Minimally Invasive Surgical Placements of Nonsubmerged Dental Implants: A Case Series Report, Evaluation of the Surgical Technique and Complications

The traditional surgical technique of dental implant placements involves careful preoperative planning,1 open flap access, osteotomy of the site adhering to well-established surgical protocol, followed by proper wound closure.

Primary stability is one of, if not the, most important prerequisites for success of osseointegration.2,3 Therefore, precise and careful surgical preparation of the site is critical to achieve this aim. The conventional open flap technique for implant site preparation allows the surgeon direct visual and instrumental access to create a congruent osteotomy for primary stability. However, this technique increases morbidity of the postoperative recovery period when compared with less invasive methods.

Minimally invasive implant surgery, commonly referred to as “flapless” implant surgery, was initially embraced by novice implant surgeons4 due to the perceived simplicity of this technique. With the introduction of in-office cone beam computerized tomography (CBCT), which improved access to dental implant treatment planning, the popularity of this technique increased further.

However, the successful use of this approach often requires advanced clinical experience and surgical judgment.4 Proper case selection should be done prior to attempting this protocol for implant placement.

This article presents a series of dental implant surgery cases restoring the functional zone, placed following a minimally invasive technique by a single oral and maxillofacial surgeon. The surgical method and encountered complications are also outlined.

This series reports 5 consecutive cases out of 10 seen and treated by a single oral and maxillofacial surgeon from the Department of Oral & Maxillofacial Surgery, National Dental Centre, Singapore, between June 2008 and March 2009 whereby the tissue punch technique was employed. All patients required dental implant replacement of missing posterior teeth, bicuspids, or molars (Table 1).

The author defined the following inclusion criteria in patient selection for this case series:

1. Noncontributory medical history

2. Nonsmoking habits including absence of past smoking history

3. ITI implants with sandblasted large-grit acid-etched (SLA) surfaces and transmucosal polished collars of uniform height 1.8 mm (StandardPlus; International Team for Implantology, Straumann AG, Waldenburg, Switzerland)

4. Adequate bone volume and density for conventional dental implant placement as determined by CBCT without the need for bone or soft-tissue grafts

5. Single tooth edentulism in the posterior mandible or maxilla

6. Presence of an adequate band of attached nonmobile soft tissue, preferably keratinized, after implant placement

In the process of selecting the cases for this report, the exclusion criterion was the total or partial lack of the above 5 inclusion criteria.

Of the 5 cases excluded from this report, 3 received implants of another system, 1 was a case of multiple teeth replacements, and 1 had a recent history of smoking but had ceased a month before the implant surgery.

A standard clinical evaluation was carried out for all patients. Significant past medical history, general health, and smoking habits were documented. None of the 5 consecutive patients included in this study presented with any significant medical or systemic issues that would have compromised dental implant success.

All of the patients were nonsmokers.

Clinical assessment included extraoral examination followed by intraoral examination. Thereafter, implant site–specific evaluation was carried out jointly with a prosthodontist. This consisted of evaluation of the inner occlusal space in addition to hard- and soft-tissue assessment.

Close attention was given to the soft tissue, including the evaluation of the biotype, volume, and dimensions of mucosa to ensure that at least 2 to 3 mm of attached soft tissue, preferably keratinized, would remain circumferentially around the healing abutments following flapless implant placement.

All patients in this series underwent further radiographic investigations with CBCT. All of the scans were taken with a radiographic guide in place, which will indicate the planned implant position in all 3 dimensions.

The surgeon then evaluated the scans to confirm the possibility of implant placement without the need for bone grafting. This was based on ridge morphology, bone volume sufficiency for the intended implant dimensions, bone quality in Hounsfield units, as well as the inferior alveolar nerve position.

All patients fulfilled the inclusion criteria for minimally invasive implant surgery as above after the clinical and radiographic evaluations.

All of the implants used in this case series were nonsubmerged parallel ITI implants with SLA surfaces (International Team for Implantology). The transmucosal polished collars of the implants were a uniform height of 1.8 mm (StandardPlus). All of the implants placed were either 10 or 12 mm in length.

In 2 patients (patients 2 and 5), 4.1-mm-diameter implants with regular necks (4.8-mm-diameter transmucosal polished collar) were used to replace missing maxillary bicuspids.

The remaining 3 patients received 4.8-mm diameter implants with wide necks (6.5-mm-diameter transmucosal polished collar), replacing mandibular first molars.

All patients received oral 1.0 g amoxicillin 1 hour preoperatively.

The surgical procedures were all carried out under local anesthesia in sterile surgical conditions.

A sharp probe guided by the surgical template was used to mark the point for implant placement through the mucosa. A bleeding spot thus generated indicated the location over which the tissue punch would be applied.

There were 2 cases (patients 2 and 5) in which 4.1-mm-diameter regular neck implants were used to replace missing maxillary second bicuspids. In both cases, a 5-mm-diameter tissue punch was used. The punch was applied onto the ridge and rotated to ensure a clean core of soft tissue would be subsequently removed. This created a uniform circular access space to the bony ridge for subsequent site preparation. The core of soft tissue was then wrapped in saline-soaked gauze and saved for possible grafting needs after implant placement.

The thickness of the soft tissue buccal, mesial, and distal to the access space was then measured. This was done to factor in the soft-tissue thickness for the drilling depth. A surgical guide was used throughout to ensure a prosthodontically favorable placement of the implant in 3 dimensions. The site preparation was then carried out to the depth of placement according to the ITI system protocol along with copious irrigation. The osteotomy sites were directly cooled with irrigation by removing the drills in the sequence. A final lavage of the osteotomized sites was done to ensure they were free of debris.

Before implant insertion, a periodontal probe was used to check for any bony fenestrations of the osteotomy. The implants were then placed after this had been confirmed.

The implants were inserted first with a hand piece at the recommended torque, and final seating was done manually with a wrench. The final seating was confirmed when the implant bottomed out at the base of the osteotomy and did not show further apical movement. The fixture mount was then removed and healing abutment placed. Immediate postoperative radiographs were done to confirm complete seating of the abutments.

The surgical protocol for the other 3 cases in which 4.8-mm-diameter wide neck implants were placed was essentially similar to the 4.1-mm-diameter implant cases. The only difference was that a 6-mm tissue punch was used instead of a 5-mm one. This was because the diameter of the wide neck transmucosal collars was 6.5 mm.

Postoperative radiographs were taken for all 5 patients. In addition, the patients also received antibiotics and analgesics as well as standard postoperative instructions before discharge.

The patients were then followed up about a week after surgery and thereafter at either 3 or 6 months after surgery before being referred for prosthodontic restoration (Table 2).

All of the 5 implant sites did not have any bony fenestrations after osteotomy as confirmed with a periodontal probe on the bony walls.

In the 2 cases (patients 2 and 5) in whom 4.1-mm-diameter regular neck implants were used, the gaps between the soft-tissue access (5-mm diameter) and transmucosal polished collar (4.8-mm diameter) were negligible. Therefore, there was no requirement to use the soft-tissue core saved from the punch technique for grafting.

In 1 case (patient 5), the initial stability of the implant was slightly compromised, but a decision was made by the surgeon to leave the implant nonsubmerged. The patient was advised to follow a soft diet for at least 1 week postoperatively and cautioned to avoid mastication on that side of the implant for a duration of 3 weeks. The lack of primary stability was due to poor bone quality of the site rather than the minimally invasive technique used.

The primary stability was good for the other 3 cases in whom 4.8-mm-diameter wide neck implants were placed.

Two of the 3 cases (patients 1 and 4) were found to have incomplete seating of the healing abutments after immediate postoperative radiographic assessment. For patient 1, it was due to soft-tissue interference (Figure 1g). This was immediately rectified by appropriate removal with a 15C blade. Proper reseating was then verified with another periapical radiograph. As for patient 4, it was due to bony interference at the mesial aspect of the transmucosal collar of the implant. Because the patient was unable to have immediate correction of this issue, a follow-up appointment was subsequently arranged about 12 days postoperatively. At that time, the healing abutment had loosened because of spontaneous resorption of the bony interference. It was then reseated without further minor surgical correction and then verified with a periapical radiograph (Figure 4g).

All 5 cases exhibited excellent soft-tissue architecture preservation at 1 week postsurgery with minimal edema, and there were no complaints of pain during the early postoperative healing period. All of the implants achieved successful osseointegration, and this included the patient with compromised primary stability (patient 5).

The soft-tissue architecture remained stable with preservation of adequate attached gingival throughout the healing period of the implants, contributing to an esthetically pleasing and biologically sound result after final restorations (Figures 1k and 2–5).

The original protocol proposed by Brånemark et al5 advocated using flaps incorporating vestibular incisions. Site osteotomy is carried out in the usual manner, and after implant placement, the surgeon accommodates the flap for closure.

Flapless implant surgery has numerous advantages over the routine open flap technique.4,6,7 Advantages include preservation of circulation, soft-tissue architecture, and hard-tissue volume; decreased surgical time; improved patient comfort; and minimization of postsurgical morbidity. The patient is able to resume normal activities and maintain oral hygiene procedures almost immediately.4 As evident in all of the cases in this series, excellent soft-tissue architecture preservation was observed at 1 week postsurgery with minimal edema. None of the patients complained of pain during the early postoperative healing period. The soft-tissue character remained stable throughout the healing period of the implants, contributing to an esthetically pleasing and biologically sound result after final restorations

However, this approach affects the ability of the surgeon to visualize anatomic landmarks and vital structures, therefore increasing the risk of implant malangulation, inappropriate placement depth, and damage to vital structures. There is also decreased ability to contour osseous structures and the potential for thermal damage of bone due to reduced access for external irrigation during site preparation. The most significant drawback would be the limited ability to manipulate soft tissues to ensure proper circumferential adaptation of adequate keratinized tissues around transmucosal implant structures.4 Therefore, before attempting minimally invasive surgery, the surgeon should be well versed with the indications and techniques of conventional open flap surgery.

All of the patients in this case series underwent detailed surgical and prosthodontic evaluation prior to surgery. The most important issues addressed at this stage were the bone volume adequacy for implant placement and soft-tissue dimensions.

The bony assessment was done with the aid of CBCT, and the implant positioning was planned to ensure that vital structures such as the inferior alveolar bundle and the maxillary sinus would not be violated and that no bony fenestration would occur during osteotomy and/or implant placement, which would necessitate converting the case into an open flap procedure.

In all cases, there was no bony fenestration after osteotomy. This was achieved because the appropriate implant dimensions were selected based on the CT findings and the surgery carried out in strict accordance to the planned positions as dictated by the surgical guide. During the CT analysis, the bony anatomy of all of the cases was assessed to be ideal for implant placement in the planned positions, and therefore, the implants could be placed in the exact locations dictated by the surgical guide (Figures 1–5b). There was no need to alter the implant angulations.

Ideally, the crest of the ridge should be flat with respect to the planned implant angulation. However, the surgeon must remember this may not be the case all of the time. The CBCT provides accurate information regarding the ridge morphology but only as far as the slice thickness allows. Therefore, minor bony discrepancies of less than 1 mm may not be detected. Hence, the surgeon must make sure that proper countersinking is done before implant insertion, so that the implant can be placed to the correct depth without interferences from minor uneven crestal bone contours. For patient 4, the healing abutment was incompletely seated due to minor bony interference at the mesial aspect of the transmucosal collar despite the countersinking. This was discovered after immediate postsurgical radiograph. The problem was resolved 12 days later on follow-up, when the bony interference had resorbed. The healing abutment was then reseated uneventfully (Figure 4g). At the time of surgery, the author felt that the countersinking could have been insufficient and thereby resulted in this complication.

Soft-tissue assessment was the other important issue. At least 2 to 3 mm of attached soft tissue, preferably keratinized, is recommended to remain circumferentially around the healing abutment following implant placement.1 ^,6 This was in fact the main criterion for case selection to undergo this noninvasive technique. All of the cases in this series fulfilled this criterion before surgery. This is an important criterion as this recommendation of soft-tissue architecture allows the implant and its restoration to better withstand the trauma of masticatory forces, restorative procedures such as impression registering, or abutment connections as well as oral hygiene measures such as tooth brushing and flossing.

It should be remembered that the tissue punch used for the wide neck implants was 6 mm in diameter, which is 0.5 mm less than that of the transmucosal smooth collar (6.5 mm). This is a special consideration as compared with flapless placement of a dental implant without such a transmucosal smooth collar or an implant with a collar of the same diameter as the tissue punch. Soft-tissue interferences due to the discrepancies of the transmucosal collar tissue punch diameters would be expected, and therefore, appropriate measures must be adopted to ensure complete seating of the healing abutment. The author overcomes incomplete healing abutment seating by actually using the healing abutment itself as a punch. This is achieved by employing a manual milling action of the healing abutment on the transmucosal smooth collar, trimming off any excess tissue interferences, and then removing them. The final seating of the healing abutment is checked manually by feeling for an abrupt snap as it fits onto the transmucosal smooth collar. This would then be verified by relevant postsurgical radiographs.

A noninvasive approach for surgical implant placement is a useful technique that can be used in situations in which ideal osseous and soft-tissue anatomy is present on a residual ridge. However, the surgeon should first be well versed with conventional flap procedures to put flapless surgery in proper perspective. With good case selection following detailed clinical and radiographic examination including CBCT, this minimally invasive technique can lead to successful outcomes.

CBCT

cone beam computerized tomography

SLA

sandblasted large-grit acid-etched