Combined Denture

Combined dentures (synonyms: combined fixed-removable dentures, combined fixed-removable dentures) are removable prostheses that are securely held to remaining teeth or implants with tight-fitting anchorage elements. Simple partial dentures are only attached to the remaining teeth with the aid of visible clasps. Although this sufficiently restores function, the esthetics can still be severely compromised. In addition, the clasp constructions facilitate the accumulation of biofilm (bacterial plaque) and can therefore result in an increased risk of caries. In addition, braces positioned in the cervical area may damage them over time due to friction during chewing and speaking.

Advantages

However, when a partial denture is attached to the remaining dentition by fixed anchorage elements, this results in a significant improvement in denture retention as well as safety during speech and eating. In addition, combined dentures can dispense with clasps in the visible area and therefore also meet high esthetic requirements. In addition, combined dentures can lead to stabilization of the residual dentition due to their defined hold and the resulting secondary splinting.

Definitions

A wide variety of anchorage systems are used in combined dentures. In each case, they have in common a primary part that is fixed to the abutment tooth, which must be crowned for this purpose, and a precisely matched secondary part that is incorporated into the denture. 1. attachments – rigid retaining elements whose retaining effect is based on friction (static friction between parallel walls). They consist of a matrix (enclosing part) and a patrix (enclosed part), which are analogous in shape to each other and allow only one defined insertion direction for the denture. The matrix is incorporated into the crown of the abutment tooth. Factory-made elements are precision attachments made of cast-on alloy. Individually manufactured attachments are called semi-precision attachments. These include the so-called partial sleeve attachments, which are milled using parallel technology and whose primary part is only partially enclosed by the secondary part. In this way, the labial side (lip side) of an abutment crown can be aesthetically veneered in tooth color. 2. telescopic crowns – are double crowns or so-called sleeve attachments, consisting of a primary crown (synonym: primary telescope) for cementation on the abutment tooth and a secondary crown (synonym: secondary telescope), which is incorporated into the prosthesis. Telescopic crowns are held in place by friction, the static friction resulting from parallel milled walls. 3. conical crowns – are also double crowns or sleeve attachments, but their primary and secondary crowns have conically shaped surfaces, which results in static friction in the sense of wedging. 4. bars – are metal bars that interlock the crowns of abutment teeth. They have round, angular or oval cross-section and represent the primary part, which is completed to the bar attachment by an abutment, the “rider”, incorporated into the prosthesis. 5. push-button anchor – following the well-known principle, the anchoring element consists of a ball button and a sleeve snapping onto it. The matrix of the system is located on the crown of the abutment tooth or in a bar, the patrix in the prosthesis. The retention is achieved by so-called clamping (press fit). The opposite is the position of a push-button anchor on implants or on root caps: here the ball button sits as a patrix on the abutment, on which the matrix located in the denture snaps in. 6. latch – a lock-like attachment of the partial denture in addition to other anchoring elements. The prosthesis can be removed only when the latch is released by the patient. Opening requires good manual dexterity.

Indications (areas of application)

Combined dentures are planned for the restoration of a partially edentulous jaw in which there are no longer sufficient teeth for a fixed bridge restoration. The anchorage elements selected again depend on the individual situation:

  1. Attachments – Crowns with inlaid or attached attachments are tooth-colored veneered labially (on the lip side), wear less labially than telescopic crowns, and exhibit less friction (rubbing) than the latter.
  2. Double crowns/telescope crowns – periodontal findings (tooth bed findings) allow chewing load, manual dexterity of patient given, symmetrical abutment distribution possible, stronger friction than attachment.
  3. Double crowns/conical crowns – periodontal findings allow chewing load, manual dexterity limited.
  4. Bars – low residual anterior teeth, e.g. two lateral incisors or two canines.
  5. Push button anchors – denture stabilization with low residual tooth stock on root-treated teeth or on implants.
  6. Latch – when the other anchorage elements can not provide sufficient retention (hold), for example, short clinical crowns with little static friction.

Contraindications

  • Periodontally insufficient teeth (with insufficient load-bearing capacity of the periodontium, e.g., due to loosening and/or bone resorption).
  • Intolerance to polymethyl methacrylate (denture acrylic).

Before the procedure

Before planning and providing combined dentures, the patient’s expectations of the new dentures are clarified. The patient is advised about alternative treatment methods such as that of a simple cast model denture. The placement of implants to avoid the need for a denture is also addressed as a treatment alternative. Due to the firm hold that the prosthesis obtains on the residual dentition via some anchoring elements, handling can be more difficult for patients with motor impairments or also with limited vision. This must be taken into account when selecting the anchorage technique. The dentition is clarified clinically and radiographically for freedom from symptoms and apical signs of inflammation (at the root tip). Any necessary root fillings on teeth to be crowned must have been successfully completed beforehand.

The procedure

The procedure is divided into quite a few treatment steps, which take place alternately between the dental practice (hereinafter “ZA”) and the dental laboratory (hereinafter “LAB”). I. Situation impression (ZA)

Impressions of the jaws are taken with standardized impression trays, usually with alginate impression material. II. situation impressions (LAB)

are made by pouring plaster over the alginate impressions and are used for the

  • Orientation about the anatomical conditions of the jaws,
  • Representation of the opposing jaw, if only one jaw is to be prosthetically restored, and
  • Production of so-called individual impression trays made of plastic, which meet the individual anatomical features of the jaws.

III. crown preparation (ZA).

  • The teeth to be provided with crowns are contoured under local anesthesia (local anesthesia) with rotary instruments in such a way that no undercuts interfere with the subsequent placement of the crown. The subsequent crown margin is prepared just below the level of the gingival margin (the gum line).
  • Preparation impression – for example, with addition-curing silicone compound.
  • Facial arch creation – serves to transfer the position of the upper jaw into a so-called articulator, in which the prosthesis is made
  • Supply of the prepared teeth with temporary crowns.

IV. Fabrication of the primary parts (LAB)

  • Fabrication of a preparation model from special plaster based on the preparation impression.
  • Fabrication of a double crown (metal or ceramic): as a telescopic crown, this must be milled exactly parallel-walled and highly polished and must not have any undercuts.
  • Alternatively, anchoring elements such as attachments, bars or press studs are incorporated into the crown.
  • Fabrication of the individual impression tray
  • Making bite templates from plastic: wax walls melted onto them simulate the future dental arch and are initially based on average values.
  • Making registration templates to determine the bite position (ZA).

V. Functional impression (ZA)

  • Before the impression is taken with the help of the custom-made tray, its edges are corrected, either by shortening the material with the plastic cutter, or by applying additional thermoplastic material: the initially heated material is applied to the tray in a soft state and slowly hardens in the mouth while the patient performs functional movements (special movements with the mimic muscles and tongue).
  • Functional impression: after positioning the tray coated with impression material in the mouth, the patient performs certain functional movements to shape the margins in a functionally appropriate manner. The aim of the functional margin design is that the marginal areas of the new prosthesis fit into the vestibule (space between the alveolar ridge and the lips or cheeks) without interference, but at the same time slightly displacing the soft tissue and thus sealing well, and, if a mandible is supplied, into the sublingual area (lower tongue area).
  • Fixation of the primary parts: Before the functional impression is taken, the primary parts are placed on the prepared teeth. They remain in the impression material after the impression is taken and are thus transferred to the next working model of the laboratory.

VI. trimming the wax walls (ZA).

The wax walls of the bite templates are individualized and aligned in three dimensions:

  • In the frontal view, the future occlusal plane (masticatory plane; plane where the teeth of the upper and lower jaws meet) must be parallel to the bipupillary line (connecting line between the pupils) and
  • Are located at the level of the lip closure.
  • In lateral view, the masticatory plane must be parallel to Camper’s plane (reference plane on the bony skull: connecting plane between spina nasalis anterior (the most anterior (front) point of the maxilla) and porus acusticus externus/outer ear opening).
  • The height of the single or both wax walls is to be designed so that the patient has a so-called resting float of 2 to 3 mm: when the masticatory muscles are relaxed, the teeth must not touch each other.
  • The centerline is drawn following the centerline of the nose.
  • The canine lines are drawn in line with the width of the nose.
  • The upper wax ridge should still be slightly visible below the upper lip when the mouth is slightly open and the upper lip is relaxed.
  • The smile line is an orientation for the future boundary between teeth and gingiva (gums).

VII. jaw relation determination (ZA).

In the same treatment session, an intraoral (“inside the oral cavity“) support pin registration is made to be able to transfer the vertical distance of the jaws as well as their sagittal (“running from front to back”) positional relationship to each other to the laboratory by keying the upper registration template with the lower registration template. In addition, an arbitrary hinge axis determination* is performed, the position of which is also transferred to the laboratory with the aid of a so-called facebow. For even more precise individualization, a recording of the sagittal condylar path (recording of the movement sequence in the temporomandibular joint during the opening movement) is possible. * Estimated axial connection between the temporomandibular joints determined by their position in relation to the porus acusticus externus (external ear opening).

VIII. Selection of anterior teeth (ZA/LAB)

The color and shape of the future anterior teeth should be selected in cooperation with the patient, because otherwise it will be difficult for the patient to accept a prosthesis whose esthetics do not match his or her expectations. The length and width of the teeth must be based on the previously determined parameters such as the midline, smile line and canine line. IX. Fabrication of the abutments and wax-up (LAB)

  • Fabrication or fitting of prefabricated abutments on the primaries – If the abutments of double crowns are fabricated by the casting method, their modeling in wax is performed first, followed by their conversion into a cast secondary crown, which is soldered to the model casting base. Alternatively, a secondary crown can be fabricated using the electroforming technique by direct electrodeposition of a gold layer onto the primary crown and then mounted into the base using a special composite (resin) adhesive. – The tooth-colored veneer of the secondary crown is layered plastic.
  • Bars, button anchors and attachments are prefabricated, precisely matched matrix-patrix systems whose abutments are incorporated into the model casting framework.
  • Placement of the denture teeth on the model casting framework in wax, with the dental arch corresponding to the individualized wax wall.

X. Wax try-in (ZA)

A try-in of the wax-up is now performed on the patient. Since the denture teeth are on a wax base, position corrections can still be made. XI.Finishing (LAB)

After the dentist and patient have determined the final position of the anterior and posterior teeth, the denture is completed. The denture material is PMMA plastic (polymethyl methacrylate). The denture is manufactured under pressure and heating in order to achieve the highest possible degree of polymerization or the lowest possible residual monomer content (monomer: individual components from which larger macromolecular compounds, the polymers, are formed by chemical combination). XII. Incorporation (ZA)

  • The completed combined denture is tried in to the patient, and corrections to margins and occlusion (final bite and chewing movements) may be required.
  • Attaching the Primaries – The denture base (bottom) and inside of the abutments are thinly coated with petroleum jelly for insulation from the luting cement. Clean and dry the prepared teeth, thinly coat the inside of the primaries with zinc phosphate cement, for example, and then place them on the teeth under pressure. Pressed-out excess cement is immediately removed with foam pellets. The denture is placed over the primary parts in the mouth while the cement is still setting.
  • After the cement has set, the denture is removed and checked for cement residue. The first removal can also be done with a few hours interval at an additional appointment.
  • The patient receives care recommendations for the new denture.
  • The insertion and removal of the denture is practiced with the patient.

XIII Follow-up (ZA).

The patient is given a short-term appointment to check for possible pressure points, as well as a recommendation for regular reappearance at the recommended interval, which is based on the state of oral health.

After the procedure

The condition of the crowned teeth, the denture, and the denture bed (tissue on which the denture is supported in the mouth), which is subject to gradual change, should be checked at six-month intervals. Timely relining of the denture can minimize damage to the tissue (e.g., pressure points or bone resorption), as well as overloading of the teeth and damage to the denture (e.g., fatigue cracks or denture fracture).

Possible complications

  • Pressure points
  • Premature loss of crowned teeth due to lack of dental care.
  • Premature denture fracture – the patient is advised to place a towel in the hand basin before cleaning the denture, or to let water in so that it lands gently if it falls out of the hand during cleaning.