This case demonstrates the successful orthodontic correction of a rare left posterior buccal crossbite, also known as a scissor bite, in an adolescent patient. Using Invisalign clear aligners in combination with cross elastics, the treatment addressed the unusual crossbite pattern, upper spacing, lower crowding, excessive overbite and overjet, and achieved a stable Class I occlusion. At one year post-treatment, the bite remained stable with proper retention.

Patient Overview

The patient was an adolescent who presented for orthodontic evaluation and treatment. The patient was at an age where remaining jaw growth could be utilized to assist in treatment outcomes, particularly in modifying the posterior crossbite relationship.

Chief Complaint

The patient presented for a Class I classification with concerns about their bite and tooth alignment. The primary orthodontic needs included correction of a crossbite and spacing irregularities.

Diagnostic Findings

The primary diagnostic finding was a left posterior buccal crossbite, commonly referred to as a scissor bite. This presentation is unusual in orthodontics. In this rare condition, the upper teeth are positioned too far outward (buccally) compared to the lower back teeth. This is the opposite of the more common crossbite pattern, where the upper teeth are positioned too far inward (lingually) relative to the lower teeth.

Additional diagnostic findings included spacing in the upper arch, crowding in the lower arch, excessive overbite, excessive overjet, and a Class I molar occlusion. The combination of these findings required a comprehensive orthodontic approach to address both the transverse and sagittal discrepancies.

Treatment Options Considered

Two primary treatment modalities were presented to the patient and parents: traditional braces and Invisalign clear aligner therapy. Both options were clinically capable of addressing the patient's orthodontic needs, including the unusual posterior scissor bite.

Selected Treatment Plan

The patient and parents selected Invisalign clear aligner therapy as the treatment modality of choice. This decision was driven primarily by aesthetic concerns, as the patient preferred the less visible appearance of clear aligners compared to traditional braces.

The treatment plan was designed to correct the left posterior buccal crossbite, close the upper spacing, resolve the lower crowding, reduce the excessive overbite and overjet, and maintain the Class I molar relationship. Because the patient was an adolescent, the treatment plan incorporated the use of remaining jaw growth to help modify and correct the posterior crossbite relationship.

Procedures Performed

Treatment began with the placement of Invisalign attachments on the teeth. These attachments provided the necessary grip and force vectors for the aligners to effectively move the teeth in the desired directions.

From the start of treatment, the patient was instructed to wear cross elastics on the upper and lower left sides to actively correct the scissor bite. The elastics provided the transverse force necessary to bring the upper posterior teeth into proper alignment with the lower posterior teeth.

After the initial set of aligners was completed, a refinement set of aligners was prescribed to fine-tune both the bite relationship and the tooth positions. This refinement phase allowed for detailed adjustments to achieve optimal alignment and occlusion.

Upon completion of active treatment, clear retainers were fabricated and delivered to maintain the corrected tooth positions and bite relationship.

Materials and Technologies Used

The primary orthodontic appliance used was Invisalign clear aligner therapy. Attachments were bonded to specific teeth to enhance aligner retention and facilitate controlled tooth movement.

Cross elastics were used on the left side to provide the directional forces needed to correct the buccal crossbite. One set of refinement aligners was utilized following the initial aligner series to fine-tune the final occlusion and alignment.

Clear retainers were provided for nighttime wear following the completion of active treatment to maintain the achieved results.

Clinical Challenges

The scissor bite is an unusual bite pattern and is not commonly encountered in orthodontic practice. Correcting this type of crossbite can present a clinical challenge due to the atypical direction of tooth movement required.

However, the patient demonstrated excellent compliance with wearing both the aligners and the rubber bands as instructed. This strong patient cooperation was instrumental in achieving successful correction of the bite and obtaining a great treatment result. Without consistent wear of the cross elastics, correction of the scissor bite would have been significantly more difficult or potentially incomplete.

Final Outcome

The patient achieved a great smile and, most importantly, the bite was fully corrected. The left posterior scissor bite was successfully resolved, the upper spacing was closed, the lower crowding was alleviated, and the excessive overbite and overjet were reduced to normal levels.

At the one-year retention follow-up after the completion of treatment, the patient's bite remained stable. The posterior crossbite that had been corrected was maintained, demonstrating long-term stability of the treatment results with proper retainer wear.

Clinical Lesson for Other Dentists

Posterior buccal crossbites, or scissor bites, are rare and can present unique treatment challenges compared to the more commonly seen lingual crossbites. While correcting this unusual bite pattern can be challenging, it is achievable with clear aligner therapy when the appropriate biomechanics are applied.

The use of cross elastics in combination with Invisalign attachments provides effective transverse control for scissor bite correction. In adolescent patients, remaining growth can be a valuable adjunct in modifying skeletal and dental crossbite relationships.

Patient compliance is critical to success in these cases. Consistent wear of both the aligners and the prescribed elastics is essential for achieving the desired tooth movements and bite correction. Clear communication with patients and parents about the importance of elastic wear, particularly in cases involving transverse corrections, significantly impacts treatment outcomes.

Long-term retention is essential to maintain the corrected crossbite relationship. Nighttime retainer wear should be emphasized to prevent relapse of the transverse correction.

Treatment Results

• Successful correction of a rare left posterior buccal crossbite (scissor bite) where upper teeth were positioned too far outward relative to lower teeth
• Complete closure of upper arch spacing and resolution of lower arch crowding
• Reduction of excessive overbite and excessive overjet to normal levels
• Achievement of proper posterior occlusion and Class I molar relationship
• Stable bite maintained at one-year post-treatment follow-up with nighttime retainer wear
• Improved smile aesthetics while utilizing clear aligner therapy preferred by patient and parents

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