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| 2010-22 |
| 22-1 |
ISSN (Print) 1013-9052
EISSN 1658-3558
P.O. Box 52500,
Riyadh 11563,
Kingdom of Saudi Arabia
| Tel. |
966-1-467-7328 |
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933-1-467-7308 / 966-1-467-7534 |
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saudidj@ksu.edu.sa |
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The effect of some dentin bonding agents on Dycal lining cement
Alaa El-Araby, Ph.D
Abed Al-Jabab, Ph.D Department of Restorative Dental Sciences,College of Dentistry, King Saud University, KSA
Dentin primer is applied as a routine
procedure prior to bonding to improve the sealing properties of direct
polymerizing resins. Some primers contain acetone or alcohol that may affect
the properties of calcium hydroxide liner which is placed as a direct or indirect pulp capping. If calcium hydroxide is
softened or smeared over the cavity walls, the bonding will be impaired.
Therefore, the cement must be removed, the walls must be cleansed and the
procedure must be repeated with careful application of dentin primer. The
purpose of this study was to determine the wear and compressive strength of a
calcium hydroxide liner (Dycal) after exposure to different kinds of
dentin primers for different periods of time. Dycal was mixed according to the
manufacturer's instructions and placed in
plastic rings of 0.5 mm x 5 mm and allowed to set at 37°C for 15 minutes under
500 gm load. To determine erosion, the height for each sample before and
after application of primers was recorded using Digital Height Measuring
Instrument (Digmar 817). Compressive
strength specimens were also prepared. Dycal treated with Optibond or Syntac
for 1 minute or 5 minutes had the highest erosion values and the lowest
compressive strength values. Gluma CPs (water based primer) had the least
effect on Dycal.
Calcium hydroxide liners are often placed in deep cavities under
restorative materials to protect the pulpal tissues
from chemical insults. It has the ability to stimulate restorative dentin
formation with direct pulp contact. It also serves as a protective barrier for
pulp tissue not only by blocking patent dentinal tubules but also by
neutralizing the attack of inorganic acids and leached products from certain
cements and Testorative materials.1 Conventional formulations of calcium hydroxide
demonstrate low physical properties.2
The materials used in the study are listed in Table1.
Erosion Test After mixing, the material was placed in plastic rings with an inner diameter of 5 mm and 0.5 mm thickness. The filled ring was placed between 2 glass plates with 500 gm applied to produce smooth surfaces and to extrude the excess material. The calcium hydroxide was allowed to set in an incubator at 37°C. After 15 minutes, the ring was separated from the glass plates and the excess material was trimmed with a scalpel. After preparation of the test specimens, they were divided into 7 groups of 15 specimens each according to the different primers used with a total of 105 test specimens. Each group was subdivided into 3 subgroups (5 specimens each) according to the primer application time of 1 minute, 5 minutes or 60 minutes. Each test specimen was immersed in 0.5 ml required dentin primer in a tight glass container, placed in a dark box for the required period and then washed with water spray for 1 minute and dried with oil free air. The amount of material lost (surface erosion) was measured in micrometers using a Digital Height Measuring Instrument "Digmar" 817. A measuring probe with spherical contact point of 2 mm in diameter was used for inside measurement. The readings before and after application of the different primers were recorded. Compressive Strength Test The specimens were prepared in a split-brass mold with internal dimensions of 12 mm height and 6 mm diameter (American Dental Association Specification No. 30). The mold was placed on a flat glass plate covered by a thin polyethylene sheet and slightly overfilled with a portion of material within three minutes after commencing the mix. A second flat glass plate and polyethylene sheet were pressed on the top of the mold and held together with a C- clamp. Three minutes after the start of the mix, the mold assembly was transferred to an incubator held at 37°C. One hour later, the ends of the cylinders were ground flat with 240-grit silicon carbide metallographic paper. The specimens were removed from the molds and kept at near 100% relative humidity at 37°C for 24 hours. The control group consisted of five specimens which did not receive any primer. The other test specimens were divided into 7 groups according to the different primers used. Each group was subdivided into 3 subgroups (5 specimens each) according to the application time of 1 minute, 5 minutes or 60 minutes. Each test specimen was immersed in 0.5 ml required dentin primer in a tight glass container, placed in a dark box for the required period. Specimens were then washed with water spray for 1 minute and dried with oil free air.3 The specimens were loaded in compression at a crosshead speed of 0.05 in/min on a Universal Testing Machine Instron 8500* each using a 1,000-Ib load cell. The value for compressive strength was reported as the average of five specimens.
Erosion Test
The solubility of calcium hydroxide in
phosphoric acid has been studied by many investigators.3-5,7 The acid
solubility of calcium hydroxide was considered an important property because of
accidental contamination during the acid-etch technique.7 High solubility of calcium hydroxide may
result in contamination of bonding agent and increased
marginal leakage.8
In this study, surface erosion of calcium hydroxide was evaluated after application of different dentin primers. The calcium hydroxide used was Dycal, which contains calcium 1-methyl trimethylene disalicylate as an ester and a mixture of ortho & para N-ethyl toluene sulphonamide as a plasticizer. Posser et al.9 found that Dycal was hydrolytically unstable, releasing calcium and hydroxide ions when in contact with water. These allow free passage of water, which then attacks vulnerable cement structure, leading to disintegration of these cements and this exerts a considerable influence on the physical properties. The rate of erosion was controlled by the plasticizer. Like all other dental cements, Dycal set by an acid-base reaction as defined by Wilson.10 An infrared spectroscopy study by Posser et al.11 showed that Dycal set by an acid-base reaction between alkyl salicylate and calcium hydroxide. During the course of cement formation, phenolic protons were replaced by calcium ions to form a chelate structure of calcium phenolate. The weakness of and friability of the cement suggested that chelates are bound together only by secondary attractions. Barnes12 observed the loss of Dycal under amalgam restoration in four clinical cases. Phillips13 suggested that calcium hydroxide bases become soft when using a water coolant during removal of amalgam from a cavity preparation and indicated that Dycal was sensitive to the base-catalyst ratio. Chong14 reported that there was no difference in the compressive strength of Dycal after seven minutes and 24 hours, respectively. This fact is important because the restorations would be placed within seven minutes after starting the mix. Shazad et al.15 found that Dycal had sufficient compressive strength 3 minutes after mixing to withstand the force of condensation of a restoration. In this study, compressive strength was measured after 1,5, or 60 minutes. The results of this study showed that Dycal responded differently upon the attack of different primers. It is interesting to note that primers are not similar in composition. They are classified as water-based, acetone- based, and alcohol-based primers. Dycal treated with Syntac or Optibond showed higher erosion values and lower compressive strength in comparison to the other specimens treated with other primers. Syntac is a self-etching primer which contains a high concentration of acetone (74%) and maleic acid (10%). This accounts for high erosion values and low compressive strength as acetone and maleic acid can penetrate through the cement, attack the chelate structure, dissolve the plasticizer, and cause disintegration of the cement. This is also the case with All-Bond 2 which contains acetone (60%) and alcohol (10%). It was noted that acetone was more aggressive than alcohol in the disintegration of the cement after one hour and that Dycal was susceptible to the attack of acetone or alcohol that is contained in some primers. Other test specimens treated with Scotchbond, Single bond, and Gluma CPS showed lower erosion values and higher compressive strength values than that obtained after application of All-Bond 2, Optibond or Syntac. These results could be related to the composition of different primers used. Scotchbond, 3M Single bond are water-based, containing an aquous solution of HEMA. Gluma CPS is water-based containing HEMA and glutraldehyde. For this reason, Scotchbond, Single bond, and Gluma have the least effect on the properties of Dycal. Washing of test specimens with water spray might also cause dissolution of the superficial layer of the test specimens.
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