Irena Sailer - Fixed Restorations

2.6.6 Posterior regions: Posterior implant- supported SC and optical impression

2.6.7 Complex situations: Tooth- and implant-supported all-ceramic SCs and fixed dental prostheses (FDPs)

2.7 Implant-supported restorations

2.7.1 Anterior regions: Implant-supported four-unit fixed dental prosthesis (FDP)

2.7.2 Posterior regions: Implant-supported three-unit fixed dental prosthesis (FDP)

2.7.3 Posterior regions: Implant-supported fixed dental prosthesis with mesial cantilever (FDP)

2.7.4 Posterior regions: Implant-supported fixed dental prostheses (FDPs)

2.7.5 Complex situations: Full-arch implant-supported fixed restoration with pink ceramics (FDP)

2.8 Maintenance

2.8.1 Intraoral direct repair of an existing restoration

2.8.2 Maintaining an existing restoration

2.8.3 CAD/CAM-fabricated Michigan splint

Part III Long-term outcomes of fixed restorations

3.1 Introduction

3.2 Tooth-supported veneers

3.3 Tooth-supported inlays and onlays

3.4 Tooth-supported SCs

3.5 Endocrowns

3.6 Tooth-supported conventional multiple-unit FDPs

3.7 Tooth-supported cantilever FDPs

3.8 Resin-bonded fixed dental prostheses (RBFDPs)

3.9 Implant-supported SCs

3.10 Implant-supported FDPs

3.11 Implant-supported cantilever FDPs 693

3.12 Combined tooth-implant-supported FDPs

3.13 References

Part IV Avoiding and managing complications

4.1 Introduction

4.2 Success of tooth- and implant-supported restorations

4.3 Tooth-supported restorations

4.4 Implant-supported restorations

4.5 References

PART I

BASICS

CHAPTER 1

Current restorative materials

Jens Fischer

1.1.1 Introduction

In this chapter:

■ Requirements for restorative materials

■ Overview of current materials for fixed restorations

■ Conclusions

In the past, material selection in fixed prosthodontics was mainly based on metal-ceramics and on a few all-ceramic alternatives. Metal-ceramic restorations were selected in clinical situations with need for high stability (eg, in the posterior region or in the case of multiple-unit fixed dental prostheses), whereas all-ceramic restorations were recommended in single tooth replacement with high esthetic demands, especially in the anterior region. These materials were traditionally processed by manual fabrication technologies such as casting, pressing, or layering 1 , 2. Restorative dentistry with all-ceramic restorations has suffered from a prolonged learning curve. Several of the early systems disappeared shortly after being introduced due to an unacceptable number of mechanical failures 3.

Nowadays, clinicians and technicians can choose from a wide range of reliable materials. Digital technologies such as intraoral optical scans and computer-aided design/computer-aided manufacturing (CAD/CAM) procedures have opened up new treatment pathways in fixed prosthodontics. New digital fabrication workflows were defined and in parallel advanced materials were developed and adjusted to the specific requirements of numerically controlled processing such as high-strength ceramics and composites. In these digital workflows, the restorations are fabricated by means of computer-aided milling from prefabricated blanks, increasingly replacing conventional manual processing.

The different materials available today exhibit differences in properties, influencing the esthetics and the long-term performance of the restorations. As multiple alternatives exist for each clinical situation, it is more difficult to select the most appropriate material for the respective clinical situation today than in the past 4 – 6. As a consequence of the transformation in present technology, selection of the restorative material requires understanding of the interaction between material properties and clinical performance 7.

After an introduction to the requirements for restorative materials and the behavior of the different material classes used in dentistry, this Chapter will provide an overview of the current material options for fixed restorations and their clinically relevant properties, indications, and limitations.

1.1.2 Requirements for restorative materials

In the oral cavity, restorative materials have to meet three requirements: biocompatibility, longevity, and esthetics .

Biocompatibility

The term biocompatibility implies that the material shall do no harm to the living tissues, achieved through chemical and biological inertness 8. As every material potentially dilutes or degrades depending on the environment, the extent of decomposition, and the quality and amount of released substances determine the degree of biological complications. A possible host response might be localized or systemic toxicity, hypersensitivity, or genotoxicity 9. The restriction to biocompatible components strongly limits the room for the development of new materials.

Due to the strict regulations for medical devices, manufacturers have to prove biocompatibility of their materials. International standards help the choosing of the appropriate tests and in interpreting the results. Tests must be done with every novel material prior to approval. Biological tests are employed in a sequence, ending up with animal tests 9. Furthermore, manufacturers of medical devices are forced by law to perform a systematic post market surveillance of the materials and devices. Measures have to be taken to minimize risk and unexpected side effects must be notified to the authorities. Fortunately, it can be concluded that biological and immunological adverse reactions attributed to dental materials are rare and the reported adverse effects are acceptable 9.

On the other hand it is unrealistic to assume that absolute material inertness is attainable and biological behavior is definitely predictable by means of biological tests 10. Hence, the biocompatibility of dental materials must always be weighed against their benefit 11. Controlled clinical trials are currently still the best way to assess the clinical response to materials. But even these tests have significant limitations. Therefore, practice-based research networks and practitioner databases are increasingly considered as a valuable alternative 10.

Longevity

The long-term success of a restoration mainly depends on its mechanical performance. From the technical side the success of a restoration can be controlled by the durability of the material , the nature of the design , the quality of the processing , and the effectiveness of the finishing .

Material

The mechanical behavior of dental materials is mainly characterized by elasticity, flexural strength, fracture toughness, and hardness. These properties are basically given by the type and strength of the bondings between the atoms.

Elasticity is the ability of the material to resume its initial shape after loading, measured in GPa (= 10 3N/mm 2). Stressing a material beyond its limit of elasticity leads to plastic deformation, a permanent distortion. Brittle materials such as ceramics only show minimal or no plasticity, which means they fracture very soon after reaching the limit of elasticity. The stress where fracture occurs is the flexural strength, measured in MPa (= N/mm 2). The resistance against crack growth is called fracture toughness, measured in MPa√m.

Elasticity, flexural strength, and fracture toughness are bulk properties. Hardness in contrast is a surface property, which is defined as the resistance to localized deformation induced by mechanical indentation or abrasion. Harder materials therefore show less risk of surface damage. Flexural strength and hardness are correlated to a certain extent.

The main risk for mechanical failure of restorations are flaws at the surface, which might act as a starting point for microcracks. In case of tensile loading, a microcrack opens and stress develops at the tip of the crack. Stress which exceeds the strength of the material leads to crack propagation. Under cyclic loading − such as mastication − crack growth happens in a micrometer scale. But over time the crack grows significantly. Finally, catastrophic failure occurs when the residual cross-section is too small to withstand the load.