Zirconia Removable Telescopic Dentures Retained on Teeth or Implants for Maxilla Rehabilitation. Three-Year Observation of Three Cases

A number of recent studies recommend the use of removable prostheses with telescopic attachments fastened to natural teeth and/or implants for prosthetic restoration.1–4 This restoration technique is preferred in Central Europe for partially edentulous and periodontologically injured dentition. It has existed as a broadly accepted and scientifically recognized approach within dentistry and predates the establishment of oral implantology.5 

In a current publication, our team also discusses the advantages of telescope-borne structures.6 Briefly, these advantages are: (1) the distribution of force on the abutment; (2) the provision of a foundation for effective oral hygiene, and maintenance of periodontal health; (3) the arrangement of teeth in the desired position; (4) circumvention of several augmentative measures in the soft and hard tissues for esthetic reasons; (5) achievement of favorable esthetics, even with there is substantial recession of the periodontal tissue or severe atrophy of the jaw; (6) creation of a gum-free structure in the maxilla; (7) longevity of the structure (eg, veneers can be reapplied at any time, and the structure remains in place even if one of the abutment teeth or implants is lost); and (8) avoidance of augmentative measures if gingival and/or peri-implant recessions arise before the construction is fabricated or while it is being worn since recessions can be covered by the lip shield.

The disadvantages of this type of construction are: (1) high costs and technical requirements; (2) the need for the dental technician to master the individual steps for creating such constructions; and (3) any psychological burden experienced by the patient provided with a removable construction.

Today, patients with periodontally reduced dentition and partially or fully edentulous patients who are to be provided with implants have become sensitized to esthetic appearance in addition to the maintenance of oral health. The introduction of zirconium oxide (zirconia) as a biocompatible material in restorative dentistry, the light weight of the structures made with this material, the development of new ceramics and composites for veneers, and the ongoing development of CAD/CAM technology were the factors that led us to manufacture telescope-borne zirconia constructions.

Three nonsmoking patients (1 female and 2 male) were selected for this retrospective study. In 2005, all 3 patients presented for treatment of advanced chronic periodontitis7 in the office of one of the authors (G.G.Z., Duesseldorf, Germany). After multiple extractions over the previous 2 years, the first patient (PERIO, female, 58 years old) had 7 natural maxillary teeth that were retained by periodontal treatment. This patient rejected the placement of an implant.

The maxillary teeth of the second patient (IMPL, male, 65 years old) had been extracted 4 years earlier, with the exception of teeth number 2 and 15. These 2 teeth possessed class II mobility but no defect in the region of the furcation. They were integrated into the existing restoration (telescopic-crown overdenture). This patient requested an implant-supported restoration of the maxilla.

The third patient (IMPL-PERIO, male, 60 years old) presented after multiple extractions of maxillary teeth due to advanced periodontal disease. Teeth number 6 and 11 were present, with class II mobility. The patient requested a palate-free, implant-supported restoration of the maxilla and periodontal treatment of the remaining dentition.

All existing mandibular teeth of the 3 patients were preserved, and a partial removable denture was not necessary for mandible restoration in any of the patients.

The full-mouth initial periodontal treatment involved oral hygiene instructions, supragingival tooth cleaning and polishing, and subgingival scaling and root planing.

In all 3 cases, subgingival scaling and root planing was followed by access flap surgery.8 Six cylindrical screw-type implants (RN, length 10 mm, 04.1 mm, SLA, Straumann, Waldenburg, Switzerland) were placed in the maxilla of the IMPL patient and 4 cylindrical screw-type implants (Straumann) were placed in the maxilla of the IMPL-PERIO patient, using a 1-stage surgical approach. Following full-thickness flap elevation, osteotomy preparation was performed at 875 rpm, and implants were manually placed at a torque of 35 Ncm (046.119/046.049 Straumann) in positions number 4, 5, 6, 11, 12, and 13 and in positions number 4, 5, 12, and 13 (IMPL and IMPL-PERIO patients, respectively).

Both IMPL and IMPL-PERIO patients were prescribed a systemic antibiotic (clindamycin, Ratiopharm, Ulm-Donautal, Germany; 600 mg/d) to be taken once a day for 6 days and the oral analgesic diclofenac (Voltaren, Novartis Pharma, Nuremberg, Germany; 100 mg/d for 4 days), starting 1 day prior to surgery and implant placement. All 3 patients were instructed to rinse twice daily with 0.1% chlorhexidine (Chlorhexamed Fluid, GlaxoSmithKline, Buehl, Germany) for 3 weeks, also starting 1 day before periodontal surgery and implant placement.

Sutures were removed 8 days postoperatively. Follow-up appointments were scheduled twice a month during the first 2 months after surgery, and once a month thereafter until loading.

The IMPL patient was provided with a provisional full denture for the maxilla. Teeth number 2 and 15, which were given telescopic crowns, were preserved to provide the denture with greater retention. The PERIO and IMPL-PERIO patients were given temporary removable partial prostheses.

Four months after implant placement (IMPL and IMPL-PERIO patients) and 3 months after periodontal treatment (PERIO patient), maxillae were restored with telescopic crown-retained palate-free removable dentures.

Impressions were taken with individual acrylic trays (the open-tray impression technique was used for implant cases) using a polyether impression material (Impregum Penta Soft, 3M ESPE, Seefeld, Germany). Casts were mounted on a semi-adjustable articulator (SAM 2P, SAM Praezisionstechnik, Gauting, Germany), using the face-bow technique and check-bite registration.

A wax-up was created and used as an orientation tool for the patient and surgeon as well as for further planning of rehabilitation. After the esthetic and functional try-in with the wax-up, a matrix of C-silicone (Zetalabor, Zhermack SpA, Badia Polesine, Italy) was manufactured. The direction of insertion and planned tooth position were determined by this silicone key (Figure 1A). In addition, it can be used to create a mock-up.

Customizable abutments were used (RN synOcta 048.642, Straumann) to fabricate the individual zirconia implant abutments. These abutments consist of a prefabricated cast-on base and a residue-free burn-out plastic channel (Figure 1a). The plastic channels of the 6 abutments were patterned with resin (Pattern Resin, GC Dental Products Corp, Leuven, Belgium) (Figure 1b). The patterns were scanned and milled in a CAD/CAM (M4820, I-MES, Eiterfeld, Germany). After scanning, the zirconia implant abutments were fixed on the abutment cast-on base using a self-curing compomer cement (AGC Cem, Wieland Dental, Pforzheim, Germany) (Figure 1c). Subsequently, the zirconia implant abutments were ground, polished and sintered, and served as primary telescopes with a minimum thickness of 0.6 mm (Figure 1d through f).

After the models were created, the tooth abutments were scanned using construction software (ZENO CAD, in CAD/CAM, Wieland Dental) and a scanner (Dental Designer, 3shape, Copenhagen, Denmark), and the primary telescopes were fabricated and milled as zirconia copings (ZENO Discs, Wieland Dental) (Figure 2a and b). An insertion key of resin (Pattern Resin, GC Dental Products Corp) and a metal wire 0.3 mm in diameter were manufactured and used for an oral try-in of the primary telescope on the abutment to determine precision of fit and direction of insertion (Figure 2c).

Subsequently, a new impression was made over the primary telescope and insertion key using a polyether impression material (Impregum Penta Soft, 3M ESPE, Seefeld, Germany). This was used to fabricate a new working model of cast plaster (Figure 2d and e).

As secondary telescopes, electroformed pure gold copings with a thickness of 0.25 mm were fabricated (AGC Galvanogold, Au > 99.9%, Wieland Dental) (Figure 3a through c).9,10 

The superstructure was created by using construction software (ZENO CAD in CAD/CAM, Wieland Dental) and a scanner (Dental Designer, 3shape, Copenhagen, Denmark) (Figure 3d). Subsequently, a milling program (ZENO CAM, Wieland Dental) was used to create a plastic mock-up (ZENO-PMMA, Wieland Dental) on a milling machine (I-MES, Eiterfeld, Germany). The mock-up was then tried in to check occlusion and the overall shape of the construction (Figure 3e). After the try-in and necessary corrections, the altered mock-up was scanned again. The zirconia framework (ZENO Discs, Wieland Dental) was then milled using a CAD/CAM system (M4820, I-MES, Eiterfeld, Germany) and sintered in a sintering furnace (ZENO Fire, Wieland Dental) for 14 hours at 1500°C (Figure 4a). To veneer the implant-retained supraconstruction, a high-fusing microceramic (Vintage ZR, Shofu Dental, Ratingen, Germany) was used. To veneer the natural tooth-retained supraconstruction, a lightly cured indirect ceramic polymer (Ceramage, Shofu Dental) and a bonding system (Bond I and II, Shofu Dental) were used (Figure 4B through E). The zirconia superstructure possessed a wall thickness of 0.6 mm, occlusal distance of 1.5 mm and 3 × 3 mm proximal connecting elements.

After veneering, the gold copings were fixed in the supraconstruction using a self-curing copolymer cement (AGC Cem, Wieland Dental) (Figure 4f). After fitting the denture, the jaw relation was rerecorded using a central tracing device and a face-bow, remounted to a semi-adjustable articulator (SAM 2P, SAM Praezisionstechnik). Final adjustments to the occlusion were made (Figure 5a through d).

The zirconia implant abutments were manually placed at a torque of 35 Ncm. The screw opening of the abutment was filled with a single-component light-cured resin (Fermit, Ivoclar Vivadent, Schaan, Liechtenstein) (Figure 5e).

In all 3 cases, the superstructures were extended only up to teeth number 3 and 14 with cantilevers. The cantilevers at teeth number 3 and 14 were supported by the veneer material on the mucosa (Figures 6 through 8).

In the IMPL patient, teeth number 2 and 15 manifested improved mobility (class I) and inflammation-free periodontal conditions at the time of the prosthetic restoration. For this reason, both teeth were retained according to the patient's wishes. Two zirconia crowns (Panavia, Kuraray Europe, Frankfurt/M, and Germany) were fabricated and adhesively inserted on the existing, old primary telescopic crowns number 2 and 15 which were intact and free of caries (Figure 6a through f).

Follow-up examinations were performed at the time of loading, and were considered the baseline examinations (BSL). At the BSL, and at the 1-, 2- and 3-year examinations after loading, the implants and/or natural teeth were examined at 4 sites per tooth. These examinations measured bleeding on probing (BOP) and plaque index11; in addition, a periodontal probe (UNC 15, Hu-Friedy, Leimen, Germany) was used to estimate probing attachment level (PAL) for implants and clinical attachment level (CAL) for natural teeth. PAL was defined as the distance in millimeters between the deepest point of the peri-implant pocket and the margin of the zirconia implant abutment. CAL was defined as the distance between the deepest point of the periodontal pocket and the margin of the zirconia primary crowns. All measurements were rounded up to the nearest millimeter.

Three patients were treated (IMPL, PERIO, and IMPL-PERIO). Ten dental implants were placed in the maxillae of 2 patients (IMPL and IMPL-PERIO), and 9 maxillary natural teeth in the maxillae of 2 patients (PERIO and IMPL-PERIO) were used as retainers for the restorations. The maxillae of all 3 patients were restored with removable telescopic dentures. Implant abutments, copings for natural tooth abutments, and superstructures were fabricated using CAD/CAM. In all cases, electroformed gold copings were fabricated as secondary telescopes.

The patients were observed over a period of 3 years. None of the patients reported any unusual pain or discomfort, abscess, swelling, or allergic reactions during the course of treatment. No implants or natural teeth were lost during the observation period. Furthermore, no fractures were observed in the zirconia abutments, the superstructures, or the ceramic veneers (Figure 9).

The small sample size and limited number of measurements in this study rendered it not amenable to statistical analysis. However, there were no observed changes in BOP and plaque index measurements between the BSL and subsequent examinations. The mean range of BOP values for the maxillary natural teeth was 5% and that for the implants was 2%–4%. Plaque index scores ranged from 5%–8%. At the BSL, the mean PAL was 1 mm. The PAL deteriorated by 1 mm at the year 1 examination and a further 0.5 mm at the year 3 examination. The mean CAL at the BSL was 2.5 mm, and the range was 3.5–4 mm between the year 1 and year 3 examinations.

In the present study, the maxillae of 3 patients were restored with removable, telescopic crown-retained, palate-free dentures. All implants and natural teeth, primary telescopes, and supraconstructions remained functional, and none of the patients suffered complications thoughout the 3-year observation period.

The use of ceramics in dentistry and dental technology has increased in recent years. Among other materials, zirconia has been used to manufacture frameworks due to its good mechanical and biocompatible properties.12–15 Importantly, during the entire observation period of the present study, no biological or mechanical complications were observed, and all reconstructions remained functional. This observation is in agreement with the few studies that have examined removable dentures retained on teeth or implants using zirconia for the fabrication of copings and/or implant abutments.12,16–20 The present study differs from other published studies in that the suprastructures were also fabricated from zirconia and not from metal. The periodontal and peri-implant findings were overall very positive.

Clinical studies of zirconia implant abutments and copings have shown them to have favorable stability and to exhibit a survival outcome similar to that of gold or titanium structures.17,18,21 Similar to prior studies, we found the bone level around the implants and/or natural tooth abutments to be stable and the soft tissue to be healthy.12,16,17,19–21 Recent studies have reported that zirconia shows a lower bacterial colonization potential than titanium in vivo.22–25 It has been further asserted that this material can help stabilize soft tissue against inflammation and contribute to the stability of the crestal bone level around the implants.17,23,25,26 

In the present study, low plaque accumulation and low BOP were also observed. The probing depth of the periodontal or peri-implant areas was stable and no gingival recessions were seen. Gingival recessions may cause esthetic complications that must be surgically managed, particularly when they occur in the anterior region. These may lead to patient dissatisfaction and caries. Although in the cases presented here no such problem was observed, the occurrence of gingival recessions in the future cannot be ruled out. In such a case, too, the removable telescopic crown-retained construction offers the great advantage that the lip shield covers these areas, and plastic periodontal surgery for the purpose of correcting the soft tissue contours is not necessary.

A number of studies have reported on the fabrication of zirconia copings for providing retention of a telescopic crown-retained overdenture.12,16,20 Other studies report positive mechanical properties of zirconia copings in fixed restorations.12,16,25,27,28 No fractures of the zirconia copings were observed in the present study. These copings proved to be a successful alternative to classic gold copings, especially when the patient's esthetic demands are high. However, the preparation angle of the natural abutments, the thickness of the zirconia, and the occlusal load must be precisely factored in.29–31 

The secondary telescopes were manufactured by galvanoforming and electroforming. This process yields a precisely-fitting secondary coping that closely mates with the primary telescope with a gap of 12–30 µm. The gold electroformed coping saves space and is made of high-quality material. In order for its shape to remain stable, it must be completely surrounded by the superstructure framework and may not merely be adhered to the veneer.9,10,16 The fixation of the electroformed copings should be done after the veneering of the supraconstruction is completed. The combination of both materials, zirconia and electroforming copings, used with the proper technologies, results in a prosthetic reconstruction of high quality, good fit. and biocompatibility.

Developments in CAD/CAM technology have resulted in discernible improvement in these methodologies.32–34 New technologies must take into account the specific requirements of dental technology and dentistry, and a great deal of time is required before they become routine. In the present study, all parts of the telescope-borne removable reconstructions were fabricated using CAD/CAM. Over the 3-year observation period, no complications were noted from the individual parts made using this technology. Nevertheless, the lack of long-term results must be borne in mind. We do not yet know whether the mechanical and prosthetic-specific properties of the material will remain satisfactory over the long term, and whether they will prove to be as valuable as the established classic methods and materials of dental technology. Randomized long-term studies with a large number of test subjects are required. Even if the overall number of restorations fabricated with CAD/CAM, especially all-ceramic frameworks made of materials such as zirconia, remain comparatively fewer than conventionally-fabricated frameworks, this technology has great potential for economical and biocompatible restorations using innovative materials that are esthetically and functionally superior.

This report presents the option of restoring the maxilla with classic techniques from oral implantology as well as prosthetic dentistry using modern dental materials. The esthetic and functional results over the 3-year observation period were very positive. Long-term results from large, preferably randomized studies would be desirable and necessary to establish greater clarity regarding the long-term potential changes in the properties of zirconia. It would, of course, be possible to reconstruct the maxillae of the patients discussed by hard and soft tissue augmentation in order to allow the fabrication of a fixed prosthetic restoration. In such cases, one is confronted with the dilemma of whether all the possibilities of modern surgery should be exhausted, or if it would be more desirable to pursue “the path of least resistance” and combine classic and modern methods. If the latter route is taken, we as surgeons or periodontists should give more weight to the option of restorative dentistry.

BOP

bleeding on probing

BSL

baseline examinations

CAL

clinical attachment level

PAL

probing attachment level

The authors report no conflicts of interest related to this study. No financial or material support was provided by any company to the authors or the patients involved in this study.