Soft tissue expansion before vertical ridge augmentation: Inflatable silicone balloons or self-filling osmotic tissue expanders?

Recent advances in periodontal plastic surgical procedures allow the clinician to reconstruct deficient alveolar ridges in more predictable ways than previously possible. Placement of implant/s in resorbed ridges poses numerous challenges to the clinician for successful esthetic and functional rehabilitation. The reconstruction frequently utilizes one or combination of periodontal plastic surgical procedures in conjunction with autogenous bone grafting, allogenic bone block grafting, ridge split techniques, distraction osteogenesis, or guided bone regeneration (GBR) for most predictable outcomes. Current surgical modalities used in reconstruction of alveolar ridge (horizontal and/or vertical component) often involve the need of flap transfer. Moreover, there is compromise in tissue integrity and color match owing to different surgical site and the tissue utilized is insufficient in quantity leading to post surgical graft exposition and/or loss of grafted bone. Soft tissue expansion (STE) by implantation of inflatable silicone balloon or self filling osmotic tissue expanders before reconstructive surgery can overcome these disadvantages and certainly holds a promise for effective method for generation of soft tissue thereby achieving predictable augmentation of deficient alveolar ridges for the implant success. This article focuses and compares these distinct tissue expanders for their clinical efficacy of achieving excess tissue that predominantly seems to be prerequisite for ridge augmentation which can be reasonably followed by successful placement of endosseous fixtures.

INTRODUCTION

The deficient alveolar ridges always present with numerous challenges to the clinician for achieving predictable augmentation.[1234567] With the up rise of implant therapy and increased esthetic, phonetic, and functional demands from the patient, the reconstruction of resorbed alveolar ridges has become the basic essentiality for placement and survival of implant and thus often requires hard and soft tissue reconstruction.[23] Preservation of alveolar ridge at the time of extraction helps in the reduction of future damage but usually requires further surgical augmentation procedures prior to final prosthetic reconstruction. Immediate ridge augmentation can be performed at the time of tooth extraction. It enables the operators to reduce the number of surgeries and to achieve optimal ridge architecture.[4] Till today, a variety of techniques and their combinations are used which include autogenous bone block grafts,[2] allogenic bone blocks,[3] GBR,[5] ridge splitting techniques,[235] distraction osteogenesis,[23] onlay grafts,[678910] or multiple heterologous cortical bone sheets,[11] that provided a predictable volume of regenerated bone after healing. Many of these reconstructive efforts are limited in the efficacy due to inadequate flap coverage and vascular perfusion. Procedures to prevent the collapse of the alveolar ridge are highly technique sensitive and require different surgical designs depending upon the size of the defect.[6] Soft tissue expansion (STE) is a new modality that generates excess tissue[1] of proper quantity and color without flap transfer or residual defect, which is so desirable during reconstruction of resorbed alveolar ridges and a variety of bone augmentation techniques used to improve the horizontal and vertical dimensions of ridge defects for placement of implants.[1213141516] When applied for lateral ridge augmentation, autogenous bone block grafts or guided bone regeneration (GBR) techniques provide a predictable volume of generated bone after healing.[17] On the other hand, the outcome of vertical ridge augmentation appears less clear. Clinical and histological data support the feasibility of vertical augmentation procedures such as onlay grafting; inlay grafting, distraction osteogenesis, or GBR.[1819] However, these surgical procedures are considered highly technique sensitive and the findings are difficult to extrapolate.[20] Although the reported incidence of post operative complications varies highly among studies, it is apparent that soft tissue dehiscence and exposure of bone grafts to the oral cavity are common complications of vertical ridge augmentation, comprising the outcome and leading to partial or complete loss of the graft material in up to 40% of the cases.[21222324]

Exposure of graft is mainly attributed to difficulties in achieving tension free closure of the flap.[25] Generally, the elevation of a flap disturbs perfusion and causes ischemia.[26] Conversely, the ischemia-reperfusion injury may cause necrosis of flap. Accordingly, a direct relation between the extent of surgical trauma and concomitant disturbance of perfusion has been shown for periodontal surgical procedures with different degree of tissue traumatization.[2027] Given that tissue mobilization for achieving tension free primary wound closure for vertical augmentation is considerably more traumatic compared with a straight forward lateral augmentation procedure, soft tissue quality and quantity appears as key factor for predictable success.[20]

Notwithstanding complications, volume maintenance during healing is another major concern, as up to 60% of graft volume may be resorbed during healing.[17] Again compromised vascularization and tension of the flap by soft tissue movement and subsequent limitation of regenerative space have been considered as causes for limited outcomes in vertical ridge augmentation in animals[28] and in humans.[21] Thus, it may be concluded that an antecedent improvement of soft tissue quality and quantity could enhance the outcome of vertical bone regeneration.[20]

Generation of soft tissue by using subcutaneous tissue expanders before reconstructive procedures is an established method of plastic surgery. After implantation, the increase of expander volume over time causes tension on the surrounding tissue and results finally in tissue gain.[2930] Presently, these expanders are used for a variety of indications, such as breast reconstruction, defect coverage after excision and preparations of tissue donor sites.[3132] Therefore, these expanders are successfully used for reconstruction of deficient alveolar ridges and thus overcome the numerous disadvantages associated with other surgical procedures. The periodontist is now able to incorporate the principles of GBR along with soft tissue modifications[3334] that permit the optimum placement of endosseous fixtures.

Soft tissue expansion using silicone balloons

Surgical procedure

Soft tissue expansion is a new modality which utilizes the “classical” type sub-periosteal tissue expander (made up of pure medical grade silicone) to produce excess gingival tissue with success.[121416] The custom fabrication of the sub-periosteal tissue expander utilizes the liquid processing unit using pure silicone which makes them inflatable. The expander is marketed by CUI (Cox Uphoff International, Santa Barbara, California[14] or Xemax Surgical products[15]) [Figure 1a and b].

Figure 1

(a) Silicone balloon expander with extension tags (Cox Uphoff Inc.). (b) Silicone balloon tested for leaks prior subperiosteal placement (Xemax Surgical Products)

The subperiosteal tissue expander consists of two parts

A silicone body (the bag with extension tags) (also called the port or “the balloon”)

The bag can be custom made[141516] both in dimensions and curvature in order to fit specific clinical requirements at the defect site which is placed under the reflected periosteum. The extension tags (custom made) can extend from the reservoir bag. These tags assist in securing it with resorbable sutures to approximate location on the ridge deformity

A tube with a self sealing valve to allow incremental inflation of the bag with saline that induces the overlying tissue to expand. A 23 gauge needle or even finer needle can be used for internal (surgical) inflation. [Figure 1b] The exit of inflation tubing through the tissue should be determined in order to avoid mechanical trauma to mobile tissue and to allow for optimal patient comfort and easy access to the valve for inflation.[1213141516]

Prior to surgery, the defect site is evaluated thoroughly for the exact dimensions, location, bony boundaries, and relationship of the defect to the oral structures. Block anesthesia is preferably given and infiltration is usually avoided at initial incision site.[15] With the patient under local anesthesia, an incision wide enough to admit the expander is placed on either side of the defect bilaterally. This incision should allow adequate reflection and undermining with minimal tension. The tissue is undermined so that the bag will be in continuous contact with bone[1314] [Figure 2].

Figure 2

Schematic representation of balloon expander in place

The other option is to create a tunnel on the lateral aspect of the defect site by making the initial incision at a location distant from the attached gingival margin of the tooth most distal to the bone level. The periosteum is lifted to allow the insertion of the expander along the bone surface. A similar incision is made on the distal end of the planned expansion site, to tunnel a suture to facilitate stabilization of the expander. The self-sealing tip is left outside the tunnel to allow external inflation of the balloon.[15]

The expander is tested for any leaks prior to its placement by inflating it with saline. The volume can also be measured to ensure functioning capacity of the balloon [Figure 1b]. The expander and its attached tubing are safely secured in place; so that it will not hinder oral tissues.[16] Extra care for suture placement and suturing technique is needed in order to avoid perforation of the reservoir bag during the procedure (needle perforation). The expander is left un inflated or only slightly inflated during first three days, as the blood supply of the flap is determined at the time of initial manipulation and thus it is essential to increase the tolerance of the flap to the initial ischemic episode which peaks at the initial 48 h.[135] The expander is then inflated with saline unless blanching of the tissue occurs [Figure 3]. Over irrigation is avoided as it may cause sequestration of the bag through the oral tissues or a break in suture line. Repeated addition of saline can be practiced with minimal patient discomfort through the tubing at timely intervals in order to generate sufficient tissue. If discomfort was reported by the patient, the pressure was relieved slightly. The process could be repeated until sufficient expansion has been achieved.[1516] Inflation with 0.3 ml saline can be done on alternate or third day for 2 weeks. After 2 weeks the expander is removed by making longitudinal incision on the palatal or lingual aspect of the expanded tissue [Figure 4].

Figure 3

Soft tissue expansion being achieved

Figure 4

Excess soft tissue gain after the removal of expander

When sufficient tissue has been generated it can thereafter be used for tissue coverage over large particulate graft material (hydroxyapatite crystals, FDBA, DMFDBA) which can then be preferably embedded in collagen and covered by a resorbable barrier membrane to facilitate primary closure of the flaps[41215] [Figure 5]. The presence of pre-existent tori or exostoses could be advantageous to obtain adequate amount of graft material.[15]

Figure 5

Ridge augmentation achieved by voluminous particulate HA or allogenic bone blocks

Simultaneous positioning of the excess tissue can be done at CEJ with particulate bone graft. However, scalloping of the gingival tissues can be achieved by gingivoplasty.[14] Prophylactic broad spectrum antibiotics are prescribed during the initial phase of expansion and also after reconstruction are achieved. The patient is asked to rinse with 0.12% of chlorhexidine mouthwash and follow up visits can be spaced every 4 weeks. After 6 months, the endosteal implant/s can be easily placed in an optimal location which is made possible by the augmented ridge.[141519]

Advantages of STE

Allows better wound closure without compromising the blood supply of the flap.[15]

Eliminates the need for harvesting connective tissue graft and avoids the multiple phases of flap transfer when ridge augmentation is contemplated by using soft tissue onlay grafts.[12131415]

Augments the keratinized tissue at the recipient sites and the color, texture and thickness of the tissue obtained is maintained.[14153335]

Expanded flaps have increased vascularity; hence, their transfer may be safer.[34]

Disadvantages of STE

Requires an altered clinical judgment for evaluation of the defect site.[14]

Multiple office visits for the addition of saline to achieve gradual expansion of the expander.[141516]

Possible infection, seroma formation, and tissue necrosis because of over expansion.[152032]

Bothersome for the patient in that expander may interfere with movements of oral soft tissues.[1315]

Possible perforation of the silicone bag (because of sharp bony projections and/or needle perforation).[1415]

Implications of STE for ridge augmentation

The need for using STE as an alternate treatment modality for ridge augmentation appears to be promising as the need for flap transfer, color match and thickness and quantity of tissue being generated especially to augment localized ridge defects poses magnitude of problems to the clinician. Also the effective primary closure of the flaps during various surgical procedures such as autogenous bone block graft, particulate bone grafts, guided bone regeneration etc., for treatment of such defects is always challenging owing to the deficiency of soft tissue. Additionally, in most of the cases compliance is questionable, regarding the need for obtaining a sizeable graft from the mandibular symphysis, ramus, iliac crest region, hard palate (onlay graft), accounts for discomfort and pain with two surgical sites being involved.[233435]

Although STE using inflatable silicone balloons finds an astute alternative for management of such defects, the concept of thick versus thin gingival biotype have different responses to inflammation and trauma.[36] The chances of perforation owing to thin gingival biotype may lead to increased chances of infection and seroma formation in the process of tissue expansion. Therefore, STE need to be judiciously performed to gain excess tissue for desired ridge augmentation and subsequent implant therapy.

The osmotic tissue expander is a new device made of hydrogel which absorbs body fluids and leads to gradual swelling of the device. The swelling phase is completed in 6 to 8 weeks and results in tissue gain. Different shapes and sizes are available to be used in almost every area of the body. The expander is 10% of its final volume and only requires a short incision and a small pocket which allows easy introduction and retrieval from the surgical area.[32]

Recently, (Kaner and Friedman 2011) application of self inflating osmotic (hydrogel) tissue expanders has been shown to be successful for vertical ridge augmentation with regard to clinical and histological outcomes and complications.[20] Twenty four sites in twelve patients were treated with STE; primary wound closure was easily achieved and the incidence of graft exposition was low (4%). At implant placement; vertical bone gain of 7.5 ± 2.4 mm was found which was comparatively higher with other studies reporting mean bone gain of 4.13-1.05 mm (range 2.2-5.1 mm)[20] and to data similarly aggregated in a systematic review (mean vertical bone gain: 4.8 mm, incidence of graft exposition 18.8%).[37] Micro CTs of bone revealed a good ratio of bone volume/tissue volume (mean BV/TV = 0.1614 ± 0.5), indicating good structural quality of bone obtained after STE.[20]

Soft tissue expansion using osmotic tissue expanders

Surgical Procedure

Osmotic self-filling tissue expanders consists of a polymer of methyl methacrylate/vinylpyrrolidone and expand due to absorption of body fluids. They are ensheathed with silicone shell containing multiple perforations which allow the influx of tissue fluids; while the rate of influx over time (and therefore speed of the volume increases) is controlled by number of perforations. Unlike the first generation of balloon expanders which were not ensheathed by silicone,[32] these swell slowly and continuously and injection dependent peaks are avoided.[38] These expanders are available as round ended hemispherical cylinders with variant sizes of 0.24, 0.35, 0.7, 1.3, or 2.1 ml final volume (“Dental Cupola slow, “Dental cylinder slow”, Osmed Ilmenau, Germany)[20] where the type and size appropriate for edentulous site with a swelling time of 60 days can be selected with surgical templates corresponding to the final expander volume[20] [Figures 6 and 7]. Initial incision was performed and a submucosal pouch was prepared with scalpel and scissors without the elevation of periosteum [Figures 8 and 9]. This offers the advantage over subperiosteal placement of the expanders as expansion of the periosteum is not to be expected; it is replaced by fibrous connective tissue after subperiosteal implantation of tissue expanders,[39] while a new periosteum is formed underneath the expander. Furthermore, subperiosteal implantation causes significant resorption of the underlying bone,[40] a finding which is not reported when hydrogel tissue expanders are used.[20]

Figure 6

Cylindrical tissue expanders before and after swelling

Figure 7

Surgical template being used prior placement of the hydrogel expander

Figure 8

Initial incision performed

Figure 9

Scissor being used for enlarging the incision to accommodate the expander

The size of the pouch was controlled with surgical template (corresponding to initial expander (volume) that the size should easily fit into the pouch. The expander was placed into the pouch with a bone fixation screw [Figure 10]. A meticulous two-layer wound closure was performed using fine monofilament sutures [Figure 11]. Administration of antibiotics (amoxicillin 750 mg or clindamycin 600 mg) was started 1 h before surgery and continued for 7 days. Ibuprofen (400 mg) was prescribed as analgesic. Patients were followed up weekly and were advised to rinse with 0.2% chlorhexidine for 2 weeks until suture removal. Abstention from removable prosthesis was required. Fixed provisional prostheses were adjusted regularly according to the increasing soft tissue volume. Bone augmentation was carried out after 6-8 weeks of expansion, when the expansion has reached its final volume [Figure 12].

Figure 10

Expander stabilized with fixation screw to achieve excess tissue at the desired defect site

Figure 11

Two layered closure using fine sutures

Figure 12

Soft tissue expansion achieved for ridge augmentation and subsequent implant placement

Expander removal and bone augmentation

Depending on the needed graft volume and the availability of intra oral donor bone, bone grafts were harvested from the mandibular ramus or the posterior ilium as block grafts with a piezoelectric device (Piezosurgery device 11 Mectron, Koln, Germany). Bone augmentation was done under local anesthesia, under sedation, antiphlogistic medication, and antibiotic coverage. Ibuprofen 600 mg was prescribed as analgesic and patient rinsed with chlorhexidine for 2 weeks.

After midcrestal incision at recipient site, a mucoperiosteal flap was reflected. The expander was removed and the bone was exposed. Generally vertical releasing incisions were avoided; in the case of adjacent teeth present, the incision was extended into the gingival sulcus for ease of reflection. The local bone was perforated and the block graft was secured with screws (Institut Straumann AG, Basel, Switzerland). The graft was covered with a granular bone substitute (Bio Oss) and a collagen membrane (Ossix plus, Colbar, Israel). The incision was closed with modified vertical mattress sutures and single interrupted sutures using fine monofilament sutures. The sutures were removed after 2 weeks. At recipient sites, mucoperiosteal flaps were elevated. Again, releasing incisions were avoided. After removal of the expanders, the local bone was exposed and perforated, and onlay grafts were fixed with screws [Figure 8]. Patients were mobilized after 24 hours and sutures were removed after 1 week. The expanders were weighed after removal and a biopsy was taken from the expanded soft tissue.

Implant placement

In patients treated with ramus grafts and GBR, implants were placed 6 months after bone augmentation, following the standard protocol of non submerged healing Figure 9. Sutures were removed after 1 to 2 weeks.

Radiographs

Cone beam computed tomographies (CBCT) were taken before implantation of tissue expanders, and 4-6 months after bone grafting, before placement of dental implants. Digital panoramic radiographs were made after bone augmentation and after implant placement. The mean vertical bone gain at the surgical site was calculated to the nearest millimeter by subtraction of bone height before grafting from bone height before implantation, using the CBCT software measurement tool after aligning investigation window at reproducible anatomical landmarks which revealed better estimation of bone regeneration.[20]

Biopsies

Biopsy is taken from the expanded soft tissue surrounding the expander was confirmed by absence of inflammatory infiltrate in the fibrin rich dense connective tissue confirming of identical thickness and color, increased vascularity with that of the resident soft tissue.[202133]

Bone core biopsies were obtained at the time of implant placement using a trephine drill for preparation of the implant site. Bone biopsies were investigated using micro CT. Three-dimensional micro CT gave better estimation of bone regeneration than classical 2D histomorphometry using histologic sections because histologic processing results in loss of biopsy material.[41] As microarchitecture reflects bone quality,[42] an appropriate ratio of BV/TV and distinct trabecular structure found in biopsies of regenerated bone further illustrate the good outcome of vertical bone augmentation subsequent to STE.[20]

Summary

“Creep” and mechanical and biologic “stretch” are responsible for tissue expansion. Although, historically surgical tissue expansion was reported by Neumann in 1957 it is being successfully practiced thereafter in various disciplines of patient care.[43] Tissue expansion is based on the simple argument that abdominal wall and breast enlarge many folds in pregnant women but still maintain their normal thickness and skin appendages.

The scientific evidence gathered so far from the clinical studies show that the invaginated areas in the edentulous ridges in which the teeth have been lost or implants have been removed, can be augmented in a vertical direction using the principles of tissue expansion.

This paper reviews two distinct tissue expanders in predictable augmentation of resorbed alveolar ridges. The intra oral use of inflatable silicone balloons for bone graft surgery has occasionally been described only in case reports.[20] Usually these expanders are filled once in a week by injection of saline in subcutaneous injection port until the overlying tissue appears blanched. However decreased tissue perfusion and hypoxia are caused by intra-luminal pressure spikes that result from the intermittent filling technique may lead to tissue necrosis and subsequent perforation of the balloon expander through the mucosa. Therefore, this technique is extremely sensitive and requires refinement of the surgical skills.

On the other hand osmotic tissue expanders increase in their size by absorption of body fluids and need for external filling is eliminated, which may explain the low incidence of infectious complications. Also the supra periosteal placement of hydrogels prevent significant resorption of the underlying bone which is seen with subperiosteal balloon expanders. Additionally, the sub mucosal pouch is easily prepared and well tolerated by the patient. However, the swelling time is 60 days for hydrogels which is four times that of silicone balloons and thus may account for prolonged discomfort but the patients reported it for initial few days and were accustomed with the process of expansion. The interference with the lip, cheek movements for balloon expander can be tolerable as it is removed just after 2 weeks of surgery. Moreover, slow and continuous expansion result in safe and effective generation of soft tissue with the osmotic tissue expanders,[44] which is confirmed histologically by absence of infiltration in the soft tissue biopsies examined.[45] Also the quality of bone obtained after the augmentation is sufficiently dense to support the implants, which additionally is confirmed by the examination of bone core biopsies obtained during the implant placement. The vertical augmentation in return effectively guarantees the success of prosthetic rehabilitation and high patient satisfaction.

CONCLUSION

STE using osmotic tissue expander is invariably advantageous over inflatable silicone balloons for vertical ridge augmentation which are compared in this systematic review. The excess tissue distinctly achieved offered easy augmentation of the ridge defect in terms of horizontal and vertical bone gain. STE is accompanied by minimal complications and the incidence of graft exposition after augmentation surgery is considerably low. The combined treatment results in comparably high vertical bone gain of well structured bone and may help to further improve the outcome and predictability of implant therapy of patients showing severe bone resorption. However, long term clinical trials preferably using osmotic tissue expanders for STE need to be undertaken for ensuring predictable long term success of the implant patient.