Bone density in human dentate and edentulous mandibles using computed tomography

Investigation of the effect of oral and internal bisphosphonate use on bone density in the jaws in patients with osteoporosis in panoramic radiography

OBJECTIVES

This study aims to quantitatively evaluate the effects of bisphosphonate use duration and route of administration on mandibular cortical and trabecular bone in postmenopausal women.

STUDY DESIGN

Ninety postmenopausal women over the age of 50 were included in this study. Trabecular bone density was specified numerically by fractal dimension (FD) in the region of interest selected on the panoramic radiograph. The width of the mandibular cortical (MCW) bone under the mental foramen of the mandible was measured. Mann-Whitney U test was used for parameters that did not show a normal distribution. Spearman rho correlation test was used to determine the relationship between continuous measurement parameters.

RESULTS

It was observed that FD and MCW of dentate and edentate individuals using bisphosphonate were statistically significantly lower than those of healthy individuals (P < .05). There was no significant correlation was found between the duration of use of bisphosphonates and the fractal values obtained from the relevant regions of the mandible (P > .05).

CONCLUSION

Fractal dimension was found to be lower in oral bisphosphonate use than in intravenous bisphosphonate use. The width of the mandibular cortical bone values was found to be lower in individuals using bisphosphonate than in healthy individuals. Fractal dimension and MCW may benefit clinicians as quantitative parameters in panoramic radiography in the diagnosis of osteoporosis.

Regional differences in microarchitecture and mineralization of the atrophic edentulous mandible: A microcomputed tomography study

OBJECTIVE

The aim of the present study was to assess mineralization and trabecular microarchitecture in atrophic edentulous mandibles and to identify regional differences and relations with the extent of resorption.

METHODS

Cortical and trabecular bone volumes in anterior, premolar and molar regions of 10 edentulous cadaveric mandibles (5 males and 5 females; mean age ± SD: 85.4 ± 8.3 years) were assessed by microcomputed tomography. Mandibular height and Cawood & Howell classes were recorded. Concerning trabecular volumes, bone mineral density (BMD), bone volume fraction, trabecular tissue volume fraction, connectivity density, trabecular number, trabecular thickness, trabecular separation, degree of anisotropy, and structural model index were measured; concerning cortical volumes porosity, BMD and cortical thickness were measured.

RESULTS

In molar regions, the bone volume fraction and trabecular number were lower, whereas trabecular separation, degree of anisotropy and cortical BMD were higher compared to anterior regions. In premolar regions, mandibular height correlated negatively with trabecular number (Spearman's correlation r = 0.73, p = 0.017) and connectivity density (Spearman's correlation r = 0.82, p = 0.004), and correlated positively with trabecular separation (Spearman's correlation r = - 0.65, p = 0.04). Cortical BMD was higher at bucco-inferior cortex of molar and inferior border of premolar region and lower at anterior cranial buccal and lingual surface.

CONCLUSIONS

In the premolar region, increased resorption coincides with local impairment of trabecular bone quality. Cortical bone BMD is higher in areas with highest strains and lower in areas with most mandibular resorption. Trabecular bone volume and quality is superior in the anterior region of the edentulous mandible, which might explain improved primary stability of dental implants in this region.

Clinical osseointegration of bone level implants with conical shape and textured surface with low primary stability

BACKGROUND

Evidence shows lower chance for osseointegration of implants without sufficient primary stability. The present retrospective study observed bone level conical screw implants with textured surface without primary stability.

METHODS

Twenty-six Stark conical screw implants, with V-Blast (Vanish Blast) surface treatment were placed with low primary stability, (insertion torque lower than 10 N/cm and visible mobility at lateral load of 250 g). A soft diet was prescribed. osseointegration was assessed applying 30 Ncm of reverse torque 6 months after placement.

RESULTS

The 26 implants that did not achieve primary stability still had a survival rate of 96% after the observation period and were classified as successful according with ICOI Pisa consensus conference success, survival, failure classification .96% of the implants showed clinical osteointegration and were successfully restored. After 12 months, all implants remained functional.

CONCLUSIONS

It can be concluded that bone-level implants with V-Blast surface in absence of functional loading are able to achieve osteointegration, even with low primary stability.

Study on bone quality in the human mandible-Alignment of biological apatite crystallites

The importance of considering bone quality during oral implant treatment is increasingly being recognized. Assessment of bone quality in response to changes in the jaw bone is extremely important when planning treatment. The present study analyzed biological apatite (BAp) crystallites, a bone quality factor, in order to investigate crystallographic anisotropy in dentate and edentulous human mandibles. Using mandibular samples from Japanese adult cadavers, a region of interest was established comprising cortical bone in the central incisors. Samples were classified into five morphological categories based on the extent of bone resorption. Bone mineral density (BMD) was measured and diffraction intensity ratios were calculated using a microbeam X-ray diffraction system. While no differences were observed in BMD, differences were observed in BAp crystallite alignment between the measurement points. In the alveolar region, samples with residual alveolar bone showed strong alignment in the occlusal direction, while samples with marked alveolar bone resorption had preferential alignment in the mesiodistal direction. The present findings suggest that tooth loss and the extent of alveolar bone resorption affects bone quality in the mandible. © 2018 Wiley Periodicals, Inc. J. Biomed. Mater. Res. Part B: 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 838-846, 2019.

The three-dimensional microstructure of trabecular bone: Analysis of site-specific variation in the human jaw bone

Purpose

This study was performed to analyze human maxillary and mandibular trabecular bone using the data acquired from micro-computed tomography (micro-CT), and to characterize the site-specific microstructures of trabeculae.

Materials and Methods

Sixty-nine cylindrical bone specimens were prepared from the mandible and maxilla. They were divided into 5 groups by region: the anterior maxilla, posterior maxilla, anterior mandible, posterior mandible, and mandibular condyle. After the specimens were scanned using a micro-CT system, three-dimensional microstructural parameters such as the percent bone volume, bone specific surface, trabecular thickness, trabecular separation, trabecular number, structure model index, and degrees of anisotropy were analyzed.

Results

Among the regions other than the condylar area, the anterior mandibular region showed the highest trabecular thickness and the lowest value for the bone specific surface. On the other hand, the posterior maxilla region showed the lowest trabecular thickness and the highest value for the bone specific surface. The degree of anisotropy was lowest at the anterior mandible. The condyle showed thinner trabeculae with a more anisotropic arrangement than the other mandibular regions.

Conclusion

There were microstructural differences between the regions of the maxilla and mandible. These results suggested that different mechanisms of external force might exist at each site.

Accuracy of Quantitative Computed Tomography Bone Mineral Density Measurements in Mandibles: A Cadaveric Study

PURPOSE

The aim was to investigate the accuracy of quantitative computed tomography bone mineral density (BMD) measurements in mandibles, comparing measured BMD with calibrated BMD.

MATERIALS AND METHODS

Seventy mandibles from adult cadavers were used. Twenty tomographic cuts were made in each mandible. In each tomographic cut, a region of interest was located, and the bone density was measured in Hounsfield unit (HU). A polymethyl methacrylate phantom containing four inserts of different predetermined densities (hydroxyapatite 100, 200, 500, and 700 mg/cm(3) ) was used to calculate calibrated bone density. Correlation between measured and calibrated bone densities was calculated.

RESULTS

Mean total correlation between measured and calibrated BMD in the 20 sagittal tomography cuts showed almost perfect positive correlation (r = 0.998, p < .001). However, when average BMD measurements in HU were compared, the measured total BMD (in the 20 sagittal tomography cuts studied) was 54.99 ± 421.59, whereas the total calibrated BMD was 49.28 ± 364.95, with statistically significant difference (p = .001).

CONCLUSIONS

There are discrepancies between measured and calibrated BMD; in this sense, a calibrated bone phantom with a predetermined mineral density should be used to determine the exact BMD before dental implants surgery.

Dentition, bone loss, and the aging of the mandible

BACKGROUND

Facial aging is a dynamic process with impact on both the soft tissues and the bones. Despite a growing body of evidence, controversy still exists regarding absolute characteristics of the aging facial skeleton.

OBJECTIVE

The purpose of this study was to investigate various mandibular measurements in different age groups and to delineate the relation of the dentition to these parameters.

METHODS

Ninety Caucasian mandibles were assessed for the following distance landmarks: gonion-gonion, infradentale-gnathion, mental foramen-mandibular crest, mental foramen-inferior mandibular border, gnathion-gonion, condyle-gonion, and gonial angle. The measurements were compared according to age, sex, and dentition.

RESULTS

The number of teeth decreased significantly with increasing age in males (P = .002) and females (P < .001). There were no other statistically significant differences between age groups for the rest of the parameters. The infradentale-gnathion distance (P = .005) and the mental foramen-mandibular crest distance (P < .001) was found to increase with total number of teeth. Other parameters did not show a significant relation to dentition. All parameters were significantly larger in the male subgroups with the exception of gnathion-gonion distance and gonial angle. Bilateral mandibular measurements were symmetric except for the gonial angle, which was more obtuse on the right side in males (P = .007) and females (P = .018).

CONCLUSIONS

Our findings support previous evidence that dentition is the main determinant of the morphology of the mandible. The skeletal characteristics are variable among individuals, and a longitudinal study is required to better understand age-related changes of the mandible.

Osteoporosis, jawbones and periodontal disease

The association between osteoporosis and jawbones remains an argument of debate. Both osteoporosis and periodontal diseases are bone resorptive diseases; it has been hypothesized that osteoporosis could be a risk factor for the progression of periodontal disease and vice versa. Hypothetical models linking the two conditions exist: in particular, it is supposed that the osteoporosis-related bone mass density reduction may accelerate alveolar bone resorption caused by periodontitis, resulting in a facilitated periodontal bacteria invasion. Invading bacteria, in turn, may alter the normal homeostasis of bone tissue, increasing osteoclastic activity and reducing local and systemic bone density by both direct effects (release of toxins) and/or indirect mechanisms (release of inflammatory mediators). Current evidence provides conflicting results due to potential biases related to study design, samples size and endpoints. The aim of this article is to review and summarize the published literature on the associations between osteoporosis and different oral conditions such as bone loss in the jaws, periodontal diseases, and tooth loss. Further well-controlled studies are needed to better elucidate the inter-relationship between systemic and oral bone loss and to clarify whether dentists could usefully provide early warning for osteoporosis risk.

Comparison of mandibular bone mineral densities in dentate and edentulous patients

PURPOSE

In contemporary implant dentistry, bone mineral density (BMD) of the jaws is a patient-associated prognostic factor. The aim of this study was to compare the mandibular body BMD of dentate and edentulous patients using the dual-energy X-ray absorptiometry (DXA) technique.

MATERIALS AND METHODS

A total of 39 patients, 20 dentate and 19 edentulous, were included in this cross-sectional study. Mandibular body BMD was measured using the DXA technique. The variables were normally distributed; thus, the independent samples t-test was used for the determination of statistical significance between the dentate and edentulous groups (age, body mass index [BMI], DXA). Chi-square test was performed for identification of the gender differences between the groups. The Pearson correlation analysis was used to analyze the relationship between age, BMI, and mandibular body BMD. Note that p < 0.01 was accepted as the significance level.

RESULTS

There was no statistically significant difference between the dentate and edentulous groups in matching variables (age, BMI, and gender) (p > 0.01). There was a statistically significant difference regarding the mandibular body BMD in the dentate and edentulous group (p < 0.01) controlling for age, gender, and BMI. The edentulous group patients had higher mandibular body BMD values (1.27 ± 0.31 g/cm(2)) than those in the dentate group (0.94 ± 0.22 g/cm(2)).

CONCLUSION

Comparison of the mandibular body BMD revealed that dentate patients had less dense bone than the edentulous patients. Further investigations are needed to determine the BMD of the jaws in different regions and for different systemic conditions.

Stability of voxel values from cone-beam computed tomography for dental use in evaluating bone mineral content

OBJECTIVES

The objective of this study was to investigate the stability of voxel values from cone-beam CT (CBCT) using a flat panel detector in changing surrounding circumstances mimicking clinical situations.

MATERIALS AND METHODS

Seven hydroxyapatite (HA) rods (0, 40, 80, 120, 160, 199, and 239 mg Ca/cm(3) ) were set in a 16 cm diameter water phantom and scanned with CBCT (FineCube) and also with multislice CT (MSCT) used as reference. The voxel values from CBCT were measured by the obtained images with OsiriX software (http://www.osirix-viewer.com), and compared with the CT numbers from MSCT. We examined the correlation between the voxel values and the HA contents, the variance of voxel values, and the influence of changing surrounding circumstances on the voxel values.

RESULTS

The voxel values from CBCT were different from the CT numbers from MSCT, but there was a linear Pearson correlation between the voxel values and the HA contents. The voxel values were greatly influenced when the samples were scanned surrounded in air. However, the voxel values were not affected significantly in the existence of materials simulating oral hard tissues and/or a metal core post.

CONCLUSIONS

There was a linear correlation between the voxel values of CBCT and the contents of HA rod samples. Our study indicated that it might be possible to evaluate bone mineral content(BMC) from the voxel values of CBCT for dental implant treatment.

Morphometrical analysis of the human mandibular canal: a CT investigation

PURPOSE

This study aimed to clarify the correct localization of the mandibular canal (MC) that is essential in order to avoid injuries to the inferior alveolar neurovascular bundle during oral surgical procedures.

METHODS

We have analyzed the position of the MC using computed tomography data bank examinations of the oral region from 50 partially dentulous Brazilian patients aging from 25 to 75 years old (mean ± SD values = 51.70 ± 4.50; females = 27; males = 23) that were obtained with the purpose of dental restoration and without any gross pathology of the mandible. Axial images were 1-mm-thick slices using bone regular algorithm, without intravenous contrast.

RESULTS

We have measured (mean ± SD) the orthogonal distances between the MC and the following selected regions of the mandible: (a) the buccal cortical plate (6.10 ± 1.52 mm); (b) the inferior border of the mandible (10.55 ± 2.28 mm); (c) the lingual cortical plate (3.98 ± 1.14 mm); and (d) the superior border of the alveolar process (16.98 ± 2.85 mm).

CONCLUSIONS

Our morphometric findings may help clarifying the detailed anatomy of the MC and its topographical relations for the planning of dental implantation.

Evaluation by quantitative magnetic resonance imaging of trabecular bone quality in mandible and cervical vertebrae

OBJECTIVE

The purpose of this study was to make a comparison between mandibular and cervical vertebral bone quality (BQ) using quantitative magnetic resonance imaging (MRI).

METHODS

The cervical MRI images included in this study belonged to 36 patients (23 women, 13 men; mean age 54 years) who had various clinical symptoms (e.g., headache, vertigo, imbalance). The mandible and cervical vertebrae BQ measurements were performed by the same investigator on these sections. Mandibular and cervical vertebral T2(*) axial cross sections were performed following receipt of consent from each patient. T2(*) relaxation time values were determined in the trabecular area.

RESULTS

The relationship between cervical vertebral and mandibular BQ was revealed by regression and correlation analysis. The correlation coefficient was r=0.04, r(2)=0.002, and P=0.818, which is not statistically significant. The relation between age and mandible BQ was very weak (r=0.001, r(2)=0.000001, and P=0.995), and the relation between age and cervical vertebrae BQ was correlated (r=-0.585, r(2)=0.342, and P<0.001).

CONCLUSIONS

There is a low correlation between the BQ measurements of cervical vertebrae and the mandible. Precise mandibular BQ measurement does not provide information that correlates with BQ in the other sites of the skeleton. Although an age-dependent decrease occurs in vertebral BQ, no significant alteration occurs in mandibular BQ.

Mineralization density and apparent density in mandibular condyle bone

OBJECTIVES

This study evaluated a method for determining the density and distribution of bone of mandibular condyles using proprietary computerized tomography (CT) software.

STUDY DESIGN

Thirty-eight condylar specimens were investigated with a high-resolution multislice CT. The density was determined by using bone density analysis algorithms available within the proprietary software. Apparent density was estimated over the total cross-sectional area, the total trabecular bone area apart from the cortical fraction, and on individually selected points. Color-coded pictures were created to demonstrate density differences.

RESULTS

The cortical bone presented significantly higher densities than the trabecular bone. The anterior cortical bone had significantly higher densities than the posterior. The central anterior cortical and the central trabecular areas showed significantly higher densities than the medial and lateral areas.

CONCLUSION

This technique proved to be a valuable method for determination of the differences in density in the mandibular condyle. It shows potential in providing clinicians with an imaging modality for specific clinical use.

Computer-assisted implantology: historical background and potential outcomes-a review

BACKGROUND

The accurate transfer of preoperatively determined implant positions to the patient mouth is very beneficial to the dental practitioner as well as patients. The objective of this paper was to review the gradual development of computer-assisted implant surgery.

METHODS

All of the major data sources including unpublished data in the internet are considered

RESULTS AND CONCLUSIONS

Computer-assisted/-guided/-aided implantology has been founded to overcome the errors encountered during implant osteotomies and to position the implants more precisely. The protocols followed by this sophisticated technique are based upon the advocated concept of prosthetic-driven implantology and CT-scan analysis recently approved. Although several attempts have been made to improve this approach more and more, little has been done regarding the patient's demands, including cost. The inherent complexity of the techniques and materials utilized necessitates several degrees of training before attempting treatment and must be taken into account.

Estrogen deficiency and its effect on the jaw bones

Estrogen deficiency-induced postmenopausal osteoporosis has become a worldwide problem, inducing low bone mass and microarchitectural deterioration of the bone scaffolding in the vertebrae and long bones. With the prevalence of such osteoporosis on the increase, the influence of this estrogen deficiency on the jaw bones has drawn the attention of researchers and clinicians in the field of dentistry. The aim of this article is therefore to review the microstructural changes occurring after ovariectomy in the jaw bones of animal subjects. Induced estrogen deficiency clearly led to structural changes in the jaw bones and alveolar bone of animal subjects (rats and monkeys). Severe bone loss in the rat alveolar bone was principally caused by high bone resorptive activity. This activity accelerated greatly immediately after ovariectomy, and was then followed by more moderate resorptive activity, which continued over an extended period. Additionally, occlusal hypofunction further greatly accelerated the fragility of the alveolar bone structure in ovariectomized rats. Microstructural damage also seen in the alveolar bone of ovariectomized monkeys was found to be directly connected to their systemic osteoporosis. Recent investigations of the relationship in humans between systemic osteoporosis and jaw bone loss have also suggested that a connection may exist between these two. However, more research is required to confirm this connection in humans as well.

Evaluation by quantitative magnetic resonance imaging of trabecular bone quality in the dentate and edentulous mandible

OBJECTIVE

To quantify the differences in mandibular trabecular bone quality between edentulous and dentate patients using quantitative magnetic resonance imaging (QMRI).

METHODS

The patients in this study had been referred to our clinic for QMRI examination for various reasons. A total of 40 male patients (18 dentate, 22 edentulous), 45-55 years of age, were examined. Mandibular T2* axial cross-sections were performed following receipt of consent from each patient. T2* relaxation time values (RTVs) were determined in the trabecular area.

RESULTS

The mean mandibular T2* RTVs of dentate and edentulous patients were 181 and 182, respectively. There were no significant differences between the two groups (P=0.929) (Student's t-test).

CONCLUSIONS

Mandibular trabecular bone quality may not be influenced by edentulousness according to QMRI.

A comparison of bone mineral density in the spine, hip and jaws of edentulous subjects

OBJECTIVES

The aim was to investigate the relationship between bone mineral density (BMD) of the jaws (mandible and maxilla) and other skeletal sites. In addition, the influence of gender, smoking and the number of years without natural teeth were examined.

MATERIALS AND METHODS

18 edentulous patients (9 females, 9 males) with a mean age of 67.1 (sd 12.6) years had DXA scans to assess the BMD of the lumbar spine and hip, together with the ramus, body and symphysis of the mandible and the anterior of the maxilla.

RESULTS

BMD values for the ramus were similar to those for the femur but significantly lower than the lumbar spine. The body and anterior mandible had higher values and the anterior maxilla lower values than both the femur and ramus. The ramus BMD showed moderately strong relationships with the standard measures of BMD in the spine and hip, but the BMD of other areas of the jaws showed no relationship with skeletal sites. The BMD for both the hip and the ramus showed an inverse relationship with increasing age. There was no statistically significant relationship between BMD of hip, spine and jaw and either years edentulous or cigarette years. (207)

CONCLUSIONS

Although the ramus of the mandible may show correlation of BMD with skeletal sites, the areas of the jaws where implants may be placed do not. Therefore BMD of the skeletal sites could not be used to predict BMD of the jaws. The BMD of the jaws as measured by DXA showed no relationship with either years edentulous or cigarette smoking.

Oral implications of osteoporosis

OBJECTIVES

The association between osteoporosis and oral health remains a matter of controversy. It is important to confirm whether there is a role of osteoporosis in bone loss in the jaws, periodontal diseases, tooth loss, and other oral tissue changes. The objective of this article is to review and summarize the published literature on the associations between osteoporosis and various oral conditions such as bone loss in the jaws, periodontal diseases, and tooth loss.

METHODS

A search of the computerized database MEDLINE was conducted. Clinical information concerning systemic osteoporosis and animal studies reporting possible associations between osteoporosis and changes in the dental and oral tissues were included. The review focus was on studies involving (1) methods for assessing bone mineral density (BMD); (2) methods for assessing osteoporosis-related changes in intraoral sites; (3) associations between mandibular BMD and skeletal BMD; (4) changes in the jaws, periodontal tissues, and temporomandibular joint concurrent with osteoporosis; (5) changes in the oral tissues following estrogen deficiency; and (6) effects of estrogen-hormone replacement therapy and/or calcium and vitamin D on oral health.

RESULTS

Ninety-seven studies conducted in various parts of the world were identified. Evidence from prospective studies supports the contention that individuals with osteoporosis may be at increased risk for the manifestations of oral osteoporosis; however, such risk is not definitively proven. Studies suggest that findings on dental panoramic radiographs may be used to detect individuals with low BMD.

CONCLUSIONS

Further well-controlled studies are needed to better elucidate the inter-relationship between systemic and oral bone loss and to clarify whether dentists could usefully provide early warning for osteoporosis risk.

Maxillary bone mineral density and its relationship to the bone mineral density of the lumbar spine and hip

OBJECTIVE

We sought to measure the bone mineral density (BMD) of various regions in the maxilla before implant treatment and to investigate correlations between these values and the BMDs of the spine and hip.

STUDY DESIGN

Eighteen patients were examined by means of quantitative computed tomography, and the BMD of the maxillary alveolar ridge was calculated. The same patients also underwent dual-energy x-ray absorptiometry of the lumbar spine and the total hip. Analysis of variance was used to compare BMD values between and within individuals. The Pearson correlation coefficient was used to correct for sex and body mass and to calculate the correlation between the BMD of the maxillary alveolar ridge and the BMD of the spine and hip.

RESULTS

The maxillary BMD varied significantly between individuals (P <.001) and within individuals (P <.001). The BMD of the anterior region of the maxilla was correlated significantly with the BMD of the lumbar spine (r=0.6; P <.05).

CONCLUSION

A site-specific evaluation of maxillary bone tissue could be of value before implant treatment.

Assessment of peripheral dual-energy x-ray absorptiometry measurements in peri-implant bone defects in dogs

BACKGROUND

The goal of this study was to assess the variability of peripheral dual-energy x-ray absorptiometry (pDEXA) measurements in peri-implant bone defects in dogs.

METHODS

Ninety dental implants were inserted in edentulous areas of nine foxhound dogs and standardized peri-implant bone defects were created on the mesial and distal aspect of each fixture (N = 144 total). The animals were sacrificed at 1, 2, and 3 months, respectively. Bone mineral density measurements (BMD) were performed with the use of pDEXA. The calibration of the system was determined by generating four quality control plots using a phantom of known density value. A series of three repeated measurements of the peri-implant sites were made with repositioning of the region of interest. The measurements were performed at the mesial and distal peri-implant sites. The variability of the three BMD measurements was expressed as the coefficient of variation (CV), which is calculated as ([SD/mean] x 100). The difference in the CV between the mesial and distal sites was evaluated using an analysis of variance model for repeated measures accounting for timing of sacrifice (month 1, 2, 3), dog (1 through 9), side (left, right), and adjacent defect regions between implants (1 through 4).

RESULTS

The calibration of the pDEXA measured by means of the phantom resulted in a deviation of 0.17%, 0.52%, -0.17%, and 0.00%, respectively, for each of the four assessments. The average CV for the 72 mesial and 72 distal peri-implant sites was 5.22% +/- 4.22% (median 3.50%; range 0.46% to 18.83%) and 5.37% +/- 3.54% (median 4.64%; range 0.22% to 15.35%), respectively. After accounting for timing of sacrifice, dog, side, and position, there was not a statistically significant difference in the CV between the mesial and distal peri-implant sites (P = 0.75). This indicates that the peri-implant site did not significantly affect the variability of the BMD measurements.

CONCLUSIONS

This study demonstrated that the pDEXA is a non-invasive, convenient, and fast method to assess BMD around dental implants in animal studies. Limitations of the technique may have a negative impact in the precision of pDEXA when measuring small regions.

The three-dimensional microstructure of the trabecular bone in the mandible

This study investigated the three dimensional (3D) trabecular microstructure of the alveolar and basal bone in the mandible using micro-CT and compared the morphometric values of the different sites. Ten specimens were prepared and scanned using a micro-CT system. Both the alveolar and basal trabecular bone of the premolar region in the mandible were measured for the structural analysis. Cross-sectional 1024x1024 pixel images were created. From the two-dimensional (2D) images produced, 3D structural images were reconstructed. After scanning the specimen, the volumes of interest (VOI) of the alveolar and basal bone regions were selected from the 3D reconstruction images, and the structural parameters such as bone volume fraction, bone surface density, trabecular thickness, trabecular separation, trabecular number and structural model index were analyzed. The trabecular structure showed a marked variation within the sites of the specimen, especially in the basal trabecular bone inferior to the mandibular canal. In both the alveolar and basal bone regions, a mixture of both plate-like and rod-like structures was observed. The alveolar region showed a more compact, plate-type trabecular structure than the basal regions. In parametric comparison with the basal bone, the alveolar bone generally had a higher bone volume fraction, bone trabecular thickness and trabecular number, and lower bone surface density, trabecular separation and structural model index. The alveolar bone consisted of a compact bone structure with a large amount of thick plate-type trabecular bone, which was effectively resistant to the masticatory forces. As the measurements were made closer to the basal bone, a loose structure was observed with lower bone volume and fewer, thin, rod-like trabeculae.

Visibility of trabecular structures in oral radiographs

OBJECTIVES

To determine whether alveolar trabecular bone is visible and quantifiable in projection radiographs. Radiographic changes in oral trabecular bone have been studied as possible indications of bone loss, but in some previous studies, observed structures have been attributed entirely to the endosteal surface.

METHODS

Computed radiography (CR) images of human mandibles in molar and pre-molar regions were compared with simulations calculated from high-resolution computed-tomography (CT) and micro-CT volumes. By digitally editing the CT volumes, the simulations were separated into trabecular and cortical components. High-pass-filtered CR images revealed structural details of cortical and trabecular bone.

RESULTS

Trabecular bone constitutes as much as 38% of the total alveolar bone, and accounts for most of the observed alveolar fine structure. Several morphological types of fine structure can be distinguished. The noise in filtered images appears to be a meaningful measure of trabecular bone.

CONCLUSION

Trabecular bone is highly visible in intraoral radiographs.

Reduced mechanical load decreases the density, stiffness, and strength of cancellous bone of the mandibular condyle

OBJECTIVE

To investigate the influence of decreased mechanical loading on the density and mechanical properties of the cancellous bone of the human mandibular condyle.

DESIGN

Destructive compressive mechanical tests were performed on cancellous bone specimens.Background. Reduced masticatory function in edentate people leads to a reduction of forces acting on the mandible. As bone reacts to its mechanical environment a change in its material properties can be expected.

METHODS

Cylindrical bone specimens were obtained from dentate and edentate embalmed cadavers. Mechanical parameters were determined in the axial and in the transverse directions. Subsequently, density parameters were determined according to a method based on Archimedes' principle.

RESULTS

The apparent density and volume fraction of the bone were about 18% lower in the edentate group; no age-related effect on density was found. The decrease of bone in the edentate group was associated with a lower stiffness and strength (about 22% and 28%, respectively). The ultimate strain, however, did not differ between the two groups. Both groups had similar mechanical anisotropy; in axial loading the bone was stiffer and stronger than in transverse loading.

CONCLUSIONS

Reduced mechanical load had affected the density and herewith the mechanical properties of condylar cancellous bone, but not its anisotropy.

RELEVANCE

The change in material properties of the cancellous bone after loss of teeth indicate that the mandibular condyle is sensitive for changes in its mechanical environment. Therefore, changes in mechanical loading of the condyle have to be accounted for in surgical procedures of the mandible.

Densitometric study of dry human mandible

The purpose of this study was to evaluate the variability of bone density among three zones of adult human dry mandible and its relationship to age, gender, and dental status. Thirty-one dried mandibles (16 female ranging between 23 and 82 yr and 15 male ranging between 34 and 85 yr; 6 samples completely edentulous and 6 edentulous only in the molar-premolar zone) were analyzed by a Hologic QDR 1000 X-ray densitometer according to three zones: the ramus, the molar-premolar zone, and the incisor-canine zone. We found a significant inverse correlation between bone density of the ramus and age (r = 0.41, p = 0.02). The bone density of the incisor-canine zone was higher than the density of the other zones; males had a higher bone density than females in all zones analyzed. Our data suggest that mandibular bone density is influenced by age and gender in different ways according to the specific mandibular portion considered, whereas the dental status does not seem to influence mandibular bone density.