Full Denture Prosthetics: The Ultimate Discipline
Craftsmanship and individual specifications in a digital age
Sebastian Guttenberger, MDT
What is the role of full dentures in the age of artificial intelligence (AI), automation, and CAD/CAM manufacturing? What relevance do manual skills still have? These questions occupy the minds of many dental colleagues. Digitization undoubtedly offers many advantages. However, full dentures still represent handcrafted work. The realization of esthetic, functional, and patient-specific aspects that make up a "good" full denture requires skills such as observation as well as creativity and an understanding of functional relationships. The basic idea behind the fabrication of dentures is always the same: A denture should be comfortable to wear and inconspicuous for the patient. The focus is on the natural shape of the teeth and—depending on the tooth replacement solution—of the gingiva. Be it digital or analog, a number of preliminary considerations are required prior to realization to prevent problems from occurring in the first place. Digitization is particularly helpful for fixed denture solutions. Digital design not only allows the frameworks to be created, but also enables a fully anatomical situation to be defined as the target. This can, for example, be realized by means of 3D printing. Digital technologies can also prove helpful for full dentures. In principle, however, full dentures are based on a sound knowledge of traditional fabrication methods and on taking the patient's individual circumstances into account.
Case Report
The following case was the winning entry in the 13th KunstZahnWerk competition, presented by Candulor. Mucosa-supported maxillary and mandibular dentures were to be created for a 69-year-old female patient. In the maxilla, the patient had been fitted with a denture for 15 years. Initially anchored via double crowns, abutment teeth Nos. 9 through 11 needed to be removed. She wore an interim denture in the mandible after teeth Nos. 20 through 28 and 30 needed to be extracted due to advanced periodontitis. The goal was to create natural-looking dentures according to the dynamic occlusion concepts tooth-to-tooth or tooth-to-two-tooth setup.
The situation was aggravated by a pronounced atrophy in the mandible, a slight flabby ridge in the region of teeth Nos. 23 through 26, and a change in the mucosa (leukoplakia) near tooth No. 20. The existing dentures exhibited several deficits. The anterior teeth were barely visible in both the upper and lower arches. Due to the low vertical proportion, the lower third of the face appeared squat and the chin pointed. The patient complained about inadequate denture retention. She could only eat by using adhesive cream to fixate the denture in her mouth. She wanted a denture with a firm hold, visually more prominent anterior teeth, age-appropriate esthetics, and adequate chewing performance. Also important to her was an appealing facial appearance, with the chin appearing less pointed. Youth photographs were utilized for orientation.
Preparatory Steps
The models of the maxilla and mandible were duplicated, and the master models were fitted with rotation locks (brass cones, milled grooves, magnet) for a split cast base (Figure 1 and Figure 2). The preliminary technical considerations were:
- Keeping in mind the increase in vertical relation when articulating.
- Adequate finishing of the denture body (buccinator support, muscle-gripping denture body, margin design), as the flabby ridge can lead to a poor suction effect of the denture.
- Utilizing a silicone matrix as a control element for an individual set-up of the maxillary teeth according to the physiognomic bite key (Figure 3).
Assignment of the Models in the Articulator
There are various methods for transferring the position of the mandible in relation to the cranium to the articulator. A common approach is the facebow to determine the position of the upper jaw. For this case, the mandibular model was transferred to the articulator (CA 3.0, Candulor) with a mean value (Figure 4). The condylar path inclination in relation to the Camper's plane (occlusal plane) was preset at 45° on the right and 47° on the left. To reflect the increase in vertical relation, the support pin was lowered by 1 mm (Figure 5). Among other things, the objective was to make the maxillary anterior teeth more visible and to make the patient's physiognomy appear more harmonious. Prior to the model analysis, the support pin of the articulator was reset to the zero position.
Model Analysis
The model analysis initially requires some time, but significantly increases the quality of the results. For instance, jaw relationships, the position of the plane of occlusion, and midline of the maxilla can be determined with the aid of model analysis. The results of the model analysis enable a precise tooth set-up according to static aspects, taking muscular balance into account.
Static lines
After marking the incisal papilla and the center of the model as an orientation guide, the positions of the first premolars in the maxilla and mandible were marked. In the maxilla, the canine was located at the level of the first large palatal fold, one premolar width to dorsal of the first premolar. In the mandible, the positions were marked in extension of the buccal frenulum attachments.
The retromolar triangles in the mandible or the tuber in the maxilla were outlined and bisected sagittally and transversely with a line. The points of intersection were connected to the marked positions of the first premolars (Figure 6). The resulting lines formed the basic static lines and were marked in red.
Inner and outer contours
The inner and outer contours indicate the tolerance range of the basic statics and create the setup area for the teeth (Figure 7). In the mandible, the intersection points of the transversal bisector line are connected with the position of the first premolars when contouring the retromolar triangles. The line passing through the lingual point represents the inner correction (green), while the line passing through the vestibular point represents the outer correction (blue). In the maxilla, the outer correction runs along the vestibular fold and the inner correction as the connecting line of the pterygomandibular plica and the position of the first premolars. The markings were extended dorsally at right angles to the occlusal plane. The overlapping area (intersection area) formed the setup area.
Alveolar ridge contour and main masticatory center
The contour of the alveolar ridge was determined with the aid of profile compasses. These were guided at right angles to the model side from mesial to distal to transfer the alveolar ridge contour of the mandible to the side of the model. The main masticatory center was defined by a tangent parallel to the occlusal plane through the lowest point of the alveolar ridge contour (Figure 8). The point of contact of the tangent marked the main chewing center and could be identified by a vertical line on the model side. In addition, a tolerance range was marked by vertical lines on both sides of the model at a distance of approximately 1 mm. As a rule, the first molar of the mandible lay within this tolerance range.
Stop line
A line was drawn through the main chewing center point at an angle of 22.5°, which extended to the dorsal. The second intersection of this line with the alveolar ridge line could be marked with a vertical line and transferred to the model margin perpendicular to the occlusal plane. This marking formed the stop line and thus the most distal point at which a tooth may be in occlusion (Figure 9). Setting a tooth behind this line can cause the mandibular denture to slide ventrally (protraction).
Setup of the Teeth
Maxillary anterior teeth
The information from the analysis was put together like a puzzle when setting up the teeth (PhysioSelect TCR, Candulor), and the ideal tooth positioning was evaluated. The bite key provided a rough guide for positioning the teeth. Attention must be paid to ensure that the labial surfaces of the teeth touch the silicone matrix (bite key) (Figure 10). According to the Gerber Condyle Theory, the central incisors and canines were set up at equal lengths—approximately 0.5 mm to 1 mm above the occlusal plane. The lateral incisors were slightly shorter. The tooth axes exhibited slight mesial inclination.
Mandibular anterior teeth
Teeth Nos. 23 through 26 (PhysioSelect TCR, Candulor) were set up oriented to the occlusal plane, whereby a small tolerance as possible due to a slightly nested setup (Figure 11). The canines could be positioned minimally above the occlusal plane (approximately 0.5 mm). When positioning the teeth to labial, the sagittal step must be considered. As the lower anterior teeth do not play a supporting role in functional loads and should only exhibit slight sliding contacts in protrusion, an individual setup was possible.
Posterior teeth in the mandible
In the posterior region, the focus was initially on the lower teeth (BonSelect TCR, Candulor), because their position was important for the articulation contacts (Figure 12 and Figure 13). The first premolars took on the main guidance function and were set up with an inclination of approximately 10° distally and 1 mm above the occlusal plane. The second premolars were at the level of the occlusal plane and were inclined to distal by approximately 5°. As there was no space for two molars dorsally, the first molar was replaced by a third premolar. For a harmonious curve of Spee, the molar was tilted slightly to mesial. The mesiobuccal cusp of the molar was level with the occlusal plane, while the distobuccal cusp stood 0.5 mm above the plane.
Posterior teeth in the maxilla
The upper posterior teeth (BonSelect TCR, Candulor) touched the silicone key with the buccal surfaces (Figure 14 and Figure 15). Again, the position of the first premolars was important as these teeth, together with the lower first premolars, provided the main guidance. They were set up at the level of the occlusal plane and inclined approximatey 10° to mesial. The palatal cusps were located in the fossa of the lower first premolars. The second and third premolars were treated in the same manner. The molars in the maxilla were slightly inclined to distal and only tangential to the occlusal plane with their mesiobuccal cusps, whereby the distobuccal cusps lay slightly above. The main contacts were located on the mesiopalatal cusp of the molars. The buccal cusps were out of occlusion and at some distance from the lower buccal cusps so as not to restrict articulation movements.
Grinding in occlusion and articulation movements
Grinding-in of the occlusion began with checking the contact points and carefully grinding interfering contacts. The main contacts were located on the palatal or mesiopalatal cusps in the maxilla and in the central fossa in the mandible. The aim was to achieve two to three points per tooth, evenly distributed between the left and right tooth rows (Figure 16 through Figure 18).
Modeling the denture body
Careful design of the denture body in the mandible was important to compensate for the lack of suction effect (flabby ridge) by means of a muscle-gripping design (Figure 19 and Figure 20). Buccinator supports were modeled to provide a counter abutment for the musculus buccinator, while the lip shield labially provided an abutment for the musculus orbicularis oris. The lower denture was modeled lingually in such a manner that the musculus mylohyoideus and the tongue nestled against the denture body in the rest position. In addition, palatal folds were designed on the maxillary denture to provide orientation for speech and assist with chewing.
Finishing of the Dentures
The transfer of wax dentures into resin was performed with the cold press technique (PolyMaster, Candulor). The advantage was that the model could be blocked out without the wax melting. By pressing the resin into the flask, a high accuracy of fit of the dentures was achieved. In addition, the denture body could be customized with lighter and darker resins as well as intensive shades before inserting the base material (Candulor 34). Prior to insertion of the models into the flask, silicone matrices (Monosil, HLW Dental) were fabricated and perforated at the cusp tips as well as incisal edges to provide selective support for the teeth (Figure 21). The lower part of the flask was filled with super hard plaster (Rocky Mountain, Class 4) and the model was pressed into the plaster. After 20 to 30 minutes, the lid of the flask could be removed (Figure 22). The teeth were provided with retention notches basally, sandblasted, and bonded into the matrices with instant adhesive (Figure 23). The vibrating line etching provided a tight seal between the denture base and the palate, and maximized the suction effect and denture bearing (Figure 24).
After the models had been wetted and insulated with alginate insulation (Iso-K, Candulor), and the teeth had been fixed in the matrix, the resin polymers were prepared (Figure 25). To provide natural esthetics, individualization and intensive color materials should be used in addition to the base material (Candulor 34) (Figure 26). The teeth were wetted with monomer and the individualization materials (AESTHETIC Intensive Colors, Candulor) were applied followed by the base material (Figure 27). After screwing the flask closed, polymerization wes performed for 20 to 25 minutes at 40 °C water temperature in the pressure pot, with a polymerization light (Bluephase, Ivoclar).
After devesting of the dentures, occlusion and articulation were checked; the support pin was set to zero (Figure 28). This was followed by the removal of the dentures from the models. Tooth necks and proximal spaces were reworked and the marginal areas as well as the areas for muscle-gripping were optimized. The dorsal prosthetic margin of the maxillary denture was shortened to the vibrating line and both dentures were carefully polished (Figure 29). Here, special attention was paid to the occlusal surfaces so as not to lose the occlusal points and ground facets.
Individualization of the Dentures
To provide the dentures with more naturalness and liveliness, the teeth should be individualized. The denture bodies were covered with wax. This served to protect the already polished gingival portions. The labial and buccal surfaces of the teeth could then be conditioned and designed with characterization materials (Optiglaze Color Sets, GC), eg, ground facets, enamel cracks, imitation of leukoplakia (Figure 30). The lower denture was furnished with a gold inlay (Aurumed Norm, Deutsche Aurumed Edelmetalle) at the level of the molar (Figure 31). After final polishing and cleaning of the models as well as dentures, the work was complete (Figure 32 and Figure 33).
Conclusion
Although dental technology is becoming increasingly digitized, the esthetic, functional, and individual aspects of full denture prosthetics require the craftsmanship and creativity of the dental technician. The challenge is to uphold these skills in a digital age. The knowledge of proven criteria and the skills of analog processes form the basis for solid full denture prosthetics. Cooperation within the dentist-laboratory team as well as an understanding of the individual needs of the patient remain indispensable for a successful result and long-term patient satisfaction.
About the Author
Sebastian Guttenberger, MDT
Master Dental Technician
Zahntechnik Hierold
Pirk, Germany
