Study of the wear of dental composites using an atomic force microscope

Rochester Institute of Technology

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2-1-1997

Study of the wear of dental composites using an

atomic force microscope

Dale E. Ewbank

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COLLEGE OF SCIENCE

ROCHESTER INSTITUTE OF TECHNOLOGY

ROCHESTER, NEW YORK

CERTIFICATE OF APPROVAL

M.S. DEGREE THESIS

The M.S. Degree Thesis of Dale

E.

Ewbank

has been examined and approved by the

thesis committee as satisfactory for the

thesis requirement for the

Master of Science degree

Dr. M. Scanlon, Thesis Advisor

Dr. V. Gupta

Dr.

M..

Jackson

Date

THESIS RELEASE PERMISSION

ROCHESTER INSTITUTE OF TECHNOLOGY

COLLEGE OF SCIENCE

Title of Thesis: STUDY OF WEAR OF DENTAL COMPOSITES USING AN ATOMIC

FORCE MICROSCOPE

I. Dale E. Ewbank, hereby grant permission to the Wallace Memorial Library ofRochester

Institute of Technology to reproduce my thesis in whole or in part. Any reproduction will

not be for commercial use or profit.

Signature:

_

Date:

'2

-2

~-~)

STUDY OF

THE WEAR OF DENTAL COMPOSITES

USING

AN

ATOMIC FORCE

MICROSCOPE

by

Dale E. Ewbank

A

thesis

submitted

in

partial

fulfillment

of

the

requirements

for

the

degree

of

Master

of

Science

in

the

Center

for Materials Science

and

Engineering

in

the

College

of

Science

of

the

Rochester

Institute

of

Technology

STUDY OF

THE

WEAR OF DENTAL COMPOSITES

USING

AN

ATOMIC

FORCE MICROSCOPE

by

Dale E. Ewbank

ABSTRACT

This

workpresents a

study

of

the

wearof

four dental

composites

(Concept, XRV,

Maxxim,

and

Belleglass)

whichare

in

commercial use.

The

wear

testing

wasperformed

using

an

Atomic Force Microscope (AFM). Several scanning

techniques

and various

cantilevers were attempted.

Finally

useof a stainless steel cantilever with a

tungsten

bead

attached resulted

in

quantifiable wear.

AFM

imaging

in

contactmode was used

for

evaluationof

the

wear

tests.

Wear

rates arereportedas volume per

100,000

scans.

The

AFM

measured wearrates rank

the tested

composites

from

most

to

least

wear as

follows:

Concept

highest

volume of wear

XRV

Maxxim

BelleGlass

least

volume of wear.

Micro-hardness

measurements werealso conducted.

ACKNOWLEDGMENTS

I

wish

to

acknowledge

Brandon

Cornelia for his

help

in

sample preparations of

the

composites.

I

wish

to thank

Dr. Marietta Scanlon for her

guidance

through this thesis

process.

Thank

you

to

JeffElings

ofDigital

Instruments,

Inc.

for

the

SS

cantilever.

And I

wish

to thank

Kerr

Manufacturing Company,

and

Ivoclar

Williams for

donating

sample composite materials

for

this

research.

Thank

you

to the

National

Science

Foundation

Grant #

DUE-9451220

for

support

funds

TABLE

OF CONTENTS

Cover

page

i

Certificate

of

Approval

ii

Thesis Release

Permission

Form

iii

Abstract Page

iv

Acknowledgments

v

Table

of

Contents

vi

List

of

Figures

viii

List

of

Tables

be

Introduction

1

Dental Composites

3

Basic AFM Operation

7

Experimental

Approach

12

Results

15

I.

Microhardness Measurements

16

n.

125

urn

Silicon Cantilever

Spring

Constant

calibration and

Force

calculation

17

HI. Wear Tests

Evolution

19

A.

Wear

scans of

10

urn

by

10

um area

using

contact

imaging

mode with

tungsten

bead

attached

to

a

125

urn siliconcantilever.

19

B.

Wear

scansof

20

um

by

2

um rectangle outline

using

nanolithography

in

contact mode with

tungsten

bead

attached

to

a

125

um siliconcantilever.

22

C.

Wear

scans of

20

um

horizontal

and vertical

lines

using

nanolithography

in

contact mode with

tungsten

bead

attached

to

a

125

um silicon cantilever.

25

D.

Wear

scans of

20

um

horizontal

andvertical

lines

using

nanolithography

in

contact mode with a

AI2O3

particle

attached

to

a

125

um silicon cantilever.

26

E.

Wear

scan of

40

um vertical

lines

using nanolithography

in STM

mode with a

tungsten

wire

tip.

26

F.

Attempting

to

fabricate

tungstenwire

tip

for

contact

mode use.

29

IV.

Results

of

SS

Cantilever Wear Tests

30

Conclusions

and

Recommendations

40

Appendices

42

References

53

Other

Reference

Sources

55

LIST

OF

FIGURES

Figure

1. Typical

force

curve

for

125

(am silicon cantilever.

8

Figure

2.

Sample

data

used

for

Spring

constantcalculation.

17

Figure 1. Duplicated

18

Figure

3

.

Sample

wear

test

of

Concept

beginning

of scans.

20

Figure 4. Sample

wear

test

of

Concept

end of scans.

2 1

Figure 5.

Wear

test

on evaporated aluminum

using

nanolithography.

23

Figure 6. Enlargement

of wear area with scan

drifts

visible.

24

Figure 7.

Wear

test

of

XRV using

STM

tungsten tip.

28

Figure 8. Applied Force

and

Applied Pressure Approximation

for SS Cantilever

31

Figure

9. Wear

test

of

XRV

for

200,000

scans.

34

Figure 10. Section

Analysis

plot of

XRV.

35

Figure 11. Section Analysis

plot of

Concept.

36

Figure 12. Section

Analysis

plot of

Maxxim.

37

Figure

13. Section

Analysis

plot of

BelleGlass.

38

LIST OF

TABLES

Table 1.

Results

of

Knoop

Microhardness for

Dental Composites.

16

Table 2.

Sample

force

calculation.

18

Table 3.

Summary

of

Wear

of

Dental Composites

39

Introduction

An

ideal dental

restorativematerial would

have

physical properties similar

to

a natural

tooth.

The dental

restorativewould

be

compatiblewith

living

tissue,

and would

duplicate

the

esthetics of a

tooth.

Over

the

years, many

different

materials

have been

usedastooth

restoratives. 1

With

the

development

of composite materials

for

tooth

restoration

the

useof amalgam and

other metal alloys

for dental

repair

has

diminished.

The

various compositesystems

have

proved

to

have

superior esthetics and physical properties.

Improvements

in

composite

materialsare

continually

being

developed

and verified.

The

properties of composite materials are

usually

studied on

the

bulk

material.

Most

of

the

reported

property

data is

on

bulk

materials

in

standard mechanical

tests

with

specimens machined

to

ASTM

standards.

Preparation

of

these test

specimens

for dental

composites

is

quite

different in

volume of material needed ascompared

to

most

tooth

restorations.

It

will

be

useful

to

have

methods

for

evaluating

the

properties of

dental

composites

that

accommodate

test

pieces

that

are

the

same as

those

in

useas

dental

restoratives.

Currently

wear

is

tested

clinically

over a period of

five

years.

An

evaluationmethodof

dental

composite wear rates

that

can

be

run

in

a

day

(or

in

a

few

hours)

and

accurately

predicts clinicalwearrates would

be

a valuable research

tool.

Use

of

the

atomic

force

microscope

(AFM)

for

wear

testing

could

be

such a

tool.

The

purpose of

this thesis

is

to

develop

a

test

method

to

measure and compare wearof

test

piecesof

dimensions

used

for

actual

tooth

restorations and

it

can

be

used

to

do

repetitive operations.

The

use of

the

AFM for

testing

also allows

duplication

of

the

Dental

Composites

The

development

of compositematerials

for

tooth

restoration

has diminished

the

use of

amalgam and other metal alloys

for dental

repair.

The

variouscomposite systems

have

proved

to

have

superior esthetics and physical properties.

Improvements

in

composite materialsare

continually

being

developed

and verified.

The ideal

restorative material will

have

physicalpropertiessimilar

to

a natural

tooth,

will

be

compatible with

living

tissue,

will

duplicate

the

esthetics of a

tooth,

will

be

adhesive,

and will not cause cavities.

One

ofthe

first

anterior restoratives used was silicate cement

that

had

good esthetic

properties and contained

fluoride

to

inhibit

cavities.

But

it

was soluble

in

oral

fluids

and

became

porous.

The

next

type

of material

to

be

tried

for

anterior restorations was an

unfilledresin.

It

wasa

two

component system of powder and

liquid first

used

in

the

1940's.

Composite

resin was

developed

in

the

early

1960's.

The

composite resin materialconsisted of a

Bis-GMA

resin matrix and quartz or glass

filler

particles

that

constituted about

75%

by

weight.

Bis-GMA

is

a methacrylic monomer

based

on

bisphenol A. Acrylates

based

on

bisphenol

A

or

epoxy

resin can

be

polymerized

by

exposure

to

ultra

violet,

electron

beam,

or visible radiationand can also

be chemically

activated

by

the

use of various peroxides.

The filler

particles were

large,

approximately

15

um and

very

hard,

whichresulted

in

the

surface

being

less

smooth,

even afterpolishing.

The

surfaceroughness

lead

to

staining

and plaque retention.

Some

ofthesecomposite

resin materials werenotcolor stable.

In attempting

to

make

the

restorative materialsmore

polishable,

composite resins were

developed

with macrofilandmicrofil.

Particles

in

the

one

to

five

micronrange

(generally

compressivestrength.

The

microfil resins were

developed

to

provide even

better

surface

polish withparticlesof colloidal silica

that

are

0.04

um

in diameter. This

size allows

the

surface

to

be

very

smooth.

But

the

microfil cannot

be

highly loaded,

meaning

that the

filler

particles make

up

a

low

percentage oftheentire

material,

usually 50%

or

less.

The

microfil resins are

less

resistant

to

fracture

than the

macrofil resins.

Both

macrofiland

microfil resins contain

the

Bis-GMA

matrix or a modified urethane-Bis-GMA matrix.

The

newest composite materials are

the

hybrid

composites which contain a range of

different

size

inorganic

filler

particles.

The

microparticles

(0.04

um)

give

the

material

the

property

of

polishability

(although less

than that

ofthe

microfils)

and

the

macroparticles

(1

.0

to

15 um)

allow

the

material

to

be

heavily

loaded (80%

or so

by

weight)

and give

the

material strength and

fracture

resistance.

These

materials at present are

probably

the

best

all around restorative materials. 1

Abrasive

particles

in

the

food

are on

the

order of

0.5

um.

Microfil

composites

tend to

have filler

particles spaced closer

together than this

distance.

Hence

the

hard filler

particles protect

the

softer resin matrix

from

abrasive

food

particles.2

Fumed

silica with

dimensions

of

between

0.020

um and

0.05

um or radio-opaque glasses

withsizes

in

the

0.5

to

60

um range are used as

the

inorganic

filler

particles.

To

make

the

glass

x-ray opaque,

elements suchas

barium,

strontium,

and

lanthanum

are

incorporated in

the

network modifier position of

the

glass structure.

These

elements also

increase

the

refractive

index

of

the

glass.

surface and

less

than

50

um per year on

the

contact area of

the

chewing

surface over a periodof

5

years.3

The

oral environment

in

which

dental

composites must perform produces

biochemical

and

mechanical stresses.

The

chemical and

biological

conditions within

the

mouthaccelerate

the

hydrolytic

degradation

processes of

the

composite.

The

hydrolytic

natureandwater absorptionpropertiesof

the

composite can result

in

failure

of

the

bonds between

the

resin

and

the

matrix material.

The

main causes of

the

bond failures

are

the

silane

coupling

agent

degradation

and

the

filler

surface

dissolving

in

the

oral

environment,

especially if it has

become

acidic

due

to

diet

or

biological

activity.4

The

breakdown

of

bonds

reduces

the

mechanical strength of

the

composite and

thus

influences

wear.

Chewing

produces stresses

in

the

dental

composite.

These

stresses

vary

depending

on

diet

and on

the

position on

the tooth.

The

maximum stress

is

20 MPa

with an application of

this

stress

3000

times

a

day.

5

This

large

number of cyclic stresses would

indicate

that

fatigue

relatedmechanisms

may

be

a part of

the

wear process.

The

complexnature of

the

environment and of

the

mechanical stresses

in

the

mouth

have

made simulation

in

awearmachine

very

difficult.

6"10

The

results

from

these

machine

tests

have been

useful

but

they

do

notalways agree with clinical wear

test

findings.

However,

subsurface

damage

has

been

shown

to

exist

in both

clinical andmachineworn

composites.10'11

And

the

mechanical wearrate

for

acomposite restorative

(Adaptic)

was

found

to

increase

dramatically

aboveacritical value ofcontact stress

(1.3-1.4

kgf

mm"2).9

Wear

resistance

generally

increases,

as

does

hardness

andmoduluswithvolume

fraction

of

filler,

while

fracture

toughnessand strength

depend

onanumber of

factors

suchas

resin

interface. The

compositesurface's

frictional

properties

may

also

be

a major

factor

in

Basic

AFM

(atomic force

microscope)

Operation

The

key

element of

the

AFM is its

microscopic

force

sensor,

orcantilever.

The

cantilever

is formed

by

silicon or silicon nitride

beam

that

is

100

to

500

um

long

andabout

0.5

to

5

um

thick.

A

sharp

tip

mounted on

the

end of

the

cantilever

is

used

to

sensea

force

between

the

sample and

tip.

The

probe

tip

is

brought

into

continuous or

intermittent

contact with

the

sample andraster-scannedover

the

surface

for

topographic

imaging.12

The

Dimension 3000 SPM

(Digital

Instruments)

consists of a

rigid

stage mounted on a

granite

block,

and

features

a

beam deflection SPM head

and

integral

on-axis video

microscope.

The SPM

head

includes

piezoelectric scanners

for

translation

in

the x, y,

and z axes.

The

head

also provides optical correction of

the

laser beam

path

to track the

movement of

the

cantileverprobe while

it is

scannedunder

the

fixed laser

beam

assembly.

Etched

silicon cantilevers of

125

um

length

are

being

used.

The

cantilever

is held in

an

AFM

tip

holder

which

is

attached

to the

SPM

head.

Force

measurements with

the

AFM

aremade

by

measuring

the

deflection

of

the

free

end

of

the

cantilever as

the

fixed

end

is

extended and retracted

from

the

sample surface.

AFMs

measure cantilever

deflections

by

reflecting

a

laser beam

off

the

free

endof

the

cantilever.

Cantilever

deflections

cause

the

reflected

beam

to

change

its

angle.

The

position changes of

the

reflected

laser beam

are

detected

by

a multiplesegment photodiode

known

as a

Position

Sensitive

Detector

(PSD).12

The relationship

of

the

PSD

voltage

to

the

cantilever

deflection

distance

is

known

assensitivity.

The

sensitivity is

calibrated

by

using

a

force

curve.

The

force

curve

is

generated

by bringing

the

cantilever

Force Calibration Plot

Si Cantilever

(sensitivity

0.0142

V/nm)

30

-90

. /

tip

dejection

at zero*setpoint of

1.0

V

retracting

*(ki lift-off from

sample

50 100 150

Z(nm)

200 250

Figure 1. Typical

force

curve

for

125

urn silicon cantilever.

The

contact

force

on

the

sample can also

be

calculated

from

the

force

curve.

The

force

curve shows

the

relationship

between

the

setpoint voltage of

the

PSD

and

the

deflection

of

the

cantilever.

The

setpoint

defines

the

value of

the

deflection

signal maintained

by

the

feedback

loop,

thus the

force

curve can

be

used

to

calculate

the

z

deflection

(Az)

of

the

tip

while

in

contact with

the

sample surface.13

The

contact

force is

defined

by

the

equation:

F

=

kAz,

(1)

where

k

is

the

spring

constant of

the

cantileverand

Az is

the

z

distance from

the

setpoint

to the

lift-off

point

(minimum

cantilever

tip

position

during

retracting)

as

in Figure 1.

The spring

constant of

AFM

cantilevers

is

a

function

of

the

elasticmodulusof

the

cantilever material and of

the

geometric

form

of

the

cantilever.

Cantilevers

are available

cantilever

to

cantilever.

Several

techniques

for

determining

the

spring

constant of cantilevers

have

been

developed.

14"19

Hutter

andBechhoefer16

have

shown

that the

area of

the

power spectrum ofthermal

fluctuations,

P,

is

related

to the

spring constant,

k,

by

the

following:

k=

kBT/P,

(2)

where

kfi

is

Boltzmann's

constant and

T

is

temperature

Kelvin. This

method

is

only

useful

for

cantilevers with resonant

frequencies

in

the

low 10's

of

kHz,

otherwise

the

effects of noise are greater

than the

power spectrum.

The

force

can

be

measured

directly

using

acapacitive

force

sensor,

17 a precision

low

force

balance18

or another

cantilever19

placed

in

the

sample position of

the

AFM.

These first

two

methods require measurement

instruments

designed for

the

range of

forces

of

interest.

Methods

for determination

of

the

spring

constant

from

physical properties of

the

cantilever

have been documented.

Sader

et

al15

has

shown

that the

spring

constant

is:

k=Mem2,

(3)

where

Me

is

the

normalizing

factor

(a

length

scale

invariant

quantity

of

the

cantilever),

and m and are

the

mass and resonant

(angular)

frequency

of

the

cantilever.

Cleveland

et

al14

states

that the

spring

constant of an end-loaded cantilever with rectangularcross section

is

given

by:

k=Et3w/413,

(4)

where

E

is

the

elastic

modulus,

t

is

the

thickness,

w

is

the

widthand

1

is

the

length.

Measurement

of

the

physical

linear

dimensions is

difficult due

to

the

smallscale and

the

continuousvariations

in

the

surfaceof

the

cantilever material.

Also,

values used

for

material properties such as

density

and elastic modulus

may

not

be

accurate

due

to

methods of

fabrication

of

the

cantilever.

Cleveland

et al14

has

also presented a method of

adding

a

known

mass

to the

endof

the

cantilever and

using

the

original and mass-added resonance

frequencies

to

arriveat

the

spring

constant.

The

resonant

frequency

withend

mass,

Mi,

added

is

defined

by:

ui

=

(2 ti)

_1

[

k /

(Mi+Mem)]

m,

(5)

where

Mem

is

the

normalized effective mass of

the

cantilever and

k is

the

spring

constant.

Rearrangement

of

the

equation

5

gives:

Mi=k(2 7tui)"2-Mem,

(6)

in

which

the

added

mass,

Mi,

is

a

linear function

of

inverse

angular

frequency

squared

(l/oa

);

the

slope of

the

line

being

the

spring

constant and

the

intercept

is

negative

the

normalized effective mass.

Using

this

relationship

various

known

masses can

be

added

to the

cantilever and

the

corresponding

resonant

frequencies

can

be

plotted

to

determine

a value

for

the

spring

constant.

The inaccuracies

of

this

method are

then the

calculation of

the

addedmass and

the

error

in

frequency

if

the

mass

is

notpositioned on

the

end of

the

cantilever.

Measurement

of

the

unloaded resonant

frequency

uo

(when

Mi

=

0)

and

the

resonant

frequency

with an added masswillyield

two

simultaneousequationsofequation

6

which

can

then

be

solved

for

the

spring

constant and

the

effective mass.

The spring

constant

is:

k=

(2

7t)2Mi/[(uf2)-(u0-2)],

(7)

and

the

effective mass

is:

Mem

=

Mi

uiz

/

(u0z

-uiz).

(8)

Experimental

Approach

The

surface properties evaluated were microhardness and wear resistance.

Knoop

microhardnessmeasurements were made

using

a

Tukon Microhardness Tester.

The

hardness

indents

wereanalyzed

using

the

filar

microscope on

the equipment,

following

the

ASTM E

384-89,

Standard Test

Method

for

Microhardness

of

Materials.

20

The

tests

for

wearresistance were performed

using

the

AFM. The

following

is

a

summary

of

the

methods attempted:

A.

Wear

scans of

10

um

by

10

um area

using

contact

imaging

mode withtungsten

bead

attached

to

a

125

umsilicon cantilever.

B. Wear

scansof

20

um

by

2

um rectangle outline

using nanolithography

in

contact mode

with

tungsten

bead

attached

to

a

125

um silicon cantilever.

C.

Wear

scans of

20

um

horizontal

andvertical

lines

using

nanolithography in

contact

mode withtungsten

bead

attached

to

a

125

um silicon cantilever.

D.

Wear

scans of

20

um

horizontal

andvertical

lines

using

nanolithography

in

contact

mode with a

A1203

particle attached

to

a

125

um siliconcantilever.

E.

Wear

scan of

40

umvertical

lines

using nanolithography

in STM

mode with a

tungstenwire

tip.

F.

Attempting

to

fabricate

tungstenwire

tip

for

contactmode use.

G.

Wear

scans of

20

um

horizontal

and vertical

lines

using

nanolithography in

contact

mode with

tungsten

bead

attached

to

a stainless steelcantilever.

Further

details

of

the

wear scanconditions

for

the

above are given

in

the

results sections

of

the

paper.

Modifications

of

the

procedure

for

wear

testing

evolved

due

to the

results

obtained with each

type

of

test.

The AFM

was used

in

contact mode

to

apply

a

known

force

and

to

scan

the

surface of

the

samples.

A

bead

of

5

to

40

um

diameter

wasattached

to the

end of a silicon cantilever.

The

displacement

along

the

z-axis of

the

cantilever and

its

spring

constantwere used

to

calculate

the

force

applied.

Spherical

tungstenpowder

(see Appendix

A)

was used

for

the

125

um cantilever

spring

constant calibration.

A

bead

of

this

powder was epoxied

to the

cantilever

tip

for

use

in

wear

testing.

The

spring

constant was calculated

from

the

change

in

resonant

frequency

for

the

oscillating

cantilever withadded mass

(Equation 7). Then

the

applied

force

wascalculated

utilizing

the

force

curve

(Equation 1). The

applied

force

wascontrolled

by

adjustment of

the

voltage setpoint

for

cantilevers of various

spring

constants.

The AFM

was used

in

tapping

or contactmode

to

image

the

wear area of

the

sample after

the tests

were run.

Then

the

volume of materialwornor

displaced

wascalculated

from

these

images.

The

materials

tested

were:

a microfilcomposite-

Concept

(see

Appendix

B);

a

hybrid

composite

XRV Herculite

(see

Appendix

C);

a micro-hybridcomposite-

Maxxim;

(see Appendix

D)

and a

hybrid

composite-

BelleGlass.

(see

Appendix

E)

All dental

composite samples were prepared per

their

manufacturer'sspecifications.

Results

The

results

have been

broken

down into

four

sections:

I.

Microhardness Measurements

n.

125

um

Silicon Cantilever

Spring

Constant

calibrationand

Force

calculation

DI. Wear Tests

Evolution

IV.

Results

of

SS Cantilever

Wear

tests

I.

Microhardness Measurements

Table

1

shows

the

results

from

the

microhardness measurements made on

the

Tukon

Microhardness Tester.

The

valuesmeasured

for

the

compositematerials are similar

to the

reported

values.22

Variations

of

the

microhardnessvalues

from

the

reported values

may

be due

to

sample preparations and/or

differences

between

Knoop

and

Rockwell

measurement

techniques.

sample

Knoop

Microhardness

(400

gram

load)

KHN

kg/mm

,22

reported

Rockwell

15

T Hardness

XRV

82.3

Concept

75.1

Maxxim

72.4

BelleGlass

82.3

84.0-87.1

76.0

-

78.0

83.0

-

84.0

87.0

-

88.0

Table 1.

Results

of

Knoop

Microhardness for

Dental

Composites.

H. 125

um

Silicon

Cantilever

Spring

Constant

calibrationand

Force

calculation

Figure 2

shows a

typical

plotofmass added

to

a

125

um silicon cantilever versus

the

inverse

angular

frequency

squared

(Equation

7.)

The

circled

data

point

is

the

tungsten

bead

epoxied

to the

cantilever

tip.

The

slope of a

line determined

by

least

squares

fit

of

the

five data

points gives

the

value of

the

spring

constant.

Mass

versus

Inverse Angular

Frequency

Squared for

a

Si Cantilever

250

200

150

M in

100

50

12 3 4

Inverse Angular

Frequency

Squared

X10M2

(sA2)

n =

5

slope =

57

kg/s2

(N/m)

intercept

=

-32ng

corr =

.989

Figure

2. Sample data

used

for

Spring

constantcalculation.

The

calculation of

force (Equation

1)

applied

by

the

cantilever

tip

is

shown

in

Table

2

with

the

value of

Az

being

determined

(Figure

1

duplicated

here) by

the

z

distance

on

the

graph

to

its

setpoint plus

the

z value adjusted

for

the

actual setpoint

(2.5

V)

used.

The

adjustment must

be

made

because

when

the

actual setpoint

(if larger

than

-1.5

V)

is

used

to

capture a

force

calibration plot

the

lift-off

pointof

the

curve

is

not

included

in

the

collected graph

data.

The force

is

equal

to the total

deflection

times the

spring

constant.

Force Calibration Plot

Si Cantilever

(sensitivity

0.0142

V/nm)

30 E c o

i

-30 Q -60 -90

^

tip

dejection

at zero~_{setpoint of}

1.0

V

v^F-retracting

extendingI^

*4~

lift-off

from

sample

50 100 150

Z(nm)

200

Figure

1 Typical

force

curve

for

125

mm silicon cantilever.

250

zgraph

zadj.

1.5

V/ 0.0142

V/nm

Az

k

F

=

84.5

nm

from

setpoint

to

lift-off

=

105.6

_nm

Voltage

_offset

=

190.1

_nm

Total

deflection

=

57

N/m

Spring

Constant

=

10836

_nN

Force

Table

2. Sample

force

calculation.

m. Wear Tests Evolution

in. A. Wear

scans of

10

um

by

10

um area

using

contact

imaging

mode withtungsten

bead

attached

to

a

125

um silicon cantilever.

Several

wear

test

scans were made on

the

Concept

and

XRV dental

composites.

The

initial

wear

test

of

approximately 6900

area scans

(10

um

by

10

um scans with

128

samples per

line

at

10.2 Hz

sampling

rate run

in

imaging

mode

for

24

hours)

at

approximately

4000

nN

force

show a change

in

surface

texture.

Figure

3

is

a surface plot

imaged in

contact mode at

the

beginning

of scans and

Figure

4

is

a plot at

the

end of

scans.

The

surface roughness

has

changed

but it is

not possible

to

measure

any

volume

change

in

the

weararea.

It

is

also

extremely

difficult

to

detect

optically

(using

metallurgical

microscope)

the

wearregion.

From

contact

images

captured at various

intervals

during

the

wear

testing

it is

also evident

that the

scanarea"drifts"with

time.

This may

be due

to

thermalchanges or

to the

piezoelectric crystals.21

In attempting

to

produce more and measurablewearchanges

to

the

scanning

technique

and

the

applied

force

on

the

surface were made.

By

using

the

nanolithography

(nanoscript)

software on

the

system

it

waspossible

to

program

the

AFM

operation.

A

subroutine or script

file

(Appendix G

and

Appendix

H)

waswritten

to

control

the

setpoint

voltage

(z

translation)

and

the

x

-y

movements of

the

cantilever

tip.

10.0

concept

E 2.0

<0l:53:02

PH Hon

Apr 29

1996>

04291353.001

Figure 3

.

Sample

wear

test

of

Concept

beginning

ofscans.

L10.0

Figure 4. Sample

wear

test

of

Concept

end of scans.

HI. B.

Wear

scans of

20

um

by

2

um rectangle outline

using nanolithography

in

contact

mode with

tungsten

bead

attached

to

a

125

um silicon cantilever.

Using

a

nanolithography

file

the

voltage setpoint

during

scans was

increased

to

double

the

force

applied.

The

technique

for

scanning

wasalso

been

changed.

Using

the

nanolithography

software on

the

AFM;

programmedscans of

25

um

length

and

2

um

offset were repeated

10000

times.

Figure 5

is

a

tapping

mode scan ofawear

test

done

on

evaporated aluminum on a glass slide.

The

aluminum was chosen asa

test

surface

for

wear

testing

due

to

its

relative softness

compared

to tungsten

and

its

smooth surface.

These

characteristic would

hopefully

permit

visibleand

possibly

measurablewearof

the

aluminum surface.

The dark

grooves

in

Figure

5

are

the

cantilever/bead path

during

the

scans.

The

light

area around

the

path

is displaced

aluminum.

Figure

6

shows an enlarged view of part of

the

wear

test

area.

As

can

be

seen

the

cantilever/bead scan

did

not

track the

same path on

every

scan.

This

makes

it impossible

to

know

the

actualnumber ofscans

for

calculating

awearrate.

Thus

changes

to the

scan

techniquewere needed.

The

visible wear

in

the

evaporated aluminum proved

that the

applied

force

of

the

bead

on

the

test

surface was

causing

wearand change

in

the

surface.

However,

it

was stillnot

known

what amount of

force

was needed

to

producewearon

the

composite materials.

20.0

-10.0

10.0

20.0

JJM

Al

wrlOOOO

<02:12:00 PM Hon

Hay

06

1996>

05061412.001

Figure

5.

Wear

test

on evaporated aluminum

using

nanolithography.

10.0

Al

wrlOOOO

<

02:

32:

46

PH

Hon

Hay

06

1996>

05061432.001

Figure 6. Enlargement

of wear area with scan

drifts

visible.

ID. C.

Wear

scans of

20

um

horizontal

and vertical

lines

using nanolithography

in

contact

mode with

tungsten

bead

attached

to

a

125

um siliconcantilever.

After

discussions

with

Digital

Instruments

the

nanolithography

schemewas changed

to

keep

the

wearscans centered around

the

origin of

the

piezoelectric crystals.

A

sample

nanoscript

file for 20

um

horizontal

and vertical wear scans

is

attached

in

Appendix

G

Wear

tests

were run with

up

to

2

million scans

in

contact mode at a setpoint of

7.0

volts

on

XRV

and

Concept

materials.

Using

the

125

um silicon cantilever

(k~57

N/m)

the

force

during

the

wear

tests

was

approximately 30,000

nN.

The scanning

rate of

the

bead

tip

was

500

urn/second.

The

length

of

scanning

time

for

the

nanoscript

files

was~16.2

hours

per

1

million scans.

The

wear

from

these tests

wasnot measurable

from

the

images

made

using

the

AFM

in

contact or

tapping

modes.

The

wear was

only

barely

distinguishable

from

the

non-wear

areas

using

a metallurgical microscope.

The force

applied

by

the

125

pm silicon cantilever at a setpoint of

7.0

volts was not

high

enough

to

produce measurable wear on

the

dental

composites.

Using

a rougher wear

materialon

the

tip

than

the tungsten

bead

would

be

tried.

HI.

D. Wear

scans of

20

um

horizontal

and vertical

lines

using nanolithography

in

contact

mode witha

AI2O3

particle attached

to

a

125

um silicon cantilever.

Tests

werealso attempted with an alumina

(AI2O3)

particle attached

to the cantilever;

in

hope

that the

rougher alumina particle might

increase

the

wear.

These

tests

were run at

conditionsas stated

in

section

HI.

C.

and

did

not give

any

measurablewearresults.

The

alumina particles

did

not

bond

well with

the

epoxy

to the

cantilever

tips,

and several of

them

came off

the

tip

during

wearscanning.

Methods

of

applying

more

force

wereneeded

to

achieve some measurable wear.

m. E.

Wear

scan of

40

um vertical

lines

using

nanolithography

in STM

mode with a

tungsten

wire

tip.

In

an attempt

to

apply

higher

forces

on

the

sample surface with

the

tip

analternative

AFM

mode was employed.

Tungsten

wireof

0.009

inch diameter

waspurchased

for

useas

tip

material

in

the

AFM in STM

(scanning

tunnel

microscopy)

mode.

The

wire as a

tip

in

STM

imaging

is

oriented such

that

it

engages

the

surface

nearly

perpendicular

to

it.

This

angle of engagement

thus

results

in

the

applied

force

being

from

the

piezoelectric crystal

movement

in

the

z

direction

rather

than

from

the

cantileverproperties of

the tip.

In STM

imaging

the

tunneling

current

between

the

AFM

tip

and

the

samplewas measured

and converted

to

height data. The

composite samples were

flashed

with gold

(-50

angstroms)

so

that their

surface could

be

electrically

grounded

to

the

stagesurface

(which

is

voltage

biased

to the

STM

tip).

Appendix H

showsa samplenanoscript

file

for

use

in STM

mode wear

testing.

The

sample surface must

be

plane captured

by

the

software

before

the

nanoscript

file

can

be

executed.

The

tunneling

feedback

loop

is

turned

off when

the

tip

is

translated

in

the

z

direction;

the

planecapture

is

used

(because

the

feedback

loop

is

off)

to

known

where

the

sample surface

is

relative

to the

STM

wire

tip.

Figure

7

shows a section analysis of a series of wear scans

in XRV. The

z

direction

offset

was

0.5

um

into

the

sample surface

for

each of

the

scan sets.

The

wearscansare

40

um

in

length,

and

the

number of scans

increases

by

ten

form left

to

right. As

can

be

seen

in

the

section analysis

the

increase in

number of scans

(10,

20, 30, 40,

50,

and

60)

corresponds

to

an

increase in

the

wear

depth.

This

method of wear

testing

was

dependent

on

the

z

translation

of

the

tungsten

tip

to

apply

the

force

on

the

sample surface.

There

is

no measured

feedback

loop

in

this type

of

scanning

and no method

for

calculation of

the

applied

force. Upon further

wear

testing

it

was

determined

that the

z

translation

by

the

piezoelectric crystals was not repeatable.

Tests

run with

100

to

10,000

scans showed variations

in

wear

depth

(hundreds

of

nanometers)

for

the

same number ofscans and some

tests

produced wear

depths

greater

than

the

0.5

umoffset of

the

z

translation.

While

these test

results were not usable

for

measurement of wear

results,

they

did indicate

that the

dental

composite materials could

be

worn

using

the

AFM. The

force

applied

by

the

STM

tungsten

tip

wasnot

known but

was

higher

than the

force

appliedwith

the

125

um silicon cantilever

tips.

A

cantilever witha

higher

spring

constant

than

the

125

um silicon cantilevers was needed.

100

-400

STM Wear Section Analysis

Xposition

(um)

100

100

JJM

Figure 7.

Wear

test

of

XRV

using

STM

tungsten tip.

m.

F.

Attempting

to

fabricate

tungsten

wire

tip

for

contact modeuse.

Making

a

tungsten

wire

tip

that

would

be

used

in

contact mode so

that

laser

feedback

could

be

used

to

control

the

applied

force

wasattempted.

The

tungsten

wire was polished

on

fine

sand paper and

then

on a

polishing

wheel with

0.5

um alumina powder.

The

wire

was

then

super-glued

to

a silicon cantilever

base.

The

alignment of

the

polished surface

withrespect

to the

base

was

difficult. This

tip

alignment

is

critical

for

the

tip

to

reflect

the

laser into

the

detector

system.

One

tip

was

fabricated

that

could

be

aligned,

however

the

polished surface was not

flat

enough

to

give repeatable alignment and

thus

force

offsets.

Therefore

it

was

determined

that this

method wasnot usable.

TV.

Results

of

SS Cantilever

Wear

tests

Wear

scans of

20

um

horizontal

and vertical

lines

using nanolithography

in

contact mode

with

tungsten

bead

attached

to

a stainless steel cantilever produced wear results which

weremeasurable.

A

stainlesssteel

(SS)

cantilever with a

tungsten

bead

attached was obtained

from

Digital

Instruments.

The

spring

constant of

this

SS

cantilever

(see

Appendix

F)

was

determined

by

Jeff

Elings

at

Digital

Instruments,

Inc.

The

tungsten

bead

attached

to this

cantilever

is

approximately

10

um

in diameter.

The

spring

constant of

the

SS

cantilever was

305 N/m. This

cantilever allowed wear

testing

withabout

ten times the

applied

force

(see Figure

8)

of

that

of

the

125

um silicon

cantilever.

Force Calibration Plot

SS

cantilever

(sensitivity

0.00541

V/nm)

tip

deflection

at zero- _{setpoint of}

0,5 V

<4-retracting

50 100 150

Z(nm)

200 250

lift-off from

sample

z graph =

1 13

_nm

from

_setpoint

to

lift-off

zadj.

4.5

V/ 0.00541 V/nm

=832nm

Voltage

offset

Az

=

945

nm

Total

deflection

=

kAz

=

305 N/m

=

288000

_nN

Spring

Constant

Force

For

the

above

force

witha projected contact area of a circle with

1

um

diameter:

contact area=_7t

(500

nm)2 =

7.85

x 105

nm2,

Then

the

applied pressure would

be:

5 2.

Pressure

=

F

/

_area=_-288,000nN

/

7.85

_x

103 nnT=

-367

MPa.

Figure 8. Applied Force

and

Applied Pressure Approximation

for SS

Cantilever

The

wear

tests

wererun

using

the

SS

cantilever with a voltage setpoint of

5

volts.

This

resulted

in

the

applied

force

being

-288,000nN.

If

this

force is

projected on a surface

contact area of

1

um

in

diameter

then the

resulting

pressure

is

-367

MPa. This

is

greater

than

fifteen

times the

maximum

stress5

expected

from

chewing.

However

the

pressure

applied

is

inversely

proportional

to the

square of

the

radius and

thus

falls

to

-92

MPa

for

a

contact area of

2

um

in diameter.

The

actualcontact area

is

not

known.

Thus,

further

studies

into

measurement of

the

contact area would

be helpful in

understanding

the

wear rates.

The

composite materials were worn

by

scanning

the

bead

20

um

for

200,000

times.

The

wear

test

for

the

BelleGlass

material was

done

at

400,000

scans as

there

wasnot

any

measurablewearat

200,000

scans.

Scans

were

done in

the

horizontal

andvertical

directions.

Figure 9

shows

the

verticalweararea of

XRV

imaged in

contact mode.

To

analyze

the

weareach composite was

imaged (10

um x

10 um)

in

contact mode

using

a standard silicon cantilever.

Section

Analysis

was used

to

evaluate

the

wear volume of

the tests.

Within

Section Analysis

the

average cursorroutine was used

to

generate aplotof an

average

line

scan

for

each wear

test

as shown

in Figures

10

though

13. The

zero

line

of

the

graphwas

taken

as

the

meansurface

level

of

the test

sample.

The

area under

the

zero

line in

the

wear

test

thus

represents

the

volume of materialremoved

during

the

scans.

The

area

between

the

curve and zero

line

was measured

using

a

Planimeter

calibrated

to

the

area

relationship

of

the

Section

Analysis

plot.

The

area was alsocalculated

from

the

plot

data

using

numerical methods.

The

Planimeter

and numerical method gave equivalent

values

for

the

area.

This

measuredareawas

then

normalized

by

multiplying

by

a constant width

(1.0

nm)

resulting in

a volume.

This

volume per number of wear scans represents

the

wearrate of

the

composite material.

Review

of

the

wear

for

the

BelleGlass

(Figure

12)

with

400,000

scans shows

that

it

is

not

possible

to

calculate a volume of wear.

It

is

assumed

that

BelleGlass'wearrate

is

less

than

the

wearrate of

the

other composites evaluated and

is

notappreciable.

Examination

of

the

wear

track

in

the

XRV

(Figure

9)

shows

lines

parallel

to the

scan

direction.

Whether

these

are a result of"drift"or

just

a product of

the

wear

is

not

known.

X

5.000

jjM/div

2

500.000

nn/div

XRU 200k

scans

vertical

01141042.001

Figure 9. Wear

test

of

XRV for

200,000

scans.

XRV Section Analysis

250

150--250

twear

track

15000

Xposition

(nm)

!2CKi00

0

10.0

Figure 10. Section Analysis

plot of

XRV.

20.0

-10.0

N

300n

200

100

0

-100

!

-200-

-300-Concept Section Analysis

wear

track^

/

-w

oo

SOOD

\10000

/

15000 ;20l

Xposition

(nm)

20.0

10.0

0

10.0

Figure 1 1

.

Section Analysis

plot of

Concept.

20.0

250 200 150

|

100

+

= ₅₀ &

N -50₍

|

-100

1

-150 -200

+:

-250

Maxxim Section Analysis

Xposition

(nm)

20<IO0

m mmmmmm

20.0

10.0

0

10.0

Figure 12. Section Analysis

plot ofMaxxim.

250 200

|

150

100

= 501

N -50

^

-100

-150

-200

-250

BelleGlass Section Analysis

i

wear

track

5000 10000 15000

Xposition

(nm)

20)00

20.0

0

10.0

Figure 13. Section Analysis

plot of

BelleGlass.

10.0

Table

3

is

a

Summary

of

Wear

for

the

dental

composites

tested.

Also included in

the table

are

the

composite

filler

size,

filler

weight percent and

the

reported clinical

wear.22,23

SUMMARY

OF WEAR

Composite

Wear

Peak to

Reported

Average

Filler

(x105nm3

Peak Width

WEAR

Filler

size

Weight

%

/100k scans)

(nm)

(tim/5yr)

(^m

)

CONCEPT

3.5

XRV

1.0

MAXXIM

0.1

BELLEGLASS

<

0.1

6.5

4.1

3.8

3.1

25.3

45

45

6.3

0.04

0.6

0.8

0.6

70

78

75

76

Reported

wear

from

references

22

and

23.

Table 3.

Summary

of

Wear

of

Dental

Composites

Evaluation

of

the

peak

to

peak widthof

the

weararea on each of

the

Section Analysis

plots shows

that the

width

increases

with

the

wearrate.

Peak

to

peak widths

in

microns

for

the

compositesare as

follows:

Concept

6.5

XRV

4.1

Maxxim

3.8

BelleGlass

3.1

This

suggests

that the

wear

track

is

mostly

influenced

by

wearand not

by

"drift" of

the

stage and/or sample or

by

"drift"

of

the

piezoelectriccrystals.

Further

studiesof

the

wear

track

widthmight also give

rise

to

better

understanding

of

the

contact area

during

the

wear

testing

scans.

The

contact area

probably

increases

as

the

surface materials are worn.

Conclusions

and

Recommendations

The

AFM

was used

to

run wear

tests

on

dental

composite materials and results were

obtained which givewearrates.

These

wearrates are summarized

in

Table 3. The AFM

measuredwearrates rank

the tested

composites

from

most

to

least

wearas

follows:

Concept

highest

volumeof wear

XRV

Maxxim

BelleGlass

least

volumeof wear.

The

measuredwearrates

do

not correspond

to

any

single

factor

of

the

dental

composite

materials.

Higher

microhardnesscomposites

tend to

show

less

wear

but

the

frictional

properties of

the

surface

(not

studied

here)

may be

of greater significance.

Larger

particle

sizeand

higher

filler

percent also

tend to

show

less

wear.

Further

evaluation of

the

wear

testing

and

the

mechanisms ofcomposite wear are needed.

Such

studies

may

lead

to

evidence of

the

interaction

of

factors

which

determine

wearresistance.

The

use of

the

AFM

for

wear

testing

is dependent

onthecantilever

type

(spring

constant)

which

limits

the

amount of

force

that

can

be

applied

to the

test

surface.

Wear

of

the

dental

composite materials was not measurable with~30,000nN of

force for

up

to

2

million

scans,

but

was quantifiable with-288,000nN of

force

for

200,000

scans.

This

supports

Bailey

and

Rice's9

findings

of a

increase in

wearrate above a criticalvalueof

stress.

Further

studies with a series of

tests

withvaried applied

forces

would

be beneficial

to

evaluate

this

critical value of stress

for

eachcomposite.

Also

further

studieswould

confirm

the

use of

the

AFM

obtainedwear rates as a valid

forecaster

of

the

clinicalwear

rates

for dental

compositematerials.

Improvements in

environmental controls and/or method of

AFM scanning

may

help

to

minimize"drift"

during

the

wearscans.

Values

of"drift"were not quantified

in

this

work.

Several

methods of

determining

the

spring

constant

have been

attempted.

Calculation

of

the

spring

constant

from

the

change

in

resonant

frequency

for

the

oscillating

cantilever

withadded mass appears

to

be

the

most reliable.

Calculation

of

the

spring

constant

from

physical

dimensions

of

the

cantilever are

very

difficult.

Measurement

errors

for linear

dimensions

are compounded with

difficulty

in

determining

edges of

the

crystaland

in

the

variations of crystaledges over

its

entire surface.

Also

the

density

or elastic modulus must

be

estimated

for

the

silicon crystal.

SYLVANIA

Chemicals/Metals

4 i

j

^

Hawes Street

Appendix

A

ini3

Towanda,

PA 18848

717 265-2121 TWX

510

671-4561

ENGINEERING

SAMPLE

University

of

California

DATE:

_10/25/91

Department

of

Physics

SALES

ORDER NUMBER: T-03097

CUSTOMER

P.O.

NO. : NEK

ITEM NUMBER: 1

LOT NUMBER:

33769-34A

QUANTITY:

0.05

ko

.

Santa

Barbara.

CA

93106

Attn: Srin Manne

DESCRIPTION:

Spherical

Tungsten Powder

20

Micron

MATERIAL: Tungsten

FORM:

Sgheroidized

SIZE:

20

micron

ENGINEERING

DATA

CHEMICAL

ANALYSIS

Carbon 10 ppm

Oxygen

160 ppm

Nitrogen 10 ppm

Al

1.0 ppm

Cu

1.0

ppm Mn 1.0 ppm

Sn

1.0 ppm

Ca

1.0 ppm

Fe

7.0

ppm

Ni

1.0 ppm Mo 16.0 ppm

Cr

3.0

ppm

Mg

1.0 ppm

Si

1.0 ppm

PARTICLE

SIZE

DISTRIBUTION

By

Screen Analysis

By

Microtrac

-325 - _100.07.

<31.0

_micron

84.2'/.

<22.0 micron 62.27.

<

5.5

micron

1.37.

MEAN

20.72

Microns

MEDIAN

IB. 60

Microns

Bulk

Density

10.66 g/cc

SIGNED:

Nelson

E.

Kopatz

Appendix B

Concept

-

indirect

_{posterior restorative}

Ivoclar

Williams

175 Pineview

Drive

Amherst,

NY 14228

composition

Weight

%

urethane

dimethacrylate

and

aliphatic

dimethacrylate

21.7-24.9

high dispersed fumed

silica,

silanated

52.3

-57.7

filler

radiopaque

20.5

-

22.5

stabilizers,

initiators,

and pigments

0. 19

-

0.21

Mechanical

properties

(N/mmA2)

Flexural

strength

120

Flexural

modulus

8700

Compressive

strength

540

Vickers Hardness

HV

0.5/30

750

Ball indentation H 36. 5/30

520

Weight % filler

of

70

-

71.2

_and

filler

_{size of}

0.04

_um

Reported

wearof

25.3

um per

5

years.

Cure

Method:

Cure in

Ivomat

(6

atmospheres pressure

in

250

degree

F

water)

for

10

minutes.

Appendix

C

XRV Herculite

micro-hybrid composite

Kerr

Manufacturing

Company

Subsidiary

of

Sybron Corporation

28200 Wick Road/Box 455

Romulus,

MI 48174

Mechanical

properties

(N/mmA2)

Flexural

strength

111

Flexural

modulus

12414

Compressive

strength

448

Weight % filler

of

78

and

filler

size average of

0.6

um

Reported

wearof

9

um per year.

Cure

method:

Forty

second exposure with

UV

light

cure unit and

10

minute

boil

in

water.

Appendix D

Maxxim

-

Micro-hybrid Indirect Composite

Ceramco

Inc.

Six

Terri

Lane

Burlington,

NJ

08016

800-487-0100

average particle size of

0.8

um

Filler Load

(by

weight):

76.5%

Wear

rate of

9

um per year.

Visible

light

cure.

Appendix

BelleGlass

-

hybrid

composite

belle de

st. claire

Subsidiary

of

Sybron

Dental

Specialties,

Inc.

1717

West

Collins Ave.

Orange,

CA

92867

800-322-6666

average particle size of

0.6

um with range of

0-1.2

um

Filled 74 %

by

weight.

Blend

of urethane

dimethacrylate

and aliphatic

dimethacrylate

resins.

6.3

um

total

wearafter

5

years.

(1.2

um annual

wear)

Heat/pressure

cured

by

high

temperature

initiator

@

135

degrees C

and

80

psi

Nitrogen

pressure.

Appendix F

Stainless

Steel Cantilever

with

Tungsten

Sphere

attached

Force

vs.

Deflection

sphere

8.0E-04

6.0E-O4-Forcel

(N)

4.0E-O4

2.0E-O4-

0.0E+O0-?

c

o

Foreel(N)

Force3 (N)

Force4(N)

y=_3l0.809x+0.001 r1

=0.999

y=306.275x+0.001

^

=0.999

y=296.470x+0.001 i2

=₁.000

Kavg

= ₃₀₅

N/m

Sensitivity

= .00326

V/nm

(Contact)

Sensitivity

= .013692

V/nm

(Tapping/Indentation

Mode)

-2.0E-O6 -1.5E-06 -1.0E-06 -5.0E-07 0.OE+00 5.0E-07

Deflection

(m)

Appendix

G

Nanoscript

file

for

contact mode wear

testing.

//

dale2h.lth

//

1-13-97 DEE

//

#include

<litho.h> void

main()

{

LITHO_BEGIN

long

i;

long

n=

100000;

long

w=

3600*36;

double

x=

20;

double

x2=

x/2;

double y

=

20;

double

y2=

y/2;

double

rate=

500;

double

stpt=

4.5;

LithoPause(5);

LithoTranslate(-x2,0,rate);

LithoSetSetpoint(stpt);

for

(i=0;i<n;i++)

{

LithoTranslate(x,0,rate);

LithoTranslate(-x,0,rate);

}

LithoSetSetpoint(-stpt);

LithoTranslate(

1

.

5

*x,-y2,rate);

LithoPause(5);

LithoSetSetpoint(stpt);

for

(i=0;i<n;i++)

//

n

times

2

scans ofwear

//

seconds per

hour

times

12

//

um

in

scan x

//

um

in

scan

y

//

rate

in

urn/sec

//

adds volts

to

setpoint

//

Pause

for

()

seconds

//

offset

for

scansat origin

//

setup for

y

scans

{

LithoTranslate(0,y,rate);

LithoTranslate(0,-y,rate);

}

LithoSetSetpoint(-stpt);

for

(i=0;i<w;i++)

{

LithoPause(

1

);

//

Pause for

(

1

)

seconds

}

LITHO_END

}

Appendix

H

Nanoscript

file

for STM

mode wear

testing.

//

newst

10.1th

//

11-13-96

DEE

//

#include

<litho.h> void

main()

{

LITHO_BEGIN

long

i;

long

n;

long

m =

5;

longd=

10;

double

x=

40;

double

x2=

x/2;

double

y

=

40;

double

y2=

y/2;

double

rate=

100;

double depth

=

-0.500;

double

z_rate=

0.050;

LithoPause(5);

LithoTranslate(-3

0,-y2,rate);

LithoPause(2);

n=

l*m;

LithoMoveZ(depth,z_rate);

for

(i=0;i<n;i++)

{

LithoTranslate(0,y,rate);

LithoTranslate(0,-y,rate);

}

LithoMoveZ(-depth,z_rate);

LithoTranslate(d,0,rate);

n=

2*m;

LithoMoveZ(depth,z_rate);

for

(i=0;i<n;i++)

//

n

times

2

scans ofwear

//

um

between

scans

//

um

in

scan x

//

um

in

scan

y

//

rate

in

um/sec

//

um

to

push

tip

down

//

move

tip

down

at .050um/sec

//

Pause

for

()

seconds

LithoTranslate(d,0,rate);

n=

7*m;

LithoMoveZ(depth,z_rate);

for

(i=0;i<n;i++)

{ LithoTranslate(0,y,rate);

LithoTranslate(0,-y,rate);

}

LithoMoveZ(-depth,z_rate);

LithoPause(5);

//

Pause

for

()

seconds

LITHO_END

}

References:

1

Vullo;

R.

P.

"Direct

Composite

Restorations";

Project D

on

Internet,

1994.

2

Bayne,

S.

C; Heymann,

H.

O.;

Swift

Jr.,

E.

J.

JADA, 1994, 125,

687-701.

3

Concise

Encyclopedia

of

Compos