Recommendations for conducting controlled clinical studies of dental restorative materials

Inspired by the recent debate, I did a literature search on clinical trials in various dental disciplines. As expected, there are loads of such studies on dental materials and clinical procedures, so the argument that something can't be tested is invalid. Everything can and must be tested using scientifically structured protocols before certain claims are made.

Two years ago, a group of scientists associated with the FDI Science Committee published recommendations for conducting clinical trials on dental materials. These recommendations are related to study design and evaluation criteria.

The following is the abstract of this paper and the full text can be obtained from J Adhes Dent or the first author, Dr Reinhardt Hickel of the University of Munich, Germany hickel@dent.med.uni-muenchen.de

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.

Hickel R, Roulet JF, Bayne S, Heintze SD, Mjör IA, Peters M, Rousson V, Randall R, Schmalz G, Tyas M, Vanherle G.

J Adhes Dent 2007; 9 Suppl 1:121-147. Erratum in J Adhes Dent. 2007 Dec;9(6):546.

About 35 years ago, Ryge provided a practical approach to the evaluation of the clinical performance of restorative materials. This systematic approach was soon universally accepted. While that methodology has served us well, a large number of scientific methodologies and more detailed questions have arisen that require more rigor. Current restorative materials have vastly improved clinical performance, and any changes over time are not easily detected by the limited sensitivity of the Ryge criteria in short-term clinical investigations. However, the clinical evaluation of restorations not only involves the restorative material per se but also different operative techniques. For instance, a composite resin may show good longevity data when applied in conventional cavities but not in modified operative approaches. Insensitivity, combined with the continually evolving and nonstandard investigator modifications of the categories, scales, and reporting methods, has created a body of literature that is extremely difficult to interpret meaningfully. In many cases, the insensitivity of the original Ryge methods leads to misinterpretation as good clinical performance. While there are many good features of the original system, it is now time to move on to a more contemporary one. The current review approaches this challenge in two ways: (1) a proposal for a modern clinical testing protocol for controlled clinical trials, and (2) an in-depth discussion of relevant clinical evaluation parameters, providing 84 references that are primarily related to issues or problems for clinical research trials. Together, these two parts offer a standard for the clinical testing of restorative materials/procedures and provide significant guidance for research teams in the design and conduct of contemporary clinical trials. Part 1 of the review considers the recruitment of subjects, restorations per subject, clinical events, validity versus bias, legal and regulatory aspects, rationales for clinical trial designs, guidelines for design, randomization, number of subjects, characteristics of participants, clinical assessment, standards and calibration, categories for assessment, criteria for evaluation, and supplemental documentation. Part 2 of the review considers categories of assessment for esthetic evaluation, functional assessment, biological responses to restorative materials, and statistical analysis of results. The overall review represents a considerable effort to include a range of clinical research interests over the past years. As part of the recognition of the importance of these suggestions, the review is being published simultaneously in identical form in both the Journal of Adhesive Dentistry and Clinical Oral Investigations. Additionally, an extended abstract will be published in the International Dental Journal, giving a link to the web full version. This should help to introduce these considerations more quickly to the scientific community.

Recent books on dental materials

This list has been updated in a new post.

Biocompatibility of Dental Materials‎ by Gottfried Schmalz, Dorthe Arenholt-Bindslev, 2009, 379 pages

Clinical aspects of dental materials: theory, practice and cases by Marcia A. Gladwin, Michael D. Bagby, 2009, 481 pages
(Preview not available)

Dental materials guide by Donna J. Phinney, Judy H. Halstead, 2008, 773 pages

Dental Materials by Lyle Zardiackas, Tracey M. Dellinger, Mark Livingston, 2007, 765 pages
(Preview not available)

Craig's restorative dental materials by John M. Powers, Ronald L. Sakaguchi, 2006, 632 pages
(Preview not available)


Materials and procedures for today's dental assistant by Ellen Dietz-Bourguignon, 2005, 269 pages
(Preview not available)


Dental materials: properties and manipulation by Robert George Craig, John M. Powers, John C. Wataha, 2004, 348 pages
(Preview not available)

Phillips' science of dental materials by Kenneth J. Anusavice, Ralph W. Phillips, 2003, 805 pages
(Preview not available)


Dental materials: clinical applications for dental assistants and dental hygienists by Carol Dixon Hatrick, W. Stephan Eakle, William F. Bird, 2003, 373 pages

Introduction to dental materials by Richard van Noort, 2002, 298 pages




The chemistry of medical and dental materials by John W. Nicholson, 2002, 242 pages



Dental materials and their selection by William Joseph O'Brien, 2002, 418 pages
(Preview not available)



Materials in dentistry: principles and applications by Jack L. Ferracane, 2001, 354 pages

Research methodology: The effect of "material A" on treatment outcome

I've recently discussed with a colleague the possibility to prove or disprove the efficacy of a certain clinical procedure on treatment outcome. Since this is the dental materials blog, I'm going to make the parallel between clinical procedures and dental materials and discuss this matter as if it was about dental materials. From the research methodology point of view, it makes no difference whether it is a dental material or a clinical procedure.

"Randomized control clinical trial" would probably be the most appropriate study design to evaluate whether a certain material (material A) has any effect whatsoever on the outcome of a particular treatment. In a recently published book "Introduction to randomized control clinical trials" by JNS Matthews, there is a very nice definition:

"A randomized concurrently controlled clinical trial is simply an experiment performed on human subjects to assess the efficacy of a new treatment for some condition. It has two key features:

1. The new treatment is given to a group of patients (treated group) and another treatment, often the most widely used, is given to another group of patients at the same time (control group). This is what makes the trial concurrently controlled.
2. Patients are allocated to one group or another by randomization. "(1)

Also, it is very important to note that:
"Trials are applied to many different modes of treatment... for example, new surgical procedures, screening programs, diagnostic procedures etc."(1)
How does this apply to our material A? A double-blind trial would be impossible in this case, because a clinician would always know the details of the treatment. On the other hand, a single-blind trial would be possible and recommended since the patient wouldn't know the details of the treatment in order to exclude the possible placebo effect.
Patient inclusion criteria should be taken into consideration at the beginning of the trial. These include, but are not restricted to, patient age, general health, the diagnosis of the current dental condition, the history of this condition etc. It would be wise to "standardise" the cohort so that the number of variables is reduced as much as possible. For example, root canal treatment of a pulpitis may have a different outcome than the treatment of periapical disease, because of the nature of the two dental conditions and variations in patients' immunological response to any of them. Therefore, it would be recommended that one of the inclusion criteria is the uniformity of clinical diagnosis.
Randomization would be easy using the table of random numbers. It excludes any potential bias and is always preferred to other ways of patient selection, as long as the number of cases in both the treated and control group is the same or as similarly-sized as possible. Most statistical tests are most powerful when the groups being compared have equal sizes.
Then, once the treatment is performed, the treated group would receive material A and the control group would receive placebo. The outcome of the treatment would be monitored over at least 3 years, using the standard parameters for monitoring the outcome of this particular treatment. After the monitoring period, (an) appropriate statistical test(s) would be used to assess the difference in treatment outcomes between the two groups of patients.
Only then would it be possible to claim that material A has any effect on the outcome of this particular dental treatment.
(1) Matthews JNS. Introduction to randomized control clinical trials. 2nd edition. Chapman&Hall/CRC; Boca Raton, FL, USA; 2006.

Upcoming event: ESE Edinburgh 2009

European Society of Endodontology Conference, Edinburgh, UK, September 24-26, 2009.

The European Society of Endodontology Conference will be held next week in the beautiful city of Edinburgh. Unfortunately, I'm not going to take part but I'm looking forward to meeting my fellow colleagues from the University of Belgrade School of Dentistry, Professors Vladimir Ivanovic and Branislav Karadzic and Dr Jugoslav Ilic, who will be presenting their research findings.

Prof. Ivanovic is one of keynote speakers and will give a presentation entitled: "Seeking where, when, why and how to locate apical terminus of the root canal preparation". He will also chair a session on the risks and controversies of local anaesthetics.

Scientific programme comprises more than 30 lectures on various topics of interest in contemporary endodontic practice and science. Dental materials will be discussed during several lectures and this year include the following issues:

• Obturation: concepts, truths and misconceptions, by Prof. G. Glickman, USA
• Changing endodontic concepts and outcomes: the multifaceted use of mineral trioxide aggregate, by Dr G. Bogen, USA
• So much for the endodontics, what about the restoration?, by Prof. R. Ibbetson, UK
• New perspectives in adhesive post endodontic restoration, by Prof. A. Cerutti, Italy
• Fibre posts and dentine adhesion: the true story, by Dr F. Mannocci, Italy

Furthemore, dental materials will be addressed in presentations on freely chosen topics including bioceramics of calcium phosphate in endodontic treatment, rheological studies, apical sealing, bond strength, biocompatibility and cytotoxicity of new and current endodontics sealers, fitting and microleakage around fibre posts.

The full scientific programme can be downloaded here.

Journal of Dental Research: Top 50 most-frequently read and cited articles

Some time ago, I wrote a post about the Top 10 'hottest' articles published in Journal of Dentistry (J Dent). Similarly to J Dent, lists of most-frequently read and cited articles are generated every month for Journal of Dental Research (J Dent Res), one of the leading dental journals with the 2008 impact factor of 3.142. These lists are based on full-text and pdf views and the latest can be found here: most-frequently read and cited.

Though both J Dent Res and J Dent cover a wide area of research in dentistry, their lists of 'hottest' articles differ significantly as to the nature of research subjects. Whilst 8 out 10 'hottest' articles in J Dent are related to dental materials, there is not a single article among the top 10 most-frequently read and cited articles in J Dent Res related to dental materials. J Dent Res does have a Biomaterials section in every issue and publishes a certain amount of articles related to dental materials. However, the majority of articles gravitate to more basic sciences, such as (patho)physiology, (patho)histology, immunology, genetics, pharmacology... This is also reflected in the lists of most-frequently read and cited articles.

IADR General Session and Exhibition, Barcelona, Spain, 2010

There's been an official announcement on the IADR website about the next IADR General Session and Exhibition in Barcelona, Spain (July 14-17, 2010).

Abstract submission is now open and the deadline is February 5, 2010. Abstracts should be submitted online following this link.

Scientific programme and keynote speakers will be announced at a later date.

Surface roughness of resin-based composites

The study "Surface characterisation of resin-based composite materials using atomic force microscopy" was successfully presented by Ana Ergic and Dejan Nedeljkovic at the IADR-CED conference in Munich. Click on the image to enlarge the poster. Ana and Dejan are my former students who were involved in this study as part of their student research project. They have recently graduated at the University of Belgrade School of Dentistry.
I'd like to point out that a custom-made device was used in this study to standardise mechanical aging which was performed as a series of brushing cycles using commercial toothbrushes and abrasive toothpaste.

More recent RBCs showed lower surface roughness values before and after aging compared to the control mycrohybrid RBC, Filtek Z250. Surface roughness for N'Durance was found to be similar before and after aging whilst Tetric EvoCeram and Filtek Silorane showed increased roughness after aging.
Keywords: dental materials, resin-based composites, roughness, AFM