d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 1570–1573

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In vitro study of edge-strength of provisional polymer-basedcrown and fixed partial denture materials

Sung-Hun Kima,∗, David C. Wattsb

a Department of Prosthodontics and Dental Research Institute, School of Dentistry, Seoul National University,275-1 Yeongeon-dong, Jongno-gu, Seoul 110-768, Republic of Koreab Biomaterials Research Group, University of Manchester School of Dentistry and Photon Science Institute, UK

a r t i c l e i n f o

Article history:

Received 25 May 2007

Received in revised form 1 June 2007

Accepted 1 June 2007

Keywords:

Edge-strength

Fracture

Polymerization

Polymer-based provisional crown

Fixed partial denture materials

a b s t r a c t

Objectives. To evaluate in vitro the edge-strength of polymer-based provisional crown and

fixed partial denture materials at increasing distances from an edge.

Methods. Three dimethacrylate-based provisional crown and fixed partial denture materials

(Protemp 3 Garant, Luxatemp, and fast set Temphase) and one monomethacrylate-based

one (Trim) were selected. Seven disk-shaped specimens of 12 mm in diameter and 2.5 mm

in thickness for each material were fabricated and stored at 37 ◦C and 80% relative humidity

for 1 month. The edge-strength was measured by using a CK 10 testing machine at a distance

of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm from the edge of the specimen. All experiments were

carried out in triplicate at each distance at 23 ± 1 ◦C. The data were statistically analyzed

using one-way ANOVA and the multiple comparison Scheffe test at the significance level of

0.05.

Results. Trim showed severe deformation without chipping during loading at all distances.

Protemp 3 Garant showed indentation at over 0.8 mm from the edge, and for Luxatemp and

fast set Temphase over 0.6 mm from the edge without chipping. At 0.5 mm from the edge,

the highest values (2073.7 N) were displayed by Protemp 3 Garant, approximately three times

those of fast set Temphase (767.3 N) and Luxatemp (697.0 N) (p < 0.05). The strengths of fast

set Temphase and Luxatemp were not significantly different (p > 0.05). Linear regression

between the distance from the edge to 0.7 mm and strength values of Protemp 3 Garant

produced a correlation coefficient, R = 0.99.

Significance. The dimethacrylate-based provisional materials tested were stronger in edge-

strength than the monomethacrylate-based one which showed severe deformation without

fracture.

lsevi

fracture. Although restorations should be properly designed

© 2007 Published by E

1. Introduction

A satisfactory provisional crown and fixed partial denture

can be fabricated from polymer-based materials which fulfillmany requirements for provisional restorations, especiallyesthetics. However, failure of the provisional restoration may

∗ Corresponding author. Tel.: +82 2 2072 2664; fax: +82 2 2072 3860.E-mail address: ksh1250@snu.ac.kr (S.-H. Kim).

0109-5641/$ – see front matter © 2007 Published by Elsevier Ltd on behdoi:10.1016/j.dental.2007.06.023

er Ltd on behalf of Academy of Dental Materials. All rights reserved.

occur if it is subjected to heavy masticatory loads [1,2]. Oneof the common failure modes of the provisional restoration is

to avoid it, they may nevertheless fail in a catastrophic way byfracture. This may lead to severe economic loss and patientdiscomfort. Thus, the mechanical strength properties of

alf of Academy of Dental Materials. All rights reserved.

3 ( 2 0 0 7 ) 1570–1573 1571

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Fig. 1 – The CK 10 testing machine used to measure theedge-strength.

Fig. 2 – Dimension of the disk-shaped specimen for

d e n t a l m a t e r i a l s 2

rovisional materials are an important factor and should beonsidered for the clinical success of provisional restorations.

Edge-strength, which means the resistance of thin materialargins to fracture [3,4], can be considered one of the crit-

cal indicators for the success of provisional restorations ashigh edge-strength is necessary to tolerate multidirectionalasticatory forces and to show an excellent marginal stabil-

ty in clinical practice. Although the mechanical properties ofolymer-based crown and fixed partial denture materials haveeen reported previously by many researchers in terms of flex-ral strength, hardness and fracture toughness [5–12], therere no papers concerning its edge-strength.

The objectives of this study were (i) to measure thedge-strength of polymer-based provisional crown and fixedartial denture materials, (ii) to investigate possible corre-

ations between the forces needed to fracture specimensnd increasing distances from the edge, and (iii) to comparehe edge-strength between monomethacrylate-based andimethacrylate-based materials. The null hypothesis to beested was that there was no difference in the edge-strengthetween monomethacrylate-based and dimethacrylate-basedaterials.

. Materials and methods

our polymer-based provisional materials used in this studyre presented in Table 1. Disk-shaped specimens wererepared in a polytetrafluoroethylene (PTFE) mould. Theimensions of each specimen were 12 mm in diameter and.5 mm in thickness. Protemp 3 Garant, Luxatemp and fastet Temphase were injected into the mould with automixingun applicators, while Trim was mixed with a clean plasticpatula for 30 s according to manufacturer’s instructions andmmediately placed into the mould. A glass plate and a plas-ic strip were placed onto the mould to prevent the inhibitionf polymerization by oxygen and to create flat end surfaces,nd then hand pressure was applied. The specimens wereeft to polymerize for 30 min at 23 ± 1 ◦C. After setting, thepecimen was removed gently from the mould, and storedt 37 ◦C and 80% relative humidity (RH) for 1 month beforeechanical testing. Seven specimens for each material were

abricated.The edge-strength was measured using a CK 10 testing

achine (Engineering Systems, Nottingham, UK) (Fig. 1). Aolycrystalline 120◦ Rockwell C diamond indenter and adap-or were mounted into the load cell. A specimen was firmly

ounted on the X–Y table base, and the crosshead was movednto its test position. The edge-strength was determined bypplying a point load at different distances from the edge ofhe specimen (Fig. 2). The distances measured from the edge

Table 1 – The polymer-based provisional materials investigated

Material Lotno. Shade

Protemp 3 Garant 646909001 A3 Dimefast set Temphase 4060 A3.5 DimeLuxatemp 120337 A2 DimeTrim 921900 Dark Mono

edge-strength. Ø = 12 mm, T = 2.5 mm, D = distance from theedge, P = load.

of the specimen were as follows: (1) 0.4 mm, (2) 0.5 mm, (3)0.6 mm, (4) 0.7 mm, (5) 0.8 mm, (6) 0.9 mm, and (7) 1.0 mm.

The load was increased to a value that produced chipping orsimilar fracture of the edge, which was detected by an incorpo-rated acoustic-emission sensor [4]. When chipping occurred,the peak force (N) displayed on the LCD was recorded at arange of distances (mm) from the edge. The plot of force ver-sus distance was examined. All experiments were carried out

in triplicate at each distance at 23 ± 1 ◦C. The crosshead speedwas 1 mm/min.

The mean values and standard deviations of the resultswere computed. The data were statistically analyzed using

Characteristics Manufacturer

thacrylate-based material 3M-ESPE, St. Paul, MN, USAthacrylate-based material Kerr, Orange, CA, USAthacrylate-based material DMG, Hamburg, Germanymethacrylate-based material Bosworth, Skokie, IL, USA

1572 d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 1570–1573

Table 2 – Mean (standard deviation) of failure strength(N) with edge-distance by the polymer-based provisionalmaterials investigated

Shaded cell denotes both indentation and crack of the materials.Superscripts (a–n) show no significant differences at P > 0.05.

one-way ANOVA and the multiple comparison Scheffe test todetermine whether statistically significant differences existedamong the materials. For all statistical analyzes, a significancelevel of 0.05 was used (SPSS, Version 10.1, SPSS Inc., Chicago,IL, USA).

3. Results

Fracture-forces of each material and the means and standarddeviations of all materials are presented in Table 2 and showngraphically in Fig. 3. The data are plotted in Fig. 4. The valueobtained at 0.5 mm distance can be defined as the specificedge-strength value [4].

Trim showed severe deformation without chipping duringloading at all distances. Thus, the data for Trim were not pre-sented. Protemp 3 Garant showed indentation and crack atover 0.8 mm from the edge, and for Luxatemp and fast setTemphase over 0.6 mm from the edge without chipping.

At 0.5 mm from the edge, the highest values (2073.7 N) weredisplayed by Protemp 3 Garant, approximately three timesthose of fast set Temphase (767.3 N) and Luxatemp (697.0 N)(p < 0.05). The strengths of fast set Temphase and Luxatemp

were not significantly different (p > 0.05).

The highest value was displayed by Protemp 3 Garant at0.7 mm from the edge, while the lowest value was displayed

Fig. 3 – Edge failure strength of provisional materialsinvestigated at different distance (mm) from the edge.

Fig. 4 – Regression of edge failure strength of provisionalmaterials investigated.

by Luxatemp at 0.4 mm. In fast set Temphase and Luxatemp,the value at 0.5 mm was not significantly different from thatat 0.4 mm (p > 0.05). All values of Protemp 3 Garant were signif-icantly higher than those of fast set Temphase and Luxatemp(p < 0.05), but fast set Temphase and Luxatemp did not showany significant difference (p > 0.05).

A correlation between the distance from the edge to 0.7 mmand the strength values of Protemp 3 Garant produced acorrelation coefficient, r = 0.99. This indicates that the ‘edge-fracture strength’ increases progressively as the distance fromthe edge increased (Fig. 4).

4. Discussion

Distances of 0.4–1.0 mm away from the edge of the specimenwere chosen as the load fracture resistance points for com-parison among the materials tested in this study, due to thefact that these distances from the edge could be more clini-cally relevant to marginal breakdown of the restorations [4].Trim did not fail by brittle fracture. Following the initial elasticdeformation, Trim suffered considerable lateral deformationat the areas of loading. On the contrary, the other three mate-rials, Protemp 3 Garant, fast set Temphase and Luxatemp,showed chipping at some distance. This can be explained by itsmolecular structure of the polymer. Chain scission or local seg-mental relaxation-movement can occur during loading andfracture of the materials. The extent to which it takes placedepends upon the structure and morphology of the polymermolecules. The dimethacrylate-based materials have a threedimensional network structure which offers greater resistanceto mechanical forces, while the monomethacrylate-basedmaterial allows movement of the polymer molecules withrelative ease under the mechanical forces. In dimethacrylate-based provisional materials, the highest edge-strength wasshown by Protemp 3 Garant, and considerable differences inedge-strength were recorded between Protemp 3 Garant andfast set Temphase, and Protemp 3 Garant and Luxatemp. The

different values between the materials shown in this studymay be explained by different composition of the material, dif-ferent filler type, different filler size, different filler distributionand different quantity of remaining double bonds, etc. [12,13].

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hus, the null hypothesis that there was no difference in thedge-strength between the monomethacrylate-based and theimethacrylate-based provisional materials can be rejected.

Fig. 4 shows that the lines drawn through the points areased on a linear regression analysis. All slopes are largerhan zero, and show positive correlation. This means thathe edge-fracture strength increased uniformly with increas-ng distance from the edge. Although Luxatemp and fast setemphase showed indentation and crack rather than chippingrom the distance of 0.6 mm, the strengths also correlated tohe distance.

The edge-strength of a polymer-based provisional materialould be an important factor to be taken into account in select-ng suitable materials for clinical use. These findings show thathe monomethacrylate-based provisional restorations woulde expected to be more susceptible to mechanical failurend less durable than the dimethacrylate-based provisionalestorations when they are exposed to heavy masticatorytresses.

. Conclusion

ithin the limitation of this study, the following conclusionsere drawn.

1) The edge-fracture strength increased as the distance fromthe edge increased. The distance from the edge overwhich chipping occurred varied with materials. The valueobtained at 0.5 mm can be accepted as a single-value Edge-strength parameter [4].

2) The dimethacrylate-based provisional materials (Protemp3 Garant, fast set Temphase and Luxatemp) tested werestronger in edge-strength than the monomethacrylate-based one (Trim) which showed severe deformation

without fracture under the conditions of this test.

3) The edge-strength of Protemp 3 Garant was significantlygreater than those of fast set Temphase and Luxatemp bya factor of 3.

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