Chris H. Chang
How to Learn Ortho
In June, I was invited by Invisalign Singapore to participate in a panel discussion session as one of the three key speakers. To prepare for this, ten questions were sent to us and we were asked to return our replies to the organizer. On the night before the session, I arrived in Singapore, and the moderator, Gigi, met me and told me that my responses were too brief compared to the other two speakers’, which were all well-written paragraphs, and she hoped that I could add some supplementary details. This got me a little nervous, especially since what I had written down was basically all I wanted to and had to say! Although a teleprompter had been prepared to remind us of what we had written, I was skeptical about whether this was a good idea or not. Despite Gigi’s best efforts to teach an old dog new tricks, I decided to stick to my way, made some minor changes and additions to my original draft, and Shufen, my trusted right and left hand, and wife, printed the draft out so I could take it with me on stage. Phew!
As it turned out, the teleprompter monitor was too far away for us to clearly decipher all the words. Even our youthful and exuberant moderator, Gigi, had difficulty reading the text properly off the monitor. In the end, those nice, short and sweet, one-sentence answers of mine came to be the most suitable form of response in an event like this…
Non-Extraction Treatment with Bite Turbo for Pseudo-Class III Malocclusion in Adult
Daisy T. Lin, Lexie Y. Lin, Chris H. Chang, W. Eugene Roberts
Introduction: A 42-year-old female presented with chief complaints of protruded chin, crowded anterior teeth, and poor smile esthetics.
Diagnosis: Cephalometric analysis showed a skeletal Class III tendency (SNA, 80˚; SNB, 83˚; ANB, -1˚) with normal mandibular plane angle (SN-MP, 38˚). An intraoral assessment revealed end-on Class III malocclusion on the left side with anterior crossbite (UR1, UR2, and UL1), and the lower midline was deviated 0.5 mm to the right. Mild crowding was present in the upper and lower anterior dentition. The Discrepancy Index (DI) was 24.
Treatment: A Damon® system appliance with passive self-ligating brackets was applied to correct the dental malocclusion. Posterior and anterior bite turbos were used to correct the anterior crossbite. Interproximal reduction (IPR) was used to relieve crowding. Space closing and midline correction were also accomplished with elastics. The active treatment time was 18 months. The dentition was aligned, and all spaces created by IPR were closed.
Results: Retraction of the lower anterior segment and lower lip was achieved to improve the profile. After 18 months of active treatment, this pseudo-Class III malocclusion was corrected to an excellent Cast-Radiograph Evaluation (CRE) of 10 points and a Pink and White esthetic score of 6. No root resorption nor periodontal problems were noted.
Conclusion: This case report demonstrates the use of a passive self-ligating appliances to resolve pseudo-Class III malocclusion in an adult patient without the intervention of orthognathic surgery. (J Digital Orthod 2023;71:4-21)
Key words: Skeletal Class III, non-surgical treatment, anterior crossbite, torque selection, bite turbos, interproximal reduction
Insertion Torque and Success of Extra-Alveolar Mandibular Buccal Shelf Miniscrews for Self-Ligation Mechanics
Lexie Y. Lin, Chris H. Chang, W. Eugene Roberts
Objectives: 1. To assess the correlation between insertion torque and the success rate of miniscrews inserted in mandibular buccal shelf (MBS) region, and 2. to evaluate the impact of the cortical bone thickness, length of endosseous engagement, insertion angle and surface angle on the insertion torque of MBS miniscrews.
Material and Methods: 128 stainless steel (SS) 2x12-mm MBS miniscrews were placed bilaterally in 64 consecutive patients (24 males and 40 females; mean age 19.5±5 years) and loaded with 10-14 oz (283-397 g) immediately. Insertion torque values were compared between failure and success groups at an interval of six months. Cortical bone thickness, length of endosseous engagement, insertion angle, and surface angle were measured blindly through cone beam computed tomography (CBCT) images.
Results: The overall success rate was 89.1%. The insertion torque value was lower in the failure (16.1±7.0 Ncm), compared to the success group (20.1±6.3 Ncm). The success rate was directly related to torque values; however, the t test failed to show any statistical significance. Cortical bone thickness and insertion angle revealed significant positive correlations with insertion torque, but only on the left side. Length of endosseous engagement and surface angle had no significant effect on the insertion torque value.
Conclusions: MBS is a region with relatively dense bone quality, where a relatively high insertion torque of the miniscrew is guaranteed compared to inter-radicular miniscrews. Therefore, primary stability of MBS miniscrews is adequate for ensuring success as orthodontic anchorage units. (J Digital Orthod 2023;71:26-39)
Key words: Miniscrews, insertion torque, primary stability, success rate, extra-alveolar orthodontic anchorage, mandibular buccal shelf (MBS)
Surgical Procedures, Mechanics, and Problems in Recovering 51 Impacted Maxillary Canines for 46 Patients with the OBS-3D Lever Arm Appliance
Chris H. Chang, Eric Hsu, W. Eugene Roberts
Objective: Assess recovery for consecutive impacted maxillary canines (I-U3s).
Material and Methods: Based on three-dimensional (3D) imaging, 51 I-U3s were recovered from 46 patients: 11 male, 35 female, mean age 16.5 years (range 10-36 yr). Orthodontics prepared a path for movement of the I-U3s as needed. Minimally invasive surgery uncovered the I-U3s and removed bone to the level of CEJ. 3D anchorage was provided with a 2 mm diameter stainless steel (SS) OrthoBoneScrew® (OBS). A rectangular slot secured a custom SS wire segment (OBS-3D lever arm) to align the I-U3.
Results: Impaction locations were according to side (22 right, 29 left), and surface (32 labial, 19 palatal). I-U3s were optimally aligned in an average of 11.7 months (M), but six more severe labial impactions required up to 17M, and six complete transpositions required 27-30M. Moderate root resorption (<2 mm) on the adjacent lateral incisor was noted for four I-U3s (3 labial, 1 lingual). Gingival recession affected 19 recovered canines (11 labial, 8 palatal); all were moderate (Miller Class I) except for one severe problem (Miller Class III).
Conclusions: The OBS-3D lever arm is a biomechanic system that enhances the probability of success by controlling treatment duration and complications. Root resorption on adjacent lateral incisors is best avoided by not bonding a bracket on them during the recovery process. (Reprint from J Digital Orthod 2020;59:24-33) (J Digital Orthod 2023;71:46-55)
Key words: Maxillary canine, impaction, transposition, bone screw, 3D lever arm, gingival recession, root resorption