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Friday, 25 March 2011

IADR Toshio Nakao Fellowship

The 89th General Session of the International Association for Dental Research was held last week in San Diego, CA, USA. I was officially awarded the IADR Toshio Nakao Fellowship during the opening ceremony. This Fellowship is generously supported by GC Corporation with the intention to "allow a young investigator to obtain training and experience in dental materials science at a center of excellence". In my case, this means six months post-doctoral research at the University of Edinburgh, Great Britain, commencing in June 2011. It was truly an honour to be among the distinguished scientists whose work has been recognized by the IADR, the leading international organisation in dental research. I am grateful to the IADR and GC Corporation for support. This Fellowship will help me continue research on dental adhesives, particularly monomer to polymer conversion and hybridisation of dentine.

Tuesday, 8 March 2011

A review of SEM and TEM studies on the hybridisation of dentine

Professors Ario Santini and Egle Milia and Dr Vesna Miletic, members of the Santini Miletic Research Group, published a chapter on dentine hybridisation in the international peer-reviewed book Microscopy: Science, Technology, Applications and Education, edited by A. Mendez-Vilas and J. Diaz and published by Formatex ( This is the 4th book in the Microscopy series. The chapter is a review of SEM and TEM studies on the hybridisation of dentine with additional findings on the subject using micro-Raman spectroscopy. The chapter can be downloaded free of charge from the publisher's website (simply scroll down to Santini, Milia and Miletic).

Santini A, Egle M and Miletic V. A review of SEM and TEM studies on the hybridisation of dentine.
In: Microscopy: Science, Technology, Applications and Education.
Editors: Mendez-Vilas A, Diaz J. Microscopy series No. 4, Volume 1, pages 256-268.       
Publisher: FORMATEX, Badajoz, Spain, 2011.
ISBN-13: 978-84-614-6189-9


Current opinion is that the hybridisation of dentine is the principal, though not the exclusive, mode of adhesion of restorations to tooth tissue. Hybrid layer formation is achieved by resin infiltration of acid-etched dentine. This layer provides micromechanical retention for resin composite restorations.

The vast literature on the development of bonding systems is summarised and the differences in the hybrid layer formation are reviewed with specific attention to SEM and TEM studies.

It is concluded that more recently marketed adhesives with simplified application procedures are less successful compared to conventional total-etch adhesives.


Visit for more references of our research group.

Tuesday, 15 February 2011

Water sorption and solubility of resin-based composites

Interaction of resin-based composites with water is a continuous process from the early stages of composite placement. Water plays an important role in the long-term stability of composite fillings and may induce hygroscopic expansion of the material, hydrolytic degradation of intra- and intermolecular bonds within the resin matrix and at the resin-filler interface, plasticization of polymer chains, elution of leachable substances and reduction in mechanical properties.

The importance of composite-water interaction has been acknowledged in the ISO standard 4049 which states the maximum values for water sorption and concurrent solubility for resin-based materials (composites and cements). In order to comply with this ISO standard, resin-based materials must have  water sorption and solubility values equal or lower than 40 micrograms per cubic milimetre (sorption) and 7.5 micrograms per cubic milimetre (solubility) for specimens 15 mm in diameter and 2 mm thick.

Water sorption and solubility values are based on mass changes of the samples before (m1) and after immersion (m2) in water and after dessication (m3) until constant mass is achieved.  Mass changes m2-m3 are divided by sample volume to calculate water sorption and m1-m3 divided by sample volume give solubility values. 

Recent papers* published in Dental Materials investigated water sorption and solubility and hygroscopic dimensional changes of several resin-based composites:

low-shrinkage Filtek Silorane
universal Gradia Kalore
micro-hybrid Gradia Direct Anterior and Posterior and
self-adhering flowable Vertise Flow.

After 150 days of storage in de-ionized water, the lowest sorption of about 13 μg/mm³ was found for Filtek Silorane and the greatest of about 72 μg/mm³ was found for Vertise Flow. Vertise Flow also showed the greatest solubility of about 16 μg/mm³ whereas other materials showed either negative values (Filtek Silorane and Gradia Kalore) or values below 4 μg/mm³. The authors suggested that the negative solubility values for Filtek Silorane and Gradia Kalore meant that the dessication was not sufficient or that some water was irreversibly bound to the resin matrix.

Hygroscopic dimensional expansion as the result of water sorption over the 150-day period was lowest for Filtek Silorane (about 0.7%) and highest for Vertise Flow (about 4.8%) whereas the values for Gradia composites were between 1.5 and 2%. Hygroscopic expansion may compensate to a certain extent polymerization shrinkage which was found to be 0.99% for  Filtek Silorane, 1.7-2.4% for Gradia composites and  4.4% for Vertise Flow. However, this expansion occurs over a much slower time scale than shrinkage and its effect on the clinical performance of resin-based composite is yet to be determined.

The greatest stability in the aqueous environment found for Filtek Silorane may be explained by the hydrophobic siloxane and low-shrinkage ring-opening oxirane units of the silorane monomer. Furthermore, cationic polymerization is relatively oxigen-insensitive with the potential of reaching higher degree of conversion than methacrylate-based composites.

On the other hand, aqueous instability of Vertise Flow was attributed to the hydrophilic monomer, GPDM, which is responsible for the self-adhesive property of Vertise Flow but also seems to attract more water uptake by the resin matrix compared to other resin-based composites.

* Wei YJ, Silikas N, Zhang ZT, Watts DC. Hygroscopic dimensional changes of self-adhering and new resin-matrix composites during water sorption/desorption cycles. Dent Mater. 2011 Mar;27(3):259-66.

[Reprints of the cited papers may be obtained from the corresponding authors]

Click here for more on Vertise Flow.

Wednesday, 2 February 2011

Monomer elution from nanohybrid and ormocer-based composites

Recently, a paper on monomer elution from resin-based composites by my research team has been accepted for publication in the leading peer-reviewed journal on dental materials. The paper is available online under "Articles in press" and awaits publication in the paper format of Dental Materials. For reprints, you may contact me at 


Dent Mater. 2010 Dec 17. [Epub ahead of print]

Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

Manojlovic D, Radisic M, Vasiljevic T, Zivkovic S, Lausevic M, Miletic V.

University of Belgrade, School of Dentistry, Department of Restorative Dentistry
and Endodontics, Rankeova 4, 11000 Belgrade, Serbia.

OBJECTIVES: To study monomer elution from four resin-based composites (RBCs)cured with different light sources.  
METHODS: Twenty-eight premolars were randomlyallocated to four groups. Standardized cavities were prepared and restored with ananohybrid (Filtek Supreme XT or Tetric EvoCeram), an ormocer (Admira) or a microhybrid RBC (Filtek Z250) which served as control. Buccal restorations were cured with a halogen and oral restorations with an LED light-curing unit. Elution of diurethane dimethacrylate (UDMA), Bisphenol A diglycidylether methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) was analyzed using high-performance liquid chromatography (HPLC) 1h to 28 days post-immersion in 75% ethanol. Data were analyzed using multivariate and repeated measures analysis of variance (α=0.05).  
RESULTS: The greatest elution of UDMA and BisGMA occurred from Tetric EvoCeram and the least from Filtek Z250 (p<0.05). LED and halogen light-curing units gave similar results for all RBCs (p>0.05) except Tetric EvoCeram which showed greater elution for the LED unit (p<0.05). TEGDMA was below the limit of quantification. HEMA eluted in similar concentrations from Filtek Supreme and Tetric EvoCeram (p>0.05).  
SIGNIFICANCE: The two nanohybrid RBCs eluted more cross-linking monomers than the ormocer and the control microhybrid RBC. Continuous elution over 28 days indicates that RBCs act as a chronic source of monomers in clinical  conditions. Light source may affect monomer elution since differences were found  for one out of four RBCs. Mathematical models for elution kinetics of UDMA and BisGMA indicated two elution mechanisms.

Monday, 24 January 2011

News from

PhD Studentship (full time, 3 years)

Toxicological Studies of Endocrine Disrupting Chemicals in Dental Patients
Peninsula College Of Medicine And Dentistry Graduate School

This studentship aims to investigate the baseline and post-treatment urine and saliva concentrations of Bisphenol A and phthalate plasticisers in paediatric and adult patient populations entering Peninsula Dental School (PDS) Clinics.

The post will involve chromatographic (LC-MS/MS) analysis of biological samples and potentially, advanced mathematical modelling of data obtained. We are therefore looking for someone with a science background (BDS, BMBS, BSc Biomedical Sciences/Biology/Pharmacology/Chemistry or similar) with an aptitude for mathematics.

Stipend:  £13,590 
UK/EU candidates only
Closing date: 21 February 2011

For more information, click here

Saturday, 15 January 2011

Dental Materials Conferences 2011

89th General Session & Exhibition of the IADR
40th Annual Meeting of the AADR
35th Annual Meeting of the CADR
March 16-19, 2011
San Diego, California, USA
More information on the IADR website. Click here for the online scientific programme. More than 4000 abstracts are expected to be featured at the conference. Traditionally, the greatest number of sessions will cover many aspects of dental materials, from chemistry and properties to clinical performance.

45th Meeting of the Continental European Division (CED) and Scandinavian Division (NOF) of the IADR
August 31-September 3, 2011
Budapest, Hungary
More information on the IADR CED website. Deadline for abstract submission is March 25, 2011. Click here to submit your abstract. The CED-IADR will provide considerable support to young researchers through as many travel stipends as possible.

21st European Dental Materials Conference
August 24-26, 2011
Turku, Finland
“Current trends in moving toward non-metallic materials”
More information on the conference website. Click here for the tentative scientific programme. Dental Materials Summer School will be organized prior to the conference.

2011 Conference of the Academy of Dental Materials
October 13-15, 2011.
Bahia, Brazil
For more information, click here. Topics at this conference: What is the future? When to market? Where will the material be used?

International Dental Materials Congress
May 27-29, 2011
Seoul, Korea
"Moving Dental Materials from the Laboratory to the Clinic"
Visit the Congress website for more information. Click here for the scientific programme.

Sunday, 26 December 2010

Clinical evaluation of dental restorative materials - Part III: FDI criteria

In 2007, recommendations for conducting clinical trials approved by the FDI were published in several peer-reviewed journals. These recommendations not only addressed designing protocols for clinical trials but also challenged the Ryge criteria with an in-depth discussion of  clinical evaluation criteria and suggested a new approach in clinical evaluation of dental restorative materials and operative techniques.

In August 2010, an update of the "FDI clinical criteria for the evaluation of direct and indirect restorations" was published  by Hickel et al. in the Journal of Adhesive Dentistry and Clinical Oral Investigations. A lot of clinical examples were presented in the paper to illustrate various ratings.

The new FDI criteria set a different background for the evaluation of dental restorations by introducing 3 groups of criteria: esthetic, functional and biological. Each of these groups has subgroups with 16 evaluation criteria in total. These are:

Esthetic criteria
  1. Surface luster
  2. Staining: (a) surface and (b) margin
  3. Color match and translucency
  4. Esthetic anatomical form
Functional criteria
  1. Fracture of material and retention
  2. Marginal adaptation
  3. Occlusal contour and wear 
  4. Approximal anatomical form: (a) contact point and (b) contour
  5. Radiographic examination, where applicable
  6. Patient's view
Biological criteria
  1. Postoperative sensitivity and tooth vitality
  2. Recurrence of caries, erosion, abfraction
  3. Tooth integrity
  4. Periodontal response
  5. Adjacent mucosa
  6. Oral and general health
For all three groups, the following gradings are used for evaluation:
  1. Clinically excellent/very good
  2. Clinically good
  3. Clinically sufficient/satisfactory
  4. Clinically unsatisfactory
  5. Clinically poor
When judging a dental restoration using the FDI criteria, the score for each group is dictated by the most severe grading among the criteria for that particular group. Similarly, the overall score is determined by the worst grading among the groups. For example, if the functional criteria are unacceptable, the overall score is unacceptable. Detailed description of each grading is given in the previously mentioned paper: "FDI World Dental Federation - Clinical Criteria for the evaluation of direct and indirect restorations".

It is not mandatory to apply all of the FDI criteria in each study. In each particular study, the examiners should determine which criteria match their intended purposes best.

Gradings for the FDI criteria are substantially more detailed and sensitive than the Cvar and Ryge criteria and their modifications suggested by other authors. These detailed gradings challenge the training and calibration procedure of the examiners. To allow an easier and more efficient training, reduced variability in judgment and greater coherence in multi-centric studies, an online calibration system was established at It is emphasized by the authors of the FDI criteria that the e-calibration system does not replace the clinical setting but shortens clinical training significantly.

Beside their use in clinical trials, the FDI criteria are recommended for quality assessment of restorations by general dental practitioners in their everyday practice and as guidelines whether or not a restoration needs refurbishment, repair or replacement. Refurbishment is a minimal intervention such as polishing or contouring when no additional material is placed. Repair is a minimal intervention which requires additional material to be placed with or without a minimal preparation in the restoration or dental tissues.

Clinical investigators are strongly advised to use the new FDI criteria when designing and conducting clinical trials. However, the criteria are "not indefinitely fixed and defined" so investigators are asked for feedback and encouraged to contribute to the e-calib database with high quality images of clinical cases.


Hickel R, Peschke A, Tyas M, Mjör I, Bayne S, Peters M, Hiller KA, Randall R, Vanherle G, Heintze SD. FDI World Dental Federation - clinical criteria for the evaluation of direct and indirect restorations. Update and clinical examples. J Adhes Dent. 2010 Aug;12(4):259-72. doi: 10.3290/j.jad.a19262.

Hickel R, Roulet JF, Bayne S, Heintze SD, Mjör IA, Peters M, Rousson V, Randall R, Schmalz G, Tyas M, Vanherle G. Recommendations for conducting controlled clinical studies of dental restorative materials. Science Committee Project 2/98--FDI World Dental Federation study design (Part I) and criteria for evaluation (Part II) of direct and indirect restorations including onlays and partial crowns. J Adhes Dent. 2007;9 Suppl 1:121-47.