*2.2. Clinical Progress*

An eight-year-old girl visited our dental clinic for a dental eruption problem. Her medical history included a premature birth at nine months and she was taking medication for attention deficit hyperactivity disorder (ADHD). Radiographic and clinical examinations revealed root deformation of the first molars, primary molars, and cervical notch of the maxillary central incisors (Figure 1). The maxillary first molars were locked on the distal surface of the maxillary primary second molar and the mandibular first molars were mesially displaced due to the early exfoliation of the mandibular primary second molars. A lingual arch was set and periodic checks followed.

When the patient was 10, severe dentoalveolar infection and fistula occurred on the mandibular left first molar (Figure 2). Orthodontic analysis was conducted for treatment planning. She already had a space discrepancy and we decided to extract all permanent first molars affected by MIM and perform orthodontic treatment after the eruption of the secondary molars. Thereafter, the four MIM first molars were extracted sequentially and they showed twisted roots with granulation tissue (Figure 3). The crown and root of the maxillary left molar and mandibular right molar were fractured during the extraction. One year later, the second molars erupted and were relatively well-aligned.

**Figure 1. Panoramic radiographic and clinical photos at the first visit**. (**A**) In the 8-year-old girl, all the primary molars, first molars (yellow arrows), and anterior teeth (red arrows) were affected by MIM. There was a loss of space due to early exfoliation of the mandibular primary second molars. (**B**–**D**) A mandibular lingual arch was set for space maintenance. Morphological abnormalities (red arrows) were observed in the maxillary central incisors.

**Figure 2. Clinical photos.** (**A**) Two years later, a severe dentoalveolar abscess was observed on the mandibular left first molar. (**B**) The full depth of the distobuccal region was probed and a fistula was seen (yellow arrow).

**Figure 3. Extracted teeth affected with MIM.** (**A**) The maxillary right first molar (ID 16) showed twisted and fused roots after cleaning. (**B**) The maxillary left first molar (ID 26) showed a fractured crown and root with granulation tissue and an abnormal calcified surface between the crown and root. (**C**) The mandibular right first molar (ID 46) showed a small canal (red arrow) on the fractured surface. (**D**) The mandibular left first molar (ID 36) showed abundant granulation tissue and pulp necrosis in the pulp chamber.
