Effect of Autoclave and Ultraviolet Sterilization on the Surface Topography of New and Retrieved Stainless Steel and Titanium Orthodontic Mini-implants: An in vitro Scanning Electron Microscopic Study

Abstract

Background: Orthodontic mini-implants are commonly used as temporary anchorage devices, and their potential reuse requires careful evaluation of surface changes after clinical retrieval and sterilisation. Aim: This in vitro study assessed the effects of autoclave and ultraviolet sterilisation on the surface topography of new and retrieved stainless steel and titanium orthodontic mini-implants. Methods: Thirty self-drilling mini-implants were evaluated, comprising fifteen stainless steel and fifteen titanium implants. For each material, specimens were allocated into three groups: new control, retrieved and autoclaved, and retrieved and ultraviolet sterilised, with five specimens in each group. Retrieved implants had remained in situ for at least three months. Surface topography was examined by scanning electron microscopy in the head, neck, thread, and tip regions. Six surface features—dullness, corrosion, cracks, craters, fractures, and blunting—were scored using a semi-quantitative 0–5 scale. Data were analysed using Kruskal–Wallis tests, Dunn’s post-hoc comparisons, and Mann–Whitney U tests. Results: Control specimens showed no detectable surface alterations. Both sterilisation protocols were associated with region- and material-specific changes, with the thread region showing the greatest alterations. In stainless steel implants, ultraviolet sterilisation produced greater thread corrosion, whereas autoclaving produced greater thread dullness. In titanium implants, ultraviolet sterilisation produced greater neck cracking and blunting than autoclaving. Stainless steel showed greater alteration than titanium in selected comparisons. Conclusion: Autoclave and ultraviolet sterilisation were associated with measurable surface changes in retrieved orthodontic mini-implants. Titanium showed better preservation of surface integrity than stainless steel under the tested conditions.