restorative resins continued Flashcards
what are the classification of resin-based composites?
Traditional Hybrid (large particle) Hybrid (Midfiller) Hybrid (Minifiller) Packable hybrid Flowable hybrid Homogeneous microfill Heterogeneous microfill
what are traditional composites?
Large filler silica or quartz particles (1–50 μm)
Wide particle size distribution
Filler loading is 70-80 wt% or 60-70 vol%
Significant improvement of mechanical properties because of the stress transferred from matrix to particles
Water sorption, polymerization shrinkage, and thermal expansion substantially reduced
Higher resistance to abrasion
Radiolucent
what are the clinical considerations of traditional composites?
Roughness developed as a result of finishing, tooth brushing, and masticatory wear
Restoration roughness is a clinical disadvantage as they become more susceptible to discoloration and stain retention
Their poor wear resistance makes them inferior to materials designated as posterior composites
Fracture stress is not a common problem
If you have hills and valleys then you have an increase in surface area so there is more area for collecting for discoloration and stain retention
what are small-particle filled (SPF) composites?
Developed to improve surface smoothness and wear resistance, physical and mechanical properties, thermal conductivity and polymerization shrinkage
Made of silica and glasses containing heavy metals for radiopacity
Colloidal silica added ~5 wt% to adjust the viscosity
Inorganic fillers ground to a size range of ~0.5–3 μm
Wide particle size distribution facilitates increasing filler content (80-90 wt% or 65-77 vol%)
Heavy metals are like strontium, uturbium,
what are clinical considerations of small particle filled composites?
High filler content and consequently great strength
Used in high stress and abrasion prone applications such as Class IV sites
Possible to attain smooth surfaces for anterior applications
what are microfilled composites?
Uses colloidal silica particles to overcome surface roughness associated with traditional composites, and low translucency problems associated with SPF ones
Particles are about 40 nm in size; thus exhibit very smooth surfaces
Tend to agglomerate to form particles ten times in size
Difficult to wet by the monomer due to the high surface area; thus thickening of the mix occurs
High viscosity can be overcome by grinding a prepolymerized composite highly loaded with the colloidal silica particles
Filler content is 80 wt% or 60 vol%
Low shrinkage
Weak bond between particles and matrix faciitates wear by chipping mechanism
Not suitable for use as stress bearing surfaces
Inferior physical and mechanical properties to traditional composites
You have to have a very strong bond between the particle and the matrix so the weak bond is a problem.
Agglomeration is a problem, because how can you garuntee from a supply perspective that they will stay as a nano particle. So you want to avoid the agglomeration.
You’d need more mercury if you had very small particles to wet the particles with the mercury.
what are clinical considerations of microfilled composites?
Potential of fracture is greater in stress-bearing situations such as Class II and Class IV sites
Occasional debonding at the restoration’s margins is attributed to the debonding of the prepolymerized composite filler
To minimize the risk for chipping, diamond burs are used instead of fluted tungsten carbide burs
They are the resin of choice for aesthetic restoration of anterior teeth and for restoring subgingival area
what are hybrid composites?
Developed to maintain desirable properties of SPF composites but with improved smoothness
Physical and mechanical properties range between traditional and SPF composites
Competitive to microfilled composites used in anterior restorative applications with respect to surface smoothness and aesthetic characteristics
Contains colloidal silica particles (10-20 wt% of total filler content) and glass particles incorporating heavy metals (75-80 wt% of total filler content)
Average particle size of glass particles ranges between 0.4 to 1.0 μm
Radiopacity sufficient
what are the clinical considerations of hybrid composites?
Used for anterior restorations including Class IV sites, because of their smoothness and good strength
Widely employed for stress-bearing posterior restorations
The terms hybrid and SPF composites are often used interchangeably
what are flowable composites?
Emerges from the modification of SPF and hybrid composites
Have a reduced filler level; thus, they flow readily, spread uniformly, and intimately adapt to a cavity form to produce a desired dental anatomy
Used in Class II restorations in gingival areas
More susceptible to wear
More susceptible to wear because of the reduced filler material.
what are composites for posterior restorations? when might you use them?
Direct Posterior Composites
Necessity to replace amalgam out of concern of mercury toxicity
Composites are used for Class I and Class II restorations
a direct posterior composite like packable composite, what is it?
Compared to amalgams, composite replacement is far more time consuming and demanding
Composites cannot be packed vertically so that the material flows laterally for intimate contact with cavity walls
Packable and condensable composites offer a solution to the problem. Both have filler characteristics that increase strength and stiffness of the uncured material, and provide a consistency similar to that of lathe-cut amalgams
Packable and condensable composites contain elongated, fibrous, filler particles of about 100 μm long, and textured surfaces to interlock or resist flow
Uncured resins are stiff, yet moldable under force by pluggers
Takes twice the time of amalgam placement
So this is a mechanical bond because of the interlocking.
what is the problem of marginal leakage?
Attributed to polymerization shrinkage
Results in marginal leakage, which increases the risk of marginal staining and marginal carries
This is one of the greatest problems of composites used for Class II and Class V restorations
what is radiopacity in resin based composites?
Resins are inherently translucent
Radiographic contrast is required
Radiopacity is especially important for any posterior restorative material
Radiopacity is imparted by heavy metals in glass filler particles
Restorations’ radiopacity should be equal to that of enamel, which is twice that of dentin
Exceeding the radiopacity of enamel by a large degree will obscure radiolucent areas caused by gap formation and secondary caries
for resin based composites what is wear like?
Occlusal wear of composites is a clinical problem
No test method offers a valid predictor of clinical performance
Composites designed for posterior restorations wear more than enamel by 0.1-0.2 mm/year
Two principal mechanisms of composite wear are proposed: two-body wear mode, and three-body wear mode
Two-body wear mode – you have one tooth rubbing against a tooth
Three-body wear mode – you have two teeth and a particle inbetween the teeth. Like a nut between two teeth.
