Canine tooth

In humans, the upper canine teeth (popularly called eye teeth, from their position under the eyes[1]) are larger and longer than the lower, and usually present a distinct basal ridge. Eruption typically occurs between the ages of eleven and twelve years for upper canines and between nine and ten years for lower canines. Upper deciduous canines also known as the baby tooth, typically erupt between the ages of sixteen and twenty-two months and shed between ten and twelve years. Lower deciduous canines typically erupt between the ages of seventeen and twenty-two months and shed between nine and twelve years.[2]

Transposition (positional interchange of two adjacent teeth) is a development defect that most commonly found in the permanent canine, with the maxillary being more commonly seen than mandibular. The upper canine frequently transposed with the first premolar whilst the lower canine transposed with the lateral incisor.[3] Occasionally canines are congenitally missing.[4]

From a facial aspect, maxillary canines are approximately one millimetre narrower than the central incisor. Their mesial aspects resemble the adjacent lateral incisors, while their distal aspects anticipate the first premolars. They are slightly darker and more yellow in color than the other anterior teeth. From a lingual aspect, they have well developed mesial and distal marginal ridges and a well-developed cingulum. A prominent lingual ridge divides the lingual aspect in half and creates the mesial and distal lingual fossae between the lingual ridge and the marginal ridges. From a proximal aspect, they resemble the incisors, but are more robust, especially in the cingulum region. Incisally, they are visibly asymmetrical, as the mesial incisal edge is slightly shorter than the distal incisal edge, which places the cusp slightly mesial to the long axis of the tooth. They are also thicker labiolingually than mesiodistally. Because of the disproportionate incisal edges, the contacts are also asymmetrical. Mesially, the contact sits at the junction of the incisal and middle third of the crown, while distally, the contact as more cervical, in the middle of the middle third of the crown. The root of the maxillary canines are the longest root of any tooth and conical in shape.[5]

The lower canine teeth are placed nearer the middle line than the upper, so that their summits correspond to the intervals between the upper canines and the lateral incisors. From a facial aspect, the mandibular canine is notably narrower mesiodistally than the maxillary one, the root is compressed mesiodistally with well-marked grooves on both sides and may be just as long as the maxillary (and at times bifurcated).[5] A distinctive feature is the nearly straight outline this tooth has compared to the maxillary canine which is slightly more bowed. As in the maxillary canine, the mesial incisal edge (or cusp ridge) is shorter than the distal side, however, the cusp is displaced slightly lingual relative to the cusp of the maxillary canine.

Lingually, the surface of the tooth is much smoother compared to the very pronounced surface of the maxillary canine, and the cingulum is noted as less developed. The cusp may be lost with attrition over time and may resemble an upper second permanent incisor.[5]