principals of cavity preparation Flashcards
what are some properties that determine cavity design
- structure and properties of the dental tissue involved
- the disease (caries, PDD, surface loss)
- properties of restorative materials
need to consider if the cavity will need to modified to accommodate a specific restorative material because the binding will differ depending on the surface
which factors of cavity preparation must be reviewed and assessed continually when preparing a tooth to receive a restoration
- position of the caries
- extent of the caries
- shape of the prepared cavity
- final restorative material
what are the different positions caries can be found in
- pit and fissure
- inter proximal (anteriorly or posteriorly)
- Smooth surface caries (also relevant when looking at erosion, abrasion, abfraction or hypoplasia)
- root caries
when should there be operative intervention to a tooth (ie when would a cavity need to be prepared and restored)
when the lesion is caveatted
when the patient cannot access the lesion for prevention
when is operative management something that should be considered for a lesion without necessarily being essential
if the lesion is into dentine radiographically
lesion is causing pulpits
lesion is unaesthetic
explain the features of enamel in relation to cavity prep and restoration
brittle
fractures run along prisms
any fragile enamel under occlusal load should be removed before restoring because it will not support the restoration
dry tissue
which dental tissue is wet
dentine
why are gingival tissues important to consider when restoring teeth
can be inflamed in the presence of plaque
margins of the restorations should be easy to clean so need to consider using a provisional restoration that is replaced when the swelling goes down
why is tertiary dentine harder to restore
the tubular structure is less organised than primary and secondary dentine
if there are multiple dentine types exposed which material would be used - one to match primary or secondary
you would have to treat the dentine types differently so there would be a combination
does the area on the tooth and the way enamel has been cut make a difference to the type of restorative material being used
no it does not make a large difference
describe the significance of linings in relation to operative management of caries
can impact bonding, enamel contamination, protection of pulpal therapeutic agents, risks if micro leakage occurs and secondary caries
this means it is important to assess the quality of the proposed dentine bond
what are the different features of exposed dentine that should be considered when deciding on the bonding and restorative agents
the type (primary secondary or tertiary)
if it is intra inter or peri tubular dentine
the diameter
the density
the mineralisation
if it healthy, diseased or reactive dentine
what are the principles of cavity preparation driven by
caries removal
necessary finishing ( modification of the cavity) to allow for
- maximising adhesion
- occlusal relationships
- ease of patient cleaning
- properties of the materials used
why should an attempt be made to remove healthy tooth tissue
if the material used for the restoration requires it or if the margins of the cavity cross an occlusal contact
outline the principles of caries removal and cavity preparation (know this card!!)
- identify and remove carious enamel
- remove enamel to identify the maximal extent of the lesion at the ameldodentinal junction and smooth the enamel margins
- progressively remove the peripheral caries in the dentine from the ADJ first, then circumferentially deeper
- only then remove the deep caries over the pulp
- outline form modification (Cavo surface margins) for enamel finishing, occlusion and requirements of the restorative material
- internal design modification including internal line and point angles, and to match the requirements of the restorative material
what is the Cavo surface margin
junction of the outline form of the external surface and the internal surface of the tooth
what steps should be taken for the final Cavo surface margins during cavity preparation
remove enamel that will not be supported by the etch technique
smooth cavosurface margins and line angles
ensure there are no excessively acute line angle transitions and that the outline form is smooth and rounded
check for stress concentrators
why should sharp lines be avoided when preparing cavities
they can cause fractures
what is the line angle
the junction between two surfaces
what is the point angle
the junction between three surfaces
what are the steps to final cavity design
- where an existing restoration has been removed, ensure that no traces of restorative material remain unless placing a repair
- smooth external enamel sharp line or point angles
- create appropriate Cavo surface margin angles
- removal internal dentinal sharp line or point angles
- check for stress concentrators
the final seal of the restoration is critical. which elements need to be met for this seal to be effective
- smooth margins
- approvate cavo surface margin angle
- no unsupported tooth tissue
- no stress concentrators
- internal anatomy that allows adaptation of material
why do marginal seals need to be perfect when restoring teeth
because bacteria can get in and form plaque leading to further caries
what is secondary caries
caries caused by failed restorations allowing build up of plaque
what should be done once the prepared cavity is satisfactory
clean the cavity to ensure it is free from debris generated during preparation
what is the first principle of cavity preparation
access the caries
- apply the dental dam
- remove overlying enamel with a high speed bur to gain access to carious dentine
- follow the cares at the ADJ
- do not extend into non carious areas
what is the access point for removal of inter proximal caries
occlusal surface
what is the second principle of cavity preparation
extent of the cares
the caries spread at the ADJ determines the outline form and encloses the extent of caries
clear all caries at ADJ and check staining
smooth enamel Cavo surface margins and examine adjacent contact for caries
avoid trauma to the adjacent tooth
how many direct plastic restorations are replacement restorations
80%
which bur should be used to remove restorations
high speed
what may happen if the angle between the restorative material and the internal surface of the cavity was not considered
cavo surface margin would become exposed
why it is important to not remove a restoration by cutting around the edges
this will increase the size of the cavity unnecessarily
how to remove a restoration properly
start from the centre of the restoration and cut toward the edge of the cavity
use the high speed bur to cut the restoration into pieces
try to chip out chunks of the restoration where possible
remove all the restoration and any of the underlying base material
why may there be a crack in an amalgam restoration
if the cavity is not deep enough - amalgam needs at least 2mm of thickness or it will fracture
what is the third principle of cavity preparing
remove dentinal caries
this is detected as a brown stain or softened tissue when using a sharp probe
sound dentine should not yield under probing
any sticking of the probe indicates residual carious dentine which should be removed
residual carious dentine must be removed first from the ADJ and last from the pulpal floor
what is used to remove carious dentine
hand held excavator
round bur
chemo mechanical caries removal
caries detector dyes may be helpful
how to know if dentine is carious
it will be detected as brown stains or softened tissue when using a sharp probe
if dentine is hard and scratchy leave it alone as it has no decalcified yet
the stained dentine should only be left if it is hard to probe but it needs to be removed from the ADJ
what is used to remove carious dentine from the pulpal floor
the largest instrument which will conveniently work in the cavity ie
large round bur
large hand held excavator
chemo mechanical caries removal
why should large instruments be used for the removal of carious dentine from the pulpal floor
smaller burs and excavators will cut deeply more quickly and this risks pulp exposure
what should be done if carious pulp exposure is a necessity
pulp therapy
- direct and indirect pulp cap (CaOH)
- exposing a healthy pulp
- importance of symptoms
what is the fourth principle of cavity preparation
modifications
- one caries is removed/ an existing restoration is removed, a decision should be made on which restorative material to use
- the cavity preparation should be modified to match this material, including changes to
- enamel margins, cavosurface margin angle, occlusion, internal anatomy and dentine quality
- ensure the cavity is rounded internally with no points or sharp angles and determine the dentine type to influence the use of materials
what are the most commonly used restorative materials for direct plastic restorations
composite and amalgam
what are the advantages of composite
- aesthetics
- conservation of tooth tissue
- support for remaining tooth tissue
- adhesion and bonding to both enamel and dentine so no tooth tissue needs to be removed so it can stay in
- command cure
- low thermal conductivity
- elimination of galvanism (like seen with amalgam)
- amalgam alternative
- mechanical properties, thermal expansion and contraction
what is the con of composite
operator sensitive
what are the cons of amalgam
does not bond to enamel or dentine
does not support the tooth
bad for environment
what holds amalgam to a restoration
retention and resistance form
any cut dentine may require a sealed resin layer
what prevents amalgam from fracturing
adequate bulk - at least 2mm deep
how to remove healthy tissue
retention and resistance
pros of amalgam
strong under occlusal load and less moisture and technique sensitivity
what does retention mean for restorations
features of the cavity which prevent the restoration being dislodged in any occlusal direction eg when the internal dimensions of the cavity are greater than the access into it
anatomical cavity design features like undercuts and dove tail
not essential for adhesive restorations but required for non adhesive restorations
what retention method is required for adhesive restorations
when the cavesurface angles are adjusted to increase the bonding area and ensure there is no unsupported enamel
what are the three labels pointing to
bevel
line angle
point angle
features of cavity margins for amalgam restorations
- caries fre
- free of contact with the adjacent tooth
- accessible for cleaning
how should the cavity margin and restoration interface be designed
for maximum strength and minimum leakage
what is the function of the bevel on cavity margins
align orientation with prisms for composite and consider the best approach to achieve and cut prisms
what is the Cavo surface angle between for amalgam
90-120 degrees
what is AMA
amalgam margin angle
what is USE
prisms unsupported by underlying dentine
what is CSMA
cavo surface margin angle
what happens if there is caries left at the dentine enamel junction
this will result in unsupported enamel and early breakdown of the restoration margin if micro leakage occurs
what does a high configuration factor mean
there will be increase polymerisation contraction stress - volumetric shrinkage
what to think about when using amalgam
design
properties
how to place
steps for cleaning up after preparation
once the cavity is prepared, it will contain loose enamel and dentine clippings, as well as organic and inorganic dentine debris smeared into the walls of the cavity
wash the cavity with air and water to remove the loose debris
rinse with chlorhexidine and remove
rinse with water and leave the surface moist
what should be used to rinse the walls of a prepared cavity
chlorhexidine and then water
should choice of restorative material be made before or after removal of the caries
after
what are the three elements to consider when designing cavities
the remaining tooth tissue
the quality of the remaining tooth tissue
choice of material
list the principles of cavity preparation
- identify and remove carious enamel
- remove enamel to identify the maximal extent of the lesion at the amelodentinal junction and smooth the enamel margins
- progressively remove peripheral caries in dentine from the adj first then circumferentially deeper
- remove deep caries over pulp
- outline form modifications including enamel finishing, occlusion and matching requirements of the restorative material
- internal design modifications including internal line and point angles, and match to the requirements of the restorative material
