A developing Class III malocclusion is one of the most challenging problems confronting an orthodontic clinician. If left untreated the Class III malocclusion may worsen, with the majority of these patients ultimately requiring orthognathic surgery as adults.

For this reason, I recommend early interceptive orthodontic treatment to reduce the percentage need for surgery. Unfortunately, when such Class III treatment is initiated at the appropriate age, there is often a significant amount of time between the end of facemask treatment and the beginning of “definitive” orthodontics.

I have written this article in an attempt to clarify the correct treatment protocol for Class III patients and to suggest methods of retention during their continued period of facial growth.

A developing Class III malocclusion can present with maxillary skeletal retrusion, mandibular skeletal protrusion, or a combination of the two. In addition to these sagittal problems there may be posterior and anterior crossbites also present. Dental compensation, such as maxillary dentoalveolar protrusion and mandibular dentoalveolar retrusion tend to produce poor facial profiles with midface deficiencies often still apparent.

The prevalence of Class III malocclusion is approximately 5% in the Caucasian population, rising to as much as 50% in the Japanese and Korean populations.

TREATMENT OF THE CLASS III MALOCCLUSION:

Although traditional orthodontic treatment, for a developing Class III malocclusion, focused on the mandible as the primary cause of the discrepancy, recent studies have suggested that 63% of skeletal Class III malocclusions display maxillary retrusion. The majority of patients tend to exhibit maxillary hypoplasia in conjunction with a normal or mildly prognathic mandible.

Unfortunately, I see too many young patients, for a second opinion, who are told there is nothing the orthodontist can do but wait until their facial growth is complete and then work them up for orthognathic surgery. Yet the majority of surgical procedures to correct a Class III malocclusion involve maxillary advancements! This suggests that the problem was never excessive mandibular growth, but rather a lack of development of the maxilla. Such problems may have been caused by airway blockages when the child was younger.

Orthodontic treatment for the Class III malocclusion can be defined into the following categories:

1. Growth modification involving maxillary expansion and protraction face mask therapy,
2. Growth modification involving a chin cup to restrain mandibular growth, or
3. Waiting until growth has ceased, thereby, committing the patient to either dental camouflage treatment or orthognathic surgery.

In my orthodontic practice children exhibiting early signs of a Class III malocclusion are given priority for treatment. My current treatment approach involves protraction and development of the maxilla, but I do not use chin cups as I feel they have an adverse effect on the patient’s temporomandibular joints.

Controversy currently exists as to the optimum time to commence Class III orthodontic treatment. Takada examined maxillary protraction therapy and reported that the pre-pubertal and mid-pubertal time frame is best due to the maxilla’s natural growth.

TREATMENT OBJECTIVES FOR THE CLASS III PATIENT:

If we treat a Class III patient as early in the growth cycle as possible i.e. as soon as the Class III problem can be diagnosed, the following treatment objectives may be achieved:

1. Reduce the growth in and the size of the mandible,
2. Increase the size of the maxilla to its maximum genetic potential, and
3. Move the maxilla forward to its maximum genetic position.

A cephalometric analysis is essential to confirm the diagnosis of a Class III malocclusion and to formulate either a surgical or non-surgical treatment plan.

I personally use the Bimler cephalometric analysis as this is ideally suited to the correct diagnosis of a Class III patient. In the Bimbler analysis the size of the mandible and the position of the mandible can be easily related to the length and position of the anterior cranial base. The size of the maxilla and the position of the maxilla may also be related to the size and position of the anterior cranial base.

The Sassouni Plus cephalometric analysis provides an easy visual means to identify maxillary/mandibular disproportions, but is not as detailed as the Bimbler analysis in regard to diagnostic criteria.

CLASS III ORTHOPAEDIC APPLIANCE OPTIONS:

The cephalometric analysis should be supplemented with a clinical diagnosis and a study cast analysis. The Schwartz/Korkhaus study cast analysis enables a clinician to determine the correct dimensions of the maxillary and mandibular arches. If the maxilla is wide enough a maxillary sagittal appliance may be used otherwise a 3D appliance is indicated. In the 3D appliance the expansion screw should be placed straight and parallel to the midline palatal suture. This will ensure that there is minimum reciprocal distalising of the maxillary buccal segments during the activation of the sagittal appliance. Such an appliance may also be used for pseudo Class III patients, however, a lower Hawley retainer must be worn to minimise further mandibular growth.

I have used either a modified Frankel III, a Han appliance or a reverse twin block for the orthopaedic correction of a growing Class III malocclusion. For any of these appliances to be successful, the maxilla must be only slightly retruded and the patient must be able to provide an edge to edge bite.

The most successful treatment in my practice, however, involves the use of a maxillary 3D appliance to enlarge the maxilla, in conjunction with a reverse pull facemask (protraction headgear) to move the maxilla, as a body, forward into a more favorable position. The reverse pull headgear is fitted in combination with a “fixed lower labial” appliance and Class III intraoral elastics in an attempt to prevent further mandibular growth.

These varying forms of “interceptive” orthodontic treatment may save your patient from surgery, which itself isn’t always successful. The disadvantage of dentoalveolar base compensations to correct a skeletal III problem is that extractions of lower bicuspids are often required. Such dental camouflage is rarely indicated as the lower anterior teeth respond to retraction mechanics by simply tipping backwards. This can lead to periodontal problems on the labio-gingival portion of the anterior teeth. Such treatment is highly unstable as the lower extraction space reopens with time. If I extract to “orthodontically camouflage” a non-growing Class III malocclusion I prefer to remove a lower incisor in preference to lower first premolars.

PROTRACTION FACE MASKS (REVERSE PULL HEADGEAR):

The reverse pull facemask was first described in Germany, more than 100 years ago. The individual most responsible for reviving interest in this technique is Delaire. Petit (1983) modified the facemask of Delaire by increasing the amount of force generated by the appliance and decreasing the overall treatment time. McNamara (1987) described a version of the petit facial mask that attaches to a maxillary splint which is bonded to the posterior dentition. The splint is fitted with hooks to attach elastics to the facemask, and an expansion screw is incorporated in the appliance. Mid facial orthopaedic expansion can produce a slight anterior movement of Point A and a slight inferior, and anterior movement of the maxilla.

Downward and backward rotation of the mandible is seen with the use of maxillary protraction, particularly in facemasks which have a chin cap incorporated into the design eg. Delaire and Petit styles.

There are now reverse pull facemasks available (Grummons) for patients suffering from severe temporomandibular joint dysfunction. These reverse pull facemasks are designed to keep all reciprocal forces completely off the mandible. I tend to favor these facemasks for Class III skeletal open bite patients because the conventional facemask causes an anterior and vertical movement of the maxilla. This results in bite opening which is desirable in deep bite patients, exhibiting over closure of the mandible, but is contraindicated in open bite patients.

Correction of a Class III malocclusion using facemask and expansion therapy results from a combination of skeletal and dental changes which produce an improvement in the soft tissue profile. Patients I have treated with this technique demonstrate a statistically significant hard and soft tissue movement which favorably affects the entire dentofacial complex.

Skeletal change is primarily a result of anterior and vertical movement of the maxillae. Mandibular movement is directed backward and downward with an increase in lower face height and mandibular inclination. Dental changes also contribute to the correction. These in combination with the soft tissue changes produce a more convex profile.

Work by Has has shown that mid facial orthopaedic expansion is in itself beneficial in the treatment of certain Class III malocclusions. In the context of facemask therapy, the effect of such expansion is to disrupt the maxillary sutural system, plus possibly enhance the effect of the orthopaedic face mask by making sutural adjustments occur more readily.

ELASTIC TRACTION:

A facemask is secured to the face by stretching elastics from hooks on the maxillary splint to the crossbow of the facemask. Heavy forces are generated, usually through the use of 5/8 inch, 14 oz elastics bilaterally. Lighter forces may be used initially, but the forces should increase to orthopaedic strength as soon as the patient adjusts to the appliance.

The elastics are attached in the canine area of the maxillary splint. These elastics should be worn for a minimum of 12 hours per day with the patient exceeding the minimal amount as much as possible. I advocate full time use of the reverse pull facemask when a patient is not in public and is able to do so. If the elastics are placed too far posteriorly in the maxillae the “Kline Effect” can be seen. This causes the maxilla to tip anteriorly and leads to an unsightly display of gingiva anteriorly.

Intra oral Class III elastics may also be used if attached to a holding arch in the mandible. These elastics are placed in a Class III direction from the maxillary first molars to the soldered hooks on the holding arch. The size of these elastics is 3/16 inch, 4½ oz in the primary and mixed dentition and 5/16 inch, 4 ½ oz in the permanent dentition. It is very important to understand that the intraoral Class III elastics have a different vector of force when compared to extraoral Class III elastics. Extraoral Class III elastics pull at a horizontal or parallel relationship to the maxillary plane. Therefore, their reciprocal force is balanced between the frontal bone and the mandible. This in turn creates only a horizontal force within the temporomandibular joints.

Intraoral Class III elastics, however, place a diagonal force upon the mandible, which can in return cause the mandibular condyle to be displaced off the meniscus. Intraoral elastics, therefore, must have the following guidelines if they are to be used during the treatment of a Class III malocclusion:

a.they must never be used for any patient who is experiencing temporomandibular joint symptoms,

b. they must be terminated if the patient acquires any form of joint dysfunction, and

c. they must be worn intermittently to allow the mandibular condyles to decompress within the glenoid fossa. This permits proper circulation to be restored within the TMJ complex.

The most satisfactory combination of intraoral and extraoral class III traction is for the patient to wear the intraoral elastics during the day, removing them only for eating. The extraoral elastics should be worn at nights and as much as possible during the day in conjunction with the intraoral elastics.

MAXILLARY EXPANSION APPLIANCE DESIGN:

An essential part of the orthopaedic Class III treatment is the use of a bonded maxillary splint. This appliance is an acrylic and wire maxillary expansion appliance that is bonded to the posterior dentition. The splint usually covers the first and second deciduous molars. The maxillary canines may also be included in patients who present with a complete deciduous dentition.

The maxillary splint is made of a framework of 0.045 inch round stainless steel wire to which an expansion screw is attached. If second molars are present an occlusal rest is extended to these teeth to prevent their over eruption during treatment. Two hooks, to which elastics are attached, are soldered to the wire framework. These hooks usually lie adjacent to the canines or first deciduous molars. The minimum thickness of the splint should be no less than 1.5 mm otherwise it can promote occlusal decalcification due to abrasion of the appliance by the opposing dentition.

When bonding the maxillary splint in the mouth the teeth should be carefully etched on their buccal and lingual surfaces. The occlusal surfaces are not etched, to facilitate removal of the appliance. I advocate the use of a light cured glass ionomer cement to prevent decalcification and facilitate removal of the excess cement before activating with a light curing machine. Whichever GIC bonding agent is used it should have a low viscosity and a long working time. The tissue fitting surface of the acrylic splint should be micro-etched in the laboratory to improve retention.

The maxillary expansion appliance is activated once a day for eight days to produce a disruption in the sutural system. This facilitates the action of the facemask. Expansion is then slowed down to two turns a week to limit increases in the vertical dimension, but allow continued development of the maxilla until the desired transverse change has been achieved.

RETENTION OF ORTHOPAEDIC CHANGES DURING THE CONTINUED GROWTH PHASE:

If a patient is in a late deciduous or early mixed dentition at the conclusion of my facemask therapy I advocate the use of a modified Frankel III appliance to act as an “active” retainer. The modified Frankel III appliance has sagittal expansion screws in the pre-maxillary region. These are activated to keep the upper lip away from the pre-maxilla. The use of acrylic palots in the labial sulcus stretch the mucoperiostium to encourage bone deposition where it is needed.

A Han appliance may also be used as a functional retainer. This appliance is a bimaxillary design which resembles an upper sagittal appliance joined to a lower Hawley retainer. The Han virtually eliminates any reciprocal movement of the upper posterior teeth. I find that I get better patient compliance with a Han appliance than I do with a Frankel III. The major drawback of the Frankel appliance is its poor patient acceptance. If, however, you can motivate your patient to wear it it really works well.

One of the disadvantages of the Han appliance and the modified Frankel III appliance is that Class III elastics and reverse pull facemasks cannot be worn simultaneously with them. The Truitt III appliance, however, permits the use of intraoral Class III elastics and extraoral Class III elastics applied to a reverse pull facemask. The Truitt III appliance does, however, require a permanent dentition for retention.

The maxillary portion of the Truitt III appliance is like a modified Schwartz plate. The following modifications may be added:

a. Occlusal coverage with a minimal thickness of 1.5 mm posteriorly,

b. Anterior tongue wires to curb a tongue thrust habit,

c. Posterior palatal spinner to allow myofunctional swallowing therapy to be initiated,

d. Frankel III mucoperiosteal pads to stimulate maxillary growth,

e. Elastic hooks placed on the maxillary first molars by soldering to Adams clasps. These are designed for the placement of intraoral elastics,

f. Soldered hooks on the omega loop of the labial bow, in the canine region, for the placement of extraoral elastics,

g. Expansion screws are incorporated into the appliance to develop the sagittal and transverse size of the maxilla.

The mandibular portion of the Truitt III appliance is a modified Hawley with a labial bow. The labial bow is constructed of heavy 0.036 steel wire. It extends from the occlusal acrylic downward and is formed into a standard Hawley loop. This engages into the gingival third of the mandibular incisors.

The Truitt III appliance is activated by turning an expansion screw once a week (1/4 mm). This adjustment should be reduced to once a fortnight if the patient has an anterior open bite. The intraoral and extraoral elastics are worn as per the rules of facemask therapy. The occlusal acrylic coverage on the Truitt III appliance is adjusted just like a flat plane splint. There should be no lower cuspid guidance to prevent an anterior displacement of the meniscus within the temporomandibular joint.

The lower labial bow of the Truitt appliance must be adjusted monthly to be in firm contact with the mandibular incisors. This adjustment is done with a three-jaw plier to constrict the size of the omega loops. It is important to ensure that the labial bow contacts the gingival 1/3 of the mandibular incisors to keep tipping of these teeth to an absolute minimum.

FINISHING CLASS III MALOCCLUSIONS VIA STRAIGHTWIRE:

Once the developing Class III problem is corrected orthopaedically I advocate the use of a Han, Frankel III, or Truitt III appliance to act as a retainer until growth is complete. The patient is then ready for final orthodontic correction using fixed appliance therapy. The orthodontic portion of the treatment is best delayed until the patient has completed their pubertal growth.

Any orthodontic treatment must be centered around the principles of maintaining the Class III dentoalveolar base compensation within the lower arch and burning anchorage in the upper arch. No retrusive mechanics should ever be used on the maxillary dentition in a Class III malocclusion.

I use a “stopped archwire technique” in the maxillary arch to push the maxillary incisors forward into a Class I incisor relationship. This is achieved by placing guerin locks mesial to the first molars and allowing a 0.016 x 0.022 thermal nickel titanium archwire to lie about 4mm ahead of the maxillary brackets. When this archwire is ligated into the maxillary incisor teeth the wire is prevented from distal driving by the guerin locks, so the wire pushes the maxillary incisors forward.

To maintain my orthopaedic correction during straightwire I recommend the use of a Vesco arch. The Vesco arch is a fixed archwire appliance which is designed to correct dental and skeletal Class III malocclusions efficiently. Like Dr Frankel’s functional regulator, the Vesco arch contains maxillary lip pads to relieve restrictive forces from the upper lip. The mechanical aspect of the lip pads acts as a cleat to bridge elastics from the archwire to the reverse pull facemask. A separation is incorporated through the centre of the acrylic lip pad to allow the orthodontist the option of adapting the pad to the oral anatomy and eliminating patient discomfort. Also, due to the cantilever effect of the reverse pull elastics from the archwire, labial root torque is transmitted to the maxillary incisors to avoid their proclination during maxillary protraction. The Vesco arch permits the continued use of reverse pull facemask therapy during the straightwire phase of treatment. If orthodontic movement is required lighter forces are applied to the Vesco arch i.e. 200 gms per side, but if we wish to continue orthopaedic correction of the maxilla heavier forces are required i.e. 600 gms per side.

The fixed appliance therapy in the lower arch is completed on a round stainless steel archwire (0.018). If we were to progress to a rectangular archwire we would express labial crown torque to the incisors. This will push them into a Class III position. I finish my Class III straightwire cases with a 0.021” x 0.025” stainless steel archwire in the maxilla and a round 0.018” stainless steel wire in the mandible. As mentioned earlier, if there is still crowding in the lower labial segment when growth is complete I would advocate interproximal stripping or the removal of a lower incisor. Extraction of lower bicuspids is contraindicated as the lower anterior teeth respond to retraction mechanics by simply tipping back.

If the patient requires surgical treatment decompensation is advocated with the use of rectangular wires in both arches to place the incisors over their respective skeletal bases.

SUMMARY FOR EARLY CLASS III MALOCLUSSIONS

Most Class III malocclusions involve a maxilla which is too small (sagitally and/or transversely) or too far back in relation to the anterior cranial base. There may be a combination of both of these problems. Understanding the problem is the key to determining which type of appliance to use. A thorough cephalometric analysis is an invaluable aid in helping to make this diagnosis.

The clinician should treat Class III malocclusions as soon as they are diagnosed. I find that Class II malocclusions are sometimes treated too early, before the forward growth of the mandible. In many cases a six-year-old Class II patient may self correct when mandibular growth occurs. On the other hand, a six-year-old Class III patient is already one step out of normal and will not grow into a Class I occlusion. These patients need early intervention and require prolonged retention (throughout the post pubertal period) to maintain their orthopaedic correction.

The clinician should always warn the patient, and the parents, that it is not always possible to avoid surgery, but early treatment mechanics can at least limit surgery to one jaw or reduce the percentage chance of requiring orthognathic treatment. A deep bite Class III malocclusion always has a better prognosis than an open bite Class III problem. In the open bite, increased vertical, Class III problem it is important to observe the need for occlusal coverage and to watch for an anterior tongue thrust.