Comparing the reliability and accuracy of clinical measurements using plaster model and the digital model system based on crowding severity

Background

This study aims to clarify whether 3Shape? digital model system could be applied in orthodontic diagnostic analysis with certainty, especially under different crowding condition. Reliability, accuracy and efficiency of 3Shape? digital model system were assessed by comparing them with traditional plaster cast.

Methods

29 plaster casts with permanent dentition were transformed into digital models by 3Shape? D800 scanner. All 29 models were categorized into mild-crowding (arch length discrepancy <3 mm), moderate-crowding (arch length discrepancy >3 mm and <8 mm), and severe-crowding group (arch length discrepancy >8 mm). Fourteen linear measurements were made manually using a digital caliper on plaster casts and virtually using the 3Shape? Ortho Analyzer software by two examiners. Intra-class Correlation Coefficient (ICC) was used to evaluate intra-examiner reliability, inter-examiner reliability and reliability between two model systems. Paired t test was used to evaluate accuracy between two model systems. Kruskal–Wallis test followed by Mann–Whitney U test was used to evaluate the measurement differences between 3 groups in two model systems.

Results

Both intra-examiner and inter-examiner reliability were generally excellent for all measurements made on 3Shape? digital model and plaster cast (ICC: 0.752–0.993). Reliability between different model systems was also excellent (ICC: 0.897–0.998). Half of the accuracy test showed statistically significant differences (p < 0.05) when digital models were compared with plaster casts. Furthermore, while assessing measurement differences between 3 groups in two model systems, the mandibular required space showed significant difference (p = 0.012) between mild crowding group (0.27 + 0.01 mm) and severe crowding group (0.20 + 0.09 mm). However, the differences were less than 0.5 mm and would not affect clinical decision.

Conclusion

Using 3Shape? digital model system instead of plaster casts for orthodontic diagnostic measurements is clinically acceptable.