Dental materials Flashcards

Question

25. What is the most important property of a posterior composite? a. It requires a single cure b. It is dual cured c. It is very heavily filled d. It is very lightly filled e. It flows very easily during placement

Answer 1

 C. It is very heavily filled.  Single or dual cure is not an important property of a posterior composite. The important properly is that the composite is heavily filled so that it can withstand the heavy occlusal forces placed on it. Lightly filled composites can easy flow composites are more commonly used in the anterior region.

Answer 2

 A. Kalzinol  Kalzinol prevents bonding of composite to enamel and dentine in a cavity.

Answer 3

 C. 2mm  The maximum thickness which can be cured is 2mm. Anything thicker than this and your composite will have a ‘soggy bottom’, and will not be stable as a restoration.

Answer 4

 D. Enamel fracture  The restoration can debond and be lost a result of microleakage. Also air and fluid leakage can lead to sensitivity, and staining can occur, especially if coloured food leak around the margins.

Answer 5

A. Zinc B. Zinc is not released from glass ionomer when it sets. Aluminium, fluoride, calcium and sodium are released during the setting process.

Answer 6

 B. Hydroxyl ions  Hydroxyl ions replace the fluoride ions which leach out during the setting process.

Answer 7

 D. Light from an argon laser with activate polymerisation.  Light from an argon laser usually between 20 and 40 seconds will cure composite.

Answer 8

 D. Barium glass  Barium is a radiopaque material and is used frequently in radiographic investigation. The most common use is barium enemas. However, this technique is in decline with the increase in computed tomography (CT) scanning.

Answer 9

 A. Hybrid ionomer  Hybrid monomers have found popularity as restorative materials and as cements for crowns and fixed prosthesis. They contain about 80% glass ionomer and 20% resin. The hybrid ionomer releases the fluoride present in the aluminosilicate glass constituent, which is dissolved by the acid present in the mixture. Ongoing research has shown that these restorations release considerable amounts of fluoride during their service in the mouth. The tricure characteristics of hybrid ionomers makes them ideally suitable for the repair of opaque restorations that have become carious during service. These materials are ideal for the repair of crowns, as well as for repairs in any restorative situation with inadequate light access to allow a light-cured material to cure properly. Hybrid ionomers do not require a bonding agent for retention. They bond to dentine naturally by means of a calcium-carboxylate ion bond. Some manufacturers have suggested using primer before placement of the hybrid ionomer; however this does not appear to be needed. Ongoing research is showing that the direct contact between the hybrid ionomer and the tooth structure causes high amounts of fluoride to be released into tooth structure. Thus hybrid ionomers are one of the most adequate choices for restoring teeth in patients who have a high caries risk.  Compomers are easier to use than hybrid ionomers, but some of their characteristics are not as desirable as those of hybrid ionomers. Compomers require a bonding agent for adequate retention to dentinal surfaces. The bonding agent reduces the amount of fluoride that can penetrate into the dentine. However, compomers release considerable amounts of fluoride from their external surfaces into the oral environment. These materials are popular for restoration of children’s posterior teeth. Because compomers are easy to use, and release fluoride, they are nearly ideal for placement in voids in crown preparations resulting from removal of old silver or composite restorations (so-called fillers). These materials release less fluoride than hybrid ionomers, but more than typical resin-based composites, most of which release few or no fluoride ions.  Conventional glass ionomers continue to be popular for restoring teeth and for cementing crowns and fixed prostheses. Glass ionomer release considerable amounts of fluoride into tooth structure, as well as into the oral environment. In fact, research has shown them to release more fluoride than any other caries-preventive material. The working characteristics of glass ionomer as a restorative material make it more difficult to use than hybrid ionomer or compomer. Nevertheless, when glass ionomer is used, practitioners can expect it to release considerable amounts of fluoride.

Answer 10

 A. Modulus of elasticity  An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance’s tendency to deform elastically (ie non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region.

Answer 11

 B. Bonding to enamel is achieved by the application of an acid etchant followed by the application of a bonding agent and then composite resin.  B describes the most common pathway for placing a composite.

Answer 12

 A. Their depth of cure allows bulk polymerisation, which has been shown to be clinically effective.  The packable dental composites can be polymerised in bulk and are clinically very effective.

Dental materials Flashcards

(36 cards)