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J Med Dent Sci 2012595356

Background Although attritive and abrasive

wear of recent composite resins has been

substantially reduced, in vitrowear testing with

reasonably simulating devices and quantitative

determination of resulting wear is still needed.

Three-dimensional scanning methods are

frequently used for this purpose. The aim of thistrial was to compare maximum depth of wear and

volume loss of composite samples, evaluated with

a contact profilometer and a non-contact CCD

camera imaging system, respectively.

Method Twenty-three random composite

specimens with wear traces produced in a ball-on-

disc sliding device, using poppy seed slurry and

PMMA suspension as third-body media, were

evaluated with the contact profilometer (TalyScan

150, Taylor Hobson LTD, Leicester, UK) and with

the digital CCD microscope (VHX1000, KEYENCE,

Osaka, Japan). The target parameters weremaximum depth of the wear and volume loss.

Results The individual time of measurement

needed with the non-contact CCD method was

almost three hours less than that with the contact

method. Both, maximum depth of wear and volume

loss data, recorded with the two methods were

linearly correlated (r2> 0.97; p< 0.01).

Conclusion The contact scanning method and

the non-contact CCD method are equally suitable

for determination of maximum depth of wear and

volume loss of abraded composite resins.

Key words:Composite resin, Wear, Profilometry, CCD-

imaging

Introduction

During recent years numerous composite resins,

indicated for restoration of all cavity classes, were

introduced to the dental market, differing from previous

brands in monomer composition, yet particularly in

reduced filler size. It is likely that the size of filler

particles might affect clinical performance, as smaller

particles result in less interparticle spacing andthus better protection of the surrounding polymer

matrix 1,2,3. It is however questionable whether or not

the common concept of combining nano-sized particles

with more conventional fillers, as in several of the

current nanohybrid composites, is an adequate means

to prevent plucking of the larger filler particles 4. Filler

refinement is considered the main reason for reduced

abrasive wear. Long-term clinical trials have shown that

filler refined composites perform satisfactorily when

used in standard class / cavities; unacceptably

high wear was only observed in occlusal contact

areas of patients with severe bruxism5,6

. In spite ofsuch encouraging results, especially in vivo, yet also

Corresponding Author: Hidekazu Takahashi

Oral Biomaterials Engineering, Course of Oral Health Engineering,

School of Oral Health Care Sciences, Faculty of Dentistry, Tokyo

Medical and Dental University 1-5-45, Yushima, Bunkyo-ku, Tokyo,

113-8549, Japan.

Tel: +81-3-5803-5379 Fax: +81-3-5803-5379

E-mail: [email protected] November 7, 2011Accepted March 9, 2012

Original Article

Quantification of in vitroproduced wear sites on composite resins using contactprofilometry and CCD microscopy: A methodological investigation

Natthavoot Koottathape1), Hidekazu Takahashi

2), Werner J. Finger

3), Masafumi Kanehira

3),

Naohiko Iwasaki2)and Yujin Aoyagi

4)

1) Advanced Biomaterials, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate

School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo

2) Oral Biomaterials Engineering, Course of Oral Health Engineering, School of Oral Health Care Sciences,

Faculty of Dentistry, Tokyo Medical and Dental University

3) Division of Operative Dentistry, Graduate School of Dentistry, Tohoku University, Sendai

4) Department of Dental Materials Sciences, Kanagawa Dental College, Yokosuka


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54 J Med Dent SciN. Koottathape et al.

in vitrowear studies are still needed7, although in vitro

models cannot satisfactorily simulate the complex

clinical conditions 8. Apart from the question how to

simulate wear, it is important to decide how to measure

wear. Among the numerous methods of measuring

wear three-dimensional (3-D) scanning is probably the

most adequate approach, since quantitative data may

be generated, including volume loss, depth and area

of wear9. Three-dimensional scanners are operating

either in contact or in non-contact mode. With contact

scanners the target surface is recorded by a number

of parallel line traces that are finally put together to

digitize the surface. Non-contact profilers, in contrast,digitize the surface by a light-source or microscope

focused on the surface.

The purpose of the present study was to investigate

and compare wear traces on flat composite resin

specimens that were produced with a zirconia ball-

sliding wear testing device, using contact profilometry

and 3D imaging with a digital charge coupled device

(CCD) microscope for determination of maximum depth

of wear and volume loss. The research hypothesis was

that wear data determined with the two evaluation

methods would not yield significantly different results.

Materials and Methods

From an ongoing investigation on wear characteristics

of microfilled (DUR), nano-hybrid (MFL) and micro-hybrid

(APX) composite resins 23 abraded specimens were

randomly selected for comparative measurements of

wear traces, produced with a custom-made sliding

ball wear testing device 10 . The composite resins

used in the present study are shown in Table I. Disc-

shaped specimens, 8 mm in diameter and 2 mm thick,

were produced in aluminum molds, light-activated

using the halogen curing unit XL 3000 (3M ESPE,MN, USA; output >500 mW cm -2) for 40 seconds,

and stored in 37 deionized water for 7 days and

consecutively polished with SiC paper to the final grit

#4000. A zirconia ball (4-mm in diameter) served as

antagonist, loading the composite specimen at 15

angulation for a 3.7 mm long slide path (50 N load,

1.2 Hz, 10,000 cycles). During loading the specimens

were immersed in third-body media, either aqueous

slurry of slightly preground poppy seeds (33 mass%)

or aqueous suspension of PMMA beads (30 mass%).

The numbers of the composite resins evaluated for this

methodological study are listed in Table . The samples

were carefully rinsed and stored for at least another 7

days in 37 water prior to determination of wear. Each sample was scanned with a contact profilometer

(TalyScan 150, Taylor Hobson LTD, Leicester, UK) at 3

mm/s scanning rate with 5 m intervals between the

scanning lines. The profilometer stylus had a 2.0 m tip

radius and the force on the stylus was 0.98 mN. The

specified vertical resolution of the inductive probe is

0.06 m.

Then, the same specimen was scanned with a digital

CCD microscope at 100-fold magnification (VHX1000

with VH-Z 100R lens, KEYENCE, Osaka, Japan) at 5 m

intervals along the z-axis. Samples were randomly first

scanned with the contact or the non-contact device.With both methods, the specimens reference planes

were adjusted using three points on the non-abraded

site. Small ridge-like elevations seen next to the wear

trace, probably due to plastic deformation under the

action of the sliding ball, were disregarded for the

software-produced calculation of maximum depth and

volume loss of the wear trace by manually aligning the

reference plane.

The bivariate data for maximum depth of wear and

volume loss, determined with the two methods, were

statistically treated by regression analysis using

statistical software (SPSS Statistics ver.17, SAS, Cary,NC, USA).

Table . Composite resins and number of specimens evaluated for 3-body wear.

Material Shade Type Manufacturer Batch CodeNumber of specimen

poppy seeds PMMA beads

Durafill VS A3 microfilledHeraeus Kulzer,

Hanau, Germany010210 DUR 3 3

MI Flow A3nano-

hybrid

GC Corp.,

Tokyo, Japan0904132 MFL 5 4

Clearfil AP-X A2micro-

hybrid

Kuraray Medical,

Okayama, Japan1078A APX 5 3


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55Composite resin quantitative evaluation of wear

Results

Regarding the contact profilometer measurement,

scanning time for tracing the wear path of each

specimen was approximately 3 hours, additionally 45

minutes were needed for wear quantification. In

contrast, with the CCD microscope the scanning andquantification times for each specimen were 30 minutes

and 30 minutes, respectively. Typical wear trace

images obtained with the contact profilometer and the

CCD microscope are shown in Fig 1. Figure 2 shows the

relationship between the maximum wear depths, Fig. 3

the relationship between the volume losses, recorded

with the two scanning methods, respectively. Each

bivariate point in the diagrams reflects wear of one

composite resin specimen, abraded with one of the

abrasive slurries. The maximum wear depths and

volume loss values of DUR in poppy seed slurry and

APX in PMMA beads suspension were relatively large,whereas those of APX and MFL in poppy seed slurry

were relatively small. Linear regressions lines were

fitted using the least square approach, and the 95%

confidence intervals for mean response were drawn

around the regression lines. The coefficients of

determination, r2, for both correlations were highly

significant.

Discussion

This study aimed at comparing maximum depth and

volume loss of wears traces, produced on composite resinsurfaces using contact and non-contact profilometers.

The research hypothesis that wear data determined

with the two evaluation methods would not yield

significantly different results is accepted. Thus, bothmethods seem to be equally suitable to quantify wear.

Figure 1: Wear traces scanned by a contact profilometer (A) and

a digital CCD microscope (B).

Figure 2: Relationship between maximum wear depth (m)

recorded by a contact profilometer (PFM) and a digital CCD

microscope. Linear regression line and 95% confidence interval for

mean response (dashed lines).

Figure 3: Relationship between volume loss (mm3) recorded by a

contact profilometer (PFM) and a digital CCD microscope. Linear

regression line and 95% confidence interval for mean response

(dashed lines).


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56 J Med Dent SciN. Koottathape et al.

Interestingly, the amounts of wear recorded varied

not only with the composite resin types but also with

the third-body media used. Effects of different types of

composite resins and third-body media on wear will be

investigated and discussed in future studies.

A common problem encountered with both methods

was the necessity for manual alignment of the flat

reference plane, to define the wear trace margin by

eliminating the marginal ridge, likely produced by plastic

deformation of the resins.

The contact profilometer method has the disadvantage,

that stylus tracking, depending on the stylus geometry

and load, might deform the surface of the material. This

is primarily important for materials with low rigidity.

Although composites with very different moduli of

elasticity, such as the microfilled brand on the one

hand, and the micro-hybrid type on the other hand were

used, this effect was apparently without practical

significance, as shown by the stringent correlations

with the CCD data. The disadvantage of the CCD

method, where a light beam is used as the stylus, is

the transparency of the composite. Basically, the

method requires an opaque diffuse reflecting surface.

The shades of the composite specimens used in this

trial were A3 and A2, according to the Vita scale. The

stringent correlations with the contact profilometerreadings show, that the materials were apparently

sufficiently opaque.

Regarding the scanning and wear quantification

times, contact profilometer measurements were more

time consuming compared with the CCD microscope

measurements. The scanning time was 6 times longer

and wear quantification time was 1.5 times longer.

Thus, non-contact CCD measurements were almost

three hours faster.

The relative measuring error encountered with both

methods becomes obviously larger with decreasing

wear traces, as unequivocal definition of the tracemargin is a challenge. Therefore, a sufficiently large

number of loading cycles should be selected with in

vitroevaluations. Future studies will have to reveal the

effect of the changing contact areas between the

antagonist cusp, here the zirconia ball, and the resulting

stress exerted on the specimen surface.

Within the limitation of this in vitrotrial, it is concluded

that the contact profilometer method and the non-

contact CCD method are both equally suitable for

determination of depth of wear and volume loss of in

vitroproduced wear traces on composite resins. From

a practical view, CCD microscopy is the preferred

routine method, since measurements are contact-free,

relatively easy and fast.

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