## 2 Non-Absorbable Membranes
### Non-Absorbable Metal Membranes  
Titanium is the material of choice in making non-absorbable metal membranes. It is an inert, stable material with good mechanical strength; in addition, it has a high degree of biocompatibility [19; 20]. These qualities of titanium make it usable in high-amplitude tissue defects, where it gives a constant shape over time [21]. An economic disadvantage is the high cost of these membranes compared to other common materials [12]. Titanium membranes may be available as all-metal membranes or metal mesh membranes. In 2003, the Ultra-Ti(r) GTR titanium barrier membrane was introduced [22]. Ultra-Ti(r) membrane is a pure titanium membrane with a homogeneous structure, about 10 microns thick; due to its ultra-thin thickness, it is easy to handle and adapt to the receptor site [23]. Moreover, the surface roughness is reduced, which makes it less susceptible to bacterial contamination. In addition, it does not require setting with pins. Because it is radiolucent, \begin{table}
\begin{tabular}{c c c} \hline
**Composition** & **Commercial Variants** & **Observations** \\ \hline \multirow{4}{*}{Titanium} & Osteo-Mesh TM-300\({}^{\text{\text{\text@b{$\oplus$}}}}\) & Very good mechanical properties \\  & Frios BoneShields & Bio-inert \\  & & Frios BoneShields & High risk of oral exposure \\  & & Requires setting pins \\  & & Requires second surgical time \\ \hline \multirow{4}{*}{Silicone} & & Low cost \\  & & Bio-inert \\  & & Very low micro-porosity \\  & & Requires second surgical time \\ \hline \multirow{4}{*}{Expanded (e-PTFE)} & & Good mechanical properties \\  & & Good micro-porosity \\  & & Bio-inert \\  & & High risk of oral exposure, with \\  & & bacterial loading \\ \hline \multirow{4}{*}{Polytetrafluoroethylene (PTFE)} & & Good mechanical properties \\  & High density Gore-Tex® & Good micro-porosity \\  & & Cytoplast TXI-200\({}^{\text{\text@b{$\oplus$}}}\) & Smooth surface (low risk of \\  & & Cytoplast Regentex GBR-200\({}^{\text{\text@b{$\oplus$}}}\) & bacterial loading) \\  & & Cytoplast Regentex GBR-200\({}^{\text{\text@b{$\oplus$}}}\) & Can be left partially exposed in \\  & & & the oral cavity \\  & & High risk of oral exposure \\ \hline e-PTFE with titanium & Gore-Tex® Reinforced & Very good mechanical properties \\  & & Bio-inert \\ \hline d-PTFE with titanium & Cytoplast Regentex Ti-250\({}^{\text{\text@b{$\oplus$}}}\) & High risk of oral exposure \\ \hline \end{tabular}
\end{table} 
Table 1: Types of non-absorbable membranes. it allows the monitoring of bone formation. As a disadvantage, being a non-porous membrane, it does not allow the perfect integration of tissues, which can lead to periodontal pocket formation [23]. In 1969, titanium mesh membranes were introduced to regenerate bone defects [24]. Titanium mesh has good mechanical properties in stabilizing bone regeneration materials. Its rigidity ensures the maintenance of the space and prevents the collapse of the defect; its elasticity prevents the compression of the mucosa, and its plasticity allows bending, contouring and adaptation to the bone defect [25]. Titanium mesh has been shown to maintain space with a higher degree of predictability, even in cases of extensive bone defects [26]. In general, titanium mesh membranes are characterized by macro-porosity; this quality is considered to play an important role in ensuring blood supply, allowing the diffusion of extracellular nutrients through the membrane [27]. Moreover, soft tissue attachment, favored by high porosity, facilitates the stabilization and restriction of epithelial cell migration [28]. [PERSON] et al. claimed in their study data that the use of a pore-free titanium membrane resulted in the exposure of all meshes in three weeks [29]. Of course, this type of membrane also has a number of disadvantages; due to its sharp edges, irritation of the soft tissue components can occur, which can lead to membrane exposure and even compromise therapeutic success [30]. However, titanium membranes can tolerate some degree of exposure.