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Trouble Shooting Dental Plasters
Do you have a problem when processing our dental plasters? Maybe you will find the answer to your question here.
Setting retarding
- The mixing pot was washed with a cleaning agent.
Clean the mixing pot and rinse off the cleaning solution or other substance if required with clean water and dry thoroughly. - Water residue in the mixing pot altered the mixing ratio.
Dry the mixing device thoroughly after use. - The water used for mixing was too cold.
If possible, used distilled water at room temperature for mixing. - Borax was added to the mixing water
Setting retarders should not be used due to a possible reduction in quality. - Blood and saliva debris was not removed from the impression
Clean the impression thoroughly before pouring. - The plaster was not mixed long enough
Adhere to the manufacturer’s mixing times. - The hydrocolloid impression was not neutralised with potassium sulphate solution
Immerse hydrocolloid impressions in a 2 % potassium sulphate solution. - The plaster was stored without being sealed and absorbed moisture from the air
Store plaster in airtight containers at room temperature.
Setting acceleration
Errors, causes and troubleshooting
- Set plaster residue adhering to the mixing vessel, mixing paddles or spatula.
Clean the mixing pot with clean water immediately after use. - Trimming water was added to the mixing water.
Do not use setting accelerators (reduces the quality of tthe plaster). - Salt was added to the mixing water.
Do not use setting accelerators (reduces the quality of the plaster). - The plaster was stored without being sealed and absorbed moisture from the air.
Store plaster in airtight containers at room temperature. - Too little mixing water was used.
Adhere to the manufacturer’s recommended mixing ratio. - There were particles of set plaster in the plaster mix.
Clean the mixing pot and rinse off the cleaning solution or other substance if required with clean water and dry thoroughly. - The plaster was mixed too long/too heavily.
Adhere to the manufacturer’s mixing times.
Increased expansion
Errors, causes and troubleshooting
- Trimming water was added to the mixing water.
Setting accelerators should not be used. - Salt was added to the mixing water or stone mix.
Setting accelerators should not be used. - The plaster was stored without being sealed and absorbed moisture from the air.
Store plaster in airtight containers at room temperature. - Set plaster residue adhering to the mixing vessel, mixing paddles or spatula.
Clean the mixing pot with clean water immediately after use and dry thoroughly.
Low final hardness
Errors, causes and troubleshooting
- Trimming water was added to the mixing water.
Only mix with distilled water. - Salt was added to the mixing water.
Do not use additives with the mixing water. - The ratio of water was increased.
Adhere to the manufacturer’s recommended mixing ratio. - The plaster was mixed too long (disrupting crystal formation).
Mechanical mixing should take 30 sec. Manual mixing should not take longer than 60 sec. - More water was added during mixing.
Do not add any more water after the soaking time. - The plaster mix was poured when it had begun to set.
Always adhere to the time recommended by the manufacturer for pouring the plaster.
Porous surface
Errors, causes and troubleshooting
- The plaster was stored without being sealed.
Store plaster in airtight containers at room temperature. - Air was trapped during manual mixing.
Stir mix (do not beat) the plaster powder and water quickly for max. 60 sec. against the sides of the plaster bowl (to eliminate any lumps of plaster). - The vacuum pump was not switched on during mechanical mixing or the air outlet of the mixing vessel was blocked.
Check the functioning and seals of the pump, mixing vessel lid and air outlets. - Blood and saliva debris was not removed from the impression.
Clean the impression thoroughly and disinfect if possible before pouring with plaster. - Sections of the alginate impression were already dry.
Pour alginate impressions immediately after cleaning and disinfection.
Cracks in the model
Errors, causes and troubleshooting
- The plaster used for pouring and basing the model was not fully set before being trimmed.
Allow the plaster base to set completely without disturbance. - During setting water was removed too quickly from the plaster, e.g. due to the absorbent paper base.
Base the models on a non absorbent surface. - Too little water was used for mixing the stone.
Adhere to the manufacturer’s recommended mixing ratio. - The model was dry before removing wax and had not been wetted.
The model should be briefly wetted beforehand (do not soak, as it would increase the expansion). Do not use boiling water to remove wax.
Streaky, distorted stone model surface
Errors, causes and troubleshootingDeformed/damaged impression.
- Deformed/damaged impression.Retake impression.
- Model removed too early from the impression.
Wait until the stone is completely set. Depending on the type of stone, allow 30 to 45 minutes before removing the model from the impression.
Some soft areas on the surface of the model
Errors, causes and troubleshooting
- Residual wetting agent or disinfectant are still in the impression.
Liquid residue, which could inhibit setting, should be carefully removed (e.g. by blowing dry).
Broken off teeth
Errors, causes and troubleshooting
- Model removed too early from the impression.
Wait until the stone is completely set. Depending on the type of stone, allow 30 to 45 minutes before removing the model from the impression. - Inclination of the anterior teeth not taken into consideration when removing the model.
Remove the impression according to the inclination of the anterior teeth. - Impression material too hard.
With highly resistant, hard impression materials, first remove the tray from the impression material and then carefully remove the now more flexible impression material from the model
Increase in the expansion and reduction in the strength of the set model
Errors, causes and troubleshooting
- Too much water came into contact with the model after it was removed from the impression (e.g. during trimming and boiling off wax).
Keep contact with water to a minimum. Do not use boiling water. Use dry trimmers if possible.
Reduction in detail reproduction on finished model
Errors, causes and troubleshooting
- The impression was poured using a stone with reduced flowability and the stone had begun to set.
Adhere to the manufacturer’s recommended working time. Only use flowable stone. - The model was cleaned in an ultrasonic cleaner.
Models should not be cleaned in an ultrasonic cleaner.
Non parallel saw cuts on the model
Errors, causes and troubleshooting
- The saw blade was blunt.
Change the saw blades before they become blunt and ensure the teeth of the saw are correctly positioned. - The plaster is too hard
It is best to saw the dies within 2 hours of setting. - Too much pressure was applied to the saw, causing distortion of the saw blade.
Saw without applying pressure.
Damage to the preparation margin when trimming (e.g. rounded preparation margins)
Errors, causes and troubleshooting
- Incorrect/too coarse trimmer was used.
Only use trimmers that ensure the dies are not damaged during trimming. Ensure the handpiece is set to the correct rpm (too low = “chatter marks”).
Unsatisfactory fit of removable dies in the model base
Errors, causes and troubleshooting
- Grinding dust, stone particles etc. prevent exact repositioning of the stone die in the model base.
Clean all connecting parts, e.g. with a brush. Compressed air should always be used with caution. - Plasters with very different expansions were used for the dental arch and model base.
Fabricate the dental arch and model base using materials with the same expansion if possible.