Age-related changes in microarchitecture and mineralization of cancellous bone in the porcine mandibular condyle

Mineralization and thickness of the condylar cortex in skeletal remains of children's mandibles: A preliminary study

OBJECTIVE

To explore the relationship between the volumetric bone mineral density (vBMD), the thickness of the condylar cortex (Tcortex) and the hemimandibular volumes (Vhemimandible) of symmetrical and asymmetrical mandibles of children.

DESIGN

The data collection consisted of 92 archeological skeletal remains of children's mandibles between 1 and 12 years old. The mandibles were digitalized with a computed tomography (CT) scan, and three dimensional models were obtained. Vhemimandible was calculated using the optimal symmetry plane. The volumes were used to calculate the asymmetry index (AI). Mandibles with an AI of ≥ 3% (N = 9) and a sample of the most symmetrical mandibles (N = 9) were selected for this research. Three groups were created: a symmetrical, an asymmetrical and a pooled group. Micro-CT was used to measure the vBMD and Tcortex in four volumes of interest. The AI was calculated for these parameters as well.

RESULTS

Significant correlations were found between the vBMD and the Tcortex in the pooled group (P < .01) and between the AI of the vBMD and the AI of the Tcortex in the pooled (P < .01) and symmetrical group (P < .05). No significant correlations were found between the vBMD and the Vhemimandible and between the respective AIs. Between the Tcortex and the Vhemimandible a significant correlation was found in the pooled and asymmetrical group.

CONCLUSION

There is a relationship between the vBMD and the Tcortex. The correlations between the Tcortex and the Vhemimandible are insufficient to draw firm conclusions. A relationship between the vBMD and Vhemimandible was not confirmed in this study.

Three-dimensional radiological anatomy of condyle trabecular bone based on a Volume-of-Interest analysis

OBJECTIVES

Three-dimensional radiological anatomic characteristics of condyle trabeculae was obtained quantitatively based on a volume-of-interest (VOI) analysis.

METHODS

Nine human mandibular condyle specimens were scanned by micro-computed tomography (micro-CT). A total of 34 VOIs were selected from each condyle specimen, which were divided into six layers and four parts to analyze the morphological characteristics of trabeculae based on cylindrical VOIs with a diameter and height of 2 mm. One-way analysis of variance was used to compare the regional differences of morphological parameters among each layer and part.

RESULTS

Values for bone mineral density, bone volume/total volume, trabecular thickness, and trabecular bone number were greater in the anterior part compared with the posterior part; and the lateral part was larger than the medial part in the first, second, and third layers, while the medial part was larger in the fourth and fifth layers; these values in the first and sixth layers were much larger, while those in the third and fourth layers were smaller. Bone surface area/bone volume, trabecular spacing, and trabecular bone pattern factor were larger in the posterior part than in the anterior part; and the lateral part was larger than the medial part in the fourth and fifth layers, while the medial part was larger in the first and second layers.

CONCLUSIONS

The morphological distribution of VOIs was anisotropic within trabecular bone of human mandibular condyles. The upper and lower ends of trabecular bone were much more compact, with higher bone density, trabecular thickness, and trabecular number than in the middle layers.

Condylar morphometry in adults with sagittal intermaxillary relationship class I, II and III using Cone Beam Computed Tomography in a Colombian population

OBJECTIVE

This study established the morphometry of the mandibular condyle in individuals with complete craniofacial growth and sagittal intermaxillary relationships class I, II and III using cone beam computed tomography (CBCT).

MATERIALS AND METHODS

Cone beam computed tomography was obtained for orthodontics diagnostic purposes. The sample was divided taking into account the ANB angle in sagittal classes I, II and III (age ranged from 18 to 40 years old). Linear measurements and shapes of 144 mandibular condyles were analyzed.

RESULTS

Statistically significant differences were found in measurements of the mediolateral diameter when compared with gender (P 0.000) being larger for males. Statistically significant differences between the mediolateral diameter and the coronal shape for the right as well as the left sides with P values of 0.000 and 0.47 respectively were found.

CONCLUSION

In this sample, it was not possible to conclusively determine the relationship between the skeletal class and the mediolateral diameter. However, more studies are required.

Internal architecture of the mandibular condyle of rabbits is related to dietary resistance during growth

Although there is considerable evidence that bone responds to the loading environment in which it develops, few analyses have examined phenotypic plasticity or bone functional adaptation in the masticatory apparatus. Prior work suggests that masticatory morphology is sensitive to differences in food mechanical properties during development; however, the importance of the timing/duration of loading and variation in naturalistic diets is less clear. Here, we examined microstructural and macrostructural differences in the mandibular condyle in four groups of white rabbits (Oryctolagus cuniculus) raised for a year on diets that varied in mechanical properties and timing of the introduction of mechanically challenging foods, simulating seasonal variation in diet. We employed sliding semilandmarks to locate multiple volumes of interest deep to the mandibular condyle articular surface, and compared bone volume fraction, trabecular thickness and spacing, and condylar size/shape among experimental groups. The results reveal a shared pattern of bony architecture across the articular surface of all treatment groups, while also demonstrating significant among-group differences. Rabbits raised on mechanically challenging diets have significantly increased bone volume fraction relative to controls fed a less challenging diet. The post-weaning timing of the introduction of mechanically challenging foods also influences architectural properties, suggesting that bone plasticity can extend well into adulthood and that bony responses to changes in loading may be rapid. These findings demonstrate that bony architecture of the mandibular condyle in rabbits responds to variation in mechanical loading during an organism's lifetime and has the potential to track dietary variation within and among species.

Age-related changes in size, bone microarchitecture and volumetric bone mineral density of the mandible in the harbor seal (Phoca vitulina)

Detailed knowledge of age-related changes in the structure and mineralization of bones is important for interpreting osseous changes in wild mammals caused by exposure to environmental contaminants. This study analyzed mandibular size, microarchitecture and volumetric bone mineral density (vBMD) in harbor seals (n = 93, age range 0.5 months to 25 years) from the German North Sea. Bone microarchitecture and vBMD were assessed using high-resolution peripheral quantitative computed tomography (HR-pQCT). Significant differences were observed between the analyzed age classes (i) young juveniles (0.5–10 months), (ii) yearlings (12–23 months), and (iii) adults (12–25 years) for several of the variables, indicating an overall increase in cortical and trabecular area, cortical thickness and total and cortical vBMD with age. Furthermore, for juvenile animals (≤ 23 months), significant positive correlations with age were observed for mandible length and perimeter, cortical area, cortical thickness, trabecular separation, and total and cortical vBMD. The findings demonstrate a rapid increase in overall size, cortical dimensions and the degree of mineralization of the harbor seal mandible during the first two years after birth. Negative correlations with age existed for trabecular number and thickness as well as for trabecular bone volume fraction in the juveniles. The findings suggest a reduction in trabecular bone volume fraction with age, due to the bone trabeculae becoming thinner, less numerous and more widely spaced. Given the strong age dependence of most analyzed parameters, it is recommended to standardize samples with respect to age in future studies comparing microarchitecture and mineralization of harbor seal mandibles from different populations or different collection periods.

Association between condylar position and vertical skeletal craniofacial morphology: A cone beam computed tomography study

OBJECTIVE

Condylar position may play an important role in the establishment of different craniofacial morphologies. The aim of the present study was to determine the possible association between condylar position and vertical skeletal craniofacial morphology in subjects with normal sagittal skeletal pattern using CBCT.

METHOD AND MATERIAL

The CBCT images of 45 patients with Class I sagittal skeletal pattern were classified into three balanced groups on the basis of SN-MP angle. Each group contained 15 subjects: low angle, normal angle and high angle. The condylar position was determined for the left and right joints. Chi square test was applied to assess the association between condylar position and vertical skeletal growth pattern.

RESULTS

The condyles were more anteriorly-positioned in patients with high angle vertical pattern than in those with normal and low angle vertical pattern. No significant differences were found in condylar position between low angle and normal angle subjects.

CONCLUSION

A significant correlation between condylar position and vertical skeletal pattern was found in the present study. This relationship can be considered for predicting and establishing a proper treatment plan for temporomandibular diseases during orthodontic treatment.

Correlation between condylar position and different sagittal skeletal facial types

OBJECTIVE

Condylar position may play a key role in the stability of orthodontic treatment of patients presenting with different skeletal patterns. The aim of the present study was to assess via cone beam computed tomography (CBCT) correlations between condylar position and sagittal skeletal relationship.

PATIENTS AND METHODS

Condylar positions in CBCT images of 20 patients presenting with a Class I skeletal pattern, 20 with a Class II skeletal pattern, and 20 with a Class III skeletal pattern were evaluated retrospectively. The χ (2) test was used to assess the correlation between condylar position and sagittal skeletal relationships.

RESULTS

The condyles were anteriorly positioned in patients with Class II skeletal pattern in comparison with those with Class I and III skeletal patterns. No significant differences in condylar position between Class I and Class III subjects were detected.

CONCLUSION

A significant correlation between condylar position and sagittal skeletal patterns was observed in the present study. This relationship should be considered when planning and carrying out the appropriate orthodontic treatment for temporomandibular anomalies.

Influence of the lateral pterygoid muscle on traumatic temporomandibular joint bony ankylosis

BACKGROUND

The pathogenesis of traumatic TMJ ankylosis remains unclear. This study aimed to verify the role of the lateral pterygoid muscle in the pathogenesis of traumatic temporomandibular joint (TMJ) bony ankylosis.

METHODS

Eight 6-month-old male sheep were used in this study. Bilateral TMJ osteotomies were performed to induce sagittal fractures of the mandibular condyle. The lateral one-fourth segment of the disc was removed to establish a model of TMJ bony ankylosis. Subsequently, the function of the left and right lateral pterygoid muscles was blocked (experimental group) or maintained (control group), respectively. At 12 weeks postoperatively, animals were sacrificed and TMJ complex samples were evaluated by gross observation, spiral computed tomography (CT), micro-CT, and histological examinations.

RESULTS

Gross observation revealed bony ankylosis in the control TMJs and fibrous adhesions in the experimental TMJs. Spiral CT and micro-CT demonstrated that, compared to the experimental group, the control group showed calcified callus formation in the joint space and roughened articular surfaces after new bone formation, which protruded into the joint space. Maximum mediolateral and anteroposterior condylar diameters were significantly larger in the control group than in the experimental group. Micro-CT also showed that the primary growth orientation of new trabeculae was consistent with the direction of lateral pterygoid traction in the control group, but not in the experimental group. Histological examination showed fibro-osseous ankylosis in the control group, but not in the experimental group.

CONCLUSIONS

The lateral pterygoid simulates the effects of distraction osteogenesis, which is an important factor in the pathogenesis of TMJ bony ankylosis during the healing of sagittal condylar fractures.

Higher number of pentosidine cross-links induced by ribose does not alter tissue stiffness of cancellous bone

The role of mature collagen cross-links, pentosidine (Pen) cross-links in particular, in the micromechanical properties of cancellous bone is unknown. The aim of this study was to examine nonenzymatic glycation effects on tissue stiffness of demineralized and non-demineralized cancellous bone. A total of 60 bone samples were derived from mandibular condyles of six pigs, and assigned to either control or experimental groups. Experimental handling included incubation in phosphate buffered saline alone or with 0.2M ribose at 37°C for 15 days and, in some of the samples, subsequent complete demineralization of the sample surface using 8% EDTA. Before and after experimental handling, bone microarchitecture and tissue mineral density were examined by means of microcomputed tomography. After experimental handling, the collagen content and the number of Pen, hydroxylysylpyridinoline (HP), and lysylpyridinoline (LP) cross-links were estimated using HPLC, and tissue stiffness was assessed by means of nanoindentation. Ribose treatment caused an up to 300-fold increase in the number of Pen cross-links compared to nonribose-incubated controls, but did not affect the number of HP and LP cross-links. This increase in the number of Pen cross-links had no influence on tissue stiffness of both demineralized and nondemineralized bone samples. These findings suggest that Pen cross-links do not play a significant role in bone tissue stiffness.

The correlation between mineralization degree and bone tissue stiffness in the porcine mandibular condyle

The aim of this study was to correlate the local tissue mineral density (TMD) with the bone tissue stiffness. It was hypothesized that these variables are positively correlated. Cancellous and cortical bone samples were derived from ten mandibular condyles taken from 5 young and 5 adult female pigs. The bone tissue stiffness was assessed in three directions using nanoindentation. At each of three tested sides 5 indents were made over the width of 5 single bone elements, resulting in a total number of 1500 indents. MicroCT was used to determine the local TMD at the indented sites. The TMD and the bone tissue stiffness were higher in bone from the adult animals than from the young ones, but did not differ between cancellous and cortical bone. In the adult group, both the TMD and the bone tissue stiffness were higher in the center than at the surface of the bone elements. The mean TMD, thus ignoring the local mineral distribution, had a coefficient of determination (R(2)) with the mean bone tissue stiffness of 0.55, p < 0.05, whereas the correlation between local bone tissue stiffness and the concomitant TMD appeared to be weak (R (2) 0.07, p < 0.001). It was concluded that the mineralization degree plays a larger role in bone tissue stiffness in cancellous than in cortical bone. Our data based on bone from the mandibular condyle suggest that the mineralization degree is not a decisive determinant of the local bone tissue stiffness.

The microstructural and biomechanical development of the condylar bone: a review

BACKGROUND

Bone constantly strives for optimal architecture. Mandibular condyle, which is subjected to various mechanical loads forcing it to be highly adaptive, has a unique structure and a relatively high remodelling rate. Despite the eminent clinical relevance of mandibular condyle, literature on its structural and biomechanical development and on the mechanical role of its mineralized and non-mineralized bone components is scarce.

OBJECTIVE

The aim of the present review is to provide a brief introduction to basic bone mechanics and a synopsis of the growth and development of human mandibular condyle. Subsequently, the current ideas on the relationship between the structural and biomechanical properties of bone in general and of mandibular condyle in particular are reviewed. Finally, up-to-date knowledge from fundamental bone research will be blended with the current knowledge relevant to clinical dentistry, above all orthodontics.

METHODS

A comprehensive literature study was performed with an emphasis on recent and innovative work focusing on the interaction between microarchitectural and micromechanical properties of bone.

CONCLUSIONS

Mandibular condyle is a bone structure with a high bone turnover rate. Mechanical properties of mandibular condyle improve during adolescence and are optimal during adulthood. Local mineralization degree might not be a decisive determinant of the local bone tissue stiffness as was believed hitherto. Bone collagen and its cross links play a role in toughness and tensile strength of bone but not in its compressive properties. Clinical procedures might affect mandibular condyle, which is highly reactive to changes in its mechanical environment.

In vivo evaluation of immediately loaded stainless steel and titanium orthodontic screws in a growing bone

The present work intends to evaluate the use of immediate loaded orthodontic screws in a growing model, and to study the specific bone response. Thirty-two screws (half of stainless steel and half of titanium) were inserted in the alveolar bone of 8 growing pigs. The devices were immediately loaded with a 100 g orthodontic force. Two loading periods were assessed: 4 and 12 weeks. Both systems of screws were clinically assessed. Histological observations and histomorphometric analysis evaluated the percent of “bone-to-implant contact” and static and dynamic bone parameters in the vicinity of the devices (test zone) and in a bone area located 1.5 cm posterior to the devices (control zone). Both systems exhibit similar responses for the survival rate; 87.5% and 81.3% for stainless steel and titanium respectively (p = 0.64; 4-week period), and 62.5% and 50.0% for stainless steel and titanium respectively (p = 0.09; 12-week period). No significant differences between the devices were found regarding the percent of “bone-to-implant contact” (p = 0.1) or the static and dynamic bone parameters. However, the 5% threshold of “bone-to-implant contact” was obtained after 4 weeks with the stainless steel devices, leading to increased survival rate values. Bone in the vicinity of the miniscrew implants showed evidence of a significant increase in bone trabecular thickness when compared to bone in the control zone (p = 0.05). In our study, it is likely that increased trabecular thickness is a way for low density bone to respond to the stress induced by loading.

Variations in nanomechanical properties and tissue composition within trabeculae from an ovine model of osteoporosis and treatment

Osteoporosis and treatment may affect both composition and nanomechanical properties and their spatial distributions within the individual trabeculae of cancellous bone at length scales that cannot be captured by bulk measurements. This study utilized 25 mature adult ewes divided into 5 treatment groups. Four treatment groups were given a dietary model for human high-turnover osteoporosis, and two of these were treated with antiresorptive drugs, either zoledronate (ZOL) or raloxifene (RAL), to examine their effects on bulk tissue properties and nanoscale tissue composition and mechanical properties within trabeculae. Treatment effects were most pronounced at the nanoscale, where RAL increased indentation modulus and hardness throughout trabeculae by 10% relative to the osteoporosis model. In comparison, ZOL increased these properties exclusively at the surfaces of trabeculae (indentation modulus +12%, hardness +16%). Nanomechanical alterations correlated with changes in tissue mineralization, carbonate substitution, crystallinity, and aligned collagen. Despite only minimal changes in bulk tissue tBMD, the nanomechanical improvements within trabeculae with both treatments greatly improved the predicted theoretical bending stiffness of individual trabeculae when idealized as cylindrical struts. Hence, small tissue-level alterations in critical locations for resisting trabecular failure could account for some of the discrepancy between the large reductions in fracture risk and the only modest changes in BMD with antiresorptive treatments.

Condylar volume and condylar area in class I, class II and class III young adult subjects

AIM

Aim of this study was to compare the volume and the shape of mandibular condyles in a Caucasian young adult population, with different skeletal pattern.

MATERIAL AND METHODS

200 Caucasian patients (15-30 years old, 95 male and 105 females) were classified in three groups on the base of ANB angle: skeletal class I (65 patients), skeletal class II (70 patients) and skeletal class III (65 patients). Left and right TMJs of each subject were evaluated independently with CBCT (Iluma). TMJ evaluation included: condylar volume; condylar area; morphological index (MI). Condylar volumes were calculated by using the Mimics software. The condylar volume, the area and the morphological index (MI) were compared among the three groups, by using non-parametric tests.

RESULTS

The Kruskal-Wallis test and the Mann Whitney test revealed that: no significant difference was observed in the whole sample between the right and the left condylar volume; subjects in skeletal class III showed a significantly higher condylar volume, respect to class I and class II subjects (p < 0.05); significantly lower condylar volume was observed in class II subjects, respect to class I and class III (p < 0.05). In the whole sample condylar volume (699.8 ± 63.07 mm3 in males and 663.5 ± 81.3 mm3 in females; p < 0.01) as well as condylar surface (423.24 ± 63.03 mm2 in males and 389.76 ± 61.15 mm2 in females; p < 0.01) were significantly higher in males than in females.

CONCLUSION

Skeletal class appeared to be associated to the mandibular condylar volume and to the mandibular condylar area in the Caucasian orthodontic population.

Mechanical and microarchitectural analyses of cancellous bone through experiment and computer simulation

The relationship between microarchitecture to the failure mechanism and mechanical properties can be assessed through experimental and computational methods. In this study, both methods were utilised using bovine cadavers. Twenty four samples of cancellous bone were extracted from fresh bovine and the samples were cleaned from excessive marrow. Uniaxial compression testing was performed with displacement control. After mechanical testing, each specimen was ashed in a furnace. Four of the samples were exemplarily scanned using micro-computed tomography (μCT) and three dimensional models of the cancellous bones were reconstructed for finite element simulation. The mechanical properties and the failure modes obtained from numerical simulations were then compared to the experiments. Correlations between microarchitectural parameters to the mechanical properties and failure modes were then made. The Young's modulus correlates well with the bone volume fraction with R² = 0.615 and P value 0.013. Three different types of failure modes of cancellous bone were observed: oblique fracture (21.7%), perpendicular global fracture (47.8%), and scattered localised fracture (30.4%). However, no correlations were found between the failure modes to the morphological parameters. The percentage of error between computer predictions and the actual experimental test was from 6 to 12%. These mechanical properties and information on failure modes can be used for the development of synthetic cancellous bone.

Analysis of the roles of microporosity and BMP-2 on multiple measures of bone regeneration and healing in calcium phosphate scaffolds

Osteoinductive agents, such as BMP-2, are known to improve bone formation when combined with scaffolds. Microporosity (<20 μm) has also been shown to influence bone regeneration in calcium phosphate (CaP) scaffolds. However, many studies use only the term "osteoconductive" to describe the effects of BMP-2 and microporosity on bone formation, and do not assess the degree of healing that occurred. The objective of this study was to quantify the influence of BMP-2 and microporosity on bone regeneration and healing in biphasic calcium phosphate scaffolds using multiple measures including bone volume fraction, radial distribution, and specific surface area. These measures were quantitatively compared by analyzing microcomputed tomography data and used to formally define and assess healing. A custom image segmentation program was used to segment >100 samples, with 900 images each, that were implanted in porcine mandibular defects for 3, 6, 12 and 24 weeks. The assessment of healing presented in this work demonstrates the level of detail possible in evaluating scaffold-guided bone regeneration. The analysis shows that BMP-2 and microporosity accelerate healing up to 4-fold. BMP-2 and microporosity were shown to have different and complementary roles in bone formation that effect the time needed for a defect to heal.

Determination of the relationship between collagen cross-links and the bone-tissue stiffness in the porcine mandibular condyle

Although bone-tissue stiffness is closely related to the degree to which bone has been mineralized, other determinants are yet to be identified. We, therefore, examined the extent to which the mineralization degree, collagen, and its cross-links are related to bone-tissue stiffness. A total of 50 cancellous and cortical bone samples were derived from the right mandibular condyles of five young and five adult female pigs. The degree of mineralization of bone (DMB) was assessed using micro-computed tomography. Using high-performance liquid chromatography, we quantified the collagen content and the number of cross-links per collagen molecule of two enzymatic cross-links: hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP), and one non-enzymatic cross-link: pentosidine (Pen). Nanoindentation was used to assess bone-tissue stiffness in three directions, and multiple linear regressions were used to calculate the correlation between collagen properties and bone-tissue stiffness, with the DMB as first predictor. Whereas the bone-tissue stiffness of cancellous bone did not differ between the three directions of nanoindentation, or between the two age groups, cortical bone-tissue stiffness was higher in the adult tissue. After correction for DMB, the cross-links studied did not increase the explained variance. In the young group, however, LP significantly improved the explained variance in bone-tissue stiffness. Approximately half of the variation in bone-tissue stiffness in cancellous and cortical bone was explained by the DMB and the LP cross-links and thus they cannot be considered the sole determinants of the bone-tissue stiffness.

The masticatory system under varying functional load. Part 2: Effect of reduced masticatory load on the degree and distribution of mineralization in the rabbit mandible

A reduction in mechanical loading of the mandible brought about by mastication of soft food is assumed to decrease the remodelling rate of bone, which, in turn, might increase the degree of bone mineralization. The effect of a reduction in masticatory functional load on the degree and distribution of mineralization of mandibular bone was investigated in male juvenile New Zealand White rabbits. The experimental animals (n=8) had been raised on a diet of soft pellets from 8 to 20 weeks of age, while the controls (n=8) had been fed pellets of normal hardness. The degree of mineralization of bone (DMB) was assessed at the attachment sites of various jaw muscles, the condylar head, and the alveolar process. Differences between groups and among sites were tested for statistical significance using a Student's t-test and one-way analysis of variance, respectively. The DMB did not differ significantly between the experimental and control animals at any of the sites assessed. However, in the rabbits that had been fed soft pellets, both cortical bone at the attachment sites of the temporalis and digastric muscles and cortical bone in the alveolar process had a significantly higher DMB than cortical bone at the attachment site of the masseter muscle, while there were no significant differences among these sites in the control animals. The results suggest that a moderate reduction in masticatory functional load does not significantly affect the remodelling rate and the DMB in areas of the mandible that are loaded during mastication but might induce a more heterogeneous mineral distribution.

Trabecular bone structure in the mandibular condyles of gouging and nongouging platyrrhine primates

The relationship between mandibular form and biomechanical function is a topic of significant interest to morphologists and paleontologists alike. Several previous studies have examined the morphology of the mandible in gouging and nongouging primates as a means of understanding the anatomical correlates of this feeding behavior. The goal of the current study was to quantify the trabecular bone structure of the mandibular condyle of gouging and nongouging primates to assess the functional morphology of the jaw in these animals. High-resolution computed tomography scan data were collected from the mandibles of five adult common marmosets (Callithrix jacchus), saddle-back tamarins (Saguinus fuscicollis), and squirrel monkeys (Saimiri sciureus), respectively, and various three-dimensional morphometric parameters were measured from the condylar trabecular bone. No significant differences were found among the taxa for most trabecular bone structural features. Importantly, no mechanically significant parameters, such as bone volume fraction and degree of anisotropy, were found to vary significantly between gouging and nongouging primates. The lack of significant differences in mechanically relevant structural parameters among these three platyrrhine taxa may suggest that gouging as a habitual dietary behavior does not involve significantly higher loads on the mandibular condyle than other masticatory behaviors. Alternatively, the similarities in trabecular architecture across these three taxa may indicate that trabecular bone is relatively unimportant mechanically in the condyle of these primates and therefore is functionally uninformative.

Age-related changes in collagen properties and mineralization in cancellous and cortical bone in the porcine mandibular condyle

Collagen is an important constituent of bone, and it has been suggested that changes in collagen and mineral properties of bone are interrelated during growth. The aim of this study was to quantify age-related changes in collagen properties and the degree of mineralization of bone (DMB). The DMB in cancellous and cortical bone samples from the mandibular condyle of 35 female pigs aged 0-100 weeks was determined using micro-computed tomography. Subsequently, the amount of collagen and the number of pentosidine (Pen), hydroxylysylpyridinoline (HP), and lysylpyridinoline (LP) cross-links were quantified by means of high-performance liquid chromatography. The amount of collagen increased with age in cancellous bone but remained unchanged in cortical bone. The number of Pen and LP cross-links decreased in both bone types. In contrast, the number of HP cross-links decreased only in cancellous bone. The sum of the number of HP and LP cross-links decreased with age in cancellous bone only. The DMB increased in cancellous and cortical bone. It was concluded that the largest changes in the number of mature collagen cross-links and the mineralization in porcine cancellous and cortical bone take place before the age of 40 weeks. The low number of mature cross-links after this age suggests that the bone turnover rate continues to be high and thereby prevents the development of mature cross-links.

Intratrabecular distribution of tissue stiffness and mineralization in developing trabecular bone

The purpose of this study was to investigate the relation between bone tissue stiffness and degree of mineralization distribution and to examine possible changes during prenatal development. Understanding this may provide insight into adaptation processes and into deformation mechanisms of the bone microstructure. Mandibular condyles from four fetal and newborn pigs were used. Tissue stiffness was measured using nanoindentation, the degree of mineralization with microCT. Eight indents were made over the trabecular width of 15 trabeculae in each specimen, leading to a total of 960 indents. Subsequently, the degree of mineralization of these locations was determined. Intratrabecular variations in bone tissue stiffness and degree of mineralization showed a similar pattern; low at trabecular surfaces and higher in the cores. A strong correlation was found between the two variables, which remained unchanged during development. It was concluded that bone tissue in fetal and newborn trabecular cores resembles adult trabecular bone tissue properties and is distributed in a regular radial pattern in trabeculae. For the first time, it was shown that the intratrabecular tissue stiffness develops along the same path as the degree of mineralization. Knowledge regarding intratrabecular tissue stiffness and mineralization results in a better understanding of trabecular bone mechanical behavior on a structural and tissue level.