Accuracy of tooth‐implant impressions: Comparison of five different techniques

Abstract Purpose To compare the accuracy of five different tooth‐implant impression techniques. Materials and Methods In this in vitro, experimental study, an acrylic model containing one bone‐level Straumann dental implant at the site of maxillary first molar and an adjacent second premolar prepared for a porcelain fused to metal restoration was used. Impressions were made from the model using five different one‐step tooth‐implant impression techniques including scanning with an intraoral scanner, occlusal matrix, wax relief, closed‐tray, and open‐tray techniques. Each technique was repeated 15 times. The impressions were poured with dental stone, and the obtained casts were scanned by a laboratory scanner. The scan file of each technique was compared with the scan file of the original acrylic model by Geomagic Design X software. Data were analyzed by one‐way analysis of variance, and Tamhane's post‐hoc test (α = 0.05). Results For dental implant, intraoral scanning had the highest accuracy (0.1004 mm2) followed by open‐tray (0.1914 mm2), occlusal matrix (0.2101 mm2), closed‐tray (0.2422 mm2), and wax relief (0.2585 mm2) techniques (p < 0.05). For the prepared tooth, wax relief (0.0988 mm2) had the highest accuracy followed by occlusal matrix (0.1211 mm2), open‐tray (0.1663 mm2), closed‐tray (0.1737 mm2), and intraoral scanning (0.4903 mm2) technique (p < 0.05). For both dental implant and prepared tooth, occlusal matrix (0.2431 mm2) had the highest accuracy followed by open‐tray (0.2574 mm2), wax relief (0.2693 mm2), closed‐tray (0.2862 mm2), and intraoral scanning (0.3192 mm2) technique (p > 0.05). Conclusion The compared simultaneous tooth‐implant impression techniques had comparable accuracy with no significant difference.


| INTRODUCTION
Dental impression is a negative or positive imprint of the teeth and adjacent structures for use in dentistry. It is used as a permanent record for the fabrication of restorations or dentures (Alikhasi et al., 2012(Alikhasi et al., , 2015Malik et al., 2018). Impression accuracy can significantly affect the accuracy of the gypsum cast, and the accuracy of the final impression sent to a laboratory plays a fundamental role in marginal adaptation and the internal gap of final restoration (Alikhasi et al., 2012;Malik et al., 2018). Thus, a precise impression is a prerequisite for optimal fit of restoration and treatment success (Malik et al., 2018).
Dental implants are a standard well-accepted modality for replacement of the lost teeth. Long-term success of implantsupported restorations depends not only on implant osseointegration after the surgical phase, but also on durability of osseointegration after prosthetic loading .
To achieve this goal, the restoration framework must have a passive fit on dental implants. Precise impression making from dental implants is one of the influential factors in achieving passive fit (Alikhasi et al., 2015). Inaccurate impressions or prosthetic fabrication can lead to incomplete seating of restoration, which results in insufficient adhesion, microleakage, tooth hypersensitivity, dental caries, need for endodontic treatment, and gingival inflammation (Di Fiore et al., 2019; and inflict delayed pain and discomfort on the patient (Shadmehr et al., 2021). Utilizing digital tools has been lucrative in various fields of dentistry including radiology and prosthodontics. Digital impression systems emerged at the start of the 1980s as Werner Mörmann started to consider how to create one session treatments. The development of digital impression devices with optical reading technologies has therefore begun (Mörmann, 2004(Mörmann, , 2006Mehdizadeh et al., 2023;Rekow, 2006). Comparing digital and traditional impression processes reveals some similarities and differences Amin et al., 2017;Christensen, 2008;Rehmann et al., 2013;Su & Sun, 2016;Wöstmann et al., 2005). A higher number of stages in the conventional impression technique raises the risk of further errors (Alikhasi et al., 2017;Chochlidakis et al., 2016;Ender & Mehl, 2015;Revilla-León et al., 2021;Tomita et al., 2018;Wöstmann et al., 2008). The standardization of the milling stage in the digital impression process, as well as the use of fewer step numbers, reduces the chance of errors and enhances adaptability (Gimenez-Gonzalez et al., 2017;Lin et al., 2015;Papaspyridakos et al., 2016;Wöstmann et al., 2005). In terms of time and physician choice, digital approaches are preferred more (Lee & Gallucci, 2013;Schepke et al., 2015;Yuzbasioglu et al., 2014).
However, to increase the accuracy of implant impressions and minimize misfits in conventional techniques, such as the open-tray and closed-tray techniques have been proposed, which can be adopted depending on the case. For instance, the closed-tray technique is more suitable for cases with limited edentulous space, or difficult placement of impression coping in the posterior region (Burns et al., 2003;Carr, 1991). Although impression technique is an important parameter in accuracy of impressions, impression material is another important factor determining the precision of the final cast. For instance, in the occlusal matrix technique, apical pressure applied to the impression material results in more accurate recording of dental margins. For the direct dental impression technique, the impression material should have two properties: adequate stiffness to prevent the rotation of impression coping in the impression, and optimal dimensional stability (Alikhasi et al., 2012).
In partial edentulism, some clinical scenarios may necessitate simultaneous impression making from both implant and an adjacent prepared tooth. Simultaneous tooth-implant impression techniques decrease the possible errors that may occur during adaptation of final restoration of the prepared tooth and dental implant, save time, and prevent impression material waste.
Thus, it is imperative to adopt an acceptable impression technique with a suitable impression material in terms of dimensional accuracy and recording of details (Alikhasi et al., 2015). In such conditions, a common strategy is to use impression copings and two-phase one-step impression technique. However, this technique does not address the necessary differences in reconstruction of the prepared tooth and dental implant. Thus, several strategies have been proposed to solve this problem: (i) treatment is divided into two phases, and tooth and implant restorations are fabricated separately; (ii) two impression techniques are employed in one-step such that a custom tray for the prepared tooth is filled with impression material and seated on the respective area, and then impression copings are placed, and a second impression is made, which includes the first tray and impression copings; (iii) tooth and dental implant frameworks are fabricated after making separate impressions from each of them, and are tried-in; next, a pick-up impression is made (Chee & Alexander, 1998;Lorenzoni et al., 2000;Rehmann et al., 2013;Wöstmann et al., 2005). Since studies on the accuracy of simultaneous tooth-implant impression techniques are limited, this study aimed to compare the accuracy of five different toothimplant impression techniques.

| MATERIALS AND METHODS
In this in vitro, experimental study, the accuracy of five different one- The sample size was calculated to be 15 in each group based on previous similar studies (Alikhasi et al., 2012(Alikhasi et al., , 2015Malik et al., 2018). A reference phantom model of the maxilla with simulated gingiva, soft tissue, and acrylic teeth (HT207U; Hoss) was used in this study, which included one dental implant at the site of maxillary first molar, and an adjacent second premolar prepared for a porcelain fused to metal restoration. To insert dental implants, an implant hole was prepared parallel to the teeth at the site of the maxillary first molar with 4.1 mm diameter and 12 mm height. A bone-level dental implant (Straumann) was placed in the hole and fixed with autopolymerizing acrylic resin such that the implant surface was at the level of the acrylic surface. Next, impressions were made from the acrylic model with five different techniques as follows ( Figure 1):

Scanning with a digital scanner
An impression coping was placed on the dental implant, and the acrylic model was scanned with a scanner (Omnicam CEREC).
The values were measured and recorded by Sirona Connect version 4.6 software.

Occlusal matrix technique
A putty impression was made from the prepared second premolar, and after setting, the putty was removed and trimmed to the size of the prepared tooth margins.
Next, an open-tray impression coping was placed on the dental implant. Wash material was injected into the putty impression made from the prepared tooth, and the impression was placed over the tooth. Wash material was also injected around the implant and coping with the respective syringes.
Next, a pick-up impression was made with a proper-size prefabricated perforated tray filled with putty and wash material.

Wax relief technique
After placing the open-tray impression coping, it was relieved with two layers of red dental wax. Next, a suitable prefabricated tray was used to make a putty impression from the tooth and implant. After the setting of putty, the wax around the coping was removed. Wash material was injected into the tray, and around the tooth and implant, and an impression was made.

Closed-tray technique
The impression coping of closed-tray technique was placed, and a putty impression was made. Wash material was injected into the putty impression and around the tooth and implant, and an impression was made.

Simultaneous one-step tooth-implant impression technique
After the placement of open-tray impression coping, wash material was injected around the tooth and implant. Putty and wash material were also applied in the tray, and a one-step impression was obtained from the tooth and implant.
All impressions were poured with type 4 dental stone (Vel-Mix). The obtained gypsum casts and the acrylic model were scanned by a laboratory scanner, and the data were recorded.
All scan files of the casts in STL format were superimposed on the gold standard file through central and lateral fossae ( Figure 2).
Next, for better comparison of casts, the implant and prepared tooth areas were cut out of the master cast, and trimmed for more accurate comparison. The casts were compared with the gold standard cast using Geomagic Design X software (Oqton). Accordingly, the mean difference in adaptation of different cast areas with the gold standard was calculated in square millimeters (mm 2 ), and reported in three

| Prepared tooth impressions
Among the prepared tooth impression techniques, wax relief had the highest accuracy followed by occlusal matrix, open-tray, closed-tray, and intraoral scanning (p < 0.05; Table 1).
The Shapiro-Wilk test showed normal distribution of data.
Considering the nonhomogeneity of variances, one-way ANOVA was applied to compare the accuracy of different techniques within each group, which revealed a significant difference among the five impression techniques for dental implant alone (p < 0.001) and also for prepared teeth alone (p < 0.001). However, the difference in the accuracy of the five techniques was not significant for simultaneous tooth-implant category (p = 0.094).
F I G U R E 4 Comparison of occlusal matrix cast and the gold standard for prepared teeth alone.
F I G U R E 5 Comparison of occlusal matrix cast and the gold standard for both implant and prepared tooth.

| DISCUSSION
Since studies on the accuracy of simultaneous tooth-implant impression techniques are limited, this study aimed to compare the accuracy of five different tooth-implant impression techniques.
Precision of each impression method is influenced by a number of aspects, including perfect manipulation of impression materials, materials utilized for impression creation, materials used for pouring dental stone, and suitable timing of cast fabrications (Corrente et al., 1995;Daoudi et al., 2001;Hiochwald, 1991;Kupeyan & Lang, 1995;Phillips et al., 1994;Tomita et al., 2018). To evaluate the accuracy of each impression technique in this investigation, a single material (except for intraoral scanning) and all previously indicated criteria were employed. Putty-wash impression material has qualities that make it a good choice for implant impressions, including exceptional dimensional stability, enhanced accuracy, and replication of fine features (Craig, 1989). Nonetheless, the intraoral scanner and the related software used in this comparison is an accurate and effective intraoral scanner setting (Yuzbasioglu et al., 2014). The results showed that for dental implants alone, intraoral scanning had  Also, the accuracy of different impression techniques should be compared using a higher number of prepared teeth and dental implants.

| CONCLUSION
The compared tooth-implant impression techniques had comparable accuracy with no significant difference. For dental implants alone, digital scanning had the highest and wax relief had the lowest accuracy, while for prepared teeth, wax relief had the highest and digital scanning had the lowest accuracy.

AUTHOR CONTRIBUTIONS
Amirhossein Fathi conceived and designed the study, collected and analyzed the data, and wrote the initial draft of the manuscript.
Mansour Rismanchian contributed to the study design, performed data analysis, and revised the manuscript critically for important intellectual content. Atousa Yazdekhasti contributed to the acquisition and interpretation of data, provided technical support, and revised the manuscript critically for important intellectual content.
Masih Salamati contributed to the interpretation of the data, provided scientific and editorial guidance, and revised the manuscript critically for important intellectual content. All authors approved the final version of the manuscript for submission and take responsibility for the integrity of the work as a whole.

CONFLICT OF INTEREST STATEMENT
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.