Tooth-coloured fixed restorations are becoming increasingly popular with patients and dentists. If high-strength all-ceramics such as zirconia are used as the restoration material, a maximum of two adjacent missing teeth can be replaced with the aid of fixed partial dentures (FPDs). For the replacement of a missing anterior or posterior tooth by FPDs, a very good clinical performance similar to that of metal-based, ceramic-veneered restorations can be expected. However, evidence-based statements on the clinical performance of long-span all-ceramic FPDs are difficult because there are only very few studies on this topic, which are also inhomogeneous with regard to the study conditions. Randomized studies to compare monolithic (consisting only of the high-strength framework material) or partially veneered (weaker veneering ceramics in esthetically relevant tooth areas) all-ceramic and classic (completely veneered) metal-ceramic FPDs are lacking. The aim of the current explorative, prospective, randomized, two-arm clinical interventional study is therefore to compare the clinical performance of long-span FPDs (≥ 4 Pontics) made of monolithic / facially veneered zirconium dioxide with a gold standard (completely veneered cobalt chromium (CoCr)-based FPDs). Forty patients will be recruited. Once all inclusion criteria have been established, including the signed informed consent of the patients informed of the content, effort, advantages and disadvantages of the study, patients are assigned to the two study groups by stratified block randomization (main strata: tooth-supported / (tooth-)implant-supported). After placement of the restorations, follow-up examinations are performed after 1 week (baseline) and after half a year, one year, two years and three years. In addition to the main target criterion (veneering defects), further complications (related to FPDs or supporting tissues / structures) and parameters of oral health are recorded. Depending on the distribution and structure of the data, parametric and non-parametric statistics are used. Group differences with respect to the main target criterion ceramic defects are to be investigated by log-rank and chi-square tests. The significance level is set at α < 0.05. Since this is an explorative study, all p-values are descriptive.

Inclusion Criteria:

• The patient is at least 18 years old.
• The patient has unrestricted legal capacity.
• The patient has two posterior teeth (premolars and / or molars) that are to be replaced next to each other.
• The patient is reliable and willing to take part in follow-up examinations regularly and over the entire study period (three years).
• The information about the study has been understood by the patient and the signed declaration of consent has been received.

Exclusion Criteria:

• Pregnancy and lactation

• Local and / or systemic acute and / or chronic (also in the past) general medical diseases and conditions that contradict participation in the study and / or expose the patient to a higher risk in the case of participation in the study.

• Severe bruxism diagnosed by a portable electrocardiomyography device (BruxOff) (> 4 bruxism episodes / night)

• Reduced clinical crown height (< 5 mm before tooth preparation)

• Limited periodontal health:

  • probing depths > 4 mm or = 4 mm and bleeding on probing,
  • Furcation involvement > I (first band of the periodontometer after Naber disappears completely)
  • Degree of loosening of the abutment teeth > Grade I (> 1 mm horizontal mobility)

• Untreated endodontic problems of abutment teeth

• Lack of antagonistic support from fixed dentures or natural teeth

• Known allergies or intolerances to the materials used in the study

• Lack of oral hygiene

• Lack of compliance

• Planned change of residence

• Rejection of randomisation