Home Merz Dental



  Denture base acrylics
Denture base acrylics

FAQs denture base acrylics


Merz Dental acrylics are formulated up-to-date. Several quality controls from raw material to the finished product guarantee impeccable process ability and optimal properties. Regular application related observations and researches insure safety and longevity for high-quality prosthetics. The processing of denture base acrylics is the key to success and requires care and providence for the well-being of our patients.

Additonal monomer or polymer was added during the doughing phase

The stated mixing ratio of powder and liquid, mixing time and doughing phase to be complied with the instruction for use; use original Merz Dental measuring cups.
Please note: surplus monomer can cause tissue irritations.
Water temperature too low and/or polymerisation time too short
Polymerise cold-cured acrylics 15 - 30 min (acc. to each product, also refer to applicable instruction for use) at 45°C and on 2 - 2.5 bar pressure in the water bath (pressure pot).
Warm-up heat-cured acrylics to 70°C in the water bath, holding-time 20 min. Heat-up water bath subsequently to boiling temperature and boil for 30 min, then let water bath cool down slowly.
Models, plaster counter, matrixes and flasks too cold
Polymerisation runs imperfectly on cold areas. That can result into soft, not cured areas. Water models preferably at room temperature.

Components for hot and cold-cured acrylics (powder/liquid) were mixed up, or different not compatible components or third-party products were used
Pay attention to suitability and usability of materials. Make sure containers are labelled. Use additional labelling form Merz Dental
Labels for REFILL:
Polymer 100g container – REF 10909313
Monomer 1,000/100 ml bottle – REF 10909314
Polymer 1,000 g container – REF 10909315

Expiry date exceeded
Pay attention to expiry date before use. Avoid direct sun light, store in cool place.

Components contaminated
Use clean containers for storage of the material as well as when measuring and mixing.

Incorrect handling of the impression
The impression has to be carefully cleaned of blood, saliva and disinfectant solution. Rinse impression with water thoroughly.

Plaster surface not sufficiently grease, oil or wax free
Fully remove any wax of plaster model. Remove any alcohol contained wax-against-plaster isolation solution thoroughly.

Isolation solution stored too long, wrongly stored or contaminated
Before using the isolation solution always check expiry date. Do not expose the isolation solution to daylight, store at cool place. Always use new and clean isolation solution, use a clean brush when applying. Protect isolation solution from contamination; always apply with a clean brush. Rinse brush with clear water thoroughly after every use.

Not sufficient or lacking isolation
Apply isolation thinly 1 to 2 times maximum. Further layers do not improve the isolation. Rinse off any residue under soft running water carefully, no isolation puddles! The islolated area should look shiny.

Unsuitable isolation solution used
PremEco Line alginate isolation solution is recommended for Merz Dental acrylics.

Composite refined plasters as their components prohibit a continuous isolation film and could react with denture acrylics.
Where applicable a different plaster should be used.

Wrong plaster class used
It is recommended to use always plaster of type class IV. Plasters of type class I and II have a porous surface and absorb the isolation solution too intensely.

Watering the plaster models in the pressure pot
Watering in the pressure pot presses water into the plaster pores. The models sweat out the remaining water when they are exposed under atmospheric pressure again. This will lift the isolation film of the plaster surface. Water the models always without pressure.    

Wax solvent and/or boil out duration have an impact on the plaster surface
When using boil out devices make sure to use applicable additives and dosage. Warm up models for 5 min., remove any wax in its plastic condition. Under no circumstances do not wait for any wax to dissolve in the boil out device. Steam off models again immediately after boil out. Do not leave the plaster surface unnecessarily exposed under thermal stress by boiling out. Clean boil out device regularly.

An isolation solution wax against plaster was used. These materials often contain essential oils, which prevent a correct isolation of the plaster through the alginate isolation solution  The oil film on the plaster surface prevents the sealing of the plaster with the alginate isolation solution.
Clean models thoroughly.

Contamination/dirt in the alignate isolation solution through plaster particles (calcium ions) in the storage container, working tray etc.
Always use clean isolation solution (one-way). Clean brush before applying the isolation solution, do not place brush back into the container of the isolation solution.

Acrylic not mixed enough, doughing time too short
Mixing ratio of powder and liquid, mixing and doughing time to comply with instructions of use.

Wrong polymerisation pressure
Please make sure that the pressure in the polymerisation device does not exceeds or falls below 2 - 2.5 bar. The exactly set pressure prevents the formation of boiling bubbles during the exothermal reaction phase.

Heat-curing polymers
Wrong polymerisation control, formation of boiling bubbles through fast heating-up. Heat-curing polymers need to be heated up to 70 °C in the water bath, then hold for 20 min. Subsequently raise water bath to boiling temperature and boil for 30 min, then let the water bath slowly cool down.

Cold-curing polymers
High water temperature in the water bath; do not exceed water bath temperature above 50 °C

Flasks and/or plaster models too hot after boiling out
Cool down to room temperature, plaster model not sufficiently watered; before applying the acrylic water plaster models in clear water at room temperature for at least 10 min.

Mixing ratio are not being complied with
Use measuring aids. Fill powder into the measuring aid, but do not tap/dense, if necessary re-measure! Too much monomer leads to high shrinkage of acrylic.

Not enough acrylic (pressing technique)
Ensure that there is a sufficient acrylic, press reservoir
Not enough acrylic in under cuts (pressing technique), thus trapped air
Place small amounts of acrylic dough in under cuts. When heat-curing it is recommended to press in between by using a polyethylene foil. 

Pressure loss during polymerisation; if the pressure falls during polymerisation, the boiling point of the monomer sinks and boiling bubbles will occur.
Checks permitted parameters and keep conditions.
Too much monomer used
Use measuring aids. Too much monomer leads to high shrinkage of the acrylic.

Isolation layer too thick
Apply isolation thinly, max 1 to 2 times. Further layers do not improve the isolation. Rinse excess carefully under soft running water. No islolation puddles should remain. The isolation area should have a shiny appearance.

Cooling-off period too fast
Allow the flask to cool down slowly after heat-curing polymerisation in order to avoid tension within the acrylic. 

Too much pressure during polishing
Polish moistly with little pressure. Thermal stresses cause tension, deformation and burns on the polished surface.

Wrong polymerisation pressure
Cold-curing polymers need 15-20 min in a 45 °C water bath under 2 – 2.5 bar pressure

Setting time of the acrylic not followed
The acrylic needs setting before it is placed into the pressure pot.

Polymerisation temperature too high with cold-curing polymers
Do not exceed water bath temperature of 50°C.

Thermal and mechanical tension of the acrylic after polymerisation
If possible avoid any thermal and mechanical stresses after polymerisation.

Teeth were not sufficiently supported within the silicon matrix technique
Apply a tiny amount of super glue onto the teeth and fix in the matrix. Remove any residue of glue after polymerisation.

Acrylic excess within the flasking technique
Depending on the system, excess remains between the parts of the flasks. This excess causes a bite raise of 0.5 to max. 1.0 mm and can be corrected in the articulator on the occlusual surface through specific grinding. Should the excess be extraordinarily thick, the pressure of the hydraulic press needs to be checked to see whether it is sufficient. If applicable, check with a pressure gauge. In addition check flask clamps for its stability. Check consistency of the set acrylic, setting time exceeded (see instructions for use), cover the mixing container to avoid that the acrylic dough is drying-out.

The acrylic working time was too slow during the start of the polymerisation in the pressing technique
If the polymerisation of the cold-cured polymer has already started during the pressing technique, the acrylic will set too quickly. In this case the flask will not close correctly and will result in bite raise.
Monitor the acrylic during the setting time carefully. An exact timing for the correct working time is essential and may take a little practise when handling with cold-cured polymers. If necessary keep the monomer refrigerated, this prolongs the working time. 

Undercut trimmed models using gel during the pouring technique
Always trim model in right angle, otherwise they wouldn’t fit back into the flask and would deform the gel.

Shrinkage of the base due to high monomer content (pouring technique)
It is resolve by using an underlay foil of 0.1 mm between the model and the base of the flask (PremEco Line).

Acrylic on the teeth 
Insufficient fixation in embedding or matrix. For fixation use a tiny drop of super glue on labial surfaces of the teeth. Please make sure that all excess is removed after polymerisation. Before embedding, please make sure that there is no wax left on the teeth. When embedding in gel remove any water in the gel cavities so that the teeth can be re-positioned and are not pushed up through any residual water.
Water content in the gel through evaporation too little (pouring technique)
When re-heating add some water again.

Gel melting point was too high, strong loss of water (pouring technique)
After use, store duplicating gel in a closed container. Add enough water when reheating. When using gel melting machines make sure of an exact temperature control during the melting phase. The gel must not come to the boil, as in this case it destroys the structure. It is recommended to check the temperature during the melting phase with an external thermometer every now and again, as the temperature in the gel machine can differ from the temperature required (see instruction for use). Should the gel only be needed sometimes, a microwave can be used for melting (see instruction for use).

Impression insufficient
When taking the impression, please check on tuber and/or trigonum retromolare.

High shrinkage in the denture base due to high monomer content
Mixing ratio of powder and liquid and doughing time to be complied with instruction for use.

When doughing time of acrylic is left too short, suction shrinkage will occur on thicker areas of the denture base.
Mixing ratio of powder and liquid and doughing time to be complied with instruction for use. Powder/liquid ratio to be checked via measuring aids or weighing.

Mixing ratio not complied with, too higher monomer content during mixing
Pay attention to mixing ratio, use measuring aids. In order to reduce monomer content, please leave the polymerised acrylic piece in the unpolished condition in water at room temperature for 48 hours prior to insertion.

Sore spots due to occlusion irritation or inaccuracy of fit
Bite raising especially in denture processed in the pressing method have to be rearticulated and grinded.

Rough basal areas
Pay attention to plaster processing. Disinfect and neutralise impression according to manufacturer’s advice. Avoid thermal impact, steaming off and boiling off to be narrowed down to a minimum. Thinly apply isolation solution twice. Apply isolation thinly, max 2 times. Further layers do not improve the isolation. Rinse excess carefully under soft running water. No isolation puddles should remain. The isolation area should have a shiny appearance. Always use clean isolation solution from the bottle. Use a brush to apply with. Rinse brush thoroughly after use to protect isolation against contamination.
Possible hypersensitivity: Check whether patient has an allergy record. Check which denture materials were used before. If no information, a doctor should be consulted.

© Merz Dental