A beautiful smile...
Dedicated to Esther Lafair
Based on the Doctoral Dissertation thesis presented to the The Department of Physical Anthropology
University of Pennsylvania
“Find out the cause of this effect: Or, rather say, the cause of this defect; for this effect defective, comes by cause.” –William Shakespeare
On the nature of Buck Teeth: Is this condition on average caused by an under-grown jaw?
(See the “ruler without numbers”: how the jaws and teeth are analyzed)
Lateral Head (“Cephalometric”) X-Ray of a patient with “buck teeth: (Its scientific name was first applied to it by the father of modern orthodontics– Dr. Edward Angle as “Class II, division 1 Malocclusion”). It is also called “distal-occlusion”, “retro-occlusion”, retrognathia and simply overbite. It occurs in 25% of the population. Orthodontists diagnose and treat this problem quite often. The big diagnostic question is how to treat this problem. Is the lower jaw retruded/small/ under-grown/set backward? Or is the upper jaw protruded/large/over-grown/set forward? How the orthodontists decides which is which determines how he is going to treat this problem.
He based his classifications on the relative position of the maxillary first molar. According to Angle, the mesiobuccal cusp (the front cusp) of the upper first molar should rest on the mesiobuccal groove (the middle) of the mandibular first molar. The teeth should all fit on a line of occlusion which is a smooth curve through the central fossae and cingulum of the upper canines, and through the buccal cusp and incisal edges of the mandible. Any variations from this resulted in malocclusion types. It is also possible to have different classes of malocclusion on left and right sides.
Class I: Neutrocclusion Here the molar relationship of the occlusion is normal or as described for the maxillary first molar, but the other teeth have problems like spacing, crowding, over or under eruption, etc.
Class II: Distocclusion (retrognathism, overjet) In this situation, the upper molars front cusp) are placed NOT in the mesiobuccal groove but anteriorly to it. Usually the mesiobuccal cusp rests in between the first mandibular molars and second premolars. Below see photo of this fairly common malocclusion:
Actually the founding father of orthodontics (Edward Angle, Ca. 1904) strongly believed that when you had a buck-teeth like condition the problem was caused by the lower jaw being small (under-grown) or retruded (shifted backward in position–”retrognathic”). He thought the upper back teeth never shifted into a forward position. The data in my study (1971), the first computerized study of its kind, utilized (LARGE SAMPLES, GROUPED BY AGE AND SEX) indicated his belief was erroneous, and on average the lower jaw of the children with buck-teeth is most often identical in size and position to those children who do not have buck-teeth. In fact, it is the upper jaw and teeth that are forward in position. No other study of this magnitude has been done to dispute the findings of this study completed in 1971.