Dentition crowding is the most common malocclusion, which can be manifested as crowded, dislocated and irregularly arranged teeth; The incidence of dental caries and periodontal disease in crowded teeth is higher than that in normal teeth. At the same time, the crowded dentition obviously affects the appearance, which can cause difficulty in closing the mouth and lips and lead to the opening of the lips and teeth.

diagnose

1. The bone mass is small, the width of proximal and distal middle diameter of teeth is normal, and the length of dental arch is insufficient. In particular, the hypoplasia of the anterior maxilla is easy to cause crowding of the teeth in the anterior maxilla.

2. There are a lot of teeth, such as too many teeth in the maxillary anterior teeth area or too wide dentition, which leads to crowded dentition.

3. Classification In order to meet the needs of clinical diagnosis, dentition congestion is generally divided into mild, moderate and severe according to its severity.

Mild crowding (ⅰ) The gap between dental arches is less than 5 mm ..

Moderate crowding (Ⅱ) The gap between dental arches is less than 65438 00 mm. ..

In case of severe crowding (Ⅲ), the gap between dental arches is greater than 65438 00 mm. ..

Treatment measures

Corrective principle

The main mechanism of dentition crowding is irregular tooth quantity and bone quantity, with more teeth quantity but less bone quantity. Therefore, the principle of correction is to increase the bone mass or decrease the tooth mass, so as to achieve the coordination between the tooth mass and the bone mass and create conditions for the alignment of dentition. In other words, to align the crowded teeth, a gap must be made to align the teeth.

1. Increase bone mass, and expand the length and width of dental arch through various appliances to achieve the purpose of increasing bone mass, that is, to obtain a gap, but the gap obtained by this method is limited.

2. Reduce the number of teeth by slicing, reducing the diameter of teeth or extracting teeth by meiosis to obtain gaps. The gap obtained by reducing the diameter is also very limited, which is easy to cause secondary caries of teeth and is rarely used in clinic. However, meiosis extraction method can obtain a large number of gaps, which has become the main correction method for moderate and severe congestion in clinic.

No matter how to correct the crowding by increasing the bone mass or reducing the number of teeth, the crowded teeth must get enough clearance before they begin to bear stress, which is an important condition for successful correction.

Correction of mild congestion

Clinically, mild crowding is often manifested as torsional dislocation of upper and lower incisors or slight labial dislocation of canine teeth, and dental arch expansion is generally used for correction.

1. Maxillary external lip arch pushes molars backward.

Device: ① welding buccal tube belt ring; ② Open coil springs or bow springs are attached to the ends of both sides of the maxillary external labial arch; ③ headgear for traction; ④ Elastic ring of afterburner.

It is a common clinical method to push the maxillary first permanent molar backward by using the maxillary external lip arch to obtain the anterior tooth space and slight crowding. This method is mainly used before the eruption of the second permanent molar, especially in the case of moving forward to the distal or distal position. Generally, the posterior teeth on each side can move 3 ~ 4 mm distally, and the degree of posterior movement should be controlled according to the need, but the limit of posterior movement should be based on the molar moving to the middle.

The correction mechanism of this appliance is to insert the external lip arch into a circular tube with a ring at the end, and then add an elastic ring with a headgear. Traction acts on the molars through the compression of the spiral spring at the end of the labial arch. The elastic force of the spiral spring must be sufficient, and the length of the spiral spring should be 2 ~ 3 mm away from the front teeth after all compression.

Orthotics must be worn for at least 12 hours every day, and still need to be worn when sleeping.

With the backward movement of molars, slightly crowded anterior teeth can be aligned or adjusted by themselves, or aligned with other removable and fixed appliances.

2. The technique of expanding the gap locally is a common method to expand the gap of dental arch. Mainly used for individual teeth crowded dislocation gap is insufficient.

Device: Ligate the molars on both sides, clamp the adjacent teeth of the crowded and dislocated teeth with square arch brackets, place the labial arch with the lingual reinforcing branch against the lingual arch, and place a large coil spring between the adjacent teeth of the crowded and dislocated teeth to partially develop the gap (Figure 1).

Figure 1 local development

The gap source of partially developed dental arch is mainly due to the increase of curvature of anterior dental arch, so attention should be paid to the coverage of anterior teeth when using, and the coverage of anterior teeth should not be increased too much to form a deep coverage error. After solving the problem of insufficient space for crowded teeth, correct the dislocated teeth to their normal positions.

3. filament arch develops dental arch

(1) The end of the labial arch is bent into an ω shape. When it abuts against the end of the circular tube, the front arch wire leaves the arch of the front tooth and is ligated into the bracket, and then the arch is unfolded by the elasticity of the arch wire.

(2) Vertical force applying unit: vertically placed on the teeth that need to develop dental arch to enlarge dental arch.

4. The whole dental arch with split spring removable appliance was developed.

Device: Place a split spring or spiral arch expander on the maxillary base, and use the split spring spiral arch expander to expand the dental arch through the base to divide the gap needed by the crowded anterior teeth.

When using this kind of appliance, it is generally necessary to replace other removable or fixed appliances to arrange the teeth that are crowded and dislocated after the dental arch is enlarged, so as to obtain a gap. There are certain restrictions when using this kind of appliance, and the dental arch cannot be expanded indefinitely, so as to avoid contact obstacles caused by the deep coverage or locking relationship of the posterior teeth.

Correction of moderate and severe congestion

Moderate and severe crowding is usually treated with meiosis tooth extraction and appliance.

1. Correction of canine lip dislocation. Insufficient gap of canine lip dislocation, commonly known as "tiger tooth", is a common clinical mistake. When the labial dislocation of canine exceeds 1/2 crown width, the treatment of meiosis extraction is often considered.

(1) Selection of tooth reduction position: Generally speaking, in the treatment of labial dislocation of canine, the removal of displaced canine itself is not considered, because canine is of great significance for maintaining dental arch shape and full facial shape. If canine is removed, it will cause facial asymmetry. At the same time, canine is the strongest root in dentition, which is beneficial to the restoration of missing denture as abutment. The preferred tooth position is the first bicuspid, so pulling out a bicuspid has little effect on chewing function.

However, when the first pair of canines is normal, and the second pair of canines or the first permanent molar has caries defect or abnormal development, the dental caries should be reduced without pulling out the first pair of canines, which increases the difficulty of correction, but keeps the normal first pair of canines.

In addition, in the special case of canine teeth with lip dislocation, tongue inversion, or abnormal tooth decay and development, it can also be removed by meiosis and then corrected. After correction, the shape can be modified to approximate the shape of the lateral incisors.

Before determining the tooth position of tooth extraction, if the second deciduous molar still exists, the tooth germ should be examined by X-ray. If the tooth germ of the second bicuspid is congenitally missing or the teeth are misaligned or abnormally developed, the unreplaced deciduous molar should be the tooth position.

(2) Corrective methods

1) manual pressure method: when the patient is a growing child, and after the first pair of canines are removed by meiosis, the space between canines is sufficient and the canines are not seriously dislocated, manual pressure method can be used to arrange canines without wearing an appliance. Patients can press the dislocated dentition with their fingers, three times a day, 40-50 times each time, and canine teeth can also be adjusted under the natural pressure of labial muscles.

2) Orthodontic appliance: The appliance can be removed, and a movable distal bow spring or longitudinal spring can be welded on the labial arch, or a hooked attachment can be attached to the labial side, and the dentition can be pulled through an elastic ring.

When using fixed appliance, square arch or begg appliance can be used to correct, and stainless steel or nickel-titanium arch wire can be ligated to press the whole dental arch bracket into the dentition.

2. Correction of severe crowding of upper and lower front teeth. Severe crowding of upper and lower anterior teeth can often be manifested as labial dislocation of canine teeth, insufficient tooth space and different degrees of tooth distortion. Calibration design is mostly carried out after extraction.

(1) Correction of movable appliance: The commonly used upper and lower movable appliances include hyperbolic lip arch, bow spring and tongue spring, and the maxillary appliance has pad. First, push the bow spring to the distal end to create a crowded gap between the front teeth, and then push the tongue to the dislocated teeth with the tongue spring to release the gap when the occlusal pad is lifted, so as to further align the front teeth.

(2) edgewise appliance correction

1) adhesive tape and adhesive bracket often affect the bonding of brackets because of the crowded front teeth. First, pull the fangs away. In this process, the crowded front teeth will move far away to reduce the congestion.

2) When the fangs move far away and the crowded teeth have enough clearance to align, the upper and lower incisors are attached with brackets, and the arch wires are aligned with NiTi.

3) Using the square arch appliance, due to the continuous stress and the patient's usual rest posture, the crossbite can be shifted and aligned to the labial side without occlusal pad.

4) When arranging the front teeth, adjust the traction in or between jaws according to the molar relationship to ensure the neutrality of molar relationship.

5) When the molar relationship is neutral and the upper and lower front teeth are aligned, if there is still a residual gap in the dental arch, the whole dental arch is ligated continuously with elastic thread or continuous elastic ring to close the residual gap.

The principle of meiosis extraction:

1. Make sure to measure and analyze the tooth model before tooth extraction during meiosis, especially to know the gap needed by tooth arrangement test and calculate the bolton index of upper and lower teeth.

2. Generally, the upper and lower front teeth should be examined by X-ray to check the periodontal root condition, whether there is alveolar absorption, short root deformity and so on. And if conditions permit, it should also show whether there are embedded teeth or congenital missing teeth in other parts according to the curved section of the whole mouth.

3. When the front teeth are crowded, the extraction of the first pair of canines is often considered as the tooth position that determines the extraction of the teeth, because it is adjacent to the front teeth, and there are four teeth in the whole dental arch that have little effect on the extraction of the first pair of canines. However, if there are severely decayed or poorly developed teeth in the dental arch, the extraction of decayed teeth should be the first choice to correct the tooth position by meiotic extraction.

4. After calculating the number of gaps needed to arrange crowded teeth, add the number of anchorage teeth moving forward during orthodontic treatment to the required gaps. Generally, each side of fixed appliance will lose about 2mm anchorage, and the amount of movable appliance will lose more anchorage.

etiology

1. Genetic factors Dentition crowding has obvious genetic characteristics. From the crowding dislocation of individual teeth or the crowding of multiple teeth, even the degree of torsion of one tooth, parents and offspring can have the same performance. This genetic feature exists objectively, but its detailed genetic mechanism is not very clear.

2. Failure during dentition replacement is a common cause of dentition crowding. For example, because the deciduous teeth fall off prematurely, the adjacent teeth move forward and occupy the missing teeth, resulting in insufficient time gap between the eruption of permanent teeth and dislocation. Another example is retention of primary teeth, which can lead to eruption of continuous permanent teeth.

3. Jaw hypoplasia. The underdevelopment of jaw leads to a large number of irregular bone mass, and the teeth are irregularly arranged in the alveolar space, so they are crowded and dislocated.

4. The teeth are too big. Because the width of teeth near, far and middle is too large, it will cause teeth to be crowded and dislocated.

5. Bad habits Some bad oral habits, such as children sucking fingers and oral breathing, will cause dental arch stenosis or affect jaw development, leading to crowded teeth arrangement.