Revealing the Effect of Impacted Canines on the Adjacent Teeth. A Three Dimensional Study Using CBCT

ABSTRACT

Objective:

The current cross-sectional study aimed to assess the relationship between impacted maxillary canines and their effect on root resorption of neighboring teeth using cone-beam computed tomography (CBCT).

Materials and Methods:

The study evaluated the effect of 24 impacted maxillary canines on the adjacent tooth roots. We used a CBCT to evaluate the position and size of the dental follicle of impacted maxillary canines and the severity of root resorption on adjacent teeth. We used a t-test to compare the significant differences between the width of the dental follicle and the severity of root resorption. The inter- and intra-rater agreements were assessed.

Results:

A number of 12 impacted canines had resorbed the roots of adjacent teeth. Lateral incisors were most affected (83.3%), followed by central incisors (16.7%). Mild root resorption was found in 10 cases, while severe resorption was found in two cases. We found no relation between the size of the dental follicle and the degree of root resorption. The inter- and intra-rater agreements were high.

Conclusion:

In cases with maxillary impacted canines, special consideration should be directed to the roots of the maxillary lateral incisors. Our findings could not confirm any relationship between the size of the dental follicle width of the maxillary impacted canines and the degree of root resorption of the adjacent incisors. More studies are needed to assess the proximity and path of eruption of impacted maxillary canines and their effect on the neighboring teeth.

INTRODUCTION

Impaction of teeth is defined as the failure of the eruption of teeth within the normal physiological and time limits.[1] The permanent maxillary canines are one of the most impacted teeth, with a prevalence of 1–3%.[2,3] The mandibular and maxillary canines are of great importance for both functional and aesthetic reasons.[4] Among the permanent teeth, the maxillary canine develops deep within the bone and has the longest eruption path, which may explain the high prevalence of impaction in maxillary canines.[4] The exact localization and early detection of an impacted canine are clinically critical to reduce or completely avoid permanent complications such as root resorption of surrounding teeth.[5,6] Palatally impacted canines are more frequent than buccally impacted canines.[7] However, both labially and palatally positioned canines can lead to the resorption of neighboring tooth roots, which might affect the long prognosis of the resorbed teeth.[1,8]

Accurate localization involving unerupted canines, revealing the resultant resorption of roots of neighboring teeth by radiographic three-dimensional (3D) methods, has a significant influence on the orthodontic management and treatment plan.[9,10] The impacted canine can be either aligned with orthodontic treatment or removed surgically. With early detection and appropriate intervention, impacted canines may be correctly positioned into the dental arch.[11,12] However, highly, horizontally, and distally displaced maxillary canines are challenging to align with orthodontic appliances and might be better to surgically remove them.[13]

Cone-beam computed tomography (CBCT) has been used in recent years to produce high-quality diagnostic 3D images.[14] The produced images from CBCT are highly accurate in localizing the angulation and Bucco-palatal position of the unerupted teeth. They also provide a clear indication of the degree of resorption and the proximity of the impacted tooth to the adjacent teeth.[3,15] The dental follicle size of impacted and displaced teeth can be easily and precisely measured with CBCT images.[16] It has been suggested that dental follicle width of impacted teeth is correlated to the degree of resorption of the roots of the neighboring teeth.[17] Regardless of the most advanced benefits from the CBCT, two dimensional (2D) conventional radiographs, such as periapical, occlusal, and panoramic projections, are widely prescribed for the initial detection and evaluation of impacted canines.[18] However, the 2D radiographs exhibit unsatisfactory information regarding the unerupted teeth and their effect on the surrounding tissues.[16]

The present cross-sectional study aims to record and evaluate cases with maxillary permanent impacted canines and their influence on the roots of the adjacent teeth. The study also aims to record other related local conditions such as the existence of root dilacerations, supernumerary teeth, and the width of the dental follicles.

MATERIALS AND METHODS

The current study was approved and received the ethical certificate by the Research Ethical committee, Deanship of Scientific Research, Qassim University (Date: November 24, 2021 – Number: 21-04-11). For this research, the need for written consent was waived by the ethics committee. All patients who visit the Qassim University dental clinics give their initial consent for their records to be used for research and educational purposes. However, their personal data should be protected and remain anonymous. The reporting of this study followed the STROBE guidelines.

The samples were collected retrospectively from the radiographic department at the dental clinics of the College of Dentistry, Qassim University. We examined all of the available CBCT images between the period of January 2020 and February 2022. All of the 3D images were taken with a Sirona GALILEOS ComfortPLUS machine. We used the SIDEXIS XG software (version 2.61) to evaluate the CBCT images.

Two examiners assessed the obtained CBCT images. To evaluate the intra-rater agreement, both examiners assessed the CBCT images two times. The time interval between the two examinations was two to four weeks. We applied no restrictions related to gender or age. However, we excluded patients with osseous lesions and/or systemic bone diseases. Also, we excluded patients with cleft lip and palate, as they may affect our readings of the CBCT scans.

A canine was considered impacted when it deviated from the normal track of eruption and had at least 2/3 of its root develop. We collected the following data from each CBCT image: the patient’s file number, age, gender, and the presence of bone diseases or a cleft palate. Also, we recorded the side, type, and position involving impacted canines, presence, and degree of resorption on the roots of the adjacent teeth. Other factors, such as the dental follicle width of impacted teeth and the presence of root dilacerations or supernumerary teeth, were recorded.

We graded the severity of root resorption according to Ericson and Kurol’s classification.[5] They classified root resorption into four main categories: absence of evidence of root resorption (=0), presence of slight resorption (=1), resorption involving half of the dentin), moderate resorption (=2), more than half of the dentin is resorbed, and the pulp remains intact), and severe resorption (=3, pulp involvement).[6]

The dental follicle widths of the unerupted maxillary canines were measured from the widest area between the outer surface of the involved impacted canine crown and the inner surface of the follicle. A reading of >3 mm was considered an enlarged follicle.[17]

All obtained data were statistically analyzed using SPSS (IBM SPSS Statistics for Windows: Version 27.0. Armonk, NY: IBM Corp). The student’s t-test was applied to assess significant differences between the severity of root resorption of maxillary lateral incisors and the dental follicle size of impacted maxillary canines. The level of significance was set at <0.05. Unweighted Kappa values are calculated by the method of Fleiss and Conger to assess intra- and inter-rater agreement.[19]

RESULTS

We initially examined 415 CBCTs and found four patients presenting with bilaterally impacted canines and 16 patients involving unilaterally impacted canines. The prevalence of impacted permanent canines in our sample was 5.8%. Of all of the 24 impacted canines, we found 12 cases with no signs of resorption, 10 cases with mild resorption, and two cases with severe resorption [Figure 1]. The most affected teeth with root resorption were lateral incisors (n = 10, 83.3%), followed by central incisors (n = 2, 16.7%). Table 1 shows detailed information regarding the findings of this study.

Figure 1.

The CBCT image on the left shows that the impacted maxillary canine (A) is erupting buccally and severely resorbing the buccal surface of the maxillary lateral incisor root (B). The right CBCT image shows that the palatally erupting canine (A) is severely resorbing the disto-palatal surface of the maxillary lateral incisor root (B)

Table 1.

Correlation of impacted maxillary canines with the other variables

Variables	n	%
Gender
Male	14	70%
Female	6	30%
Type of occurrence
Unilateral	16	80%
Bilateral	4	20%
Side (Unilateral)
Right	7	43.8%
Left	9	56.2%
Labio-palatal position
Mid-alveolar	0	0%
Labial	2	8.3%
Palatal	22	91.7%
Root resorption
Yes	12	50%
No	12	50%
Root dilacerations
Yes	2	8.3%
No	18	91.7%
Dental follicle width
Normal (≤3 mm)	21	87.5%
Wide (>3 mm)	3	12.5%
Supernumerary tooth
Yes	1	4.2%
No	19	95.8%

n=Numbers

The dental follicle widths ranged from 0.53 mm to 6.87 mm. Cases with severe resorption showed a slightly larger mean follicle size in comparison to mild or no resorption cases. However, there were no statistically significant differences between the size of the dental follicle width and the severity of root resorption. Table 2 shows the statistical results of teeth with root resorption. The severity of root resorption on neighboring teeth and the means of the dental follicle size widths are shown in Table 3.

Table 2.

Statistical results of teeth with root resorption

Variables	n	Severity (n)
		Mild	Moderate	Severe
Gender
Male	6	4	0	2
Female	6	6	0	0
Labio-palatal position
Labial	2	1	0	1
Palatal	10	9	0	1
Affected teeth
Central incisors	2	2	0	0
Lateral incisors	10	8	0	2
Dental follicle width
Normal (≤3 mm)	10	8	0	2
Wide (>3 mm)	2	2	0	0

n=Numbers

Table 3.

Severity of involvement of root resorption on neighboring teeth and means of the follicle size widths of unerupted canines

Grade of Resorption	Number of teeth (%)	Means of follicle size width (sd)	P (Grades vs follicle size)
No resorption (0)	12 (50)	1.6 mm (±1.9)	(0-1) = 0.426 (0-3) = 0.154
Slight resorption (1)	10 (41.7)	1.7 mm (±0.9 mm)	(1-0) = 0.426 (1-3) = 0.231
Moderate resorption (2)	0 (0)	-
Severe resorption (3)	2 (8.3)	1.9 mm (±1.3 mm)	(3-0) = 0.154 (3-1) = 0.231

SD=Standard deviation, statistically significant difference level is P<0.05

The intra-rater reliability results were considered high (93.75% and 100%). The inter-rater reliability finding was considered high as well (95%).

DISCUSSION

The current study was designed to evaluate the presence and degree of involvement of root resorption in cases with impacted maxillary canines using CBCT scanning. Maxillary impacted canines have always been a great challenge to treat as they are difficult to align. They have the longest path of eruption, and they might lose their space during the process of erupting. As a result, they might resorb and rotate the adjacent teeth. In the current study, we found that 50% of unerupted canines in the maxilla involved mild-to-severe root resorption of adjacent teeth. Several other studies also showed that there is a tight relationship between the impacted canines and root resorption.[1,4,6]

The dental follicle size was suggested to be a factor in the presence and severity of root resorption.[17] Ericson et al. (2002) found that the increase in the size of the dental follicle, the higher the chance of resorption of root.[17] However, in the current study, a correlation between the dental follicle size and the degree of root resorption was not found. On the contrary, the widest dental follicles were found in cases with no or mild root resorption. Dağsuyu et al. reported that the largest dental follicles of unerupted maxillary canines occurred more commonly in mild resorption cases.[16] Ericson and Kurol evaluated the thickness of maxillary canine dental follicles and the occurrence of root resorption on permanent incisors using periapical radiographs.[13] They could not confirm the relationship between the width of the dental follicle and the severity of resorption on the neighboring teeth. There might be other factors that have a closer relationship with the degree of root resorption than the follicle size, such as the proximity, direction, and position of the impacted canines.

It has also been suggested that the lateral incisors play a critical role in the path of eruption of the maxillary canines. The canine guidance theory suggests that the maxillary canines lose their eruption guidance in cases with congenitally missing or malformed lateral incisors. There is a close relationship between the lateral incisor root and the erupting canine. In the present study, about 83% of the affected teeth were lateral incisors. Also, grade 3 root resorption occurred mainly on the lateral incisor roots. Other studies also found that the impacted maxillary canines mostly resorbed upper lateral incisor roots.[3,17] We would suggest that a closer evaluation of the lateral incisor roots be carried out in cases with impacted canines. It is crucial to assess the lateral incisors carefully before attempting any surgical or orthodontic treatment.

The occurrence of root resorption of maxillary incisor roots was similar in males and females. However, severe cases existed mainly in male patients. Cernochova P. et al. found that root resorption in cases with impacted maxillary canines was equally common in males and females.[12] However, several studies highlighted the significantly higher prevalence of root resorption among females compared to males.[7,16] The severity of root resorption might be affected by the metabolic and cellular activities around the teeth. Hormones and growth factors might also influence the degree of root resorption.[16] However, it would be difficult to draw a clear conclusion about the relationship and severity of resorption between male and female groups.

CBCT images provide a significant improvement in understanding the relationship between impacted canines and the prevalence of adjacent tooth root resorption. It allows clinicians to evaluate the impacted teeth and surrounding tissues in three dimensions. The findings of this study prove that predicting the severity and occurrence of root resorption in cases of impacted canines is not possible. We would suggest evaluating each case with impacted maxillary canines carefully with a CBCT. Special consideration should be directed to the maxillary lateral incisor roots. The current study has a limited number of participants, as the CBCT machine has only recently been implemented in our clinic. Such limitations might introduce bias into the current conclusions and limit their generalizability. Accordingly, further studies are needed to compare different variables with the occurrence of incisor root resorption in cases with impacted canines, such as the degree of proximity and angulation of impacted maxillary canines with the neighboring teeth.

CONCLUSION

Impacted maxillary canines can severely resorb the roots of the neighboring teeth. It is recommended for a detailed evaluation of the roots of adjacent maxillary lateral incisors before attempting orthodontic or surgical treatment. There was no relationship between the dental follicle width of the unerupted maxillary canines and the severity of resorption of the involving roots of neighboring teeth. Also, there was no relationship noticed among the gender and degree of involvement of adjacent root resorption. Wide dental follicles involving impacted maxillary canines were found in cases presented with no or mild resorption. CBCT images help clinicians assess the degree of impaction and root resorption.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.