Guided bone regeneration (GBR) describes the use of membranes to regenerate bony defects. A membrane for GBR needs to be biocompatible, cell-occlusive, non-toxic, and mouldable, and possess space-maintaining properties including stability. The purpose of this pilot study was to describe a new method of GBR using individualized ceramic sheets to perfect bone regeneration prior to implant placement; bone regeneration was assessed using traditional histology and three-dimensional (3D) volumetric changes in the bone and soft tissue. Three patients were included. After full-thickness flap reflection, the individualized ceramic sheets were fixed. The sites were left to heal for 7 months. All patients were evaluated preoperatively and at 7 months postoperative using cone beam computed tomography and 3D optical equipment. Samples of the regenerated bone and soft tissue were collected and analyzed. The bone regenerated in the entire interior volume of all sheets. Bone biopsies revealed newly formed trabecular bone with a lamellar structure. Soft tissue biopsies showed connective tissue with no signs of an inflammatory response. This was considered to be newly formed periosteum. Thus ceramic individualized sheets can be used to regenerate large volumes of bone in both vertical and horizontal directions independent of the bone defect and with good biological acceptance of the material.
When optimal anatomical conditions for implant installation do not exist, the situation must be changed, if possible. Several techniques to improve the height and width of the alveolar process, including block grafts and particulated grafts, distraction osteogenesis, bone splitting techniques, sinus floor elevation, and membranes, have been reported. Unfortunately, the use of these methods may result in undesirable side effects such as infection, material exposure, and absence of healing linked to the material or surgical techniques.
Guided bone regeneration (GBR) describes the use of membranes to regenerate lost bone. The basic requirements of membranes for GBR are biocompatibility, cell-occlusive properties, possibility of integrating, mouldability, and space-maintaining properties including stability. Regarding resorbable membranes, they should not produce any rest products, as these may have an adverse effect on the bone regeneration. Membranes described in both experimental and clinical studies have been the same for a long period of time, e.g. expanded polytetrafluoroethylene (ePTFE), collagen, and titanium mesh. None of these materials presents material properties that fulfil the defined basic requirements for an optimal membrane material.
Titanium mesh membranes offer superb mechanical properties for GBR treatment in larger areas. Unfortunately, exposure all too often presents clinically, which can lead to unaesthetic results and infection and thereby failure of the treatment.
Inert high-strength ceramics such as zirconia form a group of materials that has not previously been used for the treatment of patients by GBR. This is a group of materials with properties that might solve the most obvious clinical dilemmas, like exposure of the materials and lack of stability in terms of larger GBR treatments.
When bone regeneration treatments prior to the installation of dental implants are evaluated, the terms ‘implant success’ and ‘implant survival’ are often used. The measurement of these values helps the clinician very little in the selection of an appropriate bone regenerating technique, as the evaluation is focused on the titanium implants rather than the bone volume or the aesthetic results achieved. The use of superimposed cone beam computed tomography (CBCT) images and of optical shape alterations in the soft tissue are examples of techniques easily used to more adequately describe the potential of a bone regeneration technique, thereby not diverting focus onto the secondary treatment, the dental implant.
The purpose of this pilot study was to describe a new method using individualized ceramic sheets to regenerate bone, aimed at optimizing the anatomical situation in order to facilitate implant installation; furthermore it was aimed to present visual evaluation techniques besides traditional histology, using three-dimensional (3D) volumetric changes in both bone and soft tissue.
The successful outcome of this case series study has encouraged an extended series of investigations to further elucidate the potential of individualized ceramic sheets.
Materials and methods
The study was approved by the regional ethics committee. Three patients, two female and one male, were included in this pilot study. They were referred to the clinic for the installation of implants. All patients had inadequate bone volume for the optimal installation of implants and required bone regeneration prior to implant surgery. The patients were selected according to the specific site of bone regeneration: patient 1 had a posterior maxillary bone deficiency, patient 2 had an anterior maxillary bone deficiency, and patient 3 had a posterior mandibular bone deficiency. Thus, the patients represented areas known to be a challenge to the surgeon with regard to the bone regeneration technique prior to implant surgery. All patients were examined preoperatively, and one panoramic image and one CBCT scan of the area of interest were obtained.
Patient 1: posterior maxillary bone deficiency
Patient 1 was a 68-year-old woman referred to the clinic for implant installation in the upper right jaw. She was edentulous from tooth 12 and posteriorly due to earlier periodontal disease and wished to have permanent rehabilitation of this area. Her medical history was significant for hypothyroidism, hypotension, and depression. She was on treatment with levothyroxine, etilefrine, and nortriptyline. She was allergic to sulfa. She was a non-smoker.
In region 12–13, the alveolar crest was 2–3 mm in width and 7–8 mm in height. In region 14, the alveolar crest was 2 mm in width and 5 mm in height. In region 15–17, the width of the alveolar crest was 2 mm with a height of 0–1 mm. The clinical situation at insertion can be seen in Fig. 1 .
Patient 2: anterior maxillary bone deficiency
Patient 2 was a 32-year-old man who had suffered a road traffic accident. He was brought to the emergency department with major pan-facial fractures, including a severe dentoalveolar crest fracture in the upper right side of the jaw, as well as exarticulation of his upper right central and lateral incisors which were never found. After primary treatment and healing of the facial fractures, it was decided to rehabilitate his occlusion by bone regeneration and dental implants. He was otherwise fit and well, without any regular medication or allergies. He was a non-smoker.
In region 11, the alveolar crest was 2–5 mm in width, varying within the interval, and the height was 14 mm to the floor of the nasal cavity. In region 12, the alveolar crest was 2–3 mm in width and the height was 8 mm to the floor of the nasal cavity. The clinical situation at insertion can be seen in Fig. 2 .
Patient 3: posterior mandibular bone deficiency
Patient 3 was a 52-year-old woman referred for the installation of implants bilaterally in the lower jaw in regions 34–35 and 44–45. She was fit and well, had no allergies, was taking no medication, and was not smoking. On examination, she presented a greatly resorbed alveolar crest bilaterally. Her teeth in these areas had been lost due to periodontal disease and caries.
In region 34–36, the height of the alveolar crest to the inferior alveolar nerve was 6–10 mm and the width approximately 5 mm. In region 44–46, the height of the alveolar crest to the inferior alveolar nerve was 7–8 mm and approximately 5 mm in width. The clinical situation at insertion can be seen in Fig. 3 .
The CBCT images of each patient were used to build a digital model. Based on this model, a five-axis CNC machine (Dechel-Maho, DMU 60, Deckel Maho, Pfronten, Germany) was used to mill a cold isostatically pressed (CIPed) and presintered green body of zirconia (TZ3YSEB; Tosoh) to the desired macroscopic shape. The size of the machined sheet was enlarged in order to compensate for the sintering shrinkage performed at 1450 °C.
After manufacturing, the sheet was cleaned in an ultrasonic bath of 70% alcohol for 15 min, followed by a brief heating to 1200 °C. It was again cleaned in an ultrasonic bath for 3 × 15 min using 90% alcohol. Thereafter the sheet was placed in an autoclave (Getinge Quadro Avanti; Getinge, Sweden) and sterilized using a standard program (134 °C). The sheets had a thickness of approximately 0.7 mm, as can be seen in Fig. 4 .
The topography of the outer surface of the ceramic sheet was characterized using an interferometer (MicroXAM; ADE Phase Shift Technology, Inc., Tucson, AZ, USA). Each device per group was measured at four positions: one in the inner (lingual) flank area, one in the top area, and two in the outer (buccal) flank area. The parametric calculation was performed after form errors and waviness were removed with a 50 μm × 50 μm Gaussian filter. The following 3D parameters were selected: S a (μm) = the arithmetic average height deviation from a mean plane, S ds (μm −2 ) = the density of summits, and S dr (%) = the developed surface ratio. Unfortunately the inner surface was impossible to measure as the flank areas collided with the optic.
The intraoral area was initially cleaned with chlorhexidine 1 mg/ml (Hexident; Meda AB, Solna, Sweden). Local anaesthetic, 20 mg/ml lidocaine + 12.5 μg/ml epinephrine (Xylocaine Dental adrenaline; Dentsply Ltd, Surrey, UK) was administered. Horizontal crestal incisions were made lightly and lingual/palatal of the mid-crest within the keratinized tissue. Vertical releasing incisions were placed on the buccal aspect of the surgical site in the usual manner to provide adequate access and to allow for eventual coronal repositioning. A full-thickness flap reflection was completed, and the cortical plate of the defect was perforated with a round bur to provoke bleeding. Fixation of the individualized ceramic sheets was done with Synthes fracture screws (Synthes, Solna, Sweden) (1.5 mm diameter, 4–6 mm in length depending on the depth). No adaptation was needed and the sheets were stable with the use of only one screw. The ceramic sheets were cleaned with 3% hydrogen peroxide prior to soft tissue closure.
For patient 3, bone chips were harvested with a Safescraper (Ostegenics, Texas, USA) and placed within the defect during the placement of the left sheet. The ceramic sheet on the right side was placed without any bone chips, as for patients 1 and 2.
After fixation of the sheets, the buccal flaps were coronally repositioned with significant apical undermining. Split-thickness periosteal release incisions were completed to aid in primary tension-free closure using Vicryl 4–0. The patients received antibiotics postoperatively (phenoxymethylpenicillin 1 g three times per day for 1 week). After a mean of 7 months of uneventful healing, the augmented sites were reopened. The ceramic sheets and fixation screws were identified and removed, followed by dental implant placement. It was found that the sheets were not attached to the underlying bone or to the soft tissue covering them; they were therefore very easy to remove.
Measurement of the bone volume gained using overlay of CBCT data
DICOM data from the pre- and postoperative CBCT investigations were analyzed through an overlay function in 3D software SimPlant Pro (Materialise Dental, Leuven, Belgium). The procedure revealed the amount of bone volume gained postoperatively in three dimensions compared to the same area in the preoperative investigation. The new bone was measured in a 90-degree cut from the alveolar crest at the highest point.
Soft tissue topographic measurement and evaluation procedure
The intraoral soft tissue profile of the alveolar defect in patient 2 was documented using 3D metering equipment PRIMOS optical 3D (Primos 5.7 and Primos Body 6.6; GFMesstechnik GmbH, Germany). The measuring and matching procedures have been described in detail previously. The measurements were performed at two different time points: (1) preoperatively, and (2) after removal of the ceramic sheet.
Samples of the regenerated bone were retrieved using a trephine bur and placed in 4% formaldehyde for 24 h, after which they were placed in 70% ethanol. All samples were processed for undecalcified ground sectioning. In brief, after a series of dehydrations and infiltrations in resin, the samples were embedded in light-curing resin (Technovit 7200 VLC; Heraeus Kulzer, Wehrheim, Germany). Thereafter, one central cut and ground section was prepared from each sample using precision sawing and grinding equipment. The sections were ground to a final thickness of approximately 40 μm and stained with toluidine blue. Histological evaluations were performed using a light microscope (Eclipse ME600; Nikon, Japan).
Samples of the soft tissue found between the ceramic sheets and the newly formed bone were retrieved and placed in 4% formaldehyde. The samples were processed for soft tissue sectioning. After processing, the tissues were embedded in paraffin and serial sections 3 μm thick were prepared and stained with haematoxylin–eosin and van Gieson stains. Histological evaluations were performed using a light microscope (Leica DMD 108; Leica Microsystems, Wetzlar, Germany).