bubble_chart Overview

Lockbite is a type of malocclusion in the posterior teeth, where individual or multiple upper posterior teeth are locked on the buccal side of the lower posterior teeth, or individual or multiple lower posterior teeth are locked on the buccal side of the upper posterior teeth, forming a locked occlusion deformity.

bubble_chart Etiology

1. Individual tooth lock bite can be caused by early loss, retention of deciduous molars, or abnormal positioning of permanent tooth buds leading to ectopic eruption. The individual tooth lock bite of the upper and lower second permanent molars is more common, mostly due to insufficient development of the jaw arch length and inadequate space.

2. Unilateral multiple posterior teeth lock bite often occurs when multiple deciduous molars on one side have grade III caries or are lost early, forcing the patient to chew with the opposite side. Over time, the disused side is prone to developing deep overbite, which can further progress into multiple posterior teeth lock bite.

bubble_chart Clinical Manifestations

Scissor bite is more common in permanent teeth and rare in deciduous teeth.

1. Due to the locking relationship of scissor bite, it affects the lateral movement of the mandible, forcing the use of non-scissor bite side posterior teeth for unilateral chewing, thereby reducing masticatory function.

2. Scissor bite can lead to abnormal dynamic balance of the mandibular muscles, resulting in asymmetric development of the mandible and facial asymmetry.

3. Scissor bite may easily induce temporomandibular joint disorders.

bubble_chart Diagnosis

Divided into buccal crossbite and lingual crossbite.

1. Buccal crossbite refers to the lingual slope of the buccal cusp of the upper posterior teeth occluding with the buccal slope of the lingual cusp of the lower posterior teeth, with no occlusal contact on the occlusal surface (Figure 1A). Individual posterior teeth with buccal crossbite and unilateral multiple posterior teeth with buccal crossbite are relatively common in clinical practice.

A. Unilateral posterior buccal crossbite         B. Unilateral posterior lingual crossbite

Figure 1 Crossbite

2. Lingual crossbite refers to the buccal slope of the buccal cusp of the upper posterior teeth occluding with the lingual slope of the lower posterior teeth, with no occlusal contact on the occlusal surface (Figure 1B). This malocclusion is relatively rare in clinical practice.

bubble_chart Treatment Measures

Locked occlusion has a significant impact on masticatory function, maxillofacial development, and the health of the masticatory organs, and should be corrected as early as possible. The principle of correction is to elevate the occlusion and eliminate the locked occlusion relationship to achieve the following:

1. **Correction of Individual Tooth Locked Occlusion** This is commonly seen in the buccal malposition of upper posterior teeth. Correction can be achieved using a unilateral occlusal pad removable appliance. Specifically, a unilateral occlusal pad is placed on the healthy side of the upper or lower dental arch to disengage the locked teeth from their cusp interference. A band is placed on each of the locked upper and lower teeth. A traction hook is welded to the buccal surface of the upper tooth band and the lingual surface of the lower tooth band. An elastic band is stretched between the upper and lower traction hooks to achieve reciprocal anchorage for correction (Figure 2).

**Figure 2** Reciprocal traction between upper and lower posterior teeth to correct locked occlusion

After the locked occlusion relationship is resolved, the occlusal pad is gradually reduced or removed, and the cusps of the locked teeth that have not undergone physiological wear are adjusted to re-establish the occlusion of the entire dentition. Desensitization treatment may be performed concurrently during cusp adjustment.

2. **Lingual Locked Occlusion of Upper and Lower Second Molars on One Side** This is frequently observed clinically, with the upper molar often exhibiting more severe buccal malposition than the lingual malposition of the lower molar. If the third molar on the same side has not yet erupted but is about to erupt, the upper second molar may be extracted to allow the third molar to self-adjust and erupt into the position of the extracted second molar, establishing a normal relationship with the lower second molar.

3. **Lingual Locked Occlusion of Multiple Posterior Teeth on One Side** This is commonly seen in cases of a narrow lower dental arch, where the lower posterior teeth on the locked side exhibit severe lingual malposition, while the upper posterior teeth show minimal buccal malposition. For such patients, a unilateral occlusal pad appliance can be worn on the lower jaw. Specifically, an occlusal pad is placed on the healthy side of the lower posterior teeth to disengage the locked teeth from their cusp interference. A double-loop lingual spring is placed on the lingual side of the locked lower posterior teeth to move them buccally, thereby correcting the locked occlusion.

The use of the occlusal pad on the healthy side increases the tension of the buccal muscles, aiding in the lingual movement of the upper posterior teeth on the locked side and facilitating the correction of the locked occlusion.

After the locked occlusion relationship is resolved, the occlusal pad is gradually adjusted, and the excessively high cusps of the locked teeth are ground down. Desensitization measures may be applied if necessary.

When correcting locked occlusion in individual or multiple posterior teeth, attention must be paid to space issues. If space is insufficient, it must be created first. In cases of severe crowding, tooth extraction may be required.