Effect of Titanium-Nitride Coating on the Wear Resistance of Stainless Steel Crowns

Soyoung Park; Myeongkwan Jih; Nanyoung Lee; Jihan Kim

doi:10.5933/JKAPD.2025.52.4.509

J Korean Acad Pediatr Dent > Volume 52(4); 2025 > Article

Park, Jih, Lee, and Kim: Effect of Titanium-Nitride Coating on the Wear Resistance of Stainless Steel Crowns

Original Article

J Korean Acad Pediatr Dent 2025;52(4): 509-518.

Published online: November 25, 2025

DOI: https://doi.org/10.5933/JKAPD.2025.52.4.509

Effect of Titanium-Nitride Coating on the Wear Resistance of Stainless Steel Crowns

Department of Pediatric Dentistry, School of Dentistry, Chosun University, Gwangju, Republic of Korea

Corresponding author: Myeongkwan Jih Department of Pediatric Dentistry, School of Dentistry, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju, 61452, Republic of Korea
Tel: +82-62-220-3868 / Fax: +82-62-225-8240 / E-mail: mdenti@chosun.ac.kr

Funding information

This study was supported by research fund from Chosun University Dental Hospital, 2025.

Received July 24, 2025 Revised August 29, 2025 Accepted September 4, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study aimed to compare the wear resistance and surface characteristics of titanium-nitride coated crowns (TiNCs) with those of conventional stainless steel crowns (SSCs) under simulated masticatory conditions. TiNCs and SSCs for primary second molars were subjected to 200,000 cycles of wear using a chewing simulator under 50 N load with thermocycling. Volumetric wear was analyzed using three-dimensional scans before and after testing. Surface roughness and morphology were evaluated by field-emission scanning electron microscopy and atomic force microscopy. TiNCs exhibited significantly less volumetric wear than SSCs. After wear simulation, TiNCs maintained smoother and more uniform surfaces with fewer microdefects. The mean surface roughness was higher in SSCs than in TiNCs, and thermocycling alone influenced surface roughness. Compared with conventional SSCs, TiNCs exhibited superior wear resistance and surface characteristics. These findings suggest that TiNCs are a durable restorative option for primary molars under high functional stress, as their enhanced wear resistance and smoother surfaces may prolong restoration longevity and reduce replacement needs—particularly in children with parafunctional habits or strong occlusal forces.

Keywords: Titanium-nitride, Stainless steel crown, Wear resistance, Chewing simulator

Introduction

Stainless steel crowns (SSCs) are the treatment of choice for restoring carious lesions in primary teeth. Since the first application of SSCs in pediatric patients by Humphrey in 1950, they have become one of the most effective and efficient restorative options in pediatric dentistry[1]. They offer simple and cost-effective placement and have demonstrated high clinical success, partly due to their ability to protect weakened tooth structure with relatively minimal tooth reduction[2]. However, their metallic appearance is considered a major esthetic drawback.

Recently, full-coverage zirconia crowns have gained popularity as an esthetic alternative. However, they require more extensive tooth reduction and are associated with higher costs, which has limited their clinical use[3]. In response to the esthetic limitations of SSCs, a titanium-nitride coated crown (TiNC) with a gold-colored surface (Kids Golden Crown, Shinhung, Seoul, Korea) was introduced in 2019. TiNCs are based on the same stainless steel alloy (Fe-Ni-Cr) as conventional SSCs, with the primary difference in surface coating: SSCs are coated with a 1 μm layer of silicon dioxide, whereas TiNCs are coated with a 4 - 6 μm layer of TiN (titaniumnitride).

TiN is known not only for its gold-like color but also for its high surface hardness, excellent biocompatibility, and corrosion resistance, which have led to its utilization in various medical devices, such as pacemaker electrodes, dental implants, and nickel-titanium endodontic files[4-6]. The selection of full-coverage crowns in pediatric patients should consider not only esthetics but also strength and wear resistance. In clinical settings, restorations with high wear resistance can better withstand occlusal forces over time, helping maintain occlusal stability and lowering the risk of restoration failure, vertical dimension loss, and secondary caries[7,8]. TiN coating on SSCs improves resistance to occlusal wear and preserves surface quality, minimizing plaque accumulation and caries risk over time[9,10]. Its high surface hardness may also reduce the chance of structural compromise, such as perforation, which is reported in up to 2% of SSCs[11], unlike prefabricated zirconia crowns where no perforations have been observed[12]. The prevalence of bruxism in children ranges from 13% to 49%[13], and it is associated with increased tooth wear. Surface hardness and roughness significantly influence material wear, and harder surfaces generally show lower wear volume[14-16]. However, the coefficient of friction is affected by environmental factors (such as temperature and humidity), surface roughness (Ra), and contact area, which limit the ability to predict wear resistance based on surface hardness[17].

Previous studies on TiNCs have primarily focused on static properties, such as surface hardness, corrosion resistance, and color stability. Recently, a randomized controlled trial demonstrated favorable clinical performance and durability of TiNCs in primary molars, supporting their potential as an alternative to SSCs in pediatric dentistry[18]. However, to date, no study has compared the wear resistance of TiNCs and SSCs. Overcoming this limitation in previous studies is clinically important, as wear resistance directly influences the longevity of full-coverage restorations, maintenance of occlusal stability, and prevention of secondary caries or restoration replacement, particularly in pediatric patients with high masticatory loads or parafunctional habits. Therefore, this study aimed to compare changes in the wear volume and Ra between TiNCs and SSCs under simulated masticatory conditions, including thermocycling.

Materials and Methods

1. Specimen preparation

Twenty resin typodont teeth, specifically representing mandibular right primary second molars (A4AN-900, Nissin Dental Products Inc., Kyoto, Japan), were prepared with standardized tooth reduction to fit prefabricated crowns. The prepared teeth were scanned using a model scanner (Medit T710, Medit, Seoul, Korea). A scan powder (Snow Scan Powder, DK Mungyo, Gimhae, Korea) was applied to prevent scanning errors caused by surface reflection. The scan files were saved in STL format and imported into a dental CAD software (3Shape Dental System, 3Shape, Copenhagen, Denmark), where a customized die was designed beneath each crown for fixation in the chewing simulator.

The designed dies were printed using a 3D printer (IMD-C, Carima, Seoul, Korea) with a printing resin (Mazic D Temp, Vericom, Chuncheon, Korea) (Fig. 1A). Thereafter, the dies were cleaned in an ultrasonic cleaner (Form Wash, Formlabs, Somerville, MA, USA) filled with isopropyl alcohol for 20 min and then post-cured in a light-curing unit (CL 300 Pro, Carima) for 6 min. Ten each of SSCs and TiNCs of the same size were cemented onto the respective dies using a glass ionomer luting cement (Riva Luting Cement, SDI, Victoria, Australia) (Fig. 1B, 1C). The cement was dispensed to fill approximately two-thirds of the internal crown volume, and any excess cement was removed with a dental explorer. The cement was self-cured according to the manufacturer’ s recommended working and initial setting times. The sample size of 10 specimens per group was determined with reference to previous in vitro studies evaluating the wear resistance and surface roughness of full-coverage crowns, which reported this number to provide sufficient reproducibility and statistical comparison[3,19]. All specimens were stored in distilled water at 37°C for 24 h before testing[3].

2. Two-body wear test (chewing simulation)

To evaluate wear induced by direct contact between surfaces, a two-body wear test was conducted using a chewing simulator (TW-D811, Taewon Tech, Bucheon, Korea). Specimens were fixed in the lower frame, and 5 mm diameter steatite balls were mounted as antagonists in the upper frame (Fig. 2). The simulation settings are described in Table 1. To simulate masticatory function, a vertical load of 50 N was applied along with a 1.0 mm lateral movement. The 50 N load corresponds to the average physiological occlusal force (approximately 5 kg) [20]. A total of 200,000 cycles were applied to simulate approximately 1 year of clinical use[21,22]. Thermocycling between 5 and 55°C was performed simultaneously, with 30 second dwell times at each temperature. Specimens were regularly inspected for damage during testing, and digital scanning was performed before and after the wear simulation.

3. Measurement of the wear volume

Pre- and post-wear STL files were superimposed using Dentbird Studio (Imagoworks Inc., Seoul, Korea), and a color difference map was generated to visually compare the amount and distribution of wear between the TiNCs and SSCs (Fig. 3A, 3B). The aligned files were imported into 3D Builder (Microsoft, Redmond, WA, USA), where the worn regions were isolated using the “subtract” function (Fig. 3C). Noise was removed, and mesh quality was refined using Meshmixer (Autodesk, San Rafael, CA, USA). Finally, the processed STL files were imported into Rhino 8 (Robert McNeel & Associates, Seattle, WA, USA), and the “volume” function was used to calculate the wear volume (mm³).

4. Surface analysis of worn crowns

Field-emission scanning electron microscopy (FE-SEM, SU 8600, Hitachi High-Tech Corporation, Tokyo, Japan) was employed to evaluate surface characteristics. One representative specimen from each group was selected for the analyses of worn and unworn surfaces for microstructural features, wear patterns, cracks, and physical damage.

To quantitatively analyze the effects of wear and thermocycling on crown surfaces, atomic force microscopy (AFM, XE-100, Park Systems, Suwon, Korea) was performed. The AFM analysis was conducted in the contact mode, and nanometer-scale surface topography was visualized in 3D. Ra was measured on (1) pre-experimental, (2) unworn and thermocycled, and (3) worn and thermocycled surfaces. For each condition, three different points on three specimens were measured, and the average Ra was compared.

5. Statistical analysis

All data were analyzed using IBM SPSS Statistics version 29.0 (IBM Corp., Armonk, NY, USA). The Mann-Whitney U test was used to compare wear volumes between the SSC and TiNC groups. Differences in Ra among the three surface conditions within each crown type were analyzed using the Kruskal-Wallis test, with post-hoc comparisons performed using Dunn’s test and Bonferroni correction. The Mann-Whitney U test was also applied to compare roughness between the two crown types under identical surface conditions. A significance level of 0.05 was adopted for all statistical analyses.

Results

1. Wear volume

The mean and standard deviation of the wear volume for each group are presented in Table 2. Statistical analysis revealed that the TiNC group exhibited significantly lower mean wear volume compared to the SSC group (p= 0.041).

2. SEM analysis

At 40× and 150× magnifications, the SSC surfaces exhibited wide areas of irregular wear with heterogeneous grooves, whereas TiNC surfaces maintained relatively uniform and smoother patterns with fine textures and shallow cracks (Fig. 4A, 4B, 4E, 4F). At 1000× magnification, the worn SSC surfaces showed more microcracks and particle detachment, whereas the TiNC surfaces presented fewer microcracks and minimal particle loss (Fig. 4C, 4G). For the surfaces exposed only to thermocycling (not wear), SSCs appeared rougher and less homogeneous than TiNCs, which maintained a smooth and consistent surface (Fig. 4D, 4H).

3. Surface roughness

In the visualized 3D surface images, an increase in surface roughness was observed on specimens exposed only to thermocycling compared to the pre-experimental surfaces, and an even rougher surface was noted when both thermocycling and wear were applied (Fig. 5). The mean surface roughness values are summarized in Table 3. Under all surface conditions, SSCs exhibited significantly higher average roughness than TiNCs (p < 0.001, Mann-Whitney U test). In the TiNC group, statistically significant differences in surface roughness were observed among all three surface conditions (p= 0.03). In the SSC group, the worn and thermocycled condition differed significantly from the other two conditions, while there was no statistically significant difference between the pre-experimental and unworn and thermocycled surfaces.

Discussion

In this study, TiNCs exhibited significantly lower wear volume and Ra than SSCs under all experimental conditions. TiNCs have higher surface hardness than SSCs[23], and Archard’s theory states that the wear resistance of metallic materials is directly proportional to their surface hardness[24]. A study reported that SSC failure is often associated with fatigue cracks and occlusal perforation[25], which are related to the susceptibility of metals to fatigue under repeated cyclic loading. Repetitive loading can also lead to plastic deformation on the occlusal surface, thinning the surface gradually and resulting in perforation. Considering that surface hardness reflects resistance to plastic deformation, similar mechanisms may explain the irregular wear patterns and microcracks observed on SSC surfaces. An increase in Ra may also expand the actual contact area, thereby increasing the coefficient of friction and wear amount[26]. In this study, TiNCs demonstrated consistently lower Ra than SSCs across all conditions, supporting their superior wear resistance as reported previously. The oral environment is exposed to frequent temperature fluctuations throughout the day, and repeated thermal stress may occur at the interfaces of materials with varied thermal expansion coefficients. The resulting microcracks or stress concentration areas can serve as initiation sites for wear or fracture, and heat-induced fatigue may lead to changes in the Ra[27]. In this study, the Ra increased in TiNCs even under thermocycling-only conditions, indicating that structural changes may occur from thermal fatigue even in the absence of mechanical wear. Thermal expansion and contraction of the metal surface can trigger microcracks and roughening. Although thermocycling may reduce wear in certain materials, it may increase wear or have no effect at all in others[28-30]. Continuous water circulation can also reduce the polishing effect of wear debris acting as a third-body abrasive by flushing the contact area between the stylus and specimen surface[21].

To minimize variability, 5 mm steatite balls with uniform shape and mechanical properties were used as antagonists, as they are widely adopted in standardized chewing simulation studies for providing a consistent contact area and load distribution[3,19,31,32]. Steatite offers intermediate hardness between dental ceramics and natural enamel, ensuring repeatable wear patterns while minimizing specimen variability[15,33,34]. Although steatite differs from enamel in terms of surface hardness and roughness[15,33,35], it offers standardization and enhances reproducibility in vitro. Natural enamel reflects clinical conditions more accurately but introduces heterogeneity in structure and morphology, making standardized testing challenging[34]. Recently, volumetric analyses using digital 3D scanners have gained attention as a more precise method for evaluating wear. Medit T710, a scanner with clinically acceptable accuracy, was used in this study[36,37]. Although scan sprays with coating thickness of 14 - 16 μm have been used to reduce reflection during metal scanning[38], this study employed a 1 μm scan powder to minimize error. However, small measurement errors may occur during alignment and digital processing, and this should be considered when calculating wear volumes. Additionally, the dies were fabricated using a 3D printer, with a composite resin material that has an elastic modulus similar to dentin[39,40], thereby providing a model that better simulates stress distribution and crown fit in clinical conditions.

The differences in wear resistance observed in this study have important clinical implications for pediatric patients requiring full-coverage restorations. Crowns with higher wear resistance, such as TiNCs, are likely to maintain occlusal morphology longer, reducing replacement frequency and preserving vertical dimension in growing children. In natural teeth, wear is a gradual physiological process involving enamel-enamel or enamel-restoration contact, which typically occurs at a slower rate under normal functional loads[34]. In contrast, restored teeth—particularly those restored with materials of lower wear resistance—are more susceptible to accelerated surface degradation, loss of anatomical form, and increased plaque retention under high functional loads or in the presence of parafunctional habits[11,13]. The superior wear resistance of TiNCs observed in the present study is consistent with recent clinical trials reporting favorable durability, marginal integrity, and handling properties of TiNCs in pediatric patients[18]. This concordance between in vitro and clinical data further supports the suitability of TiNCs as a reliable option for full-coverage restorations in primary molars subject to high functional demands.

This study has some major limitations. First, it was conducted under in vitro conditions, rather than in the actual oral environment of pediatric patients. Intraoral wear is influenced by different factors such as food abrasiveness, parafunctional habits, neuromuscular force, and salivary properties[41,42]. Wear mechanisms are generally classified as two-body wear, resulting from direct contact between tooth and restoration; three-body wear, involving food or foreign particles; and nonocclusal wear from habits or toothbrushing[22]. In clinical settings, these mechanisms often act concurrently, which limits the generalizability of the in vitro results to real-world conditions. Nevertheless, this study is the first to directly compare the wear resistance and surface characteristics of TiNCs and SSCs under identical experimental conditions. However, further studies are needed to more precisely evaluate the clinical applicability of TiNCs by incorporating extended chewing cycles, natural enamel antagonists, and additional variables, such as corrosion resistance of the worn surfaces.

Conclusion

This study compared the wear resistance and surface characteristics of TiNCs and SSCs. Compared with SSCs, TiNCs exhibited lower wear volume and Ra, along with more uniform wear patterns. These properties suggest that TiNCs may serve as a durable restorative option for primary molars subjected to high functional stress. Furthermore, their enhanced wear resistance and smoother surfaces may help prolong restoration longevity and reduce the need for replacement, particularly in pediatric patients with parafunctional habits or strong occlusal forces. Further clinical studies are warranted to confirm these findings under long-term functional conditions.

NOTES

Acknowledgments

This study was supported by research fund from Chosun University Dental Hospital, 2025.

Conflicts of Interest

The authors have no potential conflicts of interest to disclose.

CRediT authorship contribution statement

Soyoung Park: Data curation, Investigation, Writing - original draft, Writing - review & editing. Myeongkwan Jih: Project administration, Supervision, Validation. Nanyoung Lee: Supervision, Validation. Jihan Kim: Conceptualization, Methodology, Software.

Fig 1.

Preparation of material specimens. (A) 3D-printed abutment, (B) Titanium-nitride coated crown (TiNC), (C) Stainless steel crown (SSC).

Fig 2.

Two-body wear test setup. A specimen is mounted in a sample holder within the wear simulation chamber, enabling controlled cyclic loading against a steatite antagonist.

Fig 3.

3D analysis of wear. (A) 3D height maps showing deeper wear in SSC (left) than in TiNC (right) after wear testing, (B) Superimposed pre- and post-wear STL files using Dentbird Studio to visualize wear loss, (C) Worn regions isolated by STL subtraction in 3D Builder for wear volume measurement. SSC: stainless steel crown; TiNC: titanium-nitride coated crown.

Fig 4.

SEM images of crown surfaces after testing. (A - C) Worn TiNC surfaces at ×40, ×150, and ×1000 magnifications showing relatively uniform wear with shallow cracks and fine textures, (D) Unworn and thermocycled TiNC surface at ×1000 magnification, maintaining smooth morphology, (E - G) Worn SSC surfaces at ×40, ×150, and ×1000 magnifications revealing irregular wear patterns, microcracks, and partial particle detachment, (H) Unworn and thermocycled SSC surface at ×1000 magnification exhibiting rougher and less uniform morphology than TiNC. TiNC: titanium-nitride coated crown; SSC: stainless steel crown.

Fig 5.

AFM images of crown surfaces after testing. (A - C) TiNC specimens: (A) pre-experimental surface with smooth topography, (B) unworn and thermocycled surface with slight roughening, and (C) worn and thermocycled surface showing moderate Ra increase but maintained surface integrity, (D - F) SSC specimens: (D) pre-experimental surface with moderate Ra, (E) unworn and thermocycled surface with notable roughening, and (F) worn and thermocycled surface displaying highest Ra values and irregular surface features. TiNC: titanium-nitride coated crown; SSC: stainless steel crown.

Table 1.

The experimental conditions of the chewing simulator

Parameter	Condition
Cold/hot bath temperature	5ºC/55ºC
Force	50 N
Cycle frequency	2.0 Hz
Number of cycles	200,000
Sliding movement	1.0 mm
Vertical movement	2.0 mm
Rising speed	20.8 mm/s
Descending speed	20.8 mm/s
Forward speed	20.8 mm/s
Backward speed	20.8 mm/s

Table 2.

Wear volume of the specimens (mm³, Mean ± SD)

	Wear volume	p value
TiNC	0.095 ± 0.025	0.041
SSC	0.211 ± 0.111	0.041

p-value from the Mann-Whitney U test. Statistically significant difference indicated at p < 0.05.

TiNC: titanium-nitride coated crown; SSC: stainless steel crown.

Table 3.

Surface roughness (Ra) values of the specimens (μm, Mean ± SD)

Surface condition	TiNC	SSC
Before the test	0.103 ± 0.021 ^Aa	0.187 ± 0.018 ^Ab
Unworn and thermocycled	0.162 ± 0.026 ^Ba	0.264 ± 0.026 ^Ab
Worn and thermocycled	0.235 ± 0.033 ^Ca	0.315 ± 0.032 ^Bb

Uppercase letters indicate statistically significant differences between surface conditions (p = 0.030, Kruskal-Wallis test followed by Dunn’s test with Bonferroni correction).

Lowercase letters indicate statistically significant differences between crown types (p < 0.001, Mann-Whitney U test).

TiNC: titanium-nitride coated crown; SSC: stainless steel crown.

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