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PubMed1998

On the taxonomic affinities of the Dmanisi mandible (Georgia).

The recent discovery of unexpectedly ancient human remains has fuelled interest about the first dispersion of Homo outside Africa. The Dmanisi mandible is perhaps one of the most interesting findings, as it supposedly represents one of the oldest hominids outside of Africa. Recently, different interpretations have been published about this specimen. Our comparison of the Dmanisi mandible with a large sample of mandibles and teeth has led us to a new interpretation. In our view, the Dmanisi mandible exhibits a unique combination of traits. Some of its features, taken in isolation, may be attributed to morphological extremes within the genus Homo. The architecture of the mandible as well as the morphology and dimensions of incisors, canines, and P3s are clearly primitive. However, dental traits such as the reduction of the talonid in the P4s and a distally decreasing molar series seems to be derived. Some combinations of these traits are found in specimens of Homo ergaster and differ from those generally present in later hominids. Thus, we propose that the Dmanisi mandible might be taxonomically classified as Homo sp. indet. (aff. ergaster). Furthermore, some aspects of the dentition in Dmanisi display close similarities to Asian Homo erectus. If the 1.8-1.6 Myr dating for the Dmanisi mandible is correct, the differentiation of the Asian branch of the genus Homo could be regarded as a very ancient event.

Animals↗

PubMed2000

Head-capsule design and mandible control in beetle larvae: a three-dimensional approach.

This work provides the morphological basis of mandible kinematics of beetle larvae with different types of head capsules, orientation of mouthparts, mandible design, and feeding behavior. Short descriptions are provided for the hypognathous head of Liocola marmorata (Scarabaeidae), the prognathous head of Cybister lateralimarginalis (Dytiscidae), and the hyperprognathous head of Hydrophilus piceus (Hydrophilidae). Using 3D measurements of a set of points selected on the head, 3D models of head capsules and mandible articulations were made for the larvae of these three species. Further calculations of the models showed differences in spatial positions of mandible axes and insertion points of mandible muscles. Functional consequences of these differences and evolutionary aspects of changes in head design and mandible articulations are discussed. It is suggested that the approach used in this study may be useful for further comparative studies of mandible mechanics of a broad variety of insect taxa.

Animals↗

PubMed1995

Ovariectomy decreases the bone area fraction of the rat mandible.

Although osteoporosis is a major public health concern, the effect of this condition on oral bone has not been determined. Using the ovariectomized rat, we tried to determine if estrogen depletion and aging affect the mandible of the rat. Sixty-one ovariectomized (ovx) and sham-operated (sham) 6-month-old Sprague Dawley rats were divided equally into six groups. The baseline, adult, and old rats were euthanized 14, 114, 200 days post-ovx, respectively. The bone mineral density of the mandible was measured using high resolution dual energy x-ray absorptiometry. The failure load and stiffness of the mandible were measured in three-point bending. The bone area fraction and area moment of inertia of digitized images of mandible sections were measured using image analyzing software. In adult rats, ovx led to a 15% and 28% increase in failure load and stiffness, respectively, but no change in bone area fraction or bone mineral density. In the old rats, ovx led to an 8% decrease in bone area fraction, but no change in failure load, stiffness, or bone mineral density of the mandible. In the ovx rats, aging led to a 20% and 7% decrease in stiffness and bone area fraction of the mandibles in the old rats compared with that in the adult rats. In the adult ovx rats, the increase in structural properties of the mandible may be a consequence of an increase in masticatory function as it has been reported that ovx rats eat approximately 10% more than sham controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed2005

Miniplate osteosynthesis of fractures of the edentulous mandible.

This study was performed to analyze treatment of fractures of the edentulous mandible and to discuss this method in relation to the mandibular height at the fracture site. Fifteen fracture sites in 11 patients with an edentulous mandible were retrospectively examined. These fractures were located: nine fractures in the mandibular body, three in the paramedian region, and three in the mandibular angle. Fractures in a mandible measuring more than 10 mm in the vertical height were treated with one miniplate. Fractures in an extremely atrophic mandible with 10 mm or less were treated using one or two miniplates, also using a modified Champy plate with 1.3 mm in thickness. A mandibular fracture with a height of 5 mm was treated with a combination of a microplate on the buccal side and a miniplate on the inferior border of the mandible with additional direct circumferential wiring. Oblique or splitting fractures were treated with direct circumferential wiring or a Herbert screw, at one fracture site each, respectively. Complications, including infection, fibrous union, nonunion and trismus, were not seen. In one patient, hypesthesia of the lower lip was, however, persistent 1 month after surgery. Miniplate osteosynthesis is the less invasive treatment, and it is suitable for fractures of the atrophic edentulous mandible, except for comminuted or defect fractures. To obtain stable fixation in severely atrophic mandibles, we need to consider the use of two miniplates or a combination with microplates.

Aged↗

PubMed1994

A method for measuring the structural properties of the rat mandible.

The rat mandible has been used to study fractures, ridge augmentation, bone defects, and the effects of cryosurgery, all of which affect the structural properties of the mandible. The only previously described mechanical test of the rat mandible used three-point bending with a piece of foam placed between the lingual surface of the mandible and the support. The accuracy and reproducibility of this test were not determined. Two different, three-point bending tests for characterizing the structural properties of the rat mandible have now been evaluated. Acrylic specimens representing three different-sized mandibles were tested in three-point bending with either potted ends or foam interposed between the specimen and the outer load points. Flexural stiffness and failure load were compared against data from a conventional three-point bending test. In addition, five paired halves of 90- and 210-day-old rat mandibles were tested either with interposed foam or with potted ends and the mean coefficients of variation of the stiffness and failure loads were determined. Failure loads of the acrylic specimens with the potted and foam methods were significantly higher (50 and 10%, respectively; p < 0.05) than with the conventional method. The stiffness of the acrylic specimens with the potted and foam methods was significantly different (75% higher and 21% lower, respectively; p < 0.05) than with the conventional test. In addition, there was no difference between the coefficient of variation in stiffness (26 + 11%) or failure load (10 + 4%) measured with the foam test and the comparable values (16 + 11%) and (18 + 13%) in the potted test.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗

PubMed2005

Estimation of fluoride distribution in the mandible and teeth of the red deer (Cervus elaphus L.) from industrially polluted areas in Poland.

MINI SUMMARY: Animals from areas contaminated by industrial emissions containing fluoride may accumulate it predominantly in hard tissues. Therefore, an analysis was performed for the determination of fluoride content in mandibles and teeth of deer living at large in different areas in Western Pomerania (Poland). Samples of hard tissues obtained with a dental drill, were dissolved in perchloric acid and analyzed for fluoride content with an ion-selective electrode. Using the Generalized Regression Neural Network (GRNN), it was possible to arrange definite variables according to their order of importance concerning the fluoride mean content in investigated bone material. Parametric analysis revealed in which sites of mandibles and teeth the fluoride accumulation was the highest. In our calculation, the traditional statistic as well as artificial neural network was applied. OBJECTIVE: One of the interesting properties of fluoride is its balancing accumulation in the hard and soft tissues. In this paper, we decided estimate how the changeable doses of fluoride in natural environment influence on fluoride distribution and accumulation in the examined sites of mandible and teeth. MATERIAL AND METHOD: The material consist of 103 mandibles of red deer (Cervus elaphus L.) from five forestry districts of Western Pomerania in Poland, which are located near or far away from two major industrial plants: Police Chemical Work and the Dolna Odra Coal Power Plant. Samples (10 mg of powdered bone or tooth) were dissolved in perchloric acid and the fluoride content was determined with an ion-selective electrode. Comparisons were done with the Statistica 5.5 and Statistica Neural Networks. RESULTS: Animals living in Western Pomerania (Poland) have high fluoride contents in their bones. Fluoride accumulation in mandibles and teeth is irregular. The higher content of fluoride show incisal area, but coronoid process of the mandible was not sensitive to different exposure of environmental fluoride at all. Parametric analysis revealed that the accumulation pattern of fluorine was different in the two groups of deer. CONCLUSIONS: Many biological and environmental factors may influence on incessant fluoride accumulation in osseous tissue of ruminants living at large. The use of artificial neural networks enables a more accurate insight into the process of fluorine accumulation in the mandible and teeth and helps in the ranking of factors influencing this process.

Animals↗

PubMed2004

Prostaglandin E2 enhances alveolar bone formation in the rat mandible.

Prostaglandin E2 (PGE2) induces bone formation in stress-bearing bones. The mandible, a stress-bearing bone, is loaded daily during mastication. The aim of this study was to determine if PGE2 delivered locally to the mandible over 20 days enhances alveolar bone deposition. In 18 Lewis rats, controlled-release pellets containing PGE2 were implanted on the buccal aspect on the left-hand side of the mandible, mesial to the root of the first molar. Controlled-release pellets locally delivered 0.1, 0.05, or 0.025 mg/day of PGE2. The right side of the mandible was used as a matched control for each animal. Six sham-treated animals were implanted with a placebo pellet. On days 7 and 19, animals were injected with the bone markers tetracycline and calcein, respectively. On day 21, animals were sacrificed and undecalcified tissues obtained for morphometrical analysis. Morphometrical measurements were analyzed by paired t test to determine differences between the matched samples and one-way ANOVA to compare the different treatment groups. A significant increase in alveolar bone area was observed in mandibles treated with 0.1 and 0.05 mg/day when compared with matched controls and the placebo group. This was accompanied by a significant increase in alveolar bone height and width. The proportions of double-labeled surface (dLS), the mineral apposition rate (MAR), and bone formation rate (BFR) were significantly increased in mandibles treated with the two higher doses of PGE2. The proportion of resorptive surface (RS) was significantly reduced in these two groups. It is concluded that PGE2 induces alveolar bone formation in the mandible when locally delivered at a dose of 0.1 or 0.05 mg/day for 20 days.

Animals↗

PubMed2005

Predictive accuracy of sexing the mandible by ramus flexure.

Loth & Henneberg (Am J Phys Anthrop 99 (1996) 473) described a single morphological indicator of sexual dimorphism, namely the presence or absence of flexure on the posterior border of the mandible, with a predictive accuracy of 90.6-99.0%. In the other studies, which have criticized mandibular ramus flexure as sex indicator in adult and fossils specimens by the same method, the accuracy of sexing was found between 59.0% and 80.4% which is well below the reported 90.6-99.0% (Am J Phys Anthrop 107 (1998) 363; Am J Phys Anthrop 111 (2000) 573; Am J Phys Anthrop 111 (2000) 429; Homo 53 (2002) 97). It was indicated that the method sexed males more reliably than females and consistency was low. In the current blind test, 120 mandibles from forensic cases were examined for the presence or absence of mandibular ramus flexure. Virtually identical results were obtained when a second observer examined the same sample of mandibles. The results were then compared to records of the same cases resulting in 85.8% accuracy for the total sample. A marked difference was observed between sexes where the ramus shape was diagnostic for 92.6% of the males but for only 60.0% of the females (p < 0.001). When mandibles with excessive tooth loss (more than two molars missing) (n = 35) were removed from the sample (in normative sample), the overall predictive value increased to 90.6% (95.6% accuracy in males and 70.6% in females). Our results confirm that there are marked differences between the sexes in the predictive accuracy and this indicator is better in mandibles without molar tooth loss as mentioned by Loth & Henneberg. They also pointed out that the tooth loss is a potential source of error. On the other hand, in this study, there were no sexing errors when mandibles which ramus shape scores -1, 0 and +1 were extracted from the normative sample as the "sex indeterminate group". This study suggests that further assessment should be made only when both rami are available for observation, and the mandible shows either bilateral flexure (+2) or bilateral non-flexure (-2). The consideration of this new categorization can also be useful when using Loth & Henneberg's method.

Adult↗

PubMed1998

Evaluation of the precision of dimensional measurements of the mandible on panoramic radiographs.

The purpose of this study was to evaluate the precision of dimensional measurements of the mandible on orthopantomographic images and thus to evaluate their dimensional reliability. Different distances denoted by metal markers were measured on 25 dry mandibles. The same mandibles were then positioned in an orthopantomographic machine, and radiographic images of them were made. Measurements of the same distances were made on the panoramic images and then compared with the results of the measurements on the dry mandibles. All results were statistically analyzed. The results showed significant difference between the magnification factor listed by the manufacturer and calculated magnification factors, the latter being closer to 1.00. The study also showed that linear measurements made on only one side of the panoramic image of a mandible were very close to the actual dimensions of the dry mandible, whereas measurements that extended across the midline of the mandible were greatly enlarged because of large magnification factors; therefore, such measurements should not be made.

Adult↗

PubMed2001

Mandible movements in ants.

Ants use their mandibles for almost any task, including prey-catching, fighting, leaf-cutting, brood care and communication. The key to the versatility of mandible functions is the mandible closer muscle. In ants, this muscle is generally composed of distinct muscle fiber types that differ in morphology and contractile properties. Fast contracting fibers have short sarcomeres (2-3 microm) and attach directly to the closer apodeme, that conveys the muscle power to the mandible joint. Slow but forceful contracting fibers have long sarcomeres (5-6 microm) and attach to the apodeme either directly or via thin thread-like filaments. Volume proportions of the fiber types are species-specific and correlate with feeding habits. Two biomechanical models explain why species that rely on fast mandible strikes, such as predatory ants, have elongated head capsules that accommodate long muscle fibers directly attached to the apodeme at small angles, whereas species that depend on forceful movements, like leaf-cutting ants, have broader heads and many filament-attached fibers. Trap-jaw ants feature highly specialized catapult mechanisms. Their mandible closing is known as one of the fastest movements in the animal kingdom. The relatively large number of motor neurons that control the mandible closer reflects the importance of this muscle for the behavior of ants as well as other insects.

Animals↗

PubMed1999

Morphological variation in great ape and modern human mandibles.

Adult mandibles of 317 modern humans and 91 great apes were selected that showed no pathology. Adult mandibles of Pan troglodytes troglodytes, Pongo pygmaeus pygmaeus and Gorilla gorilla gorilla and from 2 modern human populations (Zulu and Europeans from Spitalfields) were reliably sexed. Thirteen measurements were defined and included mandibular height, length and breadth in representative positions. Univariate statistical techniques and multivariate (principal component analysis and discriminant analysis) statistical techniques were used to investigate interspecific variability and sexual dimorphism in human and great ape mandibles, and intraspecific variability among the modern human mandibles. Analysis of interspecific differences revealed some pairs of variables with a tight linear relationship and others where Homo and the great apes pulled apart from one another due to shape differences. Homo and Pan are least sexually dimorphic in the mandible, Pan less so than Homo sapiens, but both the magnitude of sexual dimorphism and the distribution of sexually dimorphic measurements varied both among and between modern humans and great apes. Intraspecific variation among the 10 populations of modern humans was less than that generally reported in studies of crania (74.3% of mandibles were correctly classified into 1 of 10 populations using discriminant functions based on 13 variables as compared with 93% of crania from 17 populations based on 70 variables in one extensive study of crania). A subrecent European population (Poundbury) emerged as more different from a recent European population (Spitalfields) than other more diverse modern populations were from each other, suggesting considerable morphological plasticity in the mandible through time. This study forms a sound basis on which to explore mandibular variation in Neanderthals, early Homo sapiens and other more ancient fossil hominids.

Adult↗

PubMed2000

Controlled multiplanar distraction of the mandible. Part III: Laboratory studies of sagittal (anteroposterior) and horizontal (mediolateral) movements.

Distraction osteogenesis has proven to be an effective technique for the correction of mandibular deficiencies. However, problems have been encountered in achieving a final, idealized form of the mandible when using distraction devices capable of moving the bone segments in only one dimension (uniplanar). Specifically, occlusal irregularities and deficiencies in lower facial contour have been seen following uniplanar distraction. To address these problems, a distraction device capable of independent movements in three planes (multiplanar) was developed. Previously reported studies in a canine model have demonstrated that this device can successfully distract the mandible along both the sagittal axis (anteroposterior or z-axis) and the vertical axis (superoinferior or y-axis). This study examines the ability of the multiplanar device to distract along the sagittal and horizontal axes (mediolateral or x-axis). A total of 12 dogs were included in the study. All animals underwent unilateral or bilateral mandibular distraction using an external multiplanar device. After a latency period of 5 days, primary distraction along the anteroposterior axis at a rate of 1 mm/day for 10 days (10 mm total) was performed. During the following 10 days, along with an additional 11 mm to 20 mm of anteroposterior axis distraction, concomitant secondary distraction was performed along the horizontal (mediolateral) axis at a rate of 5 degrees/day (50 degrees total). Cephalometric radiographs were obtained preoperatively and at the conclusion of both anteroposterior and combined anteroposterior-mediolateral distraction. Computed tomography (CT) scans were obtained preoperatively and at the end of consolidation (28 days), after which all animals were sacrificed and the dry skulls examined. In all animals, distraction along the mediolateral or x-axis was found to change the anteroposterior projection of the mandible. Varus angulation of the device with respect to the midline of the mandible caused compression of the distracted segments and reduced the anteroposterior thrust of the mandible. In contrast, valgus positioning of the device, with respect to the midline of the mandible, created the opposite effect, increasing the distracted length in the anteroposterior direction. The bone (mandibular) segments being distracted assumed the orientation of the device only for valgus positioning of the device (producing a decrease in the bigonial distance). Conversely, there was no effect from the mediolateral angulation on the distracted segments during varus positioning of the device. A possible explanation for this finding may be a greater resistance to an increase in the bigonial distance (varus positioning of the device) posed by obstruction of lateral movement of the condyle. This stands in contrast to a decrease in the bigonial distance observed following valgus positioning of the device. These findings confirm the clinical impression that distraction along the anteroposterior or sagittal axis remains the critical or keystone therapeutic maneuver in distraction of the mandible. Mediolateral or horizontal axis distraction is best used only as a supplementary movement; in essence, it only affects the anteroposterior dimension with little impact on clinically relevant changes to the bigonial distance.

Animals↗

PubMedDate not supplied

MR signal changes in bone marrow of mandible in hematologic disorders.

OBJECTIVE: Signal intensity changes in bone marrow of the mandible were observed in cases with hematologic disorders. MATERIALS AND METHODS: Using MRI, bone marrow intensity of the mandible was observed in six patients with polycythemia vera, acute leukemia, myelofibrosis, and malignant lymphoma. A control group was also evaluated for comparison. RESULTS: The bone marrow of the condyloid process of the mandible converts to yellow marrow in early childhood. Therefore, T1-weighted imaging showed the marrow of the mandible to have a high signal intensity similar to that of fat in the control cases. In contrast, the bone marrow of the mandible in the patients exhibited lower intensity than that of fat and was enhanced after Gd-DTPA injection. CONCLUSION: In hematologic diseases MRI detected the signal changes of the mandible. More attention should be focused on the marrow intensity of the mandible in the routine cranial MR examinations in patients with hematologic disorders.

Adolescent↗

PubMed2000

Quantitative radiographic changes in the mandible and the tibia in systemically loaded rats fed a low-calcium diet.

The combined effect of the duration of loaded physical exercise and the percentage of calcium intake on the mandible and tibia were studied in developing male rats. For the loaded exercise, rats ran on a treadmill at a rate of 12 m per min for either 1 or 2 h per day. A total of 54 4-week-old male Wistar rats were randomly assigned to one of six groups. After 4 weeks of the diet and loaded exercise, the rats were killed and their mandibles and tibia were removed. Each individual bone was assessed by radiography and the radiographs were then used for measurements of cortical thickness, bone length and bone width. All radiographic images were analyzed using a computer-based scanner image analysis system. In addition, we measured the dry weight both of the tibia and mandible. The results demonstrated that significant differences in cortical thickness, bone length, bone width, and bone weight, both of the tibia and the mandible, were detectable between the normal diet group and the low-calcium diet group. Among the normal diet groups, significant differences were found in cortical thickness, bone length, bone width, and bone weight of the tibia, whereas no significant differences in either cortical bone thickness, bone length or bone weight of the mandible were detected. In contrast, among the low-calcium diet groups, no significant differences were detected in cortical thickness, bone length, bone width or bone weight for either the tibia or the mandible. Our results suggested that systemic exercise, such as running, promote the linear dimensions and the cortical thickness of the tibia in response to local stimuli. Furthermore, sufficient calcium intake appears to be necessary to allow the effect of systemic exercise on tibial bone growth to occur. In contrast, systemic loaded exercise does not promote either bone growth or development of the mandible even under conditions of sufficient calcium intake.

Animals↗

PubMed1999

Stability after sagittal split ramus osteotomy without post-operative maxillomandibular fixation in the treatment of prognathic patients with asymmetric mandibles.

OBJECTIVE: To examine post-operative stability in prognathic patients with mandibular asymmetry who underwent sagittal split ramus osteotomy (SSRO) of the mandible and titanium screw fixation without post-operative maxillomandibular fixation (MMF). DESIGN: Skeletal and dental changes after surgery with and without post-operative MMF were compared between prognathic patients with symmetric and asymmetric mandibles. SETTING AND SAMPLE POPULATION: Second Department of Oral and Maxillofacial Surgery at Tokyo Medical and Dental University. Twenty prognathic patients were examined. EXPERIMENTAL VARIABLE: An appliance for repositioning the proximal segment was applied in all 20 patients. Ten patients with symmetric mandibles received post-operative MMF with stainless steel wires and intermaxillary rubber traction after the removal of MMF (Group I), while the other 10 patients with asymmetric mandibles underwent post-operative intermaxillary rubber traction only (Group II). OUTCOME MEASURE: Posteroanterior cephalograms were obtained pre-operatively; 2-3 days post-operatively; and 3, 6, and 12 months after surgery. Changes in the positions of the gonion points (Go) and upper and lower incisors (U-1 and L-1) were examined. RESULTS: In both groups, the Go tended to shift laterally as a consequence of the operation. Although the tendencies of the post-operative changes in the Go points of Groups II and I were different, statistical analyses revealed no significant differences between the two groups. At the last stage of the follow-up period, the absolute value of the change in L-1 tended to be larger in Group II than in Group I, but without any statistical significance. CONCLUSION: This study suggests that post-operative change in prognathic patients with asymmetric mandibles treated without post-operative MMF is comparable to that in patients with symmetric mandibles treated with post-operative MMF. Accordingly, post-operative MMF may be avoided, even in prognathic patients with asymmetric mandibles.

Adolescent↗

PubMed1980

Evidence that the human jaw stretch reflex increases the resistance of the mandible to small displacements.

1. Small 'step' or sinusoidal displacements were imposed on the mandible while human subjects maintained an average biting force of 10 N. Phase-related changes in the force resisting sinusoidal displacement were used to determine the mechanical stiffness of the human mandibular system as a function of the frequency of stretching. 2. Jaw-muscle electromyographic (e.m.g.) responses to 'step' stretches were of 8 msec latency and generated a very substantial force response. Jaw-muscle e.m.g. responses having longer latency were not observed. 3. The mechanical stiffness of the human mandible was relatively constant as a function of the frequency of stretching, having a typical magnitude of about 15 N/mm (+/- 200 micrometers stretch) or 10 N/mm (+/- 1500 micrometers stretch) at mean biting forces of 10 N. The force resisting displacement was phase-advanced at all frequencies. 4. Modulation of jaw muscle electrical activity evoked by sinusoidal stretches increased in amplitude as a function of increasing stretch frequency. E.m.g. modulation was 60--100 degrees advanced at frequencies of 1--10 Hz, but the phase decreased at higher frequencies, becoming negative (lagging stretch) at frequencies of 30 Hz and above. These characteristics are consistent with the idea that the jaw stretch reflex is dependent on jaw muscle spindle afferent fibres exciting jaw-closing motoneurones by relatively direct (but not necessarily monosynaptic) connexions. 5. The relationship between jaw-muscle activity and voluntary fluctuations of isometric biting force suggests that human jaw muscles can be modelled as a second-order linear 'filter'. The corner frequency for human jaw muscle is about 3 Hz; thus it would appear to be considerably slower than jaw muscle of monkeys. 6. The reflex stiffness of the human mandible, estimated quantitatively on the assumption that human jaw muscle stiffness is similar to the intrinsic stiffness of the gastrocnemius of the cat, ranges between 5 and 9 N/mm at frequencies between 1 and 8 Hz. Since this reflex stiffness is about the same as muscle stiffness in this frequency range, we conclude that the stretch reflex of the human mandible contributes functionally to its postural stability. 7. Reflex stiffness appears to be greater in the monkey mandible relative to muscle stiffness than in the human mandible. The difference is argued to be a manifestation of the difference in jaw muscle contraction speed between the two species. 8. The fact that the mandibular stretch reflex appears to be stronger than the stretch reflex of the limbs of intact animals and humans is discussed in terms of the special anatomical and functional features of the mandible.

Adult↗

PubMed2004

Mechanical testing of recombinant human bone morphogenetic protein-7 regenerated bone in sheep mandibles.

A new method was developed in this study for testing excised sheep mandibles as a cantilever. The method was used to determine the strength and stiffness of sheep hemi-mandibles including a 35 mm defect bridged by regenerated bone. Recombinant human bone morphogenetic protein-7 (rhBMP-7) in a bovine collagen type-I carrier was used for the bone regeneration. Initial tests on ten intact sheep mandibles confirmed that the strength, stiffness and area beneath the load-deformation curves of the right and left hemi-mandibles were not significantly different, confirming the validity of using the contra-lateral hemi-mandible as a control side. Complete bone regeneration occurred in six hemi-mandibles treated with rhBMP, but the quality and mechanical properties of the bone were very variable. The new bone in three samples contained fibrous tissue and was weaker and less stiff than the contra-lateral side (strength, 10-20 per cent; stiffness, 6-15 per cent). The other half had better-quality bone and was significantly stiffer and stronger (p < 0.05), with strength 45-63 per cent and stiffness 35-46 per cent of the contra-lateral side. Hemi-mandibles treated with collagen alone had no regenerated bone bridge suggesting that 35 mm is a critical-size bone defect.

Animals↗

PubMed2003

Effect of dental floating on the rostrocaudal mobility of the mandible of horses.

OBJECTIVE: To evaluate the effect of dental floating on the position of the mandible relative to the maxilla (a measure of rostrocaudal mobility [RCM] of the mandible) during extension and flexion of the head of horses. DESIGN: Randomized controlled blinded trial. ANIMALS: 59 horses housed in 1 barn. PROCEDURE: Horses were formally randomized into a treatment (n = 33) or control (26) group. All horses were sedated, and the distance between rostral portions of the upper and lower incisor arcades were determined with the head fully extended and flexed at the poll (the difference in measurements represented the RCM of the mandible). The oral cavity was examined. For the treatment group, dental floating was performed, and the incisor arcade measurements were repeated. RESULTS: Dental correction resulted in a significant increase in RCM of the mandible in 31 of 33 horses. The mobility was greater in heavy horses than that detected in other breed classifications. Age and number of dental lesions did not significantly affect mobility before or after dental floating. CONCLUSIONS AND CLINICAL RELEVANCE: Dental floating increased RCM of the mandible, but measurement of this variable was not an indicator of the number or extent of dental lesions, and no specific dental abnormality appeared to significantly affect RCM of the mandible in horses. In horses, measurement of RCM of the mandible can be used as a guide to determine whether dental correction is necessary; after dental floating, it can be used to ensure that irregularities of the occlusal surface have been corrected.

Animals↗