Reproducibility of 3 different tracing methods based on cone beam computed tomography in determining the anatomical position of the mandibular canal

Towards clinically applicable automated mandibular canal segmentation on CBCT

OBJECTIVES

To develop a deep learning-based system for precise, robust, and fully automated segmentation of the mandibular canal on cone beam computed tomography (CBCT) images.

METHODS

The system was developed on 536 CBCT scans (training set: 376, validation set: 80, testing set: 80) from one center and validated on an external dataset of 89 CBCT scans from 3 centers. Each scan was annotated using a multi-stage annotation method and refined by oral and maxillofacial radiologists. We proposed a three-step strategy for the mandibular canal segmentation: extraction of the region of interest based on 2D U-Net, global segmentation of the mandibular canal, and segmentation refinement based on 3D U-Net.

RESULTS

The system consistently achieved accurate mandibular canal segmentation in the internal set (Dice similarity coefficient [DSC], 0.952; intersection over union [IoU], 0.912; average symmetric surface distance [ASSD], 0.046 mm; 95% Hausdorff distance [HD95], 0.325 mm) and the external set (DSC, 0.960; IoU, 0.924; ASSD, 0.040 mm; HD95, 0.288 mm).

CONCLUSIONS

These results demonstrated the potential clinical application of this AI system in facilitating clinical workflows related to mandibular canal localization.

CLINICAL SIGNIFICANCE

Accurate delineation of the mandibular canal on CBCT images is critical for implant placement, mandibular third molar extraction, and orthognathic surgery. This AI system enables accurate segmentation across different models, which could contribute to more efficient and precise dental automation systems.

The role of implants and implant prostheses on the accuracy and artifacts of cone-beam computed tomography: an in-vitro study

To assess the accuracy of CBCT in implant-supported prostheses and to evaluate metal artifacts with and without implants or implant prostheses. Accuracy and artifacts were assessed in the dried mandible at three points on the buccal and lingual cortical plates on the mandible's body near the crest and the base. On the buccal cortical plate, these points were labelled as A, B and C near the crest and D, E and F near the base of the body of the mandible. Similarly, points a to f were marked on the lingual cortical plate corresponding to points A to F. The study had two control groups, C0 for physical linear measurement (PLM) and C1 for radiographic linear measurement (RLM) and artifact assessment. There were seven test groups, TG 1 to 7, progressing from a single implant to implant full-arch prosthesis. For accuracy assessment, PLM was compared to RLM. CBCT artifacts were investigated in images integrated at 0.25 mm, 10 mm, and 20 mm at regions of interest on concentric circles at different intersecting angles by comparing grayscale values at C1 and TG1 to 7. The data were collected and statistically analyzed. A significant difference was observed between C0 and C1, and RLM in test groups at the superior axial plane. Similarly, PLM and test RLM in the sagittal plane at A-B, B-C, and D-E were statistically significant. A significant difference between PLM and RLM was also observed in the vertical plane at A-D, B-E, and C-F. Quantification of CBCT artifacts in the presence of implants or prostheses revealed that full-arch prostheses had the highest mean grayscale value, whereas single implants with a prosthesis had the lowest. The mean grayscale change was greatest around the implant and implant prosthesis. The mean grayscale value was maximum at 20 mm voxel integration scales (VIS) and lowest at 0.25 mm. CBCT is a clinically reliable device. Metal in implants or implant-supported prostheses prevents true assessment of the peri-implant area; therefore, lower VIS is suggested in the presence of implants or implant prostheses.

Accurate mandibular canal segmentation of dental CBCT using a two-stage 3D-UNet based segmentation framework

OBJECTIVES

The objective of this study is to develop a deep learning (DL) model for fast and accurate mandibular canal (MC) segmentation on cone beam computed tomography (CBCT).

METHODS

A total of 220 CBCT scans from dentate subjects needing oral surgery were used in this study. The segmentation ground truth is annotated and reviewed by two senior dentists. All patients were randomly splitted into a training dataset (n = 132), a validation dataset (n = 44) and a test dataset (n = 44). We proposed a two-stage 3D-UNet based segmentation framework for automated MC segmentation on CBCT. The Dice Similarity Coefficient (DSC) and 95% Hausdorff Distance (95% HD) were used as the evaluation metrics for the segmentation model.

RESULTS

The two-stage 3D-UNet model successfully segmented the MC on CBCT images. In the test dataset, the mean DSC was 0.875 ± 0.045 and the mean 95% HD was 0.442 ± 0.379.

CONCLUSIONS

This automatic DL method might aid in the detection of MC and assist dental practitioners to set up treatment plans for oral surgery evolved MC.

Automatic segmentation of inferior alveolar canal with ambiguity classification in panoramic images using deep learning

Background

Manual segmentation of the inferior alveolar canal (IAC) in panoramic images requires considerable time and labor even for dental experts having extensive experience. The objective of this study was to evaluate the performance of automatic segmentation of IAC with ambiguity classification in panoramic images using a deep learning method.

Methods

Among 1366 panoramic images, 1000 were selected as the training dataset and the remaining 336 were assigned to the testing dataset. The radiologists divided the testing dataset into four groups according to the quality of the visible segments of IAC. The segmentation time, dice similarity coefficient (DSC), precision, and recall rate were calculated to evaluate the efficiency and segmentation performance of deep learning-based automatic segmentation.

Results

Automatic segmentation achieved a DSC of 85.7% (95% confidence interval [CI] 75.4%-90.3%), precision of 84.1% (95% CI 78.4%-89.3%), and recall of 87.7% (95% CI 77.7%-93.4%). Compared with manual annotation (5.9s per image), automatic segmentation significantly increased the efficiency of IAC segmentation (33 ms per image). The DSC and precision values of group 4 (most visible) were significantly better than those of group 1 (least visible). The recall values of groups 3 and 4 were significantly better than those of group 1.

Conclusions

The deep learning-based method achieved high performance for IAC segmentation in panoramic images under different visibilities and was positively correlated with IAC image clarity.

Is Intraoral Scanning Accurate to Evaluate Dental Implant Position? An In-Vitro Study

PURPOSE

The position of dental implants is generally verified through imaging exams, even though its use exposes patients to radiation. Intraoral scanning (IOS) may be a suitable alternative to using radiographic imaging to verify implant position. Using polyurethane jaw models, the purpose of this in-vitro study was to measure and compare implant positions determined by IOS and cone-bean computed tomography (CBCT).

METHODS

One hundred twenty implants were installed in 30 edentulous polyurethane jaws, 4 dental implants in each prototype. Four scanbodies were attached to the implants, and a scanning of each mandible was acquired using an intraoral scanner (CS 3600). All prototypes were also submitted to CBCT. Then, the 3D scan files in STL (Standard Tessellation Language) format were superimposed on the DICOM (Digital Imaging and Communications in Medicine) images of the tomographic mandibles. The accuracy of IOS was evaluated by the metric analyses of deviations between the position of the implants projected by the IOS versus the detected tomographically, in which CBCT served as the gold standard, using a free software for digital planning (Bluesky 4 - Grayslake, IL, USA). The following measures were analyzed: radial deviations at the shoulder (Xc) and at the apex of the implants (Xa), height deviation (Xh) and axial deviation. Bland-Altman and a paired t-test were applied to verify the reproducibility between measurements and a t-test for a mean was applied to compare the measurements with zero value.

RESULTS

The results showed Xc and Xa deviation means of 0.14 ± 0.09 mm and 0.12 ± 0.12 mm, respectively. The Xh mean was 0.2 ± 0.12 mm and the axial deviation mean was 0.71° ± 0.66°. T-test showed a statistically significant difference when the 4 means were compared to zero value, represented by the CBCT (P < .0001).

CONCLUSIONS

There was a statistically significant difference IN the scanned measures compared to CBCT as the standard, but the differences may not be clinically significant. The IOS utilization to evaluate the position of dental implants is a radiation-free and reproducible method, with the advantage of not generating metal artifacts. Further clinical studies are needed to validate this new method of postoperative evaluation.

Assessment of the Proximity of the Inferior Alveolar Canal with the Mandibular Root Apices and Cortical Plates-A Retrospective Cone Beam Computed Tomographic Analysis

Various endodontic interventions often lead to iatrogenic damage to the inferior alveolar nerve present in the inferior alveolar canal (IAC). The purpose of the present study was to analyze the relationships of IAC with the root apices of mandibular teeth and with the mandibular cortical plates.

MATERIALS

116 cone beam computed tomography (CBCT) scans were examined and the shortest distance of IAC with the root apices of mandibular canines, premolars and molars, and with cortical plates was analyzed. The data were statistically analyzed using SPSS.

RESULTS

The shortest mean distance between IAC and lingual cortical plate (LCP) was found in the third molar area, and between IAC and buccal cortical plate (BCP) in the second premolar area. A high incidence of 60% direct communication (DC) was present in mandibular second molars; 38% in mandibular third molars; 13% in mandibular second premolars; 12% in mandibular first molars; and 1% in mandibular first premolars.

CONCLUSION

Anteriorly, IAC was found to be significantly present in close approximation to the roots of mandibular canines. Posteriorly, IAC was found to be in significant proximity to the distal roots of mandibular second molars.

Validation of different protocols of inferior alveolar canal tracing using cone beam computed tomography (CBCT)

OBJECTIVES

The objective of this study was to evaluate, compare and validate different protocols of inferior alveolar canal tracing.

METHODS

60 DICOM files with a total of 80 inferior alveolar canals were retrieved and imported to a third-party software where all proposed protocols can be performed. Initially, inferior alveolar canal was traced by two oral and maxillofacial radiologists together on cone beam CT cross-sectional images and considered as the baseline for future comparisons. Oral and maxillofacial surgeon performed the proposed different protocols. The protocols were color-coded differently by the surgeon before being compared with the baseline canal by the radiologists through a 5-point scale.

RESULTS

Results showed that no single protocol was successful in all cases, even the cross-sectional protocol. According to the present study, the hybrid protocol was the most accurate while the automatic protocol was the least accurate.

CONCLUSIONS

The hybrid protocol was reliable and showed the highest number of successful applications followed by the commonly used cross-sectional protocol. Dental practitioners should be aware of the application of multiple protocols and their pros and cons as no single protocol was successful in all the cases. Applying the same protocols on a larger sample size using different cone beam CT and multislice CT machines with different exposure parameters is recommended.

Development and validation of a novel artificial intelligence driven tool for accurate mandibular canal segmentation on CBCT

OBJECTIVES

The objective of this study is the development and validation of a novel artificial intelligence driven tool for fast and accurate mandibular canal segmentation on cone beam computed tomography (CBCT).

METHODS

A total of 235 CBCT scans from dentate subjects needing oral surgery were used in this study, allowing for development, training and validation of a deep learning algorithm for automated mandibular canal (MC) segmentation on CBCT. Shape, diameter and direction of the MC were adjusted on all CBCT slices using a voxel-wise approach. Validation was then performed on a random set of 30 CBCTs - previously unseen by the algorithm - where voxel-level annotations allowed for assessment of all MC segmentations.

RESULTS

Primary results show successful implementation of the AI algorithm for segmentation of the MC with a mean IoU of 0.636 (± 0.081), a median IoU of 0.639 (± 0.081), a mean Dice Similarity Coefficient of 0.774 (± 0.062). Precision, recall and accuracy had mean values of 0.782 (± 0.121), 0.792 (± 0.108) and 0.99 (± 7.64×10^-05) respectively. The total time for automated AI segmentation was 21.26 s (±2.79), which is 107 times faster than accurate manual segmentation.

CONCLUSIONS

This study demonstrates a novel, fast and accurate AI-driven module for MC segmentation on CBCT.

CLINICAL SIGNIFICANCE

Given the importance of adequate pre-operative mandibular canal assessment, Artificial Intelligence could help relieve practitioners from the delicate and time-consuming task of manually tracing and segmenting this structure, helping prevent per- and post-operative neurovascular complications.

A Novel Treatment Concept for Advanced Stage Mandibular Osteoradionecrosis Combining Isodose Curve Visualization and Nerve Preservation: A Prospective Pilot Study

Background

Osteoradionecrosis (ORN) of the mandible is a severe complication of radiation therapy in head and neck cancer patients. Treatment of advanced stage mandibular osteoradionecrosis may consist of segmental resection and osseous reconstruction, often sacrificing the inferior alveolar nerve (IAN). New computer-assisted surgery (CAS) techniques can be used for guided IAN preservation and 3D radiotherapy isodose curve visualization for patient specific mandibular resection margins. This study introduces a novel treatment concept combining these CAS techniques for treatment of advanced stage ORN.

Methods

Our advanced stage ORN treatment concept includes consecutively: 1) determination of the mandibular resection margins using a 3D 50 Gy isodose curve visualization, 2) segmental mandibular resection with preservation of the IAN with a two-step cutting guide, and 3) 3D planned mandibular reconstruction using a hand-bent patient specific reconstruction plate. Postoperative accuracy of the mandibular reconstruction was evaluated using a guideline. Objective and subjective IAN sensory function was tested for a period of 12 months postoperatively.

Results

Five patients with advanced stage ORN were treated with our ORN treatment concept using the fibula free flap. A total of seven IANs were salvaged in two men and three women. No complications occurred and all reconstructions healed properly. Neither non-union nor recurrence of ORN was observed. Sensory function of all IANs recovered after resection up to 100 percent, including the patients with a pathologic fracture due to ORN. The accuracy evaluation showed angle deviations limited to 3.78 degrees. Two deviations of 6.42° and 7.47° were found. After an average of 11,6 months all patients received dental implants to complete oral rehabilitation.

Conclusions

Our novel ORN treatment concept shows promising results for implementation of 3D radiotherapy isodose curve visualization and IAN preservation. Sensory function of all IANs recovered after segmental mandibular resection.

Computed Tomographic Study of Remarkable Anatomic Variations in Paranasal Sinus Region and their Clinical Importance - A Retrospective Study

INTRODUCTION

With the advent of functional endoscopic sinus surgery and coronal computed tomography (CT) imaging, more attention has been paid toward paranasal region anatomy. Detailed knowledge of anatomic variations in paranasal sinus region is critical for surgeons performing endoscopic sinus surgery as well as for the radiologist involved in the pre- and post-operative assessment. The anatomical variants with some accompanying pathologies would directly influence the success of diagnostic and therapeutic management of paranasal sinus diseases. Our study intends to explore the anatomy of paranasal air sinus through CT and to describe its variants, which may predispose to chronic sinusitis and complications in endoscopic sinonasal surgery.

MATERIALS AND METHODS

This was a retrospective study carried out in a tertiary institution. Two hundred and fifty patients without paranasal sinus symptoms who presented for head CT studies and gave consent for a coronal section scan of the paranasal sinuses to be taken in addition to the axial section of the head were included in the study. The CT examination was performed with GE Hispeed-NX/I Base-2002 Dual Slice Helical CT machine.

RESULTS

Among 250 study population, 100 were females and 150 males. Among these 423 cases of anatomical variants were observed. The most common anatomical variants were pneumatization of the middle nasal turbinates 30.73%. This is followed by agger nasi cells 21.64%, Haller's cells 22.91%, septal deviation 21.91%, and sphenoid sinus septation (20.18%).

DISCUSSION

CT is the gold standard in the radiologic investigation of the paranasal sinuses, sinonasal lesions, and inflammatory disease or pre- and post-surgical assessment. It has the capability of disclosing in greatest detail any anatomical variations, which could be causing or precipitating the sinusitis.

Accuracy of the measurements from multiplanar and sagittal reconstructions of CBCT

OBJECTIVES

The purpose of this study was to assess the accuracy of linear measurements performed in multiplanar reconstructions (MPR) and sagittal reconstructions (SR) of the left hemiface obtained from cone-beam computed tomography (CBCT) with 3D^® Dolphin Imaging software by comparing them with the same measurements made on lateral cephalograms and on dry skulls.

SETTING AND SAMPLE POPULATION

Lateral cephalograms and CBCT (with voxels of 0.25, 0.3 and 0.4 mm) were taken of 10 dry skulls.

MATERIALS AND METHODS

Linear distances were measured using the software's electronic rulers. Measurements performed on dry skulls using a digital caliper were considered the gold standard. The measurements were performed twice by two evaluators.

RESULTS

No significant difference was found in the measurements performed with the different imaging modalities and on the dry skulls. The highest mean error was observed in the lateral cephalograms, followed by MPR and SR.

CONCLUSIONS

Cephalometric measurements performed on multiplanar and sagittal reconstructions from CBCT, with different spatial resolutions, are accurate when compared with the measurements obtained in lateral cephalograms.

Comparing the precision of panoramic radiography and cone-beam computed tomography in avoiding anatomical structures critical to dental implant surgery: A retrospective study

Purpose

The aim of this study was to evaluate the correlations between measurements made using panoramic radiography and cone-beam computed tomography (CBCT) based on certain anatomical landmarks of the jaws, with the goal of preventing complications due to inaccurate measurements in the pre-surgical planning phase of dental implant placement.

Materials and Methods

A total of 56 individuals who underwent panoramic radiography and a CBCT evaluation before dental implant surgery were enrolled in the study. Measurements were performed to identify the shortest vertical distance between the alveolar crest and neighboring anatomical structures, including the maxillary sinus, nasal floor, mandibular canal, and foramen mentale. The differences between the measurements on panoramic radiography and CBCT images were statistically analyzed.

Results

Statistically significant differences were observed between the measurements on panoramic radiography and CBCT for all anatomical structures (P<.05). The correlation coefficients (r) between the paired samples obtained from panoramic radiography and CBCT were closely correlated (P<.05), with r values varying from 0.921 and 0.979 for different anatomical regions.

Conclusion

The results of this study support the idea that panoramic radiography might provide sufficient information on bone height for preoperative implant planning in routine cases or when CBCT is unavailable. However, an additional CBCT evaluation might be helpful in cases where a safety margin cannot be respected due to insufficient bone height.

Association between impacted third molars and position of the mandibular canal: a morphological analysis using cone-beam computed tomography

Our aim was to assess the association between the angle of impaction of the third molar and the position of the mandibular canal on cone-beam computed tomography (CT). We designed a retrospective study of 100 cone-beam CT images of 173 mandibular third molars that were obtained between January 2012 and December 2015, and recorded the angle of impaction of the third molar, the position of the mandibular canal in relation to the impacted tooth, and the potential contact between the roots of the tooth and the mandibular canal. Most third molars tilted mesially (n=33), while the mandibular canal was positioned below the roots of the third molar in most cases (n=73). Contact between the two was most likely when the mandibular canal was between (RR=1.49; 95% CI 1.27 to 1.75, p<0.001), or to the lingual side (RR=1.49; 95% CI 1.27 to 1.75, p<0.001) of the roots of the tooth. These outcomes indicate a greater likelihood of contact between the canal and the roots when the canal is between, and to the lingual side, of the roots. We found no association between the angle of impaction and the position of the canal. These findings illustrate the importance of surgical planning using complementary imaging tests such as cone-beam CT.

Assessment of the Inferior Alveolar Nerve Canal Course Among Saudis by Cone Beam Computed Tomography (Pilot Study)

Background

The aim of this study was to identify the relative position and course of the inferior alveolar canal (IAC) in relation to the apices of the teeth in Saudi dentate subjects. Measurements were taken using cone beam computed tomography (CBCT).

Patient and Methods

In this cross-sectional retrospective study, 124 cases were selected from the archived images in "Galileos" CBCT machine in Riyadh Colleges of Dentistry and Pharmacy. The sample included both males and females with their ages ranging from 15 to 61 years. The distance between the apices of the teeth from the first premolar till the second molar was measured. Also, the distance between the buccal and lingual alveolar plates and the inferior alveolar canal and the distance from the inferior border of the mandible to the alveolar canal were assessed utilizing the cross-sectional images.

Results

The buccolingual linear measurements indicated a lingual course of the canal in both males and females. A significant difference existed between males and females regarding the vertical distance inferior to the IAC at first premolar on the right and left sides, On the right side in females the linear distance was (9.2 mm ± 1.03), and in males (10.9 mm ± 1.5), while on the left side in females the distance was (8.9 mm ± 1.7), while in males (11.3 mm ± 0.34). In 57% of the study group the mental foramen was found between the first and second premolars, while in 35% of the studied cases it was located below the second premolar.

Conclusion

The inferior alveolar canal acquires a lingual course in this selected sample of the Saudi population detected by cone beam computed tomography.

Prevalence evaluation and classification of bifid mandibular canals in CBCT exams in different facial types

Abstract Objetive The aim of this study is to establish the prevalence and classification of mandibular canal alterations using cone beam computed tomography (CBCT) in different facial types. This research was submitted and approved by the research ethics committee, registration number 2.065.839. Material and method The sample consisted of 90 CBCTs from the São Leopoldo Mandic Dental School database (Campinas-SP), divided into three groups according to brachycephalic, dolichocephalic and mesocephalic facial types. Result Of the 90 patients, 23 presented bifid mandible canals (25.6%), of which 60.9% were in males and 39.1% in females. In 39.1%, the canal bifurcation occurred towards the retromolar region (class D), 21.7% had a trajectory to an alveolar or upper direction (class C) and 13.1% were classified as C-E. For the remaining classifications (A, E, F and A-E), the frequencies were in the range of 8.7% to 4.3%. None of the 23 cases of mandibular canal bifurcation was classified as B (mesial direction). Conclusion According to the results obtained from this study, the prevalence of bifid mandibular canals was found to be 25.6%, with class D being the most prevalent for the retromolar region and the highest occurrence was unilaterally on the left side. When evaluating the occurrence of bifid mandibular canals in relation to facial types, brachycephalic patients were the most affected.

The Risk Factors that Can Increase Possibility of Mandibular Canal Wall Damage in Adult: A Cone-Beam Computed Tomography (CBCT) Study in a Chinese Population

Background

The objective of this study was to analyze the factors that can increase the possibility of mandibular canal (MC) defect in Chinese people, to evaluate the risk of nerve impairment, and to choose the proper operative method to reduce the risk of mandibular alveolar nerve injury during the extraction of mandibular third molar (MTM).

Material/Methods

A total of 954 patients (1,304 MTMs) who underwent orthopantomography (OPG) and cone-beam computed tomography (CBCT) between July 2014 and December 2014 were included in this study. The age and gender of patients, impacted type (high impaction, moderate impaction, and low impaction), Winter classification of MTM, position of MTM relative to MC, vertical classification of MTM and MC, and the feature images of OPG were collected and compared to the imperfection of the MC wall in CBCT images.

Results

The wall situation of MC was significantly correlated with the age of the patient, the depth of the molar, the position of the roots, and six imaging appearances on OPG. There was no significant difference based on gender.

Conclusions

Most incomplete walls of MCs could be inferred by OPG. However, images based on CBCT could clarify the defect of the MC and also could clearly display the spatial relationship between the root and inferior alveolar canal.

Measurement of Lingual Cortical Plate Thickness and Lingual Position of Lower Third Molar Roots Using Cone Beam Computed Tomography

Objective:

The objective of the study was to determine the potential risk of tooth/root displacement into the soft tissue during the third molar surgery. While performing third molar surgeries, one of the many complications is displacement of the tooth into the soft tissues. This can be due perforation of the lingual cortical bone during surgery or the position of the tooth root which may be close to the lingual bone.

Materials and Methods:

Retrospective samples of 251 patients were collected who had undergone cone-beam computed tomography (CBCT) for various reasons. Measurements were performed independently and recorded twice by one surgeon and one radiologist; the average of the two measurements was calculated and evaluated using MyRay CBCT.

Results:

On the right and the left side, the average distances in males for AL were 3.31 and 2.96 mm, respectively, whereas in females was found to be 3.98 and 3.56 mm which were statistically significant. On the right and left side, the average distances in males for RL were 2.03 and 1.78 mm, respectively, whereas in females, it was 2.41 and 1.99 mm, respectively, with the significant P value in the right side.

Conclusion:

Despite the sample size being of 251 patients, a large number of root of the third molar (95.62%) were not in contact with lingual cortical bone, but still practitioner should be careful during surgery as there might be the risk for displacement of the tooth. The images used were of impacted molar used in this study and these teeth were not subjected to surgery. Hence, the results can be only correlated theoretically, i.e., there would be a risk of displacement of the tooth during extraction.

Tracking of the inferior alveolar nerve: its implication in surgical planning

OBJECTIVES

The objective of the study is to assess the correlation between the mandibular canal tracing done on cone beam CT (CBCT) data, with the size, shape, and position of the neurovascular bundle (NB) obtained by magnetic resonance imaging (MRI).

MATERIAL AND METHODS

Six human cadaver mandibles were scanned with a CBCT Promax® scanner (Planmeca, Helsinki, Finland) and with an Ingenia® 3.0 T MR system (Philips, Amsterdam, The Netherlands). The NB was segmented from the MRI dataset, while the mandibular canal (MC) tracing was done on the CBCT images. Quantitative 3D analysis was made for the full-segmented nerves and for three defined regions of specific clinical interest, namely angle, body, and mental region.

RESULTS

From the 3D MRI analysis, the nerve thickness (for the angle, body, and mental region) ranges from 0.8 to 5.2 mm, while the thickness of the mandibular canal tracing is approximately 2.00 mm on both sides as chosen in the tracing software. The mean volume of the NB on the left is 828.49 ± 215.54 mm³ and on the right 792.98 ± 264.57 mm³. For the nerve tracing, the mean value is 351.92 ± 16.42 and 339.69 ± 16.12 mm³ on the left and right sides, respectively. Wilcoxon signed-rank test showed significant differences between NB and MC volume measurements (p = 0.0005). The Bland-Altman plots show an increasing slope for thickness and volume, indicating that the absolute differences between neurovascular bundle, estimated by MRI, and the mandibular canal, drawn on the CBCT images, increase with larger mean values.

CONCLUSIONS

Surgeons should be aware of the shortcomings of nerve tracing in the different regions of the mandible.

CLINICAL RELEVANCE

Tracing of the inferior alveolar nerve (IAN) underestimates shape and volume. Whenever nerve tracing instead of well-recognizable anatomical bony landmarks is used for surgical planning that need precision, a wider safe margin is recommended.

Cone Beam Computed Tomographic Analysis of the Course and Position of Mandibular Canal

PURPOSE

Estimation of the relative position of infra alveolar nerve (IAN) canal and its relation to the mandibular anatomical landmarks can be clinically useful in minimizing the risk of surgery complications such as neurosensory disturbances that may occur after invasive mandibular surgical procedures. The purpose of the present study was to investigate the anatomic location and radiographic course of the mandibular canal compared to anatomic landmarks on CBCT and to discuss its clinical significance and also to determine the possible correlations between the mandibular position and the age of the patients.

METHODS

This cross sectional study was conducted on 242 CBCT of patients (99 males and 143 females). The location of canal was evaluated in 4 different regions. The first section in trans-axial view after mental foramen, in which the loop of mandibular canal is formed, was selected as point 1 for measurement and intervals of 10 mm, respectively, points 2, 3, 4 were selected for measurement. On these sections, the shortest linear distances (mm) from the most buccal and lingual aspects of the canal to the corresponding cortical plates of the mandible and also the minimum linear distance between the inferior aspect of canal and inferior border of mandible in these regions were calculated.

RESULTS

There was statistically significant correlation between the anatomic course of the canal and the patients' gender. The mean vertical position of the canal, as measured from the lower border of the IAN canal to the inferior border of the mandible, was 8.50 mm, ranging from 4.80 to 14.50 mm. On average, the mandibular canal was situated more lingually at all sites to the point it reached the mental foramen. However, at the mental foramen region (Point 1), it was located closer to the buccal cortical plate.

CONCLUSION

Assessment of the exact course of the IAN preoperatively along the body of the mandible by using CBCT might contribute to efficient and accurate surgical planning and therefore positively influence the surgical results. The results of this study confirm the necessity of using CBCT before invasive surgical procedures to determine the variations in the relative position and course of IAN canal.

Prevalence of bifid mandibular canals by cone beam computed tomography

PURPOSE

The aim of this study was to evaluate the prevalence of bifid mandibular canals (BMC) by cone beam computed tomography (CBCT).

MATERIALS AND METHODS

We examined CT scans from 300 patients both male and female, aged 25 to 87 years. The subjects were divided into groups according to gender, male group (MG) and female group (FG) as well as subgroups according to the side, right (R) and left (L). Tomographic acquisitions were performed on the device I-Cat ® Classic. Image analysis was performed on the XoranCat ® software of the equipment itself, aided by image filters associated with transverse, oblique, and panoramic reconstruction cuts for analysis of the BMC. The results were displayed as descriptive analysis of the values and comparisons between factors were performed using ANOVA at a significance level of 95 %.

RESULTS

BMC was observed in 80 cases (26.67 %), of which, 39 (48.75 %) were in males and 41 (51.25 %) in females; no difference was seen between genders, neither by affected side, although the right side was more frequently affected (66.67 %) when both genders were combined.

CONCLUSION

The prevalence of BMC is significant and should not be overlooked.

Accuracy of software designed for automated localization of the inferior alveolar nerve canal on cone beam CT images

OBJECTIVES

The aim of this study was to design and evaluate a new method for automated localization of the inferior alveolar nerve canal on CBCT images.

METHODS

The proposed method is based on traversing both panoramic and cross-sectional slices. For the panoramic slices, morphological skeletonization is imposed, and a modified Hough transform is used while traversing the cross-sectional slices. A total of 40 CBCT images were randomly selected. Two experts twice located the inferior alveolar nerve canal during two examinations set 6 weeks apart. Agreement between experts was achieved, and the result of this manual technique was considered the gold standard for our study. The distances for the automated method and those determined using the gold standard method were calculated and recorded. The mean time required for the automated detection was also recorded.

RESULTS

The average mean distance error from the baseline was 0.75 ± 0.34 mm. In all, 86% of the detected points had a mean error of <1 mm compared with those determined by the manual gold standard method.

CONCLUSIONS

The proposed method is far more accurate and faster than previous methods. It also provides more accuracy than human annotation within a shorter time.

Assessment of the Anterior Loop of the Mental Nerve Using Cone Beam Computerized Tomography Scan

The purpose of this study is to use cone-beam computerized tomography (CBCT) scans with oblique-transverse reconstruction modality to measure and compare the anterior loop length (AnLL) of the mental nerve between gender and age groups and to compare the difference between the right and left sides. Sixty-one female and 61 male CBCT scans were randomly selected for each age group: 21–40, 41–60, and 61–80 years. Both right- and left-side AnLLs were measured in each subject using i-CATVision software to measure AnLLs on the oblique transverse plane using multiplanar reconstruction. The anterior loop was identified in 85.2% of cases, with the mean AnLL of the 366 subjects (732 hemimandibles) being 1.46 ± 1.25 mm with no statistically significant difference between right and left sides or between different gender groups. However, the mean AnLL in the 21–40 year group (1.89 ± 1.35 mm) was larger than the AnLL in the 41–60 year group (1.35 ± 1.19 mm) and the 61–80 year group (1.13 ± 1.08 mm). In conclusion, when placing implants in close proximity to mental foramina, caution is recommended to avoid injury to the inferior alveolar nerve. No fixed distance anteriorly from the mental foramen should be considered safe. Using CBCT scans with the oblique-transverse method to accurately identify and measure the AnLL is of utmost importance in avoiding and protecting its integrity.

Development of a Three-Dimensional Hand Model Using Three-Dimensional Stereophotogrammetry: Assessment of Image Reproducibility

Purpose

Using three-dimensional (3D) stereophotogrammetry precise images and reconstructions of the human body can be produced. Over the last few years, this technique is mainly being developed in the field of maxillofacial reconstructive surgery, creating fusion images with computed tomography (CT) data for precise planning and prediction of treatment outcome. Though, in hand surgery 3D stereophotogrammetry is not yet being used in clinical settings.

Methods

A total of 34 three-dimensional hand photographs were analyzed to investigate the reproducibility. For every individual, 3D photographs were captured at two different time points (baseline T0 and one week later T1). Using two different registration methods, the reproducibility of the methods was analyzed. Furthermore, the differences between 3D photos of men and women were compared in a distance map as a first clinical pilot testing our registration method.

Results

The absolute mean registration error for the complete hand was 1.46 mm. This reduced to an error of 0.56 mm isolating the region to the palm of the hand. When comparing hands of both sexes, it was seen that the male hand was larger (broader base and longer fingers) than the female hand.

Conclusions

This study shows that 3D stereophotogrammetry can produce reproducible images of the hand without harmful side effects for the patient, so proving to be a reliable method for soft tissue analysis. Its potential use in everyday practice of hand surgery needs to be further explored.

Anterior Loop of the Mandibular Canal-A Source of Possible Complications

INTRODUCTION

Recognizing the radiographic position of the mental foramina is not sufficient to avoid complications during dental implant surgery. In many cases, the inferior alveolar nerve extends mesially as an "anterior loop" (AL). The aim of this study was to investigate the prevalence and spatial extension of the AL on computed tomography (CT).

MATERIALS AND METHODS

Thirty-seven human mandibles from an anatomical collection underwent CT analysis. Cross-sectional views and panoramic reconstructions were obtained. Prevalence and length of the AL were investigated.

RESULTS

Recognition of the AL on CT was 100%. Prevalence of the AL was 97.3% (n = 36). AL mean length was 2.26 mm (maximum: 7.0 mm).

CONCLUSION

Recognition of the AL on CT scans (100%) is higher compared with data in literature for detection on panoramic radiographs (38.2%). To avoid complications, it is important to detect the AL presence and its mesial extension from the mental foramen. Safety distance of at least 2 mm from the mesial extend of the AL is recommended. Therefore, 3D imaging techniques are advised for loops which courses are not clearly identifiable on panoramic radiographs.

Development of a three-dimensional hand model using 3D stereophotogrammetry: Evaluation of landmark reproducibility

BACKGROUND

Using three-dimensional (3D) photography, exact images of the human body can be produced. Over the last few years, this technique is mainly being developed in the field of maxillofacial reconstructive surgery, creating fusion images with computed tomography (CT) data for accurate planning and prediction of treatment outcome. However, in hand surgery, 3D photography is not yet being used in clinical settings.

METHODS

The aim of this study was to develop a valid method for imaging the hand using 3D stereophotogrammetry. The reproducibility of 30 soft tissue landmarks was determined using 3D stereophotogrammetric images. Analysis was performed by two observers on 20 3D photographs. Reproducibility and reliability of the landmark identification were determined using statistical analysis.

RESULTS

The intra- and interobserver reproducibility of the landmarks were high. This study showed a high reliability coefficient for intraobserver (1.00) and interobserver reliability (0.99). Identification of the landmarks on the palmar aspect of individual fingers was more precise than the identification of landmarks of the thumb.

CONCLUSIONS

This study shows that 3D photography can safely produce accurate and reproducible images of the hand, which makes the technique a reliable method for soft tissue analysis. 3D images can be a helpful tool in pre- and postoperative evaluation of reconstructive trauma surgery, in aesthetic surgery of the hand, and for educational purposes. The use in everyday practice of hand surgery and the concept of fusing 3D photography images with radiologic images of the interior hand structures needs to be further explored.

In vitro correlation of the level of inferior alveolar canal with CBCT imaging

PURPOSE

The aim was to correlate the level of the inferior alveolar canal on cadaver specimens and as evaluated with three-dimensional radiographic cone-beam computed tomography (CBCT) imaging.

METHODS

Twenty-one skulls with intact mandibles (42 inferior alveolar canals) were imaged with an I-CAT Cone-Beam 3D Imaging System and multi-planar reformatted images obtained were scored to assess the level of the canal (Level I, Level II, and Level III). The mandibles were later dissected and level of the canal was directly visualized, scored, and further correlated with results from CBCT imaging.

RESULTS

There was no difference in the level of the inferior alveolar canal between the dissected cadaver specimen and CBCT images. Also, there was no statistically significant difference in the level of the canal among the gender assigned to the specimens and corresponding CBCT images. There were no statistical differences in the level of the canal (cadaver specimen vs. CBCT) between the left and right sides of the specimens, as studied individually.

CONCLUSION

Our study indicates that there is close correlation of the level of the inferior alveolar canal between cadaver specimens and CBCT images. Well-designed studies would be required to further validate the findings in this study.

Does cone-beam CT alter treatment plans? Comparison of preoperative implant planning using panoramic versus cone-beam CT images

PURPOSE

The present study was performed to compare the planning of implant placement based on panoramic radiography (PAN) and cone-beam computed tomography (CBCT) images, and to study the impact of the image dataset on the treatment planning.

MATERIALS AND METHODS

One hundred five partially edentulous patients (77 males, 28 females, mean age: 46 years, range: 26-67 years) seeking oral implant rehabilitation were referred for presurgical imaging. Imaging consisted of PAN and CBCT imaging. Four observers planned implant treatment based on the two-dimensional (2D) image datasets and at least one month later on the three-dimensional (3D) image dataset. Apart from presurgical diagnostic and dimensional measurement tasks, the observers needed to indicate the surgical confidence levels and assess the image quality in relation to the presurgical needs.

RESULTS

All observers confirmed that both imaging modalities (PAN and CBCT) gave similar values when planning implant diameter. Also, the results showed no differences between both imaging modalities for the length of implants with an anterior location. However, significant differences were found in the length of implants with a posterior location. For implant dimensions, longer lengths of the implants were planned with PAN, as confirmed by two observers. CBCT provided images with improved scores for subjective image quality and surgical confidence levels.

CONCLUSION

Within the limitations of this study, there was a trend toward PAN-based preoperative planning of implant placement leading towards the use of longer implants within the posterior jaw bone.

Accuracy of vertical height measurements on direct digital panoramic radiographs using posterior mandibular implants and metal balls as reference objects

OBJECTIVES

Conventional panoramic radiography, a widely used radiographic examination tool in implant treatment planning, allows evaluation of the available bone height before inserting posterior mandibular implants. Image distortion and vertical magnification due to projection geometry is well described for rotational panoramic radiographs. To assess the accuracy of vertical height measurements on direct digital panoramic radiographs, implants and metal balls positioned in the posterior mandible were used as radio-opaque reference objects. The reproducibility of the measuring method was assessed by the inter- and intraobserver agreements.

METHODS

Direct digital panoramic radiographs, performed using a Kodak 8000C (Eastman Kodak Company, Rochester, NY), of 17 partially edentulous patients (10 females, 7 males, mean age 65 years) were selected from an X-ray database gathered during routine clinical evaluation of implant sites. Proprietary software and a mouse-driven calliper were used to measure the radiological length of 25 implants and 18 metal reference balls, positioned in mandibular posterior segments. The distortion ratio (DR) was calculated by dividing the radiological implant length by the implant's real length and the radiological ball height by the ball's real height.

RESULTS

Mean vertical DR was 0.99 for implants and 0.97 for balls, and was unrelated to mandibular sites, side, age, gender or observer. Inter- and intraobserver agreements were acceptable for both reference objects.

CONCLUSIONS

Vertical measurements had acceptable accuracy and reproducibility when a software-based calibrated measurement tool was used, confirming that digital panoramic radiography can be reliably utilized to determine the pre-operative implant length in premolar and molar mandibular segments.

Accuracy of bone surface size and cortical layer thickness measurements using cone beam computerized tomography

OBJECTIVES

The purpose of this study was to determine the accuracy of Cone Beam Computerized Tomography (CBCT) reconstructions in displaying bone surface size and cortical layer thickness.

MATERIALS AND METHODS

Two fresh frozen cadaver heads were scanned using a CBCT (i-CAT(™) 3D Imaging System; Imaging Sciences International Inc.). The mandibles were sectioned and digitalized for histological evaluation. Dimensions as measured on these sections were compared with CBCT measurements of the same region with the use of 3D image-based planning software (Procera System NobelGuide(™); Nobel Biocare). To allow optimal comparison between histological and CBCT sections, reference markers were placed into the mandibles. The Student t-test was utilized to analyze the data. Differences with P-values <0.05 were considered significant.

RESULTS

The total height and width of the mandibular body, as measured on CBCT views, were larger compared with the histological values with a maximum difference of 0.33 mm (SD ± 0.34). Cortical thickness measurements were significantly thicker on CBCT sections (P < 0.006) with absolute differences ranging up to ±0.63 mm (SD ±0.28) and relative differences ranging up to 82.6%.

CONCLUSION

CBCT images (i-CAT 3D Imaging System), viewed on the planning software Procera System NobelGuide, tend to overestimate the anatomical truth in assessing both bone height and width; especially cortical thicknesses are depicted thicker than in reality. When using CBCT images for presurgical assessment, one should be aware of this phenomenon of exaggeration of dimensions.

Inferior alveolar nerve canal position among South Indians: A cone beam computed tomographic pilot study

Purpose:

To document a clinically relevant position of the inferior alveolar nerve (IAN) in complete dentate south Indian patients in the age group of 20–29 years using cone beam computerized tomograms.

Materials and Methods:

The investigators used a cross-sectional study design and a study sample of subjects who had a radiographically identifiable IAN canal with complete set of 28 permanent teeth excluding 3^rd molars. Predictor variables were age, tooth position, and side. Outcome variables were the linear distances between the buccal and lingual aspect of the IAN canal, buccal and lingual cortical thickness, IAN canal diameter, and the superior aspect of the IAN canal from the periapex of first and second mandibular molar. Descriptive statistics and Mann–Whitney U test were performed. P value of ≤ 0.05 was taken as significant.

Results:

The study sample was composed of 10 male and 10 female patients with a mean age of 24.2 ± 3.00 years. On average, the lingual cortical thickness was 1.68 mm at 1^st molar and 1.44 at 2^nd molar level. Gender and side influenced the outcome with varying statistical significance.

Conclusions:

The range of linear dimension of mandibular canal, cortical bone thickness, and distance between tooth apex and IAN canal have been presented for the South Indian population in the age group of 20–29 years. The implications of the findings will influence on the course of surgery. Further large-scale studies are needed to validate the findings of this study.

The clinical relevance of bifid and trifid mandibular canals

Background

Bifid mandibular canals (BMC) and trifid mandibular canals (TMC) are variations on the normal anatomy with incidences ranging from 0.08% to 65.0%. Such aberrations have an important clinical impact. For example, an extra mandibular canal may explain inadequate anesthesia, especially when two mandibular foramina are involved. Furthermore, during mandibular surgery, a second, or even third, neurovascular bundle may be damaged causing paresthesia, neuroma development, or bleeding.

Case report

Two cases are presented in this article. One patient had a BMC on both sites, and the other patient had a TMC on one site and a BMC on the other site.

Discussion

Initial screening for the presence of a BMC or TMC can be executed by conventional panoramic radiography. BMCs or TMCs are diagnosed, before executing mandibular surgery; additional CBCT scanning is indicated.