For millennia, we were unable to understand why teeth can be moved by finger pressure, as advocated by Celsus around the dawn of the Common Era, but it was working. Indeed, our ancestors were keenly aware of malocclusions, and the ability to push teeth around by mechanical force. The modern era in dentistry began in 1728 with the publication of the first comprehensive book on dentistry by Fauchard. He described a procedure of “instant orthodontics,” whereby he aligned ectopically erupted incisors by bending the alveolar bone. A century‐and‐a‐half later, in 1888, Farrar tried to explain why teeth might be moved when subjected to mechanical loads. His explanation was that the teeth move either because the orthodontic forces bend the alveolar bone, or they resorb it. The bone resorption idea of Farrar was proven by Sandstedt in 1901 and 1904, with the publication of the first report on the histology of orthodontic tooth movement. Histology remained the main orthodontic research tool until and beyond the middle of the twentieth century. At that time medical basic research began evolving at an increasing pace, and newly developed research methods were being adapted by investigators in the various fields of dentistry, including orthodontics; Farrar’s assumption that orthodontic forces bend the alveolar bone was proven to be correct, and the race was on to unravel the mystery of the biology of tooth movement. During the second half of the twentieth century, tissues and cells were challenged and studied in vitro and in vivo following exposure to mechanical loads. The main fields of research that have been plowed by these investigations include histochemistry, immunohistochemistry, immunology, cellular biology, molecular biology, and molecular genetics. From this broad research effort it has been concluded that teeth can be moved because cells around their roots are enticed by the mechanical force to remodel the tissues around them. This conclusion has opened the door for quests aimed at discovering means to recruit the involved paradental cells to function in a manner that would result in increased tooth movement velocity. The means tried in these investigations have been pharmaceutical, physical, and surgical. In all these categories, experimental outcomes proved that the common denominator, the cell, is indeed very sensitive to most stimuli, physical and chemical. Hence, the way ahead for orthodontic biological researchers is clear. It is a two‐lane highway, consisting of a continuous stream of basic experiments aiming at uncovering additional secrets of tissue and cellular biology, alongside a lane of trials exploring means to improve the quality of orthodontic care. Gazing toward the horizon, these two lanes seem to merge.
Biological research has exposed differences between individuals based on molecular outlines and entities. In people who possess similar facial features and malocclusions, this variability, which should be reflected in the diagnosis, may require the crafting of treatment plans that address the individual molecular peculiarities. These differences may be due to genetic and/or environmental factors and should be addressed by a personalized orthodontic treatment plan, adapted to the biological profile and needs of each individual patient.
Introduction
Orthodontics, the first specialty of dentistry, has evolved and progressed from its inception to the present time, and the credits for this evolution belong to pioneers, who aimed at improving their clinical capabilities. The evolution of clinical orthodontics is rooted in strong foundations, based on scientific studies and mechanical principles. However, as the specialty began prospering, interest in its association with biological facts began to decline. For a while, orthodontics was taught predominantly as a mechanical endeavor. It can be taught in a short course lasting a few days, usually without any associated clinical exposure. However, recent advancements in medicine have provided orthodontic researchers with investigative tools that enable them to pave new roads toward the target of personalized orthodontics, adapted to the biological profile and needs of each individual patient.
The unfolding of science behind the biology of orthodontic tooth movement (OTM) has been slow and tedious. Our ancestors, as far back as the dawn of history, in all civilizations, cultures, and nations, were interested in images of bodies and faces, covered or exposed. Their artists painted these images on cave walls, cathedral ceilings, and on canvas pieces that were hung in private homes. They also created a huge array of sculptures as monuments, religious fixtures, or outdoor decorations. These works of art reflected images of faces that were carved and crafted along guidelines unique for each tribal, ethnic, and cultural group. Figure 1.1 presents a profile view of a marble statue of a man’s head, found in an archeological dig in Greece. Typically, the facial profile is divided into three equal parts (upper, middle, and lower), and the outline of the nose is continuous with the forehead. Figure 1.2 shows a contemporary sculpture of a shrine guardian in Korea. The features are exaggerated, but the facial proportions are similar to those of the ancient Greek statue. Some artists, like Picasso, attracted attention by intentionally distorting well established facial features. Frequently, facial features in old and contemporary paintings and sculptures express a variety of emotions, ranging from love to fear, and a wide array of shapes, from the ideal to the grotesque.
Figure 1.1 Ancient Greek marble statue of a man’s head.
(Source: National Museum of Greece, Athens.)
The importance of possessing a full complement of teeth was very evident in ancient times as evidenced by the complimentary words of Solomon to the queen of Sheba “Thy teeth are like a flock of sheep that are even shorn, which came up from the washing” (Song of Solomon 4:2). Even the first code of Roman law, written in 450 BCE, specifies the importance of teeth by incorporating penalties for the master or his agent if they dare to pull out the teeth of slaves or freemen. If this happens, the law stated that the slave is eligible for immediate freedom. The prose and poetry of the Greek and Roman era portrays numerous references to teeth, smiling faces, and the importance of having a regular arrangement of teeth, indicating a desire to correct dental irregularities. There was an emphasis on a correct relationship between the dental arches, and its importance in defining female beauty, and a correct enunciation in oratory. With attention focusing on correction of dental irregularities, orthodontia in that era was already divided into biological and mechanical fields, and it was assumed that a successful practitioner should have clear idea of both. The first orthodontic investigators adopted the biological knowledge of the day and concluded that success or failure in the treatment of malocclusions depends on these fields. The superstructure of orthodontics is built upon this fundamental relationship.
Figure 1.2 Contemporary bust sculpture of a shrine guardian, Seoul, Korea.
Naturally, therefore, orthodontic research has followed closely the scientific footsteps imprinted by biologists and physicians. Present day orthodontists are aware of scientific advances in material and biological sciences, that gradually move us all closer to an era of personalized medicine and dentistry, in which a high degree of diagnostic accuracy and therapeutic excellence is required.
Orthodontic treatment in the ancient world, the Middle Ages, and through the Renaissance period: Mechanics, but few biological considerations
Archeological evidence from all continents and many countries, including written documents, reveal that our forefathers were aware of the presence of teeth in the mouth, and of various associated health problems. These early Earth dwellers confronted diseases like caries and periodontitis with a variety of medications, ranging from prayers to extractions, and fabrication of dentifrice pastes. Gold inlays
