Operative Dentistry Flashcards
glass ionomer cements
hybrids of silicate and polycarboxylate cements
powder (calcium aluminofluorosilicate glass) + liquid (polyacrylic acid)
pros of GI cements
cons
releases fluoride, chemical adhesion to tooth, micromechanical to composite, high biocompatibility, good thermal insulators (equal to dentin), thermal expansion similar to tooth, after setting it has low solubility in mouth (least soluble cement!)
higher cement film thickness, limited strength and wear resistance
only __ cement is used as a luting agent and a permanent restorative material
GI
types of GICs
- conventional - luting agent ex. ketac-cem
- light-cured GIC - liner or base, ex. vitrebond and XR ionomer
- resin-modified (hybrid) light cured - ex. Fuji-II
GIs have higher or lower? compressive strength, tensile strength, hardness than composites
LOWER
zinc oxide eugenol (ZOE) cements
SEDATIVE or temporary filling, insulative base, interim caries tx
advantage - eugenol has palliative effect on pulp
powder is zinc oxide, liquid is eugenol
soluble in oral fluids, difficult to remove from cavity preps
properties of improved zinc oxide eugenol materials
good marginal seal, palliative on pulp, easily removed from cavity prep
do NOT have thermal insulation qualities that compare to dentin
ZOE contraindications
on dentin or enamel prior to bonding, as base or liner for composites -> eugenol interferes with composite polymerization!
pt allergy to egenol or oil of cloves, not for direct pulp cap (it’s irritating)
NOT NOT NOT for composites
4 types of ZOE materials
Type I - temporary cement
Type II - permanent cement
Type III (Reinforced) - temp filling material (IRM) and thermal insulating base
Type IV - cavity liner
basic composition = zinc oxide, eugenol, resin
zinc phosphate cement
oldest luting cement, longest track record
powder = zinc oxide, liquid = orthophosphoric acid
primary use as a cement for cast restorations, initial mix is ACIDIC, so use varnish first
has been replaced by polycarboxylate or GIC
superior strength compared to other cements, retention is mechanical
use cool glass slab to incr. working time
zinc phosphate cements can provide good pulpal pretection from ___ but can damage the pulp due to __
protection from thermal, electrical, pressure stimuli
damage pulp due to initial acidic/low pH
zinc polycarboxylate cement
first cement system developed with potential adhesion to tooth structure
liquid = polyacrylic acid + copolymers
powder = zinc oxide + magnesium oxide
how do zinc polycarboxylate cements compare to zinc phosphate cements? in compressive strength and tensile strength?
zinc polycarboxylate strength slightly LOWER than zinc phosphate cements, but HIGHER tensile strength
thermal conductivity of zinc polycarboxylate cement is high/low?
low - good protection against thermal stimuli
main advantage of zinc polycarboxylate cement is
con?
it can bond to tooth structure cause carboxylate groups can CHELATE TO CALCIUM in the tooth
con - short working time
bases are
1-2 mm thick, barriers against pulpally irritating agents, thermal insulation, resistance to compressive strength
a replacement or substitute for protective dentin destroyed by caries
materials used as bases (5)
- zinc phosphate cement - need varnish
- zinc polycarboxylate cement - provides ADHESION
- ZOE (type III or reinforced) - not under composites cause eugenol inhibits setting
- GIC - fluoride, adhesion
- calcium hydroxide Dycal - promote secondary dentin formation
all ok for amalgam and composite, except ZOE can’t work with composite
primary bases are placed on dentin close to the pulp. under amalgam and composite, __ is the primary base. under gold, it’s __, __, or __.
amalgam and composite - calcium hydroxide
under gold - zinc phosphate, zinc polycarboxylate, GIC
secondary bases, most common is __ cement
zinc phosphate cement over calcium hydroxide base
most important consideration for pulp protection is
thickness of remaining dentin
only difference btw a base, cement, and cavity liner is their final application thickness
cements 15-25 microns
cavity liners 5 microns
bases 1-2 mm
cavity liners are used to protect the pulp by
sealing the dentinal tubules
being replaced by new dentin bonding agents
2 types of cavity liners are
- cavity varnish (solution liner, Copalite) - reduces microleakage, NOT for composites, not a thermal barrier
- suspension liner (ZOE, CaOH) - thicker, CaOH prevents thermal shock
cavity varnish in amalgams is for
improving marginal seal, prevent dentin discoloration, prevent acid epenetration
2 types of bleaching
- office - light activated 35% H2O2
2. home - 10% carbamide peroxide
caries is initiated at the tooth surface by growth of __, which produce __
streptococci (mutans, mitis, sanguis (most in oral cavity), salivarius)
produce DEXTRAN SUCRASE (glucosyltransferase), forms extracellular glucans from dietary sucrose -> plaque -> holds lactic acid against tooth
predominant bacteria found in plaque
- strep sanguis (found earliest)
- actinomyces viscosus, naeslundii
- strep mutans, mitis, salivarius
- veillonella, lactobacilli casei, fusobateria
2 most common cariogenic bacteria found in man are
streptococcus mutans
streptococcus sobrinus
main cause of enamel decalcification is
lactic acid produced by acidogenic bacteria
main cause/etiology of caries is
bacteria, or plaque formation
-initiation of caries requires lots of strep mutans in plaque
pulp defense mechanisms to protect from irritation include
sclerotic dentin - peritubular - initial defense
reparative - irritation - 2nd line of defense
vascularity - inflammation
microorganism most assoc. with root caries is
actinomyces viscosus
zones of caries
zone I - normal zone II - carious, subtransparent, can remineralize zone III - transparent, can remineralize zone IV - turbid, must be removed zone V - infected, decomposed, remove
4 zones of incipient caries in enamel
- translucent - deepest zone
- dark - no light, demin and remin
- body - demin
- surface - unaffected
enamel demin occurs at pH
5.5
ductility is
metal’s ability to easily be worked into desired shapes
depends on PLASTICITY and TENSILE STRENGTH
expressed in terms of % elongation
decreases as temp increases
malleability
metal’s ability to be hammered (compressed) into a thin sheet without rupture
depends on PLASTICITY
increases as temp increases
base metal alloys
less resistant to corrosion than noble metals, but they’re strong and are less dense
noble metals
resistant to corrosion, don’t oxidize
4 types of high gold alloys
Type I: highest content, small inlays, easily burnished cause high ductility
Type II: larger inlays and onlays
Type III: onlays, crowns, can be heat treated, quenched so malleability and dicutility are increased
Type IV: bridges, RPDs, can be heat treated
__ against __ materials is the combo that results in least occlusal wear?
gold alloy against gold alloy
disadvantages of cast gold
high thermal conductivity, need to use cement which is weakest point in the restoration
primary retentive feature for onlay prep is
parallelism of vertical surface (axial walls)
sharp point and line angles incr. retention
cap or shoe
cap - complete coverage of cusp, ALWAYS PREFERRED over
shoe - minimal or partial cusp coverage, NEVER indicated on functional cusps
while prepping an inlay or onlay, a gingival bevel is used to
remove unsupported enamel and compensate for casting inaccuracies
crystalline gold (mat gold) is used for
bulk filling of cavities
flow and adaptation not as good as gold foil or powdered gold
cause of porosities/pits in gold foil is related to
improper condensing technique and using oversized pellets
most important factor in securing adapation of gold foil to all parts of a prep is
direction the force is applied
during condensation, __ of gold foil is always increased
surface hardness
main indication for using a direct filling gold is a
small initial class III lesion
amt of force needed to compact direct gold is influenced mainly by
during condensation, what 3 properties of direct filling gold increase?
surface area of the condenser
surface hardness, tensile strength, yield strength
Class V prep retention vs resistance form
retention - sharp internal line and point angles, at axiogingival and axioocclusal line angles
resistance form provided by flat mesial and distal walls, and convex axial wall parallel to tooth
components of gypsum bonded investments
- refractory filler - regulates thermal expansions
- binder - decrease setting expansion, increase porosity of set material
- modifiers
strength of investments for gold alloys depends on amount of GYPSUM
gold alloys shrink upon solidification. dimensional compensation is accomplished by these 2 methods
- setting expansion - result of normal crystal growth, can be enhanced by allowing investment to set in water
- thermal expansion - upon heating, depends on refractory material, the MAIN CAUSE of MOLD EXPANSION
parts of a flame in gas-air blowtorch
- mixing zone - cool and colorless
- combustion - green blue, oxidizing
- reducing - dim blue tip, HOTTEST, only part that should be used to HEAT ALLOY
- oxidizing - outer zone, if it touches metal then “dross” scum develops
if a cast restoratio is in hyperocclusion, pt will complain of
cold sensitivity and pressure in the tooth
minimal reduction of working (functional) cusps is how many mm for amalgam, and cast gold?
minimal reduction of non-working (non-supporting) cusps is how many mm for amalgam, and cast gold?
- 5-3 mm amalgam
- 5 mm cast gold
2 mm amalgam
1 mm cast gold
for metal-ceramic (PFM), occlusal clearance is __ mm and __ facial and lingual reduction
occlusal clearance 1.5-2 mm
1.5 mm facial lingual reduction
enamel is etched with 37% phosphoric acid to
roughen enamel surface to form tags 10-25 micrometers for mechanical retention, increase surface area, better sealing of margins
will look dull white and chalky
most significant advantage to acid-etch technique is
reduction of microleakage
function of dentin conditioner
remove smear layer of dentin and etch intertubular dentin (after enamel etch)
unfilled resin adhesive (bonding agent)
after primer, cured, can bond to composite or amalgam
- LOWEST thermal conductivity and diffusivity (good!)
- offsets the HIGH coefficient of thermal expansion
- lower modulus of elasticity than filled resins
unfilled resin compressive strength is __, yield and tensile strengths are
LOW, even LOWER
marginal leakage related to temp change occurs the most with
unfilled resin
-because it has high thermal expansion (bad!)
acrylic provisionals are usually cemented with
ZOE
main disadvantage of methyl methacrylate as a permanent restorative material is its
low resistance to abrasion
high coefficient of thermal expansion
filled resins (composite resin)
inorganic inert filler (silica or quartz)
harder, stronger, more resistant to abrasion, lower coefficient of thermal expansion than unfilled
most based on BIS-GMA or UDMA, diluted with TEGDMA
dental sealants are generally made of
Bis-GMA
__ is the property of filled resins that is primarily to blame for failure of CLass II composites
low wear resistance
composites are inferior to amalgam in what qualities?
compressive strength and wear resistance
no anti-caries effect like GIs
composites classified on filler particle size and polymerization method. 2 kinds
- chemically activated (self cured) - 2 paste system (benzoyl peroxide initatior and tertiary amine activator)
- light activated - one paste system, photoiniator (camphor quinone) and amine activator
resin filler particles include
colloidal silica, quartz, silicate glasses, ion
macrofills (traditional) 10-100 microns diam. midfills 1-10 minifills 0.1-1 microfills 0.01-0.1 (smoothest finish) nanofills 0.005-0.01 (new!)
what size particles result in better finishing and greater resistance to occlusal wear?
small size
hybrid and microfills use __ fibers to increase hardness and wear resistance while keeping polishability and esthetics
colloidal silica fillers
composite filler particle fxns
decrease coefficient of thermal expansion and polymerization shrinkage
increase tensile and compressive strengths, hardness, improve wear resistance
composite matrix is
bis-GMA or UDM
difficulty in finishing is due to softness of resin matrix and hardness of filler particles
most desirable finished surface for composites is obtained with
aluminum oxide disks
couple agent (silane) acts as a
adhesive btw inert filler and matrix
visible light cure at wavelengths
advantages over UV
400-500 nm
greater depth can be cured, resin can be polymerized thru enamel
DL of canines for class III should be filled with
amalgam NOT composite
-cause composite wont maintain MD dimension of tooth
when 2 adjacent class II lesions, prepare which lesion first? fill which one?
prepare large lesion first and fill smaller one first
retention form definition
form of prep to resist DISOLDGEMENT or DISPLACEMENT
ex. dovetail, retention grooves
resistance form definition
form the walls take to RESIST FORCES OF MASTICATION to prevent fracture
ex. round the axiopulpal line angle, prep perpendicular to forces
purpose of titration is to
coat alloy with mercury
pins
largest one that can be safely placed should be used, place at line angles
if it enters pulp -> CaOH -> new site
should be 2 mm into dentin, 2 mm within amalgam, 1 mm from DEJ
what tooth requires special attention when preparing the occlusal for a restoration?
mand 1st premolar, tilt lingually to avoid encroachment on pulp horn
what margins are beveled in a class II amalgam
gingival cavosurface of box - only if in enamel
occlusal cavosurface
difficult to adapt matrix band to what surface of what tooth
mesial of max 1st premolar
thickness of a good class II matrix should be __ inches
0.002
delayed expansion of amalgams is assoc. with
insufficient titration and condensation, amalgam contamination by moisture
how does amalgam’s coefficient of thermal expansion compare to normal teeth
how does its tensile strength compare to compressive strength
2x
tensile is 1/5-1/8 its compressive
most important in amalgam’s strength is its __ content
mercury
55% + shows loss in strength, fracture, corrsion, etc
factors that influence final mercury content include
original mercury-alloy ratio
amt of trituration
condensation pressure
strongest phase of set amalgam is the __ phase
weakest is
GAMMA
gamma-2
amalgam facts
- smaller particle size -> higher strength, low flow, better carvability
- spherical amalgams high in copper have best tnesile and compressive strengths
amalgam composition (5)
- silver 40-70: decrease set time, incr. setting expansion and strength
- tin 25-27: opposite effects of silver; causes contraction
- copper <3: more free mercury = more setting expansion
amalgam’s strength
BRITTLE, but good compressive strength
brittle describes
high compressive strength
low tensile strength
mercury vaporization most likely to occur during
condensation
high copper amalgam alloys
10-30% copper to decrease gamma-2 (tin-mercury) phase
- spherical - sets faster
- comminuted - zinc or zinc-free, cut or microcut
- combination (admix) - dispersed phase alloy, MOST COMMONLY USED ALLOY TODAY
better than amalgams cause less likely to corrode, less marginal breakdown
creep
deformation with time in response to constant stress
high copper and low mercury content DECR. creep
under and overtrituration increase creep
creep of a metal indicates it will deform under
static load
corrosion produces tin __ and tin __accumulate in the gap btw restoration and tooth to make a good seal
tin oxide
tin sulfide
amalgams should be finished and polished to
reduce marginal discrepancies, create more hygienic restoration, reduce marginal breakdown, prevent tarnishing, make it look better
avoid heat (damages pulp and draws mercury to surface)
most common problem after placing amalgam is
cold sensitivity
cause POOR THERMAL INSULATOR
so place base of CaOH or ZOE
restoring a cusp with amalgam requires at least __ mm removed to provide resistance form
2 mm
adhesive potential is predicted by measuring
spreading or wetting of adhesive over a substrate surface
-the smaller the angle, the greater wetting and potential for adhesion
3 types of stresses
- compression - squeezing of material from external forces
- tension - pulling, resulting in increase in length
- shear - sliding of one layer of a material relative to another layer
toughness
total energy absorbed to point of fracture
-affected by yield strength, % elongation, modulus of elasticity
brittleness
opposite of toughness, vulnerable to fracture at or near its proportional limit
has high compressive strength but low tensile strength
ex. amalgam (why it cant have beveled margins, need butt joints)
modulus of elasticity
material’s stiffness or rigidity
the higher, the stiffer
resilience
energy a material can absorb before onset of any plastic deformation
galvanic shock
electrical charge created when 2 dissimilar metals contact
consequence of thermal expansion and contraction is
percolation
rank order of coefficient of thermal expansion
tooth (lowest ) -> direct gold (best) -> amalgam -> composite -> unfilled resin (highest, worst!)
elastic limit
greatest stress a material can be subjected to and still return to its original dimensions when forces are released
proportional limit
greatest stress produced in a material such that the stress is directly proportional to strain
-high limit has more resistance to permanent deformation
yield strength
stress slightly higher than proportional limit
% elongation of a metal is a measure of
ductility; related to permanent strain at fracture
property that most closely describes ability of a cast gold inlay to be burnished is
% elongation
4 types of excavators (remove caries and refine internal prep)
- hatchet
- hoe
- angle former
- spoon
chisels are used to
cut enamel
instruments used to trim restorative materials
- knives
- files
- discoid cleoid
3 major parts of hand cutting instruments
- handle
- shank
- blade
cutting instrument formulas
1-2-3-4 correspond with?
blade WIDTH-primary cutting edge angle-blade LENGTH-blade angle
bur blades - 2 sides, 3 angles
- rake face - side toward direction of cutting, contacts tooth
- clearance face - away from direction of bur rotation
- rake angle - most important design characteristic of a bur blade, angle btw edge of blade to axis of bur
- soft materials cut best with + angle burs
- hard materials best with - angle burs
- carbides usually have - rake angles - edge angle - btw rake and clearance face
- clearance angle - eliminates friction, the greater the less friction
on a carbide bur, greater number of cutting blades results in __ efficient cutting and a __ surface
LESS efficient cutting
smoother surface
rotary instrument that produces the roughest tooth surface after use is a
cross-cut tapered fissure bur at slow speed
less # of blades results in __ cutting
more efficient, but rougher surface
ex. cross cut fissure burs
4 types of dentin
- primary - forms initial shape of tooth
- secondary - after completion of apical foramen
- reparative - formed rapidly in response to irritants, more irregular
- sclerotic - tubules that become calcified
property most characteristic of current available cement bases is
low coefficient of thermal conductivity
material with high proportional limit has more resistance to
permanent deformation
when deep carie is excavated and cavity is close to the pulp,
place liner of calcium hydroxide, coat with cavity varnish, then zinc phosphoate cement
__ registration of dynamic occlusion is the functionally generated occlusal registration in an indirect gold casting technique
static
these cannot be used on dentin as a cavity medicament
alcohol, CaOH, ethyl chloride, silver nitrate, 10% H2O2
__ is the agent most likely to cause necrosis of the sulcular epithelium and adj. CT when impregnated into retraction cord.
zinc chloride
you can use epi, aluminum sulfate, aluminum chloride
locals reduce saliva during operative by
reducing sensitivity and anxiety during tooth prep
a typical plymer reinforced ZOE cement retains 20% by weight of __ in the powder
polymethyl methacrylate
relationship most used to design restorations is
acquired centric occlusion
reason for cavosurface bevel on inlay is to
improve marginal adapation
binder in casting investments does what?
strengthens investment, contributes to expansion through setting and hygroscopic expansions
fluoride is easily exchanged with hydroxyl ion because
fluoride is smaller and it has a greater affinity for the hydroxylapatite crystal
main disadvantage to using polymethyl methacrylate as a restorative material are its
low resistance to abrasion; high coefficient of thermal epansion
symptoms of hyperemic pulp
pain of short duration, intensified by cold, respond to low levels of EPT
porcelain of PFM separated at ineterface, this might have been caused by
degassing metal at too low of a tempo and fusing the porcelain at too low of a temp
effects of cold working a metal are
decrease in ductility
increase in hardness
drugs that act as anti-sialogogues (2)
atropine
methantheline (banthine)
adding __ __ is the procedure indicated to produce cross-linking during polymerization of a linear polymer
difunctional monomers
__ is the component that could replace eugenol in a zinc oxide paste
carboxylic acid
chelation is a chemical phenomena common to these 2 cements
ZOE and polycarboxylate
if fluoride level is 0.6 ppm, and it’s raised by 0.4 ppm, decay in kids should decrease by __% in 7 years
40
if fluoride in water is upped from 1 - 4 ppm, how does this affect caries
no effect, but mottling of enamel increases
2 properties that allow composites to be bulk placed with reasonable adaptation are
low polymerization shrinkage
low coefficient of thermal expansion
2 materials contraindicated under/in contact with composites are
varnish
ZOE
propantheline bromide (Pro-Banthine) to control salivary secretion is contraindicated in pts with
glaucoma or cardiovascular distress
pit and fissure sealants are retained best on what teeth
max and mand premolars
least likely microbial species found in dental plaque is
staph aureus
Class II in a primary molar for amalgam doesn’t require a bevel because
enamel rods incline occlusally
most effective way to reduce injury to pulp during restorative is to
minimize dehydration of the dentin
to determine caries rate for older adults, epidemiologist uses what index
DMFT
diff btw CLass V prep for amalgam and composite is the
angulation of the enamel cavosurface margins
__ is the most rigid syringe material
polyether
bonding of composites to detin depends on __ __ agents
difunctional coupling
pulp chamber retained amalgam should be __ mm deep for retention
3 mm
materials in ‘walking bleach’ are
sodium perborate
30% aqueous H2O2
what determines outline form for Class III composite
convenience for access, size, shape, locaiton of caries
NOT extension for prevention
reasons to bevel a prep for composite
increase surface area of enamel for etching, expose ends of rods, enhance marignal seal
what color stain is used to change hue of porcelain
orange
green and orange stains on mx incisors are from
poor oral hygiene
stiffness or rigidity is best measured by
modulus of elasticity
__ is an enzyme when incorporated into mouthwasy is most likely to interfere with microbial aggregation in plaque
dextranase
most frequent cause of failure of amalgams is
improper cavity design
pit and fissure caries has what configuration at the DEJ
conical on both sides, so bases of BOTH cones at DEJ
