INTRODUCTION

Permanent canines have primary roles in determining functional occlusion and a pleasant smile, and disturbances of normal development and eruption can have major consequences (for review, see Bedoya and Park1). Regarding the maxillary canine, an important and effective treatment modality to prevent impaction is based on intercepting and eliminating any factor that may interfere with eruption.2 However, although a precise diagnosis of delayed eruption, that is, displacement or impaction, is needed, this cannot be done on the basis of chronological age or phase of dentition.3,4 On the contrary, early studies,3,4 confirmed by recent evidence,5 have shown that permanent maxillary canines undergo spontaneous eruption until late puberty, that is, during prepubertal and pubertal growth phases. These results were determined using the statural height peak3,4 or the maturation of the hand and wrist or cervical vertebrae5 methods to identify the pubertal growth-spurt period in individual subjects. Therefore, the use of indicators of the timing of spontaneous maxillary canine eruption has been advocated as an adjunct to the diagnosis and management of canine displacement/impaction.5

Of interest, a recent primary study6 on white subjects and a meta-analysis7 on different ethnicities have consistently shown a significant association of the complete maturation, that is, complete root formation, of the mandibular second molar with attainment of a postpubertal growth phase. Therefore, considering how the maxillary canine eruption and mandibular second molar maturation are both parts of the same whole dentition development, a relation between the two processes may be hypothesized.

Thus, considering the relevant clinical implications reported earlier, the present study focused on the relation between the spontaneous eruption of the permanent maxillary canine and the maturation of the mandibular second molar to propose the monitoring of the latter as a means of predicting the timing for the spontaneous eruption of the former in individual subjects. Moreover, the potential confounding effects from such factors as age, growth phase, and facial features were also explored.

MATERIALS AND METHODS

A sample of 106 subjects (48 females and 58 males; age range, 9.4–14.3 years) at the Unit of Orthodontics of the University of Trieste with both permanent maxillary canines during the final phase of intraoral eruption were retrospectively included. Signed informed consent was obtained from the parents of the subjects before entry into the study, and the protocol was reviewed and approved by the local ethical committee. Thirty-three subjects of the present sample were included in a previous study6 with a different purpose.

At their first clinical examination, intraoral photographs, a dental panoramic radiograph, and a lateral cephalogram were obtained from each subject as part of the pretreatment clinical recording. The following inclusion criteria were observed: (1) white ethnicity, (2) good general health with absence of any nutritional or developmental problems, (3) never orthodontically treated, (4) negative for any dental or facial anomaly (including massive caries, tooth loss, multiple agenesis), (5) no history of previous trauma in the orofacial region, and (6) absence of any pathologic obstacles to the eruption pathway of the maxillary canines, such as odontomas, cysts, or supernumeraries.5 Moreover, only patients with minimal crowding or differential eruption degree between the two contralateral canines were considered. In case of a slight delay in the eruption of one canine over the other, the less erupted tooth was considered.

The final phase of canine eruption was defined as previously reported.8 Briefly, it was the emergence of the canine from the initial appearance of the tip of the cusp in the dental arch to a 1-mm distance of the tip of the cusp from the maxillary occlusal plane (traced on the panoramic radiograph).

Skeletal maturity was assessed through the cervical vertebral maturational (CVM) method.9 This method comprises six stages (CS1 to CS6). An experienced orthodontist, blinded to the age and sex of the subjects, assessed the skeletal maturity of the subjects. Finally, the subjects were clustered, according to their growth phases, as prepubertal (CS1 and CS2), pubertal (CS3 and CS4), and postpubertal (CS5 and CS6).

Assessment of Mandibular Second Molar Maturity

Mandibular second molar maturity (Figure 1) was assessed through the calcification stages, according to the method of Demirjian et al.10 (stages E to H), from the panoramic radiographs of the left-side mandibular teeth. Alternatively, when the left side was not clearly visible, the right side was assessed. Briefly, these stages are defined as follows:

• Stage E: (1) The walls of the pulp chamber form straight lines, the continuity of which is broken by the presence of the pulp horn, which is larger than in the previous stage; and (2) the root length is less than the crown height.

• Stage F: (1) The walls of the pulp chamber form a more or less isosceles triangle, with the apex ending in a funnel shape; and (2) the root length is equal to or greater than the crown height.

• Stage G: The walls of the root canal are parallel, and its apical end is still partially open.

• Stage H: (1) The apical end of the root canal is completely closed; and (2) the periodontal membrane has a uniform width around the root and the apex.

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An experienced orthodontist, blinded to the skeletal maturation stages and the age and sex of the subjects, assessed the dental maturity of the mandibular second molars using the distal root as the reference structure.

RESULTS

For appraisal of the stages of both cervical vertebrae and second molar maturational stages, the weighted kappa coefficients for repeatability were above 0.92. The method error for the cephalometric recordings was lower than 1°.

The mean ages of the subjects, along with the SN/MP angle and ANB angle, for females and males are summarized in Table 1. All of these parameters were similar between the sexes, and there were no significant differences.

Table 1. Chronological Age, SN/MP Angle, and ANB Angle for Females (n  =  48) and Males (n  =  58)^a

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The relative distributions of the different growth phases and second molar maturational stages for females and males are summarized in Table 2. A greater percentage of subjects in the pubertal growth phase was seen for females (66.7%) compared with males (31.0%; P < .01). Overall, the prevalences of the different second molar maturational stages were 36.8%, 37.8%, and 27.4% for stages E, F, and G, respectively. No stage H was seen, and the distributions of the other stages were similar between the sexes, with no significant difference.

Table 2. Relative Distributions of the Different Growth Phases and Second Molar Maturational Stages for Females and Males ^a

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The ordered multiple regression model for the association of each explanatory variable with the second molar maturational stage is summarized in Table 3. With the exception of age (β, 0.543; P < .01), none of the explanatory variable yielded a statistically significant interaction with the second molar maturity.

Table 3. Ordered Multiple Regression Model for the Association of Each Explanatory Variable With the Second Molar Maturational Stage^a

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Chronological ages among the different mandibular second molar maturational stages for females and males as retrieved from a previously investigated sample6 are shown in Figure 2. The overall mean (standard error) values were 8.5 ± 0.1, 9.4 ± 0.1, 10.9 ± 0.1, 12.5 ± 0.1, and 14.6±0.2 years for stages D, E, F, G, and H, respectively. Mean time intervals between stages E to F and stages F to G were 1.5 and 1.6 years, respectively. The slight differences seen between females and males were not statistically significant.

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DISCUSSION

This cross-sectional study was undertaken to evaluate the relation between the spontaneous eruption of maxillary canine and mandibular second molar maturation. All the subjects had canine eruption of the mandibular second molar within maturational stages E, F, and G (see Figure 3), irrespective of growth phase and other investigated factors.

Being that spontaneous eruption of maxillary canines and mandibular second molar maturation are parts of the same dental maturation process, a correlation between them was expected. However, whether the eruption of the former may be predicted by the maturation of the latter with satisfactory reliability, and whether other factors may influence this prediction, has still not been reported. Subjects included herein were seeking orthodontic treatment; therefore, a greater prevalence of malocclusion in the present sample was seen compared with a similar group in the general population.15 In particular, a general tendency toward hyperdivergent skeletal class II was encountered (Table 1).

The overall prevalence of subjects at the prepubertal growth phase seen herein (52.8%) was similar, though lower, than that reported previously (56.6%).5 According to previous results,4,5 no subject herein showed spontaneous eruption of the maxillary canine at the postpubertal growth phase.

In the present study, the correlation between the spontaneous maxillary canine eruption and maturation of the mandibular second molar was not influenced by sex, growth phase, or dentofacial growth features. On the contrary, a previous study5 reported an earlier eruption for hyperdivergent subjects but only when the maxillary canine eruption is attained at a prepubertal growth phase. This finding is consistent with the evidence that dental maturation would occur earlier in subjects with an extreme vertical face type.11 However, previous studies5,11 did not adjust correlations by the use of multiple regression models. Regarding the sagittal skeletal facial features, the present evidence is in agreement with previous findings.5 Nevertheless, potential effects by other factors, such as genetic or hormonal features, may be responsible for the intersubject variation seen in the timing of the spontaneous eruption of the maxillary canines.

In comparison with the growth phase, maturation of the mandibular second molar may thus be considered more strictly related to the spontaneous eruption of the maxillary canine. This may be expected as these are two events of the same overall maturation of the dental arches. Therefore, as reported for the attainment of the postpubertal growth phase,5 canine impaction can be suspected when not erupted after the complete root formation of the mandibular second molar. In this case, an implementation of the diagnosis would be deemed.

Consistently for both females and males, intervals of 18 months were seen as the time required for a mandibular second molar to mature from stage E to F and from stage F to G (Figure 2). This information on the timing of maturation of the mandibular second molar may be helpful when managing interceptive treatments for maxillary displaced canines. Indeed, knowledge of the timing at which the maxillary canines can still undergo spontaneous eruption is useful for determining the expected appearance in the oral cavity. On the contrary, if a canine has not erupted by the attainment of mandibular second molar stage H, even after an interceptive treatment, a surgical approach may be considered, especially if other diagnostic features of canine impaction are noted.1 Considering that all subjects undergo spontaneous eruption of the maxillary canine when the mandibular second molar maturation is between stages E and G, information regarding timing of eruption may be available in all the subjects, irrespective of sex, growth phase, and vertical and sagittal skeletal facial features.

Even though the CVM method has been shown to be a reliable indicator of the timing of canine eruption, this analysis requires a lateral head film, which is available as a pretreatment record. However, in several instances, optimal treatment timing is delayed until after the diagnosis, making a later reevaluation of the growth phase necessary. Moreover, the cervical vertebrae might be partially covered by the protection collar, which would be necessary to reduce radiation exposure.16 On the other hand, radiographic recording of the hand and wrist requires additional x-ray exposure and a dedicated x-ray machine. Importantly, for both methods, re-execution of recordings to reevaluate growth phases only is not indicated according to some recent guidelines.17 In this view, the use of the mandibular second molar maturation to predict the timing for eruption of the maxillary canines offers the advantage of easy interpretation, and it does not require additional x-ray exposure to the patient when a dental panoramic record is available. The radiographic recording of the region of the mandibular second molar also avoids doubling or superimposition of the recorded structures with anatomic features of the distal root that are clearly visible. Moreover, the same panoramic radiograph may be used to retrieve other relevant information regarding the identification of a potential displaced/impacted canine.18 Finally, if needed, an intraoral periapical radiographic record of the mandibular second molar may be taken during follow-up visits with minimal irradiation to the patients.

CONCLUSIONS

• Spontaneous eruption of the maxillary canine occurs between stages E and G of the mandibular second molar, irrespective of sex, growth phase, and facial features.

• The maturational stage of the mandibular second molar may be a reliable indicator for the timing of spontaneous eruption of the maxillary canine.