Objective To investigate the damage characteristics of peri-implant bones with varying densities under impact and occlusal forces using numerical simulation.Methods A finite element model of the microstructure of an implant and bones with different densities was established.Impact and occlusal forces were applied sequentially to the implant.A user material subroutine was created for failure judgment using stress-based failure criteria,enabling the analysis of bone damage caused by impact and occlusal forces.Results No cortical bone damage was observed in bones of varying densities under impact force.Damage primarily occurred in the trabecular bone at the base of the implant,with the extent of damage worsening as bone density decreased.Additionally,the number of failed bone elements generated by the damage increased with reduced bone density.Bone tissues with pre-existing impact damage sustained secondary damage when subjected to occlusal force:the bonding interface between the implant and cortical bone was damaged,leading to implant displacement and fracture of peri-implant trabecular bone.The damage caused by occlusal force also worsened as bone density decreased.Conclusions The degree of damage from impact and occlusal forces is correlated with bone density,with damage worsening as bone density decreases.This underscores the protective role of cortical bone.The application of occlusal force exacerbates bone tissue damage,leading to implant displacement when the cortical bone is damaged.In clinical practice,patients with a history of impact damage should undergo thorough examination and evaluation.The occlusal force borne by damaged bones should be reduced;if necessary,the implant should be removed and reinserted after re-establishment of osseointegration.

Objective To investigate the damage characteristics of peri-implant bones with varying densities under impact and occlusal forces using numerical simulation.Methods A finite element model of the microstructure of an implant and bones with different densities was established.Impact and occlusal forces were applied sequentially to the implant.A user material subroutine was created for failure judgment using stress-based failure criteria,enabling the analysis of bone damage caused by impact and occlusal forces.Results No cortical bone damage was observed in bones of varying densities under impact force.Damage primarily occurred in the trabecular bone at the base of the implant,with the extent of damage worsening as bone density decreased.Additionally,the number of failed bone elements generated by the damage increased with reduced bone density.Bone tissues with pre-existing impact damage sustained secondary damage when subjected to occlusal force:the bonding interface between the implant and cortical bone was damaged,leading to implant displacement and fracture of peri-implant trabecular bone.The damage caused by occlusal force also worsened as bone density decreased.Conclusions The degree of damage from impact and occlusal forces is correlated with bone density,with damage worsening as bone density decreases.This underscores the protective role of cortical bone.The application of occlusal force exacerbates bone tissue damage,leading to implant displacement when the cortical bone is damaged.In clinical practice,patients with a history of impact damage should undergo thorough examination and evaluation.The occlusal force borne by damaged bones should be reduced;if necessary,the implant should be removed and reinserted after re-establishment of osseointegration.

Objective To investigate the dynamic mechanical responses and damage characteristics of peri-implant bone structures subjected to impact load.Methods A finite element model of the peri-implant bone microstructure was established,and an initial velocity was applied to the rigid body to simulate the impact load.A stress failure criterion was employed and a user-material subroutine was developed to assess failure.Subsequently,bone damage after the impact load was analyzed according to the material subroutine.Results After the impact load,the stress on the cortical bone increased rapidly,reaching a peak value(16.01 MPa)immediately.In contrast,the stress on the trabecular bone at the bottom of the implant reached its peak value(5.85 MPa)at 0.1 μs.The impact load resulted in stress waves that propagated and diffused within the bone structure,causing changes in the bone structure damage over time.The generated impact energy could be absorbed and dissipated by the trabecular bone through deformation.The deformed trabecular bone experienced damage and failure upon reaching the yield limit,whereas the cortical bone did not experience damage or failure under an impact load.Conclusions Structural changes in the trabecular bone should be considered in patients with impact damage.The numerical model established in this study can effectively predict bone impact damage by combining the structural mechanical properties and geometric characteristics of the bones.These findings can serve as a reference for assessing bone damage and post-damage treatment in patients subjected to impact loads in clinical practice.

Patients with impaired quality of life associated with xerostomia need long-term treatment, and a nerve stimulator has the advantage of providing natural saliva and long-term management for patients with xerostomia by electrically stimulating the relevant secretory nerves to promote saliva production. A number of clinical trials have preliminarily demonstrated the efficacy of nerve electrical stimulation in the treatment of xerostomia. However, electrical stimulation has not yet become the mainstream treatment for xerostomia. Large prospective randomized controlled clinical trials are still needed to confirm its long-term effectiveness and safety. In addition, the design of nerve stimulators is of great significance for clinical application. The large volume and inconvenient treatment associated with the extra oral nerve stimulator and the first generation intraoral nerve stimulator hinder their clinical application and popularization. The second- and third-generation intraoral nerve stimulator devices are small, convenient to use and have great application prospects. Research on electrical nerve stimulators for xerostomia treatment is mainly concentrated in European and American countries, while there is very little domestic research. It is urgent to master the core technology for the research and development of electrical nerve stimulators. The innovation of miniaturization, efficient power supply, data feedback and packaging will be the key issues of electrical nerve stimulators in the future. In this paper, the treatment and research of electrical nerve stimulation for xerostomia are reviewed to provide a reference for related basic research and the clinical application of electrical stimulators treating xerostomia in China.

Objective:To investigate the surface characterization,cell adhension and proliferation of ultrafine grained titanium (UFG Ti) after different sand blasting and acid-etching(SLA).Methods:The billets of UFG Ti and commercially pure titanium Ti(CP Ti) were incised into cylindrical specimens with 7 mm in diameter and 2 mm in height.The specimens were sand blasted at the air pressure of 0.2,0.4,0.6 and 0.8 MPa respectively(n =10) and then acid-etched.The surface morphology,roughness and surface wettability of the specimens were examined.Rat embryo osteoblasts MC3T3-E1 were cultured on the speciments for 1 d,3 d and 5 d respectively,the cell morphology and cell density were observed.Results:The different hierarchical porous topographies were formed on the surface of UFG and CP Ti after modified by SLA.The sizes of blasted holes on the surface and the surface roughness of both materials increased with the increase of blast pressure,but the values of UFG Ti were lower than those of CP Ti correspondingly(P ＜ 0.05).The surface wettability of them was also changed with the blast pressure,but the values of UFG Ti was significantly smaller than those of CP Ti(P ＜ 0.05).When the blast pressure was 0.6 Mpa,the UFG Ti exhibited excellent wettability,the cell density was the highest,the morphology of MC3T3-E1 cells on UFG Ti was superior to that on CP Ti.Conclusion:UFG Ti exhibits proper surface morphology,roughness and excellent wettability,which is more appropriate for adhension and proliferation of MC3T3-E1 cells after modification by SLA at blast pressure of 0.6 Mpa.