Title	Chamfer and Rounded Shoulder Finish Lines Provide Slightly Better Marginal and Internal Fit Than Shoulder Designs for Zirconia Crowns, Though All Are Clinically Acceptable
Clinical Question	In adult patients requiring all-ceramic zirconia crowns, do chamfer or rounded shoulder margin designs, compared with traditional shoulder designs, result in improved (decreased) marginal discrepancy and internal gap?
Clinical Bottom Line	For patients requiring all-ceramic zirconia crowns, chamfer and rounded shoulder finish lines demonstrate slightly better marginal and internal adaptation compared with shoulder designs, though all preparation types remain within clinically acceptable limits (≤120 µm). This conclusion is supported primarily by two recent systematic reviews showing statistically significant but clinically small differences favoring chamfer margins. Because all included studies were in vitro and lacked long-term clinical data - the evidence is of moderate strength, and all three designs remain suitable for clinical use.
Best Evidence
PubMed ID Author / Year Patient Group Study type (level of evidence) 40383701 Sengottaiyan/2025 27 in vitro studies Systematic review of non-randomized trials Key results Preparation design significantly affected marginal and internal fit (p<0.001). Mean marginal gaps ranged from 16.2 ± 3.1 µm (chamfer) to 162 ± 14.4 µm (shoulder). Internal gaps ranged from 50 ± 6.8 µm to 100 ± 9.5 µm. Although differences are statistically significant, the effect sizes (mean differences ≤60 µm) are unlikely to affect clinical outcomes. 40611068 Pal/2025 50 in vitro studies Systematic review and network meta-analysis Key results Chamfer margins showed superior internal adaptation with a mean difference of 34.2 µm (95% CI: 6.5–63.5, p=0.020) compared with shoulder designs. Rounded shoulder designs performed similarly to chamfer margins (MD = 9.8 µm, p=0.12). Although statistically significant, the differences remain within clinically acceptable limits; thus, all finish lines provide acceptable adaptation, with minor advantages favoring chamfer. 39261857 Ashour/2024 80 crowns fabricated on 40 resin dies from premolars. In vitro. In vitro experimental study Key results Mean marginal gap values before cementation ranged from 57.8 ± 8.4 µm (chamfer), 61.3 ± 9.1 µm (deep chamfer), and 65.6 ± 7.9 µm (shoulder). After cementation, marginal gaps increased significantly across all groups (p<0.0001), reaching 94.2 ± 10.5 µm, 98.5 ± 11.2 µm, and 101.6 ± 9.8 µm, respectively. Two-way ANOVA showed no statistically significant effect of preparation design (p=0.516) or material type (p=0.269) on marginal adaptation, while cementation significantly increased gap values (p<0.0001).
Evidence Search	“margin design” OR “finish line design” OR “chamfer” OR “shoulder” OR “rounded shoulder”) AND (“marginal fit” OR “internal gap” OR “marginal adaptation”) AND (“crown” OR “fixed dental prosthesis”) Filters applied: English language, publication date 2014–2025
Comments on The Evidence	The two systematic reviews (Sengottaiyan 2025; Pál 2025) provide the highest-quality evidence on this topic and were both PROSPERO-registered and conducted according to PRISMA guidelines. Each applied structured quality appraisal tools (such as QUIN), which improved transparency and reduced bias. Both reviews reported statistically significant differences among finish-line designs, favoring chamfer and rounded shoulder preparations for marginal and internal adaptation. However, the 95% confidence intervals for mean differences (typically < 60 µm) fell well within the clinically acceptable threshold of ≤ 120 µm. The Ashour 2024 experimental study adds corroborative data, showing no statistically significant differences among preparation types (p=0.516) and mean marginal gaps below 120 µm after cementation. These findings suggest that while margin design may exert a measurable influence in vitro, the effect size is small and unlikely to alter clinical outcomes. Overall, greater weight should be given to the systematic reviews, which show consistent trends but limited clinical magnitude. The body of evidence is moderate in validity due to laboratory-based methodologies, medium risk of bias in included studies, and absence of long-term clinical trials. Future randomized clinical studies are needed to confirm whether the slight in-vitro advantages of chamfer and rounded shoulder designs translate to clinically meaningful improvements.
Applicability	All included studies were performed in vitro using extracted teeth, resin dies, or typodont models rather than actual patients. Therefore, environmental factors such as saliva, occlusal load, and intraoral temperature fluctuations were not represented. Despite these limitations, reported marginal gaps (≤120 µm) and internal gaps (≤100 µm) for all finish-line designs were within clinically acceptable ranges. The chamfer and rounded shoulder designs demonstrated slightly smaller gap values — on the order of 20–40 µm — likely due to smoother internal geometry that enhances CAD-CAM milling precision. However, this difference is clinically negligible and does not warrant changing standard practice. In the clinical setting, factors such as impression accuracy, scanner calibration, CAD-CAM system type, and cementation protocol are likely to exert a much greater influence on marginal adaptation than the specific margin design itself. Consequently, practitioners can confidently select margin designs based on esthetic, periodontal, or structural considerations rather than internal fit alone, with a modest preference for chamfer or rounded shoulder if optimal precision is desired.
Specialty	(Prosthodontics)
Keywords	Margin design, chamfer, shoulder, zirconia, fixed partial denture
ID#	3587
Date of submission	10/13/2025
E-mail	yuw2@uthscsa.edu
Author	Wendy Yu
Co-author(s)	Jeffrey Orchard, Shuto Terasaki
Co-author(s) e-mail	orchardj1@uthscsa.edu, terasaki@uthscsa.edu
Faculty mentor	Dr. Kyumin Whang
Faculty mentor e-mail	whang@uthscsa.edu
Basic Science Rationale (Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?) None available
Comments and Evidence-Based Updates on the CAT (FOR PRACTICING DENTISTS', FACULTY, RESIDENTS and/or STUDENTS COMMENTS ON PUBLISHED CATs) None available