orthodontics as a science

8/18/2019 Orthodontics as a Science

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The scientific basis of orthodontics rests ona knowledge of anatomy, physiology and growth, and

in particular, biomechanics—the relationship between

force systems and dental or orthopedic correction. Yet

much of clinical orthodontics is delivered without con-

sideration of forces or force systems. This suggests that

many clinicians believe that a fundamental knowledge

and application of biomechanics has little relevance ona daily basis in their treatment. Let us consider why

biomechanics should be at the core of clinical practice.

Optimization of Tooth Movement

The application of correct forces and moments are

necessary for full control of tooth movement, influ-

encing the rates of tooth movement and accuracy in

producing different centers of rotation. Knowing

or estimating the force system is relevant to sliding

mechanics, intermaxillary elastics, headgear, and

functional appliances.

Anchorage Control

Anchorage control is based on combining force

levels and selective moments. All archwires produce

multiple effects. Many of the effects are undesirable,

which not only leads to anchorage loss, but to new

problems created during treatment. Biomechanics

allows the clinician to place proper bends or to use

special configurations to minimize or eliminate these

undesirable side effects.

Selection of Wires Brackets and Clinical Devices

There has been a proliferation of new materials,

wires, attachments, and other clinical devices. Which

are the best to use for treatment, and how do we indi-

vidualize their selection for patients? These mecha-

nisms are not interchangeable. For instance, a .014”

superelastic NiTi wire is not the same as a .014” Niti-

nol, and hence its application is different.

Development and Use of a Scientific Terminology

Orthodontic appliances work by the delivery of

force systems. The terminology to describe forces and

the geometry of tooth position is part of a broader

knowledge used in science. Some specialized ortho-

dontic terms have produced a jargon that may not be

precise and is certainly unintelligible for other disci-

plines. Universal biomechanical language is the sim-

plest way to describe how an appliance works and is to

be used. It allows communication with other disci-

plines so joint research becomes simpler and more rel-

evant. It also enhances the teaching of clinical ortho-

dontics to new residents; emphasis is on principles

rather than techniques. The student better understands

how an appliance will work and how it is to be used. It

aUniversity of Connecticut Health Center, Department of Orthodontics.

Reprint requests to: Dr Charles Burstone, DDS, MS, University of Connecticut

Health Center, Department of Orthodontics, Farmington, CT 06030.

Copyright © 2000 by the American Association of Orthodontists.

0889-5406/2000/$12.00 + 0 8/1/106013

doi.10.1067/mod.2000.106013

Orthodontics as a science:

The role of biomechanics

Charles Burstonea

Farmington, Conn

Charles Burstone


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American Journal of Orthodontics and Dentofacial Orthopedics Burstone 599Volume 117 , Number 5

shortens what has been referred to as clinical experi-

ence. It is said that clinical experience is nothing more

than the repetition of mistakes. If the student under-

stands the biomechanical basis of his appliance many

common mistakes will never be made. As new appli-

ances are developed the experienced orthodontist canbenefit from biomechanics. Explanations of both fabri-

cation and use based upon how forces are delivered

greatly simplifies the presentation of new material.

Explanation and Evaluation of Treatment Results

In clinical practice when patients return for a visit

many times, puzzling things are observed. Sometimes

this is attributed to biological variation. In reality, much

of the variation is in the biomechanics that has been

applied. An understanding of biomechanics allows the

clinician to more accurately determine what has hap-

pened and what should be done to correct the problem.

To predict outcomes of treatment requires a more precisecontrol and understanding of the force systems used.

Research

Clinical studies require control of important vari-

ables. Much of the clinical research does not define

the force systems that were used during treatment or

during one aspect of treatment. It is not enough to say

that headgear was used or even to specify it as an

occipital headgear in a study. Occipital headgears

have many different lines of action of force and

points of application. It is little wonder that results

sometimes are either imprecise or confusing. A bio-

mechanical approach to orthodontics opens up newareas for research as what is the relationship between

force magnitudes, moment to force ratios, force con-

stancy on dental and orthopedic responses.

Minimization of Tissue Destruction

Orthodontic tissue destruction includes alveolar bone

loss, root resorption, and the clinical responses of patient

discomfort. Histologic studies can demonstrate a rela-

tionship between force magnitude and tissue destruction.

Clinical studies are less clear because many more vari-

ables are involved, particularly in root resorption where

major cases of root resorption seem to be associated with

other factors other than the force system. Nevertheless,

the quality of our treatment suggests control over force

magnitude. As in medicine, dosage does count.

Reduction of Patient Cooperation

The reduction of undesirable side effects and the

concomitant reduction in treatment time can minimize

the use of intermaxillary elastics or headgears and

other appliances that require patient compliance. We

should not ask our patients to cover up our mistakes

with the use of these devices.

Evaluation of New Appliances

New appliances and variations of old appliances are

continually presented in the literature and at meetings.These appliances can be evaluated with the use of fun-

damental biomechanical principles. The other approach

is to try these appliances clinically and see how they

work. This trial and error approach is time consuming

and is not fair to our patients. A high percentage of sug-

gested appliances do not stand the test of time.

Development of New Appliances

Orthodontics has always been a very creative field

with many clinicians developing new and exciting

appliances. An analysis and diagrams on a sheet of

paper are far better than unneeded experimentation on

our patients with new approaches.

Knowledge Transfer From Appliance to Appliance

Certain clinical procedures can be successful, and the

orthodontist may want to apply the force systems from

that used in the past to a new appliance, For instance, if

one wants to used a different type of wire or different

material, or if the orthodontics is going to be done on the

lingual rather than on the facial surfaces, biomechanical

principles allow an easy transfer of equivalent force sys-

tems that should produce the same results.

Reducing Commercialization

There has been much commercialization in ortho-dontics with exaggerated claims made by both clini-

cians and orthodontic companies. Wires, brackets, sys-

tems, and devices are claimed to be superior.

Hyperbole is used to describe these appliances such as

“controlled ... hyper,” “super”(“superelastic wires” is a

correct term for NiTi wires and is descriptive), “effi-

cient,” “biological,” and “space-age.” Knowledgeable

clinicians with good biomechanical background are not

easily swayed by such presentations.

Biomechanics and its derivative orthodontic biome-

chanics applies to all appliances and techniques. At a

minimum it would enhance any given technique used

by a clinician. Currently, not all graduate students are

being trained in biomechanics in any depth. When a

student graduates from a program, an understanding of

biomechanics should be second nature. Otherwise he

or she will be not able to apply it clinically on a daily

basis. The training of students and clinicians in biome-

chanics can include a broad array of topics. It is sug-

gested that the central core of such training should

include the following:


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600 Burstone American Journal of Orthodontics and Dentofacial Orthopedics May 2000

1. The basics of forces, moments, equivalent force

systems, resultants, and components

2. Static equilibrium and its application to solving

orthodontic problems

3. The biomechanics of tooth movement: moment

to force ratios, force deflection ratios, and therelationship of the force system to the biology

of tooth movement

4. Principles of appliance design, including the rela-

tionship of design, wires, friction, materials, and

other variables to the forces produced

5. Material science applied to wires and appliances

in general

6. The ability to develop a mechanics plan for a

patient that has as its starting place the force sys-

tem to optimize tooth movement with minimal

undesirable side effects

The conventional wisdom in orthodontics hasemphasized the appliance. Graduate students and ortho-

dontists were taught to fabricate appliances, make

bends or adjustment in these appliances, and perhaps in

some approaches (as straight wire orthodontics), no

bends or adjustments at all. Perhaps there was some lip

service given to biomechanics forces or biology, but

basically the clinician was a fabricator and user of

appliances. Treatment procedures were organized in a

cookbook fashion. This rather unscientific approach to

clinical practice led to the development of different

schools of thought, sometimes identified by the name of

a leading clinician with cookbook sequences.

A new wisdom is needed in orthodontics that is notappliance oriented. It involves a thinking process

where the clinician identifies goals at least in 3-dimen-

sional space, establishes a sequence of treatment, and

then develops the force systems that will be used to

achieve that goal. Only after force systems have been

carefully established are the appliances selected and

adjusted to obtain those force systems. This is quite

different than orthodontics where the clinician is only

aware of wire shape, bracket formulas, tying mecha-

nism, and friction and play, without any consideration

whatsoever of the forces produced.

Orthodontic biomechanics is not just a theoretical

subject for graduate students and academics. It is thecore of clinical practice; orthodontists are biophysicists

since daily “bread and butter” orthodontics is the cre-

ative application of sound biomechanical principles. The

21st century in orthodontics will be characterized by a

major shift from orthodontic techniques to a biomechan-

ical approach to treatment; and with it will come rapid

changes in treatment and procedures and concepts.

orthodontics as a science

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