Mucosal Coverage of Deeply Protruded Implant in the Maxillary Sinus: A Case Report Open Access

Maxillary sinus augmentation (MSA) can be performed using a transcrestal or lateral approach.^1,2  Because of the risk of complications in the lateral approach, clinicians want to use the transcrestal approach as long as there is a certain level of residual bone height.³  In this process, the implant may be displaced into the maxillary sinus or placed without apical bone support or membrane perforation. If the sinus mucosa is perforated, bone grafting is generally not performed.⁴ 

Indeed, there have been reports of side effects and risks of implant surgery in which the implant apex is perforated into the maxillary sinus.⁵  Various complications have been reported, ranging from short-term nasal bleeding to long-term dysventilation due to thickening of the sinus mucosa and maxillary sinusitis.^4,6  Therefore, treatment methods were introduced, such as placing a short implant or postponing implant placement.⁷ 

Conversely, many reports show that a perforated implant does not show significant long-term clinical and radiological complications.^4,6  This is presumed to be because the implant protrusion on the radiograph differs from the actual exposure, or it means that the sinus mucosa around the exposed implant apex is well-tolerated. Confirming implant protrusion with a nasal endoscope or visual inspection during intraoral surgical intervention is most accurate. In the nasal endoscopic approach, accessing the healthy maxillary sinus is impossible, and access is possible only when the ostium is surgically expanded for surgery on the pathological maxillary sinus.⁸  Direct visual confirmation is possible during lateral sinus floor elevation adjacent to the protruded implant.⁹ 

The implant apex, which perforates less than 3 mm into the maxillary sinus, is covered with sinus mucosa. This is known to be due to the regenerative potential of sinus mucosa.^10,11  This is the result of cone-beam computerized tomographic (CBCT) images and animal experiments, and direct visual confirmation is not easy. The purpose of this case report is to visually confirm the condition of the implant protruding deeply into the maxillary sinus and adjacent sinus mucosa during lateral sinus floor elevation.

A 54-year-old female nonsmoker presents to the clinic with severe mobility in the left maxillary posterior region and discomfort during mastication. Panoramic radiography and CBCT were taken. Panoramic radiography showed severe alveolar bone resorption around #14 and #15 teeth and thickening of the mucous membrane in the maxillary sinus. In addition, a Ø4.5 × 12 mm implant #13 protruding deep into the maxillary sinus was also observed (Figure 1a). The implant at the #13 site was placed and subsequently restored approximately 5 years ago. At the time of implant placement, the patient reported experiencing nasal bleeding that persisted for 2–3 days postoperatively. The CBCT panoramic image showed a thickening of the maxillary sinus mucosa (Figure 1b). On the coronal image, implant #13 protruded deep into the maxillary sinus (Figure 1c). The cystic appearance of the dome-shaped lesion was also observed on the axial image of the CBCT (Figure 1d).

Panoramic radiography and CBCT were taken 3 months after removal of #14 and #15 teeth. Severe vertical bony discrepancy was present at the #14 and #15 extraction sites. The deeply protruded implant #13 was decided to be explanted during lateral sinus floor elevation to reduce the risk of infection and contamination of the maxillary sinus bone graft (Figure 2a). On the panoramic image of the CBCT, the maxillary sinus mucosal thickening was significantly reduced (Figure 2b), and in the coronal image of the CBCT taken before surgery, implant #13 protruded very deeply into the maxillary sinus (protruding depth: 6.5 mm). A slight thickening of the maxillary sinus mucosa was observed around the implant on the sinus floor, but no mucous membrane was observed around the implant apex, indicating exposure (Figure 2c). The previous cystic appearance was not seen in the axial image of CBCT (Figure 2d).

Three months after teeth #s14 and 15 were extracted, a buccal flap was reflected under local anesthesia for lateral sinus floor elevation (Figure 3a). An oval lateral access window was prepared. The lateral bony lid was removed, and a sinus elevation instrument was used to separate and elevate the sinus floor mucosa. The sinus mucosa attached to the protruded implant was also carefully separated. Remarkably, there was no perforation or tearing in the elevated sinus mucosa. Sinus mucosa did not appear to have tight adhesion to the implant body. There was no visible contamination of the implant apex (Figure 3b). Treatment of the exposed implant body during sinus augmentation was unnecessary. The elevated sinus cavity was filled with xenograft. The removed lateral bony lid was separated into two pieces and repositioned. A barrier membrane was not used (Figure 3c). The flap was closed using 4–0 nylon and black silk (Figure 3d). An antibiotic (Ciprofloxacin 500 mg, Yuhan Co., Seoul, Korea) and a nonsteroidal anti-inflammatory drug (Etodol 200 mg, Yuhan) were prescribed for 1 week, and chlorhexidine for mouth rinsing twice a day for 1 week was recommended. Healing was uneventful during the 6 months after surgery. Uncovering of implants was performed 6 months after maxillary sinus augmentation. Upon uncovering, bone formation was well established at the lateral access window site (Figure 3e). A prosthesis was delivered after an additional 2 months (Figure 3f).

A bone graft substitute around the apex of implant #13 was observed on a panoramic radiograph taken immediately after surgery (Figure 4a). There was no leakage of bone graft particles in the panoramic image of the CBCT taken immediately after surgery (Figure 4b). In the coronal image of the CBCT taken immediately after surgery, the bone graft around implant #13 that had protruded was observed (Figure 4c). The ostium is patent in the CBCT coronal image that shows implant #14 (Figure 4d).

Radiographs were taken 1 year after the prosthesis was delivered. On panoramic radiograph, a well-consolidated bone was observed in the left maxillary sinus (Figure 5a). In the panoramic image of CBCT, there were no abnormal findings of the bone graft around the previously protruded implant #13 (Figure 5b). In the coronal images of CBCT, a well-consolidated bone graft was observed around implants #14 and #15 (Figure 5c and d).

This case showed that the implant apex was presumed to be exposed because the implant protruded deep into the maxillary sinus on the radiographic image, but it was actually covered with a thin sinus mucosa. Therefore, successful MSA could be achieved without explantation or surface treatment of protruded implants.

Sinus mucosal thickening is one of the objective parameters that can determine sinus health and physiology. Among the various potential causes, Park et al have reported that mucosal thickening may result from a bacterial infection of the ostiomeatal complex.¹²  In particular, periodontal/endodontic infection originating in the maxillary posterior teeth can be transmitted to the maxillary sinus mucosa without sinus floor perforation.¹³ 

This can be confirmed by the fact that sinus mucosal thickening was reduced after the periodontally/endodontically compromised tooth was extracted without sinus floor perforation.¹²  Other causes of mucosal thickening include damage to the cortical layer of the sinus floor and damage to the sinus mucosa by implant protrusion/perforation.¹⁰  In the present case, it is difficult to ascertain whether the cause of the mucosal thickening was the protruding implant, the periodontally compromised tooth, or both. In CBCT imaging, the severe mucosal thickening around the protruded implant disappeared after the adjacent periodontally compromised tooth was extracted. This suggests that the protruding implant did not cause the existing mucosal thickening. In this situation, the question remains whether the protruded implant is exposed in the maxillary sinus or covered with a mucous membrane.

The exposed implant apex is covered with the maxillary sinus mucosa to some extent.^10,14  However, if the protruding depth of the implant is increased, the perforated sinus membrane is not spontaneously repaired, and debris may accumulate around the exposed implant apex, leading to mucosal inflammation.¹⁵ However, in a systematic review, even if the implant apex perforated the sinus mucosa and was exposed in the maxillary sinus, the complication rate was 0–14.3% (mean: 3.4%). In addition, there was no difference in complications and implant survival rate (99.5% vs 98.5%) between groups with an exposure size smaller or larger than 4 mm.⁶  Park et al also suggest that most perforated implants (perforation depth: mean 4.3 ± 1.0 mm) placed in the maxillary sinus do not cause clinical or radiological complications.⁴  In fact, heterogeneity exists among researchers regarding the harmfulness of perforation.

In the present case, although the 3-dimensional image showed a very deep protrusion of 6.5 mm, it was covered with mucosa without implant exposure. Initially, explantation of the protruding implant during sinus floor elevation was planned to be performed in the adjacent area of the protruding implant. However, no signs or evidence of mucosal perforation or damage were found during sinus floor elevation through the lateral window approach. This means that the implant apex, which was radiographically protruded deep into the maxillary sinus, was judged to be exposed, but in reality, the implant apex was not exposed and was covered with sinus mucosa. Therefore, decontamination of the protruding implant was not required, and conventional MSA was performed. Healing after MSA was uneventful, and there were no findings of thickening of the sinus mucosa or infection of the sinus graft. If the sinus mucosa adjacent to the protruding implant was perforated and if the exposed implant was contaminated, the future of the protruding implant may vary depending on the accessibility of instruments for surface decontamination.⁹ 

Since the thin sinus mucosa covering the protruding implant was not observed in the CBCT image, radiographic findings and surgical observation may lead to conflicting results.⁸  Even if the implants placed in the maxillary sinus have the same protruding depth on radiographs, there may be heterogeneity in the patient’s clinical symptoms, degree of mucosal thickening, and actual exposure of the implant apex. Additionally, it is unknown to what extent the protruding depth can be covered with sinus mucosa and whether the surrounding tissues can tolerate it. This is expected to be due to differences depending on the anatomical structure of the sinus floor, the damage of the sinus floor cortical layer, the tolerance of the adjacent sinus membrane, and the functions of ciliated cells responsible for mucociliary clearance. According to a report by Park et al., radiographic findings that most of the implant apex (mean perforation depth; lateral side: 3.39 ± 1.79 mm, medial side: 5.06 ± 1.76 mm) penetrated to the nasal cavity was covered with mucosa in the nasal endoscopy.¹⁴  Based on these results, and because the maxillary sinus is connected to the nasal cavity and shares the same epithelial cells, it can be assumed that the results of implant protrusion in the maxillary sinus will be similar to those in the nasal cavity. Therefore, there is a limit to predicting the exposure of the implant based only on the protruding depth.

There is much confusion among clinicians and researchers regarding terms such as implant perforation, implant protrusion, and implant exposure. If the implant apex is exposed after healing of the sinus mucosa, implant perforation, implant protrusion, and implant exposure share the same meaning. However, if the perforated sinus mucosa covers the exposed implant, implant protrusion, and implant exposure have different meanings. This confusion of terms is an event that occurred because the results of the regenerative potential of the Schneiderian membrane cannot be directly observed during the healing process. Currently, confusing terminology is inevitable based on radiographic images alone. This case involved implant perforation and protrusion but ultimately was not implant exposure.

The disadvantage of this case report is that there is insufficient evidence to obtain reasonable results due to the lack of case numbers. It is considered that additional cases should be reported in the future.

Within the limitations of this case report, MSA can be performed without the need for implant removal or surface treatment if the implant protrudes deep into the maxillary sinus and is covered with sinus mucosa.

CBCT:

cone-beam computerized tomography

MSA:

maxillary sinus augmentation

The authors report no conflicts of interest with this report.