Mechanical inlay/onlay Anne Peutzfeldt, Erik Asmussen,

properties technique Dentist, DrOdont,

of three composite

CandOdont,* CandScientb

resins for the

and

Royal Dental College, Copenhagen, Denmark The present study measured the diametral compressive strength, flexural strength, and modulus of elasticity of composite resins used in inlay/onlay systems. The effect of additional curing also was determined. SR-Isosit material had the highest diametral compressive strength, and SR-Isosit-Dentin material had the lowest flexural strength. The SR-Isosit composite resins had lowest elastic modulus and Estilux posterior C VS resin the highest. A negative correlation was found between diametral compressive strength and elastic modulus of the materials. It was concluded that the additional curing of Brilliant resin did not result in improved mechanical properties. For Estilux resin, additional curing increased flexural strength and modulus of elasticity. (J PROSTHET DENT 1991;66:322-4.)

C

omposite resins do not yet constitute a perfect replacement for amalgam. In an attempt to improve properties, the so-called inlay/onlay technique, including extraoral polymerization of the composite resin, has been introduced.lp 2 Two of three proprietary inlaylonlay systems are based on photocuring composite resins, which after initial cure with a polymerization unit are transferred to a light or light/heat curing oven. The third system involves hydrhpneumatic heat polymerization of the restorative resin. After extraoral polymerization, the inlay/ onlay is cemented with a self-curing as well as photocuring resin cement. The main aims of the inlay/onlay technique are to improve mechanical properties by reduction of the quantity of double bonds remaining in the polymer and to minimize marginal gap formation caused by polymerization shrinkage of the composite resins. The present study (1) measured the diametral compressive strength, flexural strength, and modulus of elasticity of composite resins used in three inlay/onlay systems and (2) determined the influence of extraoral polymerization on these properties.

MATERIAL

AND METHODS

The materials investigated are listed in Table I. Six specimens (3 mm X 6 mm) of each material were made for testing diametral compressive strength and six specimens (2 mm X 2 mm X 10 mm) for testing flexural strength and elastic modulus. After application in brass molds of the

This investigation was supported by grant 12-8227 from the Danish Medical Research Council. BResearch Associate, Department of Dental Materials and Technology. bProfessor, Department of Dental Materials and Technology. 10/l/28107

322

above dimensions, the materials were cured as follows. Brilliant resin. The specimens were covered with transparent plastic film on both sides and polymerized with a Translux CL unit (Kulzer & Co,) for 60 seconds on each side of the specimens. The specimens were separated from the molds and additionally cured in a D.I. 500 light/heat curing oven (Coltene AG) for 7 minutes. Estiluxposterior C VS resin. The specimens covered with matrices were polymerized for 20 seconds on both sides, separated from the molds, and additionally cured in a Dentacolor XS photocure unit (Kulzer & Co.) for 6 minutes. SR-Isosit resin. One side of the specimens was covered with tinfoil, the other with a thin layer of SR-IsositN-Fluid agent (Ivoclar AG). The specimens were cured in an Ivomat IP3 hydropneumatic pressure polymerization apparatus (Ivoclar AG) for 10 minutes at approximately six times atmospheric pressure and 120’ C and were then separated from the molds. After polymerization, the specimens were stored in water at 37’ C for 1 week. The specimens were ground on carborundum paper No. 1000 and subjected to testing in a Universal Testing machine (Instron Ltd., Buckinghamshire, England). The diametral compressive strength was determined as described in American Dental Association specification No. 27 for direct filling resins. A crosshead speed of 1 mm/min was used to determine flexural strength and modulus of elasticity. The flexural strength was calculated by means of the equation

where F is the maximum force exerted on the specimen, 1 (1 = 6 mm) is the distance between the supports, b the breadth, and d the depth of the specimen.

After calibration with chemically pure Cu with a modulus

SEPTEMBER1991

VOLUME66

NUMBER3

MECHANICAL

Table

-

PROPECTIBG

OF COMFOSITE

RESINS

I. List of m,aterials inves,tigated Hrand

Shade

Table II. Diametral compressive value and standard deviation -

Material

of elasticity determined

strength,

flexural

Diametral compressive strength (MPa)

of 12!1.8 gPa,3 the modulus of elasticity by means of the following equation -X-

1”

,l”xhx4

strength,

was

F MPa h

where h is cleflection

The statistical treatmf:nt of the results involved analyses of variance (ANOVA), hewman-Keuls’ multiple range tests. and regression analyscas.4

RmESULTS The resu1t.s of the investigation are shown in Table II. ANOVA found the seven values of each of the three mechanical properties to differ with statistical significance @ < 0.01). The results of the Newman-Keuls tests then performed are indicated in Table II. With respect, to diametral ‘2ompressive strength, SRIsosit resin had higher strength than the other composite resins. The extra Cure in respective ovens did not cause an increase in d.iametral compressive strength. As for flexural strength, a higher strength was found after the additional curing process of Estilux posterior C VS resin. Without additional curing, this series together with that of SR-Isosit-IDentin resin resulted in the lowest flexural strengths. The SR-Isosit composite resins had the lowest moduli of elasticity and Estilux resin the highest.. Only with the latter material was an increase observed when the tempering procedure was carried out. Covering the Estilux resin

THE

JOURNAL

OF PROSTHETIC

No.

and modulus of elasticity

of ertormrd between the values of the three met:h:,rllcai ij:,)perties. only one revealed a coefficient of correiwt i.:l: -:6:ni!icantiy different from zero. Thus, a negatk.61 q+lrrcbla:i,~: was found between diametral compressi\-e 51t‘en:!! 11a!l:i modulus of elasticity ir -0.81; p < O.O.ii.

DISCUSSION Additional light and heat curing h I’ ht-r>!l reported t.o reduce the quantity cbi rernaii:l+ &):ible bonds.’ Asmussen” found tensile strengt 11 ! jj i::;rcase with a decreasing quantity of remaining d(aut,le hinds. Further, Kullmann6 measured 108” (1 in the Fi4liiar!t 11.1. 500 unit and 135” C in the Dentac.olor. Xt; \I*:‘! lttc : T minutes of functioning, and Bausch iat. al.: i’c~:l~~tic!i;irri t rai c’ompressive strength to improve when tht, t*.~~)~!~ture was elevated during curing of compcjsite :Y. 11.. \‘~‘!:h this background, it is surprising that no erfrc: i :I lditional polymerization on diametral cclmpresii\ + ..’ 1:c:i: I! was detected in the present investigation. iXo 4m:1:. 1~1) ;.nation can be offered for these discrepancit-, Thus, ail values of diarrietral comi>:‘.+yi uk 71reugth measured on the hybrid composite resin+ 1’31iili.iilt and Estilux posterior C L’S) belong in rhe lower ~r?!i 11I be s

onlay technique.

The present study measured the diametral compressive strength, flexural strength, and modulus of elasticity of composite resins used in inlay/onlay sy...
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