Low-intensity pulsed ultrasound attenuates replacement root resorption of avulsed teeth stored in dry condition in dogs

Abstract

This study aimed to investigate the effects of low-intensity pulsed ultrasound (LIPUS) on replacement root resorption after replantation of avulsed teeth stored in a dry condition in dogs. A total of 73 premolar roots from four male mongrel dogs were intentionally avulsed with forceps and divided into four groups-HN, HL, DN, and DL-according to storage conditions and whether or not they received LIPUS treatment. Thirty-eight roots were kept in Hanks' Balanced Salt Solution for 30 min (HN and HL groups), whereas the remaining 35 roots were left to dry in the air for an hour (DN and DL groups) prior to replantation. Following replantation, the roots in the HL and DL groups (21 and 18 roots, respectively) received a 20-min daily LIPUS treatment for 2 weeks. The animals were euthanized 4 weeks after the operation. Micro-computed tomography images were acquired for each root and the amount of replacement root resorption was measured three-dimensionally. Histological assessments were also carried out. There was significantly less replacement root resorption for the roots in the DL group compared to the DN group (p < 0.01). Histological findings in the DN group demonstrated evident replacement root resorption, whereas the DL group revealed less severe resorption compared to the DN group. Within the limitations, these results suggest that LIPUS could attenuate the replacement resorption of avulsed teeth stored in a dry condition, thereby improving their prognosis.

Figure 1

Clinical photographs during experimental periods. (a, b) Pre-operation. (c) After root canal treatment. (d) Post-operation. Replanted roots were covered by gingiva and sutured. (e) LIPUS treatment (f, g) 4 weeks after the operation.

Figure 2

Representative serial radiographs and micro-CT images of roots in the HL group. (a) Pre-operation. (b) After root canal treatment. (c) After replantation. (d–f) 4 weeks after the operation. Note that the roots were surrounded by intact lamina dura.

Figure 3

Representative serial radiographs and micro-CT images of roots in the DN group. (a) Pre-operation. (b) After root canal treatment. (c) After replantation. (d–f) 4 weeks after the operation. Note that the lamina dura became indistinct and the evidence of replacement root resorption was seen in the micro-CT images.

Figure 4

Representative micro-CT images and 3D reconstruction for quantitative measurement of the amount of root resorption. The root embedded in the alveolar bone alone was included. (a) Normal root surface without any root resorption. Regular and continuous radiolucent areas between the root surface and the alveolar bone, indicating PDL space, can be seen. (b) Replacement root resorption presenting direct connection between the root surface and the alveolar bone without interposition of a radiolucent area (yellow arrowheads). (c) Surface root resorption presenting craters or holes in the root surface (red arrowheads) (d) Visualization of the root by 3D reconstruction. (e) Distribution of replacement root resorption. (f) Distribution of surface root resorption.

Figure 5

Percentage of root resorption area in each group. (a) Replacement resorption. (b) Surface resorption. Different letters denote significant different among the groups (p < 0.05).

Figure 6

Histologic overview of sections of the replanted roots. (a, b) A root in the HL group, pointing to minimal root resorption. Note that normal periodontium organized PDL with collagen fibers and cementum layer. (c–f) A section of root in the DN group, showing replacement root resorption. (e, f) TRAP staining showed osteoclastic cells (black arrows) confined to the cementum surface. (D dentin, C cementum, PDL periodontal ligament, AB alveolar bone).