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Frequently Asked Questions


Contents

Tips
C&B Alloy and Investments
Equipment and DEMCO
FlexStar Flexible Partials
Partial Denture Casting - Chrome Cobalt Technique
Partial Denture Casting - Nickel Chrome Technique
Acrylics - Impak

TIPS

Random Tips

    1. Place your electronic scale into a clear Ziploc bag to protect from spilled investment when measuring.  Makes for easy clean up and will extend the life of your scale.
    2. Post a calendar on the side of your duplication machine.  Mark which day you put new hydrocolloid into your machine and also mark each day you cook down.  This will help you know exactly when it is time to change the material and will eliminate the guesswork.
    3. Don’t try to get that one last melt on your duplicating material-money spent on trying to fit inaccurate castings not worth money saved on duplicating material.
    4. Check calibration on duplicating machine.  Material lasts longer when not overheated and kept at lowest temperature possible in holding tank (130 degrees F).
    5. Always measure investment material and liquid!  This is important for great fits!
    6. When opening a new container of investment-mix by kneading investment in bag it comes in, or roll container on floor before opening.  Settling can occur during shipment and particles can separate.
    7. Frequently clean out your wax pots-keep your wax up debris free.
    8. Attend partial denture trainings (we have several) to keep abreast of changes and learn from fellow technicians.  Learning spurs excitement in your technicians.
    9. Use timers!  Play close attention to setting times-difference between a great fitting casting and a so-so fitting casting.
    10. Make sure when do subsequent melt downs of duplicating material, that you add liquid left in the bottom of the bucket, this will help reconstitute material and help life expectancy. Keep survey table clean of wax -this will assure an accurate survey and block out.
    11. During partial denture framework duplication process, the temperature of the water for cooling should be approximately 55 degrees F. Colder water may cause too rapid chilling, freezing or distortion of the hydrocoloid.
    12. Always use a wax pencil for transferring design to your refractory.   Never use a graphite pencil as the deposits left by this type of pencil may not be completely burned-out in the furnace causing pitting and other imperfections.
    13. When spruing your wax up-care must be taken that the connection points do not produce and sharp angles.

 

Trouble-Shooting Microfire Investment

      CRACKING: Generally, when we speak of cracking, most of the time the cause is the bulk powder taking on moisture from the environment. That’s to say, the material is kept open and the container is not sealed when the investment is not in use. It is important to keep the investment container closed so that it does not take on moisture from the atmosphere. If the investment is allowed to take on this atmospheric moisture it alters the water power ratio when the investment is mixed and may cause cracking in the furnace during burn-out. In addition this extra moisture may alter the fit of the appliances.
      Another reason for cracking could be the use of 100% special liquid when using the Microfire investment. It is very important to remember while you may use all water for mixing the Microfire, we recommend using at least 10% water with the special liquid during the investing process. Most often we find laboratories that use 100%’s special liquid will have cracking, blow-throughs or blowouts.
      Another aspect to consider is their mixing process. It is important that the investment have enough mixing time to achieve the exothermic reaction. Without this exothermic reaction the investment will be weak and will crack in the furnace. That is why we recommend they give the investment at least 30 second hand spatulation, and 45 to 60 seconds mixing under vacuum in order that the exothermic reaction take place.
      What is the temperature of the power and the liquid being mixed? If the environment is very warm, (Greater than 75°F, or 24°C) will alter the setting of the investment therefore giving cracking because the investment was not mixed long enough in order that the exothermic reaction take place. Sometimes in warm environments, technicians tend to hurry the mixing process due to the fact the warmer the environment the faster the investment will set. The investment already has a very short working window, therefore, the technician is concerned they will not have enough time to pour the investment if they spend too much time mixing.

 

Trouble-Shooting Pits in Frameworks

      There are 4 types of pits, and there are different sources of each one.
      1. White pits - These are due to investment getting in the case - usually due to sharp edges in the sprues, or dust in the cone hole. Check sprues and stop grinding the molds. There is no need for grinding!
      2. Black round pits - These are from carbon buildup in the furnace. To remove carbon, do the following: after casting, bring the furnace up to it's highest temperature and hold for 1 hour - let it cool down and this should fix the problem.
      3. Irregular shaped holes - These are shrinkage holes - Sprues too long, button too small (often seen from using flat cone formers). If spruing over the top, make sure the bottom of the cone former is at the same level as the top of the highest point of the wax, any higher will require longer sprues and suck backs will show up.
      4. Irregular black lumps in the metal: This is from dross in the crucible. Clean out the crucible after every casting to avoid dross.

Crown and Bridge - Alloy and Investments

1)  CASTING - Porosity

Porosity is normally the result of:

1. Metal too hot during casting process
2. Improper spruing

2)  INVESTMENT - Cracking

If you are having problems with CB-30 investment fracturing in the burnout furnace, try these solutions:
1. First, check the rate of climb of your furnace. Normally the rate of climb for CB-30 and most crown and bridge investments is 15°F to 20°F per minute.
2. Second, check the water powder ratio for the mixture of the investment. If you're using a special liquid with the investment, revisit and the water to special liquid ratio for the investment. Normally,with CB-30 investment you cannot use 100% special liquid.
3. Third, check the mixing time for the investment. Often if you do not allow the investment to be spatulate sufficiently it does not give the proper exothermic reaction during setting. If the exothermic reaction does not take place, the investment may be weak and therefore fracture when in the furnace, or during casting.
4. Lastly, check the bench setting time for the investment. Make sure you're following the DFU (Directions For Use) of the manufacturer and giving the investment sufficient time to mature on the bench before introduction into the furnace.

3)  INVESTMENT - Liquids

CB-30 liquid is the same liquid that is used with Microfire. The liquids are interchangeable.
CB-30 Hi-Expansion liquid is used with both CB-30 Regular and MicroFire Investments. This liquid is designed to be give more expansion then the regular liquid. Normally, this high expansion liquid is used in conjunction with casting non-precious alloys. The starting ratio for Hi-Expansion Liquid should be 50% water and 50% Hi-Expansion Liquid. At no time should you use 100% Hi-Expansion Liquid for your CB-30 or Microfire Investment. 100% concentration of Hi-Expansion Liquid may cause cracking or exploding rings in the burnout oven.

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Equipment and DEMCO

1) DUPLICATOR

A. Colloid not lasting long enough.
There may be several potential reasons:

1. Not cleaning stone from colloid after breaking-out of flask
2. Not keeping colloid hydrated after breaking-out of flask and sitting in bucket waiting to be remelted.
3. Duplicator getting too hot.

B. What is the proper cook-down temperature for hydrocolloid?
We manufacture several types of colloids, both for ethyl silicate products and all-purpose. Please consult the container for your specific material's cook down temperature. Generally, the cook down temperature for our hydrocolloid ranges from 190°F (88°C) to 195°F (91°C). The holding temperature is 130°F to 136°F.

C. How often should I replace the bearing in the bottom of my duplicator tank?
The bottom tank bearing should be examined for excessive wear each time hydrocolloid is replaced. The bearing should be changed annually to prevent excessive wear on stirrer shaft.

D. Why does my hydrocolloid turned brown only after several cook downs?
1. Hydrocolloid usually turns dark when it is overheated or aged. The cook-down temperature for most of our hydrocolloids is 190°F (88°C) to 195°F (91°C).
2. When using direct heat colloid processor, make certain the amount of colloids inside the processor is sufficient to cover the external heating source. If the colloid inside is at a lower height than the heater the material will become super heated during cook-down and burn. This is recognizable by a burn or scorch ring around the wall of the tub. Using our processors (direct heat) cooking down hydrocolloid, the tank should always be 2/3 - 3/4 full.
3. Low temperature or holding temperature of the hydrocolloid is too high. Hold the low temperature at 130°F (54°C) - 136°F (58°C) degrees. The lower the holding temperature and the lower the cook-down temperature of the hydrocolloid the longer the life of the colloid.

E. 407311 Duplicator: The dispensing valve dropped out of the bottom of the tank.
Problem: The retaining ring that secures the valve to the tank has worn away causing the valve to drop.
Solution: This can be repaired by removing the tank assembly from the cabinet and replacing the valve assembly with part # 65394. When replacing this valve, place a small bead of silicone around the valve where it comes in contact with the tank to make a good seal to the tank, then replace the tank assembly back in the duplicator.

F. 405811 Duplicator. The temperature is not holding on the low heat setting but is working on the high heat setting.
The relay off to the side of the controller board tells the controller to set temperature. Simply remove the relay from its socket and replace it back in and out of the socket several times. This will renew the metal-to-metal connection of the relay to the controller board.

G. How do I change the tank bearing on my duplicator?

  • As always unplug the power cord to the Duplicator from its power source.
  • You will need to remove the cover assembly to have access to the bearing.
  • The old bearing can be removed by turning the bearing off the retaining screw by turning it counter clockwise until it is fully removed.
  • Clean the bottom of the tank assembly around the location where the tank baring was attached.
  • Apply a small amount of silicon cement to the bottom of the bearing, and screw it back down on the retaining screw until it is tight against the bottom of the tank.
  • Wipe away any extra silicone cement.
  • Inspect the bottom of the stirrer assembly to make sure that the stirrer is not worn away and is flat across the bottom. If the stirrer assembly is worn away, and is not flat, this will ware away the new bearing and will eventually cut the tank causing that to have to be replaced.
  • Install the top cover assembly.

2) SPINDLE

A. Demco spindle makes a high pitch squeal.

There are several causes for squeal in the spindle:
1. The tension on the belt. Belt may be too tight, there should be about 3/8 inch play in the belt when depressed.
2. Dirty Collet, clean the collet.
3. Collet out of adjustment, make adjustment on collet, may be gripping the mandrel too tightly.
4. Spindle may be worn out, return the spindle to manufacture for factory replacement of inner parts.
To check the video on You Tube CLICK HERE

B. How do I get my Demco spindle repaired?

1. Send your spindle to 413 North Pearl St.; Albany, New York, 12207
2. Make sure to enclose with the shipment a business card or letter-head stationary, with your address and business name
3. There is normally a 72 hour in-house turnaround time for spindle repairs
4. Normal repairs or rebuilds for spindles will be carried out without notification, if there are any unusual circumstances or if spindle cannot be repaired you will be notified
5. If you have an account with Nobilium, your spindle repair may be billed to that account, if you do not have an account someone will contact you to verify method of payment for the repair of your spindle

C. What is the warranty on a new OR repaired spindle?

Spindles have a 90 day warranty beginning the date received back in your laboratory.

3) DEMCO GRINDER AND DUST COLLECTOR - What is the warranty on the Demco Grinders and the D1 Dust Collector?

The Demco units are guaranteed for one year.

4) CASTING MACHINES

A. MOD4, MOD5, MODX: I hear a clacking sound is in the back of the machine as soon as the melting process starts after closing the hood. The green light turns on and off along with the clacking sound.

Answer:
The problem you describe can be caused by these issues:
1. The water pressure is low and the water pressure switch needs adjusting, the filter in the pump needs cleaning, or the water level is too low.
2. The filter is attached to the water pump and can be removed by taking off the acorn nut on the bottom of the pump.
3. The water pressure switch can be adjusted by either turning the screw on the top of the switch or turning the thumb screw under the switch depending the style switch you have.
4. Water lever should be at minimum ¾ of the tank should be full of water.
5. The lid switch is faulty and in need of replacing.

B. MOD4, MOD5, MODX: Casting arm does not spin when I drop the coil.

Answers:
Problem 1: When you drop the coil to make a casting, the coil drops to the bottom and bounces. When this happens, the switch that is activated (when the coil is at the bottom of the drop) suddenly de-activates - causing the spin relay to de-energize, thus stopping the motor from spinning. This is apparent when the casting arm lunges forward and stops.
Solution 1: When you cast, press the drop lever down by hand to see if the arm spins, if so, adjust the switch up so the coil drop will press on the switch with more force.

Problem 2: The spin relay is receiving power to its coil but the coil is not energizing.
Solution 2: Replace the coil.

Problem 3: The spin relay energizes with no spin motor.
Solution 3: Replace the spin motor capacitor or replace the spin motor.

C. Mini Mod: How do I change the Mainboard on our Mini Mod Casting machine?

  • As always unplug the power cord to the Mini Mod Casting from its power source.
  • Remove the left side panel of the machine by unscrewing the two small Philips head screws on the top part of the panel.
  • Remove the cover off the gray box by unscrewing the small Philips screws.
  • De-solder wires number 15 and 14 from G11 rectifier.
  • Remove wire numbers 84, 86, 25, 22, 025, and 23 from the terminal strip on the right hand side of the Mainboard.
  • Remove the two red wires from the terminal strip located on the top left corner of the Mainboard.
  • Remove the Yellow/green ground wire from the Mainboard by removing the small Philips screw.
  • Remove the (4) four retaining bolts located one in each corner of the Mainboard.
  • Lift out the Mainboard and replace it with the new one.
  • Replace all retaining bolts and wires as removed.

D. Mini Mod: Why is my DC voltage indicator on my Mini Mod casting machine reading a voltage when I am not melting metal? Then when I try to melt metal to cast the machine will not melt?.
  • As always unplug the power cord or disconnect power to the Mini Mod from its power source.
  • The problem is that the bleeding resistor is burnt out and needs to be replaced.
  • This resistor is attached between the JCR relay and terminal #22.
  • To replace this resistor, remove the right side access panel from the machine.
  • The JCR relay is the last relay to the rear of the machine.

E. Mod4, Mod5, ModX: How do I replace a Melt Switch/Potentiometer on my Modular 4 casting Machine?

  • As always unplug the power cord of the Casting from its power source.
  • Remove the retaining screws that hold the front panel attached to the machine.
  • Remove the black knob from the top of the Melt switch by using a 3/23 Allen wrench.
  • Remove the 7/16 retaining nut from the top part of the Melt switch by turning the nut counter clockwise until fully removed.
  • Drop the switch down from its retaining hole, being careful not to lose any of the washers.
  • Remove one wire at a time from the old switch, attach that wire to the new switch in the same location it was removed from. The new switch should have attached to it, new wires with butt splices added. Attach the old wire to the butt splice and crimp it to make the electrical connection. Do this to all remaining wires one at a time.
  • Add the washers from the old switch to the new stitch and install in place making sure wires from the switch do not short out on the frame of the machine.           Note: If you arrange the switch so that the three wires attached to the side of the switch point at 7 8 and 9 O’clock position before tightening the switch in place there will be no possibility of shorting the switch out.
  • Attach the black know to the switch and tighten in place lightly. Turn the black knob counter clockwise until the switch clicks into the off position.
  • Loosen the knobs set screw and turn the knob so the pointer points to 0 or the last line, then tighten the knob in place securely with the set screw.
  • Install the front panel using the screws removed.
  • Apply power and test the machine for melt power
F. Mini Mod: I have AC voltage on my Mini Mod casting machine but have no melt of the metal when the melt switch is pressed.

The problem you describe usually is caused by one thing as follows:

  • As always, remove the power source to the casting machine before performing any service to this machine.
  • The most typical cause to this problem is a loss of electrical connection to the melting coil.
    • Check to make sure you have a good connection between the brushs and the coper electrode of the White resin cap.Mini_mod_casting_machine_resin_cap
    • This connection should be clean with no impurities between them. Is dirty, clean the connections with 600 grit paper
  • The fins of the melting coil are shorted out electrically to one and another.
    • There should be no layer of copper fins touching an adjacent set, nor should a copper fin touch any metal of the casting arm.Mini-Mod_copper
    • Use a mirror to check this often, the copper fins should look like the above picture; if not gently move the fins to achieve no shorts.
  • Metal splashed inside the coil assembly shorting out the fins.
    Mini-Mod crucible holding plate
    • You can see in the above picture, metal has shorted out the copper fins of the air cooled melting coil.
    • This material needs to be remover so as to leave no shorts. Then investment or furnace patch material used to insulate the copper fins from the crucible area. This insulation should be maintained at all times and replaced when chipped away.

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FlexStar Flexible Partials

1)  FINISHING - What is the ideal combination of burs, stones, abrasives to get a quick high shine finish?

Use FlexStar finishing kit (item 24000P9) and finish with pumice and a rag wheel. Second, tripoli. For final buff, use Shining Star Hi-Shine (item 301) to get a nice glossy shine with minimal effort.

2)  POROSITY-This is usually caused by HEAT.

What is your oven temperature set at? (550 degrees) Have you checked to see that temperature is correct? Are you heating your flask? (room temperature) If these questions are all answered correctly-ask them how many sprues are you using and what is the diameter? If 3 sprues are being used-the material may be flowing in too quickly and this can also cause porosity. 2 sprues at approximately 6-7 mm in diameter are sufficient.

3)  CARTRIDGE DID NOT POP-This is usually caused by the material not being melted.

Is your cartridge sleeve being preheated for 15 minutes? Any subsequent injections 10 minutes. Is the crimped end toward the flask when injecting. Are you using the bronze disc? If doing all these things correctly and cartridge still will not pop, double check the oven temp and see if it is correct. If everything is still good-retighten the springs on top of the injector. These sometimes will loosen. As an additional measure-you can place a crisscross with a blade knife over the cap end of the cartridge to help it inject. Lastly, your heating furnace may not be delivering the required heat. Use a temperature probe to measure the actual heat being delivered inside the cartridge furnace.

4)  MATERIAL DID NOT FLOW THROUGH TO LABIAL OR BUCCAL

Make sure there was atleast 1 mm space underneath the necks of the teeth.

5)  COLOR INCONSISTENT

This is caused by heat. Either the temperature set too high-or being left too long in the oven will cause the color to change or lighten. The pigments are food-grade and will tend to "burn-out" if heated too long.

6)  SOFT CARTRIDGE - Using the Success System

Success is a Trademark of Dentsply International

POROSITY- Caused by heat. Do not pre-heat the flask. Make sure temperature is at 550 degrees and that only 2 sprues are being used. PSI should be at 90 lbs of pressure.

MATERIAL LOCKING AROUND PISTON- Make sure flask is not heated and times and temperatures are correct. Make sure air pressure is 90 PSI. Double check that cartridge sleeve is held completely vertical. If all these things are correct- we have some specially milled piston heads that can replace the piston heads normally used. It will make it easier to clean the material off-and may eliminate this from happening all together. Some labs have reported using the thin bronze disk with success.

7)  FLEXITE SYSTEM - Cartridge will not inject

Flexite is a trademark of Rapid Injection Systems

This can happen if the material is not melted completely. With this system, several cartridge sleeves are loaded into the oven and it may take longer for the material to melt. Try heating the cartridge sleeve at 14 minutes. As an additional measure-you can place a crisscross with a blade knife over the cap end of the cartridge to help it inject.

8)  FLEXIBLE PARTIALS - I'm getting a seam in my Flex Star, it looks like the material does not join.

Seams or folds may be caused by:

1. Improper time and temperature, processing the material. Review processing times and temperatures for the oven, 15 minutes preheating the oven; 12 minutes heating the cartridge prior to injecting.
2. Oven temperature incorrect, should be 550 F (290 C) when heating the cartridge.
3. Separating material not completely dry. Make sure the separating medium is completely dry before closing the flask for injection.

9)  FLEXIBLE PARTIALS - Can I use WD-40 as a lubricant spray on cartridges?

NO! WD-40 is a flammable material. WD-40 will build-up on the walls of the heating sleeve making insertion difficult.

 

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Partial Dentures - Chrome Cobalt Technique

1)  CASTING - Incomplete framework

The most likely problem is that the alloy was not hot enough.
Incorrect spruing

2)  CASTING - Porosity

Porosity can be caused by several issues:
1. Metal is too hot when casting
2. Improper size sprues used
3. Investment particles flowing into the mold
4. Dirty crucible
5. Using lead on the refractory model
6. Debris in your wax or dipping pot-getting carried into the mold

See website for Nobilium partial denture technique. Look for Nobilium alloys, and then click on DFU (Directions for Use).

3)  PARTIAL DENTURES - Why are my Ethyl Silicate rings cracking during burnout?

Rings may be cracking due to:

1. By passing low fire stage.
2. The rate of climb for low fire is too fast.
3. The low fire temperature may be too high.

4)  PARTIAL DENTURES - What is the maximum temperature refractory model may be dried?

1. The maximum temperature for the dehydration process is 450 degrees Fahrenheit.
2. Thermal expansion for most investments begins at 500 degrees Fahrenheit. If you are taking the investment to 450 degrees Fahrenheit make sure the oven is properly calibrated. Otherwise, you will wax the framework on a model that has begun the thermal expansion process.

5)  PARTIAL DENTURES - Can I use Investic to cast Chrome Cobalt Alloy?

Investic is a Gypsum Bonded investment, which has a 1500-1550 degrees Fahrenheit threshold before it begin to breakdown. Chrome cobalt burnout temperature is between 1800-2100 degrees Fahrenheit. Oxy-Phosphate and Ethyl Silicate investments are designed to withstand these temperatures, Gypsum Bonded Investment will not.

6)  PARTIAL DENTURES - How often should I change the sand in my sandblaster?

This is a difficult question to answer, as it has a lot to do with how often you use your sandblaster. For those using the sandblaster on a daily basis for removable partial dentures, 3+ frames daily, you probably should change your sand once every 6-8 months. For those doing more frameworks daily, you might want to consider a different schedule, changing the sand perhaps once every 2-3 months. The bottom-line line is that you want to change the sand in your sandblaster on a regular basis to make it more efficient when processing your frameworks.

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Partial Dentures - Nickel Chrome Technique

1)  PARTIAL DENTURES - Can I use Investic to cast Chrome Cobalt Alloy?

Investic is a Gypsum Bonded investment, which has a 1500-1550 degrees Fahrenheit threshold before it begin to breakdown. Chrome cobalt burnout temperature is between 1800-2100 degrees Fahrenheit. Oxy-Phosphate and Ethyl Silicate investments are designed to withstand these temperatures, Gypsum Bonded Investment will not.

2)  PARTIAL DENTURES - My stone duplicate models are taking longer to set-up in the hydrocolloid. The surface is coming out soft, chalky and lack detail, what is the problem?

Several reasons for stone and oxy-phosphate models to give this appearance;

1. Taking longer for the investment or stone to set-up may be directly related to the water temperature use to chill the hydrocolloid. Water bath should be about 55 degrees Fahrenheit; therefore, the colloid should be at that temperature when pouring the gypsum or oxy-phosphate material. The colder the temperature of the colloid the longer it will take gypsum and investment to set properly.

2. Chalky , soft and smudged surfaces may be due to;
a. Insufficient set time
b. Colloid temperature too cold
c. Improper liquid powder ratios
d. Insufficient mixing time of the gypsum or investment material

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Acrylics - Impak

1)  LATEX ALLERGY - I have a patient that is allergic to latex. I delivered an Impak Denture and she had an allergic reaction. Could she be allergic to the latex in impact?

Impact does not have latex in its composition. It is an ethyl-methacrylate.

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