Restorative Dentistry Flashcards
What are the determinants of a cavity design?
- Structure/properties of the dental tissues
- The diseases involved (caries, periodontal disease, tooth surface loss)
- Properties of restorative materials
What are the principles of cavity design?
- identify and remove carious enamel
- Remove enamel to identify maximal extent of the lesion at ADJ and smooth enamel margins
- Progressively remove peripheral caries in dentine - from ADJ and then circumferentially deeper
- Only then remove caries over pulp
- Outline form modificaiton - enamel finishing, occlusion etc
- Internal design modification - internal line and point angles, requirements of the restorative material
What are possible position of caries?
Caries can be located - pits and fissures - Proximally (anterior/posterior) - Smooth surface - Root Intervene when the lesion is cavitated - Intervene when the patient can't access the lesion for prevention
What is the extent of the caries (think of tissues)?
Enamel is brittle - can fracture along prisms, unsupported enamel removed before restoration
Dentine - porous, more elastic, think of primary, secondary and tertiary
Dentine-pulp complex - operative procedures involving dentine affect pulp
Gingival tissues - inflamed in the presence of plaque, margins of restorations should be easy to clean, consider provisional restorations
Preserve healthy tissue where possible
What is the shape of the prepared cavity?
External walls: - distal - facial - buccal - gingival Internal walls: - pulpal - occlusal floor - axial -pulpal axial wall
- Cemento-enamel junction
What are 3 main examples of final restorative materials and what are their specific requirements?
- Composite - bevel, acid etch
- Amalgam - undercuts, isthmus, flat surfaces, grooves
- GIC - dentine conditioner
In pickards operative manual what does it say about enamel preparation?
Aims of cutting through enamel to view gain access to carious dentine are:
- gain visual access to carious dentine requiring removal
- remove demineralised and often unsightly carious enamel
- create a sound peripheral enamel margin to which an adhesive restorative material can form a seal
In pickards operative manual what does it say about carious dentine removal?
- Anatomical extent of the lesion > peripheral caries to caries overlying pulp at level of ADJ
- Histological depth of the lesion - i.e. the collagen and mineral content of the carious dentine
In pickards operative manual what does it say about peripheral caries?
Prevention of secondary caries is entirely dependent on the seal between restorative material and tooth at the cavity periphery
Should never leave necrotic dentine at the level of the ADJ (cannot be adhered to)
In pickard operative manual what does it say about caries overlying pulp?
Give consideration to its proximity to the pulp
Is the pulp symptomatic?
If risk of pulpal exposure high, and good restorative seal can be achieved, and pulp asymptomatic, a small amount of carious dentine can be left
What are problems encountered with restorations?
- Configuration factor - “ratio of bonded to unbonded surfaces” - important for composite
High (bad) = increased polymerisation contraction stress
Low (good) = reduced polymerisation contraction stress - Contraction stress - “poor enamel preparation margin”
composite dimensional change
etch/bond is stronger than interstitial enamel strength
composite will fracture with weak enamel and dentine attached to it - Cavity toilet phenomenon
Cavity will contain loose enamel and dentine chippings following prep
Wash out with mix of air water and CHX
Rinse with water and leave moist
What are the two classifications for dentinal caries? (p.s. not primary, secondary, tertiary)
- Affected dentine Softened Demineralised, not yet infected by bacteria Sensitive more pulpally Doesnt stain acid red should be LEFT to REMINERALISE
- Infected dentine Outer carious dentine Bacterial plaque Softened, contaminated w bacteria Highly demineralised Lacks sensation Stains acid red w propylene glycol Should be EXCAVATED
What is a cavosurface margin angle?
The cavo surface angle is the angle of a tooth structure formed by the junction of a prepared (Cut) wall and the external surface of the tooth. The actual junction is referred to as cavosurface margin.
What is a line angle?
It is formed by the junction of two surfaces, name derived from both surfaces
What is a point angle?
It is formed by the junction of 3 surfaces
What are the risk factors for caries?
- Socio-economic status
Poor knowledge of dental disease
Irregular attender
Siblings have high caries rate - Medical history
Immunocompromised
Disabled individuals ability to brush teeth
Xerostomia - reduced plaque clearance - Dietary habits
High lvl of fermentable carbs - Fluoride use
No fluoride toothpaste
Non-fluoride area - Saliva
Poor saliva flow
Low buffering capacity - Prior dental interventions
RPDs - plaque traps
Ortho appliances - ditto RPDs
Multiple restorations and history of failed resto’s
What are the causes of secondary caries?
- Marginal failure of existing restoration
- Due to poor adaptation of restorative material
- Fracture of unsupported enamel leaving exposed area
- Amalgam ditching of margins
- Failure to remove all of initial lesion
What is the hybrid layer?
It is a resin impregnated dentine layer
Formed after dentine smear layer conditioned by acid
Sufficient bond strength cannot be achieved unless all the smear layer is removed by conditioning
The smear layer must be rinsed off prior to primer being applied otherwise the smear plugs will be redeposited
Removal of the smear layer also leads to decalcification of the intertubular dentine to a depth of a few microns leaving just a collagenous dentine matrix
Hence why its called the hybrid layer
What are the reason why restorations fail?
- Misjudgment of selection of restorative material - putting amalgam and gold near each other can cause corrosion due to galvanic activity
- Incorrect cavity prep - if done incorrectly it can affect both the tooth and restorative material
- Material manipulation - if composite overworked it reduces wear resistance but also gives poor aesthetic
- Oral environment
Poor access, thermal changes, forces, microbes, aqueous nature
What is the bond strength in different types of dentine?
- V high in sound coronal dentine
- High in sound root dentine
- Secondary dentine worse than primary due to less mineralisation
- Medium in caries AFFECTED dentine
- Low in caris INFECTED dentine
