Bases and Liners 2025 PDF

Presented by Dr. Hanan Nabil Lecturer in Operative Department The ideal amount of dentin required between an amalgam restoration and the pulp for insulation is : 2.0 mm. Pulp protection against: a) Thermal irritation due to conductivity of metallic restorations to thermal changes....

Presented by Dr. Hanan Nabil Lecturer in Operative Department The ideal amount of dentin required between an amalgam restoration and the pulp for insulation is : 2.0 mm. Pulp protection against: a) Thermal irritation due to conductivity of metallic restorations to thermal changes. b) Chemical irritation due to acids and monomers in non-metallic restorations that may lead to pulpal damage and necrosis. c) Mechanical irritation due to the force of condensation. Some of these materials could improve adaptation and peripheral sealing ability of the cut dentinal tubules.  Cement Bases Bases should have sufficient strength so as to withstand forces of mastication and condensation of permanent restorations. (cement bases, typically l-2mm) Functions of bases can be as the following: Protective bases: They protect the pulp before restoration is placed. Sedative bases: They help in soothing the pulp which has been irritated by mechanical, chemical or other means. Insulating bases: They protect the tooth from thermal shock. The thickness of base 1 - 2 mm The initial increment of powder is thoroughly mixed into the liquid. When zinc phosphate cement is used for Luting, it must possess a surface gloss but with no evidence of a web formation when the spatula is left from the mix. When used as a base under restoration, it must have a putty consistency by mixing more powder to the liquid. The material strings one inch when lifted from the mixing pad. The dental cement should be used before its glossy appearance becomes dull  Zinc phosphate cement & polycarboxylic cement both have 90% zinc oxide Acid- base reaction  The cavity should be then washed thoroughly and dried lightly without dehydration. Complete isolation is recommended. Trim any excess cement. Matrix application for application of final restoration.  The consistency of the mix a soft creamy consistency, and display a surface gloss. Now, include the second finishing the mixing within a further 15 seconds. The finished mixed material should be “glossy wet” working time between 60 to 90 seconds. The fresh mix must quickly be transported into the preparation using a Teflon-tipped or gold-plated plastic instrument.