Comparison of anterior and posterior mini-implant-assisted maxillary incisor intrusion: Root resorption and treatment efficiency

Abstract

Objective: To compare, through cone-beam computed tomography (CBCT), the root resorption and treatment efficiency of two different mini-implant-assisted modalities in intruding the maxillary incisors.

Materials and methods: Thirty-two adults who had deep bite and elongated maxillary incisors were randomly allocated to two groups: anterior mini-implant group (AMG) and posterior mini-implant group (PMG). In the AMG, approximately 40 g of force was applied per side with elastic chains from mini-implants placed between the lateral incisors and canines and in the PMG, with beta-titanium wires from mini-implants placed between the second premolars and first molars. This study was conducted on CBCT scans taken before intrusion and after 4 months of intrusion. Data were analyzed by means of a paired t-test, independent t-test, and Pearson's correlation test.

Results: One patient was excluded from the AMG due to mini-implant loosening. While the incisors showed a significant reduction in length and volume, this amount was greater in the AMG, especially in the central incisors (P < .05). Together with the mean intrusion rates of 0.62 and 0.39 mm/mo in the AMG and PMG respectively, the center of resistance of the incisors showed distal movement with labial tipping; these changes were greater in the PMG (P < .001). Volumetric root resorption was correlated with the amount of intrusion (P < .05).

Conclusions: Intrusion anchoring from posterior mini-implants is preferred in cases of upright incisors, as the use of such mechanics directs the roots into the spongiosa where they undergo less root resorption and more labial tipping.

Keywords: Cone-beam computed tomography; Incisor intrusion; Mini-implant.

Figure 1.

Frontal and lateral views of the intrusive mechanics applied to the AMG and PMG.

Figure 2.

Linear and angular CBCT measurements: (1) 1 length, distance from apex to cementoenamel junction on long axis of the tooth (carried out for all the incisors); (2) 1-PP, angle between long axis of upper central incisor and palatal plane; (3) C_R-PP, perpendicular distance from C_R of the central incisor to palatal plane; (4) C_R-T, perpendicular distance from C_R of the central incisor to T plane (plane passing through posterior nasal spine and perpendicular to the palatal plane).

Figure 3.

Manual segmentation in axial, coronal, and sagittal slices.

Figure 4.

Volumetric reconstruction after manual segmentation.

Figure 5.

Volumetric measurements: (A) Reconstruction of whole tooth. (B) Separation of root from the crown. (C) Volume calculated.