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Monolithic Zirconia Complete-Arch Reconstructions Esther Grob, cdt Mario Sisera, cdt
Zirconia has established itself as a durable material for prosthetic frameworks. However, the interface between the veneering material and the zirconia frame, when exposed to high stress, has proven to be the weakest part of the reconstruction. The introduction of more translucent and multilayered zirconia has allowed elimination of the veneering process in highstress areas. Even in esthetically demanding areas, the veneering material can be applied in a minimal layer on the labial surface. Monolithic zirconia restorations can provide maximal strength with minimum tooth reduction and still achieve adequate esthetics. This chapter presents two case reports to illustrate the restorative potential of zirconia ceramic materials.
Case 1: Stained Monolithic Zirconia Prosthesis An 84-year old man in excellent physical health presented with a history of trauma to the maxillary anterior teeth. This trauma resulted in root fractures that led to the loss of a three-unit fixed partial denture extending from the right central incisor to the left lateral incisor (Figs 10-1a and 10-1b). The patient’s panoramic radiograph revealed that the root tips of the maxillary right central incisor, left lateral incisor, and left first premolar had been retained (Fig 10-1c). They were deemed unrestorable and needed to be extracted. The clinical findings revealed generalized plaque accumulation and subgingival calculus that was visible in the panoramic radiograph. Most teeth exhibited probing depths of up to 6 mm, which had to be eliminated before final prosthodontic treatment. In the maxilla, just four teeth were considered to have a good prognosis. Both the right and left canines and second premolars had adequate periodontal attachment and tested negative for endodontic involvement. In the mandible, all the teeth present were considered maintainable. Periodontal treatment was needed followed by periodic maintenance by a dental hygienist.
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b Fig 10-1 (a and b) Initial clinical situation. (c) Pretreatment panoramic radiograph.
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Initial treatment plan
Evaluation
The patient expressed a strong preference for a fixed rehabilitation. Therefore, an initial treatment plan was formulated with that in mind. The maxillary posterior segments could be restored with two three-unit fixed partial dentures on the remaining natural teeth. In the anterior section, implants were planned for the positions of the right lateral incisor and left central incisor. These would be restored with an implant-supported four-unit fixed partial denture. In the mandible, the dentition was intact up to the first premolar on both sides; no further tooth replacements were planned initially. If the patient felt that his chewing capacity was not adequate with just one premolar on each side, one premolar more could be added to each side using implants. Initially, a 10-unit provisional resin prosthesis supported by the maxillary canines and second premolars was planned. This provisional fixed partial denture would facilitate optimal periodontal treatment, because the existing prosthetic restorations had significant overhangs that prevented proper debridement and plaque control. This fixed provisional restoration would also serve during the placement and healing of the implants. To fabricate this provisional restoration, initial impressions were taken and sent to the dental laboratory.
This patient was referred to the laboratory for an evaluation. Discussions with the patient and the referring dentist and evaluation in the laboratory led to the establishment of the clinical goals for this patient’s treatment plan: an increase in the vertical dimension of occlusion, a reduction in the length of the maxillary anterior teeth, replacement of posterior teeth to reestablish the fullness of the buccal corridors, and an improvement in esthetics. The patient also gave input regarding his esthetic goals, including his desired shade for the reconstruction.
Initial treatment Preliminary impressions were made, and gypsum diagnostic casts were fabricated. A diagnostic wax-up that incorporated the goals of treatment was prepared. This wax-up was used to fabricate an acrylic resin “eggshell” provisional restoration (Fig 10-1d). Following a first visit with the dental hygienist, the periodontal situation improved significantly. In a long clinical appointment, after local anesthesia was administered, the patient’s existing metal-ceramic restorations were removed. The four vital maxillary teeth (left first premolar and
Case 1: Stained Monolithic Zirconia Prosthesis
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Fig 10-1  (cont) (d) Acrylic resin eggshell provisional restoration. (e) Intraoral view after extraction of root fragments. (f ) The relined provisional prosthesis is ready to be trimmed. (g and h) Postoperative view with provisional prosthesis in place.
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molar and right canine and second premolar) were built up directly with a dentin bonding agent (Syntac, Ivoclar Vivadent) and a composite resin (Tetric EvoCeram, Ivoclar Vivadent). Next, the root fragments from the maxillary right second premolar, right and left central incisors, and left first premolar were extracted (Fig 10-1e). The eggshell provisional prosthesis provided by the dental technician was relined in the mouth using a polymethyl methacrylate (TAB 2000, Kerr Dental; Fig 10-1f ) after the teeth and the soft tissues were coated with petroleum jelly.
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The relined provisional prosthesis was trimmed and polished extraorally and cemented in place with a temporary cement (Temrex, Temrex) (Figs 10-1g and 10-1h). The patient functioned with this provisional denture for several months. During this time, the provisional restoration served as a prototype of the definitive reconstruction. The patient was reexamined several times, and the esthetics and function of the prosthesis were evaluated. He provided feedback that resulted in some minor modifications to the provisional prosthesis. 191
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Monolithic Zirconia Complete-Arch Reconstructions Fig 10-1  (cont) (i) Postoperative view after 6 months showing the soft tissue healing and the final preparations on the remaining maxillary teeth.
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Definitive treatment
Final impression
Six months after placement of the provisional prosthesis, the patient exhibited a healthy periodontal situation with maximal probing depth of 3 mm. Oral hygiene had improved significantly. He reported no difficulty with oral function and was satisfied with the esthetics but reported that some photographs taken of his face revealed that other people could detect that teeth were missing in the maxilla. The provisional prosthesis showed good stability on the four abutments, and tooth mobility had not changed. The additional use of implants was discussed again, and the initial treatment plan was modified. It was decided that the provisional prosthesis should be copied for the definitive fixed partial denture. Clinical studies have shown that such long-span fixed partial dentures supported on few natural teeth with reduced periodontium have good long-term prognoses, as long as the patient is maintaining good oral hygiene.1 Furthermore, it was decided that the maxillary prosthesis would be extended distally with a premolar on each side. These additional teeth were not going to be in occlusal contact but would help in two ways. First, esthetics would be improved, because wide smiles revealed black spaces distal to the second premolar, indicating missing teeth. Second, this additional tooth on each side represented better guidance for the use of an interdental brush to clean the distal aspect of the maxillary premolars.
After removal of the provisional prosthesis, retraction cords were placed to better expose the preparation. Following periodontal treatment, the gingiva had shrunk; therefore, the preparations had to be extended to the new gingival level. The definitive preparation involved a rounded shoulder with a depth of approximately 0.5 mm at the gingival margin (Fig 10-1i). The definitive restoration margin was to be located approximately 0.5 mm intrasulcularly after completion of the procedure. The final impression was taken with both an intraoral scanner (Trios, 3Shape) and a conventional polyether impression material (Permadyne, 3M ESPE). Both types were prepared to allow comparison of digital and conventional complete-arch impressions to determine if digital results were as precise as conventional. This case showed that the digital impression was as accurate as the conventional impression, but working time and patient comfort were much more favorable with the digital technology. The provisional prosthesis was relined and recemented with TempBond (Kerr Dental). After cementation, an additional digital impression was taken of the provisional denture so that the tested occlusion and tooth form and arrangement could be transferred to the laboratory. The mandibular arch impression and the bite registration were also completed with the intraoral scanner. All data were sent into the laboratory digitally via the internet. The patient was told that the next appointment would be in the dental laboratory.
Case 1: Stained Monolithic Zirconia Prosthesis
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Fig 10-1  (cont) (j) Try-in of the wax-up. (k) Shade selection.
Laboratory procedures For this patient, it was preferrable to do a wax mock-up or setup, and, after try-in, a pre-preparation scan of the mockup was made in the laboratory on the D800 (3Shape). With the dental design software, it was then possible to use the scan of the mock-up as the basis for the design of the definitive prosthesis. From the photographs taken by the dentist, it was clear that the provisional reconstruction was still too long, so a copy of the provisional prosthesis was created in wax and the length adjusted before try-in. However, it is also possible to scan the provisional prosthesis with an intraoral scanner and have it serve as a model for the design of the definitive prosthesis. The tooth-colored wax-up was tried in at the laboratory and adjusted with input from the patient (Figs 10-1j). At this stage, it was possible to work with the patient to understand his demands and incorporate them, when possible, into the wax-up. The same appointment was used to select the shade, surface texture, and luster for the definitive reconstruction (Figs 10-1k). CAD procedure. The uncut cast of the remaining denti-
scanned with the D800 model scanner in the laboratory. It is always essential to keep the connectors as large as possible, especially on the lingual surfaces of the reconstruction, where esthetics is secondary. Control over the occlusion was critical for the long-term survival of this restoration. Therefore, it was essential to exactly reproduce the occlusal aspect of the mock-up (Figs 10-1l to 10-1o). Finishing the presintered zirconia. The reconstruction
was milled from a translucent zirconia disk (Biodenta). Once the milling was completed, the presintered restoration was returned to the laboratory. The burs used at the milling center are fairly large, and the final finishing of the occlusal surfaces and connectors is best done in the laboratory prior to sintering. Fine burs were used carefully, without pressure, to finish the prosthesis without creating small flaws or cracks in the presintered zirconia (Fig 10-1p). Once the details on the presintered zirconia frame were finished, it was sent back to the milling center for basic staining and sintering. It is important to have the shape and details of the presintered frame mostly finished. This will avoid heavy grinding on the sintered ceramic, which could create initial cracks and flaws.
tion, as well as the single dies and the mock-up, were now
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Fig 10-1  (cont) (l to o) The digital impressions of the cast and mock-up are used to design the zirconia framework.
Case 1: Stained Monolithic Zirconia Prosthesis Fig 10-1 (cont) (p) Use of a fine bur to finish the occlusal surfaces prior to sintering. (q) Presintered zirconia prosthesis on the blank. (r) The presintered zirconia is 20% bigger than the wax-up. (s) Application of stain for the basic shade of the zirconia prosthesis. (t) The sintered prosthesis is finished with fine burs and stones and polished manually.
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Sintering and basic staining. During the sintering proc
ess, the prosthesis was left connected to the zirconia disk to prevent distortions (Fig 10-1q). The presintered and milled zirconia construction was about 20% bigger than the waxup (Fig 10-1r). The prosthesis was stained before sintering (which is done at a temperature between 1,450°C and 1,550°C for 8 to 14 hours) at the milling center (Biodenta). Ultimately, a little less chroma in the body of the tooth, a darker interdental shade, and a grayish shade on the incisal areas were ordered. The gray color helped provide the illu-
sion of a low-value translucent incisal edge. This information was communicated to the milling center, where it was stained individually according to the given description (Fig 10-1s).The zirconia construction was finished with diamond burs, establishing the final shape, occlusion, contacts, interdental separation, and surface texture, and then polished to a high shine to minimize occlusal abrasion of the opposing teeth (Fig 10-1t). The construction was steam cleaned before individual staining.
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Fig 10-1 (cont) (u to w) Definitive prosthesis. (x) Try-in at the laboratory. (y) Definitive prosthesis on the stone cast.
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Case 1: Stained Monolithic Zirconia Prosthesis
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Fig 10-1 (cont) (z and aa) Final try-in.
It is best to have photographs of the patient’s natural dentition as a guide for staining. Depending on the shade selection, an illusion of translucency is created by adding, in small increments, a variety of dark gray, blue, pink, or violet stains to the incisal edge. Broad incisal staining has to be avoided, because it often appears blotchy and results in an unnatural appearance. The addition of white stain to the body shade gives a lustrous surface effect (glow, or higher value). The addition of violet, pink, gray, or occasionally black can give the appearance of depth or translucency (Figs 10-1u and 10-1v). Once individual staining was finished, two layers of glaze were fired before the prosthesis was polished manually with pumice, rubber wheels, and diamond paste. Final try-in. By the final, or bisque, try-in at the laboratory,
the fixed partial denture was already finished and ready for cementation (Figs 10-1w and 10-1x). (If necessary, esthetic and occlusal adjustments can be made at try-in, and the prosthesis can be glazed or polished manually.) The final try-in at the laboratory included the following steps: 1. Occlusal and proximal contacts were verified. 2. Interdental spaces were examined to ensure that they appeared closed visually but were still easily cleansable. 3. Each pontic was examined with respect to its gingival contact and, if necessary, readapted to achieve proper pressure. (Initial blanching of the gingiva is desired and should disappear in 2 to 3 minutes.)
4. The prosthesis was cleaned, sandblasted inside the crowns with 2-bar pressure and 50-µm aluminum oxide, and steam cleaned. The zirconia ceramic fixed partial denture was sent to the dentist for final cementation (Fig 10-1y).
Final cementation The provisional restoration was removed, and retraction cords were placed to expose the entire preparation. The preparations were carefully cleaned with a rubber cup and a pumice paste. Careful intraoral sandblasting is a valuable alternative to rubber cup and pumice cleaning. The all-ceramic monolithic zirconia fixed partial denture was tried in again to confirm fit, esthetics, and occlusion (Figs 10-1z and 10-1aa). Resin cement was selected as the luting agent to optimize the retention as well as the marginal seal. Because the zirconia used in this case was quite transparent, all efforts had to be undertaken to avoid microleakage that could result in marginal discoloration. After final checking of the zirconia reconstruction, the prosthesis was prepared for final cementation. This preparation consisted of mechanical and chemical processes. Sandblasting was used to create a roughened surface that would improve the mechanical interlocking. A grit size of 50-µm alumina and low pressure of 0.5 bar are recommended for this process. With a black marker, the inner aspects of the four abutment crowns of the prosthesis were
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Fig 10-1  (cont) (bb) Intaglio of the abutment crown stained black. (cc) Air abrasion of the crown intaglio. (dd) Dural-curing resin cement is applied to the prepared teeth. (ee) Seated prosthesis. (ff ) Removal of excess cement. (gg) Use of interdental brushes to clean the prosthesis.
stained (Fig 10-1bb). Air abrasion was used in a pulsating manner to remove the black stain (Fig 10-1cc). As soon as all stain was removed, the surface was ready for the next step. This procedure prevented overblasting or underblasting of the inner surface. Next, the chemical preparation process was initiated. An adhesive containing phosphate monomer (methacryloyloxydecyl dihydrogen phosphate [MDP]; Monobond Plus, Ivoclar Vivadent) was applied as a chemical pretreatment. MDP will chemically bond to metalloxides such as zirconia via phosphate bonding. After 1 minute, the MDP-containing adhesive was dried with the use of an air syringe. The next step was the application of the final dual-curing resin cement (Multilink Automix, Ivoclar Vivadent). Because no enamel remained on the prepared teeth, etching with phosphoric acid was not indicated. Multilink DBA was applied as a dentin bonding agent in accordance with manufacturer instructions (Fig 10-1dd). The prosthetic abutments were then filled with the cement and seated with high pressure in the final position (Figs 10-1ee). The excess 198
cement was slightly precured with a curing light for easier removal (Fig 10-1ff ). After complete removal of excess cement, all four preparations were exposed to the polymerization light, each spot for 60 seconds. A careful inspection was made to guarantee overhang-free margins. The retraction cords were removed, and the patient was reinstructed in the use of interdental brushes (Figs 10-1gg).
Follow-up One week later, the patient returned for a follow-up examination. A final panoramic radiograph was taken to check the margins for excess cement and as documentation (Fig 10-1hh). The definitive zirconia ceramic prosthesis provided excellent esthetics and function (Figs 10-1ii and 10-1jj). Once again, the patient was reminded that only adequate oral hygiene and regular visits to a dental hygienist would lead to long-term success.
Case 1: Stained Monolithic Zirconia Prosthesis
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jj Fig 10-1 (cont) (hh) Final panoramic radiograph. (ii and jj) Clinical appearance 1 week after cementation.
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Fig 10-2  (a) Occlusal plane before treatment. (b) Provisional prosthesis after placement.
Case 2: Labial Veneering on a Translucent Zirconia Frame A 37-year-old woman reported that she had insufficient posterior function, compromised anterior esthetics, posterior bite collapse, and anterior open bite. An accident at the age of 17 years resulted in the loss of teeth and extensive loss of bone structure. Her removable partial denture was uncomfortable and no longer acceptable to the patient, especially the severe labial inclination of the maxillary anterior teeth (Fig 10-2a). At the consultation stage, she expressed a strong preference for a nonsurgical approach to reconstruction.
Initial treatment After consultations with the dentist and the patient, a diagnostic wax-up was performed and acrylic resin eggshell provisional restorations were made. The existing fixed partial denture was removed, and all caries lesions were treated. Several endodontically treated teeth had to be re-treated. The canines had titanium posts, which were removed and replaced with glass-fiber posts. The canines were built up using an adhesive technique (OptiBond, Kerr Dental) with resin (Tetric EvoCeram). After all these procedures, the involved teeth were prepared and the provisional prosthesis, with improved function and esthetics, was relined intraorally using the same resin material (TAB 2000, Kerr Dental) as in the laboratory. The provisional prosthesis was placed during this initial treatment to test the new vertical dimension, increased incisal edge length, improved inclination and shape of the maxillary incisors, and the new crown length of the canines 200
(Fig 10-2b). The long-term use of the provisional prosthesis provided the opportunity to test the function and esthetics while allowing the soft tissue to completely heal.
Definitive treatment After 5 months, a stable dental and gingival situation was reached. At this time, the preparations were finalized to harmonize with the new gingival contours. After final preparation was completed, an impression was taken with polyether material. Because of the great esthetic demands, the material chosen for the reconstruction was a translucent zirconia framework (Biodenta), which would be supplemented with a minimal amount of labial veneering. All the posterior units were planned to be monolithic zirconia, which would be surface stained and glazed.
Laboratory procedures Impressions of the provisional prosthesis provided the basis for the wax mock-up. The patient was seen in the laboratory for try-in and modifications to the wax mock-up. Once approved by the patient, the mock-up was scanned and integrated into the digital protocol. At this time, the final shade was selected and photographs were taken with the shade tabs in the mouth (Fig 10-2c). Because of the high value of zirconia, a darker low-value coloration of the frame was ordered to mask the opacious white influence of the zirconia core material. The frame was to be veneered with a brighter enamel to achieve the correct shade. Because the framework was going to be layered with veneering ceramic, it was even more important to design the connectors to be as large as possible to achieve maximum strength in the definitive restoration.
Case 2: Labial Veneering on a Translucent Zirconia Frame
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Fig 10-2  (cont) (c) Shade selection. (d) Stone cast for scanning. (e) 3Shape scanner and design software. (f and g) Digital scan of the wax-up before labial reduction on the anterior teeth. (h) Lower value of sintered zirconia compared with the chosen shade tab and natural tooth.
After the uncut casts, single dies, and complete wax-up were scanned (Figs 10-2d to 10-2g), the data was transferred to the milling center (Biodenta), where the frame was milled and returned presintered (white stage) to the laboratory. The interproximal areas and occlusal anatomy were finished in the laboratory, on the presintered framework, before it was sent back for final sintering and basic coloring at the milling center (Fig 10-2h).
The sintered zirconia frame was highly polished, especially in the areas of the occlusal contacts to minimize wear to the opposing dentition. The finishing steps for the minimally veneered reconstruction were the same as previously described for the monolithic prosthesis. Application of liner is critical because it not only improves the bonding of the veneering ceramic to the zirconia but also enhances the esthetics. Precise application of a liner 201
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m Fig 10-2 (cont) (i and j) Definitive prosthesis on stone cast. (k) Try-in at the laboratory. (l) Veneered anterior crowns and stained posterior crowns. (m) Appearance 2 weeks after cementation.
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Reference can aid in creation of mamelons and enhance translucency. The liner is selected based on the intended shade of the veneer and is applied in one or two firings. Because the veneer is fired at a lower temperature than is needed for the glazing and staining of the monolithic portion of the zirconia frame, the liner is applied and glazing is completed before the veneering. A layer of stain is frequently applied to the surfaces intended for veneering to intensify the color of the veneering ceramic. When pontics are combined with crowns, there is a variation of thickness, resulting in different translucency and value of the framework. In these situations, use of deep dentin ceramics on the pontics and dentin ceramics on the crowns will equalize value and translucency on the definitive restoration. The first dentin firing is done about 30°C higher than manufacturer’s directions to obtain a more natural glazed appearance. Because zirconia is a good insulator and absorbs the heat much slower than the layering porcelain, very slow heating rates of 35°C to 40°C are set on the firing furnace, depending on the size and bulk of the reconstruction. At each firing of veneering material, the monolithic part is stained according to the shade selection. Long-term cooling for the last glaze firing is important on layered reconstructions to prevent initial development of cracks on the interface between the veneering material and the zirconia because of the different coefficients of thermal expansion and the different thermal conduction properties of the two materials. The veneered ceramic was finished with diamond burs and stones to achieve the desired shape and natural-looking surface texture. The labial layering and the buccal and posterior staining were finalized with two layers of glaze. The reconstruction was highly polished manually with pumice, rubber wheels, and diamond paste to obtain a natural-looking surface luster (Figs 10-2i to 10-2l). By the final try-in at the laboratory, the following steps were verified: 1. 2. 3. 4.
Gingival contact of the pontics Ease of cleaning the prosthesis Occlusal contacts Esthetics, phonetics, and function
If necessary, esthetic and occlusal adjustments can be made and glazed or polished manually before the definitive restoration is sent to the dentist for cementation.
Cementation After the accuracy of fit was confirmed with a black fitchecker, the prosthesis was cleaned with 80% alcohol to remove any residual stain. The pontics were adjusted as
previously described. The preparations were treated with OptiBond to optimize an adhesive cementation. The fixed partial denture was cemented adhesively with dual-curing resin cement. The occlusal interferences in the posterior region were adjusted and repolished (Fig 10-2m).
Conclusion Zirconia ceramic has been an important part of the authors’ dental laboratory for nearly 10 years, and it has proven to be a durable restorative material for prosthetic frameworks. It is essential to use high-quality zirconia disks and process the material according to manufacturer indications. When the authors first used this type of material, they were concerned about the stability of the material and the bond with the layering material, which has proven to be the weakest part of the reconstruction. Therefore, they decided to design the frame to be as thick as possible and to minimize the veneering layer. The introduction of more translucent and multilayered zirconia ceramics has allowed them to eliminate the veneering process entirely in highstress areas. Monolithic zirconia restorations can provide maximal strength and require minimal tooth reduction and yet still achieve acceptable esthetics. For esthetically demanding reconstructions or when desired visual effects cannot be achieved with staining, it may be necessary to apply a minimal layer of veneering material to the labial surface. However, in such cases, the occlusal contacts and the functional areas of the anterior and posterior teeth should remain completely on the monolithic part of the prosthesis. The result should be a collaborative effort incorporating the patient’s opinions and the dentist’s and dental technician’s technical knowledge to achieve optimal esthetics and function. Only time will tell if these zirconia ceramic materials will endure as a material for use in long-span reconstructions. At present, the translucency, shading, and bond strength to veneering ceramics need further improvement.
Acknowledgments The authors give special thanks to Dr Urs Brodbeck (Zurich, Switzerland) and Dr Massimiliano Sisera (Baar, Switzerland).
Reference 1. Nyman S, Lindhe J, Lundgren D. The role of occlusion for the stability of fixed bridges in patients with reduced periodontal tissue support. J Clin Periodontol 1975;2:53–66.
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