3.1. Material Preparation
This study was cross-sectional. Direct observation of CBCT images was carried out by three observers in two different with and without artifact reduction technique modes, and data was recorded. A total of 62 extracted human premolars without root fracture were evaluated via direct observation and staining with methylene-blue. Given the study type, minimum sample size in fracture and non-fracture groups was determined as 31 per group (62 samples in total). These teeth had been extracted due to periodontal problems or orthodontic treatments. Teeth were non-randomly selected according to inclusion criteria. In the 31 teeth with fracture that were included, the vertical fracture line created by the Instron machine ascertained the presence of a fracture, and this was confirmed by methylene-blue staining. Absence of a fracture in the 31 samples without fracture was confirmed by methylene-blue staining. Teeth deemed with calcification in root treatment were replaced by other eligible samples. Samples with fracture breaking into two under Instron machine pressure were excluded, and only samples with non-displaced fractures were included.
3.2. Preparation of Samples
Trial group in the present in-vitro study consisted of 62 human premolars with no fracture. Samples were selected irrespective of the patient's age, gender, and reason for extraction. The extracted teeth were placed in the volatile disinfectant solution of 0.5% sodium hypochlorite (Golrang-Tehran-Iran) and their crowns were cut off from the cement-enamel junction (CEJ) using a micro-motor and metal disc to eliminate errors caused by enamel fracture (19). Then, all samples received root treatment and the root crowns were preflared by Gates Glidden number 2 or 3 (Dentsply Maillefer, Ballaigues). All teeth received peripheral filing by 15 to 50 file (Dentsply Maillefer, Ballaigues. Switzerland) and the debris inside canals were removed by rinsing. After preparation, canals were filled by Gutta-Percha (Aria Dent, Tehran, Iran) and sealer (Dentsply Maillefer, Ballaigues. Switzerland). A week later, in preparation for the post space, all teeth were emptied by Pizzo number 2 or 3 (Dentsply Maillefer, Ballaigues. Switzerland) to two-thirds of the root length. Periapical radiographic images confirmed suitability of the post spaces. Prefabricated bronze posts (Nordin, Chaily, Switzerland) were placed in the canals but were not cemented due to the likelihood of cement flow into the fracture line (19).
Each tooth was covered with a 2-3mm layer of red wax (Dentsply, DeTrey, Weybridge, UK), and mounted in separate blocks made from a mixture of gypsum and saw dust (to resemble the jaw trabeculation). This ensured absence of a gap in the root, easy removal of teeth from their blocks, and also avoided disintegration of pieces while creating fractures (8).
Vertical root fractures were created in 31 randomly selected teeth by an Instron machine (Zwcik/roell, GmbH & Co. KG, Germany). This system creates an increasing compressive force on the pin until the fracture sound is heard. Then, this force is immediately cut off according to the diagram on the system monitor. Samples from fracture group that split into two under Instron machine force were excluded and replaced by new eligible samples. As the control group, no fracture was created in the other 31 teeth.
During the study, all samples were kept in a hydrated medium, and removed only during construction of posts, fracturing roots, and preparing images.
3.3. Imaging Method
In preparation for CBCT images, the teeth were randomly divided into 11 groups consisting of 10 of six and one of two teeth. Six gypsum and sawdust blocks were placed on a sample similar to the jaw arch that was made from Putti on the chinrest of CBCT device (Promax3d, planmeca. Helsinki. Finland) and images were taken in two modes, with mild artifact reduction (AR) and without AR (Figure 1).
Figure 1.
Axial view of cone-beam computed tomography (CBCT) without artifact reduction (AR) technique. Metal artifacts are detected in the images
In promax3d system, AR has three options of low, mild and high. A total of 22 exposures were taken (Figure 2). Imaging was carried out in 8 × 8 cm2 field of view (FOV) at a voltage of 74 kvp, with slice thickness of 1mm, voxel size 0.15, and 12 mA, which was adjusted for each sample by the system. Axial, coronal and sagittal planes were analyzed.
Figure 2.
Axial view of cone-beam computed tomography (CBCT) with artifact reduction (AR) technique
3.4. Data Collection
Three maxillofacial radiologists who had no knowledge of the root groups assessed images for presence or absence of root fracture. All observers were blinded regarding all aspects of data gathering. They were able to adjust contrast and brightness of images when necessary with no time restriction. All images were reviewed on LG Flatron W175s with a resolution of 1440 × 90 pixel, and Planmeca Romexis Viwer 3.0.1.R software (Helsinki, Finland). CBCT images were assessed in axial, coronal, and sagittal planes). Observers recorded their answers regarding probability of VRF as a five-option scale as follows:
1) Definitely no fracture
2) There is probably no fracture
3) Uncertainty about presence or absence of a fracture
4) There is probably a fracture
5) There is definitely a fracture
Observers recorded their detection according to this scale.
To apply the gold standard, teeth were removed from gypsum sawdust blocks, and examined for fracture by 1% methylene-blue staining and rinsing.
With a fracture present, the dye penetrated in the line of fracture was visible as a dark blue line on the surface of the root. Thus, presence or absence of vertical root fracture in samples was confirmed.
3.5. Analysis
To calculate the intra-observer coefficient, observers viewed the scanned images and re-identified fractures according to the mentioned five-option scale two weeks later, without knowledge about fractured samples.
Data were analyzed in SPSS for Windows version 16 (SPSS Inc., Released 2007, Chicago, SPSS Inc.)
At first, the observers' diagnostic performance was determined separately (versus the gold standard) in each voxel size and accordingly, diagnostic indices were calculated. These indices included sensitivity, specificity, positive predictive value and negative predictive value. As the observers’ remarks on fracture were based on a five-option scale (including definite or probable presence or absence of fracture, as mentioned before), diagnostic indices could be calculated in two situations; first, considering definite cases only, and second, considering definite and probable cases together. Therefore, the indices included definite sensitivity (number of teeth diagnosed as definite fracture divided by the number of fractured teeth, based on gold standard), total sensitivity (number of teeth diagnosed as definite or probable fracture divided by the number of fractured teeth based on gold standard), definite specificity (number of teeth diagnosed as definite no-fracture divided by the number of intact teeth based on gold standard), total specificity (number of teeth diagnosed as definite or probable no-fracture divided by the number of intact teeth based on gold standard), definite positive predictive value (fractured teeth diagnosed as definite fracture divided by the number of teeth diagnosed as definite fracture), total positive predictive value (number of fractured teeth diagnosed as definite or probable fracture divided by the number of teeth diagnosed as definite or probable fracture), definite negative predictive value (number of intact teeth diagnosed as definite no-fracture divided by the number of teeth diagnosed as definite no-fracture), total negative predictive value (number of intact teeth diagnosed as definite or probable no-fracture divided by the number of teeth diagnosed as definite or probable no-fracture).
To compare the diagnostic efficacy of CBCT with AR versus CBCT without AR technique option, all diagnostic indices (including definite and total sensitivity, specificity and positive and negative predictive values) were compared between two techniques separately. For this purpose, each index was calculated when the radiologist used AR technique or did not; then two groups (each group included results of three radiologists evaluations, with and without AR option) were compared (using U Mann-Whitney test). Also, inter-observer and intra-observer reliabilities were assessed using agreement coefficient.
Definite VRF was considered when the radiolucent line extended from the external border of the tooth to pulp chamber in all three axial, coronal, and sagittal planes. While probable VRF was considered when the line could not be detected in any of the three multiplanar images (axial, coronal or sagittal) or detected in just one of them.
Scientific honesty in assessing the results was observed, care was taken in proper use of equipment, and consideration was given to the welfare of the study team to avoid their discomfort.
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