cortical neuroplasticity in individuals affected by impaired oral motor coordination and function. Training or relearning of oral motor tasks could be important to optimise masticatory performance in dental prosthesis users and may represent a much-needed paradigm shift in the approach to oral rehabilitation procedures., (© 2018 John Wiley & Sons Ltd.)

Sensory information from periodontal mechanoreceptors (PMRs) surrounding the roots of natural teeth is important for optimizing the positioning of food and adjustment of force vectors during precision biting. The present experiment was designed to test the hypothesis; that reduction of afferent inputs from the PMRs, by anesthesia, perturbs the oral fine motor control and related jaw movements during intraoral manipulation of morsels of food. Thirty healthy volunteers with a natural dentition were equally divided into experimental and control groups. The participants in both groups were asked to manipulate and split a spherical candy into two equal halves with the front teeth. An intervention was made by anesthetizing the upper and lower incisors of the experimental group while the control group performed the task without intervention. Performance of the split was evaluated and the jaw movement recorded. The experimental group demonstrated a significant decrease in measures of performance following local anesthesia. However, there was no significant changes in the duration or position of the jaw during movements in the experimental and control group. In conclusion, transient deprivation of sensory information from PMRs perturbs oral fine motor control during intraoral manipulation of food, however, no significant alterations in duration or positions of the jaw during movements can be observed.

Objective: The study was designed to investigate if alteration of different orofacial afferent inputs would have different effects on oral fine motor control and to test the hypothesis that reduced afferent inputs will increase the variability of bite force values and jaw muscle activity, and repeated training with splitting of food morsel in conditions with reduced afferent inputs would decrease the variability and lead to optimization of bite force values and jaw muscle activity., Material Methods: Forty-five healthy volunteers participated in a single experimental session and were equally divided into incisal, mucosal, and block anesthesia groups. The participants performed six series (with ten trials) of a standardized hold and split task after the intervention with local anesthesia was made in the respective groups. The hold and split forces along with the corresponding jaw muscle activity were recorded and compared to a reference group., Results: The hold force and the electromyographic (EMG) activity of the masseter muscles during the hold phase were significantly higher in the incisal and block anesthesia group, as compared to the reference group (P < 0.001). However, there was no significant effect of groups on the split force (P = 0.975) but a significant decrease in the EMG activity of right masseter in mucosal anesthesia group as compared to the reference group (P = 0.006). The results also revealed that there was no significant effect of local anesthesia on the variability of the hold and split force (P < 0.677). However, there was a significant decrease in the variability of EMG activity of the jaw closing muscles in the block anesthesia group as compared to the reference group (P < 0.041), during the hold phase and a significant increase in the variability of EMG activity of right masseter in the mucosal anesthesia group (P = 0.021) along with a significant increase in the EMG activity of anterior temporalis muscle in the incisal anesthesia group, compared to the reference group (P = 0.018), during the split phase., Conclusions: The results of the present study indicated that altering different orofacial afferent inputs may have different effects on some aspects of oral fine motor control. Further, inhibition of afferent inputs from the orofacial or periodontal mechanoreceptors did not increase the variability of bite force values and jaw muscle activity; indicating that the relative precision of the oral fine motor task was not compromised inspite of the anesthesia. The results also suggest the propensity of optimization of bite force values and jaw muscle activity due to repeated splitting of the food morsels, inspite of alteration of sensory inputs., Clinical Relevance: Skill acquisition following a change in oral sensory environment is crucial for understanding how humans learn and re-learn oral motor behaviors and the kind of adaptation that takes place after successful oral rehabilitation procedures.

Background: Chewing and masticatory function constitutes one of the most important oral health factors that affect quality of life, especially in older individuals. Little consensus currently exists regarding ways to objectively assess clinical masticatory performance (in this context, performance refers an individual's objective ability to mix or comminute food bolus). That said, many methods were developed to assess masticatory performance. Consequently, systematic review of the literature would be of great value when it comes to identifying various methods for objectively assessing clinical masticatory performance and for evaluating these methods., Design: This study protocol describes a systematic review that intends to (i) identify methods to objectively assess clinical masticatory performance and (ii) evaluate psychometric properties (such as validity and reliability) of the identified methods. A systematic literature search is required to do so in these sources: MEDLINE (Ovid), Embase (embase.com), Web of Science Core Collection (Thomson Reuters), Cochrane (Wiley), and Cinahl (Ebsco)., Inclusion Criteria: studies in scientific, full-text articles; development articles; validation articles; studies of the general adult population, ages ≥18., Exclusion Criteria: topics and article types that cover interview methods and self-reported questionnaires; methods/instruments that measure subjective masticatory performance; qualitative studies and case studies; opinion and editorial pieces; animal studies; studies of humans with severe oral health complications., Discussion: This systematic review will result in a comprehensive assessment of various methods designed to objectively measure clinical masticatory performance. This systematic review will rate these methods, assess their reliability and validity, and identify one or more methods that can be recommended for use in clinical and scientific environments. From what is currently known, no systematic evaluation of various methods for objectively assessing clinical masticatory performance has been published., Systematic Review Registration: PROSPERO CRD42016037700.

Objectives: Appropriate sensory information from periodontal mechanoreceptors (PMRs) is important for optimizing the positioning of food and adjustment of force vectors during precision biting. This study was designed to describe motor behavior during the first cycle of a natural chewing task and to evaluate the role of such sensory input in this behavior., Material and Methods: While 10 subjects with natural dentition, 11 with bimaxillary fixed tooth-supported prostheses (TSP) and 10 with bimaxillary fixed implant-supported prostheses (ISP) (mean age 69 [range 61-83]) chewed a total of five hazelnuts, their vertical and lateral jaw movements were recorded. Data obtained during the first chewing cycle of each hazelnut were analyzed., Results: The amplitude of vertical and lateral mandibular movement and duration of jaw opening did not differ between the groups, indicating similar behavior during this part of the chewing cycle. However, only 30% of the subjects in the natural dentate group, but 82% of those in the TSP and 70% in the ISP group exhibited slippage of the hazelnut during jaw closure in at least one of five trials. The TSP and ISP groups also exhibited more irregular and narrower patterns of motion (total lateral/vertical movement = 0.15 and 0.19, respectively, compared to 0.27 for the natural group)., Conclusions: Subjects with fixed tooth- or implant-supported prostheses in both jaws show altered behavior, including inadequate control of the hazelnut, during the first chewing cycle. We propose that these differences are due to impairment or absence of sensory signaling from PMRs in these individuals., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Sensory information from the orofacial mechanoreceptors are used by the nervous system to optimize the positioning of food, determine the force levels, and force vectors involved in biting of food morsels. Moreover, practice resulting from repetition could be a key to learning and acquiring a motor skill. Hence, the aim of the experiment was to test the hypothesis that repeated splitting of a food morsel during a short-term training with an oral fine motor task would result in increased performance and optimization of jaw movements, in terms of reduction in duration of various phases of the jaw movements. Thirty healthy volunteers were asked to intraorally manipulate and split a chocolate candy, into two equal halves. The participants performed three series (with 10 trials) of the task before and after a short-term (approximately 30 min) training. The accuracy of the split and vertical jaw movement during the task were recorded. The precision of task performance improved significantly after training (22% mean deviation from ideal split after vs. 31% before; P<0.001). There was a significant decrease in the total duration of jaw movements during the task after the training (1.21 s total duration after vs. 1.56 s before; P<0.001). Further, when the jaw movements were divided into different phases, the jaw opening phase and contact phase were significantly shorter after training than before training (P=0.001, P=0.002). The results indicate that short-term training of an oral fine motor task induces behavior learning, skill acquisition and optimization of jaw movements in terms of better performance and reduction in the duration of jaw movements, during the task. The finding of the present study provides insights into how humans learn oral motor behaviors or the kind of adaptation that takes place after a successful prosthetic rehabilitation., (Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.)

Objective: To investigate if repeated holding and splitting of food morsel change the variability of force and jaw muscle activity in participants with natural dentition., Methods: Twenty healthy volunteers (mean age=26.2±3.9 years) participated in a single session divided into six series. Each series consisted of ten trials of a standardized behavioural task (total 60 trials) involving holding and splitting a flat-faced tablet (8mm, 180mg) 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., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Jaw actions adapt to the changing properties of food that occur during a masticatory sequence. In the present study, we investigated how the time-varying activation profile of the masseter muscle changes during natural chewing in humans and how food hardness affects the profile. We recorded surface electromyography (EMG) of the masseter muscle together with the movement of the lower jaw in 14 healthy young adults (mean age 22) when chewing gelatin-based model food of two different hardness. The muscle activity and the jaw kinematics were analysed for different phases of the chewing cycles. The increase in the excitatory drive of the masseter muscle was biphasic during the jaw-closing phase showing early and late components. The transition between these components occurred approximately at the time of tooth-food contact. During the masticatory sequence, when the food was particularised, the size of the early component as well as the peak amplitude of the EMG significantly decreased along with a reduction in the duration of the jaw-closing phase. Except for amplitude scaling, food hardness did not appreciably affect the muscle's activation profile. In conclusion, when chewing food during natural conditions, masseter muscle activation adapted throughout the masticatory sequence, principally during the jaw-closing phase and influenced both early and late muscle activation components. Furthermore, the adaptation of jaw actions to food hardness was affected by amplitude scaling of the magnitude of the muscle activity throughout the masticatory sequence., (© 2014 John Wiley & Sons Ltd.)

Objectives: Sensory information provided by the periodontal mechanoreceptors (PMRs) is used by the nervous system to optimize the positioning of food, force levels, and force vectors involved in biting. The aim of this study was to describe motor performance during a novel manipulation-and-split task and to assess the extent to which control of this performance involves information from the PMRs., Materials and Methods: A total of 10 subjects with natural teeth, 10 with bimaxillary tooth-supported fixed prostheses (TSP) and 10 with bimaxillary implant-supported fixed prostheses (ISP) (61-83 [mean 69] years of age) were asked to perform an intraoral manipulation-and-split task that involved positioning a spherical chocolate dragée between the front teeth and then splitting it into two parts of equal size. The vertical jaw movement, sound of food cracking and masseter muscle activity were monitored during this task and the accuracy of the split was evaluated., Results: The group with natural teeth was significantly better than the other groups at splitting the candy with high precision. The jaw movements were similar between groups, but the contact phase prior to the split was significantly longer for those with natural dentition., Conclusions: The present findings support the conclusion that the nervous system collects rich information about contact between the teeth and food from the PMRs prior to powerful jaw action. Impairment (TSP) or absence (ISP) of this information alters motor behavior and impairs performance during the natural biting task employed here., (© 2012 John Wiley & Sons A/S.)

Masticatory function is an important aspect of oral health, and oral rehabilitation should aim to maintain or restore adequate function. The present qualitative review is the joint effort of a group of clinicians and researchers with experiences ranging from basic and clinical oral neuroscience to management of patients with dental implants. The aim is to provide a short summary for the clinician of the many aspects related to masticatory function (including quality of life) and rehabilitation with dental implants. While there are many reviews on the tissue responses to dental implants and technical aspects, the functional aspects have received relatively little focus., (© 2012 Blackwell Publishing Ltd.)

Objectives: To determine whether there is an association between tooth loss, chewing ability, and cognitive function in a general elderly population., Design: Data from the Panel Study of Living Conditions of the Oldest Old in 2002 were analyzed. Stepwise logistic regression analyses were used to examine the relationship between cognitive function and tooth loss and chewing ability., Participants: Five hundred fifty-seven persons who were nationally representative of the Swedish population aged 77 and older., Measurements: Cognitive function was measured using the abridged version of the Mini-Mental State Examination. Information on dental status and chewing difficulty was obtained according to self-assessment., Results: Persons with multiple tooth loss and persons with difficulty chewing hard food had significantly higher odds of cognitive impairment. When adjusted for sex, age, and education, the odds of cognitive impairment were not significantly different between persons with natural teeth and with multiple tooth loss, but the odds of impairment remained significantly higher for persons with chewing difficulty even when adjusted for sex, age, education, depression, and mental illness., Conclusion: Sex, age, education, and certain illnesses do not explain the association between cognition and chewing ability. Whether elderly persons chew with natural teeth or prostheses may not contribute significantly to cognitive impairment as long as they have no chewing difficulty. The results add to the evidence of the association between chewing ability and cognitive impairment in elderly persons., (© 2012, Copyright the Authors Journal compilation © 2012, The American Geriatrics Society.)

Objectives: We aimed to determine whether people with implant-supported bridges in both jaws, thus lacking periodontal receptors, adjust jaw muscle activity to food hardness during mastication., Materials and Methods: Thirteen participants with implant-supported bridges in both jaws and 13 with natural dentition chewed and swallowed soft and hard gelatine-based model foods, while electromyographic (EMG) activity of the masseter and temporal muscles was recorded bilaterally together with the position of the mandible. Data were compared by using a mixed-design anova model and a P-value<0.05 was considered statistically significant., Results: The number of chewing cycles and the duration of the masticatory sequence increased with food hardness in both groups, whereas vertical and lateral amplitude of the jaw movements, and the jaw-opening velocity, increased significantly with food hardness only for the dentate group. Although both groups adapted the EMG activity to the hardness of the food, the implant participants showed a significantly weaker increase in EMG activity with increased food hardness early during the masticatory sequence than the dentate participants did. In addition, the implant group showed significantly less reduction of muscle activity during the progression of the masticatory sequence than the dentate group., Conclusions: People with implant-supported bridges show an impaired adaptation of the muscle activity to food hardness during mastication. We suggest that a lack of sensory signals from periodontal mechanoreceptors accounts for the impairment., (© 2011 John Wiley & Sons A/S.)

The purpose of the study was to analyze how increases in the bite force, during the splitting of food morsels of different hardness, are modulated, and to evaluate the role of periodontal mechanoreceptors in this control. Fifteen subjects were instructed to hold and split food morsels of different hardness (peanuts and biscuits) between a pair of opposing central incisors before and during anesthesia of the teeth. The split occurred at an average bite force of 9 N for biscuits and at an average bite force of 18 N for peanuts. The duration of the split phase was longer, and the split force rate higher, for peanuts compared with biscuits. Furthermore, a steeper force trajectory was observed for the peanut. During anesthesia of the teeth, the duration of the split phase increased and the mean split force rate decreased for peanuts. Force trajectories for peanuts and biscuits were indistinguishable during anesthesia. The present results show that when higher bite forces are needed to split a morsel, both the duration and the rate of the bite force produced is increased. Furthermore, adaptation of the bite force rate to the hardness of the food is dependent on information from periodontal mechanoreceptors.

This overview summarises current knowledge on the force-encoding properties of periodontal mechanoreceptors supplying the human postcanine teeth and describe their signalling during chewing. Microneurographic experiments reveal that these receptors adapt slowly to maintained tooth loads. Similar to periodontal receptors at anterior teeth, about half respond to forces applied to more than one tooth and their receptive fields are broadly tuned to direction of force application. However, population analyses demonstrate that periodontal receptors supplying anterior and posterior teeth differ in their capacity to signal horizontal and vertical forces, respectively. Most periodontal receptors exhibit a strongly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in force at forces below 1N for anterior teeth and 4N for posterior teeth. Also the dynamic sensitivity is markedly reduced at high forces. According to a quantitative model of responses in periodontal receptors based on these data, most receptors efficiently encode food contact during chewing, but due to the marked saturation tendencies at higher forces these receptors poorly encode the magnitude of the strong chewing forces and the force changes occurring at these high loads. Information provided by periodontal receptors is critical for the specification of manipulative forces used when food is positioned between the teeth and prepared for chewing. When the strong chewing forces are applied to crush the food, the receptors signal functionally important information about the mechanical properties of food as well as the spatial contact patterns between the food and the dentition.

Hold-and-split tasks were performed by 20 subjects (12 females and 8 males) using the right central incisors, canines, 2nd premolars, and 1st molars, respectively. Half a peanut was positioned on a transducer-equipped plate and the subject was instructed to hold the plate with the peanut between two antagonistic teeth, and not using more force than necessary. After ca. 3 s the subject was instructed to split the peanut in a natural manner. Each session consisted of a series of three in which the subject performed the hold-and-split task five times for each tooth. Thus, in total, data were obtained from 60 trials for each subject. The magnitude of the forces and the force rates used to split the peanut increased distally along the dental arch. However, the duration of the split phase was similar for the various teeth examined. During anesthesia of the periodontal ligament (four subjects), no significant changes were seen in the split phase. The forces used to hold the peanut between the teeth also increased distally along the dental arch: 0.60 N for the incisor, 0.77 N for the canine, 1.15 N for the 2nd premolar, and 1.74 N for the 1st molar. The difference in hold forces for the various teeth can be explained by the different sensitivity characteristics of the periodontal afferents innervating anterior and posterior teeth. During periodontal anesthesia, the magnitude and variability of the hold forces increased for all types of teeth, thus supporting the suggestion that periodontal afferent information is used in the regulation of the level of forces used to hold and manipulate morsels between the teeth.

Background: Mechanoreceptors situated in the periodontal ligament provide detailed information about intensive and spatial aspects of tooth loads, which support the neural control of masticatory forces. We asked whether a reduced periodontal ligament due to periodontitis, and, thus, an altered mechanoreceptive innervation of the teeth, would affect masticatory behavior when subjects used incisors to hold and split food., Methods: We tested 11 subjects with reduced periodontal tissue support that rendered 30% to 70% alveolar bone loss for at least one pair of opposing anterior incisors. Forces were recorded when subjects used their affected incisors to hold half of a peanut for approximately 4 seconds and then split it. Age- and gender-matched healthy subjects served as the control group. None of the participants showed acute oral symptoms or massive periodontal inflammation., Results: The test group used greater force when holding food between the teeth (1.1+/-0.4 N [ mean+/-1 SD]) compared to the control group (0.4+/-0.2 N). Hold forces used by subjects in the test group were also more variable, both within and between trials. The increase in bite force applied to split the peanut was slower and more hesitant for subjects in the test group compared to the control group., Conclusions: Reduced periodontal tissue support accompanies impaired regulation of masticatory forces. Faulty mechanoreceptive innervation of the periodontal ligament explains the elevated hold force, whereas a change in biting strategy due to the weakened support of the teeth may account for the more defensive food-splitting behavior.

Natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the basic force-encoding properties of human periodontal receptors will be presented along with a discussion about their likely functional role in the control of human mastication. Microneurographic recordings from single nerve fibres reveal that human periodontal receptors adapt slowly to maintained tooth loads. Most receptors are broadly tuned to the direction of force application, and about half respond to forces applied to more than one tooth. Populations of periodontal receptors, nevertheless, reliably encode information about both the teeth stimulated, and the direction of forces applied to the individual teeth. Information about the magnitude of tooth loads is made available in the mean firing rate response of periodontal receptors. Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at very low force levels (below 1 N for anterior teeth and 4 N for posterior teeth). Thus, periodontal receptors efficiently encode tooth load when subjects contact and gently manipulate food using the teeth. It is demonstrated that signals from periodontal receptors are used in the fine motor control of the jaw and it is clear from studies of various patient groups (e.g. patients with dental implants) that important sensory-motor functions are lost or impaired when these receptors are removed during the extraction of teeth.

Microneurographic recordings were obtained from 20 periodontal mechanoreceptive afferents in the inferior alveolar nerve while force profiles of different amplitudes and rates were applied to a premolar or the first molar in the most sensitive direction. The majority of afferents (17/20) showed a hyperbolic relationship between the steady-state discharge rate and the amplitude of the stimulating force, featuring a pronounced saturation tendency. These afferents were also characterized by a similar decline in dynamic sensitivity with increasing amplitude of background force. However, a few afferents (3/20) showed nearly linear stimulus-response relationships and a small decline in dynamic sensitivity with increasing tooth load. Quantitative models developed for all afferents successfully predicted the afferent discharge rates for novel force stimulations. Application of the transfer function to chewing forces predicted that the discharge rates of periodontal afferents rapidly increased at initial tooth contact and continued to discharge as long as the tooth was loaded. However, due to the marked saturation tendencies at higher forces, most periodontal afferents poorly encoded the magnitude of the strong chewing forces. In addition, the discharge rates of a minority of afferents continued to reflect the force profile during high chewing forces. The results revealed that periodontal afferents of posterior teeth were less sensitive at low tooth loads compared with afferents of anterior teeth. During each chewing cycle, periodontal afferents may provide information about the mechanical properties of food shortly after tooth contact that can be used to scale the muscle commands of the upcoming power phase.

1. When dental implants are loaded mechanically, a sensation, often referred to as osseoperception, is evoked. The sensory signals underlying this phenomenon are qualitatively different from the signals evoked when loading a natural tooth. In contrast with osseointegrated dental implants, natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the functional properties of human periodontal mechanoreceptors will be presented, along with a discussion about their likely functional role in the control of human jaw actions. 2. Microneurographic experiments reveal that human periodontal mechanoreceptors adapt slowly to maintained tooth loads. Populations of periodontal receptors encode information about both which teeth are loaded and the direction of forces applied to individual teeth. 3. Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at surprisingly low forces (below 1 N for anterior teeth and 4 N for posterior teeth). Accordingly, periodontal receptors efficiently encode tooth load when subjects first contact, hold and gently manipulate food by the teeth. In contrast, only a minority of receptors encodes the rapid and strong increase in force generated when biting through food. 4. It is concluded that humans use periodontal afferent signals to control jaw actions associated with intra-oral manipulation of food rather than exertion of jaw power actions. Consequently, patients who lack information from periodontal receptors show an impaired fine motor control of the mandible.

Previous studies have suggested that information provided by periodontal mechanoreceptors is particularly important for the fine motor control of the mandible, i.e., when humans hold and carefully manipulate food particles between the teeth with low biting forces. In the present study, we further evaluated this hypothesis by comparing the performance of three age- and gender-matched groups of subjects for which the integrity of the periodontal sensory apparatus differed. Specifically, the subjects had either natural teeth (natural group), dental prostheses supported by oral mucosa (denture group), or dental prostheses supported by osseointegrated implants (implant group). Each subject was instructed to hold half a peanut between the upper and lower central incisors for ca. 3 sec, and then to split it. The force applied by the anterior teeth was continuously monitored by a transducer-equipped bar on which the morsel rested. While the peanut was held, the force generated by subjects in the denture and implant groups was more variable and averaged four times that generated by subjects in the natural group. The peanut was split by a distinct, rapid ramp-increase in force that was similar for all three groups. In subjects lacking periodontal receptors, the morsel frequently escaped from the incisal edges during both phases of the task. The results demonstrate a marked disturbance in the control of precisely directed, low biting forces in subjects lacking periodontal receptors and suggest that the receptors play a significant role in the specification of the level, direction, and point of attack of forces used to hold and manipulate food between the anterior teeth. Moreover, other types of mechanoreceptors can not fully compensate for the loss of periodontal receptors.

The method of microneurography was used to record activity in trigeminal cutaneous and mucosal mechanoreceptive afferents during natural orofacial behaviors such as speech gestures, chewing, licking and swallowing. Multi-unit activity and impulses in single nerve fibers were recorded from the infraorbital nerve. It appeared that these mechanoreceptors respond to contact between the lips, air pressures generated for speech sounds, and to the deformation/strain changes of the facial skin and mucosa associated with various phases of voluntary lip and jaw movements. The relatively vigorous discharge of cutaneous and mucosal afferents during natural movements of the face are consistent with the claim that mechanoreceptors found within the facial skin provide proprioceptive information on facial movements.

Oral rehabilitation restores form and function and impacts on general health. Teeth provide a discriminating sense of touch and directional specificity for occlusal perception, management of food with mastication and swallowing, and awareness of its texture and hardness. Peripheral feedback for control of jaw muscles includes the enamel-dentine-pulp complex and mechanoreceptors in the periodontal tissues. The implications of feedback from periodontal and other intra-oral mechanoreceptors as well as changes in central representation are significant for function and adaptation to oral rehabilitation. With implants, in the absence of the periodontium and periodontal mechanoreceptor feedback, fine motor control of mastication is reduced, but patients are still able to function adequately. Further, there is no significant difference in function with full-arch fixed prostheses on teeth in comparison with implants. Predictable implant outcomes depend on bone support. Optimum restoration design appears to be significant for bone remodelling and bone strains around implants with occlusal loading. Finite element analysis data confirmed load concentrations at the coronal bone around the upper section of the implant where bone loss is commonly observed clinically. Load concentration increased with steeper cusp inclination and broader occlusal table and decreased with central fossa loading and narrower occlusal table size. It is recommended that occlusal design should follow a narrow occlusal table, with central fossa loading in intercuspal contact and low cusp inclination to minimise lateral loading in function and parafunction. Acknowledging these features should address potential problems associated with the occlusion in implant therapy. [ABSTRACT FROM AUTHOR]