Managing MIH-affected teeth is challenging due to inflammation, sensitivity, rapid caries development, and difficulty achieving anesthesia.

This study aims to compare the effectiveness of intraosseous and conventional anesthesia in providing analgesia during restorations of MIH-affected molars in children aged 6-14.

Using a split-mouth model, each child will receive both anesthesia types on different molars, with conventional anesthesia as the control.

The study will assess the effectiveness of intraosseous anesthesia in achieving analgesia and reducing anxiety, helping dentists choose the best anesthesia technique.

Introduction. Molar-incisor hypomineralization (MIH) is a qualitative defect in the development of the enamel that affects at least one first permanent molar (FPM), often also impacting permanent incisors. Although MIH is considered to be an idiopathic condition, its concise etiology remains unclear. The porous nature of MIH enamel and the presence of post-eruptive enamel breakdown leads to hypersensitivity and pain, which is often the patient's main complaint and can affect the quality of life. There is also the increased risk of dental fear and anxiety.

Dental anaesthesia, because it is mainly associated with pain, is one of the most important factors related to fear and discomfort in children and adolescents. The delivery of local anaesthetic solutions and the puncturing the mucosa by the needle during traditional infiltration procedures can be uncomfortable in spite of topical anaesthesia and computerized systems to deliver the anaesthetic at a constant rate and pressure. Infiltration methods (buccal infiltration, mandibular nerve block, etc.) may also be associated with mucosal numbing and self-biting of soft-tissues.

Clinical management of young patients with MIH-affected teeth becomes challenging due to chronic subclinical inflammation caused by ingress of bacteria in the exposed dentin, sensitivity and rapid caries development in the affected teeth, difficulty in achieving local anesthesia as a result of altered nerve potential, and limited cooperation of the young child due to hypersensitivity-related apprehension.

In the case of MIH, clinicians might be tempted to give a greater than usual dose of anesthetic to overcompensate for the hyper-reactive tooth. Treating a pediatric population limits anesthetic administration by weight and age, so the practitioner may reach the maximum dose before the desired anesthetic effect is achieved. An alternative anesthesia technique, which has been more widely used in endodontics, is the intraosseous injection.

Intraosseous (IO) injections consist of injecting local anaesthetic directly in the cancellous bone adjacent to any tooth to be anaesthetised. Since the anesthetic solution is targeted directly to the tooth requiring treatment, the surrounding soft tissues are usually not affected. Unlike other IO injections, Quicksleeper (Dental Hi-Tec, Cholet France) is a computer-controlled anesthetic system. Because there is an array of carriers and needles which serve a variety of different purposes, it is possible to administer IO injection (transcortical, osteocentral), periodontal ligament injection (PLE), intraseptal injections, infiltration, and nerve block anesthetics in this system. Owing to its asymmetric triple bevel, the needle tip makes possible a painless and easy perforation into the bone.

Also, pain during injection would be decreased because IO anesthesia can be delivered by a computerized system (QuickSleeper™ system), which delivers local anaesthesia at a constant rate and pressure. Indeed, some authors showed that 83.9% of 50 children felt no pain or only mild discomfort with QuickSleeper™ system (scores 0 to 2 on the visual analogue scale [VAS]), and that 69.7% of 30 patients preferred IOA compared to CIA.

Aim This study aimes to compare the effectiveness of intraosseous (IO) and conventional anesthesia in providing analgesia during restorative procedures for molars affected by MIH in children between the ages of 6 and 14 years.

The study will be conducted at a tertiary pediatric dental care center and will follow strict ethical guidelines in accordance with the Declaration of Helsinki, with prior approval from the institutional Ethics Committee.

Eligible participants will undergo restorative procedures on two first permanent molars affected by MIH. The study will employ a split-mouth design, where each child will receive IO anesthesia for one molar and conventional local anesthesia for the other, with treatment sessions scheduled 7 to 21 days apart. IO anesthesia will be delivered using the QuickSleeper™ system, while conventional anesthesia will be administered according to standard dental protocols. The administration technique, including needle insertion, depth, and injection speed, will be standardized to ensure consistency across participants. One clinician will perform all procedures. An assistant will record the duration of anesthesia application, from the moment the topical anesthetic is applied to the end of the anesthetic injection. Anesthesia onset will be assessed using cold air (air blower, cold test) at 5, 10, 30, and 60-second intervals. Heart rate will be monitored throughout the procedure using a pulse oximeter. Pain intensity will be assessed before and after anesthesia and restorative treatment.

The study will include a convenience sample of 50 patients. Literature review supports this sample size based on comparable study outcomes.

Prior to each treatment session, the child's behavior will be assessed using the Frankl behavior scale. All participants will complete the CMDAS questionnaire to evaluate anxiety before the procedure. An orthopantomogram (panoramic X-ray) will be performed to exclude periapical pathology and to ensure there is sufficient space for intraosseous needle placement. Baseline data will include age, gender, presence of MIH on the first permanent molars, tooth sensitivity complaints, and Frankl behavior scale rating. At the first visit, participants will receive intraosseous local anesthesia using the QuickSleeper™ system (Dental Hi Tec, Cholet, France).

Participants. The participants will be children aged 6 to 14 from Croatia referred to the Department of Paediatric and Preventive Dentistry at the School of Dental Medicine, University of Zagreb, and diagnosed with MIH through a specialist examination.

This trial will provide a comprehensive evaluation of IO versus conventional anesthesia in MIH-affected pediatric patients, combining technical procedural details with standardized clinical and behavioral assessments to generate clinically relevant and reproducible outcomes.

Inclusion Criteria:

• Diagnosis of molar-incisor hypomineralization (MIH)
• At least two first permanent molars affected by MIH
• No prior dental procedures on those molars
• Mentally and physically healthy
• Cooperative behavior (Frankl score 3 or 4)
• No use of analgesics in the 48 hours prior to treatment

Exclusion Criteria:

• Periodontal changes (e.g., periodontal pockets, tooth mobility)
• Radiographic bone loss, furcation involvement, or periapical radiolucency

Individual participant data will not be made available due to restrictions related to patient confidentiality and local ethical regulations.