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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Free live dental webcast/webinar @ Pentron Clinical Technologies

How, When and Why of Restorative Posts Cores
Presenter: Dr. Gregori Kurtzman, D.D.S.
Thursday 14 - Jan - 2010 at 6:00 pm ET (11 pm GMT)
About 150 seats left.Prior to claiming a seat, you must create a free account at Pentron Clinical Technologies HERE. This course is CE approved (1 CE credit). Instructions how to enter this virtual class are on the Pentron website.

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Free live dental webcasts/webinars @ Kerr Learning Source

Register for upcoming live webcasts at Kerr Learning Source

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(1) Simplifying the Placement of Exquisite Direct Resin Restorations
Presenter: Dr. Bob Lowe

Wed 13-Jan-2010 at 7 pm ET (14-Jan-2010 midnight GMT)
About 20 seats left !!!

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(2) Simplifying Restorative Dentistry Using Self Adhesive Flowable Composites
Presenter: Dr. Martin Jablow

Wed 10-Feb-2010 at 7 pm ET (11-Feb-2010 midnight GMT)
About 170 seats left.

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Prior to claiming a seat, it is essential to create an account for free at Kerr Learning Source HERE.

Both webcasts are CE accredited (1 CE credit). All instructions on how to enter the virtual classroom and attend these live course are given on the Kerr Learning Source website.

Both webcasts are supported by Kerr Dental.

Dental materials in practice

Endodontic treatment (obturation phase): lower premolar with 3 roots by Dr Lang

Dental materials - online learning resources

Dental materials lectures by professors Stephen C. Bayne and Jeffrey Y. Thompson for UNC and Michigan DDS students. Other users need special permission but the files can be accessed and viewed free of charge. The lectures cover topics from operative dentistry (pulpal capping, adhesives, composites, amalgam, glass-ionomer cements), fixed prosthodontics (impression materials, waxes, alloys, ceramics) and removable prosthodontics (alloys, bases and teeth). The files are in the form of PDF and PPT handouts, self-study modules and audio files and include study and discussion questions.

University of Berkley webcasts - Structural Aspects of Biomaterials , Instructor Lisa Pruitt. Tooth and bone tissues are addressed in a basic manner necessary to understand the interaction with materials. Dental materials (filling materials, implants) are discussed in terms of mechanical and structural aspects. Mechanical design for longevity includes topics of fatigue, wear, and fracture. Very well explained and understandable to dentists without almost any previous engineering knowledge. This webcast is free to view but cannot be downloaded.

Dental materials webinars by various speakers at dentallearning.com. There are 13 webinars covering topics such as contemporary adhesives, dentine bonding , anterior and posterior composite restorations, sealants and glass ionomers, zirconia, impression materials, CEREC restorations. Among the speakers are renowned lecturers Dr David Pashley and Dr Jorge Perdigao who address the advances in adhesive dentistry and explore the science of dentine bonding. The cost of webinars by Drs Pashley and Perdigao is USD$35 whereas most other webinars direct you to Kerr Learning source where they can be viewed but registration (free) is required. There are even more free webinars at Kerr Learning. All these webinars are CE approved.

Dental ED live lectures and online courses - cost from USD$50 to USD$260. Online courses include composite restorations, endodontic obturation, dental implants, porcelain building techniques, shade selection, direct laminate veneers, zirconica restorations. Upcoming live lectures can be viewed at Dental ED website. Basically, all lectures and courses are audio-visual presentations with more or less theoretical background but with excellent clinical cases.

Scientific journals focusing on dental materials

Two journals in the Science Citation Index (SCI) database focus exclusively on dental materials: (1) Dental Materials and (2) Dental Materials Journal.

Dental Materials is published monthly by the Academy of Dental Materials and is currently ranked 4/55 in the Dentistry, Oral Surgery & Medicine discipline and 5/19 in the Materials Science, Biomaterials discipline. Its impact factor for 2008 is 2.941. It is available through ScienceDirect but requires personal or institutional subscription for full text access. Abstracts can be accessed for free. January 2010 issue of Dental Materials is a free sample and full texts can be downloaded as PDF files. This issue is available HERE.


Dental Materials Journal is published bi-monthly by the Japanese Society for Dental Materials and Devices and is currently ranked 51/55 in the Dentistry, Oral Surgery & Medicine discipline and 15/19 in the Materials Science & Biomaterials discipline. Its impact factor for 2008 is 0.713. Dental Materials Journal is available through FreeMedical journals or at publisher's website HERE. All issues are free and full texts can be downloaded as PDF files.

Though I access full texts in most dental journals through my University online library, occasionally there are articles which cannot be obtained this way. Another way of obtaining an article in its entirety is to send a reprint request to the corresponding author. Fortunately, there is an email address attached to most abstracts on PubMed/MEDLINE. I have been able to obtain almost all articles from the authors whom I sent reprint requests. The only problem may arise when the provided email address becomes inactive. This often happens when an author changes institutions and institutional email addresses. This is why I, for example, always provide my gmail address for correspondence when submitting an article for publication.