5 materials & methords

7/30/2019 5 Materials & Methords

http://slidepdf.com/reader/full/5-materials-methords 1/7

Materials & Methodology

Page

An in-vitro study was conducted in the Department of Prosthodontics, St. Joseph

Dental College, Eluru, to evaluate the dimensional stability and accuracy of polyether,

vinyl polysiloxane and Vinylsiloxanether impression materials in dry condition and when

immersed in different disinfectant solutions. The dimensional stability and accuracy were

measured by using a measuring microscope available at C.R. Reddy Engineering College,

Eluru, Andhra Pradesh.

I. Sample preparation (making impressions)

a. Materials used:

1.

Medium body polyether impression material (Impregum penta soft; Lot no –

31730;3M; Germany)

2. Medium body VSE impression material (Identium; Lot no-37402/1010;

Kettenbach; Germany).

3. Medium body VPS impression material (Affinis; System 360; Art # 6480;

Coltene- Whaledent; Switzerland)

b. Disinfectant solutions used:

1. 2% Gluteraldehyde solution – (Raman & Weil India, pvt ltd, batch number-A9156)

2.1% Sodium hypo chlorite solution-(SURNI labs, Vadodara, India,

batch number- 2F01-JAN 2012)

c. Instruments used:

1. Stainless steel die (ADA No. 19)

2. Auto-mixing device (Pentamix)

3. Catridges for each material

4. Glass plate

5. Plastic discs

6. C clamp

7. Measuring microscope

8. Solution jars

24




5

Methodology

Standardized die preparation:

Standardized stainless steel die (similar to that described in ADA Specification

No. 19) scored with three horizontal lines was used for impression making. The

horizontal lines were named A, B and C. The width of each horizontal line was 0.016mm.

Two cross points at the intersection of the vertical lines with the horizontal line B were

labeled as X and Y and served as the beginning and end points of measurements for

dimensional accuracy.

The die consisted of three components: the test block, the mold and the metal

riser.

Before impression making, the die was ultrasonically cleaned to remove any

residue and allowed to air dry. Care was taken to avoid contamination of the surface of

the die before making impressions.

Impression procedure:

Impressions were made using an auto-mixing device and pre-packed cartridges of

the impression material. Latex gloves were not worn during material application because

of their potential inhibitory effect on polymerization of VPS materials. The cartridge was

used in compliance with manufacturer’s recommendations to ensure proper dispensing

ratios.

Impressions were made under dry conditions, after placing the mold onto the test

block to contain the material and to ensure a uniform thickness of 3 mm of impression.

The material was loaded into mixing tips from automixing device and applied to the lined

areas of the die.




Page 26

A plastic disc was placed on the impression and a glass plate was pressed over

this impression so that the excess material extruded out. Plastic disc served to hold and

support the impression for further procedures.

The plate and die were held together using a Clamp. The clamp is tightened until

the metal ring is completely exposed and seen through the plastic disc supporting the

impression disc thus standardizing the pressure used for making the impression.

Recovery of impression from die:

The impressions were allowed to set three minutes longer than the manufacturer’s

recommended minimal removal time (3-8 minutes), as indicated in ADA Specification 19

for laboratory testing. The mold and test block were then separated. The impression was

pressed out of the mold using the riser.

The above procedure was carried out for thirty samples for each material.

Grouping of Samples:

Ten impressions of each material were made under each of the three conditions:

dry, immersion in 2% gluteraldehyde and immersion in 1% sodium hypochlorite solution.

Group 1- (PE)

Subgroup A1 - 10 Samples - Dry Conditions

Subgroup A2 - 10 Samples – immersed in 2% gluteraldehyde solution

Subgroup A3 - 10 Samples – immersed in 1% sodium hypochlorite solution

Group 2- (VSE)

Subgroup B1 - 10 Samples - Dry Conditions

Subgroup B2 - 10 Samples – immersed in 2% gluteraldehyde solution

Subgroup B3 - 10 Samples – immersed in 1% sodium hypochlorite solution




Page 27

Group 3- (VPS)

Subgroup C1 - 10 Samples - Dry Conditions

Subgroup C2 - 10 Samples – immersed in2% gluteraldehyde solution

Subgroup C3 - 10 Samples – immersed in1% sodium hypochlorite solution.

After each impression was allowed to air dry, an alphabetic-numeric coding

system was used (alphabet represents the material, number represents different

conditions). Each impression base was marked with a alphabet-number , corresponding to

the impression material used and the condition under which the impression was

subjected. The polymerized impressions made from the three materials were of different

colors; thus though investigators could not distinguish the conditions under which the

impressions were made, they could distinguish the different materials.

II Immersion in disinfectant solutions

Each impression after removal from the die was dried properly and 2 groups of

impressions (10 each) were immersed in the disinfectant solutions (2% glutaraldehyde

and 1% sodium hypochlorite) for 10 min each. After a lapse of predetermined time, each

impression is rinsed under running water for 30 sec to remove the residual disinfectant

solution. The specimens were allowed to dry completely before they were evaluated for

stability and accuracy.

III Evaluation of dimensional stability and accuracy

a. Equipment used:

Measuring microscope with an accuracy of 0.001cm




Page 28

Dimensional accuracy was evaluated immediately after making each impression

and immediately after the impressions was removed from the disinfectant solutions. A

single investigator measured the length of line B between cross points X and Y for each

impression. This measurement was made three times to the nearest 0.001cm at original

magnification X10 using a measuring microscope.

The measurements were made using the formula:

X = MSR + (CVD X LC) mm

Y = MSR + (CVD X LC) mm

XY = (X-Y) mm

Where,

MSR = Main Scale Reading

CVD = Coincident Vernier Division

LCD = Least Count (i.e. 0.001 cm)

XY = Distance between the points X and Y on line B.

The 3 measured lengths were averaged and compared with the length of line B on

the metal die used to make the impression. The percent change from the metal die was

computed using the following equation:

[(Mean impression measurement - standard die measurement /standard die

measurement) ×100].

Method of Statistical Analysis:

MEAN:

The mean is the average value, or the sum of all the observed values divided by

the total number of observations.




Page 29

Mean = x = ∑ (xi)

N

STANDARD DEVIATION: Root Mean Square Deviation

Square root of the squared mean deviations from the arithmetic mean.

S = ∑ (Xi-X)2

N-1

ANOVA: TWO WAY ANALYSIS

After the F statistic has been calculated, its P value can be looked up in a table of

the F distribution to determine whether the results are statistically significant. (P >0.05 is

significant)

MEAN PERCENTAGE CHANGE:

(Mean impression measurement−standard die measurement / standard die measurement) ×

100.

Standard measurement of the middle line of the ADA specification no. 19 metal die is

2.5cm.




Page 30

90IMPRESSIONS

30PE

30PVS

10 DRY 10 DRY 10 DRY

30VSE

10 immersed in

2%

lutaraldeh de

10 immersed in

2%

lutaraldeh de

10 immersed in

1% sodiumh ochlo rite

10 immersed in

1% sodium

h ochlor ite

10 immersed in

1% sodium

h ochlo rite

10 immersed in

2%

lutaraldeh de

5 materials & methords

Documents