Comparative Evaluation of Bioflx Crowns, Preformed Zirconia Crowns, and CAD/CAM Crowns—Resistant to Fracture: An In Vitro Study

ABSTRACT

The most prevalent childhood illness, early childhood caries (ECC), is frequently accompanied by severe comorbidities that have an impact on children's quality of life as well as that of their families, the community, and the medical system. Carious primary teeth have been widely treated with a variety of materials, with varied degrees of effectiveness. These materials include amalgam, glass ionomer, stainless-steel crowns (SSCs), and, more recently, zirconia and Bioflx crowns. SSC has been the gold standard for restoring carious primary molars for almost 70 years because of its affordability, longevity, and very easy process. Parents are frequently unsatisfied with SSCs' esthetic qualities, despite the technology's benefits.

In this study, we assessed the link between dimensional variation and the fracture resistance of Bioflx crowns and commercially available prefabricated primary zirconia crowns. The crowns were randomly divided into three groups. A universal testing machine was used to perform fracture tests on each sample.

Computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia posterior crowns had the greatest mean load (1413.80 ± 7.085 N), followed by preformed zirconia crowns (391.20 ± 3.564 N) and Bioflx crowns with the least mean load (104.80 ± 2.280 N). In general, the examined zirconia and Bioflx crowns exhibited the best mechanical qualities to endure the stresses of mastication.

How to cite this article

Gupta N, Ghambir N, Singh D, et al. Comparative Evaluation of Bioflx Crowns, Preformed Zirconia Crowns, and CAD/CAM Crowns—Resistant to Fracture: An In Vitro Study. Int J Clin Pediatr Dent 2025;18(6):632–636.

INTRODUCTION

Early childhood caries (ECC) is the most prevalent illness in children and is frequently associated with major comorbidities that have an impact on children's quality of life as well as that of their families, the community, and the healthcare system.¹ Caries has the potential to seriously harm tooth structure if left untreated, necessitating the restoration of one or more tooth surfaces. Further advancement may cause irritation when it affects the tooth pulp. This point may necessitate pulp treatment for the tooth, and a crown will almost certainly be necessary to cover the remaining tooth structure.² Primary teeth play a crucial role in speech and mastication, as well as maintaining room in the arch for permanent teeth. Therefore, primary molars with several afflicted surfaces, massive carious lesions, or pulp preservation should be treated as soon as possible.² Many materials, including amalgam, glass ionomer, composite resin, stainless-steel crowns (SSCs), and, more recently, zirconia crowns, have been widely employed to repair carious primary teeth with variable degrees of effectiveness.¹ For a very long time, SSC full coverage restorations were thought to be the best option for treating developmental and hereditary problems in primary and permanent molars, as well as multiple surface caries and cervical caries with exceptional durability.³ Nowadays, restoring posterior teeth with esthetic restorations is becoming more and more popular as a result of the ongoing rise in socioeconomic standards.³ With the invention of computer-aided design/computer-aided manufacturing (CAD/CAM) by Dr Francois Duret and Werner Mormann in 1997 significant advancements have occurred.⁴ These days, dental offices may immediately provide this technology, which can create (customized) entire ceramic crowns, inlays, onlays, and veneers for permanent dentition in a single session, thanks to its software. Zirconia blocks, resin ceramic, hybrid ceramic, and ceramic are among the materials utilized in CAD/CAM. Because CAD/CAM produces a high restoration survival rate with a low restoration fracture rate and long-term clinical survivability, the superior mechanical qualities of these materials validate their usage as a reliable technique for dental patients.⁴

Recently introduced, Bioflx crowns, which are flexible, strong, and customizable, are esthetically pleasing prefabricated pediatric crowns with zirconia and stainless steel crown characteristics. In comparison to conventionally accessible solutions, there is limited literature to evaluate the characteristics of Bioflx crowns and their impact on clinical results and parental satisfaction.⁵ In pediatric dentistry, dental crowns are more than just a restoration. They are essential to controlling decay, especially with cutting-edge techniques like Hall crowns, which are supported by their superiority over traditional restorations in controlling decay in primary teeth.⁶ Despite the obvious advantages, there is evidence that general dentists have an adequate understanding of the indications for SSCs, but that their actual usage in practice is very low, pointing to a knowledge gap.⁶

This article aims to assess the link between:

• Evaluate fracture resistance: Assess and compare the fracture resistance of Bioflx crowns, preformed zirconia crowns, and CAD/CAM crowns under controlled conditions.

• Material performance analysis: Analyze the mechanical properties of each crown type, focusing on how material composition affects their strength and durability.

• Clinical implications: Investigate how the findings can inform clinical practices regarding crown selection based on their fracture resistance.

• Failure modes identification: Identify the failure modes of each crown type to understand how and where they are likely to fail.

MATERIALS AND METHODS

The study was carried out in CiMEC Infralabs Private Limited, Mohan Nagar, Ghaziabad. Mandibular and Maxillary primary molar crowns were included in the study. The crowns were divided into three groups:

1. Group I: Kids-e-Dental Bioflx crown (eight sample size).

2. Group II: Kids-e-Dental preformed zirconia crown (eight sample size).

3. Group III: CAD/CAM crown (eight sample size).

The fracture resistance (Newton = N) was tested using a measured universal testing machine (UTM) (Fig. 1) with registered number (CIL/EQ/M/004) with a 90° angle at a ramp rate of 1 mm/min.

Fig. 1:

Universal testing machine

METHODOLOGY

The experimental setup involved 24 sample size of crown groups of Bioflx crown, preformed zirconia crown, and CAD/CAM crown. Each group has eight sample size. Each crown was carefully positioned within a specifically designed metallic holder. This holder ensured that the crown remained stable and securely in place throughout the testing procedure. To apply the forces onto the crowns, a lateral rounded tip was utilized. This tip was chosen for its ability to distribute force evenly across the surface of the crown, minimizing any localized stress concentrations. The force was incrementally increased until the crown fractured, at which point the value of the force at the time of fracture was recorded. The fracture resistance (N) was tested using a measured UTM at a 90° angle at a ramp rate of 1 mm/min. The samples were placed into an appropriate metallic holder, and the forces were applied onto the crowns with two different tips (chisel for anterior and flat rounded for posterior) until the crown fractured. The values were recorded at the time of fracture, and the Instron was reset after each value was recorded. Furthermore, the load was balanced, and the tip attached was returned to its starting position to ensure standardization.

Statistical analyses were performed using SPSS (IBM Corp. Released 2013. IBM SPSS Statistics for Macintosh, Version 22.0). Data were compared using one-way analysis of variance (ANOVA) at 95% confidence intervals (CIs), and a significance level of 0.05 was used. Tukey's post hoc test was used for intergroup comparisons. ANOVA was considered as there were more than two groups, and the mean value for each group was compared. Data were explored for normality by checking the data distribution and using Kolmogorov−Smirnov and Shapiro−Wilk tests.

RESULTS

In this study, a total number of 24 crowns were tested. The force required to break different types of dental crowns was measured. Failure was not noted in any of the samples; therefore, no samples were excluded. It was found that Bioflx crown had the lowest mean force of 104.80 N, followed by preformed zirconia crown 391.20 N, and CAD/CAM zirconia crown requires the highest mean force of 1413.8 N (Fig. 2).

Figs 2A to C:

Pre- and postphotos of crowns after UTM testing: (A) Bioflx crowns, after 104.8 N force; (B) Preformed zirconia crowns, after 391.2 N force; (C) CAD/CAM zirconia crowns, after 1413.8 N force

Since the mean value for Bioflx crown is minimum, the force value does not deviate that much from its mean, i.e., there is less variation, while the standard deviation (SD) value for CAD/CAM zirconia crown is maximum; it shows that the force values deviate more, so it has significant variation (Table 1). Preformed zirconia crown also has less variation in values as its mean is also low. Series 1 provides a clearer comparison between fracture load of three different crowns (Fig. 3).

Table 1:

Intergroup comparison showing mean fracture resistance of Bioflx, preformed zirconia, and CAD/CAM crowns

Sr. no.	Crown name	Mean force (N)	Standard deviation (N)
1	Bioflx crown	104.80	2.280
2	Preformed zirconia crown	391.20	3.564
3	CAD/CAM zirconia crown	1413.80	7.085

Fig. 3:

Graphical representation showing mean fracture resistance of Bioflx, preformed zirconia, and CAD/CAM crowns

DISCUSSION

Zirconia crowns offer an excellent choice for primary teeth affected by conditions such as ECC, traumatic dental injuries, and developmental enamel defects.⁶ They also deliver a visually appealing, natural look. Notably, they are well-received by both parents and children, promoting good gingival health and biocompatibility.⁶ However, significant advancements in zirconia core technology and materials in 2009 and 2012 revolutionized pediatric dentistry.⁷ These advancements demonstrated that the mechanical properties of all-ceramic crowns, particularly those made with zirconia, were on par with traditional metal−ceramic crowns. The introduction of Bioflx crowns in 2022 allows for a more forgiving fitting process due to their flexibility, which is particularly advantageous in pediatric dentistry, where patient cooperation can be limited.⁵ This flexibility means the crown can be adapted to fit the tooth with less need for precise customization, reducing the stress on both the dental practitioner and the child. Additionally, the malleable nature of the material can lead to a better fit over the contours of the child's tooth, ensuring a more comfortable and natural feeling for the patient.⁵

In recent years, pediatric zirconia crowns have gained traction as viable alternatives to SSCs and preveneered crowns. In a study comparing various types of pediatric zirconia crowns, CAD/CAM zirconia crowns exhibited the highest fracture resistance, followed by Kids-e-Dental preformed zirconia crowns. Conversely, Kids-e-Dental Bioflx crowns demonstrated the least fracture resistance among the tested options.

These findings underscore the growing popularity and efficacy of pediatric zirconia crowns, particularly those fabricated using CAD/CAM technology, in addressing the clinical needs of young patients.

In a study conducted by Al Shobber and Alkhadra,⁸ the fracture resistance of esthetic crowns was examined, specifically comparing two available commercial brands, NuSmile and Cheng Crowns, and two types of esthetic crowns: zirconia and preveneered stainless steel. The methodology involved mounting the samples onto negative replicas and cementing them before subjecting them to fracture resistance testing using an Instron model 5965 at a 90° angle and a ramp rate of 1 mm/min. The results revealed that NuSmile zirconia exhibited the highest fracture resistance, measuring at 937 ± 131 N, followed closely by Cheng crowns zirconia at 751 ± 102 N. In contrast, NuSmile preveneered and Cheng Crowns preveneered did not display significant differences in fracture resistance, with values of 482 ± 76 and 415 ± 12 N, respectively. Overall, the study concluded that zirconia crowns generally demonstrated greater fracture resistance compared to preveneered crowns.

Beattie et al.⁹ conducted a study where the fracture resistance of three different brands of primary esthetic stainless steel crowns was evaluated. The methodology involved bonding the crowns onto idealized epoxy dies using glass ionomer cement (GIC). Subsequently, the samples underwent testing using a universal testing apparatus to simulate a cusp contact environment, a ball mixture was applied to exert pressure on the samples at a ramp rate of 1 mm/min. The collected data were then subjected to a one-way ANOVA for analysis. The study revealed that the pressures required to break any of the three brands of stainless steel crowns (measuring at 1730 ± 50, 1826 ± 62, and 1671 ± 68 N) were quite comparable to one another.⁹

In December 2022, Osama and Maha conducted an in vitro study to compare the fracture resistance of prefabricated crowns (PZCpri) and custom-made crowns. The study involved subjecting both groups of crowns to increasing loads until fracture occurred. The data obtained from the experiments were then analyzed using an independent t-test to determine any significant differences between the fracture resistance of prefabricated and custom-made crowns. The results of the study revealed that the fracture resistance of prefabricated crowns was measured at 1793.54 ± 423.82, whereas custom-made crowns exhibited a fracture resistance of 1987.38 ± 414.88. This suggests that custom-made crowns demonstrated a slightly higher fracture resistance compared to prefabricated crowns, as indicated by the mean values.³

Additionally, Singh et al.¹⁰ assessed how biting forces in pediatric dentistry patients with primary and mixed dentition were affected by full-mouth rehabilitation. This study had 30 volunteers, almost equal numbers of males and females. Prior to the commencement of dental treatment and 1 month after its conclusion, each subject's maximum biting force was voluntarily recorded. Variables including gender, age, height, weight, and the degree of dental caries were taken into consideration while analyzing the data that had been gathered. Before treatment, the mean maximum force recorded by all participants was 167 N. The mean biting force of the male subjects was 175 N, while the mean biting force of the female subjects was 166 N. The subjects' biting forces were evaluated once again before the dental procedure was completed, and a mean maximum bite force of 182 N was noted.¹⁰

LIMITATIONS

• Material variability: Differences in manufacturing processes and material properties among the crowns may not be fully accounted for, affecting the outcomes.

• Testing methods: The methods used to assess fracture resistance may not replicate real-life conditions. For example, the type and direction of force applied might differ from actual occlusal forces experienced in the mouth.

• Short-term study: If the study only evaluates immediate results, it might not account for long-term durability and performance over time.

• Absence of biological factors: The study may not consider the influence of biological factors such as the periodontal environment, which can affect the longevity and performance of dental crowns.

• Lack of clinical relevance: Findings from in vitro studies may not always translate to clinical success, as factors such as patient behavior, oral hygiene, and systemic health can influence outcomes.

CONCLUSION

The study suggests that the CAD/CAM zirconia is more fracture resistant than preformed zirconia crown and Bioflx crown. Although the fracture resistance of Bioflx crown is low, it is clinically esthetic with no evidence of allergic reaction and gingival swelling.

ACKNOWLEDGMENTS

The authors would like to thank CiMEC Infralabs Private Limited, Mohan Nagar, Ghaziabad, for their support.

ORCID

Nidhi Gupta https://orcid.org/0000-0002-1086-1336

Natasha Ghambir https://orcid.org/0000-0002-1301-0502

Divya Singh https://orcid.org/0000-0003-4714-1217