Mineral trioxide aggregate (MTA) in endodontics

Mineral trioxide aggregate (MTA) is a mixture of a refined Portland cement and bismuth oxide, and also contains trace amounts of SiO2, CaO, MgO, K2SO4, and Na2SO4. MTA was first described for endodontic applications in the scientific literature in 1993. Nowadays, there are two forms of MTA on the market, the traditional gray MTA (GMTA) and white MTA (WMTA), which was introduced in 2002. WMTA has less Al2O3, MgO, and FeO and, also, smaller particles than GMTA.

MTA is prepared by mixing the powder with sterile water in a 3:1 powder/liquid ratio. This results in the formation of a colloidal gel that solidifies to a hard structure in approximately 3–4h. It is believed that moisture from the surrounding tissues favours the setting reaction.

Similar or less microleakage has been reported for MTA compared to traditional endodontic sealing materials [gutta-percha and pastes] when used as an apical restoration, furcation repair, and in the treatment of immature apices. 3mm of MTA is recommended as the minimal amount against microleakage and 5mm in the treatment of immature apices. In vitro and in vivo studies support the biocompatibility of freshly mixed and set MTA when compared to other dental materials

Clinical applications of MTA include:
pulp capping,
pulpotomy dressing,
root-end filling,
root repair [resorption and perforations] and
apexification.

Clinical prospective studies suggest that both GMTA and WMTA have similar results as traditional calcium hydroxide in non-carious mechanical pulp exposures in teeth with normal pulp tissue. However, further clinical studies are needed, particularly involving pulp exposures in carious teeth.

Clinical prospective studies using MTA as pulpotomy dressings for primary and permanent teeth reported similar or better results for MTA materials compared to formocresol or calcium hydroxide in the formation of dentine bridges and continued root development. Histological analysis has suggested a more homogenous and continuous dentine bridge formation by MTA than calcium hydroxide at both 4 and 8 weeks after treatment and less inflammation associated with MTA than calcium hydroxide.

There are several case reports in which MTA has been successfully used to repair horizontal root fractures, root resorption, internal resorption, furcation perforations and apexification and/or apexogenesis which was confirmed clinically and radiographically.

Overall results on the use of MTA in endodontics are favourable, but more well-designed and controlled clinical longitudinal studies are needed to allow systematic review and confirmation of all suggested clinical indications of MTA.

You may be interested in a list of free full text scientific articles published in international peer-reviewed journals.

Biocompatiblity of resin-based materials: Bisphenol-A

Bisphenol-A is an organic compound with two phenol functional groups, commonly used in the production of many plastic products. Studies have shown that bisphenol-A may have adverse health effects such as hormonal, developmental, neurological as well as carcinogenic.

In spite of this, bisphenol-A may be part of dental resin-based materials as a direct ingredient, as a by-product of bio-degradation of other ingredients or as a trace material left-over from the manufacture of other ingredients. Though bisphenol-A is rarely used as a direct ingredient in dental composites, adhesives or sealants, it is a starting ingredient in the manufacture of the most commonly used resin - BisGMA. Also, some other, less frequently used resins, such as Bis-DMA, are also produced using bisphenol-A.

Concerns about bisphenol-A have been raised since studies have shown that various components of dental composites, adhesives and sealants may leach out and have potential local or systemic adverse effects. An in vivo study using an ELISA system showed that up to 100 ng/ml of bisphenol-A may be released into saliva from resin-based composites immediately after placement (Sasaki et al. 2005). Also, a more recent study showed that BisGMA, but also BisGA and BisDMA, all bisphenol-A - based monomers, may leach out from in vivo placed composite restorations (Uzunova et al. 2008). On the other hand, no traces of bisphenol-A were found from chemically and light-cured orthodontic adhesives after in vitro accelerated aging and elution (Eliades et al. 2007).

Over the past few years, both the FDA and ADA have supported research on biocompatibility and safety of resin-based materials containing bisphenol-A. Both organizations issued statements in 2007 (FDA) and 2008 (ADA) that the low-level of BPA exposure that may result from dental materials poses no known health threat. However, further research on this subject is encouraged by the ADA.

References:

• Sasaki N, Okuda K, Kato T. Salivary bisphenol-A levels detected by ELISA after restoration with composite resin. J Mater Sci: Mater in Med 2005;16:297-300.
• Uzunova Y, Lukanov L, Filipov I, Vladimirov S. High-performance liquid chromatographic determination of unreacted monomers and other residues contained in dental composites. J Biochem Biophys Methods 2008;70:883-888.
• Eliades T, Hiskia A, Eliades G, Athanasiou AE. Assessment of bisphenol-A release from orthodontic adhesives. Am J Orthod Dentofacial Orthol 2007;131:72-75.
  

Pre-fabricated, direct, single-visit, ceramic inserts

Ceramic inserts have been designed as single-visit systems and an alternative to conventional ceramic restorations produced in two appointments by means of indirect technique. Luting ceramic inserts with a small amount of composite resin is expected to reduce the amount of polymerisation shrinkage by reducing the bulk of resin composite needed to restore the tooth. Another advantage is that the occlusal contacts can be placed on the ceramic surface, rather than on the composite, for longer-term stability.

One of the most studied systems is Cerana, which utilises pre-etched and silanated leucite inlays with matched diamond burs. After caries removal and the preparation of a usual adhesive-type preparation for bonded restorations (Figure 1), the cavity is refined using one of three conical burs (Figure 2). Enamel and dentine are etched if etch-and-rinse adhesive is used or self-etch systems are applied and cured. Composite is then applied to the cavity, filling it to or just above the enamel-dentin junction (Figure 3). A thin coat of composite can be applied to the ceramic insert which is then pressed into the cavity. Excess resin composite is removed and the restoration is cured for 20 s or 40 s depending on the light-curing unit (Figure 4). The occlusal contour of the inlay is shaped to match the surrounding enamel and the occlusion adjusted (Figure 5). The restoration is cured for a further 20 s or 40s and polished.

(Figures from manufacturer's recommendations for use. Nordiska Dental AB, Sweden)
A 3-year prospective clinical trial has shown that “The results indicate that Cerana is an alternative to composite resin restorations in Class I situations, but should be avoided in connection with Class II tunnel preparations.” (Odman 2002)

Another 8-year prospective clinical trial has shown that “Cerana is acceptable in terms of aesthetics, patient acceptance, occlusal wear and ease of use and is a good alternative for a single-visit, tooth coloured restoration in suitable cavity shapes.” (Millar & Robinson 2006)

In an in vitro study Cerana inserts luted with flowable composite in Class V cavities showed significantly less microleakage than those cemented with the high-viscous material only at the gingival margins. Microleakage was reduced around inserts compared to the bulk filling with flowable composites but no difference was observed between inserts and bulk filling with high-viscous composite material (Salim et al. 2005).

It was also shown that in vitro thermocycling 4000 times between 5 and 55 degree C does not increase microleakage around Cerana inserts (Santini et al. 2006). After thermocycling, Cerana inserts showed siginificantly less microleakage along both occlusal and gingival margins compared to Beta Quartz glass-ceramic inserts and Tetric Ceram resin-based composite. Both findings were attributed to the coefficient of thermal expansion of Cerana inserts which approximates that of enamel (Tan & Santini 2005; Santini et al. 2006).

References:

1. Odman P. A 3-year clinical evaluation of Cerana prefabricated ceramic inlays. Int J Prosthodont 2002; 15: 79-82.
2. Millar BJ, Robinson PB. Eight year results with direct ceramic restorations (Cerana). Br Dent J 2006; 201:515-520.
3. Salim S, Santini A, Safar KN. Microleakage around glass-ceramic insert restorations luted with a high-viscous or flowable composite. J Esthet Restor Dent 2005;17: 30-38.
4. Santini A, Ivanovic V, Tan CL, Ibbetson R. Effect of prolonged thermal cycling on microleakage around Class V cavities restored with glass-ceramic inserts with different coefficients of thermal expansion: an in vitro study. Prim Dent Care. 2006 Oct;13(4):147-53.
5. Tan CL, Santini A. Marginal microleakage around class V cavities restored with glass ceramic inserts of different coefficients of thermal expansion. J Clin Dent. 2005;16(1):26-31.

News from jobs.ac.uk

Research Fellow in Biomaterials for Skeletal Regeneration
(Click for more information)

Leeds Dental Institute

University of Leeds - Faculty of Medicine and Health

Salary: £29,704 to £35,469 p.a. It is likely that an appointment will be made at or below GBP 31,513 p.a. since there are funding limitations which dictate the level at which the appointment can start.

Application deadline: 3 November 2009

Essential toolkit for a dental materials scientist: Search engine (Part II)

ISI Web of Knowledge (Web of Science)

ISI Web of Knowledge (also known as Web of Science) is a research platform by Thomson Reuters that comprises seven databases containing information gathered from thousands of scholarly journals, books, book series, reports and conferences. It contains three multidisciplinary indexes to the journal literature of the sciences, social sciences and art and humanities; two conference proceedings citation indexes for sciences, social sciences and humanities and two chemistry databases (Index Chemicus and Current Chemical Reactions).

Search panel is very intuitive and user-friendly and allows search by various categories, similar to Medline, such as topic, title, author, title, journal, year of publication, address, conference, language, document type, funding agency and grant number.



A search can be saved under Marked List and forwarded to an email address as plain text or html.

ISI web of Knowledge offers an option to create citation reports which include the total and average number of times certain items (e.g. journal articles) have been cited and also the number of citations per year. Furthermore, ISI Web of Knowledge displays a list of articles in which an article of interest has been cited.


Cited Reference Search is an option to search for articles that cite a certain person’s work. A search can be done using a person’s name, the journal where an article is published and/or the year of publication.


Another useful tool is that EndNote Web version is integrated with ISI Web of Knowledge. This allows a search to be saved as an Endnote bibliography and directly cited while typing. A search can also be exported to other types of Reference software if you have it installed on your computer (EndNote, Reference Manager or ProCite). I will address EndNote as part of the essential toolkit of a dental materials scientist in a separate blog post.

Essential toolkit for a dental materials scientist: Search engine (Part I)

MEDLINE

For many clinical researchers, MEDLINE is probably the starting point for any article search. MEDLINE comprises over 5000 journals published worldwide and is the largest part of the PubMed database, a service of the U.S. National Library of Medicine. PubMed also contains other life science journals.

As a result of U.S. National Institutes of Health Public Access policy aimed at increasing free access to articles, Pubmed Central (PMC) has been created as a free digital archive of biomedical and life sciences journal literature. It contains journals which submit articles regularly but also articles published by NIH-funded researchers in journals currently not on the PMC list. Full text is available in either HTML or PDF format.

A particularly useful tool available at PubMed is “MyNCBI” which allows searches to be saved and filtering options and automatic searches set up. It is located in the top right corner of the PubMed homepage and requires registration (free). MyNCBI offers various features but among the most useful are automatic searches and collections.

Automatic search: Once you enter keywords and search results are generated, you should save the search by clicking the “Save Search” option next to the search box. The search is saved to MyNCBI. Then, you can enable automated search in MyNCBI and the results will be emailed to you daily or once a week or month, according to the settings. The same keywords from the initial search will be used every time in the automated search.

Collection: Once you enter keywords and search results are generated, you should save the search by clicking the “Send to” option and selecting “Collections” from a drop down menu. A collection can be made public by selecting the appropriate option in MyNCBI, in which case a direct URL or HTML for web pages and blogs are generated.

You can access MyNCBI through PubMed homepage, but if no PubMed search is intended, then you can use a direct link to MyNCBI

News from jobs.ac.uk

Lecturer in Restorative Dentistry
(Click on the link for more information)

University of Leeds - Leeds Dental Institute
Salary on the Clinical Lecturer scale (£30,685 - £57,084 pa)

Application deadline: 24 October 2009