Material selection for tooth-supported single crowns—a survey among dentists in Germany

Dentists providing restorative and prosthetic treatment are confronted with a vast and steadily increasing variety of dental materials that are available on the market. Precious and base metal alloys have been available for decades. Consequently, evidence-based statements can be given regarding their long-term performance in fixed prosthodontics [1]. However, while fixed prosthetic restorations fabricated from alloys are still the standard treatment option in the posterior dentition in formalities of German national health care insurance companies, these restorations do not meet the patients’ expectations associated with favorable esthetic appearances. While partial or complete veneering of alloy restorations (i.e., porcelain fused to metal, PFM) can relevantly improve esthetic appearance, shortcomings such as gray shimmering or complications such as chipping of the veneer are frequently described [2, 3]. With regard to this aspect, the use of tooth-colored materials might be helpful to overcome some of these problems. However, especially for recently introduced materials such as translucent zirconia, resin composites, or some lithium-X-silicate ceramics [4] fabricated with computer-aided design/computer-aided manufacturing (CAD/CAM) techniques, clinical outcomes in view of quality and longevity are sparse or missing [5, 6]. Moreover, current and future advances in digital dentistry can lead to the implementation of novel fabrication techniques and materials in daily dental practice that might serve as easy-to-use tooth-colored alternatives in fixed prosthodontics [7‐9].

The restorative materials that are currently available on the market feature a wide range of mechanical properties that have an impact on the indication spectrum, adequate preparation design, and appropriate luting methods. Regarding the selection of the materials, it might be helpful to rely on results from randomized controlled clinical trials (RCTs). A recent review by the Cochrane Review Group emphasized that only a few RCTs are available for comparisons between metal-free and metal-based restorations, concluding that there is no evidence regarding the superiority of any of these materials. As a consequence, the authors suggested that dentists should base their decisions on their clinical experience, the individual circumstances, and the opinion of the patient [10]. In comparison to the results presented by the Cochrane Review Group, another research group included a wider range of study designs in a systematic review on the survival and complication rates of ceramic or metal-ceramic single crowns (SC). The authors concluded that SCs fabricated from ceramics showed similar survival rates as PFMs, yet layered zirconia SCs were more prone to technical complications such as chipping of the veneer [2].

In recent years, the National Dental Practice-Based Research Network (PBRN) Collaborative Group has surveyed dentists in the United States (US). Among others, the topics of interest included the frequency of specific dental procedures, general health aspects in dentistry, and questionnaires related to tooth-supported SCs [11‐13]. Regarding the selection of materials for fabricating SCs in the anterior area, the study identified that lithium disilicate (54%), layered zirconia (17%), and glass ceramics (13%) were favored by the participating dentists. For posterior SCs, monolithic zirconia (32%), PFM (31%), and lithium disilicate ceramics (21%) were preferred. The authors concluded that the selection of the materials was significantly associated with the individual characteristics of the participating dentists and their patients [12].

In comparison to the US, guidelines of the German national health care insurance companies compile minimum standards for both the type of restoration and the restorative material depending on the individual clinical setting. One of these companies has shared data for scientific purposes over the last years [14], yet only general information can be retrieved from that database. Specific but relevant aspects of prosthetic restorations, such as the type of materials or the individual clinical situation (i.e., marginal preparation design), were not documented in detail. Thus, no valid estimation regarding the preferred materials of dentists in Germany for the fabrication of SCs is possible from that dataset. Moreover, it is unclear whether these preferences depend on the individual characteristics of the dentist, the dental practice, or the patient.

Thus, the aim of this study was to survey dentists in Germany to identify their favored materials for the fabrication of tooth-supported SCs depending on the location of the abutment teeth and the preparation margin. The working hypothesis was that dentists in Germany recommend the same materials for the fabrication of SCs independent of the individual clinical scenario, the characteristics of the dentists, or their dental practice.

The results of the current survey entitled “Versorgungskompass Festsitzender Zahngetragener Zahnersatz” revealed that ceramic materials are favored by dentists in Germany for the fabrication of SCs, which was independent of the location of the abutment tooth and preparation margin. Only a few participants favored CAD/CAM resin composites or full metals. However, in scenarios with subgingival preparation designs, we observed that participating dentists preferred PFMs more frequently than in settings with supragingival preparation margins. Sex, the time since graduation, and the number of inhabitants of the village/city the dental practice/university was located did not influence the dentists’ preferences except for a single scenario (11 subgingival), which revealed a dependency on the time since graduation. Consequently, the working hypothesis of this investigation can be partially rejected, as characteristics of the participating dentists had—at least for one specific clinical scenario—an impact on the material recommendations.

The data of the current study suggest that the influence on preferences for the material selection of SCs are different between German and US dentists as the latter are more likely to base decisions on their own characteristics or those of their dental practice [12]. Nonetheless, ceramics were favored in both nations, followed by PFMs. The US survey comprised a clinical scenario that also included the fabrication of an SC for abutment tooth 11. The participating US dentists favored lithium disilicate as the restorative material, followed by layered zirconia and classical glass ceramics. In contrast to the US study, the current survey further distinguished between a supra- and subgingival location of the preparation margin. For supragingival preparation margins, the results of our survey were similar to the results from the US as lithium-X-silicate was recommended by most of the participants. However, for the scenario with subgingival preparation margins, the proportion of participants who preferred PFM increased compared to the material of choice for supragingival preparation margins. Both the US and the current survey included a setting that required the selection of an SC material for abutment tooth 36. German dentists recommended lithium-X-silicate ceramics (supragingival preparation margin) and monolithic zirconia, as well as PFM (subgingival preparation margin), whereas US dentists favored predominantly monolithic zirconia, followed by PFM and lithium disilicate. The authors assume that in scenarios in which moisture is difficult to control and clinical access and the view are limited, dentists tend to use materials that can be inserted using conventional cementation methods. Moreover, it might be possible that dentists are not aware or do not rely on the fact that lithium disilicate or zirconia ceramics are approved for conventional cementation techniques in most clinical situations. Although all materials offered in the questionnaire were indicated for SCs in the given location of the abutment tooth or preparation margin, these results also assume that in technically complicated settings, esthetic aspects are estimated to be less important than easy handling and evidence. Nonetheless, the data of the current survey suggest that the application of monolithic zirconia is widely established for molar restorations, although evidence on the long-term performance and survival, as well as that on the effects on the masticatory system, is still sparse.

Surprisingly, some of the participating dentists did not complete the questions about specific ceramics. However, numerous dentists entered a free answer, such as the manufacturer or the trade name. This result might be due to the high fluctuation rates of tooth-colored materials on the dental market [17] and might indicate confusion over existing classifications. Nonetheless, it is important that dentists are informed about the differences between ceramics as this knowledge is relevant when choosing the correct cementation method or indications of the material. These considerations might also explain the few recommendations of CAD/CAM resin composites or polymer-infiltrated ceramic-network materials in the present survey. Regarding their composition and structure, these materials are highly complex and require careful handling in strict accordance with the guidelines issued by the manufacturer. The vast number of different materials that are available on the German market might also produce uncertainties and confusion, which indicates that improved postgraduate education might be required, for instance, by overview articles in the German language or utilizing more detailed curricula.

The limitations of this study include the number of clinical scenarios that were offered to the participants. It might have been interesting to elucidate potential differences in restorative approaches for the lower incisors, equigingival preparation margins, or patients with parafunctional activities. Moreover, it would have been interesting to introduce clinical scenarios with different layer thickness of the SCs as this parameter might also influence the choice of tooth-colored materials. However, the estimated time required for completion of the survey was set to a maximum of 7 min to ensure that a high percentage of participants completed the survey [15]. Nevertheless, the scenarios in the survey covered both esthetically (11, 34) and technically challenging settings (molars). Despite all our efforts, questions were more frequently left uncompleted at the end of the survey. Even though an easy-to-use drop-down menu was employed to answer, e.g., the area of expertise, solely half of the participants completed the question (58.6%).

One percent of the dentists working in Germany responded to the survey, and postal codes indicated a similar percentage of participating dentists from all parts of the country. Moreover, sex- and age-related characteristics of the participants were similar to the overall demographics of dentists in Germany. Nonetheless, for an entirely representative approach, it would have been best to directly address each dentist in Germany, e.g., by e-mail or letter service to ensure that every dentist was invited to take part in the survey and to calculate an actual rate for non-respondents.

The results suggest that dentists selected their restorative materials depending on the individual clinical scenario. Nevertheless, improvements in postgraduate information and education might help to extend the expertise for newly introduced tooth-colored materials.