An apparatus for performing in-vitro measurements on a dental sample (320, 820), the apparatus comprising: a housing; an optical detection module provided within said housing, wherein said optical detection module is configured to direct an incident optical beam over a measurement region and to detect optical radiation responsively emitted by the dental sample when at least a portion of the dental sample is positioned at or near the measurement region; a control and processing unit provided within said housing, wherein said control and processing unit is configured to control said optical detection module and to generate an image by processing signals provided by said optical detection module in response to the detection of the optical radiation; a sample holder (140, 800) for supporting the dental sample; and an attachment mechanism (810, 815) provided within said housing for removably securing said sample holder in a pre-selected position and orientation relative to the measurement region; wherein said attachment mechanism and said sample holder are configured such that said sample holder can be removed from the housing and subsequently secured by said attachment mechanism (810, 815) without requiring recalibration of a relative position and orientation between the dental sample and the measurement region; wherein said sample holder includes a height adjustment mechanism for adjusting a difference in height between said dental sample and said measurement region; wherein said sample holder further comprises a mounting device for mounting the dental sample, wherein said height mechanism is configurable for positioning said dental sample such that at least a portion of said dental sample is located at a reference location, wherein said reference location corresponds to a position of said measurement region when said sample holder is secured by said attachment mechanism; and wherein said mounting device includes a marker indicating said reference location. a housing; an optical detection module provided within said housing, wherein said optical detection module is configured to direct an incident optical beam over a measurement region and to detect optical radiation responsively emitted by the dental sample when at least a portion of the dental sample is positioned at or near the measurement region; a control and processing unit provided within said housing, wherein said control and processing unit is configured to control said optical detection module and to generate an image by processing signals provided by said optical detection module in response to the detection of the optical radiation; a sample holder (140, 800) for supporting the dental sample; and an attachment mechanism (810, 815) provided within said housing for removably securing said sample holder in a pre-selected position and orientation relative to the measurement region; wherein said attachment mechanism and said sample holder are configured such that said sample holder can be removed from the housing and subsequently secured by said attachment mechanism (810, 815) without requiring recalibration of a relative position and orientation between the dental sample and the measurement region; wherein said sample holder includes a height adjustment mechanism for adjusting a difference in height between said dental sample and said measurement region; wherein said sample holder further comprises a mounting device for mounting the dental sample, wherein said height mechanism is configurable for positioning said dental sample such that at least a portion of said dental sample is located at a reference location, wherein said reference location corresponds to a position of said measurement region when said sample holder is secured by said attachment mechanism; and wherein said mounting device includes a marker indicating said reference location.