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Clinical


Fig 1


Fig 2


Figures 1 and 2: Preparation of tooth 46 for a three-quarter crown is more conservative than providing a full coverage crown


Fig 3


High Nobel Type II Gold Alloy (Labwork by Kenn Scott, A-Plus,Dundee)


Fig 5 Fig 4


High Nobel Type II Gold Alloy (Labwork by Kenn Scott, A-Plus,Dundee)


Three quarter-crown preparation. This technique allows the buccal wall of the tooth to be left intact. The preparation is characterised by a chamfer finishing line and proximal grooves that are aligned parallel with the palatal surface


Fig 6


MOD onlay – second premolar: Character- ised by a chamfer marginal finishing line located at least 1mm from the occlusal contact on the functional cusp


the following major headings: case selection, composition, restoration design, prepara- tion, try-in and cementation and finishing.


Case selection On the basis of current infor- mation, the provision of cast gold restorations should be based on the following considerations:


• Aesthetics: Aesthetics are a matter of opinion and some patients regard gold as unsatisfactory. Others state that under the right circumstances, cast gold restorations can be provided without showing the gold. If the buccal surface of the tooth is intact, careful place- ment of the margin can allow the use of gold on the


Conventional Extra coronal Full veneer crown


7/8 crown 3/4 crown MOD onlay


Intra coronal


MOD onlay Class I


Class II inlay Class IV inlay


occlusal surface, and yet satisfy aesthetics.


• Occlusal considerations: According to Wiseıı, the basic principles of correct occlusal management are to ensure that occlusal forces are directed down the long axes of teeth and that posterior restorations separate immediately in all excursive movements. This applies to the choice


of restorative material by the fact that more space is needed for the disclusion of ceramic and ceramo-metal restorations than for gold. Steep anterior guidance creates more space for posterior disclusion and shallow anterior guidance implies reduced space. There- fore, steep anterior guidance can permit the use of porce- lain, whereas shallow anterior


Adhesive Occlusal onlay


guidance indicates the need for gold.


• Conservation of tooth structure: There is more danger to the pulp when greater amounts of tooth structure are removed during tooth preparation. Cast gold restorations require removal of less tooth structure and are therefore less trau- matic than all-ceramic and ceramo-metal restorations. (Figures ı and 2)


• Bruxism: The prognosis is poor when porcelain occlusal surfaces are provided in a wearing denti- tion whereas gold does not wear or abrade the opposing dentition.


• Laboratory support: The production of high- quality cast gold restorations is dependent on excellent laboratory support.


• Cost: Gold restorations incur high costs. However, it should be realised that accurate, carefully cemented gold resto- rations have a long history of reliability6-8,ıı. Ceramo-metal restorations last for approxi-


mately ı5 years, though carry a significant biological cost to the tooth. Adhesively retained porcelain and composite indirect restorations are relatively untested. Recogni- tion of these factors will allow both patient and clinician to make a cost benefit analysis.


Composition Some clinicians consider that the American Dental Asso- ciation (ADA) provides a more useful classification of gold alloy than the British Standard (BS 4425)ı3. The ADA classifi- cation refers to the proportion of noble metals (gold, platinum and palladium) in the alloy. The classification is: High noble: at least 60 per cent noble metals, including at least 40 per cent gold. Noble: at least 25 per cent noble metals. Base metals: less than 25 per cent noble metals. (Figures 3 and 4). Typically, high noble alloys


are used to produce cast gold restorations. The ADA has divided high gold alloys into four types based on their mechanical properties. • Type I alloys are weak, soft


Continued » Scottish Dental magazine 43


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