Material and nanomechanical properties of bone structural units of cortical and trabecular iliac bone tissues from untreated postmenopausal osteoporotic women.

The differences in bone nanomechanical properties between cortical (Ct) and trabecular (Tb) bone remain uncertain, whereas knowing the respective contribution of each compartment is critical to understand the origin of bone strength. Our purpose was to compare bone mechanical and intrinsic properties of Ct and Tb compartments, at the bone structural unit (BSU) level, in iliac bone taken from a homogeneous untreated human population. Among 60 PMMA-embedded transiliac bone biopsies from untreated postmenopausal osteoporotic women (64 ± 7 year-old), >2000 BSUs were analysed by nanoindentation in physiological wet conditions [indentation modulus (elasticity), hardness, dissipated energy], by Fourier transform infrared (FTIRM) and Raman microspectroscopy (mineral and organic characteristics), and by X-ray microradiography (degree of mineralization of bone, DMB). BSUs were categorized based on tissue age, osteonal (Ost) and interstitial (Int) tissues location and bone compartments (Ct and Tb). Indentation modulus was higher in Ct than in Tb BSUs, both in Ost and Int. dissipated energy was higher in Ct than Tb, in Int BSUs. Hardness was not different between Ct and Tb BSUs. In Ost or Int BSUs, mineral maturity (conversion of non-apatitic into apatitic phosphates) was higher in Ct than in Tb, as well as for collagen maturity (Ost). Mineral content assessed as mineral/matrix (FTIRM and Raman) or as DMB, was lower in Ct than in Tb. Crystallinity (FTIRM) was similar in BSUs from Ct and Tb, and slightly lower in Ct than in Tb when measured by Raman, indicating that the crystal size/perfection was quite similar between Ct and Tb BSUs. The differences found between Ost and Int tissues were much higher than the difference found between Ct and Tb for all those bone material properties. Multiple regression analysis showed that Indentation modulus and dissipated energy were mainly explained by mineral maturity in Ct and by collagen maturity in Tb, and hardness by mineral content in both Ct and Tb. In conclusion, in untreated human iliac bone, Ct and Tb BSUs exhibit different characteristics. Ct BSUs have higher indentation modulus, dissipated energy (Int), mineral and organic maturities than Tb BSUs, without difference in hardness. Although those differences are relatively small compared to those found between Ost and Int BSUs, they may influence bone strength at macroscale.

In vitro retention force changes during cyclic dislodging of three novel attachment systems for implant overdentures with different implant angulations.

OBJECTIVES: This in vitro study aimed to compare changes in retentive force due to cyclic dislodging of three novel un-splinted attachments. MATERIALS AND METHODS: Experimental models simulating a mandibular two-implant overdenture situation, with implants positioned with various interimplant discrepancies (0°, 20°, 40°, and 60°) were fabricated. Three attachment systems were tested, "N": a straight or 15°-angulated stud; "L": a sole straight stud; and "C": a straight or individually angulated stud. All models underwent wet testing and were subjected to 10,000 insertion-removal cycles in a universal testing machine. The mean retentive forces were calculated for cycles 10, 100, 1,000, 5,000, and 10,000. Multiple mixed-effects linear regression models were applied for statistical analyses (⍺ < 0.05). RESULTS: "N" demonstrated an increasing retention until 1,000 cycles, which subsequently diminished back to its initial retention at 10,000 cycles, showing no significant loss during the entire experiment. Statistical models demonstrated no effect of implant angulation on retention, except for 60° after 10,000 cycles (p < .05). "L" showed an early peak at 100 cycles and did not significantly lose retentive force before 5,000 cycles. Angulations of 40° or higher were shown to lead to lower retentive forces (0° vs. 40° cycle 5,000: p < .05; 0° vs. 60° cycle 100: p < .05, ≥cycle 1,000: p < .001). "C" showed stable retentive forces with no significant loss only at 10,000 cycles (all angles: p < .001) or 5,000 cycles (0° vs. 60°: p < .05). CONCLUSIONS: All systems showed retentive forces promising successful clinical use in implant overdentures, even in situations with extremely angulated implants. Specific abutments compensating interimplant angulation maintain retention longer in situations with high axe divergencies.

Influence of different lubricants on the retentive force of LOCATOR(®) attachments - an in vitro pilot study.

OBJECTIVE: The aim of this in vitro pilot study was to evaluate the influence of an artificial saliva (AS) lubricant on the retentive force of a stud-type attachment (LOCATOR(®) ) for implant overdentures (IODs). METHODS: Twenty custom-made models simulating a two-IOD with parallel implant situation were fabricated using LOCATOR(®) attachments. The in vitro testing was carried out with an Instron(®) universal testing machine for a total of 10,000 insertion-removal cycles, for each model, in two different aqueous test mediums (Group 1: 0.9% sodium chloride solution (NaCl), n = 10; Group 2: AS, n = 10). Changes in the mean retentive force (F) were plotted against the cycle numbers #10, #100, #1000, #5000, and #10,000. Mixed regression models were applied for statistical analyses. RESULTS: A mixed regression (not considering interactions) predicted, compared to cycle #10, higher retentive forces at cycles #100 (P < 0.0001), #1000 (P = 0.017), similar forces at #5000 (P = 0.277), and lower forces at #10,000 (P = 0.012); there was no overall effect of the medium (P = 0.159). A second statistical model, employing the interaction term "cycle##medium", confirmed similarly the effect. Although the interaction term was significant at cycle #100 (p = 0.045), there was no significant difference between the two groups (P = 0.140). CONCLUSION: In this in vitro pilot experiment, there was no difference in mean retentive forces of the LOCATOR(®) attachments when tested with either 0.9% NaCl or a Glandosane(®) -like artificial saliva lubricant. A larger scale study may still confirm the superiority of either lubricant for quasiclinical bench experiments.

Influence of implant angulation and cyclic dislodging on the retentive force of two different overdenture attachments - an in vitro study.

OBJECTIVE: This in vitro study evaluated the influence of implant angulations on the retentive behavior of two overdenture attachments during cyclic dislodging. METHODS: Models simulating a two-implant overdenture situation were fabricated. They were divided into five groups based on their simulated implant angulations (Groups: 1 = 0°; 2 = 20°; 3 = 30°; 4 = 40°; and 5 = 60°; n = 90). Each group was further divided into two subgroups based on its attachment system (control attachment: LOCATOR(®) ; test attachment: SFI-Anchor(®) ) except for group 5 which had no LOCATOR(®) group. All models underwent 10,000 insertion-removal cycles in a wet environment. Mean retentive forces were recorded. ANOVA and linear regression models were used for statistical analyses, and the level of significance was at P < 0.05. RESULTS: The ANOVA model revealed an effect of dislodging cycles for both attachments (P = 0.0070). The linear regression model with repeated measures revealed a significant effect of angulation within the LOCATOR(®) groups (0° vs. 20°: P < 0.0001; 0° vs. 30°: P < 0.0001; 0° vs. 40°: P < 0.0001), but was insignificant within the SFI-Anchor(®) groups (0° vs. 20°: P = 0.544; 0° vs. 30°: P = 0.134; 0° vs. 40°: P = 0.254; 0° vs. 60°: P = 0.979). It further revealed a significant increase in the retentive force between the LOCATOR(®) and the SFI-Anchor(®) (20°: P = 0.041; 30°: P < 0.0001; 40°: P < 0.0001), although there was no significant difference between the attachments at 0° (P = 0.623). CONCLUSIONS: This study confirms that the retentive behavior of SFI-Anchor(®) is not influenced by implant axial inclination even at angulations of up to 60°. The SFI-Anchor(®) may therefore be particularly indicated for clinical situations with marked implant axial discrepancies.

Clinical and histological evaluation of postextraction platelet-rich fibrin socket filling: a prospective randomized controlled study.

OBJECTIVES: The aims were to investigate whether the use of platelet-rich fibrin membranes (PRF) for socket filling could improve microarchitecture and intrinsic bone tissue quality of the alveolar bone after premolar extraction and to assess the influence of the surgical procedure before implant placement. MATERIAL AND METHODS: Twenty-three patients requiring premolar extraction followed by implant placement were randomized to three groups: (1) simple extraction and socket filling with PRF, (2) extraction with mucosal flap and socket filling with PRF, and (3) controls with simple extraction without socket filling. Implant placement was performed at week 8, and a bone biopsy was obtained for histomorphometric analysis. RESULTS: Analysis by microcomputed tomography showed better bone healing with improvement of the microarchitecture (P < 0.05) in group 1. This treatment had also a significant effect (P < 0.05) on intrinsic bone tissue quality and preservation of the alveolar width. An invasive surgical procedure with a mucosal flap appeared to completely neutralize the advantages of the PRF. CONCLUSIONS: These results support the use of a minimally traumatic procedure for tooth extraction and socket filling with PRF to achieve preservation of hard tissue.

Strontium ranelate improves implant osseointegration.

INTRODUCTION: Endosseous implantation is a frequent procedure in orthopaedics and dentistry, particularly in the aging population. The incidence of implant failure, however, is high in situations where the bone at the site of implantation is not of optimal quality and quantity. Alterations of bone turnover and changes in intrinsic bone tissue quality have potentially negative effects on optimal osseointegration. Strontium ranelate, which acts on both resorption and formation, and improves biomaterial properties, is hypothesized to improve osseointegration and this hypothesis was tested here. MATERIALS AND METHODS: Titanium implants were inserted into the proximal tibias of thirty 6-month-old Sprague-Dawley female rats. During the 8 weeks following implantation, animals received orally strontium ranelate (SrRan) 5 days a week (625 mg/kg/day) or saline vehicle. Pull-out strength, microCT and nanoindentation were assessed on the implanted tibias. RESULTS: SrRan significantly increased pull-out strength compared to controls (+34%). This was associated with a significant improvement of bone microarchitecture around the implant (BV/TV+36%; Tb.Th+13%; Conn.D+23%) with a more plate-shape structure and an increase in bone-to-implant contact (+19%). Finally, strontium ranelate had a significant beneficial effect on parameters of bone biomaterial properties at both cortical (modulus+11.6%; hardness+13%) and trabecular areas (modulus+7%; hardness+16.5%). CONCLUSIONS: SrRan is an antiosteoporotic agent that increased mechanical fixation of the implant. The improvement of pull-out strength was associated with an improvement of implant osseointegration with both a positive effect on bone microarchitecture and on bone biomaterial properties in the vicinity of the implant. These current results may support potential benefits of strontium ranelate in orthopaedic and dental surgery to enhance osseointegration.

Defective implant osseointegration under protein undernutrition: prevention by PTH or pamidronate.

UNLABELLED: Protein deficiency is associated with impaired titanium osseointegration. We studied whether systemic treatment with PTH or pamidronate could influence the resistance to pull-out of titanium rods implanted into rats proximal tibia under normal and isocaloric low protein intake. PTH or pamidronate prevented the deleterious effects of protein undernutrition on bone microarchitecture close to the implant and on mechanical fixation. PTH even significantly improved implant osseointegration. INTRODUCTION: Protein deficiency is highly prevalent among elderly patients hospitalized in orthopedic wards. Reduced protein intake impairs titanium osseointegration in rats. Whether stimulator of bone formation or inhibitor of bone resorption could improve implant osseointegration under protein deprivation is not known. We studied the effects of systemic treatment with PTH or pamidronate on the resistance to pull-out of titanium rods implanted into rats proximal tibia under normal and isocaloric low protein intake. MATERIALS AND METHODS: We measured the resistance to pull-out 1-mm-diameter titanium rods implanted into the proximal tibias of 49 adult female rats receiving a normal or an isocaloric low protein diet. After 2 wk on either diet, the implants were inserted, and the rats received PTH(1-34), pamidronate or saline vehicle for 8 wk. The tibias were removed for microCT morphometry, followed by the evaluation of pull-out strength. RESULTS: Pull-out strength was lower in rats fed an isocaloric low protein diet compared with rats fed a normal protein intake (-29%). PTH and pamidronate significantly increased pull-out strength in animals fed a normal or a low protein diet, the effect of PTH being of higher magnitude. The PTH- or pamidronate-mediated increase in pull-out strength was associated with significant increases of relative bone volume, bone-to-implant contact, and trabecular thickness, whereas trabecular spacing was reduced, in the vicinity of the implants. CONCLUSIONS: We confirmed that isocaloric low protein intake impairs titanium implant osseointegration. PTH or pamidronate prevented the deleterious effects of protein undernutrition and even significantly improved the implant osseointegration. These results indicate that systemic administration of PTH or pamidronate could be considered for preventing uncemented arthroplasty loosening in protein undernourished patients.

Strontium ranelate treatment improves trabecular and cortical intrinsic bone tissue quality, a determinant of bone strength.

UNLABELLED: Beside its influence on determinants of bone strength (geometry, microarchitecture), which is likely to be related to a cellular effect, strontium ranelate improves bone tissue quality as evaluated by nanoindentation, increasing elastic modulus, hardness, and dissipated energy in vertebrae of rats treated for 104 wk with daily dose from 0 to 900 mg/kg. INTRODUCTION: We previously showed that strontium ranelate treatment improves the mechanical properties of the vertebral body and long bone midshaft in intact rats. The increased energy to failure obtained with strontium ranelate is essentially caused by an increase in plastic energy, suggesting that bone formed during treatment can withstand greater deformation before fracture. In the bone mineral phase, strontium is mainly located in the hydrated shell and could thus potentially influence intrinsic bone tissue quality. MATERIALS AND METHODS: To study whether strontium ranelate treatment could positively influence intrinsic bone tissue quality (elastic modulus, hardness, and dissipated energy), nanoindentation tests were performed at the level of trabecular nodes and cortex under physiological or dry conditions in vertebrae of rats treated for 104 wk with strontium ranelate at a daily dose of 0, 225, 450, or 900 mg/kg (n = 12 per group). Ex vivo microCT measurements and axial compression tests of adjacent vertebral bodies were also performed. Significance of difference was evaluated using ANOVA. RESULTS: In agreement with previous results, strontium ranelate (900 mg/kg/d) [corrected] increased versus controls in maximal load (+23%), total energy (+71%), and plastic energy (+143%). At the level of trabecular bone, strontium ranelate treatment resulted in a significant increase in elastic modulus (+15.1%, p < 0.01), hardness (+11.5%, p < 0.05), and dissipated energy (+16.2%, p < 0.001) versus controls in physiological, but not in dry, conditions. The effect was less pronounced in cortex. CONCLUSIONS: These results show for the first time a direct action of strontium ranelate on bone tissue quality. Beside its shown influence on classical determinants of bone strength (geometry, microarchitecture), which is likely to be related to a cellular effect, strontium ranelate improves bone tissue quality. This could contribute to the increase in bone strength and thus be involved in the reduction of fracture risk in postmenopausal osteoporotic patients treated with strontium ranelate.