Page 46 - Clinical relevance of current materials for cranial implants

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Chapter 2
Beside the clinical results evaluated in this review, physical properties of the various materials may also influence procedure safety. A better understanding of these properties is vital in the development of future materials for cranioplasty. Of the products commonly used, titanium has a good biocompatibility, shows resistance to infection, and appears to be mechanically stable11,72. However, titanium is expensive. Furthermore, it is radiopaque and easily conducts heat and cold10. PMMA is widely used for cranioplasty, relatively inexpensive, light in weight, easy to use, and radiolucent. Nonetheless, PMMA is associated with disadvantages, such as a greater infection rate, and it does not facilitate bone ingrowth and revascularization10. In addition, the residual monomer is considered to be toxic73-76. In this systematic review, an overall infection rate of 7.8% was noted. PMMA is mostly formed intraoperative, without polishing. Bacterial adhesion and biofilm deposition is stimulated by irregularities, which could contribute to an increased infection rate77. HA is an established material for cranioplasty. It is biocompatible and similar to the mineral structures of human bone. This allows the implant to be broken down over time and replaced by newly formed bone. However, before remodeling has taken place the HA is brittle and vulnerable to fracture. It therefore seems most suitable for small defects78. PEEK is a relatively new material for cranioplasties. It has high structural stability and can be sterilized using various methods without deformation. However, PEEK has some disadvantages: the material itself is costly and it has no bioactive potential71,79.
Combining multiple existing materials allowed for the development of new cranioplasty products, for example, a titanium mesh used in combination with different types of bone cement10. In addition to commonly used materials, other new materials for cranioplasty are being developed, such as bioactive fiber-reinforced composite implant, hard tissue replacement polymer and carbon fiber reinforced polymer80-82. Most of these materials, however, have merely been evaluated in preliminary studies with small patient groups.
Resorption rates up to 50%83 have been observed for autologous cranial reconstructions, and there is evidence suggesting that younger patients may have significantly greater resorption rates. Greater metabolic activity in younger patients could lead to quicker resorption, but the exact mechanism responsible for this complication is unclear84. This phenomenon suggests that young patients may be better served by an immediate alloplastic reconstruction.