Page 1

Introduction

Glass ionomer cements were introduced by Wilson and Kent in 1972.1

Their development arose from the research into silicate and

polycarboxylate cements. This material has unique properties, such as chemical adhesion to moist tooth structure, anticariogenic due to fluoride release and biocompatibility. This tooth colored restorative material is becoming increasingly popular in recent years. Water plays an important role in the setting reaction and cement structure of glass ionomer cement. Water lost during the early setting reaction, may stop the reaction resulting in surface crazing.

Water

sorption on the other hand will lead the cement to loose its translucency.7 In essence, glass ionomer cements form a class of materials known as acid-base reaction cements. Initial setting occurs in 3-4 minutes, but precipitation, gelation and hydration occurs for atleast 24 hours and setting continues slowly for much longer periods.1 These materials set and harden by a transfer of metal ions from the glass to the polyacrylic acid to form a salt hydrogel which is the binding matrix. Water is the reaction medium and also serves to hydrate the silicious hydrogel and the metal polyalkeonate that are formed. It is an essential part of the cement structure.

Therefore the water balance must be controlled to permit

1


Introduction sufficient maturation of the glass ionomer cement before the restoration is exposed to the oral environment. Some form of surface protection during the early phases of setting reaction is essential for the development of optimum physical properties.1 If the setting cement is exposed to an aqueous environment soon after placement the setting process may be upset. Only after 1 hour the glass ionomer set cement is sufficiently resistant to hydration and dehydration to allow its exposure to oral environment with the setting reaction continuing upto 24 hours.12 Correlations between early exposure to water and reduced mechanical properties that lead to poor clinical performance have been demonstrated. Lower compressive strengths and reduced degrees of hydration of the set matrix have also been reported. 5 On the other hand if left exposed to air after the initial setting, the glass ionomer cement will loose water rapidly leading to shrinkage and crazing. This will leave the restoration surface susceptible to staining and place heavy stresses on the newly formed ionic bonds, thus possibly leading to a loss of adhesion.10 Restoration of glass ionomer cement should be covered with a water proof protectant like varnish to protect them from hydration and dehydration for the first one hour.17

2


Introduction

Antonucci (1988) and Mithra (1989) developed hybrid version of glass ionomer cement by incorporating HEMA which were called the Resin modified glass ionomer cements.2

These were developed to

overcome the problems of low initial mechanical strength and moisture sensitivity associated with conventional glass ionomer cements, while preserving their clinical advantages (ionic-adhesion to dental tissues and fluoride release). Although its supposed that the occurrence of photochemical reaction and the presence of a resin network reduces the diffusion of water into the cement. Studies have shown that there is a detriment in the esthetic properties and failure at the tooth restoration interface of the resin modified glass ionomer cements due to dehydration and imbibition respectively.9 Investigations on these materials have shown that addition of resin has not significantly reduced the susceptibility of glass ionomer materials to hydration and dehydration problems which lead to detriment in the esthetic properties and failure at the tooth-restoration interface.29 But the application of surface protection soon after the restoration is placed in the oral cavity preserved the water balance in the system and also filled small surface voids and defects preserving the restoration color by reducing the uptake of stains.7

3


Introduction The purpose of this study was to evaluate the effectiveness of surface protectants such as nail varnish, Fuji varnish, Heliobond (light activated bonding resin) and Fuji Coat LC for a resin modified glass ionomer

cement–Fuji

II

LC

with

spectrophotometer.

4

the

help

of

absorbance


Aims & Objectives

The aim and objective of the study was ; • To evaluate the effectiveness of surface protectants applied on restorative resin modified glass ionomer cement immediately after setting in maintaining the water balance.

5


Review of Literature

Douglas W.H., K.L.Zakariasen U. (1981)35 in their study of volumetric assessment of apical leakage, developed

and utilized a

spectrophotometric dye recovery method for determining the volume of apical leakage for obturated root canals.

Teeth to be tested were

obturated and coated with sticky wax except for the apical foramen and submerged in 2% aqueous methylene blue dye. After appropriate dye exposure, the wax coating is removed, the cementum surface cleansed of any dye, and the tooth dissolved in dilute nitric acid to return the dye into solution. Utilizing the linear relationship that exists between dye concentrations and their corresponding spectrophotometric readings, the test solutions were analyzed spectrophotometrically and their dye concentrations were determined. Given the dye concentrations and the volume of test solutions, the volume of leakage of the original 2% dye solution into obturated root canals was calculated. The method has been found easy to utilize, is subject to minimal human measurement error and provides determination of volumes of leakage, rather than linear measurements. Mount Graham J. (1981)10 in his study on requirements for clinical success of glass ionomer cement restorations based on six years of laboratory experiments and clinical experience, stated that glass

6


Review of Literature ionomer cements can bond chemically to enamel and dentin but a proper technique must be followed for success. Moisture sensitivity problems can be readily avoided by controlling the environment of the cement after 3-4 minutes of initial set with an immediate application of a water proof varnish generally supplied by the manufacturer specifically, and is not interchangeable with copal varnish used under amalgam. Within 1 hour the restoration will be sufficiently resistant to absorption of water to remain undamaged if varnish is lost. On the other hand it will be at least 24 hours and possibly longer, before its mature enough to withstand exposure to dehydration for longer than few minutes. Therefore a further application of this varnish is required if its necessary to isolate this restoration within 24 hours. Mount G.J., Makinson O.F. (1982) 12 in their study on clinical implications of glass ionomer restorative cement setting reaction, said glass ionomer cements undergo a prolonged setting reaction.

At 4

minutes the matrix can be removed without disturbing the restoration but it is approximately 60 minutes, before the material is sufficiently resistant to hydration and dehydration, to allow its exposure to the oral environment. During this time the restoration must be protected with a coat of water proof varnish. An additional 24 hours should pass before its contoured and polished concluding that restorations of glass ionomer

7


Review of Literature cements need to be covered with a water proof varnish to protect them from hydration and dehydration for the first hour. Earl M.S.A., Hume R.W., Mount G.J. (1985) 24 studied the effect of various proprietary and non-proprietary varnishes and other surface treatments on the movement of tritium, out of the surface treated tritium labelled glass ionomer cement samples by using liquid scintillating spectrometry. No treatment reached the ideal goal of prevention of water movement for the first hour of mixing. The authors felt that there is a need for further development of varnishes to meet the ideal requirement. Earl M.S.A. and Ibbetson R.J. (1986)26 studied the effectiveness of two varnishes to protect the glass ionomer cement from damage due to early moisture contact. Neither varnish afforded adequate protection to the setting cement and damage to the surface exposed to oral environment was observed. They concluded that depletion of aluminium and silicon ions from immature glass ionomer cement exposed to an aqueous environment needs to be prevented by developing a better surface protectant. Earl M.S.A., Mount G.J., Hume W.R. (1989) 25 have studied the potential varnishes and light activated, chemically activated bonding resins in inhibiting the outward flow of water across the surface of glass

8


Review of Literature ionomer cement. Light activated bonding resins of very low viscosity were effective, while the varnishes and chemically activated bonding resins were not able to control the outward water flow significantly. The authors opinion was the union between the glass ionomer cement and composite resin may be the reason for its better performance and this may not be expected with all light activated bonding resin as the chemistry of these resins vary.

While the volatile solvent in the varnish became

porous on evaporation of the solvent. Mathis S.Ferrancane L. (1989)29 in their study on properties of glass ionomer, examined the solubility in water, adhesion to dentin and surface roughness for light cured glass ionomer material to that of conventional glass ionomer. They concluded with the results that the mechanical properties, brittleness and solubility of the material are less than those of commercial glass ionomer, while adhesion to dentin is also unaffected among the RMGICs. Most importantly surface crazing, a documented problem with conventional glass ionomer, when they become desiccated is alleviated with this hybrid formulation. Wilson Alan D. (1990)2 studied resin modified glass ionomer cements and compared their chemistry and properties with conventional glass ionomer cements and stated that resin modified glass ionomers have

9


Review of Literature the advantage of long working time, rapid set and higher early strength and easy bond to resins. Their strength is compatible to conventional glass-ionomer cements rather than to composite resins. The disadvantage of containing free monomers and HEMA makes it hydrophilic. U.M.Chung Moon, Gudbrand Oilo (1992)5 observed the effect of immersion in water at 3, 5, 7 and 10 minutes after mixing, on the surface of three regular and one light-curing glass ionomer cements by measuring the penetration of methylene blue solution. Early solubility of these cements was also measured and compared with ZnPO4 and zinc polycarboxylate cement.

They concluded that extending the time

between start of mixing and immersion in water decreased the dye penetration and lowered the loss of substance from the surface of regular glass ionomer cements. However the time after mixing had no or only a limited effect on the loss of substance from the light cured glass ionomer cement, the zinc phosphate cement or the zinc polycarboxylate cement. McLean John W. (1992)18 in his study of clinical applications of glass-ionomer cement stated that strength of glass-ionomer cements is related to their water content and the clinical success of these cements depends on early protection of the cement from hydration or dehydration, and the current use of light cured bonding agents has largely solved this

10


Review of Literature problem. In the early stages of set, the vital cement forming ions Al +++ and Ca++ can be washed out by contact with saliva. The damage is permanent; water will be absorbed, the cement will lose its translucency and the weakened surface will erode. Dehydration at this stage can be equally disastrous since water needed for cement formation will be reduced and surface crazing may occur. To prevent this, immediately upon removal of the matrix a coat of light-polymerized bonding resin should be applied and treated as oily lubricant followed by removal of excess cement with sharp scalers, knives or excavators external to cavosurface margins. During trimming, the surface of the cement should be constantly lubricated with low viscosity bonding agent. Only after finishing procedure should the resin bonding agent be light cured. Glass ionomer cements still remain the only hydrophilic restorative material. Nicholson J.W., Anstice H.M. (1992)17 studied two commercially available light curable glass ionomer cements, Vitrebond and XRIonomer measuring their compressive strengths measured following storage under wet and dry conditions for varying length of time upto 3 months. The strongest cements were those stored in air and allowed to age. Cements that were stored in water became progressively weaker with time. Air stored specimens became barrel-shaped as they were loaded and exhibited considerable plastic deformation prior to fracturing.

11


Review of Literature They concluded that properties of these particular light cured cements changed markedly on exposure to moisture, a fact which is of clinical significance. Hotta M., Hirukawa H. et al (1992)22 studied the effect of coating materials on to the surface of restorative glass ionomer cement. Three restorative glass ionomer cements, Fuji Ionomer II, Chemfil II, Chelonfil and Ketac varnish, occlusion bonding agent, Ketac glaze, Bellfeel brightner (bonding agent) were the four coating materials used. The specimens bonded with light cured bonding or glazing agents and stored in moisture showed smooth surface and the bonding agent remained intact on the surface. However coating of varnish was observed to have peeled away resulting in water penetrating the surface. This resulted in chalky surface of cement rapidly eroded. They concluded that coating with light cured bonding or glazing agents is a useful and effective means of protecting restorative glass ionomer cements in clinical practice. Hallett K.B., F.Garcia-Godoy (1993)19 studied the microleakage of two resin modified glass ionomer restorations with two conventional glass ionomer restorative materials on extracted human molars.

The

results showed that one resin modified glass ionomer cement showed significantly less microleakage against enamel and dentin / cementum

12


Review of Literature compared to conventional glass ionomer cement. Marginal gap formation for both resin modified glass ionomer cement restorations was limited to axial wall of restorations. They concluded from their study that the clinical marginal seal between the resin modified glass ionomer cement restorations examined and tooth structure, is unable to completely prevent the leakage of fluid as shown by the microleakage results. M.C.Serra, M.F. Navarro et al (1994)30 evaluated the effectiveness of various surface treatments such as light cured bonding resins, nail varnishes, vaseline for glass ionomer cement through spectrophotometer. All the surface agents were effective in protecting setting restorative glass ionomer cement, but nail varnish provided the best results. Cho Elizabeth, Hugh Kopel et al (1995) 9 studied to determine if resin modified glass ionomer cements are less sensitive to moisture than conventional glass ionomer cements, and investigated the effect of barrier coatings and different setting environments. They concluded that resin modified glass ionomer cements are less sensitive to moisture than is the conventional glass ionomer cement control. Drier environments produced stronger resin modified glass ionomer specimens. Use of fissure sealant as a barrier coating increased overall specimen strength.

13


Review of Literature Attin Thomas, Buchal L.A., Wolfgang et al (1995)34 studied the initial curing shrinkage and volumetric change during water storage of 6 resin modified glass ionomer cements (Dyract, Fuji II LC, vitremer, Ionosit Fil, Variglass, Photac-Fil) and Chemical cured glass ionomer cement.

The curing shrinkage of most of the resin modified glass

ionomers was greater than the chemical cured glass ionomer cement. There was volumetric expansion in resin modified glass ionomer and volumetric loss in conventional glass ionomer after 28 days water storage.

They concluded that the volumetric expansion of the resin

modified glass ionomer cement due to water storage is not enough to compensate the shrinkage and its questionable whether these resin modified glass ionomer cements could overcome the known short comings such as marginal gap formation, reduced wear resistance and chemical degradation of conventional glass ionomer cements. Beltrao H.C.P. et al (1996)15 studied the clinical evaluation of a conventional glass ionomer cement and a light cured glass ionomer cement after two years. They evaluated for color match and marginal degradation.

Results showed no statistically significant difference

between the restorative materials for marginal degradation after 2 years, but light cured glass ionomer cement showed statistically significant difference for color match criteria.

14

They concluded that at 2 years


Review of Literature clinical evaluation, the conventional glass ionomer cement presented best clinical performance than light cured glass ionomer cement regarding to color match criteria. A.U.Yap (1996)36 studied to quantify and compare the amount of water absorbed by six commercially available resin-modified glass ionomer cements and to investigate the possible influence of time and resin content on water sorption. Fuji II LC, Variglass, Vitrabond, Vitremer, Photoca bond Z100 a composite resin as control. He concluded that composite resin had significantly less water sorption than the remaining resin modified polyalkeonate cements.

He concluded that

degree of water sorption was influenced by the resin (HEMA) content and there is a potential relationship between time (cement maturity) and water sorption. Uno Shigeru, Finger J.Werner et al (1996) 32 compared in their study the effects of long term water storage on the mechanical characteristics of four resin modified glass ionomer restorative materials with those of a conventional glass ionomer cement and a resin composite material. Diametral tensile strength (DTS) was lowest for the conventional glass ionomer cement and highest for composite resin. Resin modified glass ionomer were intermediate. Water storage reduced

15


Review of Literature DTS between 24 hours and 1 week or 1 month but remained unaffected after 6 months. They concluded that water storage for 6 months has little adverse effect on the mechanical properties of resin modified glass ionomer cement. W.Kanchanavasita, Anstice H.M. (1997)20 studied the effect on dimensional and structural integrity of four resin modified glass ionomer cements when they take up water. They concluded that all cements expanded on immersion in water and contracted during desorption. Greater weight increase and greater volumetric expansion were observed on long term storage in artificial saliva than in distilled water. Sidhu S.K., Sherriff M. (1997)27 used confocal microscopy to study the effects of dehydration stress on the glass ionomer tooth interface in specimens of various degrees of maturity. Generally gap formation at the interface occurred within 15 minutes of dehydration. All the materials were susceptible to dehydration shrinkage upto 3 months of maturity.

At 6 months and 1 year Fuji II and Fuji II LC showed

insensitivity to dehydration.

Vitremer and Photac-Fil showed less

sensitivity to dehydration at 1 year than at 6 months. They concluded that addition of resin has not significantly reduced the glass ionomer susceptibility to dehydration problems.

16


Review of Literature

Sidhu S.K., Watson T.F. (1998)28 studied the interface of resin modified glass ionomer cements (RMGICs) especially with dentin, Fuji II LC, Vitremer, Photac-Fil, Fuji Cap II were observed with a confocal microscope. Examination with confocal microscope showed that the dye uptake by the restoration varied among materials. A “structure less” non particulate, highly stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width and was prominent where the dentin were cut “end on” and in areas closer to the pulp and was not seen adjacent to enamel.

Vitremer showed minimal dye uptake and the

“structure less” layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Conventional GIC did not show any dye uptake. They concluded, the “absorption layer” is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in wet tooth. Riberio A.P.G., C.H, Sera et al (1999)1 have studied the need for surface protection in resin modified glass ionomer against hydration and dehydration. Surface protectants used were nail varnish, heliobond light cured bonding resin and proprietary glazes (Fuji varnish, Ketac glaze, Finishing gloss). The authors opinion was that the set structure of resin

17


Review of Literature modified glass ionomer contains high proportion of hydrophillic functional groups in a highly cross linked matrix, which are affixed to take up water and swell due to the presence of Hydroxy Ethyl Methacrylate (HEMA) copolymers. They concluded that best surface protection was obtained with Heliobond light activated bonding resin. Cattani-Lorente M.A., Dupuis V. et al (1999) 23 studied the effect of water on the physical properties of resin modified glass ionomer cements. They observed that resin modified glass ionomer cement’s absorb large amounts of water during the first 24 hours compared to conventional glass ionomer cement water altered the physical properties. With decrease in flexure strength and hardness. Water immersed samples became more plastic and deformed greatly before fracture, whereas air stored specimens were brittle and failed with much less deformation. They concluded that water has two main effects on these materials. First, it diffuses into the material and acts as a plasticizer reducing their flexural strength and hardness, which is reversible once excess water is removed. Second, water dissolves the components of the cement altering the network of resin modified glass ionomer cement resulting in decreased flexural strength and hardness.

18


Review of Literature Mount G.J. (1999)14 in his review of the current status of glass ionomer stated that the finished set cement of resin modified glass ionomer has 5% of resin which is HEMA, which is strongly hydrophilic and this material tends to perform like a mild hydrogel with rapid water uptake over the first 5-7 days after placement leading to small amount of expansion of the restoration and possible stain uptake in the short term, needing for a surface protection immediately after placement to stabilize the water content of the cement and delayed finishing and polishing if possible at the next appointment. Cefaly D.F.G., B.G.M. Seabra et al (2001) 7 have studied the effectiveness of four surface protectants for resin modified glass ionomer cements by spectrophotometrically evaluating the dye up take. The tested prospective materials were effective in preventing dye up take. Except for nail varnish which gave better protection for Photac-Fil than proprietary glaze and also an over all agreement that resin modified glass ionomer cements need surface protection. The difference observed between the nail varnish and proprietary glaze may be due to the difficulty in spreading and irregular distribution of the glaze over the specimen surface due to presence of petroleum jelly.

19


Review of Literature Shu-Fen Chang, Ying Tai J.N. et al (2001) 33 investigated the effect of various surface protection on microleakage with Class V resinmodified glass ionomer cements.

Fuji Varnish, resin adhesive, acid

etching and resin adhesive were the different protectants on Fuji II LC. None of the protectants demonstrated complete marginal sealing at either occlusal or cervical margins better being resin adhesive. They concluded that although resin modified glass ionomers can be finished immediately, they remain moisture sensitive.

They suggested that resin adhesive

should be used as surface protection to reduce marginal microleakage of resin modified glass ionomer restorations.

20


Materials & Methods

The present in-vitro study was carried out in the Department of Conservative Dentistry and Endodontics, College of Dental Sciences, Davangere. MATERIALS USED :  Resin modified glass ionomer cement – Fuji II LC (GC America)  Nail varnish  GC Fuji Varnish  GC Fuji Coat LC  Heliobond – Light activated bonding resin (Ivoclar Vivadent)  0.1% Methylene blue solution  65% Nitric acid  De-ionized water INSTRUMENTS USED :  Agate spatula  Locking tweezer  Glass slides  Petridish  Composite finishing kit (Shofu)  Transparent matrix strips

21


Materials & Methods  Plastic filling instrument  Brush applicator  Mixing pad  Acrylic rings (3 mm inside diameter and 2 mm height)  Micromotor EQUIPMENT USED :  Light curing unit (3 M)  Thermostat  Centrifuger  Absorbance spectrophotometer (UV 160 IPC) METHOD : The resin modified glass ionomer cement used in the study was Fuji II LC. The four surface protectants compared were ; 1. Nail varnish 2. GC Fuji Varnish 3. GC Fuji coat LC 4. Heliobond – Light activated bonding resin A total of 60 specimens were divided into 6 groups of 10 specimen each. Group 1

Positive control

- 10 Specimens

Group 2

Negative control

- 10 Specimens

22


Materials & Methods Group 3

Nail varnish

- 10 Specimens

Group 4

Fuji varnish

- 10 Specimens

Group 5

Fuji Coat L.C.

- 10 Specimens

Group 6

Heliobond

- 10 Specimens

The cement – Fuji II LC was manipulated according to the manufacturers instructions and placed into the acrylic rings (3 mm inside diameter and 2 mm height). The specimens were held between 2 glass slides separated by Mylar strips, and pressed with a weight of 500 gms for 30 seconds and light cured for 30 seconds each on both exposed sides of the ring. Then the excess cement was trimmed off and the test specimens were protected with one of the surface treatments, except for the positive and negative control groups, on both the exposed surfaces. All the surface treatments were applied with a brush. The light cured bonding resin and Fuji Coat LC were light cured according to the manufacturers directions. Nail varnish and Fuji varnish were allowed to dry for two minutes. After the surface treatment the experimental group specimens, except for the negative control group specimens were immersed in 0.1% methylene blue solution at 37 oC while the negative control group specimens were immersed in de-ionized water for 24 hours.

23


Materials & Methods

After 24 hours all 60 specimens were removed and rinsed with deionized water and the surface coatings were trimmed off with medium Sof Lex disc (3M) for 5 seconds. The specimens were now removed from the acrylic rings and immersed separately in 60 tubes, each containing 1 ml of 65% Nitric acid for 24 hours. Standard solutions of methylene blue in 1 ml of nitric acid were prepared containing 0 – 10 µg dye/ml. After 24 hours the standard and experimental solutions were diluted with 2 ml of de-ionized water. The solutions were filtered and centrifuged and the supernatant was used to determine the absorbance in a spectrophotometer at 606 nm. The method used to quantify the effectiveness of surface protection was adapted from that of Douglas and Zakariasen (1981).35 The effectiveness of surface protectants were recorded as µg dye per specimen, with lower values corresponding to better protection. Dye penetration values are presented as Mean and standard deviation. One way ANOVA was used for multiple group comparison followed by Newmann-Keul’s test for pairwise comparisons. P-value of less than 0.05 was considered for statistical significance.

24


Results & Observations

The present in vitro study was undertaken to evaluate the effectiveness of Nail varnish, Fuji varnish, Fuji Coat LC, Heliobond (bonding resin) as surface protectants, when applied on restorative resin modified glass ionomer cement (Fuji II LC) immediately after setting, in maintaining the water balance. Comparison of dye penetration between positive control group (Group I) and surface protectants (Group III, IV, V, VI) was done by one way ANOVA (F-test) as shown in Table 1. TABLE 1 Groups

Sample

1. Positive Control

Dye Penetration Mean

SD

10

0.5370

0.2248

2. Negative control

10

0.00

-

3. Nail varnish

10

0.0692

0.0230

4. Fuji Varnish

10

0.0668

0.0213

5. Fuji Coat

10

0.0739

0.0102

6. Helio Bond

10

0.0421

0.0131

F-Value* P-Level

43.53 P<.001, HS

The positive control group allowed the greatest dye penetration with a mean value 0.537 Âľg/specimen and negative control group showed no dye. Statistically high significance (P<0.001) was found between the positive control group and the surface protected groups (Group III, IV, V and VI). 25


Results & Observations

Comparison of dye penetration in Fuji II LC among different protectants (Group III, IV, V, VI) was done by Newman-Keul’s Range test as shown in Table 2. TABLE – 2

Groups

Sample

Dye Penetration in Fuji II LC Mean

SD

1. Nail varnish

10

0.0692

0.0230

2. Fuji Varnish

10

0.0668

0.0213

3. Fuji Coat LC

10

0.0739

0.0102

4. Helio Bond

10

0.0421

0.0131

FValue* P-Level

6.49 P<.01

Difference between groups** Groups SigniCompared ficance 3 vs 4 3 vs 5 3 vs 6 4 vs 5 4 vs 6 5 vs 6

NS NS P<.05, S NS P<.05, S P<.01 S

Among the surface protected groups the dye penetration was significant (P<.01). Difference of dye penetration between Group 3 (Nail varnish) with a mean value of 0.069 Group 4 (Fuji varnish) with a mean value of 0.067 and Group 5 (Fuji Coat LC) with a mean value of 0.074 had dye penetration which was not statistically significant.

26


Results & Observations

Difference of dye penetration between Group 3 (Nail varnish) with a mean value of 0.069 and Group 6 (Heliobond) with a mean value of 0.042 Was statistically significant (P<0.05) with Heliobond showing better protection compared to nail varnish. Difference of Dye Penetration between ; Group 4 (Fuji varnish) with a mean of 0.067 and Group 6 (Heliobond) with a mean of 0.042 was statistically significant (P<0.05) with Heliobond showing better protection than Fuji varnish. Difference in Dye penetration between ; Group 5 (Fuji coat LC) with a mean of 0.074 and Group 6 (Heliobond) with a mean of 0.042 was statistically significant (P<.01) with Heliobond showing better surface protection than Fuji coat LC. Observation of the results shows that among the four surface protectants Heliobond gives the best protection. One way ANOVA technique was used for multiple group comparison. Pairwise group comparisons were made by Newman-Keulâ&#x20AC;&#x2122;s range test.

27


Results & Observations

Formulae used : ∑xi Mean x = ------n

i = 1, 2,……… n

Standard deviation SD =

∑ (xi – x)2 --------------n -1

= SD2

Variance One Way ANOVA, F

Between group variance = -----------------------------Within group variance

Newman-Keuls Range test, Minimum significant range. K=K

*

Ve = -----Nm

K* = Table value Ve = Error variance Nm = Sample size

28


Discussion

Resin modified glass ionomer materials consist of a complex mixture of components. A typical material is composed of a polyacrylic acid or a modified polyacrylic acid, a photo curable monomer (Hydroxy ethyl methacrylate (HEMA) or Bis-GMA), an ion leachable glass and water (Sidhu et al 1997.Mount GJ 1999).27,14 In these materials the traditional acid base reaction of conventional cements is supplemented by a second curing process, which is activated by light or by chemical inhibitors. The acid base reaction takes place after mixing and continues after light activation; it is responsible for the final physical properties of the material. (Sidhu et al 1998).28 Because some of the water in the cement is replaced by water-soluble monomers. The acid base reaction proceeds more slowly than in traditional cements. According to Lorentte et al 199923 in these materials, the photopolymerization of resin components has been claimed to protect against the attack of moisture during initial setting. It has been suggested that the resin network reduces the diffusion of water into the materials. However, studies on the effects of storage in water have indicated that the physical properties of these materials change markedly when exposed to moisture (Hotta 1992).22

29


Discussion Earl 198524 observed that specimens of resin-modified glassionomer cements take up considerable amounts of moisture when stored either in water or in physiologic saline solution. Compressive strength has been found to decrease with increasing storage time, and specimens stored in water have been found to be consistently weaker than specimens of similar age stored in air (Earl 1989).25

The esthetic properties and color stability are also affected by

water sorption. Color changes may result from ongoing water sorption and continuing reaction.(Moon1992).5 According to Nicholson.J.W.199217 the set structure of resinmodified glass ionomer materials contain a high proportion of hydrophilic functional groups in a highly cross linked matrix and can be compared to the structure of synthetic hydrogel. Hydrogels are materials that imbibe water, swell and weaken.

They are often prepared for

copolymers of HEMA, which are designed to take up large amounts of water.(Hotta 1992).22 According to Yap A.U. 199636 Although its known that water sorption of resin modified glass ionomer is time dependent,

its not

known for how long such materials take up water and to what extent their physical properties are affected. A potential relationship between time

30


Discussion (cement maturity) and water balance has been observed.

Water sorption

also appears to be dependent on the resin (HEMA) content. Lining materials which have high resin content should not be exposed to the oral environment. A reduction in powder to liquid ratio will result in an increase in the

proportion of resin (HEMA), which is strongly

hydrophilic, resulting in a potential for greater water uptake. In addition, these materials have been found to swell more in pure water than in aqueous solutions of electrolytes.

The sorption of water by resin

modified glass ionomer materials will therefore be less marked clinically than it was found to be in pure water. None the less, water sorption, and thus dimensional changes of these materials would be expected in saliva although the extent of the in vivo is not known.36 According to Riberio.A.P.G. 19991 Studies with dye penetration showed the occurrence of imbibition in the resin-modified glass ionomer specimens. Resin modified glass ionomer materials also appear to be sensitive to dehydration (Sidhu S.K 1997).27 Desiccation of these materials causes severe loss of water, resulting in considerable shrinkage and irreversible change in the form of failure at the tooth restoration interface within minutes (H.Ngo, 1986).16 The ratio of bound to unbound water in

31


Discussion conventional glass ionomer cements has been found to increase with time. It is the unbound water that is readily lost by evaporation when the cement is exposed to air (H.Ngo, 1986).16

Complete maturity and

resistance to water loss is not available for at least 2 weeks for fast setting cements and possibly upto 6 months for slow setting conventional cements. How long it takes resin modified glass ionomer materials to reach maturity is not yet known. Sidhu, Watson 199727 in their

recent study stated, all of the

evaluated resin-modified glass ionomer cements were susceptible to dehydration shrinkage for upto 3 months of maturation. After 6 months, 2 materials showed insensitivity to dehydration, while the other 2 showed low sensitivity to dehydration at 1 year than at 6 months. Therefore, the addition of resin has not significantly reduced the susceptibility of glass ionomer materials to hydration and dehydration problems. In opposition to what has been supposed initially surface protection is necessary and recommended for resin-modified glass ionomer restorations.

32


Discussion The application of surface protection seems to preserve the water balance in the system. In addition, the great advantage of using such surface protectors is that they fill small surface voids and defects and may help to preserve the restorationâ&#x20AC;&#x2122;s color by reducing the uptake of stains. (Sidhu ,Watson 1997).28 Cattani-Lorente M.A., Dupuis V. et al (1999) 23 studied the effect of water on the physical properties of resin modified glass ionomer cements.

They observe that resin modified glass ionomer cementâ&#x20AC;&#x2122;s

absorb large amounts of water during the first 24 hours compared to conventional glass ionomer cement. properties.

Water altered the physical

With decrease in flexure strength and hardness, water

immersed samples became more plastic and deformed greatly before fracture, whereas air stored specimens were brittle and failed with much less deformation. They concluded that water has two main effects on these materials. First, it diffuses into the material and acts as a plasticizer reducing their flexural strength and hardness, which is reversible once excess water is removed. Second, water dissolves the components of the cement altering the network of resin modified glass ionomer cement resulting in decreased flexural strength and hardness.

33


Discussion Mount G.J. (1999)14 in his review of the current status of glass ionomer stated that the finished set cement of resin modified glass ionomer has 5% of resin which is HEMA, which is strongly hydrophilic and this material tends to perform like a mild hydrogel with rapid water uptake over the first 5-7 days after placement leading to small amount of expansion of the restoration and possible stain uptake in the short term needing for a surface protection immediately after placement to stabilize the water content of the cement and delayed finishing and polishing if possible at the next appointment. Alan D.Wilson (1990)2 studied resin modified glass ionomer cements and compared their chemistry and properties with conventional glass ionomer cements and stated that resin modified glass ionomers have the advantage of long working time, rapid set and higher early strength and easily bond to resins, their strength is compatible to conventional glass-ionomer cements rather than composite resins. The disadvantage of containing free monomers and HEMA makes it hydrophilic. The hypothesis verified on this work was that incorporation of resin into glass ionomer has not overcome the moisture susceptibility of Glass ionomers and that resin modified glass ionomer cement surface

34


Discussion should be protected soon after its initial set till the cement completely matures. The effectiveness of the surface protectants applied to resin modified

glass

ionomer

(Fuji

II

LC)

was

evaluated

by

a

Spectrophotometric dye recovery method a volumetric analysis developed and utilized by Douglas W.H. and Zakariasen K.L. (1981) 35 in their study for determining the volume of apical leakage for obturated root canals. The study method has been found easy to utilize, is subject to minimal human measurement error and provides determination of volumes of leakage , rather than linear measurements. The present study was conducted to evaluate the effective surface protectant among nail varnish, Fuji varnish, Fuji coat LC, Heliobond (Light cure bonding resin) for a resin modified glass ionomer cement (Fuji II LC) by using Spectrophotometric dye recovery method . Earl M.S.A., Hume R.W., Mount G.J. (1985) 24 studied the effect of various proprietary and non-proprietary varnishes and other surface treatments on the movement of tritium, out of the surface treated tritium labelled glass ionomer cement samples by using liquid scintillating spectrometry. No treatment reached the ideal goal of prevention of water

35


Discussion movement for the first hour of mixing. The authors felt that there is a need for further development of varnishes to meet the ideal requirement Earl M.S.A., Mount G.J., Hume W.R. (1989) 25 have studied the potential varnishes and light activated, chemically activated bonding resins in inhibiting the outward flow of water across the surface of glass ionomer cement. Light activated bonding resins of very low viscosity were effective, while the varnishes and chemically activated bonding resins were not able to control the outward water flow significantly. The authors opinion was the union between the glass ionomer cement and composite resin may be the reason for its better performance and this may not be expected with all light activated bonding resin as the chemistry of these resins vary.

While the volatile solvent in the varnish became

porous on evaporation of the solvent. According to the results obtained, the non-protected resin-modified Glass ionomer cement specimens immersed in methylene blue (Positive control) presented a statistically significant higher dye uptake than other groups (P<. 001). This suggests that Resin modified glass-ionomers are susceptible to take up oral fluids. The mean values for negative control group (0.00 Âą 0.00) shows that there was no dye in the resin modified glass ionomer restorative

36


Discussion tested (Fuji II LC). Consequently, the values of the experimental groups represent only the methylene blue that was taken up. All the tested protective materials were effective in preventing the uptake of dye. Furthermore Heliobond light cured bonding resin (Group VI) cited as the best surface agent for protecting resin modified glass ionomer cement from water imbalance. These results are in accordance with ; Riberio G.P. Ana C.H, Sera et al (1999) 1 in their study stated that the set structure of resin modified glass ionomer contains high proportion of hydrophillic functional groups in a highly cross linked matrix, which are affixed to take up water and swell due to the presence of Hydroxy Ethyl Methacrylate (HEMA) copolymers. The best surface protection was obtained with Heliobond light activated bonding resin. As it is a low viscosity bonding resin low viscosity means a low contact angle between the resin and the surface of the restorative material, which provides the best surface protection. Hotta M., Hirukawa H. et al (1992)22 studied the effect of coating materials on to the surface of restorative glass ionomer cement. Three restorative glass ionomer cements, Fuji Ionomer II, Chemfil II, Chelonfil and Ketac varnish, occlusion bonding agent, Ketac glaze, Bellfeel

37


Discussion brightner (bonding agent) were the four coating materials used. The specimens bonded with light cured bonding or glazing agents and stored in moisture showed smooth surface and the bonding agent remained intact on the surface. However coating of varnish was observed to have peeled away resulting in water penetrating the surface resulted in chalky surface of cement rapidly eroded. They concluded that coating with light cured bonding agent is a useful and effective means of protecting restorative glass ionomer cements in clinical practice. The higher performance of Heliobond (P<.01)in this study can be probably explained by ; 1) Its low viscosity, which means a low contact angle between the resin and the surface of the restorative material, leading to uniform distribution on to the restoration and resistance to disintegrate.1 2) Interaction and the resin compatibility between the bonding resin and the resin components of the resin modified glass ionomer restorative evaluated leading to a chemical bond between them.1 Among Group III (Nail varnish), Group IV (Fuji varnish), Group V (Fuji Coat LC). Fuji varnish (Group IV) showed better protection with less dye penetration value, followed by Nail varnish (Group III) and Fuji Coat LC

38


Discussion (Group V). But there was no statistically significant difference among their effectiveness as surface protectants. When compared between Group III (Nail varnish) and Group VI (Heliobond). The Nail varnish poor performance over Heliobond was statistically significant,(p<.05) which can be probably due to its highly volatile solvent which became porus after the solvent evaporated. This result is in accordance with ; Riberio G.P. Ana C.H, Sera et al (1999)1 have studied the effectiveness of surface protection for resin modified glass ionomer materials against hydration and dehydration. Surface protectants used were nail varnish, heliobond light cured bonding resin and proprietary glazes (Fuji varnish, Ketac glaze, Finishing gloss). When compared between Group IV (Fuji varnish) and Group VI (Helio bond), the effectiveness of Heliobond was statistically significant (P<.05). Presumably the Fuji varnish with low volatile solvent could not be better than Heliobond due to its inability to interact with the resin components of Resin modified glass ionomers to form a complete marginal seal which may explain its poor performance.

39


Discussion

These results were in accordance with previous studies ; Shu-Fen Chang, Ying Tai J.N. et al (2001) 33 investigated the effect of various surface protection on microleakage with Class V resinmodified glass ionomer cements.

Fuji Varnish resin adhesive, acid

etching and resin adhesive were the different protectants on Fuji II LC. None of the protectants demonstrated complete marginal sealing at either occlusal or cervical margins, better being resin adhesive. When compared between Group V (Fuji coat LC) and Group VI (Helio bond), the effectiveness of Heliobond was statistically significant (P<. 05).the poor performance of Fuji coat LC may be probably due to Fuji coat LC being a proprietary glaze, their chemistry varies and therefore their physical properties vary forming a high contact angle. This is in accordance with the previous results reported by Earl M.S.A. 198925 and Riberio G.P. Ana et al (1999).1 The results of this study support the working hypothesis that incorporation of resin into glass ionomer has not overcome the moisture susceptibility of Glass ionomers and that resin modified glass ionomer cement surface should be protected soon after its initial set till the cement completely matures and that the surface protectant should :

40


Discussion • Be less volatile, • Have low contact angle • Should be able to bond with the chemical components of the resin in the resin modified glass ionomer. • Be able to seal the cement structure from external environment and allow the cement to completely mature. The Heliobond light activated bonding resin promises to fulfill the above requirements. However, additional in vivo and in vitro test and clinical trials are desirable in order to elucidate the effectiveness of this surface protectant.

41


Summary

The present in-vitro study was aimed at evaluating the effective surface protectant for a Resin Modified Glass Ionomer Cement (Fuji II LC) through spectrophotometry. 60 specimens, each with 3 mm diameter and 2 mm height were made with Fuji II LC â&#x20AC;&#x201C; Resin modified glass ionomer cement. These 60 specimens were divided into 6 groups of 10 specimens each. Group I specimens were positive control group, these 10 specimens were placed in 0.1% methylene blue solution at 37 oC after initial set (i.e. 30 secs Light Cure) without applying any surface protectant for 24 hours. Group II specimens were negative control group, these 10 specimens were placed in de-ionized water at 37oC without applying any surface protectant for 24 hours. Group III specimens were coated with nail varnish after initial set and placed in 0.1% methylene blue solution at 37oC for 24 hours. Group IV specimens were coated with Fuji Varnish after initial set and placed in 0.1% methylene blue solution at 37oC for 24 hours.

42


Summary Group V specimens were coated with Fuji Coat LC and Group VI specimens were coated with Heliobond-Light cured bonding resin and these protectants were light cured according to manufacturers instructions and were placed in 0.1% methylene blue solution for 24 hours at 37oC After 24 hour all the specimens were removed from methylene blue solution, rinsed with de-ionized water and the surface coatings were trimmed off using medium soflex disc (3M) for 5 seconds. The specimens were separated from acrylic rings and were immersed in separate tubes each containing 1 ml of 65% nitric acid for 24 hours. Standard solutions of methylene blue in 1 ml of nitric acid were prepared containing 0 â&#x20AC;&#x201C; 10 Âľg dye /ml. After 24 hours, the standard and experimental solutions were diluted with 2 ml of de-ionized water.

The solutions were filtered,

centrifuged and the supernatant was used to determine the absorbance in a spectrophotometer at 606 nm.

43


Conclusion

The present study concludes that : 1) Incorporation of resin into glass ionomer has not overcome the moisture susceptibility of Glass ionomers. 2) Resin modified glass ionomer cement surface should be protected soon after its initial set till the cement completely matures. 3) Heliobond Light cured bonding resin is effective in protecting the surface and there by preserving the water balance in resin modified glass ionomer cement.

44


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