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.


Source- http://dental-materials.blogspot.com/search?updated-min=2009-01-01T00:00:00%2B01:00&updated-max=2010-01-01T00:00:00%2B01:00&max-results=48

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

Source- http://dental-materials.blogspot.com/2009/11/nano-filled-resin-modified-glass.html

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.


Source- http://dental-materials.blogspot.com/

DENTAL ALGINATE – A clinical overview

Alginate Mixing Technique

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• Literally impression means the negative replica of the oral structures, so it must be accurate enough to simulate the surface and  surrounding structures with precision.

• IMPRESSION IS ALWAYS MADE BY A DENTIST/DENTAL ASSISTANT 

• Alginate is an elastic, irreversible hydrocolloid impression material

• They form a major bulk of our clinical practice ; therefore, it becomes mandatory to understand the material and follow certain fundamental guidelines for flawless, predictable impression.

• The most popular form of alginate is supplied as a powder, which is mixed with water. Many alginates are supplied with a reaction indicator that changes color of the impression when the material is set;.Paste type of alginate is also available. The best surface quality can be obtained with the paste-type material.

• Colder water can be used if longer working time is desired. Setting time should be controlled by varying water temperature, and not the consistency of mix. Mixing should be rapid with a wide-bladed spatula. The resultant mix should be creamy in consistency but must not drip off the spatula when lifted from the bowl

• Once set, the impression has to be removed with a firm, quick snap. During removal of the maxillary impression, the operator's index fingers (of both the hands) should be in the buccal sulci to break the seal while thumb holds the tray handle and the other fingers support the impression tray.

• A thin layer of dental stone powder can be sprinkled onto the surface of the impression. The stone adheres to saliva and acts as a disclosing agent. When impression is placed under running tap water, the saliva will be seen and can be removed by light brushing with wet camel's hair brush.

• Set alginate undergoes imbibition and syneresis if left in a normal clinical environment. The time before cast-pouring is critical. After being removed from the mouth, alginate impressions should be washed with a water spray, disinfected by means of the practitioner's choice of disinfection procedures, and dried until the shine just disappears. The impression has to be covered with damp gauze and left in a zip-lock plastic bag until the cast is poured. Cast-pouring must be delayed for 10 minutes, as the elastic recovery of alginate impression material is slow.

• The stone should be allowed to set in trays with the teeth down. If tray is turned upside down onto base of stone, there would be a tendency for water to rise to the highest point (cusp tips). This can result in faulty, very soft cusps on the model. Cast has to be removed immediately after adequate set; otherwise, the model would have “moth-eaten” appearance.

• Alginates should always be kept in an airtight container.

• The surface of d tissue should be free from any extra saliva or debris,

• While making the maxillary impression for d prepared tooth crown,,,,no need to load extra material in palatal area,as we need only d crown part impression,,,,,

• Its adviced to apply some mixed alginate nicely in the desired area before inserting the tray with the material.

Written by Dr. P. Kunal


Dr. Kunal did his BDS from Maruti Dental College, Bangalore. Currently he is pursuing private practice in New Delhi. He is a workaholic and loves dentistry!