## 2 Materials and Methods  
This review is based on publications found through the University of Sydney CrossSearch--ProQuest portal between January and April 2016. The inclusion criteria encompassed publications from 2005 onward with a cranioplasty/craniofacial implant focus, a total patient sample of 10 or greater, provision of a numerical value for total number of implants per material, as well as a numerical value for cases of infection per material. Points of examination included number of patients, materials utilized, fabrication method utilized (where applicable) and infection rate. Only first-time cranioplasty implants are considered in this study. The data from the studies was broken down based on material, leading to the following analysis groups:  
* [noitemsep]
* Autologous bone (craniotomy bone flap)
* Polymethylmethacrylate (PMMA)  
* Prefabricated *
* Templated ***
* Titanium  
* Hydroxyapatite (HA)
* Polyetheretherketone (PEEK)
* Polyethylene (PE)
* Calcium Phosphate  
* [noitemsep]
* _Hand-formed is defined as a cranioplasty implant formed intra-operatively by the surgeon using no specialized tools_
* [noitemsep]
* _Prefabricated is defined as a cranioplasty implant which has been manufactured independent from and prior-to the surgical procedure_
* [noitemsep]
* _Templated is defined as a cranioplasty implant formed intra-operatively by the surgeon using specialized, prefabricated tools._  
It must be noted that the combined utilization of materials, size and cause of defect, overlying soft tissue coverage, patient characteristics and complications other than infection (such as extrusion and migration) were not considered as a part of this study. Whilst these are critical issues in examining the effectiveness and survivability of cranioplasty implants from a clinical view-point, the purpose of this study is to examine only infection risk and, as such, these components are excluded. However, they provide points for examination in future reviews.  
The search was conducted using the following key words: cranioplasty, craniofacial, implant, material, manufacture, infection, failure, autologous bone, polymethylmethacrylate, PMMA, hand-formed, prefabricated, rapid templated, titanium plate, titanium mesh, hydroxyapatite, polyetheretherketone, polyethylene and calcium phosphate.  
Each biomaterial was provided by the authors with an estimated interactive surface form ranking (\"ISF\") and a tissue attachment bioactivity ranking (\"TAB\"), based on material surface and bioactive properties. The ISF ranking is defined as a relative measure of interaction between the implant surface and the bodies tissues and immune system--where a higher ranking represents high interconnected porosity and, as a result, greater access to vascularized tissue ingrowth and the immune system--and the TAB ranking as a relative measure of the ability for a material to support attachment of growing tissue--where a higher ranking represents an increased support for tissue ingrowth. The purpose of these values is to provide a comparison point between implant material, manufacturing method, surface characteristics, bioactivity and infection potential. ISF and TAB rankings have been defined by the authors in Tables 1 and 2.  
Each material was provided with a relative risk value in order to provide a degree of comparison. In this review, autologous bone is considered as the gold standard, based on the consideration of full regeneration and integration as a potential patient outcome [12; 13; 14; 15]. This calculation was taken as follows:  
Finally, a one-way ANOVA test was conducted in order to determine if there was any statistical significance between the mean infection rates for each implant material.