|Year : 2007 | Volume
| Issue : 1 | Page : 1-4
|The role of oxygen inhibited layer on the shear bond strength of composites - An in-vitro evaluation
Seema Merwade, Jagadish
Department of Conservative Dentistry & Endodontics, R. V. Dental College, Bangalore, India
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| Abstract|| |
Light or chemically cured dental composite resins leave a soft, sticky superficial layer upon polymerization. The layer is commonly referred to as Oxygen Inhibited Layer and it is always present when a composite or bonding resin is polymerized in air. For years. it wa s believed that Oxygen Inhibited Layer is required before adding more layers of bonded composite.
But reports on how Oxygen Inhibited Layer affects the bond strength have been inconsistent and contradictory.
The aim of the present study was to compare the shear bond strengths of composite composite bonded specimens prepared with or without Oxygen Inhibited Layer. The shear bond strengths were tested using Universal Testing Machine.
The results of the present study show that the presence of Oxygen inhibited layer increases the shear bond strength values at the interphase of incrementally built 2 layer composite specimens. Within the limitations of the present study, it can be conclusively stated "a higher shear bond strength results from Oxygen Inhibition on the surface layer of composite".
|How to cite this article:|
Merwade S, Jagadish. The role of oxygen inhibited layer on the shear bond strength of composites - An in-vitro evaluation. J Conserv Dent 2007;10:1-4
|How to cite this URL:|
Merwade S, Jagadish. The role of oxygen inhibited layer on the shear bond strength of composites - An in-vitro evaluation. J Conserv Dent [serial online] 2007 [cited 2019 Sep 19];10:1-4. Available from: http://www.jcd.org.in/text.asp?2007/10/1/1/42273
| Introduction|| |
Light or chemically cured dental composite resins leave a soft sticky superficial layer on polymerization  . Research has shown that Oxygen inhibits polymerization of the monomer systems used in dentistry  . The effect of oxygen is formation of an inhibition zone on the surface of the resin in contact with the air. This layer is commonly referred to as "Oxygen inhibited layer"  .
Reports on how Oxygen inhibited layer affects the bond strength have been inconsistent and conflicting.
While, Truffler- Boutry et al and Velazquez E et al, in their study of interfacial characterization in dental composites reported that the shear bond strength was improved when a oxygen inhibited layer was preserved between successive layers of composites, Rueggeberg FA et al. and Li J et al. concluded from their studies that presence of Oxygen Inhibited Layer was in fact detrimental to bonding.
Further, Byoung In Suh. and Finger WJ reported from their studies that bond strength tests resulted in no significant difference between samples with or without oxygen inhibited layer.
The aim of the present study was to compare the shear bond strengths of composite - composite bonded specimens prepared with or without the Oxygen inhibited layer.
| Materials and Methods|| |
Resin composite used for the study was a hybrid light curable composite (Charisma - Heraeus Kulzer). The composite was photopolymerized using visible light curing unit from Heraeus Kulzer. Curing time recommended by the manufacturer was 20 seconds.
The study comprised of two test groups of 10 samples each. Two layer composite specimens were made using gelatin capsules (5mm diameter and 5mm height) [Figure 1].
GroupA - Oxygen Inhibited Layer absent.
Group B - Oxygen Inhibited Layer present.
First increment of composite was condensed in the gelatin capsule against a Mylar strip The capsule was inverted and surface against mylar strip was cured [Figure 2].This cured surface which is devoid of oxygen inhibited layer is made the interface and a second layer of composite was condensed against it and cured without Mylar strip [Figure 3].
To obtain samples with Oxygen inhibited layer at the interphase of two increments, both the increments were cured without the use of Mylar strip  [Figure 4]
The samples [Figure 5] and [Figure 6] were stored in distilled water for two hours. The shear bond strength was determined using an Instron Universal Testing machine [Figure 7]
A fixture was prepared to hold the samples [Figure 8] and this fixture was placed in the lower arm of the testing machine. A shear force was applied parallel to the interface at a crosshead speed of 0.75mm/min. [Figure 9]
[Figure 10] shows the fractured specimen.
The shear strength was calculated using the equation
Shear Bond St = Force/Area
where Area is πr 2
r is the radius of the sample.
| Results|| |
The shear bond strength values were recorded in Newtons as shown in [Table 1].
When these values were subjected to statistical analysis using the Student t test, the p value obtained was <0.01. [Table 2] This indicates that the shear bond strength values of samples with Oxygen inhibited layer are significantly higher than those without Oxygen inhibited layer.
| Discussions|| |
It has been stated by many authors that Oxygen Inhibited Layer is viscous and contains unreacted monomers and of igomers. These are able to improve the adhesion between the substrate and the second layer of composite. The Oxygen inhibited layer readily adopts the overlying material to increase the contact area.
The unreacted molecules allow the materials on both the sides to cross the interface and blend together to form an interdiffused zone, where copolymerization can take place to produce a covalent bond  .
In the previous studies which negatively correlate bond strength and Oxygen inhibited layer, the results were attributed to the fact that Camporoquinone, the photoinitiator has been consumed or decomposed during the initial phase of light activation.
But since the fresh layer of composite overlaying the Oxygen inhibited layer contains Camphoroquinone, it can diffuse into the Oxygen inhibited layer resulting in complete polymerization of the Oxygen inhibited layer at the interphase.
Curing time more than that recommended by the manufacturer may negatively impact the ability of the oxygen inhibited layer to be post-cured by depletion of the photoinitiator.
It appears that the residual photoinitiator present in the Oxygen Inhibited Layer actually contributes to improved bonding thus exhibiting enhanced shear bond strength.
| Conclusion and Clinical Significance|| |
The conservation of photoinitiator as a result of appropriate curing at composite composite interphase appears to exhibit higher shear bond strength between layers. Hence the clinician should stick to manufacturer's instructions and cure the composite and avoid overcuring the composite, which depletes the photo initiator.
| Acknowledgement|| |
3M India, Bangalore for technical support
| References|| |
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|2.||Lewis G, W. Johnson, W Martin, A Canerdy, C laburn. Shear bond strength of immediately repaired light cured composite resin restorations. Oper Dent 1998:23: 121-127. |
|3.||Li J Effects of surface properties on bond strength between layers of newly cured dental composites. J Oral Rehab 1997,24:358-360. |
|4.||Suh BI: Oxygen inhibited layer in adhesion dentistry. J Esthet Restor Dent. 16: 316 323, 2004. |
|5.||Suh BI , Feng L, Hayes K. Is an oxygen inhibited layer necessary for bonding of composite resin? J Dent Res 2003: 82: B-237. |
|6.||Truffier- Bouty O , lace E, Devaux J, Leloup G: Interfacial layer characterization in dental composites. J Oral Rehabil 2003: 30: 74-77 |
Department of Conservative Dentistry & Endodontics, R. V. Dental College, Bangalore
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2]