In recent years, the effectiveness of dental implants in the treatment of missing dentition has been recognized, and the possibilities of prosthetic design have expanded to include cases that are difficult to treat with conventional methods. In this report, we describe a case in which an implant was used to retreat a lower left bridge with poor conditions and a good prognosis was obtained.

Outline of the Case

1. Patient: 63 years old (at the time of initial examination), female
2. Date of initial examination: July 9, 2009
3. Complaint: Swaying of the left lower bridge
4. Medical history: None to be mentioned
5. Present medical history: About 10 years ago, she was treated for 67 defects with a single pontic tooth, 5) 6) 8) bridge design. She has felt discomfort in the same area since one week before her visit and became aware of shaking yesterday.
6. Present condition: The affected area had a proximal inclination of 8 in relation to the 67 defect, and the defect space was decreasing, so we designed a bridge with one pontic tooth. The bridge with 58 abutments was shaken, and difficulty in mastication was observed.
7. Examination results: There was no redness and swelling of the gingiva, the average pocket probing depth was 3 mm, and there was no excessive resorption of the alveolar bone in the radiographic examination, so the periodontal tissue was normal. ?In addition, there was sufficient keratinized gingiva in the defect area (Figure 1). In addition, there were sixty-six other defects, which were replaced by a bridge and were in good condition. There was no abnormality in the overall occlusal relationship.
8. Diagnosis: Masticatory disorder due to dehiscence of the bridge.

Figure 1: Panoramic radiograph taken at first examination and study cast mounted on articulator.

Treatment Policy and Plan

When the bridge was removed, it was diagnosed that the bridge had detached early because the abutment tooth formation of 8 was excessively tapered due to the living teeth (Figure 2).

Figure 2: Intraoral views of the detached lower left bridge and dental radiographs taken at first examination.

The patient had no symptoms of pulpitis and was able to use the living tooth as an abutment, so it was decided to form a single crown abutment and apply implants to the 67 defects. Preoperatively, impressions of the study model, dental radiographs, orthopantomographs, and computed tomography (CT) were taken to examine the condition of the defect. The distance to the inferior alveolar canal was about 13 mm, and the bone width was about 9 mm. The distance to the inferior alveolar canal was about 13 mm, and the bone width was about 9 mm. The bone quality and morphology were good for implant placement. The bone quality and morphology were good for implant placement. (Figure 3) Since the proximally inclined 8 was not upright, the 67 defect could be designed with a single implant fixture.

Figure 3: Preoperative panoramic and computed tomography radiographs.

The implant placement surgery was performed under local anesthesia in March 2010. After incision and dissection of the gingival periosteal valve from the top of the alveolar bone, bone was drilled using a stent that simulated the fixture placement position on CT, and a single 4.1 mm diameter, 10.0 mm long Stroman Standard Plus implant was placed. (Figure 4,5). (At this time, the bone quality was Lekholm & Zarb's bone quality classification type III, and the implantation torque was 35N.

Figure 4: Stent preparation and implant surgery.

Figure 5: Postoperative panoramic radiograph.

The healing cap was placed and the mucoperiosteal valve was sutured so that the head of the cap was exposed in the mouth.

After one and a half months of unloading, the ISQ value (Implant Stability Quotient) was measured by the resonant frequency analyzer Oster Mentor, and it showed a good value of 70.

After the provisional restorations were placed and the upper-lower occlusal relationship was stabilized, a precision impression was made in May 2010. (Figure 6) After facebow transfer, the working model was mounted on a Dinner Mark II semi-adjustable articulator, and zirconia crowns were fabricated using the Zenotech® system. (Figure 7) The completed crowns were laminated after temporary adjustment. The occlusion of the implant was such that the implant prosthesis made light contact when the patient occluded strongly in the central occlusal position, but did not make contact sliding during lateral and anterior movements (Figure 8).

Figure 6: Resonance frequency analysis (implant stability quotient 70), intraoral view before impression and pickup impression.

Figure 7: Preparation of zirconia crowns with CAD/CAM.

Figure 8: Intraoral view, dental radiograph, and panoramic radiograph after treatment.

Postoperative Course and Postoperative Functional Evaluation

One month after the prosthesis was installed, the patient underwent follow-up observation and maintenance, followed by regular maintenance once every three months to check the occlusion and oral hygiene. Dental floss and interdental brushes were recommended to maintain oral hygiene. In addition, a night guard was made and the patient was instructed to use it at night.

After 3 years, the occlusal condition is stable and there is no wear or chipping of the prosthesis (Figure 9). Radiographic examination showed no bone resorption around the implant (Figure 9). There was no bone resorption around the implant in the radiographic examination, and there was no inflammation of the gingiva around the implant (Figure 10).

Figure 9: Intraoral views taken two and three years after operation.

Figure 10: Dental radiographs taken two and three years after operation and panoramic radiograph after three years.

In the case of bridge dehiscence, the bridge abutment 8 was inclined proximally, so the bridge was 5, 6, and 8, but the cause of the dehiscence was inferred and a higher-quality implant prosthetic treatment was selected instead of simply rebuilding the bridge. As a result, 58 well-conditioned teeth were replaced by single crowns with living teeth. A single implant was used to shape the crown of the 67 missing teeth, resulting in a highly predictable aesthetic and functional result.

In the past, occlusal restoration with a bridge was often used for prosthetic treatment of intermediate defects. However, bridge prosthetic treatment places an excessive occlusal burden on the abutment teeth, resulting in secondary caries, pulpitis, root and crown fractures due to cement loss. In addition, it is difficult to clean the pontic base surface for plaque control, and there is concern about the effect on the periodontal tissues around the abutment teeth.

On the other hand, prosthetic treatment with implants can reduce the occlusal burden on the remaining teeth compared with conventional bridges, and is effective in stabilizing the occlusion for a long time. However, regular checking of occlusion and oral hygiene is essential for the long-term function of implants in the mouth.

The implant prosthetic treatment instead of a bridge prosthesis for a patient with a mandibular midline defect made it possible to reduce the overload of the bridge abutment teeth and to achieve aesthetic and functional recovery.

If conditions permit, the use of implants for prosthetic defects is a treatment method that can provide a good prognosis.