Despite the growing adoption of 3D-printed resin materials, limited evidence exists on how clinical procedures such as scaling impact their surface integrity. This in vitro study evaluated the effect of different scaling methods on the roughness of five 3D-printed resin materials. Disc-shaped specimens from five commercially available 3D-printed crown materials (Crowntec, Varseosmile, Freeprint, Ezprint, and C&B Nextdent) were fabricated. Each material group (N = 30) was subjected to three scaling techniques: stainless-steel manual, plastic, and piezoelectric ultra-sonic scalers. Surface roughness (Ra) was quantified using a non-contact profilometer before and after scaling. One-way ANOVA was used to analyze the data. All the crowns exhibited increased roughness when treated with ultra-sonic scalers compared to the other scalers, and this was significant (p < 0.05) for all except VarseoSmile. Compared to the other crowns, Freeprint crowns (0.07 ± 0.04 µm) showed the greatest roughness change with plastic scalers, which was significant (p < 0.05) compared to C&B Nextdent crowns (0.001 ± 0.03 µm). For hand and ultra-sonic scalers, no significant differences were found among the crown types (p > 0.05). In conclusion, ultra-sonic scalers, while efficient, may increase surface roughness, potentially enhance plaque retention, and compromise prosthesis longevity.

Aim: To compare the fracture resistance of teeth with varying degrees of residual coronal dentine after restoration using two fibre-reinforced composite core materials. Materials and Methods: Seventy extracted human lower premolars were divided into four groups: sound (control), one missing proximal wall (Cl-II), two missing proximal walls (MOD), and endocrown (EC). Subgroups were restored with either a short fibre-reinforced flowable composite (EverX Flow) or an experimental fibre-reinforced composite. Except for the control, teeth underwent endodontic treatment and were restored accordingly. Fracture resistance was tested using a universal testing machine. Statistical analysis compared fracture resistance across groups. Results: Teeth in EC exhibited the highest fracture resistance (1153.43 ± 332.52 N), comparable to sound teeth (1114.03 ± 185.58 N) and not significantly different from the experimental composite group (1006.89 ± 200.51 N) (p = 0.304). Cl-II restorations with EverX had significantly lower strength (652.48 ± 314.04 N) compared to MOD (773.02 ± 261.18 N) and EC (p < 0.05). The experimental composite showed a similar trend, with MOD having the lowest strength (408.6 ± 168.85 N). Significant differences were noted between materials in the MOD group (p = 0.009). Scanning electron microscopy revealed distinct fracture patterns. Conclusions: Endocrowns using direct fibre-reinforced composites provided protection for endodontically treated teeth with higher fracture resistance compared to teeth with MOD and Cl-II cavities. This gives direct composite endocrowns a potential for high-stress applications, though design and material selection remain critical.