Dental caries is a common disease in the primary dentition, particularly affecting proximal surfaces, with studies showing that approximately 80% of caries in young children occur on interproximal surfaces due to their difficulty in cleaning [1]. Proper restorative treatment with suitable materials is essential for prevention. Preformed metal crowns (PMCs) are commonly used for extensive caries in primary molars due to their durability and flexibility [2,3]. However, adjusting PMCs often involves cutting, crimping, and polishing the crowns to achieve proper marginal fit, which can inadvertently create surface defects and roughness. These imperfections provide retention sites for plaque accumulation and microbial adherence, increasing the risk of oral hygiene challenges [4]. Therefore, effective oral hygiene management is critical, especially in the cervical area where plaque tends to accumulate, which can lead to gingivitis in children who are less adept at brushing [5].

Recent studies have highlighted the limitations of toothbrushing in plaque removal on lingual and proximal surfaces. To address this issue, the COMORAL^Ⓡ oral irrigator (SMDsolutions, Seoul, Korea) has been developed [2,6]. This device uses a high-pressure water jet to remove food debris and plaque while massaging the gums. The water is dispersed at an angle of 15°-30° via a specialized WATERET^Ⓡ mouthpiece, making it effective for cleaning both teeth and gums [7,8].

This study aims to evaluate and compare the efficacy of the COMORAL^Ⓡ oral irrigator in removing artificial dental plaque from the buccal and lingual surfaces of PMCs.

1. Experimental device

COMORAL^Ⓡ Oral Irrigator: high-pressure water is applied through the WATERET^Ⓡ mouthpiece (Figure 1), which features 60 small holes for optimal water dispersion. The irrigator operates with a suction mechanism that minimizes the risk of aspiration.

Figure 1. Holes of WATERET^Ⓡ - COMORAL^Ⓡ mouthpiece (SMD solutions, Seoul, Korea).

2. Model preparation

Artificial tooth models (dental typodonts) with PMCs were used to simulate mandibular primary first and second molars (Figure 2). Artificial dental plaque was applied using Occlude^Ⓡ (Pascal International, USA), a marking agent, evenly coated on the buccal and lingual surfaces. The plaque was allowed to dry for 30 minutes. The reliability of Occlude^Ⓡ as a simulation material for artificial plaque has been validated in prior studies, which have demonstrated its consistency in adherence and visibility on dental surfaces, making it a standard choice for in vitro experiments [9,10].

Figure 2. Artificial tooth model with Stainless Steel Crown (Kids Crown, Shinhung, Seoul, Korea).

3. Plaque removal protocol

The WATERET^Ⓡ mouthpiece was positioned to simulate clinical usage, and 500 ml of water was applied at the highest pressure (5 out of 5) for 1 minute. The procedure was repeated 10 times [11].

Plaque removal was evaluated by dividing the tooth surface into three sections: cervical third, middle third, and coronal third.

4. Quantitative analysis

Digital photographs were taken before and after each irrigation. The cleaned area was measured in square pixels using image analysis software Image J (National Institute of Health, Bethesda, MD, USA). The percentage of plaque removed was calculated for comparison.

5. Statistical analysis

Data were analyzed using the SPSS software (Version 21.0). The normality of data was first tested with a one-sample Kolmogorov-Smirnov test. Spearman and Kendall tau correlation was used to correlate the relationship between repeat times and cleaning capacity. Mann-whitney test was used to compare plaque removal efficiency between buccal and lingual surfaces. Statistical significance was set at p<0.05.

1. Plaque removal efficiency

The COMORAL^Ⓡ oral irrigator showed significant plaque removal on the buccal surfaces compared to the lingual surfaces (Table 1, Figure 3).

Table 1 . Artificial plaque removal ratio on buccal and lingual surfaces (n=10)

	Mean	SD	p-value
			Paired t-test	Wilcoxon test
Buccal surfaces	74.64	1.24	<0.001	0.005
Lingual surfaces	24.28	3.34

Figure 3. Clinical photographs of plaque removal on the buccal and lingual surfaces after performing 10 sessions of cleaning from the baseline (0) to the 10th session.

Buccal surface removal rate: 74.64% (most effective at the cervical third).

Lingual surface removal rate: 24.27% (most effective at the coronal third).

2. Effect of repeated applications

Repeated use (up to 10 times) did not significantly improve plaque removal (Figure 4, Table 2, 3). This could be attributed to the water pressure reaching its maximum cleaning capacity during the initial application. Additional factors, such as the inability of the water jet to target deeper or less accessible areas effectively, may also explain why repeated applications showed no further improvements. A single 1-minute application with 500 ml of water was sufficient for effective plaque removal.

Table 2 . Correlation between repeated times and plaque removal efficacy of buccal surfaces

Test	N	Sig. (2-tailed)	Correlation coefficient
Kendall’s tau_b	9	0.532	−0.167
Spearman’s rho	9	0.637	−0.183

Table 3 . Correlation between repeated times and plaque removal efficacy of lingual surfaces

Test	N	Sig. (2-tailed)	Correlation coefficient
Kendall’s tau_b	9	0.144	−0.389
Spearman’s rho	9	0.125	−0.550

Figure 4. Graph of buccal and lingual surfaces after cleaning.

The study results demonstrated that the COMORAL^Ⓡ oral irrigator effectively removes artificial plaque from the buccal surfaces of PMCs, particularly in the cervical third [1]. The reduced efficacy on the lingual surfaces can be attributed to anatomical factors, such as the lingual tilt of mandibular primary molars, which limits water jet access.

The findings suggest that a single use of the COMORAL^Ⓡ irrigator can complement toothbrushing for children, particularly those with limited manual dexterity. To improve cleaning on lingual surfaces, adjustments to the water jet angle or minor repositioning of the WATERET^Ⓡ mouthpiece during use may enhance plaque removal [12].

Comparatively, devices like Water Flosser have been widely studied for their plaque removal efficiency. Systems have demonstrated superior interproximal cleaning and gingival health improvement compared to manual toothbrushing alone. A clinical study by Barnes et al. [13] showed that removed up to 99.9% of plaque biofilm in a 3-second application, emphasizing its efficacy. However, COMORAL^Ⓡ differs in its unique mouthpiece design, which allows for continuous high-pressure water dispersion while minimizing aspiration risks. This advantage may make it more practical for pediatric use, especially in younger children or individuals with special needs [14].

Furthermore, other studies have reported that high-pressure oral irrigators generally show better plaque reduction on accessible surfaces, such as buccal areas, while their efficiency on less accessible regions (e.g., lingual surfaces) remains lower [15]. The findings of the current study are consistent with these trends.

Additionally, plaque adherence on PMCs may be higher compared to natural teeth due to surface roughness introduced during crown adjustments. Studies have suggested that polishing protocols for PMCs can reduce roughness, thereby minimizing plaque retention [6]. Combining COMORAL^Ⓡ with enhanced PMC surface treatments might further improve its efficacy.

Lastly, the clinical relevance of this study is strengthened by its practical implications for pediatric oral hygiene. Devices like COMORAL^Ⓡ are particularly beneficial for young children or individuals with special needs who struggle with manual toothbrushing. Incorporating such devices into daily hygiene routines could significantly reduce the risk of caries and gingivitis.

However, this study has several limitations that should be acknowledged. Firstly, the use of artificial dental plaque in the experiments may not fully replicate the actual oral environment, potentially leading to discrepancies in results. The scarcity of previous studies utilizing stainless steel crowns presents another limitation, as even with the use of artificial dental plaque similar to that employed in earlier research, outcomes could vary. Furthermore, while oral irrigators are typically used as a supplement to regular brushing, this study analyzed plaque removal rates when using oral irrigators in isolation. This approach, while providing valuable insights, may not fully represent typical usage patterns in real-world scenarios.

These limitations highlight opportunities for future research. Subsequent studies should focus on either more accurately recreating the oral environment or isolating specific variables to observe their effects under controlled conditions.

The novel COMORAL^Ⓡ oral irrigator is an effective adjunct to toothbrushing for removing dental plaque from PMCs, particularly on the buccal cervical areas. Its ease of use and short application time make it ideal for improving oral hygiene in children. Future modifications to the WATERET^Ⓡ mouthpiece could further enhance cleaning efficacy on lingual surfaces by adjusting the angle and pressure of the water jets to better target hard-to-reach areas. Additionally, incorporating flexible or adaptive nozzle tips that conform to lingual anatomy may improve access and ensure more even plaque removal.

Clinically, the COMORAL^Ⓡ irrigator is suitable for children who struggle with effective toothbrushing.

A single 1-minute application is sufficient for plaque removal, highlighting its practicality for daily oral hygiene routines.

No potential conflict of interest relevant to this article was reported.