 Hello everyone, welcome back to another session in dentistry and more. So today we have a genetical theory in orthodontics that is butler's field theory. So as we all know, everything in our body, the growth, the pattern of growth, the distribution, so everything in our body is determined by genes, not completely but to an extent. So genes have a very significant role in determining the pattern and the growth of various bones and other supporting structures. So coming to the oral cavity, so the growth of oral bones or the eruption of teeth or the distribution of teeth and its morphological changes and the variability within the arch or within the quadrant. So everything is just like our body is also to an extent is determined by genes. So genetical control over the growth of structures or bones is very obvious. So butler postulated a genetical theory which is known as field theory. So well coming to the oral cavity, he said there are three fields in one quadrant. So this is just one quadrant, this is the second quadrant, I have just drawn one quadrant. So we have four quadrant, one, two, three and four. So he said there are three fields, the incisor region, the canine region and molar premolar region. So the incisor region, canine region and premolar molar region or fields. So this theory says that the dental variability that is a change in tooth shape or size manifests itself in a distal direction than in a measly direction from the more stable key tooth. So the first field we have the central incisor is a key tooth and the last field that is a premolar molar field we have the first molar is a key tooth. Anyway this canine we do not have more than one tooth. So it is not mentioned in the theory. So the key tooth are central incisor and the first molar tooth. So considering each quadrant separately, the molar premolar field would consist of the first molar as a key tooth and the second and third molar on the distal end of the field and the first and second premolars on the mesial end. So this theory predicts the third molar and the first premolar would most variable in size and shape. So this theory predicts the third molar and the first premolar would be the most variable in size and shape because this is towards the distal end of the key tooth. So we need to consider this as a separate field. So considering this key tooth the third molar and first premolar are at the distal extremant. So towards molar the variability decreases. That is why this has become the more stable tooth or the key tooth. Similarly in the incisor region the central incisor is a key tooth. So definitely the distal tooth or towards the distal side is a lateral incisor. So lateral incisor shows more variability in size and shape. So as we all know the lateral incisor first premolar and third molars are very different in size and shape. But the field theory is not well accepted because of many factors because it is not actually decided by the gene itself. So it cannot be exclusively predicted by the genetical factors that the change in first molar, third molar and lateral incisor. There are other factors which involves in determining the size and shape or the variability of size and shape of these 3 teeth or the lateral incisor first premolar or the third molar. But this theory says that the distal ends of the key tooth would be most variable. So least variable will be towards the misal side and most variable towards the distal side. Now 2 key tooth that is central incisor and first molar. Canine is anyway excluded it is not anywhere mentioned in the theory. So that is all about Butler's field theory. He mentioned 3 fields canine incisors premolas and molars and the variability depends on the key tooth and its positioning towards the distal side. So you do not get confused about the distal side. Usually we consider everything here towards the misal and this is distal but considering this tooth this is distal and this is distal. Distal means away from the key tooth. So that is all about Butler's field theory. The concept is very simple towards distals the variability increases. So I will come up with a new topic in orthodontics. Thank you.