What Is an Overdenture?

In terms of indications, covered dentures can be used when the remaining teeth can not be used as fixed dentures and the patient wants the dentures to be more stable than ordinary removable dentures. From the manufacturing method, the covered dentures can use various modern restoration technologies, such as: Casting technology, porcelain technology and fixed-movable joint repair technology, etc. From the application timing, covering dentures can maximize the time for patients with many missing teeth to become edentulous jaws. When there are only 1-2 patients in the mouth Overlays can still be used as an abutment to repair and use for many years. Therefore, with the development of dental preservation and people's awareness of the desire to retain teeth, this repair method will be increasingly used. ^[1]

Pan Shaoxia	(Deputy Chief Physician)	Department of Prosthodontics, Peking University Stomatological Hospital
Feng Hailan	(Chief physician)	Department of Prosthodontics, Peking University Stomatological Hospital

Overdenture refers to a type of full denture or removable partial denture that the base of the denture covers and supports on the tooth root or crown (in a broad sense, implant-overdentures are also included). Covered dentures are a kind of removable dentures for dentition defects, especially when there are few remaining teeth, and the periodontal conditions of the abutment are poor, and they cannot be used directly as the abutment of removable partial dentures. Because the tooth root is covered under the base of the denture, the alveolar bone can be reduced, the periodontal ligament receptor can be retained, and the denture can be supported, retained and stabilized.

Chinese name: Overdenture
Foreign name: overdenture

Indication: Dentition defect
Affiliated Department: Department of Prosthodontics

Covered Dentures

Overlay Denture Biology Basics

Covered dentures retain their natural teeth as part of the denture support, so they have advantages over ordinary mucosal supported dentures. Retained roots not only improve the support and retention of removable partial dentures, but also have unique effects on maintaining alveolar bone height and retaining periodontal proprioceptors. These characteristics improve the denture's ability to restore chewing function and other aspects. At the same time, the retention form covering the denture also has a health effect on the abutment itself. The vertical force of the abutment can improve the periodontal condition of the abutment and delay the life of the abutment. In addition, reducing tooth extraction has an important impact on patients' psychological acceptance.

1. Retaining the root of the tooth improves the support and retention of the denture

Retaining the root is used to cover the abutment of the denture, and its supporting effect is greatly improved compared with the mucosal supported denture.

Depending on the height of the covering abutment, the retention force provided by the denture varies. If the covering abutment is less than the gingival part, it will play a smaller role in retaining and mainly support. The higher the covering abutment, the greater the retention effect. If additional attachments are placed on the abutment, retention is further enhanced.

The amount and degree of dispersion of the abutment also have an effect on the retention and stability of the denture. As with ordinary partial dentures, the more abutments, the greater the retention force; the more scattered the abutments, the better the stability of the denture.

2. Retaining roots is good for maintaining alveolar bone height

Retaining the root not only allows the alveolar bone around the root to be retained, but also the bone tissue between the roots can slow down absorption. Crum and Roney used a skull X-ray in 1978 to compare 8 patients with full dentures and 8 patients with full dentures. After 5 years of follow-up observation, those who wear overdentures lose an average of 1.7mm bone, while those who wear full dentures lose an average of 5.2mm bone.

Tallgren conducted a seven-year study of patients with partial dentures wearing a tooth, and found that the vertical loss of alveolar bone surface around the natural teeth of the lower jaw was only 0.8mm, while that of patients with full denture wearing a mandible was 6.6mm. It is clear that the difference in bone loss levels improves significantly with the retention of natural teeth. Crum and Rooney (1978) reported a four-year study and found that retaining mandibular canines as overdentures helps to maintain existing alveolar ridges. In addition, the alveolar crest height of the intercanine area was reduced in patients with canine teeth less than in patients without any natural teeth. ^[2]

3. Preserving the role of periodontal proprioceptors

A number of studies have shown that patients wearing overdentures can better distinguish between different thicknesses of stainless steel wire. Patients with overdentures have a better perception of occlusal thickness than patients with full dentures.

Because patients treated with covered dentures retain the periodontal ligament proprioceptors, the range and type of chewing cycle in chewing-swallowing reflexes are more effectively controlled. The ability of the tooth root to disperse under the covered denture can be used as a signal to prevent bone resorption and regulate the physiological load system. Therefore, if the periodontal, abutment and economic conditions of the abutment allow, covering the denture with more root support will be more conducive to extending the life of the abutment.

4. Health effects of covered dentures on abutment teeth

When making overdentures, the height of the clinical crown needs to be greatly reduced, so as to improve the ratio of the crown root of the abutment.

5. Retaining the root of the tooth to improve the function of the denture

Studies have shown that patients who wear covered dentures chew more slowly and effectively than patients who wear full dentures while consuming the same chewing muscle strength.

6. Psychological impact of retaining roots on patients

Retaining some of the remaining teeth can not only provide retention, but also provide great comfort to the patient. Even if there is only a single tooth root, the patient does not become an edentulous jaw. Especially young adults or postmenopausal women, because of emotional and social pressure, feel that they cannot accept the removal of all remaining teeth and use full dentures. The degree of psychological improvement is different. For some patients, emotional depression from tooth loss is severe. As you grow older, the need to have glasses with dentures by the bed is unacceptable to some people. The replacement of fixed restorations with removable denture restorations is already an emotional trauma to the patient, so it cannot be ignored that retaining a tooth root can improve the patient's psychology. ^[3]

Overdenture classification

There are different descriptions and names for overdentures: such as Hybrid Prosthesis, Telescoped denture, Overlay denture, and Overdenture. Generally referred to as "Overdenture" and describes the shape it covers.

1. Classified according to the function of the abutment

Because the height, shape and presence of retention devices covering the abutment are different, the support, stability and retention

The effect is different. Generally divided into the following categories according to the function of the abutment:

(1) Simple coverage of dentures

After a complete root canal treatment, and the residual root of a certain height (more than 1.5 mm) in the section can be used

Make simple overdentures. After trimming the root surface and filling the mouth of the root canal with silver mercury or resin, no further processing is performed, and an overdenture is made on it. This overdenture is called a simple overdenture. The abutment that covers the denture can only support and maintain the height of the root periodontal alveolar bone. It is generally used when the abutment is in poor condition, the root is short, and the looseness is obviously not suitable for further treatment; or because of economic reasons, the patient does not want to spend further. Sometimes, because there are more teeth remaining in the mouth, or better conditions of the alveolar ridge in the edentulous area, it is estimated that the abutment can be simply covered when the denture has sufficient retention.

(2) Cap-shaped overdenture

After the abutment has undergone a complete root canal treatment, a protective metal root cap is made on the surface after the crown is cut, and then

Overlay dentures are made on the surface, and this overdenture is called a metal root cap overdenture. The abutment that covers the denture can only support and maintain the height of the alveolar bone around the root. It has a certain protective effect on the abutment than simply covering the denture. After the abutment is truncated and the shape is modified, the exposed dentin is prone to secondary caries.

(3) Sleeve crown-type overdenture

The outer surface of the abutment is made of a metal inner crown with a vertical outer wall or an outer wall with a certain degree of convergence, and the tissue surface of the denture base is placed with

A metal outer crown with a highly consistent inner crown, and a covering denture that is retained by friction between the inner and outer crowns is called a sleeve-type crown covering denture. Such an abutment covering the denture not only has a supporting effect, but also has a stabilizing and retaining effect. Generally, a good grinding crown manufacturing technology is needed, while using precious metal materials is better, so the cost is higher. ^[4]

(4) Attachment-type overdenture

Attachments such as root cap attachments, rod attachments, and magnetic attachments are placed on the root surface of the abutment to increase retention. Attachment preforms are required for production. If used with sleeve crown technology, a grinding device is also required.

2. Classification by Overlap Area of Overdentures

According to the classification of the coverage dentures, they can be divided into two categories: full dentures and removable partial dentures. The former means

The denture covers the entire dental arch. The shape is like a full denture. The remaining natural teeth are only the roots. The latter means that the denture is covered on part of the arch, and some natural teeth retain the complete crown. With or without a retainer on your natural teeth.

3 Classification by Abutment's Composition

(1) Supported overdenture with natural teeth

A covering abutment is a covering denture that is the root or crown of a natural tooth. Generally, there is no specific covering denture that is a covering denture.

(2) Implant-supported overdenture

Refers to a covered denture that is overlaid on an abutment supported by an implant. Overdentures are sometimes supported by implants and natural roots. ^[5]

Cover denture indication

Covering denture treatment is suitable when the remaining teeth in the oral cavity cannot be used for fixed denture repair, and the abutment condition is poor and cannot be directly used as the abutment of removable denture. Covered dentures are more suitable if:

1. At least 1-2 teeth can be retained. The position of these teeth is beneficial for the support, retention and stability of the denture.

2. Oral hygiene is good, or good oral hygiene is achieved through practice and learning, which can delay or prevent further caries or periodontal damage of the covered abutment.

3. Due to severe alveolar ridge absorption, xerostomia, sensitivity to oral foreign bodies, lack of learning ability or psychological factors, etc., it is estimated that wearing full dentures directly is not effective.

4. Poor remaining teeth (such as inconsistent crown-root ratio) If other treatments are applied, the remaining teeth will be more severely damaged.

5. According to the price-performance ratio, and the final restoration effect of the denture, when there is no other better repair and treatment method.

Sometimes it is initially designed to retain the teeth. When it is found that further restoration is difficult or unnecessary after dental pulp and periodontal treatment, it can also be temporarily reserved for covering the abutment. ^[6]

Contraindications for covering dentures

1. Dental pulp and periodontal disease are not cured, can not be used to cover dentures

2. The root surface of the remaining tooth is under the gingival or equal to the gingival without crown extension, because this type of root does not support the denture, on the contrary, it will stimulate the gum to cover the root surface, causing permanent inflammation.

3. Poor oral hygiene or systemic disease who cannot maintain oral hygiene by themselves. ^[5]

Advantages and disadvantages of covered dentures

Covered dentures have the advantages of support, retention and stabilization, which can improve the chewing function of dentures, at the same time have a health effect on the roots of the teeth, preserve the height of the alveolar ridge, and delay the time for patients to become edentulous. I won't go into details here.

Disadvantages of covering dentures:

1. Abutment teeth are prone to caries or periodontitis. Because the abutment is covered under the denture base, it is hardly affected by the self-cleaning effect of the oral cavity. In addition, food residues sometimes remain under the denture base, making bacteria easy to grow and reproduce. If patients have poor oral hygiene, the incidence of dental caries and periodontitis is high.

2. Increased treatment cycle, treatment cost and production difficulty. Since a series of treatments are required for the remaining teeth, the treatment time and cost are increased. If an attachment or a sleeve crown is placed on the abutment, the added time and cost are even more. At the same time, the difficulty of making dentures has also increased: To prevent dentures from breaking and take effective strengthening measures, it is necessary to consider that the placement of the retainer does not affect the aesthetics. Sometimes the retained roots make local bone processes obvious, and the tissues are large, which affects the position and aesthetics of the denture.

Therefore, choosing to cover denture treatment should weigh the advantages and disadvantages, consider various factors in detail, and make the best design. ^[7]

Overlay denture oral education

Promoting and teaching patients to maintain overdentures is vital to their long-term success. Periodontal treatment and the careful design and manufacture of dentures need to play a role through proper oral hygiene. The ultimate goal is to reduce periodontal damage or secondary caries.

Health care covering denture hygiene

The oral hygiene procedure performed by the patient after the overdenture is worn is learned during the preparation phase. But sometimes it can't be achieved, especially in older patients. Common reasons are: Many older patients increasingly think that oral hygiene is not important; changes in eating habits (eat more carbohydrates and soft foods), saliva Decreased flow promotes plaque buildup; due to its small size, the retaining device covering the dentures is very difficult to clean; as the age increases, the sensitivity and vision of the hand decreases, and learning efficiency decreases for elderly patients, so urge and teach to patients and help them practice The oral hygiene process requires a lot of time, patience, and psychological skills; third parties can also be taught to help them with oral health care; and personal hygiene plans for patients must be made within their capabilities. Regular review that is suitable for individuals is very important.

Health care of denture abutment

For those who wear covered dentures, cleaning your teeth with a regular toothbrush is the foundation of home health. All abutments and their gingiva with or without root caps must be cleaned on all sides. Brush all adjacent roots and gums with an adjacent brush. Dental floss is used to clean the lower part of the retaining rod and the part where the rod and the root cap are welded together. The open denture base around the abutment can simplify the maintenance of the abutment.

If mechanical cleaning is not possible or inadequate, chemical methods are recommended. as follows:

1. Fluorogel: can be used directly on the exposed root or indirectly in the denture above the abutment. Mouthwash can also be used daily with a 0.025% fluoride solution.

2.0.1-0.2% chlorhexidine solution: it can be rinsed daily or its gel can be put into denture base or attachment type. Pay attention to the side effects of long-term use, such as altered taste, burning sensation in the mouth, exfoliation of mucous membranes, and coloring.

Covering dentures

Cover the denture mechanically with a regular toothbrush or special denture brush. Low-wear toothpaste and non-alkali soap can be used together. Denture cleaners (mostly Peroxide Based) are useful adjuncts, but are not a substitute for mechanical cleaning.

Moniliasis can be treated by immersing the denture in 0.2% chlorhexidine solution daily for 10-15 seconds. When adequate mechanical cleaning of the denture is not possible for some reason (ie, physical or mental disability, bedridden, etc.), the denture should be soaked in chlorhexidine or salicylate (0.05%) solution daily. Chlorhexidine is absorbed by the denture resin and slowly released within a few hours. But long-term use will cause discoloration of the denture. ^[5]

Covered Denture Patients Follow-up

The Importance of Regular Follow-up

In order to protect the denture support organizations and keep them as long as possible, it is necessary to compensate for the gradual and continuous changes that occur in the denture support area. This requires regular review.

Many denture wearers believe that once they put on artificial dentures, no further treatment is needed, and changes in the supporting structure of the dentures are rarely noticed because their occurrence does not cause pain. Patients usually return to the doctor only when they feel that the dentures are not functioning satisfactorily or that repairs are necessary. The above points are indirect causes of excessive absorption of the remaining alveolar ridges and the formation of soft alveolar ridges. Patients often show poor alveolar ridge conditions and even undergo surgery before making new dentures. Clinically worn prostheses should be re-evaluated for fitness, occlusion and function after 6 months, if possible annually thereafter. In this way, dentures can be worn for an average of 7 or 8 years without subjective and objective symptoms, and then a professional physician determines whether a large revision or new denture is needed.

Second, the common problems after wearing dentures (Postoperative Problems)

There are three aspects of the problems that occur after covering dentures: problems related to dentures; problems related to covering abutments; problems related to the mechanical strength and attachments of dentures.

1. Problems related to dentures. Problems in this area include: retention, pain, pronunciation, chewing, etc., which are similar to those that occur after full dentures are worn. See related chapters. The difference from full dentures is that only the mucosa and remaining alveolar ridges will be affected after wearing full dentures, and the abutment will also be affected if there is a problem with covering dentures.

2. The problem of overdenture abutment

(1) Root surface caries

Root caries is a central issue in the follow-up maintenance of patients who cover dentures. 30% of the abutments protected by root caps and 15% of the abutments covered with root caps can develop root caries. The most important factors that cause root surface caries are loss of periodontal adhesion, consumption of fermentable carbohydrates, and dry mouth caused by any factor.

The purpose of maintenance after wearing is mainly to prevent the occurrence of caries. This includes the daily use of a fluorochemical, or a fluorinated mouthwash or a fluorogel. The gel can be applied directly to the abutment with fingers, toothbrush or cotton swab or indirectly on the denture before wearing the denture. A proper nutrition plan can also prevent caries.

Root surface caries can be detected with a probe during clinical examination. X-rays are mainly used to determine the depth of large defects under the root cap. The earlier you find caries, the easier it is to treat.

Root surface caries above the local alveolar crest can usually be filled with filling material after preparing the hole. The lesions above the alveolar crest under the root cap are rarely filled directly. If the root can be used directly for a period of time, the root cap must be removed and re-prepared. Most of them require periodontal surgery to create conditions for making a new root cap. Treatment of root caries below the alveolar ridge crest has a poor prognosis, especially when the root canal wall of the post is also affected. At this time, the price / benefit ratio of the treatment needs to be strictly estimated to decide whether to treat or remove the affected tooth.

(2) Periodontal problems

Early review and examination of periodontal damage and caries are important for covering denture patients. In principle, the first review is scheduled 3 months after the restoration is worn, and the review period is determined by the individual's condition. When oral hygiene is good, periodontal resistance is strong, the interval between restorations is slightly longer, and the period can be up to 12 months. In all other cases, review every 6 months. Periodontal examinations include the patient's ability to clean abutments and dentures, periodontal pocket depth and tooth mobility, and determine the width of the attached gingiva and the degree of marginal gingival inflammation. Regular radiographs of the abutment can help determine its prognosis.

Periodic maintenance is not only to remove plaque and tartar, but also to urge and oral hygiene education again. The development of periodontal lesions is related to the quality of oral hygiene and the degree of stress on the teeth.

(3) Evaluation and coverage of denture base

Progressive atrophy of the remaining alveolar ridge can often cause changes in vertical and horizontal relationships, which can cause interference and require periodic adjustments. Inconsistencies in overdentures can be diagnosed in the same way as total dentures. Look for abrasion marks on artificial teeth, record contact in the mouth, or return the dentures for inspection.

When assessing occlusion, the amount of alveolar ridge absorption must be considered. For example, early contact of the anterior teeth is caused by the sinking of the rear of the denture, which cannot be eliminated by grinding. Because doing so will reduce the vertical distance. It is best to restore the molar contact by properly performing the relining process so that the original vertical distance is maintained or restored.

Denture base closeness is a measure of how much alveolar ridges absorb. It is therefore important to carefully evaluate the denture base. Since the covering denture is partially supported, the base is not sunk in the abutment area.

According to the number and distribution of abutments, improper dentures can cause dentures to shake and be confined to tender points in an area on the alveolar ridge. The results include loosening of the abutment, accelerated alveolar ridge absorption, broken dentures, and interference.

Third, mechanical damage covering the dentures

1. Cover denture base fracture

Fracture of the base near the attachment is common in unreinforced overdentures. Covered dentures with cast stents rarely break. A force in the wrong direction often shows a crack in the resin near the attachment rather than a break in the entire base. Cracks are the basis of excessive stress in the denture base. The excessive stress should be eliminated in a timely manner, that is, lining or adjusting the shaking base to prevent greater damage in the future.

2. Attachment damage

(1) Wear

All attachments are subject to wear during use. Retention is usually affected a few years later. Retaining force can be obtained by replacing the male type or by redoing the root cap with a new attachment.

(2) Contact with teeth

In many cases, when the covering denture is not worn, the unprotected attachment body positive wears out due to repeated contact with the natural or artificial teeth of the pair. This can cause severe damage in a short time. Therefore, those who have real teeth on their jaws must wear their dentures for a long time, even at night. If you wear a total denture or overdenture, it is recommended to remove both restorations at night. Studies have shown that if local dentures are worn at night, dental caries and periodontal damage in the remaining dentition will increase. Soft tissue under the denture is also more prone to inflammation. Poor oral hygiene or dry mouth are also detrimental to wearing dentures at night.

(3) Replace the female part of the attachment

The attachment will lose its original retention force over time. This is caused by abrasion of the male and friction females, or the weakening of the spring of the female part of the retainer. Most female types are replaceable. There will be some technical difficulties when replacing.

4.Replacing Overdenture by Complete Denture

When the last abutment is lost, the overdenture is changed to a total denture. It can be directly relined by self-setting resin or indirect impression. It is difficult to modify the open metal bracket around the abutment to cover the denture. If there are too many parts to be added to the lingual side of the denture base, you need to make impressions. In addition, when the metal tongue plate of the original abutment area cannot provide sufficient retention for the added resin, an additional retention ring needs to be welded to the bracket. This restructuring is relatively expensive because it requires more processes. ^[8]