Model:     Contact-air 632 E
Make:      KaVo
Owner:    From Vadodara, Gujarat

This service case came to us in a bizarre circumstance. Though, it came from Vadodara, Gujarat, the lead came from one of our acquaintance from a far-eastern country. With minimum idea of this antique before it could land with us, we asked it to be sent to our service centre.

Contact-air 632 is one of the earliest Multiflex coupling Air-turbine from KaVo Dental GmbH which had an open configuration cartridge. The instrument was made in West Germany around mid-1980s and was completely broken. The bearing had steel bearings and with time, both the bearings were either rusted or broken. Relatively thick red iron oxide layers had bonded to the spindle and coated over the impeller. The cartridge was soaked with paraffin-alkane based solvent to separate the bearings, spindle, and the impeller.

Spindle and impellers were recovered from the cartridge and underwent through repetitive de-rusting process. As expected, the de-rusting process lead to mass unbalance. Mass unbalance was diagnosed and found to be excessive as per our expectations. Precise diagnosis of the unbalance mass determines the amount of unbalance at 1.05 mg and its angular position. Appropriate amount of mass was needed to be removed from the impeller and spindle combination for imparting balance to the cartridge.

Mass to the tune of 980 micro-grams was removed by grinding a spherical dent with surgical accuracy on the radial surface of the impeller to bring the unbalance mass down to the permissible limit of 200 µg (0.2 mg). Final unbalance mass was a mere 70 µg (0.07 mg) to our much pleasure. Once the impeller/rotor is rectified over a repeated process of testing and fine-tuning, pair of pre-lubricated ceramic service radial ball bearings for KaVo of Myonic GmbH make were mounted.

The instrument, in its original German configuration, had the Midwest type Multiflex coupling with four pin configuration. In Indian context, most dental treatment units have simplified 2-pin type Borden couplings (One for the compressed air and the other for water inlet). Earlier, the user had to use an additional `Midwest-Borden’ converter to make it compatible to the dental chair air-turbine connection ports which had its leakage and pressure drop issues. Besides, the additional connector makes the instrument longer and thus ergonomically unsuitable.

The Borden type Multiflex coupling has been given as an option to fit into Indian dental treatment units to an otherwise three and half decade old handpiece. It improves the performance by reducing the pressure drop and bringing the handpiece to the standard length.