Class II amalgam restorations Flashcards
Embrasure
V-shaped valleys between adjacent teeth
-provide spill way for food to escape during chewing which essentially aids in self-cleansing process
Retention
Use pear-shaped bur
Undercut
Manipulation and adaptation of amalgam
Good condensation / effective packing to ensure marginal seal
What needs to be considered
Method of retention for material of choice
Prevention of recurrent caries - elimination of microleakage
Assist remineralisation of tooth tissue
Longevity under occlusal load - fracture and wear resistance
Protect tooth from mechanical failure
Aesthetics
Class II
Lesions occurring between posterior teeth only
Size can vary from moderate involvement to bulk loss of tooth structure
Direct restorative materials
Classified as plastic i.e. readily deformable when first mixed
Placed into prepared cavity whilst still in that condition
Modelled/ moulded into appropriate shape e.g. amalgam
Class II cavity preps if interproximal
Have to drill all the way down through marginal ridge
Try to keep thin enamel at base
Define D1, D2, D3, D4
D1: initial caries
D2: enamel caries
D3: caries of dentine
D4: pulpal involvement
Isthmus
Central portion of cavity prep on the occlusal surface of a bicuspid or molar
You have cut it too wide
Try to keep it as narrow as possible
Iatrogenic damage
Operator damage e.g. on adjacent tooth
Would fail exam
Must inform patient - candour
Avoid by using matrix band
Axial grooves or locks
For added retention
Locks in dentine not enamel (enamel will shatter)
Axial wall
Wall closest to pulp
Don’t cut too deep
Maybe put liner there to protect it
Principles of cavity prep
Do not damage adjacent tooth
Access should be sufficient to allow adequate visualisation of caries and to allow complete removal
Prepare below contact point
Prepare just into embrasures so that margins are visible and can be finished well
Do not leave unsupported enamel at margins
Removal of caries at ADJ
Wooden wedge
To separate contact point
-for adapting a matrix band to the proximal part of a cavity
Ditching
Marginal breakdown
Marginal ridge
Rounded borders that form the mesial and distal margins of the occlusal surface of a tooth
Meant to deflect food from fossa, stops food from getting trapped in contact area
Indirect restorative materials
Materials usually formed in lab and finished restoration cemented into placed, e.g. Full Gold Crown
Slot and box
1 - 1.5mm deep box like grooves prepared in dentine to > SA
Occlusal lock
Dovetail
Changing concepts
Improved amalgams Instruments with v small working points Amalgam bonding systems Adhesive restorative materials 'If in doubt prevent' rather than 'if in doubt fill'
Principles of cavity prep
Do not damage adjacent tooth
Access should be sufficient to allow adequate visualisation of caries and to allow complete removal
Prepare below contact point
Prepare just into embrasures so that margins are visible and can be finished well
Do not leave unsupported enamel at margins
Allow sufficient depth for amalgam, at least 2mm
Remove all caries from ADJ
When to extend or not: if proximal lesion visible
If proximal lesion visible & access good then marginal ridge can be conserved
When to extend or not: if proximal lesion is not visible, access is difficult or there is <2mm tooth structure below marginal ridge (occluso-gingivally)
Access through marginal ridge advised
This will produce a small box form sufficient to eliminate lesion
When to extend or not: if tooth is caries free occlusally
NOT necessary to cut out the fissure
Extension is a balance
Between conservation of tooth structure and need to remove defective tooth structure
When to extend or not: where occlusal caries and/ or removal of an old restoration have required extending occlusally
An occlusal lock/ dovetail can be prepared to retain the approximal part of the restoration
Where is initial cut made in Class II prep? What bur should be used?
Initial cut made through marginal ridge to penetrate caries and then widened bucco-lingually
Diamond pear shaped bur or tungsten carbide bur
Proximal plate
Can be fractured off with a hand instrument to avoid damage to adjacent tooth (or can you use a matrix band)
What would you remove the proximal wall with?
Gingival margin trimmer
Most important place for caries to be removed from
ADJ
What is the size of the cavity determined by?
Determined by size of carious lesion, extension beyond this should be minimal
How is retention from occlusal forces derived?
From a 2-5 degree divergence of the walls towards floor in both parts of the prep
Where should the margins of the box extend to
Just outside the contact area unless caries dictates otherwise
Exception to box design
When using adhesive materials e.g. composite
Principles of retention for amalgams
Relies on mechanical interlocks
A degree of adhesion can be developed through use of luting or bonding agents
What type of restorative material is an amalgam classed as?
Direct plastic restorative material
Cavo surface angle
Above 70 degrees, preferably 90 degrees to prevent ditching
Accepted minimal dimensions for amalgam
2mm occlusally and 1mm - 1.5mm elsewhere i.e. proximal box
Sufficient bulk to prevent fracture, max thickness of dentine protecting bulk
Deep preps
May require base or liner
Proximal box area
Fractured margins need to be planed with gingival margin trimmer to remove fragile enamel prisms, which could break off and affect marginal seal
Proximal box design amalgam
Retention grooves places B&L 0.5mm deep to ADJ (dentine) gingivally, fading away occlusally, rounded in cross section
Directed laterally not pulpally
Extension onto occlusal surface
Prone to fracture at isthmus therefore sufficient depth must be provided here
Width of isthmus should not be over-cut
Axio-pulpal line angle should be rounded or bevelled to reduce risk of amalgam fracture
Matrix bond and wedges
Avoid creation of overhang at cervical margin
Ensure good contact point with adjacent tooth
Matrix systems purpose
Substitute for missing walls
Create contact point
Restrict extrusion of amalgam and formation of overhangs or ledges
Provide contour for proximal surface restoration
Allow adequate surface texture in areas inaccessible to burnishing
Types of matrices
Siqveland Tofflemire Automatrix Omnimatrix and luciwedges 'V' ring/ half band matrices
Contour
Conves side of spoon excavator used to impart convex contour to matrix band
Achieve good contact area with adjacent tooth
Ensure dental floss placed below contact point to assist removal of ledges & excess amalgam
Condensing amalgam
Using amalgam pluggers or condenser
Adaptation of amalgam to walls of prep
Eliminating voids
Incremental placement of 1mm thickness essential to ensure max condensation
Carving
Wards carver e.g. No 2 or excavator
Marginal ridge should be carved, taking care not to over carve or miscarve
Post carve burnishing
Light rubbing over surface of carved amalgam with burnisher
Do not use heavy forces, avoid margins
If amalgam soft after carving
Wipe with cotton roll saturated in water to proved additional smoothing
After burnishing
Check occlusion
