EP 3 318 218 B1 relates to a dental cutting zirconia blanks having a high relative density .
Brief outline of the case
The OD decided maintenance according to AR2 and the opponent appealed.
The board held that the claim as maintained infringed Art 123(3). The same applied to AR1-5.
As AR6 had not been dealt with by the OD, the board remitted the case for further prosecution.
Claim 1 as granted relates to a “dental cutting zirconia blank“
Claim 1 of as maintained relates to a “pre-sintered body of a dental cutting zirconia blank“.
The proprietor’s point of view
The proprietor argued that the term “dental cutting blank” implied an item that is being cut or milled. Therefore, according to the proprietor, claim 1 as granted was directed to a pre-sintered body from the outset.
For the proprietor, claim 1 as granted would be understood by the skilled person to cover a dental cutting blank irrespective of its sintering state.
The proprietor argued that the skilled person would understand the term “powder” in in granted claim 1 to encompass the different sintering degrees assumed until the blank is perfectly sintered.
Specifically, the skilled person would reasonably interpret the term “powder” in light of the technical context of the claim as also referring to a pre-sintered state.
The board’s decision
In the field of dental prosthetics, the term “dental cutting blank” can indeed be used to refer to a dental prosthesis in its raw state, i.e. before final shaping and sintering.
However, this term is not used exclusively for pre-sintered articles. In particular, the term “dental cutting blank” is not a standard term with such a meaning. Rather, it leaves open whether or not a shaping or sintering process has already taken place, thereby encompassing both a pre-sintered body and an unsintered green body.
The description of the patent in suit, which is to be consulted to interpret claim 1 as granted, does not lead to a different conclusion.
In paragraph [0068] the term “dental cutting blank” is used for designating the unsintered green body, as it is the pre-sintered body of the dental cutting zirconia blank that undergoes cutting and machining. Therefore, the term “dental cutting blank” does not imply specifically a pre-sintered body.
If according to the proprietor, claim 1 as granted would be understood by the skilled person to cover a dental cutting blank irrespective of its sintering state, it precludes the term “dental cutting blank” from being limited to a pre-sintered body.
In claim 1 as granted, feature A states that the dental cutting zirconia blank has at least one layer consisting of zirconia powder. Furthermore, feature C defines a relationship between the density of the dental cutting zirconia blank after pre-sintering, and the density of the dental cutting zirconia blank in use in the oral cavity.
For the board, the term “powder” is an established term for matter in a finely divided state. More specifically, a powder is a loose, dry substance that consists of many fine particles that can flow freely when shaken or tilted.
The description of the patent in suit also does not use the term “powder” in a manner that would deviate from this general understanding.
A pre-sintered item, in contrast, is no longer composed of many fine particles as pre-sintering leads to inter-particle bonding. Paragraphs [0004] and [0041] of the patent in suit, for example, describe that pre-sintering results in an item that can be machined and that has a relative density of usually around 50% of the perfect-sintering density.
Feature A requires that it has at least one layer consisting of zirconia powder. Therefore, for technical considerations, the skilled person would exclude that the term “dental cutting blank” designates a pre-sintered body, and would interpret granted claim 1 as relating to an item in an unsintered state.
The proprietor argued that feature C made no sense for an unsintered green body, so that the skilled person would not interpret claim 1 in accordance with the second possibility.
It is correct that feature C specifies a characteristic only of a pre-sintered item. Therefore, it does in fact not characterise the claimed subject-matter, if the latter is interpreted to relate to an item in an unsintered state. This is, however, a possible lack of clarity or conciseness of the claim within the meaning of Art 84.
While this possible legal deficiency in the claim may lead the skilled person to seek an interpretation of the claim that resolves the deficiency, it would not lead them to interpret an established term contrary to its generally accepted meaning.
This is particularly pertinent in the present case, where not even the description of the patent in suit interprets the term “powder” in a manner that deviates from the general understanding.
It follows that granted claim 1 only covered an unsintered item and did not cover a pre-sintered body.
Therefore, the amendment to claim 1, directing the claim to a “pre-sintered body of” a dental cutting zirconia blank, shifted the scope of protection to an aliud.
Consequently, the claim as maintained did not meet the requirement of Art 123(3).
Comments
It is interesting to note that the decision having been issued on 10.07.2025, the board applied G 1/24 without saying so.
It is relatively rare that a claimed allowing maintenance in amended form infringes Art 123(3) and needs such a fine analysis.
Alleging that a powder still exists in a pre-sintered state, i.e. when some sintering had already taken place, was however quite daring.
The proprietor was nevertheless lucky as, thanks to AR6, the case could be remitted.
Otherwise the patent would have gone.
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