What Is a Fixed Bridge?

Fixed dentures are restorations that repair one or more missing teeth in the dentition. Adhesives or fixing devices are connected to the prepared abutments or implants on both sides of the missing tooth, thereby restoring the anatomic form and physiological function of the missing tooth. Because this type of prosthesis cannot be taken and worn by the patient, it is simply referred to as a fixed denture. Because its structure is similar to a bridge, it is also called a fixed bridge.
Fixed bridge

Yang Jian

(Attending physician)

Department of Prosthodontics, Peking University Stomatological Hospital

Chinese name: Fixed denture

Other name: Fixed bridge
Affiliated Department: Department of Prosthodontics

The origin of fixed dentures

In ancient times, people tried to install dentures in the missing dentition to restore chewing function. People used bamboo, firewood, stones, human teeth with ivory missing, and cattle bones to sculpt artificial teeth. Wait for ligation on adjacent teeth on both sides of the gap. The method is relatively rough and simple, which is confirmed from the excavated ancient skull.

Composition of fixed dentures

The fixed denture is composed of a retainer, a bridge and a connector.

Retainer refers to the part of the structure that is fixed on the abutment, including full crown, post and core crown, partial crown, inlay, wing plate fixed bridge, etc., and is connected to the abutment with retention force to obtain retention. Among them, intracrown retention is commonly used. The bridge is connected to the abutment by the retention of the retaining body and transmits the occlusal force to the abutment through the retaining body. Therefore, the retainer should have good retention and resistance.

The bridge body, or artificial tooth, is the part of the fixed bridge that restores the shape and function of the missing tooth.

The connecting body is a connecting part between the bridge body and the retaining body, and can be divided into a fixed connection and a non-fixed connection according to different connection methods.

Fixed dentures

It can not only restore the anatomical shape and physiological function of the chewing organ, but also maintain the health of the organ for a long period of time and prevent the occurrence of dental and jaw diseases, such as preventing the extension of the teeth on the jaw and the tilting of adjacent teeth. And can make patients feel beautiful, comfortable and chewy feeling similar to real teeth.

Types of fixed dentures

According to the structure, it can be divided into: double-ended fixed bridge, semi-fixed bridge, single-ended fixed bridge and can be extended into composite fixed bridge, bonded bridge, fixed movable joint fixed bridge, implant abutment bridge and so on.

According to the material can be divided into: plastic bridge, metal bridge, porcelain bridge, all-ceramic bridge and so on.

Indications for fixed denture bridges

Number of missing teeth

(1) The fixed bridge is most suitable for repairing one or two missing teeth, that is, the two abutment teeth are suitable for supporting the bridge body of one or two missing teeth. The fixed bridge can generally repair 1-4 teeth in the incisor area and 1-2 teeth in the posterior area.

(2) If there are more than two missing teeth, the interval is missing, that is, there is increased support for the intermediate abutment.

(3) When choosing a fixed bridge repair, the number of missing teeth and the ability of the abutment at both ends of the missing area to withstand the occlusal force must be considered, otherwise the fixed bridge repair will fail.

2. Missing teeth

(1) Missing teeth in any part of the dentition, as long as the number of missing teeth is not large. Abutment conditions meet the requirements, and fixed dentures can be used for repair.

(2) For patients with missing free posterior teeth, if a single-end fixed bridge is used for repair, the bridge is stressed and the leverage effect is large, which may easily cause damage to the periodontal tissue of the abutment.

(3) If the second molar is free and missing, the jaw is a mucosal supported removable denture, because its occlusal force is significantly smaller than that of ordinary natural teeth, and the second bicuspid and the first molar can be used as the abutment. The periodontal condition of the abutment is good, and it can also be repaired with a single-ended fixed bridge.

3. Conditions of the abutment

(1) The clinical crown height as a fixed bridge abutment should be appropriate. If the dental crown has a defect in the dental tissue, or the crown shape is abnormal, as long as it does not affect the retention shape preparation of the retainer and can meet the requirements of the retainer retention, it can also be considered as the abutment. The crown defect area is large. If it can be repaired by post and core, it can still be selected as the abutment. If the clinical crown of the abutment is too short, measures to enhance the retention of the retainer should be taken, such as preparing auxiliary retention shapes on the abutment or increasing the number of abutments, otherwise it is not suitable for fixed bridge repair.

(2) Roots Roots should be large and stable. The support of multiple teeth is the best. There should be no pathological looseness.

(3) The dental pulp is the most active one. If the endodontic lesions already exist, thorough endodontic treatment should be performed, and after a long period of observation, it can be confirmed that it will not affect the effect after repair before they can be used as the abutment. Dead pulp teeth become brittle after root canal filling. When selecting abutment teeth, the strength of the root should be considered.

(4) Periodontal Tissues A healthy periodontal tissue can support the strength of the bridge that is transmitted to the abutment via the retainer. Therefore, the requirements for the periodontal tissue of the abutment are: no progressive inflammation of the gums, no inflammation of the periodontal ligament, no periapical lesions; alveolar bone structure is normal, and the alveolar process is not absorbed or absorbed less than 1 / 3 and absorbed for stagnant levels. If individual teeth are missing and the abutment is loosened to varying degrees due to periodontal disease, you can consider designing a multi-abutment fixed bridge based on the principles of orthodontic treatment of periodontal disease.

(5) The position of the abutment requires that the axial position of the abutment is basically normal, without excessive tilting or twist dislocation, and does not affect the preparation of the retainer and the common seating path between the abutments.

4. Occlusal relationship

(1) The occlusal relationship in the missing tooth area is basically normal, that is, there is a normal gingival distance from the alveolar ridge mucosa of the missing tooth area to the maxillofacial tooth surface. There is no elongation on the maxillary teeth and no tilting of the adjacent teeth.

(2) If the missing tooth is too long, the relationship will be disordered, such as the tilting of adjacent teeth, the formation of interdental locks on the extension of the maxillary teeth, and the mandibular movement is limited. Generally, it is not suitable to use fixed bridge for repair. . The restoration of extended and inclined teeth to the normal position can still be considered for fixed bridge repair.

(3) The occlusal contact in the missing tooth area is too tight. The distance between the alveolar ridge top mucosa and the maxillary tooth surface in the missing tooth area is too small. Because of the retainer, bridge and connecting body, there is not enough thickness and strength to support the chewing force. It is generally not appropriate to use fixed denture repair.

5. Alveolar ridge in missing tooth area

(1) The wound healing in the missing tooth area is generally 3 months after extraction. After the extraction wound is completely ovulated, the alveolar ridge is basically stable and the fixed denture is made. For those who must be repaired immediately due to special reasons, first prepare the fixed abutment teeth, use resin to temporarily fix the bridge to repair the missing teeth, wait for the wound to fully heal, and then perform a permanent fixed bridge repair. If the tooth extraction wound does not heal and the alveolar ridge is not stabilized in absorption, the fixed bridge is repaired immediately. After repair, it is easy to form a gap between the gingival end of the bridge and the mucosa, which affects the self-cleaning effect and aesthetics.

(2) Alveolar ridge absorption in the missing tooth area Alveolar ridge absorption in the missing tooth area should not be too much, especially in the anterior tooth area. If the alveolar ridge is absorbed too much and the fixed bridge is made, it is difficult to shape the shape of the bridge, which will affect the appearance. The alveolar crest absorbs too much of the posterior area, and a sanitary bridge can be designed. In short, for those who have too much alveolar ridge in the missing tooth area, careful consideration should be taken when choosing a fixed bridge for repair. If necessary, a special shape shaping treatment is used, such as the bridge body surface or incision edge to the mucosa of the missing tooth area is too long, the bridge neck can use gum color, shorten the bridge length by visual difference, and coordinate with the adjacent tooth neck.

6. Age

(1) If the age is too young, the clinical tooth crown is short, the medullary cavity is large, the medullary angle is high, and sometimes the apical part is not completely formed. It is easy to damage the pulp during the preparation of the abutment.

(2) If the age is too large, the periodontal tissues will shrink significantly, and the teeth will become loose. At this time, the compensation function of the periodontal tissues will decrease, and fixed bridge repair is not suitable.

(3) The suitable age for fixed bridge repair is 20 to 60 years. But it also depends on the specific circumstances of the patient. Such as elderly patients, the general body and oral conditions are good, with the exception of individual teeth missing, the remaining teeth are healthy and stable, at this time can also be fixed bridge repair.

7. Oral hygiene

Patients with poor oral hygiene, tartar deposits, and plaque accumulation can easily cause dental caries and periodontal disease, leading to the destruction of abutment periodontal tissue. Therefore, when such patients choose fixed bridge repair, periodontal cleaning must be performed, and patients are instructed to keep their mouths clean and hygienic. Otherwise it is not suitable for fixed dentures.

8. Remaining tooth condition: stability of dentition.

Contraindications of fixed dentures

1. Not suitable for adolescent patients.

2. Severe deep overlap, crossover, excessive wear, etc. who cannot coordinate the occlusal relationship through adjusting the grinding.

3. Those who have missing teeth for a long time and the relationship is disordered, which results in those with restricted jaw movement.

4. The alveolar ridge defect in the missing tooth area is too large, especially in the anterior tooth area.

5. Progressive inflammation of the gums, alveolar bone resorption over root length 1/3.

6. Those with missing posterior teeth.

How to choose abutment for fixed dentures

The abutment teeth should have sufficient clinical length, relatively normal tissue structure and large volume to ensure the good retention of fixed dentures.

1.Ante's rule: the periodontal ligament area of the abutment is greater than or equal to the total area of the missing periodontal ligament.

2. Crown-to-root ratio: ideally 2: 3, at least 1: 1.

3. Root shape and structure: Relative support is better with long and thick roots and large root spacing.

4. Tilt and displacement of the abutment: The tilt of the abutment generally does not exceed 25 degrees.

Conditions and design of fixed denture bridge

The bridge should have a good self-cleaning effect, meet sanitary requirements, have sufficient strength, and have no adverse irritation to the soft and hard tissues of the oral cavity.

The design of the bridge should consider the following aspects: the gingival surface of the bridge, the strength of the maxillofacial surface, and the external shape.

The maxillofacial region can be considered to reduce the buccal-lingual diameter, increase the abduction gap, deepen the buccal-lingual groove or add an accessory groove, reduce the slope of the tooth tip to reduce the pressure on the abutment, and benefit the periodontal tissue health

The gingival surface can adopt a modified lid-type bridge according to the actual situation of the patient.

Retention of fixed dentures

Retention is more important. Poor retention can lead to many problems, which can cause secondary caries in the abutment. Damage to the periodontal tissue can not play well in chewing function or even swallowing.

Types of Retainers: Intra-crown Retainers, Out-crown Retainers and Intra-root Root Retainers

Improve the retention force of the retainer: Because the fixed denture connects the abutments into one body, its response to the force is different from that of a single tooth, and the retention force is required to be higher than that of individual teeth.

(1) The retention force of the full crown is the best, and the occlusal polymerization of the retainer should not be too large. The 3/4 crown should be adjacent to the groove to prevent rotation and dislocation. The inlays should have clear point and line angles.

(2) The design of the retention force of the retainer is adapted to the size of the occlusal force, the span of the bridge and the curvature of the bridge. The longer the bridge span, the more curved, the greater the occlusal force, the higher the retention force required by the retainer.

(3) The retention forces of the abutment retainers at both ends of the double-ended fixed bridge should be basically equal: if the retention forces of the retainers at both ends are very different, the retainer at the end with the poor retention force is liable to loosen. However, the retaining body at one end with a strong retention force has not fallen off temporarily, and it is difficult for the patient to detect the secondary caries caused by the loose end abutment.

(4) When selecting a retainer, it must be considered that there should be a common seating path between the various retainers.

(5) If there is a defect or deformity of the abutment, it should be repaired together when designing the retainer. If the abutment crown has a filler, the edge of the retainer should be covered with the filler as much as possible, so as to avoid the filler from loosening and affecting the retention of the retainer.

(6) The design of the retainer should prevent the abutment from cracking, and the external crown retainer is completely covered with metal because the abutment surface of the abutment is covered by metal, so that the crack will not occur. Intracoronary retention, especially if the maxillary bicuspids are adjacent to the adjacent teeth, the cheeks and tongue tips are very steep, which can easily cause cracks in the teeth.

(7) Retainer design for teeth with severely damaged crowns: These teeth are mostly dead pulp teeth. As long as the defect does not reach deep below the gums, the teeth are stable and should be retained as much as possible. First, after thorough root canal treatment, a retention nail or post is inserted and fixed in the root canal, a nucleus is formed with amalgam or resin, and then a full crown retainer is made.

(8) Retainer design for tilted abutment: Firstly, the axial direction of the abutment can be changed by orthodontic method; secondly, modified 3/4 crown is used for retention; again, sleeve crown retainer can be used for repair

Repair of fixed dentures

Preparation for fixed dentures

1. Based on the number of missing teeth. Location, relationship and abutment morphology, tissue structure and periodontal support tissue to select abutments and determine the number of abutments.

2. Check whether the tooth extraction wound is healed in the missing tooth area, the size of the missing tooth space, the alveolar ridge and the oral mucosa.

3. The crown of the abutment should be tall and the roots grow up. If there is a tooth or periodontal disease, treatment is needed first, and the pulpless tooth should be treated with a perfect root canal.

4. The occlusal relationship should be basically normal. If the abutment is tilted and displaced, the jaw teeth are elongated, twisted or misaligned, it is necessary to adjust the grinding or change the design method of the retainer.

Fixed denture method

l. Preparation of abutment teeth: Refer to the restoration of tooth defects, when preparing teeth according to the type of retainer, it is required that the corresponding axial surfaces of all abutment teeth are parallel to each other, no undercut or slightly square or cut end polymerization 2o-5o, In order to obtain the common seat of each bit, at the same time, attention should be paid to enhancing the retention of the bit.

2. Impressions and molds: Impressions must be accurate, complete and clear. Cast fixed bridges and metal-ceramic bridges use double-layer silicone rubber impressions to obtain full-tooth impressions, infuse them with anhydrite, and then use mold pins to form removable models.

3 Production of fixed bridges: Generally completed in the laboratory.

4. Fixation of fixed dentures: try the preliminary polished retainers on each abutment respectively. If the retainers are correct, they will be tightly fitted to the neck of the abutment. The edges should be stretched properly. The abutment relationship is good. In the case of no warpage and good retention, if there is a problem, it can be polished and fixed after appropriate treatment. The metal porcelain bridge is tried on before glazing, after the shape trimming and bite adjustment, it is then glazed and fixed.

5. Doctor's advice: Patients are advised to fast within 2 hours after cementing, and do not use a fixed bridge to chew hard food within 24 hours. If necessary, make an appointment for a review. ^[1-3]