Routine Mechanics and Aligners (Extraction/Nonextraction)

Summary

Clear aligner therapy has become a common treatment modality within the orthodontic practice. Cases ranging from simple Class I malocclusion to complex Class II and Class III malocclusions, with or without extractions, may be attempted. Although computer-aided appliance design and digital virtual treatment planning have helped us in many ways to improve our skills in treating patients with this relatively new technique, it is still not foolproof. This chapter highlights the essence of routine orthodontic treatment in various types of malocclusions, offering concise explanations on staging patterns, the use of elastics and their various configurations, attachment designs, and other important considerations.

Introduction

Modalities of orthodontic treatment have changed much over the last 10 to 15 years. With the advent of digital technology, fast internet speeds, and various digital mobile platforms, modern orthodontic treatment planning and execution have never been so much at our fingertips. However, with the convenience of advanced technology, the biology of dental movement still has not changed and the complex nature of orthodontic treatment should not be trivialized.

Aligner treatment has broadened our scope of choice of orthodontic appliances. Especially esthetically conscious adult and/or adolescent patients who may never have considered orthodontic treatment with conventional therapies now have a viable option. It is important for the clinician to understand the intricacies of digital treatment planning and their innate shortfall to allow a seamless incorporation of such techniques into their daily orthodontic practices.

Initial Appointments and Informed Consent

ClinCheck virtual treatment plans do not translate absolutely into clinical outcomes. Dental movements cannot be completely mimicked by digital manipulation, at least not yet. The biology of orthodontic movement is complex, involving a cascade of exchange of biochemicals, hormone precursors, and enzymes.1 The components of the periodontium supporting this movement have different physical properties, and the dynamic nature of this system, namely, the constant changing of stress/strain patterns within the periodontal ligament, has made its in vitro duplication difficult, if not impossible.

Hence, it is essential for new clinicians to present a more realistic treatment goal to the patient during the initial consultation appointments. Without fully considering the patient’s dental biology, studying the physical anatomy of the dentition, and understanding the intricacies of aligner mechanotherapy, it would be unwise to assume that the virtual treatment outcomes can be readily achieved.

Routinely, it is important to note patients’ chief concerns and relate to them if that was achievable. Generous treatment time frames, absolute compliance with appliance wear (including elastics for anchorage), the need to place attachments, and/or other auxiliaries need to be intimately discussed. Skeletal versus dental discrepancies contributing to the malocclusion need to be carefully considered. Additional aligners, multiple staging patterns with updated impressions, or intraoral scans will be required. Retention appliances and regimes need to be discussed during these initial appointments as well.

Nonextraction Plans (Class I, II, and III Malocclusions)

Nonextraction treatment plans do not always mean a shorter treatment duration or an easier orthodontic journey. There are different considerations in Class I, II, and III dental malocclusions.

Class I Malocclusion Considerations

The essences in obtaining space in a Class I malocclusion characterized by dental crowding are (1) dental arch expansion, (2) anterior dental proclination, and (3) interproximal reduction (IPR).

Dental Arch Expansion

Scrutinizing the dentoalveolus to ensure all expansion done is kept within the thickness of the bone is important. Existing buccal recession and/or bone loss is a contraindication. Successful cases are those where the buccal segments are lingually inclined (Fig. 5.1). Cases with bilateral posterior crossbites with no functional shift need not always be corrected (Fig. 5.2a, b).

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Fig. 5.1 Case showing lingually rolled in buccal segments ideal for dental arch expansion.

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Fig. 5.2 (a)Before and > (B)after images of bilateral posterior crossbite left uncorrected.

The soft- and hard-tissue resistance to dental arch expansion has to be considered. Although for every 1 mm of dental arch expansion the dental arch perimeter increases by approximately 0.7 mm,2 the tissue resistance prevents us from obtaining this. Therefore, during the ClinCheck planning process, it is important to have a certain degree of overexpansion planned—usually, approximately 50% more dental expansion, or about 2 mm more on either side. However, due to the lack of rigidity of the aligners at the terminal molars, overexpansion has to be greater there as compared to the midarch (premolar) regions.

During upper dental arch expansion, the center of rotation of the maxilla is positioned superior to the palatal vault. The inevitable buccal tipping of the posterior dentition usually results in the palatal cusps of these teeth being extruded, increasing the vertical dimension. In a case that has a vertical or hyperdivergent skeletal pattern, or with an anterior open bite tendency, this would worsen the anterior open bite and makes its correction extremely difficult. Therefore, during the ClinCheck treatment planning process, overcorrection movements including increased buccal root torque and intrusion of the posterior dentition need to be considered (Fig. 5.3a–c).

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Fig. 5.3 Images of (a)before and (b)after treatment with bilateral posterior arch expansion, in a case with an anterior open bite. (c)ClinCheck planning with increased buccal root torque of the upper posterior teeth and no occlusal contacts between the upper palatal cusps and the lower central fossae.

Anterior Dental Proclination

Anterior labial recession, low gingival attachments, and bone loss are contraindications of anterior dental proclination. Otherwise, this is a very efficient way to gain space in a crowded arch. Retroclined incisors are effectively proclined using the aligner appliance. For every 1 mm of incisor proclination, there is approximately 2 mm of dental arch perimeter obtained. This translation from the digital planning clinically is usually absolute due to less tissue resistance of the dentoalveolus in the anterior region (Fig. 5.4a–c).

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Fig. 5.4 (a)Before and (b) after images of a nonextraction case with proclination of anterior teeth to obtain space for alignment. (c)ClinCheck treatment planning showing superimposition of the amount of proclination of anterior teeth with measuring grid. One square is 1 mm.

In a case where lower anterior crowding is accompanied by a deep dental overbite, the proclination of the lower incisors while relieving the lower dental crowding will inevitably help in opening the deep overbite. The proclination of the lower incisors effectively allows an intrusion moment as well. This relative intrusion (proclination and intrusion), as opposed to absolute intrusion, is more readily achieved clinically (Fig. 5.5a–c).

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Fig. 5.5 Images of (a) before and (b) after of a case with an increased overjet and deep overbite. (c)ClinCheck treatment plans showing the degree of intrusion obtained with the proclination of the lower incisors.

Interproximal Reduction (IPR)

Upon submitting the prescription form, if we select all three ways to create space in a nonextraction crowded condition, IPR will be the default, last consideration. If space was not sufficient after dental arch expansion and anterior dental proclination, IPR will be indicated (Fig. 5.6a–c). This is a nonreversible clinical procedure and has to be indicated with care. Traditional orthodontic therapies using fixed appliances seldom require IPR, usually only in cases where Bolton discrepancy is eminent.

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Fig. 5.6 (a)Before and (b)after images of a nonextraction case with IPR creating sufficient space for dental alignment. (c)ClinCheck treatment plans showing the range of IPR required for alignment.

IPR is contraindicated in cases in which this procedure was done in previous orthodontic treatment, in cases with thin and slender dental anatomy, or in cases where there is poor oral hygiene or other enamel defects such as dental imperfecta.

Class II Malocclusion Considerations

There are many various plans to correct nonextraction Class II malocclusions. How the anteroposterior correction is performed or staged is the crux of treatment planning in these cases. The decision largely lies on the age of the patient and the severity of the correction required.

Staging Patterns

The staging pattern in Class II malocclusion correction could be (1) sequential staging pattern, (2) simultaneous staging (elastic simulation), or (3) simultaneous staging (en masse movement).

  • Sequential staging pattern is the default staging pattern in upper molar distalization in the correction of a Class II dental relationship using Invisalign clear aligners. The terminal molars are first moved followed by the premolars, canines, and the anterior teeth, sequentially (Fig. 5.7a, b). While this staging pattern is rather predictable, these movements need to be supported with intraoral use of Class II elastics clinically. This staging pattern is also time-consuming: while the posterior teeth are being distalized, the anterior crowding is usually not corrected till the later stages of treatment. This may contradict our patients’ chief concern which usually is the anterior crowding. To overcome this slight roadblock, request for an “esthetic start” while planning the ClinCheck treatment. This will allow the commencement of simple alignment of the anterior teeth while the terminal molars and premolars are distalizing (Fig. 5.8).

  • The anchorage control in Class II dental correction in adolescence is usually less demanding as there remains vertical dentoalveolar growth which helps with the anteroposterior correctio. It is useful to use peak growth charts as guidelines (Fig. 5.9a, b) and also ask leading questions during the consultation appointment. For instance, how rapidly the child has grown recently? Whether clothes and/or shoe sizes have changed? Age of sexual maturation in older siblings. Comparison of the child’s height–weight with parents/older siblings. Planning active orthodontic treatment to coincide with the child’s growth spurt often makes the treatment more effective.3 ,​ 4

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Fig. 5.7 (a)Treatment progress of a Class II malocclusion, upper molar distalization case demonstrating the sequential movement of the posterior teeth backward supported with Class II elastics clinically. (b)ClinCheck plans showing the staging pattern with a “V”-shaped pattern.

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Fig. 5.8 Staging pattern of a Class II malocclusion, molar distalization case showing modified sequential staging with an “esthetic start.”

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Fig. 5.9 (a, b) Peak-height growth in adolescence.

The compliant wear of aligners and Class II elastics can usually correct routine half-unit molar Class II relationship, and sometimes a full-unit molar correction is possible if conditions are ideal (Fig. 5.10a, b). Ideal conditions include good clinical crown heights, good biological response, and compliant wear of aligners and elastics. Features of the Invisalign product for suitable younger patients (Invisalign Teen or Invisalign First) includes compliance indicators, free replacement aligners, and compensatory eruption tabs, which help to overcome some roadblocks in teen treatment. Recent release of the mandibular advancement feature with precision wings (Fig. 5.11) also attempts orthopedic correction in these growing patients.

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Fig. 5.10 Images of (a)before and (b)after treatment of an adolescent patient with full-unit Class II molar correction with Invisalign and Class II elastics.

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Fig. 5.11 Precision wings integrated into Invisalign aligners as a mandibular advancement feature.

Elastic simulation staging is effective in adolescent Class II correction and is the staging pattern of choice. Augmented with compliant elastic wear, routine half-unit correction is easily achieved (Fig. 5.12a–c).

  • En masse Class II malocclusion correction requires more anchorage and it can be augmented by having temporary anchorage devices (TADs) placed in concurrent with elastics wear (Fig. 5.13a, b).

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Fig. 5.12 Images of (a)before and (b)after of a half-unit Class II correction in an adolescent case. (c)ClinCheck plans showing an “elastic simulation” in the staging profile.

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Fig. 5.13 (a)Images of progressive treatment using en masse retraction of the overjet and upper arch distalization with the placement of a TAD on the upper posterior segment. Position “x” is the position of the TAD, and elastics are worn to an esthetic button bonded on the canines. (b)An attachment is placed on the canine tooth to negate any side effects of the elastic traction.

Oct 9, 2021 | Posted by in Orthodontics | Comments Off on Routine Mechanics and Aligners (Extraction/Nonextraction)
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