Depth of cure of composites - acetone/ethanol shaking test

This method is based on the ISO 4049 standard. An important difference is that the uncured material is dissolved in acetone or ethanol instead of being removed with a spatula. The acetone shaking test was used and explained in a paper by Kleverlaan and De Gee (Eur J Oral Sci 2004;112:84–88). Equally effective is ethanol according to Miletic et al. (Serb Dent J 2012;59(4):190-197).

The image is a step by step explanation. A material complies with the ISO requirements if the remaining thickness of the specimen divided by 2 exceeds 1.0 mm for opaque shades and 1.5 mm for all other shades. Since manufacturers' recommended layer thickness is often 2.0 mm this reference may be used as well.

The acetone/ethanol shaking test is a simple yet reliable method of testing the efficiency of light-curing units and curing conditions used in clinical practice (e.g. time, distance). It may also be used to compare various composite materials/shades.

Similar post:

How to measure the depth of cure of composites according to ISO 4049?

Clinical reproducibility of three electronic apex locators

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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Miletic V, Beljic-Ivanovic K, Ivanovic V. Clinical reproducibility of three electronic apex locators. International Endodontic Journal, 44, 769–776, 2011.

Abstract

Aim  To compare the reproducibility of three electronic apex locators (EALs), Dentaport ZX, RomiApex A-15 and Raypex 5, under clinical conditions.

Methodology  Forty-eight root canals of incisors, canines and premolars with or without radiographically confirmed periapical lesions required root canal treatment in 42 patients. In each root canal, all three EALs were used to determine the working length (WL) that was defined as the zero reading and indicated by ‘Apex’, ‘0.0’ or ‘red square’ markings on the EAL display. A new K-file of the same size was used for each measurement. The file length was fixed with a rubber stop and measured to an accuracy of 0.01 mm. Measurements were undertaken by two calibrated operators. Differences in zero readings between the three EALs in the same root canal were statistically analysed using paired t-tests with the Bonferroni correction, Bland–Altman plot and Linn’s concordance correlation coefficients at α = 0.05.

Results  Mean and standard deviation values measured by the three EALs showed no statistically significant differences. Identical readings by all three EALs were found in 10.4% of root canals. Forty-three per cent of readings differed by less than ±0.5 mm and 31.3% exceeded a difference of ±1 mm.

Conclusions  The clinical reproducibility of Dentaport ZX, RomiApex A-15 and Raypex 5 was confirmed with the majority of readings within the ±1.0 mm range. However, the small number of identical zero readings suggests that EALs are not reliable as the sole means of WL determination under clinical conditions.

Upcoming event: CED IADR 2011

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.

Free e-learning resources on glass ionomers

Vivalearning.com is a popular e-learning resource featuring lots of webinars on various dental topics. All webinars are free and CE credited! All webinars premier as live presentations and then are accessible on demand.

The Wonderful World of Glass Ionomer in Clinical Dentistry
Presentedby Dr Jeff Brucia

LIVE ON (click here to register and reserve seat)
Thursday June 6, 2011 8:00 PM ET / 5:00 PM PT
Friday June 7, 2011 0:00 AM UTC (former GMT)
CE Credits: 1

From Vivalearning.com: "A comprehensive discussion of the ever-changing world of Glass Ionomers will address the following questions. Do they still cause sensitivity? Are they any more aesthetic? Are they strong enough? How and where should they be used? Do they adhere to tooth structure? This presentation is a must for any practitioner that is considering an operative procedure in a less than ideal clinical situation."


Modern Glass Ionomers Used as Liners in the Composite Resin Sandwich Technique
Presented by Greg Gillespie DDS, Lou Graham DDS and Mark A. Latta DMD, MS
CE Credits: 1
On Demand (click here to register and access class)

This presentation was released on January 7, 2011. It is now in the form of a downloadable PDF file. The authors give a short history of glass ionomers, explain the concept of the "sandwich" technique and provide several cases to illustrate this clinical procedure.

How to measure the depth of cure of composites according to ISO 4049?

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:

1. Place the mould on the glass slab and fill it with composite.

2.  Place the Mylar strip on top of the composite.

3. Light-cure the composite according the manufacturer's instructions (i.e. 40 s using a conventional or 20 s using a high-power halogen or LED light).

4. Discard the Mylar strip and remove the cured material from the mould.

5. Peel off the uncured material from the bottom side of the sample using the spatula or scalpel.

6. Measure the remaining thickness of the sample and divide this number by two. The ISO 4049 standard requires that the result should be at least 1.5 mm for non-opaque shades and 0.5 mm for opaque shades.

Free webinar on posterior composites

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 - Composite "sandwich" technique: when is the time to etch?

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.