1: an involuntary contraction of the muscles of the soft palate or pharynx that results in retching 2: a surgical device for holding the mouth open
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Membranes have been used in dental medicine since about 1980 for covering naturally existing, pathologically caused or synthetically created areas of tissue. They function as a barrier. They are intended forpreventing the growth of unwanted tissue into the boundary area as… Membranes have been used in dental medicine since about 1980 for covering naturally existing, pathologically caused or synthetically created areas of tissue. They function as a barrier. They are intended forpreventing the growth of unwanted tissue into the boundary area as well as shielding and promoting the formation of tissue required within the area using GTR/GBR. The ideal membrane should have the following characteristics: not trigger immune response, non-toxic (biocompatibility), no risk of infection, formable, adaptable and trimmable, adequately firm/rigid and positionally stable, if necessary permeable for substances yet impermeable to cells, time-determinable spacer function, predictable biological degeneration where required. Non-resorbable membranes Non-resorbable membranes can, for example consist of cellulose ester, PTFE or titanium. A second surgical intervention is always required to remove them. Cellulose ester membranes The first generation of membranes used (approx. 1980) for shielding against bacteria. PTFE membranes Flexible, tear-resistant membranes made from ePTFE (expanded polytetrafluorethylene =Teflon®) with micropores, which make exposure a low risk as no cells or microorganisms can pass through. Sometimes they are reinforced with titanium mesh, making them firm and dimensionally stable; highly suitable for covering extensive augmented areas. Titanium membranes These approx. 30 µm thick titanium foils are highly suitable for GBR and alveolar ridge augmentation. They are completely impervious and can be prestressed. Resorbable membranes No second intervention is required for removing resorbable membranes due to their integration in the tissue. They are the preferred choice where anticipated that permanent full coverage of the membrane by tissue will be possible and tissue support is not the main priority. The only resorbable membranes used in the dental sector consist of alloplastic materials. In dentistry we differentiate between hydrophobic, synthetic polymer membranes (e.g. made from polylactide) and hydrophilic, xenogeneic (e.g. bovine or porcine) collagen membranes. Polylactide membranes These mostly multi-layer membranes are initially rigid but formable intraorally and mainly used for GTR in periodontology and less commonly for GBR. They comprise polymers of the two enantiomers (D and L form) of lactic acids, if necessary supplemented by portions of glycolide. After a 20-week period in situ these membranes begin to degrade hydrolytically over intermediate stages into the end products water and CO2. This process is complete after approx. one year. Collagen membranes These membranes are of animal origin (mostly cattle or pigs) and require careful pretreatment in order to prevent the transfer of pathogens. The collagen structure is differentiated between more rigid (synthetic), cross-linked materials and more flexible (native, natural), non-cross-linked materials. Indications for collagens are stabilising extraction alveoli, coverage of bone defects and augmentation materials, prerestorative alveolar ridge augmentation and periodontal surgery. |