Influence of acquisition parameters on the evaluation of mandibular third molars through cone beam computed tomography

Accepted Manuscript Influence of Acquisition Parameters on the Evaluation of Mandibular Third Molars Through Cone Beam Computed Tomography Larissa Pereira Lagos De Melo, Anne Caroline Costa Oenning, Mariana Rocha Nadaes, Yuri Nejaim, Frederico Sampaio Neves, Matheus Lima Oliveira, Deborah Queiroz Freitas PII:

S2212-4403(17)30112-8

DOI:

10.1016/j.oooo.2017.03.008

Reference:

OOOO 1732

To appear in:

Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology

Received Date: 6 December 2016 Revised Date:

2 March 2017

Accepted Date: 4 March 2017

Please cite this article as: Lagos De Melo LP, Oenning ACC, Nadaes MR, Nejaim Y, Neves FS, Oliveira ML, Freitas DQ, Influence of Acquisition Parameters on the Evaluation of Mandibular Third Molars Through Cone Beam Computed Tomography, Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology (2017), doi: 10.1016/j.oooo.2017.03.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT INFLUENCE OF ACQUISITION PARAMETERS ON THE EVALUATION OF MANDIBULAR THIRD MOLARS THROUGH CONE BEAM COMPUTED TOMOGRAPHY

Larissa Pereira LAGOS DE MELOa, Anne Caroline Costa OENNINGb, Mariana Rocha NADAESa, Yuri NEJAIMb, Frederico Sampaio NEVESc, Matheus Lima OLIVEIRAb, Deborah

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Queiroz FREITASb

a

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DDS, MS, Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, University of Campinas (UNICAMP), Av. Limeira, 901, 13414-903, Piracicaba, São Paulo, Brazil. b

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DDS, MS, PhD, Department of Oral Diagnosis, Division of Oral Radiology, Piracicaba Dental School, University of Campinas (UNICAMP), Av. Limeira, 901, 13414-903, Piracicaba, São Paulo, Brazil.

c

DDS, MS, PhD, Department of Propedeutics and Integrated Clinic, Division of Oral Radiology, Federal University of Bahia (UFBA), Rua Araújo Pinho, 62, 40110-150, Salvador, Bahia, Brazil.

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Corresponding author: Larissa Pereira Lagos de Melo. University of Campinas. Piracicaba Dental School, Department of Oral Diagnosis. Av. Limeira, 901, Zip Code 13414-903, Piracicaba, São Paulo, Brazil. Phone: +55 – 19 – 2106-5327. E-mail: [email protected]

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Conflicts of interest related to this study: none.

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Funding: This study was partially supported by CAPES

Word count (abstract): 217 Word count (complete manuscript): 4273 Number of references: 35 Number of figures: 1 Number of tables: 5

ACCEPTED MANUSCRIPT ABSTRACT

Objectives: To assess the influence of cone-beam computed tomography (CBCT) acquisition parameters on the evaluation of mandibular third molars and their relation to

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the mandibular canal.

Study design: Eight dry human mandibles with thirteen mandibular third molars were scanned with one CBCT unit. Voxel size (0.2 and 0.3 mm), field of view (FOV) size

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(12x8.5cm and 5x5cm), and number of basis images (450 and 720) were the variables studied. Two examiners evaluated the images, and the resulting data was compared

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through McNemar, McNemar-Bowker, and Student’s t tests. Additionally, dosimetry was determined for all protocols tested and radiation doses were compared through ANOVA.

Results: The variables did not influence third molar evaluation, except for the voxel

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size when assessing contact between tooth and canal (p= 0.021). While FOV and number of basis images affected radiation dose, voxel size did not. Conclusion: FOV size and number of basis images did not influence the evaluation of

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third molars and their relation to the mandibular canal in the CBCT unit used. Conversely, smaller voxel size affected the assessment of contact between the tooth and

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the mandibular canal. In units in which voxel size does not influence radiation dose, the most appropriate CBCT protocol is the one using a smaller voxel size and delivering the lowest radiation dose to the patient.

Keywords: Molar, Third; Cone-Beam Computed Tomography; Diagnostic Imaging

ACCEPTED MANUSCRIPT Introduction Imaging of mandibular third molars provides essential information for predictable treatment planning. Ideally, it must reveal information about not only the tooth, but also about the surrounding bone, the adjacent teeth, and the relation to

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neighboring anatomical structures, especially the mandibular canal.1

Panoramic radiography is commonly used for third molar evaluation due to its wide availability, low cost, and low radiation doses. Unfortunately, its two-dimensional

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nature hinders depth assessment in the bucco-lingual direction.2 Thus, cone-beam computed tomography (CBCT) has been advocated when there is suspicion of contact

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between the mandibular third molar and the mandibular canal or when one is unsure about the canal’s position or course.3,4 While CBCT delivers lower radiation doses and is not as costly as multislice computed tomography, it is not a substitute for panoramic radiography regarding those two parameters; therefore, oral surgeons normally request

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CBCT scans only after deciding that the information provided by panoramic radiography is insufficient for predictable pre-surgical planning.5 The many CBCT units available in the market offer a wide variety of acquisition

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settings that can be adjusted to the surgeon’s or the patient’s individual needs. These parameters include exposure factors (kVp and mA), voxel size, field of view (FOV)

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size, and number of basis images.6,7 These factors can influence image quality and/or the radiation dose delivered to the patient. However, CBCT scanning optimization is centered on reducing the radiation dose without losing diagnostic quality, in compliance with the ALARA principle (keeping radiation exposure As Low As Reasonably Achievable). Since one main indication for CBCT imaging is the pre-surgical evaluation of mandibular third molars8,9, studies assessing the influence of CBCT acquisition

ACCEPTED MANUSCRIPT parameters on the visualization of teeth and the surrounding anatomy or on the radiation dose produced during scanning are important to determine the most suitable acquisition protocols. For instance, one study assessed variables such as different examiner profiles and CBCT units from different manufacturers and found no significant influence on

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diagnostic quality.10 Since that study was performed in humans, one tooth could not be scanned more than once with different units and hence no direct comparisons were possible. Therefore, the aim of this study was to assess the influence of CBCT

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acquisition parameters (i.e., voxel size, FOV, and number of basis images) on the evaluation of mandibular third molars and on the determination of the relationship

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between the tooth and the mandibular canal. The null hypotheses stated that there would be no differences attributable to the parameters regarding the anatomy of the teeth, the relationship of teeth and canal, or radiation doses.

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Materials and Methods

This study was approved by the Local Research Ethics Committee (protocol #52425316). Eight dry human mandibles containing thirteen lower third molars were

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used in this study. Proximity between the lower third molar and the mandibular canal visualized in periapical radiographs was used as the inclusion criterion.

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Image Acquisition The dry mandibles were positioned in a cylindrical polyethylene container filled

with enough water to cover the jaws in order to simulate X-ray attenuation by the soft tissues of the maxillofacial region.11 The mandibles were then scanned with a Picasso Trio cone-beam computed tomography unit (Vatech, E-WOO Technology Co, Ltd, Republic of Korea). For the initial scanning, the mandibles were positioned with the occlusal plane parallel to the horizontal plane and the midsagittal plane perpendicular to

ACCEPTED MANUSCRIPT that plane. Positioning was then adjusted according to FOV size and the location of the third molar on the right or left side when a reduced FOV was used. The energy parameters were fixed at 80 kVp and 3.5 mA to test the following factors and their variations: voxel size (0.2 and 0.3 mm), FOV (12x8.5cm and 5x5cm), and the number

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of basis images (450 and 720) (Table I). Thus, eight images were obtained for each tooth (Figure 1). The images were saved as DICOM files, which were encoded and randomized for further evaluation.

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Image Assessment

After a calibration session, two oral and maxillofacial radiologists with 10 years

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of experience with CBCT images evaluated the images together on a 24.1’’ LCD monitor with a resolution of 1920x1200 pixels (MDCR-2124, Barco, Kortrijk, Belgium) in a dimly lit, quiet environment using the CS 3D Imaging® software (Carestream Dental, New York, NY, USA). The calibration session consisted of evaluation and

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discussion of ten CBCT scans not included in the study sample. The examiners were allowed to adjust brightness and contrast and use the zoom tool freely. Moreover, a dynamic assessment was performed to adjust the images to the best plane representing

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the aspect studied using the long axis of the third molar as reference. For each variable, the examiners discussed their impressions until a consensus

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was reached. The following aspects were evaluated concerning the mandibular third molars:

1. number of roots (1, 2, 3, or more); 2. tooth angulation (adapted from Winter, 192612: vertical, horizontal,

mesioangular, distoangular, others); 3. direction of root curvature (assessed on the oblique sagittal plane, categorized as straight, mesial, or distal);

ACCEPTED MANUSCRIPT 4. bucco-lingual root position in relation to the mandibular canal (assessed on the oblique coronal plane, categorized as buccal, lingual, or aligned); 5. direct contact with the mandibular canal (assessed on the oblique coronal plane, categorized as yes or no);

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6. shortest distance between the roots and the mandibular canal, measured in millimeters in the absence of contact between the two structures (assessed on the oblique coronal plane).

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Variables 1, 3, 4, and 5 were adapted from Matzen et al. 201310. For the variables “tooth angulation” and “number of roots”, there was only one answer per

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tooth. For the remaining variables, each root was evaluated individually. Thirty days after the initial assessment, 30% of the sample was reassessed by the examiners under the same conditions to determine intra-examiner reproducibility. Dosimetry

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An anthropomorphic tissue-equivalent phantom was used to evaluate the radiation doses delivered according to the different protocols tested. Seven sets of three calibrated thermoluminescent dosimeters (TLD) (TLD-100 LiF:Mg, Ti, Thermo Fisher

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Scientific Inc., Waltham, MA, USA) were positioned on the phantom at the anatomical regions corresponding to the eye lens (right and left), parotid glands (right and left),

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submandibular glands (right and left) and thyroid, resulting in a total of 21 TLDs.13 A set of three TLDs was kept out of the examination room to measure the average background radiation that was be subtracted from the doses derived from the study’s protocols. The phantom was positioned as the dry mandibles were and scanned with the same equipment and protocols. For the small FOV, two acquisitions were performed (right and left) without changing the TLD to simulate bilateral imaging. Due to the

ACCEPTED MANUSCRIPT small amount of radiation released by a single CBCT scan regardless of the FOV size and given the great number of dosimeters out of the primary irradiated area when small FOVs were used, two repeated exposures for each protocol were performed to produce measurable values, i.e., two acquisitions were performed for large FOVs and four for

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small FOVs.

All dosimeters were read with a thermoluminescent reader (Harshaw Thermoluminescent Scanner, Model 2000, Thermo Fisher Scientific Inc., Waltham,

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MA, USA). The background radiation was subtracted from the results, which were divided by two (number of repeated exposures). Each set of three TLDs was averaged

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and the mean values of the seven anatomical regions were added. After 30 days, this procedure was repeated with new dosimeters to assess reproducibility. Statistical Analysis

Data analysis was conducted with the SPSS® v.22.0 (SPSS Inc., Chicago, IL,

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USA), and a significance level of 5% was considered for all statistical tests. To compare the results of image assessment for the different protocols, McNemar and McNemarBowker tests were used for categorical variables, while the Student’s t test was used for

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the parametric variable of distance between root and mandibular canal. The null hypothesis stated that there was no significant difference among protocols. For intra-

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examiner agreement analysis, a weighted kappa test was performed for the categorical variables (0- 0.19 – poor agreement; 0.20-0.39 – fair agreement; 0.40-0.59 – moderate agreement; 0.60-0.79 – substantial agreement; 0.80-1.00 – almost perfect agreement, according to Landis and Koch,14 and the Intraclass Correlation Coefficient (ICC) for the parametric variable. To compare the absorbed doses obtained in each protocol, a multifactor analysis of variance (ANOVA) was used. The null hypothesis stated that

ACCEPTED MANUSCRIPT there were no significant differences among the obtained doses. ICC was also performed to test the reproducibility of dosimetry.

Results

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Table II presents the influence of voxel size on image assessment. Voxel size did not significantly affect image evaluation (p>0.05), except when contact between the tooth and the mandibular canal was assessed (p=0.021). In addition, FOV size and

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number of basis images did not influence image assessment significantly (Tables III and IV, respectively).

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In the absence of contact between the structures, the mean distance between the roots and the mandibular canal was 1.94 ± 0.68 millimeters. The tested variables did not affect these measurements (p>0.05).

Intra-examiner agreement for the categorical variables ranged from substantial to

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excellent (0.65 to 1.00). Furthermore, ICC showed an excellent replicability for the distance between the mandibular canal and the roots (ICC=0.87). The absorbed doses obtained with the different protocols are shown in Table V.

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The values represent the sum of readings from all seven anatomical regions described above. As mentioned, the doses presented for the 5x5 FOV refer to two acquisitions of

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CBCT, one for each side (right and left). ANOVA indicated that total dose was affected by the number of basis images and by FOV size (p<0.001) but not by voxel size (p=0.065), suggesting that the larger the FOV size or the number of basis images, the larger the absorbed dose. ICC also showed an excellent reproducibility for dosimetry (ICC=0.92).

ACCEPTED MANUSCRIPT Since the voxel size influenced the evaluation of contact between the tooth and the canal, and the FOV size and number of basis images influenced on the radiation

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dose, the null hypothesis was rejected for these two findings.

Discussion

CBCT has been regarded as the most valuable imaging modality for the

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preoperative assessment of mandibular third molars when two-dimensional radiographs suggest an intimate relationship between the teeth being assessed and the mandibular

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canal.1,3,4,15 In this context, the goal of this study was to determine the most suitable acquisition protocol for CBCT imaging requested as part of the pre-operative workup for mandibular third molar removal, with attention to different settings of voxel size, FOV size, and number of basis images. To date, only one study has evaluated the

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factors related to CBCT scans that could affect the image assessment in that very context, but it assessed factors such as examiners’ background and differences in the image quality of two different CBCT units with similar exposure parameters.10

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Unfortunately, the degree of influence of image acquisition factors on image interpretation is difficult to answer in human studies since repeated exposures of the

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same region in humans are limited by ethical concerns. Our study has clinical relevance, therefore, since direct comparisons among different acquisition parameters was possible, even if in a laboratory setting. Voxel size seemed to affect the assessment of the relation between the tooth and the mandibular canal. This aspect is of great relevance for surgeons since studies reported that an intimate relation between the tooth and the canal may influence the decision of performing an alternative procedure, i.e., a coronectomy.16,17 Our results

ACCEPTED MANUSCRIPT ratify reports concerning the influence of voxel size on the assessment of anatomical and pathological features of the oral and maxillofacial region (periodontal defects, root fractures, root resorptions, and erosion in the temporomandibular joint).18-22 Alternatively, others have not been able to identify any relevant influence of

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voxel size on image assessment.23,24 We assume that the different voxel sizes or anatomical structures evaluated could account for these discrepant results, given that when voxel size is greater than the structure evaluated, voxel value would not represent

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the tissue or its limit, but instead it would be an average of the values for the different neighboring tissues.25

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Voxel size affects image quality because it is one of the factors affecting spatial resolution and noise. Dental professionals should consider this when setting this parameter. As a reconstruction parameter, voxel size alone does not have an effect on radiation dose.6 However, this is true only for CBCT units in which acquisition

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parameters can be set independently of each other. This could explain our results showing that voxel size did not affect radiation dose, even though this occurred only because energy parameters were fixed for all protocols. In units in which voxel size

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changes along with energy parameters, the radiologist should consider not only the dose, but also the effect of these parameters on spatial resolution and noise.

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One would expect that FOV size could influence image assessment, since some

studies suggest that smaller FOVs decrease the relative scattered radiation that reaches the detector, thus reducing noise and artifacts and improving image quality.6 In our study, however, image acquisition with a smaller FOV did not improve image assessment. Comparing our results to those from studies assessing the influence of FOV on the diagnosis of conditions such as periapical diseases and TMJ pathologies, some have reached similar conclusions26-28 while some have not.29-32 As the anatomical

ACCEPTED MANUSCRIPT structures evaluated in these studies were different from those assessed here, it is rather difficult to establish a straightforward comparison. On the other hand, we were able to identify an influence of FOV size on the radiation dose, in agreement with another report.33 It is known that FOV size influences the dose directly as it relates to the area in

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the patient’s body that is irradiated. However, mandibular third molars are usually present bilaterally, and it might not be advantageous to use a smaller FOV for preoperative imaging as there is a need for two exposures. For this reason, the dose

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values for the 5x5cm FOVs refer to two CBCT acquisitions: one from the right and another from the left side. We found that even if bilateral evaluation is needed, the dose

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delivered during acquisition of two 5x5cm FOV scans was smaller than that of one 12x8.5cm FOV scan, showing that a limited FOV restricted to the area of interest is advantageous even if two exams are necessary. Therefore, considering dose and image assessment, it is reasonable to choose a small FOV size.

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The number of basis images did not affect the evaluation of the structures of interest in this study, similar to what was reported previously.7,28,34,35 On the other hand, the more images, the higher the radiation dose, since this parameter is closely related to

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exposure time6,7 Therefore, protocols with a smaller number of basis images are suggested for the preoperative assessment of lower third molars to avoid unwanted and

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unnecessary exposure to radiation. Our intra-examiner agreement ranged from substantial to excellent, which was

even higher than that reported by Matzen et al. 20138, in which the kappa values ranged from 0.34 to 0.78 if we consider the parameters evaluated congruently in both studies. The lack of a gold standard is one limitation of our study, since the mandibles were not evaluated histologically or with other destructive techniques for practical reasons. However, this is an issue often found in clinical studies and does not discredit

ACCEPTED MANUSCRIPT the scientific information derived from them. On the other hand, a relative advantage of our study design is the possibility of scanning the same tooth as many times as necessary. It is worth mentioning that our results apply to CBCT units similar to that used

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in the present study, for which acquisition parameters can be selected independently of each other. Moreover, radiation dose can vary among different units because dose results from many factors, and the statement that two smaller FOV scans produce a

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lower dose than one larger FOV scan may not be valid for all machines. Indeed, the relation among parameters may be different in different CBCT units; however, our

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findings serve to alert dental professionals that it is possible and advisable to use lowdose CBCT protocols for this purpose.

In addition, it is important to stress that this study by no means has the purpose of stimulating the use of CBCT in the pre-surgical workup of mandibular third molars;

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instead, it is aimed to suggest the most suitable acquisition protocol that offers maximum quality in imaging and image interpretation while avoiding unnecessary

Conclusion

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exposure to radiation.

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It seems to be prudent to select a low-dose CBCT protocol for the pre-surgical

workup of mandibular third molars. In machines with such a protocol, images for that specific purpose should be acquired with a small FOV and a reduced number of basis images, since these settings decrease radiation dose but do not interfere with image quality. Moreover, the use of a smaller voxel size has affected the assessment of contact between the tooth and the mandibular canal, which is an interesting feature especially in CBCT units in which the setting of this parameter does not affect the radiation dose.

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Acknowledgments The authors would like to thank the Dr. Cassiana Viccari Sacilotto, from the

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Physics, University of São Paulo, Ribeirão Preto, Brazil.

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Center for Instrumentation, Dosimetry and Radiation Protection, Department of

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ACCEPTED MANUSCRIPT 35. Neves FS, Vasconcelos TV, Campos PS, Haiter-Neto F, Freitas DQ. Influence of scan mode (180°/360°) of the cone beam computed tomography for preoperative

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ACCEPTED MANUSCRIPT Figure Captions Figure 1. Cone-beam computed tomography images acquired with the different

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protocols tested (oblique coronal plane).

ACCEPTED MANUSCRIPT Table I. Protocols used in image acquisitions in CBCT Picasso Trio unit Voxel (mm)

Standard (3.5mA; 80kVp; t=15s; Rot.=360º; Basis images=450)

0.2

High density (3.5mA; 80kVp; t=24s; Rot.=360º; Basis images=720)

0.3 0.2 0.3

FOV (cm)

ROI

5x5

Mandible (posterior region for each side)

12 x 8.5 5x5 12 x 8.5

Mandible Mandible (posterior region for each side) Mandible

5x5

Mandible (posterior region for each side)

12 x 8.5 5x5 12 x 8.5

Mandible (posterior region for each side) Mandible

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ROI: region of interest.

Mandible

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Scanning mode

ACCEPTED MANUSCRIPT Table II. Contingency table comparing the responses obtained with voxel sizes 0.2mm and 0.3mm 0.2mm

Voxel size 2

Tooth angulation p=1.000

2

46 (88.5%)

0 (0%)

3

0 (0%)

6 (11.5%)

Vertical

Horizontal Mesioangular

Vertical

36 (69.2%)

Horizontal

0 (0%)

Mesioangular

0 (0%)

Straight

66 (60.0%)

Mesial

2 (1.8%)

4 (3.6%)

0 (0%)

Distal

5 (4.6%)

1 (0.9%)

24 (21.8%)

Direction of root curvature p=0.644

Root position in relation to the canal p=0.508

Contact between the tooth and the canal p=0.021*

9 (17.3%)

1 (1.9%)

1 (1.9%)

5 (9.6%)

Mesial

Distal

1 (0.9%)

7 (6.4%)

Aligned

Lingual

Aligned

50 (45.5%)

3 (2.7%)

Lingual

6 (5.5%)

51 (46.3%)

No

Yes

No

50 (45.5%)

9 (8.2%)

Yes

1 (0.9%)

50 (45.5%)

Statistically significant difference, according to McNemar test (p < 0.05).

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0.3mm

0 (0%)

SC

Straight

0 (0%)

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Number of roots p=1.000

3

ACCEPTED MANUSCRIPT Table III. Contingency table comparing the responses obtained with FOV sizes 12x8.5cm and 5x5cm 5x5cm

FOV size

Tooth angulation p=0.061

3

2

44 (84.6%)

4 (7.7%)

3

0 (0%)

4 (7.7%)

Vertical

Horizontal Mesioangular

Vertical

36 (69.2%)

Horizontal

0 (0%)

Mesioangular

0 (0%)

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Number of roots p=0.125

2

Straight

Root position in relation to the canal p=1.000

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8 (15.4%)

4 (7.7%)

0 (0%)

4 (7.7%)

Mesial

Distal

4 (3.7%)

5 (4.6%)

Straight

64 (59.3%)

Mesial

2 (1.9%)

2 (1.9%)

0 (0%)

Distal

6 (5.6%)

1 (0.9%)

24 (22.2%)

Aligned

Lingual

Aligned

50 (46.3%)

5 (4.6%)

Lingual

4 (3.7%)

49 (45.4%)

No

Yes

No

49 (45.4%)

3 (2.8%)

Yes

5 (4.6%)

51 (47.2%)

TE D

Contact between the tooth and the canal p=0.727

0 (0%)

SC

Direction of root curvature p=0.624

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12x8.5cm

0 (0%)

ACCEPTED MANUSCRIPT Table IV. Contingency table comparing the responses obtained with 450 basis images and 720 basis images Number of basis images

720 3

2

46 (88.5%)

0 (0%)

3

0 (0%)

6 (11.5%)

Vertical

Direction of root curvature p=0.515

Root position in relation to the canal p=0.065

0 (0%)

0 (0%)

Horizontal

0 (0%)

9 (17.3%)

1 (1.9%)

Mesioangular

0 (0%)

1 (1.9%)

5 (9.6%)

Straight

Mesial

Distal

Straight

64 (58.2%)

5 (4.5%)

6 (5.5%)

Mesial

2 (1.8%)

2 (1.8%)

1 (0.9%)

Distal

6 (5.5%)

0 (0%)

24 (21.8%)

Aligned

Lingual

Aligned

49 (44.5%)

9 (8.2%)

Lingual

2 (1.8%)

50 (45.5%)

No

Yes

No

49 (44.5%)

8 (7.3%)

Yes

4 (3.6%)

49 (44.5%)

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Contact between the tooth and the canal p=0.388

36 (69.2%)

Horizontal Mesioangular

SC

450

Vertical

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Tooth angulation p=1.000

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Number of roots p=1.000

2

ACCEPTED MANUSCRIPT Table V. Comparison of absorbed radiation doses obtained with different protocols (mGy) Voxel (mm)

FOV* (cm)

Basis images**

Mean

Standard deviation

450

23.25

1.61

720

40.00

0.79

450

19.78

2.93

720

29.56

450

23.92

720

38.47

450

16.46

720

29.86

12x8.5

5x5a

12x8.5

5x5a *

1.79 1.10 1.39 0.88

SC

0.2

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0.3

3.48

Doses from different FOV sizes show statistical significant difference. Doses from different numbers of basis images show statistical significant difference. a Corresponds to two exposure.

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**

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Statement of Clinical Relevance

CBCT parameters should be selected based on diagnostic task while attempting to minimize patient exposure. FOV size and basis images do not influence the evaluation of third molars and mandibular canal, whereas smaller voxel improves the assessment

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of their contact.