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> Light Cured Glass Ionomers
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Light Cured Glass Ionomers
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Are light-cured fluoride releasing liners the ideal material to use under an amalgam?
Generally speaking, amalgam preparations should be based to a flat pulpal floor to reduce the likelihood of tooth fracture. This flat floor does not need to be an ideal depth but to the deepest level that a flat floor can be achieved. Their use in shallow amalgams restorations is usually not necessary.
What is the ideal material for use under an amalgam?
In most situations, amalgam bases should be adhesive and able to be placed in bulk. A popular and clinically successful method of basing or lining amalgams is with the use of conventional glass ionomer liners and bases.
Could you name specific conventional GIC products?
A number of glass ionomer products can provide similar results. Lining materials which have been popular in study groups are Ketac-Bond® (Espe) in capsules, a thick mix of Dentin Cement® (G-C) and for larger build-ups a thin layer of lining cement (e.g. G-C Lining®, Ketac-Bond®, Shofu Lining Cement®, etc.)
Base material are far more popular and include a Shofu Base Cement® (Shofu), Fuji-9® or Fuji GP® (G-C), and Ketac-molar®. Fuji 9 or GP and Ketac-molar in available in capsules which makes them very easy to use.
Are calcium hydroxides necessary any more? If so, when should I use them and which are best?
In deep preparations, where the remaining dentin thickness is estimated at less than 1 mm, calcium hydroxides are the liners with over 40 years of clinical success. They are best used in thicknesses of less than 0.5 mm over the deepest areas of the preparation and not covering the entire dentin surface.
Due to the water solubility of calcium hydroxides, they should always be covered with another liner. This is very important under amalgams where studies have shown these materials can be washed out, increasing the likelihood of recurrent caries. Glass ionomers are well suited for this use.
In terms of selecting a calcium hydroxide liner, the three most popular products, Life® (Kerr), Dycal® (Caulk) and a new liner called Alkaliner® (Espe-Premier), seem to have equal clinical success.
How may liners do I need in my office to provide optimal dentistry for my patients?
At least three. First, a calcium hydroxide for deep areas and for use as a temporary cement over preparations with near exposures. Second, a lining cement to place under composites Light cured ionomers are usually preferred. Third, a base cement for bulk in build-ups.
Do zinc phosphate, IRM, or polycarboxylate have any place as bases under amalgam?
All have had many years of clinical success. However, they suffer when compared to glass ionomer systems. Zinc Phosphates: 1) do not inhibit recurrent decay, 2) have poorer physical properties, 3) lack many desirable features found in the glass ionomers (especially dentin adhesion), and 4) they increase the likelihood of tooth fracture when used as a large base under an amalgam.
IRM has been used for its sedative properties. Although useful in some situations the value of eugenol in a base is disputed due to high solubility and potential pulpal irritation.
Polycarboxylate cement is pulpally one of the kindest materials available. Where recurrent caries is not a concern it could be used as a base or liner. Its major disadvantages are its difficulty in placement (due to stringiness), higher solubility, and poor physical properties when compared to glass ionomer products.
Considering all of these factors, glass ionomers are exceptionally well suited as bases and liners where leakage, recurrent decay, and tooth weakening are major concerns. They are the material of choice.
Are light-cured glass ionomers suitable for use in tunnel preparations? If not, what would you recommend?
No, due to the poor access of most internal preparations, as are tunnel preparations, only chemically cured bases and liners should be used. Light cured liners usually will not be adequately cured in these areas since the surrounding tooth structure inhibits light curing.
The materials of choice for the internal aspects of a tunnel preparation are the glass ionomer lining cements which are available in capsules (e.g. Ketac-Bond capsules by Espe).
Does drying etched enamel desicate the glass ionomer liner and weaken it?
Yes. This is particularly critical immediately after placement. Excessive drying can result in severe damage, detectable by cracks on the ionomer surface, as well as peeling of the edges. With careful drying desication can be kept to a minimum. Should damage occur, placement technique, setting time, and enamel drying should be reevaluated.
If desication of the ionomer is unavoidable, coat it with a thin layer of light-cured resin.
Should I acid etch the glass ionomer liner with phosphoric acid prior to placing a composite resin?
The main reason to etch a glass ionomer is to improve its mechancial bond to composite resin. Although the benefits of etching glass ionomers are controversial, considerable research has shown that improvements in bonding can occur.
Unfortunately risks are associated with etching glass ionomer liners. The most important is that the etching solution can be retained in the liner and result in post-operative sensitivity. This is most critical in liners which are thin and not throughly rinsed with water.
Etching can also weaken the ionomer if it is etched soon after placement or if it is etched too long.
All liners should be a minimum of 0.5 mm thick, should be etched no longer than 5-10 seconds, and should be rinsed for 5-10 seconds or more. Thorough rinsing with water is critical to remove as much residual acid from the liner as possible.
I routinely use glass ionomers to line my indirect inlay and onlay preparations. Would light-cured glass ionomers be more suitable?
Most dentists find these easier to work with than conventional glass ionomers under indirect restorations. Their faster set, increased toughness, and higher bond strengths have made them more likely to stay in place for lining and blocking out undercuts.
Often when I remove my temporary at the cementation appointment the underlying glass ionomer liner looks very stained and chipped. In addition, I have had a number of cases with severe post-operative sensitivity. What am I doing wrong?
Indirect bonded restorations are a new area and there are a lot of things we do not yet know.
It is possible that if the ionomer is badly stained it contains plaque and/or bacteria containing debris. Since glass ionomers are poor barriers to bacterial invasion the sensitivity may be due to bacterial invasion of the pulp. There are a number of ways to treat this situation.
1. The easiest way is to remove the entire glass ionomer liner and cement the unit with a glass ionomer luting cement. This will provide less mechanical retention than cementing with resin, but, in units with adequate retention this can work very nicely.
2. A better way is to remove the liner, condition the dentin for 10 seconds to remove any attached surface debris and place a new, thinner liner. This is easy to say but difficult to do. Be sure the unit is checked for fit after placement.
3. Remove the entire liner, treat the dentin with a resin bonding primer (e.g. GLUMA, Scotchprep Dentin Primer, or XR Primer), and then cement the unit in place with a resin luting agent. This does not allow for any fluoride release under the restoration but does offer excellent bond strengths.
What should a dentist be looking for in the ideal lining material?
The ideal liner would be a product which is as strong as dentin, has no setting shrinkage, prevents decay, is pulpally kind, easy to place, light-cured, shaded as dentin, and is totally insoluble. To achieve all this may take a while. However, progress is continually being made and it is highly likely that lining and base materials will continue to improve over the years to come.
At this time the glass ionomers and light-cured fluoride-releasing liners seem to meet the most of these criteria. In addition, the long term clinical success of glass ionomer liners and bases makes me comfortable with their use.
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