Molar-incisor hypomineralization (MIH) frequently affects permanent first molars and increases the risk of rapid post-eruptive breakdown and restorative failure. Stainless steel crowns (SSCs) are considered a reliable treatment option for severely affected molars; however, SSC placement may temporarily alter the occlusal vertical dimension and occlusal contacts. Quantitative evidence describing the occlusal adaptation process following SSC placement in MIH-affected permanent molars is limited.

This prospective longitudinal clinical study aims to evaluate occlusal adaptation after SSC placement using the modified Hall technique in MIH-affected permanent first molars. Forty-six children will be included. Intraoral scans will be obtained at baseline, immediately after treatment, and during follow-up visits up to 3 months. Digital models will be superimposed to measure three-dimensional changes in cusp position, occluso-vertical dimension, and occlusal contact area. Temporomandibular joint function and periodontal parameters will also be assessed. The results are expected to provide quantitative evidence on occlusal adaptation following SSC treatment in MIH-affected molars.

The aim of this study is:

• to evaluate the occlusal adaptation process following SSC placement using the modified Hall technique in first permanent molars affected by MIH.
• to quantify three-dimensional occlusal changes, including cusp displacement, occluso-vertical dimension changes, and occlusal contact area alterations over time using digital model superimposition.
• to investigate the potential effects of this treatment on surrounding structures by assessing temporomandibular joint function and periodontal parameters.

MIH is a developmental enamel defect primarily affecting permanent first molars and often leading to hypersensitivity, rapid post-eruptive enamel breakdown, and significant coronal destruction. Recent literature has increasingly recommended biologically oriented and minimally invasive approaches for restoring MIH-affected molars, including the Hall technique and its modifications, which allow SSC placement without conventional tooth preparation. Although SSC placement is clinically successful, it may temporarily increase the occluso-vertical dimension and alter occlusal contacts. While clinical observations suggest that occlusal relationships gradually adapt over time through dentoalveolar compensation, no studies to date have quantitatively evaluated three-dimensional occlusal adaptation following SSC placement in MIH-affected permanent molars.

This prospective longitudinal clinical study will include 46 children with MIH-affected first permanent molars requiring SSC restoration. SSCs will be placed using the modified Hall technique.

Teeth will be equally distributed between maxillary and mandibular arches (23 maxillary and 23 mandibular molars), with only one tooth included per participant. Eligibility for SSC placement will be determined using the MIH-TNI index; teeth with scores 2 and 4 will be considered for inclusion. In cases where more than one first permanent molar meets the inclusion criteria within the same patient, the tooth showing the greatest degree of coronal breakdown will be selected for SSC placement. If multiple teeth present with similar severity level, tooth selection will be determined by computer-generated randomization. To minimize potential occlusal interference during treatment, all other necessary restorative procedures will be completed before SSC placement. Any additional teeth requiring SSC restoration will receive caries management during initial visits, while crown placement for those teeth will be postponed for three months to avoid interference with occlusal assessment.

In cases with tight proximal contacts, orthodontic separators will be placed prior to the procedure and left in situ for 3-5 days to achieve adequate interproximal space. At the SSC placement visit, lip and cheek retractors will be positioned to facilitate clear visualization of the teeth and surrounding soft tissues. Saliva will be removed using high-volume suction, and the tooth surfaces will be dried with an air syringe. Intraoral digital scans of both arches, together with the intercuspal occlusal relationship, will be obtained using a standardized scanning protocol.

Local anesthesia will be administered when clinically indicated. Unsupported hypomineralized enamel and defective restorations will be removed while maintaining a minimally invasive approach and avoiding conventional tooth preparation. Carious dentin will be removed according to selective caries removal principles: to firm dentin in shallow and moderately deep lesions and to soft dentin in deep lesions in order to prevent pulpal exposure.

An appropriately sized SSC (KidsCrown Permanent Molar SSC; Shinhung Co., Ltd., Korea) will be selected and tried in. Marginal adaptation and crown seating will be evaluated, and adjustments will be performed if necessary. The tooth will then be cleaned, dried, and isolated with cotton rolls. A glass ionomer cement (Ketac Cem Easymix; 3M ESPE, USA) will be prepared according to the manufacturer's instructions and placed inside the crown. The crown will be seated using finger pressure, and the patient will be asked to bite on a cotton roll until complete seating is achieved. Excess cement will be removed and interproximal remnants will be cleared using dental floss.

Following SSC placement, intraoral scanning will be repeated. Marginal adaptation of the crown will be verified using a bitewing radiograph obtained as part of the routine post-placement clinical assessment.

Occlusal changes following SSC placement will be monitored using digital models obtained at T0 (immediately before crown placement), T1 (immediately after crown placement), T2 (two weeks after crown placement), T3 (one month after crown placement), and T4 (three months after crown placement). In addition, temporomandibular joint examination and periodontal evaluation of the tissues surrounding the crowned tooth will be performed at T0, T2, T3, and T4 follow-up visits, and the findings will be recorded.

Inclusion Criteria for Participants

• Absence of any skeletal anomalies
• ASA physical status I or II according to the American Society of Anesthesiologists classification
• Frankl behavior rating score of 3 or 4
• All permanent first molars erupted and in contact at maximum intercuspation
• Emergency dental needs (e.g., toothache or acute conditions) previously managed
• Presence of at least one permanent first molar with an MIH-TNI score of 2 or 4 requiring SSC restoration
• No pain, clicking, or functional limitation in the temporomandibular joint region
• Children and their legal guardians who read, understand, and provide written and verbal informed consent Inclusion Criteria for Tooth
• Permanent first molars with MIH Treatment Need Index (MIH-TNI) score of 2 or 4 indicating the need for SSC restoration
• Occlusal contact with the opposing tooth maintained at maximum intercuspation despite post-eruptive enamel breakdown, with a noticeable reduction in posterior occluso-vertical dimension
• Absence of clinical and radiographic signs or symptoms associated with irreversible pulp inflammation or necrosis
• Absence of gingival or periodontal pathology in the surrounding soft tissues

Exclusion Criteria

• Individuals with serious systemic or psychological conditions
• Participants who fail to attend follow-up appointments
• Those who exhibit excessive fear or anxiety reactions and are unable to cooperate during treatment

The biostatistician performing the data analysis will be blinded to group allocation. The clinician performing treatment and model analysis will not be blinded.