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Cementation/Sensitivity with Glass Ionomers
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Cementation with Glass Ionomers: Cementation with glass ionomers or other cements can result in sensitive teeth. This cementation technique reduces the incidence of postoperative sensitivity.
CLINICAL CONCERNS with glass ionomers

Concerns: Cementation with glass ionomers or other cements can result in sensitive teeth. This cementation technique reduces the incidence of postoperative sensitivity.

I. Powder/Liquid Ratios. The correct powder/liquid ratio is very important since physical properties drop off exponentially as the mix becomes too fluid. Generally speaking, get as much powder into an ionomer as possible while still allowing for adequate working properties.
       Drops dispensed slowly, since they are determined by the fluid's weight, are usually accurate. (Increased speed makes larger drops.) Dispense the drop on a glass, plastic, or waxed pad. Untreated paper may absorb some of the liquid and alter the P/L ratio.
       Glass ionomer powder can change volume by over 50% depending on how long it has have been on the shelf and how long it has been since it was been shaken or tapped.
       The amount of glass ionomer powder should be calibrated to a special scoop-to-drop ratio. Packed powders are more consistent than fluffed powders although either can be used. The mix can be adjusted depending on the intended use. Encapsulated systems are the most accurate.
       Because of the inherent problems in working with powder and liquid bottles The same glass ionomer powder bottle that has been shaken. Note the increase in volume. we highly recommend use of encapsulated glass ionomer cements.

II. Adhesion to Casting and Tooth Structure. Cementation: Adhesion abilities; Polyacrylic acid–based systems, including glass ionomers and polycarboxylate cements, can bond to tooth structure and metal castings.
       Eugenol–based cements (e.g. Temp-bond, IRM, ZOE) can inhibit glass ionomer's to bond to tooth and in excess, can inhibit hardening. Use non-eugenol temporary cements when an ionomer will be used for final crown cementation. Some popular non-eugenol cements are Temp-Bond NE (Kerr), Freegenol (G-C), Nogenol (Coe), Zone (Cadco), and Varibond (Van–R).
       Polyacrylic acid-based cements will bond to clean oxidized metals and only slightly to non-oxidized metals.
For maximum retention, the crown should be sandblasted, tin-plated, and scrubbed with a tooth brush, water, and mild detergent before bonding.

III. Remaining Dentin Thickness. A critical determinant of good pulpal health and reduced postoperative pulpal problems is remaining dentin thickness, especially when virgin teeth are prepared for full coverage all-porcelain or porcelain fused to metal restorations. Radiographs can help estimate remaining dentin thickness proximally.

IV. Dentin Conditioners: A conditioner is usually a weak acid. Almost all conditioning treatment are time acid concentration dependent.
       A number of conditioners can be used to remove the smear layer and prime the surface before cementing with a glass ionomer. Most are 10% to 25% solutions of polyacrylic acid. Most studies show they improve ionomer bond strength to dentin. Used properly, they do not increase tooth sensitivity. 37% phosphoric acid can also used for 5 seconds to provide a similar result.
       Conditioners are generally indicated before placing Class V glass ionomer restorations. They should not be used before crown cementation or under liners and bases because doing so increases the incidence of postoperative sensitivity by allowing the glass ionomer liquids to penetrate too deeply into the dentin.


RECOMMENDED CEMENTATION TECHNIQUE

This cementation technique has a less than 1.5% incidence of pulpal sensitivity or death when teeth are matched by sensitivity and type as previously discussed.

Step 1. Isolate the tooth as well as possible using cotton rolls, dry angles, or a rubber dam if possible. Place a dry retraction cord in the sulcus of all restorations with subgingival margins to stop hemorrhage or gingival fluid oozing.
Step 2. Clean the tooth thoroughly with pure pumice mixed with water. Be sure no saliva, blood or intersulcular fluid contaminates the tooth before cementation.
Step 3.Select the cement and the correct amount of powder. (This should have been previously calibrated with each new bottle of cement.)
Step 4. Hydrate the tooth for 2 minutes (with a damp gauze or cotton) before cementation. With sensitive teeth topically apply local anesthetic, which is a saline solution, to the desiccated tooth. Just before cementation dry with a cotton pellet to remove any pooled moisture. The dentin should not look chalky white before cementation.
Step 5. Mix cement rapidly (ideally within 45 seconds), coat all crown walls with 1 mm of cement and start to seat within 30 seconds after the mix is complete. Slowly (about 10 seconds) press the crown in place allowing excess cement to extrude around all margins. This eliminates the need for a varnish coating at this point. Leave in place until after the initial set. Setting time is temperature dependent. Use a cold glass slab above the dew point if more working time is needed.
Step 6. Maintain isolation Keep the cemented crown totally isolated until it reaches its initial set. A damp (not wet) gauze can be placed over the tooth to establish 100% humidity until the cement reaches a more final set, at least 10 minutes. Hardness can be verified with an explorer.
Step 7. Remove excess cement bead from margins with a sharp instrument. Removing the retraction cord will remove much of the proximal cement.
Step 8. Protect margins from early cement loss by covering with methyl cellulose varnish. Some clinicians prefer unfilled resin for this.

Post-Cementation Sensitivity: The following information will help you correctly diagnose tooth sensitivity prior to cementation, and provides a review of proper cementation technique with glass-ionomer cements to avoid the potential for postoperative discomfort.

Classifying Prepared Teeth by Sensitivity
       Teeth can be categorized as very sensitive, moderately sensitive, and slightly/not sensitive. The time to determine tooth sensitivity is when the temporary crown is removed from an unanesthetized tooth, just prior to cementation.
       Very Sensitive Teeth. A very sensitive tooth is a tooth that a patient reports as painful when they draw air over the tooth after removal of a temporary. This is often found with full coverage restorations on young patients, or whenever the remaining dentin is very thin.
       Moderately Sensitive Teeth. A tooth is considered moderately sensitive if the patient can draw a slight to moderate amount of air over the tooth without pain, but cold air from a syringe is uncomfortable. Most patients with typical crown and bridge preparations are in this class.
       Nonsensitive and Slightly Sensitive Teeth. A nonsensitive tooth experiences little or no discomfort from air, not even from a moderate blast from an air syringe. Such nonsensitive teeth are commonly found in very mature patients with receded pulps, or in teeth with large buildups where little dentin is exposed on the axial walls.
       Another way to evaluate sensitivity is to touch an uncovered prepared tooth with a dry cotton pellet or the tip of an explorer. A very sensitive tooth reacts very strongly. Moderately sensitive teeth feel the gentle rubbing but little pain. The least sensitive group feels no sensation, even from forceful rubbing.

Causes of Sensitivity
       Dessication is suspect as the main cause of post-cementation tooth sensitivity. The problem begins with air entrapment in the dentin during drying of the prepared tooth.
       Air is hard for any tissue to resorb, and it can take months for dentin tubules to absorb air. Despite the slowness of the process, air entrapment is usually self-correcting.
       Entrapped air is implicated in pain because air is easily compressed and expanded, and changes in air pressure alter the hydrodynamics of dentin. Thus, biting compresses air in the dentin tubules. The compressed air dislodges nerve endings, which stimulates pain.
       Symptoms of Entrapped Air. The typical symptoms of postoperative sensitivity from entrapped air include: Sensitivity to biting, No signs of pulpitis (sensitivity to hot or cold)
       Mistaken Endodontics. The symptom of sensitivity to biting is also associated with an abscessed tooth. The discomfort can resemble that of pulpitis but usually does not result in acute pain on tapping; instead, it responds mainly to steady loading. When endodontics is performed on these teeth it is a mistake, for they are vital.
       A detailed patient history is key to achieving a proper diagnosis of reversible pulp disease (entrapped air) and avoiding unnecessary endodontics. If all other symptoms and tests are negative, it is highly likely the symptoms will self-correct, but it can take 1–12 months for the symptoms to completely resolve.
       Prevention. A hydration period of 2 to 10 minutes prior to cementation can greatly reduce the potential for air entrapment.
       Treatment. The best thing to do for a symptomatic tooth is wait for things to resolve. If the symptoms give evidence of lessening over time, the prognosis is good. Alternatively, in cases with severe pain, make an opening in the unit just into the dentin but not near the pulp. Then hydrate this opening for 10 minutes with a topically applied local anesthetic. Seal the opening with traditional glass-ionomer cement. This procedure usually eliminates sensitivity within a few days, even when the sensitivity has lasted over a year.


Posterior Composite Techniques: Esthetic direct restorations using Matrixx P posterior hybrid composite material
By Dr. Michael J. Koczarski, Woodinville, Wash. Information provided by Discus Dental Inc.
Posterior Composite - 3 Surface - Dr. Koczarski I

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