Principles and Biomechanics of AlignerTreatmentRavindra Nanda BDS, MDS, PhDProfessor Emeritus, Department of Orthodontics, University of Connecticut Health Center,Farmington, Connecticut, USAProfessor Emeritus, Department of Orthodontics, University ofConnecticut Health Center, Farmington, Connecticut, USATommaso Castroflorio DDS, PhD, Ortho. Spec.Department of Surgical Sciences, Postgraduate School of Orthodontics, Dental School,University of Torino, Torino, ItalyDepartment of Surgical Sciences, Postgraduate School ofOrthodontics, Dental School, University of Torino, Torino, ItalyFrancesco Garino MD, Ortho. Spec.Private Practice, Torino, ItalyPrivate Practice, Torino, ItalyKenji Ojima DDS, MDScPrivate Practice, Tokyo, JapanPrivate Practice, Tokyo, Japan

Table of ContentsCover imageTitle pageCopyrightDedicationContributorsForeword1. Diagnosis and treatment planning in the three-dimensional eraIntroductionIntraoral scans and digital models3D imagingReferences2. Current biomechanical rationale concerning composite attachments in alignerorthodonticsIntroductionGeometry (active surface orientation)LocationSize

FunctionsBasic attachment configurations in current aligner orthodonticsReferences3. Clear aligners: Material structures and propertiesIntroductionPolymer molecular structure and thermal propertiesPhysical and chemical aging of aligner polymersConclusions and outlookReferences4. Influence of intraoral factors on optical and mechanical aligner material propertiesIntroductionWater absorptionOptical changesShort-term mechanical loading of aligner materialsLong-term loadingClinical loading patterns of aligner materialsReferences5. Theoretical and practical considerations in planning an orthodontic treatment withclear alignersIntroductionTheoretical and practical considerations in CATBiologic considerations in aligner orthodonticsPatient complianceCAT fundamentals recap

References6. Class I malocclusionIntroductionDiagnostic referenceTreatment planClass I conditionsReferences7. Aligner treatment in class II malocclusion patientsIntroductionThe clinical protocolMaxillary distalization case reportsReferences8. Aligners in extraction casesIntroductionDiagnosis and treatment planTreatment progressTreatment resultsDiscussionConclusionReferences9. Open-bite treatment with alignersDiagnosis of anterior open biteBiomechanics for anterior open-bite correction

Aligner protocols for open-bite treatmentCase report 1Case report 2References10. Deep biteIntroductionLeveling of the curve of speeLeveling the upper incisorsCase report 1Case report 2References11. Interceptive orthodontics with alignersIntroductionMaxillary expansionExpansion case reportsClass II malocclusionMandibular advancement case reportsConclusionsReferences12. The hybrid approach in class II malocclusions treatmentIntroductionTooth-borne hybrid approach with distalizing deviceCase report 1

Case report 2References13. Aligners and impacted caninesIntroductionEarly diagnosis and treatmentLate diagnosisTreatment planning and orthodontic managementLabial impactionsPalatal impactionsClinical caseReferences14. Aligner orthodontics in prerestorative patientsIntroductionSpace management in the anterior regionCase studySpace management in the posterior regionManagement of posterior overerupted molarsManagement of patients with a history of temporomandibular disordersCase studyReferences15. Noncompliance upper molar distalization and aligner treatment for correction ofclass II malocclusionsUpper molar distalization in aligner treatmentClinical procedure and rational of the Beneslider

Clinical caseClinical considerationsConclusionsReferences16. Clear aligner orthodontic treatment of patients with periodontitisMalocclusions related to periodontal diseaseOrthodontic treatment in patients with periodontal diseaseDiagnosis and treatment planningOrthodontic movementsRetentionConclusionsClinical caseReferences17. Surgery first with aligner therapyHistoric backgroundSplint-aided maxillary and mandibular fixation without labial fixed appliancesTransitioning into and out of surgery with clear alignersSurgery first and catCase studyConclusionsReferences18. Pain during orthodontic treatment: Biologic mechanisms and clinical managementThe importance of orthodontic pain

Biologic mechanisms of orthodontic pain and clinical correlatesOrthodontic tooth pain in clear aligner therapyModulators of pain: Psychological factorsClinical considerations for the management of orthodontic painReferences19. Retention and stability following aligner therapyRetention and stability in orthodontic treatmentRetention protocols and the choice of retention applianceReferences20. Overcoming the limitations of aligner orthodontics: A hybrid approachIntroductionTransverse expansion of the posterior teethCanine and premolar rotationExtrusion, intrusion, and overbite controlMolar distalizationConclusionsReferencesIndex

CopyrightElsevier3251 Riverport LaneSt. Louis, Missouri 63043PRINCIPLES AND BIOMECHANICS OF ALIGNER TREATMENT, FIRSTEDITIONISBN: 978-0-323-68382-1Copyright 2022 by Elsevier, Inc. All rights reserved.No part of this publication may be reproduced or transmitted in any form or by anymeans, electronic or mechanical, including photocopying, recording, or any informationstorage and retrieval system, without permission in writing from the publisher. Detailson how to seek permission, further information about the Publisher’s permissionspolicies and our arrangements with organizations such as the Copyright ClearanceCenter and the Copyright Licensing Agency, can be found at our book and the individual contributions contained in it are protected undercopyright by the Publisher (other than as may be noted herein).NoticesPractitioners and researchers must always rely on their own experience andknowledge in evaluating and using any information, methods, compounds orexperiments described herein. Because of rapid advances in the medical sciences, inparticular, independent verification of diagnoses and drug dosages should be made.To the fullest extent of the law, no responsibility is assumed by Elsevier, authors,editors or contributors for any injury and/or damage to persons or property as amatter of products liability, negligence or otherwise, or from any use or operation ofany methods, products, instructions, or ideas contained in the material herein.ISBN: 978-0-323-68382-1

Content Strategist: Joslyn DumasContent Development Manager: Ellen Wurm-CutterContent Development Specialist: Rebecca CorradettiPublishing Services Manager: Shereen JameelProject Manager: Nadhiya SekarDesign Direction: Patrick FergusonPrinted in IndiaLast digit is the print number:987654321

DedicationTo Catherine, for her love, support, inspiration, and encouragement.RNTo Katia, for showing me what love is and for keeping my feet on the ground. To Alessandro,Matilda, and Sveva, because you made the world a brighter place. To my friends, Francesco andKenji, for your passion, enthusiasm, commitment, and support: you are always an example tofollow. To Ravi, for your trust and friendship, for your guidance and leadership: you havetranslated a vision into reality. It was a wonderful journey with you; thanks for your time andfor sharing your experience.TCI would like to dedicate this book to all my family with a special thought to my dad, mentor and avisionary, who shared with me a passion in aligner orthodontics for 20 years.FGMy thanks to Francesco and Tommaso for sharing their friendship with me over so many years.The time I spent writing this book with Ravi was amazing, like a dream for me. I am trulygrateful to my family for all of their support.KO

ContributorsMasoud Amirkhani, PhD,GermanyInstitute for Experimental Physics, Ulm University, Ulm,Sean K. Carlson, DMD, MS, Associate Professor, Department of Orthodontics,School of Dentistry, University of the Pacific, San Francisco, California, USATommaso Castroflorio, DDS, PhD, Ortho. Spec.Researcher and Aggregate Professor, Department of Surgical Sciences, PostgraduateSchool of Orthodontics, Dental School, University of Torino, Torino, ItalyOrthodontics Unit, San Giovanni Battista Hospital, Torino, ItalyChisato Dan, DDS,Private Practice, Smile Innovation Orthodontics, Tokyo, JapanIacopo Cioffi, DDS, PhD, Associate Professor, Division of Graduate Orthodonticsand Centre for Multimodal Sensorimotor and Pain Research, Faculty of Dentistry,University of Toronto, Toronto, Ontario, CanadaDavid Couchat, DDS, Ortho. Spec.,Couchat, Marseille, FrancePrivate Practice, Cabinet d’Orthodontie du dr.Fayez Elkholy, DDS, Senior Physician, Department of Orthodontics, UlmUniversity, Ulm, GermanyFrancesco Garino, MD Ortho. Spec.,Garino, Torino, ItalyPrivate Practice, Studio Associato dott.riAldo Giancotti, DDS MS, Researcher and Aggregate Professor, Department ofClinical Sciences and Translational Medicine, University of Rome “Tor Vergata”, Rome,ItalyJuan Pablo Gomez Arango, DDS, MSc, Associate Professor, Orthodontics Program,Universidad Autonoma de Manziales, Manziales, ColombiaMario Greco, DDS, PhDVisiting Professor, University of L’Aquila, L’Aquila, ItalyVisiting Professor, University of Ferrara, Ferrara, ItalyLuis Huanca, DDS, MS, PhD, Research Associate, Department of Orthodontics,University of Geneva, Geneva, SwitzerlandJosef Kučera, MUDr., PhDAssistant Professor, Department of Orthodontics, Clinic of Dental Medicine, FirstMedical Faculty, Charles University, Prague, Czech RepublicLecturer, Department of Orthodontics, Clinic of Dental Medicine, Palacký University,

Olomouc, Czech RepublicBernd G. Lapatki, DDS, PhD, Department Head and Chair, Department ofOrthodontics, Ulm University, Ulm, GermanyLuca Lombardo, DDS, Ortho. Spec., Chairman and Professor, Postgraduate Schoolof Orthodontics, University of Ferrara, Ferrara, ItalyTiantong Lou, DMD, MSc, Division of Gradual Orthodontics and Centre forMultimodal Sensorimotor and Pain Research, Faculty of Dentistry, University ofToronto, Toronto, Ontario, CanadaKamy Malekian, DDS, MSc,Private Practice, Clinica Bio, Madrid, SpainGianluca Mampieri, DDS, MS, PhD, Researcher and Aggregate Professor,Department of Clinical Sciences and Translational Medicine, University of Rome “TorVergata”, Rome, ItalyEdoardo Mantovani, DDS, Ortho. Spec., Research Associate, Department of SurgicalSciences, Postgraduate School in Orthodontics, Dental School, University of Torino,Torino, ItalyIvo Marek, MUDr., PhDAssistant Professor, Department of Orthodontics, Clinic of Dental Medicine, PalackýUniversity, Oloumouc, Czech RepublicConsultant, Department of Orthodontics, Clinic of Dental Medicine, First MedicalFaculty, Charles University, Prague, Czech RepublicRavindra Nanda, BDS, MDS, PhD, Professor Emeritus, Division of Orthodontics,Department of Craniofacial Sciences, University of Connecticut School of DentalMedicine, Farmington, Connecticut, USAKenji Ojima, DDS, MDSc,JapanPrivate Practice, Smile Innovation Orthodontics, Tokyo,Simone Parrini, DDS, Ortho. Spec., Research Associate, Department of SurgicalSciences, Postgraduate School in Orthodontics, Dental School, University of Torino,Torino, ItalySerena Ravera, DDS, PhD, Ortho. Spec., Research Associate, Department of SurgicalSciences, Postgraduate School in Orthodontics, Dental School, University of Torino,Torino, ItalyGabriele Rossini, DDS, PhD, Ortho. Spec., Research Associate, Department ofSurgical Sciences, Postgraduate School in Orthodontics, Dental School, University ofTorino, Torino, ItalyWaddah Sabouni, DDS, Ortho. Spec., Private Practice, Cabinet d’Orthodontie du dr.Sabouni, Bandol Rivage, Sanary-sur-Mer, FranceSilva Schmidt, DDS,Department of Orthodontics, Ulm University, Ulm, GermanyJörg Schwarze, DDS, PhD, Ortho. Spec.,Private Practice, Kieferorthopädische

Praxis Dr. Jörg Schwarze, Cologne, GermanyGiuseppe Siciliani, MD, DDS, Chairman and Professor, School of Dentistry,University of Ferrara, Ferrara, ItalyAli Tassi, BSc, DDS, MClD (Ortho), Assistant Dean and Chair, Division ofGraduate Orthodontics, Schulich School of Medicine and Dentistry, The University ofWestern Ontario, London, Ontario, CanadaJohnny Tran, DMD, MClD, Division of Graduate Orthodontics, Schulich School ofMedicine and Dentistry, The University of Western Ontario, London, Ontario, CanadaFlavio Uribe, DDS, MDentSc, UConn Orthodontics Alumni/Nanda OrthodonticsEndowed Chair, Program Director and Chair, Division of Orthodontics, Department ofCraniofacial Sciences, University of Connecticut, School of Dental Medicine,Farmington, Connecticut, USABenedict Wilmes, DDS, MSc, PhD, Professor, Department of Orthodontics,University of Düsseldorf, Düsseldorf, Germany

ForewordRavindra Nanda, Tommaso Castroflorio, Francesco Garino, Kenji OjimaAligners represent the new frontier in the art and science of orthodontics. This newfrontier offers new opportunities and challenges, but also requires the need foradditional knowledge. A rethinking of biomechanics and force delivery concepts isneeded along with the role of materials used for aligners. There is a need for combiningestablished concepts with new tools and technologies which aligner treatment requires.When considering new methodologies, orthodontists should always remember thattechnology is a tool and not the goal. Diagnosis, treatment plan, and biomechanics arealways the key elements of successful treatment, regardless of the treatmentmethodology. Aligner orthodontics is quite different than traditional methods withbrackets and wires. Force delivery with aligners is through plastic materials. Thus, theknowledge of the aligner materials, physical properties, attachment design, and thesequentialization protocol is crucial for treatment of malocclusions. It is also imperativeto understand limitations of aligner treatment and how to overcome them with the useof miniscrews and auxiliaries.Aligner treatment requires new knowledge; the number of clinical and scientificreports about all the different aspects of aligner orthodontics is increasing year by year.This book represents an up-to-date summary of the available research in the field aswell as a clinical atlas of treated patients based on the current evidence. We have madean attempt to provide benchmark for clinicians, researchers, and residents who want toimprove their skills in aligner orthodontics.We would like to express our great appreciation to all the friends and colleagues whohave contributed to this book. It was a pleasure to work with all these talentedorthodontists.We would like to say thank you to the Elsevier team for their support, patience, andguidance during the challenging Covid pandemic.

List of TablesTable 5.1 Suggested Amount of Movement per AlignerTable 9.1 Case Study 1: Problem ListTable 9.2 Case Study 1: Treatment ObjectivesTable 9.3 Case Study 1: Summary of Cephalometric ChangesTable 9.4 Case Study 2: Problem ListTable 9.5 Case Study 2: Treatment ObjectivesTable 9.6 Case Study 2: Summary of Cephalometric ChangesTable 11.1 Pre- and post-treatment volumetric and linear measurements obtained in thereported cases.Table 13.1 Factors Affecting PrognosisTable 15.1 Cephalometric SummaryTable 16.1 Framework for Staging and Grading of PeriodontitisTable 16.2 Periodontitis StageTable 16.3 Orthodontic Movements And Malocclusion FeaturesTable 16.4 Stages of PeriodontitisTable 16.5 Grades of PeriodontitisTable 18.1 Strategies to Reduce Pain During Orthodontic Treatment

List of IllustrationsFig. 1.1 Steps in diagnosis and treatment planning in the digital orthodontics era.Fig. 1.2 Integration of cone-beam computed tomography data, facial three-dimensionalscan, digital models from intraoral scans, and virtual orthodontic setup.Fig. 1.3 (A) Digital models and measurements obtained from cone-beam computedtomography data. (B) Digital models and measurements obtained from intraoral scans.Fig. 1.4 New generation of intraoral scanners with integrated near infrared (NIR)technology. (A) Itero Element 5D (Align Technology, San José, CA, USA) decaysdetection scheme. (B) 3Shape Trios 4 (3Shape A/S, Copenhagen, Denmark) fluorescenttechnology for surface decay detection (left) and NIR technology for interproximaldecay detection (right).Fig. 1.5 Cone-beam computed tomography data elaboration for enhancing diagnosisand treatment planning.Fig. 1.6 Case of impacted lower canine in which the cone-beam computed tomographydata are helpful in defining the right mechanics.Fig. 1.7 Occasional report of misunderstood right condyle neck fracture results in a 9year-old child being prescribed cone-beam computed tomography for orthodonticreasons.Fig. 1.8 Airway measurements from cone-beam computed tomography data.Fig. 1.9 Example of cone-beam computed tomography data integration in a surgerythree-dimensional planning software.Fig. 1.10 Cone-beam computed tomography data used to plan an orthodontic expansionin a subject with poor periodontal support (upper). Orthodontic expansion,corticotomies, and bone grafts were planned to obtain an excellent final result withoutbone dehiscence (lower).Fig. 1.11 Stereophotogrammetry (A) and laser scan (B) three-dimensionalreconstructions of the face of the same patient.Fig. 1.12 Superimposition of the virtual setup on the smile picture of a patient withunilateral agenesis, visualizing from left to right the initial situation, thepostorthodontic situation, and the final smile with restorative simulation.Fig. 1.13 The virtual patient in which cone-beam computed tomography data, facialthree-dimensional reconstruction, and virtual setup obtained after teeth segmentationare superimposed.Fig. 2.1 (A) Mesial tipping moments (red curved arrows) produced by aligner forces (redarrows) occurring during space closure. Antitipping moments (blue curved arrows)produced by forces (blue arrows) acting at rectangular vertical attachments (B).Opposing moments are canceled out, promoting bodily movement.Fig. 2.2 The typical force couple generated during bracket-based alignment of rotated

tooth with a fully engaged 0.014 NiTi archwire consists of two force vectors: one thatpushes against the posterior wall of the slot (red arrow) and a second that pulls awayfrom the same wall (blue arrow).Fig. 2.3 (A) Aligner-tooth mismatch. (B) Elastic aligner deformation and activation offorces upon aligner insertion. (C) Tooth alignment after aligner sequence.Fig. 2.4 (A) Active surfaces of attachments. (B) Direction of forces acting at activesurfaces. (C) Resultant force affecting the first premolar will produce extrusion andclockwise, second-order rotation.Fig. 2.5 (A) Due to the distance between the center of resistance (blue dot) and the line ofaction (red dotted line), large mesial tipping and negligible mesiolingual rotationalmoments should be expected. (B) A more mesial and apical attachment location willresult in reduced mesial tipping and increased mesiolingual rotational moments,increasing clinical efficacy.Fig. 2.6 During expansion, labial attachment location (A) produced smaller net buccalmolar tipping moments than lingually bonded attachments (B).Fig. 2.7 (A) Attachments located on teeth adjacent to force application increase alignerretention when using intermaxillary elastics. (B) Attachment position close to thegingival margin and occlusally beveled geometry is ideal for aligner retention.Fig. 2.8 (A) Multiple tangential forces (red arrows) acting during aligner-based, bicuspidrotation. (B) Due to slipping effect, incomplete expression of expected rotation withspace between tooth and aligner (in yellow) will be observed.Fig. 2.9 (A) Properly designed attachments produce complementary force vectorsrequired for predictable tooth movement. (B) Polymer stress relaxation and creep, alongwith incomplete rotation and unintended force (blue arrow), may occur during sequenceof aligner-based, tooth rotation stages.Fig. 2.10 (A) Image from ClinCheck treatment plan. (B) Loss of tracking with incompleteexpression of rotation and extrusion of left upper bicuspid. Lack of coincidence betweenattachment (green shaded area) and its corresponding recess in the aligner (green outline)is observed.Fig. 2.11 (A) Converging buccal and lingual crown surfaces. (B) Undesired alignerdislodgment during extrusive movement.Fig. 2.12 (A) Optimized Extrusion Attachments (Align Technology, Santa Clara, CA) oncentral incisors. (B) Gingivallyoriented inclined plane with optimal active surfaceangulation.Fig. 2.13 (A) Forces transmitted by the aligner (red arrows) and resultant forces (purplearrows) acting on the tooth. (B) A reduction of the angle between active attachmentsurface and buccal tooth surface produces stronger resultant extrusive forces.Fig. 2.14 Intrusion in the posterior segment (red arrows) produces reactive forces thatwill tend to dislodge the aligner anteriorly (blue arrows). Adequate attachment selectionon anterior teeth will counteract this undesired occurrence.Fig. 2.15 (A) Rotational forces produced by the aligner (purple arrows) are transmitted tothe tooth as normal force components (red arrows), which are perpendicular to toothsurface tangents (purple dotted lines). (B) Incorporation of bonded attachment increasesthe magnitude and efficacy of rotational moment by increasing the perpendicular

distance (green dotted line) between the line of action (red dotted line) and the center ofresistance (CRes).Fig. 2.16 (A) Without attachment, the tooth lagged behind the aligner almost by 30%.With attachment incorporation, this lag dropped to 5%. (B) Intrusive forces observed atthe periodontal ligament without attachments was 0.078 N for every degree of rotation,while with attachments the load was reduced to 0.021 N for every degree. ATT,Attachment.Fig. 2.17 (A) Digital image of occlusal view of right upper canine. Occlusal view of finiteelement method simulation of upper right canine during mesiolingual rotation. (B)Distinctly intrusive pressure areas (red) on mesiolabial and distolingual aspects of thetooth crown appear upon aligner insertion. The dotted line represents the aligner’sprofile.Fig. 2.18 Optimized Rotation Attachment (Align Technology, Santa Clara, CA) withactive surface oriented to provide a compensatory extrusive force.Fig. 2.19 (A) Force couple produced during bracket-based correction of excessive mesialtip. (B) Equivalent force couple produced at Optimized Root Control Attachments(Align Technology, Santa Clara, CA) during aligner-based tipping.Fig. 2.20 Tooth displacement patterns during aligner-based distalization of upper rightcanine. (A) Without attachments, distinct uncontrolled distal tipping was observed,with center of rotation between apical and middle thirds of the root (red arrow). (B) Withattachments, the canine expressed distal bodily movement.Fig. 2.21 Periodontal ligament strain patterns during aligner-based distalization ofupper right canine. (A) Without attachments, distocervical pressure (in blue) anddistoapical tension (in red) areas were observed, typical of uncontrolled distal tipping.(B) With attachments, uniform pressure along the distal root surface (in blue) anduniform tension (in red) along the medial surface, typical of distal bodily movement,were observed.Fig. 2.22 (A) Uprighting moment produced at single rectangular horizontal attachment.(B) Alternative twin attachment configuration.Fig. 2.23 Producing equivalent moments (curved arrows), an increase in intervectordistance proportionately reduces force magnitude (blue arrows) acting at attachmentsurface. Two degrees of distal tipping with a 4-mm rectangular attachment (A) willproduce higher forces on the aligner than with a two-attachment configuration thatsignificantly separates the force vectors (B) of the acting couple.Fig. 2.24 Class II case in which reciprocal moments between anterior and posteriorsegments during extraction space closure (A) will result in 50% anchorage loss and classII occlusion (B).Fig. 2.25 Clockwise moments (blue curved arrows) produced by attachments bonded toposterior teeth (A) will counteract posterior anchorage loss, reducing it to 25%, resultingin class I occlusion (B).Fig. 2.26 (A) By preactivating (red shaded) and subsequently inserting (red) thearchwire, a force couple (blue arrows) and its corresponding counterclockwise moment(blue curved arrow) will be produced. (B) The same positive torque can be achieved withaligners by producing an equivalent couple, with lower forces and increased intervector

distance.Fig. 2.27 (A) Aligner-based expansive force (red arrow) applied at a distance from thecenter of resistance (CRes) will produce counterclockwise moment (red curved arrow). (B)Without preventive measures, buccal tipping with center of rotation (CRot) above thefurcation will occur, followed by aligner deformation and loss of control.Fig. 2.28 (A) Opposing forces (blue arrows) acting at the occlusal surface and gingivalaspect of a rectangular horizontal buccal attachment will provide a clockwise moment(blue curved arrow) that reduces buccal tipping, with apical migration of the center ofrotation (CRot) (B).Fig. 2.29 (A) Programmed expansive mismatch between aligner and dental arch. (B)Once inserted, the resultant expansive forces will have a distally decreasing magnitudegradient.Fig. 2.30 Low angle patient (A), with bilateral posterior crossbite (B, D) and midlinediscrepancy (C).Fig. 2.31 (A) Initial ClinCheck stage. (B) Aligners inserted, prior to bonding of upperpalatal and lower buccal buttons. (C) Crossbite elastic.Fig. 2.32 A 100-gmf intermaxillary elastic force will produce a 90-gmf effectivetransverse force, expanding the upper arch and compressing the lower arch.Additionally, 42 gmf of extrusive force will equally influence upper and lower arches.Fig. 2.33 In the upper arch, the moments provided by upper buccal attachments (bluecurved arrows) will counteract moments (red curved arrows) produced by elasticexpansive forces (red arrows), reducing undesired upper tipping. In the lower arch,unopposed lingual elastic forces (dotted red arrows) will result in expected lingualtipping (dotted red curved arrows).Fig. 2.34 (A, B) Initial bilateral crossbite and midline discrepancy. (C, D) Aligner-basedcorrection with complementary use of intermaxillary elastics.Fig. 3.1 Chemical structure of polyethylene terephthalate glycol material (PET-G).Fig. 3.2 Chemical structure of polyurethane material (PU).Fig. 3.3 Specific volume versus temperature. Tm represents the melting temperature andTg the glass transition temperature.Fig. 3.4 Differential scanning calorimetry of polyethylene terephthalate glycol (PET-G).Fig. 4.1 Bending forces depending on the (dry or wet) storage conditions and theunloaded or loaded condition. Note 0.75-mm polyethylene terephthalate glycol (PET-G)specimens were investigated in a three-point bending setting with a span length of 8mm at a deflection of 0.1 mm. The specimens were either only thermoformed and thenunderwent only one short deflection with simultaneous force, stored for 24 hours inwater without loading, loaded continuously for 24 hours without water immersion, orloaded continuously for 24 hours with water immersion. The error bars represent thestandard deviation for the different measurements.Fig. 4.2 Invisalign aligners. (A) Prior to first intraoral application. (B) After a 1-weekwearing period.Fig. 4.3 Forces measured for 0.75-mm polyethylene terephthalate glycol (PET-G)specimens in a three-point bending setup with a span length of 8 mm. The centralsupport was deflected by 0.1 mm. Two short loading-measuring cycles with 0.1-second

duration, separated by a 2-minute recovery break, were performed.Fig. 4.4 (A) Forces measured during multiple 5-minute loading and 5-minute loadingcycles for a 0.5-mm polyethylene terephthalate glycol (PET-G) specimen in a three-pointbending setup with a span length of 8 mm and a deflection of 0.2 mm. (B) Enlargementof a data segment (see top of A) showing the gradual force decrease during the 5-minuteloading time. (C) Enlargement of a data segment (see bottom of A) showing the slightforce increase during the 10-minute minimal load time at the corresponding deflections.Fig. 4.5 Average force reduction reported for polyethylene terephthalate glycol (PET-G)aligners in the course of 50 aligner seating-removal procedures based on the datapublished by Skaik et al.20 The error bars indicate the standard deviation.Fig. 4.6 Schematic modeling of viscoelastic material behavior using a standard linearsolid model. (A) Maxwell representation of a standard linear solid model. (B) Kelvinrepresentation of a standard linear solid model. Such models combine springs anddashpots in a certain arrangement to describe the overall behavior of a system underdifferent loading conditions. Springs represent the elastic component of a viscoelasticmaterial, whereas dashpots represent the viscous component.30 Due to combination ofsuch elements, an applied stress varies with the time-dependent change of the strain.Fig. 4.7 Two fundamentally different experiments and parameters, respectively,describing the time-dependent behavior of a viscoelastic aligner material. (A) The creepphenomenon is observed if the load (and stress level, respectively) is kept constant overtime. (B) The stress relaxation behavior is characterized by loading the material underconstant strain and deflection, respectively.Fig. 4.8 Normalized stress relaxation for polyethylene terephthalate glycol (PET-G)materials loaded for 1 week in a three-point bending setup with a constant deflection ofthe specimen leading to a constant strain.Fig. 4.9 Decay of the forces measured after the loading and unloading periods duringthe 1-week observation time.Fig. 5.1 Thresholds of acceptance of smile esthetics from laypeople point of view.Fig. 5.2 Rectangular attachments on posterior teeth in CA Digital software.Fig. 5.3 Rectangular attachments on anterior teeth

Orthodontic treatment in patients with periodontal disease Diagnosis and treatment planning . Assistant Professor, Department of Orthodontics, Clinic of Dental Medicine, First Medical Faculty, Charles University, Prague, Czech Republic . Flavio Uribe, DDS, MDentSc, UConn Orthodontics Alum