Maximum Bite Force Research Articles

Craniodental divergence associated with bite force between hybridizing pine squirrels (Tamiasciurus).

Bite force can be a limiting factor in foraging and can significantly affect the competitive ability and lifetime fitness of mammals. Tamiasciurus squirrels feed primarily on conifer seeds and have a strong bite force to mechanically extract seeds from conifer cones with their mouths. In the North Cascades region, Douglas squirrels (Tamiasciurus douglasii) and red squirrels (T. hudsonicus) occupy ecologically different forests with different hardnesses in conifer cones. The ranges of these species overlap in a narrow hybrid zone where these forests meet near the crest of the North Cascades. We examined interspecific divergence in dietary ecomorphology in allopatry, in sympatry within the hybrid zone, and between hybrids and each parental species. We focused on three craniodental traits, including the incisor-strength index as a proxy measure for maximal bite force, cranial-suture complexity, and mandible shape. We find that these sister squirrel species differ in bite force and suture complexity in allopatry and sympatry and that mandible shape changes with the expected hardness of accessed food items, but is not significantly different between species. Furthermore, we find that hybrids display morphologies that overlap with hybrid zone red squirrels but not with hybrid zone Douglas squirrels. This work shows how important ecological processes at shallow evolutionary timescales can impact the divergence of morphological traits in taxa with extreme conservation of craniomandibular shape.

Effect of access cavities on the biomechanics of mandibular molars: a finite element analysis

IntroductionThis study aimed to predict the fracture resistance of a mandibular first molar (MFM) with diverse endodontic cavities using finite element analysis (FEA).MethodsFive experimental finite element models representing a natural tooth (NT) and 4 endodontically treated MFMs were generated. Treated MFM models were with a traditional endodontic cavity (TEC) and minimally invasive endodontic (MIE) cavities, including guided endodontic cavity (GEC), contracted endodontic cavity (CEC) and truss endodontic cavity (TREC). Three loads were applied, simulating a maximum bite force of 600 N (N) vertically and a normal masticatory force of 225 N vertically and laterally. The distributions of von Mises (VM) stress and maximum VM stress were calculated.ResultsThe maximum VM stresses of the NT model were the lowest under normal masticatory forces. In endodontically treated models, the distribution of VM stress in GEC model was the most similar to NT model. The maximum VM stresses of the GEC and CEC models under different forces were lower than those of TREC and TEC models. Under vertical loads, the maximum VM stresses of the TREC model were the highest, while under the lateral load, the maximum VM stress of the TEC model was the highest.ConclusionThe stress distribution of tooth with GEC was most like NT. Compared with TECs, GECs and CECs may better maintain fracture resistance, TRECs, however, may have a limited effect on maintenance of the tooth resistance.

Measurement of voluntary bite forces in large carnivores using a semi-automated reward-driven system.

Bite force is a key performance trait of the feeding system, but maximal in vivo bite force has been measured in few large mammals. The alternative, modelling of bite force from anatomy, cannot be validated without in vivo measurements. To overcome existing limitations of ethics, safety, and animal well-being, we here propose a semi-automated method to obtain voluntary maximum bite forces from large mammals using bite plates that automatically dispense a food reward if an incrementally increasing threshold force value is reached. We validated our method using two Malayan sun bears, two Andean spectacled bears and a lioness. We show that voluntary bite force measurement using positive reinforcement is a non-invasive and reliable method to record maximum voluntary bite force performance in large mammals. Our results further show that in vivo data are critical as modeling efforts from osteology have greatly underestimated bite forces in Andean bears.

Digital Occlusion Analysis after Orthodontic Treatment: Capabilities of the Intraoral Scanner and T-Scan Novus System

Digital technology is becoming increasingly popular in dentistry. The aim of this article is to demonstrate and compare the capabilities of two different digital approaches, namely, intraoral scanning and digital examination of occlusion, in the final analysis of occlusion after orthodontic treatment. The capabilities and limitations of both systems are emphasized to help clinicians determine which system to use in specific cases. Materials and methods: The study included 32 patients (15 males and 17 females) in the retention phase after orthodontic treatment. Patients were aged 15 to 28 years with a mean age of 18.62 years (±4.17), and 62.2% were aged under 18 years. At the beginning of the orthodontic treatment, 18 patients had Angle Class I and 14 had Angle Class II. Overall, 18 patients were treated without extractions and 14 with extractions, while 12 had impacted teeth. All patients wore an Essix retainer in the upper jaw and a fixed canine-to-canine retainer in the lower jaw. Intraoral scanning was performed using Trios color (3Shape, Copenhagen, Denmark, 2014), and digital occlusion imaging was performed using T-Scan Novus (Tekscan, Norwood, MA, USA, 2018). SPSS 23.0 was used to perform descriptive statistical analysis. Result and Conclusion: With the 3Shape system, the contacts are marked based on the proximity between dentitions. The T-Scan system measures the strength of the contacts, regardless of their area. Despite its many advantages, intraoral scanning is not a reliable method for recording occlusions. The results obtained are not incorrect, but they include limited parameters for analysis. The T-Scan system provides comprehensive results and allows analysis and treatment of occlusal dysfunctions. The T-Scan system can provide information on the first contact, strength of the contacts, contact distribution on each tooth, sequence of contacts, maximum bite force and maximum intercuspation, path of the lower jaw movement, and occlusion and disocclusion times as well as record videos with active sequences and distributions of the contacts. There is a good collaboration between intraoral scanning and digital occlusion determination.

Maximum bilateral bite strength and RMS EMG for the diagnosis of myogenic TMD

Aim: The study aimed to evaluate the accuracy of the maximum bilateral molar bite force and the Root Mean Square (RMS) Electromyography (EMG) index of the masticatory muscles in the maximum bilateral molar bite (MMBMax) of women with myogenic Temporomandibular Disorder (TMD) and asymptomatic. Methods: This is a cross-sectional study, composed of 86 women allocated to the TMD Group (n=43) and Control Group (n=43) diagnosis through the Diagnostic Criteria for Temporomandibular Disorders. The maximum bilateral molar bite force was evaluated using a bite dynamometer and the RMS EMG index of the masticatory muscles (anterior temporalis, masseter) during 5 seconds of the MMBMax task. Student t-test was used for data comparison between accuracy of the bite force and RMS EMG of masticatory muscles during the MMBMax. Results: The maximum bilateral molar bite force showed high accuracy (AUC=0.99) for the diagnosis of women with myogenic TMD and asymptomatic women, and the RMS EMG index evaluated during the MMBMax showed a moderate level of accuracy for all masticatory muscles (AUC=0.70 to 0.75). Conclusion: The bilateral bite dynamometer with a surface EMG during bilateral bite can be used to diagnose TMD in young women.

Impact of Acrylic and Silicone-Based Soft-Liner Materials on Biting Force and Quality of Life of the Complete Denture Wearers: A Randomized Clinical Trial.

This rerandomized clinical trial evaluated the influence of soft liners (SL) on biting force, pain perception, and the oral health-related quality of life (OHRQoL) of complete denture wearers. Twenty-eight completely edentulous patients complaining of ill-fitting lower complete dentures were selected to participate in the study from the Dental Hospital, College of Dentistry, Taibah University. All patients received new complete maxillary and mandibular dentures; then they were randomly divided into two groups (14 patients in each group): the acrylic-based SL group, in which the mandibular denture was lined with an acrylic-based soft liner, and the silicone-based SL group, in which the mandibular denture was lined with a silicone-based soft liner. OHRQoL and maximum bite force (MBF) were assessed in this study before denture relining (baseline), then at one month and three months after relining. The finding showed that both treatment modalities significantly improved the OHRQoL of included patients at one-month and three-month periods compared to baseline records (i.e., dentures before relining) with a statistically significant difference (p < 0.05). However, there is no statistical difference between groups at the baseline, one-, and three-month follow-up periods. Regarding maximum biting force, when acrylic-based SL is compared to silicone-based SL, there is no statistical difference between groups at baseline (75 ± 31 and 83 ± 32 N) and one-month follow-up periods (145 ± 53 and 156 ± 49 N); however, after three months of function, the silicone-based group recorded 166 ± 57 N statistically significant high biting force compared to the acrylic-based group that recorded 116 ± 47 N (p < 0.05). Permanent soft denture liners positively affect maximum biting force, pain perception, and OHRQoL more than conventional dentures. After three months, silicone-based SL outperformed acrylic-based soft liners in maximum biting force, which may indicate better long-term results.

Bite Force Evaluation in Implant-Assisted Prosthetic Rehabilitation of Reconstructed Jaws Utilizing Vascularized Free Fibula Flap: A Retro-Prospective Cohort Study.

Maxillary and mandibular defects due to tumor ablation pose considerable challenges to the reconstructive surgeon and in prosthetic management. Dental implants placed in vascularized fibula free flaps are considered to be a dependable technique for prosthetic rehabilitation in head and neck cancer patients. Although, there is evidence of survival of dental implants in the reconstructed jaw bones, there is lack of information regarding the masticatory performance and prosthetic success. The maximum bite force achieved through the prosthetic appliance is a measure of the therapeutic outcome. The purpose of this study was to determine the maximum bite force achieved through implant-assisted prosthetic rehabilitation in reconstructed jaw bones utilizing vascularized free fibula flap. The study included a total of 65 implants, from 16 patients who underwent surgical resection of jaw bones due to benign tumors followed by rehabilitation with implant-assisted fixed or removable prosthesis. The maximum bite force was determined with a transducer. Occlusal interferences were analyzed with mounted casts. The parameters were reviewed every 3months have T 0 marked the baseline assessment, and T 3, T 6, T 9, T 12, and T 15 were subsequent review periods. The mean occlusal force was increased in most of the patients through 15months (P < 0.01). The maximum bite force measured in the reconstructed mandible and maxilla were 225.63N and 176.51N, respectively. Occlusal interferences were absent in 68.8% of the study population. The bite force measured in reconstructed maxilla and mandible is comparable to the masticatory force measured with conventional implant supported prosthesis in native mandible and maxilla.

Comparative Analysis of Sensory Responses from Dental Implants vs Natural Teeth: An In Vivo Study

Purpose: To compare subjects' sensory responses to horizontal and vertical forces on tooth- and implant-supported restorations. Materials and Methods: In this prospective study, three protocols simulating the horizontal or vertical forces that occur during mastication were used to obtain subjective responses from subjects. These protocols included the measurement of horizontal force intensity during excursive movements and the identification of initial contact during guided and free vertical closure. Responses were recorded using a 1- to 10-point visual analog scale (VAS) and/ or monitored with electromyography (EMG) and Tekscan. Results: The study included 30 patients with a single implant-supported restoration (ISR) with a contralateral tooth-supported restoration (TSR). For horizontal forces similar to those of mastication (0.6 N), subject VAS scores were similar for both ISRs and TSRs at 6.3 vs 6.1, respectively. At reduced forces (0.2 and 0.4 N), subject responses were greater for the TSR at 3.4 and 5.4, respectively, as opposed to 1.2 and 2.6 for ISR, respectively (P < .01). During vertical guided closure (Test 1) at 25% of maximum bite force (MBF), subjects were more successful at correctly identifying initial contact of TSRs at a rate of 12 out of 17, compared to ISRs, which achieved a rate of 4 out of 13 (P < .1). In vertical free closure (Test 2), subject responses for the correct identification of initial contact at 50% MBF were similar for both TSRs and ISRs at 13 out of 17 and 9 out of 13, respectively. However, comparing the correct responses for subjects whose initial contacts were ISR showed a significant improvement in correct answers from Test 1 to Test 2, from 4 out of 13 correct to 9 out of 13 correct (P < .05). Conclusion: While the mechanism is not clear, subjects' ability to discern the horizontal and vertical forces at levels comparable to mastication appear similar between TSRs and ISRs.

Self-ligating brackets do not reduce discomfort or pain when compared to conventional orthodontic appliances in Class I patients: a clinical study.

To compare the intensity, location, and short-term impact of the periodontal discomfort/pain, as well as the related functional parameters of bite force and masticatory efficiency, between self-ligating and conventional orthodontic appliances. In 20 patients referred for orthodontic treatment, samples were collected from the gingival sulcus to evaluate the level of substance P using enzyme-linked immunosorbent assay. Orthodontic devices were randomly bonded, with self-ligating appliances on one side and conventional brackets on the contralateral side. Pain threshold (PT), maximal bite force (MBF), and masticatory efficiency (ME) were assessed using standard validated techniques at the beginning of the treatment and 24 hours post-orthodontic activation with an 0.016-inch nickel-titanium wire. There were no significant differences (P > .05) in the substance P levels, PT, MBF, and ME between the self-ligating and conventional orthodontic appliances. There was no difference between conventional and self-ligating appliances in the parameters of pain: substance P and pressure. Functional aspects, such as pain, discomfort, and masticatory efficiency, should not be considered when making a therapeutic decision regarding the use of self-ligating vs conventional orthodontic appliances.

Relationship between the Mandibular Condyle Position and the Bite Force in the People with Normal Temporomandibular Joint

Statement of the Problem. The mandibular condyle position is important in temporomandibular joint (TMJ) disorders. The bite force is a mechanical force that may affect the condylar position. Purpose. To investigate the relationship between condylar position in the glenoid fossa and maximum bite force in adults with normal temporomandibular joint. Materials and Methods. In this cross-sectional study, 23 subjects (21 females and 2 males; mean age 38.88 ± 11.7 years) with 41 joints participated. Right and left joints were examined using cone-beam computed tomography. Maximum bite force was measured using the strain gauge transducer in the regions of right molar, left molar, and incisors. Pearson correlation coefficient, paired sample t-test, and binary logistic regression were employed for analysis. Results. The mean maximum bite force was 169.09 ± 87.7 N. The most common position of the condyle was anterior (n = 36) and inferior (n = 31). The mean of mandibular condyle joint spaces for right and left sides were not statistically significant ( P &gt; 0.05 ). There were no relationships between the condylar positions and the mean maximum bite force ( P &gt; 0.05 ). Conclusion. The condylar positions in the glenoid fossa are not related to the bite force in the people with normal temporomandibular joint.

Effect of gender and age on the maximal bite force and the electromyographic activity of the masticatory muscles

Effect of gender and age on the maximal bite force and the electromyographic activity of the masticatory muscles

Comparison of Occlusal Digital Analysis Using T-Scan in Orthognathic Surgery with Only Conventional Orthodontic Patients.

The aims of this study were to compare the changes in occlusal parameters, TMJ status clinically in patients after the completion of orthognathic surgery, and patients undergoing only orthodontic treatment and with patients having normal occlusion, using T-Scan. This prospective controlled clinical trial, consisting of three groups with a sample size of twelve. Group 1 consisted of patients who underwent orthognathic surgery and orthodontic treatment. Group 2 consists of patients who underwent only orthodontic treatment (camouflage). Clinical examination of the patient (TMJ and Occlusal status) and T-Scan was performed at the time of debonding of the orthodontic brackets, 6months and 1-year after first evaluation for group 1 and 2 patients. The collected data between groups are compared and interpreted. The statistical analysis was performed using STATA/IC version 16.1 statistical software. Intragroup comparison for the study variables occlusion time, disocclusion time and maximum bite force between different time periods (T1, T2, T3) for all the three intervention groups using repeated measures. Hypothesis testing for maximum bite force, occlusion time and disocclusion time in orthognathic group (Group 1) as compared to orthodontic group (Group 2) for three different time periods using repeated measures ANOVA and Bonferroni test showed P value < 0.05 which is statistically significant. In conclusion, evaluation of occlusion using T-Scan give us an insight of the discrepancies in occlusion which is useful during pre-operative planning and especially in the post-operative follow-up period during the retention phase. Examination of TMJ in these patients at various intervals is necessary as any minor occlusal disturbances may lead to TMJ disorders.

Clinical and Technical Validation of Novel Bite Force Measuring Device for Functional Analysis after Mandibular Reconstruction.

Bite force measuring devices that are generally suitable for edentulous patients or patients undergoing mandibular reconstruction are missing. This study assesses the validity of a new bite force measuring device (prototype of loadpad®, novel GmbH) and evaluates its feasibility in patients after segmental mandibular resection. Accuracy and reproducibility were analyzed with two different protocols using a universal testing machine (Z010 AllroundLine, Zwick/Roell, Ulm, Germany). Four groups were tested to evaluate the impact of silicone layers around the sensor: no silicone ("pure"), 2.0 mm soft silicone ("2-soft"), 7.0 mm soft silicone ("7-soft") and 2.0 mm hard silicone ("2-hard"). Thereafter, the device was tested in 10 patients prospectively who underwent mandibular reconstruction using a fibula free flap. Average relative deviations of the measured force in relation to the applied load reached 0.77% ("7-soft") to 5.28% ("2-hard"). Repeated measurements in "2-soft" revealed a mean relative deviation of 2.5% until an applied load of 600 N. Maximum bite force decreased postoperatively by 51.8% to a maximum mean bite force of 131.5 N. The novel device guarantees a high accuracy and degree of reproducibility. Furthermore, it offers new opportunities to quantify perioperative oral function after reconstructive surgery of the mandible also in edentulous patients.

Masticatory biomechanics of red and grey squirrels (Sciurus vulgarisandSciurus carolinensis) modelled with multibody dynamics analysis

The process of feeding in mammals is achieved by moving the mandible relative to the cranium to bring the teeth into and out of occlusion. This process is especially complex in rodents which have a highly specialized configuration of jaw adductor muscles. Here, we used the computational technique of multi-body dynamics analysis (MDA) to model feeding in the red (Sciurus vulgaris) and grey squirrel (Sciurus carolinensis) and determine the relative contribution of each jaw-closing muscle in the generation of bite forces. The MDA model simulated incisor biting at different gapes. A series of 'virtual ablation experiments' were performed at each gape, whereby the activation of each bilateral pair of muscles was set to zero. The maximum bite force was found to increase at wider gapes. As predicted, the superficial and anterior deep masseter were the largest contributors to bite force, but the temporalis had only a small contribution. Further analysis indicated that the temporalis may play a more important role in jaw stabilization than in the generation of bite force. This study demonstrated the ability of MDA to elucidate details of red and grey squirrel feeding biomechanics providing a complement to data gathered via in vivo experimentation.

Reliability and measurement error of anterior maximum voluntary bite force in children with juvenile idiopathic arthritis and healthy children.

In children with juvenile idiopathic arthritis (JIA) the temporomandibular joint (TMJ) can be involved. As a consequence, the oral function can be impaired due to joint and/or muscle involvement of the masticatory system with a negative influence on the maximum bite force. The aim of this cross-sectional study was to establish the reliability of AMVBF in children with JIA and healthy children. Children with JIA and healthy children conducted three attempts of AMVBF. The reliability of AMVBF measurement was determined by the intra-class correlation coefficient (ICC) by age, standard error of measurement (SEM), smallest detectable change (SDC), and limits of agreement (LoA). A total of 298 children with JIA and 168 healthy children were examined. The AMVBF measurements showed an good to excellent reliability in children with JIA based on the ICCs corrected for age (0.782-0.979). In healthy children, the reliability was moderate to excellent (0.546-0.999). The SDC in our study indicated that values above 11.4N might be a clinical relevant change over time in children with JIA. The LoA showed a wide spread of variability in both children with JIA (-72.6-44.4N) and healthy children (-79.9-72.8N). The Bland-Altman plots indicated that the differences between the test and retest increased in value proportionally to the biteforce value.

CHANGES IN THE BIOELECTRIC ACTIVITY OF MUSCULUS MASSETER IN CASE OF MANDIBLE EDENTULOUSNESS TREATMENT

The objective of the research: to define the dynamics of changes in bioelectric activity of mm. masseter dexter et sinister in patients with mandible edentulousness treated by means of four implant-supported dental prostheses of various types.&#x0D; 105 patients were examined at the premises of the Center of Dentistry of the University Clinic of Ivano-Frankivsk National Medical University. 30 individuals out of 105 at the age of 23-28 with intact dentition, without somatic pathology were included in the control group.&#x0D; 75 patients with mandible edentulousness underwent clinical examination, prosthodontic treatment, and follow-up. 3 clinical groups (Group I; II; III) were formed from this cohort of patients depending on the structural features of the manufactured dental prostheses.&#x0D; We conducted electromyography of mm. masseter dexter et sinister to the patients of the examination groups (n = 75) and the control group (n = 30) in order to achieve the objective of the research. The examination was performed by means of two-channel electroneuromyographic complex “Neuro-EMG-Micro” (“Neurosoft”) in the functional diagnostics office at the premises of the Department of Dentistry of Postgraduate Study Faculty at IFNMU.&#x0D; Quantitative indicators of bioelectrical activity of the right and left masticatory muscles were analyzed. Namely, the average values of the maximum amplitudes (μV) when performing the test of maximum bite force were analyzed. Recording of electromyographic indicators was performed before the prosthodontic treatment, 14 days after the fixation of the dental prosthesis, in 6 months and 12 months after the dental prosthesis functioning in order to study the dynamics of changes in the indicators of the examination groups.&#x0D; Electromyography recording and analysis of the findings in the individuals of the control group was performed once.&#x0D; Analyzing quantitative indicators of electromyographic examination significant differences in the dynamics of an increase in the indicators in 12 months compared to the initial indicators depending on the type of fixed dental prosthesis (subgroup A рІ-ІІІ&lt;0.001; subgroup B рІ-ІІІ&lt;0.001) and the order of prosthodontic treatment (рА-Б &lt;0.001 for all groups of patients) were observed.&#x0D; &#x0D; Despite the fact that bioelectric indicators of mm. masseter dexter et sinister activity in the patients of the examination groups approximated to the indices of the control group, the dynamics of change was not equivalent and depended on the type of the dental prosthesis.&#x0D; The dynamics of an increase in the indicators of the patients in the examination groups differed by growth, however, the greatest increase was recorded in the period of “14 days” – “6 months” after the fixation of the dental prosthesis.&#x0D; On performing the test of maximum bite, the indicators of the masticatory muscles bioelectrical activity increased during the period named “before the treatment” – “12 months of functioning” most of all in IIIA examination group – by 66.52% (рd&lt;0.001) on the right and by 76.37% (рd&lt;0.001) on the left; and IIIB examination group – by 61.63% (рd&lt;0.001) on the right and 67.20% (рd&lt;0.001) on the left. The lowest indicators have increased in patients of IA examination group – 39.98% (рd&lt;0.001) on the right and 39.95% (рd&lt;0.001) on the left and IB examination group – by 32.48% (рd&lt;0.001) on the right and by 34.75% (рd&lt;0.001) on the left.&#x0D;

Shear Wave Elastography in Bruxism-Not Yet Ready for Clinical Routine.

Ultrasound shear wave elastography (SWE) is an emerging modality for the estimation of stiffness, but it has not been studied in relation to common disorders with altered stiffness, such as bruxism, which affects almost one-third of adults. Because this condition could lead to an increased stiffness of masticatory muscles, we investigated SWE in bruxism according to a proof-of-principle and feasibility study with 10 patients with known bruxism and an age- and gender-matched control group. SWE of the left and right masseter muscles was estimated under three conditions: relaxed jaw, 50% of the subjective maximal bite force, and maximal jaw opening. Rejecting the null hypothesis, SWE was significantly increased during relaxed jaw (bruxism 1.92 m/s ± 0.44; controls 1.66 m/s ± 0.24), whereas for maximal mouth opening, the result was vice versa increased with 2.89 m/s ± 0.93 for bruxism patients compared with 3.53 m/s ± 0.95 in the healthy control, which could be due to limited jaw movement in chronic bruxism patients (bruxism 4.46 m/s ± 1.17; controls 5.23 m/s ± 0.43). We show that SWE in bruxism is feasible and could be of potential use for diagnostics and monitoring, though we also highlight important limitations and necessary methodological considerations for future studies.

How to Survive a (Juvenile) Piranha Attack: An Integrative Approach to Evaluating Predator Performance.

Cory cat panel figureDrawing of bite force measuring equipment and indentation rig Pygocentrus nattereri jaw muscle morphology and skull anatomyBox plot grid of number of Pygocentrus nattereri bites before puncture along different body regions of Corydoras trilineatus during feeding trials resultsDrawing of color-coded Corydoras trilineatus with attack frequencies and average bites until puncture by Pygocentrus nattereriBox plot of average voluntary juvenile Pygocentrus nattereri bite forces to standard lengthPanel of linear ordinary least-squares regressions of Pygocentrus nattereri bite force to adductor mandibulae mass, standard length, and body massOrdinary least-squares regressions of voluntary bites to restrained bites of Pygocentrus nattereriPanel of indentation tests for intact and removed Corydoras trilineatus scutesPanel of indentation tests for Corydoras trilineatus body region. There is an evolutionary arms race between predators and prey. In aquatic environments, predatory fishes often use sharp teeth, powerful bites, and/or streamlined bodies to help capture their prey quickly and efficiently. Conversely, prey are often equipped with antipredator adaptations including: scaly armor, sharp spines, and/or toxic secretions. This study focused on the predator-prey interactions between the armored threestripe cory catfish (Corydoras trilineatus) and juvenile red-bellied piranha (Pygocentrus nattereri). Specifically, we investigated how resistant cory catfish armor is to a range of natural and theoretical piranha bite forces and how often this protection translated to survival from predator attacks by Corydoras. We measured the bite force and jaw functional morphology of P. nattereri, the puncture resistance of defensive scutes in C. trilineatus, and the in situ predatory interactions between the two. The adductor mandibulae muscle in juvenile P. nattereri is robust and delivers an average bite force of 1.03 N and maximum bite force of 9.71 N, yet its prey, C. trilineatus, survived 37% of confirmed bites without any damage. The C. trilineatus armor withstood an average of nine bites before puncture by P. nattereri. Predation was successful only when piranhas bit unarmored areas of the body, at the opercular opening and at the caudal peduncle. This study used an integrative approach to understand the outcomes of predator-prey interactions by evaluating the link between morphology and feeding behavior. We found that juvenile P. nattereri rarely used a maximal bite force and displayed a net predation success rate on par with other adult vertebrates. Conversely, C. trilineatus successfully avoided predation by orienting predator attacks toward their resilient, axial armor and behavioral strategies that reduced the predator's ability to bite in less armored regions of the body.

Factors related to masticatory performance in patients with removable dentures for jaw defects following oral tumor surgery.

Purpose In the treatment of oral tumors, extensive jaw defects due to surgical resection can reduce masticatory performance. Herein, we aimed to clarify the factors related to masticatory performance in patients with jaw defects.Methods In total, 76 patients (42 male and 34 female) underwent prosthetic treatment with a removable denture for a jaw defect following oral tumor surgery. Data on history of radiation therapy, period of time since surgery, period of use of the present denture, number of remaining teeth, and site of the jaw defect were collected. Masticatory performance was evaluated using test gummy jelly. In addition, maximum bite force, tongue pressure, tongue-lip motor function (oral diadochokinesis /pa/, /ta/, /ka/), and oral dryness were evaluated. Logistic regression analysis was performed with lower masticatory performance scores as the dependent variable. Since multicollinearity was suspected between the oral diadochokinesis /ta/ and /ka/ syllables, two logistic regression analyses were conducted: Model 1 with the /ta/ syllable as an explanatory variable, and Model 2 with the /ka/ syllable as an explanatory variable.Results In Model 1, a history of radiation therapy, maximum bite force, number of remaining teeth, tongue pressure, and oral diadochokinesis /ta/ were significant explanatory variables. In Model 2, a history of radiation therapy, maximum bite force, number of remaining teeth, and tongue pressure were significant explanatory variables.Conclusions A history of radiation therapy, maximum bite force, tongue pressure, number of remaining teeth, and motor function of the proglossis are related to decreased masticatory performance in patients with jaw defects.

Influence of awake bruxism behaviors on fatigue of the masticatory muscles in healthy young adults.

The present cross-sectional study aimed to analyze the relationship between awake bruxism and fatigue of masticatory muscles in healthy young adults. For this purpose, 121 graduate students participated in this study. Frequency of awake bruxism was collected for 7 consecutive days by ecological momentary assessment (EMA) using an online survey (mentimeter). Muscle fatigue was tested one day after EMA assessment, which consisted of voluntarily and continuously clenching at 30% (kgf/cm2) of maximum bite force (MBF) until exhaustion. The percentage of change in MBF after the clenching task, as compared to the MBF before the clenching task was measured. The average frequency of awake bruxism was 45.5% during 7 days. Sustained clenching resulted in a significant reduction in MBF values in the total sample (p < 0.05). Nevertheless, no significant correlation was found between frequency of awake bruxism behaviors and percent of change in MBF and endurance time during the fatigue test. Therefore, it can be concluded that young healthy adults present a relatively high frequency of awake bruxism behaviors that do not seem to impact the degree of masticatory muscle fatigue.