News from jobs.ac.uk

Postdoctoral Research Assistant

Centre for Oral Growth & Development
Barts and The London - Institute of Dentistry

Salary: £30,229 to £35,532

Application deadline: 26-February-2010.

Click here for more information.

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Statistics in dental research: A book review

In a addition to the previous post on statistics in dental research, I'd like to mention that Medical Statistics at a Glance is the best book on the subject I've seen. It contains all the basic things a dental materials scientist needs to know, from study designs, types of data and descriptive statistics to hypothesis testing, correlation and regression, survival analysis and Bayesian methods. The book is written in an exceptionally succinct and reader-friendly way, understandable to researchers with very little previous knowledge on statistics.

Theory is only given in the amount which is necessary to understand each concept. A very good feature of the book is that it explains most commonly used statistical tests in dental research: t-tests, analysis of variance (ANOVA), the non-parametric Mann-Whitney and Kruskal-Wallis test, chi-squared and McNemar's test. The assumptions for these tests are given but situations with departures from these assumptions are mentioned in terms of their effect and possible solutions.

Also, statistics for some more complex study designs is also presented, such as generalized linear models, multiple linear regression or methods for clustered data.

Medical Statistics at a Glance also serves as a fantastic reminder with an informative glossary and a detailed index of terms. It is an excellent value for money. I bought a new copy on eBay for about £20 but I'm sure it can be found elsewhere on the internet.

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Statistics in dental research: A challenge for a dental materials scientist

Dental research relies heavily on statistics and in the majority of studies some sort of statistics is necessary. This goes beyond the descriptive statistics (the measures of central tendency and spread) and includes hypothesis testing using parametric or non-parametric tests. Sometimes other tests are used depending on the research question and the hypothesis. As far as I can remember, the only type of research where I haven't seen any statistics done in dental materials science is finite element analysis which involves computer simulation of stresses and strains on bone and/or tooth models. This approach does not require sampling and therefore no statistics is performed.

The validity of results and conclusions depends, among other things, on the appropriate statistical test(s). I'm pretty sure dentists and material scientists who conduct research but are not familiar with statistics feel this may be their main weekness. In all research methodology courses, it is strongly advised to consult a statistician prior to conducting a study because even in the planning stage of the study, statistics is unavoidable as it is necessary to perform sample size and power calculation. However, consulting a statistician is easier said than done simply because there are not very many statistians out there available for quick (and free of charge) consultations. It seems to be a matter of personal initiative to establish some contacts since many academic institutions don't have statisticians among their employees.

Having said that, I can't help asking myself the following when I read scientific papers: how did these authors perform statistical analysis? Did they consult a statistician? Did they do statistics themselves? What's their knowledge on this subject and did they test the hypothesis based on the correct assumptions? Did they just copy the same test from a similar paper published previously? These questions arise because in many papers only the applied test and the p value are stated. Very little or nothing is known about the assumptions for parametric testing, how the departure of the required assumptions were dealt with, possible outliers and their effect on the results, correction in multiple testing etc.

I would appreciate some input from fellow scientists so please feel free to comment on this and write your opinion. Your own or other people's experience is welcome.

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IADR/Heraeus Travel Award

Supported by Heraeus
Deadline: February 5, 2010

The IADR is inviting applications from young investigators who have submitted an abstract which has a dental materials component for a travel award to support their attendance at the IADR General Session in 2010.

Young investigators (up to five years post-graduation from dental, material science, specialty training, or pre-PhD) are eligible to apply for a travel award. Applicants must be IADR members.

In 2010, five (5) awards will be granted—one person from each of the following regions: North America, Latin America, Europe, Africa/Middle East; and the Asia/Pacific Region. The winner of each award will receive US $2,500 for expenses to attend the IADR General Session & Exhibition in Barcelona, Spain, July 14-17, 2010.

Interested? Click HERE for more details on the application and peer-review process.

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Vertise Flow: the first self-adhering composite (flowable, though)

A long time ago, Michael Buonocore, one of the pioneers of adhesive dentistry, suggested four approaches to overcome the lack of adhesion between filling materials and dental tissues:
"(1) the development of new resin materials with adhesive properties;
(2) modification of present materials to make them adhesive;
(3) the use of coatings as adhesive interface materials between filling and tooth and
(4) the alteration of the tooth surface by chemical treatment to produce a new surface to which present materials might adhere." (Buonocore 1955)

In many respects, this was not only a suggestion but a visionary prediction for modern adhesive dentistry. We now know that all 4 of Buonocore's suggestions have been addressed by dental science which has led to the development of composite resins, adhesive systems and glass ionomer cements. These are three major groups of materials in adhesive dentistry today but there is a number of modifications and subgroups within each of them.

The latest news in adhesive dentistry is the development of self-adhering flowable composite, Vertise Flow by Kerr. Vertise Flow comes as a result of ongoing efforts to rationalize clinical treatment, currently including the use of adhesive systems and resin-based composites to create popular "white" fillings. Although a flowable composite, Vertise Flow clearly indicates the direction of current research by Kerr - the creation of the ultimate self-adhering composite for posterior teeth.

The manufacturer claims that Vertise Flow is based on Optibond technology which utilizes GPDM (glycero-phosphate dimethacrylate), a functional monomer, to obtain etching of enamel and dentine and HEMA, another functional monomer, most commonly used in dental adhesives to enhance wetting and resin penetration in dentine. It has been stated in many scientific papers that BisGMA is the main resin component of Optibond adhesives, though not clearly stated in manufacturer's safety data sheet. It can be expected that Vertise Flow contains BisGMA as the main cross-linking monomer as well.

One of the main questions that a dental material scientist would ask is: How does this material overcome the hydrophobic-hydrophilic mismatch between composite resins and human dentine to produce an interface that would ensure optimal bonding for long-term clinical success? This is currently achieved by the use of adhesive systems as an intermediary layer that is supposed to bridge hydrophobic composite and hydrophilic dentine.

Manufacturer's data suggest that the shear bond strength of Vertise Flow to enamel and dentine is comparable to self-etch adhesive systems. Furthermore, it is suggested that the tooth-restoration interface prevents microleakage, the passage of fluids, bacteria, molecules and ions between the restoration and cavity walls. This phenomenon has been proved to exist for all current resin-based materials due to polymerization contraction of composite resins.

Undoubtedly, Vertise Flow will soon be subjected to a vast array of studies by independent researchers that will address various properties of this material and compare it with other materials on the market. Independent evidence-based results, if in favor of this material, will be the best marketing for Vertise Flow. As always, the last word lies upon the dental practice.

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Click here to read the latest post on water sorption, solubility and dimensional changes of resin-based composites including Vertise Flow.

Free live dental webcast/webinar @ GC America Online Learning

GC I.Q.One Body Concept: The Fusion of Esthetics and Production
Presenter: Mr. Rick Sonntag, RDT

19-Jan-2010 7 pm ET (12 pm GMT)
About 150 seats available

Rick Sonntag RDT will show how production laboratories can reach their esthetic potential and how boutique labs can maximize their production potential. Viewers will also see the flexibility of the system that can be adapted to conventional layering techniques, micro-layering techniques, or internal stain techniques, on metal and zirconia.

Prior to claiming a seat for this webinar, you must create a free account at GC America Online Learning HERE.

Also, check out other free webcasts @ Pentron and Kerr
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Mineral Trioxide Aggregate (MTA): Free Full Text Articles I

This is the list of scientific articles on mineral trioxide aggregate (MTA) available in full text. All articles can be downloaded following the links on MEDLINE. You may also be interested in other posts on MTA. Click here for part II of the list of free full text articles on MTA.

Pulp capping

1. Bogen G, Kim JS, Bakland LK. Direct pulp capping with mineral trioxide aggregate: an observational study. J Am Dent Assoc. 2008 Mar;139(3):305-15; quiz 305-15.

2. Ford TR, Torabinejad M, Abedi HR, Bakland LK, Kariyawasam SP. Using mineral trioxide aggregate as a pulp-capping material. J Am Dent Assoc. 1996 Oct;127(10):1491-4.

Endodontics

3. Ghaziani P, Aghasizadeh N, Sheikh-Nezami M. Endodontic treatment with MTA apical plugs: a case report. J Oral Sci. 2007 Dec;49(4):325-9.

4. Winik R, Araki AT, Negrão JA, Bello-Silva MS, Lage-Marques JL. Sealer penetration and marginal permeability after apicoectomy varying retrocavity preparation and retrofilling material. Braz Dent J. 2006;17(4):323-7.

5. Witherspoon DE, Small JC, Harris GZ. Mineral trioxide aggregate pulpotomies: a case series outcomes assessment. J Am Dent Assoc. 2006 May;137(5):610-8.

6. Silberman A, Cohenca N, Simon JH. Anatomical redesign for the treatment of dens invaginatus type III with open apexes: a literature review and case presentation. J Am Dent Assoc. 2006 Feb;137(2):180-5. Review.


7. Schwartz RS, Mauger M, Clement DJ, Walker WA 3rd. Mineral trioxide aggregate: a new material for endodontics. J Am Dent Assoc. 1999 Jul;130(7):967-75. Review.

Chemical analysis

8. Oliveira MG, Xavier CB, Demarco FF, Pinheiro AL, Costa AT, Pozza DH. Comparative chemical study of MTA and Portland cements. Braz Dent J. 2007;18(1):3-7.

(The link to each article is in the top right corner as shown in this image. Click to enlarge.)


The following articles are available from PubMed Central.

Immunology

9. Taia Maria Berto Rezende, Leda Quercia Vieira, Antônio Paulino Ribeiro Sobrinho, Ricardo Reis Oliveira, Martin A. Taubman, and Toshihisa Kawai. The influence of Mineral Trioxide Aggregate (MTA) on adaptive immune responses to endodontic pathogens in mice. J Endod. 2008 September; 34(9): 1066–1071.

Tissue engineering (Genetics)

10. Paul C Edwards and James M Mason. Gene-enhanced tissue engineering for dental hard tissue regeneration: (2) dentin-pulp and periodontal regeneration. Head Face Med. 2006; 2: 16.

11. Rebecca S. Prescott, Rajaa Alsanea, Mohamed I. Fayad, Bradford R. Johnson, Christopher S. Wenckus, Jianjun Hao, Asha S. John, and Anne George. In-vivo Generation of Dental Pulp-Like Tissue Using Human Pulpal Stem Cells, a Collagen Scaffold and Dentin Matrix Protein 1 Following Subcutaneous Transplantation in Mice. J Endod. 2008 April; 34(4): 421–426.

(The link is shown in the image below. Click to enlarge.)


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