Leakage Path Ways Of Class V Cavities Restored With Different Flowable Composite Resin Restorations: A Scanning Electron Microscope Study WEDAD AWLIYA Associate Professor, Department of Restorative Dental Science and ALI M EL-SAHAN Professor, Department of Restorative Dental Science.

IntroductionIntroduction

Polymerization shrinkage of composite resin may induce mechanical stresses on tooth structure via the bond to enamel and dentin. These stresses can contribute to failure of the weakest adhesive attachment of composite- dentin interface.2,3 This process can cause micrometer wide marginal gap thus opening a path for migration of microorganisms, and potentially induce secondary caries.4

Several materials and methods have become advocated to minimize the development of the gap at tooth/restoration interface.

Dentin adhesive systems that created a hybrid layer between resin and dentin have shown improved marginal seal due to the application of the total-etch technique and improved bonding technology.5

Another approach to create gap-free bond is the use of an elastic intermediate layer of resin between composite and adhesive resin that may absorb the contraction stress of the composite during polymerization such as flowable resin. 6,7

Sano and others,8 in 1994, described a leakage pathway through the porous zone at the hybrid layer-adhesive interface without gap formation. This leakage is not the classical microleakage that can be seen by conventional X10-30 microscopic magnification

it represents a leakage occurring within nanometer-sized spaces in the base of the hybrid layer that have not been filled with adhesive resin or which were left when poorly polymerized resin was extracted by oral dentinal fluid. To distinguish this leakage from the typical microleakage it was called nanoleakage.

The aim of this study was to investigate by the SEM the leakage pathway of class V cavities restored with different flowable composites using one bonding agent.

Materials and methods Twenty freshly extracted caries were used for the study

Saucer-shaped cervical cavities (approximately 3 mm in diameter and 1.5 mm deep) were prepared on both buccal and lingual surfaces of each tooth using round carbide burs in a high- speed hand piece and under water spray.

40 preparations Single Bond Grandio Flow 10 Filtek Flow 10 Admira Flow 10 Z250 Hybrid 10

All experimental teeth were then thermocycled 1500 cycle in a thermocycling apparatus with a bath of 5± 2 0C and 55±2 0C, a dwell time of 60s, and transfer time of 30 s between each bath.

After thermocycling, the root apices of each tooth and occlusal portions were sealed with a Silux plus composite resin material (3M Dental products). The entire surface of each tooth was coated with clear non fluorescent nail polish to ensure perfect seal with the exception of 1 mm all around the circumference of restoration margins.

The teeth were then placed in 50% (w/v) silver nitrate solution for 24 hours in total darkness, thereafter, they were rinsed under running water for 5 min., immersed in photodeveloping solution, and exposed to fluorescent light for 8 hours so that silver ion reduction to metallic silver would be completed 9,10.

The teeth were then removed from the developing solution, rinsed thoroughly, then sectioned bucco-lingually with low-speed, water-cooled diamond saw

All cut surfaces were cleaned ultrasonically, air dried, mounted on stubs, left to rest for 24 h, gold sputter coated (Polaron E-5200 Energy Beam Sciences, Agawan, MA, USA), and examined by SEM (JSM, 6360LV, JEOL, Tokyo, JAPAN)

The length of the gap and the internal cavity walls or silver penetration along the preparations was quantitatively analyzed directly on SEM monitor, using multi-point measuring device.

The leakage scores were calculated as the percent of the total cut dentin surface that was penetrated by silver nitrate or P/L X 100, P= length of the gap or length of silver nitrate penetration along resin/dentin interface and L= total length of dentinal cavity wall on the cut surface.

Table 2. Mean Percentage and standard deviations (SD) of silver nitrate penetration with and without gap formation MaterialN Mean (SD) Percentage of silver nitrate penetration with gap formation MicroleakageN Mean (SD) Percentage of silver nitrate penetration with out gap formation Nanoleakage Z (7.2) a (5.7) d Grandio Flow (5.1) e Admira Flow (5.1) b 00 Filtek Flow (7.5) c 00 Means with the same letters are not significantly different at P<0.05

Different nanoleakage patterns were observed in the groups restored with Grandio Flow and Z250 composite resin. The sliver nitrate deposition was observed mostly at the base of the hybrid layer Figure (5) and within the adhesive layer Figure (6)

R D Figure 1. High magnification SEM image (X1000) of the interface between Filtek Flow composite resin and dentin with gap formation and silver nitrate deposition at the restoration side. D= Dentin, R= Restoration, Arrow indicates gap

D R Figure 2. Low magnification SEM image (X200) of the sever deposition of silver nitrate within the dentinal tubules shown by some Filtek Flow samples D= Dentin, R= Restoration, Arrow indicates gap

D R Figure 3. High magnification SEM image (X1000) of the microleakage pattern shown at interface between Admira Flow and dentin. Gap was noticed at the interface with silver nitrate deposition at dentine side. D= Dentin, R= Restoration, Arrow indicates gap.

Figure 4. High magnification SEM image (X1000) showing excellent adaptation of the restoration (Grandio Flow) to the dentin with the adhesive in between. No silver penentration could be detected along the interface. D= Dentin, R= Restoration, A= Adhesive, H= hybrid layer.

H R A D Figure 5. Low magnification (X200) and higher magnification (X1000) SEM image of the interface between Grandio Flow composite resin and dentin. No gap was seen at the interface. However, Silver nitrate deposition was noticed at the bottom of the hybrid D= Dentin, R= Restoration, A= Adhesive, H= hybrid layer, Arrow indicates silver nitrate

R D R D H A Figure 6. Low magnification (X200) of SEM image at the interface between Z250 composite resin and dentin. Excellent adaptation of the restoration and no gap can be seen. At higher magnification (x1000) silver nitrate deposition can be seen within the hybrid layer. D= Dentin, R= Restoration, A= Adhesive, H= hybrid layer

Discussion

Silver nitrate was selected in this study because it has been accepted as a suitable method for measuring both microleakage and nanoleakage.21 Silver ion is very small (0.059 nm-diameter) when compared to the size of typical bacterium ( µm).22 This small size and high reactivity to stain, binding tightly to any exposed collagen fibril that are not enveloped by the adhesive resin, which makes sliver nitrate the most appropriate agent to detect the nanoporosities within the hybrid layer.23

Clinical failure of composite resin restoration due to disruption of the bonded interface between composite and dentin remains a frequent occurrence.1 such interfacial defects may develop as a consequence of long-term thermal and mechanical stresses, or during the restorative procedure itself, due to stresses generated by composite polymerization shrinkage.24,25

Gap formation was observed at composite/dentin interface mostly in cavities restored with Filtek Flow, and Admira Flow. The gap formation was possibly due to polymerization shrinkage of composite resin which results in resin pulling away from dentin leading to the gap formation. Using silver nitrate staining, the artifactual gaps created upon high vacuum dehydration during specimen preparation for SEM can easily be differentiated from true gaps by the absence of silver staining along the gap border.28

One bonding agent was used with the four restorative materials in order: to study the leakage path way of the composite resins and to exclude the variation that might result from using different bonding systems Nevertheless, the different materials showed different leakage pathways.

Garndio Flow showed similar behavior to the hybrid restorative Z250 were gaps were rarely seen. They showed the typical leakage path way that was described by Sano et al and termed as nanoleakage.

The different behavior of the four materials could be attributed to the different chemistry of these materials. Volumetric shrinkage experienced by composite is determined by several factors including its filler volume.15 Flowable composites present higher volumetric shrinkage than hybrid composite due to their reduced filler content and increased resin matrix.29

Filtek Flow has 47% filler by volume and Admira flow has 50% filler by volume which might explain the reason of their volumetric shrinkage. On the other hand, Grandio Flow (65.6%) than the hybrid Z250 composite resin (60%). This might explain the low volumetric shrinkage of Grandio Flow and subsequently its resistance to gap formation.

Silver nitrate deposition was noticed within the hybrid layer which indicate that even if the restorative material resist shrinkage the adhesive systems still unable to completely eliminate marginal leakage. The bonding system that was used (Single bond) is single-bottle system where the adhesive and the primer are combined in one bottle. It is possible that lack of separate primer may reduce the infiltration depth of the adhesive resin, thus reducing adhesion and sealing capacity.

CONCLUSIONS and clinical significant This study suggest that volumetric shrinkage in composite resins still a problem. Although, some new technology trying to solve the problem of composite shrinkage. Bonding system used in this study did not achieve perfect sealing at the restoration/dentine interface. This might affect the durability of the bond to dentin.