Effect of the level of alveolar atrophy on implant placement accuracy in guided surgery for full-arch restorations supported by four implants: An in vitro study

doi:10.21203/rs.3.rs-2830650/v1

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Research Article

Effect of the level of alveolar atrophy on implant placement accuracy in guided surgery for full-arch restorations supported by four implants: An in vitro study

https://doi.org/10.21203/rs.3.rs-2830650/v1

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Journal Publication

published 30 Aug, 2023

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Background

Fixed screw-retained full-arch restoration supported by four implants is a popular treatment option for edentulous arches. Optimal alignment of implants is quite challenging in extremely atrophied edentulous cases, and a small amount of deviation is expected during guided surgery. This study aimed to compare implant accuracy among edentulous jaws with various levels of atrophy.

Methods

Five separate copies of each Cawood model (III–V) were produced for the maxilla and mandible. A total of 120 implants were placed (30 models). The implant accuracy was assessed based on angular deviations at the base (angle, 3D offset, distal, vestibular, and apical) and tip (3D offset, distal, vestibular, and apical).

Results

The atrophy level of the jaws had a statistically significant effect on deviation; implants showed greater deviation from the planned location as the atrophy level increased.

Conclusion

Given that implant deviation increased with the degree of atrophy, a greater safety margin from important anatomical structures is recommended when planning implant location for guided surgery in Cawood V cases.

dental implant

computer-aided designs

CAD-CAM

edentulous jaw

bone screws

atrophy

Placement of dental implants in cases with limited alveolar bone volume is quite difficult. Cross-arch fixed dental prostheses, supported by four implants, are widely used for atrophied edentulous jaws. Efficient use of the existing bone is important; in this respect, 3D implant planning and guided surgery could be advantageous [1, 2].

Judicious intraoperative decision-making during implant site preparation is critical in cases of limited alveolar bone volume because of the proximity of important anatomical structures to the atrophied alveolar bone. There is a risk of inferior alveolar nerve damage and maxillary sinus membrane perforation. Use of longer implants that extend to the cortical borders of the alveolar bone is preferable to ensure bicortical anchorage and immediate stability to allow loading. In this scenario, guided surgery could be useful for placing implants [3, 4]; however, a small amount of deviation can occur even during guided surgery. The deviation between the planned and actual implant positions might cause problems in cases of bone atrophy, which can undermine adaptation and complicate the use of surgical guides. Various factors affecting the accuracy of guided surgery have been investigated, including the flap approach, type of support (tooth/mucosa), template position, fixation method, fabrication process, and implant insertion protocols [5, 6]. However, the effect of atrophy on guided surgery itself has not been investigated despite its frequent occurrence.

This study aimed to compare the accuracy of axial and tilted implants, placed via guided surgery, according to the atrophy level of edentulous jaws. To our knowledge, this is the first study to investigate the effects of atrophy on implant accuracy.

The study was designed to evaluate the in vitro accuracy of implant placement. Approval was obtained from our University Faculty of Dentistry Ethical Committee (approval no. 2018/157). Digital Imaging and Communication in Medicine (DICOM) data of a real clinical case were used to produce the base model. Materialise Mimics (Materialise Medical Software, Leuven, Belgium) was used to obtain standard tessellation language (STL) data. Input parameters were between 226 and 3,071 Hounsfield units. In the 3D models, maxillary and mandibular regions were distinguished.

Meshmixer software (Autodesk, Mill Valley, CA, USA) was used to derive maxillary and mandibular models. The Cawood and Howell classification was used to differentiate among levels of atrophy [7]. Cawood III–V residual ridge types were designed for both the maxillary and mandibular models. Additionally, 3-mm molds of the gums were designed, and silicone was poured into these molds. Digital light processing technology (Moonray S 3D printer; Sprintray, Los Angeles, CA, USA) was used to print five copies of each design for the maxilla and mandible. RTV-2 silicone rubber was used for the gum model.

The sample size was calculated with G*Power software (ver. 3.1.3; Heinrich-Heine Universität, Düsseldorf, Germany) based on an alpha value of 0.05 and statistical power of 90%. A sample size of 120 implants was required (20 implants per group). Five copies of each Cawood model (III–V) were reproduced for the maxilla and mandible. In total, 30 models were produced (Fig. 1).

Three 2.4-mm screws were placed to demarcate the anterior midline and posterior lateral lines on each side of the model. Computer-aided design/computer-aided manufacturing (CAD-CAM) wax (MarmoScan; Siladent, Goslar, Germany) was used to cover the screw heads and facilitate recognition during optical scanning (Fig. 2). Cone-beam computed tomography (CBCT) (Planmeca, Helsinki, Finland) scans of all models were obtained. White CAD-CAM spray (Dr. Mat, Istanbul, Turkey) was applied to the models to obtain higher-quality scans. The scanned gingival surface texture was transferred to the software of the NeWay optical 3D scanner (Open Technologies, Rezzato, Italy) (Fig. 3).

coDiagnostiX software (Dental Wings Inc., Montreal, Canada) was used for implant planning and designing surgical guides. The radiopaque wax-covered screw heads were used for accurate superposition of the STL and DICOM data. After segmentation and marking of anatomical landmarks, virtual implants were positioned considering the available bone volume. Straumann (Basel, Switzerland) bone-level tapered implants (3.3 mm × 12 mm) were used in all regions. Four implants (two axial and two tilted) were planned in all models. In the mandibular models, the axial implants were located close to teeth #32 and #42. Two posterior angulated implants were positioned in front of the mental foramen at an approximately 30° angle. In the maxillary models, the axial implants were located close to teeth #12 and #22. Posterior angulated implants were placed in front of the anterior maxillary sinus wall at an approximately 30° angle. A constant anterior-posterior distance was maintained between the virtual implants. The surgical guide was designed using a sleeve 5.0 mm in diameter and height. The guide design was sent to the laboratory and printed using the CARES P30 printer (Straumann). The entire process, from implant planning to surgical guide design, was overseen by a Straumann digital product consultant (Fig. 4).

Surgical guides were fixed to the models using three pins passed through the sleeves (1.3 × 28 mm). The implants were placed in accordance with the recommended surgical protocol. Following implant placement, CBCT scans of the models were obtained. DICOM data were used to assess deviation from the planned locations. Marker screws were used for superimposition. The comparison module of the coDiagnostiX software was used for the assessment. Positional accuracy was evaluated by comparing the virtually planned and actual implant positions (Fig. 4). The implant placement accuracy was assessed based on angular deviations at the base [angle (A), 3D offset (B3D), distal (BD), vestibular (BV), and apical (BA)] and tip [3D offset (A3D), distal (AD), vestibular (AV), and apical (AA)].

Statistical analysis was performed using SPSS Statistics software (version 23.0; IBM Corp., Armonk, NY, USA). A two-way analysis of variance was conducted for analysis of jaw shape and region. Multiple comparisons were made using the Duncan test. The quantitative data are presented as mean ± standard deviation. Statistical significance was set at p < 0.05.

There was a statistically significant effect of atrophy level on BV, BA, BD, AV, AA, and AD (p < 0.001). This significant result was due to higher average values for Cawood V than for Cawood III ridges (Table 1).

The atrophy level and region (maxilla or mandible) had statistically significant effects on BA, BD, AA, and A (p < 0.001). The highest mean BA value was 1.04 for the implant at site 32 in the Cawood V model, while the lowest mean BA was 0.43 for the implant at site 45 in the Cawood III model. The highest mean BD was 1.13 for the implant at site 32 in the Cawood V model, while the lowest mean BD was 0.62 for the implants at sites 32 and 42 in the Cawood III model. The highest mean AA was 1.02 for the implant number at site 34 (Cawood V model), while the lowest mean AA was 0.4 for the implant at site 42 (Cawood III model). The highest mean A was 2.74 for the implant at site 44 (Cawood V model), while the lowest mean value was 1.52 for the implant at site 32 (Cawood III model). Implant location had no statistically significant effect on any parameter (Tables 2 and 3).

For clinical improvements in planning, design, and implementation, it is necessary to understand the limitations of each step of guided implant surgery to identify the reason for implant deviation from the planned position [8].

Careful positioning of implants near important anatomical structures and achieving immediate stability is important. In these respects, guided surgeries are facilitative, although deviations from the planned implant position still occur [9]. It is therefore important to analyze the factors that may increase this deviation. Deviations may be caused by errors during examination, planning, or surgery [5]. To minimize these errors, their origins must be identified [10]. Patient movement during the acquisition of 3D images may lead to image distortion, which can cause significant deviations at the apex and hex implant levels [11]. The thickness of the mucosa and the large maxillary surface area, which provides support for the surgical guide, can influence implant stability and placement accuracy [12]. It has been reported that tooth-supported guides provide better results than mucosa- and bone-supported guides [13]. The surgical technique, guide type, and implant position may also affect the accuracy of guided implant placement [14]. In our study, all other factors were controlled for, and only the effect of atrophy on deviation was examined.

Studies have shown that bone density can affect implant placement accuracy [15]. The degree of atrophy is related to bone density. As this was an in vitro study, it was not possible to assess the relationship between bone density and the extent of atrophy, which was a limitation of our study. However, all factors were controlled for except for the atrophy level. All planning and surgeries were performed by the same individuals; all implants had the same diameter, length, and design; the same software was used throughout; and all models and guides were fabricated using the same 3D printer and resin. Therefore, the bone density can be considered consistent among all evaluations. The factors that we controlled for could not have been controlled in clinical studies [16, 17].

Various methods of evaluating implant deviations have been reported in the current literature. Direct comparison of the planned and actual implant locations was performed by superimposing the CBCT images or by transferring the implant positions to the software environment with the help of abutments [18]. Although comparison of pre- and post-procedure tomograms is useful, an additional tomogram is required specifically to measure implant deviation, which might be an ethical issue in clinical studies. However, this was not an issue in our in vitro study.

The effects of various factors on implant placement accuracy have been extensively investigated. Yeung et al. measured the placement accuracy with three implant systems [19]. They reported mean implant displacements of 0.02 ± 0.13 mm mesially, 0.07 ± 0.14 mm distally, 0.43 ± 0.57 mm labially, 1.26 ± 0.80 mm palatally, 1.20 ± 3.01 mm vertically in the mesiodistal dimension, 0.69 ± 2.03 mm vertically in the labio-palatal dimension, 1.69 ± 1.02° in terms of mesiodistal angulation, and 1.56 ± 0.92° in terms of labio-palatal angulation. The average displacements were similar between our study and a previous study [19]. An important issue for guided surgery in edentulous cases is the difficulty in accurately transferring mucosal thickness data into the software environment because of the lack of radiopaque structures (such as teeth) to guide superimposition [20]. In general, scans are used to estimate gingival thickness. In our study, we aimed to overcome the problem of transferring mucosal thickness data into the software environment by using screws as a guide. This approach can increase accuracy; we obtained satisfactory outcomes in terms of implant deviation, similar to those of implants placed using tooth-supported guides [21].

The maxillary surface area is wider than the mandible and provides greater support for surgical guides; this might enhance implant placement accuracy and stability [22]. However, the degree decreases with the progression of bone atrophy over time. In our study, implant deviations increased with increasing atrophy. However, no statistically significant difference was observed between the maxillary and mandibular implant deviations.

We found that the level of alveolar atrophy was significantly associated with implant deviation. Some degree of deviation from the planned implant position is to be expected. The deviation observed in our study was similar to that observed in other studies. The outcomes were particularly similar to those of surgeries using tooth-supported guides. This could be due to our use of screws as a guide. Further studies on the clinical applications of these “superimposed screws” are merited.

In our study, no significant difference was observed in implant deviation between the upper and lower jaws. However, implant deviation increased with the degree of atrophy. Therefore, when planning the implant locations for guided surgery in Cawood V cases, a greater safety margin from important anatomical structures should be used. As this study was performed in vitro, further clinical studies are required on this subject.

Acknowledgments

None

Funding

This study supported by Straumann Turkey.

Author contributions

All authors contributed extensively to the work presented in this paper. GG, AB, FB conceptualized the study. GG, FB performed formal analysis and investigation. GG, AB, FB drafted and wrote the manusucript. All authors read and approved the final version of the manuscript.

Conflict of Interest

The authors have stated explicitly that there are no conflicts of interest to disclose in connection with this article.

Ethical Approval

This study was obtained by Marmara University Faculty of Dentistry Ethical Committee (approval no. 2018/157)

Consent for publication

All authors are aware of the publication of this work.

Availability of data and materials

All data generated or analyzed during this study are included in this published article.

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Tables 1 to 3 are available in the Supplementary Files section.

No competing interests reported.

Download PDF

Journal Publication

published 30 Aug, 2023

Read the published version in Head & Face Medicine →

Editorial decision: Major revision
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Reviews received at journal
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Reviewers agreed at journal
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Reviewers agreed at journal
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Reviewers agreed at journal
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Reviewers invited by journal
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Editor assigned by journal
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Submission checks completed at journal
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First submitted to journal
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You are reading this latest preprint version

Effect of the level of alveolar atrophy on implant placement accuracy in guided surgery for full-arch restorations supported by four implants: An in vitro study

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Abstract

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Introduction

Materials And Methods

Results

Discussion

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References

Tables

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Supplementary Files

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