Patient-reported outcome measures (PROMs) of digital and conventional impression methods for fixed dentures

Abstract

BACKGROUND:

Digital impression technique or computer-aided impression (CAI) has been recently concluded as a clinically acceptable alternative to conventional impression method (CIM) in the fabrication of crowns, short fixed partial dentures (FPDs), and implant-supported crowns.

OBJECTIVE:

The purpose of this study was to investigate the patients’ opinion and subjective perception of two different ways of impression – digital and conventional.

METHODS:

A total of 45 patients were treated with CAI and CIM for the fabrication of tooth or implant-supported crowns. They fulfilled a questionnaire including 11 questions regarding the treatment time, gag reflex, discomfort related to manipulation, and other aspects of treatment.

RESULTS:

CAI was considered the preferential method for future treatment in 53% of patients, whereas 28.9% of the respondents preferred CIM. The preference for the impression method was influenced by the total time spent with the procedure, discomfort during manipulation with the tray or scanning head, size of the tray or scanning head, maximal opening discomfort, and (the tendency towards) gag reflex.

CONCLUSION:

CAI was considered a more comfortable and preferential method. Discomfort or difficulties during CAI negatively affected the patients’ attitude to CAI, whereas the difficulties associated with CIM did not have any influence on the preferred method.

Keywords

Dentistry conventional impression digital impression implant-supported crown tooth-supported crown PROMs

1. Introduction

Recent advancements in digital technologies have revolutionized clinical workflows in dentistry, particularly in the field of fixed prosthodontics. Moreover, the research development in this field is highly dynamic [1]. Numerous studies have compared digital impression methods, such as computer-aided impressions (CAI), with conventional impression methods (CIM) [2, 3, 4, 5, 6]. In CIM, a metal or plastic impression tray is filled with soft impression material and inserted into the patient’s oral cavity. The tray remains in place until the material sets, typically within five or more minutes. On the other hand, CAI involves capturing edentulous jaw [7] or the dental arch with a scanning head to generate a digital impression, which creates an accurate virtual 3D image displayed on a computer [2]. Additionaly, CAI can also be used for simulation of future implant position, direction, and depth of bone insertion [8]. While most studies have focused on improving the workflow of dental offices and operators, there has been relatively less emphasis on the patient’s perception of treatment [6, 9]. More studies have compared CAI and CIM for implant-supported restorations rather than tooth-supported crowns and fixed partial dentures (FPDs) [3, 9].

The most commonly cited attributes for comparison in these studies are accuracy and time efficiency. According to ISO 5725-1, accuracy is described by two measurement methods: trueness and precision [10, 11], where trueness refers to the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value. For trueness measurements, the real strict geometrical dimension of the subject must be known [12]. However, inside the oral cavity, this method is not applicable. Therefore, in vivo, studies are performed as a precision measurement from repeated impressions [13]. Precision refers to the closeness of agreement between the test results, reflecting the reproducibility of different impression methods. According to Seelbach et al., the accuracy of tooth-supported crowns fabricated by CAI and CIM was at the same level [14]. This conclusion was also presented by Abdel Azim et al., Almeida e Silva et al., and Vennerstrom et al. [15, 16, 17]. Additional studies reported on higher accuracy of tooth-supported single-unit crowns and FPDs made via CAI [18, 19]. However, the accuracy of CAI in implant-supported restorations is negatively influenced by an increase in the inter-implant span between multiple implants, where the scan protocol can significantly affect the precision [20, 21]. CAI was significantly less accurate with 0–15^∘ divergence of implants than 30–45^∘ [22], but the height of the abutment can improve any angulation error (7 vs. 5 mm) [21]. The 3D accuracy of implant-supported restorations can vary according to the impression technique and implant level [23]. Many studies identified the lack of clinical experience with CAI [24] and the dentists’ experience, the convergence in dental preparation, and the type of restoration as factors influencing scan accuracy [25].

Another important factor for the operator is time efficiency. CAI is considered overall faster than the conventional impression. According to a study by Siquiera et al., the mean working time for CAI was 7.74 min for tooth-supported restorations and 15.55 min for implant-supported restorations. In comparison, CIM took 13.94 min for tooth-supported restorations and 16.74 min for implant-supported restorations. For CAI, no clear trend was seen regarding the influence of the size of the scanned area on working time [26]. Other studies also confirmed the time benefit of CAI [6, 27]. Furthermore, the operator’s experience can also influence the overall comfort of the patient [28].

The objective of this study was (i) to explore the patients’ opinions and subjective perceptions of CAI and CIM and (ii) to investigate the factors influencing patients‘ preferences for future treatment.

2. Methodology

2.1 Participants

The sample of respondents consisted of all patients ( $n=$ 45) treated with single-unit tooth or implant-supported crowns in the regular treatment procedure from January 1, 2022, to April 30, 2022, at the Department of Dentistry, Charles University, Faculty of Medicine in Hradec Kralove, and University Hospital Hradec Kralove, the Czech Republic. Participation in the study was voluntary, and each participant signed the informed consent form. No remuneration or benefits were provided for participants.

Figure 1.

Questionnaire.

2.2 Treatment procedure

The tooth and implant-supported crowns were localized in posterior region (premolars or molars) of maxilla or mandible. For the conventional impression technique of implant-supported single-unit crowns, the open tray impression technique (resin custom tray, impression copings) was used (A-silicone Hydrorise, Zhermack, Italy). For vital tooth preparation, local anesthesia was applied. Tooth-supported crowns were impressed in a metallic stock tray with A-silicone Hydrorise. The double retraction cord technique was used after the preparation of single-unit crowns. Opposing jaw impressions for all restorations were performed with alginate impression material (Hydrogum, Zhermack, Italy). Occlusal records were prepared by elastomeric bite registration material based on A-silicone (Futar, Kettenbach, Germany).

For both types of restorations, the IOS system 3Shape TRIOS Move $+$ (3Shape, Denmark) was used as a digital impression method. The implant-supported crowns were scanned with scan bodies for accurate digital implant impressions. All the procedures were performed by one operator.

2.3 Data collection

Immediately after both procedures, CAI and CIM, the patients filled out a questionnaire containing 11 closed questions (Fig. 1). These questions reflected on the preferences of impression methods and their association with eliciting the gag reflex. Additionally, high emphasis was placed on the description of discomfort and sensitivity in the oral cavity caused by various factors. The questionnaire was developed in collaboration with experts from the field of prosthetic dentistry and the academic community. The preliminary version of the questionnaire was tested with a sample of random patient representatives ( $n=$ 7) and adapted accordingly before proceeding to the study stage.

Data collection took place from January 1, 2022, to April 30, 2022. The study was approved by the Ethics Committee of the University Hospital Hradec Kralove (Ref. no. 201903S08P).

2.4 Statistical analysis

The data were sorted and primarily analyzed in Microsoft Office Excel (version 2106 for Windows, Microsoft Corporation, Redmond, WA, USA). Statistical analysis was performed using an NCSS 2021 Statistical Software (NCSS, LLC, Kaysville, Utah, USA, ncss.com/software/ncss). Data were presented by counts and percentages. Median and interquartile range were used to describe age. The chi-square test and Fisher’s exact test were used to evaluate the association between factors. Nonparametric tests, Mann-Whitney, Kolmogorov-Smirnov, and Kruskal-Wallis analysis of variance, were used to evaluate the impact of age on answers. The level of statistical significance was set to 0.05.

3. Results

A total of 45 patients were asked for cooperation. All of them agreed with study participation, resulting in a 100% response rate. There were 19 men (42%) and 26 women (58%) among the respondents. Sex did not have a statistically significant influence on any of the questions asked.

The age range was from 24 to 70 years, with a mean age of 48.3 years and a median of 49 years. There was no statistically significant influence of age, except for the question on the treatment procedure speed. The age of patients who considered CIM faster was statistically significantly lower than the age of the patients who considered the speed of both methods the same ( $p=$ 0.039).

Figure 2.

Distribution of reconstruction types.

Figure 3.

Participants’ responses regarding the faster impression method.

Figure 4.

Participants’ responses regarding the more comfortable impression method.

Figure 5.

Occurrence of difficulties related to impression types according to participants.

The distribution of the type of reconstruction is presented in Fig. 2. The perception of the speed and comfort of CAI and CIM is summarized in Figs 3 and 4, respectively. Figure 5 shows the difficulties perceived during CAI and CIM procedures. The total sum of all difficulties was 58 for CAI and 76 for CIM; this difference between the methods was not statistically significant. A total of 8.9% of patients reported the gag reflex using CAI, whereas 46.7% using CIM. The temperature increase was felt in 17.8% for CAI and in 11.1% for CIM. The unpleasant manipulation with the scanning head was confirmed in 31.1% and with the impression tray in 40%. The bulkiness of the scanning head was a problem for 22.2% of patients, and the size of the try was problematic for 28.9% of patients. 17.8% of respondents felt difficulties related to maximal depression of the jaw during CAI and 11.1% during CIM. The pressure discomfort was felt in 13.3% of cases for the scanning head and in 15.6% of cases of the impression tray. Sensitivity of teeth during CAI was confirmed by 4.4% of patients, and sensitivity related to drying the oral cavity during impression by 13.3% of them. During CIM, the sensitivity of teeth was felt by 6.7% of respondents, and sensitivity related to drying with air by 8.9% of them. The preferred method for future impressions is presented in Fig. 6.

Figure 6.

Participants’ preferences for future impression methods.

The procedure speed perception statistically significantly differed between the patients with different types of restoration ( $p=$ 0.039). Patients with implant-supported reconstructions considered CAI faster more often (CAI 51.6%; CIM 22.6%), whereas patients with tooth-supported reconstructions considered CIM faster (CAI 21.4%; CIM 64.3%). The respondents preferred the particular method, which they considered faster ( $p<$ 0.001) and more comfortable ( $p<$ 0.001).

CIM was perceived as more comfortable than CAI by the patients, who declared having gag reflex ( $p=$ 0.024), unpleasant scanning head manipulation ( $p<$ 0.001), bulkiness of scanning head ( $p<$ 0.001), mouth opening difficulties ( $p<$ 0.001), pressure of scanning head ( $p<$ 0.001), and sensitivity to air drying ( $p=$ 0.006) during the scanning.

In terms of CAI, neither the perceived temperature increase ( $p=$ 0.174), the pressure caused by the scanning head ( $p=$ 0.099), nor the tooth sensitivity during the scanning ( $p=$ 1.000) presented a statistically significant influence on the further preference. Respondents who perceived some difficulties during CAI more often preferred CIM for the future. The difficulties during CAI with statistically significant influence on the preference were the gag reflex ( $p=$ 0.005), the unpleasant manipulation with the scanning head ( $p=$ 0.002), the scanning head bulkiness ( $<$ 0.001), the mouth opening difficulties ( $p<$ 0.001), and tooth sensitivity to drying ( $p=$ 0.016). In the cases of the gag reflex and the mouth opening difficulties during CAI, all respondents preferred CIM for the future. The difficulties perceived during CIM did not have a statistically significant influence on further preference.

4. Discussion

Patient-reported outcome measures (PROMs) comparing CAI and CIM methods usually describe the patient’s perception, including factors such as comfort, taste, gag reflex, pain, and treatment time. In a review and meta-analysis of PROMs by Bishti et al., it was found that the subjective assessment of impression time did not show a statistically significant difference between CAI and CIM. However, CIM was associated with a significantly worse perception of bad taste. Patients also reported feelings of anxiety, nausea, discomfort, and inconvenience more frequently with CIM. On the other hand, less pain was reported when optical impressions were used. Some studies also described shortness of breath during the CIM impression [29]. Kunavisarut et al. also reported a worse perception of bad taste related to CIM [30].

In their systematic review, Gallardo et al. pointed out the lack of clinical studies addressing patient outcomes regarding digital prosthodontic procedures, and patients’ preference for the digital workflow, and as mentioned in the conclusion, patients were more likely to prefer the digital workflow [31]. Delize et al. concluded that patients exhibited higher satisfaction with CAI, but CIM resulted in better esthetic outcomes from both the patients’ and operators’ perspectives. This particular study focused on screw-retained single-implant crowns [32]. Another study involving young patients undergoing orthodontic therapy demonstrated a preference for CAI over the alginate impressions, despite the alginate impression requiring less chairside time [33]. De Angelis et al. reported that patients, in general, accepted and had a positive attitude towards the use of CAI [34]. Furthermore, CAI was significantly preferred over the CIM procedure in terms of taste, nausea, discomfort, anxiety, and pain for implant impressions [9, 35, 36].

For comparison with other literature, the present study was designed similarly and highlighted the patients’ perception during digital impressions with an intraoral scanner in prosthodontic treatment [30, 32]. The number of participants surveyed in this study was slightly higher compared to other studies, as other authors typically referred to a sample size of 30–40 participants [9, 27, 32, 37]. Two studies included five more participants [38, 39]. In all these studies, men and women participated in nearly equal proportions.

The age range of participants in this study varied from 24 to 70 years, with a median age of 49 years. Middle-aged patients are usually prone to experience clinical crown loss due to factors such as deep caries, fractures related to extensive fillings, or tooth loss due to periapical lesions and endodontic conditions. Therefore, they are likely to need a fixed prosthodontic reconstruction. Similar age samples were observed in all the PROMs studies found [9, 27, 32, 34, 37], except for the study by Burhardt et al., which focused on the perception of young patients undergoing orthodontic treatment [33].

As mentioned by Bishti et al. in their review of 14 meta-analyses and 7 articles, more studies have been published regarding only CIM and CAI implant impressions (De Angelis et al. 2020, Delize et al. 2019, Joda & Bragger 2016, etc.), while only three studies compared whole conventional and digital fabrication of veneered and monolithic restorations, evaluating outcomes such as function, esthetics and general satisfaction with the final restoration [29, 32]. Implant-supported restorations were preferred over tooth-supported restorations for comparing CIM and CAI [9, 27, 32, 34, 37]. However, there is a significant variation in the methodology and the parameters investigated, challenging the comparison and synthesis of the findings.

Joda et al. conducted a study demonstrating the greater efficiency of CAI compared to CIM for single implant impressions, and it also showed a high level of CAI acceptance among operators. Their study of operator’s perception showed ( $n=$ 100, 50 dentists, 50 undergraduate dental students) that 88% of students and 64% of dentists considered CAI more efficient (in the case of CIM, it was 8% of students, 12% of dentists). The applicability of CAI (Visual Analog Scale, 0 to 100) was scored 82.8 by dental students and 86.8 by dentists (CIM by students 36.1, CIM by dentists 53.9) [3]. Similar results were obtained by Yuzbasioglu et al., who found CAI to be more time-efficient and preferred by patients [6]. Gjelvold et al. concluded that CAI was more efficient and convenient than CIM [5]. However, a study by Benic et al. assessed CIM as more time effective than CAI, with no statistical differences in patients’ discomfort related to the technique of impression [4].

42.2% of our patients considered the CAI to be faster, 35.6% of respondents declared CIM faster, and 22.2% were unsure. In general, our study found that CAI was the preferred method based on the perceived speed of the procedure. However, objectively, there was no statistically significant difference in speed between CAI and CIM, both in our study and in other studies by different authors [32, 34, 37]. While some studies indicated that CIM may be slightly faster, the time difference was too small to be considered significant [4, 29]. Moreover, respondents strongly preferred the method they perceived to be faster for future use. The finding that patients with tooth-supported restorations considered CIM to be faster could be attributed to the absence of scanning body manipulations and impression coping during impressions for tooth-supported restorations.

The gag reflex was more frequent during CIM (46.7%) compared to CAI (8.9%). This fact is consistent with other studies, where the described “nausea” was commonly associated with CIM as well (46–69%) [9, 37]. The authors attributed this phenomenon to the size of the impression tray and the tray manipulation in the oral cavity. The evoking of the gag reflex was one of the factors influencing the preference for future method.

The potential discomfort caused by heat generated during scanning and the sensitivity of teeth to temperature change was not evaluated in existing PROMs studies. Therefore, their impact on patient perception remains unknown. However, in our study, these factors were not statistically significant in influencing patient preference.

On the other hand, some respondents did experience discomfort during the drying of their teeth. Approximately 13.3% of participants reported sensitivity to drying with air during CAI. This finding is particularly relevant in the lower jaw, as intraoral scanners are sensitive to moisture. Interestingly, this aspect has not been extensively explored in the literature. In our study, the presence of drying-related teeth sensitivity significantly influenced the preferred method, with those experiencing sensitivity during CAI favoring CIM for future procedures. However, since this outcome did not differ depending on the type of reconstruction, i.e., tooth- or implant-supported, or on the use of anesthesia, the relevance of this finding is unclear.

Discomfort, usually characterized as slight pain or unpleasant feeling during treatment procedures, has been consistently associated with CIM in previous studies, with statistically significant importance [29, 32]. In our study, we aimed to analyze different types of discomfort and their impact on future preferences. The majority of the patients felt CAI (60.0%) more comfortable compared to CIM (26.7%); however, some of the patients did not distinguish better comfort between CAI and CIM (13.3%).

In terms of future treatment preferences, 53.3% of respondents considered CAI their preferred method for future treatment, while 28.9% preferred CIM. These results align with the findings reported by Burhardt et al., where 51% of participants favored CAI, and 29% preferred CIM [33]. Prior to conducting our study, we anticipated that our participants’ preference for individual methods would differ from the results presented by Burhardt et al., given that their respondents were younger (10–17 years) and undergoing orthodontic therapy. This assumption was not confirmed, suggesting that method preference is not dependent on the age of the respondents and the treatment type.

An interesting finding was that the attitudes of the respondents (perceived comfort and further preference) were not influenced by the declared difficulties during CIM, even though these difficulties were more frequent than during CAI. This indicates that the patients were much more critical of the new digital technology, where any perceived difficulty led to a decreased preference for this way of impression-taking.

4.1 Limitations of the study

The study has several limitations, including a middle-aged sample of patients and a higher percentage of implant-supported restorations (69%) compared to tooth-supported restorations (31%). This limitation is commonly observed in similar studies, as confirmed by the meta-analysis conducted by Bishti et al. Another limitation of the study is that it assessed responses using only yes/no answers, without utilizing the visual analog scale (VAS) commonly used in surveys for PROMs in dentistry. One significant limitation that applies not only to our study but also to PROMs, in general, is the absence of a standardized methodology for evaluating patients’ perceptions. This lack of standardization negatively impacts the reproducibility of studies in this area [2, 29]. The authors acknowledge the crucial nature of this issue and emphasize the need for standardized procedures in PROMs.

Despite these limitations, the study provides valuable insights into the contemporary integration of digital technologies into prosthodontics. Intraoral scanners are beneficial tools and are preferred by both operators and patients. CAI not only enhances precision in prosthodontics but also improves patient comfort and satisfaction. However, there are still challenges to address in this field, such as the size of the scanning head.

5. Conclusion

The majority of the patients prefer the digital impression over the conventional one. The preference was influenced by various factors, such as time perception, gag reflex, general discomfort, manipulation discomfort, size of the scanning head, maximal mandible depression difficulties, and sensitivity to tooth drying. The speed of the CAI procedure was not significantly shorter than CIM, according to the patient’s perception. Patients tended to be more cautious when feeling any discomfort during CAI. In case of any difficulty experienced during CAI, the respondents preferred CIM. Patients were more tolerant of discomfort related to the traditional CIM. This may be due to the fact that CAI is a new method that patients are not used to. Thus, in order to achieve the best patient-reported outcomes during CAI, clinicians should not only focus on precise technical execution but also take steps to familiarize patients with CAI, explain the procedure to them, and perform manipulation in the oral cavity with exceptional gentleness.

Funding

This work was supported by Charles University’s COOPERATIO Program, Research Area DENTAL MEDICINE.

Availability of data and materials

Not applicable.

Ethics statement

The study was approved by the Ethics Committee of the University Hospital Hradec Kralove (Ref. no. 201903S08P). All participants signed the informed consent form.

Footnotes

Acknowledgments

The authors would like to thank RNDr. Eva Cermakova (Computer Technology Center, Faculty of Medicine in Hradec Kralove, Charles University, Czech Republic) for statistical analysis; prof. Ing. Anna Krejcova, Ph.D. (Department of Environmental and Chemical Engineering, Faculty of Chemical Technology, University of Pardubice, Czech Republic) and all participants for their cooperation, patience, and time for survey filling.

Conflict of interest

The authors declare no conflicts of interest related to this article. The authors are not in any relationships with the producers of the devices and materials used in this study.

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