Today, amalgam is still the best plastic restoration material for some class I cavities, and for class II cavities and all multi-surface restorations. Some patients and dentists prefer tooth-colored materials, however, these alternatives are more sensitive to the technique than amalgam. Amalgam is the end result of mixing approximately equal parts of mercury (43 to 54%) and an amalgam alloy powder (57 to 46%); it consists of silver, tin, copper and zinc. Crushing is the process by which mercury and alloy powder are mixed to form the amalgam mass needed to restore the tooth.
The pre-filled amalgam-mercury alloy capsule contains a mortar that helps in the mixing process. Before placing the capsule in the amalgamator, many brands require the use of an activator, which breaks the separator membrane. The activated capsule is placed in the amalgamator and the lid is closed to prevent mercury vapors from escaping during grinding. The amalgamator is configured to operate for the period of time specified in the manufacturer's instructions.
A suitable mixture must appear free of dry alloy particles and held together as a unit. Composite resin is a tooth-colored dental material that is becoming the material most used by dentists and the most requested by patients. At the beginning of its use, this material had a composition that made it aesthetically pleasing, but it could not withstand some of the properties discussed earlier in the chapter. Nowadays, this tooth-colored material is capable of withstanding the environments of the oral cavity; adapting easily to the anatomy of a tooth; matching the natural color of the tooth; and adhering directly to tooth surfaces for greater strength.
The composition of composite resins includes the resin matrix, inorganic fillers and a coupling agent. Composite resins are supplied in paste form, in light-resistant syringes and in capsules. This material is placed and adapted to the tooth preparation area. Once the application process has been completed, the material is polymerized (hardened) with the use of a curing light.
The exact cure time depends on the manufacturer's instructions, the thickness of the material, the size of the restoration and the tone of the material. Dentin sealant, also known as a primer, is designed to seal the dentinal tubules of the tooth, thus preventing oral fluids from leaking between the tooth and the restoration, which could eventually cause hypersensitivity. Cavity varnish is being used less and less frequently in amalgam restorations, and dentin sealants are replacing tooth decay varnish as the preferred coating. Cavity varnish is a liquid material that is placed throughout the cavity, in preparation for sealing the dentinal tubules.
It helps reduce microleaks from saliva and fluids surrounding the restoration, and acts as a barrier to protect the tooth from highly acidic cements, such as zinc phosphate. This material is contraindicated with composite resins and restorations with glass ionomers due to interference with the bonding and setting properties of the material. Many of the dental cements discussed later in this chapter are used as a basis by altering the measurements to obtain the right consistency. Acid etching, also known as dental conditioning, is a technique that is applied to a tooth surface prepared before using many permanent restorative materials.
This system was first designed to prepare enamel structure for composite materials and sealants, but research has found that by etching an enamel or dentin surface, dental material will have better retention on tooth surface. The main ingredient of engraving material is phosphoric or maleic acid. This liquid or gel substance is applied to surface of enamel or dentin for specific period of time to prepare tooth for bonding material. Bonding systems are liquid materials that flow towards engraved surface of tooth, creating micromechanical retention.
This self-healing or photopolymerizing material improves adhesion between tooth and permanent restoration. Enamel bonding allows placement of sealants, orthodontic brackets, resin-bonded bridges and bonded veneers. Attachment of dentin allows adhesion of other permanent material to engraved dental structure. A major success associated with bonding to dentin is removal of smear layer through etching process.
Smear layer is thin layer of waste that consists of liquids and dental components that have remained in dentin after preparation of cavity and that must be removed. Type of temporary restorative material selected depends on location and amount of dental structure that needs to be restored. Dental material most commonly used for temporary restoration is intermediate restorative material, also called MRI. IRM is zinc oxide-eugenol reinforced material; eugenol in this material has sedative effect on pulp and fillers are added to improve strength and durability of material.
Dental cements represent category of dental materials that are commonly used when working with indirect restorations (see chapter 22 for types of castings). Depending on dental procedure and specific cement, three methods can be used for preparation of cement product; differences include way in which liquid and powder are dispensed as well as liquid-to-powder ratios. When learning new material, make sure that one best kept secrets in adhesive dentistry today is use of glass ionomer cements as useful complement to restorative process. Since their discovery, glass ionomers have been one most researched dental materials; in many countries they are preferred restorative material because low cost and their anticariogenic properties.
According to Ngo et al., glass ionomer cement forms “chemically fused seal” with dentin which according many superior to dentine adhesive technology especially when there no enamel; it has been argued that dentinal bond hydrolyzes over time allowing microfuges.
