Trabecular alveolar bone microarchitecture in the human mandible using high resolution magnetic resonance imaging

Bone quality assessment techniques: geometric, compositional, and mechanical characterization from macroscale to nanoscale

This review presents an overview of the characterization techniques available to experimentally evaluate bone quality, defined as the geometric and material factors that contribute to fracture resistance independently of areal bone mineral density (aBMD) assessed by dual energy x-ray absorptiometry. The methods available for characterization of the geometric, compositional, and mechanical properties of bone across multiple length scales are summarized, along with their outcomes and their advantages and disadvantages. Examples of how each technique is used are discussed, as well as practical concerns such as sample preparation and whether or not each testing method is destructive. Techniques that can be used in vivo and those that have been recently improved or developed are emphasized, including high resolution peripheral quantitative computed tomography to evaluate geometric properties and reference point indentation to evaluate material properties. Because no single method can completely characterize bone quality, we provide a framework for how multiple characterization methods can be used together to generate a more comprehensive analysis of bone quality to complement aBMD in fracture risk assessment.

Influence of object location in different FOVs on trabecular bone microstructure measurements of human mandible: a cone beam CT study

The aim of this study was to assess the influence of different object locations in different fields of view (FOVs) of two cone beam CT (CBCT) systems on trabecular bone microstructure measurements of a human mandible. A block of dry human mandible was scanned at five different locations (centre, left, right, anterior and posterior) using five different FOVs of two CBCT systems (NewTom™ 5G; QR Verona, Verona, Italy and Accuitomo 170; Morita, Kyoto, Japan). Image analysis software (CTAn software v. 1.1; SkyScan, Kontich, Belgium) was used to assess the trabecular bone microstructural parameters (thickness, Tb.Th; spacing, Tb.Sp; number, Tb.N; bone volume density, BV/TV). All measurements were taken twice by one trained observer. Tb.Th, Tb.Sp and Tb.N varied significantly across different FOVs in the NewTom 5G (p < 0.001) and the Accuitomo 170 (p < 0.001). For location, a significant difference was observed only when measuring BV/TV (p = 0.03) using the NewTom 5G. The trabecular bone microstructural measurements obtained from CBCT systems are influenced by the size of FOVs. Not all trabecular bone parameters measured using different CBCT systems are affected when varying the object location within the FOVs.

Diagnostic imaging of trabecular bone microstructure for oral implants: a literature review

Several dental implant studies have reported that radiographic evaluation of bone quality can aid in reducing implant failure. Bone quality is assessed in terms of its quantity, density, trabecular characteristics and cells. Current imaging modalities vary widely in their efficiency in assessing trabecular structures, especially in a clinical setting. Most are very costly, require an extensive scanning procedure coupled with a high radiation dose and are only partially suitable for patient use. This review examines the current literature regarding diagnostic imaging assessment of trabecular microstructure prior to oral implant placement and suggests cone beam CT as a method of choice for evaluating trabecular bone microstructure.

Augmented mandibular bone structurally adapts to functional loading

Long-term changes in trabecular bone structure during the 10 years following onlay grafting with simultaneous mandibular implant placement were studied. Extraoral radiographs of both mandibular sides in eight patients were taken regularly. Bone structure was analysed using a custom-written image analysis program. Parameters studied were trabecular area and perimeter and marrow cavity area and perimeter. After skeletonisation of the trabecular network, the number of end points and branching points, skeleton length, and branch angle were determined. The observed structural changes agree with the development of a more complex and more delicate or fine osseous structure. The bone shows more trabecular branching. All changes are most pronounced in the graft spongiosa, but are also found in the graft cortex and in the original mandible. The mean trabecular branch angle becomes more horizontal. The applied technique can be used to analyse long-term changes in the architecture of bone grafts. Changes found in the graft architecture correspond to changes expected after functional adaptation to loading.

Differences in 5 anatomic parameters of mandibular body morphology by gonial angle size in dentulous Japanese subjects

This study aimed to determine the differences in 5 anatomical parameters of the mandibular body on dental panoramic radiographs (DPRs) of 234 dentulous Japanese subjects (21-78years; mean, 25.76; median, 27 teeth) according to gender and gonial angle (GA) size, and to analyse the correlations between GA size and each variable by gender. The subjects were divided into low (LGA≤120°) and high gonial angle (HGA≥125°) groups. Linear, angular, and morphological measurements were obtained using the DPRs. Statically significant differences were determined using the Mann-Whitney U and χ(2) tests and simple regression analysis. Mandibular cortical width - MCW, antegonial notch depth - AD and angle - AA, and panoramic mandibular index - PMI in the LGA group were significantly larger than those of the HGA group. In men, a significant difference was observed in the distribution of the 3 mandibular cortical index categories between both GAs. Sexual dimorphism for MCW and AD was significantly greater in men than in women. There were significantly negative low correlations between the GA and variables of the MCW, AD, and PMI. These results suggest that the MCW and AD can show significantly different morphology according to gender and GA size.

Ambiguity in bone tissue characteristics as presented in studies on dental implant planning and placement: a systematic review

OBJECTIVES

To survey definitions of bone tissue characteristics and methods of assessing them in studies of dental implant planning and placement.

MATERIAL AND METHODOLOGY

Three databases were searched using specified indexing terms. Three reviewers selected from the titles and retrieved abstracts in accordance with inclusion and exclusion criteria. Descriptions of bone tissue characteristics (bone quality, density and quantity) used before or during dental implant placement were searched for and categorized.

RESULTS

The search yielded 488 titles. One hundred and fort-nine publications were selected and read in full text. One hundred and eight were considered relevant. There were many different definitions and classification systems for bone tissue characteristics and examination protocols. Approximately two-third of the included publications reported the Lekholm & Zarb classification system for bone quality and quantity. However, only four studies implemented the Lekholm & Zarb system as originally proposed. A few publications described bone quality in accordance with the Misch or Trisi and Rao classifications systems. Assessment methods were often described only briefly (or not at all in one-fifth of the publications). Only one study presented the diagnostic accuracy of the assessment method, while only two presented observer performance.

CONCLUSION

The differing definitions and classification systems applied to dental implant planning and placement make it impossible to compare the results of various studies, particularly with respect to whether bone quality or quantity affect treatment outcomes. A consistent classification system for bone tissue characteristics is needed, as well as an appropriate description of bone tissue assessment methods, their diagnostic accuracy and observer performance.

Assessment of trabecular pattern on periapical and panoramic radiographs: a pilot study

OBJECTIVE

This methodological study aimed to determine whether the mandibular trabecular bone assessment from panoramic radiographs, using a visual index, corresponds to the evaluation obtained from periapical radiographs.

MATERIAL AND METHODS

A panoramic radiograph and corresponding periapical radiographs of the region of the lower premolars and molars were collected from each of 32 patients (mean age 18.5 +/- 5.5 years). Two calibrated observers assessed randomly the interdental sites between the first molar and second premolar and between the two premolars on all the radiographs using a visual index. Evaluations were repeated with an interval of 60 days. The results of the repeated evaluations were used to assess intra- and inter-observer agreements, employing Kappa statistics. Spearman's correlation was used to determine the association between assessments of panoramic and periapical radiographs.

RESULTS

In total, 79 interdental sites were evaluated on the panoramic and periapical radiographs. The visual analysis of periapical radiographs revealed intra-observer agreements of 0.88 for observer 1 and 0.93 for observer 2, and an inter-observer agreement of 0.82. The intra-observer agreement for panoramic radiographs was 0.79 and 0.83 for observers 1 and 2, respectively, and the inter-observer agreement was 0.79. A substantial correlation was found between periapical and panoramic radiographs (rho = 0.737, p = 0.001).

CONCLUSIONS

Although panoramic radiographs are less reliable than periapical radiographs, they can be used for assessment of the trabecular bone pattern with the aid of a visual index. Training on the method is recommended to obtain results with a high reproducibility.

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.

Fractal dimension analysis of periapical reactive bone in response to root canal treatment

OBJECTIVE

Mathematical morphology and box counting were used to extract trabecular pattern and to evaluate changes of reactive bone following root canal treatment.

STUDY DESIGN

Periapical radiographs were digitized and processed with mathematical morphology operations known as skeletonization. The trabecular patterns resulting from this skeletonization process were further analyzed with fractal dimension (FD) analysis using the box-counting method. Two groups of regions of interest (ROI) were selected from 19 subjects for the analysis.

RESULTS

Seventeen patients in one group and 13 patients in the other showed decreased FD in the reactive bone region after clinically successful root canal treatment (RCT). Significant changes in FD were noted 6 months after RCT (P < .05). Kappa analysis indicated significant reproducibility between the 2 groups of ROIs.

CONCLUSIONS

Mathematical morphology combined with box counting showed decrease of FD in reactive bone regions after clinically successful endodontic treatment.

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.

Direct measurement of trabecular bone anisotropy using directional fractal dimension and principal axes of inertia

OBJECTIVE

Precise in vivo measurement of the trabecular bone's mechanical properties is very important for endosseous dental implant treatment and design in clinical practice. The fractal structure of trabecular bone shows directional anisotropy of the architecture, as is shown in most biological fractals. To analyze the anisotropy of the trabecular bone, the fractal geometry technique was applied to 2-dimensional plain radiographs.

STUDY DESIGN

The power spectrum was used to calculate the fractal dimensions (FD) of the trabecular bone. The FDs calculated as a function of orientation yielded the fractal information reflecting the spatial characteristics of the trabecular bone in each direction. A polar plot of directional FDs was defined as an ellipse of inertia. The principal loading direction in a local region of the trabecular bone was determined from the minimum moment of inertia for the ellipse of FDs. The anisotropy was calculated directly as the ratio of the 2 principal moments of inertia from the ellipse.

RESULTS

The anisotropies were measured for radiographs from the angle and incisor region of 21 human mandibles based on the principal axes of inertia and the best-fitting ellipse. The anisotropy of the angle region was significantly greater than that of the incisor region of the mandibles.

CONCLUSION

The method using directional FDs as determined by the principal axis of inertia measures the anisotropy directly, using 2-dimensional plain radiographs. It can quantify the anisotropy of trabecular bone in vivo. The investigation can be applied to the analysis of the relationships between in vivo 2-dimensional parameters and 3-dimensional mechanical properties, which enables us to predict the bone mechanical properties such as strength in vivo in various regions of the mandible.

Comparison of trabecular bone anisotropies based on fractal dimensions and mean intercept length determined by principal axes of inertia

The mechanical quality of trabecular bone depends on both its stiffness and its strength characteristics, which can be predicted indirectly by the combination of bone volume fraction and architectural anisotropy. To analyze the directional anisotropy of the trabecular bone, we applied the fractal geometry technique to plain radiographs. The anisotropy of the bone was quantified from an ellipse, based on the directional fractal dimensions (FD), by the principal axes of inertia. The anisotropies based on the FD were compared with those determined using the common method of mean intercept length (MIL). The directional FD gave the fractal information obtained from a projection along the MIL orientation. For this reason, the spatial variations associated with the bone length in any direction were manifested in a related frequency band of the power spectrum determined along the direction. The directional FD and MIL plots were highly correlated, although they originated from quite different geometries. Of the angle, premolar, and incisor regions of the human mandible, the anisotropies calculated using both FD and MIL showed the highest correlation in the trabecular bone of the angle region. The method using directional FDs as determined by the principal axis of inertia measures the anisotropy directly, using two-dimensional plain radiographs. This kind of method will be a useful to provide better estimates of bone quality in vivo compared with the density measurements alone, especially for the indirect diagnosis of jawbone quality in dental clinics.

Bone density measurements in intra-oral radiographs

Jaw bone density measurements are applicable in many clinical situations to assess bone tissue. To be able to implement research findings in clinical reality, tools must be simple and low cost. Intra-oral radiographs including a reference material perform well as a densitometric tool. However, the inclusion of a reference material, usually in the form of a metal wedge, is an additional burden for the dentist. The aim of this study was to evaluate whether a reference step wedge is required for accurate densitometric results. Dual energy X-ray absorptiometry measurements and densitometric measurements on intra-oral radiographs using a custom-made software were performed on bone samples from the premolar region of the mandible. Observer agreement of bone density expressed as grey value was high. The correlation between mandibular bone mineral density and the densitometric values on intra-oral radiographs was substantially higher when the aluminium step wedge was included. The Wilcoxon test revealed no significant difference between the density measurements using nine or three steps of the Al reference wedge. Density determination of grey value and mm Aleq thickness value both have good intra- and inter-observer agreement. However, jaw bone densitometry is far more accurate when including a reference wedge.

Relationship between two-dimensional and three-dimensional bone architecture in predicting the mechanical strength of the pig mandible

OBJECTIVES

To investigate the relationship between two-dimensional (2D) and three-dimensional (3D) bone imaging parameters.

STUDY DESIGN

Bone specimens were obtained from the mandibles of five male pigs weighing around 110 kg each. A total of 111 samples were measured two-dimensionally with using solid state digital intraoral radiography. Of these 111 samples, 43 were selected for 3D analysis and measured by microcomputed tomography. Through destructive mechanical testing, strength parameters were obtained.

RESULTS

Correlations between the 2D and 3D parameters were rare; however, both 2D and 3D parameters separately showed significant correlations with strength. Multiple linear regression analyses using both 2D and 3D parameters together showed greater predictability than those using only 2D or only 3D parameters.

CONCLUSION

Architectural parameters in 2D and 3D independently affect trabecular strength; the combination of the two can be used to improve bone strength predictability.