Can premolars be canines? Premolar substitution in orthodontics
This second blog will focus on maxillary 1st premolar substitution as a canine
Why is it done?
1st premolar substitution is carried out due to two main scenarios; firstly missing lateral incisors and secondly ectopic canines.
Missing maxillary lateral incisors affect 2% of the population (Peck 1996), with space closure being the preferred aesthetic option where possible (Silveiria 2016). The canine substitutes as the lateral incisor, the 1st premolar substitutes the position of the canine.
Ectopic maxillary effect 2% of the population, (‘2’ is the magic number in orthodontics!). Where canine removal is indicated, the 1st premolar substitutes the position of the canine
First we will consider the bracket positioning options and modifications to make the 1st premolar like a canine. kE
What bracket modifications can we make?
1. Mesial-distal position:
Distal bracket positioning. This achieves a mesiobuccal rotation. There are two benefits from this for premolar substitution, firstly the rotated premolar occupies greater space similar to a canine, and secondly the rotation helps to hide the palatal cusp when viewed from a frontal view, by rotating the palatal cusp distally.
2. Vertical position:
A bracket placed occlusally will help intrude the premolar and gives a higher gingival margin, mimicking the gingival margin of a canine.
3. Torque: Placing greater labial root torque via the lower contralateral bracket will achieve -12o torque, which will move the smaller root of the 1st premolar into a labial position, which helps to mimics the eminence of the canine root.
What restorative options can we take?
1. Occlusal build up
Occlusal build up of the premolar to compensate for the intrusion we made by the bracket positioning, giving a crown length and cusp shape similar to a canine.
2. Grinding of the palatal cusp if it interferes with the occlusion.
What is the evidence?
A recently published in the Journal of Orthodontics March 2021, by Leonie Seager assessed the aesthetics of premolar substitution.
This survey compared the perception among dental professionals, patients and parents to a variety of treatment options including premolar substitution for impacted canines
Seager et al concluded that:
“The patient and parent groups showed similar perception in smile aesthetics for aligned canines and substituted premolars and all groups showed a strong dislike to the presence of gaps. The orthodontist group showed the most critical aesthetic perceptions.”
Here is a link to the paper:
This is interesting as it confirms how aesthetic differences are still present with premolar substitution however this difference is not perceived by patients. It also highlights orthodontists as “sensitive and critical” in our assessment of premolar substitution. This is not always a merit, as the patient and the parents are not really concerned with the smile of a canine or a premolar!
Of course, I am not encouraging surgical removal of all impacted canines and getting the 1st premolar in place regardless. this survey made me think of the how many times I could have made it easier for me and for the patient but I didn’t, just because I saw the problem only from my orthodontic perspective and perception.
Wait for our next post where we will talk about more clinical and educational topics in orthodontics.
This post was written by Kerolos AlHakeem and edited by Farooq Ahmed. Kerolos will be contributing to blogs and educational recourses as part of the orthodontics in summary team
1 minute animation below to showing premolar substitution