Dental Materials Flashcards
From what age should fissure sealants on the permanent molars be done on a patient at high risk of caries/predisposing factors/ortho appliances etc?
children from age 7
What are 4 contraindications for placement of fissure sealants?
- adequate isolation cannot be achieved
- hypoplastic teeth
- proximal/occlusal decay is present
- uncooperative patients
When should susceptible teeth be fissure sealed?
as soon as the occlusal surface is fully erupted into the mouth
What are 5 ideal properties of fissure sealants?
- cariostatic action (fluoride release)
- resistant to oral fluid and diet
- low viscosity
- should be detectable
- non toxic
What is the most common reason for sealant failure?
saliva contamination during placement
What are 2 indications for sealant restorations (PRR)?
- caries confined to one part of fissure system
- cavitation has occurred (either micro cavity in enamel or cavity with dentine at base)
What is the most commonly used dental composite?
BisGMA (bisphenol glycidyl methacrylate)
Which composition of composite give it radio opacity?
glass particles
What are 6 roles of fillers in composite materials?
- strength
- reduction in polymerisation shrinkage
- reduction in thermal expansion
- improved optical properties
- radio opacity
- reduced water absorption
How much polymerisation shrinkage do you get for most composites?
2-3%
What depth of composite is the maximum to be packed at a time?
2mm
What is meant by C factor?
number of bonded surfaces / unbounded surfaces
What are 4 clinical impacts of polymerisation shrinkage for direct restorations?
- loss of adaptation to cavity walls - micro leakage
- sensitivity
- restoration fracture
- caries
What are 4 advantages of indirect composites?
- potential improvement of degree of cure
- potential improvement in mechanical/physical properties
- reduced impact of polymerisation shrinkage
- improved shape/finish
Which phase of amalgam can be described as?
- most electropositive phase in amalgam
- most susceptible to corrosion
- weak and soft phase - reduces strength of amalgam
- causes static creep (gradual plastic deformation at loads well below the yield point)
gamma 2
What is the function of copper in amalgam?
less than 6% = increased strength
more than 6% = excessive expansion
What is the function of zinc in amalgam?
- prevents alloy becoming brittle
- at 1-2% scavenges contaminants
- increases toughness and ease of polishing
Which 4 metals are constituents of dental amalgam?
- silver
- tin
- copper
- zinc
What are 5 advantages of amalgam?
- good wear resistance
- antibacterial
- good compressive strength
- radio opaque
- chemical set
What are 4 disadvantages of amalgam?
- non-adhesive
- weak in thin sections
- thermal conductor
- not tooth coloured
What is the cavosurface angle for amalgam cavity preps?
90 degrees for retention and resistance
Amalgam cavity preps need which minimum depth?
2mm
What are 6 indications for the use of amalgam?
- class I and class II occlusal and proximal
- where heavy occlusal forces are encountered
- where aesthetics are not important
- building up broken down teeth prior to crowning
- where moisture control is limited
- high caries rate
Which phase of amalgam can be described as the strongest phase due to presence of silver?
gamma 1
