## 3 Discussion  
The current case report presented a novel approach by utilizing digitally designed and additively manufactured, individualized matrices for the restoration of severely destructed and/or subgingival cavities. Laser-sintered individualized matrices serve dual purposes in the current setting. Firstly, due to the individualized design, the matrices are able to follow the natural curvature of the teeth allowing for a gapless fit and a more natural emergence profile of the finalized restoration. Secondly, the wings of the individualized matrices ensure that the rubber dam is held firmly in a slight apical position, therefore an ideal working area can be created for the restorative process. Based upon the so far gathered experience, an individually designed matrix is mainly indicated for the restorative treatment of deep and extensive subgingival cavities or hard tissue destructions not invading the biological width (e.g., grade 1 and grade 2 classifications from [PERSON] et al.) [15]. In any DME procedure, optimal marginal adaptation of restorative materials is crucial for preventing microleakage, ensuring longevity, and maintaining periodontal health, making it essential for clinicians to select materials like lithium disilicate, zirconia, or other advanced ceramics that provide superior adaptation to the tooth structure in order to achieve durable and biologically compatible restorations [27]. To the best of the authors' knowledge, no similar methods can be found in the literature for aiding the DME procedure, although previously, a few articles have described a 3D-guided direct composite restoration method utilizing CAD and 3D printing [28; 29; 30]. However, all of these articles have utilized 3D printed guides in conjunction with direct composite veneers in the upper anterior region. With the above-proposed method, DME or core build-up can be performed in a more reproducible way under adequate isolation ideal for adhesive treatment. 3D printing has been proven to increase the reliability and reproducibility of dental interventions. In different surgical fields, stereolithography (SLA) 3D printing is utilized to manufacture surgical guides that translate the digital plan into surgical practice. Currently, 3D-printed surgical guides are most used in implant dentistry [31], bimaxillary orthognathic surgery [32], and maxillofacial oncological rehabilitation [33]. Other technologies, such as metal SLS 3D printing technology, are most commonly used to manufacture patient-specific implants and customized titanium meshes for vertical guided bone regeneration [34]. In the field of prosthetic dentistry, various 3D printing technologies have recently surfaced for the manufacturing of fixed and removable prostheses [35; 36]; however, the effectiveness of 3D printing compared to subtractive manufacturing (standard of care) is still under debate. Table 1 summarizes the main differences between the use of a prefabricated traditional matrix and a customized matrix. Figure 16: Situation at the 1-year follow-up. (**A**) occlusal view of the final restoration; (**B**) periapical X-ray. Despite the obvious clinical benefits of this method, there are a few shortcomings that have to be addressed and improved in the future. The 3D design process is relatively time-consuming, has a learning curve, and utilizes software that is not specifically meant for this purpose. However, there are alternative solutions. As an option, Blender is a free and open-source 3D computer graphics software tool, which is suitable for creating such matrices. Furthermore, there is a YouTube channel that discusses the direct dental application of the Blender software (Blenderfordental). It is also possible that the design of matrices, like other indirect restorations, would be designed by dental technicians using the software available to them or via Blender. The general management method of the Blender software is also available on YouTube in the form of free videos. This could aid the learning process of designing such individualized matrixes.