bubble_chart Overview

Abnormal mesiodistal relationship of the dental arches can manifest as mandibular protrusion, mesial malocclusion, and anterior crossbite. This is often caused by improper breastfeeding posture, retained or prematurely lost deciduous anterior teeth, congenital absence of permanent maxillary incisors, bad habits, insufficient wear of deciduous canines, systemic diseases, and hereditary mandibular protrusion. Depending on the severity, it may present as anterior crossbite with neutral molar occlusion, or in severe cases, a combination of anterior crossbite, posterior mesial occlusion, and mandibular protrusion.

bubble_chart Etiology

1. Bad Oral Habits

(1) Poor breastfeeding posture, such as improper bottle feeding, where the jaw needs to exert forward force to suck, can cause anterior crossbite.

(2) Habits like biting the upper lip or protruding the lower jaw can lead to anterior crossbite and mandibular protrusion.

2. Local Obstacles During Tooth Replacement Period

(1) Retention or premature loss of deciduous teeth can result in individual or multiple anterior crossbites.

(2) Premature loss of upper deciduous molars and posterior movement of upper permanent anterior teeth can form anterior crossbite.

(3) Insufficient wear of deciduous canines, which are higher than the occlusal plane of the dental arch, may cause the mandible to move forward or laterally to avoid premature contact between the upper and lower deciduous canines, forming pseudo mandibular protrusion with anterior crossbite or anterior crossbite.

(4) Congenital absence of upper permanent incisors, such as the common congenital absence of upper lateral incisors, can lead to insufficient development of the upper anterior region, forming anterior crossbite.

3. Diseases

(1) Chronic inflammation of the palatine or lingual tonsils stimulating the mandible to protrude can, over time, lead to anterior crossbite and mandibular protrusion.

(2) Patients after cleft palate surgery often exhibit insufficient maxillary development, easily causing anterior crossbite and mesial malocclusion, with the mandible relatively protruding.

(3) Rickets patients, with calcium and phosphorus metabolism disorders and abnormal dynamics of facial and jaw muscles, often lead to severe mandibular protrusion or anterior open bite deformity.

(4) Endocrine diseases, such as hyperfunction of the anterior pituitary gland, can cause mandibular protrusion deformity.

4. Hereditary Anterior Crossbite Combined with Mandibular Protrusion has a significant family background, and the mandibular and facial deformities are exceptionally prominent.

bubble_chart Clinical Manifestations

Anterior crossbite, sometimes accompanied by mesial malocclusion of the posterior teeth, may present with a concave facial profile characterized by mandibular protrusion and maxillary underdevelopment.

bubble_chart Diagnosis

1. Dentogenic: Mostly caused by local obstructions during tooth eruption or replacement, often manifesting as a simple anterior crossbite. The overjet is small, and the molar relationship is neutral or close to neutral. The shape and size of the mandible are basically normal, with no significant abnormalities in the maxillomandibular relationship. The chin does not protrude, and the facial appearance is generally normal. The mandible can retract on its own to an edge-to-edge relationship of the anterior teeth. X-ray cephalometry shows no morphological or structural abnormalities in the bones, making orthodontic treatment easy with a good prognosis.

2. Skeletal: Mostly caused by genetic and disease factors, often showing a large overjet in addition to anterior crossbite. The molars exhibit mesial malocclusion, accompanied by jaw deformities. This may manifest as an obtuse mandibular angle, a long mandibular body, a short mandibular ramus, or underdevelopment of the anterior maxilla. The chin is noticeably protruded, and the mandible often cannot retract on its own. The face often appears concave, sometimes accompanied by an open bite deformity. Orthodontic treatment is difficult, and simple orthodontic treatment may not yield satisfactory results.

This type of anterior crossbite can be further divided into three types based on mechanism:

(1) Underdevelopment of the anterior maxilla with normal mandibular development.

(2) Normal maxillary development with excessive mandibular development.

(3) Underdevelopment of the maxilla accompanied by excessive mandibular development.

3. Functional: Caused by factors such as improper breastfeeding posture, leading to functional excessive protrusion of the mandible and anterior crossbite. However, the shape and size of the mandible are basically normal, and the mandible can retract to an edge-to-edge or shallow overbite relationship. Some refer to this as pseudo-mandibular protrusion. If not treated early, it may develop into true mandibular protrusion over time.

4. X-ray Cephalometry:

(1) An increase in the SNB angle and facial angle indicates relative protrusion of the mandible relative to the cranial base and an increase in the mandibular angle. These measurements are normal in dentogenic anterior crossbite cases.

(2) In cases of mandibular protrusion with maxillary retraction, the SNB angle decreases, and S-Ptm, Ptm-6 decreases. These measurements are normal in cases without maxillary retraction.

(3) An increase in the ANB angle and AB plane angle, along with a decrease in the AO-BO value, indicates significant maxillomandibular disharmony. These measurements are basically normal in dentogenic anterior crossbite cases.

(4) An increase in the facial convexity angle (G-Sn-Pg'), a decrease in the H angle (H line-N'P'g), and an increase in the Z angle (FH-H line) indicate a reduction in the soft tissue profile convexity. The upper lip prominence (Ls-SnPg') decreases or remains normal, while the lower lip prominence (Li-SnPg') increases. The maxillary prominence distance (Sn-G) decreases or remains normal, and the mandibular prominence distance (Pg'-G) increases.

bubble_chart Treatment Measures

1. Headgear and chin cap traction correction device (Figure 1). Suitable for patients with early skeletal anterior crossbite and mandibular protrusion. Can be used in the advanced stage of deciduous teeth, mixed dentition, or initial stage [first stage] of permanent teeth. Can be combined with intraoral appliances, such as the bite plate with tongue spring appliance.

2. Anterior traction correction device. Suitable for early skeletal anterior crossbite combined with maxillary deficiency and mandibular protrusion, can be used during mixed dentition or the initial stage [first stage] of permanent teeth (Figure 2).

Figure 1: Headgear and chin cap correction device

Figure 2: Anterior traction correction device

3. Functional appliances, such as the activator or Frankel III. Suitable for early skeletal anterior crossbite and functional anterior crossbite, can be used during mixed dentition, especially in the advanced stage.

4. Class III traction correction device. Mainly used to adjust mesial jaw relationships, commonly used for early skeletal anterior crossbite, can be used in the advanced stage of mixed dentition or the initial stage [first stage] of permanent teeth. The intraoral appliance can be a removable maxillary and mandibular bite plate or a fixed appliance, or a combination of both.

5. Removable maxillary bite plate with tongue spring appliance can be used for the correction of any anterior crossbite, either alone or in combination with other orthopedic devices such as chin caps and appliances like fixed retainers. For specific devices and applications, refer to Chapter 7.

6. Fixed appliances, including edgewise and Begg appliances, can be used to correct anterior crossbite, often during mixed dentition or permanent dentition. When using the Begg appliance, Class III traction should be applied instead of Class II, with a traction force of about 80g.

7. For adult anterior crossbite correction, if it is dentoalveolar anterior crossbite or Grade I skeletal anterior crossbite, the aforementioned non-orthopedic correction devices can be used. If it is anterior crossbite combined with significant skeletal deformity, combined orthodontic and surgical orthodontic treatment is required.

bubble_chart Prevention

1. During the lactation period, correct poor breastfeeding postures to avoid excessive protrusion of the infant's mandible.

2. Maintain the space of prematurely lost primary teeth, especially focusing on preserving the space of prematurely lost upper primary molars. Remove retained teeth, particularly promoting lactation molars, as early as possible.

3. If caused by chronic inflammation of the tonsils, promptly treat tonsil-related conditions.

4. For anterior crossbite caused by insufficient wear of primary canines, adjust the excessive occlusal interference to allow the mandible to self-reposition.

5. If caused by poor oral habits, eliminate these habits as early as possible.