Dental materials

Though it is not quite a dental materials subject, I have been involved in clinical testing of electronic apex locators with my colleagues at the University of Belgrade School of Dentistry. This paper has been published in the August issue of the International Endodontic Journal and can be found here. If you have trouble getting access, please email me.
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The 45th Meeting of the Continental European Division (CED) of IADR, organized together with the Scandinavian Division (NOF) will be held in Budapest, Hungary, from August 31 till September 3, 2011. Basic sciences and clinical topics, such as dental materials, cariology, implantology, periodonontology, oral medicine, tissue engineering, craniofacial biology, salivary research etc. will be covered by plenary lectures, symposia, oral and poster presentation sessions etc.

Scientific symposia on dental materials will cover the following subjects:

1. Adhesive technology
2. Needs and requirements of dental materials in combating caries 
3. Biomaterials in periodontal and implant surgery
4. Aesthetic and mechanical aspects of composite materials
5. Implant restoration
6. Nano biomaterials in regenerative dentistry
7. Novel tri-calcium silicate-based dentine substitute

I will present a digital image correlation study on composite shrinkage using a two-camera system which allows 3D measurement of strains and displacements. This study is a result of strengthening research ties between my team from the School of Dentistry and colleagues from the Faculty of Mechanical Engineering, University of Belgrade, Serbia. The abstract of this study is here. Also, other studies that will be presented during the same session on Composites, Shrinkage, Curing, and Fracture Toughness may be found here.

For more information on the scientific programme and registration for the 45th IADR CED&NOF conference please visit the official CED-IADR2011 website.

The ISO4049 standard explains in detail how the depth of cure is measured and what is minimum depth that composites must have in order to comply with this standard. This simple procedure does not require sophisticated equipment and may be done in every dental office. It allows testing and comparison of materials and light curing units. Even if there is a radiometer to check the light intensity, it is recommended to measure the actual thickness of the composite cured by a a particular light curing unit.

Here is what we need:

1. composite
2. light curing unit
3. cylindrical moulds (6 mm thick and 4-5 mm in diameter), originally it should be stainless steel, but plastic straws cut into moulds of this size may be used as well
4. glass slab
5. Mylar strips
6. plastic filling instrument
7. spatula or scalpel

And here is the step-by-step procedure:

Posterior Composites: Improving Esthetics and Increasing Simplicity 
Presenter: Dr. Greg Gillespie

(CE credits 1)

Date Wednesday 27 April 2001
Time 7:00 pm ET / 6:00 pm CT / 4:00 pm PT / 11 pm UTC (former GMT)


This webinar is sponsored by GC America.
From the official website: "In this webinar, Dr. Gillespie will review adhesive protocols that will help eliminate post-operative sensitivity and increase bond strengths. Dr. Gillespie will also highlight the latest advancements in composite resins regarding shrinkage and esthetics with one shade placement."

It is necessary to register and reserve a seat. If you miss the live webinar, it will soon be among On demand webinars. They are all free and may be accessed at any time.

Glass-ionomer cements (GIs) are still the only true self-adhesive materials forming the chemical bond with tooth tissues. Despite the traditional classification to types of GIs, current scientific literature is dominated by a simpler and yet more informative classification to conventional and resin-modified GIs. This indicates information about materials' chemical composition, curing mode and clinical application steps.

The difference between conventional and resin-modified GIs is in the organic resin monomers added to the latter formula which enables prompt light-curing of the material using halogen or LED units. Light curing of resin creates favourable micro-environment for the conventional acid-base reaction between polyacrilic acid and glass particles. Improvements in material composition have led to improved mechanical properties although GIs are still inferior compared to resin-based composites. On the other hand, sensitivity to water imbalance, characteristic for early GIs, has been largely overcome in modern GIs both conventional and resin-modified. More information about GIs, their composition, properties and indications may be found in an excellent review article by Hewlett and Mount, published in 2003. [Full text]

One of the indications for GIs is the so-called "sandwich" technique with composite materials for large restorations on both vital and endodontically treated teeth. According to manufacturers' instructions both conventional and resin-modified GIs may be used for this purpose. Though it is widely known that early GIs were sensitive to water imbalance during setting, there is a certain controversy regarding this issue with current GIs. Due to this controversy, a clinical dilemma exists among dental practitioners when using GIs in combination with total-etch adhesives prior to composite placement. This dilemma is not about the acid but rather water rinsing afterwards. Simply, some practitioners are not convinced that GIs should be exposed to water so early after the setting (e.g. 3 minutes for FUJI IX GP Fast) or immediately after light curing of resin-modified GIs.

The manufacturer recommends the following protocol (Figure 1):

Figure 1. GC Europe recommends enamel etching after the placement of GI intermediary layer. (1) Old amalgam restoration; (2) Cavity preparation; (3) Conditioning; (4) Application of GI ; (5) GI layer ready; (6) Enamel etching; (7) Application of adhesive; (8) Light curing and (9)-(12) Placement of composite.

An alternative protocol suggested by some dental practitioners (Figure 2):

Figure 2. Enamel etching prior to the placement of GI. From left to right upper row: Cavity preparation; Conditioning; Enamel etching. From left to right bottom row: Application of GI; Application of adhesive; Final composite restoration.

The second approach does eliminate the possible adverse effect of water during acid rinsing. However, acid etching and rinsing prior to GI placement bears an inherent weakness - this approach requires impeccable precision. Dentin should not be etched if GI is to be placed since the mineral component required for chemical bonding will be lost. On the other hand, if adhesive is to be placed on dentin as well as on enamel, dentin should also be etched for proper micro-mechanical bonding of adhesive resin.

If one does not want to follow manufacturer's instructions and acid etch after the placement of the GI layer, then they should consider the use of self-etch adhesives instead of total-etch systems. One-step self-etch adhesives have shown inferior results regarding bond strength to dentin and enamel, degree of conversion, thickness of the hybrid layer, the quality of resin tags etc. On the other hand, current 2-step self-etch adhesives have shown satisfactory clinical and laboratory properties in a number of studies and are recommended as an alternative to total-etch adhesive systems.

In my practice, I always follow manufacturer's recommendations. In this case, I use resin-modified GIs for the "sandwich" technique and acid etch enamel after light curing of the GI intermediary layer.