ORIGINAL RESEARCH


https://doi.org/10.5005/jp-journals-10019-1426
International Journal of Prosthodontics and Restorative Dentistry
Volume 13 | Issue 4 | Year 2023

Accuracy and Efficiency of Two Commercially Available Intraoral Scanners Under Different Room Lighting Conditions: A Crossover Clinical Trial


Subhabrata Maiti1, Senthamil Sindhu2, Deepak Nallaswamy3

1–3Department of Prosthodontics, Saveetha Dental college and hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India

Corresponding Author: Subhabrata Maiti, Department of Prosthodontics, Saveetha Dental college and hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India, Phone: +91 9007862704, e-mail: drsubhoprostho@gmail.com

Received: 23 September 2023; Accepted: 20 November 2023; Published on: 30 December 2023

ABSTRACT

Purpose: The purpose of the study was to evaluate the accuracy and efficiency of the two intraoral scanners (IOSs) under the influence of three different room light conditions.

Materials and methods: A crossover clinical trial was conducted with a total of 72 experimental scan samples obtained from six subjects under a three-light source (white light, chair light, and no light). Full arch scans were made in the maxillary and mandibular arches with Trios and Medit IOSs. The cone-beam computed tomography (CBCT) scan of the corresponding subject was made as the reference scan. The results were analyzed with the three-dimensional (3D) analyzing software Geomagic. The accuracy is measured in terms of precision trueness and efficiency in terms of the number of images and time taken by the IOSs under the influence of three different room light conditions. One-way analysis of variance (ANOVA) and independent sample t-test were carried out to find the significance of the results.

Result: A significant difference in trueness was observed between the two IOSs under the influence of light conditions (p < 0.05). Lesser deviations were observed in the Medit group with the least deviations found in chair light (0.23 ± 0.03) and white light (0.23 ± 0.07). The accuracy of the IOSs when compared within the light conditions (precision) showed no statistically significant difference (p > 0.05), however, least deviations were observed for Medit (0.23 ± 0.07) and Trios (0.36 ± 0.08) in chair light condition in mandibular arch and Medit (0.38 ± 0.07) and Trios (0.55 ± 0.14) in no light condition in the maxillary arch.

Conclusion: The difference between the IOSs was present under different light sources in terms of trueness and efficacy but not in precision.

How to cite this article: Maiti S, Sindhu S, Nallaswamy D. Accuracy and Efficiency of Two Commercially Available Intraoral Scanners Under Different Room Lighting Conditions: A Crossover Clinical Trial. Int J Prosthodont Restor Dent 2023;13(4):201–209.

Source of support: Nil

Conflict of interest: None

Keywords: Accuracy, Intraoral scanners, Light conditions, Precision, Trueness

INTRODUCTION

The use of computer-aided design/computer-aided manufacturing (CAD/CAM) technology as a tool in prosthesis fabrication might have been like scientific fiction decades ago but today the use of intraoral scanners (IOSs), designing software, and CAM units like three-dimensional (3D) printers and milling units are becoming the standards for fabrication of dental prosthesis.1 Among all the devices that are available for the digital fabrication of dental prostheses the optical scanners have to be considered the most important tools because they are the backbone of digital manufacturing.2-4

Digital imaging as a part of digital dentistry is gaining much importance, as it is the major tool that digitalizes the oral tissues and serves as the source for virtual models that can be used for the digital fabrication of dental prostheses. The IOSs, in particular, are preferred over the conventional impressions due to their ease of use, better accuracy, elimination of the need for several material consumptions, and increased patient comfort; the only disadvantage being the cost factor. One additional benefit of digital impressions is the ease of storage and retrieval of the data even after years, unlike the stone models that can chip, break, or consume physical clinical/laboratory working space.5-8

The data capture remarkably varies between different commercially available CAD/CAM systems. These devices should map the entire surface of the tooth while accurately maintaining the relative position of the device to the area of interest. Any technical error during the stages of scanning can cause serious misfitting issues in the final restoration.9

Just like the conventional impressions, importance should be given to the perfect recording of finish lines, surrounding anatomy, and occlusal surfaces of the abutment and adjacent teeth in digital impressions to eliminate inaccuracies in the final prosthesis. Considering both the intraoral and lab scanners for optical scanning, the IOSs have to be handled more cautiously since the IOSs have to be used in different intraoral conditions.2,3In vitro and in vivo studies have been carried out to test the performance of the IOSs and have concluded that clinically acceptable and relatively precise impressions can be made with IOSs when compared to manual impressions.10,11 Any movement by the subject or error in the path of movement of the scanner by the operator while scanning will greatly affect the stitching of the images. Several factors like illuminance;12-15 presence of liquids;16,17 scanning pattern;18,19 scanning distance;20 software updates;21 preparation type and tooth geometries;22 and the distance between the abutment and the adjacent teeth23 are said to affect the accuracy of IOSs.

The efficiency of the IOSs describes the fastness of the scanner and size of the scan file generated by the software, which is useful in reducing the load of the working file; the number of images obtained per scan, and the time taken for a scan defines the efficiency of an IOSs.24 The purpose of this clinical study was to evaluate the accuracy and efficiency of two commercially available IOSs under three different light conditions (chair light, white light, and no light). The null hypothesis stated that there is no discernible distinction in the accuracy and efficiency between the two IOSs.

MATERIALS AND METHODS

Study Design

This cross-over clinical trial was carried out in the digital dental studio of the university. The ethical clearance for the study was obtained from the Institutional Human Ethical Committee of the University (SRB No. SRB/SDC/PROSTHO-1801/21/TH-031). All ethical guidelines specified by the World Health Organization (WHO) and the declaration of Helsinki, 1954 were satisfied.25 Volunteers who needed a cone-beam computed tomography (CBCT) scan to locate and find the prognosis of the third molars without any symptoms, edentulous areas, and restorations were selected and asked for their consent to participate in the study. The entire study cohort consisted of university engineering students who willingly volunteered for their own advantage. They were screened for any calculus or debris and any deep caries lesions. Six subjects were selected based on the inclusion criteria and informed consent was collected from each subject. Within 1 month period of time, all subjects were selected and were experimented. Each subject underwent a total of six IOSs which were full arch scans obtained from both the maxillary and mandibular arches of the subjects with two IOSs Trios 3 (3Shape, Copenhagen, Denmark) and Medit i500 (Medit Co., Seoul, Korea).

Sample Size Estimation

The sample size was calculated with G*Power software version 3.0.10 with a power of 95% and a high-intensity α error of 0.05. A total of 6 subjects of age between 20 and 25 years old participated in the study and they were selected randomly.

Randomization and Blinding

A total of 20 subjects were shorted based on inclusion and exclusion criteria among them six were randomly allocated to groups using a computer-generated randomization list (randomizer.org) with the sequence being 10, 6, 18, 14, 9, and 19. Both the participants and those assessing the outcomes were unaware of the group assignments. These chosen patients underwent scans using both experimental scanners in a crossover control study. The accuracy analyzer person was completely unaware of the group identities and received only the scanned data for analysis without any information about the group names.

Informed Consent

The subjects were given a brief idea of the methods of sample collection and the willingness of all the subjects to participate in the study was confirmed. Informed consent was signed by the selected subjects before the start of the study.

Inclusion and Exclusion Criteria

Healthy subjects with normal gait, stature, and build in the age-group of 20–25 years of any gender with no history of systemic diseases were included in the study. Subjects having completely dentulous maxillary and mandibular arches, with complete eruption of all teeth till second molars and mouth opening in the range of 50–55 mm were only included. Subjects with unerupted third molars and no symptoms, with normal viscosity and flow of saliva were also included. Subjects with partial or completely edentulousness, restricted mouth opening, restorations or replacements, or deep carious lesions were excluded. Subjects with salivary gland disorder with hypersalivation or xerostomic conditions or with thin or ropy salivary conditions, and subjects with noncarious lesions like attrition, abrasion, or erosion were also excluded.

Cone-Beam Computed Tomography Scan

The subjects were asked to remove any jewelry and made to stand upright with the chin positioned on the chin rest. The position of the patient’s head was locked in position to avoid any movements. A thumbwheel was used to move the laser point to coincide with the incisors of the subject. The patient was instructed to maintain an intraoral still posture and not to swallow during the exposure. The CBCT of the patient was exported in Digital Imaging and Communications in Medicine format by the software. This file had to be changed to the Standard Tessellation Language (STL) format and that was done with the help of online solutions (Fig. 1). A single operator for standardization did all the scans at a time.

Fig. 1: The CBCT data converted into STL format showing the maxillary arch

Intraoral Scan

For the scanning process, the subjects were made to sit upright in a dental chair and asked to open their mouth to the fullest without resisting the free movement of the scanner. The scans were made with Trios IOSs followed by Medit IOSs (Table 1) under each light condition (Fig. 2). The whole procedure was done by a single operator and one observer at the same time for all the subjects under each condition for the standardization of the study. The observer was completely unaware of the scanner used for blinding to eliminate bias. All subjects were exposed to three different light conditions which were zero light which had a complete absence of light with intensity 0 lux, white light [light-emitting diode (LED) light-1000 lux], and chair light (high-intensity halogen light of a dental chair-500 lux). For scanning under a light source, the patient was positioned semisupine in the dental chair, the light source was kept approximately 2 feet away from the patient, and the light condition of the room was changed accordingly. While scanning for no light condition all the lights in proximity were switched off and a dark environment was maintained. Before scanning each time the patient was given plain water to rinse and swallow any pooled saliva in the mouth. The calibration of the IOSs was performed before every scan. The tips of the scanner were disinfected and sterilized according to the manufacturer’s recommendation.

Table 1: Comparison of the commercial IOSs used in the study
S. No Scanner Manufacturer Software technology Light source Version
1 Trios 3Shape Parallel confocal microscopy Laser 21.2.0
2 Medit i500 Medit 3D in motion video technology LED V 2.4.6

Fig. 2: Different views of a maxillary IOS

For the mandibular arch scanning, a clean scan tip was placed with the mirror facing down. The cheeks were retracted using a finger and the scanning was started with the occlusal surface of the distal-most molar and moved toward the incisors. As the scanner was moved toward the anterior the scanner was wiggled for better capture of the incisal edges and ended with the last molar. On reaching the last molar the scanner was slowly tilted toward the lingual surface with great attention to keep the soft tissues away from the path. The tongue is kept aside with the help of the tip of the scanner. For the maxillary arch, the scanner is taken along the palatal surface of the whole arch till the last molar and then rolled onto the occlusal followed by the buccal surface of the whole arch while the soft tissue is kept away with the help of the fingers. Any missed area on the surface of the tooth was scanned again by simply adding the scans the unnecessary parts which are the soft tissue here were trimmed.26,27

Superimposition of the Scan

For superimposition and surface analysis, the Geomagic Rapidform (version 2020, United States of America) was used. The CBCT scan was considered the reference scan and the X, Y, and Z coordinates were determined to be fixed. The IOSs one by one were imported into the software and made to run through an initial fit and a best-fit algorithm (Fig. 3). The values of discrepancies that arose between the reference CBCT scan and IOS were measured and displayed by the software (Fig. 4). Around 16 points were defined on the occlusal surface of the scans on the incisal edges of anterior and functional cups of the posteriors and the deviations in X, Y, and Z coordinates were measured in these points. These values were measured and displayed by the software (Figs 5 and 6).15,28-30

Fig. 3: Image showing the alignment of reference (CBCT) and sample data (IOS) after superimposition (best-fit algorithm)

Fig. 4: The 3D compare image of surface analysis with values extracted by Geomagic software

Fig. 5: The deviations in X, Y, and Z coordinate axis (occlusal view)

Fig. 6: The deviations in the X, Y, and Z coordinate axis (palatal view)

Efficiency Analysis

The efficiency of the IOS was calculated by recording the number of images formed to make one single scan and the time taken for an IOS from the display screen of the IOS software after each and every scan made under different light conditions.15,18

Accuracy

The closeness of a measured value to a standard or a known (true) value and each other (measured by the difference in distance deviation in μm). Accuracy is calculated in terms of precision and trueness. The IOSs were compared for accuracy (trueness and precision) which denoted the efficacy of the scanners. The results of the samples were analyzed for accuracy on the basis of deviations observed from the results of superimposition between the reference scan and the experimental scans in surface analysis and in specific points of the X, Y, and Z coordinates between the IOSs under different lights.15,18

Precision

The closeness of measured values between the independent results of the measurement obtained under specific conditions. It measures the repeatability and reproducibility of the results which in the study the results obtained by comparing the deviations within the subgroups (between chair light, white light, and no light).

Trueness

Trueness is a closeness of agreement between the mean obtained from repeated measurements and the true value. It depends on the repeatability of the results which is in the study the results obtained by comparing the deviations between the groups Medit and Trios.15,18

Statistical Analysis

Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) software (IBM Corporation Released 2014. IBM SPSS Statistics for Windows, version 23.0. Armonk, New York: IBM Corporation). Data collection was done with the help of the data collection sheets. Descriptive statistics (mean, standard deviation, and standard error) were carried out for each group. An unpaired t-test was carried out to find the significance between the groups. One-way analysis of variance (ANOVA) was carried out to find the significance within the subgroup light conditions.

RESULTS

The accuracy of the IOSs when compared within the light conditions (precision) showed no statistically significant difference (p > 0.05) (Table 2); however, the least deviations were observed for Medit (0.23 ± 0.07) and Trios (0.36 ± 0.08) in chair light condition in mandibular arch and Medit (0.38 ± 0.07) and Trios (0.55 ± 0.14) in no light condition in the maxillary arch. The analysis of sample results corresponding to X, Y, and Z coordinates showed no statistically significant difference for any IOS when compared under different light conditions (Table 3).

Table 2: Comparison within the different light conditions based on the deviations observed in surface analysis using one-way ANOVA
IOSs Arch Light source Mean ± standard deviation Standard error Confidence interval f-value p-value
Lower bound Upper bound
Trios Maxillary White light 0.62 ± 0.17 0.07 0.44 0.80 0.45 0.64
No light 0.55 ± 0.14 0.05 0.40 0.70
Chair light 0.64 ± 0.15 0.06 0.47 0.80
Mandibular White light 0.42 ± 0.14 0.05 0.27 0.57 0.50 0.61
No light 0.41 ± 0.08 0.03 0.32 0.49
Chair light 0.36 ± 0.08 0.03 0.27 0.45
Medit Maxillary White light 0.41 ± 0.13 0.05 0.26 0.55 0.21 0.81
No light 0.38 ± 0.07 0.03 0.29 0.46
Chair light 0.42 ± 0.12 0.05 0.29 0.55
Mandibular White light 0.23 ± 0.07 0.02 0.16 0.31 0.10 0.89
No light 0.25 ± 0.11 0.04 0.13 0.37
Chair light 0.23 ± 0.03 0.01 0.20 0.26
Table 3: Comparison of 3D discrepancies observed between each IOS and CBCT in the different tooth regions under the influence of different light conditions using independent sample t-test
IOS Trios Medit
Arch Coordinates and points Mesio-palatal cusp M1 (R) Mesio-palatal cusp M2 (L) Cuspal tip C1 (R) Cuspal tip C2 (L) Incisal edge I1 (R) Mesio-palatal cusp M1 (R) Mesio-palatal cusp M2 (L) Cuspal tip C1 (R) Cuspal tip C2 (L) Incisal edge I1 (R)
Maxillary X coordinate p-value 0.99 0.97 0.99 0.99 1.00 0.99 0.99 0.99 1.00 1.00
Y coordinate p-value 1.00 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99
Z coordinate p-value 0.99 0.99 0.99 0.99 0.96 0.99 0.99 0.98 1.00 0.81
Mandibular X coordinate p-value 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.99 1.00 1.00
Y coordinate p-value 1.00 1.00 0.99 1.00 1.00 1.00 1.00 0.99 1.00 1.00
Z coordinate p-value 1.00 1.00 1.00 1.00 0.99 1.00 0.99 0.99 1.00 0.99

C1 (R), canine cuspal tip (right side); C2 (L), canine cuspal tip (left side); I1(R), incisal edge of central incisor (right side); M1(R), mesio-palatal cusp of first molar (right side); M2 (L), mesio-palatal cusp of first molar (left side)

Maximum Deviation Value

The accuracy of IOSs when the maximum deviation was compared between the Trios and Medit groups (trueness) showed statistically significant differences (p < 0.05). Lesser deviations were observed in the Medit group with the least deviations found in chair light (0.23 ± 0.03) and white light (0.23 ± 0.07) followed by no light (0.25 ± 0.11) in the mandibular arch and no light (0.38 ± 0.07) followed by white light (0.41 ± 0.13) and chair light (0.42 ± 0.12) in the maxillary arch (Table 4).

Table 4: Comparison between Trios and Medit based on the maximum deviations observed in the surface analysis under different light conditions using an independent t-test
Arch Light sources IOS Mean ± SD SE p-value
Maxillary Chair light Medit 0.42 ± 0.12 0.05 0.02*
Trios 0.64 ± 0.15 0.06
No light Medit 0.38 ± 0.07 0.03 0.02*
Trios 0.55 ± 0.14 0.05
White light Medit 0.41 ± 0.13 0.05 0.03*
Trios 0.62 ± 0.17 0.07
Mandibular Chair light Medit 0.23 ± 0.03 0.01 0.001*
Trios 0.36 ± 0.08 0.03
No light Medit 0.25 ± 0.11 0.04 0.02*
Trios 0.41 ± 0.08 0.03
White light Medit 0.23 ± 0.07 0.02 0.01*
Trios 0.42 ± 0.14 0.05

*Level of significance p < 0.05; SD, standard deviation; SE, standard error

Root Mean Square (RMS) Value

For maxillary arch scanning, there was a significant difference between the RMS value of two scanners under chair light (p = 0.03) and no light (p = 0.02) conditions whereas for mandibular arch the difference in RMS value was significant only under white light (p = 0.02) (Table 5). Medit scan showed less RMS deviation value for both the arches under all the light conditions.

Table 5: Significance in RMS value of light conditions between IOS using independent t-test
ARCH Light conditions IOS Mean ± SD p-value
Maxillary Chair light Medit 0.97 ± 0.18 0.03*
Trios 1.23 ± 0.17
White light Medit 0.94 ± 0.20 0.08
Trios 1.16 ± 0.19
No light Medit 0.90 ± 1.55 0.02*
Trios 1.19 ± 0.22
Mandibular Chair light Medit 0.62 ± 0.06 0.06
Trios 0.74 ± 0.11
White light Medit 0.61 ± 0.09 0.02*
Trios 0.84 ± 0.20
No light Medit 0.66 ± 0.16 0.08
Trios 0.82 ± 0.13

*Level of significance p < 0.05; SD, standard deviation

Efficiency

A statistically significant difference was found in the precision of the IOSs in images recorded under chair light conditions (p = 0.02). There is no significant difference in time taken or image obtained for both the scanners for any other light condition (Table 6).

Table 6: Comparison of efficiency between Medit and Trios IOS under different light conditions
Arch Mouth opening IOS Number of images Time taken
Mean ± SD SE p-value Mean ± SD SE p-value
Maxillary Chair light Medit 1338.66 ± 257.68 105.19 0.38 61.00 ± 10.84 4.42 0.19
Trios 1161.00 ± 407.60 166.40 80.16 ± 32.09 13.10
White light Medit 1289.66 ± 431.45 176.14 0.87 70.50 ± 29.12 11.89 0.21
Trios 1244.33 ± 555.56 226.81 98.00 ± 40.93 16.71
No light Medit 1284.83 ± 470.23 191.97 0.51 61.33 ± 18.20 7.43 0.35
Trios 1098.16 ± 479.84 195.89 76.33 ± 33.12 13.52
Mandibular Chair light Medit 1424.33 ± 331.90 135.49 0.02* 70.66 ± 17.30 7.06 0.60
Trios 957.33 ± 262.17 107.03 63.66 ± 27.43 11.20
White light Medit 1252.33 ± 372.82 152.20 0.14 64.83 ± 22.75 9.28 0.77
Trios 957.33 ± 262.17 107.03 70.33 ± 39.80 16.25
No light Medit 1124.66 ± 181.57 74.12 0.10 71.66 ± 18.44 7.53 0.25
Trios 896.66 ± 254.99 104.10 57.83 ± 21.36 8.72

*Level of significance p < 0.05; SD, standard deviation; SE, standard error

DISCUSSION

Several studies carried out on the factors, affecting the accuracy of the IOSs scanning room light conditions had a significant effect on the IOSs.12 The most commonly used light conditions for study purposes are light with intensities of 0 lux no light, 1003 lux room light, 10000 lux chair light, and 500 lux natural light.14 The present study used light intensities of 0, 500, and 1000 lux considering the commonly available light sources in dental clinics. The light conditions used in this study were chair light which was a halogen light with an intensity of around 500 lux white LED light with an intensity of around 1000 lux and 0 lux condition which is the no-light condition.12,15 The surface analysis outcomes from the current research indicated that there was no substantial variation in accuracy among the IOSs. However, statistically notable disparities were observed in terms of trueness. As a result, the null hypothesis was rejected.

The Medit IOSs showed minimal deviations under all the light conditions than Trios 3 IOS, this was contrary to the results published by Wesemann et al.,14 in which Trios 3 showed the least deviations when compared to the other IOSs used in the study; but Medit i500 was not used in the study making it incomparable to the present study.

In the Medit i500 IOS group, the mandibular arch showed lesser deviations than the maxillary arch and this might be because the arch expands posteriorly in maxillary jaws.31 The results observed by Huang et al.23 suggest that the scans produced by Medit i500 IOSs tend to narrow toward the lingual direction and might have resulted in increased deviations in the maxillary arch. In the Medit mandibular arch group chair light and white light showed lesser deviations than no light. In the maxillary arch, the deviations were lesser in no light followed by white light and chair light and this was contrary to results published by Koseoglu et al.,15 which stated that the room light conditions (1003 lux) had the least deviations in terms of trueness.

It was evident that the chair light and white light mean values do not have many differences in the heterogeneity in results with regards to the arch forms and can be explained by the fact that the patient is made to sit in a semisupine position which will expose the maxillary arch directly to the light whereas there is no direct light hit on the mandibular arch.32 In Trios mandibular arch lesser deviations were observed in chair light followed by no light and white light. Trios maxillary arch showed lesser deviations with no light followed by white light and chair light which was contrary to the results published by Revilla-León et al.,12 in which the room light condition (1003 lux) showed the least deviations in Trios 3 maxillary full-arch scans.

Concerning the efficiency of the scanners, there was no significant difference in precision and trueness of IOSs with the number of images yet Trios showed lesser measurements than Medit which denotes fast scans can be achieved in Trios under any light condition which is in accordance to the results published by Wesemann et al.14 In the Trios group, the least measurements were recorded under no light conditions irrespective of the arches and the highest measurements were observed in white light which may be due to the fact that different light intensities have varied effects on the scanning accuracy as described in previous literature.33,34 There was a significant difference in trueness with the images recorded for chair light this can be owing to the response of the difference in imaging technology of the two IOSs. Also, the number of images counted might have been controlled in no light conditions because the absence of an external light source might have not produced noisy data clouds that might have increased the number of points in the point cloud leading to a higher number of images and increased distortion in the original data.35-37

One constraint of this research lies in its concentration on a limited array of lighting conditions (white light, chair light, and no light), which might not encompass the diverse environmental contexts in which IOSs are typically employed. The study omitted real-world scenarios like natural daylight and the variability in artificial lighting conditions. In the future, more extensive investigations could encompass a wider selection of newly developed scanners, under diverse lighting conditions, in a real-world, multicentric setting to provide a more comprehensive understanding of their performance.

CONCLUSION

Within the constraints of this investigation, Medit scanner for both maxillary and mandibular arch scans, consistently demonstrated superior trueness across various lighting conditions. While precision did not significantly vary with lighting, chair light is recommended for mandibular scans, no light for maxillary scans, and underlines the need for environmental control. Importantly, the mandibular arch consistently yielded more accurate results, warranting clinicians’ attention to potential maxillary arch discrepancies. The study emphasizes the clinical significance of maintaining light conditions within the 0–1000 lux range to ensure reliable scanning outcomes.

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