1 Introduction
All-ceramic materials are known for their favourable biocompatibility (Roulet and Herder, 1985; Mc Lean, 1979). Since the chemical composition3 of IPS Empress does not significantly differ from that of other dental ceramics, it is safe to assume that the general investigations on the biocompatibility of dental ceramic materials also apply to IPS Empress. Even though the composition of IPS Empress 2 differs from that of other dental ceramics, the fundamental examinations of the biocompatibility of dental ceramics also apply to IPS Empress 2.

The biocompatibility of IPS Empress (chemical durability, possible cytotoxic, subchronical toxic, and genotoxic potential as well as the potential to cause sensitization and irriation) were evaluated in accordance with ISO 10993-1 ‘Biological evaluation of medical devices’.

Since pulp reactions are associated with the cementation procedure, they are not dealt with in this report.

2 Toxicological evaluation (for patients)
2.1 Chemical durability
Dental materials are exposed to a wide range of pH-values and temperatures in the oral cavity. Therefore, chemical stability is an important prerequisite for dental materials. The investigations
conducted by Schäfer and Kappert (1993) have shown that, having a solubility of 0.2 ± 0.1 % of the original weight, IPS Empress demonstrates a high chemical stability. Consequently, the material meets the requirements of ISO 6872 (see also section 3.5). The concentrations of Na (64 ppm), Ca (2 ppm), Mag (23 ppm), Al (100 ppm), and Fe (2 ppm) found in the solvent during this investigation do not represent a health risk.

Having a solubility of 26 µg/cm², IPS Empress 2 also exhibits a very high chemical stability (Kappert 1998). The material meets the requirements of ISO Standard 6872 (see section 3.5).

Of all the dental materials known to date, ceramics are considered to be the most durable (Anusavice, 1992).

2.2 Cytotoxicity
Baumann and Heidmann (1991) determined the cytotoxicity of IPS Empress in cell cultures of gingiva fibroplasts. Lorenz (1994) examined the behaviour of explant cultures and fibroplast cells in contact with the IPS Empress material in a long-term experiment (up to 7 weeks).

The in vitro cytotoxicity of the IPS Empress 2 framework material (CCR Project 571100) and layering material (CCR Projects 590001, 590002, 590004) was assessed by means of direct-cell-contact tests.

Under the selected test conditions, no cytotoxic potential was determined for the ceramics tested.

2.3 Sensitization, irritation
Cavazos (1968), Henry et al (1966) and Allison et al (1958) have shown that, in contrast to other dental materials, dental ceramics do not cause adverse reactions when they come in contact with the oral mucous membrane. Mitchell (1959) and Podshadley and Harrison (1966) used implant tests to prove that glazed ceramic materials cause only very limited inflammation and thus cause far less irritation than other approved dental materials, such as gold and resin composites.

Since direct irritation of the mucous membrane cells through contact with ceramics can virtually be ruled out, possible irritation is generally attributable to mechanical stimulus. Generally, such irritations can be prevented by following the IPS Empress and IPS Empress 2 Instructions for Use.

Compared with other dental materials, ceramics show only a minimum potential to cause irritation or sensitization, if any at all.

2.4 Subchronical toxicity, genotoxicity, and carcinogenicity
Solubility tests have shown no signs of IPS Empress demonstrating a potential with regard to subchronical toxicity, genotoxicity, or carcinogenicity. Neither can such references be found in literature.

2.5 Radioactivity
The following levels of radioactivity have been measured in IPS Empress 2 ceramics by Y spectrometry:

	U-238 [Bq/g]	Th-238 [Bq/g]	total [Bq/g]
Framework material	< 0.005	< 0.003	< 0.008
Layering material	0.006	< 0.003	< 0.009
Glaze	0.006	0.003	0.009
Threshold value ISO 6872 and ISO 13356.2			0.2

                                                                                        Petri (1997)

The IPS Empress 2 ceramics tested fulfil the requirements of the ISO standard regarding the maximum permissible levels of radioactivity.

3 Additional toxicological assessment for dental technicians
Of all the parties involved, dental technicians most frequently come in contact with the IPS Empress and IPS Empress 2 dental material. In contrast to patients, they also come in contact with the unfinished product.

Contact with grinding dust of the investment material and the ceramic should be given particular attention (Mackert 1992).

If the safety notes in the Instructions for Use are observed (inhalation of grinding dust must be avoided) the re is no increased risk for dental technicians .

4 Conclusion
According to the current standard of knowledge and based on the data available, both an acute and a chronical health risk can be excluded for all the parties that come in contact with the product, provided IPS Empress and IPS Empress 2 are used according to the instructions of the manufacturer.

3 The IPS Empress 2 ceramics consist of >45 wt% SiO2; additional contents are Al2O3, La2O3, MgO, ZnO, K2O, Li2O, P2O5, Na2O, CaO, F and pigments. The Shade and Stain pastes contain approx. 30 wt% glycol.