November 11, 2022
by Bo Huang, DMD, MSc, PhD, MSc (Prosthodontics), FRCD(C); Mark Lin, BSc, DDS, MSc (Prosthodontics), FRCD(C)
Modern oral implantology requires comprehensive diagnosis, intricate planning, and precise execution to achieve desired prosthetic and functional outcomes to meet patients’ and clinicians’ expectations. In this context, digital dentistry has been adopted as an excellent service, especially for complicated full-mouth rehabilitation cases, to which the implant all-on-6 concept has become an established treatment option. The all-on-6 technique commonly involves teeth removal, alveoloplasty, immediate implant placement and immediate temporalization. Update streamlining digital workflow, “Smile in a box”, allows clinician to virtually pre-plan the prosthesis, surgery, and conversion, which not only helps foreseeing potential surgical and prosthetic limitations and problems prior to surgical intervention, but also can predictably reduce chairside time and adjustments at the surgical and temporalization appointment. This case report demonstrates detailed digital and surgical workflow of “Smile in a Box” (Straumann) to elaborate how to maximize the benefit gained from digital workflow to improve efficiency and accuracy of clinicians and dental laboratory technicians.
Implant therapy, in modern dentistry, has become a highly predictable and widespread treatment option to replace missing teeth in complete edentulous patients.1 A common treatment option for edentulous patients is a complete fixed dental prosthesis supported by more than 4 implants.2,3 The two distal implants are usually tilted to overcome the challenges of insufficient bone volume, to avoid vital anatomical structures and to reduce the length of distal cantilevers.4 According to the tilted implant positioning protocol, a total of 4 to 6 implants might be sufficient to support a complete-arch, implant-supported prosthesis effectively. This treatment is commonly called All-on-4/6.
Although All-on-4/6 implant treatments are widely reported with high success rate, they are not free of complications.3,5 The most common short-term complications are surgical related including infection, nerve damage, lack of primary implant stability, injuries to adjacent teeth and intraoral hemorrhage etc. and unsatisfied aaesthetics.6 In recent years, advanced digital technologies such as digital 3-dimensional (3D) imaging, virtual tooth set up and computer-guided implant planning have been well adopted and widely promoted to reduce aforementioned complications.7 The virtual teeth wax up which are usually a Standard Tessellation Language (STL) file format can be merged with cone beam computed tomography (CBCT) as a Digital Imaging and Communication in Medicine (DICOM) file in implant planning software.8,9 Then, based on the planned teeth position, computer-aided design/computer-aided manufacturing (CAD/CAM) surgical guides can be fabricated to facilitate implants placement in more accurate, efficient and “restorative-driven” ways.7,8 Therefore, it significantly reduced surgical and aesthetics complications that allows more predictable biological and aesthetics outcomes. In addition, based on the pre-planned teeth set up, the provisional prosthesis can be fabricated pre-surgically through additive or subtractive CAD-CAM technology and be inserted at same appointment to reduce chairside time and improve patient’s acceptance.
The update streamlining workflow, “Smile in a box” has combined current advanced digital and manufacturing technologies. The present paper aims to provide a comprehensive overview of the workflow to discuss and critically assess the surgical and prosthetic outcomes, and the factors determining the reliability of current technologies.
A 70-year-old male presented with mandibular terminal dentition (Fig. 1) seeking fixed solutions to replace missing and hopeless teeth, to improve chewing function and aaesthetics. Patient’s condition is characterized by full-arch implant-supported fixed prosthesis in maxilla, multiple missing teeth in mandible and non-restorable remaining mandibular teeth due to compromised tooth structure and severe mobility. The prognosis of residual teeth is poor to hopeless. After discussing different treatment options, the decision was made to extract the remaining mandibular teeth and place 6 implants in the mandible to support a fixed full-arch prosthesis.
During consultation, patient’s maxillary prosthesis was assessed for aesthetics, phonetics, and function. If additive changes are necessary, perform a direct mock-up for the maxillary prosthesis with composite resin to facilitate the determination of incisal edge position, midline, and occlusal plane inclination. Since the maxillary prothesis was deemed sufficient, the mandibular prosthesis would be designed to match opposing dentition. Occlusal vertical dimension (VDO) was held by maxillary prosthesis and remaining mandibular teeth based on the assessment of facial appearance, phonetics, and physiologic rest position, so the VDO was recorded at current position. Otherwise, if VDO is collapsed, it should be restored and recorded by occlusal wax rim, leaf gauge, or anterior deprogrammer based on established prosthodontic guidelines.7,10
Mandibular partially edentulous arche was scanned by an intraoral scanner (TRIOS® 3, 3Shape A/S, Copenhagen, Denmark) without direct mock-up. The maxillomandibular relationship at the CR position was digitally registered with the same intraoral scanner. Both scans were saved as STL files. Facial frontal photographs (same angle and distance) with the patient in retraction and with smile were taken and saved as JPEG files for future virtual teeth set up.
Mandibular arch was also scanned by CBCT which generated DICOM files. The resultant DICOM files were imported into commercially available software (co-Diagnostix®, Dental Wings GmbH, Dusseldorf, Germany) and superimposed with STL files using remaining teeth as references to obtain the maxilla/mandible relationship, VDO and aesthetics reference points. Then, the JPEG photograph files were superimposed to perform facially driven digital diagnostic teeth set-up based on the facial and intraoral measurements.
The virtual teeth set up was assessed and reviewed by clinician and patient. After the approval was gained, prosthetically driven implant planning can be achieved by using implant planning software (co-Diagnostix®, Dental Wings GmbH, Dusseldorf, Germany). Then, a series of stackable surgical templates (Smile-in-a-Box concept, Institute Straumann AG, Basel, Switzerland) were printed as surgical guides (Fig. 2). In addition, temporary teeth can also be fabricated with open channels at planned implant position to facilitate chairside pick-up (Fig. 2).
In order to gain adequate intraoral space to facilitate guided implant surgery, maxillary implant-supported fixed prosthesis was removed. In the mandible, the remaining teeth were reference for the seating of the first surgical template, which was then secured with 5 anchor pins (Figs. 3 and 4). After removing the stackable portion of first guide, second template was stacked on the same anchor pin which was used for bone reduction (Fig. 5). Once alveoloplasty was completed, the third surgical guide was positioned on top of the second one for guided implant placement (Fig. 5). After implant placement, the third template was removed, and a prefabricated 3D printed interim prosthesis was positioned on top of the second template with opening clearance in the areas of the placed implants to accommodate temporary abutments for the conversion of the prosthesis (Fig. 6). Temporary implant abutments were connected to the multi-unit abutments (SRA, Institute Straumann AG, Basel, Switzerland) and rubber dam was used to isolate the underlying soft tissue (Fig. 6).
Poly(methylmethacrylate) (PMMA) acrylic resin was injected to pick-up the temporary abutments (denture conversion technique) and convert the denture into screw-retained fixed interim prosthesis (Fig. 7). Minor occlusal adjustments were performed and then the interim prosthesis was polished.
In general, patient had positive feedback comparing to the surgical and prosthetic experience of his maxillary restoration. Improved comfort was reported by the patient due to reduced surgical and recovering time, which also decreased the risk of post-surgical complications such as infection and bleeding etc. In addition, higher aesthetics satisfaction was also reported by the patient due to several contributing factors. First, the prosthesis was pre-designed and approved by both patient and clinician. Secondly, accurate implant placement allows minimal chairside adjustment and build up which preserve the prosthesis integrity. In the current case, no occlusion adjustment was required after insertion. Minimal chairside adjustment was required to correct opening which caused by slight surgical deviations (Fig. 6). If a major misfit of the PMMA prosthesis prototype is observed, the prototype can be sectioned and reconnected intraorally. In the future, adjusted prototype can be rescanned and milled into a definitive zirconia prosthesis to eliminate teeth try in appointments.
Although digital workflow brought profound improvements to implant dentistry, there are still limitations. Appropriate case selection is critical. In addition to contraindications for implant therapies,11,12 limited mouth opening should be considered as a limitation with guided implant placement. The assessment should be completed during clinical examination and diagnostic wax-up stage to confirm the feasibility of intraoral fit of the surgical guide and instruments. In addition to confined intraoral space, patient movement and the presence of blood and saliva were considered as contributing factors of the inaccurate implant placement.13 Previous publications demonstrated mean deviations of 1.09 mm at the entry point, 1.28 mm at the apex and 3.9° in angulation.14 These deviations need to be considered at treatment planning and execution stages to avoid violating anatomical structure and preparing for minor adjustment of prefabricated temporary prosthesis.
Flat complete edentulous ridge is considered as relative limitation since it may cause inadequate seating reference for first surgical guide, which may cause inaccurate anchor pin position leading to inaccurate implant placement. In this case, bone-supported surgical guide is recommended , instead of tissue-supported, and should be pre-planned based on CBCT DICOM file.15
Limitations of the present digital protocol include the operator’s experience with treatment planning and software designing. If current teeth display or skeletal occlusion is not ideal to determine VDO, occlusal plane or tooth alignment, then extra clinical steps are necessary to aid the treatment planning, such as direct mock up, extraction of certain teeth and/or fabrication of interim prosthesis. To transfer the intraoral situation into software design, “superimposition” of intraoral presentation (STL file from intraoral scanning of mock up or interim prosthesis) to anatomical structures (CBCT file of bone, teeth, or guide) is essential. If the clinician misaligns the CBCT and STL file, the subsequent treatment planning and surgical steps will be negatively affected. Another limitation of the present technique is the lack of effective virtual facebow, which can register the hinge axis and antero-posterior inclination of the occlusal plane in the virtual articulator prior to digital teeth set-up.
The primary advantage of “Smile in a Box” is all the necessary information for accurate implant placement leading to pre-approved aesthetics outcome is acquired pre-surgically, which allows for reduction of chairside time, reduction of cost, optimization of clinical prosthodontic procedures and improvement of patient satisfaction with reduction of treatment time. In addition, its planning workflow has been simplified and modified based on previous feedback. And, technical support is well-established by lab technician and company, which significantly reduces learning curve for fresh exposed clinician.
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About the Authors
Bo Huang is an assistant professor at the Faculty of Dentistry, University of Toronto. She had been a practising dentist in China after earning her DMD at the Air Force Medicine University (formerly known as the Fourth Military Medicine University) in Xian and her Master of Science degree at Peking University in Beijing, China. After immigrating to Canada, Dr. Huang completed her PhD in biomaterials at University of Toronto.
Mark Lin completed his dental program at University of Detroit Mercy, then a one-year General Practice Residency program at the Miami Valley Hospital in Dayton, OH. He completed his post-graduate training in prosthodontics at the University of Toronto. He maintains a full-time specialty practice at Dr. Mark Lin Prosthodontic Centre.