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Research scholar student, Oral Rehabilitation Section, Department of Odontology, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark
Corresponding author: Dr Klaus Gotfredsen, Department of Odontology, Faculty of Health and Medical Sciences, University of Copenhagen, 20 Nørre Allé, Copenhagen, 2200, DENMARK
Digital scanning has become popular and has been reported to be more comfortable for patients and equally or more accurate than conventional impression techniques. However, clinical evidence to support the advantages of digital scanning is sparse.
Purpose
The purpose of this randomized crossover study was to examine and compare the patient and provider perceptions of digital scanning and conventional impression making for implant-supported single crowns (ISSCs) provided by dental students under supervision. Furthermore, the quality and patient-reported outcome of the definitive restorations were compared.
Material and methods
Forty participants in need of a single tooth replacement were enrolled. Three months after initial implant placement, recordings were made for implant-supported crowns. The participants were randomized into a conventional or a digital group but underwent both procedures. Only the designated impression or scan was sent to the dental laboratory technician to be processed. All participants and students were asked questions concerning which technique they preferred. Furthermore, the participants filled out an oral health impact profile (OHIP-14) questionnaire before and after treatment. The restorations’ esthetic and technical quality was evaluated using the Copenhagen Index Score (CIS).
Results
The participants preferred the digital technique (80%) over the conventional technique (2%), while 18% of the participants had no preference. The participants were bothered significantly more (P<.001), experienced significantly more shortness of breath (P<.001), and were significantly more anxious during the conventional impression than during the digital scan (P<.001). Most students also preferred the digital technique (65%) over the conventional technique (22%), and 13% had no preference. The students found that the conventional impression procedure was less time-consuming but more uncertain in comparison with the digital technique. The digital technique was perceived as significantly more impractical than the conventional technique (P<.05). The results from CIS showed no significant difference in the quality of the restorations. Following treatment, the OHIP-14 scores showed a significant drop, suggesting an increase in oral health-related quality of life (P<.001).
Conclusions
The perceptions of the participants and students of the digital intraoral scanning were significantly better than those of the conventional technique. No significant differences in the quality of the restorations or OHIP scores were observed using the two recording techniques.
Clinical Implications
Patients and inexperienced providers prefer digital intraoral scanning to conventional impression-making.
Treatment with implant-supported single crowns (ISSCs) is a popular and successful option for partially edentulous patients.
Thus, the conventional workflow using impression materials, gypsum casts, and lost-wax casting has been gradually replaced with digital intraoral scanning and computer-aided design and computer-aided manufacturing (CAD-CAM).
The risk of swallowing or aspiration of impression material is eliminated, and the digital workflow is equal to or more accurate than the conventional technique.
Another advantage of the digital procedure is that adjustment or rescanning is straightforward, whereas in the conventional procedure, an entirely new impression would be required.
Nevertheless, disadvantages of using an IOS include that the technique is operator-sensitive, requires a saliva-free environment, and can be complicated by fogging of the scanner head, movement of the tongue or cheek, or the presence of blood.
A successful treatment depends on the patient, the dentist, the equipment, and the quality of the definitive restoration. However, studies examining these factors are sparse, and few clinical studies have evaluated and compared the conventional and digital workflows carried out by less experienced dental students by assessing patient-reported outcome measures.
The aim of the present clinical study was to investigate and compare the digital and the conventional techniques for providing ISSCs with respect to patient perception, student perception, and prosthetic outcome quality of ISSCs fabricated on digital compared with conventional gypsum casts. The null hypotheses were that no difference in the patient-reported outcome, student-reported outcome, or definitive prosthetic outcome would be found with the use of digital versus conventional workflows.
Material and methods
This randomized, cross-over investigation compared two commonly used recording techniques: digital intraoral scanning and conventional impression making with polyether impression material. The study was incorporated into the last semester (fifth year) of the predoctoral student curriculum, where practical training in implant dentistry is provided by treating a straightforward patient situation according to the straightforward, advanced, complex (SAC) criteria by Dawson and Chen.
Forty-four participants were prescreened and recruited for clinical teaching in implant dentistry from September 2019 to December 2021 at the Department of Odontology, University of Copenhagen, Denmark.
The randomized clinical trial followed the Declaration of Helsinki and was approved by the Research Ethics Committee for Science and Health, University of Copenhagen: J. no.: H-19037743. Patient data registration: J. no.: 514-0429/19-300 and ClinicalTrials.gov Identifier NCT04546269. Participants signed an informed consent form and had the right to withdraw from the study at any time.
Inclusion criteria were participants aged ≥18 years who needed one or more single-tooth implant-supported restorations and with natural healthy adjacent teeth and sufficient bone volume for placing an implant without bone or soft tissue augmentation. Exclusion criteria were smoking ≥10 cigarettes per day, uncontrolled diabetes, metabolic bone disorders, history of radiotherapy of the head and neck, recent chemotherapy, use of drugs influencing bone or soft tissue healing, additional oral surgery in the region of interest, and the need for multiunit prostheses.
Details of the implant surgery have been reported previously.
All implants (Astra Tech Implant System, EV; Dentsply Sirona) were placed by predoctoral dental students under the supervision of faculty dentists. The prosthetic procedures were initiated after a healing period of 3 to 4 months.
The participants were randomly assigned to the test or control group based on the contents of an opaque envelope allocating them to either the digital (test) or the conventional (control) group. A single investigator (C.S.) generated the envelopes, enrolled and assigned the participants in a random sequence, and had access to the random list stored on a password-protected computer. The crossover was performed so that the participants who had drawn the digital group started with the IOS followed by the conventional impression; the opposite was true for the participants allocated to the conventional group.
The conventional impression technique included the use of implant pick-ups (Astra Tech Implant System EV; Dentsply Sirona), whose position was controlled by a radiograph (Fig. 1). A polyether impression material (Impregum; 3M ESPE) was used for the arch containing the implant, a registration material (Blue Mousse; Parkell) was used for occlusal registration, and an irreversible hydrocolloid (Alginoplast; Kulzer GmbH) was used for the opposing jaw. The digital IOS and the conventional impressions were approved by a supervising dentist who calibrated them with other supervisors according to the department’s quality control procedures. The IOS (CEREC Omnicam; Dentsply Sirona) used a software program (Sirona Connect, Version 5.2.3; Dentsply Sirona) as specified by the manufacturer’s recommendations. Four scans were made, starting with a scan of the arch with the implant healing abutment in place, then the opposite jaw, followed by a buccal scan with the teeth in occlusion. Finally, the healing abutment was removed, and a scan body (Scan-body; Dentsply Sirona) was placed, with seating confirmed by a radiograph (Fig. 2) and scanned with the adjacent teeth and tissues. The software program (CEREC Omnicam; Dentsply Sirona) approved the 4 scans, as well as the supervisor and the dental laboratory technician who received the scans through the internet using the software program (Sirona Connect; Dentsply Sirona). Participants allocated to the digital group had prosthetic reconstruction fabricated using the IOS, and the conventional impression was not used. The opposite was true for the participants allocated to the conventional group, where the conventional impression was sent to the dental laboratory and the scan was deleted. The abutment-crown fit was verified with a radiograph (Figs. 1B, 2B), and proximal and occlusal contacts were evaluated and corrected if necessary. The shade of the crowns was selected with the involvement of the participants (Figs. 1C, 2C).
Figure 1Conventional technique. A, Radiograph with impression transfer coping. B, Radiograph of definitive implant-supported crown. C, Occlusal photograph of definitive crown.
Figure 2Intraoral scanning technique. A, Radiograph of scan body on implant. B, Radiograph of definitive implant-supported crown. C, Occlusal photograph of definitive crown.
Stereolithographic casts were produced in cooperation with a 3D printer company (Carbon3D; Carbon) based on the standard tessellation language (STL) IOS file, whereas gypsum casts (Fujirock EP Premium; Forstec) were made from the conventional impression. All the prostheses were screw-retained with custom-milled titanium abutments (Atlantis; Dentsply Sirona). Porcelain (GC Initial Ceramics; GC Europe) was fused to the titanium according to the manufacturer’s specifications. The abutment crown was designed with an appropriate emergence profile and sufficient distance to the marginal bone (Figs. 1C, 2C). When the implant-supported crowns were received by the students, the healing abutment was removed and the implant-supported crown screw was retained to the implant. A radiograph was made, and the occlusion was evaluated using 40-μm-thick foil (Bausch articulation; Bausch). The mesial and distal interproximal contacts were assessed with dental floss. When the abutment-crown was accepted by the supervisor, polytetrafluoroethylene tape was put into the screw hole and covered with composite resin (Charisma bulk Flow One; Kulzer GmbH).
After the recording procedures, patient satisfaction and the convenience of both procedures were assessed by questionnaires, where answers were graded using a visual analog scale (VAS) from 0 to 100. The questionnaires for the participants and the students were modified after Schepke et al.
The quality of the reconstruction was evaluated by using the Copenhagen Index Score, including esthetic scores for harmony and symmetry, crown color, crown morphology, mucosal discoloration, and papillae, as well as a technical score for marginal fit on a scale of 1 to 4.
Clinical photographs were made for further evaluation of the esthetic outcome.
The sample size was estimated to be 36 based on the assumption of detecting at least a 25% difference in VAS scores with type I and II errors set at 5% and 20%, respectively. An estimated study participant drop-out of 8 resulted in a prescreening of 44 participants. Descriptive statistics were used to calculate the means, range, standard deviation, and frequencies of the data. Differences in patient- and student-reported outcomes, as well as differences in OHIP scores before and after treatment, were analyzed by using a paired student t test after verifying normality. Calculations were conducted with a spreadsheet (Excel v16.54; Microsoft Corp) (α=.05).
Results
A total of 44 patients were prescreened; 4 were unwilling to participate, resulting in 40 participants completing the study (Table 1). No adverse events were recorded during the clinical study.
The data collected from the questionnaires demonstrated that the digital technique was highly preferred (80%) over the conventional technique (2%), while 18% of the participants had no preference. During conventional impression making, participants were bothered significantly more (P<.001), experienced significantly more shortness of breath (P<.001), and were significantly more anxious than during the digital scanning (P<.001) (Fig. 3). Thus, the null hypothesis was rejected since a significantly better impact was observed for the digital versus the conventional technique. The students also preferred the digital technique (65%) over the conventional technique (22%), and 13% had no preference. The answers to the questionnaire provided to the students indicated that the conventional impression procedure was less time-consuming but was perceived as more uncertain in comparison with the digital technique, although the differences were not significant. The digital technique was perceived as significantly more impractical than the conventional impression technique (P<.05) (Fig. 4). Results from the OHIP-14 scores showed that the treatment led to a significant general drop in the scores, including fewer oral problems after treatment (P<.001). For a limited number of participants, the OHIP-score increased (Fig. 5).
Figure 3Mean ±standard deviation of participant responses (n=40) to questionnaire using visual analog scale (0-100) measured by negative impact caused by recording technique. Question 1: Conventional (C)/digital (D) procedure bothered me. Question 2: Conventional (C)/digital (D) procedure made me feel unpleasantly short of breath. Question 3: I am anxious about having to undergo the conventional (C)/digital (D) procedure again.
Figure 5Oral health impact profile (OHIP-14) score for participants before and after restorative treatment. OHIP-scores were significantly reduced after treatment using conventional or digital recording techniques (P<.001).
The scores for symmetry and harmony, color match, anatomy, mucosal discoloration, and papilla volume are presented in Table 2. No significant differences in the esthetic outcome or the marginal fit of the definitive restorations produced using digital scanning or conventional impressions were registered. The interproximal contact relation and the occlusion contacts did not depend on the type of recording technique and were all acceptable.
Table 2Esthetic outcome of restorations evaluated using the Copenhagen Index Score (CIS) frequency of restorations with score 1-4
The null hypothesis was rejected, as digital scanning was significantly preferred to the conventional technique by the participants and the students. The recording techniques did not influence the esthetic or technical outcome, nor did they influence the OHIP-score, which for most participants improved considerably after delivery of their implant-supported single crown.
When the participants were asked which technique they preferred after experiencing both, the vast majority said the digital technique because it was more comfortable with fewer breathing difficulties and they were less anxious about undergoing the procedure again. These responses show that the digital technique may be better for anxious patients or patients with an extreme gag reflex, which is consistent with the results of other studies.
Patients' preferences when comparing analogue implant impressions using a polyether impression material versus digital impressions (Intraoral Scan) of dental implants.
Among the students, the results showed a majority also favoring the digital technique, even though it was perceived to be more time-consuming and less practical. These negative perceptions may have been because the IOSs in the dental school were not the latest available. Furthermore, the students were not experienced with intraoral scanning, as they had mainly encountered IOSs in their preclinical training. Repeated clinical experience has been reported to be important for the perception of the procedure and affects the trueness of the scanned image.
because the students felt that it was not an uncertain technique and minimized the transport time and risk of deterioration of the impression. They reported that digital scanning was the future of dentistry, which they found captivating and interesting.
However, in vitro preclinical studies may not accurately replicate the clinical situation examined in the present study. Even though intraoral scanning is highly favored by most students, conventional impression making remains an essential part of clinical student training.
The OHIP-score questionnaire results showed that the OHIP-score significantly decreased after the treatment in most participants, consistent with the results of a previous study.
The reason for the increase in the OHIP scores of a few participants could be that the initial values were low for most items. Furthermore, the OHIP was not developed to assess single-tooth replacement in single individuals but mainly as an instrument for epidemiological studies including participants with comprehensive oral problems.
The lower scores after restoration placement may be because of improved masticatory function, improved esthetics, and the feeling of having a complete arch.
The results from the CIS evaluation show no major difference in the esthetic and technical outcome of the crowns, regardless of the recording technique, which is consistent with the results of other studies.
Furthermore, an in vitro study comparing an experienced and inexperienced operator with digital scanning reported satisfactory results regardless of operator experience.
Satisfactory results were also seen in the present study with inexperienced students, and the need for interproximal and occlusal adjustment of the single-tooth replacement was rare in both groups. Unlike the present study, others have reported that crowns made with the digital scanning technique did not require any adjustment and had improved interproximal and occlusal contacts.
The difference may be because, in the present study, the procedures were the same after the dental laboratory had scanned the casts poured from the conventional impressions.
Limitations of the present study included that time was not considered as a primary outcome variable. However, the amount of time spent by the student in the clinics depends on the clinical supervisor and the participants. Thus, although the timing of the procedures would not have been a reliable variable for comparison, the student’s perception of the time used for the two techniques was relevant. The clinical and laboratory time has been reported to be considerably reduced with the digital technique,
possibly because of reduced human involvement in the clinic, transport, and laboratory, thus skipping several fabrication steps in the digital workflow. Consequently, reduced laboratory and clinical costs may reduce the treatment cost for patients.
Patients' preferences when comparing analogue implant impressions using a polyether impression material versus digital impressions (Intraoral Scan) of dental implants.
also reported by some students in the present study and can mainly be explained by their inexperience.
Another limitation is the rapid advancement of digital technology. The equipment and software program used in the present study have been replaced by faster devices. Even though the advances are exciting and may improve clinical treatment, adopting all the changes can be prohibitively expensive. In clinical practice, sufficient production is needed to make the digital equipment affordable.
Future research comparing digital scanning with conventional impression making is suggested to focus on in vivo investigations of the accuracy of multiple implant restorations and the effect of digital processes in implant dentistry.
Conclusions
Based on the findings from this clinical study, the following conclusions were drawn:
1.
Participants and students preferred digital intraoral scanning over conventional impression making.
2.
The esthetic and technical quality of the implant-supported single crowns did not differ significantly between the two recording techniques.
3.
The OHIP-scores of the participants after the treatment were significantly reduced, indicating increased oral health-related quality of life, regardless of the recording technique used.
Acknowledgments
The authors thank the Danish Dental Association (tandlægeforening) for a 1-year research scholarship for Chahak Seth.
References
Joda T.
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Digital vs. conventional implant prosthetic workflows: a cost/time analysis.
Patients' preferences when comparing analogue implant impressions using a polyether impression material versus digital impressions (Intraoral Scan) of dental implants.
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