Operative Flashcards
Rubber Dam and amalgam
a dry field provides delayed expansion of amalgam
Pin placement dimensions
Used to retain large restorations (prevent lateral displacement in occlusion), although they weaken the material.
Max of 4 = Place one per missing line angle…not cusp!!!
Large diameter/largest pins
Coat with adhesion (4-META) materials increases fracture resistance of cores.
If hits pulp a vital tooth: stop bleeding –> dry –> CaOH
If pin perforates, place pin but don’t et it extend out to the surface
Place pins:
2 mm in amalgam (any restorative material)
2 mm in dentin
0.5 - 1.0 mm from DEJ
Sometime bending is required, but use the tool given
Pin Types:
- Self-thread
- Cemented
- Friction lock
RISK:
- pulp exposure (pulp irritation)
- tooth perforation
- weakens amalgam
- Tooth fracture or crazes in dentin
- micro leakage of pin hole channel
Burs
The GREATER the number of cutting blades on a bur, the LESS efficient but a SMOOTHER surface (polish)
Chisels vs hatchets
Both are mainly used to cut enamel
Gingival margin trimmer = bevel class II gingival margins
What does this mean on an instrument: 10-85-8-14
- Blade width (1/10 of mm) = 1.0 mm
- Primary cutting edge (centigrades)= 85
- Blade length (mm) = 8 mm
- Blade angle (centigrades) = 14
what is the nib?
working end of a non-cutting instrument (condenser, burnisher)
What is the distinction between a base, liner and cement?
The only distinction between a base, cement and liner is by application thickness (thickness of remaining dentin).
Base 1-2 mm (Function is to replace lost dentin, thickness required for thermal insulation)
Cement 15-25 μm
Liner 5 μm (Function is to seal dentin tubles = no pain)
base categories:
• Primary = placed on dentin
• Secondary = placed over the primary base (CaOH for resin/amalgam with direct pulp caps, or ZnP for gold).
ZOE, although a suspension liner, cannot be placed under composite due to its inhibition of resin polymerization.
Types of liners:
- Solution Liner (Varnish for Zn-Phosphate cement. The varnish is needed first b/c ZnP is not biocompatible due to its initial low pH)
- should not be placed under composite b/c it will inhibit polymerization (ZOE, although a suspension liner, does the same)
- Water in-soluble
- Varnishes will seal amalgam leaks, but a biocompatible base must first be dried before application. - Suspension Liner: CaOH, ZOE (water soluble)
- Acute inflam. = Eugenol (released into dentinal tubles)
- Chronic inflam. = CaOH
Both harden intra-orally by act of drying, not a chemical rxn
Which material is the only one that can be used as a cement and a permanent restoration?
GI
- As a luting cement, its function is to provide a non-permeable seal around restorative margins
- Chemically bonds to tooth structure (like Zinc Polycarboxylates)
- Bonds to composite
Occlusal reduction for gold onlay, amalgam, ceramics
Functional cusp
- Amalgam: 2.5 - 3.0 mm
- Gold: 1.5 mm
- ceramics: 2.0 mm
NOTE: Gold preps (onlays and direct gold class Vs have shard angles that are used for retention (vs. FCC). - Resistance form for gold is flat M and D walls and convex axial walls
High occlusion will produce what patient complaint?
- cold sensitivity
- percussion (+)
Ferrule Effect requires what?
- Envelopment of a tooth by a crown
- Need 1.5 mm (If less, needs B/U and crown lengthening)
- Requirements for good ferrule:
o 1.5 – 2.0 mm of B and L subgingival tooth structure
o 1 mm of tooth thickness after preparation
o 3.5 (anterior) or 4 (posterior) mm of supra bony structure (3 mm minimum)
What is the principal cause for mold expansion?
thermal expansion (not setting)
Factors affecting expansion:
- older investments, less expansion
- Higher water content, less expansion
- less spatulation time, less expansion
- longer the time between mixing and immersion in water bath, less expansion
Two class III lesions nearby, which to prep first?
Prep the larger one first
Fill the smaller one first
Restore Class III canines with?
amalgam or direct gold
Amalgam is a ___ thermal conductor? Insulator?
Poor insulator (thus, requires a base ZOE or CaOH) Good conductor
Height of contour is located where?
gingival to middle 1/3 coronal
Class I cavities are found where?
both anterior and posteriors
What to do if a patient has galvanic shock?
Nothing, it will dissipate in a few days
Retention and resistance in cavity preps
Retention = converging walls Resistance = resistance mastication damage = resist fracture fo restoration = round line angles.
Amount of enamel dissolution post etch
7 - 25 microns of enamel tags (mechanical ret.)
- etch promotes wetting and adhesion
light cure in __ mm increments
First layer is 1.0 mm
Deep fillings require no more than 2.0 mm max
(40 sec can penetrate up to 2.5 mm)
- Cause polymerization shrinkage: camphor quinone (alpha-di-ketone initiator) reach with light (474 nm blue visible light) --> the ketone reacts with an amine to make free radicals.
- results in internal stress and gaps
- “C factor” = cavity configuration = radio of bonded to unbounded teeth surfaces = higher ratio means higher polymerization stress (Class I > Class III)
fillers in resin cause
reduction in polymerization shrinkage
- reduce coefficient of thermal expansion
- increase tensile strength
- increase compressive strength
- increase hardness
Amalgam has greater wear resistance than composite resin
Polish composite resin with
fina diamonds and aluminum oxide discs
Dentin bonding occurs via
intertubular dentin decalcification (done so by the primer to expose the dentin tubles)
Bonding agent is unfilled resin.
Polishing and abrasives
Reduce polish abrasiveness = thin, water mix + low speed + light pressure + dull, round particles
Do not polish on patients with: green stain or newly erupted teeth (demineralized teeth) + respiratory problems + communicable diseases (air) + high caries risk
Abrasives comprise of 20-40% dentrifices
Final polishing of amalgams require a rubber cup + pumice flour + high luster agent (tin oxide)
Polish with large particles, thick and viscous mixture, and apply using firm and increasingly heavy constant pressure
Do not polish “green stains” as it is demineralization
Special attention must be given to this tooth when prepping the occlusal aspect (i.e. in RCT access, or Class I restorations)
Mand 1PM (Tilt bur lingually) - plural floor coincides with angle of cusp heights
Minimum distance from the margin of the medial and distal wall to the proximal surface for:
- PM
- Molars
- PM = 1.6 mm
2. molars = 2.0 mm
most difficult tooth to burnish a matrix band?
Max 1PM
In general, trim matrix band on a slot prep at least 1 mm higher than expected for the marginal ridge
only bevel the gingival cavosurface margin in a class II prep if it is in enamel. If its in cementum, no need to. This is only meant to remove unsupported enamel. B/c enamel rods in the gingival 1/3 of primary teeth extend occlusally, there is no need to do this in PEDO teeth!
Xylitol mechanism
- keeps sucrose molecules from binding to each other and form dextran (glucans and fructans), and hence can’t attach to smooth surfaces
- Makes an alkaline environment = bacteriostatic
Enamel demineralization occurs at glucosetransferase –> glucans + lactic acid + fructans
Most decay: pits/fissures > interproximals
Lactobacilli make lexan (not dextran like strep)
Stippling
they are located at the intersection of epithelial ridges that cause depression and interspersing of CT papilla between the intersections → bumps
First line of defense for pulp
secondary dentin (sclerotic, peritubular dentin), followed by territory dentin then pulpal inflammtion
Class II amalgam vs Inlay
Same occlusal isthmus width (1/3 cusp width) and depth (0.5 mm in dentin), axiopulpal line angle (beveled/rounded)
Difference:
- Internal line angles are sharp in an inlay
- walls converge/diverge
- Retention in gingival wall are reverse curves in inlay, while amalgams have retention grooves
