Sleeve Material, Height, and Drill Surface Changes in Guided Endodontics: Vicker’s Hardness and Scanning Electron Microscope Evaluation

Abstract BackgroundGuided endodontic access uses a CBCT-derived template with a guide sleeve to direct the drill for precise canal location, particularly in calcified teeth. This technique is more conservative, time-efficient, and precise than conventional methods. Guide sleeves are fabricated from various materials (e.g., zirconia ceramic, cobalt-chromium alloy, titanium alloy, or 3D-printed resin), but their hardness and durability under drilling stress are not well characterized. However, guiding long, narrow drills through sleeves may generate excess heat through friction between surfaces, potentially causing tool wear. Studies in implant dentistry show significant drill wear with repeated use, but the effects of sleeve material and height on endodontic drill wear are also not well characterized. This study used scanning electron microscopy (SEM) to examine drill surface changes after guided Minimally Invasive Endodontic Access (MIEA) with different sleeve materials (resin, zirconia [Y-TZP], Ti-6Al-4V, CoCr alloy) and heights. This study evaluated Sleeve Material, Height, and Drill Surface Changes in Guided Endodontics through Vickers Hardness Test and Scanning Electron Microscope.MethodsIn vitro, 30 guide sleeves (10 sizes: 3 mm, 5 mm, 7 mm; 4 different materials) fit a 1.5 mm carbide bur with limited clearance. Sleeve materials tested in the current study are dental photopolymer resin, Y-TZP, Co–Cr, and Ti-6Al-4V. Before and after drilling, the sleeve hardness was measured through Vickers Hardness Test (HV0.2). Hardness variations (ΔVHN) were determined. A one-way ANOVA was used to assess hardness among materials and sleeve heights, with significance at p < 0.05. Additionally, three teeth were drilled under irrigation by one-group standardized high-speed carbide drills per guide. Cleaning and imaging of drill tips and flutes were done using a 1000× SEM. Two examiners rated wear as Grade 0 (no wear), Grade 1 (minor blunting or edge rounding), or Grade 2 (severe chipping or edge loss). Five drills showing noticeable thermal discoloration (“burn marks”) were included in the analysis. This study is a pilot study or an early feasibility study. The data will be analyzed using a Descriptive approach.ResultsWhile zirconia sleeves had the highest hardness rating (mean ~ 1392 HV pre-drilling; ~1389 HV post-drilling), resin sleeves had the lowest (~ 6 to 7 HV both pre- and post-drilling), while CoCr and Ti-alloy sleeves had intermediate hardness (~ 315 and ~ 405 HV). ANOVA showed significant material differences (p < 0.001), but no significant effect of sleeve height on hardness (p > 0.8). Due to modest hardness variations, drilling cycles do not strain-harden or soften the sleeve. Four drills (30%) exhibited Grade 1 wear. Six drills (70%) had Grade 2 wear. Medium and short resin sleeves showed Grade 1 wear, whereas Zirconia, Titanium, and CoCr had Grade 2. Short sleeves produced Grade 1 wear, while medium/long sleeves frequently caused Grade 2 wear. Five drills with burn marks corresponded to the Grade 2 group. Overall, Grade 2 wear was observed in 60% of drills, and Grade 1 in 40%.ConclusionsSleeve hardness was primarily determined by the material type, with sleeve height having no significant effect. Zirconia guide sleeves were harder than CoCr, Ti, and resin, and may also offer greater wear resistance and durability for guided endodontic template sleeves. All tested materials maintained their hardness after simulated guided access drilling. Guided minimally invasive endodontic access drill wear was considerable with static sleeves. The majority of the drills experienced heat burns and Grade 2 surface damage. Drill abrasion was notably increased when using resin, zirconia, and cobalt-chromium (CoCr) sleeves, attributed to their greater hardness, wear resistance, and sleeve height. While resin sleeves may help reduce wear during minimally invasive guided endodontics, the absence of an effective root canal irrigation system limits cooling efficiency. Clinicians must be aware that more rigid guides and sleeve systems may demand additional measures, such as optimized irrigation or intermittent drilling, to avoid thermal and mechanical damage. Proper selection of guide sleeves and implementation of effective cooling mechanisms are essential to the success of guided endodontic procedures.