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Orthodontics

Authors: Dr. Faizan Ahmed Khan, Dr. Anthony Kevin Fernandes, Dr. Muraleedhara Bhat
 

The incidence ofMaxillary constriction in the deciduous and mixed dentitions is estimated at 8% to 18% of patients having orthodontic consultations.1 Orthopedic maxillary expansion (OME) was first described over 145 years ago by Angell in a case report.2,3 The treatment options are either non surgical and surgical.

These include:
  1. Orthopedic palatal expansion
  2. Surgically-assisted rapid palatal expansion.
Orthopedic Palatal Expansion

This procedure ensures success primarily in children prior to sutural closure. Various appliances have been successfully used to expand the maxilla. One such appliance is the Haas-type Appliance. This has acrylic palatal flanges incorporated into the appliance with the jack-screw. There is less dental tipping in this due to palatal anchorage. Another appliance is the Hyrax appliance with metal framework jack-screw, quite in vogue today. A modified appliance is the hybrid of Haas and a flatplane occlusal-coverage splint physically bonded to maxillary teeth recommended in periodontally compromised dentition because it incorporates more teeth. It is helpful in patients with Temporo Mandibular Dysfunction symptomatology where occlusal modifications are possible when prematurities occur during expansion of the jack-screw. These appliances are removed after 3–4 months and aretainer then placed to prevent relapse or to begin sagittal correction. This type of orthopedic expansion typically results in greater canine expansion than molar expansion at a ratio of 3:2. The changes in the rapid palatal expansion is seen in skeletal (sutural opening), dental (tipping) and alveolar (bending and remodeling) components. The possibility of high post-treatment relapse means that at least 50% overexpansion is recommended.

After sutural closure or completion of transverse growth, orthopedic expansion alone is unsuccessful and possible problems include:

  1. Inability to activate appliance
  2. Severe pain with activation
  3. Pressure necrosis under the appliance
  4. Bending of alveolar bone
  5. Unstable results with relapse
  6. The posterior teeth tip leading to poor occlusion and instability.
  7. This further leads to clockwise mandibular rotation, opening the bite and increasing facial height.
  8. The maxillary posterior teeth are displaced buccally through the alveolus leading to gingival recession, bone loss and root resorption.

Several reasons have been speculated regarding factors that limit orthopedically induced maxillary expansion in skeletally mature patients. These are all related to changes with increasing age in the osseous articulations of the maxilla with the adjoining bones. However, a few reports in the literature contradict these findings and state that nonsurgical maxillary expansion is as successful in adults as it is in children.4,5 because of more complications after attempts to orthopedically alter the transverse dimension of the maxilla with advancing age, surgical procedures have been recommended to facilitate correction of transverse discrepancies.

These procedures have conventionally been grouped into 2 categories:
  1. Segmenting the maxilla during a LeFort osteotomy to reposition the individual segments in a widened transverse dimension
  2. Surgically assisted rapid palatal expansion (SARPE).
Rationale for SARPE:

An adequate transverse maxillary dimension is one of the critical aspects of a functional and stable occlusion.6 Rapid palatal expansion allows transverse discrepancies to be treated in skeletically immature patients. The orthopedic force delivered by the expander opens the midpalatal suture and allows the maxilla to widen.7 After skeletal maturity, there is an increase of osseous interdigitation secondary to fusion of the midpalatal suture.8,9 At this stage, trying to expand the maxilla orthopedically may cause pain, and removal of the expander will be associated with a relapse of the transverse discrepancy.10 These forces may also cause periodontal problems when posterior teeth are pushed against vestibular wall.11

Surgically assisted rapid palatal expansion (SARPE) consists of a surgical liberation of the sites of resistance combined using orthopedic forces. Based on the principles of osteogenic distraction, SARPE can widen the upper arch in skeletally mature patients.12

Maxillomandibular Transverse Differential Index (MTDI)

An index has been proposed as a guide in determining the choice of treatment modality. This is the Maxillomandibular Transverse Differential Index (MTDI).

  1. Expected Maxillo Mandibular difference = Expected mandibular width - Expected maxillary width
  2. Actual MM diff = Actual mandibular width - Actual maxillary width
  3. Expected - Actual maxillomandibular differential = MTDI

If this value exceeds 5 mm then a transverse deficiency exists and SARME may be indicated.

INDICATIONS FOR SARPE

Before the application of Surgically assisted rapid palatal expansion an accurate diagnosis of maxillary transverse deficiency is essential. The following have been reported in the literature as indications for SARPE, all applying to a skeletally mature patient with a constricted maxillary arch.14,15

  1. To increase maxillary arch perimeter, to correct posterior crossbite, and when no additional surgical jaw movements are planned.
  2. To widen the maxillary arch as a preliminary procedure, even if further orthognathic surgery is planned. This is to avoid increased risks, inaccuracy, and instability associated with segmental maxillary osteotomy.
  3. To provide space for a crowded maxillary dentition when extractions are not indicated.
  4. To widen maxillary hypoplasia associated with clefts of the palate.
  5. To reduce wide black buccal corridors when smiling.
  6. To overcome the resistance of the sutures when OME has failed.
  7. To widen the arch and to provide space for alignment without the need for maxillary premolar extractions, if the space requirement could reasonably be gained as a result of maxillary expansion,10 and if other factors, such as the protrusion of the maxillary incisors on their underlying bone have been taken into account.
  8. To widen the arch following maxillary collapse associated with a cleft palate.
PATIENT SELECTION

A thorough review of the literature shows significant disparities among clinicians regarding the criteria for case selection and the indications for SARPE.

Diagnosis

The first step in the case selection process is determination of Maxillary transverse deficiency. Unlike discrepancies in the vertical and the anteroposterior dimensions, diagnosis of Maxillary transverse deficiency is difficult. Clinical evaluation, model analysis, occlusograms, and radiographic measurements have been recommended for an accurate assessment.

Clinical evaluation:

Clinical evaluation includes assessment of the maxillary arch form and symmetry, shape of the palatal vault, width of the buccal corridors on smiling, occlusion, and predominant mode of breathing (nasal or oral). Excessively wide buccal corridors, para-nasal hollowing, or narrow alar bases usually suggest Maxillary transverse deficiency. The soft-tissue thickness should also be evaluated because it can mask Maxillary transverse deficiency. Unilateral or bilateral crossbite, severe crowding, a V-shaped or an hour glass shaped occlusion, and a high palatal vault are additional visual parameters that can help the clinician make the first determination of Maxillary transverse deficiency in a patient. Another factor that needs assessment is a mandibular shift on closure. This can often be a chin deviation with a unilateral crossbite. To identify the nature of a shift, it might be necessary to use a muscle deprogramming device such as a bite plate for a few days. These devices are needed more often for adults whose muscular kinesthetic memory and proprioceptive influences are ingrained. Such a deprogramming device allows the muscles to move the mandible in coordinated function that is undisturbed by deflective tooth contacts.16,17

Another aspect that needs determination is whether the Maxillary transverse deficiency is relative or absolute.18 This is essential in the evaluation of sagittal discrepancies (especially Class III malocclusion). An attempt is made to articulate and align the models in Angle Class I molar and canine relationship to evaluate arch coordination. Relative Maxillary transverse deficiency implies that the apparent deficiency is the result of the discrepancy of the maxilla or both jaws in the sagittal plane. Absolute Maxillary transverse deficiency implies a true horizontal width insufficiency.18,19

Study models:

Study models are useful to thoroughly assess:

  • The arch form
  • The arch shape
  • Make specific measurements to evaluate for maxillary transverse deficiency. Several indices have been proposed by various authors to measure lateral discrepancies. The most commonly used indices include Pont’s index , Linder-Harth index , and Korkhaus index.20
Disadvantages of indices:

Although indices offer a guide to diagnose Maxillary transverse deficiency, they are population specific and not completely reliable.

Digital models:

With the advent of digital models in routine clinical practice, additional tools can be used to evaluate arch form and tooth inclinations.21 The evaluation of the buccolingual inclination of the posterior teeth is an essential part of the diagnosis. This allows a more accurate distinction between dental and apical base skeletal Maxillary transverse deficiency. The digital models can be viewed in desired cross-sections that permit better visualization of the buccolingual inclination of the teeth. The digital models can also generate images for occlusograms22,23 whereby the coordination of the maxillary and mandibular arches can be evaluated. They provide occlusal simulations and assist in the diagnosis of relative or absolute Maxillary transverse deficiency.

Occlusal radiograph:

Lehman et al(1984)24 recommended a palatal or an occlusal radiograph as an essential tool to evaluate the ossification of the midpalatal suture. This, however, is unreliable because of the superimposition of other bony structures on the midpalatal suture and the lack of adequate visualization of the posterior part of the intermaxillary suture. This is relevant because histologic studies have shown that obliteration of the suture is more common in the posterior region of the intermaxillary suture. The value of an occlusal radiograph is also unclear, since studies have shown that the midpalatal suture does not offer much resistance to expansion. 25,26

Cephalometric radiographs:

Betts et al(1995)27 suggested that posteroanteriorcephalograms are the most readily available and reliable means to identify and evaluate transverse skeletal discrepancies between the maxilla and the mandible.

Using cephalometric landmarks as described by Ricketts, 28 they presented 2 methods for quantification of the Mid facial Transverse Defects :

  1. maxillomandibular width differential index
  2. maxillomandibular transverse differential index.

These methods have been criticized because the transverse discrepancy between the maxilla and the mandible is measured on bony landmarks that are greatly separated from the dentition and the apical bases.

3 D imaging techniques:

The advent of 3-dimensional imaging techniques is the most recent tool for diagnosis that have enabled an accurate visualization of the craniofacial region. It allows for evaluation of the spatial relationships of various areas of the jaws.29 Cone-beam computed tomography can generate scans that enable the clinician to perform a 3 dimensional evaluation of the apical bases including horizontal sections of the apical bases at different levels. These images can help the clinician to make an accurate and detailed analysis of the nature and location of the discrepancy including asymmetries.

Age of the patient:

The patient’s age has been considered by most authors and clinicians as the fundamental basis for distinguishing the use of OME vs SARPE to treat maxillary transverse deficiency. However, conflicting views regarding when OME is successful and when to request surgical assistance for treating maxillary transverse deficiency are found in the literature. Epker and Wolford30 recommended surgical assistance for maxillary expansion in patients over 16 years of age. Timms and Vero31 used 25 years as the upper limit for recommending OME. Mossaz et al32 arbitrarily recommended “after the second decade of life” for surgical assistance of maxillary expansion. Mommaerts33 stated that OME is indicated for patients younger than 12 years, and, for those over 14 years, corticotomies are essential to release the areas of resistance to expansion. Alpern and Yurosko34 suggested that sex should also be considered as a selection criterion. According to them, men over the age of 25 and women over 20 require surgical assistance for expansion.

Further confusion is added by several case reports in which OME has been shown to be successful in much older adults34,35, 36 These authors suggested that, although an orthopedic effect was not observed, slow expansion results in a combination of membranous warpage and some sutural stretching to provide the desired end result. They also suggested that slow expansion might not be as kind to the gingivae, but it is clinically adequate and stable.37 Determination of skeletal age is an important parameter for case selection.38 It is possible that chronologically advanced patients in case reports whose OME was successful were skeletally immature. The reverse can also be true in chronologically younger patients with advanced skeletal maturity whose OME might be unsuccessful.

Medical history

In treatment planning and case selection for maxillary transverse deficiency, the patient’s medical condition must be thoroughly evaluated. Maxillary transverse deficiency can be suspected if the patient has any of the following conditions; 39

  1. Habits–thumb sucking
  2. Obstructive sleep apnea
  3. Iatrogenic (cleft repair)
  4. Palatal dimensions and inheritance
  5. Muscular abnormalities
  6. Syndromes
    • Klippel-Feil syndrome
    • Cleft lip and palate
    • Congenital nasal pyriform aperture stenosis
    • Marfan syndrome
    • Craniosynostosis (Apert’s, Crouzon’s disease, Carpenter’s)
    • Osteopatiastriata
    • Treacher Collins
    • Duchenne muscular dystrophy
  7. Nonsyndromic palatal synostosis
  8. Multifactorial

Persson and Thilander40 based on their incestigations on cadaver skull showed that ossification of the midpalatal suture has wide variations in various age groups. Since OME depends on the sutural patency and the flexibility of the craniofacial skeleton to adapt to controlled mechanical forces, it is essential to evaluate for medical conditions that can influence the results of OME.

Several metabolic conditions have been linked to sutural synostoses. These include hyperthyroidism,41,42 hypophosphatemic vitamin D-resistant rickets,43 and mucopolysaccharidoses and mucolipidoses.41,44 A common link in all these conditions is an underlying abnormality in bone metabolism The medical history must be carefully evaluated, since developmental dynamics and environmental influences can affect the ability of a suture to respond to external force application. OME would either be unsuccessful or have unfavorable consequences as discussed earlier even in a chronologically young patient with such medical conditions. Synostosis in any of these metabolic disorders can be either simple or complex. Simple synostosis involves fusion of 1 suture, but craniosynostosis syndromes and metabolic disorders are associated with complex synostosis. Individual variability with regard to fusion of sutures is significant. Recent evidence from molecular biology has shed light on the underlying mechanisms of suture fusion. These findings might have significant implications on the selection of treatment. Bony obliteration of the suture site is caused by premature or accelerated bone formation in the fibrous suture matrix. This can occur by increasing cell numbers, leading to increased cell density and inducing bony differentiation, or by directly inducing premature differentiation of cells. Cell numbers can be increased by stimulating cell proliferation or by inhibiting apoptosis. These cellular functions are controlled by various growth and transcription factors acting in concert or in parallel with each other. Several growth and transcription factors have been shown to play a role in regulating suture morphogenesis and patency, and, in many instances, the mechanisms by which they do so have begun to be elucidated. It can be hypothesized that a detailed medical evaluation including serology might elucidate biochemical profiles to assist in clinical diagnosis and decision making. A detailed medical evaluation is also necessary from the standpoint of general anesthesia that would otherwise preclude the patient from elective surgery.

Amount of expansion:

Betts et al 27,45 and others 46 have recommended that the amount of desired expansion is an important factor in case selection for maxillary expansion in adults. In general, an orthodontist can camouflage transverse maxillomandibular discrepancies less than 5 mm with orthopedic or orthodontic forces alone. When the MTD is greater than 5 mm, surgical assistance is essential. Although both SARPE and segmental osteotomy are used for surgically assisted maxillary expansion, segmental osteotomy is reported to be unstable, especially when more than 8 mm expansion is desired.14 It is also essential to evaluate the buccolingual inclination of the teeth because that may either mask or aggravate the discrepancy at the apical bases.

Two-stage vs singular surgery

Surgical correction of maxillary transverse deficiency may be achieved by either segmental osteotomy or SARPE. Segmental osteotomy is the preferred choice for correction of maxillary transverse deficiency when a single surgical procedure is planned to correct all maxillo-mandibular discrepancies. Vertical and sagittal repositioning of the maxilla and the mandible can be done at the same time when correction of MTD is done with segmental osteotomy. On the other hand, correction of MTD is done as a first step with SARPE and a separate second surgery is necessary for discrepancies of the maxilla and the mandible in the other planes of space. Bailey et al47 have recommended that SARPE should be used for patients with an isolated transverse deficiency when OME is not indicated, or with unilateral or asymmetric narrowing of the maxilla. Although it might seem that the use of SARPE is limited, it is essential to compare the long-term stability, morbidity of a 2-stage vs a 1-stage procedure, and the psychological impact of 2 procedures on the patient rather than 1 procedure. Proponents of SARPE have also hypothesized that post-SARPE orthopedic forces can be applied to the maxilla, since the 2 halves of the maxilla have been loosened. These forces might be valuable in correcting sagittal or vertical discrepancies without additional surgery. This, however, has not been used routinely because the prognosis is uncertain.

Periodontal status

Muller and Eger 48,49 and Muller et al,50 recently introduced the concept of periodontal biotype. They pointed out that it is essential to record the thickness of the gingival tissues during clinical evaluation of the periodontium. This is especially important because a thin and delicate gingiva might be prone to recession after traumatic, surgical, or inflammatory injuries. Histologic studies of the supporting tissues around extracted teeth that were initially used as appliance anchors have shown that a strong inflammatory response ensues during maxillary expansion. Orthodontic tooth movement can have a detrimental influence on the mucogingival complex, especially when the keratinized tissue and underlying bone appear to be thin. Therefore, evaluations of the gingival tissues and the biotype are essential to determine the ability of the tissues to withstand the pressure of OME; otherwise, surgical release of the sutures is needed to remove interferences to maxillary expansion. The selection of the appliance type (number of anchor teeth included or tooth-borne vs bone-borne appliances) might also depend directly on the periodontal biotype.

References:
  1. da Silva Filho OG, Boas MC, CapelozzaFilho L. Rapid maxillary expansion in the primary and mixed dentitions: a cephalometric evaluation. Am J OrthodDentofacialOrthop 1991;100:171-9
  2. Angell EH. Treatment of irregularity of permanent adult teeth. Dent Cosmos 1860;1:540-4.
  3. Timms DJ. Emerson C. Angell (1822-1903). Founding father of rapid maxillary expansion. Dent Hist 1997:3-12.
  4. Handelman CS. Nonsurgical rapid maxillary alveolar expansion in adults: a clinical evaluation. Angle Orthod 1997;67:291-305.
  5. Handelman CS, Wang L, BeGole EA, Haas AJ. Nonsurgical rapid maxillary expansion in adults: report on 47 cases using the Haas expander. Angle Orthod 2000;70:129-44.
  6. Vanarsdale R, White R: Three dimensional analysis for skeletal problems. Int J Adult OrthodonOrthognathSurg 9:159, 1994
  7. Haas AJ: Palatal expansion: Just the beginning of dentofacial orthopedics. Am J Orthod 57:219, 1970
  8. Melson B: Palatal growth studied on human autopsy material. Am J Orthod 68:42, 1975
  9. Melson B, Melson F: The postnatal development of the palatomaxillaryregion studied on human autopsy material. Am JOrthod 82:329, 1982
  10. Haas AJ: Long term post treatment evaluation of rapid palatal expansion. Angle Orthod 50:189, 1980