In-vitro und in-vivo Untersuchungen zum Prepometer®

Concentrating on the classic field of fixed partial dentures a tooth normally has to be prepared through the enamel into the dentine-surface for complete coverage restorations. With preparation there accures a dentine-wound. Its extension depends on the number and total extrusion of injured dentine tubules. Beside other parameters like for example the influence of rising temperature on the preparation-surface and effects of chemical components within dental filling materials, there was discussed intensively the importance of remaining dentine-thickness above the pulp after tooth preparation in order to keep pulp sensitivity and vitality of the tooth. The postulation to limite preparation at a minimum thickness of dentine of 0,7 mm for teeth of adults and 1,4 mm for teeth of adolescent persons is wellknown and established in Germany (Jüde et al. 1997). These differences show, that even in the past, there was considered the different structure of dentine, which could be responsible for varying permeability for supposable damaging agents. Various studies from Gente and coworkers (Gente 1987, Feige 1989, Wenz 1990, Gente and Wenz 1991, Gente 1992, Becker-Detert 1993, Gente 1995, Netsch 1995) show, that the method of measuring electrical resistance on the tooths surface to limite the depth of preparation is to prefer to other techniques like for example the preparation of depth cuts or the interpretation of x-rays. Gente developed a procedure, which was recommended to users already in 1999 by the German Society of Dentistry and Oral Medicine (GSDOM) in their official statement "preparation technique as basis for quality assurance". But in the same statement the authors again citate the established data for minimum dentin-thickness as described above (Hellwig et al. 1999). The results of the present study clarify, that these specifications have to be questioned critically within further clinical trials. The used device to limite preparation depth (Prepometer®, Hager & Werken, Germany) shows the dentist by flashing of 10 different coloured light emitting diodes (LEDs) the progress of substance reduction. The manufacturer recommends a preparation only up to LED Nr. 7 (orange coloured) to avoid pulpal injury. The results of the present experimental record (in-vitro) demonstrate, that after reducing enamel and dentine to the minimum of 0,7 mm , described as reference data for adults by Jüde and coworkers (Jüde at al. 1997), there was exceeded the recommended preparation depth, concerning to orange coloured LED Nr. 7 in nearly 93% of the examined measuring points. At this time possible symptoms of a perhaps irreversible injury of the pulp can only be proven in histology. There exists no constant data of dentin thickness, related to the different LEDs. The results of Netsch (Netsch 1995) are confirmed. He figured out, that the dentist has to pay attention more to the surface area of the dentine wound and its permeability and less to the minimum thickness of dentine to avoid pulpal injury. The functionality of the Prepometer® follows this principle by measuring local electrical resistance. The results of the present clinical record (in-vivo) attest the application of the Prepometer® positive reference data. All teeth, prepared with control-measurement by the Prepometer®, kept a positive pulpal sensitivity up to the time of 2-5 years. In the control group however 21,1% of the examined teeth had a negative pulp testing. This results are comparable with other wide spreading data between 0,06% - 25% and different study-designs in the dental literature. Based on the results of the described present studies, we can recommend an extended use of the Prepometer® for quality assurance. The data should be reevaluated in a bigger test-group within further clinical trials. Then there has to be examined also the practicability of the described method on structural alterated dentine, influenced by age or adaptation to pathologic processes.