Expansion in the absence of crossbite – rationale and protocol

Rationale for transverse correction

Inadequate transverse occlusion has been claimed to coexist with non-carious cervical wear, i.e., abfraction possibly due to increase in non-axial loading causing cuspal flexure and stress concentration in the cervical region.^[20] Gingival recession has also been reported to be induced by transverse deficiency.^[21] In terms of masticatory function Choi et al.^[22] reported in their clinical study that subjects with non-sagittal transverse malocclusion such as buccal edge to edge bite exhibited remarkably low masticatory ability index and food intake ability.

In terms of occlusal manifestation, it is clear that transverse discrepancy in the posterior area indirectly affects the incisal relationship. For instance, excessive crowding in the maxillary arch without obvious anteroposterior jaw discrepancy may reflect narrow maxilla, which necessitates active transverse correction. Unless the transverse discrepancy is corrected, it would be difficult to correct the incisor relationship and detail the occlusion optimally.^[23]

In terms of esthetics, the transverse dimension is the least studied. Patients with constricted and narrow maxillary arch will have large buccal corridors. Sarver et al.^[24] studied the effect of buccal corridor size on smile esthetic and found that large buccal corridors to be unesthetic.

Diagnosis of transverse problem

It is vital to assess the craniofacial skeleton in the transverse dimension as early as possible and accurately diagnose the need for transverse maxillary expansion, to improve the efficiency and effectiveness of treatment. This has driven the continued evolution and development of diagnostic tools for evaluating the maxillary transverse dimension.

Diagnosis of maxillary transverse deficiency can be difficult and often includes the use of one or more of the following methods:

Clinical evaluation

Clinical evaluation includes assessment of the maxillary arch form and symmetry, width of the buccal corridors on smiling, occlusion, and predominant mode of breathing.^[25] The clinical evaluation further evaluates the degree of crowding, arch width measurement at the mucogingival junction and dental crowns, perceived buccolingual inclination of posterior teeth, and the shape and height of the palatal vault.^[26] One of the problems with the clinical assessment is that it is based on clinical crowns without consideration for the buccolingual inclination of the roots, which may camouflage the true skeletal transverse deficiencies.^[27] There may be minimal soft tissue changes associated with maxillary transverse deficiency including paranasal hollowing, a narrow nasal base, deepened nasolabial folds and zygomatic hypoplasia, and wide buccal corridor. Therefore, anteroposterior and vertical maxillary hypoplasia are much easier to clinically diagnose due to observable soft tissue changes. Where anteroposterior and vertical maxillary dysplasias exist, they can clinically mask a transverse deficiency rendering clinical evaluation alone inadequate for diagnosis of transverse skeletal discrepancies.^[28,29]

Dental cast assessment

Study models are useful in assessing the archform and inclination of the posterior segments. Several indices have been proposed by various authors to measure lateral discrepancies. Most commonly used indices are Pont, Linder-harth, and Korkhaus.^[30] Although these indices offer a guide to assess the transverse discrepancy, they are population specific and not completely reliable. McNamara and Brudon^[31] recommended measuring the transpalatal width from the gingival margin of the lingual groove of the first molar to the first molar of the other side. They establish a mean normal value from age of 7 to 15 years. The patients transpalatal width can be compared with the reported values to determine if the upper arch is normal. Caution should be exercised in employing this method since the norms are combined with both genders, and the dental compensations are not considered.

WALA ridge

Andrews^[32] proposed using the WALA ridge to serve as a landmark for assessing mandibular arch form which in turn can provide a template for the maxillary arch form. Andrews^[33] observed that when an optimal arch is viewed from the occlusal perspective, the distance of FA point of the first molars to WALA ridge should be 2 mm. In this position, the mandibular first molars are decompensated, and the arch width between the central fossa of the mandibular molars is the optimal mandibular arch width. Ideally, the distance between the mesiolingual cusp tips of the right and left maxillary first molars should be equal to the distance between the mandibular right and left central fossa. Since the diagnosis is made on a dental cast, the root position in the alveolar bone is not taken into consideration.^[34]

Recently, an attempt has been made to relate the position of the root obtained from cone-beam computed tomography (CBCT) to WALA ridge evaluated from the dental cast. It was established that although teeth more closely related to WALA ridge are not centered in the alveolar bone or over basal bone, there seem to be a definitive relationship between center of resistance of the posterior teeth and to the WALA ridge, this finding implies that the WALA ridge may serve as a useful landmark for determining arch constriction and customizing archforms.^[35]

Posteroanterior cephalometric analysis

In the 1990s, PA cephalogram was considered the most readily available and reliable radiograph for evaluating transverse skeletal dysplasia. Ricketts^[36] developed Rocky Mountain analysis and had suggested norms and differentials that allow one to determine departure from the ideal and to establish the degree of treatment difficulty for a particular patient’s problem. Betts et al.^[21] developed a PA analysis method using the Rocky Mountain analysis norms and landmarks. The analysis involves calculating the maxillomandibular width differential. This differential indicates that a transverse discrepancy greater than Ricketts norm of 1.96 mm even in the absence of crossbite requires skeletal expansion and that a surgical approach may be essential in adults.^[37]

However, the PA cephalogram is not routinely used by clinicians because of the limitations related to landmark identification errors, superimposition, magnification distortion, and head rotation affecting horizontal relationship resulting in inaccuracies in estimating the maxillomandibular width.^[38]

To intercept maxillary crowding in the mixed dentition

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 upper permanent lateral incisors. When crowding is limited to few millimeters, normal growth could provide adequate space, but when the palate is narrow, and the crowding exceeds this amount RPE could represent an effective procedure. Space would be gained not only at the alveolar bone but also in the basal bone when canines and premolars are crowded too.^[40] While the benefit of this approach has been highlighted by some,^[40] the rationale for using RPE in the absence of crossbite has been questioned by others.^[41-43] Since there is a possibility of the maxillary molars tilting further buccally, it may result in further exaggeration of the curve of Wilson. Moreover, the amount of expansion needed to correct the incisor crowding may be insufficient.^[42]

To counteract the development of a scissor bite following further buccal tipping of the first permanent molars, Schepp^[44] proposed the use of transpalatal bar to create a posterior crossbite before RPE. Marshall^[45] proposed the use of crisscross elastics. McNamara^[46] suggested uprighting of lower molars with expansion plates to avoid the scissor bite and others^[40] have recommended anchoring the palatal expander on the second deciduous molar and second deciduous canines. The benefits of this approach have been documented by Rosa,^[47] da Silva Filho et al.,^[48] Cozzani et al.,^[49] Lima et al.,^[50] and Cozzani et al.^[51]

Correction of arch length tooth size discrepancy

Crowding and protrusion of teeth are two of the common manifestations of arch length tooth size discrepancy. Howe et al.^[52] have shown that dental crowding appears to be related more to a deficiency in arch perimeter than to teeth that are too large. A primary factor in dental crowding often is a maxillary transverse discrepancy. If the position of the maxillary dentition reflects the skeletal discrepancy, it results in crossbite. On the other hand, if maxillary constriction is camouflaged by the dentition, and both dental arches are constricted, crowding in the absence of a crossbite is observed. RPE in the late mixed/early permanent dentition stage is helpful in obtaining meaningful increase in arch width and perimeter in cases where there is no crossbite.^[53] [Figure 1] Yet another advantage of using the acrylic splint expander in the mixed dentition is that it can result in spontaneous widening of the lower dental arch thereby providing space for correcting crowding of the lower incisors.^[53]

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Figure 1:

(a) A 8-year-old male in mixed dentition with maxillary arch constriction and crossbite of the right lateral incisor. (b) Before and after rapid palatal expansion. (c) On completion of Phase II treatment which was initiated after the eruption of all permanent teeth and completed in 16 months.

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Correction of the Class II malocclusion

Class II malocclusion is commonly observed in orthodontic patients. Tollaro et al.^[54] documented an underlying posterior interarch transverse discrepancy of 3–5 mm in subjects with Class II malocclusion in the early mixed dentition without posterior crossbite in the centric occlusion. When these Class II subjects posture their lower jaw forward to a Class I molar relationship, the maxillary transverse discrepancy becomes apparent. It has been postulated that in these subjects, the mandible assumes a distal position relative to centric relation because of the maxillary constriction. Several authors^[55-58] have recommended widening the maxilla with rapid maxillary expansion (RME), which often leads to spontaneous forward posturing of the mandible during the retention period. It has been hypothesized that expanding the maxilla disrupts the occlusion. The patient apparently becomes more inclined to position the jaw slightly forward^[59] thus eliminating the tendency toward a buccal crossbite and at the same time improving the sagittal occlusal relationship. Presumably, subsequent growth and remodeling of the structures of the temporomandibular joint make this initial postural change permanent^[53] [Figure 2].

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Figure 2:

(a) A 9-year-old female in late mixed dentition with convex profile, retrusive mandible, constricted maxillary arch, retroclined maxillary incisor. (b) Bonded rapid palatal expansion device, before and after expansion. (c) After completion of II^nd phase of treatment resulting in improvement in facial profile in addition to eliminating arch length tooth size discrepancy.

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RPE for altering airway dimension and breathing

Sleep-related breathing disorder (SRBD) encompasses multiple conditions associated with increased upper airway resistance during sleep. OSA is perhaps the most severe forms of SRBD. OSA affects 1%–5% of school-age children.^[60] The peak onset of SRBD symptoms in pediatric population occurs between 2 and 8 years of age.^[61] Children with mouth breathing and SRBD have alteration in dental and craniofacial morphology. These alterations could include extended head posture, lower hyoid bone position, anterior and inferior posture of the tongue, more retrognathic and posteriorly inclined mandible, large anterior and total facial height, large mandibular plane angles, narrow maxilla with or without a posterior crossbite, proclined maxillary incisors, and retroclined lower incisor.

In 2004, Pirelli et al.^[62] performed RME on 31 children with a mean age of 8.7 years with normal BMI, constricted maxilla, absence of adenoid hypertrophy, and diagnosis of OSA based on PSG. The subjects had a mean baseline AHI of 12.2 events/h that dropped below one event per hour in all subjects at 4 months follow-up.

A more recent systematic review and meta-analysis by Camacho et al.^[63] looked at sleep study outcome in children who had undergone RME as treatment for OSA. It has been hypothesized that, since the maxillary bones form half of the nasal cavity’s structures, when the midpalatal suture is opened, the nasal cavity’s lateral walls are also displaced apart, and its volume increases and upper airway resistance decreases over time.^[64] Head posture had also been associated with respiratory function, and increased craniocervical angulation was observed as a functional response to facilitate oral breathing to compensate for nasal obstruction.^[65] Once RME results in increased nasal airway patency and reduced nasal airway resistance (NAR), the airway flow increases, and the craniocervical angulation consequently is reduced. Another reported consequence after RME is higher tongue repositioning, which could increase airway volume.^[66] [Figure 3] A recent systematic review,^[67] on the impact of RME on airway volume and nasal resistance concluded that there is moderate level of evidence that RME therapy during the growth period causes increases in nasal cavity width and the posterior nasal airway, associated with reduced NAR and increased total nasal flow. The stability of the results can be expected for at least 11 months after the orthopedic therapy. All changes in airway dimensions and functions might improve the conditions for nasal breathing but cannot be indicated only for this purpose [Figure 3].

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Figure 3:

(a) A 8-year-old female patient with increased anterior facial height, convex profile, lip incompetence, and occlusal feature characteristic of altered breathing. (b) Maxillary expansion with bonded rapid palatal expansion. (c) At age 13, on completion of second phase of treatment with no further increase in facial height and improved maxillary arch form.

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Expansion for altering the buccal corridor width

Recent years have seen an increasing emphasis given to face and smile esthetics by dental professionals and patients alike. Maxillary constriction is very common in orthodontic patients, which can affect occlusion, facial development, and smile esthetics. RME is a treatment often indicated for correction of transverse skeletal deficiency by means of maxillary expansion appliances.

de Carvalho^[68] conducted a study to evaluate the effect of palatal expansion in individuals with maxillary transverse deficiency. The transverse dimension of the smile and the right buccal corridor showed statistically significant differences during the study period (P < 0.05). It was found that the transverse distance of the smile had a statistically significant increase from time T₁ to times T₂ and T₃ and the buccal corridor remained virtually unchanged even in the long term. Other methods of increasing the transverse dimension to reduce the buccal corridor width include the deployment of passive self-ligating appliance with wide arch forms^[69] [Figure 4].

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Figure 4:

(a) Pretreatment appearance of a 13-year-old female with a narrow buccal corridor and blocked out maxillary left canine. (b) Treated non-extraction with a passive self-ligating system and wide arch form. (c) At the completion of treatment at age 15 with improved smile esthetics and reduced buccal corridor width.

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Bidental arch constriction

Bidental arch constriction has only recently been recognized as an orthodontic problem. Associated with the constriction of the width in both arches is the decrease in anterior arch perimeter and crowding. Handelman^[70] has defined this malocclusion as bidental arch constriction syndrome, and it has the following characteristics:

1. Narrow maxillary and mandibular transverse widths

2. Absence of posterior crossbite

3. Lingual inclination of the posterior teeth, especially the premolars

4. Decreased arch perimeter

5. Crowding of the anterior teeth

6. Insufficient anterior arch contour

7. Dark buccal corridors

Correction of this malocclusion requires maxillary palatal expansion with concurrent mandibular expansion [Figure 5].

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Figure 5:

(a) A 12-year-old male patient with retrusive profile, incompetent lips, wide buccal corridor, and bidental arch constriction. (b) Maxillary arch expansion with bonded rapid palatal expansion followed by mandibular buccal segment uprighting with multi-banded appliance. (c) At 14 years on completion of treatment with improved facial profile, reduced buccal corridor width, and elimination of bidental arch constriction.

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Gaining arch perimeter in adults

Maxillary arch constriction derived from an underlying transverse deficiency with or without a posterior crossbite is a common etiologic factor associated with dental crowding or protrusion. Therefore, improvement of the transverse arch dimension may play an important role in solving arch perimeter problems,^[7] maxillary transverse deficiency has been successfully treated in young patients by intervention on the mid-palatal suture for separating the maxillary bones with the RPE technique.^[71] However, in adults, as skeletal maturity advances there is progressive interdigitation of the sutures and increased stiffness of surrounding structures. In addition to the midpalatal suture, exerted forces must counteract the resistance provided by circummaxillary sutures and structures such as zygomatico maxillary buttress and sphenoidal structures.^[72,73] Therefore, if conventional tooth-borne RPE devices are employed in adults it can result in alveolar bending and dental tipping rather than eliciting a skeletal response.^[74] Consequently, root resorption, periodontal damages,^[75-77] failure or limited expansion,^[78] soft tissue swelling and ulcerations,^[21] and questionable long- term stability^[79] commonly results from conventional palatal expansion technique carried out in adult patients.

To overcome the dentoalveolar undesirable effects and maximize skeletal expansion potential, a non-surgical microimplant-assisted rapid palatal expansion technique was introduced.^[80] A modification of the device to further enhance the skeletal component and minimize the dentoalveolar tipping was proposed by Moon et al.^[81] The maxillary skeletal expander employs miniscrews that recruits the palatal and nasal cortices thereby augmenting the anchorage for facilitating opening of the midpalatal suture and overcoming the resistance from the circummaxillary sutures in adults.^[82] The effectiveness of this technique has been recently documented^[83] [Figure 6].

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Figure 6:

(a) 29-year-old female patient with convex profile, Class II molar relationship, constricted maxilla and arch length tooth size discrepancy. (b) Before and after expansion with miniscrew assisted rapid palatal expander (MSE) device. (c) Change in maxillary arch form, before and after completion of treatment. (d) On completion of second phase of treatment with improvement in occlusion and reduction in facial convexity.

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To facilitate sagittal correction in adults

Jacobs et al.^[84] introduced the term “relative and absolute transverse discrepancy.” A relative transverse discrepancy exists when the posterior teeth do not coordinate in centric relation but do coordinate when the canines are approximated in Class I occlusion. In patients with skeletal Class II malocclusion due to retrognathic mandible it would be difficult to surgically advance, the mandible unless the maxillary arch is widened pre surgically. Arch expansion may be indicated in a number of joint orthodontic- orthognathic cases to maintain arch coordination following correction of the sagittal skeletal discrepancy, and a good post-surgical occlusion is important for enhancing post- treatment stability.^[85] In skeletally mature patients surgically assisted rapid palatal expansion (SARPE) is indicated as a preliminary procedure even if future orthognathic surgery is planned.^[86]

SARPE procedures have traditionally been reported to have low morbidity, especially when compared with other orthognathic surgical procedures.^[87] However, many complications have been reported, and the surgeon and the orthodontist must be aware of these before recommending SARPE to a patient.^[86] The issue of long-term stability and relapse with SARPE has not been studied in detail in the literature. In general, most reports state that surgical expansion is more stable than orthopedic maxillary expansion.^[87-90] Further SARME is preferred over multiple piece maxillary osteotomy when the expansion needed is >10 mm, when significant intercanine width widening is needed and when the palatal vault is low [Figure 7].

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Figure 7:

(a) 42-year-old male with retruded mandible, increased overjet and constricted maxilla and mandible. (b) Cone-beam computed tomography evaluation revealing constricted maxillary apical bone and compensated dentition. (c) Surgically assisted rapid maxillary expansion for widening the maxilla before mandibular advancement surgery. (d) Following mandibular advancement and post-surgical orthodontics.

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