Dental caries is a biofilm-mediated, sugar-driven, multifactorial, dynamic disease that results in the phasic demineralization and remineralization of dental hard tissues. Even now the treatment of decayed primary teeth presents significant challenges in Pediatric dentistry. The prevalence of dental caries in children worldwide in primary teeth is 46.2% and permanent teeth is 53.8%. ^[1] Among school-going children in India, the prevalence of dental caries in primary teeth is 64 to 78%, and in permanent teeth, it is 18 to 67%. ^[2] An appropriate treatment strategy is essential to overcome such a high prevalence of disease in pediatric patients. A variety of restorative materials have been explored to date. Full-coverage restorations have demonstrated the highest success rates when compared to other treatment modalities. A retrospective study by Erica Wu et.al, (2021) showed a long-term survival rate of 2 years for primary teeth with multi-surface caries. The survival rate of teeth treated with SSC was 92.8% and with intra-coronal restoration was 80%. ^[3] A literature search by Chisin LA et.al (2018) found a success rate of 96.1% associated with Stainless Steel Crown (SSC) in primary teeth. The main reason for the failure of treatment with intra-coronal restoration was secondary caries (36.5%). ^[4]

Full coverage restorations have proven effective in managing primary teeth with extensive caries. ^[2] Previous studies have shown that crowns significantly reduce the risk of long-term failure and pain in deciduous molars. ^[5] Thus SSC were proposed as the sole restorative option for caries involving more than two surfaces in primary molars. The  SSC are durable, relatively inexpensive and minimally invasive; with a success rate of around 96%. ^[6] However, the Nickel chromium allergies associated with SSCs, and its constitution of heavy metals increases the risk of corrosion and are known to be cytotoxic, Also the esthetics is compromised which makes it unacceptable in anterior region [7]. With an increase in demand for aesthetic restorations, various tooth-coloured crowns have been introduced. Polycarbonate crowns, Strip crowns, Pedo jacket crowns, New millennium crowns, Pedo pearl crowns, Artglass crowns, Preformed Zirconia Crowns (PZC), Figaro Crowns and the recently launched BioFlx crowns (BFC).

PZC possesses numerous advantages over the conventional SSC. It is notably strong and provides excellent aesthetic qualities and biocompatibility. Additionally, PZC exhibits high resistance to wear and corrosion. ^[8] SM Alaki et al. reported that PZC accumulates less plaque, as observed during follow-up visits. ^[9] Whereas, according to Agarwal et al. SSC were better in terms of retention, gingival response, and tooth wear in opposing teeth when compared to PZC during clinical evaluation of these crowns in paediatric patients. ^[10]  BFC introduced in 2021 by Kids-e-Dental LLP, are monochromatic, metal-free crowns that resemble tooth-coloured crowns. They are made from a high-strength resin polymer commonly used in the medical device industry, offering strength, flexibility, and durability. These crowns are autoclavable and the manufacturer claims them to be comparable to stainless steel crowns in tooth preparation. Recently published and only randomized clinical trial with 12 months follow-up comparing BFC and SSC showed that the clinical performance of BFC was similar to SSC for the restoration of primary molars, with an edge over SSC in providing better esthetics. ^[11]

Akin to their clinical properties, physical and mechanical properties are an important aspect to be studied. Clinical studies to test these properties are time-consuming and difficult to perform. Thus, in-vitro studies have been proven to be valuable while carrying out such tests.

The current study aimed to determine the physical properties of BFC and compare them with SSC and PZC; as previous studies have assessed the physical properties of SSC and PZC, but not those of the recently launched BFC. The null hypothesis of this study was, there is no difference in the compressive strength, microhardness, wear, and antimicrobial resistance of BFC, PZC, and SSC.