ISO 23298:2023

Overview - What ISO 23298:2023 covers

ISO 23298:2023 specifies standardized test methods to evaluate the machining accuracy of computer‑aided milling machines used in dental CAD/CAM systems that fabricate indirect restorations (inlays, crowns and bridges). The standard defines two normative test methods - the metal die method and the software method - and sets out requirements for test specimens, measuring apparatus, data preparation, machining, evaluation and test reporting. It replaces ISO/TR 18845:2017 and is intended for use by manufacturers, laboratories and others involved in device validation and quality assurance.

Key technical topics and requirements

• Test methods (Clause 5): Two complementary approaches
  • Metal die method (5.1) - evaluates marginal adaptability of machined restorations against precision metal dies (class II inlay, crown, four‑unit bridge).
  • Software method (5.2) - compares a scanned file of a milled restoration to a master manufacturing file using reverse‑engineering software to assess margin, intaglio and external surface accuracy.
• Target restorations: class II inlay, crown, four‑unit bridge (manufacturer‑specified selections permitted).
• Metal die specifications: removable occlusal/shoulder parts, tight dimensional tolerances (removable occlusal diameter difference ≤ 10 μm), and surface roughness S_a < 2 μm (referencing ISO 25178‑2).
• Measuring device accuracy:
  • Die measurements: devices with accuracy ≤ 2 μm (e.g., coordinate measuring machines).
  • Discrepancy measurements: devices with accuracy ≤ 5 μm (e.g., 3D measuring microscopes, displacement meters).
• Data procedures: measurement of dies, preparation of 3D (CAD) manufacturing data, machining of restorations, alignment/data analysis, and calculation of total errors.
• Reporting (Clause 6 + Annexes): required general and specific information, averaged characteristic accuracy values, and recommended report contents; flow charts and detailed measurement guidance are provided in annexes.

Practical applications & who uses this standard

• Manufacturers of dental milling machines and CAD/CAM systems - validate machine performance, develop technical manuals, and substantiate accuracy claims in instructions for use.
• Test laboratories and QA departments - perform standardized accuracy testing for product certification, R&D, or inter‑laboratory comparisons.
• Dental laboratories and clinics - inform procurement decisions and compare machine performance for clinical restoration quality (marginal fit, intaglio surface accuracy).
• Regulators and conformity assessors - assess compliance with defined test procedures and measurement traceability.

Related standards and references

• ISO 1942 (Dentistry - Vocabulary)
• ISO 18739 (Dentistry - Vocabulary of process chain for CAD/CAM systems)
• ISO 25178‑2 (surface texture measurement)
• Supersedes ISO/TR 18845:2017

Keywords: ISO 23298:2023, machining accuracy, dental CAD/CAM, milling machines, metal die method, software method, dental restorations, crowns, inlays, bridges, CMM, measurement accuracy.