Non-extraction treatment with maxillary expansion and interproximal reduction

Introduction

Non-extraction orthodontic treatment implies the correction of malocclusion and, thereby, improving facial profile, aesthetics and smile without sacrificing any permanent tooth/teeth.

In the past, facial balance and harmony were believed to depend on having a full complement of teeth. The jaws were ‘expanded’ to attain the space required to align the crowded teeth and correct protrusion. Expansion with an E arch and similar approaches was believed to promote alveolus development as the teeth were aligned. The appliances used were ‘E arch’ and similar, which allowed dental and orthodontic expansion. Several concerns were raised with the non-extraction philosophy of treatment mainly due to poor profile outcome, unstable occlusion, relapse of crowding and iatrogenic undesirable periodontal effects in many of the treated cases. In many instances, poor facial aesthetics resulted from bimaxillary protrusion, which was created to house the full complement of teeth on poorly developed denture bases. ^,

The philosophy of non extraction treatment was promoted by Edward H Angle and practiced by his disciples in letter and spirit. However later Drs Charles H. Tweed, P. R. Begg and Robert Strang’s supported reducing dental units to relieve crowding and improve protrusion and stability of occlusion. The initial hesitation to extract in suitable cases slowly turned into a routine orthodontic practice (See chapters 51 and 52 ). The extraction of four first premolars, followed by a course of fixed orthodontic appliances, became a standard treatment approach. However, overzealous extraction of premolars in adolescent patients led to poor treatment outcomes, which were noticed after growth was completed. Other problems of non judicious extractions were as follows:

1.
Dished in faces. These children grew up with so-called ‘orthodontic profiles’.
2.
Large and dark buccal corridors.
3.
The stability of lower incisor crowding was only sometimes guaranteed because many other factors influenced the stability of dentition.
4.
Premolar extraction treatment was linked with temporomandibular joint (TMJ) disorders.

Witzig and Spahl suggested that premolar extraction caused a posterior displacement of the condyle in the glenoid fossa, resulting in the perforation of the articular disc. The TMJ attributions of dental extractions for orthodontic purposes discouraged orthodontists from considering extraction plans and think of alternative treatment modalities. The pendulum of extraction swung back to non-extraction approaches.

Over the past 20 years, orthodontic treatment approaches have shifted towards non-extraction treatments. Many methods not commonly used before have been modified to suit current practice. Examples include non-compliance implant-supported intraoral molar distalisation and mini screw-supported maxillary expansion.

Factors influencing extraction decision

The decision to extract or not to extract should not be an ‘empirical’ one but based on sound judgement derived after a thorough clinical evaluation and study of the orthodontic records. Important considerations are as follows:

1.
Quantification of space requirements in the dental arch, that is tooth size arch length discrepancy.
2.
Profile of the patient, possible soft tissue thickness, posture and thickness of lips, shape and prominence of the nose, ethnicity of the subject.
3.
Remaining active skeletal growth and expected changes of the ‘soft tissue’ integument have considerable bearing on the extraction decision. The growth of the facial skeleton and soft tissue also shows a great deal of sexual dimorphism, which has a definite significance in the decision making.
4.
In the case of mixed dentition, due consideration must be given to the molar relationship, the possible transverse relationship of the maxilla/mandible (dentition) and the pattern of craniofacial growth, a horizontal or vertical growth.
5.
‘Leeway space’: Optimise its use in attaining class I molar relationship and resolution of crowding. This approach would necessitate a kind of forecast based on precise measurements of the ‘tooth size arch length’ discrepancy, growth potential and growth trend of the face.
6.
A case with apparent hereditary ‘tooth size’ discrepancy and potential crowding of more than 8 mm, which cannot be treated without extraction, should not be attempted for non-extraction treatment.

Non-extraction case

A child with skeletal class I bases and an acceptable profile, with minimal space requirements, can be best treated without sacrificing permanent tooth/teeth.

Several methods can be used in isolation or combination to gain space and resolve limited crowding and protrusion.

1.
‘Leeway space’ or ‘E’ spaces.
2.
Maxillary skeletal expansion and arch expansion:
- a.
  Rapid maxillary expansion (RME).
- b.
  Arch development with slow expansion devices and wire framework expansion appliances such as quad helix and its variations.
3.
Interproximal reduction (IPR) of tooth substance.
4.
Maxillary molar derotation.
5.
Molar distalisation.
6.
Mild proclination of teeth on denture bases within the limits of soft tissue tolerance.
- The retroclined anterior teeth can be proclined to relieve 2–3 mm of crowding within permissible limits of soft tissue accommodation without compromising periodontal support and thickness of labial cortical plates.
7.
Functional appliances are used to correct the sagittal discrepancy and transverse development and enhance the volume of the oral cavity. Frankel’s appliance and twin block with maxillary expansion screw are known to produce transverse maxillary expansion and arch development.

This chapter will primarily focus on E space resolution, maxillary expansion and reduction of tooth material through interproximal reduction. The methods of molar distalisation are explained in detail in Chapter 60 . The other methods on non-extraction space again are explained at relevant chapters.

Preservation of leeway or ‘E’ space for resolution of crowding in the lower arch

‘E’ space can help relieve up to 4 mm of dental crowding in the mandibular arch. To benefit from E space, the molars must be prevented from moving mesially. This can help reduce crowding or the forward movement of the anterior teeth. A lingual arch is extended from the first molar on either side and attached to the lower bands. The lingual arch should be made with 0.036 in. SS wire and can be either passive or slightly active ( Fig. 59.1 ).

Image, AltText currently not available — Figure 59.1

Brennan and Gianelly preserved the ‘E’ space with a lingual arch in children with 4–5 mm incisor crowding which they could resolve it in 68% of their sample. Of the total studied subjects 19% had adequate space with only a marginal additional arch length increase of 1 mm/side. The maxillary arch was not required to be expanded. During the follow-up of 107 patients, there was a marginal increase in inter-canine and inter-premolar width and a slight (0.4 mm) loss of leeway space. The stability of such an outcome is expected to be satisfactory, as reported by Dugoni et al. in their study of 9 years post-retention follow-up. The common modalities are the lower lingual arch and the upper transpalatal arch or Nance button. Fully bonded fixed appliance therapy is successfully used in cases with minimal or no tooth-size arch length discrepancy (TSALD).

A case of non-extraction treatment in young girl with fully erupted dentition is presented in Fig. 59.2 .

Expansion of the narrow maxilla and arch development

Dental and skeletal expansion of the maxilla is required to normalise transverse deficiency within the maxilla or to accommodate a slightly wide mandible. Expansion of the maxilla is mainly indicated to correct a buccal unilateral or bilateral cross-bite and to gain arch length to relieve minor crowding or reduce proclination of the maxillary anterior teeth.

In mild or moderate crowding situations, choosing a non-extraction treatment with an expansion or extraction approach depends on the soft tissue profile and hard tissue structures. For a patient with a large nose and chin, it is advisable to expand the arch so that the labiodental sulcus does not diminish. Also, in patients with thin lips, expansion is preferable to extraction treatment to create fuller lips and decrease dark spaces.

However, in other situations, expansion of the dental arches may not be feasible. These conditions are mainly the limitations posed by the anatomy of the dental alveolus, where dental expansion will lead to roots of teeth moving labially or buccally, creating fenestration or dehiscence of the cortical plates, thus endangering their periodontal health and longevity of the dentition.

During the early mixed dentition stage in children below 9–10 years, the mid-palatine suture is not yet fully fused; therefore, skeletal maxillary expansion by mid-palatal split is a better possibility. In children aged 12 years and above who are in late permanent dentition, greater forces may be required to achieve skeletal maxillary expansion.

On average, every 1 mm increase of the inter-premolar width leads to a gain in the arch length by 0.7 mm.

Maxillary skeleton expansion constitutes a significant component of the comprehensive treatment plan to provide improved nasal respiration in children with increased nasal resistance, which can manifest as mouth breathing habit/snoring or partial obstructive sleep apnoea (OSA).

Over-expansion of the arches can move teeth ‘off their bony bases’ and into positions where the ‘soft tissue equilibrium is altered’, and the results are unstable.

Diagnosis of maxillary transverse deficiency and case selection

Transverse dimension diagnosis includes a systematic evaluation of the face and dentition in the frontal view, the sagittal dental relationships and the transverse skeletal relationships.

Clinical evaluation of a case for maxillary expansion

Frontal examination of the face requires careful attention to the chin position for any lateral deviation, which may indicate a unilateral cross-bite. A deviated chin needs detailed evaluation to determine the cause of facial asymmetry. However, immediate concern in a growing child should focus on any functional interferences of occlusion or a narrow maxilla. A narrow maxilla may lead to lateral jaw deviation, which can clinically be exhibited as a unilateral cross-bite. In primary or early mixed dentition, interference caused by a deciduous canine or retained incisor can cause a lateral shift of the mandible. Most unilateral cross-bites do not spontaneously correct and that functional changes are rarely detected in children; an untreated lateral shift can develop into asymmetry of the mandible by adulthood. The asymmetry can be largely eliminated if the cross-bite and the functional shift are treated during early mixed dentition. In the absence of a lateral shift, chin asymmetry and unilateral cross-bite are suggestive of a unilateral skeletal asymmetry. Bilateral cross-bite occlusion may be seen without lateral shift and chin asymmetry.

In sagittal advancement, clinically visible transverse discrepancies may be relative or absolute.

A relative transverse discrepancy occurs when the posterior teeth do not align properly in centric relation but fit well when the canines are brought to class I occlusion. For example, some class III malocclusions display posterior cross-bites that disappear when the mandible is brought to occluding in a class I canine relationship.

In contrast, the transverse discrepancy is absolute if a cross-bite still exists even when the dental casts are articulated in the class I canine relationship.

Study models

Dental study models with proper articulation matching intraoral centric occlusion offer a detailed review of occlusion. A narrow maxilla, asymmetrical arch development and palatal tilt of buccal segment teeth coexist with buccal cross-bite. The dental buccal cross-bite can coexist with a normal or a narrow maxilla. However, skeletal cross-bite features a constricted palate and dentoalveolar process that is mostly lean buccally.

The maxillary arch on the cross-bite side is usually narrower than the non-cross-bite side, and the mandibular arch on the cross-bite side is generally broader than the non-cross-bite side. A transpalatal width of 35–39 mm suggests the bony base is adequate to accommodate a permanent dentition of average size. The buccal crown inclinations of the molars seen at 7 years of age progressively become perpendicular to the transverse occlusal plane. Any deviation from this trend indicates dentoalveolar compensations. Posterior dental compensations can also occur as variations in arch form and symmetry.

Normal arch widths the rule of 34/27 : Handelman, in an extensive study of expansion effects, and control subjects derived norms for the trans-dental arch widths of the maxilla and mandible. Suggested average adult maxillary inter-first molar widths were 34.3 ± 2.8 mm, and the inter first premolar as 26.8 ± 2.3 mm. In the mandible, the first molar should be 32.4 ± 2.9 mm wide, and the first premolar should be 25.1 ± 2.8 mm wide. The arch widths were measured between the antimeres of the respective right and left teeth. These measurements have been conveniently called 34/27 for the maxilla and 32/25 for the mandible. If the trans-arch width of the first molar is below 34 mm in the maxilla or 32 mm in the mandible, or if the trans-arch width of the first premolar is below 27 mm in the maxilla or 25 mm in the mandible, expansion may be beneficial.
Maxilla-mandible differential : The expansion required can be determined by measuring the distance between the most gingival extension of buccal grooves on the mandibular first molars on either side. When the groove does not have a distinct terminal on the buccal surface, measure between points on the grooves located in the middle of the buccal surfaces. The maxilla is measured as the distance between the tips of the mesiobuccal cusps of the maxillary first molars. The average maxilla-mandible differential in persons with normal occlusion is +1.6 mm for males and +1.2 mm for females. In a narrow maxilla, orthodontists should attempt to overexpand the molars 2–4 mm beyond the required width to allow for post-expansion relapse. These estimates assume a malocclusion will be treated as a class I molar relationship.

The maximum limit of expansion varies between individuals and according to the severity of the malocclusion, but 10–12 mm should be considered as the upper limit of maxillary skeletal expansion correction.

Posteroanterior (PA) cephalogram

Posteroanterior radiographs are helpful in assessing the presence and magnitude of maxillary or mandibular asymmetry and transverse skeletal and dental discrepancies (also see chapter 28 ). This approach compares the left-to-right mandibular antegonial width to the left-to-right maxillary jugal width and estimates skeletal transverse discrepancies and the amount of expansion needed. The maxillomandibular differential is estimated between the mandibular width (AG-GA) and maxillary width (J-J’). A transverse differential of about 20 mm is considered satisfactory. The ratio of the maxilla to the mandible is about 80%, and the ratio of the nasal cavity to the maxilla ranges from 40% to 42%. Ruest has shown that class II division 1 malocclusions are 3 mm smaller in the maxillary skeletal width than of class I (normal) and at age 18.

Clinical and histological basis of maxillary expansion

In general, the effect of expansion on the maxillary bases diminishes as age advances. The patient’s age governs the choice of appliance and protocol (schedule) of expansion. Therefore, it is pertinent to study the fusion of the palatine suture. Melson studied postnatal development of the hard palate by histologic and microradiographic means on autopsy material aged 0–18 years. The growth in length of the hard palate until the age of 13–15 was due to growth in the transverse suture and apposition on the posterior margin of the palate. After this age, the sutural growth was found to decrease, whereas the apposition seemed to continue for some years. Based on her findings, she grouped the postnatal development of the palate into three stages. Table 59.1 shows postnatal stages of palatal development and suture fusion. ^,

TABLE 59.1

Postnatal stages of mid-palate growth and suture fusion

Stage I	During the infantile period, the mid-palatal suture is broad and ‘Y-shaped’ with the vomerine bone placed in a ‘V-shaped’ groove between the two halves of the maxilla.
Stage II	The stage II corresponds to the juvenile period. The suture becomes wavier and longer in the vertical aspect. The junction between maxilla and palatine bone becomes higher and assumes more of a ‘T-shape’.
Stage III	The stage III corresponds to the adolescent period. The suture is characterised by a more tortuous course with increasing interdigitation, which mechanically interlocks as in a ‘jigsaw puzzle’. The interdigitation of the articulation between the palatine bone and the maxilla did not permit separation without the occurrence of fracture. Closure of the mid-palatal suture progresses more rapidly in the oral than in the nasal surface of the palatal vault, and the intermaxillary suture starts to close more often in the posterior than in the anterior part.

CBCT classification of mid-palate growth

A novel method for individual assessment of mid-palatal suture morphology using cone beam computed tomography (CBCT) defines five stages of maturation of the mid-palatal suture.

The studied sample subjects, aged 5 to almost 11 years, did not exhibit any fusion of palate. Beyond that age up to 13 years, stages A and B typically were observed, and from 11 to 17 years, stage C was noted primarily but occasionally in younger and older age groups. A bony fusion of the palatine (stage D) and maxillary (stage E) regions of the mid-palatal suture was completed after 11 years only in girls. From 14 to 17 years, 3 of 13 (23%) boys showed fusion only in the palatine bone (stage D). Adults most frequently had a fusion of the mid-palatal suture (stages D and E). Accordingly, in stages A and B, a conventional RME approach, would have less resistance to forces and probably more skeletal effects than at stage C, when there are many initial ossification areas along the mid-palatal suture. Patients in stages D and E might be better treated by surgically assisted RME because of the fusion of the mid-palatal suture that has already occurred partially or fully, hampering the RME forces from opening the suture. Fig. 59.3 .i shows schematic drawing of the maturation stages observed in the mid-palatal suture fusion based on CBCT data. Fig. 59.3 .ii shows decision tree for classification of the maturation stages of the mid-palatal suture ( Table 59.2 ).

TABLE 59.2

Five stages of palatal fusion ages between 5 and 17, based on CBCT data

Correlate with age in text and sexual variations in age of the fusion

Stage A	The mid-palatal suture is almost a straight, high-density sutural line with no or little interdigitation. In the studied sample, children from 5 to almost 11 years of age did not exhibit any fusion of palate.
Stage B	The mid-palatal suture assumes an irregular shape and appears as a scalloped high-density line. Patients at stage B can also have some small areas where two parallel, scalloped, high-density lines close to each other and separated by small low-density spaces are seen.
Stage C	The mid-palatal suture appears as two parallel, scalloped, high-density lines that are close to each other, separated by small low-density spaces in the maxillary and palatine bones (between the incisive foramen and the palatinomaxillary suture and posterior to the palatinomaxillary suture). The suture can be arranged in either a straight or an irregular pattern.
Stage D	The fusion of the mid-palatal suture has occurred in the palatine bone, with maturation progressing from posterior to anterior. In the palatine bone, the mid-palatal suture cannot be visualised at this stage, and the para-sutural bone density is increased (high-density bone) compared with the density of the maxillary para sutural bone. In the maxillary portion of the suture, fusion has not yet occurred, and the suture still can be seen as two high-density lines separated by small, low-density spaces.
Stage E	Fusion of the mid-palatal suture has occurred in the maxilla. The actual suture is not visible in at least a portion of the maxilla. The bone density is the same as in other regions of the palate.

Expansion appliance devices and uses

Emerson C. Angell documented the first case of orthodontic maxillary expansion to correct a transverse deficiency in 1860. He used a jackscrew appliance on a 14-year-old girl to create space for a labially displaced canine.

Maxillary expansion appliances can be broadly grouped into two categories: fixed or removable appliances. A typical expansion screw device consists of a rectangular piece of metal which is the body, divided into two halves. Each half has a threaded inner side that receives one end of a double-ended contrarotating threaded screw. The screw has central bossing with four holes. Each turn yields approximately one-fourth of a millimetre of activation to the appliance ( Fig. 59.4 ). Conventional expansion screw appliance can produce 2–4 mm increase in intermolar width as shown in Fig. 59.5 .

Based on the expansion protocol, an expander can be called a rapid expansion appliance or a slow expansion appliance.

Rapid maxillary expansion (RME)

Expansion of the jaw is termed ‘rapid’ when the expansion appliance is activated at a rate of 0.5–1 mm/day which is made possible by either two-quarter turns of the screw/day or two-quarter turns twice in a day. RME is indicated in a variety of malocclusions showing transverse deficiency of skeletal and dental dimension; however, not all conditions and age groups are suitable. A summary of indications and contraindications of RME are compiled in Table 59.3 . ^,

TABLE 59.3

Indications and contraindications of rapid maxillary expansion (RME)

S.no.	Indications	Contraindications
1	A narrow maxilla in absolute terms. A discrepancy of 4 mm or more between the maxillary and mandibular first molar and premolar widths.	In general, subjects with anterior open bites, steep mandibular planes and convex profile are not indicted for RME. An increased mandibular plane angle is not an absolute contraindication for RME therapy.
2	Class III malocclusion with narrow maxilla/pseudo class III of dental and skeletal in nature.	Age. The upper age limit is when the synostosis of the mid-palatal suture has occurred. However, with adjunctive surgery, this is surmounted.
3	A narrow maxilla in conjunction with nasal stenosis.	Poor periodontal health provides insufficient anchorage support.
4	A severe buccal cross-bite involving multiple teeth.	A condition where the maxilla and mandible both are constricted with a long face is a normal condition for this type of face.
5	Skeletal narrowing of the maxilla.	With new modalities of miniscrew supported and surgically assisted RME, the several limitations of age and dental anchorage in traditional RME appliances are no longer applicable.
6.	A narrow maxilla shows a lack of marginal space for erupting canines, and other conditions are normal. RME in the early mixed dentition appears to be an effective procedure to enhance the rate of eruption of palatally displaced maxillary canines (65.7%) when compared with an untreated control group.

RME results in rapid correction of the cross-bite in 2–6 weeks. A midline diastema may appear, which is suggestive of the mid-palatal split. The mid palatal spit occurs in V shape with its apex at posterior nasal spine and opening at anterior nasal spine. This diastema would close spontaneously due to the recoil of the stretched trans-septal group of gingival fibres. Slight over expansion of the maxilla whereby lingual slopes of maxillary lingual cusps touch mandibular buccal cusps is a desired clinical practice. This over-expansion makes allowance for the relapse, particularly of the buccal tipping of the molars. Following the completion of the expansion, the appliance is left passive to serve as a retainer for another 6 months.

Mid-palatal suture opening during orthodontic treatment with RME amounted to 12%–52.5% of the total screw expansion. After RME, the mid-palatal suture seems to undergo recalcification, so the expansion of the mid-palatal suture is stable. This systematic review by Liu et al. could not find consistent evidence on whether the mid-palatal sutural opening was parallel or triangular.

The osteogenic reaction in the expanded mid-palatal suture and orthodontically induced osteogenesis in the periodontal ligament (PDL) of adjacent incisors show different reactions. The widened PDL resulted in direct osteogenic induction of new bone, whereas the adjacent expanded suture experienced haemorrhage, necrosis and a wound-healing response. Vascular invasion of the blood clot in the expanded suture is a prerequisite for new bone formation.

When the maxillary molars are buccally inclined, a conventional dentoalveolar expansion will tip them further into the buccal musculature; therefore, a rapid expansion is the modality of choice. In another situation of dentoalveolar compensations to a narrow maxilla, the mandibular molars may be lingually inclined. An attempt to place the mandibular dental segments on the skeletal base would result in cross-bite and a need for maxillary skeletal expansion.

Design of RME

RME appliances can be broadly grouped into a bonded appliance or banded appliance the way these are retained in the mouth

The banded expansion appliance is attached to teeth through bands on the maxillary first molars and first premolars. The original design of RME proposed by Haas included an additional cover of the palatal vault with acrylic. This appliance design has been discarded due to the difficulty associated with keeping it clean, more so on the palatal surface. Consequently, all wire framework HYgienic RApid eXpander or HYRAX appliance was introduced ( Fig. 59.6 A).

Banded appliances cannot be used in deciduous and early mixed dentition. The alternate appliance design involves a wire framework and acrylic components which help to cement or bond the appliance. Similar RME appliance design is also indicated in subjects with high Frankfurt mandibular plane angle (FMA). The molar extrusion can be minimised by extending the acrylic over occlusal and buccal surfaces.

This appliance design is particularly useful in class II conditions, as molar extrusion would cause a backward and downward rotation of the mandible, resulting in an increase in facial convexity and the vertical dimension of the lower face. The bonded expansion appliance provides a bite block type of effect to facilitate the correction of anterior cross-bite in class III young subjects. The bonded appliance design can also be used in permanent dentition for its ease of delivery and some useful clinical effects. The need for the placement and removal of separation elastics, band adaptation and transfer into alginate impression, precision wire bending and soldering is eliminated.

Cemented hygienic rapid expansion (HYRAX) appliance : The design of the cemented HYRAX appliance is extremely critical: the acrylic component of the appliance should cover the crowns of the teeth, leaving only 1 mm of clearance at the gingival margins along the buccal and palatal aspects. This ensures a maximum surface area for retention and sufficient clearance at the gingival margins to allow the maintenance of good oral hygiene. The acrylic extensions should have a chamfer finish to minimise food retention. Acrylic occlusal coverage does not need to be more than 1–2 mm in thickness, and holes should be drilled into it to allow excessive cement to escape. With the introduction of contemporary glass ionomer cement, the retention of cemented expanders has improved significantly, and there is no longer a need to use composite or acrylic-based materials that require acid-etching procedures ( Fig. 59.6 B).

Whatever the type of appliance, the screw should be mounted high in the palatal vault as much as possible. The screw is mounted in the midline of the vault with the thread axis in line with the anterior border of the first permanent molars. To have a control on location/site of the dental arch widths when you need more expansion in premolar region, a special screw is designed which permits hinge like opening at distal end and maximum opening at anterior end is required ( Fig. 59.6 C).

Manipulation of RME

When the cemented or banded maxillary expander is placed, expansion does not begin on the first day. This initial waiting period allows the patient to adjust to the appliance. The rapid expansion of the maxilla is started at the next appointment scheduled a week later. The rate of expansion is 0.5 mm/day, which is one-quarter of a turn twice daily. To facilitate easier turning of the screw by the patient, the screw is so mounted that the thread is rotated from front to back. The patient should be reviewed every week during the active activation of the appliance. The appliance has the maximum capability of approximately 50 turns, although that much activation is rarely needed. Expansion of 10–12 mm (40–48 quarter turns) should be considered as the upper limit of maxillary skeletal expansion correction .

Structural and functional effects of RME

Skeletal, dental and functional effects of RME extend into the entire nasomaxillary complex, associated dentoalveolar structures, dentition and to some extent the opposite arch in the mandible.

Maxilla and associated structures

Mid-palatal suture and maxillary complex: RME results in its effect on the mid-palatal suture. RME also leads to an activity at the suture sites, which attach the maxilla to the cranium. RME splits the maxilla into two halves at the mid-palatal suture in a V form extending down from the frontonasal suture. The apex of the V-shaped split of the maxilla lies at its frontonasal suture and base at the mid-palatal suture. In the AP direction, the base of the V-shaped split lies between two central incisors and the apex at the posterior nasal spine. The transverse skeletal maxillary increase is significant at a younger age and also relatively more stable (pre-pubertal growth peak) than in skeletally mature individuals (pubertal and post-pubertal growth peak). The long-term transverse skeletal maxillary increase is approximately 25% of the total appliance adjustment (dental expansion) in pre-pubertal adolescents but not significant for post-pubertal adolescents. Quality studies on the long-term effects of RME on sagittal and vertical changes in the maxilla and mandible are lacking.
Alveolar bone: The alveolar bone in the area adjacent to anchor teeth shows buccal bending which is due to the resilient nature of alveolar bone.
Maxillary anterior teeth: The appearance of midline spacing is the most reliable clinical evidence of maxillary separation. By 3–5 months, the midline diastema closes because of the recoiling of trans-septal fibres ( Fig. 59.7 ).

Figure 59.7

Clinical effects of RME.

(A) Pre-treatment. A case of the narrow maxilla and lateral shift of the mandible and anterior cross-bite associated with mouth breathing and recurrent throat infection. (B) The child was treated with RME and a facemask. (C,D) Note midline diastema and signs of midline split on occlusal photograph and radiograph. (E) Spontaneous closure of midline diastema due to stretch generated by the trans-septal group of gingival fibres.
Maxillary posterior teeth: The buccal segment shows some tipping and extrusion.

Mandible

The maxillary expansion leads to tipping and extrusion of the buccal segment, which directly affects the mandible and leads to a downward and backward rotation. This can be measured as an increase in mandibular plane angle.

Nasal cavity

RME leads to an increase in nasal volume and a decrease in nasal resistance to respiration. An increase in the width of the nasal cavity can be quantified on the PA cephalogram, and it is maximum at the base of the nasal cavity. Current methodologies allow the evaluation of volume and its effect on improved nasal breathing. A similar gradient is also found in an anteroposterior direction, with the greatest increase occurring in the anterior region. RME has a potentially positive effect on nasal septum asymmetry during childhood, but significant effects in adolescence from RME in patients with nasal septal deviation (NSD) should not be expected.

Adverse effects of RME

The unwanted effect of the expansion is an extrusion of the buccal segment. However, these effects could be little and probably transitory. The bonded/cemented design of the maxillary expansion appliance is now an accepted and viable appliance of choice for the narrow maxilla, regardless of the patient’s craniofacial pattern.

Patients with a vertical facial pattern are not an absolute contraindication for receiving the RME. In growing subjects, heavy forces in the short-term evaluation moved anchored teeth and the alveolar bone at the same time and with the same magnitude and direction. In the long-term evaluation, an uprighting of anchored teeth was observed.

Root resorption of the anchor teeth is an unavoidable adverse reaction during RME. Adverse tissue changes after RME are reversible, and active root resorption appeared along with increased filling with cellular cementum after 3 months. Two-dimensional periapical radiographs do not fully reveal the amount of external root resorption associated with maxillary expansion therapy, except for frank apical root resorption. Three-dimensional CBCT radiography displays statistically significant root volume loss associated with maxillary expansion therapy. However, when considering volume-loss percentages, no statistical significance was found.

Activation schedule and force levels

The activation schedule of maxillary expansion has been described in detail by Timms and Zimring and Isaacson.

Timms
- •
  Up to 15 years: 180 degrees daily rotation of the screw can be met with a turn of 90 degrees both during morning and evening (one quarter turn 90 degrees equivalent to 0.25 mm).
- •
  Over 15 years: Increasing resistance to maxillary separation may cause a force build-up and pain to patients in this age group with turns of 90 degrees, so the total overall daily rotation of 180 degrees is split into four turns of 45 degrees in a day.
Zimring and Isaacson :
- •
  Young growing patients: Two turns each day for 4–5 days and later one turn/day till the desired expansion is achieved (two turns equivalent to 180 degrees, 0.5 mm).
- •
  Non-growing adults: Two turns each day for first 2 days, one turn/day for next 5–7 days and one turn every alternate day till desired expansion is achieved.

Forces involved in RME

Isaacson and coworkers used force dynamometers to research the forces of RME. A single activation expansion screw can generate 3–10 pounds of force. With multiple daily turns of the screw, cumulative loads of 20 pounds or more have been observed. After the appliance is fully activated, residual loads were found, which dissipated in about 6 weeks.

Slow maxillary expansion

Expansion of upper jaw is termed slow when expansion takes place at a rate of 0.5 mm/week. Expansion schedule for the upper removable appliance (URA) is slow, which is one-quarter turn (0.25 mm)/third day/every week ( Fig. 59.8 ). A faster expansion tends to dislodge the appliance in the mouth. The treatment duration varies depending on the severity of maxillary constriction.

Parallel expansion screw

The expansion screw design of the maxillary expansion has an acrylic body which houses a parallel screw. The appliance is retained with clasps on the teeth, and the acrylic plate is split in the mid-palate. After the desired expansion is complete, the expansion screw and palatal split are sealed with cold cure acrylic. The same appliance may be used as a retainer for a period of 6–8 months. In some cases, occlusal coverage is desired to disengage occlusion and facilitate expansion.

Wire framework expander appliances

All wire framework maxillary expansion appliances are mainly indicated for dental arch development. The appliance can be welded/soldered to the lingual part of the first molar bands, or it can have a removable design which is housed in the lingual sheaths on the maxillary first or second molars. Coffin spring is perhaps the oldest design of the wire type of maxillary expander, which was housed in an acrylic body.

Quad helix/tri-helix appliance

Quad helix appliance is a modification of Coffin’s W-spring and was described by R.M. Ricketts initially to treat cleft palate patients who exhibited significant maxillary arch collapse.

The incorporation of four helices into the W-spring increases the flexibility, control on the region of expansion and an increase in the range of activation. The length of the palatal arms of the appliance can be tailored to suit the requirements of the arch in cross-bite.

The quad helix appliance is constructed of 0.036-in. SS wire and soldered to bands which are cemented to either the maxillary first permanent molars or the deciduous second molars, depending on the age of the patient ( Fig. 59.8 ).

Research has shown that a combination of buccal tipping and skeletal expansion occurs in a 6:1 ratio after a quad helix appliance is activated in pre-pubertal children. Chaconas et al. found that an initial 8 mm of expansion before cementation creates approximately 14 ounces of force. This is enough force to move the teeth in the buccal direction but usually not enough to create orthopaedic expansion effects on adults when the mid-palatal suture is closed. However, in children with deciduous or early mixed dentition stages of development, the resistance at the mid-palatal suture is often less than in the dentoalveolar area. Therefore, this appliance can widen the maxilla orthopaedically in children.

The expansion is considered adequate when the occlusal aspect of the maxillary lingual cusp contact the occlusal slope of the mandibular buccal cusp bilaterally in centric relation. This slight overexpansion of approximately 2–3 mm has been recommended to compensate for uprighting of the buccally tipped teeth once retention is discontinued.

The quad helix appliance is maintained in the expanded but passive position for a 6-week retention period after the adequate expansion is achieved. Sometimes the appliance can leave an imprint on the tongue. However, this will rapidly disappear following appliance removal.

Treatment with a quad helix appliance aimed to expand the maxillary arch creates optimum conditions for normal growth of jaws/TMJ/face by elimination of lateral forced bite.

Petren et al analysed early orthodontic treatment of unilateral posterior cross bite in the primary and early mixed dentition. They reported that a spontaneous correction can occur in 16% to 50% of subjects if left untreated. However, the success rate of both the quad helix appliance and RME is nearly 100%. Expansion plates are relatively less effective (51%–100%), and occlusal grinding can help, but it is not certain (27%–90%). Removal of premature contacts of the deciduous teeth is effective in preventing a posterior cross-bite from being perpetuated to the mixed dentition and adult teeth. Hence, the most effective mode of therapy based on evidence can be questionable. Each case should be treated on the merit of its severity and type of problem and must be kept under long-term follow-up.

Case study ( Fig. 59.9 ): A young boy with buccal cross-bite of the right maxillary first molar superior protrusion, mouth breathing habit and narrow nasopharynx as seen in the lateral cephalogram. (B) The child underwent adenoidectomy and maxillary expansion with a quad helix appliance in the maxilla and lower lingual arch. Post-treatment records show marked improvement in soft tissue and skeletal profile. His breathing pattern also improved. The occlusion is class I with excellent intercuspation and coordinated arches.

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Non-extraction treatment with maxillary expansion and interproximal reduction