11: Interceptive orthodontics with aligners

Tommaso Castroflorio, Serena Ravera, Francesco Garino

Introduction

Early orthodontic treatment is still a debated argument. According to the existing literature, the usefulness of interceptive orthodontics is controversial even if many sagittal, vertical, and transversal malocclusions are clearly visible and diagnosed in the early mixed dentition.¹

Some authors recommend interceptive treatment because many malocclusions tend to worsen with age.² Some other studies have underlined that orthodontic treatment during the pubertal phase may positively influence malocclusion improvements, contributing to the stability of final results.³

However, a recent review stated that removable functional appliances can produce short-term good dentoalveolar effects rather than skeletal improvements.⁴ Furthermore, a recent update of a Cochrane review claimed that on the basis of low to moderate quality evidence, providing early orthodontic treatment for children with prominent upper front teeth is more effective for reducing the incidence of incisal trauma than providing one course of orthodontic treatment in adolescence. There appear to be no other advantages of providing early treatment when compared to late treatment.⁵

The reduction of upper incisor proclination should not be underestimated because the smile appearance is important among overall esthetics for adolescents as well as for children younger than 10 years of age. Correcting smile alterations, even in young children, may be fundamental in preventing bullying or teasing from others and in improving the quality of social interactions, preserving healthy psychologic development.⁶

Interceptive orthodontics could be also recommended when detecting bad oral habits as atypical swallowing and mouth breathing have been found to be strictly related to malocclusion worsening.⁷ Moreover, early orthodontic treatment mainly consisting in maxillary expansion and mandibular advancement has been indicated to treat pediatric sleep apnea patients.⁸

The controversial results deriving from the existing literature in terms of effectiveness of interceptive orthodontics are mainly related to the lack of specific indicators of the right biologic timing of intervention. Although no skeletal maturity indicator may be considered to have a full diagnostic reliability in the identification of the maxillary growth peak and of the pubertal growth spurt or mandibular growth peak, treatment timing according to available indicators (mainly hand and wrist maturation [HWM] and cervical vertebral maturation [CVM] methods) has yielded more favorable outcomes. The use of the HWM or CVM methods (or others) may still be recommended for treatment planning, even though large individual responsiveness and dentoalveolar compensations have been reported, even in pubertal patients.⁹

In this chapter, we focus on clear aligner interceptive orthodontics of class II retrognathic patients and of patients with maxillary constrictions, highlighting the recommendations for case selection and treatment planning, showing some case reports.

Maxillary expansion

Transverse maxillary constriction and maxillary crowding in children are problems commonly encountered and treated by orthodontists.10–12 Interceptive orthodontics with maxillary expansion (ME) is one of the treatment options recommended for children with transverse deficiencies with the intent to increase the transverse widths of the maxilla. This approach is particularly important in children with posterior crossbite because it has been shown to determine abnormal chewing patterns and the development of skeletal asymmetries.¹³^,¹⁴

Expansion is especially desirable for young class II division I patients who have constricted maxillae because the transverse deficiency does not self-correct between the deciduous, mixed, and permanent dentitions.¹⁵ Increasing maxillary arch width could improve class II with retrognathic mandible, inducing a spontaneous forward repositioning of the mandible, even if there is still a lack of general consensus on this issue.¹⁶^,¹⁷ Maxillary arches are also expanded routinely to solve anterior crowding and improve the smile esthetics of kids.⁶^,^18–20 Crowding of the permanent incisors, with associated rotations and/or anterior crossbite, is commonly observed during eruption of the permanent lateral incisors. The rationale of interceptive treatment in the early mixed dentition is to generate adequate space for the spontaneous alignment of the permanent upper lateral incisors prior to complete eruption. When crowding is limited to a few millimeters, normal growth could provide adequate space, but when the palate is narrow and the crowding exceeds this amount, maxillary expansion could represent an effective procedure.²¹ As stated by Rosa et al.,²¹ when planning interceptive rapid maxillary expansion (RME) in absence of posterior crossbite, the clinician should consider that first permanent molars are often tilted buccally, and a further buccal movement will produce periodontal problems and posterior occlusal interferences related to the deepening of the Wilson curve. Furthermore, the amount of anterior expansion could not be enough to solve the anterior crowding. Ideally the expansion should be limited to the anterior region of the arch, while permanent molars should move in a palatal direction.

Considering these aspects, maxillary expansion by anchorage on deciduous teeth has been proposed. The benefit of anchoring the expander on second deciduous molars and deciduous canines was the gain of 5 to 6 mm in upper arch perimeter. The gained space is sufficient to solve anterior crowding without tilting buccally permanent molars. However, those teeth spontaneously follow the buccal movement of deciduous molars for about 60% of their movement.

When thinking about differences between several activation protocols for maxillary expansion, a recent systematic review²² helps us to understand some outcomes comparing slow maxillary expansion (SME) and RME; there is moderate evidence showing that maxillary transverse diameters increase significantly within both groups in the short-term,²³ but SME protocol is more predictive of bodily upper molar movement, while the RME protocol produces more tipping movement in the molar region.²⁴

RME uses heavier interrupted forces to maximize orthopedic effects, and slow palatal expansion uses lighter continuous forces to move teeth at rates purported to be more physiologic.¹¹ Aligners use intermittent light forces to move teeth, and intermittent forces are able to produce orthodontic tooth movement with less cell damage in the periodontium.²⁵ Since it has been stated that light, continuous forces seem to be perceived as intermittent forces by the periodontium due to its viscoelastic nature,²⁶ the expansion produced by aligners could be described as SME.

A clear aligner maxillary expansion protocol has been recently proposed (Invisalign First, Align Technology, Inc., San José, CA, USA). Aligners could overcome some of the limitations presented by palatal expander particularly in non-crossbite cases. With these appliances, it is possible to control the movement of all the teeth in the maxillary arch, aiming to produce an initial alignment and leveling while expanding the arch. Aligners can be really helpful in controlling maxillary first molars not only on the frontal plane but on the horizontal and sagittal planes, too, avoiding all the issues mentioned earlier in relation to potential periodontal problems. Furthermore, aligners can control the expansion limited to the anterior region of the arch to generate adequate space for the spontaneous alignment of the permanent upper lateral incisors prior to complete eruption.

Because of the short clinical crowns of deciduous teeth, specific attachment shapes were designed to increase aligner retention and control the tipping movement to obtain torque compensation and avoid a deepening of the curve of Wilson (Fig. 11.1).

Fig. 11.1Invisalign First optimized attachments for maxillary expansion.

Regarding staging, two options are available at the moment: (1) Permanent molars (if required by the treatment plan) will be moved buccally, using the rest of the arch as anchorage, and only once they have reached their final position will the deciduous molars and canines be moved buccally using permanent molars and incisors as anchorage units. (2) Permanent molars and deciduous teeth are moved buccally in a simultaneous manner (Fig. 11.2). Because of the geometry of the aligners, their distal portions are not stiff enough to support a predictable buccal movement of so many teeth at the same time, making this staging not the first-line treatment option.

Fig. 11.2Invisalign First maxillary expansion protocol staging.

Timing is another important factor to be considered. The best timing to expand maxillary arch is during the early mixed dentition, before upper permanent lateral incisor eruption and after the permanent molars are fully erupted and in occlusion. This timing is favorable as the midpalatal suture is more immature.²⁷ In young children, up to age 8 or 9 years, little force is needed. Up to that age, a transpalatal lingual arch releasing light continuous forces for dental expansion also will open the midpalatal suture.²⁸ Therefore, it can be assumed that intermittent forces released by aligners can be sufficient in children up to 8 or 9 years of age to act on the transversal dimension of the maxilla.

A recent clinical trial conducted at the University of Torino (Torino, Italy) in which clear aligners and RPE effects in patients with maxillary constriction were measured on digital models, suggests that:

■ A significant increase in palatal volume, so as in the other parameters, has been proved for both treatments.
■ The RPE slightly outperform clear aligners considering all the parameters tested.
■ The compliance and the clinical condition could affect the potential results achievable by the clear aligners.

The Clear Aligners demonstrated a reasonable ability to achieve palatal expansion. Since the materials have improved over the last years, so as the academic efforts to better understand the potential of CAT, substantial advances can be expected in the near future.⁵⁸

Expansion case reports

For the following case reports, three-dimensional (3D) evaluation of upper arch and palate morphology was performed according to a previous study by Bizzarro et al.²⁹ The upper arches were scanned using a 3D scanner (iTero Element). The 3D data were imported to a reverse modeling software package called Geomagic Studio (3D Systems, Inc).³⁰ Intermolar, intersecond deciduous molar, and intercanine transverse widths at the cusps and gingival levels were measured (Fig. 11.3), as well as anterior and posterior palatal depths at the cusp level, palatal surface area (Fig. 11.4), and volume (Fig. 11.5).

Fig. 11.3CG intercanine widths assessed at gingival level, CC intercanine widths assessed at cusp level, cG inter-E widths assessed at gingival level, cC inter-E widths assessed at cusp level, MG intermolar widths assessed at gingival level, MC intermolar widths assessed at cusp level.

Fig. 11.4The anterior and posterior depth of the palatal vault is defined as the vertical distance from the contact line between the cusp of the right and left canine and mesiopalatal cusp tips of the right and left first molars to the palatal vault, respectively. The palatal volume was defined by the median sagittal, distal, and gingival planes as boundaries of the palate. The distal plane *(DP)* passed through two points at the distal of the first upper permanent molars. The gingival plane *(GP)* was created by intersecting the distal and median sagittal planes *(MSP)* through the center of incisive papilla, which is considered a stable point structure.³¹ All planes were perpendicular to each other.

Fig. 11.5The palatal surface area was defined by the median sagittal *(MSP),* distal *(DP),* and gingival *(GP)* planes as boundaries of the palate. The distal plane *(DP)* passed through two points at the distal of the first upper permanent molars.

Case study 1

Consider an 8-year-old boy with upper central incisor protrusion, mild upper anterior crowding, and palatal tipping of deciduous teeth. Invisalign First was adopted, and sequential expansion of molars first and then deciduous teeth was planned within the ClinCheck, along with alignment of central and lateral incisors. The patient was instructed to change the aligners every week, and control examinations were planned every 6 weeks. Pre- and postexpansion scan screenshots are shown in Fig. 11.6. The expansion phase lasted 8 months. The palatal volume increased from 3843.54 mm³ to 5330.89 mm³ due not only to the vestibular dental tipping but also increased interarch widths measured at both gingival and a cuspal levels. Quantitative evaluations of intraarch widths, palatal areas, and volumes for this case are summarized in Table 11.1 as Case 1 reports.

Fig. 11.6Case 1 pre- (A) and post (B) therapy scans of the maxillary arch.

Table 11.1

Pre- and post-treatment volumetric and linear measurements obtained in the reported cases.

	A mm²	V mm³	CG mm	CC mm	cG mm	cC mm	MG mm	MC mm
Case 1 pre	1105.91	3843.54	22.6	29.1	28.2	32.2	32.6	36.8
Case 1 post	1316.57	5330.89	27.6	36.7	33.4	39.7	36	42.1
Case 2 pre	1111.67	4342.64	24.4	32.1	29.8	34.5	35.1	39.7
Case 2 post	1478.69	6948.68	26.3	37.5	32.9	39.5	35.4	42.1