# Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study

Octave Nadile Bandiaky, Roselyne Clouet, Pierre Le Bars, Assem Soueidan, Laurent Le Guehennec

<figure><img src="image_1.png" /></figure>

## To cite this version:

Octave Nadile Bandiaky, Roselyne Clouet, Pierre Le Bars, Assem Soueidan, Laurent Le Guehennec. Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study. Journal of Prosthodontics, 2023, 32 (9), pp.846-853. 10.1111/jopr.13639. hal-04350607

HAL Id: hal-04350607

https://hal.science/hal-04350607

Submitted on 30 May 2024

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
ORIGINAL ARTICLE

<figure><img src="image_1.png" /></figure>

AMERICAN COLLEGE OF
PROSTHODONTISTS
Your smile. Our specialty.

# Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study

Octave Nadile Bandiaky DDS, MSc<fnref n="1" /> | Roselyne Clouet DDS, MSc<fnref n="2" /> | Pierre Le Bars DDS, MSc, PhD<fnref n="2" /> | Assem Soueidan DDS, MSc, PhD<fnref n="3" /> | Laurent Le Guehennec DDS, MSc, PhD<fnref n="4" />

**Correspondence**

Octave Nadile Bandiaky, Nantes University,
Oniris, Univ Angers, CHU Nantes, INSERM,
Regenerative Medicine and Skeleton, RMeS,
UMR 1229, 1 Place Alexis Ricordeau, 44042
Nantes, France.

Email: octave.bandiaky@univ-nantes.fr

**Funding information**

UFR of Odontology of Nantes University, France

**Abstract**

**Purpose:** This study aimed to compare the marginal and internal fit of five-unit zirconia-based fixed dental prostheses (FDPs) fabricated using digital scans and conventional impressions.

**Materials and methods:** Nine master models with three zirconia abutments were scanned with an intraoral scanner (test group), and nine conventional impressions (control group) of these same models were also made. The stone casts from these impressions were scanned with a laboratory extraoral scanner (D700, 3Shape, Copenhagen, Denmark). A total of 18 five-unit zirconia-based FDP frameworks (test group, *n* = 9; control group, *n* = 9) were manufactured. Marginal and internal fit (in µm) were evaluated using the replica method under micro-computed tomography. Analysis of variance (one-way ANOVA) and Kruskal–Wallis tests were used to compare continuous variables across two groups. A level of *p* < 0.05 was accepted as statistically significant.

**Results:** The mean ± standard deviation of the marginal fit was 95.03 ± 12.74 µm in the test group and 106.02 ± 14.51 µm in the control group. The lowest marginal mean value was observed in the test group, with a statistically significant difference compared to the control group (*F* = 14.56, *p* < 0.05). The mean ± standard deviation of the internal fit was 103.61 ± 9.32 and 106.38 ± 7.64 µm, respectively, in the test and control groups, with no statistically significant difference (*F* = 1.56, *p* > 0.05). The mean values of both groups were clinically acceptable.

**Conclusions:** The five-unit zirconia-based FDPs fabricated with digital scans showed better fit than those in the conventional impression group. Within the limitations of this study, these results are encouraging, and continued progress in the digital field should allow for more accurate long-span restorations.

**KEYWORDS**

accuracy, CAD-CAM, digital impression, high resolution, intraoral scanners, micro-CT

The accuracy of marginal and internal adaptation of prosthetic restorations on their respective abutments is one of the factors guaranteeing the durability of the treatment. This adaptation is a major objective that has led to periodontal integration of restorations and is necessary for predicting the prognosis of periodontal tissues adjacent to crowns or

fixed dental prostheses (FDPs).<fnref n="1" />,<fnref n="2" /> Indeed, Knoernschild et al showed in their review that biological complications, such as advanced gingival inflammation, deep pockets, attachment, and alveolar bone loss occurring on crown-supporting teeth, are most often due to the poor fit of restorations.<fnref n="2" /> These results have been confirmed in other studies highlighting

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2023 The Authors. *Journal of Prosthodontics* published by Wiley Periodicals LLC on behalf of American College of Prosthodontists.

<footnote n="1">¹Nantes University, Oniris, Univ Angers, CHU Nantes, INSERM, Regenerative Medicine and Skeleton, Nantes, France</footnote>

<footnote n="2">²Department of Prosthetic Dentistry, Nantes University, CHU Nantes, Nantes, France</footnote>

<footnote n="3">³Department of Periodontology, Nantes University, Oniris, Univ Angers, CHU Nantes, INSERM, Regenerative Medicine and Skeleton, Nantes, France</footnote>

<footnote n="4">⁴Department of Prosthodontics, Nantes University, Oniris, Univ Angers, CHU Nantes, INSERM, Regenerative Medicine and Skeleton, Nantes, France</footnote>
ORIGINAL ARTICLE

<figure><img src="image_3.png" /></figure>

AMERICAN COLLEGE OF
PROSTHODONTISTS
Your smile. Our specialty.

# Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study

Octave Nadile Bandiaky DDS, MSc<fnref n="1" /> | Roselyne Clouet DDS, MSc<fnref n="2" /> | Pierre Le Bars DDS, MSc, PhD<fnref n="2" /> | Assem Soueidan DDS, MSc, PhD<fnref n="3" /> | Laurent Le Guehennec DDS, MSc, PhD<fnref n="4" />

**Correspondence**

Octave Nadile Bandiaky, Nantes University,
Oniris, Univ Angers, CHU Nantes, INSERM,
Regenerative Medicine and Skeleton, RMeS,
UMR 1229, 1 Place Alexis Ricordeau, 44042
Nantes, France.

Email: octave.bandiaky@univ-nantes.fr

**Funding information**

UFR of Odontology of Nantes University, France

**Abstract**

**Purpose:** This study aimed to compare the marginal and internal fit of five-unit zirconia-based fixed dental prostheses (FDPs) fabricated using digital scans and conventional impressions.

**Materials and methods:** Nine master models with three zirconia abutments were scanned with an intraoral scanner (test group), and nine conventional impressions (control group) of these same models were also made. The stone casts from these impressions were scanned with a laboratory extraoral scanner (D700, 3Shape, Copenhagen, Denmark). A total of 18 five-unit zirconia-based FDP frameworks (test group, *n* = 9; control group, *n* = 9) were manufactured. Marginal and internal fit (in µm) were evaluated using the replica method under micro-computed tomography. Analysis of variance (one-way ANOVA) and Kruskal–Wallis tests were used to compare continuous variables across two groups. A level of *p* < 0.05 was accepted as statistically significant.

**Results:** The mean ± standard deviation of the marginal fit was 95.03 ± 12.74 µm in the test group and 106.02 ± 14.51 µm in the control group. The lowest marginal mean value was observed in the test group, with a statistically significant difference compared to the control group (*F* = 14.56, *p* < 0.05). The mean ± standard deviation of the internal fit was 103.61 ± 9.32 and 106.38 ± 7.64 µm, respectively, in the test and control groups, with no statistically significant difference (*F* = 1.56, *p* > 0.05). The mean values of both groups were clinically acceptable.

**Conclusions:** The five-unit zirconia-based FDPs fabricated with digital scans showed better fit than those in the conventional impression group. Within the limitations of this study, these results are encouraging, and continued progress in the digital field should allow for more accurate long-span restorations.

**KEYWORDS**

accuracy, CAD-CAM, digital impression, high resolution, intraoral scanners, micro-CT

The accuracy of marginal and internal adaptation of prosthetic restorations on their respective abutments is one of the factors guaranteeing the durability of the treatment. This adaptation is a major objective that has led to periodontal integration of restorations and is necessary for predicting the prognosis of periodontal tissues adjacent to crowns or

fixed dental prostheses (FDPs).<fnref n="1" />,<fnref n="2" /> Indeed, Knoernschild et al showed in their review that biological complications, such as advanced gingival inflammation, deep pockets, attachment, and alveolar bone loss occurring on crown-supporting teeth, are most often due to the poor fit of restorations.<fnref n="2" /> These results have been confirmed in other studies highlighting

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2023 The Authors. *Journal of Prosthodontics* published by Wiley Periodicals LLC on behalf of American College of Prosthodontists.

<footnote n="1">¹Nantes University, Oniris, Univ Angers, CHU Nantes, INSERM, Regenerative Medicine and Skeleton, Nantes, France</footnote>

<footnote n="2">²Department of Prosthetic Dentistry, Nantes University, CHU Nantes, Nantes, France</footnote>

<footnote n="3">³Department of Periodontology, Nantes University, Oniris, Univ Angers, CHU Nantes, INSERM, Regenerative Medicine and Skeleton, Nantes, France</footnote>

<footnote n="4">⁴Department of Prosthodontics, Nantes University, Oniris, Univ Angers, CHU Nantes, INSERM, Regenerative Medicine and Skeleton, Nantes, France</footnote>
periodontal and caries complications on crowned teeth.³⁻⁵ Thus, in the study by Sailer et al, secondary caries were found in 21.7% of the three- or four-unit posterior FDPs.³ In their meta-analysis, Pjetursson et al reported that for different types of FDPs the annual rate of secondary caries ranged from 0.11% to 0.65%.⁴ Moreover, according to Goodacre et al,⁵ there is a 10% risk of failure of prosthetic rehabilitation on a crowned tooth in the case of a poor fit; this risk increases to 27% when several teeth are prepared for medium or large FDPs.⁵ Therefore, even though the proper fit of the reconstructions depends on several parameters, such as the type of cement⁶ and the quality of the cementation, only the most accurate impression technique (digital or conventional) can ultimately achieve a small thickness of the marginal joint or internal space.

Over the years, digital scan (DS) techniques using intraoral scanners have developed considerably and are now reliable, reproducible, and more comfortable for the patient.⁷⁻⁹ Digital scans can be used to design inlays, onlays, single crowns, or short-span prostheses.¹⁰,¹¹ However, several disadvantages, such as deformations when recording the full arch, difficulties in recording coronal–radicular reconstructions, or the limits of intrasulcular preparations, are still encountered.¹ Conventional impressions (CIs) continue to be widely used and are implemented daily in many dental practices. Accurate reconstructions in many clinical situations can be obtained with CIs.¹² However, CIs have many limitations reported in various studies.¹³,¹⁴

Few systematic reviews and meta-analyses have compared the accuracy of DS methods with CI techniques by evaluating the marginal and internal fit of zirconia-based FDP restorations.⁷,¹⁵⁻²³ Some authors concluded that digital scanning provides significantly better marginal and internal fit than CI.¹⁵,²³ Other authors have argued that the two impression techniques are comparable, and both achieve clinically acceptable marginal and internal thicknesses (39–120 µm).⁷,¹⁶⁻²² However, the in vitro and in vivo studies included in these reviews are only for single crowns or three-unit FDPs.¹⁵ The accuracy of these two impression techniques beyond three prosthetic abutments remains largely unstudied.²¹ Therefore, there is a lack of scientific evidence on the accuracy of intraoral scanners used for the fabrication of FDPs with more than three abutment teeth. To our knowledge, only one in vitro study to date has assessed the accuracy of the marginal and internal fit of five-unit zirconia-based FDPs fabricated with computer-aided design and computer-aided manufacturing (CAD-CAM) technology using direct digitalization and conventional methods.²⁴ The authors reported that the marginal and internal fit were similar between the two methods.²⁴ However, further studies are needed to confirm the results of this investigation. Therefore, the objective of the present comparative in vitro study was to evaluate and compare the mean values of the marginal and internal fit of three-abutment–five-unit zirconia-based FDP frameworks designed from direct scanning and CI using micro-CT. The null hypothesis states that there is no significant difference between the two impres-

sion techniques with respect to marginal and internal fit (p > 0.05).

## MATERIALS AND METHODS

This comparative in vitro study included a test (DS) and control groups (CI), as shown in Figure 1. Nine pedagogical models (Frasaco, Tettnang, Germany) were used to make full-contour preparations for a five-unit zirconia-based FDP with three abutment teeth (the right maxillary canine, second premolar, and second molar). A single operator (O.N.B.) made these preparations. The occlusal reduction was 2 mm, and the axial reduction was 1.5 mm.²⁵ The finishing line located at the juxta-gingival level was a 1-mm-wide fillet. On each model, a DS and a CI were taken by a single operator (O.N.B.).

Nine DSs were taken using an intraoral scanner (TRIOS 3, Copenhagen, Denmark) according to the manufacturer's instructions. The maxillary and mandibular arches were scanned, and the occlusion was digitized. All standard test-selllation language (STL) files were checked and transferred to the laboratory via a secure platform.²⁶ For the control group (CI), nine CIs were made with polyvinyl siloxane (PVS) (Extrude Xtra, Kerr) using a one-step two-viscosity technique, and their quality was evaluated using the form proposed by Haddadi et al.²⁷ The antagonist arch impression was taken with alginate, and the occlusion registration was made with occlusion silicone. The CIs were disinfected by glutaraldehyde-based disinfectant as described by Demajo et al.²⁸ It has been shown by these authors that chemical disinfection with this product eliminates all microbial forms of silicone without changing the dimensional stability.²⁸ Each of the nine CIs was cast with type IV gypsum (Fuji-Rock, Tokyo, Japan). This gypsum has excellent characteristics, and it is also ideal for all types of prostheses. The models obtained were scanned with an extraoral scanner (D700, 3Shape, Copenhagen, Denmark).

Based on the STL files from the DSs (n = 9) and CIs (n = 9), 18 zirconia-based FDP frameworks (IPS e.max Zir-CAD, A3 shade, Ivoclar Vivadent, Schaan, Liechtenstein) were fabricated. The space required for the luting cement was set at 50 µm for the internal space.²³ The five-unit zirconia-based FDPs were milled from presintered zirconia blocks with a five-axis milling machine (DWX-52D, DGShape, Hamamatsu, Japan). A single technician (Y.G.) performed all of the laboratory steps.

The silicone replica technique combined with micro-CT was used to determine the mean values of marginal and internal fit.²⁹⁻³¹ To do so, the underside of the framework was loaded with low-viscosity PVS (Hydrorise Light Body, Zher-mack, Badia Polesine, Italy), and then the framework was placed and held on the abutment teeth of the initial Frasaco model (Fig 2a).²² Indeed, the excess PVS was gently removed with a #15 scalpel blade. This was done while keeping the bridge in place. After 5 min, the framework was removed, leaving the thin PVS layer attached to the surface of the
periodontal and caries complications on crowned teeth.³⁻⁵ Thus, in the study by Sailer et al, secondary caries were found in 21.7% of the three- or four-unit posterior FDPs.³ In their meta-analysis, Pjetursson et al reported that for different types of FDPs the annual rate of secondary caries ranged from 0.11% to 0.65%.⁴ Moreover, according to Goodacre et al,⁵ there is a 10% risk of failure of prosthetic rehabilitation on a crowned tooth in the case of a poor fit; this risk increases to 27% when several teeth are prepared for medium or large FDPs.⁵ Therefore, even though the proper fit of the reconstructions depends on several parameters, such as the type of cement⁶ and the quality of the cementation, only the most accurate impression technique (digital or conventional) can ultimately achieve a small thickness of the marginal joint or internal space.

Over the years, digital scan (DS) techniques using intraoral scanners have developed considerably and are now reliable, reproducible, and more comfortable for the patient.⁷⁻⁹ Digital scans can be used to design inlays, onlays, single crowns, or short-span prostheses.¹⁰,¹¹ However, several disadvantages, such as deformations when recording the full arch, difficulties in recording coronal–radicular reconstructions, or the limits of intrasulcular preparations, are still encountered.¹ Conventional impressions (CIs) continue to be widely used and are implemented daily in many dental practices. Accurate reconstructions in many clinical situations can be obtained with CIs.¹² However, CIs have many limitations reported in various studies.¹³,¹⁴

Few systematic reviews and meta-analyses have compared the accuracy of DS methods with CI techniques by evaluating the marginal and internal fit of zirconia-based FDP restorations.⁷,¹⁵⁻²³ Some authors concluded that digital scanning provides significantly better marginal and internal fit than CI.¹⁵,²³ Other authors have argued that the two impression techniques are comparable, and both achieve clinically acceptable marginal and internal thicknesses (39–120 µm).⁷,¹⁶⁻²² However, the in vitro and in vivo studies included in these reviews are only for single crowns or three-unit FDPs.¹⁵ The accuracy of these two impression techniques beyond three prosthetic abutments remains largely unstudied.²¹ Therefore, there is a lack of scientific evidence on the accuracy of intraoral scanners used for the fabrication of FDPs with more than three abutment teeth. To our knowledge, only one in vitro study to date has assessed the accuracy of the marginal and internal fit of five-unit zirconia-based FDPs fabricated with computer-aided design and computer-aided manufacturing (CAD-CAM) technology using direct digitalization and conventional methods.²⁴ The authors reported that the marginal and internal fit were similar between the two methods.²⁴ However, further studies are needed to confirm the results of this investigation. Therefore, the objective of the present comparative in vitro study was to evaluate and compare the mean values of the marginal and internal fit of three-abutment–five-unit zirconia-based FDP frameworks designed from direct scanning and CI using micro-CT. The null hypothesis states that there is no significant difference between the two impres-

sion techniques with respect to marginal and internal fit (p > 0.05).

## MATERIALS AND METHODS

This comparative in vitro study included a test (DS) and control groups (CI), as shown in Figure 1. Nine pedagogical models (Frasaco, Tettnang, Germany) were used to make full-contour preparations for a five-unit zirconia-based FDP with three abutment teeth (the right maxillary canine, second premolar, and second molar). A single operator (O.N.B.) made these preparations. The occlusal reduction was 2 mm, and the axial reduction was 1.5 mm.²⁵ The finishing line located at the juxta-gingival level was a 1-mm-wide fillet. On each model, a DS and a CI were taken by a single operator (O.N.B.).

Nine DSs were taken using an intraoral scanner (TRIOS 3, Copenhagen, Denmark) according to the manufacturer's instructions. The maxillary and mandibular arches were scanned, and the occlusion was digitized. All standard test-selllation language (STL) files were checked and transferred to the laboratory via a secure platform.²⁶ For the control group (CI), nine CIs were made with polyvinyl siloxane (PVS) (Extrude Xtra, Kerr) using a one-step two-viscosity technique, and their quality was evaluated using the form proposed by Haddadi et al.²⁷ The antagonist arch impression was taken with alginate, and the occlusion registration was made with occlusion silicone. The CIs were disinfected by glutaraldehyde-based disinfectant as described by Demajo et al.²⁸ It has been shown by these authors that chemical disinfection with this product eliminates all microbial forms of silicone without changing the dimensional stability.²⁸ Each of the nine CIs was cast with type IV gypsum (Fuji-Rock, Tokyo, Japan). This gypsum has excellent characteristics, and it is also ideal for all types of prostheses. The models obtained were scanned with an extraoral scanner (D700, 3Shape, Copenhagen, Denmark).

Based on the STL files from the DSs (n = 9) and CIs (n = 9), 18 zirconia-based FDP frameworks (IPS e.max Zir-CAD, A3 shade, Ivoclar Vivadent, Schaan, Liechtenstein) were fabricated. The space required for the luting cement was set at 50 µm for the internal space.²³ The five-unit zirconia-based FDPs were milled from presintered zirconia blocks with a five-axis milling machine (DWX-52D, DGShape, Hamamatsu, Japan). A single technician (Y.G.) performed all of the laboratory steps.

The silicone replica technique combined with micro-CT was used to determine the mean values of marginal and internal fit.²⁹⁻³¹ To do so, the underside of the framework was loaded with low-viscosity PVS (Hydrorise Light Body, Zher-mack, Badia Polesine, Italy), and then the framework was placed and held on the abutment teeth of the initial Frasaco model (Fig 2a).²² Indeed, the excess PVS was gently removed with a #15 scalpel blade. This was done while keeping the bridge in place. After 5 min, the framework was removed, leaving the thin PVS layer attached to the surface of the
<figure><img src="image_2.png" /><figcaption>FIGURE 1 Experimental design with two workflows compared in flowchart form</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>FIGURE 2 Full-contour preparation of zirconia abutment teeth (the right maxillary canine, second premolar, and second molar) on the nine master models. (a) Five-unit zirconia-based fixed dental prostheses (FDPs) framework loaded with low-viscosity polyvinyl siloxane and repositioned on the abutment teeth. (b) Release of the five-unit zirconia-based FDPs after the material has set leaving the film stuck to the tooth. (c) Abutment-film assembly unscrewed and put in a tube. (d) Micro-scanning of abutment tooth-film assembly (Skyscan 1272 Bruker—Source: 20–100 kV to 10 W, spot size < 5 µm). (e) Image cutting (CTVox v3.3.1; Bruker) and visualization of the elastomer film materializing the marginal and internal fit. (f) Sagittal section abutment 17 (mesiodistal axis), site measurements S1, S2, E1, E2, E3, E4, and E5. (g) coronal section abutment 17 (vestibulo-lingual axis), site measurements S3, S4; E1*, E2* E3*; and E4*, E5*</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**FIGURE 1** Experimental design with two workflows compared in flowchart form</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**FIGURE 2** Full-contour preparation of zirconia abutment teeth (the right maxillary canine, second premolar, and second molar) on the nine master models. (a) Five-unit zirconia-based fixed dental prostheses (FDPs) framework loaded with low-viscosity polyvinyl siloxane and repositioned on the abutment teeth. (b) Release of the five-unit zirconia-based FDPs after the material has set leaving the film stuck to the tooth. (c) Abutment-film assembly unscrewed and put in a tube. (d) Micro-scanning of abutment tooth-film assembly (Skyscan 1272 Bruker—*Source*: 20–100 kV to 10 W, spot size < 5 µm). (e) Image cutting (CTVox v3.3.1; Bruker) and visualization of the elastomer film materializing the marginal and internal fit. (f) Sagittal section abutment 17 (mesiodistal axis), site measurements S1, S2, E1, E2, E3, E4, and E5. (g) coronal section abutment 17 (vestibulo-lingual axis), site measurements S3, S4; E1*, E2* E3*; and E4*, E5*</figcaption></figure>
abutments (Fig 2b).<sup>22,32</sup> After this step, each abutment tooth with the elastomer film in place was gently removed from the study model and placed in a tube for scanning in the laboratory by a single technician (J.V.) (Fig 2c,d). The PVS-coated abutment was checked before being sent to the laboratory. The tubes were previously identified (vestibular, palatal, mesial, and distal sides) to ensure proper repositioning of the abutments. Micro-CT is a high-resolution imaging technique capable of providing lower marginal and internal gap values.<sup>33</sup>

Each tooth abutment was previously assigned a unique code to ensure blind evaluation of the results and to limit the risk of measurement bias. The images were acquired at 60 kV and 166 µA with a rotation step of 0.4° using a microtome densitometer (Skyscan 1272 Bruker—source: 20–100 kV to 10 W, spot size < 5 µm) using an 11-MP camera and 14-µm resolution. The 3-D reconstruction of the tooth–abutment–elastomer film assembly was performed with NRecon v1.7.3.0 software (Bruker). The images of the samples were then cleaned using a macro in the software CTan v1.20.8 (Bruker) and then spatially oriented with DataViewer v1.5.6.2 (Bruker). Virtual visualization of the abutment–film teeth was performed in CTVox v3.3.1 (Bruker), a software program that enables slices to be made in the three views (coronal, sagittal, and transverse) (Fig 2e). These slices passed through various previously identified sites (S1, S2, S3, and S4; E1/E5/E1*/E5*; E2/E4/E2*/E4*; and E3/E3*). The choice of these sites was based on previous studies.<sup>25,29–31</sup> For the marginal fit, S1 corresponds to the distance between the cervical margin and the FDP margin mesially, S2 distally, S3 on the vestibular side, and S4 on the palatal side. With respect to the internal space, three sites—E1/E5/E1*/E5*; E2/E4/E2*/E4*; and E3/E3*—were selected to determine the thickness between the prosthetic abutment and the underside of the FDP at the mid-axial, (E1/E5/E1*/E5*), axio-occlusal (E2/E4/E2*/E4*), and centro-occlusal (E3/E3*) sites (Fig 2f,g). Figure 2a–g shows the steps implemented in this study.

Each of the image slices was inserted into another image-processing software (ImageJ, Fiji) to automatically extract the values of the thickness of the marginal and internal fit using the methods proposed by Maragos et al<sup>34</sup> and Kimmel et al.<sup>35</sup> The average marginal fit was obtained by averaging the values of S1, S2, S3, and S4 of all of the abutment teeth, whereas the average internal fit was the average value of E1/E5/E1*/E5*, E2/E4/E2*/E4*, and E3/E3*. A total of 756 measurements were performed by a single operator (O.N.B.) for both groups (4 sites × 3 abutments × 9 FDPs × 2 groups + 10 sites × 3 abutment teeth × 9 FDPs × 2 groups).

The number of FDPs or abutments was calculated based on the study by Varol et al,<sup>36</sup> who determined the number of film sections necessary to obtain a mean difference of 20 µm between the two groups.<sup>36</sup> This difference in mean was related to the marginal joint thickness, which was the primary endpoint. With a statistical power of 80%, a p-value of 0.05, and a common standard deviation of ± 14 µm, the number of FDPs per group was 8, that is, 24 abutments.

Because of the risk of abutment damage during preparation, one additional FDP per group was retained to constitute the sample size. Analysis of variance (one-way ANOVA) and Kruskal–Wallis tests were used to compare continuous variables across two groups. A level of *p* < 0.05 was accepted as significant.

## RESULTS

The mean values of marginal and internal fit were obtained from 756 microscan measurements on 54 abutments. The values of marginal and internal fit according to the two study groups (DSs and CIs) are shown in Tables 1, S1, S2. The lowest marginal fit was observed in the DS group (95.03 ± 12.74 µm), which was significantly different from that of the CI group (106.2 ± 14.51 µm; *F* = 14.56, *p* < 0.05). In the DS group, the marginal discrepancy values ranged from 91.21 to 97.61 µm, and for the CI group, these values ranged between 96.53 and 109.12 µm. When the internal fit values were examined, there was no significant difference between the two impression techniques (DS: 103.61 ± 9.32 µm; CI: 106.38 ± 7.64 µm; *F* = 1.56, *p* > 0.05). The lowest mean values of the marginal fit were obtained at sites S3 and S4 for the DSs and at sites S1 and S4 for the CIs, with a significant difference between the two techniques for sites S2, S3, and S4 (*F* = 6.56, *p* < 0.05) (Table 2). Concerning the internal fit of the five-unit zirconia-based FDPs fabricated with CAD/CAM technology and CIs, low mean values were observed at the E1/E5/E1*/E5* (mid-axial) site for the DI method and at the E2/E4/E2*/E4* (axio-occlusal) site for the CI method, where the corresponding values were significantly different at the E1/E5/E1*/E5* areas (*F* = 3.68, *p* < 0.05) (Table 3). However, the marginal and internal adaptation of all five-unit zirconia-based FDP frameworks fabricated with the two tested techniques was within a clinically acceptable range.

## DISCUSSION

The accuracy of impressions in fixed prosthetics plays a crucial role in the periodontal integration of reconstructions.<sup>1,2</sup> This comparative in vitro study investigated the marginal and internal adaptation of five-unit zirconia-based FDP frameworks produced with intraoral scan methods and CI techniques. The null hypothesis—that a significant difference would not be found in marginal and internal fit between the two workflows—was rejected for marginal fit and accepted for internal fit. Low mean values of marginal and internal fit were obtained with the DS methods, with a significant difference for the marginal fit. However, these values remain clinically acceptable. In previous studies,<sup>26,37,38</sup> acceptable values ranged from 34 to 120 µm. The standard deviations of this study (Tables 2 and 3) ranged from 6.63 to 35.27 µm. Although these values are high, they are consistent with those of other studies.<sup>32,39</sup> The results of the present study
abutments (Fig 2b).<sup>22,32</sup> After this step, each abutment tooth with the elastomer film in place was gently removed from the study model and placed in a tube for scanning in the laboratory by a single technician (J.V.) (Fig 2c,d). The PVS-coated abutment was checked before being sent to the laboratory. The tubes were previously identified (vestibular, palatal, mesial, and distal sides) to ensure proper repositioning of the abutments. Micro-CT is a high-resolution imaging technique capable of providing lower marginal and internal gap values.<sup>33</sup>

Each tooth abutment was previously assigned a unique code to ensure blind evaluation of the results and to limit the risk of measurement bias. The images were acquired at 60 kV and 166 µA with a rotation step of 0.4° using a microtome densitometer (Skyscan 1272 Bruker—source: 20–100 kV to 10 W, spot size < 5 µm) using an 11-MP camera and 14-µm resolution. The 3-D reconstruction of the tooth–abutment–elastomer film assembly was performed with NRecon v1.7.3.0 software (Bruker). The images of the samples were then cleaned using a macro in the software CTan v1.20.8 (Bruker) and then spatially oriented with DataViewer v1.5.6.2 (Bruker). Virtual visualization of the abutment–film teeth was performed in CTVox v3.3.1 (Bruker), a software program that enables slices to be made in the three views (coronal, sagittal, and transverse) (Fig 2e). These slices passed through various previously identified sites (S1, S2, S3, and S4; E1/E5/E1*/E5*; E2/E4/E2*/E4*; and E3/E3*). The choice of these sites was based on previous studies.<sup>25,29–31</sup> For the marginal fit, S1 corresponds to the distance between the cervical margin and the FDP margin mesially, S2 distally, S3 on the vestibular side, and S4 on the palatal side. With respect to the internal space, three sites—E1/E5/E1*/E5*; E2/E4/E2*/E4*; and E3/E3*—were selected to determine the thickness between the prosthetic abutment and the underside of the FDP at the mid-axial, (E1/E5/E1*/E5*), axio-occlusal (E2/E4/E2*/E4*), and centro-occlusal (E3/E3*) sites (Fig 2f,g). Figure 2a–g shows the steps implemented in this study.

Each of the image slices was inserted into another image-processing software (ImageJ, Fiji) to automatically extract the values of the thickness of the marginal and internal fit using the methods proposed by Maragos et al<sup>34</sup> and Kimmel et al.<sup>35</sup> The average marginal fit was obtained by averaging the values of S1, S2, S3, and S4 of all of the abutment teeth, whereas the average internal fit was the average value of E1/E5/E1*/E5*, E2/E4/E2*/E4*, and E3/E3*. A total of 756 measurements were performed by a single operator (O.N.B.) for both groups (4 sites × 3 abutments × 9 FDPs × 2 groups + 10 sites × 3 abutment teeth × 9 FDPs × 2 groups).

The number of FDPs or abutments was calculated based on the study by Varol et al,<sup>36</sup> who determined the number of film sections necessary to obtain a mean difference of 20 µm between the two groups.<sup>36</sup> This difference in mean was related to the marginal joint thickness, which was the primary endpoint. With a statistical power of 80%, a p-value of 0.05, and a common standard deviation of ± 14 µm, the number of FDPs per group was 8, that is, 24 abutments.

Because of the risk of abutment damage during preparation, one additional FDP per group was retained to constitute the sample size. Analysis of variance (one-way ANOVA) and Kruskal–Wallis tests were used to compare continuous variables across two groups. A level of *p* < 0.05 was accepted as significant.

## RESULTS

The mean values of marginal and internal fit were obtained from 756 microscan measurements on 54 abutments. The values of marginal and internal fit according to the two study groups (DSs and CIs) are shown in Tables 1, S1, S2. The lowest marginal fit was observed in the DS group (95.03 ± 12.74 µm), which was significantly different from that of the CI group (106.2 ± 14.51 µm; *F* = 14.56, *p* < 0.05). In the DS group, the marginal discrepancy values ranged from 91.21 to 97.61 µm, and for the CI group, these values ranged between 96.53 and 109.12 µm. When the internal fit values were examined, there was no significant difference between the two impression techniques (DS: 103.61 ± 9.32 µm; CI: 106.38 ± 7.64 µm; *F* = 1.56, *p* > 0.05). The lowest mean values of the marginal fit were obtained at sites S3 and S4 for the DSs and at sites S1 and S4 for the CIs, with a significant difference between the two techniques for sites S2, S3, and S4 (*F* = 6.56, *p* < 0.05) (Table 2). Concerning the internal fit of the five-unit zirconia-based FDPs fabricated with CAD/CAM technology and CIs, low mean values were observed at the E1/E5/E1*/E5* (mid-axial) site for the DI method and at the E2/E4/E2*/E4* (axio-occlusal) site for the CI method, where the corresponding values were significantly different at the E1/E5/E1*/E5* areas (*F* = 3.68, *p* < 0.05) (Table 3). However, the marginal and internal adaptation of all five-unit zirconia-based FDP frameworks fabricated with the two tested techniques was within a clinically acceptable range.

## DISCUSSION

The accuracy of impressions in fixed prosthetics plays a crucial role in the periodontal integration of reconstructions.<sup>1,2</sup> This comparative in vitro study investigated the marginal and internal adaptation of five-unit zirconia-based FDP frameworks produced with intraoral scan methods and CI techniques. The null hypothesis—that a significant difference would not be found in marginal and internal fit between the two workflows—was rejected for marginal fit and accepted for internal fit. Low mean values of marginal and internal fit were obtained with the DS methods, with a significant difference for the marginal fit. However, these values remain clinically acceptable. In previous studies,<sup>26,37,38</sup> acceptable values ranged from 34 to 120 µm. The standard deviations of this study (Tables 2 and 3) ranged from 6.63 to 35.27 µm. Although these values are high, they are consistent with those of other studies.<sup>32,39</sup> The results of the present study
<table><caption>TABLE 1 Mean measurement values and standard deviations (SD) in micrometers (μm) for marginal and internal fit in two study groups: digital scans (DSs) and conventional impressions (CIs)</caption><thead><tr><th rowspan="2">Areas</th><th colspan="2">DS (n = 27)</th><th colspan="2">CI (n = 27)</th><th rowspan="2">p-Values</th></tr><tr><th>Mean ± SD</th><th>Min-max</th><th>Mean ± SD</th><th>Min-max</th></tr></thead><tbody><tr><td>Marginal fit</td><td>95.03 ± 12.74</td><td>91.21–97.61</td><td>106.02 ± 14.51</td><td>96.53–109.12</td><td>&lt;0.05*</td></tr><tr><td>Internal fit</td><td>103.61 ± 9.32</td><td>100.46–115.92</td><td>106.38 ± 7.64</td><td>105.87–125.74</td><td>&gt;0.05</td></tr></tbody></table>

<table><caption>TABLE 2 Average values of marginal fit in micrometers (μm) at the different sites of interest (S1, S2, S3, and S4)</caption><thead><tr><th rowspan="2">Interest's areas</th><th colspan="2">DS(n = 108)</th><th colspan="2">CI (n = 108)</th><th rowspan="2">p-Values</th></tr><tr><th>Mean ± SD</th><th>Min-max</th><th>Mean ± SD</th><th>Min-max</th></tr></thead><tbody><tr><td>S1</td><td>96.89 ± 7.53</td><td>89.05–101.02</td><td>100.01 ± 11.73</td><td>93.02–114.03</td><td>&gt;0.05</td></tr><tr><td>S2</td><td>96.04 ± 10.22</td><td>85.89–100.07</td><td>110.22 ± 9.45</td><td>99.52–117.56</td><td>&lt;0.05*</td></tr><tr><td>S3</td><td>94.67 ± 8.64</td><td>90.22–97.71</td><td>101.13 ± 13.54</td><td>88.83–105.02</td><td>&lt;0.05*</td></tr><tr><td>S4</td><td>93.03 ± 6.63</td><td>87.36–95.89</td><td>99.70 ± 8.80</td><td>92.44–106.75</td><td>&lt;0.05*</td></tr></tbody></table>

Abbreviations: CI, conventional impression; DS, digital scan; SD, standard deviations.

<table><caption>TABLE 3 Average values (μm) for internal fit at sites of interest between two impression techniques</caption><thead><tr><th rowspan="2">Surveyed sites</th><th colspan="2">DS (n = 324)</th><th colspan="2">CI (n = 324)</th><th rowspan="2">p-Values</th></tr><tr><th>Mean ± SD</th><th>Min-max</th><th>Mean ± SD</th><th>Min-max</th></tr></thead><tbody><tr><td>E1/E5/E1*/E5* (mid-axial)</td><td>99.23 ± 9.58</td><td>94.32–108.67</td><td>120.58 ± 29.53</td><td>103.32–137.55</td><td>&lt;0.05*</td></tr><tr><td>E2/E4/E2*/E4* (axio-occlusal)</td><td>107.45 ± 15.66</td><td>99.78–116.67</td><td>109.19 ± 19.48</td><td>98.75–123.05</td><td>&gt;0.05</td></tr><tr><td>E3/E3* (centro-occlusal)</td><td>105.33 ± 32.37</td><td>98.25–117.26</td><td>112.49 ± 35.27</td><td>104.03–126.81</td><td>&gt;0.05</td></tr></tbody></table>

Abbreviations: CI, conventional impression; DS, digital scan; SD, standard deviations.

corroborate those of previous studies that reported that DS provides better marginal and internal fit than CI for fabricating zirconia single crowns or FDPs.¹¹,¹⁵,²³,²⁵,⁴⁰⁻⁴⁴ In the literature, there was a lack of scientific data on the accuracy of DSs for long-span reconstructions, especially as Kim and Kim argued in their investigation that the length of the edentulous area can influence the extent of the marginal and internal gap with the use of direct or indirect digitalization.⁴⁵ Recently, Uluc et al compared the marginal and internal fit of 60 five-unit monolithic zirconia-based FDPs fabricated with CAD-CAM technology using direct and indirect digitalization methods.²⁴ The results of this study grouped according to workflow showed that the mean marginal gap values were 78.2 ± 9 μm in the IOS group (intraoral scanner group), 82.6 ± 9 μm in the IMP group (CI scanning group), and 82.6 ± 9 μm in the STN group (stone cast scanning group), with no significant differences among groups (*p* > 0.05). Although our study is similar to that of Uluc et al in terms of the length of the restoration (five-unit zirconia-based FDPs in full contours),²⁴ our results indicate differences in the parameters evaluated. Indeed, lower average values of marginal and internal fit were obtained in the study by Uluc et al.²⁴ This could be explained by the differences in the study design and measurement method. In the present study, low marginal fit

values were obtained at sites S3 and S4 for the DS methods. These sites are located on the vestibular and palatal surfaces and appear to be easier to scan than the sites located on the mesial and distal surfaces. Indeed, Kim et al demonstrated that the adjacent tooth can be a confounding factor for accurate DSs.⁴⁶ The results of the study by Huang et al also appeared to show that the distance between the abutment teeth and adjacent teeth affects the accuracy of the abutment scan.⁴⁷ In intraoral scanning, when the distance between the abutment teeth and the adjacent teeth is more than 1.5 mm, the scan error does not increase, and more accurate scan data can be obtained.

In the present study, the plaster models were scanned with an extraoral scanner. This process does not alter the accuracy of the restorations²⁴ but instead improves the marginal and internal adaptation of the reconstructions.²³ Kernen et al reported that the precision and trueness were higher for extraoral scans than for intraoral scans.⁴⁸ These results agree with those reported by many other authors.⁴⁰,⁴⁹,⁵⁰ According to these authors,²⁶,⁵¹ scanning of the stone cast or impression is the most accurate method and the best fabrication technique with the lowest marginal gaps. However, the results of these different studies contradict those reported by some authors.⁵²,⁵³

<footnote>*Significant differences indicated by *P* < .05.</footnote>

<footnote>*Significant differences indicated by *P* < .05.</footnote>

<footnote>*Significant differences indicated by *P* < .05.</footnote>
<table><caption>TABLE 1 Mean measurement values and standard deviations (SD) in micrometers (μm) for marginal and internal fit in two study groups: digital scans (DSs) and conventional impressions (CIs)</caption><thead><tr><th rowspan="2">Areas</th><th colspan="2">DS (n = 27)</th><th colspan="2">CI (n = 27)</th><th rowspan="2">p-Values</th></tr><tr><th>Mean ± SD</th><th>Min-max</th><th>Mean ± SD</th><th>Min-max</th></tr></thead><tbody><tr><td>Marginal fit</td><td>95.03 ± 12.74</td><td>91.21–97.61</td><td>106.02 ± 14.51</td><td>96.53–109.12</td><td>&lt;0.05*</td></tr><tr><td>Internal fit</td><td>103.61 ± 9.32</td><td>100.46–115.92</td><td>106.38 ± 7.64</td><td>105.87–125.74</td><td>&gt;0.05</td></tr></tbody></table>

<table><caption>TABLE 2 Average values of marginal fit in micrometers (μm) at the different sites of interest (S1, S2, S3, and S4)</caption><thead><tr><th rowspan="2">Interest's areas</th><th colspan="2">DS(n = 108)</th><th colspan="2">CI (n = 108)</th><th rowspan="2">p-Values</th></tr><tr><th>Mean ± SD</th><th>Min-max</th><th>Mean ± SD</th><th>Min-max</th></tr></thead><tbody><tr><td>S1</td><td>96.89 ± 7.53</td><td>89.05–101.02</td><td>100.01 ± 11.73</td><td>93.02–114.03</td><td>&gt;0.05</td></tr><tr><td>S2</td><td>96.04 ± 10.22</td><td>85.89–100.07</td><td>110.22 ± 9.45</td><td>99.52–117.56</td><td>&lt;0.05*</td></tr><tr><td>S3</td><td>94.67 ± 8.64</td><td>90.22–97.71</td><td>101.13 ± 13.54</td><td>88.83–105.02</td><td>&lt;0.05*</td></tr><tr><td>S4</td><td>93.03 ± 6.63</td><td>87.36–95.89</td><td>99.70 ± 8.80</td><td>92.44–106.75</td><td>&lt;0.05*</td></tr></tbody></table>

Abbreviations: CI, conventional impression; DS, digital scan; SD, standard deviations.

<table><caption>TABLE 3 Average values (μm) for internal fit at sites of interest between two impression techniques</caption><thead><tr><th rowspan="2">Surveyed sites</th><th colspan="2">DS (n = 324)</th><th colspan="2">CI (n = 324)</th><th rowspan="2">p-Values</th></tr><tr><th>Mean ± SD</th><th>Min-max</th><th>Mean ± SD</th><th>Min-max</th></tr></thead><tbody><tr><td>E1/E5/E1*/E5* (mid-axial)</td><td>99.23 ± 9.58</td><td>94.32–108.67</td><td>120.58 ± 29.53</td><td>103.32–137.55</td><td>&lt;0.05*</td></tr><tr><td>E2/E4/E2*/E4* (axio-occlusal)</td><td>107.45 ± 15.66</td><td>99.78–116.67</td><td>109.19 ± 19.48</td><td>98.75–123.05</td><td>&gt;0.05</td></tr><tr><td>E3/E3* (centro-occlusal)</td><td>105.33 ± 32.37</td><td>98.25–117.26</td><td>112.49 ± 35.27</td><td>104.03–126.81</td><td>&gt;0.05</td></tr></tbody></table>

Abbreviations: CI, conventional impression; DS, digital scan; SD, standard deviations.

corroborate those of previous studies that reported that DS provides better marginal and internal fit than CI for fabricating zirconia single crowns or FDPs.¹¹,¹⁵,²³,²⁵,⁴⁰⁻⁴⁴ In the literature, there was a lack of scientific data on the accuracy of DSs for long-span reconstructions, especially as Kim and Kim argued in their investigation that the length of the edentulous area can influence the extent of the marginal and internal gap with the use of direct or indirect digitalization.⁴⁵ Recently, Uluc et al compared the marginal and internal fit of 60 five-unit monolithic zirconia-based FDPs fabricated with CAD-CAM technology using direct and indirect digitalization methods.²⁴ The results of this study grouped according to workflow showed that the mean marginal gap values were 78.2 ± 9 μm in the IOS group (intraoral scanner group), 82.6 ± 9 μm in the IMP group (CI scanning group), and 82.6 ± 9 μm in the STN group (stone cast scanning group), with no significant differences among groups (*p* > 0.05). Although our study is similar to that of Uluc et al in terms of the length of the restoration (five-unit zirconia-based FDPs in full contours),²⁴ our results indicate differences in the parameters evaluated. Indeed, lower average values of marginal and internal fit were obtained in the study by Uluc et al.²⁴ This could be explained by the differences in the study design and measurement method. In the present study, low marginal fit

values were obtained at sites S3 and S4 for the DS methods. These sites are located on the vestibular and palatal surfaces and appear to be easier to scan than the sites located on the mesial and distal surfaces. Indeed, Kim et al demonstrated that the adjacent tooth can be a confounding factor for accurate DSs.⁴⁶ The results of the study by Huang et al also appeared to show that the distance between the abutment teeth and adjacent teeth affects the accuracy of the abutment scan.⁴⁷ In intraoral scanning, when the distance between the abutment teeth and the adjacent teeth is more than 1.5 mm, the scan error does not increase, and more accurate scan data can be obtained.

In the present study, the plaster models were scanned with an extraoral scanner. This process does not alter the accuracy of the restorations²⁴ but instead improves the marginal and internal adaptation of the reconstructions.²³ Kernen et al reported that the precision and trueness were higher for extraoral scans than for intraoral scans.⁴⁸ These results agree with those reported by many other authors.⁴⁰,⁴⁹,⁵⁰ According to these authors,²⁶,⁵¹ scanning of the stone cast or impression is the most accurate method and the best fabrication technique with the lowest marginal gaps. However, the results of these different studies contradict those reported by some authors.⁵²,⁵³

<footnote>*Significant differences indicated by *P* < .05.</footnote>

<footnote>*Significant differences indicated by *P* < .05.</footnote>

<footnote>*Significant differences indicated by *P* < .05.</footnote>
Some factors, such as the length of the restoration, can affect the accuracy of fit regardless of the impression technique used.⁴⁵,⁵⁴⁻⁵⁶ Thus, in their in vitro study, Kim and Kim investigated the accuracy of monolithic FDPs with different numbers of pontics (no pontic, NP; 1 pontic, 1P; and 2 pontics, 2P) fabricated with different impression methods (direct and indirect digitalization).⁴⁵ The results of this study show that the length of the reconstruction can indeed alter the accuracy of the impressions. This was also demonstrated by other authors,¹,⁴⁸,⁵⁷⁻⁵⁹ who showed that the median precision of short-span scans was higher than that of complete-arch scans. The maximum accuracy values increased from 43 to 198 µm when using partial-to-complete-arch scans; thus, the accuracy decreased as the scanning scope increased.⁴⁸ Authors such as Park et al agree that intraoral scanners are useful for short scans.⁶⁰ However, recent advances in 3D technology and intraoral scanning systems enable the fabrication of large-span fixed prostheses by fully digital flows. This was demonstrated in the present study and in the study by Uluc et al.²⁴ The performance of intraoral scanning systems has been improved over the past few decades by limiting the distortion in STL files during full-arch scanning.⁶¹ This offers new perspectives in the design and fabrication of long-range reconstructions.

In previous studies,²⁴,²⁵,⁶²⁻⁶⁷ the measurement of marginal and internal fit was performed with the silicone replica technique. This process has many limitations related to the deterioration of the material and the lack of precision in the measurements made. To limit these errors, other evaluation methods such as 3D superimposition analysis (3DSA),⁶⁸ direct viewing techniques, or the use of micro-CT have been reported in the literature. The micro-CT method is a relatively expensive but nondestructive method of investigating marginal and internal fit. This 3D, high-resolution imaging system provides detailed information concerning the FDP-to-die fit without damaging the specimen.³³,⁶⁹⁻⁷² Nevertheless, our study has many limitations, especially because of its in vitro aspect. Indeed, the applicability of our results at the clinical level remains limited by the fact that many parameters specific to the patient, oral environment, situation of the cervical limit, and characteristics of the teeth are likely to alter the precision of the optical impressions.⁷³ Therefore, clinical studies evaluating the marginal and internal adaptation of large-area restorations fabricated by direct and indirect scanning are needed to confirm our results.

## CONCLUSION

Based on the results of this study, the five-unit zirconia-based FDPs fabricated with digital scans showed a better fit. This offers new perspectives in the design and fabrication of long-range reconstructions. Within the limitations of this study, these results are encouraging, and continued progress in the digital field should allow for more accurate long-span restorations. Additional in vivo studies in a large population are needed to confirm these results.

## ACKNOWLEDGEMENT

This work was supported in part by the local scientific council of the UFR of Odontology of Nantes University, France, and in part by the department of prosthesis of the UFR of Odontology of Nantes University.

## CONFLICT OF INTEREST

The authors have no conflict of interest to declare.

## ORCID

Octave Nadile Bandiaky DDS, MSc https://orcid.org/0000-0002-6556-1947

## REFERENCES

1. Abduo J, Elseyoufi M. Accuracy of intraoral scanners: a systematic review of influencing factors. Eur J Prosthodont Restor Dent. 2018;26:101-21.

2. Knoernschild KL, Campbell SD. Periodontal tissue responses after insertion of artificial crowns and fixed partial dentures. J Prosthet Dent. 2000;84:492-8.

3. Sailer I, Fehér A, Filser F, Gauckler LJ, Lüthy H, Hämmerle CH. Five-year clinical results of zirconia frameworks for posterior fixed partial dentures. Int J Prosthodont. 2007;20:383-8.

4. Pjetursson BE, Sailer I, Makarov NA, Zwahlen M, Thoma DS. All-ceramic or metal-ceramic tooth-supported fixed dental prostheses (FDPs)? A systematic review of the survival and complication rates. Part II: multiple-unit FDPs. Dent Mater. 2015;31:624-39.

5. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JYK. Clinical complications in fixed prosthodontics. J Prosthet Dent. 2003;90:31-41.

6. Maroulakos G, Thompson GA, Kontogiorgos ED. Effect of cement type on the clinical performance and complications of zirconia and lithium disilicate tooth-supported crowns: a systematic review. Report of the Committee on Research in Fixed Prosthodontics of the American Academy of Fixed Prosthodontics. J Prosthet Dent. 2019;121: 754-65.

7. Bandiaky ON, Le Bars P, Gaudin A, Hardouin JB, Cheraud-Carpentier M, Mbodj EB, et al. Comparative assessment of complete-coverage, fixed tooth-supported prostheses fabricated from digital scans or conventional impressions: a systematic review and meta-analysis. J Prosthet Dent. 2022;127:71-9.

8. Sailer I, Mühlemann S, Fehmer V, Hämmerle CHF, Benic GI. Randomized controlled clinical trial of digital and conventional workflows for the fabrication of zirconia-ceramic fixed partial dentures. Part I: Time efficiency of complete-arch digital scans versus conventional impressions. J Prosthet Dent. 2019;121:69-75.

9. Haddadi Y, Bahrami G, Isidor F. Evaluation of operating time and patient perception using conventional impression making and intraoral scanning for crown manufacture: a split-mouth, randomized clinical study. Int J Prosthodont. 2018;31:55-9.

10. Kihara H, Hatakeyama W, Komine F, Takafuji K, Takahashi T, Yokota J, et al. Accuracy and practicality of intraoral scanner in dentistry: a literature review. J Prosthodont Res. 2020;64:109-13.

11. Takeuchi Y, Koizumi H, Furuchi M, Sato Y, Ohkubo C, Matsumura H. Use of digital impression systems with intraoral scanners for fabricating restorations and fixed dental prostheses. J Oral Sci. 2018;60:1-7.

12. Zeltner M, Sailer I, Mühlemann S, Özcan M, Hämmerle CHF, Benic GI. Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit. J Prosthet Dent. 2017;117:354-62.

13. Rodriguez JM, Bartlett DW. The dimensional stability of impression materials and its effect on in vitro tooth wear studies. Dent Mater. 2011;27:253-8.

14. Thongthammachat S, Moore BK, Barco MT, Hovijitra S, Brown DT, Andres CJ. Dimensional accuracy of dental casts: influence
Some factors, such as the length of the restoration, can affect the accuracy of fit regardless of the impression technique used.⁴⁵,⁵⁴⁻⁵⁶ Thus, in their in vitro study, Kim and Kim investigated the accuracy of monolithic FDPs with different numbers of pontics (no pontic, NP; 1 pontic, 1P; and 2 pontics, 2P) fabricated with different impression methods (direct and indirect digitalization).⁴⁵ The results of this study show that the length of the reconstruction can indeed alter the accuracy of the impressions. This was also demonstrated by other authors,¹,⁴⁸,⁵⁷⁻⁵⁹ who showed that the median precision of short-span scans was higher than that of complete-arch scans. The maximum accuracy values increased from 43 to 198 µm when using partial-to-complete-arch scans; thus, the accuracy decreased as the scanning scope increased.⁴⁸ Authors such as Park et al agree that intraoral scanners are useful for short scans.⁶⁰ However, recent advances in 3D technology and intraoral scanning systems enable the fabrication of large-span fixed prostheses by fully digital flows. This was demonstrated in the present study and in the study by Uluc et al.²⁴ The performance of intraoral scanning systems has been improved over the past few decades by limiting the distortion in STL files during full-arch scanning.⁶¹ This offers new perspectives in the design and fabrication of long-range reconstructions.

In previous studies,²⁴,²⁵,⁶²⁻⁶⁷ the measurement of marginal and internal fit was performed with the silicone replica technique. This process has many limitations related to the deterioration of the material and the lack of precision in the measurements made. To limit these errors, other evaluation methods such as 3D superimposition analysis (3DSA),⁶⁸ direct viewing techniques, or the use of micro-CT have been reported in the literature. The micro-CT method is a relatively expensive but nondestructive method of investigating marginal and internal fit. This 3D, high-resolution imaging system provides detailed information concerning the FDP-to-die fit without damaging the specimen.³³,⁶⁹⁻⁷² Nevertheless, our study has many limitations, especially because of its in vitro aspect. Indeed, the applicability of our results at the clinical level remains limited by the fact that many parameters specific to the patient, oral environment, situation of the cervical limit, and characteristics of the teeth are likely to alter the precision of the optical impressions.⁷³ Therefore, clinical studies evaluating the marginal and internal adaptation of large-area restorations fabricated by direct and indirect scanning are needed to confirm our results.

## CONCLUSION

Based on the results of this study, the five-unit zirconia-based FDPs fabricated with digital scans showed a better fit. This offers new perspectives in the design and fabrication of long-range reconstructions. Within the limitations of this study, these results are encouraging, and continued progress in the digital field should allow for more accurate long-span restorations. Additional in vivo studies in a large population are needed to confirm these results.

## ACKNOWLEDGEMENT

This work was supported in part by the local scientific council of the UFR of Odontology of Nantes University, France, and in part by the department of prosthesis of the UFR of Odontology of Nantes University.

## CONFLICT OF INTEREST

The authors have no conflict of interest to declare.

## ORCID

Octave Nadile Bandiaky DDS, MSc https://orcid.org/0000-0002-6556-1947

## REFERENCES

1. Abduo J, Elseyoufi M. Accuracy of intraoral scanners: a systematic review of influencing factors. Eur J Prosthodont Restor Dent. 2018;26:101-21.

2. Knoernschild KL, Campbell SD. Periodontal tissue responses after insertion of artificial crowns and fixed partial dentures. J Prosthet Dent. 2000;84:492-8.

3. Sailer I, Fehér A, Filser F, Gauckler LJ, Lüthy H, Hämmerle CH. Five-year clinical results of zirconia frameworks for posterior fixed partial dentures. Int J Prosthodont. 2007;20:383-8.

4. Pjetursson BE, Sailer I, Makarov NA, Zwahlen M, Thoma DS. All-ceramic or metal-ceramic tooth-supported fixed dental prostheses (FDPs)? A systematic review of the survival and complication rates. Part II: multiple-unit FDPs. Dent Mater. 2015;31:624-39.

5. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JYK. Clinical complications in fixed prosthodontics. J Prosthet Dent. 2003;90:31-41.

6. Maroulakos G, Thompson GA, Kontogiorgos ED. Effect of cement type on the clinical performance and complications of zirconia and lithium disilicate tooth-supported crowns: a systematic review. Report of the Committee on Research in Fixed Prosthodontics of the American Academy of Fixed Prosthodontics. J Prosthet Dent. 2019;121: 754-65.

7. Bandiaky ON, Le Bars P, Gaudin A, Hardouin JB, Cheraud-Carpentier M, Mbodj EB, et al. Comparative assessment of complete-coverage, fixed tooth-supported prostheses fabricated from digital scans or conventional impressions: a systematic review and meta-analysis. J Prosthet Dent. 2022;127:71-9.

8. Sailer I, Mühlemann S, Fehmer V, Hämmerle CHF, Benic GI. Randomized controlled clinical trial of digital and conventional workflows for the fabrication of zirconia-ceramic fixed partial dentures. Part I: Time efficiency of complete-arch digital scans versus conventional impressions. J Prosthet Dent. 2019;121:69-75.

9. Haddadi Y, Bahrami G, Isidor F. Evaluation of operating time and patient perception using conventional impression making and intraoral scanning for crown manufacture: a split-mouth, randomized clinical study. Int J Prosthodont. 2018;31:55-9.

10. Kihara H, Hatakeyama W, Komine F, Takafuji K, Takahashi T, Yokota J, et al. Accuracy and practicality of intraoral scanner in dentistry: a literature review. J Prosthodont Res. 2020;64:109-13.

11. Takeuchi Y, Koizumi H, Furuchi M, Sato Y, Ohkubo C, Matsumura H. Use of digital impression systems with intraoral scanners for fabricating restorations and fixed dental prostheses. J Oral Sci. 2018;60:1-7.

12. Zeltner M, Sailer I, Mühlemann S, Özcan M, Hämmerle CHF, Benic GI. Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit. J Prosthet Dent. 2017;117:354-62.

13. Rodriguez JM, Bartlett DW. The dimensional stability of impression materials and its effect on in vitro tooth wear studies. Dent Mater. 2011;27:253-8.

14. Thongthammachat S, Moore BK, Barco MT, Hovijitra S, Brown DT, Andres CJ. Dimensional accuracy of dental casts: influence
of tray material, impression material, and time. J Prosthodont. 2002;11:98-108.

15. Ling C, Cheng C, Zhiyong L, Qi Z. Clinical performance of intraoral digital impression for fixed prosthodontics: a meta-analysis. West China J Stomatol. 2021;39:306-12.

16. Chochlidakis KM, Papaspyridakos P, Geminiani A, Chen C-J, Feng IJ, Ercoli C. Digital versus conventional impressions for fixed prosthodontics: a systematic review and meta-analysis. J Prosthet Dent. 2016;116:184-90.

17. Nagarkar SR, Perdigao J, Seong W-J, Theis-Mahon N. Digital versus conventional impressions for full-coverage restorations: a systematic review and meta-analysis. J Am Dent Assoc. 2018;149:139-47.

18. Ahlholm P, Pipilä K, Vallittu P, Jakonen M, Kotiranta U. Digital versus conventional impressions in fixed prosthodontics: a review. J Prosthodont. 2018;27:35-41.

19. Tsirogiannis P, Reissmann DR, Heydecke G. Evaluation of the marginal fit of single-unit, complete-coverage ceramic restorations fabricated after digital and conventional impressions: a systematic review and meta-analysis. J Prosthet Dent. 2016;116:328-35.

20. Joda T, Zarone F, Ferrari M. The complete digital workflow in fixed prosthodontics: a systematic review. BMC Oral Health. 2017;17:124.

21. Lo Russo L, Caradonna G, Biancardino M, De Lillo A, Troiano G, Guida L. Digital versus conventional workflow for the fabrication of multiunit fixed prostheses: a systematic review and meta-analysis of vertical marginal fit in controlled in vitro studies. J Prosthet Dent. 2019;122:435-40.

22. Kumar H, Kumar T, Hemchand S, Suneelkumar C, Subha A. Accuracy of marginal adaptation of posterior fixed dental prosthesis made from digital impression technique: a systematic review. J Indian Prosthodont Soc. 2020;20:123-30.

23. Mously HA, Finkelman M, Zandparsa R, Hirayama H. Marginal and internal adaptation of ceramic crown restorations fabricated with CAD/CAM technology and the heat-press technique. J Prosthet Dent. 2014;112:249-56.

24. Uluc IG, Guncu MB, Aktas G, Turkyilmaz I. Comparison of marginal and internal fit of 5-unit zirconia fixed dental prostheses fabricated with CAD/CAM technology using direct and indirect digital scans. J Dent Sci. 2022;17:63-9.

25. Benic GI, Sailer I, Zeltner M, Gütermann JN, Özcan M, Mühlemann S. Randomized controlled clinical trial of digital and conventional workflows for the fabrication of zirconia-ceramic fixed partial dentures. Part III: marginal and internal fit. J Prosthet Dent. 2019;121:426-31.

26. Akhlaghian M, Khaledi A-A, Farzin M, Pardis S. Vertical marginal fit of zirconia copings fabricated with one direct and three indirect digital scanning techniques. J Prosthet Dent. 2021;126:421-6.

27. Haddadi Y, Bahrami G, Isidor F. Accuracy of crowns based on digital intraoral scanning compared to conventional impression—a split-mouth randomised clinical study. Clin Oral Investig. 2019;23:4043-50.

28. Demajo J, Cassar V, Farrugia C, Millan-Sango D, Sammut C, Valdramidis V. Effectiveness of disinfectants on antimicrobial and physical properties of dental impression materials. Int J Prosthodont. 2016;29:63-7.

29. Laurent M, Scheer P, Dejou J, Laborde G. Clinical evaluation of the marginal fit of cast crowns-validation of the silicone replica method. J Oral Rehabil. 2008;35:116-22.

30. Dauti R, Cvikl B, Lilaj B, Heimel P, Moritz A, Schedle A. Micro-CT evaluation of marginal and internal fit of cemented polymer infiltrated ceramic network material crowns manufactured after conventional and digital impressions. J Prosthodont Res. 2019;63:40-6.

31. Ahrberg D, Lauer HC, Ahrberg M, Weigl P. Evaluation of fit and efficiency of CAD/CAM fabricated all-ceramic restorations based on direct and indirect digitalization: a double-blinded, randomized clinical trial. Clin Oral Investig. 2016;20:291-300.

32. Al-Imam H, Michou S, Benetti AR, Gotfredsen K. Evaluation of marginal and internal fit of acrylic bridges using optical coherence tomography. J Oral Rehabil. 2019;46:274-81.

33. Cunali RS, Saab RC, Correr GM, Cunha LF, Ornaghi BP, Ritter AV. Marginal and internal adaptation of zirconia crowns: a comparative study of assessment methods. Braz Dent J. 2017;28:467-73.

34. Maragos P, Schafer R. Morphological skeleton representation and coding of binary images. IEEE Trans Image Process. 1986;34:1228-44.

35. Kimmel R, Kiryati N, Bruckstein AM. Sub-pixel distance maps and weighted distance transforms. J Math Imaging Vis. 1996;6:223-33.

36. Varol S, Kulak-Özkan Y. In vitro comparison of marginal and internal fit of press-on-metal ceramic (PoM) restorations with zirconium-supported and conventional metal ceramic fixed partial dentures before and after veneering. J Prosthodont. 2015;24:387-93.

37. Holmes JR, Sulik WD, Holland GA, Bayne SC. Marginal fit of castable ceramic crowns. J Prosthet Dent. 1992;67:594-9.

38. Mclean JW, Von F. The estimation of cement film thickness by an in vivo technique. Br Dent J. 1971;131:107-11.

39. Neves FD, Prado CJ, Prudente MS, Carneiro TAPN, Zancopé K, Davi LR, et al. Micro-computed tomography evaluation of marginal fit of lithium disilicate crowns fabricated by using chairside CAD/CAM systems or the heat-pressing technique. J Prosthet Dent. 2014;112:1134-40.

40. Özal Ç, Ulusoy M. In-vitro evaluation of marginal and internal fit of 3-unit monolithic zirconia restorations fabricated using digital scanning technologies. J Adv Prosthodont. 2021;13:373-84.

41. Güth J-F, Keul C, Stimmelmayr M, Beuer F, Edelhoff D. Accuracy of digital models obtained by direct and indirect data capturing. Clin Oral Investig. 2013;17:1201-8.

42. Vecsei B, Joós-Kovács G, Borbély J, Hermann P. Comparison of the accuracy of direct and indirect three-dimensional digitizing processes for CAD/CAM systems—an in vitro study. J Prosthodont Res. 2017;61:177-84.

43. Ng J, Ruse D, Wyatt C. A comparison of the marginal fit of crowns fabricated with digital and conventional methods. J Prosthet Dent. 2014;112:555-60.

44. Pedroche LO, Bernardes SR, Leão MP, Kintopp CC, Correr GM, Ornaghi BP, et al. Marginal and internal fit of zirconia copings obtained using different digital scanning methods. Braz Oral Res. 2016;30:113.

45. Kim WK, Kim S. Effect of number of pontics and impression technique on the accuracy of four-unit monolithic zirconia fixed dental prostheses. J Prosthet Dent. 2018;119:860-7.

46. Kim JH, Son SA, Lee H, Yoo YJ, Hong SJ, Park JK. Influence of adjacent teeth on the accuracy of intraoral scanning systems for class II inlay preparation. J Esthet Restor Dent. 2022;34:826-32.

47. Huang M-Y, Son K, Lee K-B. Effect of distance between the abutment and the adjacent teeth on intraoral scanning: an in vitro study. J Prosthet Dent. 2021;125:911-7.

48. Kernen F, Schlager S, Alvarez VS, Mehrhof J, Vach K, Kohal R, et al. Accuracy of intraoral scans: an in vivo study of different scanning devices. J Prosthet Dent. 2022;128:1303-1309.

49. Kontis P, Güth J-F, Schubert O, Keul C. Accuracy of intraoral scans of edentulous jaws with different generations of intraoral scanners compared to laboratory scans. J Adv Prosthodont. 2021;13:316-26.

50. Ellakany P, Aly NM, Al-Harbi F. Accuracy of 3D printed and digital casts produced from intraoral and extraoral scanners with different scanning technologies: in vitro study. J Prosthodont. 2022;31:521-8.

51. Flügge TV, Schlager S, Nelson K, Nahles S, Metzger MC. Precision of intraoral digital dental impressions with iTero and extraoral digitization with the iTero and a model scanner. Am J Orthod Dentofacial Orthop. 2013;144:471-8.

52. Freire Y, Gonzalo E, Lopez-Suarez C, Pelaez J, Suarez MJ. Evaluation of the marginal fit of monolithic crowns fabricated by direct and indirect digitization. J Prosthodont Res. 2021;65:291-7.

53. Ellakany P, Tantawi MEI, Mahrous AA, Al-Harbi F. Evaluation of the accuracy of digital impressions obtained from intraoral and extraoral dental scanners with different CAD/CAM scanning technologies: an in vitro study. J Prosthodont. 2022; 31:314-9.

54. Arezoobakhsh A, Shayegh SS, Jamali Ghomi A, Hakimaneh SMR. Comparison of marginal and internal fit of 3-unit zirconia frameworks
of tray material, impression material, and time. J Prosthodont. 2002;11:98–108.

15. Ling C, Cheng C, Zhiyong L, Qi Z. Clinical performance of intraoral digital impression for fixed prosthodontics: a meta-analysis. West China J Stomatol. 2021;39:306–12.

16. Chochlidakis KM, Papaspyridakos P, Geminiani A, Chen C-J, Feng IJ, Ercoli C. Digital versus conventional impressions for fixed prosthodontics: a systematic review and meta-analysis. J Prosthet Dent. 2016;116:184–90.

17. Nagarkar SR, Perdigao J, Seong W-J, Theis-Mahon N. Digital versus conventional impressions for full-coverage restorations: a systematic review and meta-analysis. J Am Dent Assoc. 2018;149:139–47.

18. Ahlholm P, Pipilä K, Vallittu P, Jakonen M, Kotiranta U. Digital versus conventional impressions in fixed prosthodontics: a review. J Prosthodont. 2018;27:35–41.

19. Tsirogiannis P, Reissmann DR, Heydecke G. Evaluation of the marginal fit of single-unit, complete-coverage ceramic restorations fabricated after digital and conventional impressions: a systematic review and meta-analysis. J Prosthet Dent. 2016;116:328–35.

20. Joda T, Zarone F, Ferrari M. The complete digital workflow in fixed prosthodontics: a systematic review. BMC Oral Health. 2017;17:124.

21. Lo Russo L, Caradonna G, Biancardino M, De Lillo A, Troiano G, Guida L. Digital versus conventional workflow for the fabrication of multiunit fixed prostheses: a systematic review and meta-analysis of vertical marginal fit in controlled in vitro studies. J Prosthet Dent. 2019;122:435–40.

22. Kumar H, Kumar T, Hemchand S, Suneelkumar C, Subha A. Accuracy of marginal adaptation of posterior fixed dental prosthesis made from digital impression technique: a systematic review. J Indian Prosthodont Soc. 2020;20:123–30.

23. Mously HA, Finkelman M, Zandparsa R, Hirayama H. Marginal and internal adaptation of ceramic crown restorations fabricated with CAD/CAM technology and the heat-press technique. J Prosthet Dent. 2014;112:249–56.

24. Uluc IG, Guncu MB, Aktas G, Turkyilmaz I. Comparison of marginal and internal fit of 5-unit zirconia fixed dental prostheses fabricated with CAD/CAM technology using direct and indirect digital scans. J Dent Sci. 2022;17:63–9.

25. Benic GI, Sailer I, Zeltner M, Gütermann JN, Özcan M, Mühlemann S. Randomized controlled clinical trial of digital and conventional workflows for the fabrication of zirconia-ceramic fixed partial dentures. Part III: marginal and internal fit. J Prosthet Dent. 2019;121:426–31.

26. Akhlaghian M, Khaledi A-A, Farzin M, Pardis S. Vertical marginal fit of zirconia copings fabricated with one direct and three indirect digital scanning techniques. J Prosthet Dent. 2021;126:421–6.

27. Haddadi Y, Bahrami G, Isidor F. Accuracy of crowns based on digital intraoral scanning compared to conventional impression—a split-mouth randomised clinical study. Clin Oral Investig. 2019;23:4043–50.

28. Demajo J, Cassar V, Farrugia C, Millan-Sango D, Sammut C, Valdramidis V. Effectiveness of disinfectants on antimicrobial and physical properties of dental impression materials. Int J Prosthodont. 2016;29:63–7.

29. Laurent M, Scheer P, Dejou J, Laborde G. Clinical evaluation of the marginal fit of cast crowns—validation of the silicone replica method. J Oral Rehabil. 2008;35:116–22.

30. Dauti R, Cvikl B, Lilaj B, Heimel P, Moritz A, Schedle A. Micro-CT evaluation of marginal and internal fit of cemented polymer infiltrated ceramic network material crowns manufactured after conventional and digital impressions. J Prosthodont Res. 2019;63:40–6.

31. Ahrberg D, Lauer HC, Ahrberg M, Weigl P. Evaluation of fit and efficiency of CAD/CAM fabricated all-ceramic restorations based on direct and indirect digitalization: a double-blinded, randomized clinical trial. Clin Oral Investig. 2016;20:291–300.

32. Al-Imam H, Michou S, Benetti AR, Gotfredsen K. Evaluation of marginal and internal fit of acrylic bridges using optical coherence tomography. J Oral Rehabil. 2019;46:274–81.

33. Cunali RS, Saab RC, Correr GM, Cunha LF, Ornaghi BP, Ritter AV. Marginal and internal adaptation of zirconia crowns: a comparative study of assessment methods. Braz Dent J. 2017;28:467–73.

34. Maragos P, Schafer R. Morphological skeleton representation and coding of binary images. IEEE Trans Image Process. 1986;34:1228–44.

35. Kimmel R, Kiryati N, Bruckstein AM. Sub-pixel distance maps and weighted distance transforms. J Math Imaging Vis. 1996;6:223–33.

36. Varol S, Kulak-Özkan Y. In vitro comparison of marginal and internal fit of press-on-metal ceramic (PoM) restorations with zirconium-supported and conventional metal ceramic fixed partial dentures before and after veneering. J Prosthodont. 2015;24:387–93.

37. Holmes JR, Sulik WD, Holland GA, Bayne SC. Marginal fit of castable ceramic crowns. J Prosthet Dent. 1992;67:594–9.

38. Mclean JW, Von F. The estimation of cement film thickness by an in vivo technique. Br Dent J. 1971;131:107–11.

39. Neves FD, Prado CJ, Prudente MS, Carneiro TAPN, Zancopé K, Davi LR, et al. Micro-computed tomography evaluation of marginal fit of lithium disilicate crowns fabricated by using chairside CAD/CAM systems or the heat-pressing technique. J Prosthet Dent. 2014;112:1134–40.

40. Özal Ç, Ulusoy M. In-vitro evaluation of marginal and internal fit of 3-unit monolithic zirconia restorations fabricated using digital scanning technologies. J Adv Prosthodont. 2021;13:373–84.

41. Güth J-F, Keul C, Stimmelmayr M, Beuer F, Edelhoff D. Accuracy of digital models obtained by direct and indirect data capturing. Clin Oral Investig. 2013;17:1201–8.

42. Vecsei B, Joós-Kovács G, Borbély J, Hermann P. Comparison of the accuracy of direct and indirect three-dimensional digitizing processes for CAD/CAM systems—an in vitro study. J Prosthodont Res. 2017;61:177–84.

43. Ng J, Ruse D, Wyatt C. A comparison of the marginal fit of crowns fabricated with digital and conventional methods. J Prosthet Dent. 2014;112:555–60.

44. Pedroche LO, Bernardes SR, Leão MP, Kintopp CC, Correr GM, Ornaghi BP, et al. Marginal and internal fit of zirconia copings obtained using different digital scanning methods. Braz Oral Res. 2016;30:113.

45. Kim WK, Kim S. Effect of number of pontics and impression technique on the accuracy of four-unit monolithic zirconia fixed dental prostheses. J Prosthet Dent. 2018;119:860–7.

46. Kim JH, Son SA, Lee H, Yoo YJ, Hong SJ, Park JK. Influence of adjacent teeth on the accuracy of intraoral scanning systems for class II inlay preparation. J Esthet Restor Dent. 2022;34:826–32.

47. Huang M-Y, Son K, Lee K-B. Effect of distance between the abutment and the adjacent teeth on intraoral scanning: an in vitro study. J Prosthet Dent. 2021;125:911–7.

48. Kernen F, Schlager S, Alvarez VS, Mehrhof J, Vach K, Kohal R, et al. Accuracy of intraoral scans: an in vivo study of different scanning devices. J Prosthet Dent. 2022;128:1303–1309.

49. Kontis P, Güth J-F, Schubert O, Keul C. Accuracy of intraoral scans of edentulous jaws with different generations of intraoral scanners compared to laboratory scans. J Adv Prosthodont. 2021;13:316–26.

50. Ellakany P, Aly NM, Al-Harbi F. Accuracy of 3D printed and digital casts produced from intraoral and extraoral scanners with different scanning technologies: in vitro study. J Prosthodont. 2022;31:521–8.

51. Flügge TV, Schlager S, Nelson K, Nahles S, Metzger MC. Precision of intraoral digital dental impressions with iTero and extraoral digitization with the iTero and a model scanner. Am J Orthod Dentofacial Orthop. 2013;144:471–8.

52. Freire Y, Gonzalo E, Lopez-Suarez C, Pelaez J, Suarez MJ. Evaluation of the marginal fit of monolithic crowns fabricated by direct and indirect digitization. J Prosthodont Res. 2021;65:291–7.

53. Ellakany P, Tantawi MEI, Mahrous AA, Al-Harbi F. Evaluation of the accuracy of digital impressions obtained from intraoral and extraoral dental scanners with different CAD/CAM scanning technologies: an in vitro study. J Prosthodont. 2022; 31:314–9.

54. Arezoobakhsh A, Shayegh SS, Jamali Ghomi A, Hakimaneh SMR. Comparison of marginal and internal fit of 3-unit zirconia frameworks
fabricated with CAD-CAM technology using direct and indirect digital scans. J Prosthet Dent. 2020;123:105-12.

55. Ueda K, Beuer F, Stimmelmayr M, Erdelt K, Keul C, Güth J-F. Fit of 4-unit FDPs from CoCr and zirconia after conventional and digital impressions. Clin Oral Investig. 2016;20:283-9.

56. Shembesh M, Ali A, Finkelman M, Weber H-P, Zandparsa R. An in vitro comparison of the marginal adaptation accuracy of CAD/CAM restorations using different impression systems. J Prosthodont. 2017;26:581-6.

57. Chen J, Sun Y, Chen H, Cao Y, Ke YF, Zhou YS. Quantitative study of intraoral scanners' accuracy. J Stomatol. 2021;56:920-5.

58. Son K, Jin M-Uk, Lee K-B. Feasibility of using an intraoral scanner for a complete-arch digital scan, part 2: a comparison of scan strategies. J Prosthet Dent. 2021;S0022-3913(21)00285-7.

59. Zhang T, Wei T, Zhao Y, Jiang M, Yin X, Sun H. Evaluating the accuracy of three intraoral scanners using models containing different numbers of crown-prepared abutments. J Dent Sci. 2022;17:204-10.

60. Park G-H, Son K, Lee K-B. Feasibility of using an intraoral scanner for a complete-arch digital scan. J Prosthet Dentist. 2019;121:803-10.

61. Nulty AB. A comparison of full arch trueness and precision of nine intra-oral digital scanners and four lab digital scanners. Dent J (Basel). 2021;9:75.

62. Sakornwimon N, Leevailoj C. Clinical marginal fit of zirconia crowns and patients' preferences for impression techniques using intraoral digital scanner versus polyvinyl siloxane material. J Prosthet Dent. 2017;118:386-91.

63. Al Hamad KQ, Al Rashdan BA, Al Omari WM, Baba NZ. Comparison of the fit of lithium disilicate crowns made from conventional, digital, or conventional/digital techniques. J Prosthodont. 2019;28:580-6.

64. Berrendero S, Salido MP, Valverde A, Ferreiroa A, Pradíes G. Influence of conventional and digital intraoral impressions on the fit of CAD/CAM-fabricated all-ceramic crowns. Clin Oral Investig. 2016;20:2403-10.

65. Martínez-Rus F, Suárez MJ, Rivera B, Pradíes G. Evaluation of the absolute marginal discrepancy of zirconia-based ceramic copings. J Prosthet Dent. 2011;105:108-14.

66. Berrendero S, Salido MP, Ferreiroa A, Valverde A, Pradíes G. Comparative study of all-ceramic crowns obtained from conventional and digital impressions: clinical findings. Clin Oral Investig. 2019;23:1745-51.

67. Pradíes G, Zarauz C, Valverde A, Ferreiroa A, Martínez-Rus F. Clinical evaluation comparing the fit of all-ceramic crowns obtained from silicone and digital intraoral impressions based on wavefront sampling technology. J Dent. 2015;43:201-8.

68. El-Ashkar A, Taymour M, El-Tannir A. Evaluation of the marginal and internal gaps of partially crystallized versus fully crystallized zirconia-reinforced lithium silicate CAD-CAM crowns: an in vitro comparison of the silicone replica technique, direct view, and 3-dimensional superimposition analysis. J Prosthet Dent. 2021;S0022-3913(21)00419-4.

69. Kılıçarslan MA. Micro-CT evaluation of the marginal and internal fit of crown and inlay restorations fabricated via different digital scanners belonging to the same CAD-CAM system. Int J Prosthodont. 2021;34:381-9.

70. Krasanaki ME, Pelekanos S, Andreiotelli M, Koutayas SO, Eliades G. X-ray microtomographic evaluation of the influence of two preparation types on marginal fit of CAD/CAM alumina copings: a pilot study. Int J Prosthodont. 2012;25:170-2.

71. Rungruanganunt P, Kelly JR, Adams DJ. Two imaging techniques for 3D quantification of pre-cementation space for CAD/CAM crowns. J Dent. 2010;38:995-1000.

72. Seo D, Yi Y, Roh B. The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns. J Dent. 2009;37:374-82.

73. Rudolph H, Luthardt RG, Walter MH. Computer-aided analysis of the influence of digitizing and surfacing on the accuracy in dental CAD/CAM technology. Comput Biol Med. 2007;37:579-87.

## SUPPORTING INFORMATION

Additional supporting information can be found online in the Supporting Information section at the end of this article.

**How to cite this article:** Bandiaky ON, Clouet R, Le Bars P, Soueidan A, Le Guehennec L. Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study. J Prosthodont. 2023;32:846-853.
https://doi.org/10.1111/jopr.13639
fabricated with CAD-CAM technology using direct and indirect digital scans. J Prosthet Dent. 2020;123:105-12.

55. Ueda K, Beuer F, Stimmelmayr M, Erdelt K, Keul C, Güth J-F. Fit of 4-unit FDPs from CoCr and zirconia after conventional and digital impressions. Clin Oral Investig. 2016;20:283-9.

56. Shembesh M, Ali A, Finkelman M, Weber H-P, Zandparsa R. An in vitro comparison of the marginal adaptation accuracy of CAD/CAM restorations using different impression systems. J Prosthodont. 2017;26:581-6.

57. Chen J, Sun Y, Chen H, Cao Y, Ke YF, Zhou YS. Quantitative study of intraoral scanners' accuracy. J Stomatol. 2021;56:920-5.

58. Son K, Jin M-Uk, Lee K-B. Feasibility of using an intraoral scanner for a complete-arch digital scan, part 2: a comparison of scan strategies. J Prosthet Dent. 2021;S0022-3913(21)00285-7.

59. Zhang T, Wei T, Zhao Y, Jiang M, Yin X, Sun H. Evaluating the accuracy of three intraoral scanners using models containing different numbers of crown-prepared abutments. J Dent Sci. 2022;17:204-10.

60. Park G-H, Son K, Lee K-B. Feasibility of using an intraoral scanner for a complete-arch digital scan. J Prosthet Dentist. 2019;121:803-10.

61. Nulty AB. A comparison of full arch trueness and precision of nine intra-oral digital scanners and four lab digital scanners. Dent J (Basel). 2021;9:75.

62. Sakornwimon N, Leevailoj C. Clinical marginal fit of zirconia crowns and patients' preferences for impression techniques using intraoral digital scanner versus polyvinyl siloxane material. J Prosthet Dent. 2017;118:386-91.

63. Al Hamad KQ, Al Rashdan BA, Al Omari WM, Baba NZ. Comparison of the fit of lithium disilicate crowns made from conventional, digital, or conventional/digital techniques. J Prosthodont. 2019;28:580-6.

64. Berrendero S, Salido MP, Valverde A, Ferreiroa A, Pradíes G. Influence of conventional and digital intraoral impressions on the fit of CAD/CAM-fabricated all-ceramic crowns. Clin Oral Investig. 2016;20:2403-10.

65. Martínez-Rus F, Suárez MJ, Rivera B, Pradíes G. Evaluation of the absolute marginal discrepancy of zirconia-based ceramic copings. J Prosthet Dent. 2011;105:108-14.

66. Berrendero S, Salido MP, Ferreiroa A, Valverde A, Pradíes G. Comparative study of all-ceramic crowns obtained from conventional and digital impressions: clinical findings. Clin Oral Investig. 2019;23:1745-51.

67. Pradíes G, Zarauz C, Valverde A, Ferreiroa A, Martínez-Rus F. Clinical evaluation comparing the fit of all-ceramic crowns obtained from silicone and digital intraoral impressions based on wavefront sampling technology. J Dent. 2015;43:201-8.

68. El-Ashkar A, Taymour M, El-Tannir A. Evaluation of the marginal and internal gaps of partially crystallized versus fully crystallized zirconia-reinforced lithium silicate CAD-CAM crowns: an in vitro comparison of the silicone replica technique, direct view, and 3-dimensional superimposition analysis. J Prosthet Dent. 2021;S0022-3913(21)00419-4.

69. Kılıçarslan MA. Micro-CT evaluation of the marginal and internal fit of crown and inlay restorations fabricated via different digital scanners belonging to the same CAD-CAM system. Int J Prosthodont. 2021;34:381-9.

70. Krasanaki ME, Pelekanos S, Andreiotelli M, Koutayas SO, Eliades G. X-ray microtomographic evaluation of the influence of two preparation types on marginal fit of CAD/CAM alumina copings: a pilot study. Int J Prosthodont. 2012;25:170-2.

71. Rungruanganunt P, Kelly JR, Adams DJ. Two imaging techniques for 3D quantification of pre-cementation space for CAD/CAM crowns. J Dent. 2010;38:995-1000.

72. Seo D, Yi Y, Roh B. The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns. J Dent. 2009;37:374-82.

73. Rudolph H, Luthardt RG, Walter MH. Computer-aided analysis of the influence of digitizing and surfacing on the accuracy in dental CAD/CAM technology. Comput Biol Med. 2007;37:579-87.

## SUPPORTING INFORMATION

Additional supporting information can be found online in the Supporting Information section at the end of this article.

**How to cite this article:** Bandiaky ON, Clouet R, Le Bars P, Soueidan A, Le Guehennec L. Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study. J Prosthodont. 2023;32:846-853.
https://doi.org/10.1111/jopr.13639