Biomechanical Degradation of Nickel-Titanium Archwires Induced by Oral Streptococcal Biofilms: Effects on Superelastic Behavior and Force Delivery

Orthodontic arch wire, nickel–titanium alloy, Superelasticity; Tensile strength, microbiologically influenced corrosion, oral biofilm, Streptococcus mutans.

Abdalmawla Alhussin Ali Ali1*,
Assistant Professor, Department of Orthodontics, Faculty
of Dentistry, University of Sirte, Sirte, Libya,
E- mail: [email protected].

Samir Tobji2,
Laboratory of Oral Health and Orofacial Rehabilitation,
Department of DentoFacial Orthopedics, Monastir Dental Clinic,
University of Monastir, Monastir, Tunisia.

3Lamis Allegue,
Laboratory of Mechanical Engineering of Monastir,
National School of Engineering of Monastir,
University of Monastir, Monastir, Tunisia.

4Tarak Bouraoui,
Laboratory of Mechanical Engineering of Monastir,
National School of Engineering of Monastir,
University of Monastir, Monastir, Tunisia.

5Maha Mastouri,
Laboratory of Infectious Diseases and Biological Agents,
Faculty of Pharmacy, University of Monastir, Monastir, Tunisia.

Received-26-06-2026
Revised-03-08-2026
Accepted-12-08-2026

European Journal of Prosthodontics and Restorative Dentistry (2026) 34(7s), 1400–1408

Biomechanical Degradation of Nickel-Titanium Archwires Induced by Oral Streptococcal Biofilms: Effects on Superelastic Behavior and Force Delivery

Background: Nickel-titanium (NiTi) archwire is a fundamental component of fixed orthodontic appliances with superelasticity required for effective tooth movement. After insertion within the oral cavity, streptococcal species produce organic acids and extracellular polysaccharides that accelerate archwire. However, exposure to streptococcal biofilm changes the mechanical properties of NiTi archwires inadequately addressed. Objective: To assess the effect of oral streptococcal species (Streptococcus mutans, Streptococcus salivarius, and Streptococcus parasanguinis) on the mechanical behavior of (NiTi) orthodontic archwires and to demonstrate the implications of these changes for orthodontic force delivery. Materials and Methods: Forty-eight superelastic NiTi archwires were allocated to a test group (n = 24), immersed for four weeks in sterile medium inoculated with the three streptococcal species, and a control group (n = 24), immersed in sterile medium alone. Tensile tests to failure and cyclic tensile tests (1, 5, and 10 cycles) were performed at 37 °C on a universal testing machine, and the transformation stresses and moduli of elasticity were derived from the resulting stress–strain curves. Groups were compared using independent t-tests, (p < 0.05). Results: No archwire fractures occurred in either group. The ultimate tensile strength was significantly lower in the test group (991.66 ± 18.37 MPa) than in the control group (1522.00 ± 43.70 MPa; p < 0.001). Cyclic testing showed that the test group exhibited significant reductions in austenitic and martensitic moduli of elasticity and the direct and reverse transformation stresses (σMs, σMf, σAs, σAf), along with a significantly greater hysteresis (Δε) (p < 0.05). Conclusion: Exposure to S. mutans, S. salivarius, and S. parasanguinis significantly compromised the load–deflection behavior of NiTi archwires, indicating a reduced capacity to deliver the light continuous forces required for efficient tooth movement. No hydrogen-embrittlement fracture was observed, suggesting that the microbial environment altered archwire without causing failure.

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