Computed gray levels in multislice and cone-beam computed tomography

Evaluation of the accuracy of cone-beam computed tomography image segmentation of isolated tooth roots based on the dynamic threshold method

OBJECTIVE

Accurate quantification of the root surface area (RSA) plays a decisive role in the advancement of periodontal, orthodontic, and restorative treatment modalities. In this study, we aimed to develop a dynamic threshold-based computer-aided system for segmentation and calculation of the RSA of isolated teeth on cone-beam computed tomography (CBCT) and to assess the accuracy of the measured data.

METHOD

We selected 24 teeth to be extracted, including single-rooted and multi-rooted teeth, from 22 patients who required tooth extraction. In the experimental group, we scanned 24 isolated teeth using CBCT with a voxel size of 0.3 mm. We designed a computer-aided system based on a personalized dynamic threshold algorithm to automatically segment the roots of 24 isolated teeth in CBCT images and calculate the RSA. In the control group, we employed digital intraoral scanner devices to perform optical scanning on 24 isolated teeth and subsequently manually segmented the roots using 3-matic software to calculate the RSA. We used the paired t-test (P < 0.05) and Bland-Altman plots to analyze the consistency of the two measurement methods.

RESULTS

The results of the paired t-test showed that there was no significant difference in the RSAs obtained using the dynamic threshold method and the optical scanning image reconstruction (t = 1.005, P = 0.325 > 0.05). As per the Bland-Altman plot, the results were evenly distributed within the region of ± 1.96 standard deviations of the mean, with no increasing or decreasing trends and good consistency.

CONCLUSION

In this study, we designed a computer-aided root segmentation system based on a personalized dynamic threshold algorithm to automatically segment the roots of isolated teeth in CBCT images with a voxel size of 0.3 mm. We found that the RSA calculated using this approach was highly accurate, and a voxel of 0.3 mm in size could accurately display the surface area data in CBCT images. Overall, our findings in this study provide a foundation for future work on accurate automatic segmentation of tooth roots in full-mouth CBCT images and the computation of RSA.

Application of metal artifact reduction algorithm for CBCT diagnosis of temporary anchorage device-tooth root contact: inadequate to reduce false-positive rate

OBJECTIVES

It was recently found that when cone beam computed tomography (CBCT) was used to examine temporary anchorage device (TAD)-tooth root contact, it tends to yield high false-positive (FP) diagnoses. This study investigated whether application of a metal artifact reduction (MAR) algorithm or reducing CBCT scan voxel-size can remediate this problem.

METHODS

18 fresh pig cadaver mandibles underwent TAD placement bilaterally at first molar lingual furcation regions. CBCT scans were taken under varied MAR (absence, presence) and voxel-size (400 µm, 200 µm) settings. Then, TADs were removed and a micro-CT scan (27 µm voxel-size) of the TAD placement site was performed. Three raters, blinded of CBCT scan setting, independently diagnosed whether TADs were in contact with roots. The reliability and accuracy of CBCT diagnoses using micro-CT as the gold-standard were statistically examined.

RESULTS

Generally, CBCT diagnoses had intrarater (Cohen's κ: 0.54-1) and interrater (Fleiss' κ: 0.73-0.81) reliability, within the moderate to excellent range, which did not vary with MAR setting or scan voxel-size. For diagnostic accuracy, FP rate among all raters was mostly in the 15-25% range and did not change with MAR or scan voxel-size settings (McNemar tests, p > 0.05) while false-negative rate was relatively minimal and only occurred to one rater (9%).

CONCLUSIONS

When using CBCT to diagnose possible TAD-root contact, applying a currently available Planmeca MAR algorithm or reducing CBCT scan voxel-size from 400 µm to 200 µm may not decrease FP rate. Further optimization of the MAR algorithm for this purpose may be needed.

Obstructive sleep apnea: a review for the orthodontist

INTRODUCTION

Obstructive sleep apnea (OSA) affects an important part of the population and is characterized by recurrent total or partial obstruction of the upper airway (UA) during sleep, negatively affecting the quality of life of patients in the short and long terms, and constituting an important public health problem for the society. The field of expertise of orthodontists is closely related to the UA, placing them in a strategic position to diagnose air passage failures and intervene when necessary. Orthodontists, as health professionals, must know how to recognize respiratory problems and manage them appropriately, when indicated.

OBJECTIVE

Thus, this paper aims to review and critically evaluate the related literature, to provide orthodontists with updated knowledge on the diagnosis and therapy related to OSA. Science and technology are constantly evolving; thus, the literature was also reviewed considering new technologies available in consumer-targeted applications and devices for the diagnosis, monitoring, and treatment of sleep-disordered breathing.

Correlation between gray values of cone-beam computed tomograms and Hounsfield units of computed tomograms: A systematic review and meta-analysis

Purpose

The aim of this review was to systematically analyze the available literature on the correlation between the gray values (GVs) of cone-beam computed tomography (CBCT) and the Hounsfield units (HUs) of computed tomography (CT) for assessing bone mineral density.

Materials and Methods

A literature search was carried out in PubMed, Cochrane Library, Google Scholar, Scopus, and LILACS for studies published through September 2021. In vitro, in vivo, and animal studies that analyzed the correlations GVs of CBCT and HUs of CT were included in this review. The review was prepared according to the PRISMA checklist for systematic reviews, and the risk of bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies tool. A quantitative analysis was performed using a fixed-effects model.

Results

The literature search identified a total of 5,955 studies, of which 14 studies were included for the qualitative analysis and 2 studies for the quantitative analysis. A positive correlation was observed between the GVs of CBCT and HUs of CT. Out of the 14 studies, 100% had low risks of bias for the domains of patient selection, index test, and reference standards, while 95% of studies had a low risk of bias for the domain of flow and timing. The fixed-effects meta-analysis performed for Pearson correlation coefficients between CBCT and CT showed a moderate positive correlation (r=0.669; 95% CI, 0.388 to 0.836; P<0.05).

Conclusion

The available evidence showed a positive correlation between the GVs of CBCT and HUs of CT.

Midpalatal suture density ratio after rapid maxillary expansion evaluated by cone-beam computed tomography

INTRODUCTION

Identifying the stage of midpalatal suture (MPS) fusion is essential for rapid maxillary expansion (RME). The objective of this study was to evaluate the relationship between MPS density ratio and the skeletal response after RME using cone-beam computed tomography (CBCT).

METHODS

CBCT scans of 64 patients (age, 13.81 ± 1.68 years; 42 females and 22 males) who underwent RME as part of comprehensive orthodontic treatment were used for this study. Two CBCT records were made at T1 (pre-RME) and T2 (post-RME). MPS density was assessed by gray scale and the skeletal effects through linear measurements: greater palatine foramina, the width of the nasal cavity (NW), infraorbital foramina. The data were collected at 4 different times: baseline, 24 hours, 48 hours, and 4 weeks.

RESULTS

There was no statistically significant correlation between MPS density ratio and greater palatine foramina or infraorbital foramina. Negative correlations with MPS density ratio are presented with the difference of age post-RME and pre-RME (r = -0.46, P = 0.033) in males, and NW (r = -0.41, P = 0.007) in females. A significant association between gender and the MPS density ratio was found (P = 0.015) in females.

CONCLUSIONS

There is a weak negative correlation between the MPS density ratio and the difference of age post-RME and pre-RME in males and the NW in females. Females presented greater density ratios than males. MPS density ratio through CBCT does not appear to be an adequate parameter to predict the skeletal effect in adolescent patients and young adults.

Associations among Primary Stability, Histomorphometric Findings, and Bone Density: A Prospective Randomized Study after Alveolar Ridge Preservation with a Collagen Cone

BACKGROUND

The objective of this investigation was to examine whether determination of bone density (BD) with a cone beam computed tomography (CBCT) scan could help predict the primary stability (PS) of the implants and to investigate whether associations between the histomorphometric findings and the CBCT scan could be observed.

MATERIALS AND METHODS

In this randomized clinical study, the efficacy of alveolar ridge preservation (ARP) with a combination of a collagen cone and a collagen membrane procedure after tooth extraction was investigated. CBCT scans were obtained after a healing period of 8 (±1) weeks. Subsequently, the CBCT scans were evaluated in terms of BD at different heights of the former socket. Eleven (±1) weeks after tooth extraction, implant placement was performed and PS was measured with resonance frequency analysis. Potential associations among the radiologically measured BD, the histomorphometric results, and the PS were analyzed.

RESULTS

No direct association was observed between the radiologically determined BD and the histomorphometric findings. No significant associations could be found between the BD and the PS.

CONCLUSION

No significant associations were observed among the BD determined by the CBCT, the histomorphometric findings, and the PS.

Radiopacity of alloplastic bone grafts measured with cone beam computed tomography: An analysis in rabbit calvaria

Availability of adequate bone structure for dental implants is still a problem in dentistry. Alloplastic grafts, which promote bone regeneration, are used as bone substitutes in orthopedic and oral surgical procedures. The aim of this study was to evaluate the radiopacity of three different synthetic bone grafts in rabbit calvaria, over 3 months, using cone beam computed tomography (CBCT). Four critical-size defects were made on the calvaria of 11 rabbits. The lesions were classified into three groups according to the alloplastic grafts they received: Osteon® 70/30, Osteon collagen®, and Osteon II® groups. The fourth group received blood clot, and served as a control. The bone samples were collected and analyzed with CBCT after the 1st, 2nd, and 3rd month. One month after surgery, the lesions that received Osteon® 70/30 and Osteon collagen® grafts showed the highest radiopacity compared to the lesions with Osteon II® and blood clot. After the 2nd month, the radiopacity values between the three groups that received the grafts were more similar compared to the group with blood clot. After the 3rd month, the lesions with Osteon® 70/30 graft showed the highest radiopacity values, followed by Osteon collagen® and Osteon II® groups. The group that received blood clot showed the lowest radiopacity values. In conclusion, the grafts used in this study had higher radiopacity values compared to blood clot. Among the grafts used, the Osteon® 70/30 graft showed the highest radiopacity values in the 3-month period.

CBCT-based bone quality assessment: are Hounsfield units applicable?

CBCT is a widely applied imaging modality in dentistry. It enables the visualization of high-contrast structures of the oral region (bone, teeth, air cavities) at a high resolution. CBCT is now commonly used for the assessment of bone quality, primarily for pre-operative implant planning. Traditionally, bone quality parameters and classifications were primarily based on bone density, which could be estimated through the use of Hounsfield units derived from multidetector CT (MDCT) data sets. However, there are crucial differences between MDCT and CBCT, which complicates the use of quantitative gray values (GVs) for the latter. From experimental as well as clinical research, it can be seen that great variability of GVs can exist on CBCT images owing to various reasons that are inherently associated with this technique (i.e. the limited field size, relatively high amount of scattered radiation and limitations of currently applied reconstruction algorithms). Although attempts have been made to correct for GV variability, it can be postulated that the quantitative use of GVs in CBCT should be generally avoided at this time. In addition, recent research and clinical findings have shifted the paradigm of bone quality from a density-based analysis to a structural evaluation of the bone. The ever-improving image quality of CBCT allows it to display trabecular bone patterns, indicating that it may be possible to apply structural analysis methods that are commonly used in micro-CT and histology.

Fast three-dimensional superimposition of cone beam computed tomography for orthopaedics and orthognathic surgery evaluation

The aim of this study was to validate a method for fast three-dimensional (3D) superimposition of cone beam computed tomography (CBCT) in growing patients and adults (surgical cases). The sample consisted of CBCT scans of 18 patients. For 10 patients, as the gold standard, the spatial position of the pretreatment CBCT was reoriented, saved as a reoriented volume, and then superimposed on the original image. For eight patients, four non-growing and four growing, the pre- and post-treatment scans were superimposed. Fast voxel-based superimposition was performed, with registration at the anterior cranial base. This superimposition process took 10-15s. The fit of the cranial base superimposition was verified by qualitative visualization of the semi-transparent axial, sagittal, and coronal cross-sectional slices of all corresponding anatomical structures. Virtual 3D surface models of the skull were generated via threshold segmentation, and superimposition errors in the reoriented models and the results of treatment for the treated cases were evaluated by 3D surface distances on colour-coded maps. The superimposition error of the spatial reorientation and for growing and non-growing patients was <0.5mm, which is acceptable and clinically insignificant. The voxel-based superimposition method evaluated was reproducible in different clinical conditions, rapid, and applicable for research and clinical practice.

CBCT-based volume of simulated root resorption - influence of FOV and voxel size

AIM

To examine the influence of the field of view (FOV) and voxel size on the measurement of the volume of simulated internal root resorption (IRR) lesions through cone-beam computed tomography (CBCT).

METHODOLOGY

Eleven single-rooted teeth with IRR simulated by acid demineralization were studied. CBCT images were acquired using large FOV (voxel sizes of 0.200, 0.250 and 0.300 mm) and limited FOV (voxel sizes of 0.076, 0.100 and 0.200 mm). The IRR volumes were calculated using the Dolphin(®) software. Volumetric measurements were validated using IRR silicone putty casts. The analysis of variance (anova) for randomized block design complemented with the Tukey's test was employed.

RESULTS

IRR volumes obtained using voxel sizes of 0.200 and 0.250 mm were similar (P > 0.05). However, both these values were significantly different from that obtained using the 0.300-mm voxel (P < 0.05). There was no significant difference between IRR volumes measured through voxel sizes of 0.076 and 0.100 mm (P > 0.05), but both differed significantly from that obtained through the 0.200-mm voxel (P < 0.05). There was no significant difference between the volumetric measurements of the 0.200-mm voxel images of the restricted and large FOV protocols. The mean volumes of the silicone casts were smaller than those calculated using a 0.200-mm voxel, but were similar to those obtained using voxel sizes of 0.076 and 0.300 mm.

CONCLUSIONS

Despite the FOV protocol, voxel size can influence measurement of simulated IRR volumes. The importance of standardization of CBCT image acquisition protocols is emphasized, especially during follow-up of an IRR lesion, to prevent misinterpretation of its extent, which can create a bias in clinical decisions.

High-quality image acquisition by double exposure overlap in dental cone beam computed tomography

OBJECTIVE

With a double exposure overlapping cone beam computed tomography (CBCT) scan technique, using CBCT acquisition radiation dose, the objective was to obtain apparent density similar to that of multidetector computed tomography (MDCT).

STUDY DESIGN

Factory quality-assurance phantom and water phantom were used for the evaluation of apparent density fidelity of iCAT scans in different modes. Each scan's apparent density was analyzed for identical regions using ImageJ, version 1.42q.

RESULTS

The iCAT Classic extended height acquisition with 4-cm central overlap and reconstruction of 2 groups of 300 projections per rotation for the water and quality-assurance CBCT phantoms resulted in improved apparent density fidelity. This apparent density accuracy was superior to that of iCAT scan at high resolution (600 projections during 1 rotation).

CONCLUSIONS

Using double exposure overlapping CBCT scans allows the analysis quality to be comparable with that of MDCT.