INTRODUCTION

Dentistry is facing a transition into the age of adhesive dental restorations . Considering issues such as perceived mercury toxicity, overall restoration aesthetics and patients’ discretion, since the 1980s more and more clinicians have been choosing composite restoration materials in lieu of amalgam for posterior teeth fillings.[1]

Adhesive techniques enable the clinician to save sound tooth tissue when caries is treated in such a way that only the decayed tooth substance is removed.[2] Tooth-colored posterior restorations are now the first choice for many patients. However, microleakage is one of the important problems at the margins of the restoration.[3] Adaptation of the restorative material to cavity margins and internal cavity surfaces are crucial for long-term performance of restorations. [4]. The shrinkage of composite resins during photo-polymerisation induces stresses at the tooth/restorative interface and as a consequence may cause failures in the bond,generating gap formation.

Such micro gap formation are considered deleterious because they allow transit of fluid or bacteria between the dentin pulp complex and the oral environment, leading to postoperative sensitivity and secondary caries formation [4] Ideally, no voids or gaps should be present in the completed restoration.[5]

One technical issue which needs to be considered while restoring the tooth with adhesive composite restoration is C factor or configuration factor. Cavity configuration (c factor) is the ratio of the bonded surface area to the unbonded or free surface area.[6] Some of the ways to minimize C factor are incremental build up technique and using flowable composite as a base below the packable resin

To improve the marginal sealing of a composite restoration, many incremental techniques have been tested [1] ,of which the most commonly used are successive cusp build up technique and oblique layering technique.

Flowable composite were used as a base below packable composite to minimise C factor. The aim of this in vitro study was to evaluate the effect of different restoration techniques on the formation of internal microgaps between materials and prepared wall.

MATERIALS AND METHODS:

Thirty two freshly-extracted human mandibular premolars without decay, cracks or previous restorations were chosen. Class I cavities with 2.0mm depth were prepared and randomly grouped into 4 categories they are as follows

GROUP I –

oblique layering technique with flowable

GROUP II –

oblique layering technique without flowable

GROUP III-Successive cusp buildup technique with flowable

GROUP IV-

Successive cusp buildup technique without flowable

3M ESPE Filtek Z350XT flowable composite was used as a base in the cavities. Restoration were completed using 3M ESPE Vlux packable composite. Radiographs were taken using paralleling technique.The radiographs were analysed by 10 endodontists and scored.

Score 0- no voids

Score 1- minimal voids

Score 2 - maximum voids

RESULT:

Table : 1 Presence of voids

Restoration Technique	No voids	Minimum voids	Maximum voids
Oblique Layering Technique With Flowable (GROUP 1)	5	3	0
Oblique Layering Technique Without Flowable (GROUP 2)	1	6	1
Successive Cusp Buildup Technique With Flowable (GROUP 3)	4	3	1
Successive Cusp Builup Technique Without Flowable (GROUP 4)	0	5	3

Thirty two lower premolars were restored.

Table 1 summaries the presence of voids in restorations done with different incremental technique.5 teeth in group 1 and 4 teeth in group 3 had no voids all the other restoration had voids or porosities either in the margins or in the floor of the cavity. The best results were achieved in Group 1 and Group 3, where a flowable composite was combined with a packable composite, this technique was significantly better compared to all other two techniques without flowable. In group 2 and group 4 Packable composite was placed without the flowable base. Presence of internal voids in oblique layering technique with flowable (group 1) and cusp buildup technique with flowable (group 3) is less when compared to oblique layering technique without flowable and cusp buildup technique without flowable. Flowable composite used as a base beneath the packable composite tend to decrease the C factor and helps in better adaptation to the cavity floor even after shrinkages due to polymerisation.

DISCUSSION:

This study compared the presence of internal voids in composite restored class 1 cavities. For that purpose flowable composite was used beneath packable composite to restore standardised cavities.

The results of this study show that the presence of internal voids in cavity without flowable beneath the packable is comparatively more than the cavities restored with flowable composite. Polymerisation shrinkage occurs regardless of the system used to initiate the setting reaction, whether light cure ,dual cure or chemicak cure ,but shrinkage stresses vary with different types of curing methods used [6] The compensation of polymerisation shrinkage by relaxation of the resin monomers is increasingly restricted by increasing C factor [7] Thus, when bonding to dentin is planned, one must investigate the effects of cavity configuration factor, dentin depth, types of adhesives, method of placement of composite material and curing behaviour of composite on bond strength to expedite interpretation of the nature of adhesion within the prepared cavity. [6] Using a flowable composite may also have some disadvantages. The volumetric curing-shrinkage of flowable composites is considerably higher and most of the physical properties are less than from normal hybrid composites (Bayne & others, 1998). From other studies on homogeneity of restorations, it is known that injection of a syringable composite results in a better restoration with less voids compared to a packing technique with a highly viscous composite. [2] The technique of placing an initial thin layer of flowable composite, left uncured, followed by injecting a syringable composite, is best suited to fill a micro preparation completely. With this so-called “snowplough - technique,” the flowable composite helps to wet the cavity walls and will be pressed out of the cavity when injecting the more viscous syringable composite. Flowable composite resins exhibit a lower filler content (60-70% by weight and 46-70% by volume) and a greater proportion of resin matrix than hybrid resins.In a related sense, the elastic modulus of flowable composite resins is lower than that for hybrid resins [1].

Previous studies study revealed that flowable composite linings improve marginal adaptation. study revealed that the use of flowable resincomposites as a lining material should result in areduction in the likelihood of the formation of voids and a reduction in marginal micro leakage.

Flowable resin composites (Filtek Flow) as a base beneath packable composite were found to be superior to resin composites in preventing micro leakage.The value for interface voids in flowable resincomposites suggested effective and similar elimination of voids.[3]

CONCLUSION:
It can be concluded from this study that narrow occlusal preparations are difficult to restore completely free of voids.[2] There is a reduction in the presence of internal restoration voids when using flowable composite resins as a lining material for composite restorations as it reduces the Configuration factor which helps In better adaptation of the restorative material to the tooth structure.

REFERENCE:

1. Microleakage and Internal Voids in Class II Composite Restorations with Flowable Composite Linings S-F Chuang • J-K Liu • Y-T Jin Operative Dentistry, 2001, 26, 193-200

2. Voids and Porosities in Class I Micropreparations Filled with Various Resin Composites NJM Opdam • JJM Roeters • T de Boer D Pesschier • E Bronkhorst Operative Dentistry, 2003, 28 , 9-14

3. The Effect of Flowable Resin Composite on Microleakage and Internal Voids in Class II Composite Restorations AÖlmez • N Öztas • H Bodur Operative Dentistry, 2004, 29-6, 713-719

4. The Evaluation of Various Restoration Techniques on Internal Adaptation of Composites in Class V Cavities D. Dionysopoulos, C. Papadopoulos, and E. Koliniotou - Koumpia Hindawi Publishing Corporation International Journal of Biomaterials Volume 2014, Article ID 148057, 6 pages http://dx.doi.org/ 10.1155/2014/148057

5. Voids and interlaced gaps in class 1 posterior composite restorations : A comparison between a micro layer and a 2 layer technique. Nachum smart, DMD /Kung -Rock Kwon, DDS, MSD, PHD/Phoebe Good/Hans Peter Webber, DMD Volume 37 Number 10 November /December 2006

6. C-Factor influencing bonding of composite resins to pulpal floor dentin K. PRIYADARSHINI * # ROOPA R. NADIG ** ##.

7. Effect of Cavity Configuration (C Factor) on the Marginal Adaptation of Low-Shrinking Composite: A Comparative ExVivo Study Motaz A. Ghulman Hindawi Publishing Corporation International Journal of Dentistry Volume 2011, Article ID 159749, 8 pages doi:10.1155/2011/159749

Received on 15.06.2016 Modified on 24.06.2016

Research J. Pharm. and Tech 2016; 9(10):1596-1598.

DOI: 10.5958/0974-360X.2016.00316.4