Author and correspondence: wedad yassin awliya



Download 63.8 Kb.
Date conversion18.11.2016
Size63.8 Kb.




Leakage Pathway of Class V Cavities Restored With Different Flowable Composite Resin Restorations

Author and correspondence:

WEDAD YASSIN AWLIYA

BDS, MSC

Associate Professor, Department of Restorative Dental Science, College of Dentistry, King Saud University, Riyadh, Saudi Arabia

P.O. box 56781 Riyadh 11564


Home Tel: 0096614808037 mobile: 00966505294516

E-mail wawliya@hotmail.com


and

ALI M. EL-SAHN

BDS, HDD, MSC

Professor, Department of Restorative Dental Science, College of Dentistry, King Saud University, Riyadh, Saudi Arabia


E-mail: profelsahn@hotmail.com

SUMMARY


The purpose of this study was to investigate the leakage pathway of facial and lingual class V cavities, restored with different flowable composite resins and bonded with one bonding agent, by examining the resin/dentin interface. Forty Class V cavities were etched with 37% phosphoric acid gel, Single Bond dental adhesive was applied, then the cavities were randomly divided into four groups (n=10). Three groups were restored with one of the three flowable composite resins (Grandio Flow, Filtek Flow, and Admira Flow). The fourth group was restored with Z250 (hybrid composite resin) to serve as a control. Specimens were then placed in 50% w/v silver nitrate solution for 24 hours and immersed in a photodeveloping solution for 8 hours. Thereafter, the specimens were sectioned bucco-lingually, polished, mounted on stubs, gold sputter coated, and examined by scanning electron microscope.

Silver particle penetration length with and without gap formation was measured directly on the scanning electron microscope monitor and calculated as percentage of total length of cut dentin surface that was penetrated by silver nitrate. The data were analyzed with one way ANOVA and Tukey HSD test. The groups restored with Filtek Flow and Admira Flow showed microleakage pattern where silver nitrate penetration was observed with gap formation at the tooth/restoration interface, and Filtek Flow recorded significantly higher leakage than Admira Flow. Grandio Flow showed similar marginal adaptation to Z250 composite resin with no gap formation at the interface. However, silver ions had penetrated beneath the resin impregnated layer in cavities restored with Grandio Flow and Z250 indicating nanoleakage occurred. This study suggests that volumetric shrinkage in composite resins is still a problem. Although, some new technologies are trying to solve the problem of composite shrinkage, the 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.


Key Words: Microleakage, Nanoleakage, Composite Resin Restorations, Flowable Composite Resins, Scanning Electron Microscope.

INTRODUCTION

Despite improvements in the current formulations of composite resin, polymerization shrinkage remains a problem.1 Polymerization shrinkage of composite resin may induce mechanical stresses on tooth structure through the bond to enamel and dentin.2 These stresses can contribute to failure of the weakest portions of a composite-dentin interface.2,3 This process can cause micrometer wide marginal gaps, thus opening a path for migration of microorganisms and potentially inducing secondary caries.4 Several materials and methods have become advocated to minimize the development of this gap. Current dentin adhesive systems that created a hybrid layer between resin and dentin have shown improved marginal seal due to the use of acidic molecules and improved bonding technology.5 Another approach to create a gap-free bond is the use of an elastic intermediate layer of resin between the composite and adhesive resin that may absorb the contraction stress of the composite during polymerization.6,7 However, 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. Rather, 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 dentinal fluid. To distinguish this leakage from the typical microleakage it was called nanoleakage. In order to quantify the degree of nanoleakage, silver nitrate penetration has been used for scanning electron microscopy (SEM) investigation.9,10 The amount of silver penetration depends on the type of bonding agent and on the different parameters of the application technique such as etching time and dentin moisture.11

Flowable composites were introduced in late 1996.12 They have a filler size similar to hybrid composites but lower filler content (60%-70% by weight and 60%-75% by volume).13 The reduced filler loading of flowable composites compared with their hybrid analogs leads to enhanced flow and reduced elastic modulus.13 The lower elastic modulus indicates that flowable composites have a greater ability to flex with the tooth than stiffer restorative materials.14 Also, this material may act as a stress-breaker and seems to wet the cavity more completely than the conventional sticky resin based restorative materials.14,15 However, Braga et al16 showed that flowable composites produced polymerization contraction stress similar to hybrid composite. Also, Chimello et al17 and Estafan et al18 found no difference in occlusal or cervical microleakage of cavities restored with flowable or hybrid composite resins.

In addition to hybrid flowable composite resin, many relatively recent classes of flowable composites have been introduced. From these classes are Ormocers (organic modified ceramic) and nano technology flowable composites.19,20 Flowable composites have been advocated as a lining in class I and II hybrid composite resin restorations, and as a restorative material in small class V cavities. 19

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

Twenty freshly extracted caries free human third molars were cleaned and examined with a stereomicroscope to exclude any cracked teeth. Saucer-shaped cervical cavities approximately 2.5 mm in diameter and 1.5 mm deep were prepared on both buccal and lingual surfaces of each tooth using round carbide burs (Mid West Dental Product Corp., Des Plaines, IL, USA) in a high-speed hand piece and under water spray. Butt-joint occlusal and gingival margins were located 1.5 mm above the cemento-enamel junction, and 1 mm below the cemento-enamel junction respectively.



The teeth were randomly divided into four groups, each group contained ten cavities. One bonding agent, Single Bond (3M Dental products, St. Paul, MN, USA), three flowable composites: Grandio flow (Voco GMBH, Germany), Admira flow (Voco GMBH, Germany) and Filtek flow (3M Dental products, St. Paul, MN, USA) and one microhybrid composite resin Z250 (3M Dental products, St. Paul, MN, USA) were used to restore the prepared cavities following manufacturer recommendations. Before restoration, all cavities were etched with 37% phosphoric acid gel (Kuraray Co., Ltd., Osaka, Japan) for 15 seconds, rinsed with water for 20 seconds, and blotted dry leaving dentinal surfaces slightly moist. Two consecutive coats of the adhesive were then applied to cavity walls; lightly air dried and light cured for 10 seconds with a Heliolux light-curing unit (Vivadent USA, Amherst, NY 14228). The first three groups were then restored with one of the tested flowable composites. The fourth group was restored with Filtek Z250 to serve as a control. The flowable restorative materials were injected as one increment into the cavity, while Z250 was placed with a bulk placement technique. After light curing for 40 seconds, all restorations were finished and polished with Sof-lex disks (3M). During polishing, all specimens were checked with a light microscope (Wild Photomakroskop M400, Heerbrugg, Switzerland) at 20X magnification to ensure no flash remained along the margins of the restorations. If flash still remained, the specimen was repolished until no flash was visible under the microscope. All experimental teeth were then thermocycled for 1500 cycles in a thermocycling apparatus (MCT2, AMM 2 instrument, Sao Paulo, Sp, Brazil) between water baths of 5 ± 2 0C and 55 ± 2 0C with a dwell time of 60 s and transfer time of 30 s between each bath. After thermocycling, the root apices of each tooth and the occlusal portions were sealed with a Silux Plus composite resin material (3M Dental products). The entire surface of each tooth was coated with a clear non fluorescent nail polish to ensure a perfect seal with the exception of 1 mm all around the circumference of the 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 a low-speed, water-cooled diamond saw (Model 650, South Bay Technology Inc., San Clement, CA, USA). A total of 20 specimens were obtained for each group. All cut surfaces were cleaned ultrasonically, air dried, mounted on stubs, left to rest for 24 hours in tight container , gold sputter coated (Polaron E-5200 Energy Beam Sciences, Agawan, MA, USA), and examined by SEM (JSM, 6360LV, JEOL, Tokyo, JAPAN)

The marginal micromorphology of each restoration was examined and recorded following the method described by Sano et al8. The length of any gap or silver penetration along the preparation wall as examined under both low (X200) and high (X1000) magnification, since in some cases the loosely distributed silver particles could not be observed under the lower magnification. The length of the gap and the internal cavity walls or the silver penetration along the preparations were quantitatively analyzed directly on the SEM monitor using a 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,

Where P= length of the gap or length of silver nitrate penetration along the resin/dentin interface and L= total length of the dentinal cavity wall on the cut surface. The results were statistically analyzed by one way ANOVA and Tukey HSD tests at a 0.05 significant level.
RESULTS

Table 1 shows the mean percentage and standard deviations of the silver nitrate penetration with and without gap in the experimental groups. All the samples restored with Filtek Flow and Admira Flow demonstrated marginal gap formation at the tooth/restoration interface with silver nitrate penetration which indicates microleakage. Cavities restored with Filtek Flow showed significantly higher leakage scores than those restored with Admira Flow (P=0.024). One sample restored with Filtek Flow was excluded from the study because of sever deposition of silver nitrate inside the dentinal tubules therefore; it was difficult to quantify the silver nitrate.

On the other hand, silver nitrate penetration without gap formation was observed only in cavities restored with Z250 and Grandio Flow composite resin which indicates nanoleakage. Grandio Flow showed significantly less nanoleakage scores than Z250 (P =0.001). However, only one cavity restored with Z250 composite resin showed true gap formation.

The leakage pathways and patterns revealed by SEM imaging of representative resin/dentin interfaces are shown in figures 1-4. No penetration

of silver nitrate or gap formation was detected at the enamel margin of the restorations. Thus only the cementum/dentin margins were photographed by the SEM.

Different nanoleakage patterns were observed in the groups restored with Grandio Flow and Z250 composite resin. The silver nitrate depositions were observed mostly at the base of the hybrid layer (Figure 3) and diffused within the hybrid layer (Figure 4)




DISCUSSION
Silver nitrate was selected in this study because it has been accepted as a suitable method for measuring both microleakage and nanoleakage.21 The silver ion is very small (0.059 nm-diameter) when compared to the size of a typical bacterium (0.5-1.0 µm).22 This small size and a high reactivity to stain after binding tightly to any exposed collagen fibrils 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 restorations 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 It has been reported that marginal gaps increase as cavity design change from a V-shaped to a box shaped configuration. The term ‘cavity configuration factor’ (C-factor) has been used to describe the difference in cavity design.26 A high C- factor, which indicates a high number of bonded to unbonded composite surfaces, corresponds to a high stress value.26 Hence saucer-shaped, shallow cavities were employed in this study to reduce composite contraction stress.27 Also, all samples in this study were exposed to the same thermal stress through thermocycling. However, gap formation was observed at the composite/dentin interface mostly in cavities restored with Filtek Flow, and Admira Flow. The gaps found in the present study were considered true gaps because 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

In the present study 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 of the different bonding systems to eliminate marginal leakage. Nevertheless, the different materials showed different leakage pathways. Filtek Flow and Admira Flow showed typical microleakge manifested as gap formation at the tooth/restoration interface. This indicates polymerization shrinkage which results in resin pulling away from dentin leading to the gap formation. On the other hand, Grandio Flow showed similar behavior to the hybrid restorative Z250 where gaps were rarely seen. Instead the last two materials showed the typical leakage path way that was described by Sano et al8 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 is a nano filled composite which has higher filler loading (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. It was not the intension of this work to measure volumetric shrinkage or contraction stress of the flowable composites. However, polymerization shrinkage frequently manifests as resin pulling away from dentin, leading to gap formation.14

Although almost no gaps were found in cavities restored with Grandio Flow and Z250 hybrid composite resin, another pathway for leakage was observed. Silver nitrate deposition was noticed within the hybrid layer which indicates that even if the restorative material resists shrinkage, the adhesive systems are still unable to completely eliminate marginal leakage. The bonding system that was used (Single Bond) is a single-bottle system where the adhesive and the primer are combined in one bottle. It is possible that lack of a separate primer may reduce the infiltration depth of the adhesive resin in demineralized collagen fibrils, thus reducing adhesion and sealing capacity.

Post operative sensitivity and restoration loss have been reported to be the most frequent sequel of gap formation (microleakage) between enamel or dentin and the restorative material. However, nanoleakage within the hybrid layer cannot allow microorganism migration within the tooth structure because the pore size in partially hybridized dentin is too small.30 Nevertheless, this kind of leakage may allow the penetration of bacterial products and oral fluid along the interface which may result in hydrolytic breakdown of either the adhesive resin or collagen within the hybrid layer. This could compromise the stability of the resin dentin-interface.31



CONCLUSIONS

Within the limitations of this study, the following conclusions can be made:



  • Filtek Flow and Admira Flow composite resin showed a significant microleakage pattern with gap formation at the restoration/dentin interface.

  • Grandio Flow showed a similar leakage pattern to Z250 hybrid composite resin where no gaps were seen at the restoration/dentin interface. Silver ions penetrated beneath the resin impregnated layer consistent with nanoleakage.

  • The bonding system used in this study did not achieve perfect sealing at the restoration/dentin interface


REFERENCES


  1. Hilton TJ. (2002) Can modern restorative procedures and materials reliably seal cavities? In vitro investigations. Part I American Journal of Dentistry 15 (3) 198-210

  2. Davidson CL & Feilzer AJ (1997) Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives Journal of Dentistry 25(6)435-440

  3. carvalho RM, Pereira JC, Yoshiyama M & Pashley DH (1996) A review of polymerization contraction: The influence of stress development versus stress relief Operative Dentistry 21(1) 17-24

  4. Calheiros FC, Sadek FT, Braga RR & Cardoso PE (2004) Polymerization contraction stress of low-shrinkage composites and its correlation with microleakage in class V restorations Journal of Dentistry 32(5) 407-12.

  5. Eick JD, Miller RG, Robison SJ, Bowles CQ, Gutshall PL & Chappelow CC (1996) quantities analysis of the dentin adhesive interface by Auger spectroscopy Journal of Dental Research 75 (4) 1027-1033

  6. Condon JR & Ferracane JL (2000) Assessing the effect of composite formulation on polymerization stress Journal of American Dental Association 131(4) 497-503

  7. Montes MA, de Goes MF, Da Cunha MR & Soares AB (2001) A morphological and tensile bond strength evaluation of unfilled adhesive with low-viscosity composites and filled adhesive in one and two coats Journal of Dentistry 29 (6) 435-441

  8. Sano H, Takatsu T, Ciucchi B, Horner JA, Matthews WG & Pashley DH (1995) Nanoleakage: leakage within the hybrid layer Operative Density 20(1) 18 -25.

  9. Li H, Burrow MF & Tyas MJ (2000) Nanoleakage patterns of four dentin bonding systems Dental Material 16 (1) 48-56.

  10. Dorfer CE, Staehle HJ, Wurst MW, Duschner H & Pioch T (2000) The nanoleakage phenomenon: influence of different dentin bonding agents, thermocycling and etching time. European Journal of Oral Science 108 (4) 346-351.

  11. Li H, Burrow MF &Tyas MJ (2000) Nanoleakage of cervical restorations of four dentin bonding systems Journal of Adhesive Dentistry 29(1) 57-65.

  12. Bayan SC, Thompson JY, Swift EJ Jr, Stamatiades P & Wilkerson M (1998) A characterization of first-generation flowable composites Journal American Dental Association 129(5) 567-577.

  13. Frankenberger R, Lopes M, Perdigao J, Ambrose WW & Rosa BT (2002) Use of flowable composites as filled adhesives Dental Material 18 (3) 227-38.

  14. Kleverlaan CJ & Feilzer AJ (2005) Polymerization shrinkage and contraction stress of dental resin composites. Dental Material 21(12)1150-1157.

  15. Braga RR, Ballester RY & Ferracane JL (2005) Factors involved in the development of polymerization shrinkage stress in resin-composites: a systematic review Dental Material 21(10) 962-970.

  16. Braga RR, Hilton TJ & Ferracane JL (2003) Contraction stress of flowable composite materials and their efficacy as stress-relieving layers Journal of American dental Association 134(6) 721-728.

  17. Chimello DT, Chinelatti MA, Ramos RP & Palma Dibb RG (2002) In vitro evaluation of microleakage of a flowable composite in class V restoration. Brazilian Dental Journal 13 (3):184-187.

  18. Estafan AM & Estafan D (2000) Microleakage study of flowable composite resin systems Compendium Continuing Education Dentistry 21(9)705-708.

  19. Kugel G & Perry R (2002) Direct composite resins: An update Compendium Continuing Education Dentistry 23(7) 593-603.

  20. Mitra SB, Wu D & Holmes BN (2003) An application of nanotechnology in advanced dental materials Journal of American Dent Association 134(10)1382-1390.

  21. Mair LH (1991) Staining of in vivo subsurface degradation in dental composite with silver nitrate Journal Dental Research 70(3) 215-220.

  22. Hammesfahr PD, Huang CT& Shffer SE (1987) Microleakage and bond strength of resin restorations with various bonding agents. Dental Material 3(4)194-199.

  23. Li H, Burrow MF& Tyas MJ (2002) The effect of thermocycling regimens on the nanoleakage of dentin bonding systems Dental Material 18 (3)189-196.

  24. Truffier-Boutry D, Demoustier-Champagne S, Devaux J, Biebuyck JJ, Mestdagh M, Larbanois P, Leloup G (2006) A physico-chemical explanation of the post-polymerization shrinkage in dental resins. Dental Material 22 (5)405-412.

  25. Kleverlaan CJ & Feilzer AJ (2005) Polymerization shrinkage and contraction stress of dental resin composites. Dental Material 21(12)1150-1157.

  26. Feilzer AJ, De Gee Aj & Davidson CL (1987) Setting stress in composite resin in relation to configuration of the restoration Journal of Dental Research 66(11)1636-1639

  27. Asmussen E & Munksgaard EC (1988) Bonding of restorative resins to dentin: Status of dentin adhesive and impact on cavity design and filling techniques International Dental Journal 38(2) 97-104.

  28. Tay FR, Gwinnett AJ, Pang KM & Wei SHY (1995) Variability in microleakage observed in total-etch wet-bonding technique under different handling condition. Journal of Dental Research 74 (5)1168-1178.

  29. Labella R, Lambrechts P, Van Meerbeek B & Vanherle G (1999) Polymerization shrinkage and elasticity of flowable composites and filled adhesives. Dental Material 15(2) 128-137.

  30. Van Meerbeek B, Yoshida Y & Lambrechts P (1998) A TEM study of two water-based adhesive systems bonded to dry and wet dentin Journal of Dent Research 77(1) 50-59.

  31. Okuda M, Pereira PN, Nakajima M, Tagami J & Pashley DH (2002) Long-term durability of resin dentin interface: nanoleakage vs. microtensile bond strength Operative Density 27(3) 289-96.


Table 1. Mean Percentage and standard deviations (SD) of silver nitrate penetration with and without gap formation


Material

N

Mean (SD) Percentage of silver nitrate penetration with gap formation

Microleakage



N

Mean (SD) Percentage of silver nitrate penetration with out gap formation

Nanoleakage



Z250

1

2.10 (7.2) a

19

24.4 (5.7) a

Grandio Flow

0

0

20

13.1 (5.1) b

Admira Flow

20

19.5 (5.1) b

0

0

Filtek Flow

19

25.8 (7.5) c

0

0

Means with the same letters are not significantly different at P<0.05 for each column









Figure 1. Low and high magnification SEM image (X200 and 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.








Figure3

Figure 2.

Low and high magnification SEM image (X200 and 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.


R


D



Figure 3. Low and higher magnification ((X200 and 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




Figure 4. 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


The database is protected by copyright ©dentisty.org 2016
send message

    Main page