Bite force Research Papers - Academia.edu (original) (raw)

The purpose of this study was to evaluate the activity of digastric, sternocleidomastoid, upper trapezius, lower trapezius and cervical muscles in response to maximum voluntary clenching (MVC) of the teeth. Twenty healthy subjects aged... more

The purpose of this study was to evaluate the activity of digastric, sternocleidomastoid, upper trapezius, lower trapezius and cervical muscles in response to maximum voluntary clenching (MVC) of the teeth. Twenty healthy subjects aged 24-31 years were divided into two groups of 10: a resting group and a clenching group. The resting group simply maintained the mandible at rest with teeth apart for two 1-min periods, whereas the clenching group underwent an initial resting period followed after 1-min by a clenching period during which they were required to perform MVC. The electromyography (EMG) responses of each muscle were recorded during all periods, and means and standard deviations of the root mean square EMG were calculated. Within-group and between-group comparisons of EMG activity were made using, respectively, the Sign two-tailed test for two related samples and the Kolmogorov-Smirnov two-tailed test for two independent samples (significance level 0AE05). Data indicated a significant increase of EMG activity of the anterior neck muscles (digastric and sternocleidomastoid) during MVC as compared with EMG recorded during resting periods. If confirmed by further research, our findings suggesting an involvement of anterior neck muscles during isometric contraction of the jaw elevator muscles may have clinical implications.

Stress distribution in human tooth structure can be visualized through the use of Moiré fringes, which has improved the clinical understanding of recently identified anatomical structures in molar occlusal surfaces. This article discusses... more

Stress distribution in human tooth structure can be visualized through the use of Moiré fringes, which has improved the clinical understanding of recently identified anatomical structures in molar occlusal surfaces. This article discusses the concept of a "peripheral rim of enamel" and describes the manifestation of compressive and tensile fractures within the peripheral rim of enamel and dentin. It also emphasizes the benefits of microdentistry techniques and minimally invasive preparation designs in the long-term preservation of the natural tooth structure.

Because sexual selection pressures are high in sexually dimorphic organisms, morphological, physiological and performance traits are often studied in a sexual selection context. The proximate mechanisms underlying evolutionary change in... more

Because sexual selection pressures are high in sexually dimorphic organisms, morphological, physiological and performance traits are often studied in a sexual selection context. The proximate mechanisms underlying evolutionary change in these traits, however, remain largely unstudied. Here, we examined the role of steroids in shaping morphology and physiological performance in males of a sexually dimorphic lizard (Gallotia galloti). We compared morphology and physiological performance of males with experimentally elevated testosterone levels to sham-operated males. Before surgery, inter-individual variation in plasma testosterone levels correlated positively with bite force capacity. Administration of exogenous testosterone resulted in an increase of the mass of both jaw closing and locomotory muscles compared with sham-operated individuals, but the responsiveness varied considerably among muscle groups. In contrast to our expectations, the dramatic testosterone-induced changes in muscle masses did not result in concordant changes in bite force performance or sprint speed.

The study was approved by Khon Kaen University's Human Research Ethical Committee. Twenty-three dental students, aged 20-26 years, who had at least 28 natural teeth, with Class I a r c h i v e s o f o r a l b i o l o g y 5 3 (2 0 0 8) 5 3... more

The study was approved by Khon Kaen University's Human Research Ethical Committee. Twenty-three dental students, aged 20-26 years, who had at least 28 natural teeth, with Class I a r c h i v e s o f o r a l b i o l o g y 5 3 (2 0 0 8) 5 3 3-5 3 7

The purpose of this paper is to analyse the effects of cranial size and shape in domestic dogs (Canis familiaris) on predicted forces of biting. In addition to continuous size-shape analysis, nine size-shape groups were developed based on... more

The purpose of this paper is to analyse the effects of cranial size and shape in domestic dogs (Canis familiaris) on predicted forces of biting. In addition to continuous size-shape analysis, nine size-shape groups were developed based on three skull shape categories and three skull size categories. Bite forces were predicted from measurements made on dried skulls using two lever models of the skull, as well as simple models derived by regression analysis. Observed bite force values were not available for the database used in this study, so only comparisons between categories and models were undertaken. The effects of shape and size on scaled predicted bite forces were evaluated. Results show that bite force increases as size increases, and this effect was highly significant (P < 0.0001). The effect of skull shape on bite force was significant in medium and large dogs (P < 0.05). Significant differences were not evident in small dogs. Size × shape interactions were also significant (P < 0.05). Bite force predictions by the two lever models were relatively close to each other, whereas the regression models diverged slightly with some negative numbers for very small dogs. The lever models may thus be more robust across a wider range of skull size-shapes. Results obtained here would be useful to the pet food industry for food product development, as well as to paleontologists interested in methods of estimating bite force from dry skulls.

Background. The functional benefits of mandibular reconstruction following a composite resection remain unclear. Although microvascular surgical techniques have dramatically increased the predictability of bone and soft-tissue... more

Background. The functional benefits of mandibular reconstruction following a composite resection remain unclear. Although microvascular surgical techniques have dramatically increased the predictability of bone and soft-tissue reconstruction towards presurgical anatomic norms, the specific factors responsible for improved function remain controversial. Objective measures of masticatory function need to be more clearly determined before the predictability and efficacy of reconstructive approaches is established.

Objective: To assess periodontal parameters in a Jordanian population in individuals with three different facial types. Materials and Methods: Forty-five dental students (ages 20-26 years) with short, average, and long face heights were... more

Objective: To assess periodontal parameters in a Jordanian population in individuals with three different facial types. Materials and Methods: Forty-five dental students (ages 20-26 years) with short, average, and long face heights were divided into three equal groups. The plaque index, gingival index, gingival thickness, width of keratinized gingiva, and width of attached gingiva were measured in each group. Occlusal factors, including the dynamic occlusion and the presence or absence of premature contacts were recorded. Differences among the three groups were assessed using Student's t-test, chi-square test, and analysis of variance (ANOVA) test. Results: No differences were present in the plaque index, gingival index, gingival attachment, width of attached and keratinized gingiva and gingival thickness between the subjects in the three groups studied. None of the subjects in the long face group had canine guidance dynamic occlusion. Conclusions: There were no differences in the periodontal parameters between the different dentofacial vertical patterns, but there was a difference in the canine guidance dynamic occlusion.

Controversy remains over the rehabilitation of implant-supported restorations regarding the need to splint adjacent implant-supported crowns. This study compared the effects of simulated occlusal loading of three implants restored with... more

Controversy remains over the rehabilitation of implant-supported restorations regarding the need to splint adjacent implant-supported crowns. This study compared the effects of simulated occlusal loading of three implants restored with cemented crowns, splinted versus unsplinted. Three adjacent screw-shaped implants were passively inserted into three holes drilled in a photo-elastic model. Two combinations of cemented restorations were fabricated; three adjacent unsplinted and three adjacent splinted crowns. Strain gauges were connected to the implant necks and to the margins of the overlaying crowns. Fifteen axial static loads of 20-kg loadings were carried out right after each other via a custombuilt loading apparatus. Strain gauges located on the implant neck supporting splinted restoration demonstrated significantly (P < 0AE001) more strain (sum of strains = 3348AE54 microstrain) compared with the single crowns (sum of strains = 988AE57 microstrain). In contrast, significantly (P < 0AE001) more strain was recorded on the strain gauges located on the restoration margins of the single crowns (sum of strains = 756AE32 microstrain) when compared with splinted restorations (sum of strains = 186AE12 microstrain). The concept of splinting adjacent implants to decrease loading of the supporting structures may require re-evaluation. The clinical relevance of these findings needs further investigation.

Metriorhynchidae was a peculiar but long-lived group of marine Mesozoic crocodylomorphs adapted to a pelagic lifestyle. Recent discoveries show that metriorhynchids evolved a wide range of craniodental morphotypes and inferred feeding... more

Metriorhynchidae was a peculiar but long-lived group of marine Mesozoic crocodylomorphs adapted to a pelagic lifestyle. Recent discoveries show that metriorhynchids evolved a wide range of craniodental morphotypes and inferred feeding strategies. One genus, Dakosaurus, is arguably the most aberrant marine crocodylomorph due to its large, robust, ziphodont teeth; very low tooth count; and brevirostrine/oreinirostral snout. We here report an additional unusual feature of Dakosaurus that is unique among marine crocodylomorphs: tightly fitting tooth-totooth occlusion, whose inference is supported by reception pits along the upper and lower tooth rows, indicative of vertically orientated crowns that were in close contact during occlusion, and three distinct types of dental wear. These include irregular spalled surfaces near the apex (probably caused by tooth-food contact), semi-circular wear near the base, and elongate surfaces extending along the mesial and distal margins of the teeth, obliterating the carinae (including the denticles). Scanning electron micrographs show that these latter surfaces are marked by parallel apicobasal striations, which in extant mammals reflect tooth-tooth contact. As such, we interpret the carinal wear facets in Dakosaurus as being formed by repeated tooth-tooth contact

Objectives: To investigate the relation between occlusal loading and peri-implant clinical parameters (probing depth, bleeding on probing, gingival retraction, width of keratinized mucosa, and crevicular fluid volume) in patients with... more

Objectives: To investigate the relation between occlusal loading and peri-implant clinical parameters (probing depth, bleeding on probing, gingival retraction, width of keratinized mucosa, and crevicular fluid volume) in patients with implant-supported complete fixed prostheses in both arches. Material and Methods: This clinical study took place at the University of Valencia (Spain) dental clinic. It included patients attending the clinic for regular check-ups during at least 12 months after rehabilitation of both arches with implant-supported complete fixed ceramo-metallic prostheses. One study implant and one control implant were established for each patient using the T-Scan®III computerized system (Tesco, South Boston, USA). The maxillary implant closest to the point of maximum occlusal loading was taken as the study implant and the farthest (with least loading) as the control. Occlusal forces were registered with the T-Scan® III and then occlusal adjustment was performed to distribute occlusal forces correctly. Peri-implant clinical parameters were analyzed in both implants before and two and twelve months after occlusal adjustment. Results: Before occlusal adjustment, study group implants presented a higher mean volume of crevicular fluid (51.3±7.4 UP) than the control group (25.8±5.5 UP), with statistically significant difference. Two months after occlusal adjustment, there were no significant differences between groups (24.6±3.8 UP and 26±4.5 UP respectively) (p=0.977). After twelve months, no significant differences were found between groups (24.4±11.1 UP and 22.5±8.9 UP respectively) (p=0.323). For the other clinical parameters, no significant differences were identified between study and control implants at any of the study times (p>0.05). Conclusions: Study group implants receiving higher occlusal loading presented significantly higher volumes of crevicular fluid than control implants. Crevicular fluid volumes were similar in both groups two and twelve months after occlusal adjustment.

The present study makes a start on characterising the cognitive processes by which physical effects of eating on the senses are transformed into quantitative judgments about perceived characteristics of a food. It was hypothesised that... more

The present study makes a start on characterising the cognitive processes by which physical effects of eating on the senses are transformed into quantitative judgments about perceived characteristics of a food. It was hypothesised that there is a discrete perceptual channel for an aspect of texture sensed during each of the three initial movements of eating a piece of a cookie. The results showed that the force required for initial compression of the surface of the biscuit related to how 'crisp' it was. Scores on 'hard' were sensitive to higher forces being required to bite off a piece. Ratings of crunchiness responded to both amplitude and frequency of the cracks opened up in this heterogeneously structured material during the first crushing of the bitten piece. These findings are being pursued to identify the stimulation patterns more precisely and to measure how the percepts are integrated into judgments of overall texture. q

Growth affects the performance of structure, so the pattern of growth must influence the role of a structure and an organism. Because animal performance is linked to morphological specialization, ontogenetic change in size may influence... more

Growth affects the performance of structure, so the pattern of growth must influence the role of a structure and an organism. Because animal performance is linked to morphological specialization, ontogenetic change in size may influence an organism's biological role. High bite force generation is presumably selected for in durophagous taxa. Therefore, these animals provide an excellent study system for investigating biomechanical consequences of growth on performance. An ontogenetic series of 27 cownose rays (Rhinoptera bonasus) were dissected in order to develop a biomechanical model of the feeding mechanism, which was then compared with bite forces measured from live rays. Mechanical advantage of the feeding apparatus was generally conserved throughout ontogeny, while an increase in the mass and cross-sectional area of the jaw adductors resulted in allometric gains in bite force generation. Of primary importance to forceful biting in this taxon is the use of a fibrocartilaginous tendon associated with the insertion of the primary jaw adductor division. This tendon may serve to redirect muscle forces anteriorly, transmitting them within the plane of biting. Measured bite forces obtained through electrostimulation of the jaw adductors in live rays were higher than predicted, possibly due to differences in specific tension of actual batoid muscle and that used in the model. Mass-specific bite forces in these rays are the highest recorded for elasmobranchs. Cownose rays exemplify a species that, through allometric growth of bite performance and morphological novelties, have expanded their ecological performance over ontogeny.

Assessments of masticatory performance and occlusal force for wearers of obturator prostheses were performed as clinical objective assessments and reported in an earlier study. The purpose of the present study was to evaluate clinically... more

Assessments of masticatory performance and occlusal force for wearers of obturator prostheses were performed as clinical objective assessments and reported in an earlier study. The purpose of the present study was to evaluate clinically the chewing function of obturator prosthesis wearers by self-evaluations and to examine their relationship to the objective assessments. Twenty patients with maxillofacial obturator prostheses who were having a periodic checkup at the maxillofacial rehabilitation clinic in Kyushu University Hospital were recruited for this study. Chewing function was evaluated by 3 assessment tools: a self-assessment mastication scale, a chewing function score, and a mastication score. In addition, correlations among these assessments and objective tests--ie, masticatory performance and maximum occlusal force--were analyzed by the Spearman rank correlation coefficient. The mean self-assessment mastication scale was 63.2 (SD 31.8), the chewing function score was 54.0 ...

Tyrannosaurs, the group of dinosaurian carnivores that includes Tyrannosaurus rex and its closest relatives, are icons of prehistory. They are also the most intensively studied extinct dinosaurs, and thanks to large sample sizes and an... more

Tyrannosaurs, the group of dinosaurian carnivores that includes Tyrannosaurus rex and its closest relatives, are icons of prehistory. They are also the most intensively studied extinct dinosaurs, and thanks to large sample sizes and an influx of new discoveries, have become ancient exemplar organisms used to study many themes in vertebrate paleontology. A phylogeny that includes recently described species shows that tyrannosaurs originated by the Middle Jurassic but remained mostly small and ecologically marginal until the latest Cretaceous. Anatomical, biomechanical, and histological studies of T. rex and other derived tyrannosaurs show that large tyrannosaurs could not run rapidly, were capable of crushing bite forces, had accelerated growth rates and keen senses, and underwent pronounced changes during ontogeny. The biology and evolutionary history of tyrannosaurs provide a foundation for comparison with other dinosaurs and living organisms.

Patients with temporomandibular disorders may present with a cluster of joint and muscle disorders characterized primarily by pain, joint sounds and irregular or deviating jaw function. Maxillary stabilization-type splints represent the... more

Patients with temporomandibular disorders may present with a cluster of joint and muscle disorders characterized primarily by pain, joint sounds and irregular or deviating jaw function. Maxillary stabilization-type splints represent the best standard therapy, so the purpose of this study was to evaluate changes in local maximal clenchingrelated asymmetry patterns of masseter muscle sites associated with the immediate`application of splint therapy' using the diagnostic approach of highresolution gray-scale ultrasonography. The study included 24 patients who had signs and symptoms of temporomandibular disorders. Ultrasonographic investigation was performed with a linear (B-scan) 7á5 Mhz small-part transducer to visualize the antero-superior, antero-inferior, medio-superior, medio-inferior, postero-superior, and postero-inferior sites of the masseter muscle. To assess local maximal clenching-related muscle asymmetry patterns and to evaluate the respective effect of KEYWORDS:

as the differences in bone density make differences in bone to implant contact. b) Available remaining bone after extraction, which has a direct influence in choosing the width and the length of the implant, affecting the surface area and... more

as the differences in bone density make differences in bone to implant contact. b) Available remaining bone after extraction, which has a direct influence in choosing the width and the length of the implant, affecting the surface area and the bone to implant contact. c) Parafunctional habits, which increase time, magnitude, direction, and distribution of the forces affecting bone to implant contact. Forces and loading conditions applied on the implant Implant-related factors: a) Implant macro design (implant body, length and diameter, threads shape, pitch, lead, depth and width, and crest module), implant design is mainly responsible for 1-increase the surface area of the implant, 2-decrease the stress in addition to 3-distributing the forces on the bone and convert the stresses into favorable compressive stresses. b) Chemical composition and biomaterial of the implant and its relation to biocompatibility, enhancing healing, modulus of elasticity. c) Implant surface treatment and coatings (surface topography), responsible for increase the surface area of the BIC, decrease the stresses, enhance adhesion qualities to the bone-implant interface at initial healing.

The purpose of this study was to compare the effectiveness of splint therapy on the electromyographic activity of masticator'/muscles (anterior temporalis and masseter) before and after the application of a muscle relaxation splint.... more

The purpose of this study was to compare the effectiveness of splint therapy on the electromyographic activity of masticator'/muscles (anterior temporalis and masseter) before and after the application of a muscle relaxation splint. Electromyography recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal biting in the intercuspal position both before and after treatment without a splint. Fourteen patients whose chief complaint was masticatory muscle pain were selected for the study. After the initial evaluations muscle relaxation splints were applied, and the patients were instructed to use the splints for 6 weeks. Surface electromyographic recordings were taken from each patient before the beginning of clinical therapy and after 6 weeks of wearing the splints. The data obtained were analyzed through paired sample t tests and Wilcoxon's signed rank tests. The results of the study were as follows: (1) the electromyographic activity of the two muscles during maximal biting was not markedly changed after the muscle relaxation splint was used; and the changes observed in electromyographic activity of the involved and noninvolved sides were insignificant as well. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85:674-9)

Changes in the technology of food preparation over the last few thousand years (especially cooking, softening, and grinding) are hypothesized to have contributed to smaller facial size in humans because of less growth in response to... more

Changes in the technology of food preparation over the last few thousand years (especially cooking, softening, and grinding) are hypothesized to have contributed to smaller facial size in humans because of less growth in response to strains generated by chewing softer, more processed food. While there is considerable comparative evidence to support this idea, most experimental tests of this hypothesis have been on non-human primates or other very prognathic mammals (rodents, swine) raised on hard versus very soft (nearly liquid) diets. Here, we examine facial growth and in vivo strains generated in response to raw/dried foods versus cooked foods in a retrognathic mammal, the rock hyrax (Procavia capensis). The results indicate that the hyrax cranium resembles the non-human primate cranium in having a steep gradient of strains from the occlusal to orbital regions, but differs from most non-anthropoids in being primarily twisted; the hyrax mandible is bent both vertically and laterally. In general, higher strains, as much as two-fold at some sites, are generated by masticating raw versus cooked food. Hyraxes raised on cooked food had significantly less growth (approximately 10%) in the ventral (inferior) and posterior portions of the face, where strains are highest, resembling many of the differences evident between humans raised on highly processed versus less processed diets. The results support the hypothesis that food processing techniques have led to decreased facial growth in the mandibular and maxillary arches in recent human populations.

The influence of physiologic occlusal forces on tissue response to orthodontic tooth movement and its subsequent recovery was investigated in rats. The mandibular incisors were subjected to tipping and intrusive loads for 2 weeks. In 27... more

The influence of physiologic occlusal forces on tissue response to orthodontic tooth movement and its subsequent recovery was investigated in rats. The mandibular incisors were subjected to tipping and intrusive loads for 2 weeks. In 27 animals, the teeth remained in occlusion, while the incisors were shortened out of occlusion in 29. In each group, some rats were killed at the end of the tooth movement process, and the rest were kept alive for a 13-week recovery period. The subgroups were matched with corresponding controls. Tooth intrusion and eruption were monitored throughout the experiment; then histomorphometric and histopathologic evaluations were performed on the incisors and their periodontal tissues. Tooth movement was barely affected by the functional forces. However, immediately upon 2-week load application, damage to the pulp was more extensive in the occluding teeth; this might be due to the combined intrusive vectors of functional and mechanical loads. The effect of the physiologic function was expressed primarily during the recovery period, in which the eruptive function and distorted periodontal ligament space returned to normal significantly faster in the occluding teeth. This was also true for the healing of dental and periodontal lesions. The incidence of tooth resorption was also reduced. Normal occlusal function is imperative for rapid reconstitution of the damage caused by orthodontic forces. (Am J Orthod Dentofacial Orthop 2002;121:620-8)

It is widely accepted that the orthodontist should have a thorough understanding of the craniofacial musculature and its association with the growth and development of the dentofacial complex. There is still much controversy regarding the... more

It is widely accepted that the orthodontist should have a thorough understanding of the craniofacial musculature and its association with the growth and development of the dentofacial complex. There is still much controversy regarding the influence of the mandibular muscles on normal growth and development, and on orthodontic treatment and stability. This review presents an outline of the mandibular muscles and the vertical facial pattern. The different methods by which the mandibular muscles have been investigated are discussed. The potential influence of these muscles on normal morphologic variation in different people is also discussed, along with the implications for contemporary orthodontic treatment and stability.

Although there is consensus that Neandertal craniofacial morphology is unique in the genus Homo, debate continues regarding the precise anatomical basis for this uniqueness and the evolutionary mechanism that produced it. In recent years,... more

Although there is consensus that Neandertal craniofacial morphology is unique in the genus Homo, debate continues regarding the precise anatomical basis for this uniqueness and the evolutionary mechanism that produced it. In recent years, biomechanical explanations have received the most attention. Some proponents of the "anterior dental loading hypothesis" (ADLH) maintain that Neandertal facial anatomy was an adaptive response to high-magnitude forces resulting from both masticatory and paramasticatory activity. However, while many have argued that Neandertal facial structure was well-adapted to dissipate heavy occlusal loads, few have considered, much less demonstrated, the ability of the Neandertal masticatory system to generate these presumably heavy loads. In fact, the Neandertal masticatory configuration has often been simultaneously interpreted as being disadvantageous for producing large bite forces. With rare exception, analyses that attempted to resolve this conflict were qualitative rather than quantitative. Using a three-dimensional digitizer, we recorded a sequence of points on the cranium and associated mandible of the Amud 1, La Chapelle-aux-Saints, and La Ferrassie 1 Neandertals, and a sample of early and recent modern humans (n ϭ 29), including a subsample with heavy dental wear and documented paramasticatory behavior. From these points, we calculated measures of force-production capability (i.e., magnitudes of muscle force, bite force, and condylar reaction force), measures of force production efficiency (i.e., ratios of force magnitudes and muscle mechanical advantages), and a measure of overall size (i.e., the geometric mean of all linear craniofacial measurements taken). In contrast to the expectations set forth by the ADLH, the primary dichotomy in force-production capability was not between Neandertal and modern specimens, but rather between large (robust) and small (gracile) specimens overall. Our results further suggest that the masticatory system in the genus Homo scales such that a certain level of force-production efficiency is maintained across a considerable range of size and robusticity. Natural selection was probably not acting on Neandertal facial architecture in terms of peak bite force dissipation, but rather on large tooth size to better resist wear and abrasion from submaximal (but more frequent) biting and grinding forces. We conclude that masticatory biomechanical adaptation does not underlie variation in the facial skeleton of later Pleistocene Homo in general, and that continued exploration of alternative explanations for Neandertal facial architecture (e.g., climatic, respiratory, developmental, and/or stochastic mechanisms) seems warranted. Am Facial features exhibited by Neandertals have long been considered unique within the genus Homo. These include: elongated vertical facial dimensions; midsagittal upper facial projection; broad squared anterior palates; relatively wide and square-shaped piriform apertures; broad, projecting nasal bridges; depressed internal nasal floors; swept-back zygomatic arches; inflated infraorbital areas; and long mandibles with high coronoid and/or low condylar processes, retromolar spaces, and relatively large anterior dentition (Smith

Bite force can be defined as the force applied by the masticatory muscles in dental occlusion. Bite force is the resultant of all the forces acting on individual teeth due to various components of the masticatory system. Knowledge of... more

Bite force can be defined as the force applied by the masticatory muscles in dental occlusion. Bite force is the resultant of all the forces acting on individual teeth due to various components of the masticatory system. Knowledge of individual bite force helps dentist to understand different type of dentition, the mechanics of mastication for evaluation of the therapeutic effects of prosthetic devices and to provide reference data for studies on the biomechanics of prosthetic devices. Currently, there are direct and indirect methods to determine bite force. Direct method includes use of suitable transducers and indirect method includes use of functional relationship between bite force and physiological variables. The bite force is a function of many factors and hence difficult to compute. Although direct methods are accurate and convenient to determine individual bite force which requires sophisticated instrumentation and intervention whereas indirect methods are not accurate and require investigation of many physiological parameters. However, it is difficult to establish exact mathematical model to estimate individual bite force. This paper presents a Finite Element Analysis (FEA) based indirect method to estimate bite force. Commercial FEA software's like HyperMesh and RADIOSS are widely used in engineering and the biomedical community for diverse applications. FE model is built using 3D CAD model of jaw created using CT scan images to estimate theoretical maximum bite force as well as individual tooth load.

Finite element analysis (FEA) was used to generate 3-dimensional models of a human mandible with impacted third molars. The aim was to analyze the effects of removing various amounts of bone around an impacted mandibular third molar and... more

Finite element analysis (FEA) was used to generate 3-dimensional models of a human mandible with impacted third molars. The aim was to analyze the effects of removing various amounts of bone around an impacted mandibular third molar and to predict the possibility of iatrogenic fracture. Data were acquired from cone beam computed tomography (CBCT) scans of a patient using numerically calculated mechanical parameters. Virtual surgery was then performed on the mandibular models, and standardized chewing forces were applied to the resulting simulations. The modelling showed that the highest stress during normal clenching occurred if the surgical procedure involved the external oblique ridge. The peak stress occurred at the site of removal of the third molar, during contralateral loading of the mandible. Use of CBCT allowed production of high-quality models of an individual patient and simulation of various surgical scenarios. FEA identified the accumulation of stress and strain at speci...

Caecilians have two functionally separate sets of jaw closing muscles. The jaw adductor muscles are parallel fibered muscles positioned close to the jaw joint and their lever mechanics suggests they are well suited to rapidly closing the... more

Caecilians have two functionally separate sets of jaw closing muscles. The jaw adductor muscles are parallel fibered muscles positioned close to the jaw joint and their lever mechanics suggests they are well suited to rapidly closing the jaws. A second set of muscles, the hypaxial interhyoideus posterior (IHP), levers the jaws closed by pulling on the retroarticular process (RA) of the lower jaw. Models of the lower jaw point out that the angle and length of the RA has a profound effect on the closure force exerted by the IHP. The caecilian skull is streptostylic -the quadrate-squamosal apparatus (QSA) moves relative to the rest of the skull, a condition that seems at odds with a well-ossified cranium. Modeling the contribution of this streptostylic suspension of the lower jaw shows that rotational freedom of the QSA amplifies the force of the IHP by redirecting force applied along the low axis of the lower jaw. Measurements from several species and life stages of preserved caecilians reveal a large variation in predicted bite force (as a multiple of IHP force) with age and phylogeny.

Purpose: To assess whether splinting can counterbalance the detrimental effects of varying the crown-to-implant (C/I) ratio and crown height space (CHS) by decreasing nonaxial overload stresses. Materials and Methods: Three implants were... more

Purpose: To assess whether splinting can counterbalance the detrimental effects of varying the crown-to-implant (C/I) ratio and crown height space (CHS) by decreasing nonaxial overload stresses. Materials and Methods: Three implants were inserted into a photoelastic block model. Two strain gauges were cemented onto the neck of each implant on the buccal and lingual aspects and provided a simultaneous direct reading of strain. Four groups of splinted cement-retained restorations with C/I ratios of 1:1, 1:1.5, 1:1.75, and 1:2 were used. CHSs were 10, 15, 17.5, and 20 mm, respectively. Fifteen static loadings were carried out simultaneously with 20-kg weights via a custom-built loading apparatus at 30°t o the vertical axis. Results: Occlusal force application at 30°showed a statistically significant increase in both buccal (1,911.65 Ϯ 110 vs 3,252.06 Ϯ 150) and palatal (35.58 Ϯ 7 vs 286.85 Ϯ 15) microstrain values as the C/I ratio increased from 1:1 to 1:1.5 (P Ͻ .001). Force application at 30°in cases with C/I ratios of 1:1.75 and 1:2 resulted in fracture of the abutment screw followed by dislodgement of the crowns. Failures were noted at a CHS of 15 mm or greater. Conclusions: In this biomechanical mode, splinting does not prevent prosthetic failure when the CHS is 15 mm or greater. Vertical bone augmentation is highly recommended in cases with a CHS of 15 mm or greater.

Stable crowns that seal and protect the tooth are needed while the tissues are healing. The results of this study indicate that Unifast light-cured material demonstrated a smaller dimensional change in the oral environment, and thus, may... more

Stable crowns that seal and protect the tooth are needed while the tissues are healing. The results of this study indicate that Unifast light-cured material demonstrated a smaller dimensional change in the oral environment, and thus, may be useful in situations where provisional crowns are needed for longer periods.

To prevent relapse after orthodontic treatment, retention is often considered indispensable. Soft tissues are thought to have a significant influence on dental movements. To quantify the influence of masticatory muscles on post-treatment... more

To prevent relapse after orthodontic treatment, retention is often considered indispensable. Soft tissues are thought to have a significant influence on dental movements. To quantify the influence of masticatory muscles on post-treatment relapse, and in an attempt to avoid unnecessary procedures, 2 male orthodontic patients (13 and 30 years old at debonding) were followed up. The patients completed 2 years of fixed orthodontic treatment and received no post-orthodontic retention. After 1 week and again after 6 months, alginate impressions of dental arches and a surface electromyographic (EMG) assessment of the masseter and temporalis muscles during maximum voluntary clenching were performed. The younger patient received surface EMG monitoring once a month for the first 6 months and at the 1-year follow-up appointment. Arch dimensions and the 3-dimensional inclination of the facial axis of the clinical crown (FACC) were measured using a computerized digitizer. Symmetry in muscular co...

In Part 1 of this two-part literature review, the biomechanics of cantilever fixed partial dentures are reviewed. Theoretical constructs of implant biomechanics with special emphasis on implantsupported cantilevers are also discussed.... more

In Part 1 of this two-part literature review, the biomechanics of cantilever fixed partial dentures are reviewed. Theoretical constructs of implant biomechanics with special emphasis on implantsupported cantilevers are also discussed. Finally, an overview of the literature regarding occlusal forces generated by patients with implant-supported prostheses is presented.

This study analyzed detailed models of human mandibles at 3 different stages of life with simulation of supra normal chewing forces at static conditions. Finite element analysis (FEA) was used to generate models from cone-beam... more

This study analyzed detailed models of human mandibles at 3 different stages of life with simulation of supra normal chewing forces at static conditions. Finite element analysis (FEA) was used to generate models from cone-beam computerized tomograms (CBCT) of 3 patients aged 12, 20, and 67 years, using numerically calculated material parameters. Estimated chewing forces were then applied to the simulations. The results reflect higher elasticity in younger models in all regions of the mandible. The experimental models show that physiologic load stress and strain distributional changes of the mandible vary according to age. The CBCT-based model generation used in this study provided high-quality model definition of the 3 individual patients of different ages. FEA has great potential to predict bone responses to paradigms of mechanical activity. Future applications of FEA will include surgical planning, surgical hardware testing, and the design of scaffolds and tissue-engineered constructs.

Occlusal overload during sleep is a significant clinical issue that has negative impacts on the maintenance of teeth and the longevity of dental prostheses. Sleep is usually viewed as an 'out-of-functional' mode for masticatory... more

Occlusal overload during sleep is a significant clinical issue that has negative impacts on the maintenance of teeth and the longevity of dental prostheses. Sleep is usually viewed as an 'out-of-functional' mode for masticatory muscles. However, orodental structures and prostheses are not free from occlusal loads during sleep since masticatory muscles can be activated at a low level within normal sleep continuity. Thus, an increase in masticatory muscle contractions, by whatever the cause, can be associated with a risk of increased occlusal loads during sleep. Among such conditions, sleep bruxism (SB) is a type of sleep-related movement disorders with potential load challenge to the tooth and orofacial structures. Patients with SB usually report frequent tooth grinding noises during sleep and there is a consecutive increase in number and strength of rhythmic masticatory muscle activity (RMMA). Other types of masticatory muscle contractions can be non-specifically activated d...

The Carnivora spans the largest ecological and body size diversity of any mammalian order, making it an ideal basis for studies of evolutionary ecology and functional morphology. For animals with different feeding ecologies, it may be... more

The Carnivora spans the largest ecological and body size diversity of any mammalian order, making it an ideal basis for studies of evolutionary ecology and functional morphology. For animals with different feeding ecologies, it may be expected that bite force represents an important evolutionary adaptation, but studies have been constrained by a lack of bite force data. In this study we present predictions of bite forces for 151 species of extant carnivores, comprising representatives from all eight families and the entire size and ecological spectrum within the order. We show that, when normalized for body size, bite forces differ significantly between the various feeding categories. At opposing extremes and independent of genealogy, consumers of tough fibrous plant material and carnivores preying on large prey both have high bite forces for their size, while bite force adjusted for body mass is low among specialized insectivores. Omnivores and carnivores preying on small prey have more moderate bite forces for their size. These findings indicate that differences in bite force represent important adaptations to and indicators of differing feeding ecologies throughout carnivoran evolution. Our results suggest that the incorporation of bite force data may assist in the construction of more robust evolutionary and palaeontological analyses of feeding ecology.

The feeding behavior of the theropod dinosaur Tyrannosaurus rex is investigated through analysis of two variables that are critical to successful predation, bite force and prey body mass, as they scale with the size of the predator.... more

The feeding behavior of the theropod dinosaur Tyrannosaurus
rex is investigated through analysis of two
variables that are critical to successful predation, bite
force and prey body mass, as they scale with the size of
the predator. These size-related variables have important
deterministic effects on the predator’s feeding strategy,
through their effects on lethal capacity and choice of
prey. Bite force data compiled for extant predators
(crocodylians, carnivorans, chelonians and squamates)
are used to establish a relationship between bite force
and body mass among extant predators. These data are
used to estimate the maximum potential bite force of
T. rex, which is between about 183,000 and 235,000N for a
bilateral bite. The relationship between maximum prey
body mass and predator body mass among the same
living vertebrates is used to infer the likely maximum
size of prey taken by T. rex in the Late Cretaceous. This
makes it possible to arrive at a more rigorous assessment
of the role of T. rex as an active predator and/or scavenger
than has hitherto been possible. The results of this
analysis show that adult Triceratops horridus fall well
within the size range of potential prey that are predicted
to be available to a solitary, predaceous T. rex. This
analysis establishes boundary conditions for possible
predator/prey relationships among other dinosaurs, as
well as between these two taxa.

Starch and mucilage extracts of sweet cassava tubers were incorporated into wheat flour–cassava starch (WF–CS) composite mix to make Chinese noodle. CS was extracted from fresh 1- and 2-yr-old sweet cassava tubers and was mixed at an... more

Starch and mucilage extracts of sweet cassava tubers were incorporated into wheat flour–cassava starch (WF–CS) composite mix to make Chinese noodle. CS was extracted from fresh 1- and 2-yr-old sweet cassava tubers and was mixed at an optimized ratio of 70:30 into patent hard red Spring wheat (HRSW) flour. Noodles of proportional substitution of cassava mucilage in WF–CS blends were

Maximum bite force is a useful indicator of the functional state of the masticatory system and the loading of the teeth, and its recordings can be performed in a relatively simple way in the clinic. However, because maximum bite-force... more

Maximum bite force is a useful indicator of the functional state of the masticatory system and the loading of the teeth, and its recordings can be performed in a relatively simple way in the clinic. However, because maximum bite-force levels vary with method, sex and age, it is important that the measurements are compared against the appropriate reference values. The level of bite force is a result of the combined action of the jaw elevator muscles modified by jaw biomechanics and reflex mechanisms. Pain limits the maximum bite force and may thus impede the measurements, but this factor may also be useful in treatment control. The maximum bite force increases with the number of teeth present. The number of occlusal tooth contacts is an important determinant for the maximally attainable bite force, explaining about 10% to 20% of the variation. The association between maximum bite force and the amount of occlusal contact is closest in the posterior region, and as a consequence, loss of molar support results in reduction of force. In contrast, malocclusions defined solely on the basis of molar and canine relationships have less influence on the level of bite force. (Semin Orthod 2006;12:120-126.)