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Journal Pre-proofMechanical considerations for deep-bite correction with alignersNeal D Kravitz DMD, MS , Mazyar Moshiri DMD, MS ,Jonathan Nicozisis DMD, MS , Shawn Miller DMD, /doi.org/10.1053/j.sodo.2020.06.010YSODO 609To appear in:Seminars in OrthodonticsPleasecitethisarticleas:Neal D Kravitz DMD, MS ,Jonathan Nicozisis DMD, MS ,Shawn Miller DMD, MMSc ,tions for deep-bite correction with aligners, Seminars inhttps://doi.org/10.1053/j.sodo.2020.06.010Mazyar Moshiri DMD, MS ,MechanicalconsideraOrthodontics (2020), doi:This is a PDF file of an article that has undergone enhancements after acceptance, such as the additionof a cover page and metadata, and formatting for readability, but it is not yet the definitive version ofrecord. This version will undergo additional copyediting, typesetting and review before it is publishedin its final form, but we are providing this version to give early visibility of the article. Please note that,during the production process, errors may be discovered which could affect the content, and all legaldisclaimers that apply to the journal pertain. 2020 Published by Elsevier Inc.

Mechanical considerations for deep-bite correction with alignersNEAL D KRAVITZ, DMD, MS, Private practice in South Riding, VA. email: [email protected] MOSHIRI, DMD, MS, Invisalign Master Faculty and private practice in St. Louis, MO.JONATHAN NICOZISIS, DMD, MS, Invisalign Master Faculty and private practice in Princeton, NJSHAWN MILLER, DMD, MMSc, Private practice in Orange, CACorresponding Author: Neal D Kravitz, Private Practice, 25055 Riding Plaza, Suite 110, SouthRiding, VA 20152E-mail: [email protected]

AbstractCorrection of deep-bite malocclusions with aligners is challenging for orthodontists. Thisreview is meant to help orthodontists improve their clinical success in treating deep-bitemalocclusions with aligners. Biomechanical strategies for achieving deep overbitecorrection need to be adapted for use in patients treated with aligners. Virtual casesetup, attachment design, elastics, and bite ramp utilization are discussed in order tobetter equip orthodontists with a new “best practices” paradigm.IntroductionCorrection of deep-bite malocclusions with aligners is biomechanically challenging fororthodontists. Specifically, research has shown that orthodontists struggle to achievemandibular incisor intrusion, which remains one of the least accurate movements.1-5Unfortunately, the efficacy of deep-bite correction with aligners has not significantlyimproved despite advancements in technology.3-5 For these patients, the result is oftenprolonged aligner treatment with minimal overbite improvement.There are number of contributing factors, including, but not limited to: patientnoncompliance, inefficient or improper virtual case setup, and loss of anchorage due topoor aligner retention. Although aligners have many advantages compared to braces fordeep-bite malocclusions, such as occlusal protection and avoidance of broken brackets,their biomechanical disadvantages and challenges still need to be considered.

In this review, the aim is for orthodontists to improve their clinical success in treatingdeep-bite malocclusions with aligners. Virtual case setup, attachment design, elastics,and bite ramp utilization will be discussed in order to better equip orthodontists with anew “best practices” paradigm.Virtual case setupA patient with a small lower arch perimeter or retrognathia is prone to the developmentof a deep-bite and a steep Curve of Spee. In these situations, the incisors supra-eruptuntil they contact opposing teeth or soft tissue and the mandibular second molarssupra-erupt until they contact the maxillary second molars. Deep-bite correction usuallyrequires a reversal of this process to flatten the Curve of Spee. 6A practical starting point for this reversal is to envision the final vertical positions of theupper incisors as they relate to the smile arc and then retro-engineer the other toothmovements accordingly. To preserve smile consonance and maxillary incisor display,the mandibular incisors and canines are primarily intruded.7 Therefore, teeth should bemoved on the virtual treatment software to simulate the force vectors of a lower reverseCurve of Spee archwire (Fig. 1).

Such a prescription might read: “Intrude mandibular second molars 0.5 mm, extrudepremolars and first molars 1.0 mm, intrude canines 1.5 mm, and intrude incisors 2.0mm, to result in an open bite with heavy posterior contacts” (Fig. 2). Note that, thevirtual treatment software is a visual representation of forces and not a predictor of finaltooth positions, just as the shape of a reverse Curve of Spee archwire is not the desiredocclusal plane.8On occasion, the mandibular posterior teeth also will be excessively lingually-inclined,resulting in a steep Curve of Wilson. This inclination is best viewed by turning the digitalmodel around to the back. If this occurs, prescribing 5 degrees of buccal crown tip to themandibular premolars and molars will flatten the Curve of Wilson and create a“resultant” extrusion that will contribute to deep-bite correction.Resultant (relative) versus absolute movementsResultant (also referred to as “relative”) intrusion or extrusion differs from absoluteintrusion or extrusion in the vertical plane. These resultant movements incorporatepredictable buccal and lingual crown tip movements to achieve vertical changes. Buccaland lingual crown tip is the most accurate movement with Invisalign,1 likely because thealigner material primarily flexes in a buccal-lingual direction.

Labial crown tip of the incisors produces a resultant intrusion for bite opening andlingual crown tip of the incisors produces a resultant extrusion for bite deepening.1,8 Assuch, interproximal reduction should be used judiciously in deep-bite cases, and alwaysbe incorporated with incisor intrusion. 8 Likewise, deep-bite malocclusions withpreexisting mandibular spacing are particularly challenging. These cases may benefitfrom significant over-engineering or a hybrid technique of upper aligners with lower fixedappliances.For the most part, two types of resultant tooth movements should be considered asaiding in deep-bite correction: 1) the resultant extrusion of the mandibular posteriorteeth via buccal crown tip, which will flatten the Curve of Wilson, and 2) the resultantintrusion of the mandibular incisors via labial crown tip, which will flatten the Curve ofSpee. Glaser refers to these movements as predictable “free rides” that often do notrequire any specific attachments (Fig. 3).8AttachmentsAttachments minimize aligner lift-off and loss of retentiveness, serving as anchorage fordescribed movements. For lower reverse Curve of Spee mechanics, attachmentsshould be placed on the extruding mandibular teeth. Attachments are oftenunnecessary for teeth undergoing intrusion, with the exception of the mandibularcanines if more than 1 mm mandibular incisor intrusion is needed.

Dome-shaped, fifth-generation (G5) and seventh-generation (G7) attachments, whichare specific for Invisalign, can be placed on the posterior teeth. G5s are designated forthe premolars and G7s are designated for the molars, but there is no difference indesign (Fig. 4). If conditions are not met for these attachments or a different alignersystem is used, then horizontal beveled attachments (HBA) can be used. HBAs are alsothe preferred attachment for the mandibular canines.The orthodontist should request that HBAs are 4 mm wide and 1.25 mm thick,angulated gingivally into the crown without a ledge. Orienting the beveled surface of theattachment gingivally directs the pushing vector perpendicularly against the linguallyinclined crown. It also eliminates the attachment’s gingival undercut to minimize thechance of debonding. This gingival-orientation step can be written as a default in theClinical Preferences section or performed manually on the virtual treatment software.For Invisalign, G5/G7s or HBAs need to be prescribed in the ClinCheck instructionsbecause anchorage for deep-bite correction is one of the lowest priorities of thesoftware. Therefore, if teeth have root tip or rotations greater than 5 degrees, thesoftware will place smaller, optimized attachments to primarily address those issuesinstead. These optimized attachments are less than ideal for overbite correction as theydo not provide the necessary anchorage.9

Root tip or rotation therefore may need to be addressed during refinement, aftersignificant deep-bite correction has been achieved. Alternatively, an HBA can be rotateddiagonally across the crown in a ‘sash’ orientation.10 This enables the pushing vectorsto simultaneously effect root tip and rotation, while extruding the premolars orsupporting the intrusion of the anterior teeth (Figs. 5A and B).Generally, it is advantageous to set the Clinical Preferences to use the largestattachment possible. Posterior and mandibular anterior attachments should be movedas incisal or coronal as possible where the aligner force levels are strongest, withoutinterfering with occlusion. However, attachment shape and location may vary dependingon the use of supporting auxiliaries, such as elastics and bite ramps.Supporting auxiliariesClass II elastics and bite ramps support the mechanics for deep-bite correction. Elasticsassist in mandibular molar extrusion (when programmed into the virtual treatment plan)and mandibular incisor proclination; therefore, they can be utilized even for Class Ipatients. Bite ramps are helpful in intruding the mandibular anterior teeth anddisarticulating the posterior teeth to allow for their extrusion. They are commonly utilizedin brachycephalic patients.

Class II elastics are often connected from hooks in the aligners over the maxillarycanines to buttons on the mandibular first molars. Buttons are preferable on the molarsbecause the elastic pulls directly on the teeth. If maxillary canine intrusion or anchorageis needed, the hooks should be moved to over the first premolars as not to counteractthe aligner’s anterior intrusive forces. This may necessitate moving the buttons back tothe mandibular second molars.Bite ramps are commonly located on the lingual surfaces of the four maxillary incisors. Ifmaxillary anterior intrusion is desired, as is often the case in Class II Division 2malocclusions, the bite ramps should be moved to the canines instead. This is becausebite ramps reduce the pressure directed along the long-axes of the maxillary incisorsneeding intrusion. Bite ramps cause less plastic to be in contact with the incisors’cingula, which reduces the surface area available for the desired intrusion force vectors.For the same reason, bite ramps also limit torque expression (Fig. 6).ConclusionTo improve the efficacy of deep-bite correction with aligners, orthodontists shouldprescribe reverse Curve of Spee mechanics: specifically, extrusion of the posterior teethand intrusion of the anterior teeth, resulting in an overcorrection to a simulated anterioropen bite. Invisalign’s G5/G7s or HBAs should be placed on teeth undergoing extrusiveforces, and Class II elastics and bite ramps can be added for support. Above all, the

virtual treatment software should be used as a visual representation of forces ratherthan a predictor of final tooth position.FiguresFigure 1. Mandibular reverse Curve of Spee mechanics. The flatter the mandibularplane, the more over-engineering of the virtual case setup needs to be performed. Thisis particular true of cases where space closure or IPR is occurring. (The attachmentshave been removed for clarity.)

Figure 2. A sample Special Instructions in ClinCheck for a deep-bite patient. Thisrecommendation may need to be exaggerated in patients who are non-growing,brachycephalic, or where space closure is needed. The selection of bite ramps comesearlier in the prescription form.Figure 3. An occlusal view showing the resultant intrusion of the mandibular incisorsand the resultant extrusion of the mandibular premolars to assist in bite opening.Proclining the incisors also increases the surface area on the cingula, which aidsintrusion. (The attachments have been removed for clarity.)

Figure 4. Invisalign’s dome-shaped G5 attachments on the premolars and G7attachments on the first molars. These attachments may not be possible in youngerpatients with shorter clinical crowns. The canine receives an HBA.

Figure 5. A. HBAs (4 mm wide; 1.25 mm thick) oriented gingivally without a ledge. B. Adiagonal or sash HBA on the mandibular right second premolar for simultaneousrotation and extrusion.Figure 6. Usage of maxillary incisor bite ramps.

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