Effect of prewarming Resin Composite and Resin-modified GIC

on the microleakage of Class II Sandwich

Restorations

INTRODUCTION

Composite resins: Routinely used as restorative materials due to excellent aesthetics, strong mechanical

and physical properties and high resistance to dissolution.

However, despite improvements in resin composite formulations, polymerization shrinkage is still

considered problematic which results in unsuccessful direct composite resin restorations.

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Poor adhesion between the dentin and restorative material

Gap formation

Microleakage

To overcome the problem of microleakage many restorative

techniques have been developed, out of which, sandwich technique (McLean and Wilson), is being

successfully used especially in class II restorations.

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• As a step to further improve the marginal interface sealing, the prewarming of resin composite before placing it in the cavity was introduced by Bertolotto et al in (2003).

• Benefits of preheating of resin systems: Flow of hybrid composites greatly increased. Improved adaptation of the composite to the prepared tooth walls. Increased monomer conversion. Decreased paste viscosity free radicals and increasing polymer chains

become more fluid more complete polymerization reaction and greater crosslinking

Improved mechanical properties and increased wear resistance. Preheating devices are commercially used at a temperature range of 37ºC–

68ºC.

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Prewarming the capsules of RMGIC

Shortens the setting reaction time of RMGIC

Significantly increases the bond strength and surface hardness

Decreasing the microleakage on the cervical walls.

• However, no study has evaluated the effect of prewarming on microleakage in class II open sandwich restorations.

• Thus, this in vitro study was undertaken to assess the microleakage in class II cavities restored using open sandwich technique with and without prewarming of resin composite and RMGIC.

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MATERIALS & METHOD6

Forty non-carious, freshly extracted human mandibular

molar teeth

Cleaned and stored in 1% chloramine-t

For standardization, the mesiodistal and buccolingual

diameters of crown were measured with a digital caliper

Teeth presenting with a difference of 0.5mm or more in

mesiodistal and buccolingual dimensions were excluded.

Standardized class II tooth preparations were done on mesial and distal sides of all

teeth.

Occlusal Box Preparation: Depth of tooth preparation = 3mmBucco-lingual width = 3mmMesio-distal width = 4mm

Proximal Box Preparation :Bucco-lingual width =3mm Width of gingival seat = 3mm

Cervical margin of proximal box was placed

1mm below the CEJ. A minimum of 2mm of tooth tissue remained occlusally between the

two preparations (Mesio-occlusal and Disto-

occlusal) in each tooth.

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The samples were randomly divided into 4 groups according to the technique used for restoration:

Group I (n=20): Open sandwich technique (MO) Pre warmed RMGIC and resin composite at room temperature.

Group II (n=20): Open sandwich technique (DO) RMGIC at room temperature and pre warmed resin composite.

Group III (n=20): Open sandwich technique (MO) Pre warmed RMGIC and pre warmed resin composite.

Group IV (n=20): Open sandwich technique (DO) RMGIC and resin composite both at room temperature.

Teeth were mounted in metallic jigs followed by application of sectional matrix band and wooden wedges. GC Cavity Conditioner was applied for

10 seconds and rinsed.

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Group IFuji II LC capsules were heated in a water bath (at 40° C) for 90 seconds prior to mixing and injected according to manufacturer’s instructions. Application of etchant for 30 secondsBonding agent was applied and cured for 10 seconds. Filtek™ Z350 XT nanocomposite applied according to manufacturer’s instructions and light cured for 40 secs. Finishing and Polishing was done (Sof-Lex™).

Group IIFuji II LC RMGIC injected (1 mm) directly onto the cavity surface.Etching and bonding Composite was pre-heated in the Waxmelter that elevates composite temperature to 68ºC. Filtek™ Z350 XT nanocomposite was applied according to manufacturer’s instructions as stated above.

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Group IIIFuji II LC capsules were heated in a water bath (at 40° C) for 90 seconds prior to mixing and injected according to manufacturer’s instructions. Etching and bonding Composite was pre-heated in the Waxmelter that elevates composite temperature to 68ºC. Filtek™ Z350 XT nanocomposite was applied according to manufacturer’s instructions as stated above.

Group IVFuji II LC RMGIC was inject (1 mm) directly onto the cavity surface. Etching and bonding Filtek™ Z350 XT nanocomposite was applied according to manufacturer’s instructions.

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• Samples were subjected to thermocycling: 500 cycles at 5ºc, 37ºc and 55ºc, dwell time of 30 seconds and transfer time of 15 seconds in a customized thermocycling device.

• Apices were sealed with modelling wax and two coats of nail polish.

• Samples were soaked in freshly prepared 0.5% basic fuchsin solution for 24 hours and washed thoroughly for few minutes.

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• Samples were sectioned in mesio-distal direction from center of the restorations and observed under a stereomicroscope(12x)

• Scores for the degree of dye penetration microscopic observations were scored using the iso microleakage scoring system (iso/ts 11405:2003).

RESULTS 12

Score 0 Score 1 Score 2 Score 3

Group 1 0 14 5 1

Group 2 2 13 3 2

Group 3 0 12 6 2

Group 4 1 11 8 1

Score 0 Score 1 Score 2 Score 3

Group 1 4 1 0 15

Group 2 1 0 7 12

Group 3 3 2 1 14

Group 4 1 1 2 16

RESULTS 13

• Obtained values were recorded and subjected to Statistical analysis by “Chi Square test,” “Kruskal Wallis ANOVA test” and “Mann- Whitnney U Test”.

• The obtained values and results were depicted using tables and bar diagrams at 5% level of significance.

• The results revealed that there was no significant difference observed for microleakage amongst all the groups.

• Microleakage was significantly lower at the occlusal margins in comparison to cervical margins of Class II open sandwich restorations.

• No significant difference was observed for microleakage in the frequency distribution of scores amongst all the groups on the occlusal surface of class II open sandwich restorations.

• There was no significant difference observed for microleakage amongst all the groups on cervical margins of class II open sandwich restorations.

• However, there was a significant difference observed for microleakage in frequency distribution of scores on cervical margins of group 2 and 4.

• None of the techniques were able to completely eliminate microleakage as far as cervical and occlusal margins are concerned.

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DISCUSSION

• One of the major limitations of restoring posterior teeth with composite resins is the lack of proper adaptation of the material, particularly at the gingival margin leading to microleakage and further causing post-operative sensitivity, pulpal inflammation and secondary caries in the restored tooth.

• This has led to development of several techniques such as sandwich technique, centripetal build up technique, incremental placement method, horizontal layering technique, oblique layering technique etc. out of which Sandwich technique is the most popular which is being used extensively.

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• Use of rmgic as base material in open sandwich restoration reduces the bulk of resin composite used, thereby decreasing polymerization shrinkage of resin composite and improving the marginal adaptation.

• Fluoride releasing property of gic is considered to have some inhibitory effect on caries formation and progression around the restoration.

• Aadvantages of rmgic includes longer working time and operator control over setting reaction by light activation, reduced brittleness, increase of tensile and flexural strengths, resistance to desiccation and acid attack, lower moisture sensitivity and solubility.

• Hence, rmgic fuji ii lc capsules (gc america inc.) For open sandwich technique was used in this study.

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• Although, it has been scientifically proven that adaptation of composite improves with prewarming, there is very limited data on effect of prewarming on RMGIC.

• More recently a new category of resin composite based on nanotechnology was developed (Nanofilled composites).

• The increase in filler level results in a lower amount of resin in nanocomposites and also significantly reduces polymerization shrinkage.

• Various authors have tested nanocomposites for microleakage in Class II restorations and results were found to be promising {Raju RK et al. (2003)20, Fabianelli et al. (2010)}.

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• The concept of prewarming composites was conceived by Bortolotto et al (2003).

• It leads to improved flow with improved degree of monomer conversion, polymerization rate and hardness especially in deep class II restorations.

• Hence, in this study the composite (Filtek Z350 XT, 3M ESPE) was prewarmed to 6 °C before placement.8̊ 8̊%

• The samples were thermocycled to mimic cyclic temperature changes in oral conditions.

• The use of organic dyes is one of the most popular to assess microleakage. The samples were immersed in 0.5% basic fuchsin for 24 hrs. A most commonly used and advocated magnification device, Stereomicroscope was used to score samples.

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• Results suggested that microleakage scores were lower for the occlusal margins as compared to cervical margins in all the groups.

• It was also observed that there was no statistical difference in mean occlusal scores amongst all the groups (1, 2, 3 and 4) but a statistically significant difference was observed in frequency distribution of scores between groups for cervical microleakage.

• In our study, since all the margins of occlusal box were in enamel so that can be one of the reasons for comparatively lesser scores on occlusal surface as compared to cervical part of class II preparations.

• The reason could be higher inorganic content in enamel on account of which acid etching creates microporosities and allows better penetration of adhesive system, thus forming a strong micromechanical bond with composite resin.

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• Regarding the role of lining material, some studies have shown that there were no significant difference in microleakage with or without the use of RMGIC when the margins were placed in the enamel (Neme et al. 2002) and (Tredwin et al. 2005).

• Moreover, the choice of material i.e nanofilled composite, which has a high filler loading and lower resin matrix and hence lower polymerization shrinkage must have also added to the lower microleakage scores on occlusal surfaces.

• This is in aggrement with the studies done by Fabianelli A et al. (2010), Bichacho N et al. (1994), Belli S et al. (2007), Efes BG et al. (2006).

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REPLACEMENT /ANKYLOTIC RESORPTION

• involves the progressive replacement of tooth structure by alveolar bone and ultimately tooth loss.

• Replacement resorption follows the death of viable PDL cells due to compression or drying of the ligament cells.

• Sometimes an intact cementum/ cementoid layer may act as a biological barrier, so that ankylosis is not accompanied by replacement resorption.

(GS Heithersay, Australian Dental Journal Supplement 2007;52)

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• No statistically significant difference among the groups in occlusal microleakage also suggest that prewarming does not play a significant role in reducing microleakage in our study, inspite of increased adaptation of composites because of prewarming.

• Inspite of the lower occlusal microleakage scores, all of the groups exhibited microleakage.

• This could be the due to presence of less resin matrix available to wet cavity walls as nanocomposites have high filler loading and less resin matrix and polymerization shrinkage inherent in resins which cannot be completely eliminated.

• Similar results were obtained by Dietrich T et al (1999), Loguercio AD et al (2002), Dietrich T et al (2000), Friedl KH et al (1997), Miller MB et al (1996) and Roulet JF et al (1997)

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• The results of mean microleakage on the cervical surface when compared showed a statistically insignificant difference between the groups but there was a statistically significant difference between the groups according to frequency distribution score for microleakage.

• Group 1 and group 3 showed better performance than group 2 and group 4.

• Since in both the groups (1 and 3), RMGIC was prewarmed before placement so, it can be presumed that prewarming of RMGIC could have led to better results.

• The possible reason could be that prewarming of RMGIC resulted in better flow leading to better marginal adaptation with less voids.

• Secondly, prewarming could have initiated better movement of monomer radicals of resin component as well leading to better polymerization with improved properties.

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• Ankylosis in the developing dentition can severely disrupt arch formation.

• In some cases of ankylosis and limited replacement resorption, a surgical repositioning procedure can be attempted to restore arch integrity.

• This procedure can be supplemented with the application of Emdogain to the affected root area in an attempt to repopulate the denuded surface with cementoblasts.

• Even if re-ankylosis and replacement resorption continue, the damage to arch development can often be avoided or minimized.

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• Another probable reason could be that as RMGIC sets by acid base and polymerization reaction and each mechanism depends on reactant diffusion prior to gelation.

• The application of heat to RMGIC could have resulted in better penetration of reacting moieties in the dentinal tubules leading to a more consistent bonding.

• Since, this is a study with limited no. of samples, we suggest some more research to be done involving more no. of samples and more parameters before advocating prewarming of RMGIC or composite or both in a class II open sandwich restoration as a standard procedure to improve marginal adaptation and hence longevity of the restoration.

CONCLUSION

Within the limitations, this study concluded that prewarming RMGIC

leads to improved flow and marginal adaptation in class II open sandwich

restorations extending onto root surface and prewarming composites also has some additional advantages

but not very significant in class II open sandwich restorations.

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