Introduction
The initial position of an impacted maxillary canine might influence the outcome of surgically assisted exposure and orthodontic alignment. Therefore, the purpose of this study was to evaluate existing correlations between the initial position of the maxillary canine and the outcomes of treatment.
Methods
A retrospective cohort study was designed, containing data of 132 patients (47 males, 106 females; median age at the date of surgical exposure 14 ± 4.6 years; range, 10-39 years) with a total of 153 impacted maxillary canines. The sample was based on orthodontic referrals over 4 years at the Department of Oral and Maxillofacial Surgery, Rijnstate Hospital, Arnhem, the Netherlands. The esthetic outcome, treatment duration, and success and failure rate were investigated in relation to the initial position of the maxillary canine as assessed on pretreatment panoramic radiographs (vertical and anteroposterior sector position and angulation of the canine [α-angle]). The esthetic evaluation was performed using the Maxillary Canine Aesthetic Index. The success of treatment was defined as achieving a fully functional eruption of the canine, with an esthetically excellent result, without the need for reinterventions. Failure of treatment was defined as the need for reintervention or removal of the canine.
Results
In 96% of the impacted canines, a successful orthodontically assisted eruption was achieved. Age, vertical distance, and angulation are predictors of the esthetic outcome of impacted canines after treatment. Age, bilateral impaction, sector, vertical distance, and angulation are predictors of treatment duration. Age, vertical distance, and buccolingual position are predictors of the need for reintervention.
Conclusions
Pretreatment radiographic variables can help in predicting the outcome and treatment duration of surgically exposed maxillary impacted canines.
Highlights
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Most canines will achieve full eruption posttreatment, with or without reintervention.
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Excellent esthetic outcomes are expected after surgical exposure and orthodontic traction.
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Pretreatment radiographs can help in predicting outcome and treatment duration.
The overall prevalence of maxillary canine impaction varies between 0.9% and 2.2%. , Impaction is defined as a failure of tooth eruption at its predetermined site in the dental arch, within its normal period of growth, because of an obstacle in the eruption path or ectopic position of the tooth germ. Various etiologic factors of maxillary canine impaction are mentioned in the literature, such as dental discrepancy, the ectopic position of the tooth germ, lack of space, lack of guidance, presence of hard and soft tissue pathologies, or genetic factors. ,
The location of the impacted canine is a predictor of treatment success. There are multiple studies investigating this topic and reporting significant relationships between the initial position and the outcome. In the literature, successful treatment is defined as a complete eruption of the canine’s crown, sufficient to allow orthodontic alignment or improve its position compared with the initial situation. Root resorption of the maxillary incisors, ankylosis, treatment duration, and periodontal outcome related to the initial position of the impacted canine have been evaluated. Previous studies selected the patient population on age, anteroposterior sector position, and/or buccopalatal location of impacted maxillary canines. , , Although some authors discussed esthetic outcome, few studies analyzed the relationship between initial canine position and the final esthetic outcome. , Parkin et al evaluated the esthetics of posttreatment canines through a panel of orthodontists and laypeople. Smailiene et al used tooth color, position in the dental arch, inclination, and shape as esthetic criteria. They did not include gingival parameters in their esthetic appraisal.
As reported by Luyten et al, one of the most important shortcomings in currently available research is that it is difficult to pool data and compare the outcome of studies because of a lack of standardization in the parameters used for evaluating esthetic outcomes. Luyten et al suggested addressing this problem by determining a core outcome set such as the Maxillary Canine Aesthetic Index (MCAI).
This retrospective study aimed to evaluate the position of a maxillary canine in relation to treatment duration, success, failure rate, and esthetic outcome providing further guidance for orthodontic treatment planning.
Material and methods
This study consisted of all patients treated by the local Department of Oral and Maxillofacial Surgery between January 2015 and December 2018 for impaction of maxillary canines. All patients were referred by orthodontists.
All patients with unilateral or bilateral impacted maxillary canines referred for surgical treatment were eligible for inclusion in this study. The exclusion criteria were as follows: (1) absence of preoperative radiographs, (2) absence or poor-quality posttreatment photographs, and (3) patients with a craniofacial syndrome or cleft lip and palate.
The variables of interest were predictors and outcomes. Predictors were the radiographic position of canine (sector, vertical height, angulation), age, and crestal position (buccal, midcrestal, palatal). Outcomes were treatment duration, the success of treatment, need for reintervention, failure of treatment and removal of canine, and esthetic outcome as defined by MCAI.
An initial evaluation was performed before the surgical treatment of the impacted maxillary canines on the basis of panoramic radiographs and the report of the clinical investigation.
After the initial evaluation and diagnosis of buccolingual position, all patients underwent the same standardized treatment strategy, as outlined in Figure 1 . We differentiated between a closed and an open procedure.
The closed treatment group consisted of 113 canines (29 buccal, 18 midcrestal, and 66 palatal). A palatal or buccal full-thickness flap of the mucosa covering the site of impaction was prepared. The bone covering the impacted crown was removed, and during the procedure, a bracket or cleat was bonded to the tooth surface close to the cusp. With a gold chain or twined wire, the cleat or bracket was connected to the orthodontic appliance. After the bonding, the mucoperiosteal flap was closed and sutured in place with the gold chain or wire exiting from the surgery site.
The open treatment group consisted of 40 canines (6 buccal, 13 midcrestal, and 21 palatal). The canine was exposed for some extent. In patients with buccal impaction, a mucoperiosteal flap was made, and the overlying bone layer was removed, then the flap was repositioned apically toward the cementoenamel junction (CEJ) and sutured in place. In patients with palatal impaction, the gingiva covering the canine was excised, and the overlying bone layer was removed. A special wound packing material was applied to prevent wound closure, or a cleat was bonded by the orthodontist once the tooth was exposed to further assist eruption and alignment. All canines underwent traction after the procedure, in most patients with a gold chain or wire ligature connected to a fixed appliance and in some patients with an extrusion plate.
The duration of treatment was taken as the period from the date of surgical exposure to the debonding date. In patients with bilateral canines, separate treatment durations were considered for the individual canines.
The intraoral photographs from 1-2 weeks after debonding were collected and assessed by 2 researchers (K.G and M.S). Both were trained and calibrated to use the MCAI system for using a reference training data set. Twelve variables of the MCAI were scored according to the scoring system found in Table I . For patients with unilateral impaction, the contralateral biologically erupted canine was used as a reference. For patients with bilateral canines, the contralateral canine was used as a reference; however, in the event of severe esthetic failure, a hypothetical ideal canine was used as a reference. Only MCAI values ≤3 were considered to be associated with an excellent esthetic outcome. After evaluation, all canines included in the study were divided into 2 groups according to the esthetic outcome: MCAI ≤3 (group 1) and MCAI >3 (group 2). This procedure allowed for comparison of all other parameters between the 2 groups.
| Variable | Absent | Incomplete | Complete |
|---|---|---|---|
| Parameters investigating the previously impacted canine | |||
| Mesial papilla | 5 | 1 | 0 |
| Distal papilla | 5 | 1 | 0 |
| Marginal gingiva | 5 | 1 (<3 mm) | 0 (>3 mm) |
| Recession | (apical to MGJ) | (coronal to MGJ) | (no recession) |
| 5 | 1 | 0 | |
| Marginal gingival thickness | Thin | Thick | |
| 1 | 0 | ||
| Mesiodistal crown angulation | Distal | Straight | Mesial |
| 2 | 1 | 0 |
| Major discrepancy | Minor discrepancy | No discrepancy | |
|---|---|---|---|
| Parameters investigating comparison between both canines | |||
| Curvature of marginal gingiva | 2 | 1 | 0 |
| Soft tissue color and texture | 2 | 1 | 0 |
| Root convexity | 2 | 1 | 0 |
| Tooth morphology | 2 | 1 | 0 |
| Vertical tooth position | 2 | 1 | 0 |
| Parameters investigating relation previously impacted canine and neighboring teeth | |||
| Buccolingual angulation crown acc. neighboring teeth | 2 | 1 | 0 |
Disagreements between the researchers were resolved through discussion. Grisar et al showed a good intraclass correlation for the MCAI (0.71).
The location of the impacted canine was identified through the clinical and radiological assessment. On a panoramic radiograph, the angulation of the canine, the vertical position, and the anteroposterior position of the crown were determined ( Fig 2 ). Angulation was determined by measuring the angle between the canine and the vertical line parallel to the central incisor. For the purpose of statistical analysis, the results of the angulation measurements were divided into 3 groups: group 1 (<15°), group 2 (15°-30°) and group 3 (>30°). The vertical distance to the canine cusp tip was measured perpendicular to the occlusal plane. The occlusal plane was determined by drawing a line through the incisal edge of the central incisor and the mesiobuccal cusp of the first molar. The vertical height was divided into 4 levels as described by Stivaros and Mandall : level 1 (vertical position of the canine cusp tip at the level of the CEJ of the adjacent incisor), level 2 (canine cusp tip between the CEJ and the middle of the root of the adjacent incisor), level 3 (canine cusp tip within the apical half of the adjacent incisor), and level 4 (canine cusp tip above the apex of the adjacent incisor). Ericson and Kurol introduced a classification system describing the anteroposterior position of the tip of the canine crown related to the neighboring teeth according to 5 sectors: 1, normal position (primary canine); 2, distal to the long axis of the lateral incisor; 3, mesial to the long axis of the lateral incisor; 4, distal to the long axis of the central incisor; or 5, mesial to the long axis of the central incisor.
Digital tracings on panoramic radiographs were repeated with a 1-month interval by the same trained operator (K.G) on 25 subjects randomly selected. Intraobserver reproducibility for the image analysis was measured using the intraclass correlation coefficient for the identification of anteroposterior sector, angulation, and vertical height. Disagreements were resolved through discussion between 2 observers (K.G and M.S).
Statistical analysis
The analysis was performed in S-Plus for Linux (version 8.0; TIBCO, Palo Alto, Calif). Univariate relations with outcome variables were fitted using a generalized linear model for binary responses using a logit-link for binary variables and a general linear model for variables that are normally distributed around their mean. The normality of the residual values of the general linear model was assessed by a normal quantile plot. If an explanatory variable consisted of more than 2 groups, the groups were compared with each other, and a correction for simultaneous hypothesis testing according to Tukey was applied. A stepwise model selection procedure was applied to find the combination of explanatory variables that have the closest relation to the outcomes.
Results
A total of 259 patients with 319 impacted maxillary canines were eligible for inclusion in the study. Unfortunately, many patients were excluded because of (1) no follow-up (53 canines), (2) absence or poor quality of posttreatment photographs (41 canines), and (3) missing preoperative radiographs (72 canines). After exclusion, a total of 153 impacted maxillary canines from 132 patients remained and were included in the analysis. Patients with missing posttreatment photographs or preoperative radiographic imaging were excluded as both parameters are fundamental in the assessment of the relation of the initial position of the canine and the main outcome of this survey: success, failure rate, and esthetic outcome. Patients’ characteristics are described in Table II .
| Variable | Impacted canines (n) | Percentage (%) | |
|---|---|---|---|
| Patient age | ≤16 | 122 | 80 |
| >16 | 31 | 20 | |
| Patient sex | Male | 47 | 31 |
| Female | 106 | 69 | |
| Unilateral vs bilateral | Unilateral | 111 | 73 |
| Bilateral | 42 | 27 | |
| Buccopalatal position | Buccal | 35 | 23 |
| Midcrestal | 31 | 20 | |
| Palatal | 87 | 57 | |
| Angulation | 0°-15° | 31 | 21 |
| 15°-30° | 45 | 29 | |
| >30° | 77 | 50 | |
| Sector | 1 | 52 | 34 |
| 2 | 33 | 22 | |
| 3 | 33 | 22 | |
| 4 | 25 | 16 | |
| 5 | 10 | 7 | |
| Vertical position | 1 | 12 | 8 |
| 2 | 70 | 46 | |
| 3 | 59 | 39 | |
| 4 | 12 | 8 | |
| Choice of treatment | Open technique | 40 | 26 |
| Closed technique | 113 | 74 | |
The distribution of the 153 impacted maxillary canines according to the classification, as described by Ericson and Kurol and Stivaros and Mandall, is also presented in Table II . Impacted maxillary canines were most frequently found in sector 1 at the level of the deciduous canine (n = 52; 34%), canine angulation >30° (n = 77; 50%), and level 2 vertical position (canine cusp tip between the CEJ and the middle of the root of the adjacent incisor; n = 70; 46%).
A closed approach was more frequently performed (n = 113; 74%) than an open approach (n = 40; 26%).
The mean treatment time was 22.2 months (standard deviation, 8.9; range, 4-48.2). The success of treatment was defined as achieving a fully functional eruption of the canine, with an esthetically excellent result, without the need for reinterventions. Out of the 153 impacted canines included in the study population, 147 canines (96%) achieved a fully functional eruption with an excellent or good esthetic outcome.
Failure of treatment was defined as the need for reintervention and/or the removal of the canine. In the course of the orthodontic treatment, 19 surgically exposed canines (12%) needed reintervention. Six canines (4%) were removed because of failure of eruption after a mean of 21 months of treatment (range, 15-30) and multiple attempts of surgical re-exposure. These failed canines did not receive an MCAI score.
Table III and Figure 3 demonstrate the significant ( P <0.05) relationship between duration of treatment and anteroposterior sector position, angulation, vertical height, and buccolingual position. A high vertical position, anterior sector position, angulation >30°, and palatal location were significant predictors of prolonged treatment duration.
| Variable | Treatment duration | |||
|---|---|---|---|---|
| No. of canines | Mean (mo) | SD | P ∗ | |
| Patient characteristics | ||||
| Age | ||||
| <16 | 122 | 21.5 | 8.3 | 0.05 |
| ≥16 | 31 | 25.0 | 10.6 | |
| Position | ||||
| Unilateral | 111 | 21.1 | 9.2 | 0.01 |
| Bilateral | 42 | 25.2 | 7.4 | |
| Canine characteristics | ||||
| Buccopalatinal position | ||||
| Buccal | 35 | 21.5 | 8.9 | 0.05 |
| Midcrestal | 31 | 19.6 | 8 | |
| Palatal | 87 | 23.5 | 9.1 | |
| Sector | ||||
| I | 52 | 17.9 | 6.6 | 0 |
| II | 33 | 22.1 | 9.1 | |
| III | 33 | 23.7 | 8.3 | |
| IV | 25 | 27.9 | 9.3 | |
| V | 10 | 25.9 | 9.8 | |
| Angulation | ||||
| I | 31 | 18.6 | 7.6 | 0.0001 |
| II | 45 | 19.7 | 8 | |
| III | 77 | 25.2 | 9 | |
| Vertical height | ||||
| I | 12 | 16.9 | 6.5 | 0.005 |
| II | 70 | 21.2 | 9.2 | |
| III | 59 | 23.2 | 7.9 | |
| IV | 12 | 28.7 | 10.2 | |
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