Try in and esthetic problem in crown and

bridge Dr.Emad Farhan Alkhalidi

MSc, phD conservative dentistry

• When the laboratory procedures have

been completed the restoration is ready to

be evaluated in the patient’s mouth before

final finishing and cementation.

• Remove the interim restoration firstly by gently positioning hemostats or a Backhaus towel clamp on the buccal and lingual surfaces and rocking it gently in a buccolingual direction to break the seal of

the interim luting agent. Then clean the prepared tooth /teeth with warmed water from remnant cement.

Try in procedure:The recommended sequence for try in of crown or bridge is as follows:1. Proximal contacts.2. Marginal integrity.3. Stability.4. Occlusion.5. Characterization and glazing.

1-proximal contact:The proximal contact of a restoration should be neither too tight nor too light. If they are too tight they will interfere with correct seating of the restoration, produce discomfort and make it difficult for the patient to floss.A proximal contact that is too light will allow impaction of strands of food, which is deleterious to the gingiva and annoying to the patient.The restoration is placed on the tooth and seated with finger pressure, occlusal pressure should not be used because forcing the restoration onto the tooth at this time may make it extremely difficult to remove.

• A crown should be able to remove if it is grasped with a dry gauze sponge and rocked slightly.

• For gold restoration the tight contact point leave a satin finish on a gold restoration which becomes apparent because there will be a shiny burnished area where the tight contact occurred. A blue or cratex wheel is used to remove the shiny mark, and then the casting is tried back on the tooth. This is repeated until floss can pass through with the same amount of resistance offered by the other contacts.

• If both proximal contacts feel too tight, the tighter contact should be adjusted first. Some times this will relieve the pressure on the second contact, precluding the need for its adjustment.

A tight proximal contact will not produce a visible

burnished area on base metal or porcelain (all ceramic

or metal ceramic restoration), so that a thin coating of a

pressure indicator such as occlude (pascal) can be

applied to these materials before seating to reveal the

exact location of the contact, red pencil or thin marking

tape also can be applied.

To avoid fracture of (all ceramic or metal ceramic restoration) only gentle forces should be used for inserting and testing the restoration. A tight proximal contact in unglazed porcelain is easily adjusted with a cylindrical stone.While tight proximal contact of base metal is adjusted using blue wheel.

2- marginal adaptation

The completed restoration should go into place

without binding of its internal aspect against the

occlusal surface or the axial walls of the tooth

preparation; in other words, the best adaptation

should be at the margins. There should be no

noticeable difference between the fit of a

restoration on the die and that in the mouth.

After the proximal contacts have been corrected the restoration is seated and the margins are examined closely. An acceptable margin is not overextended, under extended, too thick, or open.

A margin is generally considered to be open if the gap is greater than 50 µmµm which means the tip of a sharp explorer can be inserted between the restoration and tooth.

A restoration that rocks perceptibly on the tooth can not have closed margins on both sides at once.

Subgingival marginal discrepancies are the most difficult to detect and the most detrimental to gingival health.The most common cause of poorly adapted margins is failure of the restoration to seat completely. If the proximal contacts are not too tight and the margins are still short or open, there may be some minute under cut, unseen defect, or distortion preventing seating.

There are a number of materials that can be used for locating internal discrepancies like disclosing wax or aerosol indicator (occlude, pascal) these materials indicates not only points of interference but also the thickness and configuration of the future cement film, Relief of impinging area with bur usually allow the restoration to seat.

• elastomeric paste its material similar to a silicone impression material and is obtained as a two-paste system. Its viscosity is similar to that of the final luting agents, and so it can be used not only to identify unwanted internal contacts but also to assess adequate marginal fit.

• The degree of clinically acceptable marginal opening is hard to define.

• Obviously, to limit dissolution of the luting agent, the thickness of the cement film at the margins should be kept minimal. Through careful technique, a marginal gap width of less than 30 µmµm can be obtained consistently.

Elastomeric detection paste, recommended for evaluating the internal surface of a restoration

The interference is seen as aperforation in the film of silicone material.

3- StabilityThe restoration should then be assessed for stability on the prepared tooth. It should not rock or rotate when force is applied. Any degree of instability is likely to cause failure during function. If instability is caused by a

small positive nodule, this can usually be

corrected; however, if it is caused by distortion, a

new casting is necessary.

4- occlusal adjustmentAfter the restoration has been seated and the margin integrity and stability are acceptable, the occlusal contact with the opposing teeth is carefully checked.Any undesirable eccentric contact as well as centric interference must be identified and removed.

Only restorations in supra occlusion can be adjusted. For those that are out of occlusion, there is no satisfactory solution other than remaking (if in metal) or adding porcelain and re firing (if a metal ceramic restoration).To provide a basis for comparison the patient is instructed to close into the customary position of maximal intercuspation with the restoration removed. The position of the teeth and the completeness of closure and contact are noted.A pair of teeth near the prepared tooth where the patient can hold a strip of 13 µmµm shim stock is located.The restoration is inserted and it is determined whether the patient can still hold the shim between the same pair of nearby teeth, if not the crown is high in the intercuspal position.

Seat the restoration, have the patient close, andreassess the contacts. The new restoration shouldhold the shim stock and yet not alter the existingtooth relationships. If a discrepancy is detected, adecision must be made whether this can beadjusted intraorally or whether a remount

procedure is necessary.

Mark any interferences that are detected. Have the patient close on articulating ribbon or tape.Adjust the marked interferences with thediamond rotary instrument or white stone, always checking the thickness of the casting with calipers before an adjustment is made.

Be careful not to misinterpret occlusal markings. Note that a true interocclusal contact leaves a mark with a clean center (like a bull’s-eye), but a false contact leaves a smudge. Marking ribbon or tape is useful for helping determine the location of an interference. Shim stock, however, is a more reliable indicator than ribbon or tape for confirming the presence or absence of an occlusal contact and should be used to evaluate the result when the end point is reached.

Use two colors of ribbon for the different types of movement. Excursive movements and interferences are first marked in one color (e.g., green or blue ).Then a different color (e.g., red) is inserted for centric contacts. Any excursive interferences (i.e., green marks not covered by red) are adjusted with the diamond or white stone.

Characterization and glazing.

Contours Improper contours may impair gingival health and detract from a natural appearance. They must be corrected before cementation, excessive convexity near the gingival margin promotes accumulation of plaue. Surfaces directly occlusal to furcations are usually concave, and the concavity should extend occlusally on the axial surface of the restoration to improve access for a tooth brush.

Esthetic The restoration should be viewed from a conversational distance to determined if its contours harmonize with the rest of the patient's dentition. The patient should be allowed to look in a mirror so that any objections to the appearance can be dealt with before the restoration is cemented.

Surface texture characterization When the contour of the restoration has been finalized, the next goal is to duplicate the surface detail of the patient’s natural teeth. Dry the teeth, and examine their surfaces carefully. Perikymata and defects can be simulated by grinding the porcelain with a diamond stone of appropriate texture. (Be careful not to overemphasize such details.) Flat or concave areas reflect light in a characteristic manner, producing highlights.

Special illusionsForm and position are the most important factors in achieving an attractive result. However, restoring the original form may not always be possible. Loss of supporting tissue, the size of a pontic space, or a poor occlusal position may impede the attempt.

An FDP pontic may be very long because of loss of supporting bone. Simulating a root surface can partially improve the appearance. The root extension is contoured for length and width, and then an orange-brown mixture is placed over the extension. Pink stain can be used to simulate gingival tissue, but results are better with pink body porcelain.

TranslucencyTranslucency can be mimicked with violet stain, although the results are usually disappointing in comparison with those achieved with correct application of the incisal porcelain. For optimum results, both labial and lingual surfaces should be coated. Decreasing the translucency is accomplished by adding the dominant hue over the labiolingual surface.

Incisal haloTranslucent incisal edges are more common on theincisors of younger patients. Often, although theincisal area is translucent, the edge is totally opaque.This may be difficult to reproduce internally.A mixture of white and yellow stains in the ratio of4 : 1 is placed in the linguoincisal area, with anextension just onto the labial area, to produce thehalo effect.

Stained crack line Cracked enamel stains quickly on natural teeth. An orange-brown mixture applied in as thin a line as possible will effectively simulate a crack.