Definition
Cement has many definitions but can be considered as a binder
-A substance which sets and hardens independently, and can bind other materials together
Direct restorative materials that are placed in dentine in close proximity to the pulp
-Number of direct restorative materials are placed in dentine that are in close proximity to the pulp
- Immediate restorative materials (cavity varnishes/liners/bases)
- Luting- fitting crowns
- Temporary restorations
- Endodontics
Intermediate restorative material definition
Temporary restorative material
Barrier, intermediate restorative materials
- Barrier between filling material and dentine
- Provides a thermal, chemical and electrical barrier
- Protects the pulp from bacterial invasion
- Pulp may be damaged and may die
- Effects of bacteria and their metabolic products
- Due to effects of microleakage post restoration
- Thermal insulation
- Chemical barrier: prevents diffusion of irritable chemicals, for example monomer leakage
- Electrical barrier: protection from galvanic pain
Calcium Hydroxide Cements constituents and chemistry
2 paste cements:
-One paste contains 50% calcium hydroxide, 10% zinc oxide and 40% ethyl toulene sulphonamide
- Other paste contains 40% butylene glycol disalicylate, titanium dioxide and calcium sulphate
- Setting reaction is one of chelation between the ZnO and butylene glycol disalicylate (initial hardening)
- Freshly mixed cement has a high pH (12) and is thought to enhance the formation of secondary (tertiary??) dentine
Properties and indication of calcium hydroxide cements
- Very brittle
- No mechanical integrity
- Dissolve easily
- Compressive strength is low
- Mainly used as a sub-liner/pulp cap under zinc phosphate
- Calcium hydroxide: for direct pulp capping when a pulp exposure is suspected
MTA cements components and chemistry
- MTA has been suggested for use as a pulp capping material
- MTA mixed with water hydrates to form calcium silicate hydrate and calcium hydroxide
- Needs moisture to set
- Made up of fine hydrophilic particles that set in the presence of water, forming a solid cement
-Composed of tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, calcium sulphate dihydrate and bismuth oxide (radioopacifier)
Types of MTA and difference
- Grey and white
- Only difference is the presence of iron in grey MTA
Initial use of MTAs
Root-end filling material
Subsequently been used for pulp capping, pulpotomy, apexogenesis, apical barrier formation in teeth with root apices, repair of root performations
-Seals off the pathways of communication between the RC system and surrounding tissue, significantly reducing bacterial migration
Biodentine definition and constituents
- Calcium-silicate based cement
- Can be used in pulp capping, root perforations and dentine replacement
Powder:
- Tricalcium silicate
- Dicalcium silicate
- Calcium carbonate
- Oxide filler
- Iron oxide shade
- Zirconium oxide
Liquid:
- Calcium chloride as an accelerator
- Water soluble polymer that serves as a water reducing agent
Properties of biodentine
- Setting time must shorter than tradiitonal MTAs (9-12mins)
- Increase in particle size, addition of calcium chloride to the liquid component results in a shorter setting time
- Has the ability to release calcium when in solution and is a source of hydroxyapatite in contact with synthetic tissue fluids
- Biodentine is designed to treat damaged dentine both for restorative and endodontic indications
- Can be veneered with composite
Luting cements ideal properties
-Used when cementing a crown
- Easy of manipulation
- Low film thickness (high thicknesses result in increased chance of cohesive failure)
- Long working time with rapid setting at mouth temperature
- Low solubility in oral fluids
- Adhesion to tooth structure and restorative material
- Adequate tensile and compressive stregnth
- Biocompatible
- Anticarogenic properties
Examples of luting cements
- Zinc phosphate
- Zinc oxide eugenol
- Zinc polycarboxylate
- Resins
- GICs
Zinc phosphate cement and use
pH is around 2 of a freshly mixed cement
- Rises to 5.9 with 24 hoyrs and is nearly neutral after 48 hours
- Setting rxn is exothermic and this limits the mixing time
- Mixing time is 5 mins, setting time is 15 mins
Variables
- High powder:liquid ratio accelerates the rxn
- Moisture accelerates the rxn
- Low temperature retards the rnx thus mixing can be done on a cool slab but not below the dew point
- Rapid addition of powder accelerates the rxn
- Limited value as a lining cement
- No therapeutic effect on pulp
- Type II used as a luting cement but may cause post insertion sensiticity
Zinc polycarboxylate cements
Composition on slides
- Formation of zinc polyacrylate
- Physical properties are comparable to zinc phosphate and the setting exotherm is lower and initial pH is higher
- Adhesive to the tooth structure
Zinc oxide egenol cements
- Temporary use only
- pH is relatively neutral
- Natural bacterucude
- Mild pulp irritant
- Eugenol can act as a free radical sink and should not be used with composites as it inhibits polymerisation
- Can also cause discolouration of the composite
EBA cement
-Lower solubility and higher strength than conventional ZoE
Temporary restorations requirements
- Good retention
- Fast setting
- Easy to clean up
- Low sensitivity
- Ease to remove
Root canal therapy
- Remove the pulp and all its remnants
- Canal and pulp chamber are cleaned and sealed
- Sealed to prevent infection to adjacent bone
- Permanent restoration intended to obturate pulp space of the tooth
Properties of RCT materials
- Ability to seal completely
- Retain seal over extended periods (indefinite)
- Bactericidal
- Good compatibility with bone/tooth interface
- Appropriate mechanical strength
Types of root fillings
Rigid root fillings
- Metallic
- Polymeric
Plastic root filling
- Zn-O-eugenol
- Epoxy resins
- GIC
- Calcium hydroxide
Gutta Percha definition
- Semi-plastic, structural isomer of natural rubber
- Trans-poly (1,4 isoprene)
- Properties diffuer from natural rubber (cis isomer)
- Harder, lacks resilience and cannot be stretched reversibly
-Polymeric cones of gutta percha with other constituents such as ZnO, barium sulphate, plasticisers and pigments
Advantages and disadvantages of gutta percha
+:
- Semi plastic nature allows reshaping and remoulding
- Biocompatible at the root tip
- Radioopaque
- Can be removed and replaced if required
- :
- Lack of rigidity makes the placement difficult
- Root canal preparation is critical
- Must be confined to prevent excess material being expressed beyond the apex
- Ages rapidly, becomes brittle
Amalgams definition and pros/cons
- Via orthograde approach (ie from the crown of the tooth)
- Retrograde approach (directly into the apex via a surgical approach)
- Well tolerated by tissues
- Build up of amalgam in the oral mucosa results in so called amalgam tattoos
+:
- Inexpensive
- Radiopaque
- Long shelf life
- Plastic on insertion with a quick setting time
- :
- Difficult to condense into the root canal
- Tends to be expressed beyond the apex of the tooth
- Usually shows considerable leakage
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Biocompatibility of materials for use in the body21
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Failure of Materials54
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Polymers in Dentistry33
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Ceramics59
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Polyalkenoate Cements27
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Composites39
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Metals in Dentistry56
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Adhesion to Enamel and Dentine40
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Amalgam39
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Impression Materials36
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Elastomeric Impression Materials36
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Acrylic Materials22
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Cements27
