DentAI – Notes on Finish Line Design and Intraoral Scanner Accuracy

This article is a consensus statement from the joint SSRD, SEPES and PROSEC conference on minimally invasive restorations, summarizing the findings of two separate systematic reviews with meta-analysis across two different areas of restorative dentistry: finish line design, and intraoral scanner (IOS) accuracy.

1. Evaluating Finish Lines (Horizontal vs. Vertical)

• Based on systematic reviews with a 3-to-7-year follow-up period, there is no significant difference in survival rate, success rate (65% to 100%), or periodontal health indices (plaque index and gingival index) between horizontal and vertical finish lines for veneers, crowns and fixed partial dentures (FPDs).
• Both finish line designs are clinically validated and citable.
• Executing vertical preparations (such as the BOPT technique) is highly technique-sensitive and requires careful case assessment and full coordination with the dental laboratory technician.
• The choice between the two approaches still has no evidence-based criterion and is made on a case-by-case basis. Factors involved in the decision include finish line location (supra-, sub- or juxta-gingival), the current and desired gingival margin position, supracrestal tissue height, embrasure space, the tooth's restorative status, material selection and contouring, and how invasive the preparation is.

2. Intraoral Scanner Accuracy for Partial-Coverage Restorations

• Intraoral scanners are considered an accurate and reliable replacement for conventional impression methods in fabricating single-unit inlays and onlays.
• The type of impression method (digital vs. conventional) shows no effect on the marginal and internal fit of inlay and onlay restorations.
• Because of the scarcity of scientific evidence, no definitive, standardized recommendation can currently be made for using intraoral scanners to fabricate veneers.
• All existing studies were conducted on single restorations, and no data is available on scan accuracy for multiple simultaneous restorations (several veneers or several inlays at once).
• To achieve maximum scan accuracy, clinical factors must be assessed before digital scanning: preparation geometry, surface finishing quality, finish line position and design, interproximal space, and the presence of build-up on the prepared tooth or an adjacent restoration. This set of factors is collectively known as scanability.
• A newer scanner generation does not necessarily lead to a better-fitting restoration, because fabrication-stage parameters also play a role in the final result.

3. Limits of the Evidence Level

The section on scanners rests almost entirely on in vitro studies, conditions in which saliva, sulcular bleeding, tongue movement and limited mouth opening space were absent. Expecting the exact same accuracy to be reproduced under real clinical conditions is not reasonable.