The MPA 5

Drs. Fabio Oliveira Coelho, Francesca Scilla Smith, and Larry W. White discuss the evolution and efficacy of the mandibular protraction appliance (MPA)

Introduction

As far back as 1880, dentists have had an obsession with correcting overbites and overjets by protracting the mandible. Kingsley¹ was one of the first to describe his vulcanite plate for “jumping the bite,” and it became the ancestor of the myriad functional appliances that now exist. In the United States, Angle’s² influence and development of the edgewise bracket combined with Case’s³ discovery and use of elastics gave orthodontic clinicians a fixed alternative for protracting the mandibular dentition to correct malocclusions with excessive overbites and overjets. In Europe, orthodontists continued using removable functional appliances such as the Andresen⁴ activator, the Bionator,⁵ the Bimler⁵ appliance, and most important after WW II, the Fränkel⁶ appliances.

Permissive appliances have never found a large acceptance in the United States, and as a result of that prejudice, fixed functional appliances have found an enthusiastic audience. Even in the European cradle of removable functional appliances, fixed functional appliances were being developed more than 100 years ago and were first described in a publication by Emil Herbst.⁷ World War II interrupted orthodontic information coming from Germany for several decades until the Herbst* rediscovery by Pancherz⁸ in 1979. This created renewed interest in fixed functional appliances and gained new traction in the United States.

The MPA Nos. 1-4

Dr. Carlos Martins Coelho Filho⁹ first described the mandibular protraction appliance, aka MPA, in 1995, and this first iteration was about as simple a Class II corrective mechanism as could be imagined. The MPA consisted of a single .036 stainless steel wire that connected the maxillary molar and mandibular archwire and protruded the mandible, held it there, and formed a template for the eruption of the posterior teeth into a Class I occlusion while simultaneously correcting the overbite, overjet, and midline (Figure 1). The MPA provided patients with an effective corrective for excessive overbite, overjet, and Class II malocclusion but limited their opening to about 30 mm.

More versions quickly followed.^10-12  Each of these MPAs connected to the maxillary molar through the distal opening of the headgear tube with a .036 pin that was turned up or down on the mesial to lock it in. The second iteration (Figure 2) began to use a Guerin lock as a stop on the mandibular wire. The third version (Figure 3) started the use of a stainless steel tube with a rod that slid through it and contained a compressible coil spring on its mesial end that allowed greater opening and a softer closure.

Dr. Coelho Filho details the construction and use of the fourth version¹³ in the ascribed Journal of Clinical Orthodontics article (Figures 4 and 5). The MPA No. 4 has endured much longer than the others and differs from the third iteration by using a small occlusal circle on the mandibular archwire between the canine and the first premolar into which the rod enters from the lingual before inserting into the tube, which then attaches to the maxillary molar via a .036 pin through the distal opening of the headgear tube.

MPA No. 5

Before Dr. Coelho Filho died in 2015, he developed a final iteration that greatly simplified the placement of the appliance and improved its function. The following illustrations show the instrumentation and a protocol for the MPA 5 implementation (Figures 6-10).

Protocol for placement of the MPA

Step 1

Construct a .017 x .025 or a .019 x .025 SS mandibular archwire (according to the bracket size the clinician uses) with extremely small occlusal circles for the MPA rod between the mandibular canines and first premolars. Ligate the wire in the brackets with 3M™ AlastiKs™ and turn down the ends distal to the mandibular molar tubes (Figure 11).

Step 2

Dry and mark the maxillary and mandibular incisors with a Sharpie pen, and with a patient-held mirror, guide the bite into a proper corrective occlusion (Figure 12).

Step 3

Place the headgear locking pin of the MPA tube into the mesial opening of the right maxillary molar band. With the patient holding the bite with desired overbite, overjet, and midline position, measure the length of the tube needed by marking it in the center of the small circle between the mandibular canine and premolar (Figure 13).

Step 4

Cut off the measured tube with a small disc in the air turbine, and smooth off any frayed ends of the tube. Make certain that the MPA mandibular rod will move through the MPA tube without any resistance (Figure 14).

Step 5

With the mandibular rod in the newly adjusted MPA tube, cut the rod so that no more than 2 mm-3 mm of rod protrudes from the distal end of the maxillary MPA tube (Figure 15).

Repeat steps 3, 4, and 5 for the left side.

Step 6

Insert the mandibular MPA rods into the mandibular archwire small circles from the lingual, and turn them upwards, making sure that the ends of the rods do not escape from the small circles. If the circles are too large, use Weingart or Howe pliers to squeeze the circle until the rod does not escape (Figure 16).

Step 7

On the right side, slide the maxillary tube over the mandibular rod, and insert the maxillary headgear locking pin that should extend no more than 3 mm-4 mm distally from the maxillary headgear tube, and stretch the two AlastiK O-rings over the protruding locking pin to secure the MPA (Figure 17).

MPA No. 5 patient therapies

Patient No. 1 (Figures 18-20)

Patient No. 1 displays an adolescent female with a Class II, Division 1 malocclusion with a large overjet, deep overbite, a lip bite habit, a lower lip curl, short mandible, a large A-B discrepancy, protrusive maxillary incisors, retruded mandibular incisors, and excessive space in the maxillary arch.

Patient No. 2 (Figures 21-25)

Patient No. 2 displays a female adolescent with a Class II, Division 1 malocclusion with a large overjet and deep overbite, lip incompetence, a lip bite habit, maxillary spacing, a large A-B discrepancy, protrusive maxillary incisors, retruded mandibular incisors, and only marginal growth potential.

Patient No. 3 (Figures 26-28)

Patient No. 3 is a male adolescent presenting with a Class II malocclusion characterized by a maxillary arch length discrepancy, mandibular arch spacing, an overbite, overjet, posterior crossbite, root canal therapy on No. 30 and limited growth potential. Correction with the MPAs will be almost entirely with dentoalveolar effects.

Summary

The MPA has proven its effectiveness, safety, and value in the treatment of Class II malocclusions for more than 25 years and has proven that this new iteration — the MPA 5 — is a significant improvement: It places pressure on the maxillary dentition through the mesial opening of the molar headgear tube and attaches via a double AlastiK chain. This has several distinct advantages:

• Makes it much easier to attach.
• Makes adjustments much easier.
• Increases the attachment angle of the tube and rod, thereby avoiding interference with the mandibular molar.
• Allows easier repairs when breakage of any part of the appliance occurs.

As with all other variations of the MPA, the MPA 5 does not require a laboratory technique and can be delivered with one appointment chairside.

Even so, as with any beneficial mechanism, it has distinct advantages and some disadvantages. Since orthodontic clinicians have to construct this appliance, it loses its appeal for many. This disadvantage, however, is offset by its inexpensive and simple fabrication. Dr. Coelho resisted several requests from companies to make the appliance because he knew that would require a patent and ultimately a more expensive appliance, while he wanted everyone to have the opportunity to use the appliance without restriction. Although the MPA is small compared to other functional appliances, it has proven equal in effectiveness to the Herbst*^14,15 and other fixed, functional appliances,^16,17 while it offers stability,¹⁸ more clinician control, and patient comfort than removable functional appliances and many of the larger fixed Class II correctors.