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Ceramic Dental Implants Ralf Kohal, dmd, dr med dent, phd Eric Van Dooren, dds

The use of dental implants to replace missing teeth is a well-documented treatment modality. Because of its biocompatibility and biomechanical properties, commercially pure titanium has been the material of choice.

However, some people believe that metal titanium can cause undesirable host reactions, such as allergy and sensitization toward titanium, and may result in elevated titanium concentrations in the vicinity of titanium dental implants and regional lymph nodes. Furthermore, titanium implants may impair the final esthetic outcome of the restoration, because its gray color can be apparent through thin, soft peri-implant tissues. Some patients refuse to be treated with metallic implants and request an entirely metal-free reconstruction for the replacement of missing teeth. For these patients, the use of titanium implants may not be acceptable. Because of these possible drawbacks to the utilization of titanium as a dental implant material, different alternatives have been proposed.

A ceramic material that has been utilized for total hip replacement in the orthopedic field for quite a while is zirconia.1 This ceramic material, also called ceramic steel, has similar biomechanical properties to and is as biocompatible as titanium. The advantages of zirconia ceramic implants can be summarized as follows: • The esthetic appearance of a reconstruction can be improved because zirconia ceramic has a white color and therefore presents greater esthetic appeal than titanium.

• As a ceramic material, zirconia is not prone to corrosion or to other chemical reactions.

• If implant-borne restorations are necessary, patients who request metalfree reconstructions can only be treated with ceramic implants.

This chapter aims to address the information available in the literature regarding the mechanical and biologic aspects of zirconia implants (Figs 12-1 and 12-2) and to present some clinical cases that illustrate important surgical and prosthetic aspects that must be considered in order to achieve success when such an implant system is used.

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Fig 12-1 One-piece zirconia implant fabricated from yttria-stabilized tetragonal zirconia polycrystal (Y-TZP).

Support for the Use of Zirconia Dental Implants Materials science research The most commonly used zirconia ceramic material for fixed partial denture reconstruction as well as for the fabrication of dental implants is tetragonal zirconia polycrystal stabilized with 3 mol% yttrium oxide (Y2O3), otherwise known as 3Y-TZP (or simply Y-TZP).2 Pure zirconia—without the addition of the stabilizing oxide Y2O3—would be prone to spontaneous fracture after sintering when it cools down from the sintering temperature to room temperature. There is a change from the tetragonal (t) phase to the monoclinic (m) phase in zirconia, and this change in the crystalline phase (called the t-m transformation) leads to a volume increase of about 5% that entails crack initiation and propagation in the sintered zirconia material. The result is a complete breakdown of the zirconia body.

With the addition of the stabilizing oxide, Y2O3, the transformation from the tetragonal phase to the monoclinic phase can be avoided during cooling from the sintering

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Fig 12-2 Two-piece zirconia implant fabricated from Y-TZP.

temperature to the room temperature. However, the tetragonal phase is not entirely stable but is in a metastable state that can transform into a monoclinic phase if mechanical energy such as a crack initiation or propagation acts on the tetragonal grains, leading to a local increase in volume.

This change of phases under the influence of a crack in the material is called transformation toughening because this counteracts crack propagation locally through volume increase. The high fracture toughness of that material is attributed to this t-m phase transformation and its release during the initiation and propagation of a crack.2 According to Chevalier and Gremillard,3 3Y-TZP possesses the best combination of toughness and strength among oxide ceramics, as a direct benefit of its fine grain size and transformation toughening. The flexural strength of various TZP materials typically ranges from 900 to 1,200 MPa and the fracture toughness from 6 to 8 MPa ∙ m1/2.4 In comparison, the strength and toughness of alumina, the previously used ceramic material for dental implants, ranged from 350 to 500 MPa and from 3.5 to 4.0 MPa ∙ m1/2, respectively.4 Due to its biomechanical characteristics, zirconia in the form of Y-TZP seems to be the ceramic material of choice for dental implants.4

Support for the Use of Zirconia Dental Implants However, Y-TZP is affected by hydrothermal aging, or low thermal degradation, which in principle is a similar process to the t-m phase change of the crystalline structure that leads to transformation toughening.2,3 The underlying mechanism of low thermal degradation is that moisture catalyzes the transformation from t to m zirconia. An explanation given in the literature is that moisture, in the form of hydroxide (OH–) ions, diffuses into the zirconia ceramic and fills oxygen vacancies, thereby destabilizing the tetragonal phase.3 The process involves the chemical adsorption of H2O on the zirconium oxide (ZrO2) surface. The water reacts with oxygen on the zirconia surface, leading to the production of OH– ions. These ions penetrate the inner part by grain boundary diffusion and subsequently fill so-called oxygen vacancies. This will finally lead to the t-m transformation on the surface. The consequences may be material uplift and crack initiation. Due to this crack production, the grains in the surrounding area transform because of stress release.

As a result, water species gain the ability to penetrate deeper into the material, maintaining the process of t-m transformation.

Through this process, the material may lose its stability and catastrophic fracture may occur.2,3 However, when Chevalier et al5 evaluated zirconia dental implants and the impact of the transformation through accelerated aging on the structural integrity of a specifically produced implant and implant surface, they showed that hydrothermal aging had no effect on the bending strength and stability of the tested zirconia implants.

Laboratory studies evaluating the biomechanical stability of zirconia dental implants There are some reports available regarding the in vitro biomechanical stability of zirconia dental implants.6–10 Some of these publications presented results on the tests of oneand two-piece zirconia implant systems. However, only one investigation tested a commercially available zirconia implant product.9 Other investigators have only tested prototype zirconia implants that are still not available on the market.

In the study performed by Kohal et al,9 the zirconia implants were either not loaded or were artificially loaded in a chewing simulator at 98 N for 1.2 and 5.0 million cycles.

No implant fractured during the artificial loading tests.

Subsequently, all implants were subjected to catastrophic fracture in a universal testing machine. The results of that investigation showed that long-term loading can decrease the stability of these implants, but the authors stated that

“even the lowest values of mean fracture strength seem to withstand average occlusal forces even after an extended interval of artificial loading.”

Three other investigations examined the same prototype of a one-piece zirconia implant system.7,10,11 Silva et al10 compared the impact fracture resistance of a single-piece ceramic implant with that of two titanium implant–abutment systems. The authors found that the fracture energy of the two titanium implant–abutment systems was not different from that of the single-piece Y-TZP implant in foam blocks.

However, no information on the fracture stability of the implants was given.

In a further investigation,7 data were presented on the reliability of one-piece zirconia ceramic implants either as received or after complete crown preparation. The authors stated that crown preparation did not influence the reliability of the one-piece zirconia ceramic implant. Furthermore, fatigue did not influence the survival of the implants at loads under 600 N.7 Two studies presented the fracture strength outcomes of prototype two-piece implants.6,12 The values for the fracture strength after artificial loading of these implants were lower than values for the one-piece zirconia implants; the biomechanical stability of the tested two-piece prototype implants seemed to be insufficient for clinical use.

Within the limits of these investigations, it can be concluded that one-piece zirconia implants can withstand normal occlusal forces over an extended period of time.

However, whether two-piece implants will withstand these forces over a longer time period might be questioned, considering the outcomes of the previously mentioned investigations.

Animal investigations New implant designs as well as implants fabricated from new materials have to show a performance that is equal to or better than that of well-documented titanium implants.

This is true for both the biomechanical and the biologic behavior. With regard to osseointegration, specifically the amount of bone-to-implant contact, zirconia implants have to show at least the same values as titanium implants do in order to be successful. Many preclinical investigations have been performed to evaluate the bone-to-implant contact of zirconia dental implants. Table 12-1 presents the results of animal investigations evaluating the osseointegration of different zirconia implants and surfaces. In general, it can be stated from the available (newer) literature that zirconia dental implants with an adapted surface topography (rough surface) show osseointegration values similar to those of roughened titanium implants.

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Ceramic Dental Implants TABLE 12-1 Osseointegration of zirconia (ZrO2) and titanium (Ti) implants: Results of their application in animal experiments

Author

Animal model

Akagawa et al

13

Dog

Bone-implant contact (%) or removal torque (N/cm) ZrO2 Unloaded: 82% Loaded: 70% (3 months)

Akagawa et al14

Scarano et al

Monkey

Rabbit

15

ZrO2 Loading period 12 months

Loading period 24 months

Single freestanding: 54%–71%

Single freestanding: 66%–81%

Connected: 58%–77%

Connected freestanding: 66%–77%

Implant-tooth–supported: 70%–75%

Implant-tooth–supported: 66%–82%

4 weeks ZrO2: 68%

Monkey

Kohal et al

16

9 months ZrO2 (Y-TZP): 68% Ti: 73%

Sennerby et al17

Rabbit

6 weeks ZrO2 control group Femur: 46% Tibia: 19% ZrO2-A Femur: 60% Tibia: 31% ZrO2-B Femur: 70% Tibia: 22% Ti-oxidized Femur: 68% Tibia: 24%

Hoffmann et al

18

Depprich et al

19

Lee et al20

Kohal et al21

Rocchietta et al22

Rabbit Miniature pig

Rabbit

Rat

Rabbit

2 weeks

4 weeks

ZrO2 (Y-TZP): 55%

ZrO2 (Y-TZP): 71.5%

1 week

4 weeks

12 weeks

ZrO2 (Y-TZP): 35%

ZrO2 (Y-TZP): 45%

ZrO2 (Y-TZP): 71%

Ti: 48%

Ti: 99%

Ti: 83%

3 weeks

6 weeks

ZrO2 (ZiUnite): 70.5%

ZrO2 (ZiUnite): 69.7%

ZrO2 nanomodified surface A: 64.6%

ZrO2 nanomodified surface A: 68.6%

ZrO2 nanomodified surface B: 62.2%

ZrO2 nanomodified surface B: 64.5%

TiUnite: 77.6%

TiUnite: 67.1%

14 days

28 days

ZrO2 (modified): 45.3%

ZrO2 (modified): 59.4%

TiUnite: 36.4%

TiUnite: 55.2%

3 weeks ZrO2 (ZiUnite): 27.5% ZrO2 (Promimic): 42.5% ZrO2 (CoAT sputtered): 36.1% TiUnite: 58.3%

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Support for the Use of Zirconia Dental Implants TABLE 12-1 Osseointegration of zirconia (ZrO2) and titanium (Ti) implants: Results of their application in (cont)

animal experiments

Author

Animal model Pig

Gahlert et al

23

Dog

Koch et al24

Bone-implant contact (%) or removal torque (N/cm) 4 weeks

8 weeks

12 weeks

ZrO2: 51.1%

ZrO2: 53,7%

ZrO2: 64.2%

SLA Ti: 55.1%

SLA Ti: 70.4%

SLA Ti: 54.4%

4 months Uncoated ZrO2: 59.2% Coated ZrO2: 58.3% Ti: 41.2% Synthetic material (polyetheretherketone): 26.8%

Miniature pig

Stadlinger et al

25

4 weeks Submerged ZrO2 and Ti: 53% Nonsubmerged ZrO2: 48%

Pig

Gahlert et al26

Schliephake et al

27

Bormann et al28

Mรถller et al29

Gahlert et al30

Hoffmann et al31

Aboushelib et al32

Pig

Pig

Pig

Miniature pig

Rabbit

Rabbit

4 weeks

8 weeks

12 weeks

Acid-etched ZrO2: 42 N/cm

Acid-etched ZrO2: 70 N/cm

Acid-etched ZrO2: 69 N/cm

SLA Ti: 42 N/cm

SLA Ti: 75 N/cm

SLA Ti: 73 N/cm

4 weeks

13 weeks

Sandblasted ZrO2: 58%

Sandblasted ZrO2: 55%

Sandblasted and etched ZrO2: 67%

Sandblasted and etched ZrO2: 58%

Sandblasted and etched Ti: 69%

Sandblasted and etched Ti: 79%

4 weeks

8 weeks

12 weeks

Acid-etched ZrO2: 110 N/cm

Acid-etched ZrO2: 97 N/cm

Acid-etched ZrO2: 147 N/cm

SLA Ti: 131 N/cm

SLA Ti: 128 N/cm

SLA Ti: 180 N/cm

4 weeks

12 weeks

ZrO2: 59%

ZrO2: 67%

Ti: 64%

Ti: 74%

4 weeks

8 weeks

12 weeks

Acid-etched ZrO2: 60%

Acid-etched ZrO2: 65%

Acid-etched ZrO2: 63%

SLA Ti: 61%

SLA Ti: 64%

SLA Ti: 68%

6 weeks

12 weeks

Sintered ZrO2: 33%

Sintered ZrO2: 34%

Laser-modified ZrO2: 40%

Laser-modified ZrO2: 44%

Sandblasted ZrO2: 40%

Sandblasted ZrO2: 41%

Acid-etched Ti: 34%

Acid-etched Ti: 35%

4 weeks

6 weeks

SI-etched ZrO2: 65%

SI-etched ZrO2: 75%

As-sintered ZrO2: 53%

As-sintered ZrO2: 62%

Ti: 57%

Ti: 68%

SLA, sandblasted and acid-etched; SI, selective infiltration.

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Ceramic Dental Implants Box 12-1 Zirconia implant systems Sigma (Incermed) Z5 (Z-Systems) White Sky (Bredent Medical) CeraRoot (Oral Iceberg) White Implant (White Implants Development) Omnis (Creamed) Zeramex (Dentalpoint) PURE Ceramic Implant Monotype (Straumann) Ziraldent (Metoxit) Vitaclinical ceramic.implant (Vident)

Clinical research Zirconia dental implants were introduced to the market before the positive biomechanical and preclinical behaviors of these implants6–12 were published in the literature. One of the first zirconia dental implant systems that became commercially available was the Sigma system (Incermed), developed by Sandhaus and Pasche in the late 1980s.33 Today, at least 10 manufacturers are selling zirconia implants (Box 12-1).

The available clinical scientific literature on zirconia dental implants was recently regarded as qualitatively questionable.34 In a recent review on zirconia dental implants, Depprich et al35 found 17 clinical studies published between 2006 and 2011. Up to 2013, further clinical investigations emerged.36–39 Further data on zirconia implants have been presented at international congresses.40,41 So far, only a few short-term studies have presented clinical and radiographic data prospectively.36,37,39,42 For the Sigma implant system, no investigations have been published. There is no information, therefore, on the success or survival rate of this system. The Z-Systems zirconia implants have been the subject of several investigations.38,42–46 The White Sky implant system was the focus of research in a few clinical reports or investigations.36,47–49 Two scientific investigations were found for the CeraRoot 240

system.50,51 Scientific abstracts were found for the Ziraldent system and the Vitaclinical ceramic.implant system (Vident).40,41 At the time of writing, no published scientific information about implant survival or success rates could be found for the remaining systems listed in Box 12-1. Case reports of the different implant systems were not considered for this compilation of investigations.52–58 The survival rate of the investigated Z-Systems implants was reported to be 85% after an observation period of 12 months and immediate loading42 and 98% after an observation period of 12 to 24 months with delayed loading.43 Lambrich and Iglhaut44 reported a survival rate of approximately 84% for the Z-Systems implants placed in the maxilla after a mean observation period of 21.4 months.

One investigation45 reported on fractures of Z-Look3 implants (Z-Systems). Thirteen of 170 inserted implants fractured after a mean observation period of approximately 36 months. Twelve of the implant fractures occurred with narrow-diameter implants with an implant diameter of 3.25 mm, and one 4.0-mm implant fractured in that investigation. The fracture rate reported by Gahlert et al45 amounted to almost 8%, which is several times the fracture rate seen with titanium implants.59 No other investigation so far has reported on the fracture rate of zirconia implants. Only one of the aforementioned investigations42 reported on periimplant bone remodeling or bone loss.

Surgical and Prosthetic Considerations Cannizzarro et al,42 in a multicenter pragmatic randomized clinical trial, compared immediate occlusal and non– occlusal loading of single zirconia implants (Z-Systems).

In their investigation, all implants were restored with provisional crowns on the day of implant placement; in one study group, the provisional crowns had occlusal contacts constituting immediate occlusal loading, and the other group had no contacts (non–occlusal loading). One year after loading, five implants (12.5%) had failed: three implants that were loaded and two that were not loaded. Implants that had not been immediately loaded had a mean of 0.7 mm of marginal bone loss. The immediately loaded group showed a loss of bone of 0.9 mm. No implant fractures were reported.

The survival rate of the White Sky implants was reported to be in the range of 89% (74% survival of implants placed in augmented bone and 97% survival of implants placed in native bone)48 after 12 months to 96%49 and 95%36 after 24 months.

CeraRoot implants were clinically evaluated by the system inventors.50,51 In their first investigation, Oliva et al50 reported a survival rate of 98% after 12 months. In the second investigation, the survival rate of the implants was 95% after a mean observation period of 24 months. Interestingly, the CeraRoot system offers five different implant designs for the different tooth positions. Furthermore, in the investigations published on the CeraRoot system, three different surface modifications have been tested (uncoated, coated with a stable bioactive ceramic coating, and acid-etched).50,51 Two prospective, clinical cohort investigations have evaluated an implant system that has not been made commercially available (ZiUnite, Nobel Biocare).37,39 The immediately loaded one-piece zirconia implants showed a survival rate of 95% after 1 year. However, when the peri-implant bone loss was included as a criterion of success, the success rate of the implant system dropped to 66% when bone loss of 2 mm or less was accepted and to 86% when bone loss of 3 mm or less was accepted for the single-tooth reconstructions.37 The results for the implants supporting three-unit prostheses showed an implant survival rate of 98%, bone loss of at least 2 mm in 40% of the patients, and bone loss of at least 3 mm in 28% of the patients. Again, the success rate of the implants was far below the positive survival rate.

The results of various abstracts presented recently at scientific meetings reporting on prospective investigations using the Ziraldent implant system or the Vitaclinical ceramic.implant system were very encouraging.40,41 Sperlich et al40 evaluated the survival and success rates and the bone remodeling as well as the soft tissue response of a one-piece alumina-toughened zirconia (Ziraldent) dental implant after 3 years. Of the 20 patients included in the re-

search project, 17 were seen at the 3-year follow up. Two patients lost their implants after 3 and 4 weeks (implant survival rate of 90% at the 3-year follow-up). The average marginal bone loss from implant placement to the 1-year follow-up amounted to 0.72 mm and from implant placement to the 3-year follow-up to 0.43 mm. The authors reported a slight bone gain from the 1-year to the 3-year follow-up.

Grohmann et al41 evaluated the safety and efficiency of zirconia dental implants after 1 year of function. Two centers treated patients in need of implant-supported singletooth restorations or three-unit fixed partial dentures. A total of 57 patients with 66 implants participated in the investigation. Nine patients received fixed partial dentures and 48 patients received single crowns. No implant loss was detected at the 1-year follow-up. The mean marginal bone loss from implant insertion to the 1-year follow-up of the definitive prosthetic restoration was 0.8 mm.

Discussion Long-term, high-quality clinical investigations (randomized controlled clinical trials, controlled clinical trials, and prospective cohort investigations) that would allow appraisal of the survival and success of zirconia dental implants are lacking. Therefore, the indiscriminate use of zirconia implants as an alternative to titanium implants cannot yet be recommended. However, emerging data from prospective investigations36,40,41 suggest that zirconia dental implants have very good potential for the replacement of missing teeth.

Regarding the stability of zirconia implants, the evidence in the literature indicates that the low thermal degradation of Y-TZP has no negative impact on implant stability.

However, one investigation reported a high fracture rate in small-diameter implants.45 Therefore, it is recommended that the clinician avoid using small-diameter implants made from Y-TZP. Tougher all-ceramic materials must be developed and evaluated to overcome the fracture problems associated with Y-TZP.

Surgical and Prosthetic Considerations This section addresses clinical aspects related to zirconia implant design and clinical concerns that may influence the success of zirconia implant therapy. Three clinical scenarios are presented to demonstrate the concept and surgical protocol associated with prosthetic rehabilitation using zirconia implants.

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Case 1: Surgical considerations A 30-year-old woman presented with a fractured maxillary left lateral incisor (Fig 12-3a). A microscopic evaluation revealed a crack in the labial aspect of the root. The fractured coronal part was bonded provisionally to the root with a metal post. Radiographically, the supracrestal fracture line was visible (Fig 12-3b). No bleeding was present during probing, and the labial bone was intact. The patient exhibited a very thin gingival biotype61,62 and a moderate to high smile line63 with full exposure of the dentogingival complex and surrounding soft tissues.

The patient was willing to undergo comprehensive treatment to achieve her esthetic goals; however, she was reluctant to proceed unless minimally invasive surgery was performed. A treatment plan was proposed involving extraction of the lateral incisor followed by the immediate placement of a zirconia implant and provisional restoration for subsequent prosthetic replacement.

Periotomes were used with a nontraumatic extraction technique64 to preserve the facial bone contour. Care was taken to completely debride the socket with a curette and to remove the periodontal ligament before implant placement. A one-piece zirconia implant (Nobel Biocare) with narrow prosthetic diameter was placed in the extraction socket. The implant was secured by engaging the palatal bone of the extraction socket to obtain primary stabilization and by avoiding contact of the facial bone plate, allowing a 2-mm gap for the grafting procedure (Bio-Oss, Geistlich).65 Subsequently, a connective tissue graft was harvested from the tuberosity region and secured into a split-thickness facial pouch with a sulcular approach (Figs 12-3c to 12-3e).

Sutures were placed, and care was taken to ensure a passive, tension-free fit of the connective tissue graft into the facial pouch (Fig 12-3f ). The connective tissue graft allowed for partial compensation of the crestal bone resorption that commonly occurs after extraction.66,67 With this graft approach, thick connective tissue could be formed around the transmucosal zone where the zir-

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conia implant prototype presents a concave design. The prosthetic component of the implant, with the faciolingual angulation of 15 degrees, allowed immediate provisionalization (see Fig 12-3f ).

The postoperative radiograph shows the position of the most coronal scalloped interdental thread (Fig 12-3g).

With conventional implant systems, implants are frequently placed excessively deep and therefore have the potential to induce bone resorption. With the utilization of the prototype described, it is possible that less interdental bone resorption might be observed because the interdental threads are more coronally positioned.

After 3 months of healing, the marginal soft tissue form was excellent. This might be a result of the combination of connective tissue grafting and the implant’s concave transmucosal profile, which allowed for soft tissue thickness and stability in the critical zone. Compared to baseline (see Fig 12-3a), papillary height and volume decreased very slightly initially because of surgical trauma. At this stage, initial healing was complete and osseointegration achieved.

The provisional crown was removed, the preparation of the coronal portion of the implant was finalized to establish adequate marginal soft tissue contours and position of the mucosal zenith, and retraction cord was inserted (Figs 12-3h to 12-3k) to allow final impression taking. A Procera Alumina coping (Nobel Biocare) was fabricated with the double scanning technique (Fig 12-3l), and the porcelain veneer (NobelRondo, Nobel Biocare) was applied (Fig 12-3m). Care was taken to provide the optimal prosthetic gingival support to ensure optimal long-term soft tissue stability.

At the 3-year recall, the soft tissue levels remained stable (Fig 12-3n). The 3-year postoperative radiograph showed only minor changes of interdental bone levels (Fig 12-3o).

The impact of the proper design of the transmucosal component in the soft tissue health and stability was evident in the clinical scenario described. The combination of concave zirconia implant design and connective tissue grafting seemed to play a significant role in the long-term esthetic and functional outcome.

Surgical and Prosthetic Considerations

a

b

c

d

e

f

Fig 12-3  Case 1. (a) At initial presentation, the maxillary left lateral incisor is fractured and discolored. (b) Pretreatment radiograph revealing the provisional repair with a post as well as the normal crestal profiles. (c to e) Immediate placement of a narrow, one-piece zirconia implant followed by hard and soft tissue grafting. (f ) Provisional crown after relining and cementation.

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Ceramic Dental Implants Fig 12-3  (cont) (g) Postoperative radiograph on the day of implant placement. (h and i) Clinical situation 3 months after implant surgery. Note the healthy and stable soft tissue conditions. (j) Placement of retraction cord. (k) Final preparation of the implant.

g

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h

i

j

k

Surgical and Prosthetic Considerations

l

m

n

o

Fig 12-3  (cont) (l) Cast with coping wax-up prior to scanning. (m) Definitive restoration. (n) Clinical situation 3 years after treatment. (o) Radiographic evaluation 3 years after surgery. (Reprinted from Van Dooren et al60 with permission.)

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Case 2: Prosthetic considerations A 28-year-old man presented with a severe esthetic problem associated with trauma of the anterior dentition (Figs 12-4a and 12-4b). The maxillary left central incisor was endo­dontically treated and restored with a fiber post followed by a composite buildup. The right central incisor exhibited a vertical fracture line, necessitating extraction.

Neither bleeding nor facial bone loss was detectable by probing. A two-unit provisional fixed prosthesis was fabricated prior to tooth extraction and implant placement.

A one-piece zirconia implant was placed with the same surgical protocol as described in the prior clinical example (Fig 12-4c). For this clinical scenario, the implant design with a wider prosthetic diameter was used. This implant configuration allowed for better anatomical form of the definitive crown to match the dimensions of a central incisor.

However, even with these advanced asymmetric designs, utilization of one-piece implant systems requires a greater understanding of the prosthetic rehabilitation. In general, two-piece implant systems allow individualized transmucosal designs, whereas one-piece implant systems have limitations. It is important that both the prosthodontist and the laboratory technician understand the impact of soft tissue contouring and prosthetic support to achieve longterm stability of the soft tissue.

Although provisional restoration and relining could promote soft tissue architecture during the provisionalization stage, it is imperative that the technician optimize the soft tissue contour on the master cast. For this procedure, two master casts are needed: a first die cast with silicone soft tissue mask and a solid cast to check the contact points.

The master cast represents an exact replica of the existing clinical situation. For the case presented in this section, there was a clear discrepancy between the diameter of the implant and that of the contralateral natural tooth (Figs 12-4d and 12-4e). This discrepancy could result in a deeper cement margin when compared with a two-piece implant system with a custom transmucosal abutment design. At this stage, the objective is to mimic the preparation configuration of a natural tooth, with the abutment margin being positioned slightly within the gingival sulcus. With a one-piece implant system, the crown emerges in the last 25% to 30% of the transmucosal space to allow for proper

246

prosthetic soft tissue support. Although the provisional prosthesis was relined for the patient in case 2, the technician needed to optimize the peri-implant soft tissue contour on the master cast.

Figures 12-4f to 12-4l illustrate the removal of the dies and the reshaping of the soft tissue mask with a diamond bur to simulate the gingival emergence angle, contour, and zenith position of the contralateral tooth. Two Procera Alumina copings were fabricated. The dental technician applied an additional volume of marginal ceramic (Nobel­ Rondo) to the facial aspect of the coping (see Figs 12-4k and 12-4l) to mimic the contour and shade of the natural tooth. The marginal ceramic is believed to be stable after processing because of its high firing temperature and seems to have minimal shrinkage during multiple firings throughout the layering process.

The subgingival contour and the emergence angle of the implant crown are completely different from those of the natural tooth. Care must be taken to avoid excessive pressure on the transmucosal mask tissue. A slightly concave subgingival contour or negative submergence profile is essential to minimize pressure and to leave the space for connective tissue in the critical zone (Figs 12-4m and 12-4n).

Because it is virtually impossible to exactly duplicate the profile and soft tissue contour of the contralateral natural tooth on the zirconia implant restoration, and because papillary thickness and height are lacking on the distal aspect of most implant restorations, clinicians need to rely on the dental technician’s skills to create an optical illusion to obtain the optimal esthetics (Figs 12-4o and 12-4p).

The greatest challenge in constructing implant-supported restorations in the esthetic zone involves creating the ideal position and shape of a natural tooth. Any excessive gingival pressure of the prosthetic components might lead to apical tissue migration or recession. Therefore, for anterior implant restorations, the dental technician is advised to employ optical illusions to achieve the best esthetic result without compromising the soft tissue stability.

After the crowns were finalized, the right lateral incisor was restored with a composite resin restoration to match the esthetics of the anterior crowns (Figs 12-4q to 12-4t).

The composite restoration was fabricated according to a wax-up and silicone index fabricated in the laboratory with the definitive crowns in situ.

Surgical and Prosthetic Considerations

a

b

Fig 12-4  Case 2. (a and b) Initial clinical presentation showing fractured maxillary right central incisor. (c) Soft tissue healing and maturation 3 months after placement of a zirconia implant. (d) Placement of retraction cords. Note the difference in diameter between the natural tooth and the implant at the marginal soft tissue level. (e) Note the soft tissue contour on the resulting cast.

c

d

e

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Ceramic Dental Implants

f

g

h

i

j

k

l

248

Fig 12-4 (cont) (f ) Die preparation ensures a precision fit. (g) Procera alumina copings in place on the cast. Note the soft tissue around the implant (arrow). (h and i) Removal of the dies and trimming of the gingival mask for ideal crown contour, particularly around the implant (circle). (j to l) Initial layering allows for compensation of the difference in diameter between the implant (circle and arrows) and the natural teeth.

Surgical and Prosthetic Considerations

m

n

o

p Fig 12-4  (cont) (m) Ideal positioning of the line angles for optimal light reflection. (n) The intaglio view of the definitive crowns clearly demonstrates the difference in diameter. (o and p) Cemented definitive crowns at 2-week follow-up. Note the initial lack of papillary volume.

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q

r

s

t

Fig 12-4  (cont) (q to t) Composite resin layering of the right lateral incisor to match the esthetics of the anterior crowns. A palate-incisal silicone index is used. (Courtesy of Dr Claudio Pinho, Brasilia, Brazil.) (u) Clinical situation 6 months postoperatively. (v) Substantial improvement in papillary volume 4 years postoperatively, resulting in better esthetics. (w and x) Baseline and 4-year postoperative radiographs allow comparison of interdental bone levels. (y) Definitive crowns and composite resin restorations at 4-year follow-up. Soft tissue maturation has contributed to excellent final esthetics. (Reprinted from Van Dooren et al60 with permission.)

At 6 months postoperatively (Fig 12-4u), the soft tissue appearance was satisfactory, although the papilla lacked height and especially volume at the distal aspect of the implant-supported restoration. The lack of volume resulted in a slight shadow at the mesial and distal angles of the crown.

However, the clinical outcome had improved substantially by the 4-year postoperative recall, showing a clear gain in papillary height and volume (distal papilla) of the implant-supported crown, resulting in a better match with the restored natural tooth (Fig 12-4v). The baseline and 4-year postoperative radiographs revealed stable bone 250

levels (Figs 12-4w and 12-4x). The authors speculate that the soft tissue thickness associated with the O-ring effect of the connective tissue fibers might have resulted in the long-term bone level stability observed in Figs 12-4u and 12-4v. Figure 12-4v reveals a minor change in bone levels into the interdental concavity. The authors speculate that soft tissue maturation may occur over a period of 2 years and that the phenomenon is the key to a long-term esthetic outcome of zirconia implant restorations (Fig 12-4y). More clinical experiences with long-term observations are needed to confirm these observations.

Surgical and Prosthetic Considerations

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v

w

x

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Case 3: Surgical and prosthetic considerations A 43-year-old man sought fixed dental restorations for treatment of the edentulous areas in the mandibular right and left quadrants. His main problems were the significantly reduced masticatory function in general and the severely extruded teeth of the maxillary right quadrant. During recording of the specific case history, the patient reported tooth loss due to untreated severe caries lesions.

A panoramic radiograph revealed that the maxilla was fully dentate with the right third molar missing (Fig 12-5a).

In addition, the mandibular left second premolar (tooth 35), first molar (tooth 36), and second molar (tooth 37) as well as the right first molar (tooth 46), second molar (tooth 47), and third molar (tooth 48) were missing. The postextraction sockets of teeth 37, 36, and 48 were still visible in the panoramic radiograph. With the exception of some small restorations in the maxillary right and left second molars and mandibular left third molar, and the elongated maxillary right second premolar and first and second molars, there were no further radiographic findings.

No systemic diseases were reported. The patient took no medication and was a nonsmoker.

Dental examination revealed opaque alterations of the enamel and enamel defects (Fig 12-5b). The periodontal status was unremarkable, and probing depths of only 2 to 3 mm were found. The alveolar ridge showed a slight degree of resorption horizontally in the mandibular left quadrant at tooth position 35 and soft tissue lesions in the area of the keratinized soft tissue at former tooth position 36 (Fig 12-5c).

After the history was recorded, impressions of the maxillary and mandibular arches were taken for pretreatment analysis of the intraoral situation. A bite registration was also performed.

Diagnosis After a thorough clinical and radiographic examination, the patient’s dentition was found to have received sufficient conservative treatment. A moderate Class III alveolar ridge defect (horizontal and vertical) was observed in the mandible in the areas of former tooth positions 35 to 37 and 46 to 48.

Treatment planning The patient expressed the wish for a functional prosthetic restoration of the edentulous space in the mandibular left quadrant and the free-end situation in the mandibular right quadrant. After the various treatment methods were ex252

plained, the patient agreed to receive an implant-supported fixed restoration in the left quadrant. Because the situation in the right quadrant was complex, the patient favored a wait-and-see approach after hearing the different treatment options.

The casts were mounted in an articulator and analyzed.

A wax-up/setup of the missing teeth in the mandibular left quadrant was performed. After evaluation of the stone casts and the radiographic images, the patient was found to fulfill the inclusion criteria for a clinical study of a singlecomponent (one-piece) ceramic implant. In the frame of the investigation, the edentulous spaces of the patients were restored with fixed all-ceramic reconstructions (either single-tooth restorations or three-unit fixed partial dentures41) supported by ceramic implants.

A three-dimensional evaluation of the alveolar bone was performed with the aid of digital volume tomography. On the basis of the results, an implant with a length of 10.0 mm and a diameter of 4.5 mm was planned for the region of former tooth 35 and an implant with a length of 10.0 mm and a diameter of 5.5 mm for the region of former tooth 37.

The utilized implant system (Vitaclinical ceramic.implant) was a single-component ceramic implant made of yttrium oxide–reinforced zirconium dioxide. The endosseous portion of the implant exhibited a rough, porous surface.

The treatment plan consisted of ceramic implants placed in the region of teeth 35 and 37, immediately restored with a provisional acrylic resin restoration. After a 2-month healing phase in the mandible, an impression of the implants was taken for the fabrication of an all-ceramic fixed partial denture. The follow-up examinations of the patient were to be performed according to the study protocol of the clinical investigation.

Treatment procedures Hygienic phase. The patient was instructed in optimal oral hygiene. No further measures were indicated.

Prosthetic pretreatment. Prior to implant placement, a standardized x-ray film holder for reproducible radiographic images was manufactured for the purpose of the clinical study. A standardized apical radiograph was performed showing the situation before treatment (Fig 12-5d).

Surgical intervention. Before the implant surgery, the patient rinsed his mouth for approximately 1 minute with a chlorhexidine solution. This was followed by local infiltration anesthesia of the surgical site. The surgical site was accessed via an incision of the alveolar ridge in the region of teeth 35 to 37 and an extended marginal incision along the first molar and third molar. No vertical relieving incisions

Surgical and Prosthetic Considerations

a

b

c

Fig 12-5  Case 3. (a) Panoramic radiograph. (b) Situation before treatment on the left side of the mandible. The mandibular left second premolar and first and second molars are missing. An enamel anomaly can be seen on the mesiobuccal cusp of the maxillary left second molar. (c) Occlusal view of the edentulous mandibular left segment. Small mucosal alterations caused by the processing of food can be observed on the alveolar ridge. (d) Standardized radiograph of the edentulous region.

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e

f

g Fig 12-5 (cont) (e) Surgical site with the implant bore holes in the region of the second premolar and second molar. (f ) Ceramic implants to be placed in the second premolar region (4.5 × 10 mm; left) and second molar region (5.5 × 10 mm; right). (g) Implants in situ. (h) Standardized radiograph taken immediately after placement of the implants.

h

were made. Two mucoperiosteal flaps were prepared buccally and lingually to expose the alveolar ridge.

The implant bed was prepared with the spiral and shaping burs intended for this purpose in accordance with the implant position planned on the cast (Fig 12-5e). The implant bed was prepared under external cooling with a sterile saline solution. After the bore holes were cleaned with a saline solution, an implant measuring 4.5 × 10.0 mm was placed in position 35 and an implant measuring 5.5 × 10.0 mm was placed in position 37 (Figs 12-5f and 12-5g).

Normally, the horizontal groove below the smooth surface of this type of implant should be positioned slightly below the bone margin. Because of the upward slope of the bone distal to tooth 37, the groove was positioned slightly higher mesially and slightly lower distally to permit 254

parallelism of the implants. A primary stability of 30 N/cm was achieved for both implants. The surgical site was subsequently closed with a loose suture.

Before final suture closure, a shell provisional prosthesis fabricated in the laboratory was relined directly with a coldcuring acrylic resin on preformed provisional acrylic resin copings belonging to the system. These copings fitted exactly on the implant heads. The provisional restoration was then finished extraorally, polished, and seated with a eugenol-free temporary adhesive cement. The excess cement was removed carefully.

The mucoperiosteal flaps were now sutured without tension around the supracrestal portion of the implants. The laboratory-fabricated provisional restoration was adjusted in such a way that no static or dynamic contacts occurred.

Surgical and Prosthetic Considerations Fig 12-5  (cont) (i) Prefabricated impression caps placed on the implants for the impression taking. The position of the impression caps on the implants is secured by a click-lock mechanism. (j) Impression caps left in the impression material after completion of the impression. Prefabricated laboratory implants will be inserted into the impression caps for the production of the master cast.

i

Approximal contacts with the adjacent teeth were also removed. A standardized radiograph was taken postoperatively to verify the implant position (Fig 12-5h).

The patient received postsurgical pain medication, was informed with regard to correct postoperative behavior, and was instructed to avoid oral hygiene measures in the surgical area for 1 week. To prevent plaque accumulation, a chlorhexidine solution was prescribed for daily rinsing.

After 1 week, the sutures were removed and a professional cleaning of the surgical site was performed with a polishing cup and chlorhexidine gel. From this stage onward, the patient was allowed to clean his implants carefully using a soft toothbrush. Follow-up examinations to evaluate the progress of the healing took place after 2, 4, 8, and 12 weeks.

Prosthetic phase. The prosthetic phase followed after an 8-week healing phase. After removal of the provisional restoration, the implant abutments were cleaned using a polishing cup and polishing paste. Special transfer caps were attached to the implant abutments (Fig 12-5i). The exact positioning was facilitated by a click mechanism. The impression was taken using an individual impression tray and an elastomeric impression material (Fig 12-5j). The impression of the opposing arch was taken using an alginate impression material. A bite registration and a facebow transfer followed. After the impression taking, the provisional restoration was again seated with temporary cement.

j

The master cast and opposing arch cast were fabricated and mounted in the articulator in the dental laboratory. The master cast and the occlusal bite registration were scanned with a Cerec inEos scanner (Sirona) for digital manufacturing of the prosthetic framework. The framework was designed on the computer monitor with the aid of Cerec InLab software (Sirona) on the basis of the digital information. After data were transferred to the milling unit, the framework was milled from a zirconium dioxide blank (InCeram YZ, Vident) in the Cerec inLab MX XL milling unit. The framework was veneered with veneering ceramic (VITA VM 9, Vident; Fig 12-5k).

After completion of the restoration, at the clinical try-in, the fit was checked and the esthetic evaluation took place.

Prior to cementation of the definitive prosthesis, the intaglio surfaces of the abutments were sandblasted carefully with corundum (50 Âľm, 0.5 bar). The surfaces of the implant abutments were cleaned using an intraoral sandblasting unit and bicarbonate powder. The prosthesis was seated with RelyX Unicem (3M ESPE) after retraction cords were placed around the implants (Figs 12-5l and 12-5m). The cementation material was inserted in the abutment crowns, and the prosthesis was placed on the implants and held in place with slight manual pressure. Excess composite resin cement was removed with cotton pellets. The restoration was cleaned, and the retraction cords were removed. After the occlusion and articulation were checked and adjusted, the prosthesis was polished.

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k

l

m Fig 12-5  (cont) (k) All-ceramic prosthesis fabricated from a zirconium dioxide framework (In-Ceram YZ) that is veneered with a silicate ceramic (Vita VM 9). (l) Implants and soft tissues prior to placement of the prosthesis. (m) Prosthesis cemented in place. (n) Standardized radiograph taken after placement of the prosthesis for evaluation of the fit and the peri-implant bone remodeling.

n

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References After placement of the restoration, soft tissue and reconstruction parameters were recorded for the clinical study, and a standardized dental radiograph was taken to confirm the good fit of the reconstruction (Fig 12-5n).

Conclusion At present, the biggest challenge to the future of zirconia implants is the need to provide clinical investigations that are long-term and of higher quality and that deliver meaningful outcomes that allow the evaluation of the survival and success of zirconia dental implants. Because of the small number of investigations available as well as the quality of those that do exist—in general, short-term—it is not yet possible to recommend the unrestricted use of zirconia implants as an alternative to titanium implants. However, prospective investigations36,40,41 suggest that zirconia dental implants have the potential to emerge as an excellent choice for the replacement of missing teeth.

Acknowledgment The first two case reports presented in this chapter were published previously in the European Journal of Esthetic Dentistry (Quintessence Publishing). They are reprinted here with permission.

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