September 2016
Volume 37, Issue 8


Case Report of Posterior Crossbite: Description of an Effective Treatment Protocol

Marcos Rogério de Mendonça, DDS, PhD; Ana Caroline Gonçales Verri, DDS, PhD; Lídia Pimenta Martins, DDS, PhD; and Osmar Aparecido Cuoghi, DDS, PhD


Early treatment of functional unilateral posterior crossbite during the mixed dentition stage is extremely important, as it provides the correct positioning of osseous bases, teeth, and the temporomandibular joint when the stomatognathic system is in growth and development. This article reports on a 9-year-old patient who presented with functional unilateral posterior crossbite and was treated with a modified Hyrax expander. The case report highlights a simple, low-cost, effective treatment protocol. The malocclusion was corrected with 15 days of active use of the appliance, 5 months of use for retention purposes, and 5 years of post-treatment follow-up. The stability in the long-term treatment is highly dependent on early diagnosis by the clinician and the elimination of the etiological factor through use of the proper appliance.

Posterior crossbite can be defined as a transversal discrepancy between jaws and is a common finding in children in both the primary and mixed dentition, with prevalence between 7% and 23%.1,2 Such prevalence makes this malocclusion an especially important consideration for clinicians practicing pediatric dentistry.

Children presenting with this malocclusion show a constricted craniofacial complex.3,4 The etiology is multifactorial and includes nasal breathing, muscle dysfunction, and/or a prolonged non-nutritive sucking habit.2,5 Among the cases with unilateral posterior crossbite, 97% present with a premature dental contact during movements in habitual intercuspation of the mandible, which produces a lateral shift of the mandible, establishing functional unilateral posterior crossbite.2,6,7 Findings from tomographic studies have shown condylar asymmetry in children with posterior crossbite, but symmetry is reestablished after treatment.8-10 If the condition is not treated, the condyle may undergo remodeling during growth to compensate for the asymmetry.8,11 Self-correction is rare, and it is believed that early diagnosis following malocclusion correction solves problems related to the craniomandibular bases during growth and development.12 Moreover, in most cases of functional posterior crossbite, an appliance is required to expand the maxilla.

Although a large number of articles focusing on this correction have been published,13-15 the purpose of this article is to report a case of functional posterior crossbite and present clinicians a simple, low-cost, effective treatment protocol.

Case Description

The patient, a boy aged 9 years and 10 months at the beginning of treatment, was evaluated at the program of preventive orthodontics at Araçatuba Dental School of State University of São Paulo with the chief complaint of an unesthetic appearance when he smiled. The medical and dental histories were irrelevant.


The intraoral evaluation from the front view revealed that the patient was in the first period of mixed dentition. A lack of space was observed for the permanent maxillary right lateral incisor and negative vertical overlap of approximately 3 mm semicircular. Posterior crossbite extended from the primary canine to the permanent first molar, and on the left side involved only the primary canine. In addition, an excessive lingual inclination of both the maxillary and mandibular alveolar processes was noted, as was a slight deviation from the dental midline in the position of habitual maximum intercuspation (MIP) (Figure 1). The right-side view revealed normal sagittal relationship of the primary canines and showed the primary second molars with a slight mesial degree and the first permanent molars with Angle’s Class I relationship, despite the crossbite (Figure 2). On the left side, a normal sagittal relationship of the primary canines was verified despite the total crossing, and the primary and permanent molars were in a normal position (Figure 3).

The maxillary occlusal view revealed an atresic maxilla, with lack of space for the permanent maxillary right lateral incisor and moderate crowding between the permanent maxillary right central incisor and permanent maxillary left central incisor (Figure 4).

The clinical signs described were observed with the patient in the MIP position. Dynamic analysis demonstrated a difference in the mandibular position during centric relation and habitual MIP, which is an important factor in determining functional crossbite. The definitive diagnosis was functional posterior crossbite with a favorable prognosis.

Treatment Appliance

The patient received a modified Hyrax expander. The appliance was constructed with a 9-mm expander screw supported on the primary molars and canines and with rigid wires, and cemented on the primary second molars using glass-ionomer cement (Figure 5).

Treatment Sequence

The treatment sequence used in this case was as follows: (1) insertion of the Hyrax appliance; (2) occlusal radiography before expansion (Figure 6); (3) 2 activations of 1/4 turn per day, one in the morning and one at night; (4) grinding of the primary canines to eliminate locking of the expansion; (5) obtainment of transversal overcorrection (Figure 7); (6) occlusal radiography after final expansion (Figure 8); (7) retention stage for 150 days, with use of the appliance itself; and (8) removal of the appliance and periodic controls every 6 months.


Regarding the intraoral results, the front view showed a clearly noticeable improvement in vertical overlap and reestablishment of transversal dimension, with a recovering of the vestibular inclination of the teeth and an allowance of the morphogenetic development of the maxilla (Figure 9). Notably, the midline was centralized after correction.

In the occlusal view, the lack of space for the permanent maxillary right lateral incisor was evident, and crowding was present in the initial phase (Figure 10). However, there was a distinct improvement in the outline of the maxillary arch and axial inclination of the posterior teeth, increasing the intercanine and intermolar distances.

The results obtained showed satisfactory stability during the postretention period of 1 year (Figure 11). The control accomplished with the expansion 5 years post-treatment shows the patient with normal occlusion (Figure 12 and Figure 13) and illustrates the importance of treatment of this malocclusion at the proper time.


The treatment protocol described in this article involved the use of a fixed appliance known as a modified Hyrax, with 2 daily activations of 1/4 turns until overcorrection was achieved, along with 150 days containment and post-treatment control every 6 months. This protocol has been widely used in children with functional posterior crossbite with high success rates.

The appliance used was designed based on Biederman’s appliance.16 It was a simplified form with hooks on the canines and distal extensions to the palatine face of the permanent first molars. This appliance featured a rigid structure, was easy to adapt and fix to the supporting teeth, was easily cleaned, and made it possible to achieve the position of overcorrection in a more controlled manner. Various types of appliances can be used for the correction of functional posterior crossbite, such as an acrylic plate with an expander screw and the quad-helix. The description given in the present protocol does not suggest the superiority of one appliance over another, but offers the clinical data of a simple and effective treatment method.

Activations of a half turn per day were recommended in a previous study,17 which used the bonded expander appliance, simulating rapid maxillary expansions. However, in the present protocol, the option was to use this amount of activation with the parameter being the absence of pain or discomfort experienced by patient. Overcorrection up to the limit of contact between the tips of palatine cusps of the maxillary molars with the tips of vestibular cusps of the mandibular molars showed how it was possible to obtain a clinical parameter and reproduce it in various treatments. The retention period of 150 days corresponds with the literature,17 in which the authors conducted a clinical trial in children under the same clinical conditions as in the present case.

In 2013 Lippold et al18 performed a randomized clinical study to evaluate the effects of orthodontic treatment in children at primary or mixed dentition affected by functional posterior crossbite compared with children in normal growth using tridimensional digital cast methodology. They concluded that appliances used to correct this problem were effective and promoted improvement of occlusal relationships and craniofacial growth. The authors emphasized the importance of early intervention.

A functional posterior crossbite will not allow normal maxilla development in the transverse plane if the crossbite is present at the end of the pubertal growing period of the patient. Therefore, a problem of dentoalveolar origin could become a skeletal problem and possibly require a surgical procedure to achieve correction.19

According to Pinto et al in 2001,11 during the craniofacial growth period, no correction of functional posterior crossbite can generate increased growth of the non-affected side of the maxilla, while the affected side will present limited growth.11 Some studies have shown this growth will generate facial asymmetry.8,13

Children in primary or mixed dentition may not necessarily present with signs of craniomandibular dysfunction but may develop some signs in a later growing period.20 Therefore, the correction of this malocclusion in patients that are in the growth and development phase of dentition is vital, with the main goal being to allow normal development of the craniomandibular bone bases.


As presented in this protocol, the modified Hyrax appliance is easy to use and is efficient for the correction of functional posterior crossbite in a short intervals. Furthermore, strict patient cooperation is not needed to allow the normal development of the maxilla at the transverse plane.

About the Authors

Marcos Rogério de Mendonça, DDS, PhD, MSc
Adjunct Professor
Department of Pediatric and Community Dentistry
Dental School of Araçatuba
UNESP - Univ Estadual Paulista
Araçatuba, São Paulo, Brazil

Ana Caroline Gonçales Verri, DDS, MSc
PhD Student
Department of Pediatric and Community Dentistry
Dental School of Araçatuba
UNESP - Univ Estadual Paulista
Araçatuba, São Paulo, Brazil

Lídia Pimenta Martins, DDS, MSc
PhD Student
Department of Pediatric and Community Dentistry
Dental School of Araçatuba
UNESP - Univ Estadual Paulista
Araçatuba, São Paulo, Brazil

Osmar Aparecido Cuoghi, DDS, PhD, MSc
Adjunct Professor
Department of Pediatric and Community Dentistry
Dental School of Araçatuba
UNESP - Univ Estadual Paulista
Araçatuba, São Paulo, Brazil


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