Three-Dimensional Analyses of Surface Morphology of Posterior Paediatric Zirconia Crowns

Background: Paediatric zirconia crowns for primary teeth were introduced in the market. They have fulfilled the increased esthetic desires of paediatric patients and their parents. The purpose of this study was to evaluate surface morphology of posterior paediatric zirconia crowns and to compare with surface morphology of posterior stainless steel crowns (SSCs) using digitalized 3-dimensional reconstructed images.

Methods: Paediatric zirconia crown (NuSmile ZR crown; Orthodontic Technologies, Houston, Texas, USA) and SSC (KIDS CROWN; Shinhung, Seoul, Korea) used for left maxillary and mandibular molars were tested. Lab scanner (Rainbow scanner; Dentium, Seoul, Korea) was used to record digital scans of the inner and outer surface morphologies of both crowns. And obtained data were evaluated and superimposed by 3-dimensional analysis software (Gom Inspect 2017, GOM, Braunschweig, Germany). The 3-dimensional discrepancy between the outer and inner surface for each crown was measured.

Results: The discrepancy differences between paediatric zirconia crowns and SSCs differed by tooth surfaces. In the occlusal surface, the differences between two crowns were greater at the cusp tip than on the fossa. At the axial level, the differences between two crowns were decreased toward areas close to the gingival margins.

Conclusions: Tooth preparation for paediatric zirconia crown needs special considerations. Greater amounts of tooth reduction are necessary for posterior paediatric zirconia crowns compared to posterior SSCs. Especially, greater amounts of tooth reduction in occlusal surface are required than axial surface and gingival margin.