The aim of this study was to evaluate the influence of changes in maxillomandibular positioning during cone beam computed tomography (CBCT) imaging on the planning of dental implants. Ten skulls were marked bilaterally with metal spheres in four regions: incisors, canine, premolars, and molars. CBCT scans were obtained in seven positions: standard position (SP), displacements of 10° and 20° above and below the SP, and lateral displacements of 10° and 20° from the SP. Subsequently, bilateral measurements of the height and width of the maxilla and mandible were performed on all images. The results showed that the position with a displacement of 20° above the SP presented the greatest differences in the measurements of bone height and width. In the bilateral comparisons, the maxillary bone width showed the greatest differences, especially for the regions of the premolars and molars. It is concluded that alterations of positioning during the acquisition of CBCT images can lead to alterations in the measurements of bone height and width, which may result in errors in implant planning and cause damage to anatomical structures.
Since the concept of osseointegration was introduced, dental implants have been demonstrated to be a successful treatment for the replacement of absent teeth, representing one of the greatest advancements in dentistry in terms of oral rehabilitation. For the correct planning of implants, it is necessary to use complementary methods to examine the quantity and quality of the remaining bone to establish the ideal conditions for rehabilitation in each case.
Panoramic and peri-apical X-rays are complementary resources that are frequently used for the planning of dental implants. However, when using panoramic X-rays, it is necessary to perform corrections related to the enlargements produced by the machinery. Furthermore, distortions are inherent in the panoramic technique and may also result from changes in the positioning of the head of the patient, resulting in errors in the measurements. An alternative method to improve the interpretation of images is the use of conventional radiographic examination in association with computed tomography (CT).
At present, dentistry relies on the specific tomographic examination of the maxillary–mandibular region. Cone beam CT (CBCT) is widely used to guarantee the best preoperative planning for dental implants. This new technology provides a three-dimensional image of the mineralized maxillofacial tissues with minimum distortion.
Measurements carried out on CBCT images have been shown not to present a significant difference from those obtained directly from the anatomical objects, demonstrating the usefulness of these images for the planning of implants. However, to ensure that the linear measurements are reliable, it is important that all of the image acquisition protocols are followed carefully. Alterations in the positioning of the patient during the acquisition of radiographic examinations can cause distortions that will lead to planning mistakes, and consequently to failures in the treatments.
Numerous articles have highlighted the problems caused by the incorrect positioning of patients while obtaining panoramic radiographs, especially those that are to be used for implant planning. Changes in aspects such as the configuration of the dental arch and distortions in the inclination of a tooth can arise, and errors in the linear measurements for preoperative planning can occur. Though the CBCT is the examination method that is most frequently indicated for the planning of osseointegrated implants, few studies have investigated the real effects of the incorrect positioning of the patient during image acquisition or the influence of positioning variations on the measurement of the height and width of the remaining alveolar bone. Therefore, the objective of the present study was to evaluate the influence of maxillary–mandibular positioning during the acquisition of images by CBCT for the preoperative planning of dental implants.
Materials and methods
Ten dry, fully edentulous skulls were used. Skulls that presented bone openings and/or perforations, fractures, maxillary–mandibular bone injuries, or unscarred alveolar rims were excluded from the sample.
The skulls included in this study were classified according to the methodology proposed by Cawood and Howell. Based on this study, the skulls were classified with scores of III to VI.
For each skull, the regions of the incisors (I), canine (C), premolars (PM), and molars (M) were marked bilaterally with metal spheres. These spheres were fixed on the rim using a layer of red wax. In the maxilla, the incisor region was defined 0.5 cm distal to the anterior nasal spine, the canine was defined at the longitudinal centre of the canine cavity, the premolar was defined 0.5 cm distal to the canine cavity, and the molars were defined 1 cm distal to the premolar region. In the mandible, the incisor region was defined 0.5 cm distal to the sagittal medium plane, the canine was defined 1 cm distal to the sagittal medium plane, the premolar was defined as the height of the mental foramen, and the molars were defined 1 cm distal to the premolar region.
To evaluate the influence of the superior–inferior and side displacement of the head of the patient on the measurements that are used for implant planning, a standardized ‘positioner’ was developed (patent registered; No. 020110074053), which allowed the positioning of the skulls in different positions. The positioner is made of acrylic plates to avoid interference with the image. It has coupled transferors that allow the standardized angular adjustment of the positions and an external box (also made of acrylic) that simulates soft tissue and reduces the radiation ( Fig. 1 ).
The images were acquired by CBCT using an I-Cat scanner (Imaging Sciences International, Hatfield, PA, USA). The following protocol was established for all the acquisitions performed in this study: 26.9 s, 0.25 mm voxel, and HiRe (high resolution). The field of view (FOV) was standardized individually in accordance with the extension, established as 6 cm for the skulls in standard position and 10 cm for those with inclinations.
For evaluation of the influence of the superior–inferior dislocation, five image acquisitions were carried out. The first was acquired on an occlusal plane parallel to the horizontal plane, and the image was designated as the standard position (SP). Two images were acquired with the skull rotated superiorly by 10° (P10+) and 20° (P20+) in relation to the horizontal plane. Two last acquisitions were taken with the skull rotated inferiorly at the same angles, designated as P10− and P20−, respectively.
To evaluate the influence of the side inclination of the head, two more acquisitions were carried out with the long longitudinal axis of the skull inclined laterally at angles of 10° and 20°. These positions were designated as PL10 and PL20, respectively. The inclinations were carried out in a standardized way for the right side, chosen randomly.
Axial and orthoradial reformatting were performed using the program XoranCat, version 3.1.62 (Xoran Technologies, Ann Arbor, MI, USA) for the images with the correct positioning and those that were intentionally modified. Subsequently, orthoradial slices were obtained with a thickness of 1 mm and a spacing of 1 mm between them.
On the image with the most central visualization of the radiopaque marker (most clear image) for each studied region, a line was defined passing through the centre of the bone, equidistant from the vestibular and lingual cortexes. This was referred to as the so-called bone profile line (BPL). With this line taken as the base, representing the point and angle of insertion of the implant, vertical and horizontal measurements were carried out, designated as the implant bone height (IBH) and the bone edge width (BEW), respectively ( Fig. 2 ).
For the maxilla, the IBH was parallel to the BPL, spanning from the alveolar rim to the floor of the nasal cavity, to the incisor and canine regions. For the premolar and molar regions, the upper limit was the floor of the maxillary sinus. For the mandible, the IBH was parallel to the BPL, spanning from the alveolar rim to the internal outline of the basilar cortex of the mandible, to the incisor and canine regions. For the premolar region, the lower limit was the superior outline of the mental foramen, and for the region of molars, the limit was the superior wall of the mandible channel.
For the maxilla, the BEW was perpendicular to the BPL, spanning between the external cortex to half the distance of the IBH for each of the regions evaluated. For the mandible, the BEW, as for the maxilla, was perpendicular to the BPL, spanning between the external cortex to half the distance of the IBH for the incisor and canine regions. For the premolar region, this measurement was obtained at the height of the superior outline of the mental foramen, and for the region of molars, the measurement was taken at the height of the superior wall of the mandible channel.
All linear measurements were performed digitally on a single computer using XoranCat, by a single investigator who is a radiologist experienced with CT images based on CBCT. These measurements were performed twice at an interval of 30 days between measurements to calculate the intra-observer error.
For comparison of the values of bone height and width in the different tomographic positions, the Friedman test was used for each of the studied regions. The Wilcoxon test was used to evaluate the two-by-two crossings in the regions that showed a significant difference according to the Friedman test. The same statistical procedure was used for comparisons between the right and left sides for each region studied and in all the tested positions. The level of significance was set at 5% ( P ≤ 0.05). Statistical analyses were carried out using SPSS (Statistical Package for the Social Sciences) version 15.0 (SPSS Inc., Chicago, IL, USA).
The intra-observer error was 0.03. The values of bone height and width, when the Friedman and Wilcoxon tests were applied, showed significant differences for some of the regions studied. For the maxillary bone height, only the regions of the left canine, right and left premolars, and right molars were statistically significant. Regarding the maxillary bone width, the regions that presented significant differences were the left incisor and the left molars.
When the mandible measurements were evaluated, it was possible to observe significant differences for the following regions: the left canine and both the left and right molars for the values of bone height, and the right and left premolars and right and left molars for the values of bone width.
The percentage difference between the means of the values for bone height and width obtained from the SP are presented and compared with the other positions in Tables 1 and 2 . Positive percentage values indicate that the tested positions presented means that were greater than those obtained in the SP. Negative percentage values indicate that the tested positions presented means that were less than those obtained in the SP.
|P10+||−1.60||1.75||1.54||−3.12||13.75 a||28.22 a||18.97 a||10.21|
|P20+||−0.06||2||5.12||15.23 a||32.48 a||35.89 a||21.31 a||27.32|