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Cortical Tenting Technique Versus Onlay Layered Technique for Vertical Augmentation of Atrophic Posterior Mandibles: A Split-Mouth Pilot Study Golnaz Morad, DDS,* and Arash Khojasteh, DMD, MS†

he progressive decrease in the alveolar bone volume after tooth loss impedes the use of dental implants for rehabilitation of edentulous regions. This fact is of utmost significance in the posterior areas of mandible, where the presence of inferior alveolar nerve further complicates the proper insertion of dental implants.1 Placement of short-length implants in areas with 7- to 8-mm bone over the inferior alveolar nerve canal minimizes the risk of nerve encroachment.2,3 This treatment modality is, however, prone to criticism due to the dubious survival rate associated with short-length fixtures.3,4 Moreover, utilization of short implants may not be feasible in cases of severely resorbed alveolar ridges.2 However, lateralization of the inferior alveolar nerve allows for implant placement in atrophic alveolar ridges; yet, this technique-sensitive procedure might lead to transitory or perman-

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*Research Fellow, Dental Research Center, Research Institute of Dental Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran. †Associate Professor and Director of Basic Science Research, Department of Oral and Maxillofacial Surgery, Dental Research Center, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran.

Reprint requests and correspondence to: Arash Khojasteh, DMD, MS, Department of Oral and Maxillofacial Surgery, Dental Research Center, School of Dentistry, Shahid Beheshti University of Medical Sciences, Daneshjou Boulevard, Evin, Tehran 19839, Iran, Phone: +98-912-1060032, Fax: +98-21-88507688, E-mail: [email protected] ISSN 1056-6163/13/02206-566 Implant Dentistry Volume 22  Number 6 Copyright © 2013 by Lippincott Williams & Wilkins DOI: 10.1097/01.id.0000433590.33926.af

Purpose: This study intended to compare the efficacy of onlay layered and cortical tenting grafting techniques for vertical alveolar augmentation. Materials and Methods: Six patients with bilaterally edentulous atrophic posterior mandibles received 2 thin ramus blocks, covered with bovine bone mineral on 1 side (onlay layered technique), whereas in the opposite side (cortical tenting technique), a thin ramus block was placed over the ridge keeping a distance that was filled with particulate autogenous bone and bovine bone mineral (50:50). Bone height over the mandibular canal was measured on panoramic radiographies taken preoperatively,

and 2 weeks and 4 months postoperatively. Results: The amount of augmentation in the tenting group (5.2 6 0.76 mm) was higher than the onlay group (4.48 6 0.51 mm). Graft resorption was 1.75 6 1.08 mm in the onlay group and 1.17 6 0.41 mm in the tenting group. Neither of the differences regarding the amount of augmentation and graft resorption was statistically significant (P ¼ 0.345 and 0831, respectively). Conclusion: Both of the examined techniques might be favorable methods for vertical augmentation. (Implant Dent 2013;22:566–571) Key Words: vertical bone augmentation, alveolar ridge augmentation, onlay bone graft, block bone graft

ent nerve damage.5,6 Considering the drawbacks of the non-reconstructive treatment options, restoring deficits of alveolar ridges by reconstructive procedures might still be more practicable, despite the invasiveness.1,7,8 The majority of reconstructive techniques involve a process of bone grafting. The onlay bone grafting technique, being associated with minimal complexity of procedure and promising results, has become a prominent method for vertical ridge augmentation.9 The unpredictable amount of graft resorption, however, remains a major draw-

back.10 Introduction of guided bone regeneration (GBR) principles into practice has led to encouraging outcomes, as regards the reduction of graft resorption. Still, potential complications associated with membranes, namely membrane exposure and infection, counter the favorability of membrane usage.11 Within the last 2 decades, different modifications to conventional augmentation methods have been brought into the literature. The 3-dimensional reconstruction technique12 successfully applied the concept of exploiting high-strength cortical bone

IMPLANT DENTISTRY / VOLUME 22, NUMBER 6 2013 blocks for protection of particulate bone substitutes in vertical and horizontal deficiencies. The efficacy of this concept was subsequently approved with cortical tenting technique in which cortical blocks were tented over the particulate material to increase the ridge width.13 However, resorption of block bone grafts has been successfully diminished using particulate bovine bone mineral as a protective layer over onlay bone grafts.14–16 However, the experiments involving this type of protective layer have mainly focused on the enhancement of ridge width, and its efficacy in vertical ridge augmentation has remained unclear. Considering the scarcity of experiments evaluating these 2 concepts, this splitmouth pilot study aimed to appraise and to compare their efficacy for vertical augmentation of atrophic posterior mandibles. The amount of augmentation and graft resorption associated with an onlay layered technique, using 2 layers of cortical ramus bone covered with a layer of particulate bovine bone mineral, was compared with those of a cortical tenting technique, with a thin block of ramus cortical bone stabilized over a mixture of particulate autogenous bone and particulate bovine bone mineral.

MATERIALS

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Fig. 1. Onlay layered technique. A, The ipsilateral ramus graft was cut in width and the 2 blocks were fixed upon each other. B, Particulate bovine bone substitute was applied to the periphery of the graft. Additional material was applied on top of the graft immediately before the flap closure.

Fig. 2. Cortical tenting technique. A, The ramus block was fixed over the edentulous ridge with a distance. B, The underlying gap was filled with a mixture of particulate bovine bone and autogenous bone.

METHODS

This prospective pilot study included patients who were scheduled for a vertical augmentation procedure before the implant placement in posterior mandibular edentulous regions. Patients with unremarkable medical history were enrolled in this study. To be eligible, participants were also required to be bilaterally edentulous in the posterior mandible. Vertical alveolar ridge deficiency, defined as the bilateral lack of adequate bone for receiving 8-mm dental implants with a 2-mm safety distance to mandibular canal, was approved based on the clinical examinations and the cone beam computed tomography (CBCT) scans taken before treatment planning. Patients were subjected to alveolar ridge augmentation with a split-mouth approach. Randomly, 1 side of the posterior mandible received 2 layers of thin lateral ramus bone grafts covered with particulate bovine bone mineral (the onlay layered group), whereas the opposite side was reconstructed in a tenting fashion via a combination of bovine

Fig. 3. At the time of re-entry for implant placement, 4 months after grafting, residual particulate xenogenic material was observed in both the onlay layered group (A) and the cortical tenting group (B).

bone mineral and autogenous bone (50:50 ratio), filling the space beneath a thin layer of lateral ramus block (the cortical tenting group). After a comprehensive explanation of the procedure, possible complications, and alternatives, a written informed consent was obtained from each participant. All surgeries were performed by the same surgeon (A.K.).

Surgical Procedure

The premedication prescription included 500 mg amoxicillin (Tehran Chemie, Tehran, Iran), 400 mg ibuprofen (Rouz Darou, Tehran, Iran), and 0.5 mg dexamethasone (Iran Hormone, Tehran, Iran). Bilateral local anesthesia was achieved by lidocaine 2% with adrenaline 1:100,000.

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A mid-crestal incision was made on the edentulous alveolar ridge with an intrasulcular extension to the adjacent teeth. Furthermore, extending the incision over the oblique ridge provided access to the ramus area for graft harvesting. A full-thickness flap was fully retracted. To obtain cortical ramus blocks, vertical and horizontal osteotomies limited to the cortical bone were performed using a fissure bur under copious irrigation with saline. Extreme care was made to avoid inferior alveolar nerve injury. The outlined graft was subsequently levered and disengaged from its bed by means of careful application of a chisel. In the mandibular sides, scheduled to receive the onlay layered technique, the ipsilateral harvested graft was cut in width into 2 separate blocks by a wheel saw. Using a large round bur, sharp edges of the harvested graft were rounded and the graft was properly trimmed to adapt to the recipient bed. Fixation screw holes were created on the blocks using a drill. As depicted in Figure 1, A, to achieve the required amount of augmentation, 1 block was placed over the other and the 2 blocks were firmly fixed to the alveolar ridge by means of fixation screws (10–12 mm; Jeil, Seoul, South Korea). Before graft fixation, the recipient bed was decorticated to enhance the vascularization of the augmented area. The periphery of the onlay blocks was covered with a layer of particulate



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anorganic bovine bone mineral (Cerabone; Botiss medical, Berlin, Germany) (Fig. 1, B). Immediately before the flap closure, additional particulate material was applied on top of the grafts. The flaps were subsequently closed with periosteal traction on both lingual and buccal sides, using continuous horizontal mattress sutures (5-0 Vicryl; Ethicon, Inc., Sint-Stevens-Woluwe, Belgium). In the opposite side of the mandible (the cortical tenting group), the harvested block was placed over the deficient edentulous area with a distance of at least 4 mm (Fig. 2, A). A periosteal elevator placed between the bone block and the recipient site maintained the desired distance while the fixation microscrews (10–12 mm in length; Jeil) were tightened. The underlying gap was filled with a mixture of particulate anorganic bovine bone mineral (Cerabone) and particulate autogenous bone provided during the cortical graft harvest and trimming (Fig. 2, B). The flap closure was similar to the opposite site. Postoperatively, patients were prescribed an antibiotic prophylactic regimen (amoxicillin 500 mg 3 times a day, for 7 days), analgesics (ibuprofen 400 mg alone or with acetaminophen codeine 300/10 mg, for moderate and severe pain, respectively), as well as a single intramuscular injection of 8 mg dexamethasone (Alborz Darou, Tehran, Iran) and 75 mg diclofenac (Troge Medical GmbH,

Hamburg, Germany). The patients were also instructed to use chlorhexidine mouthwash 0.2% (Behsa Pharmaceutical, Tehran, Iran) for a week from the day after surgery. Sutures were removed 14 days after surgery. The patients were visited biweekly during the first month, and the follow-up examinations were continued at a monthly interval before implant placement. A 4-month healing period was considered for graft integration before the implant surgery. Bone Gain Measurements

The height of alveolar bone over the mandibular canal on both sides of the mandible was measured using panoramic radiographies taken before the augmentation surgery (Bone height 0; BH0), 2 weeks after ridge augmentation (BH1), and 4 months postoperatively, at the time of implant placement (BH2). Using BH0 measurements, the amount of initial vertical deficiency for receiving 8-mm dental implants with a 2-mm distance from the alveolar nerve was calculated. The amount of bone augmentation 2 weeks after surgery, considered as the initial bone gain (BH1 − BH0) and the amount of final bone gain at the time of implant placement (BH2 − BH0) was also measured. The difference between the initial and the final bone gain (BH2 − BH1) demonstrated the amount of graft resorption within the 4-month healing period. To minimize the effect of radiographic magnification on the accomplished

Table 1. Demographic Information and Data Regarding the Amount of Bone Augmentation and Graft Resorption, Obtained From the Panoramic Radiographs

Patient

Gender

Age

Type of Edentulism

Type of Augmentation

Initial Bone Height (BH0, mm)

1

F

55

Complete

2

F

58

Partial

3

F

49

Partial

4

M

54

Partial

5

F

62

Partial

6

M

57

Complete

Tenting Onlay Tenting Onlay Tenting Onlay Tenting Onlay Tenting Onlay Tenting Onlay

6.2 5.4 6.5 7.5 4.4 5.6 5.4 5.5 7 7.5 6.3 6.1

Bone Height Gain (mm) 2-wk Postoperative

At Implant Placement

Bone Graft Resorption (Total Amount of Augmentation, %)

5.8 7.6 6.5 5.5 7.6 7.4 6.6 5.5 6 4.5 5.7 5.9

4.8 4.6 5.5 4.5 6.6 4.9 4.6 3.5 5 4.5 4.7 4.9

17.24 39.47 15.38 18.18 13.16 33.78 30.30 36.36 16.67 0 17.54 28.99

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Fig. 4. Two weeks after operation. The initial amount of augmentation at this time was not significant between the 2 groups. A, Onlay layered group. B, Cortical tenting group.

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the amount of graft resorption as the percentage of the total amount of augmentation. At the time of implant placement, the mean amount of bone height gain was higher in the tenting group (5.2 6 0.76 mm) compared with the onlay group (4.48 6 0.51 mm). However, this difference was also found not to be statistically significant (P ¼ 0.051). All participants could receive 8- to 10-mm dental implants with 3.8- to 4.5-mm diameter at both sides of the mandible.

DISCUSSION

Fig. 5. Four months after operation. A greater amount of resorption could be observed in the onlay layered group (A) compared with the cortical tenting group (B).

results, all panoramic radiographies were taken in the same radiology center, using the same device. Statistical Analysis

All data were analyzed using Statistical Package for Social Sciences (SPSS software), version 17.0 (SPSS Inc., Chicago, IL). Test of significance was executed using paired-samples t test. Statistical significance was taken as a P value # 0.05.

RESULTS Six patients, 4 women and 2 men, with an average age of 55.8 years (49–62 years old), were enrolled in this splitmouth study (Table 1). Four participants had partial edentulism in the posterior mandibular regions, whereas the other 2 were fully edentulous. Soft tissue healing occurred uneventfully. No complication was observed in the bilateral donor sites. Panoramic radiographies taken at the time of implant placement, 4 months after grafting, revealed acceptable integration of grafts to the recipient bone.

On re-entering for implant placement, the residuals of particulate materials could be observed on both sides of the mandibles (Fig. 3, A and B). The bone quality on both sides was D2/D3 in all patients. The mean amount of initial vertical deficiency for placing 8-mm dental implants with a 2-mm safety distance was 3.73 6 0.98 mm (ranging from 2.5 to 4.6 mm) in the onlay group, whereas in the tenting group, this measurement was 4.03 6 0.93 mm (ranging from 3 to 4.6 mm). The average of the initial bone height gain, measured 2 weeks postoperatively, was 6.23 6 1.24 mm in the onlay group and 6.37 6 0.71 mm in the tenting group (Fig. 4, A and B). The difference of the amount of initial vertical deficiency and the initial bone augmentation between the 2 groups was not significant (P ¼ 0.374 and 0.818, respectively). Within the 4-month healing period, a greater amount of graft resorption was observed in the onlay group (1.75 6 1.08 mm) compared with the tenting group (1.17 6 0.41 mm), although not statistically significant (P ¼ 0.256) (Fig. 5, A and B). Table 1 also represents

Donor site selection for reconstruction of deficient edentulous areas of jaw via bone grafting might differ based on the physical and biological characteristics anticipated from the harvested bone.17 Among the intraoral donor sites, ramus is one of the most practicable alternatives for long-span augmentations. An approximate 25- to 40-mm length bone block can be harvested from this area using different techniques. Yet the limited thickness of the harvested block due to the critical anatomical proximities, questions its suitability for vertical augmentation of severely resorbed ridges.17–19 As has been previously proposed in the literature,19 in contrast to the conventional onlay bone grafting, the onlay layered grafting method provides greater amounts of augmentation by using 2 layers of cortical ramus blocks fixed upon each other. Similarly, in the cortical tenting technique, fixing a single ramus block over the edentulous ridge while maintaining a distance underneath to be filled with particulate bone material makes large augmentations achievable. The current experiment demonstrated both techniques as equally efficient for vertical augmentation of atrophic posterior mandibles. Osteoregeneration within a grafted area largely depends on the activity of osteogenic cells migrated from the recipient bed because a limited number of osteogenic cells within the harvested bone graft survive and function in the recipient site. Adequate number of osteogenic cells is only provided by proper revascularization of the bone graft, which is considered a major success criterion for grafting procedures.20–22 It has been proven that with particulate bone materials, neoangiogenesis is established

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more rapidly than when blocks of bone grafts are used, particularly cortical bone blocks with minimal revascularization potency.23 Because the total amount of required augmentation is provided by layers of cortical bone blocks with the onlay layered technique, the likelihood of graft loss due to lack of vascularization of the outer layers might be significant. In contrast, application of particulate bone substitutes under the cortical block in the tenting technique might facilitate the revascularization of the area, leading to more favorable augmentation results. Khoury and Khoury12 could achieve 7.8 mm of vertical augmentation by securing particulate autogenous bone grafts with cortical ramus blocks. Although not statistically significant, a greater bone height gain was achieved in the cortical tenting group in this study. The cortical bone was assumed to have protected the particulate materials from the soft tissue pressure and consequent resorption. Application of particulate bone substitutes for vertical augmentation is largely limited to GBR procedures in which membranes are used to stabilize the materials.24–26 However, membranes might not be quite desirable, given the possibility of membrane exposure, infection, and healing impediment.11 In the cortical tenting grafting technique, the cortical bone block fixed over the particulate bone substitutes, not only serves as a protective membrane preventing from displacement of particulate materials but also greatly endures resorption. In a previous retrospective study conducted by the authors,27 the cortical tenting technique was evaluated in 37 cases of vertical ridge augmentation in different areas of jaw. Enhancement of bone height allowed for proper implant placement. However, due to the lack of immediate postoperative measurements, the amount of graft resorption before implant placement could not be assessed. In this study, graft resorption after 4 months was measured to be 1.17 6 0.41 mm in the tenting group. Although not statistically significant, this measurement was less than the amount of resorption in the onlay layered group (1.75 6 1.08 mm) in which the 2 mandibular blocks, fixed upon each other, were subsequently covered with a layer of particulate xenogenic bone material. Various experiments



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have suggested a slow resorption rate for xenogenic material.20,28,29 Maiorana et al15 treated horizontal deficiencies of alveolar ridges in 26 patients with mandibular onlay bone blocks. In 12 patients (the test group), the blocks were covered with a layer of bovine bone substitute. After 5.3 months of healing, bone resorption in the test group was 9.3% compared with 18.3% in the control group. Other animal30 and human14,16,31 studies have also proved the antiresorption effect of xenogenic bone substitute layer, with or without application of membranes, in lateral augmentation models. The efficacy of this protective layer for vertical augmentation was evaluated in a study by Proussaefs et al,32 who applied a mixture of autogenous and xenogenic particulate bone materials around onlay ramus bone blocks. Considering the resorption rate reported in this study (radiographic resorption rate, 16.38%), the layer of particulate material might have not provided an antiresorption action because the bone blocks were not covered with this layer on the top, which would be the most susceptible part to resorption. In this study, all peripheral aspects of the bone blocks were completely covered with particulate xenogenic material, and additional material was applied on top of the grafts immediately before flap closure. Residual particulate material could be observed at the time of re-entry for implant placement. It is noteworthy that in this study, due to lack of a control group, no conclusion could be made on the efficacy of this xenogenic layer for graft preservation in vertically augmented ridges. However, the accomplished results indicated that cortical bone block serving as a protection for particulate bone materials might be as effective, if not more so, than particulate xenogenic bone covering layers of cortical blocks for vertical augmentation of posterior mandibles. It should be mentioned that the measurements taken on panoramic radiographies, even if taken under similar exposure conditions, are still prone to impreciseness due to distortions caused by patient motion and measurement errors. However, despite the greater precision, CBCT scans were not required for all the patients at followups in this study. Therefore, it was not

ethically acceptable to have the patients undergo CBCT scanning at all the time points considered for measurements. The split-mouth design used in this experiment allowed for a more accurate comparison of the 2 augmentation techniques by eliminating intersubject variability.33 However, the small number of participants in this pilot study might affect the validity of the accomplished results. To explicitly determine the practicability of these techniques for vertical reconstruction of atrophic alveolar ridges, more controlled trials with larger number of patients are warranted.

CONCLUSION This split-mouth study demonstrated that application of ramus bone grafts with xenogenic particulate bone substitutes in either an onlay layered or a cortical tenting fashion might be favorable for reconstruction of the vertical deficiencies in posterior mandibles.

DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.

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Cortical tenting technique versus onlay layered technique for vertical augmentation of atrophic posterior mandibles: a split-mouth pilot study.

This study intended to compare the efficacy of onlay layered and cortical tenting grafting techniques for vertical alveolar augmentation...
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