A Clinical Comparative Study of Different Methods for Correcting Lower Lip Sucking Habits in Preschool Children

Comparison of the Effectiveness of Behavioral Therapy, Maxillary Lip Bumper Appliance, and Twin-Block Appliance in Correcting Lower Lip Sucking Habits in Children

Intervention Methods Behavioral Therapy Group: Children were rewarded with their favorite candy or toys as positive reinforcement when they refrained from sucking their lower lip. When they exhibited lip-sucking behavior, corresponding punishments were applied (e.g., being prohibited from watching cartoons for 1 hour or from playing with toys) as negative reinforcement. At night, bitter nail polish or substances with unpleasant smells were applied to the lower lip as aversive stimuli. Patients attended follow-up appointments monthly.

\*\*Lip Bumper Therapy Group:\*\* The treatment involved placing arrow-shaped clasps and interproximal hooks on the maxillary molars, with a double-curved labial bow positioned on the labial side of the upper anterior teeth. A lip bumper wire was soldered at the position of the maxillary central incisors. The lip bumper wire should reach the mandibular vestibular groove to support the lower lip without obstructing the natural labial adjustment of the lower anterior teeth. Patients were required to wear the appliance at all times except during meals and oral hygiene activities. Monthly follow-up appointments were conducted, during which the double-curved labial bow could be adjusted to retract the upper anterior teeth.

Modified Twin-Block Therapy Group: Initially, occlusal reconstruction was performed, with the combined forward movement of the mandible and vertical dimension being less than 10 mm. The standard criteria were an incisal edge-to-edge bite of the upper and lower anterior teeth, with the vertical opening in the posterior region exceeding the resting occlusal gap by 2-3 mm. Patients were required to wear the appliance at all times except during meals and oral hygiene activities. Monthly follow-up appointments included progressive grinding of the maxillary occlusal pads. If discrepancies in arch width occurred, expansion therapy was implemented.

Evaluation of Therapeutic Efficacy

All children were assessed for the following indicators after 6 months of treatment:

1. Comparison of Lip-Sucking Habit Improvement: The outcome of lip-sucking habit correction was compared among the groups. Treatment was considered successful if the lip-sucking habit was completely corrected, malocclusion was improved, and parents were satisfied. It was considered unsuccessful if there was no significant improvement in the lip-sucking habit and parents were dissatisfied. Success rate = (Number of successful cases / Total number of cases) × 100%.
2. Comparison of Oral Examination and Model Analysis Indicators:\*\* Oral examinations and oral model preparation were conducted before treatment (T0) and one month after the end of treatment (T2). Changes in the overjet of the anterior teeth were measured using a vernier caliper.
3. Comparison of Cephalometric Measurements:Lateral cephalometric radiographs were taken before treatment (T0) and one month after the end of treatment (T2). SNA, SNB, ANB, U1-SN, and L1-MP angles were measured using Dolphin software (Version 11.8, Dolphin Imaging and Management Solutions, CA, USA).
4. Assessment of Oral Health-Related Quality of Life (OHRQoL) using the ECOHIS Questionnaire:The Chinese version of the Early Childhood Oral Health Impact Scale (ECOHIS) was used to assess the impact of lip-sucking habits and orthodontic treatment on children's OHRQoL. Parents completed the ECOHIS questionnaire before treatment (T0), after 1 month of treatment (T1), and 1 month after the end of treatment (T2). The questionnaire includes 13 items, covering the \*Child Impact Section\* (CIS) which assesses the impact on the child's symptoms, functions, psychology, and social interactions, as well as the \*Family Impact Section\* (FIS), which assesses the impact on parental distress and family function. Each item is rated on a scale of 0-5: never (0), hardly ever (1), occasionally (2), often (3), very often (4), don't know (5). The total ECOHIS score is calculated by summing the response codes from both CIS and FIS sections. The score ranges from 0 to 65, with higher scores indicating a greater negative impact on children's OHRQoL. The questionnaire was considered invalid if there were more than two "don't know" responses in the CIS or one in the FIS, and another child was selected for inclusion.

Eligibility Criteria:
Inclusion Criteria:

* Preschool children aged 3-6 years,
* Habit of lower lip sucking,
* No anterior crossbite or open bite,
* Missing no more than 2 incisors in a single jaw,
* No other systemic diseases,
* The child's family has a certain level of reading and comprehension ability, can effectively understand the questionnaire content, and is willing to sign the informed consent form.

Exclusion Criteria:

* Prior orthodontic treatment;
* Tooth extraction;
* Mini-implant usage;
* Chronic rhinitis, tonsil hypertrophy and other upper airway diseases.