Properties of Tungsten Carbide Rings When Compressed to Failure or Cut with a Diamond Grinding Bit: A Biomechanical...

Tungsten carbide rings are increasingly popular modern jewelry items. Tungsten carbide is an extremely dense, hard metal. Previously described methods to remove tungsten carbide rings include using locking pliers to compress the ring or cutting the ring with a high-speed dental drill.

A universal mechanical testing system (MTS) machine was used to diametrically compress tungsten carbide rings 9 mm in length and 2.4 mm in thickness with a 23.4-mm outer diameter and a 21.0-mm inner diameter while measuring the force required to fracture the rings. A computer numerical control (CNC) machine was used to cut tungsten carbide rings with a diamond grinding bit with and without a flow of normal saline solution. An infrared thermal camera was used to record the temperature at the site of contact between the ring and the grinding bit and at a site one-quarter of the circumference along the ring.

A mean force with 95% confidence interval of 3.7 ± 1.2 kN was required to fracture the tungsten carbide rings via diametral compression (p = 0.05). The rings failed at a mean displacement with 95% confidence interval of 0.32 ± 0.13 mm (p = 0.05). The maximum temperature observed at the site of contact between the ring and grinding bit averaged 160.2°C including cases with and without coolant. The time to reach maximum temperature and the duration of maximum temperature differed significantly between the cases with and without coolant (p = 0.0007 and p = 0.0108, respectively).

Tungsten carbide rings fractured with minimal displacement using a small amount of force via diametral compression. The brittle fracture pattern of the rings produced minimal comminution. Tungsten carbide rings reached extreme temperatures when cut with a high-speed diamond grinding bit despite cooling with normal saline solution.

Previously documented methods to remove a tungsten carbide ring include breaking the ring by compressing it with pliers or cutting it off with a high-speed dental drill. Clinicians should be aware of potential complications of current methods to remove tungsten carbide rings.