## 4 Discussion  
The patient showed the stereotypic characteristics of a MIM patient. Based on our study in 2014 [1], the average age of 12 MIM patients at the initial visit was about 7.8 years (range 4-13 years) and it was the same with this patient. This seems to be due to the eruption of the MIM teeth including the permanent first molars. The patient in this study was female and the sex ratio was even in a previous study [1]. However, in the study by [PERSON] et al. [8], there were 24 males out of 38, and in the study by [PERSON] et al. [3], there was a male predominance at 56.3%. The gender ratio is still controversial. Interestingly, the patient had a medical history of systemic disease, preterm birth at nine months, and medication for ADHD. Reportedly, almost 95% of the MIM patients  
Figure 6: Heatmap analysis at the genus (A) and species (B) level with >3% frequency. The perio group showed genera _Streptococcus, Veillonella, Leptotrichia, Prevotella,_ and _Fusobacterium._ The endo group showed gram-positive anaerobic cocci species, such as _Parvimonas micra_ and _Peptostreptococcus stomatitis._had diseases during infancy [8]. One of 12 in [PERSON]'s study [1], one of one in [PERSON]'s 2015 study [18], and four of 30 in [PERSON]'s 2016 study [19] were born preterm. In addition, meningitis, spina bifida, cerebral cyst, cephalohematoma, seizures, hydrocephalus, and other diseases were present in MIM patients [3,8,19]. According to a recent review, \"the exact aetiology of this condition is unknown. However, the fact that root malformations are limited to isolated teeth suggests that a non-genetic, environmental factor related to past medical history could be the cause\" [3]. The authors suggested a possible epigenetic association, which needs further investigation. In this patient, all the permanent first molars, the deciduous molars, and the maxillary central incisors were MIM teeth. This case seemed more serious compared to those in previous studies [3,8,19]. MIM teeth occurred in the permanent first molar, and often only in the mandible or in the maxilla. In many cases, the primary second molar was affected, but rarely the primary first molar or the permanent second molar. In the future, a classification for MIM is needed. The prevalence of incisors affected by MIM was about half [1] or one-third [3]. Sampling was the most crucial part for identifying the microbiome by collecting plaque and obtaining accurate data. If the sampling is incorrect, the disease-related bacteria may not be accurately identified. In this study, the sampling method applied was the one used by researchers in previous studies [13, 14, 15]. The NGS method MiSeq was developed in 2011 by Illumina. The characteristics of MiSeq consists of minimization while maintaining the chemistry of HiSeq (Illumina) and is suitable for reading V3 and V4 of 16S rRNA applied to microbial community analysis [20]. A total of 17 samples were categorized into the perio and endo groups. The perio group had higher average OTUs and alpha diversity compared to the endo group. At the genus level, _Streptococcus, Veillonella_, and _Leptotrichia_ were present in most of the perio group samples, but not in the endo group. These genera were usually found in healthy Korean preschool children [21]. Particularly, sample 36-2 with a clinically severe dentalveolar abscess showed only the presence of the _Spirochetes_ phylum. _Spirochetes_ were present in subgingival plaques and elevated in advanced periodontal disease and endodontic infection [22]. _Treponema socranskii_ and _Treponema medium_ appeared at 1% frequency in sample 36-2. _Treponema_ genera belonging to oral _Spirochetes_ were isolated from the periodontal inflammation site [23]. In the heatmap, the perio group was subtly divided into three clusters: (1) 11-2, 11-1, Nor-2, 26-2, 26-1, Nor-1, and 36-1; (2) 16-2, 16-1, 46-3, 46-2, and 46-1; and (3) 36-2. The first group included the MIM-incisor and non-MIM teeth, and the maxillary left MIM-molar.