## 4 Discussion
A reflection to be made from this examination is that implant material does provide an effect on potential infection risk, as greater levels of surface interaction and active support of tissue ingrowth can be considered as indicators of greater infection resistance. This can be seen as occurring in part due to the capacity of increased vascularization and access for the body's natural system to access the implant and assist in either preventing and/or combating possible sources of infection. Such characteristics are due to the physical structures of the implants and, as a result, it can be said that the method of production can, through alteration of these physical properties, assist in minimizing implant infection risk. It is to be noted that interconnected porosity is fundamental in tissue regeneration as this allows propagation of appropriate cells (osteoblasts) through the implant and the eventual formation of appropriate vascularization. Whilst the size of the pores may vary, it is generally accepted that a pore size of approximately 100 um is required to regenerate bone tissue [88]. As such, a trend can be seen where those implant materials with higher ISF and TAB rankings trend towards a lower infection risk; however, the true validity of this remains a point for future study. Building on this, manufacturing methods can further minimize infection risk through influences of prime sources of infection risk. By removing the implant contouring and/or alteration requirements from cranioplasty/craniofacial repair, the processes become simplified, providing better outcomes with fewer surgical requirements. Using the example of PMMA implants for cranioplasty and craniofacial reconstruction, it can be observed that both the prefabricated and templated methods of implant production are considered to minimize potential surgical timeframes, whilst also reducing variance in surgical time between surgeries. This is reflected particularly in relation to the templating method by [PERSON] et al. 2012, with cranioplasty surgery taking 184.36 \(\pm\) 26.07 min for PMMA (templated), as opposed to previously recorded values of 285 \(\pm\) 128 min for alternative fabrication methods [11]. The ability to either prefabricate patient specific implants, or template these intra-operatively external to the patient, provided clear benefits by removing the risk of thermal necrosis or hypotension associated with the curing process of PMMA [74; 75; 76; 77]. In addition, the nature of geometry generation becomes controlled through accepted physical design methodologies and computer-aided design (CAD), allowing for better form, fit and function [26; 89; 90]; which in turn leads to less chance of abnormal biomechanics and fit-based complications, without the need to shape or alter the implant by hand, as well as minimizing the complexity of the surgical procedure. This example can be considered in the case of easily alterable materials (PMMA, porous polyethylene, titanium mesh, etc.) which can be readily shaped using commonly available surgical tools [11; 25; 84; 85; 91] and adapted to meet anatomical requirements which may not be visible or known prior to surgery. However, for certain applications, such as titanium plate, this is not appropriate as intraoperative alteration of the implant is near impossible without specialized tools. A fundamental consideration not discussed within the body of this review is the relationship between implant graft material and patient context. Different injury profiles and patient lifestyles require different outcomes, which may provide a degree of preference to certain reconstructive materials. Features such as size, shape, cause, complexity and functional outcomes can drastically impact the pool of applicable implant materials and the potential associated fabrication and implantation cost. However, this topic is beyond the scope of this review.