WEEK 4 Flashcards
Outline G.V Blacks classification for carious lesions
CLASS I
- p/fs carious lesions
- occ surface of posterior teeth
- lingual surface of max incisors
CLASS II
- restos on proximal surfaces of post. teeth
- eg MOD, DO, MO
CLASS III
- restos on proximal surfaces of ant. teeth [not incl incisal edge]
CLASS IV
- Class III + incisal edge
CLASS V
- involves gingival 1/3 of all teeth, facial or lingual
- not incl p/fs
objectives of MID
- remin of early lesions
- reduction of cariogenic bacteria to eliminate risk or further demin
- minimal surgical intervention
- repair rather than replace
- disease control
list and describe the 7 steps to cavity preparation
- outline form
- access to caries
- reach sound tooth structure
- remove unsupported enamel
- retain restoration in tooth - resistance form
- shape and placement of prep should enable restoration to withstand fracture
- flat floor, slight rounding of internal line angles, sufficient dentin support - retention form
- shape form of prep - resists dislodgment from tipping or lifting forces - convenience form
- allows adequate observation, assessment and instrumentation - removal of carious dentin
- with spoon excavator or SSHP - finish enamel margins
- remove faults and walls smoothed - cavity debridement
- commonly with triplex air/water
- removal of debris from prep
explain the significance of a 90degree cavosurface margin
enamel rods usually perpendicular to enamel surface, with inner ends on sound dentin
the strongest enamel margin results in 90 degree angle
state the advantages of composite resin
- lower polymerisation shrinkage
- coefficient of thermal expansion similar to tooth structure
- high fracture/ water resistance
- high radiopacity
- colour match to tooth
- high bond strength to enamel/dentin
- high compressive strength
disadvantages of composite resin
- bacterial adhesion
- polymerisation shrinkage
- technique sensitive - tooth needs to be completely dry
- low tensile strength
describe polymerisation shrinkage and how to avoid it
shrinkage of material towards source of light
- amount of fillers in material will reduce amount of shrinkage [more viscous composite = more shrinkage]
reducing shrinkage
- incremental placement [place base like GIC to reduce filling dimension and act as shock absorber
- strong bonding agent
- good intensity light cure and hold close to restoration
explain c-factor and its relation to polymerisation shrinkage
configuration factor describes ratio of bonded to unbonded surface in restoration
influences polymerisation [high cf = associated w ^ shrinkage stress = debonding, marginal leakage, post op sens
eg class I preps have 5 bonded surfaces [walls + floors] and 1 unbonded [occ opening] = 5:1 C factor
- indicating high cf
CRs shrink as they polymerise, high cf means more of the CR is constrained by bonded surfaces = higher internal stress
describe etch and its function
37% phosphoric acid
creates microtags on enamel enabling a resin based material to bond micromechanically
describe bond and its function
bond = resin w less filler material
func = adheres composite to tooth surface, keeping restoration in place
describe dentine conditioner and its function
10% polyacrylic acid
removes smear layer [tooth prep debris spread on surface after prep] of dentine allowing material to bond chemically to tooth
dentin requires weaker shorter conditioning [to avoid harming collagen fibrils]
describe liner and its function
RMGIC [Vitrebond] used for cavity preps exceeding 2mm
- seals dentin tubules
- prevents thermal conductivity
- reduces post op sens
- protects pulp from toxins and stimulates repair
- reduces microleakages
- enables retention
vitrebond used under CR and amalgam [not to be placed directly on pulp]
- working time just under 3 mins
describe challenges with bonding composite resin to dentin compared to enamel
enamel has higher inorganic content [96%] compared to dentine [70%]
- dentin less mineralised and more porous
dentin tubules surround by collagen matrix
- makes surface less dense and heterogenous
smear layer
- during prep, smear layer forms on tooth = interferes with adhesion if not removed
hydrophilicity
- dentin more hydrophilic than enamel due to higher water content and dentinal fluid
- makes it harder for hydrophobic adhesives to bond effectively
briefly describe flowable resin and its properties
LESS filler than CR = more viscous = higher polymerisation shrinkage
lower compressive strength = not recommended for load bearing restorations
describe the sickle scaler and its function
- periodontal instrument - typically used on ant. teeth
- removes med-large supragingival calc depo
- triangular cross section not suitable for subgingival use
- two cutting edges/ working end
sickle scaler: describe how to find the working end on BOTH anterior and posterior teeth
inner cutting edge [closer to handle] = D surfaces
outer cutting edge ised on facial, lingual, mesial surfaces
ANTERIOR
1. work at midlines
2. position tip at midline in direction of work
3. tilt lower shank towards tooth to establish 70-80 degree angulation
4. roll instrument at line angles to main adaptation
POSTERIOR
1. position tip at distofacial line, with tip facing distally
2. tilt shank to enable 70-80 degree angulation and make distal strokes
3. tilt shank mesially at distofacial line and make strokes across facial surface
4. roll to maintain adaptation
describe GIC
- bonds chemically to enamel and dentin
- acts as reservoir for fluoride and promotes fluoride uptake
- available in capsules to form water based cement when mixed [undergoes acid/base reaction]
- lower compressive strength and wear resistance compared to CR
list advantages and disadventages of GIC
advantages
- fluoride content = makes GIC plaque resistant
- biocompatibility
- fluoride release aids remin
- ease of handling
disadvantages
- short working time
- brittle [cracks on dessication]
- poor resistance to acid attack
- inferior mechanical properties
- 24 hr setting time - needs coating agent
describe the GIC setting mechanism
- after powder/water mixed = acid dissolves on surface of glass particles
- in initial setting –> ca ions = released and react with polyacrylic acid = 3D cross linked structures
- setting reaction continues during next 24H [material matures by absorbing water], then final material strength is increased
list and describe the function of each adhesive system component
- etch = clean surface for bonding, removes smear layer - enabling primer to form hybrid layer
- primer = promotes adhesion to dentin - coupling agents between hydrophilic dentin and hydrophobic resin
- bond = provides better curing and seals dentin tubules - helps reduce shrinkage
describe the selective etch protocol
etching dentin frequently = post op sens
- universal adhesives [eg dentin conditioner] have eliminated the need to etch dentin
- now etch is typically used on enamel margins
list the indications for GIC
restorative material
fissue protectants
luting cement for crowns, bridges
pulp protection
ART
what are things that would be incl on a hard tissue chart
soft tx findings [I/E - E/O]
hard tx exam
periodontal exam findings [recession, pocket depths, furcation, mobility]
presence/ absence of teeth
caries
existing restorations and surface
prosthetics
defects
describe the role of water in GIC setting
GIC = 11-24% water when set
- evaporating too much air [w/ water] or too much water contamination during packing = can cause dissolution of matrix and material failure
- too much water uptake/ water loss = weak cement
- can be prevented by coating restoration surface immediately after it is placed eg vaseline
