What do we check for in metal casting and ceramic one?
Metal castings need to be evaluated in terms of proximal contacts, margin integrity, stability, internal fit, external contours, occlusion, and surface finish.
Metal-ceramic restorations often require two evaluations: a metal evaluation stage, followed by reevaluation after the esthetic veneer has been applied.
What’s Evaluation Sequence of try in
- Proximal contacts.
- Marginal integrity.
- Stability.
- Occlusion.
- Characterization and glazing
How do we check for proximal contacts? How the ideal contact should be?
- The location, size, and tightness of a restoration’s proximal contacts should resemble those of the natural teeth.
- the use of floss is a convenient method for comparing the contacts with other contacts between
- adjacent teeth in the arch. If the floss does not pass, the contact is excessively tight; if it goes through too easily, food impaction may result.
- Ideal contacts—–Contacts that allow unwaxed floss to “snap” through “relatively easily.”
- The use of shim stock (thin Mylar film) is a more reliable indicator of proximal contact than floss. A passive contact allows the Mylar film to be pulled from the interproximal with some slight resistance. If the strip tears, the contact is too tight.
- The ideal contact allows for positional stability of the abutments and adjacent teeth, as well as easy maintenance of the supporting structures.
What do we do when there’s excessive tightness in metal and porcelain? Glazed and an-glazed
All-metal restorations If a tight contact prevents the seating of an all- metal restoration, adjustments are readily made with a rubber wheel.
Identifying the location of a tight proximal contact.. A shiny mark is formed where the contact is excessive.
Porcelain restorations A tight proximal contact in unglazed porcelain is easily adjusted with a cylindrical stone. The location of tight porcelain contacts can be identified with thin marking tape.
If adjustment of a glazed, restoration is needed, it can be repolished with diamond-impregnated silicone points, pumice, or diamond-polishing paste.
What do we do when there’s deficiency?
All-metal restorations A gold casting with a deficient proximal contact can usually be corrected by soldering .
A deficient proximal contact in porcelain requires additional firing. This is time Consuming, but adding additional porcelain is not a problem. However, if a restoration has been completely finished, glazed, at that time the deficient contact is discovered, a lower fusing “add-on” or correction porcelain can be used to solve the problem .
Hour should marginal integrity be? How do we fix it?
How do we detect it?
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.
If the indirect procedure is handled properly, there should be no noticeable difference between the fit of a restoration on the die and that in the mouth.
A deficient proximal contact in porcelain requires additional firing. This is time Consuming, but adding additional porcelain is not a problem. However, if a restoration has been completely finished, glazed, at that time the deficient contact is discovered, a lower fusing “add-on” or correction porcelain can be used to solve the problem . Several techniques have been used to detect where a casting binds against an occlusal or axia Wall.
Nevertheless, elastomeric paste has some advantages. The material is 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.
What should ideal marginal integrity be?
Also talk about adaptation
After the proximal contacts have been corrected, the restoration is seated, and the margins are examined closely. An acceptable margin is not overextended, underextended, too thick, or open.
The degree of clinically acceptable marginal opening is hard to define.A margin is generally considered to be open if the gap is greater than 50 μm, which means the tip of a sharp explorer can be inserted between the restoration and tooth.
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 um can be obtained
Supragingival margins are generally finished with the casting seated on the tooth.
What about Finishing of Subgingival margins ??????? On the cast
Gold margin finishing golds differ from other materials in that they can be burnished against the tooth to some extent. This must not be attempted until it is certain that the casting is seated as far as it will go.
Talk about stability in try in
The 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.
Talk about occlusion in try in?
After 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 contacts as well as centric interferences must be identified.
By using of shim stock , teeth relationship should be recorded, if there is an interference so articulating paper should be used
- Ask the patient to close without restoration and assess the contacts with using a shim stock between opposing teeth adjecent to the prepared teeth .
- Seattherestoration,havethepatientclose,and reassess the contacts. With the new restoration the previous teeth should hold the shim stock and yet not alter the existing tooth relationships.
- Mark any interferences that are detected.
- Have the patient close on articulating tape.
Adjust the marked interferences with the diamond rotary instrument or white stone, always checking the thickness of the casting with calipers before an adjustment is made.
On occasion, adjusting an opposing cusp rather than cementing a restoration that is too thin may be the preferred method,
Talk about Characterization and glazing
- The surface luster or degree of gloss of a porcelain restoration depends on the autoglazing procedure.
- Both time and temperature must be carefully controlled. During the glazing firing, the surface layers of porcelain melt slightly, fill the surface defects.
- some dentists prefer to glaze porcelain restorations in the office.
- During the clinical evaluation, the patient should be instructed to moisten the restoration because saliva affects its appearance. A dry crown looks misleadingly underglazed.
- If restoration is not sufficiently glazed, it will retain more plaque and may be more liable to fracture. After glazing, the metal surfaces of the restoration, which have oxidized during firing, are polished.
What’s alternative to glazing?
- An alternative to glazing is to polish the porcelain surfaces of the restoration. This provides greater control of the surface luster and distribution than glazing. For example, having a higher gloss on the cervical area and a lower gloss on the incisal area is possible. This is not possible with glazing because the entire crown is subjected to the same time- temperature combination.
- A number of commercially available polishing kits are available for this purpose, should be used correctly.
- Despitetheestheticadvantagesofpolishing, it also reduces flaws,
- In laboratory studies, polishing has not been found to reduce physical properties, in comparison with glazing
What do we do when restoration that does not blend well with the adjacent teeth?
- In many situations, a restoration that does not blend well with the adjacent teeth can be improved by simple chairside color modification or characterization procedures.
- These are done concurrently with final glazing, and it is therefore recommended that restorations be tried in the patient’s mouth when contoured but unglazed
- Characterization. Characterization is the art of reproducing natural defects, and it can be particularly successful in making a crown blend with the adjacent natural teeth. In general, defects should be reproduced to a slightly lesser extent on the restoration than as they appear on the natural teeth.
