or eugenol free (phenols) zinc oxide impression. If patient irritant to eugenol use rubbers imp.Eugenol irritant, cause burning sensation of lips.and moisture ↓ ST….accelerate reaction…drop of water accelerate setting.
stearic acid to improve flow properties (plasticizer). Talc or shalk 50%.gives body increasing viscosity of the softened materials, reduce thermal contraction. Thermoplastic materials, natural or synthetic resin and waxes….47% characterizes the softening temp.Stick single crown impression (copper ring technique).close fitting special tray used with zinc oxide eugenol wash. Sheet primary impression of edentulous mouth.Good dimensional stability and accuracy.Can be combined with impression compound.Mucostatic impression of edentulous ridges.Rarely used these days as they are brittle and fractures very easily.The thin areas of impression material, which are most prone to fracture are arrowed. View of a material being used to record an impression of a crown with subgingival shoulders. during removal- the impression is subjected to both compressive and tensile stresses. Oversized impression space results in an oversized dieĪ. Do not mix adhesives and impression materialsĭimensional change of impressions High Medium Low.Wait appropriate time before taking impression.Improve adaptation of gypsum so as to prevent voids in the casts.Displace water and other oral fluids from the surfaces in the mouth so as to prevent voids in the impression and consequent bubbles in the casts.Wettability of Impression materials Excellent Good Fair Wettability….ability of liquid to cover the surface of the substrate completely Hydrophobic Hydrophilic.Viscosity High- muco-compressive Low- muco-static.įlexibility of Impression materials Easy Moderate HardĪccurate reproduction of surface details depends on degree of permanent deformation. A fast setting material can be removed from the mouth in about 3 min.Using auto-mixing device for direct injection reduce working time to one minute.A total working and setting time of 4 min is adequate for most crown and bridge procedures. Dentist's time requirements must be balanced with patient's comfort.Automatic mixing reduces mixing time and bubbles use correct mixing tip.Low viscosity less viscous is easier silicones are easiest to mix followed by polyether and polysulphides.Elastomers Polysulfide (PS).set by polymerization Silicon rubber (AS and CS) Polyethers (PE) Hydrocolloids Reversible (agar)……sol.↔ gel (temp) Irreversible (alginate)….sol.→ gel b.Can be disinfected without any changes of properties. Should give accurate reproduction of tissue details. Adequate strength so that will not tear or break on removal from the mouth.Ĩ. Should be elastic to allow removal from undercuts without permanent deformation.Should have acceptable taste, colour and smell.Biocompatible, non toxic and non irritant.Ideal requirements of impression materials Impression tray is a device used to carry and control impression material while making an impression. The impression materials must be in a plastic or fluid status which become hard or set while in contact with oral tissues. What is a dental impression? It’s a negative likeness of the teeth and/or other tissues of the oral cavity. Dental impression materials Libyan International Medical University
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