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To quantify the performance characteristics of D-Lub9™ as they relate to use in a dental handpiece, an independant testing laboratory conducted Coefficient of Friction and Viscosity Index tests on D-Lub9™ and other hand piece lubricants.

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comparison of kavo to D-Lub9™

Dental Handpiece Lubricants
(November 30, 1999 Testing Data)

History
           
Increasing concern over patient safety has driven improvement in dental handpiece lubricants.  When requirements by the U.S. government’s Occupational Safety and Health Administration (OSHA) mandating autoclaving were implemented, significant increases in handpiece failure were observed as traditional lubricants failed to stand up to the high temperatures required to assure sterility. 

The challenge was to create a long-life lubricant for air-driven instruments providing for significantly improved hydrolytic stability, oxidative resistance, extended bearing life and wear protection.  It had to be designed to eliminate deficiencies inherent in the performance of other lubricants, specifically, thermal/oxidative degradation (varnish/sludge formation), oil/water emulsification leading to rust and excessive wear problems, lubricant degradation and loss due to hydrolytic insta­bility or high temperature vaporization during autoclaving. In addition, it had to be palatable and safe for use intra-orally.

This challenge was met in a relationship between a frustrated dentist and a synthetic lubrication engineer resulting in the formulation of D-Lub9™ Dental Handpiece Lubricant (distributed by High Speed Lubricants International, LLC. The unique chemistry of D-Lub9™ ensures deposit-free operation with repair intervals 8 to 12 times longer than when other lubricants are used.

Historically, satisfactory lubricants such as KaVo Spray were developed prior to OSHA Standards driven by the HIV epidemic have been found to be unable to sustain their integrity in their new role lubricating handpieces that must be autoclaved.  D-Lub9™ was developed with these challenges mindful of the following and other issues:

1. The KaVo material is composed entirely of a synthetic ester that has acceptable high temperature stability and lubricity.  However, esters are created by reacting an alcohol with an acid to produce the ester and a molecule of water:

Alcohol (R-OH) + Acid (H-R)   è     Ester + H-OH

The reaction is driven by drawing off the water from the ester side of the above equation.  What this means, however, is that if water (or steam) is added to the ester, (i.e. by autoclaving) the reaction can be driven the other way, breaking the ester back into alcohols and acids, which are poor lubricants and can be corrosive.  This process is called hydrolysis.

Ester + H-OH    è     Alcohol (R-OH) + Acid (H-R)  

To measure the hydrolytic stability of fluids, we measure the amount of acidic by-products formed.  This measurement is called the Total Acid Number (abbreviated TAN), and is conducted by the ASTM (American Society for Testing and Materials) Method D-664.  The test method is used to indicate relative changes that occur in the oil.  Acid numbers were measured upon completing the oxidation testing. The TAN values for these two products are as follows:

Acid numbers are considered to be excessive, and in many cases corrosive, if they reach the 2.0 range.  Neither product reached this level.  However, KaVo has approximately twice the acidic concentration as D-Lub9™.

D-Lub9™ contains a variety of synthetic base fluids which are much more resistant to hydrolysis and generate significantly less acidic byproducts.

2. Esters have varying degrees of emulsibility, the ability to mix with water.  The water that is “picked up” by the ester causes significant increases in bearing wear.  A study conducted by SKF Bearing found that 1% water emulsified in a lubricating fluid resulted in a 10X increase in bearing wear and shortened the bearing life by the same factor.  What this means is that if the bearing should have lasted 100 days (approximately 3 months) the bearing actually failed after only 10 days of use.  Given the small volume of lubricant in the handpieces, 1% water from the autoclaving process is easily attainable.  If the water content climbs to 5%, the failure climbs by another factor of 10, which means that in the above example the bearing only lasts one day.

Emulsibility testing is conducted by the ASTM (American Society for Testing and Materials) Method D-1401.  The test results are reported as follows:  Oil (ml) – Water (ml) – Emulsion (ml)  (time, minutes).  Forty (40)-milliliters of oil are mixed with 40 milliliters of water and then subjected to a high shear mixer for 5 minutes in a graduated cylinder.  At the end of the mixing period, the mixer is removed and the cylinder is observed until there is clear separation of the oil and water mixture.  Perfect separation would be represented by the following:
 
40 – 40 – 0 (15)            i.e., after 15 minutes, there are 40 mL of oil, 40
mL of water and no emulsion.

Our testing yielded the following:

Again, the emulsion generated by the KaVo product is due to the affinity the synthetic esters in the KaVo product have for water, which goes back to how esters are manufactured.  The emulsion of 3 ml would equate to approximately 3.75% of water, which is a significant amount as demonstrated by the bearing testing conducted by SKF.

3. Esters are not Generally Recognized As Safe (GRAS) by the U.S. FDA, nor do they meet the U.S. FDA requirements associated for ingestion (i.e. incidental food contact).  The materials used in D-Lub9™ are GRAS approved.

4. The viscosities of the products are as follows:

This indicates that D-Lub9™ maintains its viscosity (and thus its lubricating performance and fluid film thickness) better than the KaVo at operating temperatures.   

5. When reviewing the oxidation testing conducted, detailing the deposits generated by the KaVo product, please note the following:

The radial clearance, or “play”, in the turbine bearings used in dental handpieces is typically 0.0002 to 0.0006 inches, which equates to 5 to 15 μm (micron).  A human hair is 80 microns, a red blood cell is 5 microns, and a white blood cell is 20 microns.  With such small clearances, any depositing will result in significant bearing wear and failure.

In summary, although the KaVo product is produced with high quality synthetic esters, it is designed more typical of Type II, jet aircraft turbine lubricants, which have their own unique lubrication properties and requirements.  In contrast, D-Lub9™ was specifically formulated to meet the needs of the dental handpiece turbines, their unique lubrication requirements and cognizant of recent requirements associated with stem autoclaving.

Thin film thermal oxidative testing was conducted on the samples utilizing a ceramic furnace at 210°C (410°F) and aluminum pans.  The initial photos were taken after 2 hours in the furnace.  The samples were then placed back in the furnace for 6 additional hours, then removed and re-shot.  As you can see, at the two-hour mark, there is a slight darkening of the KaVo fluid with a hint of deposit beginning to develop along the rim of the aluminum pan.  At the end of the eight hours, the depositing of the KaVo material is significantly greater than that of the D-Lub9™.  This testing was similar to the Panel Coker Test. The results are significant only when conducted in a head-to-head comparison.

This depositing is significant because the clearances between the rotor and the housing in a dental hand piece are so small that this type and level of deposit will lead to shortened component life and premature equipment failure.

OXIDATION TEST COMPARISONS

Oxidation Test-Comparison after 2 hours

                        Oxidation Test-Comparison after 8 Hours

Other testing specifics are as follows:

• Coefficient of Sliding Friction

• The coefficient of sliding friction test simulates the “one-armed bandit” that we have seen used to demonstrate that “other” lubricants outperform D-Lub9™.  As has been previously discussed, sliding friction is an extreme pressure phenomenon that has nothing to do with the operation of dental handpieces.  One of the issues that should be mentioned, is that to increase the extreme pressure (EP) performance of a lubricant typically leads to increased deposits.

• In the sliding friction tests, the KaVo slightly outperformed the D-Lub9™.  This would be important if we were using this product in an industrial gearbox running at low speeds (less than 200 rpm) and extremely heavy loads.  Again, this is exactly the opposite of the operating conditions experienced by the dental handpieces and has little to do with the operation or protection required in the dental handpieces.

• Coefficient of Rolling Friction

• The loads, friction and wear experienced by dental handpieces are best represented by conducting the Shell 4-Ball testing for Coefficients of Rolling Friction. D-Lub9™ outperformed the KaVo in this test.  It should be pointed out that these numbers should not be compared to other test results due to repeatability and reproducibility variations in test equipment.  You should compare the results only when run head-to-head as in this test.

• Thin Film Thermal Oxidation Stability Test

• Thin film thermal oxidative testing was conducted on the samples utilizing a ceramic furnace at 210°C (410°F) and aluminum pans.  After 2 hours in the furnace the samples where then placed back in the furnace for 6 additional hours, then removed. At the two-hour mark, there is a slight darkening of the KaVo fluid with a hint of deposit beginning to develop along the rim of the aluminum pan.  At the end of the eight hours, the depositing of the KaVo material was significantly greater than that of the D-Lub9™.  This testing was similar to the Panel Coker Test previously run.  Again, the results cannot be compared except in a head-to-head comparison.

This depositing is significant because the clearances between the rotor and the housing are so small that this type and level of deposit will lead to shortened component life and equipment failure.