Abstract: Bone augmentation procedures are routinely required before dental implant placement. Several techniques for this procedure may be considered, such as guided bone regeneration, bone block grafting, and ridge splitting for bone expansion. These case reports describe the technique for ridge splitting and gradual expansion in the maxilla and the mandible. Simultaneously, dental implants were placed within the split ridge, surrounded by the particulate bone graft and covered by a resorbable membrane. Six months later, the implants were uncovered followed by impression and final restoration with implant-supported porcelain-fused-to-metal crowns.

The resorption process of the alveolar ridge after tooth loss is routinely encountered in patients requiring dental implant treatment. Several methods have been described to augment the alveolar crest using bone graft from various sources (block or particulate) in conjunction with membranes.^1,2

Another method to increase bone availability in the narrow alveolar ridge is the ridge-splitting technique. This approach creates a sagittal osteotomy of the edentulous ridge using instruments such as chisels between the two cortical plates to expand the ridge width and consequently allow for the placement of implants. Tatum described a technique to expand the cortical wall in cases with inadequate buccolingual thickness of bone using various sizes of channel formers.³ Subsequently, other clinical cases were reported with some variation of this technique, allowing placement of implants simultaneously.^4,5

To start, adequate bone height for implant placement should be present because the splitting of the crest will not increase bone volume vertically. A minimum of 3 mm of bone width, including at least 1 mm of cancellous bone, is desired to insert a bone chisel between cortical plates and consequently expand the cortical bones.⁶ A pyramidal form ridge with a wider base is the ideal indication for this technique because it will prevent the risk of buccal plate fracture.

This approach allows simultaneous placement of implants, shortening the overall treatment time. In some cases, the expansion of the buccal plate with the ridge-splitting technique may correct the buccal concavity caused by ridge resorption. Morbidity related to second donor site also is eliminated with this approach.

Figure 1A through Figure 1C—The preoperative CT scan for implant surgery planning of the area near tooth No. 11 (A), No. 12 (B), and No. 13 (C) revealing a narrow ridge with 3 mm to 4 mm width at crestal level

Because this technique does not add vertically to the alveolar ridge, its use is limited when the alveolar ridge is overangulated, especially in the maxillary anterior areas. This condition makes implant restoration a challenge. Also, when a single site is planned, this technique is difficult to perform in the mandible because of space. The main complication is fracture of the buccal plate, especially in the mandible. If this occurs, bone fixation screws need to be used to stabilize the buccal plate.

This article describes implant placement in atrophic maxillary and mandibular alveolar crests using the ridge-splitting technique.

CASE REPORTS

Ridge Splitting in the Maxilla

A 65-year-old woman was referred for implant placement and prosthetic treatment in the area of teeth Nos. 11 through 14. The teeth had been extracted 3 years before and the patient was not wearing any denture. The computerized tomography (CT) scan evaluation revealed adequate bone height for implant placement, but a narrow ridge of 3 mm to 4 mm at the crest (Figure 1A through Figure 1C). The CT scan also revealed a posterior pneumatized maxillary sinus. Because the patient wanted to avoid a sinus elevation procedure, it was decided not to place an implant in the area of tooth No.14. It was decided to place a 10-mm length, 3.7-mm diameter Tapered Screw Vent® MTX (Zimmer Dental, Carlsbad, CA), with a rough, acid-etched surface, using the ridge-splitting technique in the area of teeth Nos. 11 through 13.

Figure 2—Clinical aspect of the alveolar crest after full-thickness flap elevation.	Figure 3—Expansion of 2 mm to 3 mm of the buccal plate achieved by splitting the ridge with chisels and a mallet.
Figure 4—Placement of three implants at the expanded ridge.	Figure 5—Periapical radiograph of implants at uncovering phase 6 months after the implant surgery.
Figure 6—Delivery of final implant-supported PFM restoration.	Figure 7A and Figure 7B—The preoperative CT scan for implant surgery planning of area near tooth No. 19 (A) and No. 20 (B) revealing crestal ridge width of 3 mm to 4 mm.

At the time of the surgery, local infiltrative anesthesia was administered (lidocaine 2%, epinephrine 1:100,000). A full-thickness mucoperiosteal flap was raised, confirming the presence of a narrow crest ridge previously observed in the CT scan (Figure 2). The initial osteotomy was performed on midcrestal bone using a No. 15 blade. Chisels of increasing width and a mallet were used to further enlarge the osteotomy to a point 3 mm shorter than the final length of the implants to be placed. Approximately 2 mm to 3 mm of expansion was achieved without performing vertical incisions in the bone (Figure 3). To prepare the osteotomy site for implant placement, sequential surgical burs according to standard implant placement protocol were used up to the final length of the implants (10 mm). The implants presented initial primary stability (Figure 4), the cover screws were placed, and the implants were submerged for a healing period of 6 months. The widened space between cortical plates was filled with a mix of bovine anorganic bone filler, Bio-Oss® (Osteohealth, Shirley, NY), and demineralized freeze-dried bone allograft (DFDBA) (Pacific Coast Tissue Bank, Los Angeles, CA), and covered with a bioresorbable membrane, Bio-Gide® (Osteohealth). The tissue was approximated and the patient was instructed not to wear any denture or to place pressure on the healing site.

Second-stage surgery was performed 6 months later, healing abutments were placed (Figure 5), and the soft tissue was allowed to heal for an additional 5 weeks. Splinted porcelain-fused-to-metal (PFM) crowns supported by custom gold abutments then were delivered (Figure 6).

Ridge Splitting in the Mandible

A 60-year-old woman without medical complications presented for the replacement of a missing mandibular right second premolar and first molar. The teeth had been extracted 2 years before. The CT scans revealed the presence of 16 mm of bone above the mandibular inferior alveolar nerve at each implant site, with a crestal ridge width of approximately 3 mm to 4 mm (Figure 7A and Figure 7B).

At the time of the surgery, a full-thickness mucoperiosteal flap was raised. For the initial midcrestal osteotomy, a carbide tungsten bur, Flat-end Fissure 701 (Brasseler USA, Savannah, GA), was used. Because of the thickness of the cortical bone in the mandible, two vertical osteotomies were required, extending from the edges of the initial midcrestal osteotomy. The length of these "vertical bony release" osteotomies is usually tailored to the length of the implant. Typically the length of the bony cut will be 3 mm shorter than the final length of the implant.

To prevent a fracture of the buccal plate during the expansion process, an apical osteotomy with a carbide round bur was performed connecting the apical ends of the two "bony verticals" (Figure 8). Expansion of 3 mm between cortical plates was achieved using chisels with gentle hand motion buccolingually. Two implants, 4 mm x 11.5 mm (Osseotite®, parallel walled, Biomet 3i, Inc, Palm Beach Gardens, FL), were placed following standard protocol (Figure 9). The expanded site was filled with a mixture of bovine anorganic bone filler, Bio-Oss, and DFDBA and covered with a bioresorbable membrane, Bio-Gide.

After 6 months of healing, the second-stage surgery was performed to expose the implants (Figure 10 and Figure 11). Custom abutments were fabricated to be restored with the splinted PFM crowns (Figure 12).

Figure 8—To facilitate the bone expansion, vertical osteotomy was performed in the buccal plate joint by osteotomy with a round bur at the apical portion.	Figure 9—Placement of two implants at site of teeth Nos. 19 and 20 after the ridge expansion.
Figure 10—Periapical radiograph of the implants at uncovering phase 6 months after the implant surgery.	Figure 11—Clinical aspect of the surrounding bone at the uncovering phase 6 months after the implant placement.
Figure 12—Delivery of the final splinted implant-supported PFM restoration.

DISCUSSION

The ridge-splitting technique allows placement of implants in a narrow crestal ridge in a single procedure. Chiapasco and colleagues evaluated the success of different surgical techniques for ridge reconstruction and success rates of implants placed in the augmented areas.⁷ The surgical success and the implant survival rates were as high as the guided bone regeneration and onlay graft procedure, with the advantage of a shorter treatment time.

Several authors have suggested the use of a partial thickness flap to help immobilize the displaced buccal cortical plate.^5,6,8 In the presented cases, the use of a full-thickness flap helped to avoid excessive bleeding, resulting in better visualization of the operating sites and better handling of the surgical steps. In cases where there is thin connective tissue, the partial-thickness flap procedure becomes extremely difficult, and the remaining tissue over the alveolar bone is too thin to protect the bone adequately.⁹ In cases of buccal plate fracture, the mobile plate may be retained with bone fixation screws.¹⁰ Finally, when the primary stability of the implants is compromised, implants are placed only after the healing period of the augmented site.

Generally, mandibular bone has higher density compared with maxillary bone, requiring a different approach in ridge splitting. In the maxilla, the osteotomy of the crest may be achieved with chisels and without the assistance of surgical burs. A mallet may be used to expand the plates without vertical osteotomy. In the mandible, however, the initial osteotomy is achieved using a surgical carbide bur on the alveolar crest and two vertical osteotomies. Additionally, an apical osteotomy connecting both verticals with a round bur allows the expansion and minimizes any chance of bone fracture. Instead of a mallet, hand motion is used with the chisels, resulting in slow bone expansion. To separate the ridge gently, Chiapasco et al¹¹ reported 45 cases using a wedge-type device with two surgical steel arms hinged apically and a transversal screw, which allows a progressive activation of the device. A fracture of the mandibular buccal plate occurred in one patient. In nine patients, the expansion was achieved gradually in 4 to 5 days by activating the device 1 mm per day.

CONCLUSION

This article described implant placement in atrophic maxillary and mandibular alveolar crests using the ridge-splitting technique. The correct indication associated with careful clinical maneuver of the ridge-splitting technique allows predictable placement of implants even in narrow alveolar ridges.

ABOUT THE AUTHORS

Samuel Koo, DDS, MS: Faculty, Department of Restorative Dentistry and Biomaterials Sciences, Harvard School of Dental Medicine, Boston, Massachusetts.

Serge Dibart, DMD: Associate Professor and Clinical Director of Postdoctoral Periodontology, School of Dental Medicine, Boston University, Boston, Massachusetts.

Hans-Peter Weber, DMD: Professor and Chair, Department of Restorative Dentistry and Biomaterials Sciences, Harvard School of Dental Medicine, Boston, Massachusetts.

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This paper was presented at the 12th Annual Northeast Postgraduate Implant Symposium, which was held November 10-11, 2006, at the University of Connecticut Health Center in Farmington, and sponsored by the Prosthodontic Residency at University of Connecticut School of Dental Medicine.