 hello everyone welcome back to another session in dentistry and more so this topic in conservative dentistry is DFG direct filling gold so pure gold which can be used as an restorative material so the most noble metal which rarely tarnishes in oral cavity so the basic restorations where the gold can be applied is pits and small class 1 restoration class 2 and class 5 restorations for repair of casting margins and also for the repair of cement vent holes in gold crowns so the vent holes in the gold crowns so it can always stand a bigger masticated force so it is basically useful small class 1 then class 2 and class 5 restorations so this is the classification of DFG the basic three categories the foil powder and mat gold so mat gold is the electrolytic precipitate so foil can be sheet can be cohecy or non-cohecy then ropes cylinder laminated ones and the mat gold which is mat type mat foil and alloyed the first one gold foil so it is the oldest one okay so the oldest one so it's manufactured by a cast ingot of 15 millimeter thickness is beaten to so 15 millimeter thickness is beaten to a sub microscopic thickness of 15 to 25 micrometer then supplied as flat square sheets of varying thickness like number four weight or number three weight that is four grains and this is three grains that means it is 0.259 gram this is 0.194 grams also it can be in preformed foils that is ropes and cylinders are available in preformed shapes made from number four foil that has been carbonized or corrugated okay so carbonized corrugated that is especially for the ropes and cylinders okay then platenized foil so that I forgot to mention platenized foil so it is pure platinum foil sandwiched between two sheets of pure gold so it is bonded by cladding process so the cladding process where this is sandwiched between the sheets of pure gold and it increases hardness because of the platinum and available in number four sheets so whereas the cohesive and non-cohesive gold the cohesive one so for cold welding gold should have a very clean surface so gold attracts gases and any absorbed gas filling prevent cohesion of in individual increments of gold so cohesive gold is supplied free of contaminants okay whereas a non-cohesive one called is subjected to volatile agents such as ammonia which is absorbed on surface which acts as a protective filling so this volatile filly can be easily removed by heating so it is rarely used nowadays so the most commonly used cohecy one which is free of any impurities which is having a very clean surface after that we have the second category that was electrolytic precipitate or mat so the crystalline gold powder is formed by electrolytic precipitation crystalline powder so powder is formed into shapes by sintering that is a heat fusion sintering process heat fusion process so this powder is changed into various shapes so it is available as I mentioned mat then mat foil then alloy type so the mat gold it is crystalline formed in strips easy to build up the internal bulk more easily compacted and adapted which results in pitted external surface so covered with a veneer of foil gold whereas a mat foil which is a sandwich of electrolytic precipitated gold powder between sheets of number three gold foil actually which is done to eliminate the need to veneer the restoration with a layer of foil so because here we have a veneering of a gold foil layer so to avoid this we keep mat foil that is a sandwich process of gold powder between the sheets of number three but anyway this is no no longer marketed the last one is alloyed electrolytic precipitate which is the newest form okay so alloy of gold and calcium calcium so this calcium produces stronger restoration by dispersion strengthening so the alloy is sandwiched between two layers of gold so this calcium will be sandwiched between two layers of gold now the last one we have powdered gold so third category is powdered so this is enclosed in number three gold foil which is manufactured by the chemical precipitation or atomizing the metal pellets mixed with soft wax burned off later and wrapped in gold foil so it available as foil acts as an effective container and matrix for the powdered metal then powdered gold petal increases cohesion and reduces the time required for placing it because each pellet contains more metal by volume than the same sized pellet of gold foil so that is the importance of powdered gold it has more metal by volume than the pellet of gold foil so the powdered gold petal have cylindrical or irregular shape and the ratio of gold foil to powder varies from one to three for small pellets to one to nine for the largest one so how do we manipulate how do we apply this so there are two pressures involved so the first process is so the manipulation we have two process the first process is known as de-gassing de-gassing and second one is compaction so desorbing or de-gassing desorbing or de-gassing so as the name suggests it is a removal of impurities from the surface because during storage and packing of cohesive gold they absorb gases from atmosphere it prevents it from fusing so we can remove it by heating so that process is known as de-gassing heating done in two ways basically in bulk on a tray by gas flame or electricity or piece by piece in a well adjusted alcohol flame so totally dry cavity needed to hello complete cohesion so the second one as a procedure is known as compaction so the gold may be compacted by hand mallet or by vibrateic vibratory condenser vibratory condenser or electrically driven condenser electric condenser so what are the properties of a compacted gold so the strength so the greatest strength is the most dense area weakest part it has got porous structure and direct filling gold failure occurs from incomplete cohesion the transfer strength is measure of cohesion whereas the hardness it indicates overall quality or the presence of porosity density of pure gold we know 19.3 gram per centimeter cube so the density less than pure gold because it is not for our DFG it will be less than this pure gold because it is not possible to eliminate voids during the compaction compaction is unavoidable so what is the effect of voids amount of voids estimated by apparent density of compacted gold voids on surface increases susceptibility to corrosion and deposition of plaque so voids at the restoration tooth interface causes gross leakage and secondary caries development and there can also be tarnished and corrosion so resistance to this tarnished and corrosion is good if it is well compacted biocompatibility pulpal response is very minimal if a compacted well this procedure causes a certain amount of trauma to the tooth and supporting structures so mechanical condensers causes less trauma than the manual technique so the advantages are the tarnishing and corrosion resistant good mechanical properties good biocompatibility the disadvantages are poor aesthetics high coefficient of thermal expansion and manipulation also it's very difficult so that's all about direct filling gold so short notes are frequently been asked from this topic direct filling gold de-gassing desorbing and the three types of our direct filling gold they are the gold foil then the powder or matte gold so anything can be asked as a short note so I'll come up with a new topic in consumer video industry thank you