Exam2 Flashcards
The Dental advisor
In vitro studies (biomaterials, microbiology)
clinical marketing studies (restorative materials [placement and long-term]; infection control products; equipment)
Enspire Dental
CERAC AC, E4D Dentist, PlanScan, iTero Imaging System, Lava C.O.S, 3M True Definition Scanner
Apex Dental Milling
Full contour zirconia- anterior and posterior; zirconia framework and copings; pressed lithium disilicate, printed orthodontic and crown/bridge models
Digital Impressions- Factors in selection of digital impression system
Type of restoration (silica based ceramic, zirconia, resin ceramic, metal, provisional, wax pattern) in office milling or milling center, cost of equipment (10,000- 125,000), powder required, ortho and implant integration available, special features
In office scanning and In office milling
CEREC (DENTSPLY/Sirona), APOLLO DI, BLUECAM, OMNICAM, e4d Dentist (Planmeca), PlanScan & PlanMill 40 (Planmeca), TRIOS Pod (3shape), TRIOS color (3shape), Galaxy BioMill (BIOLASE), CS 3500 & 3600 Intraoral Scanner and CS 3000 Mill (Carestream Dental), 3M True Definition Scanner (3M), TS 150 Mill (Glidewell Laboratories), new- 3M Mobile True Definition Scanner, Whip Mix corporation, TRIOS Pod (3Shape), DWX- 50 mill (Roland)
New Intraoral Scanner- 3M True Definition Scanner
Scan and Send- scan the preparation using this device then send the highly accurate scan file through the 3M connection center- a secure cloud based digital hub- to a broad range of open and trusted connections
Open connections- send STL files directly to your lab, export STL files and send to virtually any open CAD/CAM system, provide options for clear aligners and night guards
Trusted connections- in office chairside mills, digital implant workflows, orthodontic appliances, access to digitally produced SLA working models
Ownership of Digital System
65% do not own a system
10% own a digital impression system
25% own a full system with in office mill
In office CAD/CAM- steps
prepare tooth (and soft tissue)- dentist, scan- dentist, design- assistant, mill- assistant, polish- stain and glaze- assistant, seat- dentist
Intra- oral scanning In- office
training requirements
initial scanning and “hole filling”, initial design if available (margin marking), lab script completion, file transfer to laboratory
Desktop scanning in office
Initial requirements
workstation dedicated to software (desktop or laptop); WIFI or LAN network- shielded cable to send files; proper network specs to maintain speed of file transfer and storage of files; stead counter/cabinet to hold weight of scanner
Infection control concerns
Disinfection of wands and keyboards
Plan scan-smart tips, autoclavable covers; ITero and Element: disposable covers, ~2.80 each; CS 3500 and 3600: autoclavable covers; Straumann cares/ DWIOS: disinfection with wipe; Tru Def- reportedly immersable in disinfectant; CEREC- Dry Heat or disinfection with wipe
Available In office Mills
PlanMill 40 (Planmeca), CEREC MCXL (DENTSPLY/Sirona); [best for in office work]
TS-150 (Glidewell), Carestream CS3000
Milling in office initial requirements
workstation dedicated to software (desktop or laptop), WiFi or LAN network- shielded cable to send files; proper network and memory to maintain speed of file transfer and storage of files; steady counter/cabinet to hold weight of mill and footprint; compressed air connection, water connection, distilled water, lubricant specific to mill
Milling in office use and maintenance requirements
Software update applied, bur life and changes, chuck maintenance, filter changes for compressor, cleaning spindle and unit, lubricant specific to mill
milling in office training requirements
Operation and maintenance of mill and furnace, file acquisition and initial design (margin marking), restoration design, material selection and milling, firing, staining, and glazing
Maintaining and Troubleshooting- what if something doesn’t scan or mill as expected
Help lines, dial- in support, reviewing maintenance, network issues
selection of restorative materials
Materials, CERAC, PlanMill
Resin ceramic ( yes, yes) Feldspathic porcelain (yes, no) Leucite- reinforced (yes, yes) Lithium disilicate (yes, yes)
CAD/CAM- Lab Work Flow
- Dental office (impressions, model, digital scan)
- Lab (pour model, scan impression, scan model, import scan to design software)
- CAD (Design center or Lab- design restoration)
- CAM ( milling center or Lab- no model, mill restoration, Sinter if necessary, finish and glaze OR print model or wax pattern for investing, pressing or layering PFM or all ceramic restorations. Printed models are also used for orthodontics and prosthodontics appliances)
SLA Die
Dies are fabricated using SLA (3D) printing
SLA (3D) printing
ProJet 1200 (Whip Mix)
Objet Eden 260V (stratasys) Objet30 OrthoDesk (stratasys)
Chairside Oral Scanners- Digital Transfer to Milling/Printing CEnter
Lava Chairside Oral Scanner C.O.S (3M)
iTero Imaging System (Align Technology, Inc)
Milling Center equipment
Scanners, design software, milling machines, and sintering ovens; proprietary and open architecture, 3D printing ( orthodontic and C/B models)
Computer Aided Machining (CAM)
Lava Milling Machine
Milled Zirconia
Lava vs Crystal
Shading
New ceramics are pre-shaded and layered
Sintering
Monoclinic to Tetragonal…stopping short of cubic
Lava COS vs Elastomeric Impressions- Clinical Study
Occlusion
COS, Impression
Perfect: 74, 48%
High: 18%, 46%
Light: 8%, 6%
Lava COS- better results (P <0.05)
Lava COS vs Elastomeric Impressions- Clinical Study
Contacts- Mesial
COS, Impression
Perfect: 62,43%
Tight: 38%, 57%
Lava COS- better results (P <0.05)
Lava COS vs Elastomeric Impressions- Clinical Study
Fit
COS, Impression
Perfect: 92%, 70%
Loose:8%, 30%
Lava COS- better results (P <0.05)
Lava COS vs Elastomeric Impressions- Clinical Study
Clinically Acceptable
COS, Impression
Yes: 95, 89%
No: 5, 11%
Lava COS- better results ( p< 0.05)
Lava COS vs Elastomeric Impressions- Clinical Study
Patient Preference
COS 63%, Impression 8%, No preference 29%
CAD/CAM Ceramics
Factors in Selection of CAD/CAM ceramics
Strength (120 to 1200 MPa),
Esthetics (anterior vs posterior)
patient factors
CAD/ CAM Ceramics Silica based
Feldspathic porcelain (CEREC Blocs), Leucite-reinforced porcelain (IPS Empress CAD), Lithium disilicate ceramic (IPS e.max CAD)
CAD/CAM Ceramics
Flexural Strength of Silica based Ceramics
Feldspathic porcelain (100-120 MPa) , Leucite- reinforced porcelain (120-140 MPa), Lithium disilicate ceramic (375 MPa) (IPS e.max CAD)
CAD/CAM Ceramics
Non silica based CAD/CAM Ceramics
Zirconia (BruxZir Solid Zirconia, BruxZir Anterior, Lava Crowns & Bridges, Lava Plus, NexxZr) Flexural strength (500-1500 MPa), Veneered core and framework and full-contour restorations
What is Zirconia?
Yttrium- stabilized Tetragonal Zirconia (Y-TZP)
> 90% zirconium oxide (ZrO2), stabilized with 3-5.4%, Y2O3, HfO2, Al2O3; small grains with no glassy phase, no silica- special primer for bonding
Benefits of Zirconia Ceramics
Esthetics- excellent, strength- very high, fit- excellent, metal- free, clinical track record (10 year Lava recall, 4 year BruxZir recall, 1 year, NexxZr recall, 1 year BruxZir Anterior recall)
Units of BruxZir vs IPS e.max vs PFR
Material, 2010, 2016
BruxZir, 10,000/mo, 143,000/mo*
IPS e.max, 10,000/mo, 26,000/mo
PFM, 25,000/mo, 19,000/mo
*BruxZir Solid Zirconia 87%
BruxZir Anterior 13%
Lava Recall at 10 years
over 1300 Lava restorations placed since 2003, 1008 restorations recalled, molar crowns, pre-molar crowns, anteriors, bridges, and implant abutments
Resistance to fracture and chipping- fracture rate (6% required), replacement- molar> premolar, chipping rate 4.7%, No fracture/chipping 89%
Zirconia based Restorations
Lava Failures
Undersupported, underfired
BruxZir Solid Zirconia Crowns and Bridges at 4 years
1392 zirconia restorations placed- cemented with self- adhesive and adhesive resin cements; 913 restorations recalled at 4 years; single crown (77%) bridges (16%) and implant crowns (7%)
most restorations had no chipping or fracture, one crown and 2 implants failed; esthetics- excellent great for patients who wanted B1 shade; 5 restorations exhibited slight marginal discoloration, minimal wear on restorations and on opposing dentition, 39 of 913 (2.8%) crowns debonded and were recemented
NexxZr Full contour restorations at 1 year
278 NexxZr T full contour restorations placed; 4% of restorations required minor occlusal adjustment at placement; single crown (88%) bridges (11%) and implant crowns (1%)
NexxZr Full contour restorations at 1 year- rating 97%
179 restorations recalled at one year, one premolar crown exhibited chipping, no restorations required replacement, esthetics- excellent; excellent resistance to marginal discoloration with self adhesive and adhesive resin cements; no wear observed on restorations or on opposing dentition
What’s new
Esthetic Zirconia
BruxZir Anterior (Glidewell Laboratories), Katan UTML (Kuraray Noritake Dental), Lava Plus (3M), Origin Beyond (B&D Dental technologies) Vericore ZR HTX (whip Mix Corporation) * improved translucency but lower flexural strength
What’s new
Multilayered Zirconia
Katana UTML, Kuraray Noritake Dental
35% enamel layer, 15% transition layer 1, 15% transition layer 2, body (dentin) layer 35%
CAD/CAM Ceramics- Translucency Parameter
Zirconia (7.1-7.8) Lithium disilcate (13.8-15.8) Resin ceramic (14.9- 17.7) What value of TP is ideal clinically? Stump shade important
CAD/CAM Ceramics- Surface Roughness (polished)
Zirconia- (0.1-0.15um), lithium disilicate (0.28-0.37um), resin ceramic (0.34-0.46)
BruxZir Anterior Full Contour Restorations at Placement- Rating 98%
306 BruxZir Anterior full-contour restorations placed; 96% of restorations received a rating of 5 at placement. Only 2 restorations were redone because of loose fit and light contacts; single crown (88%), bridges (10%) implant crowns (2%)
BruxZir Anterior Full Contour Restorations at 1 year- Rating 100%
108 restorations were recalled at one year, no restorations exhibited chipping, no restorations required replacement; esthetics- excellent; excellent resistance to marginal discoloration, no wear observed on restorations or on opposing dentition
Pressed Lithium Disilicate (IPS e.max) at 5 years
Over 670 pressed lithium disilicate restorations placed- cemented with self adhesive (87%) and esthetic resin (13%) cements; 381 restorations recalled- 68% at 5 years, 32% less than 5 years; molar crowns (46%) premolar crown (38%), anterior crowns (8%), inlays, onlays, bridges
most restorations had no chipping or fracture, Fracture (required replacement) <2%, chipping 1.5%; esthetics- excellent, 6% of restorations slightly opaque; resistance to marginal discoloration- excellent, 2% slight graying at margins; 12 posterior crowns debonded
What’s new
Milled Resin Ceramics
CeraSmart (GC America),
Enamic (Vident- VITA),
Lava Ultimate (3M)
*higher translucency but lower flexural strength
What’s new Milled Fully Sintered Zirconia
BruxZir Now (Glidewell Laboratories)
limited milling options
What research is needed?
Color and optical properties of monolithic, shaded and layered milled restorations; wear of opposing teeth with full contour zirconia restorations; properties of milled resin ceramics vs zirconia vs silica based ceramics; longevity of lithium disilicate vs zirconia restorations
Mechanical Properties
Reaction to applied force
Elastic modulus, strength (yield, flexural, compressive, tensile) creep, ductility, malleability, hardness, fracture toughness
elastic modulus
“young’s modulus” “modulus of elasticity” a measure of rigidity ; a measure of a material’s ability to resist elastic deformation; a measure of the stiffness of a material; the higher the elastic modulus, the less elastic and more stiff is the material
Yield Strength
The measure of a material’s ability to resist permanent (plastic) deformation; offset is the measure of plastic deformation in test or calculation (can be as little as 0.01%, typical is 0.2%, can be as much as 0.5% or more)
Flexural strength
“Modulus of rupture”; a measure of a material’s ability to resist fracture when a bending force is applied; a measure of both compressive (on top) and tensile (on bottom) strengths
Compressive strength
the measure of a material’s ability to resist being crushed or broken with the application of a pushing force
Tensile strength
The measure of a material’s ability to resist being separated from itself, or broken with the application of a pulling force
Creep
“creep modulus” a measure of the amount of plastic deformation of a material subjected to a compressive force over a given period of time
Elongation percent
The measurement of a material’s ability to be stretched up to its breaking point; the formula (final length - initial length) X100
a measurement of brittleness vs ductility
ductility
a solid material’s ability to be plastically deformed under tensile forces without fracture; a solid material’s ability to be stretched into a wire
malleability
a solid material’s ability to be plastically deformed under compressive forces without fracture; a solid material’s ability to form a thin sheet by hammering or rolling
Gold
Is so ductile that 1 oz can be stretched into a thin wire measuring only 5um in diameter and 50 miles in length; is so malleable that 1 oz can be beaten into a thin, continuous sheet measuring ~100 sq. ft.
Hardness
The measure of a solid material’s ability to resist plastic deformation on its surface when a compressive force is applied
fracture toughness
the measure of a material’s ability to resist fracture in the presence of an existing crack
Physical properties
“observation” dimensional change, dimensional stability, corrosion resistance, tarnish resistance
Dimensional change
The volumetric change that can occur when the components of a material react to form a product
Dimensional Stability
The volumetric change that can occur in a set material over time
Corrosion
Defined as the progressive destruction of a metal by a chemical or electrochemical reaction
Galvanism is a corrosive process that occurs when an electrical current is generated between dissimilar metals in a solution of electrolytes (such as the mouth)
Tarnish
A thin layer of corrosion that can form on the surface of some metals; usually the result of an oxidation reaction with the metal; a tarnish layer can serve as a protection to the underlying metal (silver used to fight off infection)
Amalgam
An alloy of Hg (mercury) and one or more other metals; produced by mixing liquid Hg with solid particles of an alloy containing predominately Ag, Sn, and Cu;
Zn, In, Pd, and Pt may also be present in small amounts
amalgamation
to blend, unite, combine, mix, merge or make a combination of 2 or more things;
in metallurgy: to mix or alloy with Hg
Trituration
to crush, grind or pound into small particles, to pulverize and comminute thoroughly
Amalgam alloy freshly mixed
Once the amalgam alloy is freshly mixed (triturated or amalgamated) with liquid Hg, it has the plasticity that permits it to be conveniently packed or condensed into a prepared tooth cavity
Amalgam alloy vs dental amalgam
the combination of solid metals vs amalgam alloy mixed with Hg
Alloy is the solid part of amalgam filling- dental amalgam is the finished product
Advantages and Disadvantages of amalgam
relatively easy to place, not overly technique sensitive, relatively long service life, inexpensive relative to other materials
color, patient concerns over reported toxicity, concern about impact of amalgam disposal on wastewater and the environment
History
618- 907- possibly used in the first part of Tang Dynasty in China
1528- reportedly used in Germany
1800s- became the restorative material of choice due to its low cost, ease of application, strength and durability
1895- GV Black formulation published
Circa 1900- first broad based research into dental amalgam (balanced composition)
1962- Dispersalloy introduced (addition of a spherical Ag- Cu eutectic particle to the lathe cut Ag3Snɣ particle)
1972- Tytin introduced (unicompositional spherical particles)
Balanced Composition
Ag3Sn ɣ
small amount of Cu
occasionally Zn; 10-20 year durability
Marginal fracture
also referred to as “crevice corrosion”
likely due to Sn- Hg phase (Sn7-8Hg) ɣ2 [weakest phase in the hardened amalgam]
acceptable characteristic of dental amalgam fillings at the time
Eutectic
From the greek “eutektos” meaning “easily melted”
relating to or denoting a mixture of substances (in fixed proportions that melts and solidifies at a single temperature that is lower than the melting points of the separate constituents or of any other mixture of them
Ag- Cu Eutectic
72% Ag 28% Cu
Eutectic point- low point; Silver and copper alone have higher melting points
Types of Alloy
Low Cu,
Hi Cu
Admixed Regular (different Cu amounts)
Lathe Cut- Low Cu
Spherical- Hi Cu
Admixed Unicompositional
Lathe Cut- Same Cu
Spherical- Same Cu
Unicompositional - spherical
Low Cu
Ag3Sn; Ci (2-8wt%)
irregular in shape- lathe cut
Admixer Regular
Ag3Sn; Cu (2-30wt%) lathe cut
+
Ag3Sn; Cu (20-40 wt%) spherical
Admixed Unicompositional
Ag3Sn; Cu (29-30wt%) lathe cut
+
Ag3Sn; Cu (29-30wt%) spherical
ex. dispersilode is this
Unicompositional
Ag3Sn; Cu 13-20wt%) spherical
Elemental Composition of Alloy
Ag- 40-60% (increase strength)
Sn- 26-30% (increase regulates expansion and setting)
Cu- 13-30% strength and hardness decrease corrosion and creep
Zn <0.01% (Zn free) during manufacture; prevents oxidation
In- 0-5% increase strength, decrease creep
Pd 0-1% decreases tarnish and corrosion
Pt 0-1% increases tensile and compressive strength
Why Zn
Included to help produce clean, sound ingots from which the lathe cut particles are made
>0.01% can’t be classified as Zn free
Why is Zn bad? When moisture contamination occurs during amalgam placement, Zn will cause delayed expansion of the set amalgam
Metallic Phases in Alloy
Ag3Sn (ɣ)
Cu3Sn (ɛ) [small amounts]
Cu6Sn5 (ƞ’) [small amounts]
Ag4Sn (β)
Ag-Cu (eutectic)
Amount of liquid Hg
The amount of liquid Hg used to amalgamate the alloy particles is not sufficient to react with the particles completely
more Hg is required to react with lathe cut alloy because of the increased surface area of the irregular, lathe cut shape
Low Cu Reaction
Ag3Sn +Hg –> Ag2Hg3 + Sn7-8Hg + (unreacted) Ag3Sn
Composition of Set Low- Cu Amalgam
Ag3Sn (ɣ) (27-35vol%)
Ag2Hg3 (ɣ1) (54-56vol%)
Sn7-8Hg (ɣ2) (11-13vol%) [weakest of all phases]
Cu6Sn5 (ƞ’) (eta prime) (2-5vol%)
Admixed High Cu Reaction
Ag3Sn + Ag-Cu +Hg –> Ag2Hg3 + Cu6Sn5 + (unreacted) Ag3Sn + (unreacted) Ag-Cu
Composition of Set Admixed High- Cu Amalgam
Ag2Hg3 (ɣ1)
Cu6Sn5 (ƞ’)
Ag3Sn (ɣ)
Ag-Cu eutectic
Unicompositional High Cu Reaction
[Ag3Sn + Cu3Sn] + Hg
—> Ag2Hg3 + Cu6Sn5 + (unreacted)[Ag3Sn + Cu3Sn]
Components of Set Unicompositional High- Cu Amalgam
Ag2Hg3 (ɣ1)
Cu6Sn5 (ƞ’)
Ag3Sn (ɣ)
Cu3Sn (ɛ)
Adding Ag-Cu eutectic to alloy
By adding the Ag- Cu eutectic to the alloy, the formation of the Sn7-8Hg phase was replaced by the Cu6Sn5 phase. This created a harder, more corrosion resistant amalgam
Lathe Cut and/or Admixed Alloys
vs Spherical Alloys
More condensable, easier to establish proximal contacts, less post operative senitivity
vs
better early strength, smoother surface, more easily adapted around retentive pins, requires less Hg
When amalgam achieves strength
Most amalgams will achieve 40-60% strength within 1 hour
Most amalgams will achieve 100% strength by hour 24
Mechanical and Physical Properties of Dental Amalgam
Mechanical (compressive strength, tensile strength, elastic modulus)
Physical ( dimensional change, dimensional stability, corrosion resistance, tarnish resistance)
High Cu Compressive Strength
1 hour (118 to 292 MPa) 7 days (387 to 516 MPa)
High Cu Tensile Strength
15 min (3.8- 8.1 Mpa) 7 days- (43 to 56 MPa)
Elastic Modulus Comparison
Amalgam (40-60 GPa) Composite Resin (5-20 GPa)
Amalgam Creep
The “Creep Test” 7 day set amalgam cylinder, 37C, 36 MPa Compressive force, 104 hours, measured by the shortening of the specimen, ADA/FDI acceptable limit (1%), 0.05-0.45% is standard for Hi Cu Am; >1% creep indicates Sn7-8Hg is in the mix
High Cu Dimensional Change
Change in length of 8mm cylinder between 5 min and 24 hours after trituration; -1.9 to -8.8 um/cm of length (shrinkage); less shrinkage with admixed lathe cut alloys, more shrinkage with unicompositional spherical alloys –> increased PO sensitivity
bonding agents –> decreased PO sensitivity
bonding of amalgam
(4-methacryloyloxyethy trimellitate anhydride)
4META is most successful (for amalgam); 10 MPa shear bond strength to dentin; no true chemical adhesion, bond is produced by commingling of bonding agent with amalgam at interface; fracture resistance of bonded MOD amalgam is equal to that of bonded MOD composite resin and more than twice that of un-bonded MOD amalgam
Dimensional Stability; delayed expansion in Zn containing alloys
Delayed expansion in Zn containing alloys resulting from moisture contamination; this contamination can occur anytime during mixing/ condensing; expansion begins 3-5 days after placement and may continue for months; can exceed 400 um/cm (4%)
caused by the electrolysis of water by Zn which releases ZnO and H2 gas; H2 collects within the mass of the restoration, increasing internal pressure enough to cause the amalgam to creep and expand; can cause pain, typically 10-12 days after placement
High Cu Corrosion
Corrosion can occur on or within the amalgam through the interaction of dissimilar metals; corrosion can lead to increased porosity, reduced marginal integrity, loss of strength and the release of metallic products into the oral environment ; high Cu amalgam restorations are cathodic with respect to other metals within the mouth, such as Ay alloy; Galvanism can occur between these metals (a short term battery effect can be created; long term clinical significance is unknown); the accumulation of corrosion products in the micro-gap at the margin decreases microleakage over time ; consequently, post operative sensitivity can be more prolonged with high Cu amalgams
Corrosion Resistance
Ag2Hg3 (ɣ1) Ag3Sn (ɣ) Cu3Sn (ɛ) Cu6Sn5 (ƞ’) Sn7-8Hg (ɣ2)
(as go down, decrease corrosion resistance)
High Cu Tarnish
Tarnish occurs on the surface of the amalgam restoration as Ag is oxidized in a reaction with salivary chlorides and sulfides in the presence of O2. Although unsightly, it does not affect the mechanical properties of the amalgam
Process Overview
Dispensing and mixing, placing, condensing, carving, polishing
Size of mix (historically- dispensing)
400 mg( 1 spill), 600 mg (2 spill), 800 mg (3 spills) 1200mg
Amalgam Safety
The safety of amalgam restorations has been scrutinized since they were first introduced. To understand the possible side effects of dental amalgam, the differences between allergy and toxicity will be discussed
Amalgam Safety (Anusavice) Allergy
Allergic responses are an antigen- antibody reaction marked by itching, rash, difficulty breathing, swelling and other signs and symptoms; a small percentage of people may be allergic to mercury, just as a certain number of people are allergic to any number of metals; contact dermatitis or Coombs type IV hypersensitivity reactions are the most likely physiologic side effect to dental amalgam (these are experienced by <1% of the treated population); Lichenoid reaction (most common site: buccal mucosa immediately opposite a buccal amalgam; may occur on ventral surface of tongue adjacent to lingual amalgam; not very common- shows within a few days)
To confirm suspicion of a true hypersensitivity to dental amalgam, the patient should be evaluated by an allergist
Mercury Safety (Anusavice) Toxicity
Fewer than 100 documentable reports of mercury allergy and toxicity attributable to dental amalgam have been published in the past 70 years in the scientific literature; the real hazard that may exist is the inhalation of mercury vapor during the mixing, placement and removal of dental amalgam personnel
Mercury Vapor Toxicity
The magnitude of vapor exposure for a patient with 8-10 amalgam restorations is between 1- 4.4 ug/day; the toxicity threshold for workers in the mercury industry is 350-500 ug/day
Mercury Blood Level Toxicity
Mercury blood levels in one study indicated that the average blood level for patients with amalgam restorations was 0.7 ng/mL, compared to 0.3 ng/mL for subjects with no amalgam; a Swedish study demonstrated that one saltwater seafood meal/week elevated blood mercury levels from 2.3-5.1 ng/mL
Normal daily intake of mercury
15ug from food, 1 ug from air, 0.4 ug from water
Three forms of mercury
Elemental Hg (released into air with fossil fuel combustion), inorganic Hg (found in the environment in combination with sulfur and oxygen), organic Hg (methylmercury found in soil and water; thimerosal, phenylmercuric acetate and other organic mercury compounds are synthesized and used as preservatives)
Conversion of mercury
microorganisms in the soil and water can convert both elemental and inorganic mercury into methylmercury which can bio-accumulate in the food chain
Methylmercury exposure over long periods of time can cause
Neurological disorders, fetal and infant developmental abnormalities, cerebral palsy in the developing fetus
ALL forms of mercury can have toxic effects, however ORGANIC MERCURY is often the most insidious in its nature
Amalgam vs Composite Resin
Composite Resin components
bisphenol A- BPA- estrogen mimicker
aluminum- possible links to Alzheimer’s Disease
Barium- heavy metal
mercury hygiene in dental offices
operatory should be well ventilated, all excess mercury including disposable capsules, should be collected and stored in well sealed containers, scrap and waste amalgam should be disposed of through reputable vendors, amalgam and mercury should not be incinerated or subject to heat sterilization, use disposable, single use pre-sealed capsules, only condense manually
Regulation of amalgam use by government
There is no evidence to suggest that dental amalgam causes illness in the general population, several countries are phasing out amalgam because of ENVIRONMENTAL concerns. Denmark, Norway, and Sweden announced general bans in 2008-2009 on the use of mercury in any product including dental amalgam; Austria, Germany, Japan, and Canada have restricted the use of dental amalgam
Dental Casting Alloys
Noble Metals (metals that retain their surface luster in dry air; metals that resist oxidation, tarnish and corrosion)
base metals (metals that don’t retain their surface luster in dry air; metals that oxidize, tarnish and corrode more easily)
Noble Metals
Au – yellow, soft, malleable, ductile
Pt – bluish white, tough, malleable, ductile
Pd – white, improves quality of castings (as little as 5% profoundly whitens Au)
Ir (Iridium) – grain refiner
Rh (Rhodium) – grain refiner
Ru (Ruthenium) – grain refiner
Os (Osmium) – not used in dentistry
Iridium, Ruthenium, Rhodium
Used in small amounts; very high melting points; don’t melt while casting; serve as nucleating centers for the molten metal as it cools, resulting in fine grain structures that improve the properties of the allow
Carat and Fineness
Carat refers to Au content in units of 1/24 (18K is 75% gold); fineness refers to parts of Au per 1000 parts of alloy (18K is 750 fine); both systems are less useful now in dentistry
nobel casting alloys
Type I: soft; simple inlays
Type II: medium; complex inlays, onlays, single unit crowns
Type III: hard; crowns and fixed dental prostheses
Type IV: extra hard; partial denture frameworks
Noble and High Noble Casting Alloys
High Noble - ≥ 60% Noble and ≥ 40% Au
Au-Ag-Pt
Au-Cu-Ag-Pd-I
Au-Cu-Ag-Pd-II
Noble - ≥ 25% Noble Au-Cu-Ag-Pd-III Au-Ag-Pd-In Pd-Cu-Ga Ag-Pd
Noble Ceramo- Metal Casting Alloys
Au-Pt-Pd
yellow color, good corrosion resistance, lower strength
Au-Pd
excellent mechanical properties, good corrosion resistance
Au-Pd-Ag
high mechanical properties, easy to cast, lower density and cost
Pd-Ag
low density, low cost, good mechanical properties
Pd-Cu
high strength, easy to cast, low cost, form dark oxides
Affects of Minor Elements in Metal- Ceramic Alloys
Indium, Tin, Gallium, Cobalt -enhance metal-ceramic bond, increase strength of alloy, lower the fusion temperature
Iron- strengthens alloy
Copper and Cobalt- produce dark oxide
Silver- can cause “greening”
Requirements of Ceramo- Metal Alloys
The alloy must have a melting temperature substantially higher (> 100C) than the firing temperature of the ceramic and the solders that may be used to join segments of the bridge. The alloy must form surface metal oxides that help create the bond between the ceramic and the metal.
The alloy must have a compatible, but slightly higher, coefficient of thermal expansion than the ceramic. This tends to keep the ceramic in compression (where it is stronger) rather than in tension. The alloy must have adequate stiffness and strength to not permanently deform under masticatory forces.
The alloy must have a high sag resistance ex. no distortion of the metal can occur during the firing of the ceramic. The alloy must create accurate castings, even with the high melting ranges of ceramo- metal alloys (more shrinkage upon cooling); preparation design is critical to allow for adequate thickness of restorative materials
Coefficient of thermal expansion
ceramic over metal
firing temperature –> room temperature
The metal contracts more upon cooling, putting the ceramic in compression
Base Metal Alloy uses in Dentistry
Removable Partial Denture (RPD) Frameworks
Copings for Ceramo-Metal (PFM) Restorations & Fixed Partial Denture (FPD) Frameworks
Endodontic Instruments
Orthodontic Wires & Brackets
Pre-Formed Crowns
Implants [Titanium]
Base metals
Chromium(Cr) Cobalt(Co) Nickel (Ni)** Molybdenum(Mo) Tungsten(W) Carbon(C) Aluminum (Al) Iron(Fe) Manganese(Mn) Beryllium(Be)** Indium (In) Tin (Sn) Gallium(Ga) Copper (Cu) Silver (Ag) Niobium(Nb) Silicon(Si)
metalloid- having properties of both a metal and a non-metal
Biocompatibility/ Toxicity Concerns
Be in both vapor and particulate form, is associated with contact dermatitis, chronic lung disease, lung carcinoma, and osteosarcoma.
Ni is an allergen. Sensitivity to Ni is 5-10x higher for females than males; 5-8% of females show sensitivity to Ni
Base Metal Influence on Base Metal Alloy Properties
Cr- tarnish resistance, >29% —> increase brittle
CO- increase elastic modulus, strength and hardness, increase strength of porcelain/metal bond
Ni- increase elastic modulus, strength and hardness
(Co and Ni generally interchangeable)
Mo- increase strength
W- increase strength
C- increase hardness (typically only <0.1-~0.5wt%)
Exact amount of C is critical!
Al- forms Ni3Al (Nickle Aluminide)–> properties similar to ceramic and metal tensile and yield strength
Fe- increase strength
Mn- increase fluidity and castability
Be- increase improves castability by decrease the alloy’s melting temp ~ 100C and decrease surface tension of the molten alloy, also increase strength of porcelain/ metal bond
In- increase strength, decrease fusion temperature, increase strength of porcelain/metal bond
Sn- increase strength, decrease fusion temperature, increase strength of procelain/metal bond
Ga- increase strength, decrease fusion temperature, increase strength of porcelain/ metal bond
Cu- can prodcue a dark oxide
Ag- can cause “greening”
Nb- similar to Ti in it’s properties
Si- enhances fluidity and castability
Base Metal Alloys
Co-Cr (Vitalium) Co: ~ 63 wt% Cr: 30 wt%: Mo: 5 wt% Fe: 1 wt%
Ni-Cr (Ticonium) Ni: ~ 66 wt% Cr: 17 wt%: Mo: 5 wt% Al: 5 wt% Be: 1 wt% Mn: 5 wt%
Ni-Cr c Be (Rexillium III) Ni: ~ 77 wt% Cr: 13 wt%: Mo: 5.5 wt% Al: 2.5 wt% Be: 1.9 wt%
Ni-Cr s Be Ni: ~ 64 wt% Cr: 22 wt%: Mo: 9 wt% Nb: 3.5 wt%
Co-Cr Co: 62 wt% Cr: 26 wt% Mo: 6 wt% W: 5 wt% Si: 1 wt%
Co-Cr c Noble Metal Co: ~ 62 wt% Cr: 20 wt% Mo: 4 wt% Al: 2 wt% Mn: 4 wt% Au: 2 wt% Ga: 6 wt
Base Metal Alloy Uses
Co-Cr (Vitallium) – RPD Frameworks
Ni-Cr (Ticonium) – RPD Frameworks
Ni-Cr (Rexillium III) with Be – PFM Metal
Ni-Cr without Be – PFM Metal
Co-Cr – PFM Metal
Co-Cr with Noble Metal – Used for High Expansion Porcelain
Base Metal Alloy features
Have higher hardness values than noble metal alloys; have a higher elastic modulus than noble metal alloys; are more difficult to cast and solder than noble metal alloys; are more technique sensitive than noble metal alloys; undergo more solidification shrinkage than noble metal alloys
Physical Properties of Metal Alloy-
Melting Temperature
Most melt between 1400-1500 C, Ni-Cr-Be melts at 1275C, Types I to IV Au alloys melt between 800-1050C
Physical Properties of Metal Alloy- Density
Between 7-8g/cm3, half the density of Au alloys, lower density can be an advantage for larger maxillary appliances, more difficult to cast!
Physical Properties of Metal Alloy- Corrosion
Dependent upon: Electrolytic media (the solution or salivary composition), alloy composition, alloy microstructure, surface state of the alloy (usually a different composition than the bulk of the alloy), corrosion coupled with wear: 3x Ni ions released
Mechanical Properties of Metal Alloy- Elastic modulus
Elastic modulus of base metal alloys is twice that of Au alloys; Greater rigidity allows the fabrication of restorations with reduced dimensions
Mechanical Properties of Metal Alloy- Hardness
Base metals are harder than Au alloys; polishing techniques are more complicated
Mechanical Properties of Metal Alloy- Yield Strength
Minimum of 415 MPa needed to maintain RPD clasp integrity
Mechanical Properties of Metal Alloy-Tensile strength
Base metal alloys are all greater than 800 MPa
Mechanical Properties of Metal Alloy-Percent Elongation
Wide variability among base metal alloys; too high –> the RPD clasp can’t maintain it’s shape
Too low –> the RPD clasp is too brittle and breaks
Mechanical Properties Percent Elongation; Alloy Type (RPD);% Elongation
Alloy Type (RPD);% Elongation
Au Alloy (Hardened) 5-7
Co-Cr (Vitallium) 1.5
Ni-Cr (Ticonium) 2.4
Mechanical Properties Percent Elongation; Alloy Type (PFM);% Elongation
Au-Pt-Pd (Noble) 3-10
Co-Cr (Base) 6-15
Ni-Cr (Base) 8-20
Mechanical Properties Yield Strength;
Material; Yield Strength (0.2 % offset) MPa
Au-Pt-Pd (Noble) 480-510
Co-Cr (Base) 644
Ni-Cr (Base) 710
Mechanical Properties Elastic Modulus;
Material; Elastic Modulus (GPa)
Co-Cr alloy 218 Au Alloy (Type IV) 99 Feldspathic Porcelain69 Enamel 84 Dentin 18 Composite Resin 17
Base Metal Alloys Info
Have higher melting ranges than cast Au alloy types I through iV
1150 C to 1500C for base metal alloys; 800C to 1050C for cast Au alloys
Have lower densities than cast Au alloy types I through IV; ~1/2 that (7-8g/cm3) of cast Au alloys; can create difficulties with casting
RPD base metal alloys
In general, RPD base metal alloys, such as Vitallium and Ticonium, contain more C than base metal alloys used in PFM fabrication. RPD base metal alloys, such as Vitallium and Ticonium, are harder, stronger, and stiffer than base metal alloys used in PFM fabrication.
Preparation of Alloys for the application of Porcelain
Pre- oxidation- relieves internal stresses, forms an outside layer of metal oxides with which the porcelain forms a chemical bond, this process is unique and specific to each of the metal alloys; sometimes referred to as “Degassing”
Other applications of Co-Cr Metals
Wide range of surgical applications “surgical Vitallium”, bone plates, surgical screws, fracture repair appliances of various sizes and shapes, can be implanted directly into bone for long periods without harmful reactions, seems to be bio-inert with no initiation of an inflammatory response
Rutile “roo- teel”
a black or reddish-brown mineral consisting of titanium dioxide (TiO2), typically occurring as needle- like crystals; the most common natural form of titanium dioxide (TiO2)
Titanium
Ninth most abundant element in the earth’s crust; fourth most abundant structural metal; commercial production began in 1950s; worldwide titanium production is now over 25,000 tons, annually; high strength/density ratio; excellent corrosion resistance
Titanium uses
Aerospace and defense industry (aircraft engines, aircraft frames, missiles, spacecraft), deep sea marine application, navy ship components, automotive industry, recreation/sport equipment, biomedical devices
physical properties of Titanium
Resistant to electrochemical degradation, benign biological responses, relatively light weight and low density (4.4-4.5g/cm3) [make it difficult to cast], high melting point (CP Ti-1700C, Ti Alloys (+/- 1350C), rapidly passivates (10^-9sec) by forming a very stable and protective oxide layer on the surface
passivate
To make a metal or other material unreactive by altering the surface layer, or coating the surface with a thin inert layer; To coat a material with an inert substance to protect it from contamination
Mechanical Properties of Titanium
Variable Tensile Strength (240-890 Mpa)
Variable Yield Strength (170-830 Mpa) 0.2% Offset
High Fracture Toughness
Low Thermal Expansion Coefficient
Low Elastic Modulus (103-114 Gpa)- somewhat elastic
Elongation Percent (10-20%) quite ductile
Alloying has significant effect on mechanical properties – most common alloy for implants is Ti-6Al-4V
Commercially Pure Titanium (CP Ti)
CP Grade I
CP Grade II
CP Grade III
CP Grade IV
Each grade varies according to oxygen (0.18-0.40 wt%) and iron (0.20-0.50 wt%) content
These slight concentration differences have a profound effect on the physical and mechanical properties of the titanium
alloptropy or allotropism
The property of some elements that can exist in 2 or more different forms, in the same physical state. These different different forms are known as allotropes; Titanium exhibits allotropism
Titanium allotropism
α Phase – Hexagonal close-packed (HCP) crystal lattice
β Phase – Forms at temperatures above 883˚ C, body-centered cubic (BCC) form
Alloying Ti with other metals preferentially stabilizes either the α or the β phase to influence the properties of the Ti alloy
Titanium Phase Properties
α- Al is an α phase stabilizer; good weldability, excellent strength characteristics, difficult to form or work at room temp
β- Vanadium, copper and palladium are β phase stabilizers; malleable at room temp, useful in orthodontics
α+β- good strength properties; difficult to weld
Mechanical Property comparison
The mechanical properties of cast CP Ti are similar to those of types III and IV gold alloys
The mechanical properties of cast Ti- 6Al- 4V and Ti-15V are similar to those of Ni-Cr and Co-Cr alloys
Ti Alloys under investigation
Ti-6Al-4V Ti-15V Ti-20Cu Ti-30Pd Ti-Co Ti-Cu Ti-Cu-Ni Ti-6Al-4Nb
Titanium in Dentistry
Implants (machined), Crown (computer aided machining; electric discharge machining or spark erosion cast), FDP Frameworks (Computer Aided Machining (CAM), electrical discharge machining or spark erosion cast), RPD Frameworks (computer aided machining (CAM), electrical discharge machining or spark erosion cast)
Dental Implants
Machined from billets of Titanium; CP Ti, Ti-6Al-4V
A billet is a length of metal that has a round or square cross section. A billet is created directly via continuous casting or extrusion, or indirectly via hot rolling an ingot (large rough casting) or blood (an ingot that has been rolled into a smaller cross sectional area)
Ti crowns, FPD, and RPD
Abrasive machining (CAM) of titanium is slow and inefficient; spark erosion technology is expensive and technique sensitive; currently, technologies to cast, machine, weld and/or veneer titanium with porcelain are very technique sensitive and expensive
Consequently, our focus on titanium will be in the area of implantology. The passivating oxide on the implant surface permits close apposition of physiological fluids, proteins, and hard/soft tissues to the metal surface. The process whereby living tissue and an implant become structurally and functionally connected is called osseointegration.
Increasing Implant Surface Area
Grit Blasted (metal-oxide, hydroxyapatite particles) plasma sprayed with Ti, coated with hydroxyapatite
Wrought
Beaten out or shaped by hammering, “cold worked”, the work done to the alloy is usually at a temperature significantly below the solidus line; worked and adapted into prefabricated forms for use in dental applications (precision attachments, backings for artificial teeth, wire in various cross sectional shapes)
wrought wires
Can be soldered to an existing RPD framework. They can be cast to a new RPD framework.
wrought forms
Wrought forms have a fibrous microstructure that results from the cold work applied during the operations that shapes the metal.
This cold work increases both tensile strength and hardness.
Prolonged heating of wrought forms can cause them to recrystallize and develop a grain structure similar to their cast form.
Recrystallization adversely affects the mechanical properties. Severe recrystallization can cause wrought forms to become brittle. Heating operations must be minimized when working with wrought forms.
Wrought Alloys
High Noble Pt-Au-Pd Au-Pt-Pd Au-Pt-Cu-Ag Au-Pt-Ag-Cu Au-Ag-Cu-Pd
Noble- Pd-Ag-Cu
Titanium
Ni-Ti
β-Ti
Stainless Steel
Martensitic(Cr-Co)
Ferritic (Cr-Co) Cr
Austenitic (Cr-Ni)
Wrought Noble and High Noble Alloys in Dentistry
Clasping wires for removable prostheses
Not commonly used due to high cost
Wrought Titanium Alloys in Orthodontics
β-Ti
78%Ti-11.5%Mo-6%Zr-4.5%Sn
This alloy composition stabilizes the β phase at 37° C
Less force than stainless steel wires
Low elastic modulus
High springback* (max elastic deflection)
Low yield strength
Good ductility, weldability & corrosion resistance
Ni-Ti – “Nitinol” 55%Ni-45%Ti High Resiliency Called “Shape Memory Alloy”or “Thermal Memory” Wire can be plastically deformed below the TTR (temperature transition range), then when warmed above the TTR will assume its original shape Lowest elastic modulus Highest springback* Lowest yield strength
Wrought Titanium Alloys in Endodontics
Ni-Ti – “Nitinol”
50-60%Ni-40-50%Ti
Co, up to 2%, substituted for Ni will lower TTR
2-3X the Memory of stainless steel
Unique shape memory
Super-elasticity
Most bio-compatible of the super-elastic alloys
Excellent corrosion resistance
Resists torsional (twisting) fractures
Can be strained up to 8% with full recovery of shape (1% for stainless steel)
Transformation fatigue cycles for endodontic Nitinol
6% Strain ; Several 100 Cycles
2% Strain; 10^5 Cycles
1% Strain; 10^5 Cycles
Nitinol Phase Transformations
Austenite Phase (Parent Phase); Body-Centered Cubic Lattice (BCC)
Above 100° C —-(cooling)—–>
37° C
Martensitic Phase (Daughter Phase)
Hexagonal Close-Packed Crystal Lattice (HCP)
super elasticity
Austenite(BCC)–(cooling)—> martensite (HCP, twined HCP) —(Deformation)–> Martensite (HCP; De-twined HCP)—-(heating)–> Austenite
What is steel?
Iron alloyed with carbon; carbon gives steel strength, but also makes it more brittle; steel is not corrosion resistant, steel can also be alloyed with varying amounts of Ni*,Cr, Mo, B, Ti, V, W, Co & Nb
What is stainless steel?
A steel that contains a minimum of ~11% Cr; chromium passivates the surface via the formation of a strongly adherent Cr2O3 layer; Stainless steels are much more corrosion resistant than high carbon steels; stainless steels are not as hard as high carbon steels
Three major stainless steels
martensitic, ferretic, austenitic
Martensitic Steel
Corrosion resistant, hardenable by heat treatment, magnetic, high hardness, high strength, high wear resistance, 11.5-18% Cr, No Ni*, is a very brittle crystalline structure of C and Fe that is the main constituent of hardened steel. Named after the German metallurgist, Adolf Martens (1850-1914)
Ferritic Steel
More corrosion resistant than Martensitic, but less than Austenitic; non hardenable by either heat or work, can be cold-worked, can be softened by annealing; magnetic, 10-20% Cr, no Ni*, Ferrite (Fe2O3) or ferric oxide, or rust, is a type of ceramic compound; name is a derivation of ferrous or ferric, “having to do with iron”
Austenitic steel
Most corrosion resistant; added corrosion resistance is from the formation of a solid solution of Cr-Ni-Fe; can’t be hardened by heat treatment, can be hardened by cold-working; non- magnetic (~10% Cr, ~8% Ni) Gamma phase iron(ɣ-Fe)
Named after Sir William Chandler Roberts-Austen (1843-1902)
Stainless Steels Comparison
Martensitic (hardenable by heat, corrosion resistant)
Ferritic (not hardenable, more corrosion resistant)
Austenitic (hardenable by heat or cold work, most corrosion resistant)
Wrought Stainless Steel Alloys in Dentistry
Ferritic Steel (Cr-Co)- dental instruments, some dental equipment parts
Martensitic steel (Cr-Co) Dental instruments, ortho appliances
Austenitic Steel ( Cr- Ni*)- stayplate/flipper claps, ortho wires
The last 2 are the most common wrought wires used in dentistry today
Cementation Objectives
Objectives of cementation or luting are to help maintain restoration in place, maintain integrity of remaining tooth structure
Cementation retention
Retention is achieved by: friction, adhesive joint, the cement, the restoration, or both mechanisms
Cementation
an effective interfacial seal depends on the ability of the cement to fill the irregularities between the tooth and the restoration and to resist the oral environment short and long term
Strong bond between the luting agent and dental substrates is also important because it can prevent infiltration of bacteria and fluids that can cause caries and sensitivity to the patient
Bonding to other substrates
Cast alloys, ceramics, indirect (lab) composites, amalgam, fiber posts, repair of composite, ceramic, and ceramic- metal restorations
Classification of Luting Agents according to length of time
According to the length of time that they are expected to stay in function
provisional (low strength and easy handling, no irritate pulp) such as Zinc oxide and non-eugenol cements and calcium hydroxide pastes
Definitive (remain in function for the longest time possible, must have sufficient properties)
Classification of Luting Agents according to setting
Acid based reaction: GI, RMG, zinc oxide- eugenol, zinc polycarboxylate, and zinc phosphate
setting by polymerization: resin cements, compomers, and self- adhesive cements
Some materials that are capable of creating a chemical interaction with hydroxyapatite are
zinc polycarboxylate, Gi, RMG, Self adhesive resin cements
Minimal invasive dentistry
“preservation of a healthy set of natural teeth for each patient should be the objective of every dentist”; all work in the health field is aimed basically at conservation of the human body and it’s function
Tooth Adhesion Steps
Adhesives- dentin morphology and physiology, adhesive systems, adhesive dentistry (case reports)
The adhesive revolution
Micromechanical retention (dentin, adhesive resin tags, composite resin restoratives)
Buonocore 1955
Finding in 1955 that acid etching of the enamel increases the bond strength of resin to enamel; The practice of bonding to enamel has become a routine procedure in many fields of dentistry
Enamel etching vs Dentin etching
surface not even- better mechanical retention
Evidence Based
Approximately 1/2 of all restorations placed in general dental practice are done to replace a defective or failed restoration; the reasons that restorations are replaced may be divided into 3 major categories: clinical factors (technique), material properties (will surface withstand stress ex. bruxism), and patient factors (want a white filling)
Dental adhesion challenges
morphology, physiology, smear layer, saliva, structure of tubules
Adhesive dentistry- closer look at Dentin
Dentinal tubule (large)–> peritubular dentin (around tubule) –> intertubular dentin (around peritubular)
Composition of dentin
50% mineralized apatite crystals, 20% water, 30% organic matrix (collagen fibrils)
Superficial vs Deep dentin
water content varies from superficial to deep dentin (diameter and number of tubules increase near pulp, 20,000 tubules/mm2 at DEJ vs 45,000 tubules/mm2 close to pulp)
superficial dentin hybrid layer is a form of intertubular resin infiltration while deep dentin hybrid layers are mainly composed of resin tag formation (an example of intratubular permeation; peritubular dentin matrix below the depth of acid etching)
Sclerotic and caries- affected dentin
hypermineralized (like a scar- protecting pulp), tubules occluded with CaPO4 crystals, acid resistant (etching won’t occur easily- must use phosphoric acid with higher %)
Wet vs Moist vs dry dentin
collagen fibers susceptible to collapse upon over- drying
keep dentin moist when restoring or else collagen network will collapse- cross linking will not occur- keep dentin moist for good bonding
Changes in the matrix when dentin is decalcified with phosphoric acid
1. mineralized dentin matrix 2. demineralized dentin matrix filled with water (plasticized) 3. collapsed stiffened air dried demineralized dentin matrix 4. demineralized dentin matrix stiffened by organic solvents in air
The “overwet phenomenon”
producing bubbles- PG won’t infiltrate tubules properly
*look at slide 25
*Smear layer of dentin
0.5-2um thick, can’t be removed with rinsing, composed of bacteria, saliva, blood cells, denatured collagen
*Hybrid
A thing made by combining 2 different elements (a mixture)
ex. a car with gasoline engine and an electric motor each of which propel it
Dr. Nakabayashi about hybrid layer
“the structure formed in hard dental tissues by demineralization of the surface and subsurface, followed by infiltration of monomers and subsequent polymerization”
remove smear layer, add primer (all adhesives have 3 types of solvents acetone, ethanol, water)
- adhesive (monomer- any polymer that is liquid; once cured it’s a polymer) solvent helps primer penetrate; air dry; apply adhesive, then cure (hybrid layer is formed)
different adhesives- have dif. solvents
Adhesive systems
“understanding the anatomy and physiology of dentin has been critical to the development of high- performance dentin bonding systems”
utilize A/Phys of dentin for max bond strength; resin monomers infiltrating demineralized dentin
(denting exposed to phosphoric acid- resin tag open use morphology of substrate to your advantage)
Composition of dentin adhesives
primer (allows penetration; hydrophilic monomer (HEMA), water soluble solvent- water, acetone, ethanol)
adhesive (unfilled or lightly filled resin [Bis-GMA])
Adhesive Categories
*** slide 34
Conditioner (etchant), primer, adhesive
4th generation-1. remove smear layer (phosphoric acid etching), 2.primer, 3.adhesive
5th generation[golden standard]- 1. remove smear layer (phosphoric acid etching), 2. combined primer and adhesive resin; resin tags are longer
6th generation- * improves over time 1. dissolve smear layer [ no phosphoric acid, primer dissolves the smear layer], 2.self etching primer, 3.adhesive
4th vs 5th generation adhesive systems
4th- primer and adhesive are in separate bottles, more steps, slightly more predictable
5th- primer and adhesive are mixed together in one bottle, less steps, less predictable, more susceptible to differences in wetness
Self etching adhesives
newer generation; significant difference in technique, user-friendly (no more phosphoric acid etching); acidic monomer dissolves smear layer and primes dentin simultaneously; one step or two step system
Latest research on self etching adhesives
Higher bond strength in deep dentin than 4th and 5th generation adhesives [ bond strength when closer to pulp is usually weak, this makes it stronger], bonds well to CUT enamel [restoration/prep], not as well to uncut enamel [ braces], resin tag formation not as pronounced, doesn’t seem to affect bond strength, 2 step self etching adhesives more predictable than one step products
7th generation or all in one adhesives
Dissolve smear layer, self etching primer and adhesive all in one bottle
4th generation or “two step” adhesives
• Scotchbond Mul’Purpose Plus (3M ESPE) – Ethanol, Water; Unfilled
• AllNBond 2 (Bisco)
– Acetone, Ethanol; Unfilled
• Op’bond/Op’bond FL (SDS/Kerr) – Ethanol/Water; Filled
- adhesive has filler or no filler- add particles to make it stronger (improve mechanical properties)
5th generation or “one step” adhesives
• Prime&Bond NT and NT Dual Cure (Dentsply/ Caulk)
– Acetone, Ethanol, Filled
• Op’bond Solo Plus (SDS/Kerr) gold standard
– Ethanol, Filled
• Single Bond Plus (3M ESPE) – Ethanol/Water; Unfilled
6th generation or “self etching” adhesives
*solvent is always water
• Clearfil SE Bond (Kuraray)
– Water; 10% Filled; Light-Cured
- Adper Prompt L-Pop (3M ESPE) – Water; 2% Filled, Light-Cured
- Clearfil Liner Bond 2V (Kuraray) – Water; 10% Filled, Dual-cured
- OneNUp Bond F (fluroide) Plus (Tokuyama) – Water; 10% Filled, Light-cured *make sure material compatible with fluoride
All- In- one (7th generation) adhesives
iBond (Heraeus Kulzer)- unfilled, light cured
G-bond (GC Corp.)- 5% filled, light-cured
and more to come..
bond strength of adhesives to enamel and dentin after 24 hours vs bond strength of adhesives to enamel and dentin after thermocycling
want them to stay at same value or increase in value; SE and SB really good? look at slide 46/47
bonding generations
4th (primer, adhesive, etch) 5th (one bottle, etch), 6th (etch-primer, adhesive), 7th (one bottle)
Etch and rinse or total etch:
3 steps (etching, priming, and bonding) vs 2 steps (etching and primer and bond mixed in one bottle)
etching is 30-40% phosphoric acid (conditioners) to demineralized tooth structure
primers are hydrophilic monomers, oligomers, or polymers, usually carried in a solvent (acetone, ethanol, or water)
Self etch
two step system with a hydrophobic bonding resin in a separate bottle; all in one system; ester monomers with grafted carboxylic or phosphate acid groups dissolved in water
bonding agents
most bonding agents are light-cured and contain an activator such as camphorquinone and an organic amine; dual-cured bonding agents include a catalyst to promote self-curing; some bonding agents contain: nanofiller, fluoride (glass ionomers), antimicrobial ingredients, or desensitizers (glutaraldehyde_
In-vitro evaluation of bond performance
by far, the most important mechanical property is bond strength among in- vitro research
biocompatibility
solvents and monomers in bonding agents are usually skin irritants (HEMA can produce local and systemic reactions to dentists and dental assistants (gloves, mask, high speed suction, keep bottles closed and unit dose system)
Clinical performance
longevity of bond in general practice may be only 40% of that achieved in clinical trials because don’t follow instructions, clinical studies are highly controlled; 95% of secondary caries associated with resin composites is in the interproximal areas (hard to clean [patient], clinician [ don’t use all tools needed, don’t do increments of 2 mm- tend to fail]; clinical performance can be evaluated by (postoperative sensitivity, interfacial staining, secondary caries, retention or fracture followed for 18 months)
enamel bonding
bonding to enamel occurs by micromechanical* retention after etching
bonding penetrates the etched surface and becomes locked into place after polymerization occurs
composition of dention
50% mineralized apatite crystals, 20% water, 30% organic matrix (collagen fibrils)
dentin bonding
primers (hydrophilic components such as HEMA [wet dentin and penetrate its structure]); total etch or etch and rinse systems (phosphoric acid removes the mineral creating microsporosites within the collagen network); after etching step, the dentin contains about 50% unfilled space and about 20% remaining water, after acid is rinsed, drying of dentin must be done cautiously
dentin bonding
Dehydration of the dentin outer surface will cause that the remaining collagen scaffold to collapse onto itself then the collagen mesh will exclude the penetration of primer and bonding will fail. excess of moisture tends to dilute the primer and interfere with resin interpenetration; ideal dentin moisture levels varies according to the solvent present in the adhesive
dentin bonding
resin composite (RC), hybridization, hybrid layer (HL) resin tags (RT)
Hybrid layer
the structure formed in hard dental tissue by demineralized of the surface and subsurface followed by infiltration of monomers and subsequent polymerization
durability
durability is one of the most challenging problems of adhesive/dentin bonds
Case 1- Congenitally Missing (Agenesis) Lateral Incisors
shade match after vital bleaching, conservative preparation, bonded indirect resin FPD [splint- acrylic- gets hard and cement- cemented with resin cement and adhesive ]
Case 2- traumatic injury
8 year old male, basketball incident in which patient fell to floor, fracturing #8,9; patient had been to one dentist prior to arrival at office, dentist placed dycal and instructed patient to leave teeth alone [calcium hydroxide deep base- due to exposure of pulp want to create dentin bridge]
diagnostic aids- periapical x-ray revealed large pulp chambers, no apparent periapical pathology at this time, apices were open and still developing, father had saved fractured pieces 8,9
Pumice teeth, clean, and gently dry; applied self etching primer, dry to remove solvent (water), adhesive placed and gently dried, light cured for 10 sec, flowable composite placed on fractured surface of tooth (use flowable because mechanical properties in anteriors are not as high), also placed on lingual surface, primer and adhesive placed on surface of fractured piece and light cured prior to placement, 8 was re attached and light cured, flowable composite placed on #9, adhesive placed on fractured piece and tried in, #9 bonded to place, acid etched enamel surfaces, additional composite placed, bonding complete, prior to contouring, contoured facial surfaces and polished with Sof- Lex,
Principles of Adhesion
A strong, durable, and bonded interface with enamel and dentin provides benefits. protects the interface of the restorations against penetration of bacteria and fluids that can cause recurrent or secondary caries. Reduces the need of retentive areas in the prep that would required removal of sound tooth structure. Sometimes strengthen the remaining tooth structure.
it is very difficult to achieve chemical bonding between tooth structure and a restorative material because of the complex composition of some substrates such as dentin, presence of contaminants and water.
in daily practice, adhesion is accomplished by micromechanical interlocking between the adhesive and tooth substrate.
Aspects to create an adhesive joint: cleanliness of the surface (biofilm, debris, saliva) and smear layer
These contaminants will reduce the surface energy of the bonding substrate and its wettability
dental implant
generally speaking, anything inserted into the mandible or maxilla designed to take the place of a tooth; have been in use at least 2,300 years; modern implants usually take the form of a self tapping titanium screw or post; millions of dental implants are placed annually worldwide [better than bridgework and crowns]
endosseous implants
most common, sits inside bone (post, screws)
crew post into bone- build restoration on top; typical system;
Have blade, screw, cylinder: blade not very effective; will mostly see screws (modern- thread into bone) vs cylinder
subperiosteal
much rarer, were used in cases of atrophic bone/ sit atop bone
sit like a saddle on top; rarer because mass recession around implant- high failure rate
transosteal
quite uncommon, higher failure rates. post transverses the entire mandible, not used on the maxilla.
disadvantage: operation to place is quite brutal
alveolar bone structure
alveolar process: ridge on surface of mandible/maxilla where teeth are
basal bone: bone underlying the alveolar process
alveolar bone proper and supporting alveolar bone
Alveolar bone proper
compact bone (cribiform plate, lamina dura)
cribiform- plate with a lot of bones; radio opaque that surrounds tooth; lines tooth socket
supporting alveolar bone
both compact and trabecular bone.
cortical plates (compact bone component), central spongiosa (trabecular bone component) surrounds both sides, supports plates
Alveolar bone structure
loading via mastication critical for maintaining bone density; loss of alveolar bone in edentulous patients [ no loading= no alveolar ridge, only basal bone] ; patient selection/site preparation critical for high success rate of dental implants
- must build up bone to place implant; may have other sources that impair healing ex. Diabetes ; if can’t heal things properly or quickly will be a major challenge
Success rates are high PROVIDED THAT patients are selected well- can’t be patients that won’t change their lifestyles ex. Smokers, diabetics that don’t manage diabetes, etc.
Osseointegration
deposition of bone in close apposition to implant surface (really by oxide layer); clearly a highly desirable process, mediated by mesenchymal progenitor cells; provides mechanical stability of implant and tight seal [preventing inflammation, want good healing]
Vs biointegration (direct apposition to ceramic- bone can attach directly to ceramic surface- ceramic and titanium becomes weak spot)
Oxide layer- increases biocompatibility –
Will always see a gap between bone and titanium oxide
Survive repeated cyclical loading is the main goal of teeth
Implant anchored well to bone
osseointegration continued
wound healing (space management); extraction of tooth= hole; hole fills with a clot, which is then converted to a highly cellular granulation tissue; epithelial invasion vs bone regeneration; osteoblast differentiation and bone deposition (osseointegration)
Wound- void in tissue
Wound managing- restoring integrity of compartments
Blood is key component of wound healing- managing compartments
Osteoblasts- build bone/mesenchymal; osteoclasts- break down/hematopoietic; together make mature bone
Don’t want epithelial cells to prevent this process of bone formation- things tend to turn into what they are next to (bone growth factors are released) DON’T want epithelial ingrowth- will never get CT forming (“preparing integrity of compartment” - but don’t want it”
GT- granulation tissue (want it to give rise to tissue that you want –>new bone)
9 week- almost full closure- osseointegration is occurring
Recruitment of Cells
Stro-1, osteoblast- progenitor associated marker, F4/80, macrophage marker, TGFB1, growth factor, Osteopontin, non collagenous matrix protein
Initial inflammation must resolve- drives osseointegration
Fibrous Encapsulation
Formation of fibrous tissue (collagen) around implant; bad news for mechanical anchoring; can result from peri-implantitis brought on by a number of factors, but often problems/delays in osseointegration= microbial infiltration or poor stability after placement
If inflammation does NOT resolve- Fibrous collagenous sac around implant- bone will not lay down; will be lose and will come out; not mechanically stable
Mechanical forces acting on implants
tensile, compressive, and shear forces all brought to bear on implants; up to 1250N reported[ 1 N = force required to move 1 kilo at 1m/s^2] due to forces involved: material properties and integration of implants are critical
bite force especially strong by hinge
Mechanical forces and ceramics
bone must experience strain or it will resorb; ceramics tend to be quite stiff and don’t transfer adequate strain to surrounding bone, resulting in “stress shielding”
elastic modulus: too high= lower transfer of force to bone= lower bone loading
Mechanical forces and titanium
Titanium somewhat more elastic and transfers some strain to surrounding bone thus an implant material must be structurally sound but also must have mechanical properties which are physiologically compatible
mechanical forces acting on implants and bone
bone is strongest when compressed, weaker under tensile forces, and weakest when subjected to shear
The bone- implant interface therefore is critical when considering mechanical loading of implants
bone in apposition to smooth implants is subjected to almost total shear when the implant is loaded and less surface area for attachment
mechanical forces and texture
Adding texture (ex threads) engage bone in compression where it is strongest; interlocking also provides much better transfer of load to bone (less resorption) and increased surface area for attachment
mechanical forces and alteration in length/width
alterations in the length and width of implants also have implications for implant loading
increasing length: increase surface area of attachment= decreased stress on bone. Minimal advantage however as most force transfer happens at the upper part of an osseointegration implant (also anatomy and heating- loner it is, the more heating)
increasing width: increased surface area for attachment= decreased stress on bone. Implant stiffness increases, leading to stress shielding of bone
There is an optimal range for these parameters. Implants can be too long/short, or too narrow/wide
Implant surface modification
Titanium is the most common material employed in dental implants: CP Ti or Ti-6Al-4V alloy
has a number of excellent properties: elastic modulus lower (flexes more, avoid stress shielding)than ceramic but compared to rubber band (higher) ; strength, immune inert (non immunogenic), low corrosion (passivation- continual presence of a passive oxide layer), biocompatible (non- toxic)
Ti can be simply modified:
alterations in oxide layer (oxide layer is mainly what biological systems interact with [can make thicker and improve compatibility] ), coatings (biomemtic or ceramic), roughening/etching (grit blasting or acid etching)
surface modification generally has the aim of either enhancing osseointegration by osteoblast differentiation/migration, improving the mechanical interlocking with bone tissue, providing better loading characteristics (ex. threads)
optimal surface still unclear
implant surface topography modification
machined, Ti Grit Blasted HF Etched, Tri- Calcium Phosphate Sputter Coated (smooth surface –> roughened–> coated)
alteration of surface topography can have an impact on the biology of attached cells (smoother surfaces have rounder cells; rougher surfaces have different cells)
Implant surface chemistry modification
generally refers to increasing oxide layer; TiO2 forms the stable oxide layer, Oxide layer generally biologically favorable (protein absorption), modifications such as hydroxylation increase hydrophilicity (wettability); anodization used to increase oxide layer thickness
increase affinity to blood which increases management
Implant surface chemistry modification- coating
many coatings are also applied to implants; ceramic and glass coating (hydroxyapatite/tricalcium phosphate/bioglass)- bioactive, although only as strong as the metal- ceramic interface
ceramic coating is the weak point [metal- ceramic interface, bone-ceramic interface]
coating with short peptide sequences to increase cell attachment: integrins, RGD cell attachment sequences, collagen, fibrin
coating with growth factors associated with wound healing such as TGFB1, FGF-2, VEGF, PDGF. [doesn’t work; optimal healing comes with exposure of all of these at the same time but not just one]
patient selection and challenges
endosseous implants have a 7 year survival rate of around 95% (because of soft tissue); this is however due to careful patient selection. die to the requirements for rapid osseointegration, patient selection is critical; must have good bone around site to anchor implant during loading (many edentulous patients have atrophied bone), must not (challenge) be compromised in terms of bone healing (diabetes, immune compromised patients can pose problems depending on how compliant they are), implants have a very high success rate, the next clinical challenge is developing implants which can be placed in complex or difficult clinical situations
Tissue Engineering/ bioactive materials**
tissue engineering is a discipline which seeks to encourage the restoration of function and structure to a pre-injury state; bioactive materials (materials which are designed to drive repair/regeneration through the use of bioactive factors)
traditionally 3 components in tissue engineering: relevant cell source, biomaterial or scaffold[ what you implant cells in], bioactive component to drive cell responses
**Autograft
implanted material derived from the same individual as the implant is to be delivered into
**allograft
implanted material derived from another individual of the same species
**xenograft
implanted material derived from another species
**alloplast
implanted material is not derived from a living source or is “synthetic” very broad category
**dental pulp progenitor cells
population of mesenchymal progenitors resident in the dental pulp, derive from the neural crest; huge topic in dental pulp biology (focus of both cellular and a cellular approach to tissue engineering); can theoretically differentiate to regenerate vasculature, mineralized tissue, soft tissue, or possibly even nerves; represents a capacity of the tooth for self repair ( or other tissues- SHED banking)
Steady state turnover –> Quiescent niches –> trauma response (by stimulatory signals) –> Reparative dentine
** Cellular vs Acellular approaches
addition material containing cells vs application of materials to existing tissues; tissues need cells to regenerate, but many contain cells containing the necessary cells (ex. a capacity to self repair)
there are advantages and disadvantages to each
soft tissue: periodontal ligament, dental pulp, oral mucosa, skin
hard tissue: bone, dentin, cementum
Ex. root canal OR cells + scaffold OR scaffold +native tissue
If want to regenerate pulp; needs progenitor cells (cell source)
Acellular approach- leave native tissue and then add bioactive material
Isolation of dental pulp progenitor cells (DPPCs)
practical difficulties (relatively low cell number- possibly around 1% of cells)
practical difficulties (lack of single specific marker to ID cells; generally a panel used)
Gold standard( 1. population doubling over long periods in culture 2. multipotency: ability to differentiate in various lineages ( adipose, endothelial, chondro- osteo-)
DPPCs are adherent cells ex. they attach to tissue culture plastic, but so are many other cells found in the pulp
They typically express high levels of the α5β1 integrin receptor, which binds fibronectin: fibronectin adhesion isolation
adherent–> tissue culture
non-adherent –> disposal
Cells age- senescent (mesenchyme become senescent much slower; divide longer than the more differentiated cell)
Biomaterials
There are a huge number of potential ‘biomaterials’, both synthetic and naturally occuring
multiple challenges to overcome in oral tissue regeneration: microbial infection, inflammation, regeneration
Through tissue engineering, it may be possible to manipulate the innate capacity of oral tissue to encourage repair or perhaps regeneration
new bioactive materials= more options for practitioners= improved outcomes for patients
biomimetric
biomimetric= mimicry of tissues/processes/structures that are ‘biological’
