In the last few decades, the rehabilitation of maxillary and mandibular edentulous areas with dental implants has become a common practice, with reliable long-term results.1 In some situations, there is a lack of supporting bone due to atrophy, trauma, or surgical resection. Because dental implants can only be placed if there is sufficient bone to adequately stabilize them, bone augmentation procedures represent an effective treatment option. It has been reported that the presence of at least 1 mm in width around the implant bone crest at the buccal and palatal plane is required to achieve an adequate osseointegration and a good treatment outcome.2 In fact, in patients with long-standing edentulous arches, extreme bone resorptions (both vertically and horizontally or combined defects) are frequently observed.3
As a consequence, the use of additional techniques for bone augmentation is essential. Some of these approaches include the use of appropriate growth factors, distraction osteogenesis,1,4 guided bone regeneration, the use of revascularized bone grafts, and techniques for ridge expansion using bone expanders or osteotomes or the approach known as “split-crest.”5–7
The “split-crest” technique consists of splitting the vestibular and buccal cortical tables,5–8 displacing the vestibular cortical bone both in maxilla or mandible to create a middle gap, which is used to contain the inserted implants. The unoccupied space by the implants can be filled with biomaterials such us autologous bone grafts, particulate bone, or plasma derivatives such as plasma rich in growth factors (PRGF).9,10
The use of ultrasonic bone surgery represents an advantageous alternative technique to perform split-crest procedure over conventional surgery using disks and chisels. Ultrasonic device has the ability to cut mineralized hard tissues as teeth or bone in a very safe and precise way, with minor tissue damage.11,12 Soft tissues such as nerves, blood vessels, or the Schneiderian membrane are not altered by the cutting tip because of their ability to oscillate at the same speed and amplitude as the cutting tip.13 Some clinical studies have evaluated the potential of ultrasonic bone surgery in split expansion technique14,15 with satisfactory results in most cases. However, the use and predictability of the conventional split-crest technique is limited when the ridge is reabsorbed into the apical or occlusal points.
This study reports the clinical evaluation of a novel technique based on a modification of the conventional split ridge expansion technique with ultrasonic bone surgery. This procedure is indicated in cases of extremely resorbed ridges and consists on expanding the bone in two consecutive stages. The approach presented herein provides a twofold or even threefold increase in the width of the ridge, facilitating the placement of large diameter implants, that otherwise could not be inserted with the conventional one-stage technique.
A total of nine implants have been placed in six patients after expanding their ridges with the new two-stage split-crest procedure. The status of the soft and hard tissues surrounding the implants and the success of inserted implants have been carefully analyzed. Final clinical evaluations were carried out at least 6 months after loading the definitive implants.
Materials and Methods
This case-series study followed national and international (ICH rules)16 policies on clinical studies. Patient selection for surgical procedure was based on the absence of any local or systemic diseases that might contraindicate the treatment. The clinical histories of all patients were carefully evaluated to obtain the necessary information on demographic, anthropometric data, and the clinical backgrounds of patients.
The study selection criteria included patients of both genders, older than 18 years, with initial insufficient bone ridge for implant placement, and a very compact bone, and submitted to two-stage split-crest expansion technique using ultrasonic device for posterior insertion of dental implants and whose definitive implants were loaded at least 6 months before. Patients who underwent one-stage split technique were not included in the study. Included patients were recalled for a final clinical evaluation in an elapsed time of at least 6 months after implant loading.
Preinsertion Protocol and Medication
The same protocol for surgery and implants insertions were followed in all patients. Subjects received oral hygiene treatment and instructions during the days before the intervention. Antibiotics (1 g of amoxicillin and 1 g of acetaminophen) were prescribed to each patient for 6 days, starting 30 minutes before implant installation. If necessary, one tablet of midazolan 7.5 mg was administered 20 minutes before the intervention to promote patient relaxation and facilitate their collaboration.
At the time before the intervention, 1 minute rinses with chlorhexidine digluconate 0.20% were recommended. Lips and perioral area were also cleaned with chlorhexidine. An infiltrative anesthesia (articaine 40 mg/mL and ephinefrine 0.01 mg/mL) was applied to all patients from vestibular, lingual, or palatine. After the surgery, patients were encouraged to take, in case of pain, acetaminophen (1 g/8 h) or ibuprofen (600 mg/8 h). If the pain persisted, patients were also advised to come to the site for observation.
USBS Device and Two-Stage SPLIT-Crest Surgical Procedure
The split-crest surgical technique procedure was carried out using the piezoelectric surgery device (BTI-Ultrasonic, BTI Biotechnology Institute S.L., Vitoria, Spain). The latter allows operating between 25,000 and 35,000 cycles per second with a new model handpiece that minimizes heat due to the design of the piezoelectric device.
The procedure was performed in two stages. The first stage consisted of a conventional split-crest procedure involving the opening of a full-thickness flap; after which a scaling with the ultrasonic spoon around the bone bed was performed with the aim of stimulating bone bleeding and thus facilitating the subsequent apposition of grafts on the bone surface. The starting drill was used to localize the sites where future implants would be placed. With the use of ultrasonic flat chisel a side-to-side cut in the osseous crest was performed to connect the holes previously created (Fig. 1, A). At that point, the expansion was begun using the different motorized expanders (BTI Biotechnology Institute). The expansion was performed by means of the necessary drills (BTI Biotechnology Institute) depending on bone width and the type of implant to be placed (Fig. 1, B). The drilling sequence was 1.8, 1.8 to 2.5, and 2.5 mm, and exceptionally with 3 mm drills. Then, implants were placed (Figs. 1, C) and the “gap” on the ridge was overcorrected using an initial graft made of autologous bone mixed with liquid PRGF-Endoret (BTI Biotechnology Institute), a second layer consisting of porous bovine inorganic freeze-dried bone (BIOSS, Geistlich, Switzerland) mixed with liquid PRGF-Endoret and a final layer of fibrin membrane from PRGF-Endoret technology (Fig. 1, D). Autologous bone was obtained from a low-speed drilling procedure (50-125 rpm)14 and without irrigation. Closure was made without tension.
Once the osseointegration period was completed (4–6 months), a new full-thickness flap was performed to obtain access to the previously inserted implants that were covered by the gum (Fig. 1, E). The implants that had to be replaced by larger diameter ones were retrieved using the new BTI Extraction Kit (BTI Biotechnology Institute). The new BTI Extraction kit consists of a new wrench that allows a counter torque force of 200 Ncm (the wrench breaks back at that force and alerts us when that value is exceeded), an internal connection extractor, an extractor for external connection, and a set of ratchet handle extension pieces to adapt into different clinical situations. This Extraction Kit facilitates a predictable and a nontraumatic extraction and the insertion of a new implant in the implant bed, because the integrity of the bed is preserved.
Once the transitional implant was atraumatically removed, a new drilling sequence was performed to place the definitive implants (Fig. 1, F). The latter favored a new expansion process, compacting the native bone and enhancing the horizontal bone ridge width. The ridge was overcorrected if necessary, following the same protocol described previously. Implants were loaded in function 4 to 6 months later.
One experienced surgeon following a favorable treatment plan performed all implant installations. Rehabilitations were carried out by three prosthodontists. The latter included careful evaluation of the patient's clinical history, a complete radiological evaluation (conventional x-ray and the BTI Scan program), the elaboration of surgery guides, and the preparation of provisional and final prostheses adapted to each patient. Both transitional and definitive implants were installed without irrigation using a low-speed drilling procedure (50–125 rpm).17 Before installation, all implants were carefully embedded in liquid PRGF-Endoret with the aim of bioactivating the implant surface.9,18,19 PRGF-Endoret was prepared in 9-mL citrated tubes (BTI Biotechnology Institute) from patient's blood, by centrifugation at 580g for 8 minutes at room temperature. The milliliter fraction just located above the sedimented red cells, but not including the buffy coat, was collected and used to humidify the implants.20 In addition, the upper 2 mL of PRGF-Endoret were used to prepare the fibrin scaffold as reported elsewhere.20–22
Before the intervention, patients' general health and dental status were assessed. A computed axial tomography scan was carried out on patients before the intervention, to assess bone quality and quantity, to quantify the ridge height and width of the supporting bone and to locate major anatomical features. All these evidences helped the clinician to make a detailed study using specialized software (BTI Scan program) in implant surgery planning. Just after the intervention, a panoramic radiograph was taken too, to verify the adequate placement of the implants. Once the intervention was conducted, patients were referred to a series of periodic evaluations, consisting normally in: one evaluation 2 to 3 days after intervention, at 1 month, at 3 months, at 6 months, and from this moment ahead, once a year. Panoramic radiographies were repeated normally at least once a year.
Several items were used for data analysis. These variables include demographic items, clinical items, surgery-dependent items and prosthetic variables (Tables 1–4).
At least 6 months after definitive implants loading, patients were recalled for a final clinical evaluation. Between November 2009 and October 2010, six patients attended the final evaluation, which included the following clinical assessments:
- Smoke habits (cigarettes per day).
- Dental hygiene habits (number of brushings per day, use of dental floss, interdental brushes, and mouthwash use).
- Implant status according to the following success criteria23: (1) The implant does not cause any allergic reaction, toxic or infectious local or systemic. (2) The implant offers support for a functional prosthesis. (3) The implant shows no signs of fracture or bend. (4) The implant shows no mobility when it is scanned manually or electronically. (5) The implant shows no signs of radiolucency with an intraoral radiograph. (6) The marginal bone loss (Rx intraoral) and/or attachment loss (probing depth + recession) should not impair the function of anchoring the implant or cause discomfort to the patient for 20 years.
- Status of the soft tissue around each implant: (1) Plaque Index24; (2) Bleeding Index25; (3) probing depth: measured at four sites per implant (mesial, distal, vestibular, and lingual); and (4) suppuration (Yes/No).
- Status of bone tissue: Scanner and measuring of bone expansion achieved in comparison with the scanner before procedure. The measurement of the width of the bony ridge for each implant was made at two points: one in the basal part of the crest and in a middle zone located at 8 mm from the first measurement (defined as apical and occlusal points of the ridge).
Data collection and analysis was performed by two independent examiners (other than restorative dentists). Descriptive statistics were performed considering the implant and the patient as a unit of analysis. Absolute and relative frequency distributions were calculated for qualitative variables and mean values and standard deviations for quantitative variables. Implant survival rate was calculated using a Kaplan-Meier analysis. SPSS version 15.0 for Windows statistical software package (SPSS Inc., Chicago, IL) was used.
Nine patients were eligible for the study and were recalled for a final clinical assessment. However, only six of them attended the visit and were finally included. A total of nine implants (BTI implants) between March 2008 and June 2009 after a two-stage Split-crest procedure for bone ridge expansion with ultrasonic device were inserted. Provisional implants were replaced 4 to 7 months later by definitive larger diameter implants. Final evaluations were conducted at least 6 months after loading, between November 2009 and October 2010.
The mean age of the six patients at first surgery was 61 years (SD = 8.65; range, 52–72 years). Five were females (83.3%). Only one of the patients was smoker (16.7%). Two patients (33.3%) had previous periodontal disease, and none of them had bruxism. None of the patients showed pathologies affecting the maxilla or previous head-neck radiation. Table 1 describes the cases and implants involved in surgical procedures.
Patient's mean follow-up period between first surgery time and final examination was 19 months (SD = 2.28; range, 15–22 months). The average duration of the first stage of the technique was 5.78 months. The mean time elapsed between the loading of the definitive implants and the final evaluation was 7.67 months (SD = 1.73; range, 6–10 months).
Results at the end of the follow-up period revealed that the status of soft tissues surrounding implants was good. All implants showed low rates of plaque index. In fact, all of them showed values ≤1. Furthermore, low values of bleeding index were recorded (all implants showed values ≤1). Last, but no least, none had drainage at final assessment. The mean probing pocket depth26 measured in four different sites around implants was 2.65 mm (SD = 0.83; Table 3).
Bone ridge width was measured and compared between baseline and final computed tomography-scanner of the patients. The initial mean width of the ridge was 4.03 mm at apical (SD = 1.47; range, 2.68–6.80 mm; median, 3.29 mm) and 2.97 mm at occlusal (SD = 0.56; range, 2.48–4.01 mm; median, 2.73 mm), whereas the final measurements after two-stage split-crest technique was 9.63 mm at apical (SD = 1.12; range, 7.84–11.11 mm; median, 9.91 mm) and 10.30 mm at occlusal (SD = 1.79; range, 7.85–13.22 mm; median, 9.93 mm) (Fig. 2). Therefore, mean crest expansion for the nine inserted implants was 5.60 mm (SD = 1.93) and 7.33 mm (SD = 1.73) at apical and occlusal, respectively.
Interestingly, no implants failed during the observation period, and all of them met the defined success criteria26 showing a 100% success rate at the end of follow-up period. Figures 3 and 4 shows the clinical situation of two patients involved in the study before and after the split-crest technique and implant placement.
Results from this clinical study, although preliminary, support the predictability and safety of the two-stage split-crest technique with ultrasonic bone surgery and its potential use in patients with extremely resorbed ridges. This new approach is less aggressive than other techniques such as the use bone grafts but can provide the same, or even greater, capacity for bone expansion.
Using the two-stage split-crest approach, a mean bone gain of 5.6 and 7.33 mm was achieved at apical and occlusal, respectively. No complications related to the surgical procedure were reported in any case.
All implants were installed following BTI's general guidelines for implant insertion, using a low-speed drilling procedure and without irrigation.17,27 Implants were humidified with PRGF-Endoret to bioactivate their surfaces and create a fibrin layer that stimulates the mechanism of bone formation at the implant-bone interface and promotes faster implant osseointegration.28,19 PRGF-Endoret technology consists on a limited volume of plasma enriched in platelets, which after activation with calcium, permits the release of a wide range of biologically active proteins. Some of these molecules including platelet-derived growth factor, transforming growth factor, vascular endothelial growth factor, basic fibroblast growth factor, type I insulin-like growth factor, and hepatocyte growth factor regulate cell migration, proliferation, and adhesion, driving the tissue regeneration process.20 PRGF-Endoret technology was also applied during the crest expansion procedure, mixed both with porous bovine inorganic bone and with autologous bone. These growth factors enriched grafts helped to overcorrect the defect and promoted bone regeneration.
Edentulous alveolar ridges of less than 5 mm in width are considered to require bone augmentation procedures before or after implant placement, to establish a bony wall of at least 1 mm around screw-type implants and provide a successful long-term function and aesthetics.28,29 The use of a two-stage split-crest procedure, provides a twofold and even threefold increase in the width of the crest both at apical and occlusal, promoting a predictable implant placement and function. One important step in this technique is the use of the ultrasonic device for bone cutting. This device shows clear advantages compared with other alternatives for bone cutting in different surgical procedures. The effect of cavitation cleans the working area and improves visibility.15,30 The biological effects of mechanical instruments on the structure of bone and the viability of cells are important issues to be considered in regenerative surgery. Of note is that the biological viability of bone treated by ultrasound is comparable with bone treated with other surgical techniques.31,32 Several studies have reported the positive effects of piezoelectric surgery on bone viability.12,33 The effects of piezoelectric devices on chip morphology and the resulting cell viability when harvesting bone chips have been fully documented.31,34 Moreover, several studies have reported less damage to soft tissues, particularly neurovascular tissue, when using a piezoelectric device compared with conventional methods.35,36 In addition, ultrasonic-bone surgery seems to be more efficient in the first phases of bony healing; it induces an earlier increase in bone morphogenetic proteins, controls the inflammatory process better, and stimulates remodeling of bone earlier after treatment.37
Although conventional split-crest technique (one stage) with ultrasonic bone is now a widespread technique, few clinical studies have been reported. Blus and Szmukler-Moncler15 described the application of ultrasonic bone surgery to perform split-crest procedures on 57 patients over a period of three and a half years with the aim to place 230 implants. The initial mean value of the ridge width was 3.2 mm, whereas at the end of the surgery the final mean width was 6 mm. A 96.5% success rate was reported. After loading (at least 2 months for all implants), no implant failed. In the 3-year life-table analysis, there was a cumulative survival rate of 100% of loaded implants.
In summary, using the two-stage split-crest expansion approach, it is possible to increase ridge width avoiding the use of more aggressive techniques as bone block grafting. This new technique is especially interesting for those cases in which insufficient bone width is regarded as a major limitation factor in the placement of dental implants.
This study describes the two-stage split-crest approach using ultrasonic bone surgery and PRGF-Endoret technology. This novel technique is a modification of the conventional split technique. Results, although preliminary, support the predictability of the procedure both in terms of the bone expansion achieved, and in the status of the soft tissue around implants. A 100% implant success rate was observed at the end of follow-up period. This technique avoids more traumatic procedures such as the use of bone block grafts, which may increase patient morbidity.
Dr. Anitua declares that he is the scientific director of BTI Technology Institute in Vitoria, Spain. Drs. Begoña and Orive declare that they are researchers collaborating with BTI Technology Institute.
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