1. No tray adhesive used.
   
2. Not allowing tray adhesive to dry completely.
   
3. Poor tray support, weak or short tray walls.
   
4. Removing impressions from mouth too soon.
   
5. The disinfectant was not rinsed from tray prior to applying adhesive or tray was not completely dry.
   
6. Wrong type tray adhesive was used.
   

Possible Results:

1. Crowns too tight/high crowns.
   
2. Extensive occlusal adjustment necessary.
   
3. Tight or loose contacts.
   

Solutions:

1. Always use tray adhesive; wait ten minutes after applying adhesive before loading the tray. Using tray adhesive guides the polymerization shrinkage towards the tray. This leads to a slightly larger crown with a better fit. When no adhesive is used, the shrinkage is guided to the center of the mass. This leads to a smaller crown with a poor fit.
   
2. Use a custom tray or a strong stock tray with proper support.
   
3. Keep tray in mouth until impression material is completely set; use a timer if necessary.

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1. Pouring model too soon.
   

Possible Results:

1. Poor marginal detail.
   
2. Non fitting restorations. The lab will have to use guess work regarding the margins, undercuts, and surfaces of the restoration.
   
3. The presence of voids on the model will result in poor marginal integrity and will hinder the articulation of the model.

Solution:

1. Wait one hour before pouring the model unless a mechanically vacuum-mixed die is used. If the die stone is hand mixed, the operator should delay pouring the impression one hour in order to obtain the best surface on the model. Pouring the impressions may be delayed up to fourteen days without loss of accuracy.
   
2. Waiting one hour will alleviate the presence of small voids die to hydrogen gas released from the impression material.

Back To Impression Taking Tips Options

1. Seating partially set tray material.
   

Possible Results:

1. Poor occlusal detail.
   
2. Poor marginal detail.
   
3. Non-fitting restorations.
   

Solution:

1. Seat tray material within the specified work time.

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1. Latex glove or dam contamination. Touching the prepared teeth or surrounding areas, pulling retraction cord through gloved fingers, or through the use of a rubber dam can leave sulfur in vital areas of the impression.
   a. Contamination or non-set at the margin-retraction cords containing ferric sulfate or aluminum chloride will inhibit the set of all vinyls.
   b. Contamination or non-set at the buccal surface - when the cheek is retracted the doctor's gloved finger may come in contact with the prepared tooth.
   
2. Water used to rinse away hemostatic agents is still present at the bottom of the gums and has not been suctioned. The impression will appear to have a mottled surface. The non-set material will appear on the perimeter of the tray or away from the tooth surface.
   
3. Not rinsing area around retraction cord prior to taking impression.
   
4. Residues from temporary materials left behind.
   
5. Presence of air-inhibited layer.
   a. Contamination or non-set on the surface of the prep - an
   air-inhibited layer from composite, adhesive, core build up material, or methyl-methacrylates will cause non-set situations.
   
6. Contamination on the labial surface - a patient wearing lipstick or other makeup will recontaminate the surface each time he/she closes his/her mouth, or the doctor may be inadvertently rubbing his/her gloved fingers on the back of the patient's lips if they are not being held back.
   
7. Putty contamination - latex gloves, or germicidal agents in hand soaps. Some germicidal agents contain sulfur as a preservative; sulfur inhibits the set of vinyls.
   

Possible Results:

1. Poor occlusal or marginal detail.
   
2. Incomplete set of material.
   
3. Contamination of die stone.
   
4. Re-makes of the impression.
   
5. Re-makes of the restoration.
   

Solutions:

1. Wear latex or vinyl gloves that are guaranteed not to inhibit the set of vinyl materials. If contamination is probable, wash the affected area with a diluted hydrogen peroxide just before taking the final impression.
   a. Retract the patient's cheek using a cleaned mirror handle instead of a gloved hand.
   
2. After rinsing around the retraction cord make sure to suction thoroughly so no hemostatic agents have come in contact with the bottom of the sulcus.
   
3. Rinse the area around retraction cord thoroughly. Have assistant use pliers to dispense retraction cord, not a gloved hand.
   
4. Make the temporary crown or bridge after the final impression has been taken. If final impression was taken prior to the fabrication of the temporary make sure to prophy and rinse thoroughly.
   
5. An air-inhibited layer due to composites, bonding agents or core build-up materials must be removed. The doctor must polish the composite surface, remove air-inhibited layer with alcohol or cover with glycerin prior to curing and then rinse.
   
6. Have patient remove lipstick or other makeup prior to taking impression. Place cotton rolls or use a retractor to hold the patient's lips back.
   
7. Only mix putty with bare hands or use gloves that are guaranteed not to inhibit the set of putty. Make sure the assistant mixing the putty has not washed hands with a germicidal soap containing sulfur as a preservative. Wash hands with regular hand soap after using germicidal soap.

Back To Impression Taking Tips Options

1. Prepped tooth came in contact with side or bottom of the tray.
   
2. Prepped tooth came in contact with tray material when using a two-step technique.
   

Possible Results:

1. Crowns are too tight, too small or too large.
   

Solutions:

1. Teeth should not touch any part of the tray, only the impression material.
   
2. Create a dimple in the dray material to ensure a 2-3mm space around the teeth to allow for proper placement of the wash material.
   
3. Do not allow contact of the teeth with the tray material when
   re-seating the wash filled tray.
   
4. Use plenty of wash on the prepared tooth as well as in the lined tray.

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1. Inadequate time spent mixing base and catalyst.
2. Unequal amounts of base and catalyst were mixed.
   

Possible Results:

1. Unequal distribution of set and unset material resulting in poor fitting restorations.
   

Solution:

1. Mix base and catalyst in finger tips to ensure a homogeneous mix. Material should not appear streaky.

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1. Either tray or wash material has begun to set prior to tray seating.
   In a two-step technique, no spacer was used.
   

Possible Results:

1. Crowns will not fit.
   
2. Rough margins with lack of detail.
   

Solutions:

1. Always use a spacer in a two-step technique.
   
2. Adhere to working times of both tray and syringe material.

Back To Impression Taking Tips Options

1. Surface contamination (see Surface Contamination).
   
2. Excessive moisture present.
   
3. Wash has already begun to set prior to tray seating.
   
4. Removal of impression from mouth before it is completely set.
   
5. Use of wash material with a poor tear strength.
   

Possible Results:

1. Crowns too tight/too high.
   
2. Poor occlusal detail or marginal detail.
   
3. Contamintaion of dies stone.
   
4. Re-make of impression.
   
5. Re-make of restoration.
   

Solutions:

1. Follow directions closely for work time.
   
2. Make sure impression remains in mouth for recommended set time. Use a timer if necessary.
   
3. Allow material to set for an additional 1-2 minutes. Tear strength increases as material continues to polymerize.
   
4. Use a higher viscosity material (Extrude Medium) for tear strength.
   
5. If presence of moisture is extreme or there is excessive bleeding:
   a. Rinse and dry preparation thoroughly after removal of the retraction cord, but prior to syringing.
   b. Apply cotton pellets soaked in hemostatic agent for one minute to tissue areas which exhibit excessive bleeding.
   c. Rinse and dry thoroughly prior to syringing.
   d. Moisten retraction cord prior to removal.
   e. Replace cotton rolls as needed.
   f. Delay procedure. Have patient return when tissue has properly healed.

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Adhesive used in tray	No adhesive used in tray
With Any Tray	Rim Lock Tray
Using an adhesive directs the polymerization toward the tray. This results in a slightly larger crown with improved fit.	Without an adhesive the polymerization shrinkage is directed toward the center of the mass. This results in a slightly smaller crown with a poor fit.
No adhesive used in tray	Buttoned Plastic Tray
Button Tray
Without an adhesive the polymerization shrinkage is directed toward the center of the mass. This results in a slightly smaller crown with a poor fit.	This illustration shows views of the button tray illustrated to the left. As the number of holes increases, the more securely the putty will be held into the tray.

Back To Impression Taking Tips Options

Impressions: A Text for Selection of Materials and Techniques, 1st edition Harry Albers, DDS, p58 with permission from Dr. Harry Albers.

*Bomberg TJ, Goldfogel MH, Bomberg SE: Considerations for adhesion of impression materials to impression trays. J Prosthet Dent 60;681-684, 1988.

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