Fisher 1
Fisher 2

Figures 1 (top) and 2 (bottom) demonstrate the typical results when the new mechanotherapy is used to treat an open bite.

By Jack C. Fisher, DMD, and Jay B. Burton, DMD, MBA

 

Open bites have long been the most difficult type of malocclusion to treat and retain. The etiology is multifactorial, including: inheritance, allergies, mouth breathing, low tongue position, forward tongue position, constricted upper arch, super erupted molars, reverse swallowing habit, trauma, idiopathic condylar resorption, etc. The relationship between these factors makes it difficult to diagnose with 100% accuracy. Regardless of the etiology, we as orthodontists are responsible for treatment of open bite patients when they present to our practices.

New Modalities

In the 1980s and early ’90s, many open bite cases were treated with fixed orthodontic appliances and orthognathic surgery. During this time, most insurance companies covered this treatment modality. Unfortunately, getting approval from insurance companies for this type of treatment has become difficult, if not impossible. This has left the profession of orthodontics with the challenge of developing alternative treatment modalities to correct this malocclusion.

However, we cannot discuss new modalities of open bite treatment without first addressing the past stability of surgical treatment. With regard to the stability of surgical treatment, Espeland et al wrote that “surgical impaction of the posterior maxilla ?2 mm relapsed on average by 31% and inferior repositioning of the anterior maxilla ?2 mm relapsed by 62%.”1 If a treatment modality to close open bites, without surgery, falls within these envelopes of relapse, we can conclude that this new modality is an acceptable alternative to surgical intervention. Proffit et al states:

Successful treatment of skeletal open bite during growth requires control of downward growth of the maxilla and eruption of posterior teeth so that mandibular rotation is prevented. This can be extremely difficult to accomplish. Continued vertical growth in the late teens is a major problem that often occurs after orthodontic treatment has been completed. After excessive vertical growth has occurred, there are only two approaches to treatment of open bite: elongate the anterior teeth, which leaves the skeletal component of the deformity uncorrected, or depress the posterior teeth.

If an appropriate force system could be developed and applied, it would be possible to intrude posterior teeth. Bite blocks between the posterior teeth, with or without magnets, can prevent further eruption, but significant intrusion in adolescents or adults is difficult to document and rarely if ever achieved. Open bite can be corrected in patients who are beyond the adolescent growth spurt with multiloop edgewise technique, but the major effect is extrusion of anterior teeth rather than ?intrusion posteriorly. Once excessive vertical development has occurred, orthognathic surgery is the only way to correct the jaw rotations and reduce anterior face height.2

With this in mind, this article offers a treatment modality that meets the objectives stated by Proffit et al and falls within the surgical relapse rates regarding treatment stability. Looking at Figures 1 and 2, we see a typical result when using the mechanotherapy described below.

Use of TSADs

Fisher 3Figure 3: Here, TSADs are used in combination with an appliance incorporating bite blocks, a midpalatal acrylic button, and four nitinol springs. In the last 10 years, the use of temporary skeletal anchorage devices (TSADs) has continued to evolve as an acceptable treatment modality for anchorage control. Perhaps one of the greatest benefits these devices offer is the vertical control they can provide. TSADs in combination with an appliance that incorporates bite blocks, a midpalatal acrylic button, and a vertical force from four nitinol springs allows for intrusion of the posterior teeth and closure of the open bite (Figure 3). In this case, the springs are attached to two TSADs placed in the infrazygomatic crests bilaterally (Figure 4).

Each spring produces about 225 g of force. Using four springs, two per side, yields the resultant vertical force of around 800 g total. Additionally, it is important to incorporate an intrusive force on the lower posterior segments in cases that exhibit a lower reverse curve of spee that is the result of supra erupted posterior teeth. The lower appliance uses two to four TSADs for intrusion (Figure 5). The TSADs are placed between the first and second molars and/or mesial to the first molars (Figure 6).

Fisher 4Figure 4: The nitinol springs are attached to two TSADs placed in the infrazygomatic crests bilaterally. It should be noted that this appliance also has tongue spurs incorporated on the lingual bar that is positioned vertically off the lower anteriors. As the posterior teeth intrude, it is important to continually adjust this lingual bar so that it does not contact the anterior teeth. Occlusal rests on the second molars and bicuspids also contribute to the vertical forces created by this appliance. It is now recommended that the lower TSADs be placed under the tissue, which requires a horizontal flap as illustrated.

Force Systems

When these two appliances are combined to close an open bite, there are four active force systems:

  1. An acrylic button on the upper appliance is placed approximately 5 mm off of the palate. This provides an intermittent vertical force every time the patient swallows.
  2. Bite blocks on the upper appliance are constructed so that the only teeth contacting the appliance initially are the second molars. As the posterior teeth intrude, the first molars and the bicuspids begin to contact.
  3. A maxillary appliance attached to springs provides a vertical force.
  4. A mandibular appliance attached to springs provides a vertical force.

Results

Fisher 5Figure 5: Here, the lower appliance uses two to four TSADs for intrusion. We have utilized these appliances or some variation in approximately 120 patients. When the case is treated nonextraction, we have seen a range from zero to 6 mm of intrusion with the average being a little more than 2 mm. The mandibular appliance will result in 1 to 3 mm of intrusion of the posterior teeth as well. When upper and lower first bicuspids are removed, there is an average of 3 mm of intrusion of the upper posteriors and 3 mm of average intrusion of the mandibular posteriors. The ?maxillary anterior teeth also extrude some, ranging 1 to 3 mm. This may be due to the tongue spurs placed on the lower appliance.

When 3 mm of upper and lower intrusion is achieved (a total of 6 mm intrusion), this results in the potential closure of an 18-mm open bite and the Y-axis can close as much as 5º. Because of the amount of intrusion and rotation of the mandible, the canines often begin to occlude too soon due to the autorotation. In order to continue the posterior intrusion, it is often necessary to employ finger springs on the maxillary appliance to push the canines buccally during intrusion, as seen in Figure 3.

Fisher 6Figure 6: TSADs have been placed between the first and second molars and/or mesial to the first molars.

We have found that 5 months of wearing the appliances is usually sufficient time to close most open bites. In severe cases, the appliance can remain active for 6 months. Upon removal of the maxillary ?appliance, there is usually a posterior open bite, which is normal at this stage in the treatment protocol. Usually, some relapse is warranted because of the posterior open bite that has been created (Figure 7). The lower appliance is not removed so as to continue to take advantage of the tongue spurs placed on the lower appliance.

Fsiher 7Figure 7: Some relapse is expected because of the posterior open bite that has been created.

The patient is then instructed to return to the clinic in 4 weeks to place the fixed brackets, which are placed in an open bite position. If needed, the TSADs, which have been left in on purpose, can be used as vertical control by ligating the first molars to the TSADs. This should prevent any unwanted relapse.

As with any open bite case, retention is a major concern. We recommend an upper wrap-around type of retainer and a lower Hawley retainer with posterior bite blocks (2 to 3 mm) and tongue spurs (Figure 8).

Fisher 8Figure 8: An upper wraparound type of retainer and a lower Hawley retainer with posterior bite blocks and tongue spurs is recommended for retention.

Before attempting this mechanotherapy, it is recommended that the clinician become proficient in the placement of infrazygomatic TSADs in order to obtain consistent results. The best education to gain this competency is to first become proficient in placing these TSADs on fresh tissue specimens during a training course. This appliance meets the objectives reported in the footnoted article to close open bites.

While long-term follow-up studies are needed to compare the stability of this technique with that found in orthognathic surgical closure, the preliminary results we have observed are positive and encouraging. OP

 

Fisher Burton headshot

Jack C. Fisher, DMD, has maintained a private practice since 1982. He can be reached at jack.fisher@mac.com.

Jay B. Burton, DMD, MBA,  is an orthodontic resident at New York University. He can be reached at burton.jay@gmail.com.

 

References:

  1. Espeland L, Dowling PA, Mobarak KA, Stenvik A. Three-year stability of open-bite correction by 1-piece maxillary osteotomy. Am J Orthod Dentofacial Orthop. 2008;134(1):60-66.
  2. Profitt WR, Bailey TJ, Phillips C, Turvey TA. Long-term stability of surgical open-bite correction by Le Fort I Osteotomy. Angle Orthod. 2000;70(2):112-117.