Tissue Management Protocol: “Tunnel Bone Graft” Technique

INTRODUCTION
Resorption in the edentulous posterior mandible primarily occurs in a buccal to lingual direction with a resultant thin, vertical, bony lingual cortex. Patients who wear removable partial dentures usually exhibit greater degrees of bone loss than those who do not wear removable appliances. Increasing bone width for future implant placement can be accomplished with block bone grafts¹ or tunnel tissue bone grafting techniques.²
      Block bone grafts have proven to be a good modality to increase width with the patient’s own bone or allograft bone blocks.³ If bone is harvested from the patient’s chin or ramus area, there is a donor site invasion that must be accomplished to acquire the bone for the receptor site. An allograft bone block graft material (such as Puros Block Allograft [Zimmer Dental]) can eliminate the donor site surgery.
      An alternative to a mandibular block graft is the remote incision with tunneling approach to gain width of thin mandibular bone. A crestal incision approach on the mandible using particulate bone grafting material has not achieved predictable results, due in part because of possible suture line breakdown during swelling and allowing for tissue to separate over the surgical site.⁴ For the authors, the remote incision approach using the tunneling technique has produced favorable results with 50 prospective patients having yielded an 86% success rate of 3 to 7 mm gain in mandibular ridge width to the previous existing ridges (in 43 out of 50 procedures). Only 7 patients experienced less than 3 mm of mandibular bone width from this bone grafting technique.

Mandibular Tissue Management With the Remote Buccal Incision: The Tunneling Technique
Figure 1 illustrates a mandibular posterior edentulous area distal to the first bicuspid. As illustrated in the drawing, a full-thickness vertical incision (10 to 12 mm long) is made in alveolar mucosa, posterior to the canine fossae between the bicuspid and cuspid roots. It is imperative that the scalpel blade be “pushed hard” through the tissue and periosteum so that a full-thickness tissue reflection is produced. This allows the tunnel procedure to have less bleeding and reduce the incident of “tissue tears” in the tunnel.

Figure 1. Vertical incision in unattached gingiva.	Figure 2. Illustrates use of opposing thumb to resist tearing tissue preparing tunnel procedure reflecting unattached gingiva.

     Beginning at the incision line, a Nordent No. 14 thin periosteal elevator is then used to lift the alveolar mucosa away from the buccal aspect of the bony ridge. The dissection/reflection continues distally, in alveolar mucosa only, and terminates buccal to the pterygomandibular raphae. The operator should press his or her thumb over the site where the tissue is being elevated to minimize unwanted tissue tearing (Figure 2). The opposing thumb pressure protocol should be used for the remainder of the elevation procedure to avoid tearing tissue or pushing the periosteal elevator through the buccal tissue. Using the opposing thumb, pressure protocol should be used in the alveolar mucosa as well as the attached gingival mucosa.
      The next step is to reflect the attached gingival connective tissue fibers located on the buccal crest of the edentulous ridge. Once loosened, the occlusal portion of the attached gingivae is carefully freed (Figure 3). The attached gingival connective tissue on the lingual of the ridge must now be loosened. This is the most technically challenging portion of the tunneling procedure. Perforating the lingual tissue with the periosteal elevator could necessitate aborting the procedure; therefore, care must be taken with loosening the lingual crestal attached gingivae. On occasion, lingual tissue perforations may be sutured closed without compromising the graft, but is not recommended for the most predictable results. The authors usually abort the procedure if a lingual tissue tear occurs and will reschedule the patient to return in 4 to 6 weeks to perform the procedure again.

Figure 3. Reflecting attached gingival connective tissue fibers on buccal of ridge and on occlusal of ridge using opposing thumb to resist  tearing buccal tissue.	Figure 4. Use of dull bent wax instrument to relieve lingual attached gingival connective tissue fibers starting posteriorly and coming anteriorly to reduce risk of instrument penetrating the lingual tissue.
Figure 5. Side view showing dull wax bent instrument over on to the ingual aspect of the ridge relieving mylohyoid muscle fibers.	Figure 6. Placement of bone graft mixture under the tissue barrier using the bent dull wax instrument to push bone graft mixture over on to the lingual side of bony ridge.

     Figure 4 shows a dull waxing instrument (bent by the operator) specifically for this procedure. (There is a commercially-designed instrument called the Heller tunneling instrument [Miter].) The tunnel-reflecting instrument should be dull to the touch, and used as a blunt instrument. This bent reflecting instrument allows access to the lingually attached crestal fibers (which can extend up to 3 mm), maintains bone contact for full-thickness reflection, and follows the lingual bony contour for subsequent reduction of tissue tearing. The lingual tunnel dissection is started just anterior to the raphae, continuing anteriorly toward the distal of the bicuspid tooth (using the opposing thumb pressure protocol described earlier). It is very important to proceed from posterior to anterior, allowing for better control of the bent instrument and to reduce lingual tissue penetration. Once the crestolingual fibers are freed, the bent instrument is then manipulated to elevate the lingual mucosa to the mylohyoid muscle attachment (Figure 5). The resultant freely movable pocket of tissue can now allow for placement of grafting materials and tissue barriers (Inion GTR [Riemser]) through the vertical access incision. A straight handpiece with a No. 4 round bur is now used to either scratch the buccal bone or, if thickness allows, create perforations into the medullary bone (Figure 6).

Tissue Barrier and Grafting Material Placement Within the Tunnel
A 25- x 20-mm sheet of demineralized, freeze-dried bone laminar tissue barrier (Miter) is slightly hydrated in sterile saline and then molded into a U shape. The Inion Guided Bone Regeneration/GBR barrier (Inion GTR) can also be used as a barrier. A plasticizer liquid is used to allow the material to become firm, allowing for easier placement of the grafting material. Using cotton plier forceps, the U-shaped barrier is carried through the vertical incision to the most proximal aspect of the receptor site (ie, tunnel). The laminar tissue barrier is then manipulated to create a tent, which extends from the mylohyoid region to the buccal bone. The laminar tissue barrier will now become the superior wall of the receptor site, acting as a “roof” for the bone graft.
      Using a No. 9 periosteal elevator to hold up the laminar tissue barrier, the author suggests a bone mixture of 90% irradiated bone with 10% resorbable tricalcium phosphate (Curasan [Reimser] or SynthoGraft [Bicon]). Jensen⁵ found that the mixture of irradiated bone and tricalcium phosphate produced results equal to autogenous graft material. The use of platelet-rich plasma using centrifuges (Harvest Technologies or Clinseal Technology [Salvin Dental]) is also recommended; this can be mixed directly with the aforementioned bone combination to add increased growth factors to the site for potentially better and quicker healing.⁶ This combined mixture is then loaded into a syringe and placed into the most posterior aspect of the receptor site (pocket), where the graft mixture is extruded. The (dull) bent instrument is then used to push the graft material over the crest of the ridge and into the mylohyoid area (Figure 7). The authors suggest placing the graft material over the crest of the ridge into the lingual mylohyoid tunnel space. This is done to slow down the reattachment of the mylohyoid muscle tissue, which can cause resporption of the buccal bone graft. It is also important that the operator place adequate graft material onto the lingual side of the crest to increase case success rates. This mixed bone material is placed repeatedly into the pocket, pushing the material lingually, and then buccally, until the receptor site is filled with grafting material (Figure 8).

Figure 7. Straight handpiece with No. 4 round bur was used, penetrating cortical bone plate to produce bleeding from within bone medullary spaces.	Figure 8. Completed tunnel graft procedure showing lingual and buccal graft material in place.

     The use of thumb-and-forefinger pressure can mold the graft material under the tissue to equalize the width of the graft. The Inion GTR barrier, if used, is more difficult to mold because the plasticizer makes the barrier more rigid. Coated Vicryl (3-0) suture (Polyglactin 910 [Ethicon, a subsidiary of Johnson and Johnson]) is the suture of choice. This absorbable, synthetic, braided suture, and antibacterial suture is now used to close the vertical incision, starting at the superior portion of the incision. Interrupted sutures are placed every 3.0 mm inferiorly until the incision is closed. Finger pressure using wet gauze is applied to the area for 2 to 3 minutes to assist in achieving hemostasis, and to remold material in the tunnel pocket. Wetted gauze can also have platelet-poor plasma squirted on before placing pressure on the vertical suture site. After 2 weeks, sutures are removed and the vertical incision line is checked for small openings. If small tissue openings are found, it is suggested the patient be placed on an antibiotic, told to brush the incision site with a soft brush, and to return in 2 weeks for another examination.
      Proper suturing technique⁷ will allow the suture ties to stay in for the 2-week suture removal appointment.

Sequence of Proper Suture Tying: Figures 9 to 13

1. Two forward—gently tighten suture next to tissue (Figure 9)
2. One forward—gently tighten suture material, making granny knot (Figure 10)
3. One reverse—secure knot with tight pulling, which forms a square knot (Figure 11)
4. One forward—secure knot with tight pulling, which forms another granny knot (Figure 12)
5. The completed granny-square-granny knot is seen (Figure 13).

     Six months’ healing time will usually produce a 5- to 7-mm increase in the width of the bone. This bone is immature and will be a mixture of new woven bone and more mature bone. However, it does have sufficient strength in which to place implants. After implants are placed in the newly grafted bone, it is recommended that one does not load the implants for 5 to 6 months in order to allow for bone to mature. Future technology could allow for bone grafting mixtures that will obtain mature bone in 3 to 4 months under the tissue of the resorbed mandibular bone with a barrier using the tunneling technique.
Photos in Figures 14 to 21 show a tunneling procedure that gained 6.0 mm buccal bone growth, allowing for the placement of 3 implants and leaving 1.0 mm of both buccal and lingual bone to support the implants.

DISCUSSION AND CLOSING COMMENTS
Mandibular posterior edentulous bone can exhibit bone loss quickly after tooth removal. This bone loss usually is exhibited from buccal to lingual in the resorbing direction. Reduction of the bone width to less than 4.0 mm will not allow for placement of an implant of 3.7 to 4.0 mm in diameter, as a single implant or bridge abutment. Ideal bone conditions will have the minimum of 1.0 mm of buccal and 1.0 mm of lingual bone surrounding the embedded implant.

Figure 14. Pre-op photo.	Figure 15. Pre-op diagnostic model.
Figure 16. Vertical incision unattached gingivae.	Figure 17. Intraoperative showing laminar barrier.
Figure 18. Post-op diagnostic model.	Figure 19. Mature graft.
Figure 20. Five-year post-op x-ray.	Figure 21. Five-year post-op prosthetics.

     Block bone grafting can restore the width by securing bone from the patient donor site areas or by using cadaver bone blocks screwed into position. Drawbacks of using the bone block treatment are that autogenous bone must be obtained from the patient’s chin, ramus, or hip area; and that the donor site must be grafted and healed, which can be traumatic to the patient. Another area of caution: there must be sufficient tissue in the area to close over the block bone graft. It is important to close the tissue with a nontension tissue flap to avoid opening of the tissue site during the healing period and thus exposing the underlying grafted bone.
      The technique illustrated in this article ensures tissue closure over the grafted site, reducing the chance of graft exposure through breakdown of the sutured tissue flaps. With placement of laminar bone/Inion GTR barrier as the “roof” of the grafted site, bone maturation can occur without tissue in-growth into the grafted bone. Six months post-op exposure produces bone width of 4 to 6 mm of additional buccal bone growth over the existing ridge width. In the authors’ experiences, this procedure has proven successful in more than 85% of the cases performed.

References

1. Misch CM. Ridge augmentation using mandibular ramus bone grafts for the placement of dental implants: presentation of a technique. Pract Periodontics Aesthet Dent. 1996;8:127-135.
2. Block MS, Degen M. Horizontal ridge augmentation using human mineralized particulate bone: preliminary results. J Oral Maxillofac Surg. 2004;62(9 suppl 2):67-72.
3. Misch CM. Comparison of intraoral donor sites for onlay grafting prior to implant placement. Int J Oral Maxillofac Implants. 1997;12:767-776.
4. Block MS, Kent JN. Factors associated with soft- and hard-tissue compromise of endosseous implants. J Oral Maxillofac Surg. 1990;48:1153-1160.
5. Jensen OT, Shulman LB, Block MS, et al. Report of the Sinus Consensus Conference of 1996. Int J Oral Maxillofac Implants. 1998;13(suppl):11-45.
6. Grageda E. Platelet-rich plasma and bone grafting materials: a review and a standardized research protocol. Implant Dent. 2004;13:301-309.
7. Heller AL, Heller RL, Cook G, et al. Soft tissue management techniques for implant dentistry: a clinical guide. J Oral Implantol. 2000;26:91-103.

Dr. Alfred “Duke” Heller, founder and director of the Midwest Implant Institute, limits his practice to the placement of dental implants and has placed more than 20,000 implants since 1969. He received both his DDS (1962) and MS (1974) degrees from The Ohio State University College of Dentistry. He is a Fellow of the American Academy of Implant Dentistry, is board-certified in oral implantology, and is past president of the American Board of Oral Implantology. He has taught in 8 dental schools, teaching hands-on surgical courses where doctors place implants under his supervision. He can be reached at (614) 885-1215 or via e-mail at dukeheller@copper.net.

Dr. Robert Heller is a graduate of Ohio Wesleyan University and The Ohio State University College of Dentistry (1988). He completed a prosthetic residency at Medical College of Virginia (1990) and a hospital implant residency at Loma Linda Dental School in Calif (1997). He served as president of the Ohio Section of the American College of Prosthodontics and chairman for the Ohio Dental Association’s Sub-Council on Young Dentists. He is a teaching faculty member since 1995 and director of the prosthetic arm of Midwest Implant Institute. He can be reached at (614) 885-1215 or via e-mail at rob@implantdentist.org.

Disclosure: Drs. Alfred Heller and Robert Heller report no conflicts of interest.