ISO 11953 Dentistry - Implants - Clinical Performance of Hand Torque Instruments

The standard “ISO 11953 Dentistry - Implants - Clinical performance of hand torque wrenches” developed by the International Organization for Standardization (ISO) describes a classification system for hand-held torque wrenches designed for clinical use. This standard includes performance requirements for accuracy, reproducibility and resistance to remachining. This standard describes test methods and specifies marking and labeling requirements. However, this standard does not cover electronically controlled devices.

For the purposes of this standard, in addition to the terms and definitions given in ISO 1942, the following apply:

• Hand torque tool refers to a hand-operated mechanical device used for tightening dental implants or parts of a dental implant system by indicating or limiting the rotational force of the tool.
• Use refers to the sequence of squeezing and re-squeezing followed by reprocessing (including disassembly, cleaning, disinfection or sterilization) in accordance with the manufacturer's instructions.

Screw-retained joints are secured by a compressive force resulting from the amount of tension in the screw. Each screw has an optimum value. Torque control using a hand-held torque tool fitted with a screwdriver tip is the most commonly used method in implant dentistry. Commonly used mechanical devices use the following methods for torque control.

The classification in the ISO 11953 standard is made as follows:

• Type 1: These devices have a preset break mechanism. The break mechanism design includes a hinge located near the center long axis of the screwdriver bit or a clutch located around the long axis of the screwdriver bit. The locking mechanism is held firmly by a compression spring acting on a cam or clutch designed to unlock at the desired torque, allowing the handle to bend or slide (break point). In this way, it indicates to the operator that the desired torque has been achieved. Therefore, the device provides both tactile and auditory feedback to the operator.
• Type 2: These devices operate like Type 1 but have an adjustable compression spring that allows the value of the breakout torque to be selected.
• Type 3: These devices have a similar configuration to Type 1, but instead of a rupture mechanism, they incorporate a torque beam. This beam is linearly deformed in response to applied torque, which can be measured by the operator using a scale built into the device.
• Type 4: These devices house the torque limiting mechanism in a housing with an output shaft designed to mate with a specialized counter-angle tooth handpiece. A suitable screwdriver bit is inserted into the handpiece and torque is applied by rotating the torque applicator housing until the drive is disengaged by the torque limiting mechanism. Both tactile and auditory feedback is provided.

When tested in accordance with this standard, the accuracy and repeatability of the breaking torque or specified torque shall be within the manufacturer's stated specification. For compliance, all values, both initial and after reprocessing, shall be within the specified range. The number of uses before the device must be recalibrated or discarded shall be specified by the manufacturer.

When testing Type 1 and Type 4 devices, the tightening device is attached and applied to the prosthetic screw. It is rotated until the desired torque is reached. The drive shaft is rotated in the reverse direction until the device is unloaded and then tightened again. The tightening/torque release sequence is repeated twenty times or as many times as appropriate, and the torque achieved at the point of failure at the end of each sequence is recorded.

When testing Type 2 and Type 3 devices, the procedure for Type 1 devices is applied at the minimum and maximum torque settings specified by the manufacturer. For Type 3 devices, this is the point at which the scale indicates the desired torque derived from closing the electrical contact.

Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “ISO 11953 Dentistry - Implants - Clinical performance of hand torque instruments” standard with its trained and expert staff and advanced technological equipment.