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Define outline form and identify the specific features and criteria that address it in the class II cavity preparation
- Outline form- external form; includes occlusal and proximal outline form.
- -smooth-flowing from a dovetail through the isthmus to the s-curve (as needed, usually located on the buccal wall) to the proximal box.
- Pre-clinical evaluation- defined by laboratory standards
- Clinical evaluation- extent of caries
- Outline size
- 0.8 – 1.0 mm isthmus width
- 1.0 – 1.5 mm buccal fissure and lingual fissure extensions (molars)
- 0.25– 0.5mm dovetail extensions buccolingually
- 0.8– 1.0 mm distal and distobuccal fissure extensions (fishtail at distal cusp)
- fishtail extensions - 0.8 - 1.0 mm (RGS 2/3)
- dovetail extensions - 0.25 - 0.5 mm (RGS 1)
- proximal clearance (Buccal/lingual) - 0.5 mm (0.25 - 0.75 mm) RGS 1)
- gingival clearance - 0.5 mm (0.5 - 1.0 mm) ( RGS 1)
- -proximal wall of the non-functional cusp forms a perpendicular angle with the gingival wall
- -proximal wall of the functional cusp forms a slight acute angle with the gingival wall
2) Define resistance form and identify the specific features and criteria that address it in the class II cavity preparation Resistance form- internal form; shape and placement of the preparation walls enabling tooth to withstand masticatory forces, preventing fracture of the tooth or restorative material.
- -pulpal/gingival walls perpendicular to long axis of the tooth; flat pulpal/gingival walls buccolingually
- -pulpal depth - 1.5 - 1.9 mm
- -axial depth - 1.0 - 1.5 mm (0.5 mm into dentin clinically)
- -strong cusps/ridges with sufficient dentinal support
- -divergent dovetail wall
- -s-curve- increase strength of amalgam and tooth structure at the junction of the occlusal step and proximal box, exit angle 90degrees
- -round internal line angles (inc. rounded axiopulpal line angle and gingival "bevel" that follows enamel rods, which increases the bulk and decreases the stress concentration within the restorative material)
3) Describe all the features in a class II preparation that provide retention form Retention form- internal form; features that hold a restorative material in place
- -Convergent isthmus walls/functional cusp wall of proximal box
- -Divergent dovetail/buccal/lingual extensions
- -Retention grooves- axiobuccal/axiolingual line angles (from axioproximogingival - axioproximopulpal point angles; .25mm deep in dentin
4) Describe the minimal requirements for a successful application of the Tofflemire retainer, matrix band, and wedge for a class II restoration contra-angled/universal retainer
- Matrix- narrow opening = gingiva; wide opening = occlusal
- -covers proximal box
- -creates a seal for packing amalgam
- -1mm above marginal ridge
- Wooden wedge - for proximal contact
- -loosen and burnish band after placing wedge
5) Describe the proper technique of condensing amalgam into a class II cavity preparation that maximizes the physical and mechanical properties of the final restoration
- (1) Properly mix the amalgam (should be a homogenous, slightly reflective mass)
- (2) Have mental image of the outline form and general characteristic of the preparation to aid in locating cavosurface margins
- (3) Amalgam should be inserted incrementally and condensed with overlapping strokes. Make sure that the proximal box is equally as condensed as the remainder of the preparation
- (4) Tooth prep should be overpacked to ensure well-condensed marginal amalgam that is not mercury-rich.
- (5) To ensure a marginal ridge is properly placed, make sure the amalgam is packed solid up to the same height as the neighboring marginal ridge.
- (6) In general, move from smaller condensers to larger condensers
6) Describe the proper technique for contouring and carving the class II amalgam restoration after condensation
- (1) carving begins immediately after condensation.
- (2) use cleiod-discoids of suitable size.
- (3) large acorn burnisher used to obtain the pits & fissures since it rests on unprepared tooth structure and the tip is thus guided along the amalgam surface by the untouched enamel.
- (4) Carving: edge = perpendicular to margins; move parallel to the margins
- (5) instrument rests on unprepared tooth to prevent over carving!!!
- (6) Mesial/distal fossae slightly deeper than proximal marginal ridges
- (7) The finished margin should be regular and in the same form as the initial preparation
- (8) Remove Tofflemire retainer carefully so to keep the marginal ridge intact.
- (9) floss can be run through the proximal contact.
- (10) Post carve burnishing can produce smoother satin (not shiny) appearance but is only to be used with high-copper amalgams
- Anatomy: Reproduce ideal fossa and groove anatomy
- Surface contours: Ideal ridge and line angle contours, even marginal ridges
- Proximal contours: Proper embrasure form with adjacent tooth contact
- Margin integrity: Margins sealed and level with tooth contours
- Surface finish: Smooth, even appearance
7) Describe the proper location on a 6" X 6" rubber dam for the hole to be punched for the posterior anchor tooth on an ideal rubber dam application when treating tooth #20 #18 - #28 (second molar to contra-lateral first premolar)
- - divide dam: 3 vertical sections (2"), 2 horizontal sections (3").
- - hole for #19: intersection of the middle horizontal line and the right vertical line.
- - anchor hole (#20): above and slightly to the right of hole for #19, following the arch form.
8) Describe the recommended operator chair position and patient position when treating tooth #12 for the right-handed operator
- 9:00 - facial surface
- 11:00 - lingual and occlusal surfaces (via mirror)
- -patient's head toward operator
9) Describe the differences between affected dentin versus infected dentin that distinguish tooth structure that must be clinically removed during a cavity preparation -infected dentin = remove
- -affected dentin = DOES NOT require removal
- - Affected dentin (aka inner carious dentin) is softened, demineralized dentin that is not yet invaded by bacteria. This tooth structure is still alive and is remineralizable
- - Infected dentin (aka outer carious dentin) is the bacteria-infected, unremineralizable outer structure of a carious lesion. It is softened, dead, and senseless to touch
- -stain infected dentin to determine where to stop
What advantage and disadvantage occur with the presence of zinc in dental amalgam? How can the disadvantage be minimized or eliminated?
- Pros:-Zn oxidizes -> Zn oxide to protect other elements-longevity
- -delayed expansion from Zn
- Zn oxide rxn releasing H2
- PAIN TO AVOID WETNESS GETTING TO SITE-
- use non-Zn amalgam if isolation is difficult
10) Discuss the role of copper in high-copper dental amalgam and its impact on physical and mechanical properties -12-30% copper (typical dental amalgam: 0-6%.)
- -high compressive strength
- -corrosion resistance
- -marginal integrity
- -longevity (24-25 years)
- -reduction in creep
- -more rapid set
- • Addition of very small amounts of soluble metals (e.g. Cu) into a solution of molten gold creates a much harder alloy
- • Mixing of three ingredients
- • Ag-Sn alloy (γ)
- • Ag-Cu alloy
- • Mercury
- • High reactivity of Cu with Sn
- • In low-copper amalgams, particles react with Hg to form a matrix of Ag-Hg and Sn-Hg (the most corrosion prone phase)
- • In high-copper amalgams, the Sn-Hg phase is eliminated by the competitive reaction of Cu with Sn (Cu6Sn5, η)
- • Ag3Sn + Ag•Cu + Hg ® Ag3Sn + Ag2Hg3 + Cu6Sn5
- • γ + Cu alloy mercury ® γ + γ 1 + η
- • No γ2 phase
- • Cu-Sn phase surrounding core particles
- • Properties
- 1. Higher compressive strength
- 2. More rapid set to full strength
- 3. A reduction in creep
- 4. Reduced susceptibility to corrosion
12) Describe the basic technique for sharpening the cutting edge of a 10-7-14 hand instrument on a stationary stone
- -Rub across the stationary stone with the cutting edge leading the motion.
- Take care to maintain the angle, and keep the blade flat
- for most of the hand instruments, and even for many of the perio scalers, you will use an “Arkansas stone”- scrape against the bevel to sharpen the cutting edge
- ex. Wedelstaedt chisel- bevel is always held on the surface of the sharpening stone
- can use a little oil to plug up the pores in the stone, & to obtain a smooth run as you push from side to side
- hold bevel abt at 45 degrees- this is a happy medium btw too sharp, too dull, & longevity; the sharper the edge, the sooner it becomes dull
- keep edge of the blade perpendicular to the direction you’re pushing in
- push evenly- once you rotate, the bevel will change; your goal is to replicate the original instrument formula & shape
- -whether a hatchet or GMT, the concept is the same- hold the bevel flat on the stone, keep the cutting edge perpendicular to the force of the movement
- mechanical sharpeners can assist you, if you know how to use them; advantage is, you have a guide to hold the blade w the proper bevel
- -don’t sharpen the instrument w so much force that you shorten the blade significantly!