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This research aimed to compare the estimation error of the root axis using 3-dimensional (3D) tooth models at the midtreatment stage between the whole-surface scan (WSS) and lingual-surface scan (LSS) methods.The sample consisted of 208 teeth (26 each of central incisors, canines, second premolars, and first molars in the maxillary and mandibular dentition) from 13 patients whose pre- and midtreatment intraoral scan and cone-beam computed tomography (CBCT) were available. The 3D tooth models were constructed by merging the intraoral-scan crowns and the CBCT-scan roots obtained at the pretreatment stage. To estimate the root axis at the midtreatment stage, we superimposed the individual 3D tooth models onto the midtreatment intraoral scan obtained by the WSS and LSS methods. The midtreatment CBCT scan was used as the gold standard to determine the real root axis. The estimated root axis in terms of mesiodistal angulation and buccolingual inclination was measured in the WSS and LSS methods, and statistical analysis was performed.The estimation errors of the mesiodistal angulation and buccolingual inclination were 2.0° in both methods. The LSS method demonstrated a statistically larger but clinically insignificant estimation error than the WSS method in the mandibular canine (mesiodistal angulation, 1.95° vs 1.62°) and the total tested teeth (mesiodistal angulation, 1.40° vs 1.29°; buccolingual inclination, 1.51° vs 1.41°).Because the estimation errors of the root axis angle using the 3D tooth model by the WSS and LSS methods were within the clinically acceptable range, the root axis can be estimated by both methods.

The purpose of this study was to investigate the registration accuracy between intraoral-scanned crowns and cone-beam computed tomography (CBCT)-scanned crowns in various registration methods.The samples consisted of 18 Korean adult patients, whose pretreatment intraoral scans and CBCT images were available. A 3-dimensional (3D) dental model was fabricated using a TRIOS intraoral scanner (3Shape, Copenhagen, Denmark) and the OrthoAnalyzer program (version 1.7.1.4; 3Shape). After the CBCT image was taken, 3D volume rendering was performed to fabricate a 3D dental model using InVivo5 software (version 5.1; Anatomage, San Jose, Calif). Registration of the 3D dental crowns made from intraoral- and CBCT-scanned images was performed with Rapidform 2006 software (Inus Technology, Seoul, Korea) by a single operator. According to registration methods, 3 groups were established: individual-arch-total-registration group, individual-arch-segment-registration group, and bimaxillary-arch-centric-occlusion-registration group (n = 18 per group). After the amounts of shell/shell deviation were obtained, the mixed model analysis of variance and Bonferroni correction were performed.Although there was no significant difference in the registration accuracy between the individual-arch-total-registration group and individual-arch-segment-registration group, the bimaxillary-arch-centric-occlusion-registration group exhibited the lowest registration accuracy (maxillary and mandibular teeth, all 0.21 mm in the individual-arch-total-registration group; all 0.20 mm in the individual-arch-segment-registration group vs 0.26 mm and 0.25 mm in the bimaxillary-arch-centric-occlusion-registration group; P 0.001). Color-coded visualization charts exhibited that most red spots were localized on the occlusal surface of the posterior teeth in all 3 groups.When considering the registration accuracy and convenience of the process, the individual-arch-total-registration method can be regarded as an efficient tool when integrating CBCT-scanned crown and intraoral-scanned crown.

Introduction The purpose of this study was to assess the reproducibility of in-vivo and ex-vivo scans using an intraoral scanner. Methods Twenty adults with no missing teeth except for third molars were included in the study. Alginate impressions were taken, and plaster models were made from the impressions. Each subject underwent full-arch intraoral scanning twice with a TRIOS scanner (3Shape, Copenhagen, Denmark) at an interval of 2 weeks, and, the plaster models were scanned at the same interval with the same scanner. The first images of each scan were superimposed on the second scanned images using surface-based registration. In each case, the differences between the 2 scanned images were evaluated with color mapping. The reproducibility between the in-vivo and ex-vivo scans was compared using independent t tests and Bland-Altman analysis. Results The discrepancies between the first and second images were greater in the posterior than in the anterior regions for both the in-vivo and ex-vivo scans. Average surface differences between the first and second images were greater for the in-vivo scans (0.04 mm) than for the ex-vivo scans (0.02 mm). The Bland-Altman plots showed that the reproducibility of both scans was within the limits of agreement. Conclusions The reproducibility of in-vivo scanning was comparable with ex-vivo scanning, although it showed a slight difference (0.02 mm) compared with ex-vivo scanning.

Introduction The purpose of this study was to examine changes in registration accuracy after including occlusal surface and incisal edge areas in addition to the buccal surface when integrating laser-scanned and maxillofacial cone-beam computed tomography (CBCT) dental images. Methods CBCT scans and maxillary dental casts were obtained from 30 patients. Three methods were used to integrate the images: R1, only the buccal and labial surfaces were used; R2, the incisal edges of the anterior teeth and the buccal and distal marginal ridges of the second molars were used; and R3, labial surfaces, including incisal edges of anterior teeth, and buccal surfaces, including buccal and distal marginal ridges of the second molars, were used. Differences between the 2 images were evaluated by color-mapping methods and average surface distances by measuring the 3-dimensional Euclidean distances between the surface points on the 2 images. Results The R1 method showed more discrepancies between the laser-scanned and CBCT images than did the other methods. The R2 method did not show a significant difference in registration accuracy compared with the R3 method. Conclusions The results of this study indicate that accuracy when integrating laser-scanned dental images into maxillofacial CBCT images can be increased by including occlusal surface and incisal edge areas as registration areas.

Introduction Our objective was to investigate the dimensional accuracy of digital dental models obtained from the cone-beam computed tomography (CBCT) scans of alginate impressions according to the time elapsed after the impressions were taken. Methods Alginate impressions were obtained of 20 adults using 2 alginate materials: Alginoplast (Heraeus Kulzer, Hanau, Germany) and Cavex (Cavex Holland, Haarlem, The Netherlands). These impressions were stored in wet conditions and scanned by CBCT immediately after impression-taking and after storage times of 12, 24, 36, 48, 60, and 72 hours. After reconstruction of the 3-dimensional digital dental models, the models were measured, and the data were analyzed to determine the dimensional changes according to the time elapsed. The changes within the measurement error were regarded as clinically acceptable in this study. Results The measurement errors ranged from 0.27 to 0.29 mm in the digital dental models obtained from CBCT scans of the alginate impressions. All measurements showed decreasing accuracy with greater elapsed time after the impressions were taken. Changes above the measurement error occurred at 24 and 36 hours for Cavex and Alginoplast, respectively. Conclusions Digital dental models can be obtained from CBCT scans of alginate impressions without sending them to a remote laboratory. However, the impressions need to be scanned within 24 hours; otherwise, dimensional changes lead to errors that exceed the error of measurement.

Root damage is a significant complication of orthodontic miniscrew implant placement. Although root damage is rare, its proper management should be clearly understood by practitioners. This article reports the iatrogenic root perforation of a mandibular lateral incisor caused by the placement of a miniscrew. Despite a large radiolucent area caused by chronic apical periodontitis, the perforation was successfully repaired by using a recently developed material, mineral trioxide aggregate. The treatment, clinical implications, and clinical guidelines for preventing root damage during miniscrew placement in orthodontic practice are discussed.

Introduction: The esthetic impact of the soft-tissue profile might play a major role in deciding on premolar extraction or nonextraction treatment, particularly in borderline patients. The purpose of this study was to compare the esthetic impact of extraction and nonextraction therapy on Korean patients. Methods: Panels of 50 dentists and 50 laypersons evaluated randomly presented pretreatment and posttreatment soft-tissue profiles of 50 extraction and 50 nonextraction patients. As subjects in this study, borderline patients were selected based on their initial diagnostic records. Two panels were asked to compare the pretreatment and posttreatment profile tracings and to quantify their perceptions of the esthetic impact of treatment change using a visual analog scale. Results: Premolar extraction patients showed greater improvement in facial profile compared with nonextraction patients, regardless of the panel. Based on the results of regression analysis to determine the degree of lip protrusion at which the retraction that commonly follows premolar extraction would be needed, the intersection was about 3.0 mm behind the Ricketts’ E-line; this is far behind the Korean norm. Conclusions: The results indicate that premolar extraction is more beneficial than nonextraction treatment in terms of facial profile improvement in Korean borderline patients.

Introduction: In this study, we evaluated errors introduced into the interpretation of facial asymmetry on posteroanterior (PA) cephalograms due to malpositioning of the x-ray emitter focal spot. We tested the hypothesis that horizontal displacements of the emitter from its ideal position would produce systematic displacements of skull landmarks that could be fully accounted for by the rules of projective geometry alone. Methods: A representative dry skull with 22 metal markers was used to generate a series of PA images from different emitter positions by using a fully calibrated stereo cephalometer. Empirical measurements of the resulting cephalograms were compared with mathematical predictions based solely on geometric rules. The empirical measurements matched the mathematical predictions within the limits of measurement error (x= 0.23 mm), thus supporting the hypothesis. Based upon this finding, we generated a completely symmetrical mathematical skull and calculated the expected errors for focal spots of several different magnitudes. Quantitative data were computed for focal spot displacements of different magnitudes. Results and Conclusions: Misalignment of the x-ray emitter focal spot introduces systematic errors into the interpretation of facial asymmetry on PA cephalograms. For misalignments of less than 20 mm, the effect is small in individual cases. However, misalignments as small as 10 mm can introduce spurious statistical findings of significant asymmetry when mean values for large groups of PA images are evaluated.

Although posterior tooth intrusion in an adult patient is a difficult procedure, it can be achieved without extruding the adjacent teeth by performing a corticotomy and using magnets. In carrying out this procedure on 2 adult patients whose molars had overerupted due to the early loss of antagonists, tooth movement was rapidly achieved without discomfort or side effects.

Introduction The purposes of this study were to determine bone density at various orthodontic implant sites and compare them according to depth and area (anterior and posterior, buccal and lingual, and maxilla and mandible). Methods Maxillofacial computed tomography scan data were obtained from 30 adults with normal occlusion. Bone density was recorded in Hounsfield units with simulated placement of miniscrews with the V-Implant program (CyberMed, Seoul, Korea). Bone density was measured to a depth of 6 mm at 1-mm intervals in 60 interdental areas (30 in the maxilla, 30 in the mandible), and mean bone density was calculated at each site. Results Bone density tended to decrease with increasing depth, particularly in the posterior area. Mean bone density showed a progressive increase from posterior to anterior except for the mandibular buccal side, which had no significant differences. A comparison of the mean bone densities between the buccal and lingual sides in the mandible showed that the lingual side had higher values in the anterior area and vice versa in the posterior area. On the other hand, there were no distinct differences between the buccal and lingual sides in the maxilla. A comparison of the mean bone densities between the maxilla and the mandible showed higher values in the mandible, and these differences were more significant on the buccal side of the posterior. Conclusions The differences in bone densities according to depth and area should be considered when selecting and placing miniscrew implants for orthodontic anchorage.

Introduction The purposes of this study were to determine bone density at various orthodontic implant sites and compare them according to depth and area (anterior and posterior, buccal and lingual, and maxilla and mandible). Methods Maxillofacial computed tomography scan data were obtained from 30 adults with normal occlusion. Bone density was recorded in Hounsfield units with simulated placement of miniscrews with the V-Implant program (CyberMed, Seoul, Korea). Bone density was measured to a depth of 6 mm at 1-mm intervals in 60 interdental areas (30 in the maxilla, 30 in the mandible), and mean bone density was calculated at each site. Results Bone density tended to decrease with increasing depth, particularly in the posterior area. Mean bone density showed a progressive increase from posterior to anterior except for the mandibular buccal side, which had no significant differences. A comparison of the mean bone densities between the buccal and lingual sides in the mandible showed that the lingual side had higher values in the anterior area and vice versa in the posterior area. On the other hand, there were no distinct differences between the buccal and lingual sides in the maxilla. A comparison of the mean bone densities between the maxilla and the mandible showed higher values in the mandible, and these differences were more significant on the buccal side of the posterior. Conclusions The differences in bone densities according to depth and area should be considered when selecting and placing miniscrew implants for orthodontic anchorage.

Introduction: The purpose of this study was to investigate factors affecting lip-line canting by using musculoskeletal analyses. Methods: Fifty-six adults with lip-line canting were selected as subjects. They were divided into 3 groups according to the changes of lip line during smiling: increasing (group I), decreasing (group D), and minimal (group M). Lip-line canting at rest was correlated to craniofacial morphology and muscular activity: Regarding craniofacial morphology, various craniofacial measurements in lateral and frontal cephalograms were used, including inclination of the tongue blade placed across both first molars. The zygomaticus major was the focus of the measurement of muscular activity affecting lip-line canting, and its activity during smiling was evaluated by using a needle electrode. Results: In group I, lip-line canting at rest showed a significant correlation with the right-left (R/L) difference of muscular activity, but no significant correlation with the measurements of craniofacial morphology. In group D, lip-line canting showed a positive correlation with the measurements of craniofacial morphology, such as the inclination of the tongue blade, and a negative correlation with the R/L difference of muscular activity. In group M, lip-line canting showed no significant correlation with the R/L difference of muscular activity, but a significant correlation with inclination of the tongue blade. Conclusions: The results indicate that lip-line canting is caused by craniofacial morphology when the change of lip-line canting during smiling is minimal, whereas lip-line canting is affected by the R/L difference of muscular activity in addition to craniofacial morphology when the cant of lip line markedly changes during smiling. The findings suggest that the cause of lip-line canting can be identified easily by the change of canting during smiling, without complicated musculoskeletal analyses.