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1.
The mechanics of the first bite   总被引:4,自引:0,他引:4  
An analysis of the action of the incisor teeth in humans is presented in terms of the fracture of food particles. It is predicted that the resistance of foods with an essentially linear elastic response to an initial bite by the incisors will depend on the square root of the product of two food properties, Young's modulus and toughness. This quantity should be approximately equal to the product of the stress at cracking during a bite, and the square root of the length of a notch or indentation from which that crack initiates. As a test of the theory, the relationship between in vivo stresses and the depth of incisal penetration, measured during bites on seven 'snack' foods by 10 subjects, and food properties established from mechanical testing, was investigated. Theory and experiment were found to be in excellent agreement. A dimensionless index of the efficiency of incision is suggested, relating fracture performance by subjects to values from a testing machine. This appears to have a high level of inter-subject discrimination with efficiencies varying about threefold. The method appears to have potential applications in dentistry, food science and studies of human and primate evolution.  相似文献   

2.
Analysis of synchronously recorded cine-radiographs and electromyograms in two rodents (Aplodontia rufa and Marmota monax) demonstrates that jaw movements and muscle activiteis during incisal functions are distinctly different from those found during mastication. Movements during incisal biting are primarily along the midline, accompanied by symmetrical activity of the jaw adductor muscles. Most biting cycles do not end in contact between upper and lower incisors. When contact does occur, the lower incisors are dragged along the lingual surfaces of the upper incisors. Cropping, or tip-to-tip occlusion of upper and lower incisors, was not observed. Sharpening of the lower incisors, a behavior which may be unique to the Rodentia, was recorded in both A. rufa and M. monax. During sharpening, the lingual surface of the lower incisor is dragged across the tip of the upper incisor producing a lingual wear facet. Like incisal biting, sharpening movements are primarily confined to the midline, although there may be lateral movements in some sharpening cycles. Sharpening cycles are among the most rapid cyclic movements recorded in mammals, as the mean frequencies of sharpening are 11 cycles/s in A. rufa and 8 cycles/s in M. monax. © 1995 Wiley-Liss, Inc.  相似文献   

3.
Longitudinal ground sections of 29 Old World monkey central lower incisors were studied histologically and metrically. Labiolingual incisor width tended to scale isometrically with body weight but with important deviations in relative incisor size, which appeared to be correlated with diet in accord with work by Hylander. Lower incisors of the predominantly folivorous colobine monkeys had a substantial layer of enamel on both lingual and labial aspects and consequently had blunt incisal edges. These teeth in both cercopithecins and papionins, which are omnivorous or frugivorous, had little or no enamel on the lingual aspect, resulting in sharp incisal edges. It is suggested that colobine incisors are used mainly in gripping and tearing leaves, whereas cercopithecine incisors are better adapted to cutting and scraping. Crown height showed a positive allometric relationship with overall incisor height, so that the tall incisors of papionins, especially Papio and Mandrillus, were more hypsodont than the shorter incisors of colobines and cercopithecins. This appears to be related to differences in the rates of incisor wear between the groups.  相似文献   

4.
Allometric relationships between incisor size and body size were determined for 26 species of New World primates. While previous studies have suggested that the incisors of Old World primates, and anthropoids in general, scale isometrically with body size, the data presented here indicate a negative allometric relationship between incisor size and body size among New World species. This negative allometry was exhibited by platyrrhines when either upper or lower incisor row length was regressed against body weight, and when either least-squares or bivariate principal axis equations were used. When upper incisor length was plotted against skull length, negative allometry could be sustained using both statistical techniques only when the full sample of 26 species was plotted. The choice of variables to represent incisor size and body size, and the choice of a statistical technique to effect the allometric equation, had a more pronounced impact on the location of individual species with regard to lines of best fit. Platyrrhines as a group have smaller incisors relative to body size than do catarrhines, regardless of diet. Among New World primates, small incisors represent a plausible primitive condition; species with relatively large incisors manifest a phyletic change associated with a dietary shift to foods that require increased incisal preparation. The opposite trend characterizes Old World primates. In spite of the taxonomic differences in relative incisor size between platyrrhine and catarrhine primates, inferences about diet derived from an allometric equation for all anthropoids should prove reliable as long as the species with unknown diet does not lie at the upper end of the body size range for platyrrhines or catarrhines.  相似文献   

5.
The aim of this study was to investigate the stress distribution generated in a veneer restoration of an upper central incisor compared to intact teeth using the finite element analysis after applying a lingual buccal loading at the incisal edge. Methods: Two models were developed: one model contained enamel, dentine, cementum, periodontal ligament, cortical and trabecullar bones, and the other model was a veneer restoration; both models were developed using MSC/Nastran software (MacNeal-Schwendler Corporation, Los Angeles, CA, USA) as the pre- and post-processor. A 10-N load was applied at the incisal edge from the lingual to the buccal side to simulate oral conditions in this area (protrusion). Results: Von Mises stresses were then analysed for three different regions: A-B (enamel elements under the veneer or second enamel layer), A'-B' (buccal enamel and/or veneer element layer) and C-D (lingual enamel elements layer). A higher stress mode was observed for both models at the lingual cervical region. Conclusions: The presence of a veneer restoration on the incisors is a good alternative to mimic the behaviour of enamel under protrusion loading conditions. The use of veneers to replace enamel during rehabilitations is recommended.  相似文献   

6.
The three species of vampire bats (Phyllostomidae: Desmodontinae), Desmodus rotundus, Diaemus youngi, and Diphylla ecaudata, are the only mammals that obtain all nutrition from vertebrate blood (sanguinivory). Because of the unique challenges of this dietary niche, vampire bats possess a suite of behavioral, physiological, and morphological specializations. Morphological specializations include a dentition characterized by small, bladelike, non‐occlusive cheek teeth, large canines, and extremely large, procumbent, sickle‐shaped upper central incisors. The tips of these incisors rest in cuplike pits in the mandible behind the lower incisors (mandibular pits). Here, we use microCT scanning and high‐resolution radiography to describe the morphology of the mandible and anterior dentition in vampire bats, focusing on the relationship between symphyseal fusion, mandibular pit size, incisor size, and procumbency. In Desmodus and Diaemus, highly procumbent upper incisors are associated with relatively small mandibular pits, an unfused mandibular symphysis with substantial bony interdigitations linking the dentaries, and a diastema between the lower central incisors that helps to facilitate the lapping of blood from a wound. In Diphylla, less procumbent upper incisors are associated with relatively large mandibular pits, a completely fused mandibular symphysis, and a continuous lower toothrow lacking a central diastema. We hypothesize that symphyseal morphology and the presence or absence of the diastema are associated with the angle of upper incisor procumbency and mandibular pit development, and that spatial constraints influence the morphology of the symphysis. Finally, this morphological variation suggests that Diphylla utilizes a different feeding strategy as compared to Desmodus and Diaemus, possibly resulting from the functional demands of specialization on avian, rather than mammalian, blood. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.  相似文献   

7.
Most previously published electromyographic (EMG) studies have indicated that the temporalis muscles in humans become almost electrically quiet during incisai biting. These data have led various workers to conclude that these muscles may contribute little to the incisai bite force. The feeding behavior and comparative anatomy of the incisors and temporalis muscles of certain catarrhine primates, however, suggest that the temporalis muscle is an important and powerful contributor to the bite force during incision. One purpose of this study is to analyze the EMG activity of the masseter and temporalis muscles in both humans and macaques with the intention of focusing on the conflict between published EMG data on humans and inferences of muscle function based on the comparative anatomy and behavior of catarrhine primates. The EMG data collected from humans in the present study indicate that, in five of seven subjects, the masseter,anterior temporalis, and posterior temporalis muscles are very active during apple incision (i.e., relative to EMG activity levels during apple and almond mastication). In the other two human subjects the EMG levels of these muscles are lower during incision than during mastication, but in no instance are these muscles ever close to becoming electrically quiet. The EMG data on macaques indicate that, in all six subjects, the masseter, anterior temporalis, and posterior temporalis muscles are very active during incision. These data are in general agreement with inferences on muscle function that have been drawn from the comparative anatomy and behavior of primates, but they do not agree with previous experimental data. The reason for this disagreement is probably due to differences in the experimental procedure. In previous studies subjects simply bit isometrically on their incisors and the resulting EMG pattern was compared to the pattern associated with powerful clenching in centric occlusion. In the present study the subjects incised into actual food objects, and the resulting EMG pattern was compared to the pattern associated with mastication of various foods. It is not surprising that these two procedures result in markedly different EMG patterns, which in turn result in markedly different interpretations of jaw-muscle function. In an attempt to explain the evolution of the postorbital septum in anthropoids, it has been suggested that the anterior temporalis is more active than the masseter during incision (Cachel, 1979). The human and macaque EMG data do not support this hypothesis; during incision, the two muscles show no consistent differences in humans and the masseter appears to be in fact more active than the anterior temporalis in macaques.  相似文献   

8.
The aim of this study was to investigate the stress distribution generated in a veneer restoration of an upper central incisor compared to intact teeth using the finite element analysis after applying a lingual buccal loading at the incisal edge. Methods: Two models were developed: one model contained enamel, dentine, cementum, periodontal ligament, cortical and trabecullar bones, and the other model was a veneer restoration; both models were developed using MSC/Nastran software (MacNeal-Schwendler Corporation, Los Angeles, CA, USA) as the pre- and post-processor. A 10-N load was applied at the incisal edge from the lingual to the buccal side to simulate oral conditions in this area (protrusion). Results: Von Mises stresses were then analysed for three different regions: A-B (enamel elements under the veneer or second enamel layer), A′-B′ (buccal enamel and/or veneer element layer) and C-D (lingual enamel elements layer). A higher stress mode was observed for both models at the lingual cervical region. Conclusions: The presence of a veneer restoration on the incisors is a good alternative to mimic the behaviour of enamel under protrusion loading conditions. The use of veneers to replace enamel during rehabilitations is recommended.  相似文献   

9.
Response of the mandibular joint to loss of incisal function in the rat   总被引:2,自引:0,他引:2  
In a study of the rat mandibular joint (MJ), Simon [Acta anat. 97: 351-360 (1977)] suggested that reduction in condylar cartilage thickness noted in animals subjected to removal or trimming of incisors resulted from the lessening of joint reaction forces produced during incision. In order to explore this question further, the microanatomy of the MJ in 47-day-old rats whose incisors had been trimmed every other day was compared to that in control animals and in a third group fed a soft diet as a control for reduced joint reaction forces. Both the incisor-clipped and soft-diet groups exhibited reduced size and density of bony trabeculae underlying the condylar cartilage and diminished staining for alcian blue. The thickness of the prechondroblastic layer of the condylar cartilage was significantly (p less than or equal to 0.01) reduced relative to controls in both experimental groups on the superior aspect of the cartilage, but was reduced in the more posterior parts of the cartilage only in the incisor-clipped group. While not denying that joint reaction forces may affect MJ response, the reduced proliferative response noted in the posterior region of the condylar cartilage in incisor-clipped animals is perhaps best explained by a decrease in the frequency and extent of protrusion of the lower jaw due to a lack of incisal preparation of food items.  相似文献   

10.
In 1995-1996 two isolated hominin lower incisors were found at the middle Pleistocene site of Boxgrove in England, with Lower Palaeolithic archaeology. Boxgrove 2 is a permanent lower right central incisor and Boxgrove 3 a permanent lower left lateral incisor. They were found separately, but close to one another and appear to belong to the same individual. The Boxgrove 1 tibia discovered in 1993 came from a different stratigraphic context and is thus believed to represent a different individual. This paper describes the morphology of the incisors, which is similar to other middle Pleistocene hominin specimens and, as with the tibia, suggests that they could be assigned to Homo heidelbergensis (recognising that the taxonomic status of this species is still a matter of debate). The incisors show substantial attrition associated with secondary dentine deposition in the pulp chamber and clearly represent an adult. They also show extensive patterns of non-masticatory scratches on the labial surfaces of both crown and root, including some marks which may have been made postmortem. The roots were exposed in life on their labial sides by a large dehiscence, extending almost to the root apex. This is demonstrated by deposits of calculus, polishing, and scratching on the exposed surfaces. The dehiscence may have been caused by repeated trauma to the gingivae or remodelling of the tooth-supporting tissues in response to large forces applied to the front of the dentition.  相似文献   

11.
The first biplanar X-ray motion analysis of mastication and food processing for Castor fiber is presented. While particles are chipped off interaction of incisors involves variable movements of the lower mandible and thus incisors. After jaw opening the tip of the lower incisors can reach different positions anteriorly of the upper incisors. Then the mandible moves upwards and backwards and brings the tips of the incisors into contact. The lower incisors slide along the wear facet of the upper to the ledge when the cheek teeth occlude. The glenoid fossa and lower jaw condyle are in close contact during incisor contact and no transverse movements are observed. Mastication involves interaction of the cheek teeth with no contact of the incisors. When the cheek teeth are in occlusal contact the mandible is moved forward and transverse, or mediolateral. In consecutive power strokes the jaw is moved alternately to the right and left side. When the jaw opens it is brought into a more central but not totally centred position. During mastication the condyles are positioned posteriorly to the glenoid allowing lateral movement of the mandible. The lateral movement is particularly noticeable in the anterior part of the mandible. With the lateral movements of the incisors one glenoid has to move posteriorly, the other anteriorly.  相似文献   

12.
The structure of teeth in all living beings is genetically predetermined, although it can change under external physiological and pathological factors. The author's hypothesis was to indicate evolutional shifts resulting from genetic, functional and other differences. A comparative study about certain characteristics of incisors in humans and myomorpha, the fat dormouse (Glis glis) being their representative as well, comprised measurements of enamel and dentin thickness in individual incisor segments, evaluation of external enamel index, and also assessment of histological structure of enamel and dentin. The study results involving dormice showed the enamel to be thicker in lower than in the upper teeth, quite contrary to enamel thickness in humans. In the upper incisors in dormice the enamel is the thickest in the medial layer of the crown, and in the cervical portion of the crown in the lower incisors. The thickness of dentin in dormice is greater in the oral than in the vestibular side. These findings significantly differ from those reported in reference literature, but they are based on the function of teeth in dormice. Histological characteristics of hard dental tissues in dormice are similar to those in humans, with exception of uniserial structure of enamel and appearance of dentinoenamel junction.  相似文献   

13.
In chimpanzees, the cutting edge of the incisor battery is longer in relation to the length of the molar row than in any other hominoid, extant or fossil, the only other lineage approaching it being the orangutan. Apart from their increased mesio-distal dimensions, the upper and lower incisors of chimpanzees differ in additional ways from those of almost all other hominoids. The I2/ is enlarged, so that the difference in size between it and the central upper incisor is less than it is in the heteromorphic upper incisors of other hominoids. The lower incisors are expanded mesio-distally, so much so that isolated I/2 crowns can resemble upper central incisors. In chimpanzees the lingual surface of the lower incisors is generally more procumbent than it is in other hominoids, which have more vertically oriented incisor crowns and there is a greater difference in enamel thickness between labial and lingual sides. The re-orientation of the lower incisor crown is reflected in the root, which in lateral view is anteriorly concave in chimpanzees whereas it is more orthogonal or convex in other hominoids. The molars of chimpanzees, especially the lowers, have extensive and relatively deep occlusal basins, and the main cusps are peripheralised and labio-lingually compressed, making them more trenchant than those of other hominoids. This paper examines the incisor-lower molar proportions in extinct and living hominoids and develops a new hypothesis about the evolution of the dentition of chimpanzees and links it to their diet. It also examines the incisor-molar proportions of hominids and African apes in order to throw light on the phylogenetic relationships between them. It is shown that chimpanzees are highly derived in this respect and that several recent ideas concerning the chimp-like appearance of the last common ancestor of hominids and African apes are likely to be incorrect.This revised version was published online in April 2005 with corrections to the cover date of the issue.  相似文献   

14.
The mechanical properties of plant foods play an important role in the feeding process, being one of many criteria for food acceptance or rejection by primates. One of the simplest justifications for this statement is the general finding that primates tend to avoid foods with high fiber. Although fiber is largely tasteless, odorless, and colorless, it imparts texture, a sensation in the mouth related to the physical properties of foods. All primates encounter such mechanical resistance when they bite into plant food, and studies on humans show that an incisal bite facilitates quick oral assessment of a property called toughness. Thus, it is feasible that primates make similar assessments of quality in this manner. Here, we review methods of measuring the toughness of primate foods, which can be used either for making general surveys of the properties of foods available to primates or for establishing the mechanisms that protect these foods from the evolved form of the dentition.  相似文献   

15.
This article reports an analysis of two dimensional grasp where a convex rigid object is grasped by two contact points with friction. The purpose is to find the object orientation that minimizes the norm of the contact force vector, each element of which is composed from the normal force and friction force at each contact point. The formulation of this problem requires some equality or inequality conditions. In the analysis, the solution of the equality conditions is parameterized at first. Based on the fact that the norm of the contact force vector becomes monotonic increasing function of this parameter, the minimal parameter values are calculated by means of the piecewise analysis. Using the relation between the friction coefficient and the apex angle of the friction cone effectively, the following result is obtained: the norm of the contact force, i.e, gripping power becomes locally minimal at the object orientation where the intersection point of the upper sides of two friction cones is located in opposite direction of the gravity from the center of mass of the grasped object.  相似文献   

16.
In several primate groups enamel is reduced or absent from the lingual (tongue) side of the mandibular incisor crowns akin to other placental and marsupial mammalian groups such as rodents, lagomorphs and wombats. Here we investigate the presumed adaptation of crowns with unilateral enamel to the incision of tough foods in cercopithecines, an Old World monkey subfamily, using a simulation approach. We developed and validated a finite element model of the lower central incisor of the rhesus macaque (Macaca mulatta) with labial enamel only to compute three-dimensional displacements and maximum principal stresses on the crown subjected to compressive loads varying in orientation. Moreover, we developed a model of a macaque incisor with enamel present on both labial and lingual aspects, thus resembling the ancestral condition found in the sister taxon, the leaf-eating colobines. The results showed that, concomitant with experimental results, the cercopithecine crown with unilateral enamel bends predominantly towards the inside of the mouth, while displacements decreased when both labial and lingual enamel are present. Importantly, the cercopithecine incisor crown experienced lower maximum principal stress on the lingual side compared to the incisor with enamel on the lingual and labial aspects under non-axial loads directed either towards the inside or outside of the mouth. These findings suggest that cercopithecine mandibular incisors are adapted to a wide range of ingestive behaviours compared to colobines. We conclude that the evolutionary loss of lingual enamel in cercopithecines has conferred a safeguard against crown failure under a loading regime assumed for the ingestion (peeling, scraping) of tough-skinned fruits.  相似文献   

17.
目的:研究Le Fort I型截骨术与上颌牙根尖的关系,为临床合理制订截骨平面提供解剖学依据。方法:选择上颌牙槽清晰或出土后仍有牙保留的颅骨,在颅骨梨状孔下缘至上颌结节作一连线作为模拟Le Fort I型术式截骨水平,以上颌牙槽缘为标志,用游标卡尺测量每侧上颌各牙的牙槽缘至上述模拟截骨水平的距离及牙槽缘至各牙根尖端的长度,然后计算出上颌各牙根尖至Le Fort I型术式截骨线的距离。结果:上颌各牙相对的牙槽缘至Le FortI型术式截骨线的距离,从中切牙至第二磨牙逐渐缩小,右侧中切牙为21.09±1.53mm,左侧中切牙为20.96±1.64mm,右侧第二磨牙为14.94±1.52mm,左侧第二磨牙为14.95±1.59mm;上颌各牙根尖至Le Fort I型术式截骨水平的距离,从中切牙至第二磨牙也逐渐缩小,而两侧尖牙牙根尖距离Le Fort I型术式截骨线的距离右侧为4.49±1.74mm,左侧为4.69±2.14mm,第二磨牙牙根尖距离Le Fort I型术式截骨线的距离右侧为4.65±1.63mm,左侧为4.49±1.89,两侧尖牙牙根尖和第二磨牙牙根尖至Le Fort I型术式截骨水平的距离均比较接近。结论:上颌各牙根尖至LeFortI型术式截骨线的距离均在4mm以上,根据前牙中尖牙牙根尖的位置和后牙中第二磨牙牙根尖的位置,Le Fort I型术式截骨线水平在13、23(3|3)根尖及27、27(7|7)根尖上方4mm以上,按此平面作截骨水平较为安全,不易损伤牙根。  相似文献   

18.
Plaque pH measurements can be used to detect individual's caries susceptibility and the cariogenic potential of ingested foods. However, repeated measurements with a touch electrode at a single site may affect the metabolic state of the dental plaque and result in changes of its inherent pH values. The purposes of this study were to evaluate the influence of repeated measurements of resting plaque pH values and to determine the pH values at different interdental sites. Eleven dental students participated in the study. The dental plaque was built up after thorough oral hygiene care. The subjects were then instructed to maintain a normal diet but to refrain from any oral hygiene care for the next 48 hours. Measurement of plaque pH was performed with an antimony electrode at 6 interproximal sites, including central spaces between the upper and between the lower central incisors, and the area between the second premolar and the first molar in each quadrant. At each tested site, measurements were taken 5 times at 0, 10, 30, 45 and 60 min. The results showed that the plaque pH became slightly alkaline at all the tested locations after repeated measurements. However, only the lower incisor area showed a significant change in pH values. Interdental plaque on the lower arch showed higher pH values than did that on the upper arch. There was no significant difference between the pH values on the right and left corresponding sites as determined using the Wilcoxon signed ranks test.  相似文献   

19.
目的:比较前方牵引器及下颌支抗颌间牵引两种正畸牵引方式矫治上中切牙埋伏倒置阻生的疗效。方法:选择10例患者10颗埋伏倒置阻生上颌中切牙,在三维CT片上的位置、三维方向和埋伏阻生的程度均相似,随机分为两组,分别行前方牵引器牵引和颌间牵引,对两组的牵引时间和成功率进行比较,分别采用t检验和x2检验进行统计学处理。结果:前方牵引组牵引时间长于颌间牵引组,有显著差异(P0.05),前方牵引组成功率为100%,颌间牵引组为60%,差异有显著性(P0.01)。结论:埋伏倒置阻生的上中切牙外科开窗术后,通过前方牵引器牵引的时间显著长于下颌支抗颌间牵引,但成功率显著高于颌间牵引。  相似文献   

20.
In 1966 during a dental survey of four districts in Uganda — Acholi in the north, Bugisu in the east, and Kigezi and Toro in the southwest — 1169 Africans were examined. In the sample from Kigezi District 11.9% of the Bakiga tribe showed a form of dental mutilation consisting of the filing away of the mesial angle of the upper central incisors. In the sample from Acholi District 16.1% of the Acholi tribe showed abnormal conditions related to the ritual extraction of the primary canines. Extraction of the lower permanent incisors was seen occasionally in the Acholis (8), Batoros (1) and Bugisus (3). Removal of the primary canines is attributed to a belief that infantile fever originates from these teeth. Because the primary canines were removed in a crude fashion, malformation, non-eruption or premature eruption of the underlying permanent canines resulted.  相似文献   

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