Clinical Try-In & Adjustment

Clinical Try-In & Adjustment:
After the laboratory procedure has been completed, the casting restoration is now ready to be tried in (checked on the prepared tooth inside patient mouth) prior to final finishing and cementation.
With or Without Anesthesia?
The procedure can be accomplished in most patient without anesthesia, it give us the benefit of unimpaired tactile sensation that is of great value during occlusal adjustment. But sometime we use anesthesia if the patient unco-operative.
Seating The Casting
1. Remove temporary restoration and clean the prepared tooth from any remnant of cement because it will interfere with seating of restoration.
2. Seat the restoration on the prepared tooth with pressure.
3. Examine the inter-proximal contact area, it should be tight as the other in the mouth. Dental floss is used to check the interproximal contact by passing it between the restoration and the adjacent natural teeth, it should have slight resistance otherwise we have either;
a) Heavy resistance; the dental floss can’t pass through the contact, this indicate that the contact is heavy and it must reduced.
b) No resistance; however if the floss passes easily, it indicate that the contact area is under contoured (deficient contact) -- either you have to repeat the restoration or to correct this defect by adding solder to that area.
4. If the contact area is perfect and the crown is not seated completely this might mean that, there is interference from inside (metal bubbles or undercut) we use pressure indicating past (silicon wash) or spray to identify the interferences. We place it into the inner surface of the crown restoration. The crown were then seated on the prepared tooth with pressure , the restoration were then removed and inspected for any pressure (shiny) area which indicates an interference area that should relieved.
5. Evaluating Complete Seating, the margin of the restoration is the most critical area, we should have complete fitness between the restoration margin and finishing line of the preparation.
Types of Marginal Defects
1. Short margin (under extension, Shoulder or ledge): margin of the crown restoration lies short of finish line of prepared tooth.
2. Long margin (overextension, overhang): margin of the crown restoration lies beyond finish line of the prepared tooth.
3. Open margin: margin within finish line but there is space between the restoration margin and the prepared tooth.
4. Over contoured:
To check the marginal integrity of the crown restoration, we use sharp pointed probe (varying tip size), the probe should be move in a two direction (varying approaching angle), the direction of the movement and the angle of approach during checking with probe is very important.
How to check:
1) Move probe from the restoration toward tooth surface, if it passed smoothly without any interpretation then the margin is OK. However if there is any interpretation during this movement, this indicate under extended margin.
2) Move from tooth surface toward restoration margin, if the probe catch by the margin, this indicate over extended margin (correction might lead to open margin).
3) If the probe passes smoothly in the two direction this mean the margin extension is correct.
4) If there is space between the restoration and tooth surface at area of finishing line & the probe can go in ,this mean open margin.
The restoration should then be examined for stability, it should not rock or rotate on the prepared tooth when force is applied on.
• After complete seating, adjust the occlusal relationship in all mandible movements (centric and eccentric) using articulating paper. Any occlusal prematurities should be relieved using green stone bur. After that, the casting restoration is ready for the next step.
Margin finishing:
Objectives: is to obtain at least one mm wide margin that is closely adapted to the tooth surface at the area of finish line to prevent microleakage.
1. Sub gingival margin can be finished on the die using burnisher, no intra oral finishing is desirable because of the risk of damaging the tooth and the periodontal tissue.
2. Supra gingival margin can be finished directly on the tooth, margin adaptation can be improved by using burnisher or dull bur.

Final polishing
Objective: is to provide smooth shiny restoration surface that will be less susceptible to plaque accumulation or deposition.
Purpose of Polishing:
Polishing is performed in order to provide a restoration that have:
1) Glossy surface.
2) Plaque resistant.
3) Tarnish/corrosion resistant.
4) Good appearance.
Surface defects and roughness are removed by grinding with abrasive particles bound on grinding stone or rubber wheel or paper discs or it applied as abrasive paste.
Permanent Cementation
Dental cement doesn t contribute to the retention of the restoration. It is used only to fill the micro-spaces between the tooth structure and the restoration when it sets (into the small irregularities between the opposing surfaces), it provides a chemical and/or mechanical bond (interlocking) that prevent the restoration from removal.
Luting Agent:
A material that acts as an adhesive to hold together the casting to the tooth structure. Luting agents are designed to be either permanent or temporary.
Properties of ideal luting agent:
1. Should have good working and setting property.
2. Adequate strength.
3. Compressible into a thin layer.
4. Should provide good sealing, and must be non-toxic to the pulp.
5. Should adhere well to the inner surface of the restoration.
6. Low viscosity and solubility.
Function of cement:
1. To secure a lasting retention of the restoration to the prepared tooth.
2. To seal the gap against penetration of fluid and bacteria from oral cavity.
3. To act as an insulating barrier against the thermal and galvanic activity.
Factors affecting the retention of the cemented cast restoration
1. Geometrical relations of the preparation like retentive properties of the preparation (taper, height, surface area…..etc).
2. Biophysical factors relating to the casting; such as accuracy of fit, metallurgical characters, surface texture of the casting restoration.
3. Mechanical properties of the luting agent such as compressive strength, tensile strength, shear strength, adhesive property and film thickness.
4. Difference in the coefficient of thermal expansion between tooth, casting and cement.

Dental cementing (luting) Agents
Cements may be classified as soft or hard.
1. Soft cements: can be used for temporary cementation.
2. Hard cements: these are used for definitive (permanent) cementation. There are essentially three types of hard cement: conventional, resin or a hybrid of the two.
• Conventional cements, rely on an acid-base reaction resulting in the formation of an insoluble salt (the cement) and water e.g. zinc phosphate, zinc polycarboxylate and glass ionomer.
• Resin cements, set by polymerization.
Zinc phosphate cement
It is the traditional luting agent that have proven itself after years of work, it has compressive strength of 14000-16000 PSI, with low PH at the time of cementing (about 3.5) which might irritate the pulp.
Advantages: -
1. Good compressive strength (if correctly proportioned).
2. Good film thickness.
3. Reasonable working time.
4. Resistant to water dissolution.
5. Long track record.
6. No adverse effect on pulp although initially acidic.
Disadvantages: -
1. Low tensile strength
2. No chemical bonding
3. Not resistant to acid dissolution
Recommendations: -
1. Good default cement for conventional crowns and posts with retentive preparations.
2. Working time can be extended for cementation of multiple restorations by incremental mixing and cooled slab.
Zinc silicophosphate cement
Has compressive strength of 22000 PSI but it has highly acidic PH which may affect the health of the pulp (irritant).
1. Mixture of zinc phosphate & silicate cement.
2. Film thickness, compressive strength & tensile strength in the range of ZPhC with slight lower solubility.
3. Anti-cariogenic property due to fluoride content.
4. Low PH & pulpal irritation.
Poly-carboxylate cement
Adhere to enamel, dentine and stainless steel but not to gold alloy, the setting PH is (4.8) but because of the large size of poly-acrylic acid molecule, it has less effect on the pulp, high bond strength to enamel (1300 PSI) but its binding to dentine is considerably less 480 PSI.
Advantages: -
1. Good compressive strength (if correctly proportioned).
2. Adequate working time.
3. Bonds to enamel and dentine.
4. Adequate resistance to water dissolution (but less good than zinc phosphate).
5. Reasonable track record.
6. No adverse effect on pulp and less acidic than zinc phosphate on mixing.
Disadvantages: -
1. Low tensile strength.
2. Can deform under loading.
3. It is difficult to obtain low film thickness.
4. Not resistant to acid dissolution.
Recommendations: -
• Traditionally used for vital or sensitive teeth, but no evidence to support efficacy (dentine bonding agents used to seal preparation prior to cementation may be a better option).
• Occasionally useful to retain an unretentive provisional crown.
Glass ionomer cement
has compressive strength of 18600 PSI and it bonds to enamel and dentine (to enamel more), it releases fluoride after setting which is indication of an ability to inhibit secondary caries.
Advantages: -
1. As for polycarboxylate cement but cement has similar acidity to zinc phosphate on mixing.
2. Fluoride release.
Disadvantages: -
1. Sensitive to early moisture contamination.
2. Low tensile strength.
3. Not resistant to acid dissolution.
4. Has been accused of causing post-operative sensitivity but a controlled trial reports it is no worse than zinc phosphate
Recommendations: -
• Used empirically for conventional crowns where patient has had a previously high caries rate.
• May be used as an alternative to zinc phosphate.
Resin Luting cement
They have wide range of formulation, can be classified basis of polymerization method (chemical, light cure, dual cure) & the presence of dentin bonding mechanisms. Chemical cure for metal restoration, light cure for ceramic restorations.
Advantages: -
1. Good compressive and tensile strengths.
2. High tensile strength (relative to conventional cements).
3. Resistant to water dissolution.
4. Relatively resistant to acid dissolution.
5. Can enhance strength of ceramic restoration if bond obtained.

Disadvantages: -
1. Film thickness varies substantially between materials.
2. Excess material extruded at margin may be difficult to remove especially proximally.
Recommendations: -
• Must be used with or incorporate an effective dentine bonding agent.
• Material of choice for porcelain veneers, ceramic onlays and resin bonded ceramic crowns.
• May be used to improve retention where preparation geometry sub-optimal, but clinical studies needed to determine long-term success.
Resin modified glass ionomer cements and compomers
Resin modified glass ionomer (RMGI) cements are a hybrid of traditional glass ionomer cement with small additions of light curing resin and generally have the advantages of both, combines the strength and insolubility of resin with the fluoride release of GIC. They were introduced with the aim of overcoming the moisture sensitivity and the low strength of conventional glass ionomers.
Compomers are also composed of resin and glass ionomer but are more closely related to composites with the glass ionomer, setting reaction occurring slowly as moisture is absorbed into the set resin matrix.
The use of RMGIs for luting purposes is becoming more popular because of their relatively high bond strength to dentine, and their ability to form a very thin film layer. RMGIs leach fluoride, but it is unclear how useful this is in preventing secondary caries formation.
Advantages: -
1. Good compressive and tensile strengths (if correctly proportioned).
2. Reasonable working time.
3. Resistant to water dissolution.
4. Fluoride release.
Disadvantages: -
1. Short track record.
2. May expand and crack overlying porcelain because of water absorption.


The selection of cement for placement of cast restoration is not clear cut decision. Zinc phosphate cement is used
1. When maximum retention is required.
2. The pulp of the tooth is of no concern.
3. Also, we use it on endodontically treated teeth or teeth with heavy amalgam filling.
However more biologically compatible cement is used (polycarboxlate, GIC, Compomer):
1. On teeth, whose preparation possess adequate retentive features.
2. When the depth of the preparation raise some concern about the vitality of pulp.
Plain ZnOE Cements based on zinc oxide and eugenol are classical soft cements is not used for permanent cementation because:
1. It has poor oral durability due to continuous eugenol loss.
2. Also, it possesses low compressive strength, so we use it for temporary cementation.
Cementation Technique
Cementation procedure for ZPhC:
1. Remove the temporary crown, cleaning of the prepared tooth from any residues of cement.
2. Isolate the prepared tooth or teeth with cotton roll (dry field of operation).
3. Partial protection of pulp can be provided by application of two layers of cavity varnish.
4. Start mixing cement, mix slowly and over a wide area on a cool glass slab to ensure that a maximum amount of powder can be incorporated to reduce acidity.
5. Apply a coating of the cement to the inside of clean dry casting restoration.
6. Seat the casting crown on the tooth with pressure and have the patient to apply force to the occlusal surface of the casting by biting on wooden stick or cotton roll for 3-4 minutes (to ensure complete seating).
7. After cement setting, remove any excess cement from the interproximal area, gingival cervix and underneath the bridge using dental probe and dental floss.
8. Check occlusion.




Cementation with resin cement (all ceramic and zirconia restorations)
1. Clean the prepared tooth surface from any remnants of temporary cementation with ultrasonic scaler followed by headpiece brush and pumice.
2. Isolate the prepared tooth and acid etch the prepared tooth surface for 30 seconds with 37% phosphoric acid gel, rinse and dry gently with air syringe.
3. Apply universal bonding agent on the etched surfaces for 10 seconds, dry gently and cure for 15 seconds.
4. Etch the internal surface of the restoration with 9.5% hydrofluoric acid for 30 seconds, rinse and dry gently, apply special zircon bonding agent for 15 seconds, dry and cure for 20 seconds.
5. Mix suitable amount of resin cement according to manufacturer instructions and load it on the internal surface of the restoration and seat it over the prepared tooth with moderate pressure or asking the patient to bite on the restoration, cure for 2-5 seconds then remove the excess cement material with probe.
6. Final curing and checking of the occlusion and adjustment if needed.