The pullout strength of the pedicle screws was the functions of bone strength, screw design, and pilot hole.
In the literature, the Chapman's formula has been widely proposed to predict the pullout strength of screws with constant outer and inner diameters (cylindrical screws).
Nevertheless, our results indicate that in a synthetic material with a density similar to that of severely osteoporotic bone, screw back-out does not affect the pullout strength of screws with cement augmentation.
The results of fracture strength of screws in this study, before and after immersion in SBF for 2 and 4 weeks are shown in Fig. 2.
In order to improve the mechanical strength of screws, metal implants are in the focus of current research.
Traditionally, to improve the anchoring strength of screws in osteoporotic bone, PMMA is injected directly into the prepared pilot hole of the vertebral body prior to screw insertion.
When adequate press-fit fixation cannot be achieved, cup stability decreases considerably and depends on the strength of screw fixation, which is influenced by the length and position of the screws.
The performed experiments revealed that the strength of screw joints depended on the total area of pressure and shear.
In order to improve the rolling formability and the strength, the screw-thread of the DTB-II was fundamentally modified in this study.
Density, moisture content after submersion, thickness swelling, water absorption, modulus of rupture, modulus of elasticity, bonding strength, and screw withdrawal strength of the plywood panels were carried out according to national or international standard methods.
Existing models to predict the strength of screw anchors under tensile loading are based on the assumption that anchors are installed in mature concrete.
