Evaluation of Nickel and Titanium Releasing from Titanium-coated Stainless Steel Crowns Regarding Trimming: An In Vitro Study

Abstract

Introduction

Stainless steel crowns (SSCs) are the most durable and effective restorations for primary teeth. Titanium-coated SSCs are newer on the market, and this study was conducted to assess the amount of nickel (Ni) and titanium ions released from titanium-coated SSCs, with and without trim, in artificial saliva.

Materials and methods

A total of 60 titanium-coated SSCs were divided into two groups—group I (n = 30, without trim) and group II (n = 30, with trim) and were immersed in 5 mL artificial saliva. The amount of Ni and titanium released in each group was measured by inductively coupled plasma-mass spectrometry on days 1, 7, and 21.

Results

The amount of Ni ion released in group I on day 1 was 0.0096 ppm and reduced on day 7 (0.0091 ppm) and day 21 (0.0088 ppm). Whereas the amount of Ni ion released in group II was the same for all 3 days (0.0096 ppm). The amount of titanium ion released in both groups was the same on all 3 days (0.00108 ppm).

Conclusion

There was no significant difference seen in the mean Ni and titanium ion release between the two groups on all 3 days. The cumulative release of metals from titanium-coated SSCs in each of the groups was significantly lower than the level required to produce any harmful effects. Any of the groups of commercially available SSCs can be used in pediatric dentistry.

How to cite this article

Biradar R, Siaddaiah SB, Bhat PK. Evaluation of Nickel and Titanium Releasing from Titanium-coated Stainless Steel Crowns Regarding Trimming: An In Vitro Study. Int J Clin Pediatr Dent 2024;17(5):524-527.

Introduction

Caries is one of the most frequently seen problems in children. Stainless steel crowns (SSCs) are the most efficient way of restoring primary molars.¹

Attention to the adverse effects of dental materials used in dentistry, especially metals, has been a major concern of recent studies.^2,3 Nickel (Ni) is one of the common components used in SSCs. There isn't much research that discusses how saliva acts as a mediator and electrogalvanic current to release metal ions from SSCs.¹

Nickel has long been known as one of the causes of allergy and sensitivity⁴ and is the most common cause of allergic reactions like contact dermatitis.⁵ Titanium is considered the most biocompatible due to its corrosion resistance. However, there are studies that show the release of titanium ions in saliva.⁶

Prefabricated crowns do require trimming and adaptation to the underlying teeth, as the crown margin may interfere with crown seating or cause blanching of the marginal gingiva.¹ According to our theory, crown trimming may have an impact on the release of titanium and Ni and may even reach a critical level due to disruption of the integrity.

Titanium-coated SSCs are newer on the market, and very little research has been done on the ions released from these crowns, such as titanium and Ni. Therefore, the amount of titanium and Ni ions emitted from titanium-coated SSCs both with and without trim will be measured in this study using artificial saliva.

Materials and Methods

A total of 60 titanium-coated SSCs (Kids Golden Crowns, Shinhung Company, Korea) were used in the study. The titanium-coated SSCs were divided into two study groups— group I—without trim (30 crowns) and group II—with trim (30 crowns).

Before trimming the group II samples, a marker was used to draw a line at a distance of 1 mm from the crown margin. Each crown was cut using specialized scissors designed for cutting crowns (K-crown scissors curved, Shinhung Company, Japan). The cut margins were then trimmed using a heatless stone bur and polished using a rubber wheel. Thirty crowns from each study group were placed in centrifuge tubes containing 5 mL artificial saliva in a plastic stand, which had no contact with any metallic material during the test, and the crowns were placed in separate tubes. Each tube will be tightly closed to prevent evaporation. Two tubes containing only the artificial saliva with no crowns will be used as a control group. All the tubes will be stored at 37°C in an incubator. After 1 day, inductively coupled plasma atomic emission spectroscopy will be used to determine the concentration of titanium and Ni that have been liberated. At the end of day 1, crowns will be removed from each tube and placed in new tubes with freshly prepared 10 mL artificial saliva. All the tubes will be stored at 37°C in an incubator for a period of 1 week. Every sample will be measured, examined, and documented after 7 days. On day 21, the identical procedure will be carried out three times—crowns will be placed in an incubator, fresh artificial saliva will be replaced, and the release of titanium and Ni will be measured.

Results

In group I, the quantity of Ni ions emitted on day 1 was 0.0096 ppm (Table 1) and decreased on days 7 (0.0091 ppm, Table 2) and 21 (0.0088 ppm, Table 3), whereas the amount of Ni ions released in group II was 0.0096 ppm (Tables 1 to 3)—same on all 3 days. The amount of titanium ions released in group I and group II were 0.00108 ppm (Tables 1 to 3)—same on all 3 days. The mean did not show any discernible variation in nickel and titanium ion release between the two groups on all 3 days.

Table 1:

Comparison of mean Ni and titanium ion release between two groups after day 1 using the Mann–Whitney U test

Ion	Groups	N	Mean	Standard deviation (SD)	Mean difference	p-value
Ni	Group I	30	0.00960	0.00285	0.00000	1.00
	Group II	30	0.00960	0.00285
Titanium	Group I	30	0.00108	0.00140	0.00000	1.00
	Group II	30	0.00108	0.00140

Statistically not significant

Table 2:

Comparison of mean Ni and titanium ion release between two groups on day 7 using the Mann–Whitney U test

Ion	Groups	N	Mean	Standard deviation (SD)	Mean difference	p-value
Ni	Group I	30	0.00918	0.00300	−0.00042	0.16
	Group II	30	0.00960	0.00285
Titanium	Group I	30	0.00108	0.00140	0.00000	1.00
	Group II	30	0.00108	0.00140

Statistically not significant

Table 3:

Comparison of mean Ni and titanium ion release between two groups on day 21 using the Mann–Whitney U test

Ion	Groups	N	Mean	SD	Mean difference	p-value
Ni	Group I	30	0.00885	0.00327	−0.00075	0.11
	Group II	30	0.00960	0.00285
Titanium	Group I	30	0.00108	0.00140	0.00000	1.00
	Group II	30	0.00108	0.00140

Statistically not significant

Discussion

The British Society for Paediatric Dentistry suggests using preformed SSCs as the treatment of choice for primary molar teeth with caries involving two or more surfaces. This recommendation is made by the British Dental Association. “severe decay, big lesions, or multiple-surface lesions” are the conditions for which the American Academy of Pediatric Dentistry recommends their application.⁷

Humphrey introduced SSCs into clinical practice for the first time in 1950. These restorations can be placed with minimal technical sensitivity and are long-lasting and resistant to discoloration. The longevity of SSCs and amalgam restorations has been examined in some retrospective investigations. Consequently, these studies have shown that SSCs are superior to multilevel amalgam restorations.¹

Nickel is a material frequently utilized in the dental industry for the production of space maintainers, brackets, fillings, and crowns.^8–10 On the contrary, in the oral cavity, Ni undergoes biodegradation due to its ionic, thermal, microbiological, and enzymatic properties. Their widespread application can be attributed to the several benefits offered by Ni and chromium alloys, including their great strength, resistance to corrosion, and comparatively low cost. Because of this, their potential safety from a biological standpoint has been called into question. Burrows's research from 1986 showed that Ni is by far the most common agent that causes sensitization, attributing this to the fact that dental appliances induce Ni to leak into saliva.¹¹

Stainless steel crown shares many of the same chemical components as orthodontic braces and wires, such as iron (65–75%), molybdenum (0.6 wt%), manganese (up to 2 wt%), silicon (up to 1 wt%), and chromium (17–20%).^12,13 Dental and biomedical experts are becoming increasingly interested in learning about the adverse effects of using metallic materials, particularly biomaterials.

Clinical pediatric dentistry frequently uses prefabricated crowns for primary tooth restoration, raising concerns that the metals in the crowns could leach into the mouth and build up in the body.¹⁴ These consist primarily of iron, Ni, and chromium mixed with base metal alloys. All austenitic stainless steel alloys contain Ni to help stabilize the austenitic phase, increase the alloy's resistance to tarnish, and reduce ductility. On the contrary, chromium is added to help form the anticorrosive passivating coating on the alloy surface.¹⁵

Currently on the market, prefabricated crowns are not always perfectly adapted to the tooth being treated. Hence, it is possible that the height of the crown's margins may occasionally interfere with the seating of the crown or blanch the gingiva. In these situations, the dentist needs to “trim” the crown, which refers to narrowing the margins. According to Basir et al., due to integrity disturbance,¹ crown shearing, also known as trimming, may impact the amount of Ni released and potentially bring it to a critical level.¹

We decided to assess the impact of trimming stainless steel on Ni release because SSCs are widely used in pediatric dentistry, similar studies on SSCs and the potential negative effects of released metals are uncommon, and no research has been conducted regarding the effect of trimming on Ni release to date.

Titanium has a long history of use, is biocompatible, and is one of the most extensively used materials for dental implants. Titanium is also frequently utilized in industrial settings for paints, culinary additives, gum and candy processing ingredients, and medicinal coatings. Many implantation and fixation systems have been created in the medical industry using titanium and titanium alloys. Because titanium is used so frequently, there are concerns about the negative effects of titanium buildup and its impact on the human body. As a result, titanium's stability and potential risks need to be considered and discussed.¹⁶

Titanium is considered the most biocompatible due to its corrosion resistance.¹⁷ However, studies show that titanium ions can be released into saliva. Titanium-coated SSCs are newer on the market, and very little research has been done on the titanium and Ni ions released by these crowns. Thus, the amount of titanium and Ni ions released from titanium-coated SSCs both with and without trim in artificial saliva was measured in this study.

Studies have typically examined the accumulation of such metals in the body in vitro rather than attempting to acquire reliable data on the oral release of dental metals, as it is difficult to do so. As a result, the present investigation was carried out in vitro.

The current study utilized a total of 60 samples of titanium-coated SSCs manufactured by Shinhung Company in Korea and sold under the brand name Kids Golden Crowns. These samples were split evenly between two study groups as follows—group I consisted of crowns without trimming, while group II had a total of 30 crowns with trimming.

In the present study, the maximum release of Ni was in group I on the 1st day, at 0.0096 ppm, which significantly reduced to 0.0088 ppm on the 21st day. However, titanium release remained constant at all three intervals. The behavior of the element may change in such a way that, after the initial release of ions from the surface, a stable oxide layer may form and shield the remaining surface from corrosion.^18,19 “Corrosion” may play a role in the rise in the concentration of metallic ions in artificial saliva.

It was observed that there was no change in the amount of Ni or titanium released in group II across any of the three time intervals.

Although the release of Ni in group I was less compared to group II at all intervals, the intergroup comparison between group I and group II showed no significant difference. However, the intragroup comparison showed that in group I, the mean Ni ion emission significantly decreased from day 1 to day 21. This was not the case for group II, where it remained constant.

According to Basir et al., the hypothesis stated that we would see greater ion release as a result of alloy integrity being disturbed due to shearing the crown margins.¹

When it comes to Ni release, the graded titanium coating's major effect is to block Ni by mechanical means. This is the mechanism rendered by the coating. When titanium is coated onto SSCs, it forms a protective layer that prevents the crown from deteriorating over time. However, a coating with a total thickness of 0.9 μm cannot eradicate unprotected patches and holes, and as a result, Ni release cannot be reduced to zero.^17,18 Therefore, as trimming causes disturbance in this layer, it could have contributed to increased Ni release from group II.

In the current study, although the intragroup comparison showed a significant reduction in group I, both groups I and II released Ni and titanium ions into the medium. The World Health Organization (WHO), in 1988 and 1991, stated that 0.2 ppm/kg body weight of Ni can cause systemic manifestations.¹⁵ The release of ions in the present study was very minimal, which is not sufficient to induce allergic reactions in children.

According to the findings of this study, a measurable amount of Ni and titanium was released from titanium-coated SSCs, and the release decreased on the 7th and 21st days of immersion in artificial saliva. Because the cumulative release of metals from titanium-coated SSCs in each of the groups was significantly lower than the level required to produce any harmful effects, any of the groups of commercially available SSCs can be used in pediatric dentistry.

The minimum concentration of Ni ions required to trigger a sensitized reaction in a given person is highly variable. If the person's skin is injured earlier and is susceptible to sensitization by even small levels of solubilized Ni, then the sensitization process may proceed more quickly.

Other factors that may play a role in whether or not hypersensitivity reactions occur include pH, abrasion of the metal surface, the presence of other allergic conditions, race, age, and sex.¹⁹ For this reason, the release of metal ions such as Ni and titanium might trigger hypersensitivity reactions in individuals who are sensitive to them. Therefore, an alternative restorative material free of any contact allergen should be used for these patients. Due to the possibility of increased metal ion leaching from SSCs in saliva with an acidic pH, additional research is needed to obtain an accurate estimate of the quantity of Ni and chromium released into the mouth under various oral conditions from SSCs.

Conclusion

The mean did not show any discernible variation in Ni and titanium ion release between the two groups on all 3 days. The cumulative release of metals from titanium-coated SSCs in each of the groups was significantly lower than the level required to produce any harmful effects. Therefore, any of the groups of commercially available SSCs can be used in pediatric dentistry.

Orcid

Shakuntala B Siaddaiah https://orcid.org/0000-0002-1962-4054