A total prosthesis (complete denture) is a removable dental prosthesis for the restoration of one or both completely edentulous jaws. The following explanations can only be very general, as the development of total prosthetics has produced many different solutions.
Indications (areas of application)
All treatment concepts aim to provide the edentulous patient with esthetically pleasing dentures that are functionally flawless and atraumatic for all adjacent tissues.
Contraindications
A contraindication to total dentures made of polymethyl methacrylate exists in the case of a very rare, proven intolerance to MMA (methyl methacrylate) or other ingredients, in which case a positive epicutaneous test (synonyms: patch test, plaster test; provocation test (allergy test), which is used to determine whether a contact allergy is present) alone is not sufficient for the diagnosis of an allergy; only the presence of clear clinical symptoms completes the diagnosis.
Before the procedure
The procedure is preceded by clarification of the patient’s expectations of the future denture and his or her counseling and education about alternative treatment methods, such as preprosthetic surgical procedures to improve the denture bearing and thus improve subsequent denture retention. This also includes the placement of implants, for example, in the case of poor denture bearing in the mandible, on which, even with good conditions, in principle a significantly lower denture adhesion can be achieved compared to the maxilla.
The procedure
is divided into several treatment steps, which are carried out alternately between the dental practice (hereinafter referred to as “ZA”) and the dental laboratory (hereinafter referred to as “LAB”). I. Situation impression (ZA)
The impressions of the edentulous jaws are taken with standardized impression trays usually with alginate – impression material. II Situation impressions (LAB)
are made by pouring the alginate impressions with plaster and are used for the
- Orientation about the anatomical conditions of the jaw.
- Production of so-called individual impression trays made of plastic, which meet the individual anatomical features of the previously impression jaw.
III. tray corrections and functional impression (ZA).
Before another impression is taken with the help of the made tray, its margins are corrected, either by shortening the material with the plastic cutter, or by applying it with 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). The aim of functional margin shaping is to ensure that the marginal areas of the new denture fit into the vestibule (oral vestibule, space between the alveolar ridge and lips or cheeks) without interference, but at the same time slightly displacing the soft tissue and thus providing a good seal, and, if a mandible is being restored, into the sublingual area (lower tongue area). The functional margin design is the decisive step with which satisfactory denture retention can be achieved via adhesion and negative pressure. In the subsequent functional impression, the complete base of the tray is loaded with impression material – for example, addition-curing silicone. After positioning the tray in the mouth, the patient again performs certain functional movements in order to form the margins in a functionally appropriate manner. IV. Master model, bite templates and registration templates (LAB)
With the aid of the functional impression, the so-called master model is fabricated from special plaster. The dental technician uses this to fabricate plastic bite templates, onto which wax walls are fused. These are initially based on average values and are intended to simulate the future dental arch. In addition, registration templates are produced for the next working step with the dentist. V. Jaw relation determination and trimming of the wax walls (ZA)
The wax walls 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 jaw 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 center line is drawn following the center line 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).
In the same treatment session, an intraoral support pin registration is created to be able to transfer the vertical distance of the jaws as well as their sagittal 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 made, 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. VI. Selection of the 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. VII. anterior tooth set-up / complete wax-up (LAB)
If you want to be sure, only the anterior teeth are set up first, while the remaining wax wall remains. VIII. Wax try-in (ZA)
The bite templates are tried in on the patient. Depending on the procedure, either the anterior teeth or all the teeth are added, although they are still on a wax base and can therefore be moved in their position during the try-in. IX. Finalization (LAB)
After the dentist and patient have determined the final position of the anterior and posterior teeth, the denture is finished. Before the denture is pressed in acrylic, the dental technician ensures even better suction adhesion for future maxillary dentures by means of an “artifice”: an approx. 2 mm wide, max. 1 mm deep line is etched (abraded) on the master cast, which lies at the transition of the hard palate to the soft palate: The dorsal dam of the future prosthesis displaces soft tissue and prevents air from penetrating under the prosthesis while the soft palate moves during speech. The prosthesis 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). X. Incorporation (ZA)
The finished prosthesis is fitted to the patient, whereby corrections to margins, occlusion (final bite) and articulation (chewing movements) may be required. Care recommendations for the new prosthesis are explained to the patient. XI. Follow-up check-up (ZA)
The patient will be given a short-term appointment to check for possible pressure points, as well as a recommendation for regular re-visits every six months.
After the procedure
The condition of the denture and the denture bed (hard and soft tissues on which the denture is supported in the mouth), which may be subject to constant change, should be checked at six-month intervals. Timely relining of the denture can prevent damage to the tissue (e.g., pressure points or bone resorption), as well as damage to the denture (e.g., fatigue cracks or denture fracture).
Possible complications
Due to the large number of parameters and work steps to be taken into account, fit deficiencies may result, which in the simplest case may lead to the repetition of an intermediate step, and in extreme cases to the fabrication of a new prosthesis.A possible dissatisfaction of the patient with the esthetics of the new prosthesis can only be prevented by, as already mentioned, intensively involving the patient in the selection of color and shape, having the selection countersigned and providing information in advance regarding the limitations that may be due to the function. Premature prosthesis fracture is a frequent complication that is not caused by faulty function but by incorrect handling during prosthesis hygiene. The patient should therefore be advised to run water in the hand basin before cleaning the prosthesis so that if it falls out of the hand during cleaning, it will land gently in the water.
