Application of polychromatic µCT for mineral density determination

A 3D micro-CT assessment of composition and structure of bone tissue after vertical and horizontal alveolar ridge augmentation using CAD/CAM-customized titanium mesh

OBJECTIVES

To date, no studies have exploited micro-CT in humans to evaluate bone morphology and structure after bone augmentation with CAD/CAM-customized titanium mesh, in mandible and maxilla. The aim of this study was to assess the composition and microstructure of bone biopsy through micro-CT analysis.

MATERIALS AND METHODS

Bone augmentation at both maxillary and mandible sites was performed on 30 patients randomly treated with customized mesh, either alone (M-) or covered with resorbable membrane (M+), in both cases filled 50:50 with autogenous bone and xenograft. After 6 months, biopsies were taken and micro-CT was performed on consecutive 1-mm-thick VOIs from coronal to apical side, measuring tissue volumes, trabecular thickness, spacing, and number.

RESULTS

In both groups, irrespective of membrane use, bone tissue (M-: 29.76% vs. M+: 30.84%) and residual graft material (M-: 14.87% vs. M+: 13.11%) values were similar. Differences were site-related (maxillary vs. mandibular) with higher percentage of bone tissue and trabecular density of low-mineralized bone and overall bone in the mandible.

CONCLUSIONS

The composition and structure of bone tissue, as assessed by micro-CT after alveolar ridge augmentation using CAD/CAM-customized titanium meshes, showed similar features regardless of whether a collagen membrane was applied.

A Modern Multidisciplinary Method to Characterize Natural White Spot Lesions with 2D and 3D Assessments: A Preliminary Study

In this preliminary study, a multidisciplinary method based on high-resolution analytical techniques (such as microcomputed tomography, Raman Microspectroscopy, scanning electron microscopy, and Vickers microhardness test) was exploited to evaluate the alterations that occur in human teeth at the initial stage of the carious lesion. To this purpose, six extracted molars displaying a natural white spot lesion (WSL) were investigated. Specific morphological, structural, and chemical parameters, such as the mineral density, indentation hardness, molecular and elemental composition, and surface micromorphology were obtained on the WSL, and the results were statistically compared (t-test, p < 0.05) to those of the sound enamel on the same tooth. In the WSL, with respect to the sound area, a decrease in the mineral density and crystallinity was detected together with differences in the molecular composition and surface microstructure, such as the occurrence of micropores and irregularities. Moreover, the elemental analysis highlighted in WSL showed a statistically significant decrease in Ca and P percentages. In conclusion, this multidisciplinary approach allows us to fully characterize the area of interest, providing a deeper knowledge of these enamel lesions, which could have important clinical implications.

The accuracy of quantifying the degree of hard tissue calcification using an electron probe micro analyzer, micro-focus X-ray computed tomography, and tissue sectioning methods

OBJECTIVES

Micro-focus X-ray computed tomography (μCT) helps evaluate specimens without destroying it. However, its accuracy of quantifying bone mineral density remains to be fully elucidated. We aimed to verify the accuracy of calcification assessed by μCT, by comparing the images of identical specimens obtained via different methods such as μCT and electron probe micro analyzer (EPMA) analyses.

METHODS

The maxillae, mandibles, and tibiae of five-week-old male mice were analyzed. Calcification density was analyzed using μCT. The right sides of the specimens were decalcified and processed for Azan staining. The left side of the specimens underwent elemental mapping for Ca, Mg, and P using EPMA.

RESULTS

μCT revealed a significant increase in calcification levels in the following order: enamel, dentin, cortical bone, and trabecular bone. These results reflected the Ca and P levels observed in the EPMA analyses. μCT demonstrated significant differences in the degree of calcification among the enamel tissues or dentin tissues, except for dentin in the maxillary incisors and molars. However, EPMA analysis did not demonstrate significant differences in the Ca and P levels among the same tissue samples.

CONCLUSIONS

EPMA elemental analysis can be used to measure Ca and P levels for evaluating the calcification rate of hard tissues. Additionally, the study results validate the evaluation of calcification density via μCT. Furthermore, μCT can evaluate even minute differences in calcification rates compared with EPMA analysis.

Can locally applied risedronate be an effective agent when combined with xenografts? An animal study

BACKGROUND

To examine the effects of local risedronate application with xenografts on healing of rabbit skull defects using histological, histomorphometric, immunohistochemical, and three-dimensional radiological methods.

METHODS

Two critical-sized defects with a diameter of 10 mm were created in 16 rabbits and filled with xenogenic bone graft and xenogenic bone graft + 5 mg risedronate in the control I and risedronate (RIS) groups, respectively. Residual graft, new bone, soft tissue areas, and bone volume were evaluated in the 4- and 8-week study groups.

RESULTS

In both the 4- and 8-week samples, the RIS group samples had significantly higher mean new bone area values than the C group (p < 0.05). In both groups, the values for the new bone area were significantly higher in the 8-week-old samples than in the 4-week-old samples (p < 0.05). The h scores obtained for sialoprotein and osteopontin did not differ significantly between the groups at either time point (p > 0.05). The results of radiological evaluation showed that the bone density value was significantly higher in the C group than in the RIS group at either time point (p < 0.05).

CONCLUSIONS

Although this study aimed to demonstrate the effect of risedronate on the osteoconductive properties of xenografts when applied locally, targeted results could not be achieved.

Three-dimensional characterization of naturally developed early caries lesions using high-resolution micro-computed tomography

OBJECTIVES

The goal of this micro-Computed-Tomography (μCT) study was to characterize the structural parameters of natural, early proximal enamel caries lesions and correlate them with two-dimensional radiographic findings.

METHODS

Extracted human premolar teeth with ICDAS score 2 proximal lesions were examined using visual-tactile, μCT and simulated bitewing radiographs (BTX). Sound enamel and caries-lesions' structural and mineral density (MD) parameters were analyzed which included surface layer (SL) status and thickness, depth of lesion, and MD.

RESULTS

Thirty-six extracted premolars with 54 proximal early enamel caries lesions were analyzed. Lesions varied notably in lesion depth and MD. SL thickness ranged between 20 and 139μm. Three teeth (5.6%) had micro-cavitations upon the μCT examination despite being "clinically" non-cavitated. Cavitation status had no significant association with μCT nor BTX radiographic depth. Depth of lesions correlated weakly but statistically significantly with mineral loss (ML) at body of lesion (r=0.301, p=0.027). SL thickness also correlated negatively with ML at SL (r=-0.501, p&lt;0.001).

CONCLUSIONS

Early proximal enamel lesions with ICDAS 2 score as determined by visual-tactile examination exhibited a wide range of lesion parameters and cavitation status when examined by μCT. Visual-tactile examination may fail to detect micro-cavitations in enamel surface that are detectable by μCT.

CLINICAL SIGNIFICANCE

Clinicians have direct access to early proximal enamel lesions during orthodontic separation, exfoliation, extraction or restoration of adjacent teeth. This study invites the clinician to consider more decisive management options in high risk individuals (e.g. micro-invasive techniques), given the finding of vast structural variability of such lesions.

Comparison of the effects of different instrumentation techniques on root surface roughness and cement loss using micro-computerized tomography: An in-vitro study

OBJECTIVES

The purpose of this study was to compare the effectiveness of three different instruments on the cement loss and roughness of the root surface following scaling and root planning (SRP) using micro-computerized tomography (micro-CT).

METHODS

In this experimental study, 60 single-rooted extracted human teeth were used and divided into three groups. All teeth were scanned with micro-CT before and after SRP. Group 1: SRP was performed by Gracey-curette, Group 2: SRP was performed by using an ultrasonic device and Group 3: SRP was performed by using a piezo ultrasonic device. Cement loss and porosity of the root surface were analysed by micro-computerized tomography, which is a current imaging technique that provides high-quality images and allows for qualitative and quantitative analysis of samples.

RESULTS

Results of our study revealed that initial porosity values were 1.60%, 1.25%, 1.59% for the group 1, 2, 3, and 0.93%, 0.86 and 0.80 after SRP respectively. Although Group 3 had the least surface roughness, there was no statistically significant difference between the groups. Cement loss following SRP was 47.15 μmin the piezo ultrasonic device group, 59.44 µm in the ultrasonic device, and 134.163 µm in the Gracey-curette group respectively. The highest cement loss was seen in the Gracey-curette group, and there was a significant difference between the three groups.

CONCLUSIONS

In conclusion, it was observed that surface roughness decreased and similar surface roughness was obtained with all three methods, but more cementum loss was observed with Gracey-curette. Therefore, ultrasonic devices appear to be a viable alternative to manual instrumentation with curettes.

In-vitro trabecular bone damage following mono- and bicortical mini implants anchorage in mini-implant assisted rapid palatal expansion (MARPE)

OBJECTIVES

To assess in-vitro trabecular bone damage following mono- and bicortical mini-implant (MI) anchorage in mini-implant assisted rapid palatal expansion (MARPE).

MATERIAL AND METHODS

Sixteen self-drilling MI (four MARPE appliances) were distributed in two groups according to bone insertion (monocortical and bicortical) in bovine rib. The device was activated five times (0.5mm each). Trabecular bone damage was assessed using micro-CT scans made at baseline and after each activation by trabecular spacing parameter (Tb.Sp) (distance [mm] between the trabecular bone structure). These measurements were made in five different regions of interest (ROI) surrounding the screw (whole, superior, inferior, anterior and posterior). Two-way ANOVA with Tukey post-hoc analysis (α=0.05) was used to evaluate the effect of insertion type (monocortical vs. bicortical) and activation cycle (0-5) on trabecular damage. The time effect was evaluated using ANOVA-MR test effect with Bonferroni correction (α=0.003). The micro-CT images were also examined qualitatively.

RESULTS

When analysing the individual ROIs, only the superior ROI had a significant difference (P<0.003) beginning at the fourth activation cycle. For the monocortical group, trabecular spacing was affected when the whole ROI was analysed beginning at the fourth activation cycle, while for the superior ROI, this difference became apparent beginning with the third activation cycle (P<0.003). For the qualitative analysis, it seems that only monocortical anchorage influences the trabecular bone in the superior area.

CONCLUSIONS

Monocortical anchorage is more susceptible to bone damage around the MIs, with the superior (cervical) region most strongly affected.

Calculation of Stopping-Power Ratio from Multiple CT Numbers Using Photon-Counting CT System: Two- and Three-Parameter-Fitting Method

The two-parameter-fitting method (PFM) is commonly used to calculate the stopping-power ratio (SPR). This study proposes a new formalism: a three-PFM, which can be used in multiple spectral computed tomography (CT). Using a photon-counting CT system, seven rod-shaped samples of aluminium, graphite, and poly(methyl methacrylate) (PMMA), and four types of biological phantom materials were placed in a water-filled sample holder. The X-ray tube voltage and current were set at 150 kV and 40 μA respectively, and four CT images were obtained at four threshold settings. A semi-empirical correction method that corrects the difference between the CT values from the photon-counting CT images and theoretical values in each spectral region was also introduced. Both the two- and three-PFMs were used to calculate the effective atomic number and electron density from multiple CT numbers. The mean excitation energy was calculated via parameterisation with the effective atomic number, and the SPR was then calculated from the calculated electron density and mean excitation energy. Then, the SPRs from both methods were compared with the theoretical values. To estimate the noise level of the CT numbers obtained from the photon-counting CT, CT numbers, including noise, were simulated to evaluate the robustness of the aforementioned PFMs. For the aluminium and graphite, the maximum relative errors for the SPRs calculated using the two-PFM and three-PFM were 17.1% and 7.1%, respectively. For the PMMA and biological phantom materials, the maximum relative errors for the SPRs calculated using the two-PFM and three-PFM were 5.5% and 2.0%, respectively. It was concluded that the three-PFM, compared with the two-PFM, can yield SPRs that are closer to the theoretical values and is less affected by noise.

Remineralising effects of fluoride varnishes containing calcium phosphate on artificial root caries lesions with adjunctive application of proanthocyanidin

OBJECTIVES

To evaluate the remineralising effects of fluoride (F) varnishes containing bioavailable calcium-phosphate compound (Ca-P) based remineralisation systems and 5000 ppm F toothpaste (FTP) on root caries lesions (RCLs) and the potential effects of proanthocyanidin (PA) for the treatments of RCLs when used as an adjunct to F regimens.

METHODS

Demineralised root dentine and a pH-cycling model were used to mimic RCLs and the oral environment. Remineralising effects of MI Varnish^TM (MIV) containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and Clinpro™ White Varnish (CPWV) containing tri-calcium phosphate (TCP) along with FTP and PA were evaluated regarding the birefringence, elemental composition, mechanical properties and mineral density of remineralised dentine with Duraphat^TM as a comparison.

RESULTS

MIV, CPWV and Duraphat^TM promoted the incorporation of F into RCLs and increased mineral density but did not change microhardness of root dentine significantly. Surface microhardness increased significantly when MIV or CPWV was used with 5000 ppm FTP. Application of PA with F regimens significantly increased subsurface mineral density. When PA was applied with MIV or CPWV along with FTP, the highest ion uptake and relative mineral gain (%ΔZ) was achieved, and significant increase of microhardness was up to 30 μm depth. Generally, MIV was associated with a higher mineral content gain than CPWV.

SIGNIFICANCE

Treatment of carious root surfaces remains challenging due to the complex pathological processes and difficulty in restoring the highly organised structure of root dentine. Treatment strategies targeting both remineralisation and preservation of the dentinal organic matrix have the potential to improve the fluoride-mediated remineralisation approaches.

Analysis of enamel structure and mineral density after different bleaching protocols using micro-computed tomography

OBJECTIVE

This study aims to investigate the effect of three different bleaching applications on structural integrity, mineral volume (MV) and density of the enamel by using micro-computed tomography (Micro-CT) and evaluate the colour effectiveness using CIEDE2000.

MATERIALS AND METHODS

Twenty-four maxillary premolar teeth were divided into three groups (n = 8) (group 1: 40% HP gel with erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser activation; group 2: 40% HP gel with diode laser activation; group 3: 16% CP gel). Bleaching protocols were applied and colour alteration was obtained. Data were calculated with CIEDE2000 before and after bleaching. A Micro-CT was used to scan the specimens before and after the bleaching application. Statistical analysis was performed by ANOVA.

RESULTS

No significant difference was observed between the groups for colour changes (p > .05). Micro-CT analysis showed significant differences in structural thickness, structural separation, mineral density and MV for the different ROIs before and after bleaching for all groups (p<.05).

CONCLUSIONS

All of the bleaching methods represented similar efficiency. However, bleaching with Er,Cr:YSGG laser was less harmful to enamel in comparison with other bleaching methods. The present results may be useful for establishing a numerical standard for the change in bleaching with laser systems in dental hard tissues.

Remineralization of enamel subsurface lesions using toothpaste containing tricalcium phosphate and fluoride: an in vitro µCT analysis

Background

This study aimed to compare the efficacies of experimental toothpastes containing functionalized tricalcium phosphate (fTCP) with and without fluoride for in vitro enamel remineralization under pH-cycling conditions.

Methods

To create artificial white spot lesions, 36 bovine enamel specimens were immersed in a demineralization solution for 10 days. During pH-cycling for 12 days, the specimens were divided into four groups based on the experimental toothpaste type used: (a) fTCP-free, fluoride-free (fTCP − F −); (b) fTCP-containing, fluoride-free (fTCP + F −); (c) fTCP-free, fluoride-containing (fTCP − F +); and (d) fTCP-containing, fluoride-containing (fTCP + F +). Micro-focus X-ray computed tomography (μCT) scans of all specimens were obtained before demineralization, after demineralization, and after pH-cycling. The mineral density and mineral loss (ΔZ) in the enamel subsurface lesions were measured and the percentage of remineralization (%R) was calculated from ΔZ after demineralization and pH-cycling. One-way ANOVA with Tukey’s test was used for statistical analysis of the %R values. The treated enamel surface was investigated via scanning electron microscopy (SEM).

Results

The fTCP − F − group presented with the lowest amount of mineral gain after pH-cycling. In contrast, the fTCP + F + group showed the highest degree of remineralization within all lesion parts. The %R was highest in the fTCP + F + group (38.2 ± 7.8, all P < 0.01). SEM revealed the presence of small crystals on the enamel rods in the fTCP + F − and fTCP + F + groups.

Conclusions

The experimental toothpaste containing fTCP and fluoride increased remineralization of the artificial enamel subsurface lesions during pH-cycling. Furthermore, fTCP and fluoride appear to act independently on the remineralization of enamel subsurface lesions, although they coexisted in one toothpaste type.

Trial registration: This is not a human subject research.

Characterization of Enamel and Dentine about a White Spot Lesion: Mechanical Properties, Mineral Density, Microstructure and Molecular Composition

The study focuses on in vitro tracing of some fundamental changes that emerge in teeth at the initial stage of caries development using multiple approaches. The research was conducted on a mostly sound maxillary molar tooth but with a clearly visible natural proximal white spot lesion (WSL). Values of mineral density, reduced Young's modulus, indentation hardness and creep as well as the molecular composition and surface microstructure of the WSL and bordering dentine area were studied. The results obtained were compared to those of sound enamel and dentine on the same tooth. A decrease of mechanical properties and mineral density both for the WSL and bordering dentine was detected in comparison to the sound counterparts, as well as increase of creep for the enamel WSL. Differences in molecular composition and surface microstructure (including the indenter impressions) were found and described. WSL induces a serious change in the state of not only the visually affected enamel but also surrounding visually intact enamel and dentine in its vicinity. The results provide the basis for future studies of efficacy of minimal invasive treatments of caries.

Ten Years of Micro-CT in Dentistry and Maxillofacial Surgery: A Literature Overview

Micro-computed tomography (micro-CT) is a consolidated imaging technology allowing non-destructive three-dimensional (3D) qualitative and quantitative analysis by the observation of microstructures with high resolution. This paper aims at delivering a structured overview of literature about studies performed using micro-CT in dentistry and maxillofacial surgery (MFS) by analyzing the entire set of articles to portray the state of the art of the last ten years of scientific publications on the topic. It draws the scenario focusing on biomaterials, in vitro and in/ex vivo applications, bone structure analysis, and tissue engineering. It confirms the relevance of the micro-CT analysis for traditional research applications and mainly in dentistry with respect to MFS. Possible developments are discussed in relation to the use of the micro-CT combined with other, traditional, and not, techniques and technologies, as the elaboration of 3D models based on micro-CT images and emerging numerical methods. Micro-CT results contribute effectively with whose ones obtained from other techniques in an integrated multimethod approach and for multidisciplinary studies, opening new possibilities and potential opportunities for the next decades of developments.

Comparative analysis of sample preparation protocols of soft biological tissues for morphometric studies using synchrotron-based X-ray microtomography

The spread of microtomography as a tool for visualization of soft tissues has had a significant impact on a better understanding of complex biological systems. This technique allows a detailed three-dimensional quantitative view of the specimen to be obtained, correlating its morphological organization with its function, providing valuable insights on the functionality of the tissue. Regularly overlooked, but of great importance, proper sample mounting and preparation are fundamental for achieving the highest possible image quality even for the high-resolution imaging systems currently under development. Here, a quantitative analysis compares some of the most common sample-mounting strategies used for synchrotron-based X-ray microtomography of soft tissues: alcoholic-immersion, paraffin-embedding and critical-point drying. These three distinct sample-mounting strategies were performed on the same specimen in order to investigate their impact on sample morphology regardless of individual sample variation. In that sense, the alcoholic-immersion strategy, although causing less shrinkage to the tissue, proved to be the most unsuitable approach for a high-throughput high-resolution imaging experiment due to sample drifting. Also, critical-point drying may present some interesting advantages regarding image quality but is also incompatible with a high-throughput experiment. Lastly, paraffin-embedding is shown to be the most suitable strategy for current soft tissue microtomography experiments. Such detailed analysis of biological sample-mounting strategies for synchrotron-based X-ray microtomography are expected to offer valuable insights on the best approach for using this technique for 3D imaging of soft tissues and following morphometric analysis.

Sost deficiency leads to reduced mechanical strains at the tibia midshaft in strain-matched in vivo loading experiments in mice

Sclerostin, a product of the Sost gene, is a Wnt-inhibitor and thus negatively regulates bone accrual. Canonical Wnt/β-catenin signalling is also known to be activated in mechanotransduction. Sclerostin neutralizing antibodies are being tested in ongoing clinical trials to target osteoporosis and osteogenesis imperfecta but their interaction with mechanical stimuli on bone formation remains unclear. Sost knockout (KO) mice were examined to gain insight into how long-term Sost deficiency alters the local mechanical environment within the bone. This knowledge is crucial as the strain environment regulates bone adaptation. We characterized the bone geometry at the tibial midshaft of young and adult Sost KO and age-matched littermate control (LC) mice using microcomputed tomography imaging. The cortical area and the minimal and maximal moment of inertia were higher in Sost KO than in LC mice, whereas no difference was detected in either the anterior-posterior or medio-lateral bone curvature. Differences observed between age-matched genotypes were greater in adult mice. We analysed the local mechanical environment in the bone using finite-element models (FEMs), which showed that strains in the tibiae of Sost KO mice are lower than in age-matched LC mice at the diaphyseal midshaft, a region commonly used to assess cortical bone formation and resorption. Our FEMs also suggested that tissue mineral density is only a minor contributor to the strain distribution in tibial cortical bone from Sost KO mice compared to bone geometry. Furthermore, they indicated that although strain gauging experiments matched strains at the gauge site, strains along the tibial length were not comparable between age-matched Sost KO and LC mice or between young and adult animals within the same genotype.

Effect of platelet-rich plasma on peri-implant trabecular bone volume and architecture: A preclinical micro-CT study in beagle dogs

OBJECTIVES

To evaluate the peri-implant trabecular bone volume and architecture changes with 6-month follow-up after local application of platelet-rich plasma (PRP) and platelet-poor plasma (PPP) using high-resolution micro-CT.

MATERIAL AND METHODS

Seventy-two dental implants were placed into healed mandibular sites of 9 beagle dogs. Implants were randomly divided into 4 groups following a split-mouth design: control I; control II; PPP; and PRP. Primary and secondary stabilities were assessed using resonance frequency analyses. At 1, 3, and 6 months after implant loading, trabecular structural parameters were evaluated at 0.5, 1, and 1.5 mm away from implants using micro-CT (voxel = 20 μm).

RESULTS

Primary and secondary stabilities were equivalent in all conditions. PPP and PRP groups showed higher bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) but lower trabecular separation (Tb.Sp) and total porosity percentage (Po (tot)) at all 3 time points. A significant decrease in BV/TV and Tb.Th was found for the control groups after 3 months of healing, while this was not observed in both the PPP and PRP groups. However, no distinct difference was found between the PRP and PPP groups over time. Moreover, as the investigated distance from the implant surface increased, BV/TV and Po (tot) within the same group and time point stayed the same, yet Tb.Th and Tb.Sp continued to increase.

CONCLUSIONS

Platelet-rich plasma and PPP with conventional implant placement lead to similar primary and secondary implant stability, but improved peri-implant bone volume and structural integration. The present research does not seem to suggest a different bone remodeling pattern when using PRP or PPP.

Effect of the software binning and averaging data during microcomputed tomography image acquisition

This study describes the effect of the software binning and data averaging during micro CT volume acquisition, on the assessment of root resorption volumes. The mesial roots (n = 9), after orthodontic tooth movement during 14 days, were scanned, using a micro CT system (9 µm/pixel). All roots were reconstructed and the volumes of the resorption lacunae evaluated. The height and width of the pixels vary according to the parameters (A1, A2, A3, A4, A5, A6, A7, A8, A9) used during the scan. In the root #1 the mean volumes of resorption were similar in A4 and A7; in the root #2 there was no similarity in the mean volumes of resorption in any of the parameters; in root #3 only A4 presented mean volume different from zero (3.05 × 10°). In the root #5, the A1 and A7 presented similar mean volumes and in the A6 and A9 presented near mean volumes. In the root #9 the A1, A4, and A7 presented similar mean volumes and A6 and A9 also had similar mean volumes. Significant difference was detected in the volume of resorption among the roots #2, #5 and #9 (p = 0.04). When analyzing delicate structures such as the roots of rats’ molars, the variation of such parameters will significantly influence the results.

Functional imaging of tumor vasculature using iodine and gadolinium-based nanoparticle contrast agents: a comparison of spectral micro-CT using energy integrating and photon counting detectors

Advances in computed tomography (CT) hardware have propelled the development of novel CT contrast agents. In particular, the spectral capabilities of x-ray CT can facilitate simultaneous imaging of multiple contrast agents. This approach is particularly useful for functional imaging of solid tumors by simultaneous visualization of multiple targets or architectural features that govern cancer development and progression. Nanoparticles are a promising platform for contrast agent development. While several novel imaging moieties based on high atomic number elements are being explored, iodine (I) and gadolinium (Gd) are particularly attractive because of their existing approval for clinical use. In this work, we investigate the in vivo discrimination of I and Gd nanoparticle contrast agents using both dual energy micro-CT with energy integrating detectors (DE-EID) and photon counting detector (PCD)-based spectral micro-CT. Simulations and phantom experiments were performed using varying concentrations of I and Gd to determine the imaging performance with optimized acquisition parameters. Quantitative spectral micro-CT imaging using liposomal-iodine (Lip-I) and liposomal-Gd (Lip-Gd) nanoparticle contrast agents was performed in sarcoma bearing mice for anatomical and functional imaging of tumor vasculature. Iterative reconstruction provided high sensitivity to detect and discriminate relatively low I and Gd concentrations. According to the Rose criterion applied to the experimental results, the detectability limits for I and Gd were approximately 2.5 mg ml^-1 for both DE-EID CT and PCD micro-CT, even if the radiation dose was approximately 3.8 times lower with PCD micro-CT. The material concentration maps confirmed expected biodistributions of contrast agents in the blood, liver, spleen and kidneys. The PCD provided lower background signal and better simultaneous visualization of tumor vasculature and intratumoral distribution patterns of nanoparticle contrast agent compared to DE-EID decompositions. Preclinical spectral CT systems such as this could be useful for functional characterization of solid tumors, simultaneous quantitative imaging of multiple targets and for identifying clinically-relevant applications that benefit from the use of spectral imaging. Additionally, it could aid in the development nanoparticles that show promise in the developing field of cancer theranostics (therapy and diagnostics) by measuring vascular tumor biomarkers such as fractional blood volume and the delivery of liposomal chemotherapeutics.

Microcomputed Tomography Calibration Using Polymers and Minerals for Enamel Mineral Content Quantitation

OBJECTIVE

The aim of this paper was to develop calibration standards (CSs) that are readily available for clinical researchers for the quantitation of enamel mineral content.

METHOD

Polyethylene terephthalate (PET), acetal, polyphenylene sulfide (PPS), selenite, Egyptian alabaster, aragonite, and fluorite were fashioned into discs, and their densities were measured and stacked for microcomputed tomography examination. Frame averaging, flat-field correction, pre-filtration, and beam-hardening correction were applied. CSs were checked for homogeneity. The linear relationship between the mean greyscale value (GSV) of each disc and its physically calculated density was explored, and reproducibility was tested. A calibration function was established and then validated using a bovine enamel disc and sound enamel of extracted human premolar teeth.

RESULTS

Measured densities were PET (ρ = 1.38 g/cm3), acetal (ρ = 1.41 g/cm3), PPS (ρ = 1.64 g/cm3), selenite (ρ = 2.24 g/cm3), Egyptian alabaster (ρ = 2.7 g/cm3), aragonite (ρ = 2.72 g/cm3), and fluorite (ρ = 3.11 g/cm3). Examination of the profile sections of CSs confirmed the uniformity of GSVs with minimal beam-hardening effect. A squared Pearson correlation coefficient of R2 = 0.994 was determined between the mean GSV of each CS and its calculated density and was reproduced at different settings with R2 >0.99. A linear regression equation of density (y) versus GSV (x) was established using the least squares regression equation method. The estimated density of the bovine enamel disc (2.48 g/cm3) showed high accuracy when compared to the physically measured value (2.45 g/cm3). The -relative error was 1.2%. Densities of sound enamel in the extracted human premolar teeth were 2.6-3.1 g/cm3.

CONCLUSIONS

This is a simple, valid, and reproducible method to quantitate enamel mineral content. This simple, yet accurate system could be used to expand knowledge in the field of enamel caries research.

Evaluation of permanent and primary enamel and dentin mineral density using micro-computed tomography

OBJECTIVES

The present study was performed to investigate the mineral density distribution in enamel and dentin for both permanent and primary teeth and to establish the standard density per tooth type using micro-computed tomography (CT).

METHODS

Fifty-seven extracted human teeth (37 permanent, 20 primary) were evaluated in the present study. The enamel and dentin mineral densities in the extracted teeth were measured using micro-CT. Cubic regression curves were used to determine the mineral density distribution in the enamel and dentin for each tooth type.

RESULTS

The mean values, distributions, and regression equations of the mineral densities were obtained. The mean mineral density values for permanent enamel and dentin were significantly higher than those for their primary counterparts for each tooth type.

CONCLUSIONS

In the present study, we demonstrated the distribution of mineral density in sound enamel and dentin and attempted to determine the standard mineral density for each tooth type using micro-CT. The mineral density distributions found in this study contribute to our understanding of the mechanical properties of enamel and dentin. A positive correlation suggests that the systemic bone mineral density could be predicted based on the analysis of exfoliated teeth, such as in patients with hypophosphatasia. The present results may be useful in establishing a numerical standard for the mechanism involved in root fracture and for early detection of root fracture risk.

Beam hardening correction tool improves the diagnosis of incipient caries lesions in Micro-CT images

OBJECTIVE

To evaluate the effect of Beam Hardening Correction tool (BHC) on Micro-CT images used in the diagnosis of incipient caries lesions.

METHODS

Six posterior teeth, with 6 sound proximal surfaces and 6 natural white spot lesions, were scanned using a SkyScan1174 device. Each tooth was imaged 16 times in various acquisition parameters, and reconstructed 3 times applying different levels of BHC (0, 15 and 30%). The 288 datasets were analyzed by three examiners. Gold-standard was obtained by microscopic analyses under polarized light. Area under the ROC curve was obtained for each protocol and the BHC parameter was isolated to individually observe the influence of such parameters of reconstruction.

RESULTS

Microtomographic images were accurate for the diagnosis of incipient caries lesions even when the BHC tool was not applied. Accuracy was perfect in 50 % of the protocols without BHC. When adding the artefact correction, the number of protocols that reached perfect accuracy increased to 81.25%. No difference was found between the protocols that used 15 or 30% BHC. Statistically significant differences were found only in four comparisons, and on those the images that had BHC were more accurate. Two non-BHC protocols reached accuracy scores of 0.653 and 0.881, and were improved to perfect accuracy with BHC application.

CONCLUSION

The use of the BHC tool should be encouraged when using Micro-CT to detect incipient caries lesions, especially when low-quality parameters aiming less acquisition and processing time are used.

Interrelationships Between Morphometric, Densitometric, and Mechanical Properties of Teeth in 5-Month-Old Polish Merino Sheep

Interrelationships between morphological, densitometric, and mechanical properties of deciduous mandibular teeth (incisors, canine, second premolar) were investigated. To perform morphometric, densitometric, and mechanical analyses, teeth were obtained from 5-month-old sheep. Measurements of mean volumetric tooth mineral density and total tooth volume were performed using quantitative computed tomography. Microcomputed tomography was used to measure total enamel volume, volumetric enamel mineral density, total dentin volume, and volumetric dentin mineral density. Maximum elastic strength and ultimate force of teeth were determined using 3-point bending and compression tests. Pearson correlation coefficients were determined between all investigated variables. Mutual dependence was observed between morphological and mechanical properties of the investigated teeth. The highest number of positive correlations of the investigated parameters was stated in first incisor indicating its superior predictive value of tooth quality and masticatory organ function in sheep. Positive correlations of the volumetric dentin mineral density in second premolar with final body weight may indicate predictive value of this parameter in relation with growth rate in sheep. Evaluation of deciduous tooth properties may prove helpful for breeding selection and further reproduction of sheep possessing favorable traits of teeth and better masticatory organ function, leading to improved performance and economic efficiency of the flock.

Micro-CT assessment of comparative radiopacity of adhesive/composite materials in a cylindrical cavity

This study was performed to evaluate the comparative radiopacity of adhesive/resin composite materials in cylindrical cavities using micro-computed X-ray tomography (μCT). The two-step self-etch adhesive systems, Clearfil SE Bond (SE) and FL-Bond II (FL), and flowable resin composites, Beautifil Flow F10 (BF) and Clearfil Majesty ES Flow High (MJ), were used. The radiopacity of bovine tooth structures and restorative materials was measured by μCT. In addition, cylindrical cavities prepared in bovine teeth were restored with the following adhesive/composite combinations: SE-BF, SE-MJ, FL-BF, and FL-MJ. The mean gray values of the composite restorations were calculated. The threshold values of the μCT images were evaluated using the Otsu's thresholding method. The current results show that the comparative radiopacity of the materials and tooth structure varied, which affected distinguishing the μCT images of the composite restorations in the cylindrical cavity. The proper combination of restorative materials should be considered when conducting in vitro μCT assessments of composite restorations.

Trait independence primes convergent trait loss

The repeated, independent evolution of traits (convergent evolution) is often attributed to shared environmental selection pressures. However, developmental dependencies among traits can limit the phenotypic variation available to selection and bias evolutionary outcomes. Here, we determine how changes in developmentally correlated traits may impact convergent loss of the tympanic middle ear, a highly labile trait within toads that currently lack adaptive explanation. The middle ear's lability could reflect evolutionary trade-offs with other skull features under selection, or the middle ear may evolve independently of the rest of the skull, allowing it to be modified by active or passive processes without pleiotropic trade-offs with other skull features. We compare the skulls of 55 species (39 eared, 16 earless) within the family Bufonidae, spanning six hypothesized independent middle ear transitions. We test whether shared or lineage-specific changes in skull shape distinguish earless species from eared species and whether earless skulls lack other late-forming skull bones. We find no evidence for pleiotropic trade-offs between the middle ear and other skull structures. Instead, middle ear loss in anurans may provide a rare example of developmental independence contributing to evolutionary lability of a sensory system.

Efficacy of Fluoride Varnishes with Added Calcium Phosphate in the Protection of the Structural and Mechanical Properties of Enamel

The aim of this study was to investigate the efficacy of various fluoride varnishes in the protection of the structural and nanomechanical properties of dental enamel. Demineralized enamel specimens were imaged using a high-resolution micro-CT system and lesion parameters including mineral density and lesion depth were extracted from mineral density profiles. Nanoindentation elastic modulus and hardness were calculated as a function of penetration depth from the load-displacement curves. The average depth of the lesion in specimens with no prior fluoride varnish treatment was 86 ± 7.19 μm whereas the varnish treated specimens had an average depth of 67 ± 7.03 μm (P < 0.05). The mineral density of enamel lesions with no fluoride varnish treatment had an average of 1.85 gr/cm3 which was 25% lower than the corresponding value in varnish treated enamel and 37% lower than sound enamel. While, in the varnish treated group, elastic modulus and hardness values had decreased by 18% and 23%, respectively, the corresponding values in the non-varnish treated specimens had a reduction of 43% and 54% compared to the sound enamel. The findings from this study highlight the preventive role of fluoride varnishes. Addition of calcium and phosphate does not seem to enhance or inhibit the prevention or remineralization performance of fluoride varnishes.

Synchrotron imaging and Markov Chain Monte Carlo reveal tooth mineralization patterns

The progressive character of tooth formation records aspects of mammalian life history, diet, seasonal behavior and climate. Tooth mineralization occurs in two stages: secretion and maturation, which overlap to some degree. Despite decades of study, the spatial and temporal pattern of elemental incorporation during enamel mineralization remains poorly characterized. Here we use synchrotron X-ray microtomography and Markov Chain Monte Carlo sampling to estimate mineralization patterns from an ontogenetic series of sheep molars (n = 45 M1s, 18 M2s). We adopt a Bayesian approach that posits a general pattern of maturation estimated from individual- and population-level mineral density variation over time. This approach converts static images of mineral density into a dynamic model of mineralization, and demonstrates that enamel secretion and maturation waves advance at nonlinear rates with distinct geometries. While enamel secretion is ordered, maturation geometry varies within a population and appears to be driven by diffusive processes. Our model yields concrete expectations for the integration of physiological and environmental signals, which is of particular significance for paleoseasonality research. This study also provides an avenue for characterizing mineralization patterns in other taxa. Our synchrotron imaging data and model are available for application to multiple disciplines, including health, material science, and paleontological research.

Comparison of Different Decalcification Methods Using Rat Mandibles as a Model

Selection of decalcification agents is an essential consideration when processing mineralized tissues because the integrity and immunohistochemical characteristics of the tissues may be affected. Here, we report results obtained from the decalcification of rat mandibles using 10% ethylenediaminetetraacetic acid (EDTA) at room temperature (RT), 10% EDTA at 37C, 5% nitric acid, and 10% formic acid at RT. Decalcification endpoints were determined by microcomputed tomography. Morphological preservation and antigenicity were evaluated by hematoxylin and eosin staining and immunohistochemistry. Decalcification of the anterior and posterior portions of the mandible took 220 and 191 hr in 10% EDTA RT, 102 and 73 hr in 10% EDTA 37C, 13.5 and 4.3 hr in 5% nitric acid, and 140 and 36 hr in 10% formic acid, respectively. Decalcification in 10% EDTA at 37C was accelerated, but 10% EDTA at RT provided optimal results for immunohistochemistry and cellular and structural details. Decalcification using 5% nitric acid was accomplished in the shortest time and exhibited good cellular and architectural morphology, whereas 10% formic acid was suboptimal with respect to tissue and cellular morphology. Despite being the slowest method, EDTA at RT is still the recommended method for decalcifying mineralized tissues; however, if rapid decalcification is needed, 5% nitric acid is the best option, yielding acceptable tissue integrity and speed.

In vitro assessment of a calcium-fluoroaluminosilicate glass-based desensitizer for the prevention of root surface demineralization

The purpose of this study was to evaluate the ability of a calcium-fluoroaluminosilicate glass-based desensitizer (Nanoseal) to protect against root demineralization in vitro. Nanoseal was applied to human root dentin, which was immersed in acidic buffer for 72 h, or exposed to pH cycling by immersing in distilled water or mineralizing solution for 24 h intermediately during 48 h-acid attack. Demineralization was evaluated by μ-CT, and mineral loss (ML) and lesion depth (LD) were determined from mineral density profiles. ML and LD in all treatment groups were significantly smaller compared with control. The Nanoseal-treated group with pH cycling using mineralizing solution had the lowest ML and LD. Analysis using an EPMA demonstrated calcium and phosphorous were incorporated into the superficial layer of specimens in the Nanoseal-treated groups, suggesting Nanoseal modified the dentin surface, making it resistant to demineralization. Application of Nanoseal is an effective method for protecting root from demineralization.

Local Structural Damage Evaluation of a C/C-SiC Ceramic Matrix Composite

Ceramic matrix composites (CMCs) are structural materials, which have useful properties that combine high strength at high temperatures with moderate toughness. Carbon fibers within a matrix of carbon and silicon carbide, called C/C-SiC, are a particular class of CMC noted for their high oxidation resistance. Here we use a combination of four-point bending and X-ray radiography, to study the mechanical failure of C/C-SiC CMCs. Correlating X-ray radiographic and load/displacement curve data reveals that the fiber bundles act to slow down crack propagation during four-point bending tests. We attribute this to the fact that strain energy is expended in breaking these fibers and in pulling fiber bundles out of the surrounding matrix material. In addition, we find that the local distribution and concentration of SiC plays an important role in reducing the toughness of the material.

Elemental Contrast X-ray Tomography Using Ross Filter Pairs with a Polychromatic Laboratory Source

The majority of current laboratory based X-ray sources are polychromatic and are not tuneable. This lack of monochromaticity limits the range of applications for these sources and in particular it reduces the elemental specificity of laboratory based X-ray imaging experiments. Here we present a solution to this problem based on the use of Ross filter pairs. Although such Ross filter arrangements have been applied in proof-of-principle spectroscopy experiments, to date there have been no reports of this approach used for full-field X-ray imaging. Here we report on the experimental demonstration of Ross filter pairs being used for quasi-monochromatic, full-field imaging. This arrangement has several important benefits for laboratory based X-ray imaging including, as we demonstrate, elemental contrast enhancement. The method is demonstrated both for two-dimensional radiography and for three-dimensional X-ray tomography.

VALIDATION OF A BONE MINERAL DENSITY CALIBRATION PROTOCOL FOR MICRO-COMPUTED TOMOGRAPHY

Micro-computed tomography (micro-CT) is widely used for in vitro studies to characterize bone structure at the resolution of 10–100 microns. However, a densitometric calibration protocol is necessary to convert the X-ray attenuation coefficient provided by micro-CT in bone mineral density (BMD). The lastest one has an important role to improve the accuracy of subject-specific finite element models. This work presents a simple calibration protocol based on the use of solid hydroxyapatite phantoms with the correction of the beam hardening effect. The method was validated in comparison to ashing measures of cortical and trabecular human bone. In addition, bone samples tissue mineral density (TMD) was calculated with two different methods. The correlation between ash density and BMD was linear both for cortical ([Formula: see text]) and trabecular bone ([Formula: see text]). The analysis stratified by tissue type versus the pooled analysis confirmed the validity of a common linear model for both types of tissue ([Formula: see text]). Despite its simplicity, the correlation obtained in this work does not depend on the acquisition settings of the micro-CT. TMD was shown to be dependent on the tissue investigated, with values in the range of 1.15–1.21[Formula: see text]mg/mm3 for trabecular bone, and 1.19–1.29[Formula: see text]mg/mm3 for cortical bone. Results are of some interest for generating micro finite elements models.

Hypophosphatasia: Evaluation of Size and Mineral Density of Exfoliated Teeth

OBJECTIVE

Most cases of hypophosphatasia (HPP) exhibit early loss of primary teeth. Results of micro-computed tomography (micro-CT) analysis of teeth with HPP have not yet been reported. The purpose of the present study was to describe the size and mineral density distribution and mapping of exfoliated teeth with HPP using micro CT.

STUDY DESIGN

Seven exfoliated teeth were obtained from a patient with HPP. Exfoliated teeth sizes were measured on micro CT images and mineral densities of the mandibular primary central incisors were determined.

RESULTS

Partial dentures were fabricated for the patient to replace the eight primary teeth which had exfoliated. Most primary teeth sizes were within the normal range. The mean values of enamel and dentin mineral densities in teeth with HPP were 1.35 and 0.88 g/cm³, respectively, in the mandibular primary central incisors.

CONCLUSION

Mineral density distribution and mapping revealed that the values in teeth with HPP were lower than the homonymous teeth controls in all regions from the crown to apex. Furthermore, it was demonstrated that the differences between HPP and controls were larger on the crown side and the differences tended to converge on the apex side. These results suggested that the present patient showed mild hypomineralization in the primary dentition.

Nondestructive Microcomputed Tomography Evaluation of Mineral Density in Exfoliated Teeth with Hypophosphatasia

Most cases of hypophosphatasia (HPP) exhibit early loss of primary teeth. Results of microcomputed tomography (micro-CT) analysis of teeth with HPP have rarely been reported. The purpose of the present study was to describe the mineral density distribution and mapping of exfoliated teeth from an HPP patient using micro-CT. Four exfoliated teeth were obtained from a patient with HPP. Enamel and dentin mineral densities of exfoliated teeth were measured on micro-CT. The mean values of enamel and dentin mineral densities in mandibular primary central incisors with HPP were 1.61 and 0.98 g/cm³, respectively. The corresponding values in the mandibular primary lateral incisors were 1.60 and 0.98 g/cm³, respectively. Enamel hypoplasia was seen in the remaining teeth, both maxillary and mandibular primary canines and first and second molars. Micro-CT enables nondestructive, noninvasive evaluation and is useful for studying human hard tissues obtained from patients.

Better late than never: effective air-borne hearing of toads delayed by late maturation of the tympanic middle ear structures

Most vertebrates have evolved a tympanic middle ear that enables effective hearing of airborne sound on land. Although inner ears develop during the tadpole stages of toads, tympanic middle ear structures are not complete until months after metamorphosis, potentially limiting the sensitivity of post-metamorphic juveniles to sounds in their environment. We tested the hearing of five species of toads to determine how delayed ear development impairs airborne auditory sensitivity. We performed auditory brainstem recordings to test the hearing of the toads and used micro-computed tomography and histology to relate the development of ear structures to hearing ability. We found a large (14-27 dB) increase in hearing sensitivity from 900 to 2500 Hz over the course of ear development. Thickening of the tympanic annulus cartilage and full ossification of the middle ear bone are associated with increased hearing ability in the final stages of ear maturation. Thus, juvenile toads are at a hearing disadvantage, at least in the high-frequency range, throughout much of their development, because late-forming ear elements are critical to middle ear function at these frequencies. We discuss the potential fitness consequences of late hearing development, although research directly addressing selective pressures on hearing sensitivity across ontogeny is lacking. Given that most vertebrate sensory systems function very early in life, toad tympanic hearing may be a sensory development anomaly.

[Effect of Pinus massoniana needle extract on root dentin demineralization in vitro]

OBJECTIVE

This study aims to evaluate the effects of Pinus massoniana needle extract (PMNE) on inhibiting demineralization of root dentin.

METHODS

Root dentin blocks were randomly divided into distilled deionized water (DDW) group, fluoride sodium (NaF) group, and 4%, 8% and 12% PMNE groups according to the experimental solution used in the process of pH cycling in each group. All specimens in each group experienced pH cycling for 8 d. The dentin mineral density (DMD) of the normal dentin and demineralized dentin and their D-value (ΔDMD) were determined using micro computed tomography. The morphology of dentin surface after pH cycling was also observed using a scanning electron microscope.

RESULTS

The ΔDMD values in all PMNE groups and the NaF group were considerably lower than the ΔDMD in the DDW group (P<0.05). The ΔDMD values of the 8% and 12% PMNE groups had no difference (P>0.05), both of which were lower than the ΔDMD in the 4% PMNE group and higher than that in the NaF group (P<0.05). The dentin tubules were partly opened in the PMNE groups. The opening degrees of the dentin tubule in PMNE groups were significantly less and smaller than the opening degree in the DDW group and were larger than that in the NaF group.

CONCLUSIONS

PMNE can inhibit the deminera-lization of root dentin and can slow down the reduction in DMD. PMNE has the potential to prevent caries, and 8% PMNE can effectively inhibit dentin demineralization.

Complex Odontoma: A Case Report with Micro-Computed Tomography Findings

Odontomas are the most common benign tumors of odontogenic origin. They are normally diagnosed on routine radiographs, due to the absence of symptoms. Histopathologic evaluation confirms the diagnosis especially in cases of complex odontoma, which may be confused during radiographic examination with an osteoma or other highly calcified bone lesions. The micro-CT is a new technology that enables three-dimensional analysis with better spatial resolution compared with cone beam computed tomography. Another great advantage of this technology is that the sample does not need special preparation or destruction in the sectioned area as in histopathologic evaluation. An odontoma with CBCT and microtomography images is presented in a 26-year-old man. It was first observed on panoramic radiographs and then by CBCT. The lesion and the impacted third molar were surgically excised using a modified Neumann approach. After removal, it was evaluated by histopathology and microtomography to confirm the diagnostic hypothesis. According to the results, micro-CT enabled the assessment of the sample similar to histopathology, without destruction of the sample. With further development, micro-CT could be a powerful diagnostic tool in future research.

A comparative study of new and current methods for dental micro-CT image denoising

OBJECTIVES

The aim of the current study was to evaluate the application of two advanced noise-reduction algorithms for dental micro-CT images and to implement a comparative analysis of the performance of new and current denoising algorithms.

METHODS

Denoising was performed using gaussian and median filters as the current filtering approaches and the block-matching and three-dimensional (BM3D) method and total variation method as the proposed new filtering techniques. The performance of the denoising methods was evaluated quantitatively using contrast-to-noise ratio (CNR), edge preserving index (EPI) and blurring indexes, as well as qualitatively using the double-stimulus continuous quality scale procedure.

RESULTS

The BM3D method had the best performance with regard to preservation of fine textural features (CNREdge), non-blurring of the whole image (blurring index), the clinical visual score in images with very fine features and the overall visual score for all types of images. On the other hand, the total variation method provided the best results with regard to smoothing of images in texture-free areas (CNRTex-free) and in preserving the edges and borders of image features (EPI).

CONCLUSIONS

The BM3D method is the most reliable technique for denoising dental micro-CT images with very fine textural details, such as shallow enamel lesions, in which the preservation of the texture and fine features is of the greatest importance. On the other hand, the total variation method is the technique of choice for denoising images without very fine textural details in which the clinician or researcher is interested mainly in anatomical features and structural measurements.

Ex vivo evaluation of new 2D and 3D dental radiographic technology for detecting caries

OBJECTIVES

Proximal dental caries remains a prevalent disease with only modest detection rates by current diagnostic systems. Many new systems are available without controlled validation of diagnostic efficacy. The objective of this study was to evaluate the diagnostic efficacy of three potentially promising new imaging systems.

METHODS

This study evaluated the caries detection efficacy of Schick 33 (Sirona Dental, Salzburg, Austria) intraoral digital detector images employing an advanced sharpening filter, Planmeca ProMax(®) (Planmeca Inc., Helsinki, Finland) extraoral "panoramic bitewing" images and Sirona Orthophos XG3D (Sirona Dental) CBCT images with advanced artefact reduction. Conventional photostimulable phosphor images served as the control modality. An ex vivo study design using extracted human teeth, ten expert observers and micro-CT ground truth was employed.

RESULTS

Receiver operating characteristic analysis indicated similar diagnostic efficacy of all systems (ANOVA p > 0.05). The sensitivity of the Schick 33 images (0.48) was significantly lower than the other modalities (0.53-0.62). The specificity of the Planmeca images (0.86) was significantly lower than Schick 33 (0.96) and XG3D (0.97). The XG3D showed significantly better cavitation detection sensitivity (0.62) than the other modalities (0.48-0.57).

CONCLUSIONS

The Schick 33 images demonstrated reduced caries sensitivity, whereas the Planmeca panoramic bitewing images demonstrated reduced specificity. XG3D with artefact reduction demonstrated elevated sensitivity and specificity for caries detection, improved depth accuracy and substantially improved cavitation detection. Care must be taken to recognize potential false-positive caries lesions with Planmeca panoramic bitewing images. Use of CBCT for caries detection must be carefully balanced with the presence of metal artefacts, time commitment, financial cost and radiation dose.

Development of phantom for quantitative analyses of human dentin mineral density

The purpose of the present study was to develop a novel-designed phantom that could be scanned with a sample in the same image, that specialize for quantitative analyses of human dentin mineral density using the X-ray attenuation method. A further attempt was made to demonstrate the intracoronal dentin mineral density using this phantom in mandibular incisors. The phantom prepared with a 15 mm hole in the center of an acrylic resin bar having an outside diameter of 25 mm and 8 small holes (diameter, 3 mm) were made at equal intervals around the center. Liquid dipotassium hydrogen phosphate (K2HPO4) solutions were established at 0.4, 0.6, 0.8 and 1.0 g/cm3, and were arranged to these holes. The mean value of the intracoronal dentin mineral density was 1.486 ± 0.016 g/cm3 in the present study. As the results of the present study corresponded to previous reports, this new phantom was considered to be useful. This phantom enables the analysis of samples that are not readily available by conventional mechanical tests and may facilitate biomechanical investigations using X-ray images. It was suggested that this system is a simple, accurate and novel mineralization measuring system.

Silver diamine fluoride and glass ionomer differentially remineralize early caries lesions, in situ

OBJECTIVES

The aim of the present study was to evaluate the percent mean mineral density (MD) change of early caries lesions after the application of silver diamine fluoride (SDF) or glass ionomer cement (GIC).

MATERIALS AND METHODS

This double-blind, crossover study involved two experimental phases of 28 days each. Thirty-two pairs of enamel slabs were created from the proximal surfaces of 16 premolars. Each pair of artificial carious slabs was randomly divided into the control or test group (38 % SDF or GIC). The slabs were attached to orthodontic brackets and bonded to the maxillary first permanent molars of 16 subjects for 28 days. After a 7-day washout period between phases, the subjects received the other material for the second phase. The mean MD of the lesions was measured by microcomputed tomography.

RESULTS

SDF yielded a percent mean MD increase at a depth of 0-84 μm, although increase in the GIC group was observed at a depth of 24-108 μm. The percent mean MD changes of the SDF and GIC groups were similar (p = 0.100) and significantly higher than in control (p < 0.001, p = 0.003, respectively).

CONCLUSIONS

The two materials increased the percent mean MD change of early proximal caries lesions to a similar extent, but with different spatial patterns.

CLINICAL RELEVANCE

Due to deeper level of GIC remineralization, the refractive index of the GIC applied enamel might be closer to sound enamel. Hence, GIC is recommended for remineralization of anterior teeth. SDF staining makes it unsuitable for use in anterior teeth; thus, it is reserved for use in posterior teeth.

Bmp2 deletion causes an amelogenesis imperfecta phenotype via regulating enamel gene expression

Although Bmp2 is essential for tooth formation, the role of Bmp2 during enamel formation remains unknown in vivo. In this study, the role of Bmp2 in regulation of enamel formation was investigated by the Bmp2 conditional knock out (Bmp2 cKO) mice. Teeth of Bmp2 cKO mice displayed severe and profound phenotypes with asymmetric and misshaped incisors as well as abrasion of incisors and molars. Scanning electron microscopy analysis showed that the enamel layer was hypoplastic and enamel lacked a typical prismatic pattern. Teeth from null mice were much more brittle as tested by shear and compressive moduli. Expression of enamel matrix protein genes, amelogenin, enamelin, and enamel-processing proteases, Mmp-20 and Klk4 was reduced in the Bmp2 cKO teeth as reflected in a reduced enamel formation. Exogenous Bmp2 up-regulated those gene expressions in mouse enamel organ epithelial cells. This result for the first time indicates Bmp2 signaling is essential for proper enamel development and mineralization in vivo.

A comparison of methods for in vivo assessment of cortical porosity in the human appendicular skeleton

The recent advent of high-resolution peripheral quantitative computed tomography (HR-pQCT) provides new opportunities to measure in vivo human bone microarchitecture. Increasingly, cortical porosity (CtPo) is of particular interest due to its relationship with bone quality and turnover. The two approaches that have emerged to measure CtPo from HR-pQCT are threshold-based and density-based methods, and the purpose of this work was to compare the performance of each against a gold-standard synchrotron radiation micro-computed tomography (SRμCT) measurement. Human cadaveric cortical bone specimens (N=23) were measured by SRμCT and HR-pQCT, and high correlations were found for both methods. The density-based approach had an r2=0.939 (95% confidence interval (CI) of +6.17% to +20.99%) and consistently overestimated porosity as measured by SRμCT, while the threshold-based approach had an r2=0.977 and consistently underestimated porosity (95% CI of -2.60% to -10.76%). The density-based approach is prone to beam hardening artifacts and susceptible to natural variations of tissue mineral density (TMD), but is less affected by motion artifacts that may occur in in vivo scans. The threshold-based method has the advantage that it provides structural information that complements the cortical porosity measure, such as number of pores and connectivity, and can accurately detect the larger pores which are the most relevant to bone biomechanical strength. With the first generation HR-pQCT systems the accuracy of detecting pores larger than 140 μm diameter is excellent (r2=0.983; 95% CI of -4.88% to +2.45%). The accuracy of the threshold-based method will improve as new HR-pQCT systems emerge and provide a robust quantitative approach to measure cortical porosity.

Skeletal maturity leads to a reduction in the strain magnitudes induced within the bone: a murine tibia study

Bone adapts to changes in the local mechanical environment (e.g. strains) through formation and resorption processes. However, the bone adaptation response is significantly reduced with increasing age. The mechanical strains induced within the bone by external loading are determined by bone morphology and tissue material properties. Although it is known that changes in bone mass, architecture and bone tissue quality occur with age, to what extent they contribute to the altered bone adaptation response remains to be determined. This study investigated alterations in strains induced in the tibia of different aged female C57Bl/6J mice (young, 10-week-old; adult, 26-week-old; and elderly, 78-week-old) subjected to in vivo compressive loading. Using a combined in vivo/in silico approach, the strains in the bones were assessed by both strain gauging and finite element modeling experiments. In cortical bone, strain magnitudes induced at the mid-diaphysis decreased by 20% from young to adult mice and by 15% from adult to elderly mice. In the cancellous bone (at the proximal metaphysis), induced strains were 70% higher in young compared with adult and elderly mice. Taking into account previous studies showing a reduced bone adaptation response to mechanical loading in adulthood, these results suggest that the diminished adaptive response is in part due to a reduction in the strains induced within the bone.

High-resolution micro-CT scanning as an innovative tool for evaluating dental hard tissue development

Microcomputerized tomography (micro‐CT) allows discriminating very small changes in dental hard tissue volumes. The aim of the present study was to create a new method for obtaining high‐resolution, three‐dimensional images of dental hard tissue development using micro‐CT, and to observe the changes in dental hard tissue development and composition in growing rat pups. Tooth germs from rats at the end of the 20‐day embryonic period (E20) and during the neonatal period (D1‐14) were subjected to micro‐CT. Three‐dimensional reconstructions were analyzed to compare dental hard tissue formation and mineralization during the different development periods. Scanning electron microscopy and energy dispersive spectroscopy were used to confirm mineral density (MD). Dental hard tissue began to form during the E20, but the process was slow and resulted in minimal deposition. Hard tissue volume increased by approximately 0.040 mm³/day from E20 to D3, and by 0.12‐0.42 mm³/day after D3, peaking at 0.42 mm³/day at D12. This increase in hard tissue volume resulted in continuous increases in hard tissue thickness, from 90.0 ± 20.7 μm at E20 to 545.2 ± 14.1 μm by D14. MD was 298 ± 3.1 mg HA/cm at E20 and increased to 678.2 ± 6.1 mg HA/cm by D14. The degree of calcification also progressively increased during the first 14 days of development. Dental MD was strongly associated with calcification. This study indicates that micro‐CT is a nondestructive, high‐resolution, reliable, and innovative tool for the evaluation of volume and MD of dental hard tissues during development. Micro‐CT minimizes artifacts caused by sample preparation.

PACS number: 87