Restoration of teeth after removal of previous restorations is a common problem in the dental clinic. The situation of teeth after removal of previous restoration is complex and often requires multidisciplinary cooperation. However, there is a lack of systematic and concise guidelines for determining the treatment plan for those teeth. Through a combination of restorative clinical experience and the opinions of endodontic specialists, the author systematically described the problems that may exist after the removal of previous restorations in the teeth that have not undergone or have undergone root canal treatment (RCT) and those with post and core restorations. And summarized the corresponding treatment recommendations according to their pulpal and periapical status, the quality of RCT and the presence or absence of post and core restorations. ①For teeth without RCT, the vitality of the pulp, the occurrence of pulpal/periapical disease and the amount of re-preparation need to be assessed to determine whether RCT is necessary. ②For teeth with RCT, if the quality of RCT is good and no periradicular lesion exists, direct restorative treatment can be considered. If the quality of the RCT is unsatisfactory but no periradicular lesion exists, root canal retreatent (re-RCT), follow up or direct restorative treatment should be performed as appropriate and treatment plan can be developed in conjunction with the endodontist if necessary. If the quality of the RCT is unsatisfactory and periradicular lesion exists, re-RCT is necessary before restorative treatment.③For teeth with post and core restorations, if the quality of RCT is good and no periradicular lesion exists, direct restorative treatment can be considered. If the quality of the RCT is unsatisfactory but no periradicular lesion exists, follow up or direct restorative treatment should be performed as appropriate and treatment plan can be developed in conjunction with the endodontist if necessary. If the quality of RCT is unsatisfactory and periradicular lesion exists, for teeth with thin post and thick root canal walls, re-RCT after removal of the post can be attempted. For teeth with thick post and thin root canal walls, preservation of the post and apical surgery can be considered. For the teeth with excessively large defects or extremely poor periodontal conditions, extraction is recommended. The author refined the above recommendations into a set of treatment procedures, aiming to provide a reference for the selection of treatment options for teeth after removal of previous restorations.

Guided bone regeneration (GBR) membranes are extensively utilized in dental implantation. However, the existing GBR membranes showed insufficient space-maintaining capability and poor bone promoting ability, affecting the effectiveness of clinical bone augmentation, which in turn resulted in poor implant outcomes and even failure. In this study, we designed a novel magnesium reinforced sandwich structured composite membrane, consisting of an inner magnesium scaffold and a PLGA/collagen hybrid (mixture of poly(lactic-co-glycolic acid) and collagen) top and bottom layer. The magnesium scaffold provided mechanical support and released Mg²⁺ to enhance osteogenesis. The PLGA/collagen hybrid regulated membrane degradation and improved biocompatibility, promoting cell adhesion and proliferation (P < 0.05). The PLGA/collagen hybrid regulated the release of magnesium ions, such that the MgP10C (mass ratios of PLGA and collagen =100:10) group showed the best in vitro osteogenic effect. Further mechanism exploration confirmed that MgP10C membranes significantly enhanced bone defect repair via the MAPK/ERK 1/2 pathway by the Mg²⁺ released from the composite membranes. In rat calvarial defect and rabbit alveolar defect model (P < 0.05), the in vivo osteogenic effect of the MgP10C group was superior to that of other groups. Finite element analysis models validated the support effect of composite membranes, demonstrating lower stress and a significant reduction in strain on the bone graft in the MgP10C group. In conclusion, the magnesium-reinforced sandwich structure composite membrane, with its space-maintaining properties and osteoinductive activity, represents a new strategy for GBR and enhancing osteogenic potential that meets directly clinical needs.

In bone tissue engineering, polycaprolactone (PCL) is a promising material with good biocompatibility, but its poor degradation rate, mechanical strength, and osteogenic properties limit its application. In this study, we developed an Mg-1Ca/polycaprolactone (Mg-1Ca/PCL) composite scaffolds to overcome these limitations. We used a melt blending method to prepare Mg-1Ca/PCL composites with Mg-1Ca alloy powder mass ratios of 5, 10, and 20 wt%. Porous scaffolds with controlled macro- and microstructure were printed using the fused deposition modeling method. We explored the mechanical strength, biocompatibility, osteogenesis performance, and molecular mechanism of the Mg-1Ca/PCL composites. The 5 and 10 wt% Mg-1Ca/PCL composites were found to have good biocompatibility. Moreover, they promoted the mechanical strength, proliferation, adhesion, and osteogenic differentiation of human bone marrow stem cells (hBMSCs) of pure PCL. In vitro degradation experiments revealed that the composite material stably released Mg²⁺ ions for a long period; it formed an apatite layer on the surface of the scaffold that facilitated cell adhesion and growth. Microcomputed tomography and histological analysis showed that both 5 and 10 wt% Mg-1Ca/PCL composite scaffolds promoted bone regeneration bone defects. Our results indicated that the Wnt/β-catenin pathway was involved in the osteogenic effect. Therefore, Mg-1Ca/PCL composite scaffolds are expected to be a promising bone regeneration material for clinical application.

Statement of significance: Bone tissue engineering scaffolds have promising applications in the regeneration of critical-sized bone defects. However, there remain many limitations in the materials and manufacturing methods used to fabricate scaffolds. This study shows that the developed Ma-1Ca/PCL composites provides scaffolds with suitable degradation rates and enhanced boneformation capabilities. Furthermore, the fused deposition modeling method allows precise control of the macroscopic morphology and microscopic porosity of the scaffold. The obtained porous scaffolds can significantly promote the regeneration of bone defects.