Context: In the students dental clinic of the University of Geneva (University Clinic of Dental Medicine, CUMD) the students use two different X-ray tube units: the fixed (Planmeca ProX) and the mobile (Carestream CS 2200).

Aim: The aim is to find out if the quality of the bitewings and periapical radiographs taken by students of the last two years of their studies is depending on the X-ray tube and if they improve the quality of the radiograph by time and experience of around four months.

Material and methods: One group of students used the fixed and the other the mobile X-ray unit. The students filled a list giving the information of the exposure parameters, patient number (Zawin), X-ray tube (fix or mobile) and type of radiograph (bitewing or periapical radiograph with the number of the radiographed tooth). Totally 757 radiographs were anonymized and then analyzed with a score table. By putting back the original information the scores can be compared between the radiographs taken by the fixed and mobile unit in detail. Three time periods were divided to analyze the quality of the radiographs by the time.

Results: The results showed that the quality of the radiograph is depending on the X-ray tube for bitewings but not for periapical radiographs. Planmeca ProX (the fixed X-ray tubes) scored better for capturing the distal contacts, correct bite and superpositions than Carestream CS 2200 (the mobile X-ray tubes). The quality of the bitewings decreased by time.

Conclusion: Planmeca ProX can help to take higher quality bitewings compared to Carestream CS 2200. The adaptation of the film holder ring and the tube is better for the Planmeca ProX tube than for Carestream CS 2200. The quality of periapical radiographs is not depending on the X-ray tube used at the CUMD. The difference in exposure parameters did not conclude a difference in quality of the radiographs. Artefacts were more important in bitewings than periapical. The decrease of quality of the bitewings by time are probably due to decrease of the quality of the plate on the borders, whereas periapical radiographs did not change significantly in quality by time.