Continuing Education (CE) for Orthodontists
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Educational aims and objectives
This article aims to discuss some of the principles gained from current knowledge regarding the vertical dimension of the maxilla and mandible and a possible easily applied remedy for controlling the deleterious effects of too much vertical dimension.
Orthodontic Practice US subscribers can answer the CE questions on page 55 to earn 2 hours of CE from reading this article. Correctly answering the questions will demonstrate the reader can:
- Identify some history regarding the vertical dimension in orthodontics.
- Identify some possible treatments for correction of facial vertical excesses.
- Realize some inadequacies of previous attempts to control the vertical dimension.
- See a mechanism for applying intrusive forces to maxillary and mandibular molars simultaneously.
Dr. Larry White discusses principles gained from current knowledge regarding the vertical dimension of the maxilla and mandible
The vertical dimension in orthodontics remained unimportant and unexplored until Fred Schudy began his epochal studies and publications in the 1960s. Until then, orthodontists presumed that most maxillary-mandibular sagittal discrepancies were due to horizontal growth deviations, and subsequently, practically all orthodontic therapies were designed with horizontal interventions. Class II malocclusions in particular were typically treated with horizontal mechanics without regard to vertical growth and/or biomechanical features that might influence the vertical position of the mandible. Subsequently, orthodontists slowly began to seek remedies that addressed the vertical component of malocclusions with directional-pull headgears, limitation of classical Class II elastics, molar holding arches, repelling springs and magnets, jaw surgery, and more recently, the intrusion of molars with temporary anchorage devices (TADs). This article will illustrate some of the principles gained from current knowledge regarding the vertical dimension of the maxilla and mandible and a possible easily applied remedy for controlling the deleterious effects of too much vertical dimension.
In 1963, Fred Schudy1-5 began publishing articles regarding the influence that the vertical dimension has on occlusion, facial development, and appearance. Until that time, orthodontists were firmly convinced that the vertical position of teeth had little or no influence on the correction of malocclusions, and that conviction stayed entrenched for several more years. Convinced that controlling the vertical eruption of maxillary and mandibular molars was critical in the treatment of Class II malocclusions, Schudy and Creekmore developed a directional-pull headgear that sought to limit the eruption of the maxillary molars and possibly to intrude them.
For a time, surgical interventions via the Le Fort 1 procedure6-9, which impacted the maxillary arch, were the gold standard for certainty and stability in the corrections of facial vertical excesses.
As the truth of Schudy’s discoveries began to take hold, others attempted to control the vertical development of the posterior occlusion with various appliances. Dellinger11,12, Barbre12, Darandellier13, Joho14, Killaridis15, and Woods16 among others had some success controlling molar eruption with magnetic appliances, while others recorded some success with bite blocks17-19. Some tried spring-loaded appliances20-21, while others22 reported some success with removable apparatuses. Unfortunately, most of the previously mentioned techniques proved too unwieldy and never gained more than minimal professional endorsement and use.
In 1983, Creekmore23 excited orthodontics with his use of a surgical screw to intrude maxillary incisors and reveal the possibility of skeletal anchorage heretofore untried in orthodontics to control the vertical dimension. Within 15 years, others, notably in Japan24 and South Korea25-29, developed techniques for intruding teeth with screw-secured bone plates or mini-screws.
Carano30,31 developed an interesting concept for intruding maxillary and mandibular molars simultaneously by using a modified Jasper Jumper (Figure 1) that he called the Rapid Molar Intrusion Appliance (RMI). Although capable of closing anterior bites, the appliance has not proven popular for a couple of reasons: It required headgear tubes on both molars bands, maxillary and mandibular lingual arches, and the jumper material quickly fatigued and needed frequent, difficult, and expensive changes.
Figure 1: Rapid Molar Intrusion appliance of Carano; used with permission from the Angle Orthodontist, 2005:5(5):736-746
More recent studies by Buschang,32,33 et al., have illuminated some of the inadequacies of previous attempts to control the vertical dimension with the previously mentioned techniques. In their study, where only the maxillary molars intruded with TADs, the mandibular molars erupted and negated much of the gains from the maxillary molar intrusion. When they subsequently intruded both maxillary and mandibular molars, the anterior open bite closed, the mandible rotated forward, and the chin projected forward.
Obviously, when only one arch receives treatment, whether it is with headgears, mini-screws, bone plates, or removable appliances, it only achieves an ineffective, compromised result.
Carano’s idea takes on a new and needed cogency, and the strategy needs only improved materials and a simpler attachment method, which the illustrated therapy provides. A 35 mm NiTi closed coil spring shown in Figure 2 (Soft Spring) with eyelets provides an ideal mechanism for applying intrusive forces to maxillary and mandibular molars simultaneously.
Figures 3 and 4 illustrate this new NiTi molar intrusion spring with a typodont.
As the mouth closes, the spring assumes a U-shape that places equally light intrusive pressures on the maxillary and mandibular molars. But those pressures work constantly and do not require large forces to effect their result. Weinstein34 showed in 1967 how constant forces as low as 1.68 gm could produce measurable effects, and clearly the forces produced by the Soft Springs (50 gm to 75 gm) have that clinical capability.
Figure 2: 35 mm NiTi (Soft Spring) closed coil spring with eyelets (JES Orthodontics, Fort Lauderdale, Florida)
Figure 3: Activated 35 mm NiTi closed coil spring with eyelets Figure 4: 35 mm NiTi molar intrusion spring installed fully extended
The photos in Figures 5-8 illustrate the potential this new molar intrusion spring has. Note the maxillary and mandibular lingual arches that negate the facial moments the intrusion springs create on the molars.
Figure 5: Patient with an anterior open bite
Figure 6: The malocclusion after 1 month of therapy with intruding springs
Figure 7: The malocclusion after 2 months of therapy with intruding springs
Figure 8: The malocclusion after 3 months of therapy with intruding springs
After 3 months with molar intrusion springs, the patient is ready to complete the bonding of posterior brackets and fulfillment of treatment. Obviously, one successful anterior bite closure patient cannot offer unequivocal endorsement for universal employment. Nevertheless, this technique presents an instrument that satisfies the most current research that encourages clinicians to simultaneously intrude maxillary and mandibular molars rather than concentrating intrusion therapy in only one arch. Also, clinicians need to realize that when the banded and bonded appliance includes incisors, those teeth will receive an eruptive force even as the molars receive intrusive forces. Regardless of the primary corrective feature, the technique shows promise in correcting open bites. Additionally, these NiTi springs provide a comparatively inexpensive, noninvasive, and simply implemented method of intruding molars in both arches while concurrently aiding in the extrusion of the anterior teeth.
Greater use of the NiTi intrusion springs in anterior open bite patients will reveal any deficiencies inherent in the technique, but the limited experience thus far has shown good acceptance by patients, little interference with occlusal functions and minimum breakage.
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