Cements Flashcards
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
