1.0 Introduction

1.1 Literature Survey

Dental cements are often classified on the basis of their components into water and acid

based systems such as zinc phosphate, zinc polyacrylate (polycarboxylate) and glass ionomer.

They contain metal oxide or silicate fillers embedded in a salt matrix. Non-aqueous acid-based

cements include zinc oxide eugenol and non-eugenol types. These also contain metal oxide

fillers embedded in a metallic salt matrix. The polymer-based systems include acrylate or

methacrylate resin cements which has been sub classified into self-etch, total-etch and the latest

generation of self-adhesive resin cement systems which contain silicate or other types of fillers in

an organic resin matrix. Cements can also be classified based on the type of their matrix; eg,

phosphate (zinc phosphate, silico phosphate), polycarboxylate (zinc polycarboxylate, glass

ionomer cement), phenolate (zinc oxide eugenol and ethoxybenzoic acid) and resins (polymeric)

[41].

Dental cements have been and are used to retain restorations to the prepared teeth, to seal

the marginal gap between the prosthesis and the finishing line on the tooth and also, to

interconnect (attach) any type prosthesis to the tooth structure or an implant construct. It is also

recognized that the cement surface exposed within the oral environment may be subject to

multiple changes over time and function. These include wear, especially when it is used for

inlays against enamel [1-4,24]; resorption [5]; subsurface degradation [6]; marginal ditching [7];

1

and discoloration [8-10]. These conditions including wear could make the tooth susceptible to

caries [11], periodontal disease [12] and altered prosthesis esthetics, these type changes could

ultimately lead to loss of the prosthesis [8-10, 13-16]. These situations are most significant if the

cement marginal gap region is larger and directly exposed to occlusion [43]. Despite of these

situations, loss of marginal integrity at the exposed cement region has not always been related to

the loss of clinical restorations [7,8,10,13-15]. The wear of resin cements at margins has been

reported in some studies which showed that these did not directly influence the survival rates of

some indirect restorations [7]. In contrast, comprehensive eight-year clinical evaluation of

cemented ceramic inlays using scanning electron microscope (SEM) analyses and 3D

morphological measurements showed a relationship to cement alterations and clinical outcome

[28,29]. Also, margins cracks of ceramic and enamel reported from prospective clinical trials

[13,16] have been listed as the main reasons for a decrease in marginal integrity. Some studies

used optical scanners [4,29,30] which allowed for more detailed evaluations and interpretations

of wear degradation and the processes occurring at surfaces of dental materials subjected to

wear.

Some recently introduced dental cements do not require pretreatment of the tooth surface,

hence proposed to reduce the technique sensitivity of placement procedures. The resin cements

are usually dual-cured systems including systems that can be light-cured and/or self-cured [17].

Studies of these systems mainly, have considered bond strength, marginal adaptation,

microleakage, physico-mechanical properties and adhesion [18,23] while, the wear of dental

cements have received minimal attention [36,37]. This is especially important with the cements

that have been recently introduced for clinical applications.

2

Another aspect related to the wear of cements when contacted by enamel which could be

clinically important in the future is the possibility that the US Environmental Protection Agency

may further limit the use of amalgam restorations due to mercury contamination related to

concerns about disposal plus some issues about toxicity [25]. Alternatives to amalgam such as

some polymeric dental composite systems have been shown to exhibit shrinkage and marginal

deterioration with time which could limit longevity [26]. Also, some composite systems and

techniques have demonstrated less than ideal wear resistance, particularly along tooth to

restoration occlusal areas [32,33], difficulty in generating proximal contours and contacts [34]

and some issues with postoperative sensitivity [35]. Thus ceramic inlays especially chairside

milled inlays that are cemented into teeth are an important consideration for the future [27]. This

focused literature survey using showed that available data on the wear of cements are limited and

relatively inconsistent [31,38] . Also, minimal emphasis has been given to the various methods

for curing the cements [39].

1.2 Objective

The central objective of this study was to evaluate the in vitro wear resistance of selected

commercially available cements. The assessment of wear for different types of the nine cements

as tested in vitro using human enamel cusps as an antagonist.

3

1.3 Hypotheses

1- The light cure mode of each dual cured resin cement has higher wear resistance than its

chemical cure mode.

2- Chemically cured dual cured resin cements wear resistance is comparable to each other

and have higher wear resistance than water-based controls.

1.4 Specific Aims

1. To compare the wear resistance of a variety of commercially available cements when

tested against intact human enamel cusps.

2. To evaluate the light cured versus the chemical cured modes of each dual cured cement.

3. To compare the chemically cured modes of the dual cured resin cements with the control

cements.

1.5 Data Analysis

In consideration of the parametric data developed in this project plus council from a

biostatistician resulted in a joint decision to utilize ANOVA and Tukey/Kramer post-hoc tests

(p≤0.05) for the statistical significance.

4

2.0 Materials and Methods

2.1 Materials

The following nine cements were selected to compare relative properties of wear:

Self-adhesive resins; Maxcem Elite (Kerr), RelyX Unicem 2 (3M ESPE), G-CEM LinkAce (GC

America), self-etch resins; PANAVIA SA (Kuraray), Multilink (Ivoclar Vivadent), total-etch

resin: Variolink II (Ivoclar Vivadent), resin modified glass ionomers; RelyX Luting Plus (3M

ESPE), GC FujiCEM 2 (GC America) and zinc-phosphate; Harvard Cement (Harvard). The

details about these nine cements and the machines/materials used for wear testing are provided in

Appendix 1.

2.2 Specimen preparation for wear testing

To prepare specimens, 3.5X magnification loupes and powder free gloves were utilized

throughout all of the procedures. A rectangular elastomeric impression material mold (length,

width and depth of 9,7 and 4mm) was used to mold prepare and standardize the size for the

specimens. The overall study design is shown schematically in (Fig.1A,B). A mold was filled

with the mixed cement and placed on a vibrator (low speed) to minimize specimen porosity (Fig.

2A). Eight specimens were made for each cement curing mode which included using an

incubator and an Elipar™ S10® curing light of circa 1200 mW/cm² illuminator (Fig. 2B). the

usable wavelength range of the Elipar S10 LED Curing Light is 430 – 480 nm with a center

5

wavelength of 455 ± 10 nm. The Spectrum of the Elipar S10 LED Curing Light matched the

absorption spectrum of the dual cured cements in this study.

Calibration of the S10 was done before each curing using a FieldMate®. The light curing

tip was placed directly on the sample with the operator wearing curing light protective glasses

(Zoom®) using a curing light clean sleeve on the curing light tip. Curing was done following the

manufacturers’ instructions (Appendix 1). After curing the top surface, the specimens were

removed from the mold, the surface (air inhibited layer) was removed with clean gauze, the sides

and bottom surfaces of the rectangular specimens were treated by light curing the same way as

the top surface. The self cured specimens were made in the dark inside an incubator. The

specimens were individually stored in sealed bags using moist napkins soaked with distilled

water away from each other at 37C for 24 hours in an incubator (Fig. 2C).

The specimens were subsequently embedded in brass holders (d=15mm, h=10mm) using

a 1:2 ratio of liquid to powder acrylic, with 1mm of the sample extending above the top of brass

holder (Figs. 3A-C). The upper face of the specimen was positioned parallel to the rim of the

brass holder for polishing using 600 and 1200-grit SiC abrasive papers under copious tap water.

The specimen surfaces were finished with an alumina slurry. The method included four minutes

for each sample, (one minute for each direction of the four sides of the rectangular sample) for

the 600 and 1200-grit papers and alumina slurry finishing on a polishing cloth. Polishing and

finishing was done on medium speed with light finger pressure. Each abrasive paper was

replaced after four samples and each of the four samples were prepared using a different

concentric circle position on the abrasive papers (Figs. 4A-C).

6

The final polishing direction along the abrasive papers for each sample was oriented

along the specimen width. This was done so that this polishing direction would be perpendicular

to the sliding path of the enamel antagonist within the wear machine. Before using the alumina

slurry polishing cloth, the cloth and supporting disc were cleaned by hand washing in running

water while held on the polishing stage during rotation on high speed. The final polishing step

was followed by rinsing with distilled water for five seconds, and each specimen was sonicated

in an ultrasonic machine (Fig. 4D) separately for five minutes using fresh distilled water for each

specimen at a temperature of 37C.

2.3 Premolar preparation for the stylus

Intact extracted premolar teeth were selected without visible defects and the enamel cusps

were standardized for wear testing using Brasseler Sintered Diamond S5030.11.050 bur,

preparation was done without abrading the cusp tip (Fig. 5A). A new bur was used for each

cement curing mode group (n=8) and each bur was cleaned ultrasonically in distilled water for

two minutes after each use. Cusps were prepared using a hand-piece set at 20,000 rpm for one

minute each, with regular intervals of dipping the cusp in distilled water for cleaning and to

prevent the cusp tip alteration by cutting or overheating (Fig. 5B).

The premolar teeth were subsequently reduced using a polisher-grinder with water

cooling from the root towards the standardized cusps, screws were embedded onto the sectioned

root side for mounting in the wear machine (Figs. 6 and 7) using acrylic. The cusps were

7

positioned so that the polished cusp tip was aligned parallel to the screw center. The cusps were

subsequently polished using pumice for one minute each with slow-speed hand-piece and a

rubber cup.

2.4 Wear Measurements

The second generation UAB wear machine (Fig. 6) (which includes a contact and slide

motion with fiberglass mounting cylinders to mimic the teeth movement within the

periodontium) was calibrated to a dead-load of 10N on each station. Load was applied to the

cement specimens through the enamel cusps. The testing media was a solution of glycerol to

water 1:3 (25% Glycerol) at a pH 6.3 and temperature of 24C. The media was renewed after each

cement curing mode group (n=8), the wear machine was programmed for 70 cycles/minute and

50,000 cycles.

After 50,000 cycles, the specimens were cleaned with dry paper towels, rinsed with

distilled water then subjected to light air drying. Specimens were examined visually and scanned

using a non-contact 3D surface profilometer and software (PROSCAN 2000®) (Fig.8) of 0.1%

accuracy to determine the wear depth and volume loss of each cement specimen (Figs. 9A,B).

8

A

9

Water based controls

Zinc-phosphate

8 chemical cured

RelyX Luting Plus

8 chemical cured

GC FujiCEM 2

8 chemical cured

B

Fig. 1: schematics showing (A) Water base controls study design, (B) Dual cured resin

cements study design.

10

Dual Cured

G-CEMLinkace

8 light cured

8 chemical cured

Panavia SA

8 light cured

8 chemical cured

RelyX Unicem 2

8 light cured

8 chemical cured

Maxcem Elite

8 light cured

8 chemical cured

Multilink Automix

8 light cured

8 chemical cured

Variolink II

8 light cured

8 chemical cured

A

B

11

C

Fig. 2: Images showing (A) molding, (B) light curing and (C) storing in incubator.

A

12

B

C

Fig. 3: Images showing embedding in UAB wear machine brass holder (A and B) and an

embedded sample (C).

A

13

B

C

14

D

Fig. 4: Images showing specimen (A) polishing, (B) finishing (C) polishing & finishing direction

and (D) ultrasonic cleaning.

15

A

B

16

Fig. 5: Images showing cusp (A) standardization and (B) polishing.

Fig. 6: Image showing UAB wear, second generation machine.

17

Fig. 7: Image showing specimen mounted in the wear test machine for testing.

18

Fig. 8: Image showing the Proscan 2000 non-contact surface profilometer.

19

A B

Fig. 9: Images of Proscan wear measurements showing (A) specimen surface before wear

cycles (upper) and after wear cycles (lower) and (B) superimposition the two images to calculate

wear volume and depth.

20

Fig. 10: Image showing grinding intact human premolars to the cusps

21

3.0 Results

3.1 Data Presentation

The relative comparisons of the cement loss, measured by depth and volume within the

wear zone are summarized in (Table 1) and shown graphically in [Figs 11-13]. The volume and

depth measurements presented in mm3 and µm respectively are listed for each specimen and

summarized as means with standard deviations (Table 1). The overall data are summarized for

the cement in (Table 2). The data shown in graphical format [Figs. 11-13] present comparison

between the systems as a function of materials type [Fig. 11] and mode of curing [Figs 12,13].

3.2 Dual cured cements

The dual cured cements, Maxcem Elite showed the lowest wear resistance while G-CEM

LinkAce showed the highest wear resistance to machine induced wear against enamel [Fig. 12].

A statistically significant difference (p≤0.05) was found between the dual cured cements

(Multilink, Variolink II, Maxcem Elite) which showed less wear resistance than (G-CEM

LinkAce, PANAVIA SA, RelyX Unicem 2) [Fig. 12].

3.3 Curing modes of each dual cured cement

There was no significant difference (p>0.05) between the resin cements as a function of

curing mode of each cement except for Maxcem Elite which exhibited a significant difference

(p=0.01) when comparing the light cured and chemically cured modes [Fig. 13].

22

3.4 Cements types

All the cements in this study showed a significant difference (p≤0.05) when compared to the

control zinc phosphate [Fig. 10]. The dual cured resin cements also showed a significant

difference (p≤0.05) when compared to the resin modified glass ionomer chemical cured cements

(FujiCEM 2 and RelyX Luting Plus) [Fig. 10].

23

Table 1: Volume and depth wear data

PANAVIA SA (Kuraray) G-CEM LinkAce (GC America)

Light cured Non-light cured Light cured Non-light cured

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

A 0.005 0.620 0.011 3.070 0.006 5.980 0.024 39.780

B 0.005 1.230 0.006 4.280 0.009 16.950 0.006 10.880

C 0.009 1.240 0.038 15.380 0.006 12.810 0.007 12.330

D 0.040 13.780 0.011 1.430 0.005 11.470 0.017 26.740

E 0.007 1.230 0.014 3.700 0.005 15.600 0.011 22.150

F 0.005 0.900 0.008 1.130 0.009 16.180 0.007 22.250

G - - 0.016 3.450 0.006 12.090 0.009 13.070

H 0.034 4.270 0.040 10.560 0.006 13.070 0.007 16.880

Mea

n

0.015 3.324 0.018 5.375 0.006 13.018 0.011 20.510

SD 0.015 4.770 0.013 4.979 0.001 3.483 0.006 9.591

RelyX Unicem 2 (3M ESPE) Variolink II (Ivoclar Vivadent)

Light cured Non-light cured Light cured Non-light cured

24

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

A 0.012 27.790 0.016 51.790 0.010 17.260 0.014 59.690

B 0.021 61.750 0.023 58.780 0.032 36.400 0.022 72.380

C 0.013 28.110 0.006 17.470 0.024 27.090 0.020 34.460

D 0.008 24.500 0.005 11.140 0.013 23.620 0.034 146.97

0

E 0.037 76.520 0.011 23.440 0.048 95.800 0.028 33.940

F 0.014 53.550 0.008 26.600 0.048 54.490 0.032 45.380

G 0.031 74.300 0.007 12.940 0.007 13.630 0.066 80.230

H 0.008 14.010 0.021 52.740 0.040 56.920 0.029 39.240

Mea

n

0.018 45.066 0.012 31.862 0.027 40.650 0.030 64.036

SD 0.010 24.400 0.007 19.459 0.016 27.430 0.015 37.743

Multilink (Ivoclar Vivadent) Maxcem Elite (Kerr)

Light cured Non-light cured Light cured Non-light cured

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

A 0.048 62.500 0.065 106.340 0.038 73.900 0.073 122.39

0

B 0.029 47.780 0.041 79.250 0.019 56.320 0.059 99.060

C 0.038 61.340 - - 0.058 102.19 0.043 58.720

25

0

D 0.043 61.010 0.050 75.140 0.073 94.850 0.075 129.17

0

E 0.020 45.210 0.048 110.650 0.034 72.480 0.045 59.450

F 0.020 44.560 0.026 63.270 0.017 29.310 0.089 160.55

0

G 0.019 52.330 0.035 87.340 0.027 37.840 - -

H 0.062 82.700 0.021 70.010 0.063 86.550 0.109 108.09

0

Mea

n

0.034 57.178 0.040 84.571 0.041 70.305 0.070 105.34

7

SD 0.015 12.682 0.015 18.003 0.021 25.801 0.023 37.042

FujiCEM 2 (GC

America)

RelyX Luting Plus

(3M ESPE)

Zinc phosphate (Harvard)

Self cured Self cured Self cured

Volume

(mm3)

Depth

(µ)

Volume

(mm3)

Depth

(µ)

Volume (mm3) Depth (µ)

A 0.235 56.980 0.160 380680 0.567 100.320

B 0.154 32.640 0.065 11.480 0.523 90.680

C 0.238 38.420 0.379 75.000 1.555 156.040

26

D 0.260 32.410 0.307 73.600 0.294 37.920

E 0.244 28.180 0.181 37.260 1.347 185.590

F 0.403 61.910 0.623 77.520 1.196 124.680

G 0.306 41.850 0.140 47.930 0.389 63.680

H 0.170 23.900 0.500 97.530 0.637 103.440

Mea

n

0.251 39.536 0.294 57.375 0.813 107.793

SD 0.078 13.539 0.194 28.136 0.479 47.601

Table 2: Wear volume mean and standard deviation

27

28

Fig. 11: Wear volume (mm3) of zinc-phosphate, self-cured RMGIs and both curing modes of the

dual cured dental cements

29

Fig. 12: Wear volume (mm3) magnitude for the dual cured cements

30

Fig. 13: Wear volume magnitude for both curing modes of the dual cured cements

31

4.0 Discussion

Overall this study showed that zinc-phosphate cement was the least resistance to wear

within this simulation test, followed by the resin modified glass ionomers while the resin

cements had the highest resistance to wear which correlate with results in [31]. The previous

study of Kawai K, Isenberg BP, Leinfelder KF showed that the microfilled cement exhibited less

wear than hybrid cements. The smoother microfilled surface was shown to provide a greater

resistance to wear. The study results also showed a linear relationship between horizontal gap

and vertical cement dimensions due to wear loss. The greater the interfacial gap, the greater the

amount of wear [41].

Dental cements polymerization is started by light and/or by a chemical reaction of the

initiator system, the setting reaction is a radical polymerization during which the single monomer

molecules are chemically cross-linked to form a three-dimensional polymer network.

Simultaneously, neutralization reactions take place, which are important for the long-term

stability of the set cement material. There is a linear correlation between the degree of

conversion and the plasticization of material [44], higher degree of conversion results in

increased cross-linkage density of the polymeric matrix which is a major factor influencing the

bulk physical properties. In general, the higher the degree of conversion, the greater the

mechanical strength [45].

32

The final degree of conversion depends on the chemical structure of the cement and the

polymerization conditions i.e., atmosphere, temperature, light intensity and photo-initiator

concentration [46]. Also, The biocompatibility of a cement is related to its degree of conversion

and complaints of sensitivity may be due to incomplete polymerization of the cement [47,48]

5.0 Summary and Conclusions

Eight samples were made for each curing mode of the nine cements using a mold on a

vibrator then they were stored in the incubator for 24 hours to complete the polymerization, these

specimens were mounted on the wear machine brass holders using acrylic then polished on a

rotational machine and ultrasonically cleaned afterward in distilled water. Intact human

premolars were ground to the cusps, the cusp tips were standardized using a bur and polished

with pumice then mounted with acrylic on UAB second generation wear machine screws to act

as antagonists in 25% glycerol media against the standardized dental cements specimens for

50,000 cycles, 10N dead load and 75 cycles/minute. Proscan 2000 was used after the cycles to

determine the wear volume and depth. 2-way ANOVA, separate 1-wayANOVA and

Tukey/Kramer post-hoc test (p≤0.05) was used for statistical analysis, the first for the two curing

modes of the dual cured resin cements and the second for the chemical cured modes of all the

cements in this study.

33

The only dual cured cement in this investigation that showed a difference in its curing

modes was Maxcem Elite. Resin cements showed higher wear resistance in this study than glass

ionomer cements which showed higher wear resistance than zinc phosphate. There was a

significant difference in two groups of the dual cured cements of this study. Thus the

investigation hypotheses were rejected within the limitations of this project.

6.0 Some Limitations

Constant Media (pH, viscosity, amount & temperature).

Constant load force and force direction.

The media was not circulated and filtered while the wear testing in function

7.0 Some suggestions for future research

Conducting the wear testing on a machine that has the ability to circulate and filter the

media.

Test the materials with standardized changes in temperature, pH, media, media viscosity

and media circulating speed.

34

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40

Appendix 1

Material Manufacturer Lot # Expiry

Date

Self Cured Light

Cured

G-CEM

LinkAce

GC America

(Alsip, IL)

1205244 Not listed 4min 20sec

RelyX Unicem

2 Automix

3M ESPE (St.

Paul, MN)

Box 466325

Tube and

package

465917

Box,

package and

tube 471886

07-2013

09-2013

20sec 6min

Maxcem Elite Kerr (Orange,

CA)

Box 4568232

Tube

4579155

10-2013 4min 10sec

RelyX Luting

Plus

3M ESPE (St.

Paul, MN)

Box

N442148

Tube and

package

08-2014 5min

41

N436375

GC FujiCEM 2 GC America

(Alsip, IL)

Box and

Tube

1112141

12-2013 5min

PANAVIA SA Kuraray

America (New

York, NY)

Box

0065AAA

Tube

0065AA

Box

0067ABA

Tube

0067AB

06-2014

07-2014

5min 5sec

Harvard

ZincPhosphate

Cement

Harvard Dental

(Hoppegarten

Germany)

Powder Box

and Bottle

1111108

Liquid Box

and Bottle

1101111

06-2014

04-2014

1.5g : 1ml

90sec

mixing

time

5min

setting

time after

mixing

Multilink Ivoclar R36511 09-2014 4min 30sec

42

Automix Vivadent

(Amherst, NY)

Variolink II Ivoclar

Vivadent

(Amherst, NY)

Catalyst

Yellow

(210,A3)

High

Viscosity

R43895

Base Yellow

(210/A3)

Box R32649

Tube

R25428

R34712

10-2014

12-2013

08-2014

08-2014

1:1 ratio

10sec

mixing

time

3.5min

10sec

Genie Heavy

PVS

Sultan

Healthcare

(Hackensack,

NJ)

040925856 04-2009

Grinder Wehmer

43

Corporation

(Lombard, IL)

Elipar™ S10 3M ESPE (St.

Paul, MN)

FieldMate Coherent

(Santa Clara,

CA)

Cross Linked

Flash Acrylic

(Chicago, IL)

SiC abrasive

papers and

polishing cloth

Mark V

Laboratory

(East Granby,

CT)

Rotational

polishing

device No:

233-0-1997

Buhler (Lake

Bluff, IL)

.05µ Gamma

Alumina slurry

No:40-6301-

080

Buhler (Lake

Bluff, IL)

Branson 1200 Branson

Ultrasonics

44

( Danbury, CT)

Glycerol Acros Organics

(Fair Lawn,

NJ)

SensION pH

meter

Hach Company

(Loveland, Co)

Thermometer Control

Company

(Friendswood,

TX)

PROSCAN

2000

Scantron

Industrial

Products Ltd.

(Taunton,

England)

NSK Z500

hand-piece and

Sintered

Diamond

S5030.11.050

bur

Brasseler

(Savannah,

GA)

45