Flashcards in NEWER NOTES Deck (75):
What do biological contours do for teeth?
-stimulate natural, healthy teeth
-protect the supporting tissues
-maintain the health of gingiva + periodontum
- minimize trauma and irritation to bony tissues
What do improper contours of teeth lead too?
- often induce early breakdown of supportive structures
-result in early loss of teeth
What to check for when contouring teeth?
1) facial and lingual convexities
2) medial and distal concavities
3) transitional line
4) contact area and embrasures
5) cervical ridges
6) marginal ridges
7) tooth reduction
What are the facial and lingual convexities?
- this is where the crest of curvature (aka the height of contour) is located
- this is the greatest convexity on the axial surface of the crown
What is the height of contour (aka protective contours of the crown)?
-the contours of a tooth are curved
- when viewed from medial or distal aspects, crowns have rather uniform curvatures in the cervical third and in the middle third
-these contours play an important role in the health of the supporting structures
Why is the proper curvature/contour of a tooth important?
1) the proper degree of curvature will deflect food over the gingival margin preventing irritation
2) the proper curvature allows stimulation of soft tissue
3) if the curvature is absent, the gingival tissue will driven apically and this will result in pathological changes
4) if the curvatures is too great, the gingiva is protected too much and loses gingival tone. food and debris may pack under this area and result in chronic inflammation of the gingiva
Where is the facial contour located?
- no more than 1/2 mm facially beyond the CEJ
- height of contour is in the cervical third
Where are the lingual contours located?
- no more than 1/2 mm. lingually beyond the CEJ
- height of contour is in the middle third
**EXCEPTION: mandibular second premolar and molars - 3/4 to 1 mm. lingually beyond the CEJ
What is the emergence profile?
- tooth surface that is gingival to height of contour and above the gingival crest
- the profile of the gingival third of a restoration as it emerges from the gingival crevice
- it should be flat for 2-3 mm above the gingival
(it's the bump that sticks out of the tooth on the bottom)
** there can be an inflammatory soft tissue response as a result of over-contoured restorations
How are the proximal surfaces of posterior teeth contoured?
- proximal surfaces are always flat or slightly concave between the contact area and the CEJ to allows room for the papillae
What is the contact area on a posterior tooth?
- the area of the medial or distal surface of a tooth which touches it's neighbors.
- it is similar to a ball to ball point contact.
- it can have various locations
What are the basic functions of contact areas?
1) aids in proper development of the arches
2) prevents food from packing between the teeth
3) allows the teeth to be self-cleaning (to come extent)
4) prevents injury to the inter-proximal tissues
Where should the contact area be in posterior teeth?
1) The contact gets broader with time due to wear as the teeth move during function
2) contact areas of all posterior teeth should be buccal to the centra fossa and in the occlusal third
3) in occlusal 1/3
*** exception: between maxillary molars-junction of occlusal and middle 1/3 or middle 1/3
4) buccal to buccolingual center
*** exception: between max. molars, in middle 1/3
5) distal contacts are more cervical than medial contacts
*** exception: mandibular first premolars
why should proximal contact be always established?
- to develop arch integrity (stability)
- prevent food retention
- protect interdental papillae
What are the transitional line angles?
- between the faciolingual convexities and proximal concavities there is a surface called the transitional line
- the contours of this area should blend the convexities and concavities without excess bulk or irregularity
- improper contours present a hazard to the supporting tissue
*** transitional line angles are straight between the proximal contact point and the cementoenamel junction
What are the marginal ridges?
- on the occlusal surfaces of the teeth at the proximal border there is a ridge-like structure neighbored by two depressions
- one depression is the occlusal embrasure and the other is the proximal fossa. the structure is called the marginal ridge
- marginal ridges are rounded elevated crests.
- convex MD and concave FL
-adjacent ridges are at the same height
**except between canines and premolars
- marginal ridges converge from buccal to lingual (facial 1/2 is wider than lingual 1/2)
** except: mandibular 2nd premolar 3 cusp type and maxillary first molar
*** posterior marginal ridges should be of equal height
What to do if both adjacent marginal ridges are missing? how can I determine the height?
- use the opposing cusp to determine the height of the marginal ridge.
What are embrasures?
- an embrasure is a "v"-shaped space extending outward from the contact areas of the teeth
-an embrasure is also known as a spillway space
What are the functions of embrasures?
1) it's a spillway for the escape of food during function
2) it helps maintain the tooth clean
** lingual embrasures are always larger than buccal embrasures EXCEPT (didn't get the exception portion so don't know this)
What is the cervical curvature?
- margins of restoration often end at the cervical line or CEJ. this line curves occlusally at the proximal and apically at the facial and lingual.
-this curvature relates to the contour of the bony alveolar area.
What is the biologic width?
- 1.5-2 mm between the tooth margin and bone
- the biologic width includes both connective tissue attachment and the junctional epithelium. invasion of the biologic width due to restorations could result in crystal bone loss, gingival recession with localized bone loss, localized gingival hyperplasia with minimal bone loss, or a combo of the three. Therefore when restoring teeth with subgingival caries or fractures. Clinical crown lengthening is performed to achieved margins on sound tooth structure, maintenance of the biologic width, access for impression techniques, and esthetics.
What does an over-contoured crown result from and what does it cause?
it results directly from inadequate tooth reduction and causes a lack of room for biomaterials.
What can occur when placing the margins of restorations sub gingival?
- it can cause inflammation and reduction of gingival height
- for sub gingival margins, it is wise to consider using a metal margin, which is easily tolerated by tissues. If esthetics is a concern zirconia crowns are very compatible with tissues .
How do you establish contours in restorations?
always establish contours in restorations which are in harmony with the natural tooth structure
When making a reduction guide for teeth #1-5 where do you section it?
section guide at medial cusp tips
What is the sequence of steps for tooth prep for a maxillary teeth (CVC)?
1) occlusal depth orientation grooves
2) functions cusp bevel depth orientation grooves (lingual)
3) occlusal reduction including functional cusp bevel
4) axial depth orientation grooves
- establish path of withdrawal
- buccal guide grooves
- lingual guide grooves
5) axial reduction
- buccal axial first plane
- lingual axial reduction
- buccal axial 2nd plane reduction
- not functional cusp bevel (buccal)
6) finishing and evaluation
- interproximal reduction
How and where to place the occlusal depth orientation grooves on max molars?
- w/ a 242.6 M diamond bur
- height of each triangular cusp right and the buccal, lingual and developmental fossae grooves
- place 4 on lingual and 5 on buccal
- grooves are placed .2mm shallower than intended tooth reduction
-depth orientation grooves for the functional cusp bevel
How do you achieve occlusal reduction?
-remove "islands" of tooth structure between groovers with 242.6 M diamond
- uniform reduction which is planar corresponding to anatomic contour of unprepared tooth surface
-functional cusp (lingual on maxillary) is beveled and part of the occlusal reduction
* 45 deg to the long axis of the tooth
* POW is slightly buccal
How do you place the axial depth orientation grooves?
-establish the path of withdrawal (POW)
-place three shallow grooves on lingual and the buccal axial walls slightly coronal to intended chamfer margin
-grooves determine the POW of the final restoration
how to achieve the axial reduction?
-hold diamond bur parallel to POW
-remove the "islands" of remains tooth structure between the grooves
- concurrently, the tip of the bur prepares the chamfer
-buccal second plane reduction
* necessary for uniform reduction of 1.0 mm over buccal surface of prep
* provides adequate space for restoration material in the occlusal one half of the buccal surface
* prevents over-contoured restoration
- extend the buccal and lingual axial reduction into the inter proximal area until a narrow island of tooth structure remains
-remove remaining inter proximal tooth structure first with a 169 carbide or narrow 747.6 M diamond and then widen with 242.6M
-don't damage the adjacent tooth
how to achieve the buccal second plane reduction?
-hold 242.6 M diamond bur in a plane parallel to the occlusal half of the previously unprepared buccal tooth surface
- use adjacent tooth as a guide
-don't engage tip of the bur
-uniform reduction of 1.0 mm
-evaluation with silicone reduction guide and periodontal probe
How to finish the crown prep?
-preparation should exhibit smoothness (a surface with light striations created by the diamond bur)
- slightly round all sharp line angles
What are the properties of gold?
-most noble and corrosion-resistant metal
-most ductile and malleable metal
-too weak for dental restorations unless other alloying elements are used
-melts at 1063 degC
- not tarnished by air or water, and does not dissolved in HCL, H2SO4, and HNO3
- can be etched by aqua regis [1 HNO3: 3 HCl]
What are the properties of the noble metals?
-don't form stable oxides at room temperature
- lowest tendency to lose electrons and become positive ions
-seven metals - gold, platinum, palladium, iridium, ruthenium, rhodium, and osmium
-noble metal content of dental alloys on manufacturer packaging = Au + Pt + Pd
- silver is not a noble metal in oral environment (e.g., black AgS formation)
what are some precious metals?
-classification is based upon metal price and not electrochemistry
-relatively common and inexpensive metals become precious when very high purity is required (e.g., 99.9999% Cu)
What is carat and fineness for gold purity?
- carat (K) - parts in 24 with pure gold = 24 K
* sometime used to describe dental alloys, but provides no info about other elements
- fineness - parts in 1000 with pure gold = 1000 [ also express as a decimal - pure gold = 1.000]
* fineness used for specification of dental solders
What are the Avoirdupois and Troy weight systems?
1 lb Avoirdupois = 16 oz [common US system]
1 lb Troy = 12 oz [used for noble metals]
1 lb troy = 0.823 lb Avoirdupois (compare masses for pound of gold vs. feathers)
1 troy oz = 20 pennyweights (dwts)
1 dwts = 1.555 gm
- noble alloys are typically packaged in 1 dwt or 2 dwt pieces
What are the approximate unit metal prices (troy oz)
gold - $1,310
palladium - $975
silver - $16
platinum - $957
what would be an approximate metal cost for a small gold alloy casting?
What are dental gold casting alloys used for?
-coin gold and 22k gold were formerly used for dental restorations
-types I-IV high-gold casting alloys date from 1930's, but lower-gold compositions now used
-historic ANSI/ADA specification No. 5 for dental casting alloys have been withdrawn
-the current standard for dental casting alloys is ISO 22674 - now there are Types 0-5
What are the ISO standard 22764 Mechanical Property Requirements?
- 0.2% offset yield strength minimum (types 1-5)
- minimum percentage elongation after fracture (types 1-5)
-minimum Young's modulus is specified only for type 5
What are some additional alloy selection factors?
-cost of the metal per pennyweight
- experience of the dental laboratory
What are the ISO classifications of casting alloys?
-Type 0: very low stress-bearing restorations (small veneered one-surface inlays, veneered crowns, also metallic materials for metal-ceramic crowns produced by electroforming or sintering)
- Type 1: very stress-bearing single-tooth restorations, e.g., veneered or unveneered one-surface inlays, veneered crowns
- Type 2: single-tooth fixed restorations, e.g., crowns or inlays without restriction on number of surfaces
- Type 3: multiple-unit fixed restorations, e.g., bridges
- Type 4: thin sections subjected to very high forces (RPDs, clasps, thin veneered crowns, bridges with wide spans or small cross-sections, attachments, impact-retained superstructures)
- Type 5: appliance requiring combination of high stiffness and strength, e.g., thin RPDs, parts with thin cross-sections, clasps
What are the roles of major elements in gold casting alloys?
-gold: provides ductility, tarnish and corrosion resistance
-copper: principle element for hardening and strengthening (exceeding ~12% in traditional high-gold alloys reduced tarnish and corrosion resistance)
-silver: counteracts effect of copper on color and substitutes economically for gold without degrading mechanical properties
- platinum and palladium: also provide tarnish and corrosion resistance, as well as strengthening (limited amounts because small percentages substantially raise alloy melting temperature)
- zinc: oxygen scavenger during melting to minimize oxidation of other elements, and considered to improve castabqlity or fluidity of molten alloy
What is the schematic solidification of metallic material?
white squares represent atoms of solidifying metal, and darker background represents liquid metal. grains are microscopic single crystals. grain boundaries are last regions to solidify, have greater atomic disorder, contain higher concentrations of impurity atoms, and are more readily attacked by chemical etchants than bulk grains,
What other important elements in gold casting alloys??
- small amounts of indium and gallium may be present to provide hardening and strengthening
- very small amounts (much less than 1%) of iridium are generally incorporated to provide desired small grain size or grain refinement (improves mechanical properties, compositional uniformity in microstructure, and corrosion resistance)
What are the characteristic trends on going from ISO type 1 to type 5 casting alloys?
-increases in yield strength and hardness, decrease in ductility
-for gold alloys, increase in total amount of elements other than gold is expected (gold content decreases)
-decreases occur in ease of adjustment and burnish ability for casting
-for gold alloys, decrease in melting temperature is expected (useful for making large castings)
What are the hardening/strengthening mechanisms in gold casting alloys?
- solid solution hardening provided by copper, platinum, palladium, silver, zinc
- order hardening provided by copper (sufficient amount must be present for transformation to occur)
- grain size refinement (typically iridium, much less than 1%)
What is the ordering transformation in gold casting alloys?
-slow cooling through appropriate temperature range enables ordering to occur ("domes" for AuCu and AuCu3 regions on gold-copper phase diagram)
-quenching of casting (sprue loses "red heat appearance") give softened condition - cooling rate is too rapid for ordering transformation
-bench-cool of furnace heat-treat casting (e.g., heat to 450 deg C and cool to 250 deg C over a 30 min period) for hardened condition as result of ordering transformation
-ordered phase is AuCu for traditional (>70%) high-gold alloys and AuCu3 for lower-gold (~50%) alloys such as Midas
At what temp does gold alloy age-harden?
-the special gallium-containing gold-alloy age-hardens rapidly at room temp. The conventional gold alloy also ages very slowly as well
Compare midas to argenco Y+ (Argen)
-argenco is a new economical Pd-Ag alloy containing 2% Gold Argenco Y+ . Argenco Y+ is much harder; much weaker; lower ductility; lower elastic modulus; lower density; much higher melting range. This alloy (cast as Argen) is now used in college clinics. Midas had previously been used for over 2 decades.
What are the biological requirements for an interim restoration?
1) periodontal health maintenance
2) proper occlusal and proximal contacts
3) maintain tooth position
4) prevent enamel fracture
What are the mechanical requirements for interim restoration?
1) resist functional loads
2) resist removal forces
3) maintain inter-abutment alignment
What are the esthetic requirements for interim restoration?
- color match
- color stability
- easy contour
What are the procedures and materials needed for an interim restorations?
- the ESF (external surface form) is made of mold
- the TSF (tissue surface form) is the prepped tooth
What are the two types of external surface form?
- made of the polypropylene shell (what we made in class)
* cellulose acetate
* aluminum (plain)
* aluminum (anatomic)
What are the methods of fabrication of provisional restorations?
-direct (what we use)
What are the advantages of the direct procedure?
- the patient's prepared teeth and gingival tissues directly provide the TSF, intermediate steps of the indirect technique are eliminated
- this is convenient when office lab facilities are inadequate for efficiently producing an indirect restoration
What are the disadvantages of the direct procedure?
-potential tissue trauma from the polymerizing resin and inherently poorer marginal fit
What are the ideal properties of the material used for interim fixed restorations?
- convenient handling: adequate working time, easy molding, rapid setting time
- biocompatibility (non toxic, non allergenic)
- dimensional stability during solidification
-ease of contouring and polishing
-adequate strength and abrasion resistance
- good appearance
- good acceptability to patient: nonirritating, odorless
- ease of adding to or repairing
- chemical compatibility with interim luting agents
What materials are needed for the direct method?
-ESF: vacuum form matrix
-TSF: prepared typodont tooth
- lubricant: vaseline (brush)
- acrylic: trim powder and monomer (cups/dappen dishes, spatula, brush)
-slow speed handpiece, acrylic burs, finishing discs and burrow wheels
What are the step of the direct method?
-the TSF is the prepared typodont tooth
- take an alginate impression of the typodont
-pour in yellow stone
- sometimes need to block undercuts and block emergence profile
- then use the omnivac machine to fabricate a vacuum-formed matrix
* trim matrix to 4mm-5mm from gingival margin
* make sure the matrix fits the tissue surface form
- make an ideal prep
- lubricate teeth and gingiva with vaseline (don't obliterate margins)
- fill ESF with trim
- seat ESF
* press on unprepared adjacent teeth to seat completely
* after rubbery stage is achieved, pump ESF 2mm while setting to prevent locking in (and overheating the teeth)
* mark the important areas like the chamfer and contact areas with a red pencil
* remove excess and adjust margin - but don't trim the red marks
* adjust contact
* adjust occlusion
* contour: axial contours
- finish and polish
* use fulcrum to do this
* angle your acrylic burs and sandpaper disks with the emergence profile
* follow proper sequence
* flick the acrylic resin off once translucent thin
* polish with rubber wheels
~ fine pumice and water
~ slow speed on lathe
~ protect margin with finger
~ fabulustre polishing paste - dry
- check occlusion
Why is it important to pump?
wait until the monomer inside the ESF gets doughy (not runny) and move the ESF and provisional occlusally about 2 mm and place it back on the teeth to break the seal of resin with gingiva and prepared teeth (to prevent locking on typodont, and to avoid thermal injury)
- repeat this until polymerization is complete
- test the stage with extra material in the cup
What are the categories of the Moore Sandpaper disks?
- sand medium
- sand fine
- cuttle medium
- cuttle fine
What's the sequence of finishing and polishing?
- acrylic burs
- Moore disks
- burlow wheels (margins and axial)
- diamond (occlusal)
- rubber points (occlusal if needed)
What errors can be made when forming the margins of the provisionals?
- can have a shy/ledge
- can be open
- can be overcontoured/have an overhang
What is zirconia and why do patients and dentists like them?
- zirconia is a type of metal which is long lasting and indestructible. plus there is no fear about the body rejecting zirconia. It's safe to use and preferred by many people to porcelain fused to metal crowns.
-zirconia (zirconium oxide) is a white powdered metal used to create dental frameworks for crowns, bridges and other dental substructures. It replaces gold or stainless steel used in the past, creates the appearance of a whiter more translucent tooth.
- it behaves like a ceramic - is very strong and aesthetic at the same time
What are some indicators of a zirconia crown?
- used for anterior and posterior crowns or bridges
- used for post and core in endo
- used in implant abutments
- for orthodox brackets
What are some contraindications of a zirconia crown?
- reduced inter occlusal space
- deep vertical overlap
- opposing supra erupted tooth
- very short clinical crown
- not used when don't have much interocclusal space
What are some advantages of a zirconia crown?
- easy to prep and cement
- optimal fit (CAD/CAM)
- high strength (Fracture and crack resistance as well as good flexural strength)
- excellent insulating behavior - protect tooth from any external stimulation
- biocompatible (no allergic response to date) - no damage on the gingiva
What are the disadvantages of a zirconia crown?
-difficult to re intervene (posts for endo)
- bond between veneer ceramic and zirconia framework is the weakest component in the layered structure
- non available longitudinal study - it's new so don't have any research on how it works when worn for a long time
PFM (MCC) vs ZIRCONIA vs LITHIUM DISILICATE
- porcelain-fused-to-metal is well proven and has had over 50 years of successful use
- lithium disilicate restorations are among the most esthetic restoration in dentistry today and many labs are providing them at reasonable prices
- properly fabricated and seated cast-gold alloy restorations are still known to be the longest-lasting crown restorations
- most dentists are reluctant to use one restoration type for all of their restorations
- lithium has lower costs than zirconia crowns
-gold crowns are very biocompatible and don't require too much of reduction in teeth but aren't as aesthetic
Porcelain fused to metal = PFM = MCC disadvantages
- increase opacity
- porcelain chip off from tooth
- marginal discoloration
What restorative material is recommended today?
zirconia is mainly recommended for molar and premolar single unit or short spam posterior bridges
What restorative material will be used in the future?
- PFM will remain for some long-span prostheses, precision attachment placement, and other uses
- cast-gold alloy will continue to die a natural death due to cost of material, patient domain for tooth-colored restorations, and lack of dentists promoting it
- zirconia will continue to grow in use as better esthetic characteristics are developed