Assessment of Microbial adhesion on 3M and Kids Stainless Steel Preformed Crowns-An In-vitro Study

Introduction

Bacterial adhesion plays a considerable role in tooth decay, calculus formation and gingival inflammation [1-4]. Streptococcus mutans, which is the most prevailingmicroorganism in dental plaque of patients with active caries, plays a major role in the onset of dental caries and gingival inflammation [5,6]. Among the bacteria present in dental plaque, streptococci often show great adhesion to oral surfaces such as oral mucosa and dental structures[7]. Crowns are generally classified into four groups: partial veneers, full metals, metal ceramics, and all-ceramics[8]. Determination of suitable dental material limiting colonization of S. mutans is critical in patients at high risk of caries.

Stainless steel crowns (SSCs) were introducedby Humphrey in 1950 to pediatric dentistry. Since time, SSCs have become apriceless restorative technique for the treatment of badly broken down primary teeth. The superiority and durability of SSCs over multisurface amalgam and other restorations in the primary dentition has been documented in the literature[9]. Adhesion and colonization of oral microbes on tooth surfaces and restoratives is considered crucial in the development of secondary caries and periodontal disease[10]. In vivo and in vitro experimentshave shown that Streptococcus mutans is one of the microbes isolated in plaque samples from natural and artificial surfaces during early phases of caries development. However, it is notable that the first stage of colonization by an organism includes adherence of the organism to a host surface.

From this viewpoint, evaluation of S. mutans adhesion to tooth surfaces and restorative materials is of most importance for their success [11]. The initial adhesion and retention of S. mutanshappens through van der Waal’s attractive forces and electrostatic repulsive forces with the crown surface. Further, the microorganisms present on rough surfaces of prostheses are more ensured against shear forces which permits it to be in direct contact with them for longer periods building up an oral ecological change [12]. The higher the surface free energy, the higher will be the adhesion of microorganisms, and alternatively, the more hydrophobic the surface, the less microorganism adherence is expected[13].

SSCs are available under various brands in the market like 3M ESPE, Unitek, Rocky Mountain, ION Ni Chro. The 3M ESPE crown is the most commonly used. Marginal adaptation is required to inhibit the ingress of oral bacteria which can cause secondary caries and gingival inflammation[14].

These preformed crowns are well contoured and are accessible in different sizes for primary teeth. Alternative SSCs such as Kids crown are introduced with thin cervical margin and makes trimming and contouring simple and convenient [15]. However, the microbial plaque adhesion on these types of crowns is unknown. Hence, the study aims to evaluate the microbial adhesion on the 3M SSC and Kids crown in primary molars.

Materials and Methods

This in-vitro study was carried out at the Dental Materials Research Lab of Saveetha Institute of Medical and Technical Sciences in the month of November 2020. Ethical approval was obtained from the Institute Scientific Review Board. Ten stainless steel crowns of the first primary mandibular molar of size 6 of two commercial brands named Kids crown(Shinhung, Seoul, Korea) and 3M Stainless Steel Primary Molar Crowns(3M ESPE, St. Paul, MN, USA) were used in the study. The samples were rinsed with distilled water and autoclave-sterilized. Then, they were exposed to a typical bacterial suspension of S. mutans (RTCC1683) with a concentration of 1×106 mg/mL (0.5 McFarland standard). The specimen was immersed in a test tube of 350 mL of the bacterial suspension. The tubes were incubatedat 37°C for one hour.Then, they were all rinsed and immersed in normal saline for 20 seconds; subsequently each sample was shaken for one minute in 1mL of freshnormal saline solution;Finally, S. mutans were counted and expressed in colony forming units (CFU) (Figure 1).

Results

Two groups of 3M stainless steel crown and Kids stainless steel crown (n=10) were tested for the adhesion of S.mutans. The mean S. mutans adhesion level to 3M stainless steel crown was 5.4 ± 2.05 colonies/mm2 which was significantly lesser than that of Kids stainless steel crown with the microbial adhesion of 5.7 ± 2.47 colonies/mm2. The independent t- test results revealed that the difference between the mean S. mutans adhesion to 3M stainless steel crown samples and to Kinder stainless steel crown samples was not significant (P=0.6) (Table 1).

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Figure 1:

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Figure 1: CFU count (S. mutans) on 3M SS crown (1A) and Kids SS crown (1B).

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Table 1:

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Table 1: Comparison of the adhesion level of S. mutans to 3M stainless steel crown and Kids stainless steel crown

Discussion

Restoration of severely decayed primary teeth is usually a challenge to the clinician. The ideal requisites for a restoration to be successful is its durability, ease of placement, cost effectiveness, and natural appearance [16]. Preformed SSCs have better success rate than large multi surface amalgam restorations, which has been reviewed in the literature [17]. The SSC is cost effective as they are durable, inexpensive, and less technique sensitive and have high longevity than large multi surface restorations [18].

In the last few decades, an esthetic solution was found to replace the conventional SSC which has poor esthetic appearance [19]. In this regard, open faced SSCs, preveneered crowns, and resin bonded composite facings are introduced. However, a study by Reeves has shown that the esthetic crowns are more thick and bulky, which favored the adhesion of microbes causing periodontal breakdown[20].

The dental caries is caused by a principle microbe, S. mutans. The initial stage of developing secondary caries is due to the capability of S. mutans to adhere to the surface of the restoration [21,22] MSBA agar was used to isolate S. mutansbecause it is that the selective media for Streptococcus due to the addition of bacitracin and sucrose [23]. When the microbial count was seen on the crowns, there was no statistically significant difference seen between the 3M and Kids crown. However, the S. mutans count on the Kids crown was more than that observed on 3M crowns.

Pedrini et al. said that the substances released by the dental material can directly influence the bacterial growth [24]. The characteristics of SSCs like surface roughness and surface energy influence the microbial growth [25].

Myers et al. [26] reported that plaque will readily form on the surface of SSC regardless of the polishing procedures; therefore, oral hygiene procedures should be emphasized to minimize the accumulation of plaque. This could be due to physicochemical interaction through electrostatic and van der Waals forces between the surface of the restoration and microorganisms. The characteristics of SSCs such as surface roughness and surface energy influence the microbial growth. The higher the surface area and surface roughness of the restoration, the higher is the occurrence of bacterial adhesion.

To the best of our knowledge, very few previous study has evaluated the microbial adhesion to SSC in primary molars, where Bin AlShaibah et al. compared microbial adhesion with SSC and preveneered SSC and concluded that preveneered SSC showed higher microbial adhesion due to the greater thickness of the crown compared with SSC (4). Subramanyam D et al. (15) reported that the microbial adhesion of S. mutans was higher on the Kids crown than 3M crown which was in accordance with our results.

Conclusion

Under the limitations of this investigation,the conclusion drawn is:

• Adhesion ofS. mutans was seen higher on the kidsSS crown than 3M SS crown.

• There was no significant difference between 3M and Kids crown.