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ORIGINAL RESEARCH Table of Contents   
Year : 2008  |  Volume : 19  |  Issue : 2  |  Page : 147-149
Heat radiation vs air drying to remove interfacial water from self-etch adhesives

Department of Conservative Dentistry and Endodontics, Sri Ramachandra Dental College, Porur, Chennai, Tamil Nadu - 600 116, India

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Date of Submission27-Feb-2007
Date of Decision01-Oct-2007
Date of Acceptance04-Oct-2007


The clinician's quest for time-saving and technique-insensitive technology has led to the development of simplified self-etch adhesives that are predominantly water or solvent based. Several studies have shown that conventional air-drying procedures are incapable of eliminating all the residual water in the adhesive and that it may even cause collapse of the underlying collagen matrix. We hypothesized that heat from a light source may be effective in removing water from these adhesives. The aim of this study was, therefore, to evaluate the effectiveness of heat vs conventional air drying in eliminating water droplets from self-etch adhesive. A self-etch adhesive was applied to bur-cut dentin surfaces, which were then allotted to one of two treatment procedures for eliminating residual water from the adhesive: conventional air drying or the experimental heat application. Specimens were then prepared and analyzed using SEM. Specimens in the experimental group showed no evidence of water treeing within the adhesive layer. Thus, it was concluded that heat radiation was an effective method to remove residual water from simplified adhesives.

Keywords: Heat radiation, interfacial water, self-etch adhesives

How to cite this article:
Mathews IE, Arathi G, Balagopal S. Heat radiation vs air drying to remove interfacial water from self-etch adhesives. Indian J Dent Res 2008;19:147-9

How to cite this URL:
Mathews IE, Arathi G, Balagopal S. Heat radiation vs air drying to remove interfacial water from self-etch adhesives. Indian J Dent Res [serial online] 2008 [cited 2022 Jan 20];19:147-9. Available from:
Over the last decade the classic concept of three-step bonding to dental tissues has evolved rapidly to more user-friendly, simplified adhesive systems. These comprise the two-step etch and rinse, two step self-etch, strates. and one step self-etch adhesives. [1] Unfortunately, these adhesives also have some characteristics that are detrimental to their efficacy in providing long-lasting bond stability. The self-etch adhesives eliminate the rinsing phase, which is needed to remove the dissolved hydroxyapatite and the smear plugs of etched substrates. [2],[3] However, these simplified adhesives contain higher concentrations of ionic and hydrophilic moieties. Such hydrophilicity renders these adhesives very permeable and diminishes their ability to hermetically seal dentin. [4] Thus, air drying of bonded teeth has been recommended to eliminate the excess water droplets. The entrapped water between the adhesive surface and the slow-setting composite/cement may act as stress raisers and account for the incompatibility of these adhesives with bonding of restorations. [4] It is well documented that air drying of demineralised dentin can cause collapse of collagen and hamper resin infiltration. This led to the development of the wet-bonding technique by Kanca in the year 1992. Also, it is speculated that air drying is incapable of totally eliminating entrapped water from adhesive surfaces. We hypothesized that heat from other sources, such as a microwave, laser, or infrared, may be efficient in the removal of the interfacial water droplets. Infrared heat seemed a good choice due to its wide application in the field of medicine and physiotherapy. Therefore, the aim of this study was to investigate whether heat from an infrared light could be used to eliminate interfacial water droplets in self-etch adhesives.

   Materials and Methods Top

Twenty extracted intact human premolars were selected for the study. The teeth were sectioned with a diamond disc to expose flat dentin surfaces. All samples were coated with a self-etching primer of Panavia F 2.0, a dual-cure dental adhesive system (Kuraray Dental). Samples were then randomly assigned to one of the two groups:

Group 1: Air drying

Group 2: Infrared heat application for 20 s (infrared lamp; output 150 W; maintained at a distance of 1 ft from the sample)

After the samples were subjected to the treatment described earlier, 2 mm of composite build-up was carried out using a light-cure composite material; this was then light cured for 20 s. The teeth were then sectioned occluso-gingivally, perpendicular to the resin-dentin interface, and 1-mm-thick sections were obtained using an Isomet slow-speed saw. Sectioned specimens were immersed in 50 wt% ammoniacal silver nitrate solution for 24 h, exposed to photodeveloping solution under a fluorescent light for 8 h, and subjected to examination under the backscattered mode of SEM.

   Results Top

The samples of group 1, which were air dried as per the standard protocol, showed the uptake of metallic silver particles, which represent discrete droplets of water extending from the surface of the dentinal tubule into the bulk of the adhesive (columnar type) [Figure - 1].

Samples of group 2, which were subjected to infrared heat, did not show the uptake of metallic silver, thus suggesting the absence of entrapped water within the adhesive layer [Figure - 2].

   Discussion Top

The results of the present study showed absence of silver uptake in the specimens of the experimental group, whereas there was considerable silver staining seen in the control group; this occurred more at the top of the hybrid layer and extended into the adhesive layer. This higher concentration of droplets at the bottom of the adhesive layer, adjacent to the hybrid layer, must be attributed to the upward movement of droplets toward the surface where they emerge. [5] Also, the present study used Panavia F 2.0, which consists of HEMA, a complex mixture of hydrophilic and hydrophobic ingredients, water, and solvents, which are prone to phase separation [6] and, therefore, could be expected to provide a better background for the evaluation of the efficacy of heat drying and air drying in removing interfacial water.

The short 10 s application time of most current adhesives is not sufficient to allow all water droplets to move upward to be eliminated by air drying. Hence, light curing entrapped the droplets within the adhesive layer. Earlier, light microscopic studies have shown that complete disappearance of water droplets from the adhesive resin was achieved only after a 4-10 min delay after its application over a glass slide. The same study also suggested that very strong air drying could blow out most of the water droplets from the dentin substrate in a shorter period of time, as observed using TEM. [7] In the long term, such a void-free adhesive layer should be beneficial for bond integrity. However, the long application time of 4-10 min and the necessity for strong air drying can render these products less than practical for clinical use.

The use of infrared radiation has gained much popularity in industry and medicine. Infrared heat radiation has been utilized for the relief of pain and for the heating of water surfaces. This radiation has the capacity to penetrate to a depth of 1 mm and thus remove the surface film of water. It was in view of this ability that an infrared lamp was used for this study. The results of this study substantiate the hypothesis that infrared heat can reduce the incidence of water treeing in self-etch adhesives. However, the effects of the heat application on pulp and dentinal tubules were not examined in this study. Further research should be carried out to evaluate the harmful effects, if any, and to find out if heat application in a pulsed mode would also prove beneficial.

Thus, it may be concluded that, within the limitations of this in vitro study, infrared heat application is a promising approach to eliminate interfacial water from self-etch adhesives so as to prolong the longevity of resin-dentin bonds.

   Acknowledgement Top

The authors wish to thank the staff of IP Rings Ltd. and Dr. Sudarshan of IIT, Chennai for their technical assistance and valuable support.

   References Top

1.Van Meerbeek, De Munck. Adhesion to enamel and dentin: Current status and future challenges. Oper Dent 2003;28:215-35.  Back to cited text no. 1    
2.Chersoni S, Acquaviva GL. In vivo fluid movement through dentin adhesives in endodontically treated teeth. J Dent Res 2005;84:223-7.  Back to cited text no. 2    
3.Hashimoto M, Ito S. Fluid movement across the resin-dentin interface during and after bonding. J Dent Res 2004;83:843-8.  Back to cited text no. 3    
4.Tay FR, Carvalho RM, Pashley D. Water movement across bonded dentin-too much of a good thing. J Appl Oral Sci 2004;12:12-25.  Back to cited text no. 4    
5.Tay, Pashley. Water Treeing in simplified dentin adhesives. Dιją vu Oper Dent 2005;30:561-79.  Back to cited text no. 5    
6.Knobloch, Kerby. Solubility and sorption of resin-based luting cements. Oper Dent 2000;25:434-40.  Back to cited text no. 6    
7.Van Landuyt, J De Munck. Monomer-Solvent phase separation in one-step self etch adhesives. J Dent Res 2005;84:183-8.  Back to cited text no. 7    

Correspondence Address:
Irene Elza Mathews
Department of Conservative Dentistry and Endodontics, Sri Ramachandra Dental College, Porur, Chennai, Tamil Nadu - 600 116
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-9290.40470

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