Alignment of impacted maxillary canines

A simple mantra to follow when aligning impacted canines is to aim to keep the treatment as short as possible with efficient mechanics and maintain the health of the adjacent teeth with effective execution of the mechanics.

As a general rule of thumb (a consideration more than a rule!), if the case requires extractions, then the impacted canine should be seriously viewed as the extraction of choice. We often worry about the aesthetics of the first premolar (our new canine) and canine guidance and as a result we are, sometimes, reluctant to make that decision (extraction of the canine). Evidence does show that there is no aesthetic difference between canine extraction and premolar extraction.

We will look into the canine/premolar and lateral incisor/canine substitution in more details in a future blog.

Before we get into the clinical orthodontics aspect, let’s briefly revisit some of the facts about impacted canines:

Most impacted maxillary canines tend to be palatal, of course this was first pointed out in the 1980s by the work carried out by Eriscon and Kurol, they found that maxillary canines are positioned palatal to the dental arch in 85% of the cases and buccal in only 15% of the cases. The incidence of palatally displaced canines (PDCs), however, depends largely on the study type and the radiographic examination used for localisation. For example, in one study the incidence of palatal position was found to be almost 93%.

Palatal displacement of the maxillary canine most often leads to its impaction, and in some cases, can lead to sequelae such as root resorption of the permanent incisors and/or formation of dentigerous cysts. Root resorption of the lateral (and/or central) incisors is not uncommon. It has been reported that 66.7% of the lateral incisors and 11.1% of central incisors had root resorption associated with PDCs.

There are 5 possible treatment options to manage a PDC:

• Interceptive treatment by extraction of the primary canine (and space creation, if required);

• Surgical exposure and orthodontic alignment;

• Surgical removal of the PDC;

• Autotransplantation;

• No active treatment/leave and observe.

In this blog we will focus on the mechanical eruption and alignment of impacted maxillary canines.

Resorption…resorption…resorption!

Root resorption (RR) is not uncommon with impacted maxillary canine. Severity of RR is dependant on the type of study design, however, there is good evidence to suggest that almost one third of RR is severe. Moreover, delayed treatment and management of impacted canines can lead to an increased risk of RR of the incisor teeth.

Why does RR occur? RR is a complex process, nevertheless, we know it simply occurs when the canine is in direct contact with the incisor, as a result the alveolar bone surrounding the incisor is resorbed and the protective layer of cementoblasts and collagen fibres is lost, allowing dentinoclasts to resorb the incisor root.

There are some predictors of RR that we can look out for when deciding on the best course of action. It is worth remembering that there is higher risk of incisor RR if the canine is associated with female sex, severely mesiodistally displaced and vertically positioned canines in the middle third of the adjacent incisor root, dental follicles wider than 2 mm, and normal lateral incisors.

In another study from 2020, where CBCT analysis was used, it was found that the variables contributing to the prediction of incisor root resorption were canine contact with adjacent incisors, size of canine dental follicle, and the presence of peg-shaped lateral incisor.

Buccally impacted UR3 and UL3. The canines are high, mesially angulated and buccal. The incisors have RR pre-treatment.

The upper lateral incisors (as well as lower E’s) were part of the extraction pattern due to the pre-existing RR and to correct the Class II malocclusion.

The upper canines were left to “spontaneously” erupt before applying traction, in order to reduce the load on the central incisors.

Sectional mechanics utilised to reduce the risk of further RR on the central incisors. 17x25” TMA wires were constructed in order to apply vertical as well as rotational force vectors.

The UR1 and UL1 are not included in the set up for as long as possible to reduce any further RR.

Treatment should be kept as short as possible while applying very light forces. There is very low to low evidence for supporting positive associations between root resorption and increased force levels, force continuity, intrusive forces, and treatment duration.

Canines can sometimes become “stuck” behind the lateral incisor

It is not uncommon for the canine to be stuck lateral to the root of the lateral incisor. A distal force vector needs to be incorporated to our treatment mechanics to free up the canine before attempting labialising the tooth.

Pre-treatment: UR3 impacted palatally, not particularly high.

Mechanical eruption had been attempted for 12 months with little-no success. Elastomeric powerchain was used as well as “zing string” to attempt applying vertical and buccal force vectors.

After 20 months of active traction with elastomeric powerchain and zing string, no demonstrable change seen.

At this point, orthodontic traction with “TMA fishing rod” was used, applying force vectors in 3 planes. The aim was to “free up” the canine from the lateral incisor root.

2 visits later (approx. 12 weeks), the canine has uprighted and erupted vertically. When the TMA fishing rod is in passive state, the head is more distal, coronal and buccal. This is to move the canine distally, vertically down and buccaly.

The position of UR3 has now been idealised in the 3 planes.

Controlling the force vectors

PDC UR3, overlying the root of the UR2. The UR3 should be distalised first before buccal force vector applied.

Distal and buccal forces applied via an elastomeric lasso chain.

The UR3 is ready to be labialised now, piggyback mechanics utilised in this scenario.

It is not uncommon for PDCs to be mesially positioned. Careful mechanical consideration to distalise the canine is crucial before attempting buccal force vectors.

Buccal miniscrews

In cases where the molars are Class II and the canine requires distalisation, sectional mechanics can be relied on to achieve multiple treatment objectives at once:

• Reinforce posterior anchorage

• Distalise the canine to Class I

• Move the canine away from the lateral incisor root

• Reduce the overall duration of incisors in fixed appliances (to reduce any risk of RR)

An efficient way for distalising the canines whilst maintaining posterior anchorage.

Once the canines are back to Class I, continuous arch mechanics can be applied.

Palatal miniscrews

Multiple treatment objectives can be achieved as shown below.

We will discuss in more details the placement of palatal miniscrews in a future blog.

De-rotation and distalisation of the UR3 whilst maintaining the URC for as long as possible and reducing the duration of fixed orthodontic appliance phase.

For patients:

An impacted canine refers to a situation where a permanent canine tooth fails to erupt properly through the gum line, remaining trapped or partially emerged. This can lead to misalignment, crowding, and potential damage to surrounding teeth. Treatment for impacted canines typically involves orthodontic intervention, such as braces or clear aligners, to create space and guide the impacted tooth into its proper position. In some cases, surgical exposure/uncovering and placement may be necessary to assist the eruption process. Early detection and prompt intervention are crucial in addressing impacted canines effectively and preventing complications in the long term.