The role of tryptophan and its derivatives in musculoskeletal pains: A systematic review and meta-analysis.

BACKGROUND: Studies present ambiguous findings regarding the role of tryptophan and its metabolites, kynurenine and serotonin in chronic musculoskeletal pain. This systematic review aimed to investigate the expression of tryptophan and its metabolites, serotonin and kynurenine in patients with local and generalized chronic musculoskeletal pain in comparison with pain-free controls. METHODS: An electronic search was conducted in the databases MEDLINE, CINAHL, EMBASE, the Cochrane Central Registry of Controlled Trials (CENTRAL) and Web of Science for clinical and observational trials from the beginning of each database to 21 April 2023. Out of 6734 articles, a total of 17 studies were included; 12 studies were used in the meta-analysis of serotonin, 3 regarding tryptophan and 2 studies for a narrative synthesis regarding kynurenine. Risk of bias was assessed using the quality assessment tool for observational cohort and cross-sectional studies of the National Heart, Lung, and Blood Institute, while the certainty of evidence was by GRADE. RESULTS: All included studies showed a low risk of bias. The meta-analysis showed lower blood levels of tryptophan (p < .001; very low quality of evidence) and higher blood levels of serotonin (p < .001; very low-quality evidence) in patients with generalized musculoskeletal pain, when compared to pain-free individuals. In local chronic musculoskeletal pain, there were higher blood levels of serotonin (p=.251; very low quality of evidence) compared to pain-free individuals. Regarding kynurenine, the studies reported both higher and lower blood levels in generalized chronic musculoskeletal pain compared to pain-free individuals. CONCLUSIONS: The blood levels of tryptophan and its metabolites serotonin and kynurenine seem to influence chronic musculoskeletal pain.

Temporalis Muscle Changes Following Botulinum Toxin A Injections in Masseter Hypertrophy Patients: A Randomized Triple-Blinded Trial.

BACKGROUND: This study aimed to elucidate the effects of botulinum toxin A (BoNT-A) treatment for patients diagnosed with masseter hypertrophy on the temporalis muscle, with a particular focus on assessing alterations in muscle thickness, electromyographic (EMG) activity, and the development of muscle pain. METHODS: The present randomized triple-blinded clinical trial enrolled 26 female participants aged between 25 and 50 years complaining about masseter hypertrophy. Participants received 75U of BoNT-A (abobotulinumtoxinA) in both masseter muscles and after three months were randomized to receive a second treatment session of saline solution (S-BoNT-A) or BoNT-A (M-BoNT-A). Longitudinal assessments included temporalis muscle thickness through ultrasound, EMG activity, subjective pain, and masseter prominence severity after one, three, and six months of the first injection session. Muscle thickness, EMG, and subjective pain were analysed using two-way ANOVA with repeated measures and post hoc Sidak test, and for masseter prominence severity, Friedman and Mann-Whitney tests were used. RESULTS: Regarding inter-group comparisons, a higher muscle thickness (p < 0.02) and a higher EMG activity (p < 0.01) were found in the M-BoNT-A group at the 6-month follow-up. For subjective pain assessments, inter-group comparisons showed a higher prevalence of painful regions in M-BoNT-A group at the 6-month follow-up (p < 0.02). No significant differences were found in masseter prominence severity at the 6 months assessment between groups. CONCLUSION: BoNT-A treatment for masseter hypertrophy lead to structural and functional changes in the temporalis muscle, presenting higher changes after multiple injections of this treatment. LEVEL OF EVIDENCE I: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Psychological treatments for temporomandibular disorder pain-A systematic review.

OBJECTIVE: Temporomandibular disorders (TMD) are common. They affect abilities for carrying out daily tasks and influence different psychological aspects. In addition to standard treatment, psychological treatments have been suggested. The aim was to investigate the effects of psychological treatments on patients with painful TMD in a short- and long-term perspective. MATERIALS AND METHODS: An electronic search was conducted in the databases MEDLINE, CINAHL, EMBASE, the Cochrane Central Registry of Controlled Trials (CENTRAL), and Web of Science for randomized clinical trials (RCTs) reporting psychological interventions for TMD. Registered beforehand in PROSPERO (CRD42022320106). In total, 18 RCTs were included; six RCTs that could be used in the meta-analysis, and all 18 RCTs were used in the narrative synthesis. Risk of bias was assessed by the Cochrane's tool for assessing risk of bias and certainty of evidence by GRADE. RESULTS: The narrative synthesis indicates that psychological treatment options seem equivalent to standard treatment for painful TMD. The meta-analysis showed that a combination of psychological treatment and standard treatment and manual treatment (very low-quality evidence) are significantly better in pain reduction than just counselling and standard treatments of TMD. CONCLUSION: This study indicates that psychological treatments seem to reduce pain intensity in individuals with painful TMD, and that the effect seems to be equally good as standard treatment. However, a combination of psychological treatments and standard treatments seems to have an even better effect. This indicates that psychological treatments are promising as an additional treatment approach for painful TMDs.

Evaluation of jaw function, oral health-related quality of life, and nutritional status during oral rehabilitation procedures - a pilot study.

AIMS: To evaluate limitations in jaw function, oral health-related quality of life (OHRQoL), and nutritional status during extensive oral rehabilitation procedures. MATERIAL METHODS: Fourteen participants (mean age ± SD: 70 ± 3.8) undergoing major oral rehabilitation involving the restoration of a minimum of eight teeth were recruited in the study. Jaw function limitations scores (JFLS), oral health-impact profile (OHIP), and nutritional status were measured at different time points during, six months, and one year after the rehabilitation procedures. Nutritional status was evaluated by measuring the body weight and arm and calf muscle circumference. The effect of time points on the measured variables was evaluated with Friedman's test. Trends in nutritional status were evaluated with linear regression analysis. RESULTS: The results of the analysis showed significant main effects of time points on the JLFS (p < .001) and OHIP scores (p = .005). However, there was no effect of time points on the body weight (p = .917) and calf muscle circumference (p = .424), but a significant effect on arm circumference (p = .038). Further, there was a decreasing trend for body weight (64.3%), arm (71.4%), and calf circumference (64.3%) in the majority of the patients. CONCLUSION: The results of the preliminary study suggest that people undergoing extensive oral rehabilitation procedures show improvement in jaw function and an increase in OHRQoL after the rehabilitation procedure. Despite no major changes in the nutritional indicators, most patients showed a negative trend in their body weight, arm circumference, and calf circumference, suggesting that they may be susceptible to nutritional changes.

Food Hardness Modulates Behavior, Cognition, and Brain Activation: A Systematic Review of Animal and Human Studies.

Food hardness is one of the dietary features that may impact brain functions. We performed a systematic review to evaluate the effect of food hardness (hard food versus soft food diet) on behavior, cognition, and brain activation in animals and humans (PROSPERO ID: CRD42021254204). The search was conducted on 29 June 2022 using Medline (Ovid), Embase, and Web of Science databases. Data were extracted, tabulated by food hardness as an intervention, and summarized by qualitative synthesis. The SYRCLE and JBI tools were used to assess the risk of bias (RoB) of individual studies. Of the 5427 studies identified, 18 animal studies and 6 human studies met the inclusion criteria and were included. The RoB assessment indicated that 61% of animal studies had unclear risks, 11% had moderate risks, and 28% had low risks. All human studies were deemed to have a low risk of bias. The majority (48%) of the animal studies showed that a hard food diet improved behavioral task performance compared to soft food diets (8%). However, 44% of studies also showed no differential effects of food hardness on behavioral tests. It was also evident that certain regions of the brain were activated in response to changes in food hardness in humans, with a positive association between chewing hard food, cognition performance, and brain function. However, variations in the methodologies of the included studies hindered the meta-analysis execution. In conclusion, our findings highlight the beneficial effects of dietary food hardness on behavior, cognition, and brain function in both animals and humans, however, this effect may depend on several factors that require further understanding of the causality.

Subjective and objective evaluation of masticatory function in patients with bimaxillary implant-supported prostheses.

BACKGROUND: People perform poorly in masticatory function tests despite well-functioning prostheses. However, it is unclear whether there is an agreement between subjective and objective measures of mastication. OBJECTIVES: To investigate the association between subjective and objective measures of masticatory function in patients with bimaxillary implant-supported prostheses. MATERIALS AND METHODS: An experimental group (n = 25, age = 70.6 ± 7.5 years, eight women) with bimaxillary implant-supported fixed prostheses and a control group (n = 25, age = 69.0 ± 5.3, 13 women) with natural dentition were recruited. The participants in the experimental group were included if they had been using the prosthesis for at least a year and had no obvious complaints with their prostheses. The control group was people with natural dentition and without any prostheses or complaints related to the masticatory system. The masticatory function was evaluated objectively with food comminution and mixing ability tests, and subjectively with jaw function limitation scale (JLFS) and oral health impact profile (OHIP). RESULTS: The experimental group performed poorly in both objective tests (p < .001). However, there was no significant differences between the two groups in total JFLS (p = .114) and OHIP (p = .312) scores. Though, there were certain positive correlations between the food comminution test and JFLS subdomains in the control group, and a positive correlation between food comminution test and specific subdomains of OHIP in the experimental group indicating poor correlation between the subjective and objective measures. CONCLUSION: Although patients with implant prostheses show poor masticatory performance, there is no agreement in the objective and subjective measures of mastication.

Assessment of masticatory function in older individuals with bimaxillary implant-supported fixed prostheses or with a natural dentition: A case-control study.

STATEMENT OF PROBLEM: A clinical assessment of the masticatory performance of edentulous people treated with bimaxillary implant-supported fixed prostheses is lacking. PURPOSE: The purpose of this case-control study was to compare the masticatory performance of edentulous people treated with bimaxillary implant-supported fixed prostheses to that of those with a natural dentition by using a simplified comminution test with hard viscoelastic test food and a mixing ability test. MATERIAL AND METHODS: Thirty-six participants were recruited and divided into 2 equal groups (n=18) based on their dental status. The experimental group (7 women, mean ±standard deviation age=69.8 ±7.5 years) had bimaxillary implant-supported fixed prostheses, and the control group (9 women, mean ±standard deviation age=68.3 ±5.6 years) had a natural dentition. A hard viscoelastic food comminution test and a mixing ability test with 2-colored chewing gum were performed in both groups. The number and total area of the particles during the comminution test and the variance of hue during the mixing ability test were measured. The data were analyzed with the parametric (paired t test) and nonparametric (Mann-Whitney U) tests to assess differences between the groups (α=.05). RESULTS: The experimental group exhibited significantly fewer pieces in the food comminution test than the control group (P=.001). The experimental group also showed significantly higher variance of hue values than the control group (P<.001). CONCLUSIONS: Patients treated with bimaxillary implant-supported prostheses had reduced masticatory performance in comparison to those with a natural dentition, despite having been provided with satisfactory and well-functioning prostheses.

Chewing and its influence on swallowing, gastrointestinal and nutrition-related factors: a systematic review.

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.

Effect of apical microsurgery on force regulation of incisor teeth during unpredictable force control task.

BACKGROUND: Apical microsurgery (AMS) involves removal of the root-end which can affect the force regulation of teeth. OBJECTIVE: To investigate the force regulation of incisor teeth treated with AMS during the unpredictable force control task in comparison with their contralateral teeth with complete root apices, in humans. METHODS: Fifteen eligible participants (8 women and 7 men; mean age 52.9 ± SD 4.4 years) performed a standardised unpredictable force control task, which involved pulling and holding a force transducer with AMS-treated incisors and their contralateral control teeth (n = 30 teeth). A series of four load masses: 100, 200, 50 and 300 gm were attached to the force transducer through a string in an unpredictable manner. The obtained force profile was divided into initial and later time-segments. The peak force and peak force rate during the initial time-segment, and the holding force and coefficient of variability during the later time-segments were calculated and compared by the repeated measures analysis of variance. RESULTS: During the initial time-segment, the peak force and peak force rate were significantly lower in the AMS-treated teeth than in the controls (p = .001, p = .013, respectively). However, during the later time-segment, no significant differences in the holding force nor the coefficient of variability were observed between the AMS-treated teeth and their controls (p = .755, p = .213, respectively). CONCLUSION: In contrast to incisors with complete normal root apices, AMS-treated incisors do not show robust changes in force regulation.

Motor Performance and Skill Acquisition in Oral Motor Training With Exergames: A Pilot Study.

Objective: To investigate the effects of oral-motor training with exergames on motor performance and motor skill acquisition in two different age groups. Methods: Thirty-two healthy participants were recruited in the current pilot study and divided equally into two groups (Gen Z and Baby Boomers) according to their age. A pair of electromyographic (EMG) electrodes were placed on the participants' masseter muscles. The EMG device communicated via Bluetooth with a mobile video game in response to the electromyographic activity of the masseter muscles during clenching. During the experimental session, participants were asked to play a video game in five blocks of 5 min each, with a 3-min break between each time block. The goal of the game was to collect as many coins (game points) as possible and to dodge/avoid upcoming obstacles (game life). Motor performance was assessed by performance scores and the number of game lives. Skill acquisition was measured by task efficiency (ratio of performance scores and number of game lives) across time blocks. Results: The results of the study showed significantly lower performance scores (p < 0.001), a higher number of game lives (p < 0.001), and lower task efficiency in the Baby Boomer group compared to the Gen Z group. Specifically, the results showed that there was a significant difference in task efficiency between the first and second, third and fourth, fourth- and fifth-time blocks in the Gen Z group (p < 0.002). However, there was only a significant difference between first- and second-time blocks in the Baby Boomer group (p = 1.012), suggesting that skill acquisition in the Baby Boomer group did not change significantly over the course of the time blocks. Conclusion: The study showed higher motor performance and superior motor skill acquisition with novel exergame training in the Gen Z group compared to the Baby Boomer group. The results of the study indicate that there is an improvement in oral motor skills with short-term training, yet the differences in oral motor skills between the two groups are still evident. The Baby Boomer group, unlike the Gen Z group, did not show robust improvement in task efficiency over the course of the series.

Effect of malocclusion on jaw motor function and chewing in children: a systematic review.

OBJECTIVE: To investigate the effects of dental/skeletal malocclusion and orthodontic treatment on four main objective parameters of chewing and jaw function (maximum occlusal bite force [MOBF], masticatory muscle electromyography [EMG], jaw kinematics, and chewing efficiency/performance) in healthy children. MATERIALS AND METHODS: Systematic searches were conducted in MEDLINE (OVID), Embase, and the Web of Science Core Collection. Studies that examined the four parameters in healthy children with malocclusions were included. The quality of studies and overall evidence were assessed using the Joanna Briggs Institute and GRADE tools, respectively. RESULTS: The searches identified 8192 studies; 57 were finally included. The quality of included studies was high in nine studies, moderate in twenty-three studies, and low in twenty-five studies. During the primary dentition, children with malocclusions showed similar MOBF and lower chewing efficiency compared to control subjects. During mixed/permanent dentition, children with malocclusion showed lower MOBF and EMG activity and chewing efficiency compared to control subjects. The jaw kinematics of children with unilateral posterior crossbite showed a larger jaw opening angle and a higher frequency of reverse chewing cycles compared to crossbite-free children. There was a low to moderate level of evidence on the effects of orthodontic treatment in restoring normal jaw function. CONCLUSIONS: Based on the limitations of the studies included, it is not entirely possible to either support or deny the influence of dental/skeletal malocclusion traits on MOBF, EMG, jaw kinematics, and masticatory performance in healthy children. Furthermore, well-designed longitudinal studies may be needed to determine whether orthodontic treatments can improve chewing function in general. CLINICAL RELEVANCE: Comprehensive orthodontic treatment, which includes evaluation and restoration of function, may or may not mitigate the effects of malocclusion and restore normal chewing function.

Effect of food hardness on chewing behavior in children.

OBJECTIVE: To investigate the effects of food hardness on chewing behavior in children compared with adults. MATERIALS AND METHODS: Healthy children (3-17 years) were equally divided into five groups based on their dental eruption stages. Each participant ate soft and hard viscoelastic test food models (3 each), while the three-dimensional jaw movements and electromyographic (EMG) activity of the bilateral masseter muscles were recorded. The data from the children were compared with a control group of healthy adults (18-35 years). The data were analyzed with nonparametric tests. RESULTS: There was no significant difference in the number of chewing cycles and the duration of the chewing sequence between children groups and adults. Children with primary dentition (3-5 years) showed shorter lateral jaw movement and higher muscle activity at the end of the chewing sequence, compared with adults. Further, children's age-groups (3-14 years) failed to adapt their jaw muscle activity to food hardness. However, at the late-permanent dentition stage (15-17 years), children were capable of performing adult-like chewing behavior. CONCLUSIONS: Overall, it seems that children as young as 3-year-old are quite competent in performing basic chewing function similar to adults. Yet, there are differences in the anticipation or adaption of jaw muscle activity and jaw kinematics to food hardness. CLINICAL RELEVANCE: The study may have clinical implication in the diagnosis and management of children with chewing impairment associated with dental malocclusions and other orofacial dysfunctions.

Oral Fine Motor Control of Teeth Treated with Endodontic Microsurgery: A Single-Blinded Case-control Study.

INTRODUCTION: Periodontal mechanoreceptors (PMRs) are refined neural receptors present in abundance at the root apex and have a pivotal role in oral fine motor control. This case-control study aimed to evaluate the oral fine motor control of teeth treated with endodontic microsurgery (EMS) in comparison with the control teeth using a standardized behavioral biting task. METHODS: Fourteen eligible participants performed 5 trials of an oral fine motor control task that involved holding and splitting half of a peanut positioned on a force transducer with their EMS treated tooth and its contralateral control incisor tooth (28 teeth in total). The outcome variables were the mean food holding force, intra- and intertrial variability of the holding force, food splitting force, splitting duration, and the frequency of the stepwise splitting phase. The data were analyzed with parametric and nonparametric tests. RESULTS: The results showed no statistically significant differences in the holding force, inter- and intratrial variability of the holding force, splitting force, or splitting duration between the teeth treated with EMS and the control (P > .05). However, there was a significantly higher frequency of stepwise ramp increase during the splitting phase with EMS treated teeth compared with the control (48% and 37%, respectively; P < .05). CONCLUSIONS: EMS treated teeth showed similar force regulation and oral fine motor control as the contralateral control. The findings of this study suggest that EMS treatment does not perturb the sensory information of PMRs and maintains the force regulation and oral fine motor control of the teeth.

Comparison of Pain-Generated Functional Outcomes in Experimental Models of Delayed-Onset Muscle Soreness and Nerve Growth Factor Injection of the Masticatory Muscles.

AIMS: To compare two pain models of myalgic TMD, delayed-onset muscle soreness (DOMS) and injections of nerve growth factor (NGF), in terms of pain-related and motor function outcomes, as well as activity-related temporal summation. METHODS: Fifty age- and gender-matched healthy participants were recruited and randomized into one of three groups: to a repeated eccentric contraction task to cause DOMS (n = 20), to receive NGF injections into the masseter muscle (n = 20), or to a control group (n = 10). Mechanical sensitivity of masticatory muscles, chewing parameters, jaw function limitation, maximum bite force, and activity-related temporal summation were assessed at baseline and at days 1, 2, and 7 following the intervention. RESULTS: Compared to baseline, both model groups showed increased mechanical sensitivity, jaw function limitation, pain on chewing, and decreased chewing efficiency, lasting longer in the NGF group than in the DOMS group (P < .05). Furthermore, also compared to baseline, the NGF group showed increased pain on maximum bite and decreased pain-free maximum opening (P < .05). No increases in activity-related temporal summation were shown for any of the model groups when compared to baseline or the control group (P > .05). CONCLUSION: Both models produced similar pain-related outcomes, with the NGF model having a longer effect. Furthermore, the NGF model showed a more substantial effect on motor function, which was not seen for the DOMS model. Finally, neither of the models were able to provoke activity-related temporal summation of pain.

Age-related changes in oral motor-control strategies during unpredictable load demands in humans.

To investigate age-related changes in oral motor strategies in response to unpredictable load demands. Sixty-five healthy children (aged 3-17 yr) were divided into five age-groups based on their dental eruption stages and compared with a group of healthy adults (aged 18-35 yr). Each participant was asked to perform a standardized motor control task involving 'pulling' and 'holding' a force transducer with the anterior teeth. Different loads were attached to the force transducer in an unpredictable manner. The temporal force profile was divided into two time-segments (an initial segment and a later segment). The peak force and peak force rate during the initial time-segment, and the holding force and intra-trial variability (coefficient of variation) during the later time-segment, were measured. The results showed no differences in the peak force, peak force rate, holding force, and force variability in children compared with adults. However, the trends in the data evaluated using a segmented regression analysis showed that a breakpoint (abrupt change) consistently occurred in the late-mixed dentition group (age 9-11 yr) for most of the outcome variables. The results indicate that while the motor control strategies in children appear to be similar to those in adults, there is a shift in the oral motor developmental trend during the late-mixed dentition stage.

Experimental pain and fatigue induced by excessive chewing.

BACKGROUND: The study was aiming to optimize excessive gum chewing as an experimental model to induce jaw muscle pain and fatigue similar to those in painful TMDs with durations that would allow immediate investigations of jaw-motor function. Further, if any sex differences would be detected in the expression of pain. METHODS: This randomized, double blinded study included 31 healthy participants of both sexes. A standardized chewing protocol of either 40- or 60-min of chewing was used with a wash-out period of 1 week. Subjective fatigue, pain characteristics and functional measures were assessed. For statistical analyses, Wilcoxon Signed Rank test, Mann-Whitney Rank Sum test and Friedman's ANOVA with Tukey post-hoc test were used. RESULTS: High subjective fatigue scores that lasted up to 20 min after the end of the trial were significantly induced both in the 40- and 60-min chewing trials (P <  0.001*). Significant but mild pain was induced only in the 60-min trial (P = 0.004*) and only in men (P = 0.04*). Also, the induced pain area was significantly bigger in the 60-min trial (P = 0.009*). However, this increase in pain and pain area did not last to the first 10-min follow-up. There were no significant differences neither between the 40- and 60-min chewing trials, except regarding the pain area (P = 0.008*), nor between the sexes. CONCLUSION: Taken together, excessive chewing in its current form does not seem to be a proper pain experimental model. The model needs further adjustments in order to mimic TMD-pain especially in women and to prolong the pain duration.

Motor control strategies during unpredictable force control tasks in humans.

BACKGROUND: There are fundamental similarities and differences between the jaw and hand motor systems. However, it is unclear how the two systems respond to unpredictable task demands. OBJECTIVE: To investigate and compare the force control of the jaw motor system (OMS) and the hand motor system (HMS) during unpredictable load changes. METHODS: Seventeen healthy adults (24.0 ± 4.3 years) performed two standardised force control tasks (OMS and HMS). During the OMS, the participants asked to bite and pull a force transducer with the front teeth. While during HMS they pinched and pulled the same force transducer with their index and thumb fingers. Series of loads were added to a string attached to the transducer in an unpredictable (sequential and non-sequential) manner. The entire force profile during the task was divided into "initial" and "latter" segments. The force control was analysed and compared between the OMS and HMS in terms of peak force during the initial segment and holding force and force variability during the latter segment. RESULTS: The peak force, holding force and force variability were higher for the OMS than the HMS (P < .001). However, there were no differences in the peak force, holding force or force variability between the sequential and non-sequential load changes (P > .05). CONCLUSIONS: The results showed that unpredictable load changes did not affect the force control during the motor control task. This study suggests that both the motor systems are optimised in performing simple motor control tasks and are rather resilient to motor unpredictability.

Developmental and age-related changes in sensorimotor regulation of biting maneuvers in humans.

Previous studies indicated distinct differences in biting and chewing behaviors between children and adults. However, these studies used different methodologies and failed to study age-related changes in the fine motor control of biting from childhood to adulthood. Therefore, this study aimed to investigate age-related changes in oral fine motor control in healthy children in comparison to adults. Sixty-five healthy children (3-17 years) were equally divided into five age-groups based on their dental eruption stages. Each participant was asked to hold half a peanut rested on a force transducer between two opposing anterior teeth for 3-4 s before splitting it. The force applied on the transducer was continuously monitored and recorded during food holding and splitting. The data obtained from the children subgroups were compared to an adult group (18-35 years). Results showed that the force regulation during food manipulation was higher and more variable in children with primary to early-permanent dentition stages compared to adults. Additionally, children with primary and early-mixed dentition showed longer food splitting duration than adults and exhibited a predominantly step-wise ramp-increase of force. The results of the present study showed age-related changes in fine motor control of food biting maneuvers. The results of the study also suggested that younger children with primary dentition show signs of immature oral fine motor control. However, with an increase in age and the accompanying structural changes, the oral fine motor control eventually transits to a more matured "adult-like" biting maneuvers.

Effect of Chewing on the Expression of Salivary Protein Composition: A Systematic Review.

Salivary proteins have an imperative role in the maintenance of oral health and repairing mechanisms of injured tissues. However, there is paucity of information reported in the literature about the influence of chewing activities on the secretion or expression of salivary proteins. The purpose of this systematic review is to evaluate the effect of chewing on the expression of salivary proteins composition in healthy individuals. A thorough systematic search shows 14 eligible studies for the review. The results of the systematic review show the effect of chewing on total protein concentration, alpha-amylase (α-amylase), peroxidase, lysozyme, immunoglobulin A (IgA), and mucin. Six papers concluded that chewing has a little or no effect on total protein concentration, α-amylase, peroxidase, lysozyme, and IgA activities. Five papers reported a negative (decreasing) effect of chewing on the function of total protein, α-amylase, IgA, and mucin. Only two papers showed an increase in total protein and IgA function upon chewing stimulation. The results of this systematic review indicate that more standardized evidence-based research is required for better assessment of chewing effects on salivary proteins. Within the limitations of this review, the existing evidence suggests that chewing in healthy people has minimum effect on the expression and activities of salivary proteins.

Effects of Chronic and Experimental Acute Masseter Pain on Precision Biting Behavior in Humans.

Chronic pain in the orofacial region is common worldwide. Pain seems to affect the jaw motor control. Hence, temporomandibular disorders (TMD) are often accompanied by pain upon chewing, restricted mouth opening and impaired maximal bite forces. However, little is known on the effects of pain, in particular the effects of chronic jaw muscle pain on precision biting. The aim of the study was to investigate the effect of chronic and acute jaw muscle pain on oral motor control during precision biting in humans. Eighteen patients with chronic masseter muscle pain and 18 healthy participants completed the experiment. All participants were examined according to the Diagnostic Criteria for TMD. Experimental acute pain was induced by bilateral, simultaneous sterile hypertonic saline infusions into the healthy masseter muscles. A standardized hold and split biting task was used to assess the precision biting. The data was analyzed with non-parametric statistical tests. The results showed no significant differences in the hold forces, split forces, durations of split or peak split rates within or between the pain and pain-free conditions. The mean split rate increased significantly compared to baseline values both in the chronic patients and the pain-free condition. However, this increase was not evident in the experimental acute pain condition. Further, there were no significant differences in the mean split rates between the conditions. The data suggest that jaw muscle pain does not seem to alter precision biting in humans, however, the possibility that a nociceptive modulation of spindle afferent activity might have occurred but compensated for cannot be ruled out.