Burstone's Biomechanical Foundation of Clinical Orthodontics

Dr Charles Burstone was a pioneer in orthodontic biomechanics, and his legacy lives on this second edition of his book, with Dr Kwangchul Choy at the helm. This textbook has taught thousands of orthodontists the importance of understanding biomechanics to ensure healthy, predictable movements in clinical practice, and this new edition will undoubtedly do the same for the new generations of students. Technology continues to advance in orthodontics, but no technology can replace a sound understanding of how the teeth move in their periodontal apparatus and how they can be pushed or pulled to get where they need to be. This book is the difference between an orthodontist who can move teeth and an orthodontist who can plan cases with predictability and achieve the sought-after results.

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Why We Need Biomechanics

"Don't believe blindly in experience, but believe in theory, and think creatively."

-Charles J. Burstone

Dentofacial changes are primarily achieved by the orthodontist applying forces to teeth, the periodontium, and bone. Hence, the scientific basis of orthodontics is physics and Newtonian mechanics applied to a biologic system. The modern clinician can no longer practice or learn orthodontics as a trade or a technique. The orthodontist must understand forces and how to manipulate them to optimize active tooth movement and anchorage. Communication with fellow clinicians and other colleagues in other fields requires a common scientific terminology and not a narrow "jargon." There is no such thing as a unique "orthodontics physics" divorced from the rest of the scientific community. New appliances and treatment modalities will need a sound biomechanical foundation for their development and most efficient use.

Every profession has its trade tools. The carpenter uses a hammer and a saw. The medical doctor may prescribe medication and is therefore a student of proper drug selection and dosage. Traditionally, the orthodontist is identified with brackets, wires, and other appliances. Such hardware is only a means to an end point: tooth alignment, bone remodeling, and growth modification. The orthodontist achieves these goals by manipulating forces. This force control within dentofacial orthopedics is analogous to the doctor's dosages. An "orthodontic dosage" includes such quantities as force magnitude, force direction, point of force application (moment-to-force ratios), and force continuity.

Historically, because the end point for treatment is the proper force system, one might expect the development and usage of orthodontic appliances to be based on concepts and principles from physics and engineering. On the contrary, however, most appliances have been developed empirically and by trial and error. For that reason, treatment may not be efficient. Many times undesirable side effects are produced. If appliances "work," at a basic minimum the forces must be correct, which is independent of the appliance, wires, or brackets. Conversely, when bad things happen, there is a good possibility that the force system is incorrect.

These empirically developed appliances rarely discuss or consider forces. Forces are not measured or included in the treatment plan. How is it possible to use such mechanisms for individualized treatment? The answer is that they are shape driven rather than force driven. Different shapes and configurations are taught and used to produce the desired tooth movement. This approach is not unreasonable because controlled shapes can lead to defined wire deflections that relate to the produced forces. Unfortunately, there is so much anatomical variation among different patients that using a standard shape for a bracket or a wire or even modifying that shape will not always produce the desired results predictably.

An example of a shape-driven orthodontic appliance is what E. H. Angle called the ideal arch. In a typical application of this ideal arch, an archwire is formed with a shape so that if crooked teeth (brackets) are tied into the arch, the deflected wire will return to its original shape and will correctly align the teeth. Today, wires have been improved to deflect greater distances without permanent deformation, and brackets may have compensations to correct anatomical variation in crown morphology. The principle is the same as Angle's ideal arch, but this approach is now called straight wire. Straight-wire appliances can efficiently align teeth but can also lead to adverse effects in other situations. The final tooth alignment may be correct, but the occlusal plane may be canted or the arch widths disturbed. Inter