Collagen membranes are hydrophilic resorbable membranes. Xenogenic (e.g. bovine or porcine) collagen membranes are mainly used in the dental sector.
The collagen structure is differentiated between more rigid (artificial) crosslinked and more flexible (native, natural) non-crosslinked materials. Comparative studies show that the latter exhibit lower complication rates and advantages during wound healing.
Up till now the good properties of resorbable membranes - on the one hand maintaining the barrier function and on the other hand biointegration in the form of quicker vascularisation, penetration and resorption – appeared to be mutually exclusive. According to the latest research results, there seems to be a paradigm shift taking place in this regard.
Native collagen membranes maintain their barrier function over an appropriate period: the quantity and quality of bone regeneration under a native collagen membrane are comparable to those of membranes with an extended barrier time. Integration in the tissue is, however, quicker and triggers a much lower inflammation reaction.
The range of applications for collagen membranes includes general GBR and GTR procedures in particular preventive and preimplantological stabilisation of extraction sockets (socket grafting and ridge preservation), coverage of bone defects following apicectomies, coverage of the Schneiderian membrane and the access window with lateral sinus floor elevation, coverage of augmentation materials with immediate, delayed or late implantation, with preprosthetic alveolar ridge augmentation and with periodontal surgery indications.
Although allergic reactions to collagen membranes may occur, these are rare due to the biological similarity of the tissue. With all materials of a natural origin, particularly those of animal origin, thorough pretreatment is necessary to exclude the transference of pathogens.
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Composites also composite (from the Latin componere = to compose) are tooth-coloured filling materials with plastic properties used in dental treatment. In lay terms they are often referred to as plastic fillings, also erroneously sometimes confused with ceramic… Composites also composite (from the Latin componere = to compose) are tooth-coloured filling materials with plastic properties used in dental treatment. In lay terms they are often referred to as plastic fillings, also erroneously sometimes confused with ceramic fillings due to their tooth colour. After being placed in a cavity they cure chemically or by irradiating with light or a combination of the two (dual-curing). Nowadays, composites are also used as luting materials. The working time can be regulated with light-curing systems, which is a great advantage both when placing fillings and during adhesive luting of restorations. Dual-curing luting materials are paste/paste systems with chemical and photosensitive initiators, which enable adequate curing, even in areas in which light curing is not guaranteed or controllable. Composites were manufactured in 1962 by mixing dimethacrylate (epoxy resin and methacrylic acid) with silanized quartz powder (Bowen 1963). Due to their characteristics (aesthetics and advantages of the adhesive technique) composite restorations are now used instead of amalgam fillings.
The material consists of three constituents: the resin matrix (organic component), the fillers (inorganic component) and the composite phase. The resin matrix mainly consists of Bis-GMA (bisphenol-A-glycidyldimethacrylate). As Bis-GMA is highly viscous, it is mixed in a different composition with shorter-chain monomers such as, e.g. TEGDMA (triethylene glycol dimethacrylate). The lower the proportion of Bis-GMA and the higher the proportion of TEGDMA, the higher the polymerisation shrinkage (Gonçalves et al. 2008). The use of Bis-GMA with TEGDMA increases the tensile strength but reduces the flexural strength (Asmussen & Peutzfeldt 1998). Monomers can be released from the filling material. Longer light-curing results in a better conversion rate (linking of the individual monomers) and therefore to reduced monomer release (Sideriou & Achilias 2005) The fillers are made of quartz, ceramic and/ or silicon dioxide. An increase in the amount of filler materials results in decreases in polymerisation shrinkage, coefficient of linear expansion and water absorption. In contrast, with an increase in the filler proportion there is a general rise in the compressive and tensile strengths, modulus of elasticity and wear resistance (Kim et al. 2002). The filler content in a composite is also determined by the shape of the fillers.
Minimally-invasive preparation and indiscernible composite restoration
Composite restorations Conclusion |