Effect of voxel size in cone-beam computed tomography on surface area measurements of dehiscences and fenestrations in the lower anterior buccal region

Accuracy of facial skeletal surfaces segmented from CT and CBCT radiographs

The accuracy of three-dimensional (3D) facial skeletal surface models derived from radiographic volumes has not been extensively investigated yet. For this, ten human dry skulls were scanned with two Cone Beam Computed Tomography (CBCT) units, a CT unit, and a highly accurate optical surface scanner that provided the true reference models. Water-filled head shells were used for soft tissue simulation during radiographic imaging. The 3D surface models that were repeatedly segmented from the radiographic volumes through a single-threshold approach were used for reproducibility testing. Additionally, they were compared to the true reference model for trueness measurement. Comparisons were performed through 3D surface approximation techniques, using an iterative closest point algorithm. Differences between surface models were assessed through the calculation of mean absolute distances (MAD) between corresponding surfaces and through visual inspection of facial surface colour-coded distance maps. There was very high reproducibility (approximately 0.07 mm) and trueness (0.12 mm on average, with deviations extending locally to 0.5 mm), and no difference between radiographic scanners or settings. The present findings establish the validity of lower radiation CBCT imaging protocols at a similar level to the conventional CT images, when 3D surface models are required for the assessment of facial morphology.

Long-term bone remodeling of maxillary anterior teeth with post-treatment alveolar bone defect in adult patients with maxillary protrusion: a prospective follow-up study

BACKGROUND

Alveolar bone defects, particularly palatal bone dehiscence (PBD) and labial bone fenestration (LBF), occur frequently as a result of retraction of the maxillary anterior teeth. The study aims to explore the long-term bone remodeling of maxillary anterior teeth in adult patients with post-orthodontic treatment PBD and LBF.

MATERIALS AND METHODS

The study includes 24 adult patients with maxillary protrusion (8 males, 16 females) who were treated with extraction of four first premolars and had alveolar bone defects (PBD or LBF) in maxillary anterior teeth following orthodontic treatment. Cone-beam computed tomography imaging measurements were obtained before (T1), after (T2) orthodontic treatment, and after at least 1-year removable thermoplastic retainer retention (T3). The maxillary anterior teeth with PBD or LBF at T2 were divided into the PBD or LBF groups, respectively. The labial and palatal alveolar bone height (ABH), alveolar bone thickness (ABT), and movement of maxillary anterior teeth were measured during retraction (T2-T1) and retention (T3-T2) periods.

RESULTS

The incidence of PBD and LBF in maxillary anterior teeth significantly increased after orthodontic treatment and decreased during the retention period. In the PBD group, the palatal ABH of all maxillary anterior teeth significantly increased from T1 to T2 but decreased from T2 to T3. The ABT of the maxillary central incisor and canine significantly increased on the palatal side and decreased on the labial side during the retention period. In the LBF group, the labial ABT of the maxillary central incisor at the apical level showed a significant decrease from T1 to T2, followed by an increase from T2 to T3. In both groups, the maxillary central incisor showed significant labial movement, with a relative intrusion during the retention period.

CONCLUSION

For adult patients with maxillary protrusion, the alveolar bone defect of maxillary anterior teeth caused by orthodontic retraction significantly improved during the retention period, indicating good long-term bone remodeling. Our findings suggest that a combination of spontaneous reorientation of maxillary anterior teeth and bone remodeling contributed to alveolar bone covering in these patients.

Appraisal of the Accuracy and Reliability of Cone-Beam Computed Tomography and Three-Dimensional Printing for Volumetric Mandibular Condyle Measurements of a Human Condyle

Background This study aims to evaluate the accuracy of volumetric measurements of three-dimensional (3D)-printed human condyles from cone-beam computed tomography (CBCT) in comparison to physical condyles using a water displacement test. Methodology A sample of 22 dry condyles was separated from the mandibular body by disc, mounted on a base made of casting wax, and scanned using the SCANORA (Scanora 3DX, Soredex, Finland) CBCT scanner. Subsequently, the projection data were reconstructed with the machine-dedicated OnDemand 3D (Cybermed Co., Seoul, Korea). The Standard Tessellation Language file was prepared for 3D printing using chitubox slicing software v1.9.1. Frozen water-washable gray resin was used for 3D printing. All condyles were printed using the same parameters and the same resin. The volumetric measurements were then performed using a customized modified pycnometer based on water volume and weight displacement. Volumetric measures were performed for both the physical human condyles and the 3D-printed replicas and the measurements were then compared. Results The volume of dry condyles using the water displacement method showed an average (±SD) of 1.925 ± 0.40 cm3. However, the volume of 3D-printed replicas using the water displacement method showed an average (±SD) of 2.109 ± 0.40 cm3. The differences in measurements were insignificant (p > 0.05), as revealed by an independent t-test. Conclusions Highly precise, accurate, and reliable CBCT for volumetric mandibular condyle was applied for measurements of a human condyle and 3D-printed replica. The modified pycnometer for volumetric measurements presented an excellent volumetric measure based on a simple water displacement device. The tested modified pycnometer can be applied in volumetric measurements in both 3D-printed and mandibular condyle. For best accuracy, the highest scanning resolution possible should be used. As it directly handles irregularly shaped solid objects in a non-destructive manner with a high level of precision and reliability, this 3D scanning approach may be seen as a superior alternative to the current measurement methods.

Accurate gingival segmentation from 3D images with artificial intelligence: an animal pilot study

BACKGROUND

Gingival phenotype plays an important role in dental diagnosis and treatment planning. Traditionally, determining the gingival phenotype is done by manual probing of the gingival soft tissues, an invasive and time-consuming procedure. This study aims to evaluate the feasibility and accuracy of an alternatively novel, non-invasive technology based on the precise 3-dimension (3D) soft tissue reconstruction from intraoral scanning and cone beam computed tomography (CBCT) to predict the gingival biotype.

METHODS

As a proof-of-concept, Yorkshire pig mandibles were scanned, and the CBCT data were fed into a deep-learning model to reconstruct the teeth and surrounding bone structure in 3D. By overlaying the CBCT scan with the intraoral scans, an accurate superposition was created and used for virtual measurements of the soft tissue thickness. Meanwhile, gingival thicknesses were also measured by a periodontal probe and digital caliper on the buccal and lingual sides at 3 mm apical to the gingival margin of the posterior teeth and compared with the virtual assessment at the same location. The data obtained from virtual and clinical measurements were compared by Wilcoxon matched-pairs signed-rank analysis, while their correlation was determined by Pearson's r value. The Mann-Whitney U test was used for intergroup comparisons of the amount of difference.

RESULTS

Among 108 investigated locations, the clinical and virtual measurements are strongly positively correlated (r = 0.9656, P < 0.0001), and only clinically insignificant differences (0.066 ± 0.223 mm) were observed between the two assessments. There is no difference in the agreement between the virtual and clinical measurements on sexually matured samples (0.087 ± 0.240 mm) and pre-pubertal samples (0.033 ± 0.195 mm). Noticeably, there is a greater agreement between the virtual and clinical measurements at the buccal sites (0.019 ± 0.233 mm) than at the lingual sites (0.116 ± 0.215 mm).

CONCLUSION

In summary, the artificial intelligence-based virtual measurement proposed in this work provides an innovative technique potentially for accurately measuring soft tissue thickness using clinical routine 3D imaging systems, which will aid clinicians in generating a more comprehensive diagnosis with less invasive procedures and, in turn, optimize the treatment plans with more predictable outcomes.

Alveolar bone changes after tooth-borne surgically assisted rapid maxillary expansion: A three-dimensional study

INTRODUCTION

Surgically assisted rapid maxillary expansion (SARME) with a dental-anchorage appliance can induce dental and skeletal complications adjacent to the teeth supporting the device. The purpose of this study was to quantify the dentoskeletal changes observed after SARME using a tooth-borne device.

MATERIALS AND METHODS

Cone beam CT images from 39 patients were compared between the preoperative (T1) and the postoperative period (T2). The mean time to complete the second imaging was 13.8 ± 6.9 months after the SARME. Dental and bone parameters were assessed: the vestibular bone height (BH), the bone thickness (BT), the existence of fenestrations, and the root resorption at the level of first upper premolar (P1) and the first upper molar (M1). The maxillary expansion parameters were also collected.

RESULTS

Both vertical and horizontal vestibular bone loss were observed mainly in the first upper molar sectors: The BT decreased from 0.93 ± 0.50 mm to 0.53 ± 0.51 mm (p < 0.0001) and the BH decreased from 1.84 ± 1.05 mm to 0.93 ± 1.02 mm (p < 0.0001) for tooth #16. The bone loss also affected the first upper premolars but in a more limited manner. Significant fenestrations were observed at the apex of the mesio-vestibular root of teeth #16 and #26. We noted significant root resorption affecting the mesio-, disto-vestibular and palatal roots of tooth #16 (mean reductions of 0.32, 0.35, and 0.55 mm, respectively; p < 0.05), and the palatal root of tooth # 26 (loss of 0.58 mm; p = 0.004). The mean bone expansion was 3.76 mm and 1.41 mm at the premolar and molar levels, respectively (p < 0.0001), while a mean 6.24 mm and 4.23 mm inter-cuspid expansion was noted at the P1 and M1 levels (p < 0.0001).

CONCLUSION

Our results document the vestibular bone changes and low root resorption, mostly in the molar sectors, associated with SARME using dental-anchorage devices.

Effect of hydration on the anatomical form of human dry skulls

In radiology research soft tissues are often simulated on bone specimens using liquid materials such as water, or gel-like materials, such as ballistic gel. This study aimed to test the effect of hydration on the anatomical form of dry craniofacial bone specimens. Sixteen human dry skulls and 16 mandibles were scanned with an industrial scanner in dry conditions and after water embedding. Ten skulls were also embedded for different time periods (5 or 15 min). The subsequent 3D surface models were best-fit superimposed and compared by calculating mean absolute distances between them at various measurement areas. There was a significant, primarily enlargement effect of hydration on the anatomical form of dry skeletal specimens as detected after water embedding for a short time period. The effect was smaller in dry skulls (median 0.20 mm, IQR 0.17 mm) and larger in mandibles (median 0.56 mm, IQR 0.57 mm). The effect of different water embedding times was negligible. Based on the present findings, we suggest to shortly hydrate the skeletal specimens prior to reference model acquisition so that they are comparable to hydrated specimens when liquid materials are used as soft-tissue simulants for various radiologic research purposes.

Bone Remodeling during Orthodontic Movement of Lower Incisors-Narrative Review

The tooth movement in the alveolus is possible due to bone remodeling. This process could be the risk factor for the formation of gingival recessions-the most common side effects of orthodontic therapy. Gingival recessions are found 5.8-11.5% more frequently among the orthodontically treated patients. What is more, anterior mandibular teeth are the ones most prone to gingival recession dehiscences and fenestrations. The aim of this narrative review was to evaluate, based on CBCT (Cone beam computed tomography) scans, the changes in the alveolar bone of lower incisors in adolescent and adult patients after orthodontic tooth movements. From the pool of 108 publications, a total of 15 fulfilled the criteria of this review. Both retrospective and prospective longitudinal studies-using CBCT or CT (Computed Topography) and evaluating alveolar bone changes in mandibular incisors during orthodontic treatment performed before and after teeth movement-were included. In the group of growing patients, either proclination or retroclination of mandibular incisors led to increase of the distance from CEJ (cementoenamel junction) to marginal bone crest. The difference in bone loss was greater on the lingual side of the incisors in both types of tooth movement. The results were similar for adults patients. The thickness of the alveolar bone was reduced after proclination (total bone thickness) among growing and non-growing patients and retraction (lingual and buccal) of lower anterior teeth in the group of growing patients. The only improvement was measured for buccal thickness of mandibular incisor in bimaxillary protrusion patients treated with extraction therapy. The control of retraction movement (more root than crown movement) enhanced preservation on bone height and thickness. In order to minimize possible deterioration and place teeth in the center of alveolus, CBCT monitoring and scrupulous clinical evaluation are recommended.