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• A crystal may contain rotation axes in different directions, defining the polyaxial point-groups.[...]The general symbol for a polyaxial point group is n1 n2 n3. The simplest case is 222 in the orthorhombic system with three 2-fold axes at right angles to each other (Figure 4.13a).
• However, polyaxial screw heads can be controlled with an instrument in such a way as to mimic the monoaxial screw capability for direct vertebral rotation but ultimately retain the advantages of a polyaxial screws.
• The polyaxial screw is the most versatile. The polyaxial screw is a load-sharing device. A portion of the applied correction force is dissipated through the polyaxial connection protecting the bone-screw interface.
• More modern, polyaxial designs allow screw angulation prior to end point locking, and these can be very useful if femoral component lugs or the like are encountered during drilling.
• According to Florin, only the Taxaceae cannot be interpreted in terms of the polyaxial concept, since the single terminal ovule shows no evidence of having evolved from a bract and ovuliferous shoot system.
• However, sustainable avocado production at acceptable commercial levels remains a challenge as the polyaxial, pseudo-terminal flowering architecture of avocado (Verheij, 1986) dictates that trees must continuously increase in size to remain productive (Whiley and Schaffer, 1994).