Materials + Restorative Flashcards
Composition of amalgam
- Alloy of silver, tin, copper, zinc.
- Tin: Helps with dimensional change.
- Copper: Prevents corrosion, reduces fracture.
- Zinc: Scavenger for oxygen, forming Zinc oxide in place of copper/silver/tin oxides which would weaken the structure.
-
Mercury: Wets alloy aka wetting agent
- ~50%
What are the three forms of mercury?
- Elemental: Liquid at room temp, used in amalgam.
-
Organic: Methylmercury (most toxic), formed in water or soil by bacteria and can build up in fish.
- Can be formed in the mouth with saliva from elemental or inorganic form.
- Inorganic: Enters air from mining or deposits, burning coal/waste, manufacturing, exists in solid state.
What are the main ways that humans are exposed to mercury?
-
Mercury Vapor: Dental restorations.
- Risk is from inhalation – excreted in feces and urine, as well as passing it to a fetus and breastmilk.
- Reduce by using a rubber dam and high volume air and water - m_ost risk is removing the amalgam._
- EPA mandated amalgam separated be used in dental offices by July 2020.
- Incinerated waste can release vapor.
- Methyl Mercury: From seafood.
- Inorganic Mercury: From food.
Gamma phase: Amalgam
- Unreacted alloy particles are the gamma phase (mainly silver and tin).
- Gamma phase combines with mercury, forming gamma 1 and gamma 2 phase.
- Gamma 1: Silver and mercury.
-
Gamma 2: Tin and mercury.
- Early fracture and failure.
- Adding copper replaces gamma II phase and makes it stronger (Eta phase)
Amalgam: MOA
-
Low-copper alloy
- Higher % of Gamma 2 phase → weakest phase prone to corrosion.
-
High-copper alloy
- Lower % of Gamma 2 phase → increased mechanical strength, resistant to corrosion.
What are the three types of amalgam?
- Lathe-cut
-
Spherical
- Amalgamates more readily and condenses more.
- Less mercury.
-
Admixed
- Strongest proximal contacts
Amalgam: Creep
Max is 5% to be ADA certified, increases in size.
- Modern alloy should have not have >1% creep.
- Hydrogen gas release in when zinc reacts with water if you don’t have good isolation.
- Excess moisture causes delayed expansion.
Amalgam: Marginal seal
-
Marginal seal improves over time due to corrosion - the only one.
- Eta phase (Cu6Sn5): oxidizes and transforms into CuCl2 and CuO2, takes twice as long to make marginal seal (2 years).
- Gamma 2 corrosion can seal margins (Handbook).
FDA re-classifying amalgam in 2009?
- Class II device (having some risk) and designated guidance that included warning labels:
- Possible harm of mercury vapors.
- Disclosure of mercury content.
- Contraindications for persons w/ known mercury sensitivity.
- Limited information regarding dental amalgam and the long-term health outcomes in pregnant women, developing fetuses, and children <6yo.
Amalgam: Indications
- Replace primary and permanent tooth structure lost due to:
- Active caries that has caused visible cavitation.
- Enamel defects or malformation that do not enlarge beyond the material’s limits.
- Restoration of moderate sized carious lesions when isolation cannot be achieved.
- Strong evidence supports safety and efficacy of dental amalgam in all populations.
What is the % survival for Class I-V amalgams in primary teeth?
-
Primary teeth: 85-96% at 7yrs.
- Average annual failure rate: 3.2%
- Strength of evidence: Strong
What is the % survival for Class I amalgams in permanent teeth?
-
Permanent teeth: 90-99% at 7yrs (Handbook)
- 89.8-98.9% (Guidelines)
- Strength of evidence: Strong
What is the % survival for Class II amalgams in primary molars? In permanent molars + premolars?
-
Primary molars: 75% at 5yrs.
- Survive a minimum of 3.5yr and potentially in excess of 7yr.
-
Permanent molars + premolars: 92% at 10yrs.
- Mean annual failure rate is equal to composite = 2.3%
- Strength of evidence: Strong
Amalgam: Prep design
- Strong under compression but weak under tension.
- Ideal prep floor is 0.5mm into dentin, 1.5mm from enamel surface.
- ⅓ of the intercuspal width.
- Convergent buccolingual walls, proximal box is wider at the cervical than occlusal, gingival wall should be flat not beveled .
- 1mm wide gingival seat.
Amalgam: Trituration
- Trituration: aka mixing in capsule
- Problem is under-triturated mix: Dry, sandy, sets too rapidly, high residual Hg content.
- Higher trituration speed gives shorter working time, most of the time is under triturated and can appear dry and sandy.
Amalgam: Condensation
- Back to back should be done at the same time
- Not going to be as strong immediately, but hardens over time.
Amalgam: Longevity
- May be better than composite in the long run.
- Higher additional restorative tx when composites placed; 7x more than amalgam.
- High replacement rates of composite in general practice setting can be attributed partially to GP’s confusion of marginal staining for marginal caries and their subsequent premature replacements.
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Guidelines conclude that median success rate of composite (92%) and amalgam (94%) are statistically equivalent after 10yrs.
- Equivalent mean annual failure rate = 2.3%
- Higher additional restorative tx when composites placed; 7x more than amalgam.
Amalgam: Advantages + Disadvantages
- Advantages
- Economics
- Time efficiency
- Less sensitive to operator variables
- Historical longevity
- Wide application potential
- Disadvantages
- Esthetics
- Lack of bonding does not initially seal restoration and can increase mechanical stresses in the remaining tooth structure.
- In 2yr, Gamma 2 corrosion can seal margin.
- Mechanical retention required.
- Environmental concerns w/ proper disposal.
Amalgam: Safety Concerns
- Mercury safety for human use + environment:
-
Human use: No evidence of harmful effects from the use of amalgam in humans.
- Ingestion: Amalgam associated mercury intake below toxic thresholds.
-
Allergy: Rare (<50 cases in 100yrs); lichenoid lesions have been reported.
- Replaced ONLY if lesion + amalgam contact.
- Use of rubber dam minimizes potential toxic risks.
-
Environmental:
- WHO:53% of mercury emissions comes from dental amalgam.
- EPA: Dental amalgam is a significant contaminant of wastewaters.
- ADA: Use amalgam separators and amalgam waste recycling.
-
Human use: No evidence of harmful effects from the use of amalgam in humans.
How to minimize amalgam risks?
- Proper ventilation
- Pre-capsulated alloys
- Appropriate scrap disposal (check specific state regulations)
SSCs: Composition
-
Chrome Steel
- 18% chromium
- 9-13% nickel
- 0.8-20% carbon
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Nickel-Chrome Steel
- 15% chromium
- 77% nickel
- 7% iron
-
Surgical Grade
- 65-73% iron
- 17-19% chromium
- 9-12% nickel
- <2% manganese, silicon, carbon
SSCs: MOA
- Full-coverage restorations restore form + function.
- Protects remaining tooth surfaces from caries formation.
SSCs: Indications in primary + permanent teeth
- Primary teeth:
- Extensive caries – other restorative options likely to fail.
- Circumferential cervical decalcification.
- Developmental defects (hypoplasia, hypoplastic teeth).
- Following pulpotomy/pulpectomy.
- Strong consideration for use for high caries risk patients.
- Strong consideration for use when treatment is completed under sedation or GA.
- Hall crown technique: No removal of caries, no LA, no reduction of tooth surfaces to fit SSC.
- Fractured teeth.
- Abutment for space maintainer.
- Proximal box that extends beyond line angles.
- Permanent teeth:
- Extensive caries – other restorative options likely to fail.
- Developmental defects (hypoplasia, hypoplastic teeth).
- Financial considerations.
- Interim restorations.
- Needs full coverage but not fully erupted.
SSCs: Safety concerns
Metal or nickel allergy
SSCs: Advantages + Disadvantages
- Advantages
- Protects remaining surfaces from caries formation.
- Restores form + function.
- All surface protection.
- Disadvantages
- Traditional SSCs are non-esthetic.
- Increase in localized gingivitis (can be improved w/ optimal OH).
- Periodontal concerns.
SSCs: Longevity survival rates
- Traditional SSCs on primary teeth – 95%
- Failure usually results from crown loss or perforation.
- Hall crown survival rate – 95%
SSCs: Contraindications
- Undergoing MRI
- Scatter; May opt for alternative if full case.
- Nickel allergy
- Recommend allergy testing
- Teeth exfoliating in 6-12mo
SSCs: Technique
- Not in supraocclusion; should not interfere with occlusion.
- Look at the tooth before prepping.
- 1.5-2mm reduction.
- Restored before crown cementation.
SSCs vs. Class II amalgams/composites
- SSCs are more durable.
- Longest track record and highest degree of success.
- Dentists spend 50-60% of their time replacing restorations.
- Main reason for SSC failure is perforation.
SSCs: Gingival health
- Poor margins show gingivitis, extensions of the crown not associated w/ gingival health.
- Poor OH the most associated w/ unhealthy gingiva around SSCs.
- Takes ~2wks for healing.
- Bleeding is normal; cleaning will help to make healing faster.
SSCs: Cementation
- Resin is the best but there is usually a lot of bleeding.
- GI or RMGI are both acceptable (no difference)
- Polycarboxylate is the least effective cement.
- Chemical adhesion, but more temporary cement.
- Patch perforated crowns w/ composite, GI, RMGI – resin the least bc of the microleakage.
- Luting cements: Zinc phosphates, polycarboxylate, GIC, resin
What cement is the least effective for SSCs?
- Polycarboxylate is the least effective cement.
- Chemical adhesion, but more temporary cement.
SSCs: Bases + Liners
- At least 0.5mm of material is needed.
- CaOH (Dycal)
- ZOE
SSCs bases + liner: CaOH
- Catalyst paste: Calcium hydroxide, zinc oxide, zinc stearate in ethylene toluene sulfonamide.
- Base paste: Calcium tungstate, calcium phosphate, and zinc oxide in glycol salicylate.
- Form an amorphous calcium disalicylate.
- Alkaline pH aids in preventing bacterial invasion.
-
Hydrolysis due to fluid contamination from dentinal tubules and microleakage.
- Gingival displacement of restoration may lead to restoration breakdown.
- Not good for directly under amalgam.
-
Needs something placed over it.
- Less soluble high-strength base should be placed - use visible light curing or RMGI.
SSCs bases + liner: ZOE
- Zinc oxide-eugenol; powder is the zinc oxide, rosin, and zinc acetate, liquid is the eugenol.
- Low compressive strength, increase strength with polymethacrylate (IRM).
- Forms a chelate of zinc eugenolate.
- Sedative effect.
- Eugenol is an inhibitor for resins and impression materials, need to put a barrier in between - causes problems with polymerization of resin.
Hall technique
- Place a crown over the tooth without local anesthesia and no reduction.
- Fill with GI cement and have patient bite down to place crown.
- Effective in behavior, more accepted because of no injection, most effective.
- Better than interproximal restorations, no difference between HT and traditional SSCs.
- Opens occlusion but within a month occlusion goes back to normal.
- More negative behavior in children who received conventional treatment.
Prefabricated Esthetic Crowns: MOA
- Full coverage restorations restore form, function, and esthetics for lifetime of tooth.
- Protects remaining tooth surfaces from caries.
Prefabricated Esthetic Crowns: Indications
[Same for SSC, except where esthetics are also important.]
- Extensive caries.
- Post-pulp therapy
- Tooth surface loss – erosion, abrasion
- Primary molar hypoplasia
- Inherited defects of dentition
- Traumatic injuries
Similarities between veneered SSC + zirconia crowns
- Harder to replace.
- Prefab crowns come in predetermined sizes + contours for primary teeth.
- Color, contour and sizing differ according to manufacturer.
- Require passive fit so that circumferential tooth reduction is essential w/ subgingival feather edge finish line (overall 20% greater reduction than for SSC).
- Occlusal reduction same as SSC (1.5-2mm).
- No risk of pulp exposure due to preparation.
- Adjacent and opposing crowns possible.
- Tooth colored
- Durable
- Retentive
Differences between veneered SSC + zirconia crowns
- Veneered SSC
- Tooth preparation – increased reduction on labial surface to accommodate bulk of composite (0.6-1.5mm).
- Thicker cervical margin in composite.
- 1-1.5mm circumferential reduction; 1.5-2mm occlusal reduction.
- Easy to adjust occlusion by reducing composite.
- Exposed metal margins can be crimped, but not advised.
- High risk of facing fracture over time.
- Composite facing may be damaged by heat sterilization.
- Not as technique-sensitive as zirconia.
- Hard to replace pre-veneered facing.
- Tooth preparation – increased reduction on labial surface to accommodate bulk of composite (0.6-1.5mm).
- Zirconia crowns
- Tooth prep requires equal circumferential reduction to accommodate thickness of zirconia which varies from 0.2mm at cervical margins to 1.2mm occlusal surface.
- Occlusal reduction same as SSC (1.5-2mm); circumferential reduction w/ subgingival feather edge finish line.
- Cannot be crimped so increased tooth reduction may be required for passive fit.
- Susceptible to fracture if excess pressure used while seating.
- Zirconia adjustment requires specific burs due to physical properties of zirconia.
- Excellent gingival response due to high polish + biocompatibility.
- Cementation or color may be compromised if fitting surface of crown is contaminated w/ saliva/blood.
What are the two types of pre-fabricated esthetic crowns?
- Veneered SSC: SSC w/ composite veneer attached via physical or chemical means.
- Zirconia crowns
Both may be used for anteriors, cuspids, posteriors.
Prefabricated Esthetic Crowns: Longevity, survival rates
- Veneered SSC: Survival rate similar to SSC after 3yrs, but veneer loss increases w/ time.
- Zirconia crown: Unknown – limited studies available.
Primary anterior crowns: Indications
- Multiple surfaces
- Incisal edge involvement
- Pulp therapy
- Hypoplastic
- Poor moisture
- Large single surface
- Poor OH
- Discolored incisors
Composite crowns usually replaced 2yrs after – not for long term durability?
Zirconia Crowns:
- Zirconium dioxide (ZrO2) stabilized w/ Yittria.
-
Tetragonal form is what we use in dentistry.
- Properties:
- High strength – 1000-1200MPa
- Unreactive chemically
- Insoluble in water
- High thermal stability
- Highly polishable
- Cannot be crimped
- Not damaged by autoclave sterilization
- Properties:
- Exceed the max bite force of 6-8yo.
- Good for bruxers.
- Gingival health is better than SSC; plaque does not like zirconia.
Not as resistant to fracture as SSC.
What is the #1 reason zirconia crowns fail?
Pulpal complications
What is the biggest problem/concern w/ zirconia?
Abrasion of the opposing teeth.
Considerations when cementing zirconia crowns
- All types of cement
- Need good hemostasis
- Fill ¾ full
- Cement both incisors at the same time.
What factors can make anterior esthetic restorations in primary teeth challenging?
- Small size of teeth
- Close proximity of the pulp to the tooth surface
- Relatively thin enamel
- Lack of surface area for bonding
- Behavior
Class III (interproximal) restorations of primary incisors: Prep Design
- Labial or lingual dovetails to increase surface area for bonding and to increase retention.
- Isolation must be adequate.
- RMGIC has been recommended with poor isolation? (Handbook)
- High caries risk patients may be better served w/ placement of full tooth coverage restorations.
Class V in primary incisors
If isolation is poor, GIC or RMGIC is suggested
When are full coronal restorations of carious primary incisors indicated?
- Caries present on multiple surfaces.
- Incisal edge is involved.
- Extensive cervical decal.
- Pulp therapy is indicated.
- Caries may be minor, but OH is poor.
- Behavior makes isolation difficult.
Strip crown retention after 3yrs %?
- 80% completely retained after 3yr.
- 20% partially retained.
- None completely lost.
Recommendations for SSC’s
- SSC use is supported on high-risk children w/ large or multi-surface cavitated or non-cavitated lesions on primary molars, especially when children require advanced behavior guidance techniques [including GA].
- Using SSCs in permanent teeth as a semi-permanent restoration to tx severe enamel defects or grossly carious teeth.
Evidence of efficacy of amalgam in primary + permanent teeth: Class I-V
- Class I
- Primary: Strong evidence
- Permanent: Strong evidence
- Class II
- Primary: Strong evidence
- Permanent: Strong evidence
- Class III
- Primary: No data
- Permanent: No data
- Class IV
- Primary: No data
- Permanent: No data
- Class V
- Primary: Expert opinion
- Permanent: No data
Evidence of efficacy of composite in primary + permanent teeth: Class I-V
- Class I
- Primary: Strong evidence
- Permanent: Strong evidence
- Class II
- Primary: Strong evidence
- Permanent: Evidence in favor
- Class III
- Primary: Expert opinion
- Permanent: Expert opinion
- Class IV
- Primary: No data
- Permanent: No data
- Class V
- Primary: Evidence in favor
- Permanent: Evidence in favor
Evidence of efficacy of glass ionomer in primary teeth: Class I-V
- Class I
- Primary: Strong evidence (ART trials)
- Permanent: Strong evidence (ART trials)
- Class II
- Primary: Evidence against (conflicting evidence from ART trials)
- Permanent: Evidence against
- Class III
- Primary: Evidence in favor
- Permanent: Evidence in favor (preference when moisture control is an issue)
- Class IV
- Primary: No data
- Permanent: No data
- Class V
- Primary: Expert opinion
- Permanent: Expert opinion
Evidence of efficacy of RMGIC in primary teeth: Class I-V
- Class I
- Primary: Strong evidence
- Permanent: Strong evidence
- Class II
- Primary: Expert opinion (small restorations; life span 1-2yr)
- Permanent: No data
- Class III
- Primary: Expert opinion
- Permanent: Expert opinion
- Class IV
- Primary: No data
- Permanent: No data
- Class V
- Primary: Expert opinion
- Permanent: Evidence in favor
Evidence of efficacy of compomers in primary teeth: Class I-V
- Class I
- Primary: Evidence in favor
- Permanent: Evidence in favor (evidence from studies in adults)
- Class II
- Primary: Evidence in favor
- Permanent: No data
- Class III
- Primary: No data
- Permanent: Expert opinion
- Class IV
- Primary: No data
- Permanent: No data
- Class V
- Primary: Expert opinion
- Permanent: Expert opinion
Evidence of efficacy of SSC in primary teeth: Class I-V
- Class I
- Primary: Evidence in favor
- Permanent: Evidence in favor (for children + adolescents w/ gross caries or severely hypoplastic teeth)
- Class II
- Primary: Evidence in favor
- Permanent: Evidence in favor (for children + adolescents w/ gross caries or severely hypoplastic teeth)
- Class III
- Primary: No data
- Permanent: No data
- Class IV
- Primary: No data
- Permanent: No data
- Class V
- Primary: No data
- Permanent: No data
Evidence of efficacy of anterior crowns in primary teeth: Class I-V
- Class I
- Primary: N/A
- Permanent: N/A
- Class II
- Primary: N/A
- Permanent: N/A
- Class III
- Primary: Expert opinion
- Permanent: No data
- Class IV
- Primary: Expert opinion
- Permanent: No data
- Class V
- Primary: Expert opinion
- Permanent: No data
Resin-based composites: Composition
- Resin matrix (bis-GMA, bis-DMA) w/ fillers (Handbook).
- Resin matrix + chemically bonded filler.
How are composites classified?
- According to their filler size, because their filler size affects:
- Polishability/esthetics
- Polymerization depth
- Polymerization shrinkage
- Physical properties
- Hybrid resins combine a mixture of particle sizes for improved strength while retaining esthetics.
- Smaller filler particle size = greater polishability + esthetics.
- Larger filler particle size = strength.
Flowable resins vs. Hybrid resins
Flowable resins = lower volumetric filler % than hybrid resins.
Composite classification by filler particle size
-
Microfill
- Excellent esthetics + polishability
- Elastic = allows for tooth flexion under loading
-
Hybrids
- Bimodal or trimodal blends of fine or microfine
- Excellent long-term results
- Good for posterior + anterior use
- Low thermal expansion + polymerization shrinkage
- Relatively high resistance wear
- Up to 70% filler
-
Fine particle
- Contains >2 particle sizes
- High wear resistance
- Good mechanical properties
- Appropriate for posterior use
- Veneers needing strength
- Rougher surface than microfill or hybrid
- Higher filler loading (60-70% by volume, 77-88% by weight)
Composite classification by clinical handling characteristics
-
Flowable
- Low viscosity resin allows material to flow into prep
- 45-75% filler by weight.
- Shrinks more.
- Lower filler content increases polymerization shrinkage + wear
- Higher filler content decreases shrinkage
- Indicated for PRR, Class III + IV, strip crown
- High filler content can be considered for Class I or II
-
Packable
- High viscosity resin allows instruments to push + shape material.
- Historically contains higher % of filler particles improving wear resistance.
- Indicated for moderate to large Class I, II, III, V, strip crowns.
Composite: Indications
- Replace primary + permanent tooth structure, especially in the esthetic zones, lost due to:
- Visibly cavitated active caries
- Enamel defects/malformation
- Traumatic injuries
- Use in moderate-low caries risk patients where you have good isolation.
- Class II that do not extend beyond the line angle, except when expected to exfoliate within 1-2yrs.
- Class II restorations in permanent teeth that extent ~⅓-½ bucco-lingual intercuspal width.
- Indirect resins allow more complete polymerization of resin.
Composite: Advantages
- Esthetics
-
Micromechanical seal between tooth + restoration
- Seals cariogenic bacteria from fermentable carbs
- Mechanically bonds tooth together reinforcing structural integrity of tooth
- Better wear resistance than GI or RMGI (historically, less wear than amalgam)
- Many different forms (flowable, hybrid, packable, etc) for different applications
Composite: Disadvantages
-
Technique sensitive
- Comparable longevity to amalgam
- Minor variations in technique + moisture alters performance
-
Chair time
- Higher time investment for ideal placement
- Newer bulk-fill resins minimize this disadvantage
- Higher time investment for ideal placement
-
Recurrent caries
- Most frequent cause for replacement
-
Polymerization shrinkage
- Constriction when cured introduces stresses into tooth.
-
Incremental placement can minimize stress
- Newer bulk-fill resins minimize this disadvantage
-
Post-operative sensitivity
-
Result of polymerization shrinkage and poor bonding
- Newer bonding agents may minimize this disadvantage
-
Result of polymerization shrinkage and poor bonding
-
Wear resistance
- Larger filler particles increase wear rates
Survival rate of resin-based composites w/ PRR/small pits + fissures: Primary + Permanent teeth
- 54% retention at 9yrs
- Strength of evidence: Single report