What is the health problem?
Upper permanent canine teeth (commonly known as eye teeth or fang teeth) are positioned in the upper jaw, one on the right and one on the left. In around 1% to 3% of children, they may not erupt (appear from behind the gum and into the mouth) into their correct position. The permanent canine tooth or teeth may grow towards the palate (roof of the mouth) and remain unerupted (buried under the gum). This is known as a palatally displaced canine (PDC). If the permanent canine tooth remains displaced and unerupted, it can damage or change the position of neighbouring teeth, and occasionally it can lead to a cyst.
What are the treatments?
Management of a PDC can take a long time, involving surgery to uncover the tooth and prolonged orthodontic (brace) treatment to straighten it. Various quicker or easier alternatives have been suggested to encourage the tooth or teeth to erupt. These include extraction (taking out) of the primary (baby) canine, extraction of the primary canine and primary first molar (also called double primary tooth extraction), or using braces to create space in children's mouths.
What did we want to find out?
We wanted to find out if any of these treatment alternatives were successful for children aged 9 to 14 years, in terms of encouraging PDCs to erupt without using surgery.
What did we do?
We searched for studies that assessed the effectiveness of different ways to deal with palatally displaced canines up to 3 February 2021.
Where studies measured the same thing in the same or similar ways, we combined the results to give us a clearer idea about the effects of the treatment. We assessed whether the individual studies were at risk of being biased and we judged the overall reliability of the evidence we found.
What were the main findings?
We found four studies involving 199 children (195 analysed).
There is very weak evidence that extraction of the primary canine in children aged between 9 and 14 years may increase the probability that the PDC will successfully erupt into the mouth without the need for surgery by 12 months. There is no evidence it reduces the number of children needing surgery to correct their PDC.
There is no evidence that double extraction of primary teeth increases the proportion of erupted PDCs compared with a single primary tooth extraction by 18 months after treatment or that it reduces the number of children needing surgery to correct the PDC by 48 months.
There is some limited evidence suggesting that the severity of the displacement of the PDC towards the midline may be important in deciding whether or not to intervene. If it is very far from the midline, it may be less likely to be successful.
What does this mean?
The review authors found the reliability of the evidence to be very low so future research is necessary to help us know for sure the best way to deal with upper permanent canines that are not erupting as expected.
The evidence that extraction of the primary canine in a young person aged between 9 and 14 years diagnosed with a PDC may increase the proportion of erupted PDCs, without surgical intervention, is very uncertain. There is no evidence that double extraction of primary teeth increases the proportion of erupted PDC compared with a single primary tooth extraction at 18 months or the proportion referred for surgery by 48 months. Because we have only low to very low certainty in these findings, future research is necessary to help us know for sure the best way to deal with upper permanent teeth that are not erupting as expected.
A permanent upper (maxillary) canine tooth that grows into the roof of the mouth and frequently does not appear (erupt) is called a palatally displaced canine (PDC). The reported prevalence of PDC in the population varies between 1% and 3%. Management of the unerupted PDC can be lengthy, involving surgery to uncover the tooth and prolonged orthodontic (brace) treatment to straighten it; therefore, various procedures have been suggested to encourage a PDC to erupt without the need for surgical intervention.
To assess the efficacy, safety and cost-effectiveness of any interceptive procedure to promote the eruption of a PDC compared to no treatment or other interceptive procedures in young people aged 9 to 14 years old.
An information specialist searched four bibliographic databases up to 3 February 2021 and used additional search methods to identify published, unpublished and ongoing studies.
We included randomised controlled trials (RCT) involving at least 80% of children aged between 9 and 14 years, who were diagnosed with an upper PDC and undergoing an intervention to enable the successful eruption of the unerupted PDC, which was compared with an untreated control group or another intervention.
Two review authors, independently and in duplicate, examined titles, keywords, abstracts, full articles, extracted data and assessed risk of bias using the Cochrane Risk of Bias 1 tool (RoB1). The primary outcome was summarised with risk ratios (RR) and 95% confidence intervals (CI). We reported an intention-to-treat (ITT) analysis when data were available and a modified intention-to-treat (mITT) analysis if not. We also undertook several sensitivity analyses. We used summary of findings tables to present the main findings and our assessment of the certainty of the evidence.
We included four studies, involving 199 randomised participants (164 analysed), 108 girls and 91 boys, 82 of whom were diagnosed with unilateral PDC and 117 with bilateral PDC. The participants were aged between 8 and 13 years at recruitment. The certainty of the evidence was very low and future research may change our conclusions.
One study (randomised 67 participants, 89 teeth) found that extracting the primary canine may increase the proportion of PDCs that successfully erupt into the mouth at 12 months compared with no extraction (RR 2.87, 95% CI 0.90 to 9.23; 45 participants, 45 PDCs analysed; very low-certainty evidence), but the CI included the possibility of no difference; therefore the evidence was uncertain. There was no evidence that extraction of the primary canine reduced the number of young people with a PDC referred for surgery at 12 months (RR 0.61 (95% CI 0.29 to 1.28).
Three studies (randomised 132 participants, 227 teeth) found no difference in the proportion of successfully erupted PDCs at 18 months with a double primary tooth extraction compared with extraction of a single primary canine (RR 0.68, 95% CI 0.35 to 1.31; 119 participants analysed, 203 PDCs; mITT; very low-certainty evidence). Two of these studies found no difference in the proportions referred for surgical exposure between the single and the double primary extraction groups data at 48 months (RR 0.31, 95% CI 0.06 to 1.45).
There are some descriptive data suggesting that the more severe the displacement of the PDC towards the midline, the lower the proportion of successfully erupted PDCs with or without intervention.