Dental Problems

Method of Using Glass Ionomer Cements

How to Clean Mouth GuardGlass ionomer cements are used for the restoration of the primary tooth. Because while placing gold foils or gold inlays for primary tooth restoration they may have difficulties. In this article, there is a brief discussion on the method of using glass ionomer cements. Read on to know more.

Hand Mixing:

Divide the dispensed powder into two equal parts. Gently spread the liquid drop a little over the glass slab. Roll the first half of the powder into the liquid and incorporate the two together rapidly. This is completed in 10 seconds and the rest of the powder is brought into the mix.

No attempt should be made to try and dissolve the powder into the liquid. It is only necessary to wet the surface of each particle so that ion release can occur leading to the initiation of the acid or base setting reaction. The final mix should be completed within 25 -30 seconds.

Conditioning the cavity

Following completion of any cavity preparation there will be a smear layer left on the surface of the floor and walls. This will consist of tooth debris, bacterial plaque, pellicle and other debris and if left in place may interfere with the development of the ion exchange adhesion layer. It is therefore necessary to remove this before placing the restoration.

For this purpose a 10 percent poly acrylic acid is applied and allowed to remain in place for 10 seconds only. The surface energy of the cavity walls and floor is modified so that the high surface energy newly mixed cement will adapt better to the low surface energy cavity walls.

The cavity should be washed thoroughly and dried lightly and the cement flowed into place immediately. Do not over dry the cavity, as the glass ionomer is a water based material and may lose physical properties if dehydrated through a lack of water.

It is important to note that conditioning and etching are two different entities. A cavity for restoration with glass ionomer should always be conditioned but the enamel margin of the cavity to be restored with composite resin must always be etched.

Ion exchange adhesion

One of the greatest hazards in restorative dentistry is micro-leakage between a restoration and the cavity walls or floor. As long as they are present bacteria and their toxins will cause a continuing inflammation within the pulp tissue so elimination of micro-leakage is essential. The union between a glass ionomer and tooth structure arises as a result of an exchange of ions.

When the newly mixed cement is adapted to either enamel or dentin there will still be a quantity of free polyalkenoic acid within the cement. Because of its low pH the acid will attack the tooth surface and release calcium and phosphate ions which will be free to mix with the matrix of the cement. Further release of ions buffers the reaction and a new material containing ions from both the cement and the tooth will begin to form and set at the interface.

The new material will be firmly attached to both sides of the union and will be stronger and more resistant to acid attack than either the tooth structure or the cement. Some degree of bond is also developed between glass ionomer and the collagen fibres of the dentin. This arises through either hydrogen bonding or metallic ion bridging between the carboxyl groups on the poly acid in the cement and the collagen fibres in tooth structure.

The strength of this ion enriched material has to be properly assessed. Failure of the union will be cohesive in either the tooth or the cement rather than adhesive at the interface. Therefore it is important to understand the term bond strength in relation to the glass ionomers.

Water balance

As a water based material, glass ionomer is always susceptible to both water loss and water uptake.
All types of glass ionomer will lose water if exposed to dehydration for longer than a few minutes.
They type II, I cement remains susceptible to water uptake for at least one hour and up to 24 hours after placement and if it is not properly protected it will lose both translucency and physical properties.

The most effective method for early protection is to paint over the newly set restoration a low viscosity, light activated, resin enamel bond immediately after removing the matrix. Light activates the bond before releasing the restoration to the environment. This will ensure stability within the cement for the first one-hour during which time the calcium polyacrylate chains can complete their formation and the aluminium poly acrylate chains will then become dominant.

It must be noted that all glass ionomers may lose water for periods between 2 weeks and 6 months after placement because not all water is fully bound with in that period. The resin-modified forms of glass ionomer were developed to overcome this problem however they also remain susceptible to dehydration for some time after placement so they also should be sealed.

Biocompatibilty

The glass ionomers show a high degree of compatibility with living tissues. The polyalkenoic acids used as the liquid are mild acids with a high molecular weight and a long complex chain formation. This makes it difficult for the acid to permeate through dentin tubules and even if it does it will not produce a vigorous reaction.

Another reason for the relatively high biocompatibility is the presence of free fluoride ions within the set cement. Bacteria such as Streptococcus mutans is unable to thrive in the presence of fluoride so there will generally be a low accumulation of plaque on the surface of a glass ionomer.

Again in the absence of bacteria the pulp shows an ability to recover rapidly and defend itself from inflammation. It is possible to place a glass ionomer directly over a mechanically exposed pulp and expect to find secondary dentin formation in immediate apposition to the cement.

The above article discusses about the method of using glass ionomer cements.

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