Telescopic Prosthesis

A telescopic denture is used to replace several teeth in a partially edentulous jaw. It is a combination of a removable denture and telescoping double crowns that fit firmly in the mouth and anchor the denture without clasps. A telescopic denture differs in shape and extension from a complete denture (full denture) and also from an overdenture. The latter is a denture supported purely by mucosa, in which the chewing force cannot be supported by the severely reduced and periodontally (with regard to the tooth bed) damaged remaining teeth. The denture must be extended accordingly to distribute the load on the oral mucosa over a wide base. In contrast, with a telescopic prosthesis the force is transmitted both to the residual teeth and to the alveolar ridge or the oral mucosa covering it. The prerequisite for this is that the condition of the periodontium (tooth-supporting apparatus) of the teeth intended for double crowns still permits this load, so that they can assume the following tasks for the denture:

  • Support function
  • Holding function
  • Guide function
  • Thrust distribution function

The peculiarity of a telescopic prosthesis is parallel-walled telescopes (sleeve slides). These are double crowns, whose primary crown (synonyms: inner telescope, primary part, primary telescope) is firmly cemented to the prepared (ground) tooth, while the secondary crown (synonyms: outer telescope, secondary part, secondary telescope), which fully encompasses the primary part physically, is incorporated into the prosthesis. The primary and secondary crowns have friction (static friction) to each other due to the parallel walls, which counteracts the withdrawal forces during speech and chewing. The parallel-walled portions of the crowns ensure a defined insertion direction of the denture and, due to a defined abutment of the secondary crown on the primary part, an axial load (in the root direction) on the teeth supplied with the telescopes during mastication. The denture in which the secondary crowns are incorporated is stiffened by a model casting base in such a way that the chewing pressure is distributed from the telescopes to the denture without risk of fracture and the load on the alveolar ridge or mucosa is thus reduced. However, the load cannot be completely avoided, especially in areas with increasing distance to the telescope. Consequently, a telescopic denture is a dental prosthesis that is supported both periodontally (by the periodontium) and by the mucosa. If we compare a simple cast denture with a telescopic one, one of the advantages resulting from the exact fit of the double crown system is the high level of safety for the patient when speaking and eating. The model cast prosthesis is also at a distinct disadvantage in terms of esthetics because of its visible clasps. The only compromises that have to be made with the telescopic prosthesis are the facts that double crowns must necessarily have somewhat more volume than simple crowns and that the tooth-colored veneer of the abutment is made of plastic – and not, for example, of higher-quality ceramic.

Indications (areas of application)

A telescopic prosthesis is planned when there are no longer sufficient teeth in a partially edentulous jaw to provide gaps with a fixed bridge construction. Teeth that can be expected to bear a chewing load due to their periodontal condition (periodontal bed condition) can be restored with parallel-walled telescopes that transfer the force to the tooth-supporting apparatus and the denture base. Multiple abutments with a symmetrical distribution of abutments should be aimed for.

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 fitting a telescopic denture, the patient’s expectations of the new denture are clarified. The patient is counseled about alternative treatment options such as that of a simple cast model denture or an overdenture. Implant placement to avoid the need for a denture is also addressed as a treatment alternative.

The procedure

is divided into several treatment steps, which are carried out alternately between the dental practice (hereinafter referred to as the “dentist”) and the dental laboratory (hereinafter referred to as the “laboratory”).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
  • 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 fitted with telescopic crowns are contoured under local anesthesia (local anesthesia) with rotary instruments so that no undercuts interfere with the subsequent placement of the thimble-shaped primary crown. The later 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. Primary crown fabrication (LAB)

  • Fabrication of a preparation model from special gypsum based on the preparation impression.
  • Fabrication of the primary crown (metal or ceramic crown) – This must be milled exactly parallel-walled and highly polished and must not have any undercuts.
  • Manufacture 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 specific functional movements to shape the margins in a functionally appropriate manner. The aim of the functional edge design is that the edge areas of the new prosthesis without interference, but at the same time slightly displacing the soft tissue and thus well sealing into the vestibule (space between the alveolar ridge and lips or cheeks) and, if a lower jaw is supplied, in the sublingual area (lower tongue area).
  • Fixation of the primaries – Before the functional impression is taken, the primary crowns 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 the spina nasalis anterior and the porus acusticus externus).
  • 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 chewing muscles are relaxed, the teeth must not touch.
  • 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 created in order 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 encoding 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. * The arbitrary hinge axis is the estimated axis connection between the temporomandibular joints, which is determined by its 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. secondary crown fabrication and wax-up (LAB)

  • Fabrication of the abutments on the primary crowns – first as a wax-up, followed by conversion to a cast secondary crown, which is soldered to the model casting base. Alternatively, an abutment can be fabricated using the electroplating technique true to form by direct electrodeposition of a gold layer on the primary crown and then mounted in the base with a special composite adhesive (plastic).
  • The veneering of the abutment is made of plastic.
  • 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. Finalization (LAB)

After the dentist and patient have determined the final position of the anterior and posterior teeth, the denture is finished. The denture material is polymethyl methacrylate (PMMA)-based plastic. The denture is manufactured under pressure and heating 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 of the finished telescopic work (ZA).

  • The finished placed telescopic work is tried in to the patient, and corrections to margins, occlusion (final bite), and articulation movements (chewing movements) may be required.
  • Attaching the primary crowns – The denture base (underside) and inside of the secondary crowns are thinly coated with petroleum jelly for insulation from the luting cement. The prepared teeth are cleaned and dried, the primary crowns are thinly coated on the inside with e.g. zinc phosphate cement and then placed on the teeth under pressure. Pressed-out excess cement is immediately removed with foam pellets. The prosthesis is placed over the primary crowns in the mouth.
  • After the cement has set, the denture is removed and checked for cement residue. The first removal can also be done a few hours apart 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 may be subject to 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 loss), 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.
  • Denture fracture due to mishandling – the patient is advised to place a towel in the hand basin before cleaning the denture or to let water in so that the denture lands gently if it falls out of the hand during cleaning.