Purpose: To evaluate the impact of dental materials on stress concentration and distribution in inlay restorations and the tooth. Materials and methods: A maxillary premolar model was developed to investigate the stress concentration and distribution within the inlay restorations and the tooth. The three-dimensional inlay cavity designs featured dimensions of 2.7 mm in depth, 2.3 mm in isthmus width, and 1.2 mm in gingival wall width. Three types of restoration materials were examined: conventional composite for direct inlay restorations, and full ceramic and indirect composite for indirect inlay restorations. A load of 250 N was applied to the tooth, and stress levels were quantified using von Mises stress values. Results: The highest stress concentration occurred in the direct composite restoration (371 MPa). The stress levels for the indirect composite and ceramic were 367 and 368 MPa, respectively. Within the tooth structure, stress levels measured 148 MPa for direct composite and 108 MPa for indirect composite. The ceramic restoration distributed the lowest stress values at 41.7 MPa. At the resin cement layer, stress concentrations were 19.5 MPa for direct composite, 16.4 MPa for indirect composite, and 7.17 MPa for ceramic restoration. Conclusion: The choice of restoration material influenced the stress levels in both the restoration and the tooth. Ceramics emerged as a more appropriate material for inlay restorations, while indirect composite also offered a viable alternative for inlays.

Purpose: To evaluate and compare the effects of low-level laser therapy (LLLT) and light-emitting diode (LED) therapy on osteoclastic activity in RAW 264.7 cells cultured on titanium disks. Materials and methods: This in vitro study utilized 42 titanium disks (10 mm diameter, 3 mm thickness) divided into three groups: control (n = 6), LLLT (n = 18), and LED therapy (n = 18), with each therapy applied at 2, 4, and 6-minutes durations. LLLT used invisible infrared gallium arsenide phosphide (Ga–As–P) laser diode (940 nm, 50 mW, 6 J/cm²), while LED therapy employed visible red LEDs (660 nm, 89 mW, 10 J/cm²). Osteoclastic activity was evaluated using tartrate-resistant acid phosphatase (TRAP) staining and resorption pit area analysis after 72 hours. Statistical analysis was done with one-way analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) test. Results: Both LLLT and LED therapy significantly reduced TRAP-positive cell counts and resorption pit areas. LED therapy demonstrated superior efficacy over LLLT at all exposure times, with the most notable reduction observed at 6 minutes (TRAP-positive cells: 45 ± 4; resorption pit area: 0.5 ± 0.1 mm²; p < 0.001). Specifically, LED therapy reduced TRAP-positive cell counts by 63% compared to the control (p < 0.001) and resorption pit areas by 72% at the 6-minute mark. LLLT showed a progressive decrease in TRAP-positive cells from 97 ± 8 at 2 minutes to 82 ± 7 at 6 minutes, while LED therapy achieved significantly lower values at corresponding times (e.g., TRAP-positive cells at 4 minutes: 63 ± 5 for LED vs 89 ± 7 for LLLT; p < 0.01). Conclusion: LED therapy is more effective than LLLT in reducing osteoclastic activity on titanium disks. This suggests LED therapy's potential for enhancing bone stability around implants and improving clinical outcomes. Future research should validate these results in vivo and explore optimal parameters for both therapies.

Purpose: To explore the influence of air abrasion using alumina particles in two distinct sizes (50 and 110 μm) on the bonding strength and surface characteristics of ultra-translucent zirconia bonded to enamel. Materials and methods: Twenty-eight disk specimens were created from ultra-translucent, multilayered Katana zirconia using computer-aided design/computer-aided manufacturing (CAD/CAM) milling. The samples were divided into two groups, each containing 14 specimens (n = 14): group A, which was treated with 50 μm alumina particles, and group B, treated with 110 μm alumina particles. Surface roughness was evaluated using a profilometer after surface preparation. Prior to aging, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses were performed. To replicate approximately 15 years of intraoral use, the specimens were autoclaved for 5 hours at 134°C and 2 bars of pressure. Duo-Link Universal adhesive cement was used to bond the specimens to enamel. After artificial aging, shear bond strength tests were conducted along with SEM and EDX analyses. Fracture patterns were examined using a digital light microscope. Group comparisons were evaluated through the Mann–Whitney U test. Categorical variables were expressed as counts and percentages, with the Chi-squared test employed to analyze differences between groups. Results: The shear bond strength demonstrated no statistically significant difference between group A (15.03 ± 2.77 MPa) and group B (13.99 ± 2.76 MPa), as indicated by a p-value of 0.33. However, group A exhibited significantly lower surface roughness (0.93 ± 0.04 μm) compared to group B (0.96 ± 0.02 μm) (p = 0.03). SEM of the 50 μm zirconia specimen showed a small porous, irregular surface texture with small microretentive areas and defective crack areas, while EDX revealed a higher percentage of zirconium oxide concentration (ZrO₂). In contrast, the 110 μm zirconia specimen showed large porous, irregular surface texture with defective crack areas in SEM, and EDX revealed a higher percentage of other oxides. SEM of the debonded group A and group B specimens showed cement traces spreading homogeneously over the surface with detached areas. The predominant failure modes were mixed. Conclusion: Sandblasting with 50 μm alumina particles results in bond strength comparable to that achieved with 110 μm particles, with no significant difference in performance. Both particle sizes increase surface roughness and primarily produce mixed failure modes.

Purpose: To analyze the effects of sustained-release polylactic-co-glycolic acid (PLGA)-coated melatonin microspheres on free radical injury and osteoblastic activity around dental implants. Materials and methods: Ten patients with bilateral missing posterior teeth were recruited as study participants. Twenty edentulous sites were randomly allotted to receive PLGA-encapsulated melatonin and placebo microspheres, followed by the placement of implants of dimension 3.75 × 11.5 mm. Free radical injury was assessed through the expression of the specific marker malondialdehyde (MDA) on the 15th day after implant placement. Osteoblastic activity was assessed using alkaline phosphatase (ALP) on the 30th and 90th days after implant placement. An independent t-test was used to compare the experimental and control groups. Intragroup comparison was performed by using repeated-measures ANOVA (α = 0.05). Results: The analysis of the independent t-test revealed that, on the 15th day of implant placement, MDA values were lower at the experimental sites (6.010 ng/mL) than at the control sites (9.080 ng/mL), which was statistically significant (p < 0.05), indicating lesser free radical injury with melatonin-coated microspheres. The mean osteoblastic activity was higher in the experimental group than in the control group on the 30th and 90th days after implant placement (p < 0.001). Conclusion: Locally administered sustained-release PLGA-coated melatonin microspheres reduced free radical injury around dental implants on the 15th day. ALP levels indicated improved osteoblastic activity until the 90th day. In addition to combating free radical injury, melatonin also has a positive influence on early implant healing through improved osteoblastic activity.

Purpose: The purpose of this study was to compare the accuracy of the automatic registration of digital dental casts to cone beam computed tomography (CBCT) images vs the point-based semiautomatic registration. Materials and methods: Twenty single jaws of partially edentulous patients were included. For each patient, a CBCT scan was performed, and a dental stone cast was scanned using a desktop scanner. The acquired digital data were imported into Blue-Sky-Plan software. Image registration was performed twice: the first was the automatic registration, while the second was the point-based semiautomatic registration. For accuracy assessment, three digital surface images were exported from Blue-Sky-Plan software and then imported with the same orientation into Medit Design software. The square root of the mean square of the distance measurements [root mean square (RMS)] was used to measure the deviation between the CBCT surface and the registered cast by each technique, and also between the cast alignments in the two registration techniques. A color map was used to visually assess the error distribution. Comparison between the deviation errors in both registration techniques was analyzed using the paired t-test, while inter- and intraobserver reliability were analyzed using the intraclass correlation coefficient (ICC). Results: The RMS error was 0.33 mm for automatic registration and 0.32 mm for point-based registration, with no statistically significant difference (p < 0.05) between the two methods. For the deviation between the cast alignment of the two different registration techniques, the RMS error was 0.11 mm. Both registration techniques showed strong inter- and intraobserver agreement (p < 0.05). Conclusion: The automatic registration of the digital cast image to the CBCT scan using Blue-Sky-Plan software is as accurate and reliable as the point-based semiautomatic registration technique. The automatic registration technique can be used to decrease planning steps, save planning time, and eliminate operator-related discrepancies. Clinical trial registration number: ORAD 6-3-1 (www.clinicaltrials.gov).

Purpose: The purpose of this study was to evaluate and compare the fracture toughness and marginal adaptation of polyether ether ketone (PEEK) and cast metal crowns for restoring posterior teeth using the endocrown and Richmond crown techniques. Materials and methods: Forty-two extracted permanent first molars were divided into three groups (n = 14 each): group E (endocrown), group R (Richmond crown), and the control group. Groups E and R were subdivided based on materials (PEEK and cast metal) used into PEEK endocrown (EP), cast metal endocrown (ECM), PEEK Richmond crown (RP), and cast metal Richmond crown (RCM). Standardized endocrown and Richmond crown preparations were done, and samples were randomly divided into subgroups. Restorations were fabricated, and marginal gap evaluation was conducted using two-dimensional (2D) cross-sectional analysis. After cementation, specimens were subjected to compressive stress until failure using a universal testing machine. Failure loads and modes were recorded. Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey Honestly Significant Difference (HSD) test (p < 0.05). Results: One-way ANOVA revealed significant differences in fracture toughness, with the RCM subgroup showing the highest mean fracture toughness (3530.06 N) compared to RP (2879.89 N), EP (2249.56 N), and ECM (2919.69 N). The EP subgroup exhibited favorable fractures in 71% of samples. No significant variations in mean marginal gap were observed among groups, with all mean values within clinical acceptability. Conclusion: PEEK and cast metal crowns achieved satisfactory marginal adaptation within clinically acceptable limits, ensuring effective sealing against microleakage. Richmond crowns demonstrated superior fracture toughness but were prone to catastrophic failures. Conversely, the endocrown technique exhibited high fracture toughness with a safer, more predictable failure mode. PEEK-based restorations, particularly EPs, showed promising results in terms of fracture toughness, marginal adaptation, and favorable failure patterns.

Purpose: To evaluate the surface roughness (Ra) and microhardness of bulk-fill resin-based composites (RBCs) treated with different polishing and finishing systems. Materials and methods: One hundred twenty-eight disks were fabricated with four types of bulk-filled RBCs (n = 32 each) (SDR Plus flowable, SonicFill nanohybrid, Filtek One nanofiller, and Beautifil-Bulk packable). Each group of 32 disks was further divided into subgroups of 8 disks, corresponding to each polishing and finishing system (Enhance^® PoGo^®, HiLusterPLUS, Sof-Lex™, and Super-Snap X-TREME). The Ra was assessed with a surface profilometer. Microhardness was determined using the Vickers hardness test. The surface texture was observed using field-emission scanning electron microscopy. The differences in mean Ra values and microhardness among the groups were determined using analysis of variance (ANOVA). The Tukey test was applied for post hoc comparisons. Correlations between microhardness and bulk-fill RBCs/finishing and polishing protocols were indicated by Pearson's correlation test. Results: The polishing systems had a significant impact on Ra (p < 0.001). Among the tested combinations, SonicFill 3 RBCs polished with the Super-Snap X-TREME system demonstrated the lowest Ra (0.13 ± 0.13 µm), while SDR Plus polished with the same system exhibited the highest Ra value (0.37 ± 0.10 µm). Microhardness values differed significantly among the RBC types (p < 0.001) but were not significantly influenced by the polishing systems (p > 0.05). A weak yet significant correlation was identified between Ra and microhardness (r = 0.272, p = 0.007). Conclusion: All polishing systems evaluated in this study yielded clinically acceptable Ra values for all tested RBC materials. The smoothest surfaces were achieved with nanohybrid composites polished using the Super-Snap X-TREME system. The roughest surfaces were observed with bulk-fill flowable composites polished with the same system. Despite not being specifically tailored to the tested RBCs, the polishing and finishing systems demonstrated comparable performance in achieving satisfactory Ra.

Purpose: This study evaluated the microleakage resistance of milled and 3D-printed (3DP) polymethylmethacrylate (PMMA) provisional crowns cemented with either eugenol-based or noneugenol-based cements. Materials and methods: Forty-eight extracted human molars were prepared for full coverage crowns, scanned, and standard tessellation language (STL) files were generated for crown fabrication. Milled and 3DP PMMA crowns were divided into four groups based on the cement type: group ME (milled with eugenol-based cement), group MN (milled with noneugenol cement), group PE (3DP with eugenol-based cement), and group PN (3DP with noneugenol cement). All samples underwent thermocycling, followed by immersion in methylene blue dye to evaluate microleakage. Microleakage scores were statistically analyzed using Kruskal–Wallis and Mann–Whitney U tests with Bonferroni correction. Results: Significant differences were found across groups (p < 0.001), confirming that both crown fabrication method and cement type significantly influence microleakage resistance. Group PN showed the lowest microleakage (median score: 1, mean rank: 14.88), followed by MN (median score: 1, mean rank: 19.75), ME (median score: 2, mean rank: 30.42), and PE (median score: 2, mean rank: 32.96). Post hoc analysis indicated significantly lower microleakage for noneugenol cements compared to eugenol-based cements, especially in 3DP crowns. Conclusion: Noneugenol cements, particularly with 3DP crowns, demonstrated superior microleakage resistance, suggesting their suitability for longer-term provisional applications. Milled crowns generally showed better marginal adaptation than 3DP crowns, emphasizing the impact of both crown fabrication method and cement type on marginal seal integrity.