SINCE 1971 EMPOWERING DOCTORS AND STAFFS TO ATTAIN GREATER SUCCESS THROUGH EDUCATION AND KNOWLEDGE
|
SINCE 1971 EMPOWERING DOCTORS AND STAFFS TO ATTAIN GREATER SUCCESS THROUGH EDUCATION AND KNOWLEDGE |
|
|
Orthodontic
diagnosis of long face syndrome. General
Dentistry, 1996 vol. 44, no. 4, pp. 348-351. Dr. Jim Prittinen,DDS Abstract Management of the vertical dimension of occlusion is one of the most difficult aspects of orthodontic therapy. The vertical dimension of some orthodontic patients increases quickly when mechanics are initiated. However, other orthodontic patients show no increase in vertical dimension when the same mechanics are applied. In this article, a diagnostic method is described that enables clinicians to predict patients’ responses in the vertical dimension before treatment. An
important aspect of comprehensive orthodontic therapy is managing the vertical
dimension of the patient’s face. Many
of the most difficult orthodontic cases involve long face syndrome.
Characteristics include excessive eruption of posterior teeth, normal or
excessive eruption of anterior teeth, short posterior facial height, and a steep
mandibular plane angle.1 Common
diagnostic criteria for long face syndrome include a gonion (Go) to gnathion (Gn)
to sella-nasion (SN) line angle (mandibular plane angle) of 37°
or greater, and a posterior (S to Go) to anterior facial height (N to menton
(Me)) ratio of 0.65 or less.2 In
Figure 1, the skeletal differences between normal and long-faced patients are
illustrated. Causes and management The
primary cause of long face syndrome is an unfavorable growth pattern.3
However, extrinsic factors such as large adenoids, finger habits, or improperly
applied orthodontic mechanics can cause characteristics of long face syndrome.
Limiting the extrusion of the posterior teeth is critical in orthodontic
management of long face syndrome.1 If
the posterior teeth extrude more than normal, the bite opens.
This increases the mandibular plane angle and reduces the ratio of
posterior to anterior facial height. These
changes cause characteristics of long face syndrome.
Because the mandible opens along an arc, excessive bite opening results
in a retruded mandibular position (Fig. 2).
Sassouni3
and Prahl-Anderson et al. showed that a retruded mandible combined with
characteristics of long face syndrome result in poor facial esthetics.4
McNamara showed that more than 60 percent of patients with Class II
malocclusions exhibit 1 or more symptoms of long face syndrome.5
Long face syndrome patients with malocclusions are the most difficult
cases to treat. General practitioners who perform orthodontics must recognize
patients with long face syndrome, and patients with the potential to develop
characteristics of long face syndrome due to improper or inappropriately applied
orthodontic mechanics. These cases
should be referred to an orthodontist.
Most orthodontic systems primarily affect the teeth and alveolar
processes. Bands, brackets, and
wires cause extrusion of teeth.6
However, this bite-opening tendency is expressed differently among patients.
Some patients’ stomatognathic systems resist vertical dimension
changes, and many months often are required to erupt teeth. Tooth eruption in other patients proceeds dramatically with
only a month or two of leveling and aligning mechanics. A major challenge in performing orthodontic procedures is
predicting a patient’s response to extrusive forces. Bjork provided a reliable, convenient method of determining a
patient’s response to orthodontic appliances in terms of vertical dimension.7
Patients who may have excessive posterior eruption and develop characteristics
of long face syndrome can be recognized before treatment.
Bjork, former chairman of the orthodontic department of the Royal College
of Dentistry in Copenhagen, did his research in the 1950s and 60s.
He placed metallic implants in the maxillas and mandibles of 240 growing
patients and observed their growth for 10 to 15 years.7
He performed no treatment but kept annual diagnostic records.
His study cannot be duplicated because supervised neglect (not treating
malocclusions) and placement of metallic implants for observation violate
today’s medical ethics.
Superimposing a patient’s lateral cephalometric x-rays on the stable
metallic implants permits study of growth mechanics and direction.
Most mandibular growth occurs at the condylar head.8
Any change in mandibular shape result from apposition and resorption of surface
bone. Bjork discovered that surface
remodeling disguises about 50 percent of the growth rotation of the lower jaw.9
Untreated patients have a wide range of condylar-growth direction.10
In Figure 3, condylar growth direction is shown in some patients in Bjork’s
study. The majority of patients
show slight anterior condylar growth. Many
patients deviate from this pattern. Some
patients have more anterior condylar growth, which results in more horizontal
mandibular growth. Some patients
show more posterior condylar growth, which results in more vertical direction of
mandibular growth (Fig. 4). No one
knows why these differences occur. According
to a widely accepted theory, different location of growth cells – an inherited
trait – determines mandibular-growth direction.11
Although the reasons for growth differences are not well understood,
these differences affect the entire craniofacial complex.
The muscles of mastication act in different directions in horizontal and
vertical growers, and produce different muscular pressures and tensions in the
two types of growth. This results
in different apposition and resorption of surface bone, and, therefore,
different mandibular morphology in horizontal and vertical growers. Strong – and weak – muscle factorsWhy
are these differences in mandibular morphology important?
In horizontal growers, the angles at which the muscles work produce much
masticatory force. In vertical growers, the angles at which the muscles work
produce much less force.12 Therefore,
horizontal growers can be referred to as strong-muscled patients, and vertical
growers can be referred to as weak-muscled, patients. In Figure 5, the morphological differences are highlighted
between the two growth patterns as viewed on lateral cephalometric x-rays.
The morphological differences are numerous, but five are especially
diagnostic.
First, strong-muscled patients have relatively acute gonial angles; in
weak-muscled patients, the gonial angle tends to be obtuse.13,
14 Second, the shape of the lower border of the mandible differs in
the two types of patients. In
strong-muscled patients, a double curvature on the lower border consists of a
concavity near the gonial angle and a convexity near the anterior portion of the
lower border. Weak-muscled patients
lack this double curvature and instead exhibit a concave lower border. Third, strong-muscled patients have a radiopaque symphysis;
in weak-muscled patients, this area is more radiolucent.2
Fourth, the more acute the symphyseal inclination, the more the patient tends to
be strong-muscled. This can be
quantified by a simple cephalometric measurement of the angle between Go-Gn and
the chin line (the line from pognion (Po) to infradentale (Id) – the most
anterosuperior point on the mandibular alveolar ridge) (Fig. 6).
11 A range of 70°
± 4°
is normal: 65° or less indicates that the patient is
strong-muscled; 75°
or more indicates that the patient is weak-muscled.
Finally, condylar-head inclination indicates muscle strength.
Strong-muscled patients have an anterior condylar-head inclination;
weak-muscled patients have a posterior condylar-head inclination.
Due to superimposition of the zygomatic process over the condylar area,
condylar inclination sometimes is not visible on a cephalometric radiograph.
Some patients have a mixture of strong– and weak-muscle
characteristics. About 80 percent
of all patients are predominately strong-muscled.
A clinician’s biggest challenge is to determine which patients have
extremely strong- or weak-muscle strength characteristics.
Although no method can predict a patient’s muscle strength with 100
percent accuracy, Bjork’s structural method is reliable, especially in extreme
cases.
Extremely strong- or weak-muscled patients present different challenges.
In strong-muscled patients, the masticatory force often overpowers the
extrusive force of the orthodontic appliance.
Posterior segment extrusion and, hence, bite opening in these patients
are difficult. Weak-muscled
patients respond differently to orthodontic force: the extrusive force of the
orthodontic appliance often overpowers the weak masticatory force, resulting in
extrusion of posterior teeth and bite opening.
As this happens, long face syndrome characteristics are expressed.
Response to orthodontic appliances in terms of vertical dimension is
often contrary to the patient’s needs. Most
strong-muscled patients have deep bites; these patients’ masticatory forces
resist bite-opening. Weak-muscled
patients are likely to have long face syndrome.
By causing unwanted bite-opening, orthodontic appliances can aggravate
this syndrome.15 Application of
indiscriminate, heavy forces to weak-muscled, long-faced patients is a serious
clinical error. Further aggravation
of long face syndrome may change a nonsurgical case into one that requires
orthognathic surgery. ConclusionRecognizing
long face syndrome characteristics is an important aspect of orthodontic
diagnosis and treatment. The degree
of horizontal or vertical direction of mandibular growth varies among patients.
Proper orthodontic diagnosis involves recognizing patients (particularly
vertical growers) who demonstrate extremes in mandibular-growth direction.
Bjork’s structural method quickly and easily determines a patient’s
muscle strength and (hence) response to orthodontic appliances in terms of
vertical dimension. Prudent
clinicians treat long-faced, weak-muscled patients with care because deleterious
vertical changes occur easily. Extremely
weak-muscled, long-faced patients are best treated by orthodontists. The
method of Class II correction, the decision to treat with or without tooth
extractions, and the type of arch wires, finishing appliances, and post
treatment retention differ in strong- and weak-muscled patients. Dr. Prittinen practices general dentistry in Virginia, Minnesota, and is an orthodontics instructor for the U.S. Dental Institute. Address correspondence to: James R. Prittinen, DDS, 216 North Fifth Avenue, Virginia, and MN 55792. AcknowledgmentThe author thanks Ann Marie Larson for helping prepare this manuscript. References1. Graber T, Swain B. Orthodontics: current principles and techniques. St. Louis: C.V. Mosby Co.; 1985:81:408. 2. Viazis A. Atlas of orthodontics, principles and clinical applications. Philadelphia: W.B. Saunders; 1993:66. 3. Sassouni V. A radiographic chephalometric analysis of cephalofacail dental relationships. Am J Orthod 1965; 41: 735-764. 4. Prahl-Anderson B, Boersma H, Vander Linden F, Moor AW. Perceptions of dentofacial morphology by laypersons, general dentists, and orthodontists. JADA 1979; 98:209-212. 5. McNamara J. Integrated treatment of the orthodontic patient. Ann Arbor: University of Michigan Press; 1986:410-411. 6. Bennet JC, McLaughlin RP. Orthodontic treatment mechanics and the preadjusted appliance. Aylesbury, England: Wolfe Publishing; 1993:123. 7. Bjork A. Prediction of mandibular growth rotation. Am J Orthod 1969; 55:283-299. 8. Proffit W. Contemporary orthodontics. St. Louis: C.V. Mosby Co.; 1986:32, 88. 9. Bjork A, Skeiller V. Facial development and tooth eruption. Am J Orthod 1972; 62:339-383. 10. Bjork A. Sutural growth of the upper face studied by the implant method. Acta Odontol Scand 1966;24:109-127. 11. Litt R. Comprehensive orthodontics. Presented at the Faculty for Orthodontic Research and Continuing Education (FORCE) Session 4; January 18, 1991; Winnipeg, Manitoba, Canada. 12. Litt R. Comprehensive orthodontics. Present at FORCE Session 1;July 20, 1990; Montreal. 13. Viazis A. Atlas of orthodontics, principles and clinical applications, pp. 66, 70. 14. Bjork A. The face in profile: an anthropological x-ray investigation on Swedish children and conscripts. Svensk Tandlakare-Tidskrift 1947; 40 (suppl):27. 15.
Burstone C, Nanda R. Retention
and stability in orthodontics. Philadelphia: W.B. Saunders; 1993:13, 14.
|
Send mail to usdinstitute@juno.com with questions or comments about this web site.
|
