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"Porcelain" restorations like veneers crowns and bridges can fracture. The fracture can be partial thickness, or fully through to reveal the underlying tooth (or metal-work). The clinician needs to decide whether repair is indicated: often a complete replacement is better.
Some clinicians enjoy the convenience of ready made kits: Ultradent and Optident provide Porcelain Repair Kits.
What is the importance of analysing the occlusion before undertaking a repair?
If the fracture is due to an occlusal interference, the repair will also fracture, as the bond strength of the repair will be weaker than the original ceramic.
The interference must be corrected before repair. If this is not possible, a replacement restoration that is able to withstand the occlusal forces should be considered.
If the fracture is due to parafunction, a protective appliance such as a Michigan Splint might be considered.
It provides pores for micro-mechanical retention of the repair materials. This is achieved by preferentially dissolving the glass phase in the ceramic.
What is the problem with using Hydrofluoric Acid in the mouth? How are the risks reduced?
This is a very dangerous material, and can cause severe burns. It should only be used with rubber dam, and by experienced operators.
Risks can be further reduced by applying a caulking agent to seal the dam.
Some gingival protection can be given using a (neutralising) slurry of sodium bicarbonate.
When checking the shade of composite to be used, why is the composite cured?
Some (not all) composite resins demonstrate shade shift on polymerisation.
Curing is not necessary if you are sure you are using a composite that is colour-stable during polymerisation.
How does silane (more properly, a Silane Coupling Agent) work?
The coupling agent molecule has a silane group at one end. This bonds to the hydroxyl groups on the porcelain glass phase.
It has a methacrylate group at the other end, which bonds to the resin in the bonding system and composite.
Please take a moment to review these points, reflect on their significance, and consider how they apply to your own experiences.
Tick to confirm (optional):
Analyse occlusion before porcelain repair to avoid repeated fractures. Occlusal interferences or parafunction may require correction or protective appliances.
Hydrofluoric acid gel (9%) or APF gel can be used to etch porcelain, except for high purity alumina or zirconia ceramics like Procera and Lava, which cannot be etched.
Etching creates pores in the ceramic for micro-mechanical retention by dissolving the glass phase. Use Hydrofluoric Acid with extreme caution, applying rubber dam and caulking agents to protect soft tissues.
Additional surface roughening for bonding, such as grit blasting or using a bur, increases surface area but weakens the ceramic.
Cure composite resins to check shade stability, as some resins may change color during polymerisation.
Silane coupling agents bond porcelain to composite by connecting the glass phase of the ceramic to the resin.
Gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS) is commonly used as a silane coupling agent in dentistry.
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