Comparison of digital intraoral scanners and alginate impressions: Time and patient satisfaction


Recent technological advances have made intraoral scans and digital models a possibility and a promising alternative to conventional alginate impressions. Several factors should be examined when considering an intraoral scanner, including patient acceptance and efficiency. The objectives of this study were to assess and compare patient satisfaction and time required between 2 intraoral scanners and conventional alginate impressions.


An initial pilot study was completed to create a valid and reliable survey instrument that would measure 3 areas of patient satisfaction with the impression experience. A visual analog scale survey was developed and administered to 180 orthodontic patients receiving 1 of 3 types of impressions: (1) iTero Element intraoral scan (Align Technologies, San Jose, Calif), n = 60; (2) TRIOS Color intraoral scan (3Shape, Copenhagen, Denmark), n = 60; and (3) conventional alginate impression (imprEssix Color Change; Dentsply Sirona, York, Pa), n = 60, and the time required to obtain the impressions was recorded.


Reliability was evaluated with intraclass correlation coefficient values for 17 paired questionnaires, and all questions were found to be reliable (intraclass correlation coefficient, ≥0.65). For the main study, 180 subjects completed timed impressions and surveys. Data indicated that subjects receiving intraoral scans preferred the digital impressions, and subjects receiving alginate impressions were neutral regarding impression preference, and that efficiency varied based on the impression method.


Intraoral scanners are accepted by orthodontic patients, and they have comparable efficiency with conventional impression methods depending on the type of scanner.


  • Orthodontic patients are satisfied with and accept intraoral digital impressions.

  • Patients may show increased preference for digital impressions compared with conventional alginate impression.

  • There is a difference in patient satisfaction according to the type of intraoral scanner.

Orthodontists frequently use dental models for diagnostic and treatment planning purposes such as evaluation of tooth positions and occlusal relationships, space assessment, simulation of tooth and jaw movements, appliance design and fabrication, and treatment effects. Methods of making dental impressions have greatly evolved over the past several decades; in recent years, dental models have been conventionally made using alginate impressions and plaster casts. However, current interest in 3-dimensional and digital technology in the medical and dental fields has led to the development of 3-dimensional scanning and digital casts. Advantages of digital casts include more efficient storage and retrieval, increased diagnostic versatility, easier transferability, superior durability, and decreased processing time.

Previous studies to evaluate the accuracy of 3-dimensional models have shown that they are comparable with plaster models using both linear and angular measurements as well as shell-shell deviation and arch-registration measurements. With evidence supporting the accuracy of digital impression techniques, their adaptation in orthodontic practices is increasing. Nevertheless, intraoral scanning has not been fully integrated into orthodontic private practices because of the endurance of conventional impression methods. The advantages of conventional materials are that they are accurate, well accepted, and traditionally inexpensive. However, these types of impressions are not always favored by patients and have been reported to be unpleasant and burdensome. Additionally, conventional impression methods require inventory and stocking of raw materials as well as storage space for the plaster models. A number of dental and orthodontic suppliers have produced digital scanners, and some provide high-tech software analysis programs that allow operators to complete model analysis and diagnosis, occlusal setups, treatment predictions, and evaluation of treatment outcomes. Digital models are also compatible with many laboratories, allowing efficient digital communications while still providing quality fabrication of restorations, prostheses, and appliances.

Questions remain regarding the acceptance and use of intraoral scanners. Clinicians should consider the technical aspects of these devices, some of which have been evaluated and include performance, ease of use, portability, features and options, vendor company, compatibilities, and cost. But they also should consider patient-oriented aspects of scanner use. Some of these aspects have been investigated, but all used previous generation technology that required coating the teeth before scanning for adequate performance. These studies provided conflicting results.

Two types of information are currently missing from the literature regarding scanners: data generated from contemporary scanners not requiring the powder coating of teeth, and more information related to the patient perspective. This latter point has been emphasized in dentistry and orthodontics, in particular, in 2 recent articles. Most dental research reports disease activity as the primary or secondary outcome, whereas quality of life and functional measures were rarely considered.

In orthodontics, morphology is most frequently measured (63% of the time). Health resource usage, adverse effects of orthodontic treatment, quality of life, functional status, and physical consequences of malocclusion are evaluated much less frequently (32%-2% of the time). Evaluating patient-centered issues related to intraoral scanning then clearly addresses 2 central issues in this area—a lack of information related to contemporary scanners and a patient-centric viewpoint.

The aim of this study was to assess important factors related to digital scanners: patient acceptance and impression efficiency. We compared 2 currently available and popular digital intraoral scanners with each other and with alginate impressions. For each impression method, patient satisfaction was measured, and the time required to complete a full-mouth impression was recorded.

Material and methods

Approval to conduct this study was obtained from the institutional review board at Ohio State University. Informed consent was obtained from legal guardians and adult subjects, and assent was obtained from minor subjects.

A survey was designed to test 3 areas of patient satisfaction regarding the impression experience: comfort, time, and novelty. The proposed survey was administered to a group of orthodontic practitioners, technicians, and patients to confirm the validity of the questions. After adjustments and corrections to the survey instrument, the finalized survey ( Fig 1 ) consisted of 7 statements with a 100-mm visual analog scale (VAS) below each statement anchored with “agree” and “disagree.” The survey also included questions to determine whether the patient had previous experience with impressions.

Fig 1
Survey instrument.

Next, a pilot study was undertaken to establish reliability of the instrument. Seventeen subjects were recruited from the graduate orthodontic clinic at Ohio State University. Each had an impression made and completed the survey. Three to 4 days after the impression, each participant completed a second survey. The surveys were measured and analyzed, and the results from the 2 time points were compared to assess the reliability of each question. After the survey instrument was determined to be both valid and reliable, the main study began.

Subjects were recruited from the graduate orthodontic clinic and a local private orthodontic practice in Columbus, OH for either an intraoral scan or an alginate impression. Inclusion criteria for participants specified that they be healthy, English-speaking subjects seeking orthodontic treatment or actively undergoing orthodontic treatment. There were no restrictions for age, sex, or race. Patients were excluded if they had a history of mental disabilities, cleft lip or palate, or other craniofacial anomalies or syndromes.

Sample size calculations were completed before data collection. With a nondirectional alpha risk of 0.05 and assuming a standard deviation of 24, a sample of 50 subjects would allow detection of a difference of ±14 mm on the VAS scale with power of 0.823. To account for participant dropout and the possibility of using a nonparametric data analysis, we added 20% to the number of 50, yielding a sample size of 60 per group.

A total of 180 orthodontic patients were included in the study: 60 subjects had an intraoral scan with the iTero Element (Align Technologies, San Jose, Calif), 60 had an intraoral scan with the TRIOS Color (3Shape, Copenhagen, Denmark), and 60 had alginate impressions (imprEssix Color Change; Dentsply Sirona, York, Pa). The participants included 104 female and 76 male subjects, with a median age of 15 years (interquartile range, 13-20) and an age range of 8 to 56 years.

Each subject had either a digital intraoral scan or an alginate impression completed by an operator trained and experienced in the specific impression technique used. The scanning protocol was applied according to the manufacturers’ recommendations. For each intraoral scan with either the iTero Element or the TRIOS Color, the time required to complete a full mouth scan and bite registration was recorded. Any verbal explanation or isolation placement was not included in the recorded time. Alginate impressions were obtained with a fast-setting 120-hour alginate material and standard plastic impression trays. For each impression, the time required to mix the material and complete a full-mouth (maxillary and mandibular arches) impression was recorded.

Immediately after the impression procedure, each participant was asked to complete the VAS survey described above and return it before the end of the appointment. Each VAS score was measured to the nearest 0.5 mm, and medians and interquartile ranges were calculated for each response.

Statistical analyses

The reliability of the survey instrument was assessed using the data from the pilot study to measure intraclass correlation coefficients for each survey question.

Because the assumptions of parametric statistical analyses were not met, the data were analyzed using nonparametric tests. Medians and quartile ranges were calculated for subject sex, age, previous expression experience, impression time requirement, and each survey question. These data were analyzed statistically with the nonparametric Dwass, Steel, Critchlow-Flinger method multiple comparison analysis with a simultaneous P value adjustment, with <0.05 as the level for statistical significance. The data analysis for this study was generated using SAS/STAT software (version 9.4 of the SAS System for X64_7PRO platform; SAS, Cary, NC).


Analysis of data from the pilot study indicated that each of the 7 survey questions was reliable. Four questions had excellent reliability, and 3 had moderate-to-good reliability. The intraclass correlation coefficient (ICC) values and interquartile ranges for each question (Q) are as follows: Q1, 0.80 (0.55-0.92); Q2, 0.85 (0.65-0.94); Q3, 0.68 (0.33-0.86); Q4, 0.77 (0.49-0.91); Q5, 0.90 (0.76-0.96); Q6, 0.65 (0.28-0.85); and Q7, 0.71 (0.38-0.88).

For the main data acquisition study, analysis of participant demographic information showed that the 3 subject groups had no significant differences in sex: iTero, 39 female, 21 male; TRIOS, 33 female, 27 male; alginate, 32 female, 28 male. However, there were statistical differences in the ages of participants as well as their previous impression experiences. The median ages were 14 years for the iTero group, 15 years for the TRIOS group, and 17 years for the alginate group. For impression experience, 32% of subjects had never had any previous impressions, 37% had previous alginate impressions, 6% had previous digital impressions, and 25% had both digital and alginate impressions; previous impression experience was not even among the groups.

The 7 survey questions and the impression times were not normally distributed as indicated by the Shapiro-Wilk statistic ( P <0.0001); therefore, nonparametric analysis was completed. The analyzed data from the main survey administration study including median, interquartile range, and P value information are summarized in the Table . According to the satisfaction questionnaire, subjects had significantly more comfort and less pain with the iTero scanner than with the TRIOS scanner and alginate impressions. The iTero participants also had significantly less dry mouth related to the impressions. There was a significant difference among the subjects’ time perceptions between the iTero and alginate impressions, but no significant differences among the iTero and TRIOS impressions, or alginate and TRIOS impressions, were found. Significant differences were also found in the assessment of technician skill and importance of new technology, with iTero participants rating the technicians with higher skill levels, and believing that new technology was important in an orthodontic office. When asked whether they would rather go to an orthodontist who uses digital or alginate impressions, the iTero and TRIOS participants preferred digital impressions, whereas the alginate participants had less preference toward digital impressions. Differences in the time required to complete each impression type were found, with the TRIOS digital impression requiring significantly more time than the iTero and alginate impressions.

Median values and interquartile ranges (IQR) for survey responses and time requirements for each impression group
iTero TRIOS Alginate
Q1: Comfortable 12 (IQR, 22.5) 26.25 (IQR, 39) 33.5 (IQR, 51.5)
Q2: Painless 4.5 (IQR, 4.75) 12.5 (IQR, 26.25) 11.75 (IQR, 35.25)
Q3: Dry mouth 82 (IQR, 27) 54 (IQR, 63.75) 64 (IQR, 65)
Time and technician skill
Q4: Faster than expected 8.25 (IQR, 22.5) 13.5 (IQR, 31.5) 18 (IQR, 24.75)
Q5: Technician skilled 4.5 (IQR, 4.5) 8.75 (IQR, 9) 8.25 (IQR, 8.5)
Novelty and preference
Q6: Technology importance 5 (IQR, 4.5) 6.25 (IQR, 9.25) 11 (IQR, 17.75)
Q7: Preference 5.5 (IQR, 19.25) 10.5 (IQR, 26.5) 49.5 (IQR, 55.25)
Time required
Minutes 7 (IQR, 1) 8.6 (IQR, 3.5) 6.4 (IQR, 2.13)
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Dec 12, 2018 | Posted by in Orthodontics | Comments Off on Comparison of digital intraoral scanners and alginate impressions: Time and patient satisfaction
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