Correction of Class III Posterior Cross-bite with Maxillary Midline Diastema in an Adult Patient using Invisalign®: Report of two cases

Categories: Article

Correction of Class III malocclusions with maxillary deficiency and posterior cross bites in adults can be challenging. Depending upon the severity of the malocclusion treatment options include comprehensive orthodontic treatment with or without surgical aid. With advent of clear aligners systems as Invisalign many patients are seeking orthodontic treatment as an alternative to comprehensive orthodontic treatment with traditional fixed braces.

Two cases with posterior cross-bites are presented here. The first case of a 17-year-old female illustrates the difficulty in correcting posterior cross-bites and the second case of a 35-year-old female demonstrates the treatment of posterior cross-bite and maxillary midline diastema using clear aligners (Invisalign®).

The exploration of using Invisalign® combined with palatal expanders in conjunction with removable elastics to gain desired results was shown to be a useful device for orthodontic correction.

It is described to aid the clinician in the management of maxillary transverse deficiency in skeletally mature patients who desire non-traditional methods.

|| Introduction

Malocclusion is commonly found in adults and observed in equal or greater frequency than in children and adolescents.[1] Some of the most common problems in adults are crowding, affecting about 24% of women and 14% of men, and spacing, affecting 8% of women and 13% of men. Typically those treated by fixed orthodontics show an increase in gingivitis and plaque, while some even experience irreversible bone loss and decalcification. However, when clinicians select the appropriate appliance that produces the right force to correct the malocclusion, many enjoy the benefits of orthodontic treatment. Adults are often reluctant to wear fixed appliances despite their need for orthodontic treatment. But with the increased awareness of patients of the need for good oral health and the increase in aesthetic requirement from society, the demand of orthodontic treatment to correct malocclusions without fixed appliances have increased. In an aesthetically agreeable approach, the Invisalign® system makes it possible for adult patients requiring orthodontic treatment.

The use of clear aligners to move teeth is documented in various articles. In particular, the Invisalign® appliances for treating malocclusions have recently been described by several different authors whose cases involve extractions, deep bites, anterior and posterior cross-bites, and periodontal complications. In these patients, the appearance of the smile is their main treatment goal. This article describes the treatment of a unilateral posterior cross-bite with maxillary midline diastema with the Invisalign® system in conjunction with palatal expander and class III elastics. It describes two similar cases of posterior crossbite, similar malocclusion but with varying results.

A posterior cross-bite can be dysfunctional and unaesthetic as it is a lateral misalignment of the dental arch, where the maxillary posterior dentition is lingual in relation to the mandibular dentition. In a unilateral posterior cross-bite due to shift, one side of the dentition is affected and in order for the posterior dentition to meet together, the lower jaw will have a centric relation-centric occlusion lateral functional shift. This abnormal transverse maxillary/mandibular constriction is a major factor in several malocclusions.

Several methods have been employed to correct a maxillary transverse deficiency in patients including widening the maxilla, surgically or non-surgically. Other methods may include treating the cause of the cross-bite (e.g. thumb sucking habits, tongue thrust). Although the correction of posterior cross-bite can be complex, maxillary expansion is a common orthodontic treatment used for the correction of cross-bites resulting from reduced maxillary width. Correction of maxillary transverse deficiency is routinely done in young patients; however, in a skeletally mature patient the osseous articulations of the maxilla with the adjoining bones make it more challenging to treat. Hence, once the patient has been properly diagnosed, it is necessary to select the appropriate modality and to determine when adequate expansion has been achieved and how to retain it.

The fundamental basis for deciding between surgical vs non-surgical expansion for the correction of reduced maxillary widths, by most clinicians, has been the patient’s chronological age, as well as their skeletal age. It is possible that a chronologically advanced patient is skeletally immature, or vice versa, making skeletal age a very important parameter for case selection. For the predictable correction of posterior cross-bite in adults, it ideally requires surgical expansion; however, these can be associated with certain complications that include significant hemorrhage, gingival recession pain, root resorption maxillary nerve injury, infection, periodontal breakdown, sinus infection, and asymmetrical expansion.

Non-surgical expansion using the Haas/Hyrax rapid palatal expansion (RPE) has been, for the most part, limited to growing patients. However, a few articles state that non-surgical expansion is as successful in adults as it is in children. Most of the correction of maxillary transverse deficiency in an adult occurs at the lateral alveolar process rather than at the skeletal base of the maxilla, producing a combination of dentoalveolar modification and dental tipping to correct posterior cross-bite. Although less invasive than surgical expansion, palatal expanders do pose potential complications including pain, tissue swelling, posterior teeth tip, mandibular rotation, and gingival recession.

The attempt to correct posterior cross-bites with removable elastics is often limited to buccal flaring of the teeth as well and can cause chronic imbalance of the posterior dentition where the lingual cusps strike the mandibular teeth first. Therefore, in the case of adults, surgical expansion may be required or compromise accepted with flare.

Invisalign® might not be as effective as fixed braces for a few reasons. Primary among them is compliance. It is generally a disadvantage to the clinician where treatment efficacy lies in the hands of the patient, as the appliance can be easily removed. Removable appliances produce intermittent forces, and if not continued for enough hours of the day, they don’t have significant effects on tooth movement. When the removable appliance is taken out, intermittent forces drop to zero and only when the appliance is reinserted into the mouth do the forces return.

The optimum force for traditional orthodontic tooth movement is 10-100g, where the values depend on the type of movement and size of the tooth. These forces are not affected by the patient and produce more tooth movement than removable appliances unless the removable appliance is continuously present. Decreased tooth movement is observed when these removable appliances are worn for shorter durations of time.

Another reason Invisalign® fails is that the occlusion is minimally addressed. According to Vlaskalic and Boyd, while assessing Invisalign® occlusal outcome, it became apparent to them that similar results could have been reached with traditional braces in less time. They concluded that the most important aspects of Invisalign® over braces are that they are aesthetically pleasing, comfortable, and removable, and they reduced plaque accumulation resulting in improved periodontal health. However, there are no biomechanical advantages.

Case Report : Case 1 Diagnosis and Treatment Objectives
A 17-year-old female presented with a bilateral, symmetrically constricted posterior cross-bite (Fig. 1). She was concerned with her bite, as well as crowding of her teeth. Her facial proportions were well-balanced and intraoral examination revealed dental arches with moderate crowding. Class III molar relationships were detected and the patient admitted heavy clenching. Third molars had been extracted prior to treatment. The patient did not want traditional fixed appliances and expressed interest in the use of clear aligners (Invisalign®).

The objective of the treatment was to align the lower anterior teeth and eliminate the bilateral cross-bite. Pre-treatment, the patient was advised of the difficulty of correcting her bilateral posterior cross-bite with the Invisalign® system. However, the patient insisted on using clear aligners and not traditional fixed appliances.

Treatment Progress

The patient was prescribed 15 aligners, upper and lower and a total of 2.5 mm Interproximal Reduction (IPR) mesial to the first molars to correct the Bolton discrepancy. IPR was completed within the first two months of treatment. The patient was compliant with aligners. After completion of the 15 sets, the patient’s lower anterior teeth were well aligned but there was no change to her posterior cross-bite. Refinement impressions were taken and the patient was prescribed an additional 14 aligners for the upper and 5 aligners for the lower. At the end of refinement the patient’s poster occlusion was still not corrected. ClinCheck projection (Fig. 2) showed an improvement of her malocclusion with satisfactory resolution of her cross-bite and alignment of her teeth in both arches. Regular appointments were made in 4-6 week intervals to assess her aligner fit, patient compliance, and tooth movement.

Treatment Results The patient’s occlusion made minimal changes. The mandibular crowding was resolved; however the bilateral posterior cross-bite showed little to no improvement despite ClinCheck projections. Invisalign cannot fix posterior cross-bite as expanders can due to the lack of anchorage. Post-treatment results overall showed incomplete correction of her malocclusion (Fig. 3).

Case 2 : Diagnosis and Treatment Objective
A 35-year-old female presented with chief complaint of spacing between her front teeth and biting issues. Pre-treatment photographs, panoramic and cephalometric radiographs (Fig. 4-6) were taken along with initial records. The patient was diagnosed with class III dental and skeletal with symmetrically constricted posterior cross-bite with shift, anterior cross-bite and maxillary midline diastema. The patient was presented with multiple treatment options, including surgical expansion and comprehensive orthodontic treatment. The treatment objective was to use a Hyrax palatal expander to correct the posterior cross-bite. A Hyrax palatal expander was used to correct the posterior cross-bite followed by use of the Invisalign system to close spaces, improve class III dental relation and obtain ideal overjet and overbite.

Treatment Progress
The expander was turned once every third day for approximately 13 weeks, for a total of 6 mm at the screw. The expander after deactivation was left a month to stabilize with expander in place and subsequently removed and post-expansion records were taken (Fig.7). Invisalign ClinCheck superimpositions of predicted outcome were assessed (Fig. 8). The amount of interproximal reduction performed to correct the Bolton discrepancy was a total IPR of 0.2 mm in the upper arch and a total IPR of 3.4 mm in the