Periodontics and Orthodontics: Low Forces, Expansion, Protraction and Control of Gingival Recession

Drs. Kuo PJ, Lin JJ, Chang NNS, Roberts WE.

Abstract

Background: The periodontal aspects of orthodontics are reviewed with an emphasis on arch expansion and management of crowding in the lower anterior segment.

Gingival Recession: Gingival biotype (width of keratinized tissue) and bone morphotype (thickness of labial bone) are the critical diagnostic factors for prevention and treatment of gingival recession. Optimal post-treatment conditions are: 1. dentition positioned in the center of the alveolar ridge, 2. axial loading, 3. circumferential bone support 1–2mm below the cementoenamel junction (CEJ), and 4. alveolar bone at least 1mm thick on the labial and lingual surfaces of the root.

Arch Expansion: For non-extraction treatment of crowding, increasing arch width helps control labial tipping of the incisors. Recent animal studies reveal that very low archwire force (5cN or g-force), interacting with the resistance cheeks and lips, results in moment that produces buccal translation of molars and the alveolar process. These data help explain the mechanism of slow arch expansion with passive self-ligating (PSL) brackets and small diameter copper nickel titanium (CuNiTi) archwires.

Gingival Grafting: Gingival grafts are not indicated for moderate recession problems related to poor alignment that can be corrected with orthodontics. Free gingival grafts can prevent further recession but combined soft tissue and bone grafts with enamel matrix derivative are required to restore the periodontium. Periodontal grafts can be performed before, during or after orthodontics.

Conclusion: Very low force is necessary for expansion of the alveolar process. Prospective surgical augmentation is indicated if tooth movement poses a signi cant risk for gingival recession. Prevention is preferred over surgical intervention. (J Digital Orthod 2018;52:4-19)

Key words: Gingival biotype, bone morphotype, free gingival graft, combined soft and hard tissue graft, very low forces, archwire expansion, prevention, gingival recession
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Asymmetric Oligodontia and Acquired Class IlI Malocclusion: Space Management and Site Development for an Implant-Supported Prosthesis

Drs. Cheng J, Huang C, Chang CH, Roberts WE.

Abstract

History: A 26-year-old male presented with a severe, asymmetric Class III, partially edentulous malocclusion that was associated with decreased facial height due to a midface de ciency. The chief complaints were poor masticatory function and compromised dentofacial esthetics.

Diagnosis & Etiology: A decreased vertical dimension of occlusion (VDO) was associated a deep overbite (8mm), deviated maxillary dental midline (3.5mm to the right), skeletal Class lll (ANB -5 ̊), asymmetric absence of six permanent teeth (UR4, UR5, UL5, LR4, LR5, and LL5), and two retained deciduous teeth. The probable etiology for the anterior crossbite was ectopic eruption to the palatal of the upper central incisor(s). Severe deepbite re ected the absence of multiple posterior teeth, and the upper midline deviation was due to the loss of both upper premolars on the right side. The patient was a good candidate for camou age treatment because in centric relation (CR ) the facial pro le was acceptable, molars were near Class I, and the incisors occluded in an end-to-end relationship.

Treatment: The upper deciduous lateral incisor was extracted and the space was closed. A full xed appliance was bonded on all permanent teeth as well as the lower right deciduous second molar. Space was created in the UR4 area for an implant-supported prosthesis (ISP). The anterior crossbite was corrected by bonding bite turbos on the posterior teeth, placing an open coil spring in the UR4 area, and utilizing Class lll intermaxillary elastics. In the 29th month of treatment, the UR4 implant was placed, and all xed appliance were removed when the ISP was delivered. Retention was a lower xed 3-3, and clear overlay retainers in both arches.

Outcomes:Following 33 months of interdisciplinary treatment, this difficult malocclusion, with a Discrepancy Index of 66 points, was treated to a Cast-Radiograph Evaluation score of 15 points and a Pink and White esthetic score of 4 points. The patient was very pleased with the treatment outcome. (J Digital Orthod 2018;52:24-46)

Key words: Multiple missing teeth, oligodontia, skeletal Class lll pattern, Class lll molar relationship, dentofacial asymmetry, asymmetric mechanics, interdisciplinary treatment, open coil spring, bite turbos, Class lll intermaxillary elastics, implant site development, 2B-3D rule
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Skeletal Class ll Malocclusion with Convex Profile, Horizontal Impaction and Gummy Smile: Substituting Third for Second Molars

Drs. Cheng J, Lee A, Chang CH, Roberts WE.

Abstract

History: A 25-year-old female sought orthodontic consultation to evaluate the poor esthetics of her maxillary anterior dentition.

Diagnosis: The patient presented with a convex facial pro le (24 ̊), increased lower facial height (58%), protrusive lips (4mm/5mm to the E-line), maxillary incisors extruded to the occlusal plane, deep bite (4mm), Class II occlusion (full cusp on the right, end-on on the left), and a maxillary dental midline shifted 3mm to the left. Upper incisor display was irregular, the smile arc was not visible, and there were unesthetic exostoses underlying the maxillary anterior gingiva. Cephalometrics revealed a protrusive maxilla (SNA 89 ̊), intermaxillary discrepancy (ANB 8 ̊), and a high mandibular plane angle (38 ̊). All 32 teeth were present, but the lower right third molar (LR8) was horizontally impacted, and two lower molars (LR7, LL6) had a history of endodontic treatment with extensive restorations. The American Board of Orthodontics (ABO) Discrepancy Index was 34.

Treatment: Both maxillary second molars (UR7, UL7) and the compromised molars (LR7, LL6) were extracted, the LR8 was uprighted, and space was closed with power chains in all four quadrants. Class ll elastics and bite turbos on the maxillary central incisors were applied to correct the intermaxillary relationship. Miniscrews were placed in each infrazygomatic crest (IZC) and between the upper central and lateral incisors. A surgical crown lengthening procedure was performed to enhance maxillary anterior esthetics.

Outcomes:With 38 months of active treatment, this di cult malocclusion (DI 34 points), was treated to a good result as evidenced by an ABO Cast-Radiograph Evaluation (CRE) score of 28 points and a Pink and White esthetic score of 5 points. Two-year follow-up evaluation documented the stability of the correction. (J Digital Orthod 2018;52:50-66)

Key words: Uprighting an impacted third molar, Class II malocclusion, self-ligating brackets, bite turbos, temporary anchorage devices, infrazygomatic crest (IZC), surgical crown lengthening
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Failure Rates for SS and Ti-Alloy Incisal Anchorage Screws: Single-Center, Double Blind, Randomized Clinical Trial

Drs. Chang CH, Huang C, Lee WH, Roberts WE.

Abstract

Objective: Compare the 6 month failure rates for stainless steel (SS) and titanium alloy (Ti) miniscrews placed between the roots of maxillary central and lateral incisors. The null hypothesis was that there is no statistical di erence in the failure rates for screws made of SS or Ti.

Materials and Methods: Over a three year period (2014-17), 320 consecutive 1.5x8mm miniscrews (OBS®, iNewton Dental Ltd, Hsinchu City, Taiwan) were placed bilaterally between central and lateral incisor roots in 160 consecutive patients (26 males,134 females, mean age 25.9 yr, range 10-58 yr). All of the screws served as temporary anchorage devices (TADs) to intrude the maxillary anterior dentition. Half the TADs were made of 316LVM surgical stainless steel (SS) and the other half (160) were composed of Ti6Al4V titanium alloy (Ti). All the miniscrews were placed by the same orthodontist with a double blind, split mouth design. Torque was measured when each screw was seated to provide an index of primary stability. All TADs were immediately loaded with 2-oz (57g, 55 cN), and used for at least 6 months as anchorage to intrude the maxillary anterior segment. Anchorage loss due to a loose screw was de ned as a failure.

Results: The overall failure rate was 7.2% for incisor anchorage screws placed in cortical bone about 0.6mm thick. For the right and left sides combined (n=160 for each material), 18/160 SS (11.25%) and 5/160 Ti (3.125%) failed. A chi-square test revealed the di erence in failure rates was statistically signi cant (p≤0.05). Torque levels indicating primary stability were relatively consistent (5.8- 6.1N-cm), and appear to be unrelated to TAD failure. The hypothesis was rejected because Ti alloy has a superior success rate to SS as a material for incisal miniscrews.

Conclusions: TADs made of Ti alloy have a lower failure rate compared to SS when placed in thin cortical bone. These results are consistent with a biocompatibility-related tendency for less bone resorption at the bone screw interface. (J Digital Orthod 2018;52:70- 79)

Key words: Incisors screws, gummy smile correction, stainless steel, titanium alloy, randomized clinical trial, double blind, split mouth, failure rate, biocompatibility
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金牛頓現場報導：科技與藝術的完美結合
Live coverage from Newton’s A: The perfect synergy of art and technology

Chester Yu, Tzu Han Huang

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