Impacted Teeth Canines

Introduction

A canine is an important tooth of the dentition because it is placed strategically in the mouth. It makes the transition between the anterior teeth (central and lateral incisors) and the posterior teeth which are the first and second premolars. This tooth has a very long root, the longest of all teeth, and therefore, its position is unique in the dental arch.

 

• Function: It is a strong and solid tooth designed to tear foods. It is also used to guide the movements of the lower jaw during chewing.

• Esthetics: The color of the canine, generally darker, ensures the transition between the incisors which are often lighter in color and the posterior teeth. The sharp shape also plays a role in the transition of the visual esthetics between the anterior and posterior teeth.

• Eruption:  It erupts after the premolars in the maxillary arch. Being the last one to arrive, it often has to put up with limited space. As it is a big sharp tooth, it is not uncommon to observe its prominence and its malposition. The canine usually erupts before the first premolar in the mandibular arch, but it sometimes happens that the order is reversed and, like its counterpart in the maxillary arch, it puts up with the remaining space.

Back to top.

 

Impaction and ectopic eruption

A canine is considered impacted if it does not come into the mouth and remains in the alveolar bone in an ectopic position. Ectopic means: “that is not at the right place”.

Impacted canine in vestibular position

A canine can end up on the palatal side (palatal impaction), stay very high and horizontal above the other dental roots (see #2 on the picture and the X-ray of impacted canines) or be prominent in the oral vestibule (impaction on the vestibular position: see #1, #2 and #3 on the picture), that is on the opposite side of the palate.

We then talk about vestibular impaction, meaning that it is positioned in the oral vestibule compared to palatal impaction, where the canine is on the palatal side.

Palpating the areas identified by circles makes it possible to feel lumps revealing the presence of canines. Visual examination shows that the lateral incisors are very inclined. They are inclined because the canines represent an obstacle to the good positioning of the lateral incisors. The vestibular impactions represent only 15% of canine impactions.

Back to top.

 

Palatally impacted canine

In 85% of cases, canines are impacted on the palatal side. In the same way as previously, palpation and visual inspection make it possible to suspect the presence or the absence of such ectopia.

The circle on the picture on the opposite side represents the lump of the palatal vault that is easily palpable with the finger. A white arrow indicates the displacement on the palatal side of the lateral incisor crown, which means that the root is on the opposite side of the crown. It is thus called a vestibular root. It is like that because of the presence of the permanent canine that is just beside, on the palatal side. The persistence of the primary canine is also another visual indicator. On the X-ray, the group of white arrows defines the border of the follicular envelope that surrounds the tooth crown and it is much enlarged. At this size, the envelope is a follicular cyst and as with all cysts, it will tend to get bigger and wider, causing damages to the surrounding teeth (resorption of the root, movement of teeth or pathological evolution of the cyst).

Back to top.

 

Incidence and prevalence

Canine impactions involve 0.92% of the white American population. Epidemiological data shows different incidences among other populations.

• Finnish = 1.8 %

• Swedish = 1.7 %

• Italian = 2.4 %

• Japanese = 0.27 %

• White American = 0.92 %

Canine impactions are more frequent among females than males (F : M = 2.3 : 1) or 1.17% of females and 0.51% of males. And, as it was previously mentioned, 85% of impactions are palatal impactions compared to 15% that are vestibular impactions.

Back to top.

Etiology

Research shows that the cause of canine impactions is mainly hereditary, therefore genetic. Among other causes, there is persistence of the primary canine (the root does not resorb), an infectious chronic periapical lesion (at the apex (tip of the root) of the primary tooth), pathology issued from the follicular envelope such as dentigerous cyst or a giant cell tumor.

Proofs concerning the genetic origin of an impacted canine are the following:

• Link with other dental anomalies.

• Peg shape teeth or microteeth.

• Congenital absence of a lateral incisor.

• Infraocclusion or ankylosis of the 2^nd primary molars.

• Congenital absence of one or both lower 2^nd premolars.

• Delay in the formation or distal angulation of the lower 2^nd premolar.

• Occurs bilaterally, that is on both sides.

• Family incidence.

• Dr Ann Todd convened a research among files of the Harvard University’s orthodontics department and she found that when a member of a family has an impacted canine, 40% of the members of this family (brothers and sisters, cousins, uncles and aunts) had an impacted canine.

• Sexual dimorphism. More females have impacted canines than males.

• Difference across populations.

Peck S, Peck L, Kataja M. The palatally displaced canine as a dental anomaly of genetic origin. Angle Orthod 1994;64:249-256.

Peck S, Peck L. Palatal displacement of canine is genetic and related to congenital absence of teeth. J Dent Res 1997;76:728-729.

Todd, A. , Cephalometric and epidemiological findings in families with PDC, Angle East meeting, Charleston, 2008

On this figure composed of 3 X-rays of 3 individuals of the same family (2 brothers and 1 sister), you can see, for the girl, the first signs of the impaction of an upper right canine as well as the enlarged follicular envelope and the congenital absence (hypodontia) of a lower incisor.

Her 2 brothers each shows an impacted canine and congenitally missing of both lower 2^nd premolars. This is a single example among many more that I have come across.

Back to top.

Non-genetic etiology

Even though the genetic origin of impacted canines is confirmed, there are other factors that can cause the impaction or ectopic eruption of a canine.

Other causes can be:

• An infectious chronic lesion near the canine crown (chronic periapical lesion of a primary tooth)

• A dental or odontogenous tumor, a keratocyst, a giant cell tumor, a follicular or dentigerous cyst

• Lack of space

• Impacted canine and chronic apical lesion:

This series of X-rays shows well the problems that can create inflammation or infection to the apex (tip) of the root of a primary tooth (green “C” letter). The white arrows define enlarged follicular envelopes around the permanent canine crown (blue “C”).

The primary canines (green “C”) received a pulpotomy (partial removal of the pulp) because of a cavity or to reduce the sensitivity of the primary tooth when a cut is made through enamel and dentin. This results in chronic inflammation of the nerve and at the apex; this inflammation will be defined by an apical granuloma. This granuloma irritates the follicular envelope surrounding the permanent canine crown (blue “C” letter) and the granuloma becomes an obstacle in front of the permanent tooth. The tooth path of eruption is deflected. Therefore, a potential cause to the development of a follicular cyst would be chronic inflammation of the apical granuloma. (Becker,  A.,  The orthodontic treatment of impacted teeth 2e ed.Thieme 2007, p.97 & 240.)

Consequently, if the lack of space in the incisor-canine area necessitates proximal reduction (cut in enamel and dentin) of the primary canine, it could be more recommended to proceed with the extraction of the primary tooth. If this were the case, it becomes another chapter of the concept of interception in orthodontics which will be developed later on. You can consult the seminars Interception en orthodontie and réduction proximale sélective. Crowding of a primary canine and a lateral incisor of 1.5 mm does not justify the proximal reduction of the primary canine.

Solution: The cases shown above all required, as initial procedure, the extraction of the primary canines.  Back.

• Impacted canine and odontogenous tumor.

This kind of pathology is not very frequent. It is the reason why when we encounter one, we remember it. It is an 11-year-old young girl who comes in for misaligned central and lateral incisors and for a palate that is too narrow (there is a crossbite on the left side). Visual examination shows a bulge of the cortical plate (black circle) and a different vascularization of the mucous membrane. The radiographic appearance of the cyst, apart from an enlargement that can be seen very easily, is similar to a benign lesion. The extraction of the primary canine was prescribed as it is always the case in such situation. In short, the bulge of the plate increased in the following weeks and taking a new X-ray showed the enlargement of the cyst. The patient was referred to oral surgery and in Dr Dany Morais’ expert hands, the cystic lesion was removed entirely and pathological examinations were performed. Back.

• Impacted canine and lack of space

Here is a typical example of an impacted canine (black circle) caused by a lack of space in the dental arch. In the current case, there is no space available between the 1^st premolar and the lateral incisor to put a canine of 8 mm in width. Both sides are affected. Back.

Complications, consequences

An impacted canine, if it stays impacted, is a complication in itself.

It can also erupt late (whenever in adulthood) in a rather unusual area (ectopic). The case shown on the opposite side shows the retained primary canines (red arrows). Permanent canines finally erupted in the mouth despite the obstacles which are primary canines and the lack of space. The upper right canine (blue arrow, position 1) is on the palatal side. The upper left canine (blue arrow, position 2) has erupted in the oral vestibule in front of the lateral incisor. The lower left canine (blue arrow, position 3) has erupted on the lingual side.

In conclusion, keeping a primary canine in the mouth beyond the timeframe where it should normally shed guarantees that the permanent canine is either ectopic or impacted.

Another complication is the resorption (shortening) of the roots of the adjacent tooth. Note the resorption of the roots of lateral incisors. As a metaphor, it is as if the collision between the permanent canine and the incisor had pulverized the root.

Back to top.

Preventive diagnosis

The permanent canine normally erupts around 11-12 years of age. It is thus wise to verify its position and its evolution as early as 9-10 years of age. We must suspect that an anomaly can occur if we observe:

• A microtooth or a congenital absence of a lateral incisor

• An overall delay of eruption

• The retention of the primary canine beyond 12-13 years of age without any signs of moving

• A palpable palatal vault

• A congenital absence of premolar(s). One or more absent premolar.

• An ankylosis of a second primary molar

• A lateral incisor in labioversion, palatoversion, distoversion

Back to top.

 

Interceptive treatment

The extraction of the primary canine in relation with the permanent canine that shows an ectopic evolution is the treatment of choice of the interceptive measures to perform.

The decision is made from an early diagnosis, the patient is between 10 and 13 years old. The relative position of the permanent canine with regard to the adjacent teeth is an important factor in the success of the interception. By success, I mean that the canine will go back to a normal path of eruption.

Erikson and Kurol developed a little evaluation diagram. If the tip of the unerupted canine does not go past more than half of the root of the lateral incisor (zone 2 and 3) and the inclination angle related to the medial plane is not greater than 55^o, the average success rate (normal eruption) is about 80%. This means that 80% of the cases showed a normalization of the canine eruption in the 6 to 12 months following the extraction of the primary canine.

If the permanent canine is in zone 1-2, the success rate is about 90%. If the canine goes past the lateral incisor and the tip is in zone 4, the success rate decreases to 64%.

If no improvement is observed, then the autocorrection prognosis is weak and a procedure must be considered.

Ericson S, Kurol J. Early treatment of palatally erupting maxillary canines by extraction of the primary canines. Eur J Orthod 1988;10:283-295.

Pitt S, Hamdan A, Rock P. A treatment difficulty index for unerupted maxillary canines. Eur J Orthod 2006;28:141-144.

Often, a path correction is observed and we can anticipate that the canine eruption will be normal. A second factor then steps in our decision-making process. It is time. Some canines can take up to 2 years before erupting in the mouth. After discussing with the patient, it can happen that the decision is made to proceed with the surgical ligation of the canine to make it erupt more quickly, not to delay the evolution of the orthodontic treatment underway.

This example illustrates well how efficient the preventive extraction of primary canines (X) is to correct the path of eruption (white arrows) of permanent canines which deviated toward the palate and for which the vaults were palpable with the finger tip at the back of the lateral incisors. The X-ray on the right, taken 9 months after the extraction of primary teeth, shows favorable repositioning of the permanent canines. This case is among the several ones I was happy to manage successfully that way. Of course, in some cases, the repositioning was less spectacular and it was decided to proceed with an exposure surgery and ligation of the permanent tooth.

One thing is for sure, to not extract the primary canine guarantees that the permanent canine will remain impacted.

 

Pitt S and colleagues determined a treatment difficulty index for impacted canines. The important factors are:

• The horizontal position of the impacted tooth (degree of overlap with the lateral and central incisors).

• The patient’s age.

• The height or vertical position of the impacted tooth.

• The oro-palatal position of the impacted tooth.

Ericson S, Kurol J. Early treatment of palatally erupting maxillary canines by extraction of the primary canines. Eur J Orthod 1988;10:283-295.

 

Pitt S, Hamdan A, Rock P. A treatment difficulty index for unerupted maxillary canines. Eur. J Orthod 2006;28:141-144

Back to top.