Bite or brain: Implication of sensorimotor regulation and neuroplasticity in oral rehabilitation procedures.

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.

Temporal profile and amplitude of human masseter muscle activity is adapted to food properties during individual chewing cycles.

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.

Occlusion on implants - is there a problem?

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.

From brain to bridge: masticatory function and dental implants.

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.

Sensations evoked by microstimulation of single mechanoreceptive afferents innervating the human face and mouth.

Intraneural microneurography and microstimulation were performed on single afferent axons in the inferior alveolar and lingual nerves innervating the face, teeth, labial, or oral mucosa. Using natural mechanical stimuli, 35 single mechanoreceptive afferents were characterized with respect to unit type [fast adapting type I (FA I), FA hair, slowly adapting type I and II (SA I and SA II), periodontal, and deep tongue units] as well as size and shape of the receptive field. All afferents were subsequently microstimulated with pulse trains at 30 Hz lasting 1.0 s. Afferents recordings whose were stable thereafter were also tested with single pulses and pulse trains at 5 and 60 Hz. The results revealed that electrical stimulation of single FA I, FA hair, and SA I afferents from the orofacial region can evoke a percept that is spatially matched to the afferent's receptive field and consistent with the afferent's response properties as observed on natural mechanical stimulation. Stimulation of FA afferents typically evoked sensations that were vibratory in nature; whereas those of SA I afferents were felt as constant pressure. These afferents terminate superficially in the orofacial tissues and seem to have a particularly powerful access to perceptual levels. In contrast, microstimulation of single periodontal, SA II, and deep tongue afferents failed to evoke a sensation that matched the receptive field of the afferent. These afferents terminate more deeply in the tissues, are often active in the absence of external stimulation, and probably access perceptual levels only when multiple afferents are stimulated. It is suggested that the spontaneously active afferents that monitor tension in collagen fibers (SA II and periodontal afferents) may have the role to register the mechanical state of the soft tissues, which has been hypothesized to help maintain the body's representation in the central somatosensory system.

Weak- and strong-coupling electrostatic interactions between asymmetrically charged planar surfaces.

We compare weak- and strong-coupling theory of counterion-mediated electrostatic interactions between two asymmetrically charged plates with extensive Monte Carlo simulations. Analytical results in both weak- and strong-coupling limits compare excellently with simulations in their respective regimes of validity. The system shows a surprisingly rich structure in terms of interactions between the surfaces as well as fundamental qualitative differences in behavior in the weak- and the strong-coupling limits.

Planar screening by charge polydisperse counterions.

We study how a neutralising cloud of counterions screens the electric field of a uniformly charged planar membrane (plate), when the counterions are characterised by a distribution of charges (or valence), [Formula: see text]. We work out analytically the one-plate and two-plate cases, at the level of non-linear Poisson-Boltzmann theory. The (essentially asymptotic) predictions are successfully compared to numerical solutions of the full Poisson-Boltzmann theory, but also to Monte Carlo simulations. The counterions with smallest valence control the long-distance features of interactions, and may qualitatively change the results pertaining to the classic monodisperse case where all counterions have the same charge. Emphasis is put on continuous distributions [Formula: see text], for which new power-laws can be evidenced, be it for the ionic density or the pressure, in the one- and two-plates situations respectively. We show that for discrete distributions, more relevant for experiments, these scaling laws persist in an intermediate but yet observable range. Furthermore, it appears that from a practical point of view, hallmarks of the continuous [Formula: see text] behaviour are already featured by discrete mixtures with a relatively small number of constituents.

Development of the jaw sensorimotor control and chewing - a systematic review.

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.

Effect of friction on dense suspension flows of hard particles.

We use numerical simulations to study the effect of particle friction on suspension flows of non-Brownian hard particles. By systematically varying the microscopic friction coefficient µ_{p} and the viscous number J, we build a phase diagram that identifies three regimes of flow: frictionless, frictional sliding, and rolling. Using energy balance in flow, we predict relations between kinetic observables, confirmed by numerical simulations. For realistic friction coefficients and small viscous numbers (below J∼10^{-3}), we show that the dominating dissipative mechanism is sliding of frictional contacts, and we characterize asymptotic behaviors as jamming is approached. Outside this regime, our observations support the idea that flow belongs to the universality class of frictionless particles. We discuss recent experiments in the context of our phase diagram.

Encoding of tooth loads by human periodontal afferents and their role in jaw motor control.

Microneurography has been used to analyze the functional properties of human periodontal mechanoreceptors. Signals were recorded from single afferents in the inferior alveolar nerve while controlled forces were applied to the teeth. We have found that all periodontal afferents adapt slowly to maintained loads. Most afferents are tuned broadly to direction of force application, and about half respond to forces applied to teeth adjacent to the one to which the afferent distributes. Populations of periodontal afferents, nevertheless, reliably encode information about both the teeth stimulated and the direction of forces applied to the individual teeth. Information about the magnitude of steady forces is made available in the mean firing-rate response of periodontal afferents. Most afferents exhibit a marked "hyperbolic" relationship between the static discharge rate and the force amplitude; the highest sensitivity to changes in static force is observed at forces below 1 N. Similarly, the dynamic sensitivity is highest at low forces. These afferents efficiently encode food contact during biting and continuously discharge while food is held between the incisors. Subjects spontaneously exert low contact forces matched to the sensitivity characteristics of these periodontal afferents when holding food substances between the incisors. If periodontal afferent information is not available, the control of the hold forces is severely impaired. Moreover, since only a few afferents encode information about the rapid and strong force increase employed to bite through food, we conclude that subjects rely on signals from periodontal afferents to regulate the jaw muscles primarily when they first contact, manipulate and hold food substances between the teeth. A potential role for periodontal afferents in the spatio-intensive control of jaw actions is discussed.

A Randomized Controlled Trial of Crown Therapy in Young Individuals with Amelogenesis Imperfecta.

Amelogenesis imperfecta (AI) is a rare, genetically determined defect in enamel mineralization. Existing treatment recommendations suggest resin-composite restorations until adulthood, although such restorations have a limited longevity. New crown materials allow for minimal preparation techniques. The aim of this study was to compare the quality and longevity of 2 crown types-Procera and IPS e.max Press-in adolescents and young adults with AI. A secondary aim was to document adverse events. We included 27 patients (11 to 22 y of age) with AI in need of crown therapy in a randomized controlled trial using a split-mouth technique. After placing 119 Procera crowns and 108 IPS e.max Press crowns following randomization, we recorded longevity, quality, adverse events, and tooth sensitivity. After 2 y, 97% of the crowns in both crown groups had excellent or acceptable quality. We found no significant differences in quality between Procera and IPS e.max Press crowns. Tooth sensitivity was significantly reduced after crown therapy (P < 0.001). Endodontic complications occurred in 3% of crowns. The results show that it is possible to perform crown therapy with excellent results and without severe complications in young patients with AI. The study is registered at http://www.controlled-trials.com (ISRCTN70438627).

Effects of short-term training on behavioral learning and skill acquisition during intraoral fine motor task.

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.

Food-holding and -biting behavior in human subjects lacking periodontal receptors.

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.

Conserved features of cancer cells define their sensitivity to HAMLET-induced death; c-Myc and glycolysis.

HAMLET is the first member of a new family of tumoricidal protein-lipid complexes that kill cancer cells broadly, while sparing healthy, differentiated cells. Many and diverse tumor cell types are sensitive to the lethal effect, suggesting that HAMLET identifies and activates conserved death pathways in cancer cells. Here, we investigated the molecular basis for the difference in sensitivity between cancer cells and healthy cells. Using a combination of small-hairpin RNA (shRNA) inhibition, proteomic and metabolomic technology, we identified the c-Myc oncogene as one essential determinant of HAMLET sensitivity. Increased c-Myc expression levels promoted sensitivity to HAMLET and shRNA knockdown of c-Myc suppressed the lethal response, suggesting that oncogenic transformation with c-Myc creates a HAMLET-sensitive phenotype. Furthermore, HAMLET sensitivity was modified by the glycolytic state of tumor cells. Glucose deprivation sensitized tumor cells to HAMLET-induced cell death and in the shRNA screen, hexokinase 1 (HK1), 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 1 and hypoxia-inducible factor 1α modified HAMLET sensitivity. HK1 was shown to bind HAMLET in a protein array containing ∼8000 targets, and HK activity decreased within 15 min of HAMLET treatment, before morphological signs of tumor cell death. In parallel, HAMLET triggered rapid metabolic paralysis in carcinoma cells. Tumor cells were also shown to contain large amounts of oleic acid and its derivatives already after 15 min. The results identify HAMLET as a novel anti-cancer agent that kills tumor cells by exploiting unifying features of cancer cells such as oncogene addiction or the Warburg effect.

Repulsion between oppositely charged macromolecules or particles.

The interaction of two oppositely charged surfaces has been investigated using Monte Carlo simulations and approximate analytical methods. When immersed in an aqueous electrolyte containing only monovalent ions, two such surfaces will generally show an attraction at large and intermediate separations. However, if the electrolyte solution contains divalent or multivalent ions, then a repulsion can appear at intermediate separations. The repulsion increases with increasing concentration of the multivalent salt as well as with the valency of the multivalent ion. The addition of a second salt with only monovalent ions magnifies the effect. The repulsion between oppositely charged surfaces is an effect of ion-ion correlations, and it increases with increasing electrostatic coupling and, for example, a lowering of the dielectric permittivity enhances the effect. An apparent charge reversal of the surface neutralized by the multivalent ion is always observed together with a repulsion at large separation, whereas at intermediate separations a repulsion can appear without charge reversal. The effect is hardly observable for a symmetric multivalent salt (e.g., 2:2 or 3:3).

Sensory-motor function of human periodontal mechanoreceptors.

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.

Mechanoreceptive afferents in the human sural nerve.

Microneurography was used to characterize 104 low-threshold mechanoreceptive afferents in the human sural nerve. The afferents were readily classified into four types using criteria developed for the glabrous skin of the hand: SA I (31%), SA II (11%), FA I (49%), and FA II (9%). The distribution of fascicle fields and receptive fields of individual afferents on the lateral side of the foot indicates that the glabrous skin portion of the innervation territory of the sural nerve is more densely innervated than the non-glabrous skin portion. The different populations in the glabrous and non-glabrous skin regions were similar regarding proportion of unit types, receptive field sizes, and force thresholds. The receptive field sizes of the type I units of the present sample were about twice the size compared to those of the glabrous hand units, and the force threshold were at least three times higher for three of the unit types (SA I, FA I, and FA II). Given their receptive properties, it is likely that mechanoreceptive afferents in the sural nerve provide rich information about contact patterns between the foot and environment during stance and locomotion.

Multiple-tooth receptive fields of single human periodontal mechanoreceptive afferents.

1. Single-unit impulse activity from 25 mechanoreceptive afferents was recorded in the human inferior alveolar nerve using tungsten microelectrodes. All of these afferents were considered to originate in periodontal receptors because they showed responses to mechanical stimulation of one or more teeth but not to stimulation of the gingiva. 2. For each afferent isolated, forces with "ramp-and-hold"-shaped profiles of similar magnitudes (261 +/- 21 mN, mean +/- SD) were applied to the incisors, the canine, and the first premolar on the recording side, and the contralateral central incisor in four horizontal directions: lingual, labial, mesial, and distal. For a few of the afferents, forces were also applied in the axial directions (up and down). Both static and dynamic response components were analyzed. 3. For about one half of the tested afferents, the receptive fields were restricted to a single tooth. The remainder (52%) responded to stimulation of a group of teeth (on average 3.1 teeth), which typically showed contact between their crowns. 4. Afferents responding to loading of multiple teeth showed their strongest responses to forces applied to a particular tooth, with a gradual decline in the responsiveness to the adjacent teeth. 5. The stimulation directions eliciting the strongest afferent responses for the most sensitive tooth were approximately evenly distributed over the four stimulation directions, except for some bias toward the lingual direction. In contrast, loading of the adjacent teeth most often showed the strongest responses in the mesial or distal directions, in most cases toward the most sensitive tooth.(ABSTRACT TRUNCATED AT 250 WORDS)

Low-threshold mechanoreceptive afferents in the human lingual nerve.

Intrafascicular multiunit activity and impulses in single mechanoreceptive afferents were recorded from the human lingual nerve with permucosally inserted tungsten microelectrodes. Nylon filaments and blunt glass probes were used for mechanical stimulation of the mucosa of the dorsal surface of the tongue. The innervation territories of nine nerve fascicles were mapped during multiunit recordings. All fascicle fields included the tip of the tongue, suggesting a particularly high innervation density for this area. Thirty-three single mechanoreceptive afferents were isolated and studied. Of these afferents, 22 were characterized by very small mucosal receptive fields (range: 1-19.6 mm2; geometric mean: 2.4 mm2) and responded to extremely low mechanical forces (force threshold range: 0.03-2 mN; geometric mean: 0.15 mN). As such, it was concluded that these "superficial" units terminated near the surface of the tongue. The remaining 11 units responded to probing of large areas of the tongue (> 200 mm2) and exhibited high force thresholds (> or = 4 mN). It was concluded that these "deep" units terminated in the muscle mass of the tongue. Fourteen of the superficial units were classified as rapidly adapting and resembled the fast-adapting type I afferents described for the glabrous skin of the human hand. The rapidly adapting units responded both during the application and removal of, but not during maintenance of, the mechanical stimuli on the receptive field. Two types of slowly adapting responses were observed. One type (characteristic of only 2 units) was characterized by a pronounced sensitivity to force change during the application and removal of the mechanical stimuli and an irregular static discharge during maintenance of the stimulus on the receptive field. In contrast, the other six units exhibited a weak sensitivity to force change, a highly regular static discharge, and spontaneous activity. As such, these two types of slowly adapting units resembled the slowly adapting I and II afferents, respectively, described for the hand. All 11 deep units were slowly adapting, and 7 were, in addition, spontaneously active. The units were not equally sensitive to the application and removal of the mechanical stimuli, suggesting at least two different modes of termination in tongue muscle. The deep units reliably encoded information about tongue movements in the absence of direct contact with the receptive field. In contrast, the superficial units responded vigorously when the tongue was moved to bring the receptive field into physical contact with other intraoral structures.

Encoding of amplitude and rate of forces applied to the teeth by human periodontal mechanoreceptive afferents.

1. The encoding of force amplitude and force rate by human periodontal mechanoreceptive afferents was studied. Recordings were obtained from 19 single periodontal afferents in the inferior alveolar nerve with the use of tungsten microelectrodes. Loads consisting of a force increase (loading ramp), a phase of maintained force (static phase), and a force decrease (unloading ramp) were applied to the receptor bearing tooth, which was most often an incisor. The static forces applied ranged between 0.05 and 5 N, and the rate of force applied during the loading ramps ranged between 0.4 and 70 N/s. The forces were primarily applied in one of six directions (lingual, labial, mesial, distal, upward, or downward) that evoked the greatest discharge activity. 2. For each force application, the steady-state response was defined as the mean discharge rate during a 1-s period starting 0.5 s after the end of the loading ramp. Most afferents (15/19) exhibited a "hyperbolic" (viz., negatively accelerating) relationship between the amplitude of the stimulation force and the steady-state response, featuring a pronounced saturation tendency: the highest sensitivity to changes in static force was observed at force levels below 1 N. At higher force levels the sensitivity gradually diminished. Moreover, the dynamic sensitivity similarly decreased with increasing amplitude of static background force. For a subsample of afferents studied, comparable stimulus-response relationships were obtained in directions other than the most responsive one, but the discharge rates were lower. 3. In contrast to the response of most afferents, four (4/19) differed in that they consistently exhibited a nearly linear relationship between force amplitude and the steady-state response. Moreover, these afferents maintained their dynamic sensitivity as the amplitude of the background force was increased. 4. The steady-state response of all afferents was well described as a constant times F/ (F + c), where F represents the steady-state force, and c the force generating one-half the estimated maximum discharge rate that could be evoked by steady-state force stimulation. The c-parameter was on average 0.42 N (range 0.05-1.1 N) for the afferents exhibiting hyperbolic stimulus-response relationships. In contrast it ranged between 5 and 22 N for those exhibiting "nearly linear" relationships. A hypothetical model of the mechanics of the periodontal ligament supporting the F/(F + c) transform is proposed. 5. A general transfer function was developed to predict the instantaneous discharge rate of an individual afferent to arbitrary force profiles applied to the receptor bearing tooth.(ABSTRACT TRUNCATED AT 400 WORDS)