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.

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.

News from Esstech, Inc.

Esstech, Inc. develops and manufactures advanced materials for many biomedical fields including dental materials. In their range of products are various monomers, initiators, silanated glass etc. for resin-based composites and adhesive systems. The latest research by or using Esstech's products includes studies on physical properties of new low shrink resin , optimizing the degee of conversion and certain physical properties of various BisGMA/BisEMA/TEGDMA formulations , optimizing silanated glass , developing a high molecular mass monomer to substitute HEMA etc.

For more information, check out their website and blog.

Esstech, Inc. will be present at the IADR/AADR General Session in Barcelona, Spain (14-17 July 2010) and I really look forward to meeting their representatives, hoping that we could establish scientific collaboration.

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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.

Nano-filled resin-modified glass-ionomer cement: "nano-ionomer" Ketac N100

In addition to conventional and resin-modified glass-ionomer cements, a nano-filled resin-modified glass ionomer cement, or “nano-ionomer”, was developed by 3M ESPE a couple of years ago – Ketac N100.

It is stated by the manufacturer that indications for the use of this nano-ionomer include primary teeth restorations, small Class I, Class III and IV, temporary restorations, filling defects and undercuts, “sandwich” technique with resin-based composites, core build-ups with min 50% of the remaining tooth for support.

The nano-ionomer is based on the acrylic and itaconic acid copolymers necessary for the glass-ionomer reaction with fluoroaluminosilicate (FAS) glass and water. The nano-ionomer also contains a blend of resin monomers, BisGMA, TEGDMA, PEGDMA and HEMA which polymerize via the free radical addition upon curing and it is stated that the primary curing mechanism is by light activation. The originality of this glass-ionomer cement is the inclusion of nano-fillers which constitute up to two thirds of the filler content (circa 69 wt%).

Other advantages stated by the manufacturer are a simplified procedure which requires the priming but not the separate conditioning step and a precise dispensing and mixing “clicker” mechanism.

In spite of its uniqueness amongst other dental formulations, the nano-ionomer has not been investigated to a greater extent in the scientific dental literature. Medline search using the keyword “Ketac N100” resulted in only 4 papers in international peer-reviewed journals. Another paper was found using the keyword “nano-ionomer”. It is my pleasure to mention that the first of these 5 papers was done in Serbia by my colleagues from the Paediatric Dept of the School of Dentistry, Belgrade and the Dept. of Dentistry School of Medicine, Novi Sad.

It has been reported that fluoride concentration on material surface is similar for Ketac N100 and other glass-ionomer cements from the Fuji “family” but Ketac N100 showed less porosities and surface cracks than Fuji materials (Markovic et al 2008).

A study on bonding orthodontic brackets showed significantly lower shear bond strength for Ketac N100 compared to a conventional light-cure orthodontic bonding adhesive (Transbond XT). However, it has been suggested that this nano-ionomer may be used for bonding orthodontic brackets since the obtained shear bond strength is within clinically acceptable range (Uysal et al. 2009).

Another study using the shear bond strength as an adhesion parameter showed that Er:YAG laser dentine pre-treatment results in lower bond strength values compared to acid etching or a combined acid-etching and laser pre-treatment (Korkmaz et al. 2009).

A study on microleakage around Class V cavities showed that Er:YAG preparation results in greater microleakage than a conventional cavity preparation with a bur when a nano-ionomer (Ketac N100) and a nano-composite (Filtek Supreme XT) were used as restorative materials (Ozel et al. 2009).

In a study by Leuven BIOMAT Research Cluster it has been concluded that Ketac N100 “bonded as effectively to enamel and dentin as a conventional glass-ionomer (Fuji IX GP), but bonded less effectively than a conventional resin-modified glass-ionomer (Fuji II LC). Its bonding mechanism should be attributed to micro-mechanical interlocking provided by the surface roughness, most likely combined with chemical interaction through its acrylic/itaconic acid copolymers” (Coutinho et al. 2009).

More research is needed to investigate other mechanical properties of the nano-ionomer, its biochemical stability in the oral environment, fluoride release etc. Ultimately, well-designed randomized clinical trials will reveal the longevity and anti-cariogenic effect of this material in clinical conditions.

References:

• Markovic DLj, Petrovic BB, Peric TO. Fluoride content and recharge ability of five glassionomer dental materials. BMC Oral Health 2008; 28:8-21.
• Uysal T, Yagci A, Uysal B, Akdogan G. Are nano-composites and nano-ionomers suitable for orthodontic bracket bonding? Eur J Orthod 2009; Apr 28 [epub ahead of print]
• Korkmaz Y, Ozel E, Attar N, Ozge Bicer C. Influence of different conditioning methods on the shear bond strength of novel light-curing nano-ionomer restorative to enamel and dentin. Laser Med Sci 2009; Aug 18 [epub ahead of print]
• Ozel E, Korkmaz Y, Attar N, Bicer CO, Firatli E. Leakage pathway of different nano-restorative materials in class V cavities prepared by Er:YAG laser and bur preparation. Photomed Laser Surg 2009; 27:783-789
• Coutinho E, Cardoso MV, De Munck J, Neves AA, Van Landuyt KL, Poitevin A, Peumans M, Lambrechts P, Van Meerbeek B. Bonding effectiveness and interfacial characterization of a nano-filled resin-modified glass-ionomer. Dent Mater 2009; 25:1347-1357.

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.

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.

Filtek Silorane by 3M ESPE

In 2007, 3M ESPE launched a new resin-based composite, Filtek Silorane (FS), and its adhesive system. Both the composite and the adhesive system contain a unique resin monomer based on the combination of siloxanes and oxiranes so it is apparent where the term "silorane" comes from. The polymerisation of FS differs from methacrylate-based composites and adhesives and is claimed to result in reduced polymerisation shrinkage. The cationic polymerisation of FS occurs via the ring opening of the C-O-C epoxide group which ends up in less reduction in molecule distances compared to the free radical polymerisation of methacrylate-based composites. In the latter, monomer interaction via methacrylate C=C groups results in the greater reduction of inter-molecular distances and subsequently greater polymerisation shrinkage.

Most recent studies have shown reduced shrinkage and shrinkage stress and strain for FS compared to methacrylate-based composites. Microleakage and nanoleakage were also reported for FS. Ongoing studies will reveal other properties of FS that may affect its clinical performance.

The dedicated adhesive system is designed to bridge the gap between hydrophilic dentine and hydrophobic FS composite. It contains the Primer and the Bond in separate bottles which are cured as separate layers, unlike any other two-step self-etch adhesive system, where primer and bond are mixed before curing. In Filtek Silorane adhesive system, these layers are not visible on SEM but can be detected using micro-Raman spectroscopy (Santini & Miletic, 2008) At the BSDR symposium on Dental materials it was reported, that after 6 months of storage, the type of failure for FS changes from the adhesive to cohesive as the fracture occurs within the adhesive system. The intermediate zone between FS Primer and Bond of about 1 micron may be the weak link in the failure mechanism and certainly needs further investigation.

One-step self-etch adhesive, Adhese One F

A new one-step self-etch adhesive, Adhese One F, manufactured by Ivoclar Vivadent has been sent to the Santini Miletic Research Group for scientific evaluation. The adhesive is based on previously developed Adhese One with the inclusion of potassium fluoride which is reported to act as a fluoride releasing agent. The manufacturer's internal data state that there is a cumulative fluoride release over a 6 day period.

Micro-Raman spectroscopic studies will be conducted to evaluate the ratio of carbon-carbon double bonds (RDB) of Adhese One F under different curing conditions. Furthermore, the adhesive-dentine interface will be characterised in terms of dentine demineralisation and adhesive penetration and the RDB across this interface.

A previous study has shown significantly lower RDB values for Adhese One in both the adhesive and the hybrid layer compared to Excite (etch-and-rinse) and Adhese (2-step self-etch). In another study, Adhese One produced a thinner hybrid layer compared to G Bond (1-step self-etch), Filtek Silorane adhesive system (2-step self-etch) and Excite

Santini A, Miletic V. Quantitative micro-Raman assessment of dentine demineralization, adhesive penetration, and degree of conversion of three dentine bonding systems. Eur J Oral Sci 2008;116(2):177-83. Abstract Full text available upon request.

Santini A, Miletic V. Comparison of the hybrid layer formed by Silorane adhesive, one-step self-etch and etch and rinse systems using confocal micro-Raman spectroscopy and SEM. J Dent 2008;36(9):683-91. Abstract Full text available upon request.