Digital Three-Dimensional Visualization of Intrabony Periodontal Defects for Surgical Planning (Pilot Case Study)

Background: In the regenerative treatment of intrabony periodontal defects, surgical strategies are determined by defect morphologies. Clinical direct measurements and intraoral radiographs are the main tools in periodontal diagnostics and surgical planning, however in certain cases they don’t provide sucient amount of information. Therefore, the application of cone-beam computed tomography (CBCT) in diagnosis and treatment planning of periodontally involved patients has been proposed. The aim of this study is to present a novel method for 3D visualization of intrabony periodontal defects on digital models reconstructed from CBCT datasets for diagnostics and treatment planning. Methods: 4 patients with a total of 6 intrabony periodontal defects were enrolled in the present study. 2 months following initial periodontal treatment CBCT scan is taken. Radiographic image processing (segmentation) of CBCT datasets were performed in a radiographic imaging software to acquire anatomically accurate, virtual three-dimensional polygon models of surgical areas. Intrasurgical and digital measurements were taken, and results were compared, to validate the accuracy of digital models. Results: Difference between intrasurgical- and digital measurements in depth and width of intrabony components of periodontal defects were 0,31±0,21 mm and 0,41±0,44 mm respectively. Conclusion: It can be concluded that, the described digital workow is useful in the treatment of certain periodontal intrabony defect morphologies. However, to determine the exact use cases of such technology further studies and examination is necessary.


Background
Regenerative treatment of periodontal defects was rst published in the early 1980's (Nyman et al. 1982), but the concept of a new periodontal attachment formation in intrabony periodontal defects was emphasized from the 1970's (Melcher 1976). Since the rst concepts on regenerative periodontal therapy, many different approaches have been introduced to achieve periodontal regeneration. The introduction of various biomaterials has made regenerative surgery more predictable and more straightforward. Applied surgical modalities and regenerative strategies are determined by the morphology and the extent of the intrabony defect. Decision-trees (Cortellini 2012), described in the literature provide treatment options for different clinical scenarios.
Defect morphology is determined by (i) direct clinical measurements (probing pocket depth: PPD, gingival recession: GR, clinical attachment loss: CAL) and (ii) two-dimensional (2D) radiographic images (intraoral radiographs: IR, and panoramic x-rays: PX). These tools are used for diagnostics and treatment planning of periodontally involved patients. The aforementioned methods are considered the gold standard in periodontal diagnostics, however there are a few drawbacks and in certain cases they don't provide su cient amount of information. Clinical studies have demonstrated, that clinicians constantly underestimated the extent of intrabony defects during direct clinical measurements (Eickholz et al. 1998, Vrotsos 1999, Christiaens 2018. IRs provide two-dimensional (2D) image, where overlapping anatomical structures make it di cult to accurately determine the true three-dimensional (3D) defect morphology (Eickholz et al. 1998, Christiaens 2018  Various surgical elds in general medicine such as: cardiac surgery, orthopedic surgery and craniomaxillofacial surgery have utilized different radiographic image segmentation techniques to create patient speci c digital three-dimensional anatomical renders and 3D printed models for diagnostics and treatment planning.
Aim of this study is to present a method for 3D visualization of intrabony periodontal defects with the help of virtual, patients speci c models reconstructed from CBCT datasets and to evaluate the accuracy of the models, by comparing the results with direct intrasurgical measurements.

Methods
Patient selection and Image Acquisition 4 patients with 6 intrabony periodontal defects were enrolled in this preliminary study. Selected patients were diagnosed with Stage III/ Grade B periodontitis and were in need of complex perio-prosthetic rehabilitation. 2 months following initial periodontal treatment, CBCT scans were taken with I-CAT FLX® (KaVo Dental GmbH, Bieberach an der Riß, Germany) /300 µm voxel size; 120 kV anode voltage; 36 mA xray tube current/. In all cases prosthetic rehabilitation of all patients was planned with implant retained xed partial dentures (FPD). To acquire the best possible image quality, all metal restorations, that would be changed during the treatment were removed. If the patient had permanent metal restoration and implants, metal artifact reduction was applied. To reduce scatter at the occlusal plane, patients were instructed to bite on cotton rolls. The study was conducted with full accordance to the declaration of Helsinki (2008) and were approved by the local ethical committee (Semmelweis University Regional and  Table 1.   Table 2.  Table 3. . But application of radiographic image processing and creation of anatomically accurate 3D models of periodontal defects has never been proposed. The biggest drawback of computed tomography compared to conventional radiographic methods is the increased radiation dose and unprocessed CBCT images give relatively little additional information compared to conventional radiographic methods. Therefore, the increased radiation dose is di cult to justify. This novel method for radiographic image processing in periodontal diagnostics allows for clinicians to view periodontal defects in 3D, rotate the models, zoom in and out, measure distances and plan surgeries more precisely. If necessary, the models can be produced with additive manufacturing techniques.
This pilot study demonstrated that digital models created with this novel semi-automatic segmentation method represent an accurate clinical situation. Differences between intrasurgical and digital measurements were minor and did not have any clinical relevance. However, for further evaluation of this process prospective case study has to be carried out.
Utilizing anatomic 3D models of hard tissues is a useful tool in periodontal diagnostics, because clinicianares able to see the three-dimensional morphology of intrabony periodontal defects. However, not every case requires the application of CBCT based segmentation. Conventional diagnostic tools (direct clinical measurements, IRs) should still be the number one method in treatment planning of periodontal regenerative surgery however, if these aforementioned methods do not provide su cient amount of information, this novel digital method can be utilized as a third diagnostic modality.
To further expand on the concept of applying computer assisted technologies in periodontology, the method can help to create a digital work ow in periodontal regenerative surgery. Digital technologies can be utilized during surgical procedures, as well as in 3D postoperative evaluation. Individualized, 3Dprinted stents can be used during surgical intervention as passive guides (Lei et al. 2019). With 3D bioprinting technologies defect speci c implants can be used as grafting material (Rasperini et al. 2015).
Digital models on the other hand can also be uploaded into an augmented reality (AR) setup and be used with an AR headset (Pellegrino et al. 2019), to further increase the visualization of the surgical eld.

Conclusions
It can be concluded that, the described digital work ow is a usefuldiagnostic modality in the treatment of certain periodontal intrabony defects. However, to determine the exact use cases of such technology further studies and examination is necessary. With the aid of digital, anatomical models, intraoperative tools and postoperative validation methods can be developed to further expand the digital work ow in periodontal surgery. Patients participating in the study were fully informed and were given written consent to the participation.

Consent for publication
The identifying images and other personal or clinical details of participants are presented without compromising anonymity.

Availability of data and materials
All data generated or analyzed during this study are included in this article.

Competing interests
Francesco Guido Mangano (Associate Editor) and Peter Windisch are members of BMC Oral Health editorial board. The authors declare that they have no competing interests.  Regenerative periodontal surgery. 5a: Palatal single ap approach 5b: Volume stable collagen matrix (Fibroguide®) 5c: Enamel matrix derivatives placed into the defect 5d-e: Collagen matrix placed into the defect 5f: Double layer wound closure Comparing intrasurgical measurements with digital measurements. 6a: Intrasurgical measurement 6b: Digital measurement