Clinical prospective evaluation of zirconia-based three-unit posterior fixed dental prostheses: Up-to ten-year results.

Abstract

Objectives

Only a few studies exist, which assess the clinical long-term behavior of all-ceramic FDPs in the posterior region. The aim of the present prospective clinical study was to evaluate the clinical performance of posterior three-unit FDPs manufactured from Y-TZP after a service period up to 10 years.

Methods

55 patients received 59 three-unit FDPs in the posterior region of the maxilla or mandible. Abutment teeth were prepared and full-arch impressions were taken. Definitive casts were fabricated and optically scanned. Frameworks were fabricated with computer-aided design (CAD) and manufacturing (CAM) technology. Y-TZP frameworks were veneered and adhesively luted to the abutment teeth. Baseline and follow-up examinations (service time: ≥48 months) were recorded by applying modified United States Public Health Services (USPHS) rating criteria. Cumulative survival rate was analyzed with Kaplan–Meier. Percentage of biological and technical complication was calculated.

Results

Fifty-three patients with 57 FDPs attended the last follow-up visit and a mean observation period of the remaining was 6.3 ± 1.9 years was calculated. Biological complications occurred in 17.5%, technical complications in 28% of the FDPs. The 10-year cumulative survival rate amounted 85.0%. Three FDPs failed to survive, two due to a root fracture of the abutment tooth and one due to secondary caries.

Conclusions

Three-unit FDPs made from Y-TZP, veneered with ceramic offer a treatment option with a high rate of chipping. However, the manufacturing processes nowadays are modified in order to avoid this complication.

Clinical significance

The results of the present investigation suggest that three-unit Y-TZP posterior FDPs may are a possible treatment option. However, a high rate of chipping can be expected.

Introduction

When it comes to replace a missing posterior tooth, tooth-supported fixed partial dentures (FDPs) are a well-documented treatment option with high survival rates . Veneered gold- or metal-alloys are still the ‘gold standard’ for the fabrication of posterior FDPs . They offer good mechanical properties, while from an esthetic point of view it may be challenging to veneer the dark framework, especially in areas with limited space. All-ceramic materials offer an alternative in terms of better optical properties with a more tooth-resembling color and a higher translucency. Furthermore, the patient’s demand for metal-free restorations is increasing and all-ceramic restorations come along with a good biocompatibility . Also due to the risen costs for the production of metal-frameworks, the need of developing all-ceramic materials that withstand high occlusal forces were needed.

Nowadays, a variety of different ceramic materials are available for all-ceramic crowns, FDPs and their frameworks. Besides the conventional glass-ceramics, high-strength ceramics like alumina and zirconia have been introduced. While glass-ceramics offer good optical but low physical properties, alumina and zirconia ceramics exhibit a superior stability but lower translucency. Due to the weak optical properties of alumina and zirconia, they usually were used as a framework material and have to be veneered with tooth-colored ceramics . Existing since the early 1990s, zirconia appears as the most suitable all-ceramic material for FDPs .

Pure zirconium-dioxide (ZrO 2 ) can exist in three temperature-dependent phases: monoclinic (room temperature to 1′170 °C), tetragonal (1′170 °C to 2′370 °C) and cubic (2′370 °C up to the melting point). ZrO 2 , in its pure condition is at room temperature unsuitable for structural or mechanical applications . By adding Y 2 O 3 to ZrO 2 , it is possible to stabilize the dense tetragonal phase to a so-called yttria-stabilized zirconia (Y-TZP). This process leads to an inhibited further propagation in cases of crack-formation within the material and therefore gives Y-TZP a great potential for stress-bearing . By this reason, Y-TZP exhibits fracture strength of 900–1′400 MPa and a fracture toughness of 5–10 MPa m 1/2 , which is superior to all currently available sintered ceramics .

The productions of such frameworks, made by high-strength ceramic zirconia, have become feasible with the introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) systems in dentistry . By using CAD/CAM procedures, the time for fabrication, the material costs and the associated costs for production of FDP-frameworks can be reduced in comparison to conventionally manufactured metal-frameworks. In general, in the CAD/CAM-workflow three steps can be defined: (1) Scanning of the preparation intraorally or from a cast model; (2) Digital design of the reconstruction (CAD) and (3) Machining the digitally designed reconstruction out of a pre-fabricated blank (CAM) . Usually, the Y-TZP blanks get milled in a pre-sintered condition. In order to obtain the final density and strength of the milled framework, sintering at high temperature is necessary. Machining the work piece enlarged by this amount compensates the sinter-shrinkage of about 25–30% .

So far, numerous clinical studies have confirmed zirconia as sufficient strong to function as framework material for FDPs . However, current data indicate the chipping of the veneering ceramic is often observed as a technical complication . Since now, only a few studies exist, which assess the clinical long-term behavior of all-ceramic FDPs in the posterior region . Thus, the want for additional long-term investigations on all-ceramic FDPs is essential.

Therefore, the aim of the present prospective study was to evaluate the clinical performance of posterior three-unit FDPs manufactured from Y-TZP after a service period up to 10 years. It was hypothesized that the long-term survival rate of such FDPs would not differ from those reported in the literature for conventional metal-ceramic FDPs.

Materials and methods

Study population

Following approval by the ethical committee (Ref. Nr. StV 02/09) of the University of Zurich, 55 patients with the indication of at least one three-unit FDP in the posterior were recruited for this study. The abutment teeth had to be either a premolar and a molar or two molars. The FDP had to replace just one missing premolar or one missing molar. Patients had to be periodontally healthy and show no signs of actual parafunctional habits or untreated tempo-mandibular disorders. All patients were informed in detail about differences between metal-ceramic and full-ceramic restorations and their advantages and disadvantages. A signed informed consent was obtained from all the patients prior to any treatments.

Clinical procedure

All previous restorations and build-up materials, as well as base materials and caries, were completely removed to prepare a sound basis for the new restoration. If required, vital teeth were built up using a functional adhesive (Syntac Classic & Heliobond; Ivoclar Vivadent, Schaan, Liechtenstein) and a light-curing resin-based fine-hybrid composite (Tetric; Ivoclar Vivadent, Schaan, Liechtenstein). If endodontic treated teeth showed not enough surfaces for retention, an endodontic ceramic post was set (Cera Post; Brasseler, Lemgo, Germany/Panavia 21 TC; Kuraray, Tokyo, Japan). The abutment teeth were prepared according to the requirements for all ceramic FPDs with circular butt joint margins of approximately 0.8–1.0 mm width, a tapering angle of 10–12 degrees, an occlusal reduction of at least 1.5 mm and a minimal abutment height of 3–4 mm.

After preparation, full-arch impressions were taken using a silicone material (Honigum; DMG Dental, Hamburg, Germany). Direct temporary FDPs were fabricated (Luxatemp; DMG, Hamburg, Germany). Prior to cementation of the temporary FDP (Temp Bond NE; Kerr Hawe, Bioggio, Switzerland), dentine was sealed a self-etching primer and adhesive as well as a bonding agent (Syntac Classic & Heliobond; Ivoclar Vivadent, Schaan, Liechtenstein).

Fabrication of the Y-TZP FDPs

First, definitive casts were fabricated out of hard stone plaster (Fuji Rock; GC International, Leuven, Belgium). All frameworks were manufactured by a CAD/CAM system (in Lab; Sirona, Bensheim, Germany). An optical scan was taken from the FDP preparation, using a pinpoint laser scanner (in Lab; Sirona, Bensheim, Germany). The CAD construction of the framework was made by means of a software (in Lab; Version 3.1, Sirona, Bensheim, Germany). According to the manufacturer’s guidelines, the minimal connector dimension of the framework was 9 mm 2 . The minimal framework thickness accounted 0.5 mm at the vertical crown walls and 0.7 mm occlusally. With a milling unit (in Lab; Sirona, Bensheim, Germany), the framework was milled out of presintered zirconia blank (Vita In-Ceram 2000YZ-Cubes; Vita Zahnfabrik, Bad Säckingen, Germany). The enlarged milled framework was sintered to full density at a temperature of 1′560 °C (ZYrcomat; Vita Zahnfabrik, Bad Säckingen, Germany) for 2 h according to manufactures instruction, resulting in shrinkage to the wanted framework dimension. After checking for fit in the patient mouths, the framework was manually veneered with a veneering ceramic (Vitadur Alpha; Vita Zahnfabrik, Bad Säckingen, Germany).

Moisture control and adhesive placement

The temporary FDP was removed and the preparations were carefully cleaned using a finishing diamond (grain size: 25 μm, Nr. 2504; Intensiv, Viganello-Lugano, Switzerland). Cotton rolls (Pharmadoc; Zürich, Switzerland) and dry angle (Dry Tip; Mölnycke, Sweden) were used to manage salivation and gingival fluid during adhesive placement. Adhesive pretreatment of the dentin was applied using a self-etching primer, adhesive and a bonding agent (Syntac Classic & Heliobond; Ivoclar Vivadent, Schaan, Liechtenstein).

After air-abrasion with aluminum oxide (grain size: 50 μm, pressure: 2.5 bar) and cleaning with alcohol of the internal parts, the reconstruction was adhesively placed (Panavia 21 TC; Kuraray, Tokyo, Japan). Excess luting material was partially removed and the margins of the restoration were covered with a protective layer (Panavia F Oxyguard II; Kuraray, Tokyo, Japan) for 8 min. After polymerization, the removal of excess luting material was completed with a scaler (M23 Universal Scaler; Deppeler, Rolle, Switzerland).

Clinical examination

Baseline examination was recorded by applying modified United States Public Health Services (USPHS) rating criteria . Patients whose FDPs had been in service for at least 48 months and no such follow-up data were available, were invited for follow-up examination. Patients who did not appear to the follow-up examination where excluded from the study.

Two clinicians assessed the FDPs. The examiners had previously trained on other clinical cases until ratings were equal. In addition, Plaque- and Papillary-Bleeding-Indices were recorded for six sites (mesiobuccal, buccal, distobuccal, distoligual, lingual, mesiolingual) on abutment teeth and on Ramfjord control teeth . Ramfjord control teeth included non-restored and restored teeth.

Statistical analysis

Data were coded and analyzed in SPSS Statistics 20.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistic such as mean and standard deviation (SD) and the 95% confidence interval (95% CI) was applied to the data. The statistical unit in calculating the survival rate was the FDP. FDP survival was defined the FDP was in situ at the time of the last follow-up visit. The cumulative survival rate was analyzed with the Kaplan–Meier nonparametric method. The percentage of biological and technical complication was calculated.

For the USPHS-criteria, the number of single ratings, A, B, C, (D), (E) were expressed as a percentage of the total number of ratings per criterion.

For comparing the Plaque- and Papillary-Bleeding-Indices, the measured values were pooled and averaged for the abutment and the Ramfjord control teeth. A Wilcoxon test was applied to compare the test and control teeth. After Bonferroni correction for multiple testing, the significance level was set at p < 2.5% (α/ k = 0.05/2).

Materials and methods

Study population

Following approval by the ethical committee (Ref. Nr. StV 02/09) of the University of Zurich, 55 patients with the indication of at least one three-unit FDP in the posterior were recruited for this study. The abutment teeth had to be either a premolar and a molar or two molars. The FDP had to replace just one missing premolar or one missing molar. Patients had to be periodontally healthy and show no signs of actual parafunctional habits or untreated tempo-mandibular disorders. All patients were informed in detail about differences between metal-ceramic and full-ceramic restorations and their advantages and disadvantages. A signed informed consent was obtained from all the patients prior to any treatments.

Clinical procedure

All previous restorations and build-up materials, as well as base materials and caries, were completely removed to prepare a sound basis for the new restoration. If required, vital teeth were built up using a functional adhesive (Syntac Classic & Heliobond; Ivoclar Vivadent, Schaan, Liechtenstein) and a light-curing resin-based fine-hybrid composite (Tetric; Ivoclar Vivadent, Schaan, Liechtenstein). If endodontic treated teeth showed not enough surfaces for retention, an endodontic ceramic post was set (Cera Post; Brasseler, Lemgo, Germany/Panavia 21 TC; Kuraray, Tokyo, Japan). The abutment teeth were prepared according to the requirements for all ceramic FPDs with circular butt joint margins of approximately 0.8–1.0 mm width, a tapering angle of 10–12 degrees, an occlusal reduction of at least 1.5 mm and a minimal abutment height of 3–4 mm.

After preparation, full-arch impressions were taken using a silicone material (Honigum; DMG Dental, Hamburg, Germany). Direct temporary FDPs were fabricated (Luxatemp; DMG, Hamburg, Germany). Prior to cementation of the temporary FDP (Temp Bond NE; Kerr Hawe, Bioggio, Switzerland), dentine was sealed a self-etching primer and adhesive as well as a bonding agent (Syntac Classic & Heliobond; Ivoclar Vivadent, Schaan, Liechtenstein).

Fabrication of the Y-TZP FDPs

First, definitive casts were fabricated out of hard stone plaster (Fuji Rock; GC International, Leuven, Belgium). All frameworks were manufactured by a CAD/CAM system (in Lab; Sirona, Bensheim, Germany). An optical scan was taken from the FDP preparation, using a pinpoint laser scanner (in Lab; Sirona, Bensheim, Germany). The CAD construction of the framework was made by means of a software (in Lab; Version 3.1, Sirona, Bensheim, Germany). According to the manufacturer’s guidelines, the minimal connector dimension of the framework was 9 mm 2 . The minimal framework thickness accounted 0.5 mm at the vertical crown walls and 0.7 mm occlusally. With a milling unit (in Lab; Sirona, Bensheim, Germany), the framework was milled out of presintered zirconia blank (Vita In-Ceram 2000YZ-Cubes; Vita Zahnfabrik, Bad Säckingen, Germany). The enlarged milled framework was sintered to full density at a temperature of 1′560 °C (ZYrcomat; Vita Zahnfabrik, Bad Säckingen, Germany) for 2 h according to manufactures instruction, resulting in shrinkage to the wanted framework dimension. After checking for fit in the patient mouths, the framework was manually veneered with a veneering ceramic (Vitadur Alpha; Vita Zahnfabrik, Bad Säckingen, Germany).

Moisture control and adhesive placement

The temporary FDP was removed and the preparations were carefully cleaned using a finishing diamond (grain size: 25 μm, Nr. 2504; Intensiv, Viganello-Lugano, Switzerland). Cotton rolls (Pharmadoc; Zürich, Switzerland) and dry angle (Dry Tip; Mölnycke, Sweden) were used to manage salivation and gingival fluid during adhesive placement. Adhesive pretreatment of the dentin was applied using a self-etching primer, adhesive and a bonding agent (Syntac Classic & Heliobond; Ivoclar Vivadent, Schaan, Liechtenstein).

After air-abrasion with aluminum oxide (grain size: 50 μm, pressure: 2.5 bar) and cleaning with alcohol of the internal parts, the reconstruction was adhesively placed (Panavia 21 TC; Kuraray, Tokyo, Japan). Excess luting material was partially removed and the margins of the restoration were covered with a protective layer (Panavia F Oxyguard II; Kuraray, Tokyo, Japan) for 8 min. After polymerization, the removal of excess luting material was completed with a scaler (M23 Universal Scaler; Deppeler, Rolle, Switzerland).

Clinical examination

Baseline examination was recorded by applying modified United States Public Health Services (USPHS) rating criteria . Patients whose FDPs had been in service for at least 48 months and no such follow-up data were available, were invited for follow-up examination. Patients who did not appear to the follow-up examination where excluded from the study.

Two clinicians assessed the FDPs. The examiners had previously trained on other clinical cases until ratings were equal. In addition, Plaque- and Papillary-Bleeding-Indices were recorded for six sites (mesiobuccal, buccal, distobuccal, distoligual, lingual, mesiolingual) on abutment teeth and on Ramfjord control teeth . Ramfjord control teeth included non-restored and restored teeth.

Statistical analysis

Data were coded and analyzed in SPSS Statistics 20.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistic such as mean and standard deviation (SD) and the 95% confidence interval (95% CI) was applied to the data. The statistical unit in calculating the survival rate was the FDP. FDP survival was defined the FDP was in situ at the time of the last follow-up visit. The cumulative survival rate was analyzed with the Kaplan–Meier nonparametric method. The percentage of biological and technical complication was calculated.

For the USPHS-criteria, the number of single ratings, A, B, C, (D), (E) were expressed as a percentage of the total number of ratings per criterion.

For comparing the Plaque- and Papillary-Bleeding-Indices, the measured values were pooled and averaged for the abutment and the Ramfjord control teeth. A Wilcoxon test was applied to compare the test and control teeth. After Bonferroni correction for multiple testing, the significance level was set at p < 2.5% (α/ k = 0.05/2).

Results

Patient demographics and distribution of the FDPs

Fifty-five patients (32 women, 23 men) received 59 FDPs between 2002 and 2006. At time of insertion, the mean age of the patients accounted 52.6 ± 10.1 years. The distribution of the replaced teeth is shown in Table 1 . In total, 25 premolars and 34 molars were replaced. Twenty-nine FDPs were placed in the upper jaw and 30 FDPs in the lower jaw.

Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Clinical prospective evaluation of zirconia-based three-unit posterior fixed dental prostheses: Up-to ten-year results.
Premium Wordpress Themes by UFO Themes