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Biomaterials 1 (Adhesion, Bonding & Cementation (Key Terms: (Adhesion …
Biomaterials 1
Adhesion, Bonding & Cementation
Key Terms:
Adhesion - attraction of two surfaces:
- chemical adhesion
- mechanical adhesion (structural interlocking) or
- a combination of both
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Surface tension —A measurement of the cohesive energy present at an interface
- in the case of a liquid, it is the liquid/air interface.
- It has units of mN/m
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Adhesion Challenges
- Tooth composition is not homogeneous
- Fluid exchange through the tooth.
- Instrumentation roughening = promotes air entrapment at the interface
- Saliva contamination.
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- Adhesive must displace or incorporate water
- Adhesion must be sustained long-term in an aqueous environment
Cements
Definition: Base, liner, filling material or adhesive that bind devices and prostheses to tooth structure or to each other
Classification
According to Uses:
- Luting Agents
- Permanent Cements: Long term cast restorations
- Temporary Cements: Provisional coverage
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- Liner or base application
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Luting Interface
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Cement Thickness
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Varies:
- amount of force applied during seating
- direction of force during seating
- design potential to inhibit or facilitate the flow of cement
- the fit on the prepared tooth
- the inherent film thickness of the cement
Ranges: ranges between 17 and 50 µm
nb: For luting applications, the maximum allowable film thickness is 25 µm
Bonding & Adhesives
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Uses
- Composite restorations
- Splinting teeth
- Fissure sealant
- Attachment of orthodontic brackets
- Attachment of bridges
- Attachment of acrylic or porcelain labial veneers
- Root canal sealants
- Glass Ionomer
- Amalgam bonding
Wetting & Surface Energy
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Etching = removes passivating/smear layer, roughens the surface and increases the surface energy
Factors affecting adhesion
- Tooth
- smear layer, contaminants
- Material Stress
- elastic modulus, thermal coefficient, dimensional stability
- Cavity Prep
- resistance/retention, cavity design, finish
- Restorative Technique
- Moisture control, liner/base, c-factor
- Oral Environment
- occlusion loads, para-functional habits, oral degradation
Generations:
5th gen: Two-Step
Prevent collagen collapse/minimize post-op sensitivity. More susceptible to hydrolyitic degradation
ex. Scotch single bond
7th gen: One-Step
Multipurpose: Self Etch, etch-and-rinse, selective etch. Long term bond strength
ex. Scotch Universal Adhesives
Total Vs Self-etch
Long term performance of simplified one step is inferior in terms of durability compared to 3 or 2 steps total-etch technique
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Luting Cements
Definition
= A material used to retain an indirectly-fabricated device in place, such as an orthodontic bracket, a crown, a pin or a post
Ideal Properties
- Good pulpal/gingival health
- Dimensionally stable
- Good adhesion
- Ease of use/removal
According to Properties:
Aqueous (water-based)
Zinc-Polycarboxylate
Historical Luting cement - used in cases of pulp hypersensitivity
- short working time (2-3mins)
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Zinc Phosphate
Historical Luting Cement:
Type 1 (fine grain) Used for luting
Type 2 (medium grain) Used in luting and filing
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Advantages: Long working time, good thermal insulation
Disadvantages: No chemical adhesion, high micro-leakage risk(solubility)
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Classification
According to Uses:
- Luting Agents
- Permanent Cements: Long term cast restorations
- Temporary Cements: Provisional coverage
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- Liner or base application
GIC
Classification
- Type I - Luting agent
- Type II - Restorative Material
- a. aestheic cements
- b. reinforced cements
- Type III Lining cements & bases
- Type IV Fissure & Pit sealant
- Type V - Orthodontic cement
- Type VI - Core build-up
Types
Fuji I
- Crown/ bridge cementation (tooth-metal bond)
& Inlays, Onlays, Posts Orthodontic brackets
Fuji II LC
- Conventional restorative
- Class 3, 5 and primary dentition
- Depth of cure 1.8mm
Fuji VII
- Conventional restorative = Erupting molars/ Exposed root surfaces
- Intermediate(temp)/Caries stabilization restorations
Fuji IX GP/Extra
- Class 1 and 2 in children
- Class 1, 2, 5 in adults
- Non-load bearing areas
- Root surface
- Core-Build up
Reaction
acid/base reaction
Polycarboxylate + fluoroaluminosilica glass = gel
then set to form a cement through cross-linking
--> in post-set hardening, fluoride is released.
Tartaric acid
Added to increase working time and manipulation
Temporarily suppresses ionization of the acid
Moisture Control
The reaction occurs in a water medium, and transports released ions, whilst hydrating salts to aid in setting
Chemical Bond to tooth
Carboxyl groups react w/ hydroxyapatite in enamel and take the place of phosphate ions to bond to calcium
(ion exchange)
Properties
Adhesion
- chemo-mechanical retention - chelation btwn Ca+2 and the polyaryclic acid
- Removal of smear layer w/ dentine conditioner
- RMGIC have incraesed bond strength compared to conventional GICs
Biocompatibility
- good pulpal tolerance(<1mm RDT)
Mechanical
- Low compression strength, tensile strength and hardness when compared to other restorative materials
- Limited for use in low force areas
- Wears similar to enamel and dentine
- Increased resistance to acid-attack
Aesthetics
- available in different shades
- opacity/lack of translucency
Resin-based Restorations
Composites
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Uses
- Direct restorations
(e.g. for anterior teeth, conservative or non-retentive cavities, etc.)
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- Core build-up for crowns and Post-endo(RCT)
- Splinting of mobile dentition
- Cementation of fixed prosthesis
eg. orthodontic brackets, maryland bridge etc
Components
Contains:
- Resin-based matrix - oligomer and monomer
- Filler particles - silica or quartz
- (size determines polishability)
- (% determines mechanical properties)
- Coupling agent - silianes bond filler and matrix
- Accelerator-initiator - peroxide and tertiary amides
- Others
- inhibitors - inhibit free radicals/increase shelf life
- pigments/opacifers - Ti or AlO alter shades/translucency
Clinical Steps:
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Etch = 30-40sec phosphoric
- Enamel = 15-30s (micro-retention and wetability)
- Dentin = 15s (smear removal and collagen exposure)
Adv/Disadvantages
Advantages:
Aesthetics
Repairable/lower biological cost
Mechanical properties
Versatile use - filling material, veneers, crown, core etc.
Working time (better)
Disadvantages:
Polymerization shrinkage
Technique sensitive - hydrophobic, incremental, shade selection
Moisture Control
- Anterior Composite Restorations
- Annual failure rate: 4.9% (Collares et al., 2017)
- Posterior Composite Restorations
- Annual failure rate: 2% (Ferracane, 2011)