Dental Materials Science

Question 1

how does composite bond to tooth?

Answer 1

hybrid layer formed through DBA e.g. primer i.e. HEMA and resin i.e. bis-GMA. hydrophilic end of DBA bonds to wet dentine and fills dentinal tubules; hydrophobic end polymerises with bis-GMA resin. note that bond made is mechanical

Question 2

how does GI bond to tooth?

Answer 2

by hydrogen and mineral bonds with collagen. calcium in tooth being chelated by COO in polyacid. complex reprecipitation of CaPO4 from apatite and calcium salts from GI onto/into tooth surface

Question 3

how does amalgam bond to tooth

Answer 3

it doesn’t it is mechanically retained

Question 4

why does a bond fail and what can happen

Answer 4

normally fails due to microleakage; oral fluids/bacteria/sugar enter restoration margins causing secondary caries which untreated can lead to pulpitis and eventually a necrotic pulp that can become purulent and drain gingivally or extra orally. treatment = extraction / antibiotics

Question 5

amalgam composition + use

Answer 5

powder AgSnCu + Hg
liquid Hg
used for restoration of medium to large posterior cavities

Question 6

RMGI composition + use

Answer 6

powder: polyaluminosilicate glass + barium glass // vacuum dried polyacrylic acid
liquid: polyacrylic acid// tartaric acid // water // photo initiator

use: light curing material that acts as a base/liner for deep restorations

Question 7

composite - composition + use

Answer 7

1. filler particles - quartz/glass and silica for hybrid
2. resin - bis-GMA
3. photo initiator - camphorquinone
4. low weight dimethyacrylate - TEGDMA
5. coupling agent - silane

use - primary caries / abrasion / erosion / failed restorations i.e. secondary caries / trauma

Question 8

what is bis-GMA

Answer 8

bisphenol-A glycidyl methacrylate

is a difunctional molecule that allows for free radical addition polymerisation

Question 9

composite vs flowable composite

Answer 9

composite = filled bis GMA resin
flowable = unfilled bis GMA resin

Question 10

CaOH compostion + use

Answer 10

base - CaOH, zinc oxide filler, plasticiser
catalyst - butylene glycol disalicylate, zinc oxide filler

use - prevents gaps, acts as a protective barrier

Question 11

vitapex - composition + use

Answer 11

CaOH and iodoform

to fill root canals in paediatric pulpectomy

Question 12

hardness

Answer 12

a material’s ability to resist scratching or surface indentation

Question 13

compressive strength

Answer 13

ability to withstand direct pushing forces

Question 14

thermal expansion

Answer 14

expansion of a material due to increased molecular vibrations as they absorb heat

Question 15

creep

Answer 15

permanent deformation if a load is applied over a period of time even though the stress is below the elastic limit

Question 16

brittleness

Answer 16

high stresses to cause a small strain - material breaks with little permanent deformation occurring beforehand

Question 17

fracture

Answer 17

large force causes catastrophic destruction of material’s surface

Question 18

deformation

Answer 18

applied force may cause a permanent change in material’s dimensions but won’t fracture it

Question 19

why Cu enriched amalgam

Answer 19

higher earlier strength, less creep (so less ditching and marginal breakdown), higher corrosion resistance, increased durability of margins

Question 20

why spherical particles in amalgam

Answer 20

require less Hg, have higher tensile strength, higher early compressive strength and easier to carve

Question 21

tensile strength

Answer 21

resistance to breaking from a force acting to elongate

Question 22

gamma 2 phase

Answer 22

weakest, most electronegative, least corrosion resistant

Question 23

thermal expansion of amalgam

Answer 23

3x that of the tooth so may lead to microleakage

Question 24

factors impacting strength of amalgam

Answer 24

corrosion 
undermixing 
too high Hg content 
low condensation pressure 
slow rate of packing

Question 25

to reduce corrosion in amalgam

Answer 25

Cu enriched materials
polishing margins
avoiding galvanic cells

Question 26

liners protect pulp from

Answer 26

chemical stimuli - unreacted chemicals in / pH of filling material
thermal stimuli - exothermic setting of composite / heat conduction of amalgam
bacteria + endotoxins

Question 27

ease of use of cavity liners

Answer 27

should be command set
workable
easy to mix

Question 28

thermal properties of cavity liner

Answer 28

low thermal conductivity
same TEC as tooth
diffusivity should be similar to conductivity

Question 29

mechanical properties of cavity liner

Answer 29

high compressive strength, placement of filling without breakage, radiopaque, low solubility, marginal seal, cariostatic, biocompatibility

Question 30

ZOE zinc oxide eugenol

Answer 30

involves chelation of zinc oxide with eugenol to form a matrix bonding unreacted particles - inhibits set of comp resin so don’t use

Question 31

EBA - modified ZOE

Answer 31

modified ZOE with better compressive strength and lower solubility

Question 32

hybrid layer

Answer 32

exists between dentine and the restorative material. has several constituents i.e. primer/adhesive (HEMA + bis-GMA), exposed collagen fibrils, demineralised dentine, resin tags penetrating down dentinal tubules

Question 33

syneresis

Answer 33

loss of water

Question 34

imbibition

Answer 34

uptake of water

Question 35

what does pmma stand for

Answer 35

polymethylmethacrylate

Question 36

if too much monomer in pmma

Answer 36

contraction porosity

Question 37

if insufficient monomer in pmma

Answer 37

granularity

gaseous porosity which affects strength appearance roughens sensation to tongue and absorbs saliva

Question 38

self cure v heat cure acrylic

Answer 38

self - increased accuracy but decreased mechanical properties
heat - stronger due to higher weight monomers. more commonly used

Question 39

rmgi vs gic

Answer 39

rmgi has better physical properties // lower solubility // fluoride release // better translucency + aesthetics // better handling
gic has less polymerisation shrinkage

Question 40

rmgi dual curing

Answer 40

on mixing - dissolution
light activation causes free radical methacrylate reaction to occur = resin matrix formed
acid base reaction occurs for several hours after

Question 41

rmgi tri curing

Answer 41

on mixing - dissolution 
redox
light activation - resin matrix formed 
redox continues for 5 mins 
acid base occurs for several hours 
final hardening may take days

Question 42

3 phases of GIC setting reaction

Answer 42

dissolution
gelation
hardening

Question 42

3 phases of GIC setting reaction

Answer 42

dissolution
gelation
hardening

Question 43

properties of GIC

Answer 43

poor bond strength 
poor tensile strength 
lower compressive strength than composite 
higher solubility than composite 
usually seals well
fluoride release for short time

Question 44

mechanical properties of composite

Answer 44

smooth surface finish
technique sensitive
low setting shrinkage

Question 45

thermal properties of composite

Answer 45

TEC poor compared to amalgam + GI

under cold stimuli composite can shrink away from cavosurface margins

Question 46

requirements of DBA

Answer 46

flowability
intimate contact w dentine surface
adhesion to substrate
low viscosity