cements

Question 1

defn of cement

Answer 1

GPT 9th ed

a binding agent used to firmly unite 2 approximating objects

a material that, on hardening, will fill space/ bind adjacent objects

Question 2

defn of luting agent

Answer 2

GPT 9th ed
any material used to attach/cement indirect restorations to prepared teeth

Question 3

ideal requirements of luting agents

Answer 3

BIOLOGICAL
- non toxic
- non carcinogenic
- cariostatic

CHEMICAL
- inert
- solubility in oral cavity negligible
- bonds chemically to enamel and dentine

RHEOLOGICAL
- low film thickness which allows it to flow
- longer mixing and working time

MECHANICAL
- high compressive strength
- high tensile strength
- high MOE
- minimum dimensional changes during setting

THERMAL
- good thermal insulator

AESTHETICS
- will not alter colour of tooth and prosthesis
- stability, no colour change with time

OTHERS
- low technique sensitivity
- cost
- shelf life

Question 4

what is GIC cement susceptible to

Answer 4

1) moisture contamination during setting: water absorbed during initial set will lead to early loss of cement forming cations

2) dessication
- stress concentration occurs as water drawn out of setting cement, leading to cohesive failure and microcrack formation
- need to maintain some level of dentine hydration during cementration procedures

Question 5

what cases are RMGIC contraindicated in

Answer 5

• posts in non vital teeth because there wil be expansion due to water sorption and may induce root fracture)
• all ceramic feldspathic type restorations bc rmgic have water sorption and expands and feldspathic ceramics are brittle, susceptible to cracks under pressure and also RMGIC is opaque and can interfere with natrual shade and traslucency of resto

Question 6

factors of consideration before choosing what type of cement

Answer 6

BIOLOGICAL
1) tooth vitality
- resin: excess mnomer may irritate pulp
- if zinc polycarb, large size of the molecules will cause minimal pulp irritation

2) marginal adaptation of prosthesis
- solubility of cement more crucial if margins are open
- RMGIC has low solubility so will have good marginal seal vs ZN phosphate has greater solubility

MECHANICAL
3) type of restoration
- ceramic veneer use resin cement

4) need for additional retention
- overtapered preps, short clinical crown height
- use resin for adhesive bonding

5) others
- poor moisture control
- eugenol in ZOE may inhibit resin polymerisation

AESTHETICS
- use resin for more translucent restoration

Question 7

what is the point of a silane coupling agent, when is it used

Answer 7

the molecules contain functional groups that bond with both organic and inorganic materials, and it improves chemical bonds with resin

• need to apply silane coupling agent to fitting surface of the EMAX after etching the surfac with HF acid

Question 8

why use alginate for impressions for dentures instead of APS, and why use APS for FP?

(answer not done)

Answer 8

• undercuts in teeth for RP, perio involved teeth -> APS is too rigid? (is this the MOE…)??

ALGINATE
- fast setting
- cost effective (inexpensive so good for large impressions for dentures)
- works well in moist oral environment
- cant be used for crowns because of low dimensional stability (shrinks and distorts if not poured immediately), and lower detail reproduction (dont capture fine margins as accurately as silicones)

APS
- limitation for denture because it is less flowable for full arch impression and hence not as ideal for capturing large soft tissue areas as effectively as alginate

Question 9

ideal properties of INTERIM luting agent

Answer 9

1) seal against leakage of oral fluid

2) strength consistent with intentional removal

3) low solubility

4) obtundent effect

5) chemical compatibility with interim restoration material

6) good handling properties

7) adequate working time, short setting time

8) excess easily removed