Wear evaluation of the human enamel opposing differentY-TZP dental ceramics and other porcelains

Mi-Jin Kim a, Sun-Hee Oh b, Ji-Hwan Kim a, Sung-Won Ju c, Deog-Gyu Seo d, Sang-Ho Jun b,Jin-Soo Ahn c,*, Jae-Jun Ryu b

aDepartment of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Jeongneung 3-dong, Seongbuk-gu,

Seoul 136-703, Republic of KoreabDepartment of Medical Science, Graduate School, Korea University Medical Center, 126-1 Anam-dong 5ga, Seongbuk-gu, Seoul 136-705,

Republic of KoreacDental Research Institute and Department of Biomaterials Science, School of Dentistry, Seoul National University, 101 Daehak-ro, Jongno-gu,

Seoul 110-749, Republic of KoreadDental Research Institute and Department of Conservative Dentistry, School of Dentistry, Seoul National University, 101 Daehak-ro,

Jongno-gu, Seoul 110-749, Republic of Korea

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8

a r t i c l e i n f o

Article history:

Received 17 April 2012

Received in revised form

30 July 2012

Accepted 4 August 2012

Keywords:

Zirconia

Ceramic

Wear

Tooth

Y-TZP

a b s t r a c t

Purpose: This study examined the wear resistance of human enamel and feldspathic

porcelain after simulated mastication against 3 zirconia ceramics, heat-pressed ceramic

and conventional feldspathic porcelain.

Materials and methods: Human teeth and feldspathic porcelain cusp were tested against

ceramic discs. 5 brands were tested – 3 monolithic zirconia, Prettau, Lava, and Rainbow, one

lithium disilicate, IPS e.max Press, and one feldspathic porcelain, Vita-Omega 900. The

surface was polished using a 600 grit and 1200 grit SiC paper. Each group was loaded for

300,000 cycles in a chewing simulator. The wear resistance was analyzed by measuring the

volume of substance lost. The wear surfaces were observed by scanning electron micros-

copy to determine the wear characteristics.

Results: Vita-Omega 900 led to the greatest amount of enamel wears followed by IPS e.max

Press, Prettau, Lava and Rainbow. There was a significant difference between Vita-Omega

900 and IPS e.max Press ( p < 0.05). The wear values for human enamel were significantly

greater than those for feldspathic porcelain, regardless of the surface roughness of the

ceramic specimens ( p < 0.05).

Conclusion: The wear behaviour of human enamel and feldspathic porcelain varies accord-

ing to the type of substrate materials. On the other hand, 3 zirconia ceramics caused less

wear in the abrader than the conventional ceramic.

Clinical significance: Dental professionals should be aware of the wear effect of dental

restorations on the opposing teeth or restorations. The amount of enamel wear was highest

in feldspathic porcelains whereas zirconia ceramics caused less wear on the opposing teeth.

# 2012 Elsevier Ltd. All rights reserved.

* Corresponding author. Tel.: +82 2 740 8691; fax: +82 2 740 8694.

Available online at www.sciencedirect.com

journal homepage: www.intl.elsevierhealth.com/journals/jden

E-mail address: 937331@paran.com (J.-S. Ahn).

0300-5712/$ – see front matter # 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.jdent.2012.08.004

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8980

Table 1 – Y-TZP dental zirconia and ceramic materialsexamined.

Materials Type Manufacturer

Prettau Y-TZP Zirkonzahn GmbH, Bruneck, Italy

Lava Y-TZP 3M ESPE, St. Paul, MN, USA

Rainbow Y-TZP Dentium, Seoul, Korea

e.max Press Lithium

disilicate

glass ceramic

Ivoclar Vivadent, Liechtenstein

Vita-Omega

900

Low fusing

porcelain

Vita Zahnfabrik,

Bad Sackingen, Germany

1. Introduction

Dental prosthetic materials should have good mechanical

properties that will enable them to withstand a repetitive

masticatory pressure; be biocompatible; chemically durable so

that they can be used for a long time in the oral environment;

have aesthetic properties that are similar to those of natural

teeth; and have a high level of wear resistance, while

minimizing the wear of the opposing teeth.1 Despite the

biocompatibility and aesthetic advantages of ceramic crowns

in the early days, they had limitations in clinical use due to

their susceptibility to fracture and their excessive wear of

opposing teeth.2

First introduced to dental clinics in the late 1990s, Y-TZP

(Yttria partially stabilized tetragonal zirconia) has consider-

ably higher bending and fracture strength than other

ceramics.3,4 Generally, a zirconia ceramic crown consists of

a zirconia core in the lower part and a feldspathic porcelain in

the upper part, as in most all-ceramic crowns.

This ceramic crown has good physical properties in the

lower core as well as improved physical properties and good

aesthetic features due to the condensation of the upper

ceramic.5 A ceramic crown has disadvantages such as the

susceptibility of the upper veneer ceramic to fracture, the

possibility of structural weakening of the veneer ceramic

during the construction, and the need to remove a larger

portion of teeth for the abutment preparation. Sailer et al.6

recently reported that the most common failure of ceramic

crowns was fracture of the veneer ceramic lining, with a

failure rate of 15.2%. Such fractures are attributed to the

difference in the thermal expansion coefficients of the lower

core and upper ceramic, and to mechanical error during

condensation of the ceramic. Hence, the possibility of a

fracture is unavoidable.

All-ceramic crowns made from zirconia can replace metal-

ceramic restorative materials in terms of their mechanical

strength by employing the physical advantages of zirconia.

Despite this, ceramic crowns made only of zirconia, mono-

lithic zirconia crowns are not used widely in clinical practice

because of the absence of a sound standard and the possibility

of wear of the opposing teeth due to the hardness of zirconia.

Particularly, in relation to the possibility of wear of the

opposing teeth, the selection of an appropriate restorative

material is important for preserving the function of normal

opposing teeth and the balance of articulation.7 Among the

restorative materials, the type III gold alloy is ideal in terms of

the possibility of wear of the opposing teeth with its minimal

wear of the enamel of opposing teeth, unlike ceramics that

have a disadvantage, such as the high likelihood of wear of the

opposing teeth, despite their good aesthetic features and

biocompatibility, which limits their clinical applications.8,9

Studies on the wear of opposing teeth in relation to ceramic

crowns have been conducted. Many studies reported that the

ceramic destroys the enamel.10

These same studies also reported that although dental

ceramic is resistant to wear, it is extremely hard and causes

wear of the enamel and other restorative materials.8,9,11–14

Monasky and Taylor reported that ceramic with a rough

surface causes excessive wear of the natural opposing teeth;

more than gold alloy, amalgam, composite resin and enam-

el.15 Krejci et al.14 concluded that a ground surface causes less

wear than a glazed surface, and that the rate of enamel wear

depends on the hardness, texture and surface finish of the

opposing restorative materials. The surface roughness of

restorative materials is clinically important in relation to the

wear of opposing teeth, and has attracted considerable

attention from studies of dental restorative materials.16 The

rough surface of restorative material may cause gingivitis,

periodontitis, physical irritation of the surrounding gingiva, or

aesthetic problems due to the deposition of dental plaque or

increased retention.17,18

Turssi et al.19 reported that surface roughness plays an

important role in the wear pattern of the restorative material

itself or of the opposing teeth. Oh et al.7 reported that the

hardness and strength of the ceramic are not related strongly

to the wear of enamel, and that enamel wear is strongly

related to the microstructure of the ceramic, roughness of the

contact surface, and the environmental effect.

Many studies have reported the effect of different finishing

and grinding methods in relation to the surface roughness of

dental restorative materials.10,20,21 Although many studies

have examined the possibility of wear of enamel in relation to

the effect of veneering porcelain or composite resin on the

possibility of wear of the enamel, few studies have investigat-

ed the influence of zirconia ceramic directly on enamel wear.

Therefore, this study evaluated the possibility of wear of

the opposing teeth to establish structural criteria for the safe

intraoral use of zirconia monolithic crowns for dental

restorations. To achieve this goal, specimens were made

using three types of ceramics (zirconia, heat-pressed ceramic,

and feldspathic porcelain), and the degree of enamel wear due

to the surface roughness were observed and compared.

2. Materials and methods

Five kinds of substrates were tested. Three types of commer-

cially available zirconia blocks and heat-pressed ceramic and

low-fusing feldspathic porcelain were used for the wear test.

The three types of zirconia blocks were Prettau (Zirkonzahn

GmbH, Bruneck, Italy), Lava (3M ESPE, St. Paul, MN, USA) and

Rainbow (Dentium, Seoul, Korea). The heat-pressed ceramic

was IPS e.max Press (Ivoclar Vivadent, Liechtenstein) and the

low-fusing feldspathic porcelain was Vita-Omega 900 (Vita

Zahnfabrik, Bad Sackingen, Germany) (Table 1). The extracted

Fig. 1 – Chewing simulator CS-4.8 (SD Mechatronik,

Feldkirchen-Westerham, Germany).

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8 981

normal premolar teeth of the maxilla and mandible, and

feldspathic porcelain were used as the corresponding abra-

ders.

A total of 100 substrate specimens (20 per product) were

prepared and divided into two groups. The surface of the

specimens of one group was ground with 600-grit silicone

carbide paper (SiC), and that of the other group was ground

with 1200-grit silicone carbide paper.

2.1. Making of the abrader specimen

2.1.1. Making of the human enamel specimenThe cusps of the premolar teeth of the maxilla and mandible

extracted recently for orthodontic treatment were used as the

abrader specimens. The cusps of the teeth that had a worn or

fractured surface or were too sharp were excluded.

2.1.2. Making of the cusp specimen of the feldspathic porcelainThe low-fusing feldspathic porcelain was condensed into a

6 mm � 8 mm (width � height) right square column and fired.

The column was designed to be 6 mm tall from the bottom to

the top to have a circular arc with a diameter of 6 mm on the

apex of the cusp. All specimens were prepared by a single

dental technician.

2.2. Making of the substrate specimen

2.2.1. Making of specimens of three types of zirconiaCommercial zirconia blocks manufactured from Prettau, Lava,

and Rainbow were used, and cuboidal specimens,

20 mm � 10 mm � 5 mm (width � length � thickness) in size,

were prepared according to the instructions of the manufac-

turer by sintering the blocks.

2.2.2. Making of the heat-pressed ceramic specimenA wax pattern with a 20 mm � 10 mm � 5 mm (width � length

� thickness) cuboidal shape was made using inlay wax and

buried. The IPS e.max Press was made according to the

manufacturer’s instructions, and the specimen was embedded

in acrylic resin to fit the jig of the wear test device.

2.2.3. Making of the low-fusing feldspathic porcelain specimenA cuboid-shaped silicone mould was made for the ceramic

specimen. Vita-Omega 900 was condensed using the mould

and fired on a heat-resistant tile according to the manufac-

turer’s instructions, and a 20 mm � 10 mm � 5 mm

(width � length � thickness) specimen was made.

2.3. Wear test and measurement

2.3.1. Wear testA wear test was performed using a chewing simulator CS-4.8

(SD Mechatronik, Feldkirchen-Westerham, Germany). The

device had eight sample holders, and the vertical and

horizontal movements between the opposing specimens were

simulated using two motors controlled by a computer (Fig. 1).

The circulation of heat was possible by controlling the flow of

cold and warm water with a computer. Each of the eight

interior chambers consisted of an upper sample holder that

could be tightened with a screw, and a lower sample holder

into which the specimen could be embedded. To use the teeth

specimen as the abrader, the tooth specimens were embedded

in the lower sample holder using acrylic resin. Each of the

ceramic specimens that were embedded in the acrylic resin

was fixed on the upper sample holder using a screw. A 5 kg

load, which is equivalent to a masticatory force of 49 N was

applied,14 and heat circulation (5–55 8C) was allowed during

the test.

2.3.2. Measurement of the worn amount of the abraderspecimenThe three-dimensional surface of the abrader specimen was

scanned before and after the wear test using an MTS 3D

profiler (MTS Systems Corporation, Eden Prairie, MN, USA),

and the actual volumetric loss was calculated using the Ansur

3D software (Minneapolis, MN, USA) by superimposing the

three-dimensional surfaces before and after the wear test.

2.3.3. Observation of the wear of ceramic substrate specimensBefore the wear test, the mean roughness (Ra) of the ceramic

specimens was measured using a laser scanning microscope

(LSM 5 Pascal, Carl Zeiss, Jena, Germany). After the test, the

specimen surface was observed by scanning electron micros-

copy (SEM) (JSM-6360, JEOL Techniques, Tokyo, Japan) under

magnifications of 50� and 2000�.

2.4. Statistical analysis

The wear amount of the enamel and feldspathic porcelain

cusp was analyzed via 3-way ANOVA using SPSS (version 12.0,

SPSS, Inc., Chicago, USA), and a post hoc test was performed to

test the significance of the wear amount using a Scheffe test

(a = 0.05).

3. Results

3.1. Wear of the enamel

Table 2 lists the mean and standard deviation of the wear

amount of the enamel and feldspathic porcelain cusp. For both

of the surface roughness values, the amount of enamel wear

Table 2 – Mean values and SDs of wear volume of the enamel and feldspathic porcelain cusp (mm3).

Abrader Grit Substrate materials

Prettau Lava Rainbow e.max Press Vita-Omega 900

Enamel 600 0.04 � 0.02 0.04 � 0.02 0.04 � 0.02 0.08 � 0.03 0.13 � 0.05

1200 0.04 � 0.02 0.04 � 0.02 0.04 � 0.02 0.06 � 0.03 0.11 � 0.03

Feldspathic porcelain 600 0.03 � 0.02 0.03 � 0.01 0.02 � 0.01 0.06 � 0.02 0.03 � 0.01

1200 0.03 � 0.02 0.03 � 0.01 0.03 � 0.02 0.02 � 0.01 0.03 � 0.01

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8982

was highest in the Vita-Omega 900 group followed by the IPS

e.max Press, Prettua, Lava, and Rainbow groups, although

there was no significant difference seen between the latter

three groups, i.e. Prettau, Lava and Rainbow groups ( p > 0.05).

A significant difference was seen between Vita-Omega 900 and

IPS e.max Press ( p < 0.05) in terms of enamel wear.

3.2. Wear of the feldspathic porcelain cusp

In the 600-grit group, the wear amount of the feldspathic

porcelain cusp was highest in the IPS e.max Press group,

followed in order by the Vita-Omega 900, Prettau, Lava, and

Rainbow groups. In the 1200-grit group, the amount of wear

was lowest in the e.max group.

From the results of 3-way ANOVA, The amount of wear

significantly differed depending on the type of abrader

materials, the substrate materials, and surface roughness.

Result showed significant interaction between abrader and

substrate, and between substrate and surface roughness

( p < 0.05). However, there was no significant interaction

Table 3 – Scheffe analysis to evaluate the mean enamel volumshowing multiple comparisons (P, Prettau; L, Lava; R, Rainbow

(I) Groups (J) Groups Mean difference (I � J) S

P L 0.0071

R 0.0054

E �0.0175*

V �0.0257*

L P �0.0071

R �0.0016

E �0.0246*

V �0.0328*

R P �0.0054

L 0.0016

E �0.0229*

V �0.0312*

E P 0.0175*

L 0.0246*

R 0.0229*

V �0.0083

V P 0.0258*

L 0.0328*

R 0.0312*

E 0.0083

p < 0.05 indicates significant difference.* Difference in the mean values between group pair ( p < 0.05).

between abrader and surface roughness, and among three

factors ( p > 0.05).

A post hoc test in ANOVA was performed using the

Scheffe test. There were no significant differences in the

wear amounts of the Prettau, Lava, and Rainbow groups,

whereas the wear amounts were significantly different for

the IPS e.max Press and Vita-Omega 900 groups from

those of the Prettau, Lava, and Rainbow groups ( p < 0.05)

(Table 3).

Fig. 2 shows the mean amount of wear of the enamel and

feldspathic porcelain cusp according to the materials with

different degrees of surface roughness. When the abrader

was the enamel, the wear amount was higher in the 600-grit

group than in the 1200-grit group in all ceramic substrate

material groups. The amount of wear of the enamel was

highest in the Vita-Omega 900 group in the 600-grit group,

and lowest in the three types of zirconia groups in the 1200-

grit group. The amount of wear of the enamel group was

higher than that of the feldspathic porcelain cusp group

regardless of their surface roughness ( p < 0.01).

e loss (mm3) differences between the material groups; E, e.max Press; V, Vita-Omega 900).

td. error Sig. 95% confidence interval

Lower bound Upper bound

0.005316 0.778 �0.0098 0.0240

0.005316 0.901 �0.0115 0.0223

0.005316 0.038 �0.0343 �0.0060

0.005316 0.000 �0.0426 �0.0089

0.005316 0.778 �0.0240 0.0098

0.005316 0.999 �0.0185 0.0152

0.005316 0.001 �0.0415 �0.0077

0.005316 0.000 �0.0497 �0.0160

0.005316 0.901 �0.0223 0.0115

0.005316 0.999 �0.0153 0.0185

0.005316 0.002 �0.3983 �0.0060

0.005316 0.000 �0.0481 �0.0143

0.005316 0.038 0.0006 0.0344

0.005316 0.001 0.0077 0.0415

0.005316 0.002 0.0060 0.0340

0.005316 0.663 �0.0251 0.0086

0.005316 0.000 0.0089 0.0426

0.005316 0.000 0.0159 0.0497

0.005316 0.000 0.0142 0.0481

0.005316 0.663 �0.0086 0.0252

Fig. 2 – Mean wear volume of the enamel and porcelain

cusp. Standard deviations are shown by error bars.

Table 4 – Mean values and SDs of the surface roughnessof the ceramic substrate specimens before the wear test(mm).

Materials 600 grit 1200 grit

Prettau 0.784 � 0.069 0.284 � 0.052

Lava 0.785 � 0.123 0.459 � 0.075

Rainbow 0.678 � 0.026 0.411 � 0.034

e.max Press 0.455 � 0.066 0.249 � 0.015

Vita-Omega 900 0.823 � 0.383 0.704 � 0.094

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8 983

3.3. Wear surface of the ceramic substrate specimens

3.3.1. Average RaTable 4 lists the average Ra and standard deviation of each of

the ceramic substrate specimens measured by laser scanning

microscopy before the wear test. In the 600-grit SiC wear

group, the average Ra was lowest in the IPS e.max Press group.

In the 1200-grit SiC wear group, the average Ra was highest in

the Vita-Omega 900 group, and in both the 600-grit and 1200-

grit, the average Ra was lowest in the IPS e.max Press group.

3.3.2. Scanning electron microscopy (SEM)Figs. 3–7 show SEM images of the five ceramic substrate

specimens of 1200-grit group, which was performed after the

wear test (the marks of wear are shown in each of the

specimens). In the IPS e.max Press and three types of zirconia

substrate specimens, the inner structure was consistently

dense and air bubbles were rarely observed, whereas a large

crystalline shape and numerous air bubbles were observed in

the Vita-Omega 900 porcelain substrate specimen.

Fig. 3 – SEM images after wear test of e.max Press (1200 grit SiC

50T, (B) original magnification 2000T.

4. Discussion

Tooth wear is a complex process that involves a range of

factors, such as the food, non-functional habits, neuromus-

cular force, thickness and hardness of enamel, acidity and

other properties of saliva, masticatory pattern, and opposing

restorative materials.10 The progressive wear of natural teeth

is a normal physiological phenomenon.

This physiological wear can be affected if restorative

materials with different wear rates from that of natural teeth

are used for intraoral restorations.15,22 Lambrechts et al.23

reported that vertical wear of enamel is 20–40 mm a year under

normal condition. Seghi et al.24 reported that the wear rates of

intraoral restorative materials should be similar to that of the

human enamel.25 Therefore, it is important to evaluate the

wear resistance of restorative materials against the opposing

natural teeth and the physical properties of restorative

materials. Among the dental restorative materials, ceramic

has the best aesthetic features as well as good compressive

strength and biocompatibility,22 although it presents certain

disadvantages such as relatively low tensile strength and can

cause an excessive wear of the opposing teeth.8,9 Restorative

materials that significantly wear down the opposing teeth can

cause hypersensitivity and articular imbalance by rapidly

wearing down the opposing teeth.26 To overcome this

problem, new ceramics that produce less wear on the

opposing teeth have been developed.27

Among the improved all-ceramic crowns, the zirconia

crown has a feldspathic porcelain lining in its upper part, and

it is used in clinical practice. Recently, the construction of an

all-ceramic crown made only of zirconia has become possible.

polished) against human enamel (A) original magnification

Fig. 4 – SEM images after the wear test of Lava (1200 grit SiC polished) against human enamel (A) original magnification 50T,

(B) original magnification 2000T.

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8984

This has made it possible to overcome the susceptibility of its

veneer ceramic layer to wear, while maintaining its physical

advantages. Most studies on the wear of enamel have focused

on the veneering porcelain and resin,15,28 and few studies have

examined the effect of zirconia ceramic on enamel wear. This

study examined the possibility of wear against the opposing

teeth to establish a structural standard for the safe intraoral

use of zirconia for monolithic ceramic crowns. A clinical study

on wear takes at least 6 months to 1 year, and involves

difficulties in accurate measurements due to many uncon-

trollable variables.29

Although an in vitro study has limitations in perfectly

simulating the intraoral masticatory movement,30 it can

simulate simple movements, such as grinding and clenching

teeth,30 and the mechanism behind the wear resistance of

various materials or the order of susceptibility of various

materials to wear can be assessed at the pre-clinical stage

using specific test variables. Because of the advantages of an

in vitro study, the test devices that can simulate the intraoral

masticatory movement were developed to assess the wear of

natural teeth and restorative materials.13,29,31–34 The 2-axes

wear test device used in this study is currently being used in

many studies, and is known to be practical, durable and cost-

effective. This device has a total of 8 interior chambers, and

simulates the mandibular closing movement that occurs

Fig. 5 – SEM images after the wear test of Prettau (1200 grit SiC

50T, (B) original magnification 2000T.

during matiscatory movement by simulating the occlusal

contact followed by the sliding movement.35 In this study, a 2-

body wear test was performed. This test is used widely in wear

resistance measurements,36 and was used to simulate the

attrition caused by the occlusal contact between restorative

materials and the teeth during bruxism and clenching.

This method could also simulate the friction and fatigue

wear caused by direct contact between the maxilla and

mandibular teeth during swallowing or non-functional dy-

namic occlusal movement.37 The load of the wear test device

was 5 kg, which is the mean physiological occlusal force

without bruxism based on the intraoral occlusal force reported

in previous studies on ceramic wear.38 The subsequent sliding

movement plays an important role in simulating the intraoral

wear as microfatigue occurs during the opposing wear

material slides on the specimen.39 In the present study,

0.3 mm lateral movement was applied. Mair et al.40 reported

that as the load that accompanies the sliding factor causes 10

times greater stress than that caused by a static load, and a

crack may be formed on the surface of the ceramic. During the

test, the 8 interior chambers were filled with water, and the

continuous change of water enabled the removal of wear

particles created by the wear test from the contact surface. In

addition, heat circulation was performed during the wear test

to simulate changes in the intraoral temperature.

polished) against human enamel (A) original magnification

Fig. 6 – SEM images after the wear test of Rainbow (1200 grit SiC polished) against human enamel (A) original magnification

50T, (B) original magnification 2000T.

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8 985

Up to 300,000 masticatory movements were simulated,

which is equivalent to the masticatory movement performed

at 1 year in a clinical environment.37 After the test, the

volumetric loss was measured using an MTS 3D profiler and

Ansur 3D software by superimposing the 3D surfaces before

and after the test. Standardization of the enamel surface of

natural teeth that was used as the opposing wear material has

been a subject of considerable controversy.35 In most studies, a

standardized enamel cusp was used for the wear test of

ceramic and enamel. Krejci et al.41 reported that the non-

standardized enamel cusp of natural teeth is most appropriate

for the opposing wear materials in the wear test, which was

consistent with previous studies by Krejci et al.42 and Lutz

et al.43 In a preliminary experiment, Kunzelmann et al.44 used

an enamel cusp surface that was not treated, and reported that

the standardization of the enamel through grinding prepara-

tion altered the wear properties of the opposing wear material,

unlike that with the non-standardized cusp. Heintze et al.35

reported that a standardized enamel cusp could result in a

range of results, and the results obtained from these cusps

were slightly inconsistent. Therefore, in this study, the enamel

surface of the premolar teeth of the maxilla and mandible,

which were extracted for orthodontic treatment, was used

without standardization.

Fig. 7 – SEM images after the wear test of Vita-Omega 900 (1200

magnification 50T, (B) original magnification 2000T.

In this study, the amount of wear of the opposing abrader

shows a significant difference depending on the type of

ceramic substrate, opposing abrader and surface roughness.

Of the five types of ceramic substrate material, the amount of

enamel wear was the highest in the Vita-Omega 900 group,

followed by the IPS e.max Press, Lava, Rainbow, and Prettau

groups. In particular, the amount of enamel and feldspathic

porcelain cusp wear was the lowest in the Prettau, Lava, and

Rainbow groups, and was significantly higher in the Vita-

Omega 900, IPS e.max Press, and three types of zirconia

substrate groups.

The amount of wear in the Vita-Omega 900 group was

higher when the abrader was the enamel rather than of the

feldspathic porcelain cusp. Unlike the other wear materials,

IPS e.max Press group significantly wore out the abrader at a

600-grit surface. The mean wear amounts of the three types of

zirconia substrate specimen that were measured after the

wear test were all too small to be measured. This suggests that

compared to feldspathic porcelain, the superior physical

properties and surface features of zirconia, such as its

hardness, bending strength, fracture toughness and density,

enabled it to maintain a smooth surface during the wear test,

which is consistent with the results reported by Ghazal et al.

on the wear of a zirconia specimen.37 In this study, the amount

grit SiC polished) against human enamel (A) original

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8986

of the enamel wear of natural teeth was higher than that

of feldspathic porcelain cusp, possibly due to the higher

wear resistance of feldspathic porcelain than the human

enamel.

The lower level of enamel hardness than feldspathic

porcelain could cause greater wear of enamel than feldspathic

porcelain. Enamel generally has a Vickers hardness of 320–

380 kg/mm2 and a fracture toughness of 0.8 Mpa m1/2. Also

these values have variations caused by anatomical character-

istics in enamel such as Hunter–Schreger Band (HSB). It is

known that higher packing densities of HSB are noted in those

areas subjected to greater external forces.45,46 Feldspathic

porcelain, however, has a higher degree of hardness of 500 kg/

mm2 or more, and its wear of the opposing enamel could be

accelerated by a rougher surface and by broken particles

during the matiscatory test. Additionally the wear of enamel

could increase considerably as the fracture toughness of

enamel is significantly lower than that of feldspathic porce-

lain. This superior property of feldspathic porcelain to that of

the human enamel can affect the wear amount, which is

consistent with these results. The surface roughness of

ceramic can vary according to the methods and degree of

surface grinding, and a rough ceramic surface decreases the

physical properties of the materials, or causes an excessive

wear of the opposing teeth, surface discoloration, and

inflammation of soft oral tissue. Schuh et al.47 reported that

a high friction coefficient between low-fusing ceramic and the

opposing wear materials increases the fatigue and ceramic

wear.

The results of this study showed that the amount of enamel

wear in relation to the surface roughness differed significantly

( p < 0.05) and decreased in the 1200-grit grinding group. The

average Ra of the specimen was measured by laser scanning

microscopy before the wear test, and the surface was observed

after the test using SEM. In the SiC grinding group of 600 grit,

the average Ra was the lowest in the IPS e.max Press group and

in the SiC grinding group of 1200 grit, and the degree of

roughness was the highest in the Vita-Omega 900 group. In the

IPS e.max Press group, the average Ra was the lowest both in

the 600-grit group and 1200-grit group. In the three types of

zirconia groups where grinding was performed using 1200-grit

SiC, the mean surface roughness of the Lava, Rainbow,

Prettau, and IPS e.max Press groups were similar. Willems

et al.48 reported that the roughness of the contact surface of

the enamel after wear was 0.64 mm, and Al-Wahadni49

reported that the average Ra of the ceramic after grinding

was 0.26–0.75 mm.

The hardness of metal is related to enamel wear. Based on

the results of various studies, however, Seghi et al.24 Magne

et al.50 and Oh et al.7 reported the hardness of ceramic and the

wear of opposing teeth by ceramic restorative materials. The

hardness and wear of ceramic are closely related to each other,

and that wear is closely related to the microstructure of

ceramic, the roughness of the contact surface, and environ-

mental factors. Although the correlation between the surface

roughness and amount of enamel wear can be expected, the

correlation was not analyzed in the present study.

The effect of the surface roughness on wear was

reconsidered because in the present study, some ceramic

materials with similar degrees of surface roughness showed

significantly different enamel wear after the wear test.

Metzler et al.51 reported that although the surface condition

of ceramic is important at the initial stages of wear, the inner

properties of ceramic affected the wear rate once the effect of

roughness disappeared with wear progression. The surface

roughness is one of the factors that affect wear. This study

examined the possibility of the wear of zirconia ceramic

against the opposing teeth as part of a study to apply a

zirconia monolithic crown to clinical practice. These results

suggest that zirconia ceramic can be used as zirconia

monolithic crown with an advantage as it showed less

enamel wear than feldspathic porcelain and heat-pressed

ceramics.

As this is an in vitro study, which involves many factors,

such as occlusal force, matiscatory habits, type of food, and

location of the teeth in the maxillary and mandibular arch, the

conditions used in this study could differ from the clinical

intra oral conditions. In addition, in this study, only 2-body

wear was evaluated. Therefore, different results could be

achieved if a 3-body wear test is performed using different

wear materials, further studies with well simulated intra oral

condition are required for better clinical implication.

5. Conclusion

(I) The enamel wear was significantly greater than the

feldspathic porcelain abrader wear ( p < 0.05).

(II) The feldspathic porcelain substrate caused the most wear

of the enamel abrader ( p < 0.05).

(III) The zirconia substrates caused the least wear of the

enamel abrader ( p < 0.05) and had no difference among

them ( p > 0.05).

Acknowledgements

First two authors contributed equally to this work. This study

was supported by the Basic Science Research Program through

the National Research Foundation of Korea (NRF) funded by

the Ministry of Education, Science and Technology (2010-

0005090 and 2011-0005559).

r e f e r e n c e s

1. Kadokawa A, Suzuki S, Tanaka T. Wear evaluation ofporcelain opposing gold, composite resin and enamel.Journal of Prosthetic Dentistry 2006;96:258–65.

2. Southan DE, Jorgensen KD. Faulty porcelain jacket crowns.Australian Dental Journal 1972;17:436–40.

3. Piconi C, Maccauro G. Zirconia as a ceramic biomaterial.Biomaterials 1999;20:1–25.

4. Guazzato M, Albakry M, Ringer SP, Swain MV. Strength,fracture toughness and microstructure of a selection of all-ceramic materials. Part I: pressable and alumina glass-infiltrated ceramics. Dental Materials 2004;20:441–8.

5. Sailer I, Feher A, Filser F, Luthy H, Gauckler LJ, Scharer P,et al. Prospective clinical study of zirconia posterior fixedpartial dentures: 3-year follow-up. Quintessence International2006;37:685–93.

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8 987

6. Sailer I, Feher A, Filser F, Gauckler L, Luthy H, Hammerle C.Five-year clinical results of zirconia frameworks forposterior fixed partial dentures. International Journal ofProsthodontics 2007;20:383–8.

7. Oh WS, DeLong R, Anusavice KJ. Factors affecting enameland ceramic wear: a literature review. Journal of ProstheticDentistry 2002;87:451–9.

8. Wiley MG. Effects of porcelain on occluding surfaces ofrestored teeth. Journal of Prosthetic Dentistry 1989;61:133–7.

9. Mahalick JA, Knap FJ, Weiter EJ. Occusal wear inprosthodontics. The Journal of the American Dental Association1971;82:154–9.

10. Elmaria A, Goldstein G, Vijayaraghavan T, Legeros RZ,Hittelman EL. An evaluation of wear when enamel isopposed by various ceramic materials and gold. Journal ofProsthetic Dentistry 2006;96:345–53.

11. Hudson JD, Goldstein GR, Georgescu M. Enamel wear causedby three different restorative materials. Journal of ProstheticDentistry 1995;74:647–54.

12. Hacker CH, Wagner WC, Razzoog ME. An in vitroinvestigation of the wear of enamel on porcelain and gold insaliva. Journal of Prosthetic Dentistry 1996;75:14–7.

13. Ramp MH, Suzuki S, Cox CF, Lacefield WR, Koth DL.Evaluation of wear: enamel opposing three ceramicmaterials and a gold alloy. Journal of Prosthetic Dentistry1997;77:523–30.

14. Krejci I, Lutz F, Reimer M, Heinzmann JL. Wear of ceramicinlays, their enamel antagonists, and luting cements. Journalof Prosthetic Dentistry 1993;69:425–30.

15. Monasky GE, Taylor DF. Studies on the wear of porcelain,enamel, and gold. Journal of Prosthetic Dentistry 1971;25:299–306.

16. Al-Shammery HAO, Bubb NL, Youngson CC, Fasbinder DJ,Wood DJ. The use of confocal microscopy to assess surfaceroughness of two milled CAD–CAM ceramics following twopolishing techniques. Dental Materials 2007;23:736–41.

17. Quirynen M, Bollen CML. The influence of surfaceroughness and surface-free energy on supra- andsubgingival plaque formation in man. Journal of ClinicalPeriodontology 1995;22:1–14.

18. Quirynen M. The clinical meaning of the surface roughnessand the surface free energy of intra-oral hard substrata onthe microbiology of the supra- and subgingival plaque:results of in vitro and in vivo experiments. Journal ofDentistry 1994;22(Suppl. 1):S13–S16.

19. Turssi CP, de Moraes Purquerio B, Serra MC. Wear ofdental resin composites: Insights into underlyingprocesses and assessment methods—a review. Journal ofBiomedical Materials Research Part B Applied Biomaterials2003;65:280–5.

20. Kou W, Molin M, SjOGren G. Surface roughness of fivedifferent dental ceramic core materials after grinding andpolishing. Journal of Oral Rehabilitation 2006;33:117–24.

21. Sara D, Turk T, Elekdag Turk S, Sara YS. Comparison of 3polishing techniques for 2 all-ceramic materials.International Journal of Prosthodontics 2007;20:465–8.

22. Jagger DC, Harrison A. An in vitro investigation into thewear effects of unglazed, glazed, and polished porcelainon human enamel. Journal of Prosthetic Dentistry1994;72:320–3.

23. Lambrechts P, Braem M, Vuylsteke-Wauters M, Vanherle G.Quantitative in vivo wear of human enamel. Journal of DentalResearch 1989;68:1752–4.

24. Seghi RR, Rosenstiel SF, Bauer P. Abrasion of human enamelby different dental ceramics in vitro. Journal of DentalResearch 1991;70:221–5.

25. Sulong MZAM, Aziz RA. Wear of materials used in dentistry:a review of the literature. Journal of Prosthetic Dentistry1990;63:342–9.

26. Jacobi R, Shillingburg JHT, Duncanson JMG. A comparison ofthe abrasiveness of six ceramic surfaces and gold. Journal ofProsthetic Dentistry 1991;66:303–9.

27. Eom S, Oh S, Dong J. A study on the wear of dentalrestorative materials. Journal of Korean Academiy ofProsthodontics 1998;36:69–81.

28. McLaren E, Giodano IIR, Pober R, Abozenada B. Materialtesting and layering techniques of a new two-phase all-glass veneering porcelain for bonded porcelain and high-alumina frameworks. Quintessence of Dental Technology2003;26:69–81.

29. Ratledge DK, Smith BGN, Wilson RF. The effect of restorativematerials on the wear of human enamel. Journal of ProstheticDentistry 1994;72:194–203.

30. Suzuki S. Simulated enamel wear during occlusal contact.American Journal of Dentistry 2004;17:373–7.

31. Yip KH, Smales RJ, Kaidonis JA. Differential wear of teethand restorative materials: clinical implications. InternationalJournal of Prosthodontics 2004;17:350–6.

32. Degee AJ, Pallav P, Davidson CL. Effect of abrasion mediumon wear of stress-bearing composites and amalgam in vitro.Journal of Dental Research 1986;65:654–8.

33. Kaidonis JA, Richards LC, Townsend GC, Tansley GD. Wearof human enamel: a quantitative in vitro assessment.Journal of Dental Research 1998;77:1983–90.

34. Yap AUJ, Teoh SH, Hastings GW, Lu CS. Comparative wearranking of dental restorative materials utilizing differentwear simulation modes. Journal of Oral Rehabilitation1997;24:574–80.

35. Heintze SD, Cavalleri A, Forjanic M, Zellweger G, RoussonV. Wear of ceramic and antagonist—a systematicevaluation of influencing factors in vitro. Dental Materials2008;24:433–49.

36. Heintze SD, Zappini G, Rousson V. Wear of ten dentalrestorative materials in five wear simulators—results of around robin test. Dental Materials 2005;21:304–17.

37. Ghazal M, Yang B, Ludwig K, Kern M. Two-body wear ofresin and ceramic denture teeth in comparison to humanenamel. Dental Materials 2008;24:502–7.

38. Gibbs CH, Mahan PE, Lundeen HC, Brehnan K, Walsh EK,Holbrook WB. Occlusal forces during chewing andswallowing as measured by sound transmission. Journal ofProsthetic Dentistry 1981;46:443–9.

39. Heintze SD. How to qualify and validate wear simulationdevices and methods. Dental Materials 2006;22:712–34.

40. Mair LH, Stolarski TA, Vowles RW, Lloyd CH. Wear:mechanisms, manifestations and measurement. Report of aworkshop. Journal of Dentistry 1996;24:141–8.

41. Krejci I, Albert P, Lutz F. The influence of antagoniststandardization on wear. Journal of Dental Research1999;78:713–9.

42. Krejci I, Reich T, Lutz F, Albertoni M. An in vitro testprocedure for evaluating dental restoration systems. 1: acomputer-controlled mastication simulator. SchweizMonatsschr Zahnmed 1990;100:953–60.

43. Lutz F, Krejci I, Barbakow F. Chewing pressure us. wearcomposites opposing enamel cusps. Journal of Dental Research1992;71:1525–9.

44. Kunzelmann KH, Jelen B, Mehl A, Hickel R. Wearevaluation of MZ100 compared to ceramic CAD/CAMmaterials. International Journal of Computerized Dentistry2001;4:171–84.

45. Lynch CD, O’Sullivan VR, Dockery P, McGillycuddy CT, SloanAJ. Hunter–Schreger Band patterns in human tooth enamel.Journal of Anatomy 2010;217:106–15.

46. Lynch CD, O’sullivan VR, Dockery P, McGillycuddy CT, ReesJS, Sloan AJ. Hunter–Schreger Band patterns and theirimplications for clinical dentistry. Journal of OralRehabilitation 2011;38:359–65.

j o u r n a l o f d e n t i s t r y 4 0 ( 2 0 1 2 ) 9 7 9 – 9 8 8988

47. Schuh C, Kinast EJ, Mezzomo E, Kapczinski MP. Effect ofglazed and polished surface finishes on the frictioncoefficient of two low-fusing ceramics. Journal of ProstheticDentistry 2005;93:245–52.

48. Willems G, Lambrechts P, Braem M, Vuylsteke-Wauters M,Vanherle G. Surface roughness enamel-to-enamel contactareas compared intrinsic roughness dental resincomposites. Journal of Dental Research 1991;70:1299–305.

49. Al-Wahadni A. An in vitro investigation into thesurface roughness of 2 glazed, unglazed, and refinished

ceramic materials. Quintessence International 2006;37:311–7.

50. Magne P, Oh WS, Pintado MR, DeLong R. Wear of enameland veneering ceramics after laboratory and chairsidefinishing procedures. Journal of Prosthetic Dentistry1999;82:669–79.

51. Metzler KT, Woody RD, Miller Iii AW, Miller BH.In vitro investigation of the wear of human enamel bydental porcelain. Journal of Prosthetic Dentistry 1999;81:356–64.