Appropriate timing of treatment contributes to better root development of impacted anterior teeth in children

Introduction

This study investigated the effects of different timings of orthodontic treatment on the root development of impacted anterior teeth in children.

Methods

The cone-beam computed tomography (CBCT) data of 45 children with impacted anterior teeth were divided into unformed root (UR) group or basically formed root (BFR) group to evaluate root length (RL) and root growth length (RGL) of impacted teeth and contralateral nonimpacted teeth pretreatment and posttreatment. In addition, 22 patients with impacted dilaceration were selected to assess the effects of the crown-root angle and root development stage on RL and RGL. The Student t test, Wilcoxon test, analysis of variance, and multiple linear regression analysis were used for statistical evaluations.

Results

The RL of treated impacted teeth pretreatment and posttreatment was significantly shorter than contralateral nonimpacted teeth values ( P <0.05). Posttreatment, the RL and RGL of impacted teeth of the UR group were significantly greater than those of the BFR group ( P <0.05). The RGL of the dilacerated root in the UR group was considerably higher than in the BFR group ( P <0.05). The larger crown-root angle group had a longer posttreatment RL ( P <0.05). Multiple linear regression analysis revealed that the Nolla stage of impacted teeth and RL of contralateral teeth pretreatment significantly influenced the RL of impacted teeth posttreatment.

Conclusions

Prompt orthodontic treatment is necessary for children with impacted anterior teeth to release the impacted state and achieve better root development. The root length of a dilacerated tooth continued to develop under treatment, but the crown-root angle partly constrained it.

Highlights

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Impacted teeth treated with earlier Nolla stage can get better root prognosis.
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The crown-root angle partly constrained the root length growth of dilacerated tooth.
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Early treatment releases the impacted state and augments the root development potential.

Teeth embedded in the mucosa or jawbone that cannot erupt into a normal functional position because of the obstruction of the bone, tooth, or fibrous tissue are called “impacted teeth.” ^, Impacted anterior teeth are common eruption abnormalities in children. The prevalence of impacted maxillary canines is the most prevalent impacted anterior teeth (incidence, 0.92%-5.4%), followed by maxillary central incisors (incidence, 0.1%-2.1%) and mandibular canine teeth (incidence, 0.35%). One of the special manifestations of the impacted tooth is dilaceration (ie, abrupt deviation of the long axis of the crown or root portion of the tooth in labiolingual or mediodistal directions).

Various etiologic factors are related to the impaction of anterior teeth, including systemic illness, hereditary influence, or local factors (eg, cleft lip and palate, lack of space, chronic periapical inflammation of deciduous teeth, supernumerary teeth, or odontomas). The etiology and mechanism of root dilaceration are unclear but might be related to the trauma of the primary tooth or idiopathic developmental disturbance, for instance, ectopic tooth germ development. ^, Zilberman et al postulated that trauma to the primary tooth might exert a force on the developing permanent tooth germ, which would cause displacement of the calcified portions and form an angle with the remaining tooth germ. Recent research has shown that highly proliferative undifferentiated stem cells and an actively communicating microenvironment in the developing apical complex (DAC) contribute to tooth root development. Local factors like trauma and inflammation might affect the function and microenvironment of DAC in forming an abnormal root. ^,

Impacted anterior teeth can severely damage the integrity and symmetry of the dentition and even cause root resorption of the adjacent tooth. Impacted teeth in the maxillary anterior area may significantly impact facial esthetics, pronunciation, mastication, and psychosocial well-being. Therefore, impaction of the anterior teeth should be diagnosed and corrected promptly to help children improve oral function and esthetics.

Cone-beam computed tomography (CBCT) is widely utilized in the diagnosis and treatment planning for impacted teeth. CBCT enables a 3-dimensional (3D) spatial display of the teeth, soft tissues, and bone. ^, Consequently, CBCT can be employed to evaluate the position of the tooth, development stage of the root, and provide critical information about adjacent anatomy around the impacted tooth.

The clinical treatment of an impacted anterior tooth requires comprehensive intraoral evaluation on the basis of its position, shape, dilacerated root and direction, and relationship with adjacent teeth and bones, combined with other malocclusion deformities in the mouth. Currently, treatment for impacted anterior teeth combines orthodontic and surgical treatments. The prognosis of impacted teeth depends on the position and root development of impacted teeth. Studies have demonstrated that reduced root growth and increased frequency and severity of dilaceration occur as dental age increases. ^, Because a uniform standard for quantitative indicators of the timing of treatment is lacking, appropriate timing of treatment should be determined to fully exploit the root growth and development potential to achieve better root growth and morphology of the root apex. ^, ^,

To provide a basis for the judgment of treatment outcome, we explored the effects of different treatment timing on the root development of impacted anterior teeth in this study.

Material and methods

The protocol for this clinical study was approved by the School and Hospital of West China Stomatology Hospital ethics committee within Sichuan University (Chengdu, China). All participants provided written informed consent.

The inclusion criteria were (1) a diagnosis of an impacted anterior tooth, (2) CBCT images were available and clear, (3) full clinical information and medical history were obtained, (4) closure of the apical foramen of the contralateral normal tooth and impacted tooth at the end of the observation period, (5) regular follow-up, and (6) good compliance with the study protocol.

The exclusion criteria were (1) systemic disease; (2) impacted teeth in nonanterior areas; (3) extracted impacted teeth because of various reasons; (4) incomplete CBCT data; (5) severe oral and maxillofacial diseases, craniofacial anomalies, cysts, or cleft lip and palate; (6) frequent appointment failure.

All patients treated for impacted maxillary or mandibular anterior teeth from 2013 to 2018 at the Department of Pediatric Early Orthodontics Specialty of West China Stomatology Hospital (Sichuan University) were evaluated. Forty-five patients (25 boys, 20 girls) met the above mentioned criteria and were recruited for our study ( Table Ⅰ ). Of these, 22 patients were root dilaceration, all of which were maxillary central incisors.

Table I

Characteristics of patients and the impacted teeth

Variables	n (%)
Gender
Male	25 (56)
Female	20 (44)
Age, y
5-6	2 (4)
7-8	19 (42)
9-10	18 (40)
11-13	5 (11)
17	1 (2)
Impacted teeth position
Maxillary right lateral incisor	2 (4)
Maxillary right central incisor	22 (49)
Maxillary left central incisor	19 (42)
Maxillary left lateral incisor	1 (2)
Mandibular left central incisor	1 (2)
Impacted teeth Nolla stage
6	3 (7)
7	18 (40)
8	17 (38)
9	4 (9)
10	3 (7)
Contralateral teeth Nolla stage
7	7 (16)
8	9 (20)
9	17 (38)
10	12 (27)
Impacted teeth root
Dilacerated	22 (49)
Straight	23 (51)
Cause of impacted teeth
Periapical periodontitis of deciduous teeth	32 (71)
Supernumerary teeth	7 (16)
Adhesion of deciduous teeth	2 (4)
Retention of unexplained deciduous teeth	1 (2)
Dental tumors and compression absorption	3 (7)

The medical history, clinical examination, and imaging examination were gathered for the etiologic diagnosis. Dolphin Imaging software (version 11.8; Dolphin Imaging and Management Solutions, Chatsworth, Calif) was used for the 3D reconstruction of CBCT images. The measurement items were the: Nolla stage (description of tooth growth and development, seen in Fig 1 , G ) at the first diagnosis of the objective tooth and the contralateral nonimpacted tooth; root length (RL) pretreatment and posttreatment; crown-root angle of the dilacerated teeth. The 3D line function was applied to measure pretreatment and posttreatment RL and the angle of the dilacerated root. The length of root growth was calculated by subtracting the pretreatment RL from the posttreatment RL. The angle of dilaceration was defined as the angle between the line established by the long axis of the crown and the straight portion of the root and the axis of the dilacerated root. Measurement of the length of dilacerated roots includes the length of the straight root and curved root ( Fig 1 ).

According to the root development of the contralateral nonimpacted tooth pretreatment, all 45 patients were divided into an unformed root (UR) group (Nolla stage 7 or 8) or basically formed root (BFR) group (Nolla stage 9 or 10) (Y.P.).

Twenty-two patients with an impacted maxillary central incisor with dilacerated roots were assigned to the UR group (Nolla stage 7 or 8) and BFR group (Nolla stage 9 or 10) according to the root formation of the contralateral nonimpacted tooth pretreatment; 11 patients were included in each group. In addition, according to the measured curved angles of dilaceration, the impacted teeth with dilacerated roots were also separated into 0°-90° and 91°-180° (Y.P.).

Statistical analyses

Data analyses were completed using SPSS software (version 17.0; IBM, Armonk, NY). All measurements were repeated after 2 weeks by the same investigator. Intraexaminer error was determined by the interclass correlation coefficient on the basis of a 2-way mixed analysis of variance (ANOVA). The mean value of 2 measurements was used for statistical analyses. Significance was determined via the Student t test or ANOVA. Multiple linear regression analysis was carried out to evaluate the RL of impacted teeth posttreatment on the basis of 9 variables: sex, age, whether the roots of impacted teeth were dilacerated, Nolla stage of impacted teeth and contralateral teeth at the first visit, RL of impacted teeth and contralateral teeth at the first visit, the difference in RL between impacted teeth and contralateral teeth at the first visit, the difference in Nolla stage between contralateral teeth, and impacted teeth pretreatment of impacted teeth. P <0.05 (2- or 4-tailed) was considered significant.

Results

The mean age of the study cohort (25 boys and 20 girls) was 9.00 ± 2.07 years. Impaction was observed mainly in maxillary central incisors (which accounted for 91% of all tested teeth), followed by maxillary lateral incisors (7%) and mandibular central incisors (2%) ( Table I ).

The main cause of impacted teeth was periapical periodontitis of deciduous teeth (71% of patients), followed by supernumerary teeth (16%). The other reasons were adhesion of deciduous teeth, delayed loss of deciduous teeth, retention of unexplained deciduous teeth, dental tumors, and compression absorption ( Table I ).

Compared with contralateral nonimpacted teeth, the Nolla stage of impacted teeth was significantly lower, and the RL was shorter in all 45 patients pretreatment ( Figs 2 , A and B ). Posttreatment, the RL of impacted teeth remained substantially shorter than that of contralateral nonimpacted teeth ( Fig 2 , C ).