Adhesion to Moderate Fluorosed Enamel: Silorane Composite versus Methacrylate Composite: in vitro study.




Dental News Volume XXII, Number IV, December, 2015


By Dr. Chems Belkhir, Dr. Afef Karmandi, Dr. Rim Mabrouk, Dr. Najet Aguir, and Dr. Mohammed Semir Belkhir







Introduction

Dental fluorosis is a hypomineralisation of the dental hard tissues induced by an excessive intake of fluoride occurring during odontogenesis.4 Fluorosis is clinically manifested, depending on individual susceptibility, by opaque white spots, lines following the perikymata direction, or wavy yellowish and brownish striations of the enamel. Later, the opaque surfaces develop and turn into chalky and the enamel develops small cavities. After tooth eruption, the enamel pits and fissures turn into brown or black.22 
A fluorosed tooth requires a particular therapeutic. The fluorosed enamel is hard, brittle and acido-resistant.4, 22 These features represent a real problem for resin composite bonding to this enamel which is little studied.
Few years ago, a low shrinkage restorative material of polymerization; silorane composite; was introduced in the dental market. Several studies have shown that silorane composite present better mechanical and physical properties than conventional methacrylate based composite.7, 14, 29
This study deals with a clinically relevant problem that can influence the dental practice it is bonding on moderate fluorosed enamel. The difficulty of bonding on this enamel is the object of limited number of studies. This difficulty is in relation to the specificities of the fluorosed enamel.
The aim of the study is to evaluate the adhesion quality of silorane composite on moderately fluorosed enamel in vitro using thermo cycling and infiltration of methylene blue and to compare bonding efficacy of coronal restorations by methacrylate based composite (micro-hybrid) and those by silorane composite on fluorosed teeth. 


Materials and methods

Sample collection

Twenty four recently-extracted, non-carious human teeth (maxillary and mandibular molars) were stored in water and in a refrigerator until use after cleaning with pumice water slurry in order to remove tartar, soft tissues and any other debris.
All the collected teeth presented a moderate fluorosis according to the Thylstrup and Fejerskov index (TFI= 4). 

Cavity preparation 

Class II box cavity were prepared on the mesial and distal surfaces of each tooth. These preparations were accomplished with carbide burs in a high-speed hand piece with water spray. There was no occlusal connection between the preparations.
Each cavity was placed at two millimeters of the cemento-enamel junction and presented the following dimensions:
- 3 mm height,
- 2 mm in the bucco-lingual axis,
- 1, 5 mm in the mesio-distal depth.
Buccal and lingual walls of the preparations were approximately parallel and connected to the gingival wall with rounded angles.
Prepared teeth were stored in distilled water. 

Sample preparations

The teeth were randomly distributed between two groups of 12 teeth.

Following cavity preparation, each tooth was rinsed with distilled water and dried.


Group 1

The distal faces

The cavities located on the distal faces were etched for 30 seconds with an orthophosphoric acid gel at 35% (3M) and rinsed for 30 seconds with 5 cc of distilled water with the help of a syringe. The preparations were gently dried with an air gun and a cotton pellet.
A mono component adhesive (scotch bond®, 3M) was applied by friction on the surfaces for 10 seconds, gently air dried and light cured for 20 seconds. 
A methacrylate based composite (Valux®, 3M) was applied in three successive layers (1mm thinness each). Each layer was photo polymerized for 40 seconds with a second generation LED lamp. 
A transparent strip was tightened and held by finger pressure against the gingival margin of the cavity so that the preparation could not de overfilled at the gingival margin.

The mesial faces

The cavities located on the mesial faces were restored with a silorane composite (Filtek silorane) according to the manufacturer protocol:
Application of the self etching adhesive system of Filtek® silorane:
Apply the self etching primer on the cavity for 15 seconds, gently dry then photo polymerize for 15s.
Spread the adhesive on the cavity, dry with air, photo polymerize for 10s.
Setting the silorane composite per layer of 1mm thickness.
Photo polymerization for 10s each composite layer and final photo polymerization for 40s.
A transparent strip was tightened and held by finger pressure against the gingival margin of the cavity.




Table 1: Groups 1 and 2 repartition.




Fig 1

a: distal cavity: occlusal infiltrations, absence of cervical infiltrations; mesial cavity: occlusal infiltrations and absence of cervical infiltrations.

b: distal cavity: absence occlusal and cervical infiltrations, mesial cavity: occlusal infiltrations and  absence of cervical infiltrations.

c: distal cavity: occlusal infiltrations, absence of cervical infiltrations; mesial cavity: absence of occlusal and cervical infiltrations.




Group 2

The distal faces

The cavities located on the distal faces were obturated with a silorane composite (Filtek® silorane) according to the following protocol:
Etching the enamel with orthophosphoric acid gel at 35% for 30s while paying attention not to overflow on the dentine. Thorough rinsing for 15s and drying.
Application of the self etching adhesive system of Filtek silorane: Apply the self etching primer on the cavity for 15 seconds, gently dry then photo polymerize for 15s.
Spread the adhesive on the cavity, dry with air, photo polymerize for 10s.
Setting the silorane composite per layer of 1mm thickness.
Photo polymerization for 10s each composite layer and final photo polymerization for 40s.
A transparent strip was tightened and held by finger pressure against the gingival margin of the cavity.

The mesial faces

The cavities located on the mesial faces were restored with a silorane composite (Filtek® silorane) according to the manufacturer protocol.

Thermocycling:
The apices were sealed with a transparent orthodontic resin (Luxaself UGIM®). A complementary protection was brought with the application of two coats of transparent finger nail varnish on each crown while leaving 1mm around the restorations. 
The teeth were placed in KCI solution at o, 9 ‰ for thermocycling.
Daily cycle: 45 minutes at 6°±2°C + 45min at 60°±2°C. Repeat four times. 16 hours at room temperature.  The daily cycle was repeated for five successive days.

Infiltration at methylene blue:
A second application of two coats finger nail varnish on each crown was performed. The crowns were immersed in a methylene blue dye solution at 0,1% for 48 hours at room temperature. After withdrawing the teeth from the dye solution, they were rinsed with water and cleaned with abrasive disks to eliminate the dye traces.

Microtome sectioning:
The roots of each tooth were inserted in a numerated methacrylate resin blocks.
At the vertical plane, each tooth was sectioned mesio-distally with a microtome (Isomet® Buehler) across the center of the restorations using the 0,4mm diamond saw with continuous water irrigation.
After separating the roots of each tooth from the crown, two sections were obtained: one buccal and the other lingual.




Fig 2

a: distal cavity: occlusal infiltrations, absence of cervical infiltrations; mesial cavity: occlusal infiltrations, absence of cervical infiltrations.

b: distal cavity: occlusal infiltrations, absence of cervical infiltrations; mesial cavity: absence of occlusal and cervical infiltrations.

c: distal cavity: occlusal and cervical infiltrations; mesial cavity: absence of occlusal and cervical infiltrations.



Stereomicroscope observation

48 composite resin obturations were analyzed. 
Each cut was photographed with a stereomicroscope (Zeiss) under magnification of 3 and with a digital camera. (Figs n°1, 2).
The observations were separately performed by two observers. The infiltration degree of the product was noted in function of the following scores:
Score 0: no infiltration,
Score 1: infiltration ˂ to half the enamel,
Score 2: infiltration ˃ to half the enamel,
Score 3: infiltration of all the enamel and dentin thickness,
Score 4: infiltration exceeding the cavity.

Statistical analysis 

The Fisher exact test was used to conduct qualitative analyses of the bonding efficacy between:

The operative protocols: 
Methacrylate composite with two-step etch and rinse adhesive (distal faces) and the silorane protocol (mesial faces). 
Silorane with etching (distal faces) and the classical silorane protocol (mesial faces).  
And between the cervical enamel and the occlusal enamel of each cavity.
The absence of infiltration (0) and the presence of infiltration (1) were taken as selection criteria.
The value p is considered as significant when it is inferior to 0.05.


Fig 3: Methylene blue infiltration: Comparison between methacrylate based composite with two-step etch and rinse adhesive (distal cavity) and the silorane protocol (mesial cavity).


Fig 4: Methylene blue Infiltration: Comparison between silorane protocol with etching (distal cavity) and the classical silorane protocol (mesial cavity).


Table 2: Methylene blue infiltration: groups 1 and 2.


Results 

Adhesion efficiency of silorane composite on fluoresced teeth compared to methacrylate based composite: no significant difference: p=0,286.
No significant differences were observed for the adhesion quality between the cervical enamel and the occlusal enamel: p=0,192 for the mesial cavities and p=1 for the distal cavities.
The score attributed to each sample depending on the infiltration is reported on table n° 2. (Fig n° 3).
Adhesion efficiency of silorane composite on fluoresced teeth: no significant difference: p=1.
No significant differences were observed for the adhesion quality between the cervical enamel and the occlusal enamel: p=1 for the mesial cavities and p=0,081 for the distal cavities.
The score attributed to each sample depending on the infiltration is reported on table n° 2. (Fig n° 4).


Discussion 

The literature 4, 22 describes the fluorosed enamel as hard, brittle and acido- resistant. Despite these characteristics, few studies have been interested in the bonding properties on this enamel. 
Our in vitro study allowed to evaluate the adhesion quality of silorane composite on the moderate fluorosed enamel and to compare silorane composite bonding with methacrylate based composite.
There was no difference between adhesion on moderate fluorosed enamel of silorane composite protocol and methacrylate based composite protocol.
Silorane composite is associated with a self etching adhesive system. The advantage of these systems to simplify the operative protocol of bonding but their efficiency on the enamel remains questionable and their impact on the fluorosed enamel remains little studied.
According to Perlatti D’alpino and al.21, the Silorane protocol and the self-etching bonding procedure associated with methacrylate based composite showed a better adaptation than the separated etching-rinsing protocol. A better result was observed in methacrylate based composite associated with a self-etching adhesive system.
Hara and al.11 reported that bonding with self-etching adhesive system was inferior compared to the system using orthophosphoric acid as a separate conditioner.
The study conducted by Hannig and al.10 and that conducted by Blunck and al.5 showed, on the opposite, that the self-etching adhesive system could have been used as a satisfactory alternative to orthophosphoric acid.
In fact failures are produced inside the hybrid layer, causing a fragile bonding, favouring micro-hiatus formation and leading to micro-infiltrations. These failures are generally observed on the adhesive interface and are principally due to a divergence between the demineralization depth and the monomer infiltration. For the self-etching adhesive system, the demineralization and the monomer infiltration are simultaneously produced.19,27 
For silorane, the influence of the bonding approach cannot be studied in the same manner as this material has a dedicated adhesive system which represents an advantage. This dedicated adhesive system is conceived to fill the hiatus between a hydrophilic dentin and hydrophobic silorane.15
Mine and al.15 confirmed that silorane adhesive system was capable to present a chemical link to hydroxyapatite crystal.
In the study of Santini and Miletic23, an intermediate zone about 1µm between the primer layer and the silorane adhesive was detected with the help of Raman microscopy. According to these authors, this zone can be the weak link in the failure mechanism of silorane restoration. Papadogiannis and al.18 using cylindrical dentinal cavities noted that silorane showed a better behavior than methacrylate based composite as when comparing marginal adaptation. Silorane presented a better performance in marginal occlusal and proximal adaptation. 
Our study showed no significant difference between silorane and methacrylate composite.
Palin and al.17 noted that the cusped deviation caused by the withdrawal of polymerization was significantly weaker when the teeth are restored using silorane compared to those restored by methacrylate.
On the other hand, a clinical study of Schmidt and al.24 revealed that the good results presented by a silorane in laboratory tests were not clinically validated. However, in the works conducted by Bagis and al.2, no micro-infiltration was observed on the mesio-occluso-distal preparations restored with a silorane or a methacrylate based composite. Weinmann29 and al. noted that the ring opening chemistry of the Siloranes enables at the first time shrinkage values lower than 1% vol. and mechanical parameters as E-Modulus and flexural strength comparable to those of clinically well accepted methacrylate based composites.
Although there are controversies of the bonding system of self-eching system on normal enamel, there is sufficient proof indicating that the bonding systems are capable to provide link forces comparable to those of bonding using ortho phosphoric acid.10, 13 The performances of these systems on the fluorosed enamel remains however a little studied subject. 
In our study, on the moderate fluorosed enamel, the silorane composite protocol associated with etching didn’t give better results than the classic silorane protocol as well as the methacrylate protocol with etching.
Hoffman and al.12, Opinya and Pameijer16 showed the unpredictability of fluorosed enamel treatment and an irregular response to the etching agent. 
Al-Sugair and Akpata1 reported the etching depth of orthophosphoric acid at 37% on the moderate fluorosed enamel with Thylstrup and Fejerskov Index TFI= 4 are not significantly different from the depth obtained on normal enamel.
However, Wersarsing and al.28 showed that for moderate fluorosed enamel the etching time should be long.
De Goes and al.6 noted that orthophosphoric acid at 35% used for 15 or 60 seconds produce the same effect on normal enamel.
According to Ermis and al.8 works, bonding on normal enamel is better than on moderate fluorosed enamel. 
The study conducted by Weerasinghe and al.28 which showed the link forces after etching with orthophosphoric acid and the use of self-etching on normal enamel and mild fluorosed enamel are comparable. However long-term adhesion force is to be monitored. In  the case of severe fluorosis; where the difference was significant; the self-etching bonding system is inferior to orthophosphoric acid. 
Pashley and al.20, Tay and al.26 showed that efficiency of self-etching primer on the enamel does not depend on their etching aggressiveness. 
Through these different works, we can confirm those hypotheses that moderate fluorosed enamel reacts to etching like normal enamel and that bonding may depend on the characteristics of the enamel.
Additional studies are necessary on severe fluorosed teeth.
Shimada and al.25 have confirmed the regional variations in the adhesion to the enamel. Our study has shown no difference for the three protocols between adhesion to cervical and occlusal enamel. In another study 3 we demonstrated that on mild fluorosed enamel adhesion on the occlusal enamel is better than on the cervical enamel. A change of the prism orientation and manipulation facility on the occlusal enamel argued this study.
The results on the fluorosis teeth in our study are obtained thanks to a rigorous operative protocol, starting by small touches drilling during the cavities preparation and ending by a good application of the adhesive by mini-brush friction. In fact, the action of orthophosphoric acid combined to adhesion silorane allow to modify the enamel surface state, whether fluorosis or normal by ameliorating the wettability of the resin and by assuring a physic-chemical bond in addition to the micromechanical one, thus decreasing micro-infiltration.
These are consistent with Santini and Mileyic study.23
Thus although, the fluorosed enamel is brittle and acido-resistant, it reacts positively to bonding techniques.
Giattchi and al.9 have highlighted the practitioner’s skill ability during resin composite manipulation. For this reason, a good manipulation of silorane composite and methacrylate composite and a respect of the different steps, especially that of adhesive application, allow obtaining good results.


Conclusions

Our in vitro study allowed to evaluate adhesion quality of silorane composite on the moderate fluorosed enamel and to compare the coronal restoration sealing using methacrylate composite to those using silorane after thermo cycling and methylene blue infiltration. The stereomicroscope observation has shown that the classic silorane protocol did not have better results than silorane protocol with etching or the methacrylate resin protocol. Our Study has also show that there is no significant difference between adhesion to the occlusal and cervical enamel.

Within the framework of this study, we can conclude that:
- The self-etching systems associated with silorane composite seem to have the same consequence on the moderate fluorosed enamel as the etching-rinsing approach. The moderate fluorosed enamel reacts in the same manner independently from the etching protocol.
- The adhesion of a material to the moderate fluorosed enamel seem to be in relation to several factors,  apart from the material properties, such as the degree of fluorosis, the adhesion quality of the adhesive or the degree of the practitioner’s ability.
Additional in vitro studies are useful to optimize dental adhesion, reach a better bonding and improving the stability of the adhesive interface over the time.
Finally, in vitro investigations are necessary to fully evaluate the properties of silorane composite and methacrylate composite adhesion to the fluorosed enamel and to determine if any of the approaches provides better results.


Acknowledgments

The authors thank Mister Samir Boukottaya for language assistance and Sonia Ghoul-Mazgar for revision of the manuscript. 


References

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2. Bagis YH, Baltacioglu IH, Kahaogullari S (2009). comparing micro leakage and the layering methods of silorane-based composite in wide class II MOD cavities. Oper Dent. 34: 578-85. 

3.  Belkhir C, Arous A, Belkhir MS (2014). Adhesion to mild fluorosed enamel: a comparative study of two etching protocols. Dental News. XXI. N° II: 12-22. 

4. Belkhir MS, Triller M (1987). Modifications ultra-structurales de la dent fluorotique et conséquences cliniques. Actual Odontostomatol. 158:223-38.

5. Blunck U, Roulet JF (1999). Marginal adaptation of compomer class V restorations in vitro. J Adhes Dent. 1:143-51. 

6. De Goes MF, Sinhoreti MA, Consani S , Silva M (1998). Morphological effect of the type, concentration and etching time of acid solutions on enamel and dentin surfaces. Braz Dent J. 9: 3-10. 

7. Duarte S, Botta CA, Phark JH et  Sadan A (2009). Selected mechanical and physical properties and clinical application of a new low-shrinkage composite restoration. Quintessence Int. 8:631-38. 

8. Ermis RB, De Munck J, Cardoso MV, Coutinho E, Van Landuyt KL, Poitevin A, Paul Lambrechts P, Van Meerbeek B (2007). Bonding to ground versus unground enamel in fluorosed teeth. Dent Mater J. 23: 1250–55. Gittachi L, Scaminaci Russo D, Bertini F, Nieri M (2007). Effect of operator skill in relation to micro leakage of total etch and self etch bonding systems. J Dent. 35:289-93. 

9. Hannig M, Reinharrdt KJ, Bott B (1999). self etching primer versus phosphoric acid: an alternative concept for composite to enamel bonding. Oper Dent. 24:172-80.

10. Hara AT, Amaral CM, Pimenta LA, Sinhoreti MA (1999). Shear bond strengt of hydrophilic adhesive systems to enamel. Am Dent J; 2: 181-84. 

11. Hoffman S, Rovelstad R, McEwan WS, Drew CM (1969). Demineralization studies of fluoride-treated enamel using scanning electron microscopy. J JDent Res. 48:1296–1302. 

12. Kenemura N, Sano H, Tagami J (1999). Tensile bond strength and SEM evaluation of ground and intact enamel surfaces. J Dent. 27: 523630. 

13. Lien W et Vandewalle KS (2010). Physical properties of new silorane-based restorative system. Mater Dent J. 26: 337-44. 

14. Mine A, De Munck J, Van Ende A, Cardoso MV, Kuboki T, Yoshida Y, Van Meerbeek B (2010). Tem caracterisation of silorane composite bonded to enamel and dentin. Dent Mater J. 26:524-32. 

15. Opinya GN, Pameijer CH (1986). Tensile bond strength of fluorosed Kenyan teeth using the acid etch technique. Inter Dent J. 36: 225-29. 

16. Palin WM, Fleming GJ, Nathwani H, Burke FJ, Randall RC (2005). In vitro cuspidal deflection and micro leakage of maxillary premolars restored with novel low-shrink dental composite.  Dent Mater. 21:324-35. 

17. Papadogiannis D, Kakaboura A, Palaghias G, Eliades G (2009). setting characteristics and cavity adaptation of low-shrinking resin composite. Dent Mater J. 25:1509-16. 

18. Pashley DH, Tay FR, Breschi L,Tjaderliane L, Carvallho RM, Carrilho M R, Tezvergil Mutluay A (2011). State of the art of etch-rinse adhesive. Dent Mater J. 27:1-16. 

19. Pashley DH, Tay FR (2001). Aggressiveness of contemporary selfeching adhesives. Part II: etching effects on unground enamel. Dent Mater J;17:430-44. 

20. Perlatti D’alpino PH, Bechtold J , dos Santos PJ, Alonso RC, Di Hipólito V,  Silikas N ,Rodrigues FP (2011).  Methacrylate and silorane-based composite restoration: hardness, depth of cure and interfacial gap formation as a function of the energy dose. Dent Mater J.  27:1162-69. 

21. Piette et Goldberg (2001). La dent normale et pathologique. Paris : De Boeck université.

22. Santini A, Miletic V (2008). comparisons of the hybrid layer formed by silorane adhesive, one-step self-etch and etch and rinse systems using  confocal micro-Raman spectroscopy and SEM. J Dent. 36:683-91. 

23. Schmidt M, Kirkevang LL, Horsted-  Bindslev P, Poulsen S (2011). marginal adaptation of low-shrinkage silorane-based composite: 1-year randomized clinical trial. Clin Oral Investig. 15: 291-95. Shimada Y, Kikushima D, Tagami J (2002). Micro-shear bond strength of resing systems to cervical enamel. Am J Dentist. 15:373-77. 

24. Tay FR, Pashley DH, King NM Carvallho RM, Tsai J, Lai SC, Marguezini L Jr (2004). Aggressiveness of a self etching adhesive on unground enamel. Oper Dent. 29: 309-16. 

25. Van Meerbeek B, Yoshihara K, Yoshide Y, Mine A, De Munck J, Van  Landuyt K (2011). State of the art of self-etch adhesives. Dent Mater J. 27: 17- 28. 

26. Weerasinghe DS, Nikaido T, wettasinghe KA, Abayakoon JB, Tagami J (2005). Micro-shear bond strength and morphological analysis of a self etching primer adhesive system to fluorosed enamel. J Dent. 33:419-26. 

27. Weinmann W, Thalacker C, Guggenberger R (2005). Siloranes in dental composites. Dent Mater. 21(1):68-74. 

    







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