Who wears the crown? Comparing 3D-printed resin crowns to preformed stainless steel crowns for restoring primary molars.

Design: A multi-centre randomised controlled trial was conducted with paediatric patients requiring crowns after pulp therapy. Participants were randomly divided into two groups: Stainless Steel Crown (SCC) (n = 28) and Resin Crown (RC) (n = 28). RCs were fabricated using a 3D printer with a standardised manufacturing process. The assessment was through periapical radiographs, photographs, quantitative light-induced fluorescence, impressions, and clinical assessment. Quigley-Hein plaque index (QHI), gingival index (GI), occlusal wear, and survival were evaluated.

Case Selection: Participants were selected from two departments of paediatric dentistry at Yonsei University and Kyung Hee University of Dental College. Patients were between 4-7 years old. The tooth must require pulp therapy and crown, be in place for at least 2 years, and be in stable occlusion. Those with systemic illness, disability, poor cooperation, temporomandibular joint disorder, and bruxism were excluded.

Data Analysis: Analysis was performed at 1 week, 3 months, 6 months and 12 months. QHI and GI were compared between the two groups. Shapiro-Wilk test was used to analyse the normal distribution of occlusal wear. Comparison was completed using Mann-Whitney U and independent t-tests. Survival rates were assessed using Kaplan-Meier analysis and log-rank tests.

Results: Fifty-six teeth were included initially, with follow-up on 23 RCs and 25 SSCs due to failure or lack of attendance. RCs exhibited a statistically significant increase in wear, with mean root mean square (RMS) values of 0.064 (+/-0.02) at 3 months, 0.079 (+) at 6 months, and 0.125 (+/-0.05) at 12 months. Whereas SSCs demonstrated minimal wear, with mean RMS values ranging from 0.021 (+/-0.01) to 0.025 (+/-0.01). The QHI scores indicated no significant difference, except at 1 week where RC exhibited increased plaque. The GI scores for RCs were significantly higher at 12 months. The survival rate of RCs was significantly lower (82.1%) compared to SSCs (100%).

Conclusions: While RCs offer improved aesthetics over SSCs, they exhibit lower wear resistance and higher plaque accumulation and gingival inflammation. The survival rate of RCs is significantly lower due to fractures. The clinical effectiveness of RCs has not yet been established.