Dimensional accuracy of alginate impression

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Vol. 21, No. 1, January 2014

Introduction

Impression materials are used to register orreproduce the form and relation of the teeth andthe surrounding oral tissues.

In Prosthodontics,

impression material and prosthesis that have beenexposed to infected saliva and blood pose a main

source of cross-contamination and additionalproblems in controlling cross-infection betweendental office and laboratories (Powell et al.,1990; Samaranayake et al., 1991) .

In view of the

infectious carrier state of a signicant proportionof the population and current trends in cross-infection control, disinfection of the impressionsis seriously recommended by the AmericanDental Association (ADA) and the Centers forDisease Control to prevent possible transmissionof infectious diseases.

Despite the necessity of

additional control procedures and disinfection

during making and handling of dental impressionsimmediately after removal, it should be ensuredthat such procedures do not alter the dimensionalaccuracy of dental impressions. To issue guidelinesregarding impression disinfection, the ADAdetermined the antimicrobial agents to be usedfor different impression materials and the time,dilution, and temperature needed for the optimalperformance of each agent 3. The disinfectingprocess should be proper, but should not have anadverse effect on the dimensional stability or thesurface detail of the impression. The purpose of this

study was to evaluate the effect of the disinfectionby spray or immersion on dimensional accuracy oftwo currently available, commonly used alginateimpression materials in Myanmar.

Materials and methods

Alginate impression materials, Cavex (GCCorporation, Tokyo, Japan) and Phase (BadiaPolesine (Rovigo)- Italy) were used. A custommade metal die made of stainless steel with threereference grooves and partially edentulous plasticmodel were used to make impressions. A rigidperforated acrylic tray more than 3 mm in thicknessfor metal die and perforated plastic tray for partiallyedentulous plastic model were used to load theimpression materials. All the impressions weremixed according to manufacturers instructionsin air conditioned room (25+1) C. Impressionwas taken immediately after the material wascompletely mixed. The tray was held in situ untilsetting of impression material was completeand the tray was removed without bending.Impressions were then poured up in dental stone.

Two measurements for each metal die cast weredone by measuring width and depth of grooveon the surface of the die. The linear dimensionalchanges were measured on the metal die cast by

using an electronic digital caliper & USB microscopewith 40 times magnication. For measurements ofdepth and width of lines, photographs were takenwith USB microscope and saved in the personalcomputer. Then the measurements were done byImage J software (NIH, USA). Four measurementsfor partially edentulous plastic model were done by

measuring inter-canine line, 2 canine-molar linesand inter-molar line. These lines were measuredby using electronic digital caliper. All measureddata were recorded in spreadsheet program(Microsoft Excel, Version 2007) and analyzed byusing Paired Samples T test in SPSS (StatisticalPackage for Social Science) statistical software. The values of change between measurement ofreference points recorded from sample surfaceand measurements directly taken from test blocksurface were calculated and expressed as a linearchange in mm. Positive values indicated that

measurements obtained from sample surface werelarger than the measurements directly obtainedfrom test block surface. Negative values indicatedthat measurements obtained from sample surfacewere smaller than the measurements directlyobtained from test block surface.

RESULTS

Figure (1) USB microscope (PC Camera PAC 7302)

(A) (B)Figure (2) Photomicrographs of (A) test block and(B) cast surface obtained with USB microscopeshowing the grooved lines

(A) (B)Figure (3) Photomicrographs of (A) test block and(B) cast surface obtained with USB microscopeshowing the grooved depth


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M yanmar Dental Journal

Figure (4) The amount of change in the lines widthof stone cast. Values are shown as linear change indimension (mm) and error bars denote standarddeviation.(* p


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Figure (11) The amount of change in Left Canine-molar (BD) width of stone cast. Values are shown aslinear change in dimension (mm) and error bars denote standard deviation. (* p


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M yanmar Dental Journal

Changes were also detected in inter-caninedistance on model after spray disinfection andleft canine-molar distance after immersiondisinfection when Cavex and Phase impressionmaterials are compared (p


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References

ADA Council on Scientic Affairs and ADACouncil on Dental Practice. Infection controlrecommendations for the dental office and thedental laboratory. J Am Dent Assoc 1996; 127:672-80.

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Dimensional accuracy of alginate impression

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