Advances in Porous Biomaterials for Dental and Orthopaedic Applications

Abstract

The connective hard tissues bone and teeth are highly porous on a micrometer scale, but show high values of compression strength at a relatively low weight. The fabrication of porous materials has been actively researched and different processes have been developed that vary in preparation complexity and also in the type of porous material that they produce. Methodologies are available for determination of pore properties. The purpose of the paper is to give an overview of these methods, the role of porosity in natural porous materials and the effect of pore properties on the living tissues. The minimum pore size required to allow the ingrowth of mineralized tissue seems to be in the order of 50 µm: larger pore sizes seem to improve speed and depth of penetration of mineralized tissues into the biomaterial, but on the other hand impair the mechanical properties. The optimal pore size is therefore dependent on the application and the used material.

Porous Titanium for Dental Implant Applications

“…The concept of creation of functionally graded structures in porous materials by changing the structure of the lattice has also been investigated [80]. [19,62] -sintering hollow spheres -thermal decomposition -sintering of powders, compressing and sintering of titanium beads or fibers Removable space holder and titanium metal powder particles: [63][64][65][66][67][68][69] -saccharose crystals -NaF -NaCl -polymer granules -Magnesium -ammonium hydrogen carbonate Additive manufacturing technology: [60,66,74] -selective laser sintering -selective laser melting -electron beam melting Bandyopadhyay and colleagues suggested laser engineered net shaping (LENS™) to construct porous structures from Ti-6Al-4V alloy across the range 23%-32% porosity with low modulus (7-60 GPa) which can be tailored to match human cortical bone [81]. Nomura et al in 2010 recommended the infiltration technique in a vacuum with sintering to create porous titanium/hydroxyapatite composites.…”

“…Relatively simple techniques for the production of porous materials include sintering hollow spheres or the use of thermal decomposition of, for example, TiH2. Fairly homogenous foam structures have been made from high melting temperature metals such as titanium and its alloys [19] and this method is also suitable for the production of titanium foams with pore sizes meeting the standard requirements considered to be suitable for bone ingrowth [6].…”

“…By increasing the porosity, a structure was created which closely mimics that of trabecular bone [5]. Typically, a porosity of 75%-85% and a pore size of more than 100 μm are considered to be preferable for rapid bone ingrowth [19]. Wen et al revealed that porous titanium with pore size ranging from 200-500 μm was sufficient for adequate bone formation and fluid transport [53].…”

“…Many fabrication methods have been used to fabricate porous titanium for medical purposes. However, the size, shape, percentage and distribution of pores were variable and need further optimization [19]. This review article aims to summarize the evidence in the literature of the benefits of using porous structures to improve integration of titanium dental implants with bone tissue.…”

“…However, the Young's modulus of these materials is higher than that of mineralized tissue. Furthermore, the traditional structure of titanium for medical and dental implants is non-porous; this dense structure of implants can cause a mismatch between the Young's modulus of the titanium implant (110 GPa) and natural cortical (17)(18)(19)(20) and cancellous bone (around 4 GPa) [7][8][9].…”