The cylindrical screws maintained a constant diameter from hub to tip; in contrast, the conical screws tapered 20%, from 6.0 mm at the hub (major diameter) to 4.8 mm at the tip.
In this design, fixation is achieved using a tapered screw for engagement with cortical bone and HA coating for subsequent osseointegration.
Fig. 1 Three-dimensional solid model of the mini-implant and bone: three-dimensional solid model of a 35-mm section of the alveolar bone of the posterior maxilla with a single self-drilling titanium mini-implant with a small head-type and tapered screw.
Distally, the plate accepts five 3.5-mm locking screws and is tapered to minimize soft tissue irritation and the screw hole density is greater to allow larger number of screws to be placed in the distal fragment (Fig. 2).
This increases the radial preload of these tapered screws in cancellous bone.
If using tapered screws from the Osteotite system (Orthofix SRL, Verona, Italy), it may be advantageous to drill the near cortex with a 4.8-mm drill and the far cortex with a 3.2-mm drill only in metaphyseal bone.
First two tapered hydroxyapatite screws (length and diameter determined by age and quality of bone stock) are inserted into the supra-acetabular region using a T-clamp.
Screwdrivers did not become common tools until 1850 when automatic screw machines began the mass production of tapered, gimlet-pointed wood screws.
Both hip compression and muscular contraction were transferred to the fitting cup through the central screw and taper, thus leading to stress concentration at the cup-taper junction (40.0 MPa).
We designed the mini-implant as a small head-type tapered pure titanium screw with external diameters of 1 and 1.3 mm, lengths of 6 and 8 mm, threaded deepness flight depth of 0.2 mm, threaded angle of 60°, and thread interval of 0.5 mm, with angulation of insertion to the vertical plane, at 30° and 60° (Fig. 1).
