Inside Dental Technology
April 2021
Volume 12, Issue 4


Collaborative benefits of a detailed diagnostic approach

By Ryan Tak On Tse, BDS, and Edward Tam, BDS


This case report discusses the case of an elderly gentleman who desired a fixed implant prosthesis to replace his failing dentition and tooth-supported fixed and removable appliances. The combined use of a Kois dentofacial analyzer, Kois facial reference glasses, intraoral scans, and cone-beam computed tomography (CBCT) scans enabled the dental team to plan and complete the implant case digitally and fulfill the patient's desired outcome.

Clinical Case Overview



Diagnosis and Risk Assessment


From the laboratory's perspective, the primary periodontal issue with a full-arch prosthesis is whether the patient can clean underneath the fixed implant bridge. In some cases, a removable option such as an overdenture may need to be considered. In this case, a high-performance polymer was chosen, partly because of its biocompatibility and ability to maintain periodontal health.

The patient's biomechanical risk was assessed as high and his prognosis poor, as he presented with multiple carious lesions. His missing teeth were lost because of caries.

Functionally, the patient did not have adequate natural dentition for mastication, and because of the failing restorative appliances his chewing was gradually becoming compromised. There were no detectable neuromuscular or joint pathologies or complaints at the time of examination. Although his function was diagnosed as acceptable, the potential for loss of function due to his dentition and restorative treatment failing over time was notable. The functional risk was assessed as moderate, and the prognosis was poor.

With the functional diagnosis, the laboratory needs to consider:

• the likely loading requirement on the framework and therefore the choice of material of the framework and crowns;

• the amount of occlusal clearance so the type of prostheses and material are suitable;

• the anterior guidance and the cuspal incline of the crown;

• the possible wear if the patient has paranormal function;

• and the opposing dentition and materials.

Dentofacially, with the patient smiling, the maxillary gingival margins were not visible. However, the patient's mandibular teeth Nos. 27 through 31 (No. 30 being a pontic) were supererupted and fully visible in the patient's smile (Figure 3). The dentofacial risk was assessed as high and the prognosis poor.

From the laboratory's perspective, the position of the incisors particularly affects where the access holes of the implant connection may come out, so that should be considered at the planning stage. It is also important to determine and communicate the vertical dimension of occlusion (VDO) and anterior occlusal plane (ie, the incisors' vertical and horizontal positions in relation to the lips).

The team planned the case from the position of the incisal edge and lip dynamics. This is significantly different from the old "bone-driven" approach; conversely, the "restorative-driven" approach allows the team to plan the esthetics from the beginning. This helps to decide how much bone to reduce, where the transition zone is, whether/how much pink porcelain is required, and what material is best for the final prosthesis.

In order to optimize treatment outcomes, the clinician should be well-informed regarding laboratory procedures and materials, including limitations, advantages, and disadvantages. Similarly, technicians need to understand the clinical situation well to alert dentists to potential problems and address them while the case is still being planned. When technicians are only involved after implant placement, the restorative options are limited. By using the approach detailed above, the entire restorative team can plan the case together; in this case, the prosthodontist was also the surgeon, and two laboratories were involved (one for the fabrication of the surgical guide and temporary prosthesis, and one for the final prosthesis).

Treatment Plan


Phase 1: Dentofacial Analysis







Phase 2: Data Gathering and Digital Planning

For the digital treatment plan, four image layers were superimposed (ie, merged). The DSD Planning Center provided the digital merging of the layers.




Phase 3: Guided Implant Surgery and Immediate Prostheses


Phase 4: Provisional Prostheses

After 6 months of osseointegration, the patient was satisfied with the appearance and function of the provisional restoration (Figure 19). A Kois deprogrammer platform (Kois Center) was made directly in the mouth on the palatal surfaces of teeth Nos. 8 and 9 (Figure 20). The patient was deprogrammed for 1 hour and a bite record (Harvard Bite, Harvard Dental International) was taken for the laboratory to mount the final prosthesis (Figure 21). An open-tray PVS impression (Imprint, 3M Oral Care) was taken with splinted impression copings.

The functional pathways were adjusted by positioning the patient in an upright seated position.18He was asked to bite on 200-µm-thick articulating paper (Bausch) and bring the posterior teeth together to maximum intercuspation. The lingual contours of the maxillary incisors were adjusted until the marking ink no longer showed surface streaks during biting. The laboratory would utilize the lingual surfaces of the provisional restoration as an aid in the design of the final restoration.

Phase 5: Final Prostheses

The framework chosen for the base of the final prostheses was made of milled PEKK, a high-performance polymer (Pekkton®, Anaxdent North America), which has elastic modulus similar to natural teeth and bone and is designed to provide stress distribution and shock absorption.19 Milling the framework involves significant amounts of digital design work, which was beneficial in this case because information from the initial planning and other stages could be transferred to the design. Additionally, the temporary implant bridges could be used as templates, as the clinician had adjusted them.

The laboratory needed to make individual crowns that fit over the framework, so they opted to "split" the whole design into crowns and base in the design software (Figure 22 and Figure 23). Even in the gingiva, cutback could be pre-determined.

Once the framework design was finalized, it was precisely milled with a 5-axis machine (Figure 24 and Figure 25). After milling, the margins were carefully refined and the prosthesis was re-scanned using pre-recorded implant positions so the crown height and shape would not change and all the components could be bonded together precisely when ready.

Full-contour zirconia crowns (Katana, Kuraray Noritake Dental) were selected for the posterior, and layered lithium disilicate crowns (IPS e.max®, Ivoclar Vivadent) were used for the anterior teeth (Figure 26 through Figure 33).Strength and esthetics must be considered for all tooth-colored materials, and sometimes those factors are inversely related. The full-contour zirconia offered high strength (850 MPa), providing durability in the posterior. Lithium disilicate crowns, meanwhile, offer even more natural-like esthetics, so they were chosen for the less mechanically demanding anterior. Both materials bond similarly to the PEKK framework.

As the crowns were designed together with the framework, the final shape had already been determined. Once they were adapted to the final framework, the STL files were sent to the CAM software for milling. The zirconia crowns were milled with 5-axis dry milling, and the lithium disilicate crowns were wet-milled. The zirconia crowns were sintered in a furnace (Dekema) and the lithium disilicate crowns were crystallized in a ceramic oven (Ivoclar Vivadent). Stains and even thin layers of porcelain were added according to the desired shade and esthetic requirements such as surface textures and translucency.

The final crowns were cemented onto the framework according to bonding protocols from the PEKK manufacturer (Cendres+Metaux).



About the Authors

Private Practice
Hong Kong

Edward Tam, BDS
Vanguard Computer Assisted Laboratory
Hong Kong





















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