Impacted maxillary canines – a perennial problem

Radiographic examination

Radiographic assessment of the position of an impacted maxillary canine is usually carried out by taking two radiographs from clearly different positions and applying the principle of radiographic parallax, first introduced by Clark in 1910.

The technique was described in detail as follows:19

The best way for the clinician to remember this effect is to use the acronym SLOB = Same Lingual, Opposite Buccal.

Horizontal parallax

This can be carried out by taking the following combination of radiographs:

Jacobs19 recommended taking two occlusal radiographs, as greater tube movement is possible when compared to two periapical radiographs and the radiation dose from two occlusal radiographs is comparable with that from two periapicals, however, the direction of the radiation is towards the patient's gonads, which is considered unacceptable whilst there are alternatives.

Vertical parallax

This can be carried out by taking the following combination of radiographs:

With this combination of radiographic examination, if the impacted canine tooth moves apical in relation to the adjacent tooth root on the occlusal radiograph, the position of the impacted teeth is palatal, as can be clearly seen in Figure 3 a and b. This is invaluable information for the surgeons when planning their flaps for canine exposure and bonding.

Other, less reliable, methods of locating impacted maxillary canine include:

Ericson and Kurol13 have reported that an OPT radiograph overestimates the angulation of the canines and underestimates the proximity of the impacted maxillary canine to the midline. These authors, in their study, also found that the positions of canines could be assessed with sufficient accuracy from the conventional periapical films in 92% of cases.

Computed tomography is, without doubt, the most precise method of radiographic localization. However, its relatively high radiation dose limits the indications for its use.20 Cone-beam computed tomography (CBCT) offers a lower dose alternative to conventional CT for the localization of ectopic canine teeth and its use is increasing for more complex cases (Figure 4).

Surgical exposure and bonding a gold chain attachment to impacted maxillary canine teeth is often required in order to bring the tooth into the dental arch and to allow subsequent alignment. A study conducted by Becker et al21 showed that bonding at the time of surgical exposure is superior to it being performed at a later date. Use of an eyelet attachment has a lower failure rate as compared to the use of a conventional orthodontic bracket. His study also showed that the palatal aspect of the canine offers the poorest bonding surface and also that pumicing the exposed tooth confers no advantage over immediate etching of exposed enamel. Another study by Pearson et al22 showed that a second surgical procedure may be required for up to 30% of cases, where the adhesive bond between the bracket and the tooth breaks down before or during orthodontic traction.

The closed technique

This technique involves surgically exposing the crown of the impacted tooth and then etching the enamel and bonding an eyelet, to which is soldered a gold chain. The palatal flap is then replaced leaving the length of chain to exit the gingivae, the free end of which is sutured to the buccal mucosa. A few days after the surgery, gentle orthodontic traction can be applied to the tooth to start bringing it into its correct position within the dental arch. In the closed technique, the canine tooth is orthodontically moved into its correct position beneath the mucosa.

The open technique

This technique involves exposing a palatally displaced canine as before but instead of bonding a gold chain attachment to it at the time of surgery, the area of palatal mucosa which covers the crown of the tooth is cut out, to create a window, through which the crown is visible and the palatal flap is repositioned and sutured. A dressing pack is then used to cover the exposed area. This pack is removed in a few days and the canine is either allowed to erupt ‘naturally’ or, bonding a gold chain attachment to its crown, is carried out to allow gentle orthodontic traction to be commenced. In this technique, the canine tooth moves into its correct position above the mucosa. An advantage of this technique is that the orthodontist can bond the gold chain attachment to the crown of the canine, hopefully in the most favourable position.

In the UK, the surgical procedure of exposing a palatally impacted maxillary canine and bonding a gold chain is usually carried out under general anaesthesia. Even if general anaesthesia is used, a greater palatine nerve block, nasopalatine nerve block and local anaesthetic infiltration in the labial sulcus are recommended, as this will greatly reduce the chance of post-operative pain and discomfort (Figure 5). Local anaesthetic agents, such as lignocaine hydrochloride or longer-acting bupivacaine hydrochloride, with adrenalin as a vasoconstrictor, are commonly used.

For unilateral impactions, the incision is commenced in the gingival crevice (Figure 6a) from mesial to first molar on the impacted side and is taken around the palatal gingival margin to the canine on the opposite side (Figure 6b and c). For bilateral canine impactions, the flap margin can be extended from first molar on one side of the arch to the first molar on the other side. A palatal flap is then raised by inserting the convex surface of a curved Warwick-James elevator in the inter-dental region and peeling back the gingival margin (Figure 7a and b). A Howarth's periosteal elevator can then be used to raise a full thickness mucoperiosteal flap, thus exposing the palatal bone (Figure 8a and b). The neurovascular bundle issuing from the incisive foramen is severed in this procedure but it rarely gives rise to clinically perceptible anaesthesia. Any bleeding that is difficult to arrest with pressure alone may require bipolar coagulation.

In the case of superficial impaction of a maxillary canine, the crown of the tooth may be visible once the mucoperiosteal flap has been raised. In cases where a thin plate of palatal bone covers the impacted canine, it can be easily chiselled away to expose the crown. Chisels can be used either by hand or, if the bone covering is thick, with a mallet (Figure 9). The bevelled side of the chisel is placed against the bone and is driven along at required depth to shave off successive wafers of the bone covering the impacted crown. A rosehead or fissure bur, in a surgical drill, is usually required to expose a crown fully, if covered by thick palatal bone. When using a drill to remove bone, it is important to ensure copious irrigation with sterile water in order to avoid any necrosis of bone due to the heat produced by high speed drilling (Figure 10). The amount of bone removal should be sufficient to free the crown down to its greatest circumference. Great care should be taken to ensure no damage is done to the impacted tooth crowns or roots of adjacent teeth (Figure 11).

Once the crown of the impacted canine is sufficiently exposed, a clean dry field is essential to bond a gold chain to the exposed crown successfully. A gold chain is attached to whatever enamel is most easily accessible on the canine crown. The orthodontic bracket can later be bonded to the labial aspect of the tooth once it is sufficiently erupted, following initial orthodontic traction.

Traditionally, once adequate moisture control was achieved, acid-etch with 33% buffered orthophosphoric acid was applied to the surface of exposed crown. An etch time of 20–30 sec is usually sufficient (Figure 12). It is important to ensure that the surface of the enamel is not rubbed during the etching process as the rubbing action will break all the enamel prisms that stick up from the surface and the crevices, and cracks for resin tag formation will be lost.23 Acid etching of enamel increases the surface roughness of the enamel and hence the bonding area. It also raises the surface energy of enamel by removing surface contaminants. This provides for a better wettability of the enamel by the adhesive. The etched tooth surface is then washed with sterile water, not saline, for at least 10 sec (Figure 13) and is thoroughly dried with a chip syringe (Figure 14). Dried etched enamel appears matt, white and frosty. An eyelet attached to a gold chain is now bonded to the etched enamel using a light-cure composite material (Figure 15a and b).

More recently, self-etching primers (SEP) have become much more popular in orthodontics and it is now recommended that this is used by surgeons, as the second washing and drying phase is deemed unnecessary. Once the exposed crown is initially cleaned and dried, the SEP is applied and left in place for 15–20 seconds. The bracket base or eyelet can then be stuck to the canine crown. Not only is there a significant time saving, but the risk of crown contamination is also reduced.

Once the gold chain is attached to the crown, its loose end can be sutured to mucosa in the depth of labial sulcus using a black silk suture in order to secure it, until the orthodontist reviews the patient. It is recommended for the surgeon to tie a really loose knot, 5–10 mm diameter, so it can be easily cut and the suture removed by an orthodontist, at a subsequent appointment (Figure 16a). It is exceedingly unhelpful if a tight knot is tied in the buccal sulcus, as these can be difficult and painful to cut at a later date (Figure 16b).

The palatal mucoperiosteal flap is then replaced and sutured using 3.0 vicryl rapide sutures (Figure 17). Vertical mattress sutures can be used to minimize any chances of palatal haematoma formation. The gold chain attached to the tooth, tunnels subgingivally and comes out at the margin of flap, so it is easily accessible for the orthodontist, at a later date.

The orthodontist can review the patient in a couple of weeks' time and then gentle traction can begin to be applied to the impacted canine by including the gold chain into the fixed orthodontic appliance.