The canine is a tooth with special characteristics and adaptive significance that varies considerably between mammalian lines and the primates. No matter what the line, canine teeth are never involved in mastication and do not interfere with masticatory dynamics. Mastication, which is one of the most complex functions that monkeys and apes display, appears well before the large canines in both phylogeny and ontogeny. In apes, their size and shape have nothing to do with diet, but are linked to sexual selection. The human line of hominids possesses smaller canines that have become incisiform and have lost their sexual and social function. They are now used exclusively to tear apart meat and other types of solid foods. The development of a wide, short buccal surface that increased medial-lateral movement during the masticatory cycle, may explain this particular development in recent hominids including humans. From an evolutionary point of view this means that the human canine has been subjected to stresses imposed by the biomechanical environment of the masticatory apparatus. In other words, the human canine, as well as those of the other anthropoids, does not guide mastication but has acquired a morphology and position restricted by masticatory functions. In evolutionary terms, it is therefore referred to as an “exaptation”; it has acquired, not a function, but a passive characteristic which makes it a marker for rehabilitation – on condition that its eruption is related to normal masticatory functions in individual histories, but it never serves as a mediator of mastication.

In this paper we examine the placement of the human canine tooth in the dento-alveolar system in order to explain its phylogenesis and ontogenesis over the course of its interactions with other tissues. We explain the known genetic mechanisms that occur throughout its morphogenesis and during its eruption until the tooth takes its place in the oral cavity. We carefully examine the role that genetic and environmental factors play in causing anomalies in its form, maturation, eruption and function.

We show how environmental factors determine how well it becomes integrated into the already established dental functional schema.

Biometric study of contemporary human maxillary incisors and canine coronal morphology

The orthodontic alignment or prosthetic rehabilitation of the upper anterior sector is based on available biometric data.

The aim of this study is to measure the angle formed between the functional lingual surface of the canine and central incisor and the axial-orbital plane.

Materials and methods

This retrospective study is based on an analysis of documents of young dental students.

The measurements were made on 49 silicone models of healthy, natural, functional teeth, in class I occlusion for the maxillary anterior group.

Results

The values of slope angulations of the lingual surfaces relative to the axial-orbital plane clearly decrease by 10° from the central incisor (57°) to the canine (47°).

If there is stability in buccal morphology, there is variability in anterior lingual morphology, particularly of the canine.

These variations in an essential zone on the functional level are marked enough to warrant being taken into account in clinical practice.

When a maxillary canine has not appeared in the arch at its scheduled time of arrival, the treating dentist should make a precise analysis of the possible factors responsible for its absence and devise the best therapeutic plan for correcting the problem. Factors to be considered are its agenesis or the more likely possibility of anomalies of tooth size and eruption patterns. Deciding whether to bring an absent canine into place orthodontically or to replace it prosthetically or with an implant almost always constitutes a sort of therapeutic wager.

This article proposes a method for the systematic appraisal of the management of a missing maxillary canine using a decisional tree of the “in cases where” type. It allows for questionable issues to be grouped in logical order, starting with diagnostic procedures that lead to the beginning of a step-like therapeutic sequence that concludes, if it proves negative, with the development of an alternative to the initial treatment plan (fig. 1).

This arboreal schema is comprised of three parts:

     1 – The first deals with diagnosis;

     2 – The second takes up the start of treatment in consideration of the position of the tooth and the possibility of its being ankylosed or becoming ankylosed;

     3 – The third is concerned with replacing the missing canine tooth in accordance with the dictates of implant or prosthetic therapy, or of an orthodontic solution to the problem.

Three dimensional images derived from X-Rays, scans or Digital Cone Beam Computed Tomography (CBCT) are components of supplementary diagnostic procedures. Using them, practitioners can visualize the anatomic relationships of teeth with each other and with adjacent structures and can discern the presence or absence of root resorption.

These radiographic films can assist in the diagnostic evaluation of impacted, transposed, or duplicated teeth or those situated on the edges of facial clefts. They are indispensable in helping diagnosticians to rule out contraindications as they establish treatment plans and continue to be useful as guides when mechano- therapy starts.

Recently, CBCT has become accessible for use in dental offices even though it has been an expensive and bulky instrument with a relatively high radiation output. Today, with a more acceptable radiation dosage, it is well accepted as an alternative diagnostic procedure in the field of oro-facial implants, but overall, it cannot yet be considered as a technique that should be systematically employed in every supplementary examination.