Requirements of Filling Materials Flashcards
Conditions which need restoring
- fracture
- caries
- erosion/abrasion
Fracture is caused by…
trauma
Caries is caused by…
bacteria
Erosion/abrasion is caused by …
- acids
- wear
Properties of enamel
- outer shell
- ceramic (apatite) which is hard but brittle
- relatively translucent
Properties of dentine
- inner layer
- made of composite (apatite and collagen polymer)
- softer and tougher than enamel
- more opaque too
Requirements of direct filling materials
- done chairside
- mouldable to cavity (initially fluid and plastic)
- harden and stregthen during setting (resist mechanical forces)
- bond to tooth
- tooth colour
- protect pulp how enamel and dentine would (temp and electrical changes)
- biocompatible
- mechanically stable (fatigue, stiffness etc)
What aesthetics are needed from fillings initially?
- patients want white appearance but enamel rarely white
- match shade with possible materials (not with amalgam, gold etc)
- enamel is translucent so opaque materials don’t look lifelife
What is needed long term from filling materials aesthetically?
- needs to be stable over time
- look the same if not much different from when it was placed
List factors that affect aesthetics of fillings over time
- roughness/gloss
- location
- stains
How does roughness affect aesthetics of fillings?
- scratches can lead to gloss loss
- micro-organisms colonise rough surfaces
How does location affect aesthetics of fillings?
- forces different anterior and posterior
- aesthetics more essential anteriorly
How do stains affect aesthetics of fillings?
- depends on material
- composites stained by food/drink
- amalgams may tarnish
Regarding thermal protection, what do materials need to be?
- insulators
- low conductivity and diffusivity in enamel and dentine to protect pulp from hot and cold
Are amalgam and gold insulators?
Solution?
- no - conductors
- in deep fillings, may need insulator cement
- acts as a barrier to pulp
Are composites insulators?
- yes
- cement may not be needed
- some dentists will use it though
List protective properties of filling materials
- non-toxic and non-irritant
- cariostatic
- adhere to tooth tissue
What kind of reactions can be had to filling materials?
- setting reactions - avoided if toxic components kept to safe levels
- individual allergies - common so need a full history
What does it mean for a filling material to be cariostatic?
- prevents caries
- some release fluoride
- antibacterial agents incorporated in filling
Why is it good for materials to adhere to tooth tissue?
- allows conservative preparation
- only remove carious tissue and retain sound tooth
- reduces microleakage - bond acts as a barrier
Explain dimensional changes when material sets
- shrinkage can cause stress on adhesive bond and effect retention and microleakage
- expansion causes stress development in tooth - filling extruding beyond margins or fracture of tooth
The mouth is an aqeous environment so filling materials ideally shouldn’t do what?
absorb water
Water diffusion and absorption can lead to…
- hydrolysis
- softening
- leaching
- staining
How does hydrolysis occur?
- filling components react with water
- weakening filling
How does softening occur?
water can act as a plasticiser
How does leaching occur?
- components can diffuse from filling into oral cavity
Filling materials need to withstand temp variations.
2 ways you’re exposed to this
- hot and cold food/drinks
- thermal cycling (5-60 degrees)
Filling materials need to withstand pH variations. How are they exposed to this?
- acidic with plaque (4 ish) and drinks (1-3)
- alkaline (medicine and toothpaste pH 12)
- solvent exposure (foods like peppermint oil, alcohol)
- corrosion (galvanic effects/medals)
Thermal expansion and contraction can cause large dimensional changes. Explain issues
- contributes to stress at interface
- can lead to the interface failing
- may have a ‘pump’ effect
- can force stains and bacteria around margins
- secondary caries may initiate away from surface
Larger cavities experience … changes
greater
Fillings must withstand mechanical stress. Explain
- high stress leads to fracture
- low stress over time - fatigue
- sudden, rapidly applied stress - impact
How do differences in rate of strength development occur?
- setting time (can be hours/days for strength)
- setting mechanisms (can speed it up with light curing etc)
Abrasive factors on teeth
- hardness
- two body - opposing teeth
- three body - food and/or toothpaste
- solvents causing softening
How does bacteria affect fillings?
- breakdown of resins
- leads to weakening
Should fillings be radio-opaque?
- yes
- caries is radiolucent
- radiolucent fillings will confuse diagnosis
Polymer-based materials e.g composites - radio-opaque?
- made from low atomic number elements
- not radio-opaque
- need a radio-opacifier (more opaque but lowers strength)
- compromise needed
What is taken into consideration with working and setting time?
- sufficient time to mix and place
- long ST is uncomfortable for patient
Mixing and setting with 2 components in material
- setting starts by mixing
- technique sensitivity possible
- mix by hand - spatula on pad
- mechanical mixing - capsules in a machine
Mixing and setting with one component materials
- lower technique sensitivity
- setting starts by external source like light
The ideal filling material should be …
- easy to mix and place
- should be low waste
- safe to mix in clinic
The ideal application procedure should be …
- easy to sculpt
- transferred by spatula and syringe
- single-dose packets or as easy
Ideal technique sensitivity for materials
- moisture control - does moisture stop setting
- less stages the better - more stages requires more time
Can 1 material do everything for cavities?
- ideally
- class 1 to 5 cavities
- small and large
