Teen Class III Crossbite Correction with MARPE

Presentation

Chief complaint. I want to fix my underbite and my back teeth don't fit together

Diagnosis. Skeletal Class III malocclusion with maxillary transverse constriction and bilateral posterior crossbite. The maxillary incisors are proclined and mandibular incisors retroclined, consistent with dental compensation. He presents with an approximately 1 mm anterior open bite and near edge-to-edge anterior relationship with approximately −1 mm overjet. He has Class III molars and Class I canines on the right and Class I molar and canine relationships on the left. The mandibular midline is deviated to the left with a CR-CO functional shift to the left.

Why I chose this approach

My goal was to achieve a functional bite and camouflage the skeletal Class III relationship. This patient’s upper jaw was too narrow, resulting in bilateral posterior crossbite and contributing to a functional shift of the lower jaw to the left. Correcting the upper jaw’s width was an essential first step in helping the upper and lower teeth fit together properly. At age 16, widening the upper jaw can be more challenging as the mid-palatal suture matures and becomes more resistant to expansion. Although skeletal maturity varies between patients, simply expanding the teeth with Invisalign would not predictably correct this underlying skeletal constriction. Dental expansion alone could primarily tip the back teeth outward rather than adequately widen the jaw, potentially moving them toward the limits of their supporting bone. I chose miniscrew assisted rapid palatal expansion, or MARPE, supported by four temporary anchorage devices (TADs) to direct expansion forces to the upper jaw and reduce reliance on the teeth for anchorage. This approach allowed us to address the skeletal width discrepancy, correct the bilateral posterior crossbite, and establish a better foundation for bite correction. After expansion and stabilization, we transitioned to Invisalign. Following third molar removal, lower sequential distalization and Class III elastics helped move the lower dentition into a more favorable relationship with the upper teeth. Posterior intrusion was incorporated into the treatment plan to help close the anterior open bite, while controlled lower incisor retroclination contributed to camouflage of the Class III relationship. The objective was to improve how the teeth fit and function through skeletal expansion and dental compensation. This combined approach achieved a Class I dental occlusion with positive overjet and overbite while the underlying skeletal Class III relationship remained. Excellent aligner and elastic compliance was an important part of the successful outcome.

Measurements

Cephalometric values before and after treatment
Measure	Norm	Pre	Post
SNA	82	83	84
SNB	80	86	86
ANB	2	-3	-2
Wits	0	-4	-2
SN-MP	32	22	25
U1-SN	102	120	119
L1-MP	90	85	77
Overjet (mm)	2–3	0	2
Overbite (mm)	2–3	-2	2

Treatment

Objectives. Expand the maxillary arch, distalize the mandibular dentition to achieve Class I occlusion, and intrude the posterior teeth to close the open bite.

Plan. Expand the maxilla with MARPE, extract the third molars, then use Invisalign to sequentially distalize the lower dentition and intrude the posterior teeth to close the open bite with class III elastics

Appliances and materials

MARPE — expander supported with 4 TADS
Invisalign
Class III elastics

Progress records

Outcome

Excellent aligner and elastic compliance allowed closure of the open bite and correction to a Class I occlusion. The mandibular incisors were retroclined to help camouflage the skeletal Class III relationship, with adequate thick attached gingiva maintained in the lower anterior region.

Retention

Fixed U2-2 permanent retainer
Fixed U3-3 permanent retainer
Invisalign Vivera retainers to be worn at night