88th IADR General Session (Barcelona, 2010)

Effect of Preparation and Storage on Adhesive Monomer Conversion

V. MILETIC,  University of Belgrade, Belgrade, Serbia,  
A. SANTINI, The University of Edinburgh, Edinburgh, United Kingdom

Objectives: To study the effect of sample preparation and storage conditions on the degree of conversion (DC) of two adhesive systems using micro-Raman spectroscopy.  
Methods: Sixty samples each of an etch-and-rinse (Excite) and a self-etch (Clearfil 3S) adhesive were prepared on glass slides and allocated to groups G1-G6 (n=10). Thirty samples of each adhesive were prepared on dentine discs according to manufacturer's instructions and allocated to groups D1-D6 (n=5). In groups G1 and D1, each sample was covered with a Mylar strip and cured for 10 s with a bluephase LED unit. In groups G2 and D2, samples were cured without the Mylar strip. Micro-Raman spectra were taken 5 min post-curing. Groups G3-G6 and D3-D6 were covered with Mylar strips, cured according to the same protocol and stored for 24 h: G3 and D3 at 22±2ºC and 45±3% humidity; G4 and D4 at 37±1ºC and 90±2% humidity; G5 and D5 in distilled water at 37±1ºC; G6 and D6 in buffered incubation medium at 37±1ºC. Micro-Raman spectra were taken 5 min post-curing and after storage. Data were analyzed using t-tests and repeated measures ANOVA and the level of significance was α=0.05.
Results: Higher DC values were found on dentine than glass for both adhesives (p<0.05). Higher DC values were found for both adhesives when cured on dentine with than without Mylar strips (p<0.05). Higher DC values were found for Excite cured on glass with than without Mylar strips (p<0.05), but there was no difference for Clearfil 3S (p>0.05). Both adhesives cured on dentine gave higher DC after 24 h storage irrespective of the medium (p<0.05). Excite G3 group and Clearfil 3S G3 and G4 groups showed higher DC values after storage (p<0.05).
Conclusions: Sample preparation methods and storage conditions significantly affected the DC of Excite and Clearfil 3S.

IADR 2010

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Current status of visible light activation units and the curing of light-activated resin-based composite materials - review by professor Ario Santini in Dental Update

Abstract
Light activation units are standard items of equipment in dental practice. It is essential to understand the many factors which affect the polymerization of light-activated resin composite materials and the choice of a light curing unit. In this respect, the development of high-intensity halogen and light-emitting diode (LED) light curing units (LCUs), many with multiple curing modes, has revolutionized light curing techniques. This article reviews visible light activation unit design and development. Factors influencing the effective use of LCUs and polymerization of resin-based composite materials are discussed, as are the steps which should be taken to maintain the efficiency of units in clinical use.
CLINICAL RELEVANCE: Many LCUs produce lower output intensities than stated by the manufacturer. Newer high power LEDs may present as much of a heat problem as high power quartz tungsten halogen lamps (QTHs). The manufacturer's data should be followed to ensure that the emission spectra of the unit are compatible with the photo-initiator in the resin-based composite material.

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Professor Ario Santini is the Director for Biomaterials Research at the Edinburgh Postgraduate Dental Institute, Chair Research at Faculty of General Dental Practice (UK), Professor at Faculty of Medicine and Surgery, University of Sassari (Italy), Visiting Professor at the University of Belgrade (Serbia) and Fellow of the Academy of Dental Materials. Professor Santini's research interests are dental material sciences, dental resin-based composites and adhesives, Raman spectroscopy, high performance liquid chromatography, pulp biology and research methodology. He has published numerous articles in international, peer-reviewed journals indexed in Thomson's Science Citation Index. Browse for more articles by professor Santini at http://www.santinimiletic.com/

Dental Update is the leading dental journal of continuing professional development (CPD) in the United Kingdom. By reading the appropriate peer reviewed articles and then answering the questions in each issue of the journal, one can earn up to 40 hours of verifiable CPD per year.

Free live dental webcast/webinar @ Pentron

A Science-based Protocol for Direct and Indirect Restorations that will End Post-Operative Sensitivity In Your Practice for Good!
Presenter Dr. Jeffrey Blank, D.M.D.
Thursday 27 May 2010 at 7 pm ET (midnight GMT 28 May 2010)
This webinar is CE accredited (1 CE point)|

It is essential to create a free account at http://pentron.vivalearning.com/  to register a seat. There are about 126 seats left at this moment.

From Pentron and J. Blank:  "Reliably bonding direct and indirect restorations to both enamel and dentin is the single most important scientific discipline in modern dentistry. Over the past 18 years, adhesion has increased in effectiveness and predictability, but in turn has become complex and confusing. This CE presentation will address proper product selection, proper use of products and the variables that control the post-operative outcome."

Mineral Trioxide Aggregate (MTA) and direct pulp capping

Two papers have been published recently on the use of mineral trioxide aggregate (MTA) for direct pulp capping.

A large clinical trial was conducted between 2001 and 2006 at Ruprecht-Karls-University of Heidelberg, Germany (1). Direct pulp capping with either MTA or Calcium hydroxide was done in 167 teeth of 149 patients. Treatment outcome was evaluated clinically and radiographically by calibrated examiners 12-80 months post-treatment. The authors reported a high recall rate of more than 70% and based the statistical analysis on 108 patients and 122 treated teeth. A significantly greater success rate was found for MTA (78% of teeth) than Calcium hydroxide (60% of teeth). It seems critical to restore such teeth permanently as soon as possible after pulp capping. This study showed that teeth permanently restored ≥2 days after capping had a significantly worse prognosis irrespective of the capping material. The authors concluded that "MTA appears to be more effective than calcium hydroxide for maintaining long-term pulp vitality after direct pulp capping".

Another study is an immunohistological study on Wistar rats (2). It compared the proliferation of pulp cells 1, 3, and 7 days after direct pulp capping with either MTA or Calcium hydroxide. After 3 days, the number of proliferating cells (fibroblasts, endothelial cells and Hoell's cells) was significantly greater when capping was performed irrespective of the material compared to the control group with no capping. After 7 days, however, there were no differences between MTA and Calcium hydroxide groups and the control group. The authors concluded that "Immunohistologic analysis demonstrated that MTA showed similar results when compared with Calcium hydroxide within the first week after direct pulp capping".

(1) Mente J, Geletneky B, Ohle M, Koch MJ, Friedrich Ding PG, Wolff D, Dreyhaupt J, Martin N, Staehle HJ and Pfefferle T. Mineral trioxide aggregate or calcium hydroxide direct pulp capping: an analysis of the clinical treatment outcome. J Endod 2010;36:806-13.

(2) Dammaschke T, Stratmann U, Wolff P, Sagheri D and Schafer E. Direct pulp capping with mineral trioxide aggregate: an immunohistologic comparison with calcium hydroxide in rodents. J Endod 2010;36:814-9.

Reprints of both studies should be available from the authors: (1) johannes.mente@med.uni-heidelberg.de
and (2) tillda@uni-muenster.de

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Research Methodology in Dentistry seminar

It will be my great honour to lecture again along side my supervisor, Dr Ario Santini, at a seminar on Research Methodology in Dentistry. The seminar will take place at Belgrade University School of Dentistry on Thursday, June 10 (9am-1pm). The seminar is accredited by the Serbian Health Council and each attendee gets 4 CE points.



Programme:

9-9.15 Opening remarks
9.15-9.45 Dr Vesna Miletic: Literature search (MEDLINE and KoBSON)
9.45-10.45 Dr Ario Santini: Designing a study protocol
10.45-11 Break
11-12 Dr Ario Santini: Writing a scientific article
12-12.30 Dr Vesna Miletic: Managing references with EndNote
12.30-1 pm Discussion and practical work

The seminar is free for professors and clinical lecturers of Belgrade School of Dentistry. Contact me at vesna.miletic@gmail.com  to reserve a seat.

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News from Esstech, Inc.

Esstech, Inc. develops and manufactures advanced materials for many biomedical fields including dental materials. In their range of products are various monomers, initiators, silanated glass etc. for resin-based composites and adhesive systems. The latest research by or using Esstech's products includes studies on physical properties of new low shrink resin , optimizing the degee of conversion and certain physical properties of various BisGMA/BisEMA/TEGDMA formulations , optimizing silanated glass , developing a high molecular mass monomer to substitute HEMA etc.

For more information, check out their website and blog.

Esstech, Inc. will be present at the IADR/AADR General Session in Barcelona, Spain (14-17 July 2010) and I really look forward to meeting their representatives, hoping that we could establish scientific collaboration.

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Filtek Silorane composite: temperature changes during light-curing

Some time ago, my colleagues and I published a paper on temperature changes during curing of Filtek Silorane, Admira (ormocer) and Herculite XRV (microhybrid, control) composites. It was interesting to notice substantially higher temperature rise in Filtek Silorane compared to the other two materials. However, there was no difference in the temperature rise inside the pulp chamber, probably due to the insulating effect of the remaining dentine.

The abstract of this paper may be found on MEDLINE and I will be happy to email the full text to anyone interested in this subject. Feel free to contact me at vesna.miletic@gmail.com

J Esthet Restor Dent 2009;21(2):122-31.
Temperature changes in silorane-, ormocer-, and dimethacrylate-based composites and pulp chamber roof during light-curing.
Miletic V, Ivanovic V, Dzeletovic B, Lezaja M.

STATEMENT OF THE PROBLEM: Light-curing of resin-based composites (RBCs) is associated with temperature increase in the pulp chamber, which may have a detrimental effect on the vital pulp.
PURPOSE: The purpose of the study was to evaluate temperature changes of silorane-, ormocer-, and dimethacrylate-based RBCs at the bottom surface of the RBC and in the pulp chamber roof dentin (PCRD) during curing.  
MATERIALS AND METHODS: In part A, temperatures were measured for Filtek LS (3M ESPE, St. Paul, MN, USA), Admira (Voco GmbH, Cuxhaven, Germany), and Herculite XRV (Kerr Corp., Orange, CA, USA) with a high-power light-emitting diode (LED) unit by placing thermocouples in contact with the bottom surface of the material in standardized acrylic molds. In part B, temperature changes in PCRD were measured in extracted molars during light-curing of adhesives and RBCs in 2-mm-deep cavities with a remaining dentin thickness (RDT) of 1 mm.
RESULTS: Filtek LS showed a different temperature curve compared with Admira and Herculite XRV. Significantly higher temperatures were recorded for Filtek LS (p < 0.001) than for Admira and Herculite XRV in acrylic molds. Temperature rises recorded in PCRD for adhesives and RBCs were between 4.1 and 6.4 degrees C. No significant differences in PCRD temperatures were found between the three groups during adhesive curing and RBC curing (p > 0.05).  
CONCLUSIONS: Filtek LS showed a different heat-generation pattern from and significantly higher temperatures than Admira and Herculite XRV when the materials were tested in acrylic molds. Similar temperatures were recorded in the PCRD during curing of adhesives and RBCs.
CLINICAL SIGNIFICANCE: Although a substantial temperature rise in the bulk material occurred during light-curing of the three resin-based composites, a remaining dentin thickness of 1 mm caused a significant reduction in pulp chamber roof dentin temperatures. Temperatures measured in the pulp chamber roof dentin corresponding to the zone occupied by the postmitotic odontoblast layer were not statistically different for the three types of resin-based composites.

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