BACKGROUND:Clinical studies suggest that both bone quality and excessive crown-to-implant ratio are factors that affect the success rate of implant surgery,but there is no consensus on how large the crown-to-implant ratio under each bone quality will affect the prognosis of implant repair.OBJECTIVE:To analyze the stress and strain of bone tissue around implant restorations with different crown-to-implant ratios under different bone types after stress loading using three-dimensional finite element method.Combined with the Frost bone mechanics regulation system theory,the physiological limits of bone strain were observed for each bone type within a certain range of crown to implant ratios.METHODS:Cone beam CT data were selected from a patient to establish solid bone block models with four different bone types(class Ⅰ bone:cortical bone thickness 3 mm+dense cancellous bone,class Ⅱ bone:cortical bone thickness 2 mm+relatively dense cancellous bone,class Ⅲ bone:cortical bone thickness 1 mm+relatively low-density cancellous bone,class Ⅳ bone:cortical bone thickness 1 mm+low-density cancellous bone).Implant restorations with five different crown-to-implant ratios(1,1.5,2,2.5,and 3)were created on each bone block model,for a total of 20 models.Vertical and oblique forces were applied to the dental crown to observe the von Mises stress values,strains,and displacement of the cortical and cancellous bones,as well as the degree of implant displacement.RESULTS AND CONCLUSION:(1)In the class Ⅰ bone model,when the crown-to-implant ratio reached 3 under oblique loading,the cortical bone strain exceeded the physiological limit.In the class Ⅱ bone model,under oblique loading,when the crown-to-implant ratio reached 2.5,the cortical bone strain exceeded the physiological limit.In the class Ⅲ bone model,under oblique loading,cortical bone exceeded the physiological limit when the crown-to-implant ratio reached 2.5,while cancellous bone reached the critical physiological limit at 1.In the class Ⅳ bone model,under oblique loading,when the crown-to-implant ratio reached 1.5,2,2.5,and 3,the cortical bone strain exceeded the physiological limit.In the class Ⅳ bone model,all five crown-to-implant ratios of cancellous bone exceeded physiological limits.(2)Under vertical load,the cancellous bone strain exceeded the physiological limit when the crown-root ratio reached 1,2,2.5,and 3 in the class Ⅲ bone model,and when the cancellous bone strain of the five crown-root ratios in the class Ⅳ bone model exceeded the physiological limit.(3)Under oblique or vertical load,the implant displacement of the 20 groups of models did not exceed 100 μm.(4)From the perspective of biomechanics,when patients with insufficient bone height choose implant restoration,the crown-root ratio that class Ⅰ bone can tolerate is up to 2.5 times,the crown-root ratio that class Ⅱ bone can tolerate is up to 2 times,and the crown-root ratio that class Ⅲ and class Ⅳ bones can tolerate is up to 1 times due to excessive strain of cancellous bone;but the crown-root ratio that cortical bone in class Ⅲ bone can tolerate is up to 2 times.Whether class Ⅲ bone can tolerate implant restoration with a high crown-root ratio and whether cancellous bone can tolerate higher strains needs further study.

BACKGROUND:Clinical studies suggest that both bone quality and excessive crown-to-implant ratio are factors that affect the success rate of implant surgery,but there is no consensus on how large the crown-to-implant ratio under each bone quality will affect the prognosis of implant repair.OBJECTIVE:To analyze the stress and strain of bone tissue around implant restorations with different crown-to-implant ratios under different bone types after stress loading using three-dimensional finite element method.Combined with the Frost bone mechanics regulation system theory,the physiological limits of bone strain were observed for each bone type within a certain range of crown to implant ratios.METHODS:Cone beam CT data were selected from a patient to establish solid bone block models with four different bone types(class Ⅰ bone:cortical bone thickness 3 mm+dense cancellous bone,class Ⅱ bone:cortical bone thickness 2 mm+relatively dense cancellous bone,class Ⅲ bone:cortical bone thickness 1 mm+relatively low-density cancellous bone,class Ⅳ bone:cortical bone thickness 1 mm+low-density cancellous bone).Implant restorations with five different crown-to-implant ratios(1,1.5,2,2.5,and 3)were created on each bone block model,for a total of 20 models.Vertical and oblique forces were applied to the dental crown to observe the von Mises stress values,strains,and displacement of the cortical and cancellous bones,as well as the degree of implant displacement.RESULTS AND CONCLUSION:(1)In the class Ⅰ bone model,when the crown-to-implant ratio reached 3 under oblique loading,the cortical bone strain exceeded the physiological limit.In the class Ⅱ bone model,under oblique loading,when the crown-to-implant ratio reached 2.5,the cortical bone strain exceeded the physiological limit.In the class Ⅲ bone model,under oblique loading,cortical bone exceeded the physiological limit when the crown-to-implant ratio reached 2.5,while cancellous bone reached the critical physiological limit at 1.In the class Ⅳ bone model,under oblique loading,when the crown-to-implant ratio reached 1.5,2,2.5,and 3,the cortical bone strain exceeded the physiological limit.In the class Ⅳ bone model,all five crown-to-implant ratios of cancellous bone exceeded physiological limits.(2)Under vertical load,the cancellous bone strain exceeded the physiological limit when the crown-root ratio reached 1,2,2.5,and 3 in the class Ⅲ bone model,and when the cancellous bone strain of the five crown-root ratios in the class Ⅳ bone model exceeded the physiological limit.(3)Under oblique or vertical load,the implant displacement of the 20 groups of models did not exceed 100 μm.(4)From the perspective of biomechanics,when patients with insufficient bone height choose implant restoration,the crown-root ratio that class Ⅰ bone can tolerate is up to 2.5 times,the crown-root ratio that class Ⅱ bone can tolerate is up to 2 times,and the crown-root ratio that class Ⅲ and class Ⅳ bones can tolerate is up to 1 times due to excessive strain of cancellous bone;but the crown-root ratio that cortical bone in class Ⅲ bone can tolerate is up to 2 times.Whether class Ⅲ bone can tolerate implant restoration with a high crown-root ratio and whether cancellous bone can tolerate higher strains needs further study.

BACKGROUND:The development of calcium phosphate bone cement is limited due to its poor mechanical properties and weak osteogenic ability.Silicate bioactive glass is highly favored due to its excellent biological activity and osteogenic ability.Simultaneously,fiber structures can enhance the mechanical strength of materials.OBJECTIVE:To investigate the mechanical properties,biocompatibility,and osteogenic effect of silicate bioactive glass fiber composite calcium phosphate bone cement.METHODS:Different mass percentages(0％,10％,and 20％)of silicate bioactive glass fiber were added to the solid phase of calcium phosphate bone cement,mixed with the liquid phase and cured for 48 hours to obtain silicate bioactive glass fiber composite calcium phosphate bone cement.The mechanical properties,setting time,and ion precipitation of the cement were characterized.The three groups of bone cement extracts were co-cultured with MC3T3-E1 cells.The cell compatibility of the materials was evaluated by CCK-8 assay,live/dead staining,and phalloidin staining.After osteogenic induction,the osteogenic induction ability of the materials was evaluated by alkaline phosphatase staining,alizarin red staining,RUNX2 immunofluorescence staining,and RT-PCR.RESULTS AND CONCLUSION:(1)With the increase of silicate bioactive glass fiber content,the compressive strength and flexural strength of bone cement increased,and the setting time was prolonged.When bone cement was immersed in simulated body fluid,the precipitation of silicon ions,calcium ions,and phosphorus ions could be detected.Moreover,with the increase of silicate bioactive glass fiber content,the mass concentration of silicon ions and phosphorus ions released by bone cement increased,and the mass concentration of calcium ions decreased.(2)Live/dead staining and phalloidin staining results exhibited that silicate bioactive glass fiber composite calcium phosphate bone cement had no toxic effect on MC3T3-E1 cells.CCK-8 assay results showed that silicate bioactive glass fiber composite calcium phosphate bone cement could promote the proliferation of MC3T3-E1 cells.(3)With the increase of silicate bioactive glass fiber content in bone cement,the alkaline phosphatase activity and extracellular calcium deposition of MC3T3-E1 cells increased,the expression of RUNX2 protein increased,and the expression of alkaline phosphatase,osteocalcin,osteopontin,and RUNX2 mRNA expression increased.(4)The results indicate that silicate bioactive glass fibers can enhance the mechanical properties and osteogenic induction ability of calcium phosphate bone cement,among which 20％silicate bioactive glass fibers have a more obvious effect.

Objective:To study the consistency between post-processing bone mineral density(BMD)values of multi-slice spiral computed tomography(MSCT)scan and the BMD value of quantitative computed tomography(QCT)for lumbar vertebra,so as to explore the feasibility of utilizing MSCT scan-based post-processing BMD values for lumbar vertebra in clinical practice.Methods:The MSCT equipment and QCT equipment were respectively adopted to conduct imaging scan for the L2-L4 of lumber vertebra of QRM-ESP145 European Spine Phantom(ESP),and L2-L4 of lumbar vertebra of adult sheep,and L2-L4 of lumbar vertebra of adult volunteer.The L2-L4 of ESP lumber vertebra and L2-L4 of lumbar vertebra of adult sheep were scanned respectively MSCT and QCT for three times,so as to measure BMD values.The L2-L4 of lumbar vertebrae of volunteers were scanned respectively by the two methods for one time according to the standard of clinical examination,which were reconstructed by three times so as to obtain mean of them.The BMD values of QCT scan were set as control group,and the BMD values of MSCT scan were set as experiment group.The experiment group was further divided into experiment 1 group[two dimension(2D)regional volumetric BMD values of the lumbar vertebra]and experiment 2 group[three dimension(3D)global volumetric BMD post-processing of the lumbar vertebra]according to the reliability of experiment.Then,the consistency between the MSCT 3D post-processing BMD values of three groups and QCT-measured BMD values was compared and analyzed.Results:The MSCT 3D post-processing BMD values of L2-L4 of ESP lumbar vertebra of three groups were respectively(120.83±0.97),(199.57±0.54)and(119.19±1.04)mg/cm3,and that of L2-L4 of lumbar vertebra of adult sheep of three groups were respectively(414.89±1.72),(410.50±0.77)and(420.25±2.71)mg/cm3,and that of L2-L4 of lumbar vertebra of volunteer were respectively(141.22±0.09),(137.38±0.37)and(152.03±1.03)mg/cm3.There were not statistically significant differences in BMD values between MSCT examination and QCT examination(P＞0.05).Conclusion:MSCT 3D post-processing BMD values on lumbar vertebra has high consistency with that of QCT measurements,which post-processing technique can replace QCT to conduct BMD examination,and reduce unnecessary radiation exposure and examination costs for patients.

Objective:To analyze the clinical efficacy and learning curve for robot-assisted cortical bone trajectory (CBT) screw fixation performed by surgeons with different seniority in the treatment of lumbar degenerative disease.Methods:The clinical data of 91 lumbar degenerative disease patients underwent robot-assisted CBT screw fixation from August 2020 to December 2022 in Beijing Shijitan Hospital, Capital Medical University were retrospectively analyzed. Among them, 48 patients underwent surgery performed by the same senior surgeon (senior group), with a total of 234 CBT screws were placed; while 43 patients underwent surgery performed by the same junior surgeon (junior group), with a total of 206 CBT screws were placed. The surgical related indexes, functional improvement score, lower back pain and lower limb radiation pain scores, acceptable nail insertion rate, non invasion rate of facet joints and incidence of postoperative complications were compared between two groups. The functional improvement score was evaluated using the Japanese Orthopaedic Association (JOA) score, the pain score was evaluated using visual analog score (VAS). The cumulative sum (CUSUM) method was used to depict the learning curve with "single screw placement time" as the observation index.Results:There were no statistical difference in incision length, operation time, intraoperative blood loss and postoperative hospital stay between two groups ( P>0.05). The least squares means of JOA scores 1, 3 and 6 months after surgery in both groups increased significantly compared to baseline, while the least squares means of lower back pain VAS and lower limb radiation pain VAS decreased significantly compared to baseline; there were no statistical differences between two groups ( P>0.05). There were no statistical difference in acceptable nail insertion rate, non invasion rate of facet joints and incidence of postoperative complications between two group ( P>0.05). The CUSUM learning curves were fitting well and the inflection point for senior surgeon corresponded to 18 cases, while it was reached after performing surgery on 21 cases for junior surgeon. Conclusions:Robot-assisted CBT screw fixation performed by surgeons with different seniority could achieve similar clinical outcomes for treating lumbar degenerative disease. The senior surgeons are able to complete the initial learning stage faster than the junior surgeons, but there is not much difference in the number of surgeries performed the learning curve.

Objective:To compare the effectiveness and safety between robot-assisted percutaneous kyphoplasty (PKP) and traditional fluoroscopy-assisted PKP in the treatment of dual-segment recurrent osteoporotic vertebral compression fracture (OVCF) including in situ vertebral fracture.Methods:The clinical data of 33 patients with dual-segment recurrent OVCF including in situ vertebral fracture from January 2016 to January 2023 in Beijing Shijitan Hospital Affiliated to Capital Medical University were retrospectively analyzed. All the patients were treated with PKP. Among them, 14 patients were treated with robot-assisted surgery (robot-assisted group), and 19 patients were treated with fluoroscopy-assisted surgery (fluoroscopy-assisted group). The total surgical time, preparation time and number of fluoroscopy were recorded. The in situ and other fracture vertebral operation time, number of punctures, amount of bone cement injection, bone cement filling effect, bone cement leakage, pedicle wall breakthrough and other special intraoperative situations were separately recorded. The visual analogue score (VAS) before surgery and 1 d, 3 months after surgery was recorded.Results:The preparation time in robot-assisted group was significantly longer than that in fluoroscopy-assisted group: (30.8 ± 6.9) min vs. (19.1 ± 4.5) min, the number of fluoroscopy was significantly lower than that in fluoroscopy-assisted group: (17.1 ± 4.1) times vs. (41.0 ± 6.3) times, and there were statistical differences ( P<0.01 and <0.05); there were no statistical differences in total surgical time and VAS at any time point between the two groups ( P>0.05). For the in situ fracture segment, the operation time and number of punctures in robot-assisted group were significantly lower than those in fluoroscopy-assisted group: (15.4 ± 2.8) min vs. (22.0 ± 5.5) min and (1.1 ± 0.4) times vs. (2.4 ± 1.2) times, the amount of bone cement injection was significantly higher than those in fluoroscopy-assisted group: (2.36 ± 0.75) ml vs. (1.79 ± 0.69) ml, the filling effect of bone cement was significantly better than that in fluoroscopy-assisted group, and there were statistical differences ( P<0.01 and <0.05); there were no statistical difference in bone cement leakage and pedicle wall breakthrough between the two groups ( P>0.05). For the other fracture segment, the operation time in robot-assisted group was significantly shorter than that in fluoroscopy-assisted group: (13.8 ± 3.8) min vs. (19.2 ± 6.4) min, and there was statistical difference ( P<0.01); there were no statistical difference in number of punctures, amount of bone cement injection, filling effect of bone cement, bone cement leakage and pedicle wall breakthrough between the two groups ( P>0.05). Conclusions:Robot-assisted PKP in the treatment of dual-segment OVCF including in situ vertebral fracture, could reduce operation time, minimize punctures and fluoroscopy numbers, and provide superior bone cement filling results.

BACKGROUND:The development of calcium phosphate bone cement is limited due to its poor mechanical properties and weak osteogenic ability.Silicate bioactive glass is highly favored due to its excellent biological activity and osteogenic ability.Simultaneously,fiber structures can enhance the mechanical strength of materials.OBJECTIVE:To investigate the mechanical properties,biocompatibility,and osteogenic effect of silicate bioactive glass fiber composite calcium phosphate bone cement.METHODS:Different mass percentages(0％,10％,and 20％)of silicate bioactive glass fiber were added to the solid phase of calcium phosphate bone cement,mixed with the liquid phase and cured for 48 hours to obtain silicate bioactive glass fiber composite calcium phosphate bone cement.The mechanical properties,setting time,and ion precipitation of the cement were characterized.The three groups of bone cement extracts were co-cultured with MC3T3-E1 cells.The cell compatibility of the materials was evaluated by CCK-8 assay,live/dead staining,and phalloidin staining.After osteogenic induction,the osteogenic induction ability of the materials was evaluated by alkaline phosphatase staining,alizarin red staining,RUNX2 immunofluorescence staining,and RT-PCR.RESULTS AND CONCLUSION:(1)With the increase of silicate bioactive glass fiber content,the compressive strength and flexural strength of bone cement increased,and the setting time was prolonged.When bone cement was immersed in simulated body fluid,the precipitation of silicon ions,calcium ions,and phosphorus ions could be detected.Moreover,with the increase of silicate bioactive glass fiber content,the mass concentration of silicon ions and phosphorus ions released by bone cement increased,and the mass concentration of calcium ions decreased.(2)Live/dead staining and phalloidin staining results exhibited that silicate bioactive glass fiber composite calcium phosphate bone cement had no toxic effect on MC3T3-E1 cells.CCK-8 assay results showed that silicate bioactive glass fiber composite calcium phosphate bone cement could promote the proliferation of MC3T3-E1 cells.(3)With the increase of silicate bioactive glass fiber content in bone cement,the alkaline phosphatase activity and extracellular calcium deposition of MC3T3-E1 cells increased,the expression of RUNX2 protein increased,and the expression of alkaline phosphatase,osteocalcin,osteopontin,and RUNX2 mRNA expression increased.(4)The results indicate that silicate bioactive glass fibers can enhance the mechanical properties and osteogenic induction ability of calcium phosphate bone cement,among which 20％silicate bioactive glass fibers have a more obvious effect.

Objective:To analyze the clinical efficacy and learning curve for robot-assisted cortical bone trajectory (CBT) screw fixation performed by surgeons with different seniority in the treatment of lumbar degenerative disease.Methods:The clinical data of 91 lumbar degenerative disease patients underwent robot-assisted CBT screw fixation from August 2020 to December 2022 in Beijing Shijitan Hospital, Capital Medical University were retrospectively analyzed. Among them, 48 patients underwent surgery performed by the same senior surgeon (senior group), with a total of 234 CBT screws were placed; while 43 patients underwent surgery performed by the same junior surgeon (junior group), with a total of 206 CBT screws were placed. The surgical related indexes, functional improvement score, lower back pain and lower limb radiation pain scores, acceptable nail insertion rate, non invasion rate of facet joints and incidence of postoperative complications were compared between two groups. The functional improvement score was evaluated using the Japanese Orthopaedic Association (JOA) score, the pain score was evaluated using visual analog score (VAS). The cumulative sum (CUSUM) method was used to depict the learning curve with "single screw placement time" as the observation index.Results:There were no statistical difference in incision length, operation time, intraoperative blood loss and postoperative hospital stay between two groups ( P>0.05). The least squares means of JOA scores 1, 3 and 6 months after surgery in both groups increased significantly compared to baseline, while the least squares means of lower back pain VAS and lower limb radiation pain VAS decreased significantly compared to baseline; there were no statistical differences between two groups ( P>0.05). There were no statistical difference in acceptable nail insertion rate, non invasion rate of facet joints and incidence of postoperative complications between two group ( P>0.05). The CUSUM learning curves were fitting well and the inflection point for senior surgeon corresponded to 18 cases, while it was reached after performing surgery on 21 cases for junior surgeon. Conclusions:Robot-assisted CBT screw fixation performed by surgeons with different seniority could achieve similar clinical outcomes for treating lumbar degenerative disease. The senior surgeons are able to complete the initial learning stage faster than the junior surgeons, but there is not much difference in the number of surgeries performed the learning curve.

Objective:To compare the effectiveness and safety between robot-assisted percutaneous kyphoplasty (PKP) and traditional fluoroscopy-assisted PKP in the treatment of dual-segment recurrent osteoporotic vertebral compression fracture (OVCF) including in situ vertebral fracture.Methods:The clinical data of 33 patients with dual-segment recurrent OVCF including in situ vertebral fracture from January 2016 to January 2023 in Beijing Shijitan Hospital Affiliated to Capital Medical University were retrospectively analyzed. All the patients were treated with PKP. Among them, 14 patients were treated with robot-assisted surgery (robot-assisted group), and 19 patients were treated with fluoroscopy-assisted surgery (fluoroscopy-assisted group). The total surgical time, preparation time and number of fluoroscopy were recorded. The in situ and other fracture vertebral operation time, number of punctures, amount of bone cement injection, bone cement filling effect, bone cement leakage, pedicle wall breakthrough and other special intraoperative situations were separately recorded. The visual analogue score (VAS) before surgery and 1 d, 3 months after surgery was recorded.Results:The preparation time in robot-assisted group was significantly longer than that in fluoroscopy-assisted group: (30.8 ± 6.9) min vs. (19.1 ± 4.5) min, the number of fluoroscopy was significantly lower than that in fluoroscopy-assisted group: (17.1 ± 4.1) times vs. (41.0 ± 6.3) times, and there were statistical differences ( P<0.01 and <0.05); there were no statistical differences in total surgical time and VAS at any time point between the two groups ( P>0.05). For the in situ fracture segment, the operation time and number of punctures in robot-assisted group were significantly lower than those in fluoroscopy-assisted group: (15.4 ± 2.8) min vs. (22.0 ± 5.5) min and (1.1 ± 0.4) times vs. (2.4 ± 1.2) times, the amount of bone cement injection was significantly higher than those in fluoroscopy-assisted group: (2.36 ± 0.75) ml vs. (1.79 ± 0.69) ml, the filling effect of bone cement was significantly better than that in fluoroscopy-assisted group, and there were statistical differences ( P<0.01 and <0.05); there were no statistical difference in bone cement leakage and pedicle wall breakthrough between the two groups ( P>0.05). For the other fracture segment, the operation time in robot-assisted group was significantly shorter than that in fluoroscopy-assisted group: (13.8 ± 3.8) min vs. (19.2 ± 6.4) min, and there was statistical difference ( P<0.01); there were no statistical difference in number of punctures, amount of bone cement injection, filling effect of bone cement, bone cement leakage and pedicle wall breakthrough between the two groups ( P>0.05). Conclusions:Robot-assisted PKP in the treatment of dual-segment OVCF including in situ vertebral fracture, could reduce operation time, minimize punctures and fluoroscopy numbers, and provide superior bone cement filling results.

Objective:To study the consistency between post-processing bone mineral density(BMD)values of multi-slice spiral computed tomography(MSCT)scan and the BMD value of quantitative computed tomography(QCT)for lumbar vertebra,so as to explore the feasibility of utilizing MSCT scan-based post-processing BMD values for lumbar vertebra in clinical practice.Methods:The MSCT equipment and QCT equipment were respectively adopted to conduct imaging scan for the L2-L4 of lumber vertebra of QRM-ESP145 European Spine Phantom(ESP),and L2-L4 of lumbar vertebra of adult sheep,and L2-L4 of lumbar vertebra of adult volunteer.The L2-L4 of ESP lumber vertebra and L2-L4 of lumbar vertebra of adult sheep were scanned respectively MSCT and QCT for three times,so as to measure BMD values.The L2-L4 of lumbar vertebrae of volunteers were scanned respectively by the two methods for one time according to the standard of clinical examination,which were reconstructed by three times so as to obtain mean of them.The BMD values of QCT scan were set as control group,and the BMD values of MSCT scan were set as experiment group.The experiment group was further divided into experiment 1 group[two dimension(2D)regional volumetric BMD values of the lumbar vertebra]and experiment 2 group[three dimension(3D)global volumetric BMD post-processing of the lumbar vertebra]according to the reliability of experiment.Then,the consistency between the MSCT 3D post-processing BMD values of three groups and QCT-measured BMD values was compared and analyzed.Results:The MSCT 3D post-processing BMD values of L2-L4 of ESP lumbar vertebra of three groups were respectively(120.83±0.97),(199.57±0.54)and(119.19±1.04)mg/cm3,and that of L2-L4 of lumbar vertebra of adult sheep of three groups were respectively(414.89±1.72),(410.50±0.77)and(420.25±2.71)mg/cm3,and that of L2-L4 of lumbar vertebra of volunteer were respectively(141.22±0.09),(137.38±0.37)and(152.03±1.03)mg/cm3.There were not statistically significant differences in BMD values between MSCT examination and QCT examination(P＞0.05).Conclusion:MSCT 3D post-processing BMD values on lumbar vertebra has high consistency with that of QCT measurements,which post-processing technique can replace QCT to conduct BMD examination,and reduce unnecessary radiation exposure and examination costs for patients.