There are four canine teeth: two in the upper (maxillary) and two in the lower (mandibular) arch. A canine is placed laterally to each lateral incisor. They are larger and stronger than the incisors, and their roots sink deeply into the bones, and cause well-marked prominences upon the surface.
The crown is large and conical, very convex on its labial surface, a little hollowed and uneven on its lingual surface, and tapering to a blunted point or cusp, which projects beyond the level of the other teeth. The root is single, but longer and thicker than that of the incisors, conical in form, compressed laterally, and marked by a slight groove on each side.
In humans the upper canine teeth (popularly called eye teeth, from their position under the eyes) are larger and longer than the lower, and usually present a distinct basal ridge. Eruption typically occurs between the ages of 11 and 12.
The practice of extracting baby canine teeth to make way for adult canines that are erupting in the wrong place has no evidential basis, according to a new study by Cochrane Researchers. In a systematic review, the researchers were unable to identify a single high quality study to support the practice.
"The recommendation of extracting the baby canine is in fact based on one uncontrolled study that was carried out over twenty years ago," says lead author of the study Nicola Parkin of the Department of Oral Health and Development at the University of Sheffield.
It is common for adult upper canines to grow in the wrong place. Normally adult canine teeth erupt in the mouth around the age of 12 years and, in approximately 2-3% of the population of 12 year old children, these teeth become displaced in the roof of the mouth. Displaced canines can cause damage to neighbouring teeth as well as unfavourable movement of other teeth and, more rarely, cysts. One suggested way of avoiding canine displacement and encouraging the eruption of the adult canine is to remove a child's baby canine tooth at around 10 to 13 years, under local anaesthetic.
According to the researchers, however, the most commonly cited evidence for this practice comes from one trial, carried out in 1988, in which a group of children with canine displacement had their baby canines extracted. A major flaw of this study was the absence of a control group. Two other studies considered for the review did have an untreated control group, but had to be excluded because of inadequacies in reporting.
"Extracting the primary canine may help the secondary tooth to emerge correctly, but at this time we can't provide any hard evidence," says Dr Parkin. "Greater attention to the design and reporting of studies is needed to improve the quality of clinical trials on this topic."