Tarek El-Bialy, Donna Galante, Sam Daher
Abstract
Although it has been reported earlier in 2005 that it is difficult to achieve full correction of sagittal relationship (class II or III) either dental or skeletal using clear aligners, pioneer reports by Boyd and Dahr [1, 2] have been stimulating to the creativity of orthodontists who may modify original protocols that were provided by Boyed and Dahr. Proper designing clincheck or treatment planning in class II cases is very important utilizing the principles of both functional appliances and bioprogressive techniques. The following cases will explain how to utilize both functional appliance and bioprogressive principles using clear aligners to correct class II cases. Although, this might seem as case reports or case series, further clinical trials are required to support or otherwise provide other evidences of using clear aligners in correcting class II skeletal and dental cases.
* Corresponding author Tarek El-Bialy: Faculty of Medicine and Dentistry 7-020D Katz Group Centre for Pharmacy and Health Research University of Alberta, Edmonton, Alberta T6G 2E, Canada; E-mail: telbialy@ualberta.ca.
Introduction
Previous reports have shown that class II cases can be treated by clear aligners [1–2]. All available publications in the literature are limited to the use of Invisalign for this type of treatment with no other clear aligners being reported to correct sagittal jaw discrepancy. Different protocols have been reported for class II treatment planning, however the most common ones are: 1) Premolar extraction using 1 mm rectangular attachments for root parallelism using Boyd protocol [1]; 2) Upper arch expansion and upper molar distalization using Dahr protocol where he proposes buccal crown torque (Power Ridge™ feature) on the upper incisors as he starts retraction on the incisors and lingual root torque on the lower incisors [2]. Also, in cases where upper molars distalization is recommended, third molars are recommended to be removed to allow for distalization of upper molars. In this case, class II elastics are recommended to be used to support anterior anchorage. According to Dahr [2], if buttons are to be used on the upper canines, it would be better to bond the buttons on the labial surfaces of the upper canines to apply distalization forces closer to the center of rotation.
In my opinion, center of rotation is a function of the tooth movement and it is less predictable to estimate its position, while center of resistance of the tooth is more predictable to locate. Applying the force as cervical as the crown allows, still create moment that tends to tip the canine crown distally and the root mesially by uncontrolled tooth movement. The protocol that has been recommended by Boyed seems to be valid that recommends using vertical square attachments on the canines that can provide couple, this couple can move the canine roots distally along with the crown tips. A detailed explanation of the two views is in the following sketch (Fig. 7.1).
Fig. (7.1))
Moment on upper canine without vertical attachment leads to clockwise moment and distal crown tipping of upper canine with most likely uncontrolled tipping of the canine. With vertical attachments (Right figure), a coupe is created with class II elastics that can lead to counter-clockwise moment that automatically upright the canine while retracting with class II elastics or any distal force. Detailed biomechanical analysis of vertical and optimized attachments are underway to provide the best option of either attachments for space closure.
As mentioned before in chapter 6, in order to correct class II malocclusion with proclined upper incisors, if the treatment objectives are to retract upper incisors by bodily movement, palatal root torque (labial crown tip/torque) is required to maintain proper axial inclination of upper incisors.
In his white paper, Dahr 2011 [2] presented an interesting protocol of class II correction with emphasis on using class II elastics and upper molar distalization. This chapter emphasizes on upper and lower incisor torque consideration and possible growth modification using clear aligners.
Previous case reports and publications about treatment of class II solely by Invisalign showed improvement of buccal occlusion, overbite and overjet [1–3]. However, most of these reports showed proclination of the lower incisors, in particular when class II elastics were used to distalize upper molars [2, 3], except cases reported by Boyed that showed lower incisor inclination is actually improved after treatment [1]. Exact mechanisms of how lower incisor inclination was improved in Boyed cases were not explicitly explained. In cases where lower incisor inclination are retroclined, it is understandable that class II elastics can procline lower incisors to normal position, however in cases with proclined lower incisors, it is unclear how mechanism(s) were used to retroclined after class II elastics. One can assume that lower crown torque or lower incisor pre-retroclination was requested/performed. This technique looks like the best way of handling class II, especially when class II elastics may be used to distalize upper molars.
Case 1: Class II With Bimaxillary Protrusion
A 19 year-old-female was presented to the clinic with a chief complaint of upper and lower front teeth sticking out that required improvement. Initial records in June 2008 revealed that the patient had a skeletal class II as seen by convex profile with retrognathic mandible and slightly recessive chin (Fig. 7.2). Regardless of the convex profile, it was accepted by the patient and she did not want to change it. Cephalometric measurements revealed bimaxillary dentoalveolar protrusion and proclination (Fig. 7.3), (Table 7.1). Lower incisor inclination was planned to be retroclined (lingual crown torque). Upper incisors were requested to be retracted to close all spaces (5 mm) in the upper arch. No Class II elastics were prescribed. Clincheck is seen in (Fig. 7.4).
Fig. (7.2))
19 years old female with bimaxillary dental protrusion and retrognathic chin.
| Initial | Final | ||
|---|---|---|---|
| Skeletal | |||
| SNA (°) | 85.8 | 85.1 | |
| SNB (°) | 79.3 | 78.5 | |
| ANB (°) | 6.4 | 6.4 | |
| Wits Appraisal (mm) | 3.6 | 3.3 | |
| FMA (MP-FH) (°) | 28.5 | 28.9 | |
| Lower Face Height (ANS-Me) (mm) | 63.8 | 61.8 | |
| N-Me (mm) | 111.7 | 110.1 | |
| Y-Axis — Downs (SGn-FH) (°) | 59.6 | 57.9 | |
| Dental | |||
| Interincisal Angle (U1-L1) (°) | 103.8 | 117.9 | |
| U1 – NA (mm) | 8.9 | 5.7 | |
| U-Incisor Protrusion (U1-APo) (mm) | 13.6 | 10.4 | |
| U1 – NA (°) | 31.4 | 24.6 | |
| U1 – SN (°) | 117.2 | 109.7 | |
| L1 – NB (mm) | 10.9 | 9.7 | |
| L1 – NB (°) | 38.4 | 31 | |
| IMPA (L1-MP) (°) | 98.8 | 90.6 | |
| Soft Tissue | |||
| Lower Lip to E-Plane (mm) | 4.8 | 5.7 | |
| Upper Lip to E-Plane (mm) | 0.6 | 1.4 | |
| Nasolabial Angle (Col-Sn-UL) (°) | 99.3 | 93.1 | |
| Facial Convexity (G’-Sn-Po’) (°) | 19.7 | 22 | |
| Upper Lip to Incisor (UL-U1) (mm) | 1.4 | 2.2 |
Fig. (7.3))
Initial cephalometric radiographs showing bimaxillary protrusion.
Fig. (7.4))
Clincheck side view, show class II end to end relationship of the right and left buccal segments.
Results
Fig. (7.5) shows that Class II correction was achieved mainly by upper molar de-rotation. Since upper incisor retraction was more than the lower incisor retraction, the achieved labial root torque is assumed to be due to lingual crown torque of the lower incisors by retraction of upper incisors more than the lower (Figs. 7.6 and 7.7, Table 7.1), however due to the resultant overbite, upper incisors did not go to cross bite and instead, upper incisors’ retraction produced lower incisor lingual crown (labial root) torque. Upper and lower incisors’ inclination and protrusion were improved mainly by retraction and closing by upper and lower spaces.
Fig. (7.5))
Clinical photos of the Patient AB19 after treatment.
Fig. (7.6))
Cephalometric radiograph for Patient AB 19 after treatment.
Although FMA did not change much, Y-axis was closed and this could be attributed to the fact that the occlusal covering of posterior teeth might have been working as a posterior bite blocks that led to slight intrusion of posterior teeth and consequently slight autorotation of the mandible, improving class II as well as Y-axis and recessive chin.
Fig. (7.7))
Patient AB19 superimposition of before and after treatment cephalometric digitized tracings and clincheck. Difference of incisor position before and after treatment can be seen.
Superimpositions of before and after cephalometric digitization as well as clincheck superimposition (Fig. 7.7 and Table 7.1) show that upper incisors were retracted while lower incisors were torqued (labial root torque [lingual crown torque]). The obtained lower incisor lingual crown torque by maximum retraction of upper incisors seems to be a new and novel approach to control lower incisors’ inclination. A valid criticism would be that this acheived lingual crown torque of lower incisors could be just a cephalometric tracing error that needs further documentation. The following cases are the best proof of this principle using cone-beam-computed-tomography (CBCT).
Fig. (7.8))
Clinical photos and cephalometric radiographs generated from initial CBCT of patient LJ that show convex profile and recessive chin. Class II division 1 malocclusion with impinging overbite and median diastema. Patient was biting on the plastic bite-piece while scanning CT which could show an over presented class II. However, upon autorotation of the mandible using Anatomage and re-digitization, cephalometric analysis confirm class II as outlined in figures 7.9 and 7.10 below.
Case 2: Class II
A 15 year-old male was presented to the clinic with chief complaint of sticking out and spaced upper front teeth that needed to be fixed. No medical history of concern was recognized. Clinical records showed that he has meso-cephalic facial form and convex profile due to recessive chin (Fig. 7.8). Digital models showed a class II division 1 malocclusion with overjet 11.5 mm and 100% overbite. Mild upper spacing and minimal lower dental arch crowding (Fig. 7.9). Cephalometric records and analysis confirmed that the patient has a skeletal class II relationship due to mandibular reterognathism, bimaxillary dentoalveolar protrusion and proclined upper and lower incisors (Fig. 7.10, Table 7.2). TMJ tomograms showed forward inclined mandibular condyles, which according to Bjork [4], provides the likelihood of late forward mandibular growth.
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