In a 54-year-old patient, periodontitis was diagnosed 12 years ago, resulting in tooth mobility at positions 22 and 23 due to the formation of periodontal pockets. A review of CBCT scans (Figure 1) concluded that these teeth needed to be extracted, and an implant was placed at position 23. 

The implant was positioned high in the upper jaw in the buccal-oral direction, aiming for sufficient bone volume to ensure implant stability. Initially, at position 23 where the implant was placed, a screw-retained metal-ceramic crown with a cantilever at position 22 was mounted, as seen in the CBCT scan (Figure 1). However, due to the progression of periodontitis, teeth 13, 12, 11, and 21 became mobile, and tooth 21 was extracted due to compromised stability. To preserve the remaining natural teeth, the dentist decided to reduce teeth 13, 12, and 11 and connect them as a single unit with the implant (13–23) to improve stability and rigidity. Due to the significant axis discrepancy between the implant and the prepared abutments (Figure 2), conventional solutions were not applicable in this case. Additionally, the progression of periodontitis and gingival recession made reconstructing a metal-ceramic structure impractical for both aesthetic and practical reasons. 

Figure 1: CBCT scan of the jaw 

Figure 2: Disparity between the implant axis and prepared abutments 

Given the specific implant angulation and the requirement to create a structure from tooth 13 to 23, the coronal part of the individual abutment needed to be parallelized with the abutments. Therefore, a titanium-composite structure with a direct fit at the multi-unit abutment level was chosen. This approach ensures adequate space for the structure and composite thickness. Composite material was also selected for its flexibility, as the rigidity and stability of the abutments, due to the patient’s oral health condition, were already compromised. A softer material helps reduce the load on the restoration, thereby protecting the abutments and the implant. Additionally, in the case of gingival recession, the dentist can repair the restoration chairside using composite material to preserve aesthetics. 

Given the axis disparity and the specific implant angulation, selecting the appropriate abutment was a key part of this case. 

When assessing the feasibility of mounting the structure onto the multi-unit abutment, the sum of the abutment tilt angle (A) and the half-angle of the central cone for centering the structure (Ak) must be considered (Figure 3). 

Figure 3: Abutment tilt angle and central cone for centering 

The sum of these two angles determines the feasibility of fitting the restoration and the maximum allowable angle of insertion. 

Ad ≤ Ak+A. 

The equation shows that the axis disparity (Ad) between the implant axis and the abutment axis must be less than or equal to the sum of angles A and Ak of the abutment. A smaller tilt angle (A) than the most common commercial maximum of 30° was selected. While a larger tilt angle would improve mounting characteristics, it would result in excessive transgingival segment height, which contradicts the depth requirement for the abutment to remain below the gingival level. Additionally, the abutment was designed with a minimal transgingival segment height of 0.05 mm at its lowest point and 1.6 mm at its highest point. This ensured adequate material thickness in the lowest part of the abutment, lowering the transgingival segment below the implant level. The final structure is shown in Figure 4. 

Figure 4: Designed multi-unit abutment

The multi-unit abutment allowed for the structure to be mounted while concealing the abutment margin by lowering the seating surface 1 mm below the gingival level (Figure 5). 

Figure 5: Depth of the multi-unit abutment 

During the design of the prototype (Figure 6), and later the titanium structure (Figure 7) for the final prosthetic restoration (Figure 8), special attention was given to the cement gap size. Since this case involved a combination of cemented and screw-retained connections, it was essential to ensure a passive fit of the structure on the multi-unit abutment, achieved by increasing the cement gap. 

Figure 6: Prototype of the final restoration 

Figure 7: Titanium structure 

Figure 8: Final prosthetic restoration – titanium-composite structure 

This case demonstrates that for multi-unit abutments, as a relatively new and widely accepted mechanism for mounting prosthetic restorations in dental medicine and technology, there is significant potential for further advancements and improvements.