Introduction
This study aimed to use 3-dimensional data to investigate the factors affecting local alveolar bone thickness in unilateral maxillary canine–lateral incisor transposition.
Methods
Pretreatment cone-beam computed tomography data of 34 patients with unilateral maxillary canine–lateral transposition were imported into Dolphin Imaging software (version 11.8; Dolphin Imaging and Management Solutions, Chatsworth, Calif) for 3-dimensional reconstruction. The age, gender, and type of transposition at the beginning of treatment were recorded. The thickness and height of the transposed canine, the labiopalatal and distomedial distance from the transposed canine to the apex of the lateral incisor, the inclination of the transposed lateral incisor, the apical height of the lateral incisor, and the alveolar bone thickness in the apical plane were measured. Multiple linear regression analyses were applied to investigate the factors affecting alveolar bone thickness in the apical plane of the transposed lateral incisor. Two sample t test were applied to assess the difference of alveolar bone thickness in patients of different ages.
Results
The 10 boys and 24 girls had a mean age of 12.26 ± 2.34 years. In all 34 participants, the apical alveolar bone thickness of transposed lateral incisors was significantly higher than that of the unaffected side ( P <0.05). Based on multiple regression analyses, factors associated with a wider alveolar bone thickness were as follows: age (β = −0.237; P = 0.008), the labiopalatal distance from the transposed canine to the apex of the lateral incisor (β = 0.675; P <0.001), and the inclination of the transposed lateral incisor (β = 0.048; P = 0.032). Patients aged <11 years had significantly thicker alveolar bone than that of patients aged >11 years ( P <0.05).
Conclusions
Patients with younger age, greater lateral incisor inclination, and greater labiopalatal distance between canine and lateral incisor had more alveolar bone thickness. Early treatment permits tooth movement within the thicker alveolar bone.
Highlights
- •
The study included 34 patients with unilateral maxillary canine–lateral transposition.
- •
Age and lateral incisor inclination have been associated with local alveolar bone thickness.
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Patients aged <11 years had significantly thicker alveolar bone than that of patients aged >11 years.
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Early treatment enhances alveolar bone thickness.
Transposition is a severe form of malocclusion. The exchange of 2 adjacent permanent teeth in the same arch or the aberrant eruption of 1 tooth in a nonadjacent dental position are both examples of transposition. In complete transposition, both the root and the crown (the whole tooth) exchange positions, whereas incomplete transposition refers to the exchange in position of the crown only. , Transposition occurs most frequently between the maxillary canine first premolar and maxillary canine lateral incisor (MxCI2), and is more prevalent in females. ,
Transposition treatment options are as follows: (1) extracting 1 of the teeth, (2) maintaining the erroneous alignment of the relocated teeth and aligning them with orthodontic treatment, and (3) correcting the erroneous alignment with orthodontic or multidisciplinary combination treatment. The lateral incisors cannot take the position of the canine in the “canine-guided” role, , because of the large disparity in root surface area. In addition, it is difficult to replace lateral incisors with canines, considering that differences in crown size and shape require significant enameloplasty, labiopalatal thickness differences, and gingival margin disparity. Therefore, clinicians favor an approach that restores the canines to their proper positions for patients with MxCI2 transposition. The difficulties presented by the lack of alveolar bone thickness are usually the biggest obstacles to this treatment, along with the patient’s consideration of the pain from the surgery and the lengthier treatment period. , This is because having sufficient alveolar bone thickness, particularly on the labial side at the apical level of the transposed lateral incisors, is crucial for allowing the transposed canines to move to their normal position without experiencing root resorption, dehiscence, or gingival recession.
Certain anomalies in alveolar bone thickness are observed clinically in association with many MxCI2 transpositions. Some of these anomalies are helpful, whereas others are not. The likelihood of a favorable outcome can be significantly increased if the factors affecting the local alveolar bone thickness in these patients can be identified and the controllable factors adjusted to raise the alveolar bone thickness at the time of therapy. There is currently no literature that provides reliable information on the factors influencing alveolar bone thickness in MxCI2 transpositions. Consequently, the objectives of this study were to (1) evaluate the differences in alveolar bone thickness on the affected and unaffected side of MxCI2 transpositions and (2) determine the variables affecting alveolar bone thickness at the apical level of the affected lateral incisor.
Material and methods
School and Hospital of Stomatology, Wenzhou Medical University Approval for the clinical trial of this study was obtained from the Ethical Committee of the Hospital of Stomatology of Wenzhou Medical University (Hospital of Stomatology, Wenzhou Medical University Clinical Ethical Registry: 201101). All patients signed an informed consent form.
Study design is shown in Figure 1 . Data were recorded on 34 patients (10 males, 24 females; mean age, 12.26 ± 2.34 years) presenting with unilateral canine–lateral incisor transposition, treated between April 2011 and April 2022 at Wenzhou Medical University, Hospital of Stomatology. The inclusion criteria were (1) patients with full clinical documentation, including biographic data, contact information, and medical history; (2) pretreatment photographs of the cone-beam computed tomography (CBCT) were complete, clear, and measurable; (3) the patient’s initial diagnosis of unilateral MxCI2 transposition (12-13 or 22-23), both complete and incomplete; (4) canine was transposed labially to the lateral incisor; and (5) no systemic disease. The exclusion criteria were (1) bilateral MxCI2 transposition; (2) patients presenting with other oral or maxillofacial diseases in addition to teeth transposition, such as cleft lip and palate, giant cysts, multiple teeth; (3) canine was transposed palatally to the lateral incisor; and (4) presence of systemic disease.
All study subjects were photographed before treatment: CBCT images were taken using NewTom VG (QR srl; NewTom, Verona, Italy). The typical imaging parameters were as follows: 110 KV, 1-20 mA (pulse mode), 26-second scanning time with an axial thickness of 0.25 mm, the field of view was 15 × 15 cm, and the voxel size was 0.30 × 0.25 × 0.25 mm. NNT workstation software (QR srl, Verona, Italy) was used to obtain the patients’ original CBCT data; data were exported in digital imaging and communications in medicine format (QR sr1) and imported into Dolphin 11.8 software for 3- dimensional reconstruction and correction of skull position.
Head reorientation was carried out on the CBCT images by 1 examiner using the Dolphin Imaging software. The ANS and PNS points in the sagittal slice were connected; the plane in which the straight line is located is the palatal plane ( Fig 2 ). The following items were measured, or information was gathered to identify variables affecting alveolar bone thickness:
- 1.
Age (years): the patient’s age at the time of CBCT at the beginning of treatment.
- 2.
Gender.
- 3.
The type of transposition was based on the description of MxCI2 transposition by Shapira et al. Incomplete transpositions are when 2 teeth overlap, and the canine’s apical root is still in its normal position; complete transpositions are when the positions of both the crown and the root are switched ( Fig 3 ).
- 4.
The thickness of the transposed canine (mm) is defined as the maximum thickness of the transposed canine in the labiopalatal direction ( Fig 4 ).
- 5.
Height of the transposed canine (mm): defined as the vertical distance between point A and the palatal plane, with a positive value indicating a distance below the palatal plane and a negative value indicating a distance above it. ( Fig 5 , A and B ).
- 6.
The apical height of the transposed lateral incisor (mm) is defined as the vertical distance between the palatal plane and the apex point of the transposed lateral incisor ( Fig 5 , C and D ).
- 7.
Labiopalatal distance from the transposed canine to the apex of the lateral incisor (D in LP): rotate the axial slice such that the tangent of the dental arch is parallel to the coronal slice, then move it to the location of the transposed lateral incisor’s root apex. In this axial slice, measure the distance between the center of the canine and the coronal line as D in LP ( Fig 5 , E and F ).
- 8.
Distomedial distance from the transposed canine to the apex of the lateral incisor (D in DM): in this axial slice, measure the distance between the center of the canine and the sagittal line as D in DM ( Fig 5 , E and F ).
- 9.
The inclination of the transposed lateral incisor (°) is defined as the angle formed by the palatal plane and the long axis of the transposed lateral incisor. The greater the angle, the more labially inclined the transposed lateral incisor ( Fig 5 , G and H ).
The dependent variable was the measurement of the total alveolar bone thickness in the plane of the affected lateral incisor root apex ( Fig 5 , I and J ). In addition, the maximum thickness of 2 lateral incisors, the apical height of the lateral incisors on both sides and the labial and palatal alveolar bone thickness of the lateral incisor apex on both sides were all measured independently.
Statistical analysis
Measurements for all study subjects were performed twice by the same individual at 2-week intervals; the mean of the 2 measurements was used for statistical analysis. Descriptive statistics were expressed as mean and standard deviation.
Simple linear regression analyses were used to screen out n variables that were significantly related to total alveolar bone thickness at the affected lateral incisor root apex from 9 variables.
Multiple linear regression analysis was used to evaluate the impact of the n variables on total alveolar bone thickness at the affected lateral incisor root apex. Null and alternative hypotheses are stated as follows.
H0:β1=β2=…=βn=0
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