Impact of minimal taper canal preparation on the adaptation of glass fiber posts.

OBJECTIVES: To evaluate the adaptation of a small diameter glass fiber post in minimally prepared root canals and to compare two taper configurations (4% and 7%) within the framework of minimally invasive endodontics (MIE). MATERIALS AND METHODS: Twenty standardized resin canal models with identical internal anatomy were assigned to two groups (n = 10): Group 1 (4% taper; R-Motion, FKG Dentaire) and Group 2 (7% taper; WaveOne Gold Primary, Dentsply Sirona). Following a formal power analysis to establish sample size validity, root canals were prepared according to manufacturers' parameters and obturated using standard warm vertical compaction with an epoxy-resin based sealer (ADSEAL, Meta Biomed). Postspace patterns were fabricated using an autopolymerizing acrylic resin. A prefabricated glass fiber post (0.95 mm; Itena Clinical) served as the reference control. All experimental patterns and the reference post were scanned using a high-precision TRIOS intraoral scanner (3Shape). Digital superimposition was conducted using best-fit alignment algorithms in 3D analysis software, and root mean square (RMS) values were calculated to verify alignment accuracy. Cross-sectional post diameters were measured at five standardized levels (-5 mm--9 mm from the working length). Data normality was verified via the Shapiro-Wilk test, and differences between groups and the reference post were evaluated using Student's t-test and Wilcoxon signed-rank test (α = 0.05). RESULTS: Low mean RMS values confirmed excellent digital alignment accuracy across both groups (7% group: 0.0615 ± 0.029 mm and 4% group: 0.1496 ± 0.088 mm). At all five evaluated cross-sectional levels (-5, -6, -7, -8, and -9 mm), the canal-derived diameters were significantly smaller than the 0.95 mm reference post (P < 0.01). While the 7% taper configuration yielded significantly larger internal dimensions than the 4% configuration at all levels, neither taper configuration allowed passive adaptation of the fiber post. Consequently, none of the specimens could accommodate the reference post without secondary mechanical enlargement. CONCLUSIONS: Minimally invasive canal preparations utilizing 4% and 7% tapers effectively preserve radicular dentin structural integrity but do not provide sufficient physical space to accommodate standard small diameter (0.95 mm) glass fiber posts. To successfully bridge this gap without sacrificing the biological benefits of conservative endodontics, a balanced approach combining apical preservation with highly controlled coronal modification is required. Alternatively, the dental industry must develop reduced-taper, smaller-diameter fiber posts that match contemporary minimal-preparation file dimensions.