Effect of Low-Intensity Pulsed Ultrasound on a Rat Model of Dentin-Dental Pulp Injury and Repair

Ultrasound Therapy: Experiences and Perspectives for Regenerative Medicine

Ultrasound has emerged as a novel tool for clinical applications, particularly in the context of regenerative medicine. Due to its unique physico-mechanical properties, low-intensity ultrasound (LIUS) has been approved for accelerated fracture healing and for the treatment of established non-union, but its utility has extended beyond tissue engineering to other fields, including cell regeneration. Cells and tissues respond to acoustic ultrasound by switching on genetic repair circuits, triggering a cascade of molecular signals that promote cell proliferation, adhesion, migration, differentiation, and extracellular matrix production. LIUS also induces angiogenesis and tissue regeneration and has anti-inflammatory and anti-degenerative effects. Accordingly, the potential application of ultrasound for tissue repair/regeneration has been tested in several studies as a stand-alone treatment and, more recently, as an adjunct to cell-based therapies. For example, ultrasound has been proposed to improve stem cell homing to target tissues due to its ability to create a transitional and local gradient of cytokines and chemokines. In this review, we provide an overview of the many applications of ultrasound in clinical medicine, with a focus on its value as an adjunct to cell-based interventions. Finally, we discuss the various preclinical and clinical studies that have investigated the potential of ultrasound for regenerative medicine.

Three-dimensional printing biotechnology for the regeneration of the tooth and tooth-supporting tissues

The tooth and its supporting tissues are organized with complex three-dimensional (3D) architecture, including the dental pulp with a blood supply and nerve tissues, complex multilayer periodontium, and highly aligned periodontal ligament (PDL). Mimicking such 3D complexity and the multicellular interactions naturally existing in dental structures represents great challenges in dental regeneration. Attempts to construct the complex system of the tooth and tooth-supporting apparatus (i.e., the PDL, alveolar bone, and cementum) have made certain progress owing to 3D printing biotechnology. Recent advances have enabled the 3D printing of biocompatible materials, seed cells, and supporting components into complex 3D functional living tissue. Furthermore, 3D bioprinting is driving major innovations in regenerative medicine, giving the field of regenerative dentistry a boost. The fabrication of scaffolds via 3D printing is already being performed extensively at the laboratory bench and in clinical trials; however, printing living cells and matrix materials together to produce tissue constructs by 3D bioprinting remains limited to the regeneration of dental pulp and the tooth germ. This review summarizes the application of scaffolds for cell seeding and biofabricated tissues via 3D printing and bioprinting, respectively, in the tooth and its supporting tissues. Additionally, the key advantages and prospects of 3D bioprinting in regenerative dentistry are highlighted, providing new ideas for dental regeneration.

Effect of Low-Intensity Pulsed Ultrasound on the Expression of Calcium Ion Transport-Related Proteins during Tertiary Dentin Formation

Low-intensity pulsed ultrasound (LIPUS) is known for its positive effect on bone healing and reparative regeneration. This study investigated whether LIPUS affects reparative progression of the tooth and the expression of calcium ion transport-related proteins in odontoblasts and dental pulp cells using a rat dentin-pulp complex injury model. Forty male adult Sprague-Dawley rats underwent cavity preparation in the right maxillary first molar: 20 received LIPUS irradiation on the cavity-prepared tooth; 20 received LIPUS irradiation on the left maxillary first molar. Rats were randomly allocated into four groups: blank control group, LIPUS group, cavity-prepared group, cavity-prepared + LIPUS group. LIPUS irradiation (frequency: 1.5 MHz, 200-µs pulse width, 1-kHz pulse repetition frequency, 30 mW/cm² spatial averaged temporal averaged intensity) was administered individually for 20 min daily. Rats were sacrificed 1, 3, 7 and 14 d post-operation. The histopathological and cellular morphologic changes in the dentin-pulp complex were detected with hematoxylin and eosin staining. Expression of calcium ion transport-related proteins (Cav1.2, NCX1 and TRPV1) was determined with immunohistochemical staining and imaging analysis. Histopathological analysis revealed obvious reparative dentin formation at day 14 in the cavity-prepared + LIPUS group compared with the other groups. Expression levels of Cav1.2, NCX1 and TRPV1 increased significantly by 22%, 53% and 23%, respectively, at day 1 and increased significantly by 23%, 27% and 22%, respectively, at day 3 in the cavity-prepared + LIPUS group (p <0.05) compared with the cavity-prepared group. LIPUS has a positive effect on the expression of calcium transport-related proteins during early-stage dentin injury and facilitates tertiary dentin formation; the mechanism for this likely relates to the inflammatory reaction and a mechanical effect.