Yoon Ah Kook

The thickness of alveolar bone at the maxillary canine and premolar teeth in normal occlusion

Purpose The main purpose of this study was to investigate bone thickness on the buccal and palatal aspects of the maxillary canine and premolars using cone-beam computed tomography (CBCT). The differences between left- and right-side measurements and between males and females were also analyzed. Methods The sample consisted of 20 subjects (9 males and 11 females; mean age, 21.9±3.0) selected from the normal occlusion sample data in the Department of Orthodontics, The Catholic University of Korea. The thickness of the buccal and palatal bone walls, perpendicular to the long axis of the root were evaluated at 3 mm and 5 mm apical to cemento-enamel junction (CEJ) and at root apex. Results At the canines and first premolars regions, mean buccal bone thickness of at 3 mm and 5 mm apical to CEJ were less than 2 mm. In contrast, at the second premolar region, mean buccal bone thickness at 3 mm and 5 mm apical from CEJ were greater than 2 mm. Frequency of thick bone wall (≥2 mm) increased from the canine to the second premolar. Conclusions This result should be considered before tooth extraction and planning of rehabilitation in the canine and premolar area of maxilla. Careful preoperative analysis with CBCT may be beneficial to assess local risk factors and to achieve high predictability of success in implant therapy.

En-masse retraction with a preformed nickel-titanium and stainless steel archwire assembly and temporary skeletal anchorage devices without posterior bonding

Objective To evaluate the therapeutic effects of a preformed assembly of nickel-titanium (NiTi) and stainless steel (SS) archwires (preformed C-wire) combined with temporary skeletal anchorage devices (TSADs) as the sole source of anchorage and to compare these effects with those of a SS version of C-wire (conventional C-wire) for en-masse retraction. Methods Thirty-one adult female patients with skeletal Class I or II dentoalveolar protrusion, mild-to-moderate anterior crowding (3.0-6.0 mm), and stable Class I posterior occlusion were divided into conventional (n = 15) and preformed (n = 16) C-wire groups. All subjects underwent first premolar extractions and en-masse retraction with pre-adjusted edgewise anterior brackets, the assigned C-wire, and maxillary C-tubes or C-implants; bonded mesh-tube appliances were used in the mandibular dentition. Differences in pretreatment and post-retraction measurements of skeletal, dental, and soft-tissue cephalometric variables were statistically analyzed. Results Both groups showed full retraction of the maxillary anterior teeth by controlled tipping and space closure without altered posterior occlusion. However, the preformed C-wire group had a shorter retraction period (by 3.2 months). Furthermore, the maxillary molars in this group showed no significant mesialization, mesial tipping, or extrusion; some mesialization and mesial tipping occurred in the conventional C-wire group. Conclusions Preformed C-wires combined with maxillary TSADs enable simultaneous leveling and space closure from the beginning of the treatment without maxillary posterior bonding. This allows for faster treatment of dentoalveolar protrusion without unwanted side effects, when compared with conventional C-wire, evidencing its clinical expediency.

New classification of lingual arch form in normal occlusion using three dimensional virtual models

Objective The purposes of this study were 1) to classify lingual dental arch form types based on the lingual bracket points and 2) to provide a new lingual arch form template based on this classification for clinical application through the analysis of three-dimensional virtual models of normal occlusion sample. Methods Maxillary and mandibular casts of 115 young adults with normal occlusion were scanned in their occluded positions and lingual bracket points were digitized on the virtual models by using Rapidform 2006 software. Sixty-eight cases (dataset 1) were used in K-means cluster analysis to classify arch forms with intercanine, interpremolar and intermolar widths and width/depth ratios as determinants. The best-fit curves of the mean arch forms were generated. The remaining cases (dataset 2) were mapped into the obtained clusters and a multivariate test was performed to assess the differences between the clusters. Results Four-cluster classification demonstrated maximum intercluster distance. Wide, narrow, tapering, and ovoid types were described according to the intercanine and intermolar widths and their best-fit curves were depicted. No significant differences in arch depths existed among the clusters. Strong to moderate correlations were found between maxillary and mandibular arch widths. Conclusions Lingual arch forms have been classified into 4 types based on their anterior and posterior dimensions. A template of the 4 arch forms has been depicted. Three-dimensional analysis of the lingual bracket points provides more accurate identification of arch form and, consequently, archwire selection.

Torque control during lingual anterior retraction without posterior appliances

Objective To evaluate the factors that affect torque control during anterior retraction when utilizing the C-retractor with a palatal miniplate as an exclusive source of anchorage without posterior appliances. Methods The C-retractor was modeled using a 3-dimensional beam element (0.9-mm-diameter stainless-steel wire) attached to mesh bonding pads. Various vertical heights and 2 attachment positions for the lingual anterior retraction hooks (LARHs) were evaluated. A force of 200 g was applied from each side hook of the miniplate to the splinted segment of 6 or 8 anterior teeth. Results During anterior retraction, an increase in the LARH vertical height increased the amount of lingual root torque and intrusion of the incisors. In particular, with increasing vertical height, the tooth displacement pattern changed from controlled tipping to bodily displacement and then to lingual root displacement. The effects were enhanced when the LARH was located between the central and lateral incisors, as compared to when the LARH was located between the lateral incisors and canines. Conclusions Three-dimensional lingual anterior retraction of the 6 or 8 anterior teeth can be accomplished using the palatal miniplate as the only anchorage source. Using LARHs at different heights or positions affects the quality of torque and intrusion.

Evaluation of the facial dimensions of young adult women with a preferred facial appearance

Objective The aim of this study was to evaluate the facial dimensions of young adult women with a preferred facial appearance and compare the results with those from the general population. Methods Twenty-five linear, nine angular, and three area measurements were made and four ratios were calculated using a sample of standardized frontal and lateral photographs of 46 young adult women with a preferred facial appearance (Miss Korea group) and 44 young adult women from the general population (control group). Differences between the two groups were analyzed using multivariate analysis of variance (MANOVA). Results Compared with the control group, the Miss Korea group exhibited a significantly greater facial height, total facial height (TFH; trichion-menton), facial width (tragus right-tragus left), facial depth (tragus-true vertical line), and trichion-nasion/TFH ratio and smaller subnasale-menton/TFH and facial width/TFH ratios. Furthermore, the control group had smaller intercanthal and interpupillary widths. Conclusions The Miss Korea group exhibited longer, wider, and deeper faces compared with those from the general population. Furthermore, the Miss Korea group had larger eyes, longer but less protruded noses, longer and more retruded lower lips and chins, larger lip vermilion areas, and smaller labiomental angles. These results suggest that the latest trends in facial esthetics should be considered during diagnosis and treatment planning for young women with dentofacial abnormalities.

Treatment effects of mandibular total arch distalization using a ramal plate

Objective The purpose of this study was to evaluate treatment effects after distalization of the mandibular dentition using ramal plates through lateral cephalograms. Methods Pre- and post-treatment lateral cephalograms and dental casts of 22 adult patients (11 males and 11 females; mean age, 23.9 ± 5.52 years) who received ramal plates for mandibular molar distalization were analyzed. The treatment effects and amount of distalization of the mandibular molars were calculated and tested for statistical significance. The significance level was set at p < 0.001. Results The mandibular first molar distalization at the crown and root were 2.10 mm (p < 0.001) and 0.81 mm (p = 0.011), respectively. In the evaluation of skeletal variables, there was a significant increase in the Wits appraisal (p < 0.001). In the evaluation of the soft tissue, there was no significant effect on upper lip position, but the lower lips showed a significant retraction of 2.2 mm (p < 0.001). Conclusions The mandibular molars showed a significant amount of distalization accompanied by limited extrusion and mesiobuccal rotation of the crowns. A ramal plate may be a viable device for mandibular total arch distalization in Class III patients who are reluctant to undergo orthognathic surgery.