Korean Journal of Orthodontics最新文献

Objective: To evaluate the ideal anteroposterior position of incisors in lateral smiling profiles with different chin prominences and to relate these positions to nose and chin landmarks based on the perceptions of orthodontists and laypersons.

Methods: A lateral smiling profile image of a female subject was adjusted to create five levels of chin prominence (-6, -3, 0, +3, +6 mm). For each level, the anteroposterior positions of the maxillary incisors were adjusted across five positions (-4, -2, 0, +2, +4 mm). Thirty-six orthodontists and 36 laypersons rated the attractiveness of each profile using a visual analog scale. The maxillary incisor position (U1) was measured relative to the external nose and chin landmarks (E-lines). Differences in perceptions between orthodontists and laypersons were analyzed.

Results: For profiles with 6 and 3 mm chin retrusion, the most favored incisor positions were the 2 mm retrusion and unaltered positions, respectively. For the unaltered chin prominence, orthodontists preferred unaltered incisors, while laypersons favored 2 mm protrusion. Conversely, for 3 and 6 mm chin protrusion, both groups preferred 4 and 2 mm protrusion, respectively. The distance between U1 and the E-line is the most attractive images ranged from 8.5 to 11.5 mm. Based on the regression model, an optimal U1-E-line distance of 8.95 mm was recommended.

Conclusions: The preferred incisor position is influenced by chin prominence, with the incisor position shifting in the same direction as the chin. The U1 E-line can be a useful clinical tool for determining the proper incisor positioning. Esthetic perceptions were generally consistent between orthodontists and laypersons.

Objective: To study the influence of bracket base meshes on shear bond strength and observe them using a scanning electron microscopy (SEM) before and after debonding.

Methods: Ninety brackets were divided into nine groups of 10 samples each: G1-Alexander, G2-Mini Sprint^® Brackets, G3-In-Ovation R CCO, G4-Gemini SL Self-Ligating Bracket, G5-Classic mini 2G Stylus^®, G6-Gemini Metal Brackets, G7-Clarity^TM Advanced, G8-Crystall-Ize^®, and G9-Ceramic Series Flexx 2G^®. Groups G1 to G6 and G7 to G9 consisted of metallic and aesthetic brackets, respectively. Initial photographs of all brackets were taken through SEM at 25X magnification. The brackets were then bonded to premolars using Transbond^TM XT, and a shear bond strength test was conducted after 24 hours using an Instron machine at 1 mm/min. After debonding, the bracket meshes were observed using SEM.

Results: Before bonding, 72.22% of brackets didn't present mesh defects, while 27.77% did. SEM analysis revealed that G4 and G5 presented defects in 100%, G7 in 40%, and G8 in 10%. The average shear bond strength of 9.67 ± 2.84 MPa and 11.21 ± 4.99 MPa were obtained for both metallic and aesthetic brackets, respectively. A Pairwise-Wilcoxon test with Benjamini-Hochberg correction was conducted to determine specific statistical differences between the groups, revealing significant differences based on bracket type and shear bond strength (P < 0.009).

Conclusions: This study suggested that the shape of bracket meshes influenced shear bond strength.

Objective: This study aimed to evaluate the effects of attachment design on maxillary molar distalization and simultaneous expansion during distalization, and the influence of third molars on distalization in the clear aligner technique using the finite element method.

Methods: Six models were created to evaluate three different attachment designs on the second molars. Model I: employed a vertical rectangular attachment; Model II: used a vertical rectangular attachment with the presence of the third molar; Model III: used a combined semi-elliptical attachment; and Model IV: featured an opposed semi-elliptical attachment with buccal and palatal components. Models I through IV focused on distalization. Models V and VI were created by adding expansions to Models III and IV. The displacement amounts, clear aligner deformations, and stress distributions were analyzed using Ansys 19.2.

Results: The presence of a third molar reduced maximum total displacement by 17%. Models I and III demonstrated similar distal displacement and tipping, both of which were more pronounced than in Model IV. Model IV achieved the most parallel tooth movement, with the least distal and buccal tipping and minimal distopalatal rotation. In the comparison of Models V and VI, Model VI exhibited greater distal and buccal displacements and more tipping than Model V.

Conclusions: The presence of a third molar reduced distalization efficiency and increased clear aligner deformation. For both movements, the attachment that provided the most parallel movement showed the least displacement. When selecting attachments, it is essential to consider factors such as tooth rotation, inclination, bone support, and root health.

Objective: The effect of different attachment positions on torque control during the labialization of maxillary lateral incisors with clear aligners was evaluated using finite element analysis.

Methods: Anatomical data acquired through cone-beam computed tomography, combined with the design of 0.625-mm-thick aligners and horizontal attachments, were integrated into the software. Six distinct simulations were generated: (1) attachment-free, (2) labial attachment placed gingivally, (3) labial attachment placed mid-crown, (4) labial attachment placed incisally, (5) palatal attachment, and (6) attachment placed labially and palatally. The evaluation was performed using a default aligner activation of 0.25 mm.

Results: The crown of the lateral incisor demonstrated labial movement, while the root exhibited palatal movement in all models. Group 6 showed the lowest crown and root displacements on both axes, whereas the attachment-free group exhibited the greatest crown movement. The aligner experienced maximum deformation at the incisal edge, with deformation progressively decreasing towards the gingival region. Group 6 demonstrated the least deformation of all groups. The Von Mises stresses in the periodontal ligament (PDL) were most pronounced at the gingival level, with higher values on the palatal side than on the labial side.

Conclusions: The use of attachments, particularly the combination of labial and palatal attachments, enables a more precise labialization process, helping to reduce tipping. Increasing crown movement of the lateral incisor elevates stress within the PDL, with the highest stress observed in the palatal region at the gingival level.

Objective: This study aimed to evaluate bone remodeling in gingival crevicular fluid (GCF) during canine distalization in obese individuals and compare it to that in normal-weight individuals. Additionally, the orthodontic tooth movement rates of obese individuals were measured and compared with those of normal-weight individuals.

Methods: Thirty-six patients (18 obese and 18 normal-weight) aged 12-18 years who were candidates for maxillary first premolar extraction for Angle Class II malocclusion were included in the study. The two groups were formed according to World Health Organization guidelines. A normal-weight group (body mass index [BMI] 16-85%) and an obese group (BMI ≥ 95%). Gingival crevicular fluid samples were collected before, 24 hours after, and on the 7th, 14th, and 21st days after the application of the distalization force. Enzyme-linked immunosorbent assay was used to measure leptin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG) and interleukin-6 (IL-6) levels in GCF samples. In addition to the recorded GCF sampling times, the amount of canine tooth movement was calculated using digital models obtained on the 28th day and 3rd month.

Results: Leptin, RANKL, OPG, and IL-6 levels were significantly higher in the obese group (P < 0.05). The digital model measurements displayed high rates of repeatability (ICC 0.990). The difference in the amount of tooth movement between groups was not statistically significant (P > 0.05).

Conclusions: Although obese and normal-weight individuals showed different biomarker levels during tooth movement, there were no significant differences in the amount of movement.

Objective: Miniscrews are commonly utilized as temporary anchorage devices (TADs) in cases of maxillary protrusion and premolar extraction. This study aimed to investigate the effects and potential side effects of two conventional miniscrew configurations on the maxillary incisors.

Methods: Eighty-two adult patients with maxillary dentoalveolar protrusion who had undergone bilateral first premolar extraction were retrospectively divided into three groups: non-TAD, two posterior miniscrews only (P-TADs), and two anterior and two posterior miniscrews combined (AP-TADs). Cone-beam computed tomography was used to evaluate the maxillary central incisors (U1).

Results: The AP-TADs group had significantly greater U1 intrusion (1.99 ± 2.37 mm, n = 50) and less retroclination (1.70° ± 8.80°) compared to the P-TADs (-0.07 ± 1.65 mm and 9.45° ± 10.68°, n = 60) and non-TAD group (0.30 ± 1.61 mm and 1.91° ± 9.39°, n = 54). However, the AP-TADs group suffered from significantly greater apical root resorption (ARR) of U1 (2.69 ± 1.38 mm) than the P-TADs (1.63 ± 1.46 mm) and non-TAD group (0.89 ± 0.97 mm). Notably, the incidence of grade IV ARR was 16.6% in the AP-TADs group, significantly higher than the rates observed in the P-TADs (6.7%) and non-TAD (1.9%) groups. Multiple regression analysis revealed that after excluding tooth movement factors, the AP-TADs configuration resulted in an additional 0.5 mm of ARR compared with the P-TADs group.

Conclusions: In cases of maxillary protrusion and premolar extraction, the use of combined anterior and posterior miniscrews enhances incisor intrusion and minimizes torque loss of the maxillary incisors. However, this approach results in more severe ARR, likely due to the increased apical movement and composite force exerted.

Objective: To measure and compare the extent of root resorption in the maxillary incisors following microimplant-assisted rapid palatal expansion (MARPE) and to identify risk factors of root resorption after expansion.

Methods: Cone-beam computed tomography images were obtained from a total of 60 patients both before expansion (T1) and 3 to 6 months after expansion (T2). Measurements taken included tooth length, root length, crown length and center of resistance. Resorption length (RL) and resorption length percentage (RLp), resorption volume (RV) and resorption volume percentage (RVp) and the amount of expansion were calculated.

Results: A significant difference in tooth length and volume was observed in both the central and lateral incisors before and after expansion. The resorption index (RL, RLp, RV, RVp) was significantly higher in the central incisors than in the lateral incisor. There was a significant correlation between several factors: age and RLp of the central incisors, the amount of expansion and RVp of the central incisors, tooth length of the central incisors and RL, RLp of the central incisors, root/crown ratio of the central incisors and RL of the central incisors, as well as tooth length of the lateral incisors and the RL of the lateral incisors.

Conclusions: Significant root resorption occurs in maxillary incisors following MARPE, with central incisors root resorption being significantly higher than lateral incisors. Key risk factors for root resorption after MARPE include advanced age, a larger amount of expansion, initial tooth length, and a root/crown ratio.

Objective: Miniscrew-assisted maxillary expansion devices are frequently used for patients with calcified midpalatal sutures. This study aimed to evaluate the effects of two bone-borne maxillary expansion appliances on the cranial and circummaxillary sutures by comparing cone-beam computed tomography (CBCT) images before and after transverse maxillary expansion.

Methods: A total of 81 patients (women = 58, men = 23) were treated with either a C-expander (n = 44) or an ATOZ expander (n = 37). CBCT images were obtained before (T0) and after (T1) maxillary expansion, and the widths of 10 circummaxillary sutures were measured in the sagittal, coronal, and axial planes. The Wilcoxon signed-rank test was used to compare the changes in suture width between the C-expander and ATOZ groups, and statistical significance was set at P < 0.05.

Results: The frontonasal, frontomaxillary, pterygomaxillary, nasomaxillary, internasal, intermaxillary, and midpalatal suture widths increased significantly after maxillary expansion in both the ATOZ and C-expander groups (both P < 0.05). The frontozygomatic, zygomaticomaxillary, and temporozygomatic suture widths decreased in the C-expander group (P < 0.05), whereas the frontozygomatic suture width increased significantly in the ATOZ group (P < 0.05). The width changes of the frontozygomatic, zygomaticomaxillary, temporozygomatic, pterygomaxillary, internasal, intermaxillary, and midpalatal sutures differed significantly between the two groups (P < 0.05).

Conclusions: Both the C- and ATOZ expanders affected the suture width in the naso-maxillo-zygomatic region. The C-expander decreased the circum-zygomatic suture widths, whereas the ATOZ expander widened the frontozygomatic suture with no effect on other circummaxillary sutures.