Does substituting premolars for canines look good?
Occasionally, we decide that an impacted canine cannot be aligned and decide to remove it and replace it with a first premolar. This study provides great information on the aesthetics of this approach.
While contemporary treatment mechanics make alignment of most impacted canines possible, there are patients for whom we should consider removal of the impacted canine. Good examples are patients with arch-length discrepancy, good contact between the lateral incisor and first premolar and palatally placed canines that are very displaced. Despite the publication of heroic case reports showing canines going on a long journey of guided eruption. We should consider if this treatment is always in the best interests of the patient.
The counterargument to canine removal is based around aesthetics and occlusal function. Unfortunately, these are at the level of case report and expert opinion. As a result, I thought that this new study was timely. A team from Manchester and Chesterfield, North of England did this study. They looked at the aesthetic appearance of orthodontic patients treated by canine extraction.
The AJO-DDO published the paper.
Badri Thiruventakachari et al,
Am J Orthod Dentofacial Orthop 2017;152:509-15
They did the study to ask this question;
“Is there a difference in the perceptions of patients smiles treated by extracting either maxillary canines or premolars, as judged by orthodontists, dentists and lay people”?
What did they do?
They did a retrospective study and looked at sets of patients records selected from one orthodontic department.
The authors selected patients who had unilateral or bilateral extraction of maxillary canines and compared them to a group who had unilateral or bilateral extraction of maxillary first premolars.
They had finished all the patients to a high occlusal standard with PAR scores less than 5.
They took facial and anterior teeth photographs, blinded them and randomly showed them to a rating panel. The panel included 10 orthodontists, 10 dentists and 10 lay people. The panel rated the attractiveness of the photographs using a 10 point Likert scale. Here are examples of the anterior intra oral pictures that they used.
They calculated the mean scores for each photograph and compared the groups using the relevant statistical tests.
What did they find?
They included 24 patients in the canine extraction group and 24 in the control group. The canine extraction group included 14 unilateral and 10 bilateral extractions.
They found that there was no difference in the aesthetic ratings between the canine and premolar extraction groups. The mean difference in scores was on 0.33 (95% Ci -0.26-0.91). There were also no clinically significant differences between the rater groups.
“We found no difference in the smile attractiveness of patients treated with extraction of canines or first premolars.
“Operators should discuss the removal of canines where this approach has advantages”.
What did I think?
I will declare an interest, I know this team well and we are close colleagues. However, I thought that this was a clinically relevant study that provides us with useful information.
I will start by having a look at the potential shortcomings of their methods. Firstly, they collected a retrospective study of selected cases that they finished to a high standard. This means that the findings are only relevant to well treated cases. A better study methodology would be to enrol patients into a trial and randomly allocate them to canine removal or not. This would then include the results of treatment that is not successful. However, this type of study would take many years and involve several centres because of the low numbers of patients who would satisfy the inclusion criteria. As a result, I feel that they have done the best type of study.
The other issue is that the photographs are “still life” and not dynamic. We may consider this to be problem. Again, I feel that this is the best that can be done using routine records.
Finally, they did not carry out a sample size calculation. This means that the study may not have enough power to detect a difference between the groups. However, when I looked at the effect size, it was very small. This provides me with some reassurance, nevertheless, we should bear this in mind when we evaluate the findings.
I feel that this study is important because it is the first study that has evaluated this question and the findings are clinically useful. Some may be critical and point out they did not evaluate occlusal function and canine protected occlusion. But the evidence behind these concepts is very weak. I expect that we will get a lot of discussion about this!
This project certainly reassures me when I decide that it is the best interests of the patient to extract the permanent canine and replace this tooth with a premolar.
Emeritus Professor of Orthodontics, University of Manchester, UK.