Study design & patient selection
A controlled clinical trial was designed. The study population consisted of first year dental and medical students of the İstanbul Medipol University who had no experience with either conventional or digital impressions. The subjects were informed in detail about the possible risks and benefits, and all signed an informed consent form. The study was performed following the principles outlined in the Declaration of Helsinki on experimentation involving human subjects. The study protocol was reviewed and approved by the Ethical Committee of the Istanbul Medipol University, Istanbul, Turkey, (No:10840098-74).
Inclusion/exclusion criteria
Twenty-four subjects (12 females, 12 males, aged 21.87 ± 2.76 years) who fulfilled the following inclusion criteria were recruited after an initial examination: no experience with either conventional or digital impressions, good general health, good oral hygiene, no periodontal disease, and good mental health. Prerequisites for exclusion in the study were previous impression experience, fixed or removable prosthetic rehabilitation, orthodontic treatment and preventive appliances, history of use of space maintainers in mixed dentition, moderate to excessive dental anxiety.
Clinical scenario
A clinical scenario of an “excessive destruction of a mandibular molar and crown fracture of the lateral incisor, which would be restored by post-core and all ceramic crowns” was explained to the subjects during their orientation to the clinical settings of the study. Subjects watched an informational video illustrating the restorative steps of the clinical scenario. The impression phase was excluded from the video.
Conventional impressions
One operator selected the proper tray for both arches of the subject, and applied the adhesive (Polyether Tray Adhesive, 3 M ESPE, Dental Products, St. Paul, MN, U.S.A.). The conventional impressions of mandibular and maxillary arches were made by polyether impression material (Impregum Penta Soft Quick Step MB, 3 M ESPE, Dental Products, St. Paul, MN, U.S.A.) with stock trays using the monophase impression technique. The interocclusal relationship was recorded with a polysiloxane bite registration material (Futar D, Kettenbach GmbH & Co. KG, Eschenburg, Germany). All materials were used according to the manufacturers’ guidelines and performed by the same operator (E.Y.).
The effectiveness and clinical outcomes of the conventional impression technique was evaluated by measuring the total treatment time, including the individual steps (Figure 1): A) tray selection, B) adhesive application, C) upper/lower impression, D) bite registration. The treatment time was measured in seconds and recorded for each step by a second operator (R.T. & H.B.). Immediately after the impressions were made, the attitudes and perceptions of the subjects towards the conventional impression technique were evaluated using a standardized questionnaire. The subjects’ perceived source of stress was also evaluated using the State-Trait Anxiety Scale immediately after the impression technique.
Digital impressions
A digital impression appointment was scheduled for the same patients 2–3 weeks following the conventional impressions. The digital impressions were performed with the chairside dental CAD-CAM system (Cerec OMNICAM, Sirona Dental GmBH, Wals Bei Salzburg, Austria). The digital impression electronic data constituents of the virtual models for both arches and bite registration were recorded. All digital scanning procedures were carried out according to the manufacturer’s guidelines and performed by the same operator (EY).
The effectiveness and clinical outcomes of the digital impression technique were evaluated by measuring the total treatment time, including the individual steps (Figure 2): A) entering patient information (including name, last name, date of birth, B) laboratory prescription (including shade of restoration, material choice of restoration, form of restoration), C) upper/lower scan, and D) bite scan. Treatment time was measured in seconds and recorded for each step by a second operator (R.T. & H.B.). Immediately after the impressions were made, the attitudes and perceptions of the subjects towards the digital impression technique were evaluated using a standardized questionnaire. The subjects’ perceived source of stress was also evaluated using the State-Trait Anxiety Scale immediately after the impression technique.
The subjects were also asked to answer a 9-item comparative questionnaire including the following research questions: Which was the preferred impression technique? Which was the recommended impression technique? Which impression technique was more efficient? Which impression technique would be most comfortable regarding impression techniques?
Reliability and validity of questionnaires
The questionnaires used in this study were pre-tested, revised, and retested before use. A pilot questionnaire was tested on a representative sample of 10 patients. Test-retest reliability was performed to test the reliability and internal consistency of the questionnaires. The Cronbach Alpha reliability coefficient of the scales were found as 0.921, and 0.982, respectively. The adaptation, reliability and validity of the Turkish version of the State-Trait Anxiety Scale were evaluated by Öner and Le Compte in 1983[41].
Statistical analysis
Statistical analysis by the Wilcoxon Signed-Rank Test, with p = 0.05 as the level for statistical significance, was performed to evaluate the differences in effectiveness and clinical outcomes between conventional and digital impression techniques, using the SPSS 15.0 for Windows statistical software (SPSS Inc., Chicago, IL, USA).
The attitudes and perceptions of the subjects on both impression techniques were assessed with a self-administrated questionnaire using a Visual Analog Scale (VAS) ranging from 0 to 100. The data were analyzed statistical by the Wilcoxon Signed-Rank Test, with p = 0.05 as the level for statistical significance, using the SPSS 15.0 statistical software (SPSS Inc., Chicago, IL, USA).
The subjects’ preferences for the impression techniques were assessed with a 9-item comparative questionnaire, and the distribution of the answers were evaluated by descriptive analysis using the SPSS 15.0 statistical software (SPSS Inc., Chicago, IL, USA).