# Diamond‐like carbon coating enhances mechanical performance of NiTi rotary instruments: A multimethod analysis

## TL;DR

Diamond-like carbon coating improves the durability and performance of nickel-titanium dental instruments without affecting their structure.

## Contribution

Demonstrates that DLC coating enhances cyclic fatigue resistance and mechanical properties of NiTi rotary instruments.

## Key findings

- DLC-coated instruments showed significantly better cyclic fatigue resistance (p = 0.0028).
- DLC coating increased microhardness (p = 0.0019) and reduced bending load (p = 0.0294).
- Buckling strength remained unchanged between coated and uncoated instruments (p = 0.3569).

## Abstract

This study aimed to evaluate the impact of diamond‐like carbon (DLC) surface treatment on the mechanical properties of nickel–titanium (NiTi) rotary instruments.

One hundred and ten nickel–titanium instruments with a size of 25/.06 and a length of 25 mm, both with (n = 55) and without (n = 55) a DLC coating were selected and compared regarding their design (stereomicroscopy, scanning electron microscopy), metallurgy (energy‐dispersive X‐ray spectroscopy, differential scanning calorimetry), and mechanical performance (time to fracture, bending strength, buckling strength, cutting efficiency, and microhardness). Data were analysed using Mann–Whitney and independent Student's t‐test (α = 5%).

The design analysis confirmed that both instruments had identical geometric features, similar spiral and tip designs, with DLC‐coated instruments showing fewer surface irregularities and a multi‐coloured appearance. Metallurgical analysis revealed identical transformation temperatures for both groups, with the R‐phase starting at ~32°C, finishing at ~25°C during cooling, and the austenitic finish occurring at ~35°C. DLC‐coated instruments demonstrated significantly superior cyclic fatigue resistance (p = 0.0028), lower bending load (p = 0.0294), lower cutting efficiency (p < 0.0001), and higher microhardness (p = 0.0019), whilst no difference was observed in terms of buckling strength (p = 0.3569).

Diamond‐like carbon surface treatment significantly enhanced cyclic fatigue resistance, flexibility, and microhardness of NiTi rotary instruments without compromising their structural integrity.