Katja Nelson

Miniature pigs as an animal model for implant research: bone regeneration in critical-size defects

OBJECTIVEnStandardized experimental investigations determining the critical-size defect (CSD) in the mandible of miniature pigs are still lacking. The aim of the present study was to obtain information about the new bone formation in created defects of varying sizes.nnnSTUDY DESIGNnMarginal resection of the alveolar crest of the lower jaw was performed in 3 female miniature pigs. The animals used in the study were 3 years of age and weighed approximately 55 kg. For histologic evaluation the dental implants were harvested with the surrounding bone tissue 10 weeks after implant placement. For this, bone segments including the implants were removed from each side of the mandible. The sizes of the resected bone blocks varied, showing the following volumes: 10.1 cm(3), 4.2 cm(3), and 1.9 cm(3). Periosteal coverage of the defects was performed. Computerized tomography (CT) of the skull of the miniature pig was performed immediately after the surgical procedure as well as 6 weeks later using a 64-channel mult-slice scanner.nnnRESULTSnThe CT showed that 6 weeks after obtaining the biopsies, the filling of the defects with new bone varied. The percentage of newly formed bone in relation to the size of the original defect was 57.4% for the small- and 87.2% for the middle-sized defect. The large-sized defect showed 75.5% newly formed bone compared with baseline.nnnCONCLUSIONnConsidering the amount of new bone formation found within this study, it is questionable if the critical defect size of 5 cm(3) stated in the literature is valid. Further research concerning the mandibular model in minipigs is required and more refinement needed to assure a standardized CSD, allowing qualitative and quantitative evaluation of bone grafts and bone graft substitutes.

A prospective randomized split‐mouth study comparing iliac onlay grafts in atrophied edentulous patients: covered with periosteum or a bioresorbable membrane

PURPOSEnIn this prospective study, solid monocortical iliac onlay grafts of the maxilla were randomly covered with a bioresorbable membrane and periosteum within the maxilla. Histologic specimens were analyzed by light microscopy after a healing period of three months and the rate of resorption of the grafts were measured.nnnMATERIALS AND METHODSnFourteen patients (9 females and 5 males), with a mean age of 56 years (range 25-72) underwent augmentation with avascular iliac onlay bone grafts. The grafts were randomly covered either with a bioresorbable membrane (MC) or periosteum (PC). Resorption was measured with a digital caliper at the microscrews (slashed circle 1.5 mm) used to fixate the graft. Histologic evaluation of the specimens derived from the graft with a trephine bur (slashed circle 2 mm) from the implant site at implant placement after a 3-month healing period. Statistical evaluation of the data was performed using Analysis of variance and the Wilcoxon signed rank test.nnnRESULTSnClinical appearance of the augmented bone after 3 months showed a dense cortical layer with good vascular perfusion. Thirty-three sites in 13 patients (one dropped put) were analyzed histomorphometrically and showed an average of 46% newly formed bone with no significant difference between the groups (P=0.46). The mean resorption rate at 56 measured sites was 1.2 mm (range 0.3-3.4 mm) after 3 months, with no significant difference between the MC sites and the PC sites (P=0.38).nnnDISCUSSIONnHistomorphometry of new bone formation after 3 months demonstrates no significant difference between the PC and MC groups. Initialization of graft resorption can be seen after 3 months with no significant difference as to whether the graft was covered with a membrane or the periosteum.nnnCONCLUSIONnThis study provides evidence that after avascular iliac bone grafting, the revascularization of the graft was sufficient after 3 months regardless of the graft coverage with no effect on the amount of initial resorption of the graft.

Clinical Evaluation of a Modified Method of Vestibuloplasty Using an Implant-Retained Splint

PURPOSEnOral rehabilitation of resected tumor patients often requires, besides the use of dental implants, the improvement of the soft tissue condition. In this clinical report, we describe a simple and effective surgical and prosthetic treatment procedure to achieve adequate long-term soft tissue conditions.nnnMATERIALS AND METHODSnSeventeen tumor patients were selected for this evaluation. A total of 68 implants were placed in the mandible. At implant placement, a closed impression was taken from the implants for the fabrication of an implant-retained surgical splint. At second-stage surgery, vestibuloplasty by use of a split-thickness skin graft from the upper thigh was performed and an implant-retained splint was positioned. Pocket depths at the implants and the size of the graft were monitored over a period of 2 years. Statistical analysis by use of nonparametric 2-factorial analyses for repeated measures was performed.nnnRESULTSnThe mean mesial and distal pocket depths remained stable and measured 2.56 mm and 2.64 mm, respectively, at 24 months postoperatively. The graft showed an overall shrinkage of 18.5% in the vertical direction and 10.4% in the horizontal direction after 24 months. The shrinkage of the vertical direction compared with the horizontal direction showed a significant difference (P= .035). The shrinkage tendency was less than that described in the literature.nnnCONCLUSIONSnThe applied method described an easy, sufficient surgical procedure that minimizes shrinkage and creates a denture-bearing area that is stable over the long term, thus representing an improvement over previous methods.

Fabrication of a fixed retrievable implant-supported prosthesis based on electroforming: a technical report.

This article describes a method of fabricating a fixed retrievable implant-retained prosthesis based on electroforming. This method combines the advantages of both the cement- and screw-retained prostheses, including passive fit, ease of fabrication, and retrievability. The absence of visible occlusal screw-canals adds to its increased esthetic appeal.

Survival rate and potential influential factors for two transitional implant systems in edentulous patients: a prospective clinical study.

The aim of this present study was to evaluate the success of immediately loaded transitional implants and to identify possible influential factors. A total of 64 patients were recruited in a private specialist implant practice. Two different implant systems were evaluated (IPI, Nobel Biocare, Sweden; I-Plant, Unor, Switzerland). Primary stability, survival rate, gender, location, the type of prosthetic restoration and the tooth status of the opposite jaw were analysed using Kaplan-Meier or Pearson Chi-Square test. A total of 254 transitional implants were placed, thereof 216 were IPI implants and 38 I-Plant implants. The overall observation period ranged between 2 and 426 days. The results demonstrated a survival rate of 82·4% for the IPI system and 84·2% for the I-Plant system. None of the transitional implants with a good primary stability were lost during the observation period. The primary stability showed significant influence on the implant survival. There was no significant difference in survival of the implants between the two implant systems. Neither the gender, the kind of superstructure, the location of the implant, the tooth status of the opposing jaw or the immediate prosthetic superstructure had an influence on the survival of the implants. Both implant systems proved to be sufficient alternatives for the support of provisional restorations.

Maxillary sinus augmentation following removal of a maxillary sinus pseudocyst after a shortened healing period.

PURPOSEnDome-shaped radiopacities on the floor of the maxillary sinus are commonly interpreted as a sinus cyst on radiographs during dental implant planning. They might present an obstacle in sinus grafting, leading to bone graft failure or implant loss later. The therapeutic approaches to the removal of such cystic lesions and the following sinus augmentation are still controversial. The purpose of this article is to present a modified technique that can be used for predictable removal of a maxillary sinus cyst and sinus augmentation after a shortened healing period in patients with maxillary sinus pseudocysts.nnnMATERIALS AND METHODSnA total of 11 patients with a mean age of 43.7 years with a radiographic dome-shaped opacity in the posterior maxilla sinus were included in this study. A lateral sinus window (with a diameter of about 5 mm) was prepared, and removal of the cyst was performed with grasping forceps. Three months after removal of the cyst, a conventional sinus augmentation with xenogeneic material was undertaken. Dental implants were placed 6 months later. Panoramic radiography and coronal/axial computed tomography were performed to diagnose the sinus lesion preoperatively and for follow-up.nnnRESULTSnA total of 11 pseudocysts were removed from the sinuses of 11 patients under local anesthesia. Histologic evaluation showed antral pseudocysts in all specimens. A soft tissue scar was evident after 3 months of healing at the time of sinus augmentation. No sinus membrane perforation was seen or occurred during the sinus augmentation. A total of 17 implants were placed and restored prosthetically. No clinical complications were observed. The patients were followed up for a mean of 29.2 months (range, 17-43 months) after prosthetic loading, during which no implants were lost and no recurrence of the antral pseudocyst was observed.nnnCONCLUSIONnThe described modified surgical technique allows the minimally invasive removal of the antral pseudocyst and histologic verification of the diagnosis without compromising the nasoantral entrance as well as the anatomy of the sinus for future sinus augmentations. It can be performed under local anesthesia without endoscopic equipment while shortening the treatment period.

Stable vertical distraction osteogenesis of highly atrophic mandibles after ablative tumour surgery of the oral cavity--a salvage pathway for mandibular reconstruction prior to oral rehabilitation with dental implants.

Mandibular reconstruction is still a challenge for surgeons. Distraction osteogenesis (DO) might contribute in certain instances to solve this problem. A principal advantage of DO is the expansion of the surrounding soft tissues that accompanies the bony regeneration. In addition there is no donor site morbidity when compared with reconstruction by autologous bone grafting. However its application may be limited by the thinness of the mandible and the attendant fracture risk. This article describes a technique that combines stable internal fixation with vertical distraction of the alveolar ridge in six patients with critical mandibular thickness after ablative surgery for cancer of the oral cavity. Prior to implant insertion for further prosthodontic restoration stable vertical mandibular distraction produced an additional 11-20mm. Improvement of the surrounding soft tissues, especially intraorally was achieved and dental implants were inserted after bony consolidation. This method can be a useful salvage technique for the augmentation of the atrophic mandible in patients who are not able or willing to undergo the risks and disadvantages of established methods such as free autologous bone transfer or microsurgical techniques.

Osteogenic potential of mesenchymal cells embedded in the provisional matrix after a 6‐week healing period in augmented and non‐augmented extraction sockets: an immunohistochemical prospective pilot study in humans

PURPOSEnThe aim of the present clinical study was the evaluation of the osteogenic potential of mesenchymal cells embedded in the provisional matrix of non-augmented and with Bio-Oss collagen-augmented human extraction sockets after 6 weeks of healing time.nnnMETHODSnTwenty-five patients with 47 extraction sites participated in the present study. After tooth removal, the extraction sockets were augmented with Bio-Oss collagen or not augmented. At implant placement, bone biopsies of the extraction sockets were obtained. The immunohistochemical analysis of the osteogenic potential of the mesenchymal cells in the provisional matrix was performed using three monoclonal antibodies: core-binding factor α1 (Cbfa1)/runt-related protein (Runx)2, osteonectin (OSN/secreted protein acidic and rich in cyst [SPARC]) and osteocalcin (OC). The statistical analysis was performed using two-factorial analysis for repeated measures, Mann-Whitney U-test and Spearmans rank-order correlation coefficient.nnnRESULTSnOf 47 extraction sockets examined, 17 sockets demonstrated an almost complete ossification. Hence, the provisional matrix of the 30 remaining extraction sockets (21 non-augmented, 9 augmented) was immunohistochemically investigated. No evidence of acute or chronic inflammation was noted in any of the specimens. In the provisional matrix of the non-grafted socket, the median amount of Cbfa1/Runx2-positive cells was 72.3%, of OSN (SPARC) 66.9% and of OC 23.4%, whereas in the grafted sockets the median rate of immunopositive cells staining with Cbfa1/Runx2 was 73.3%, of OSN (SPARC) 61.4% and of OC 20.1%. There was no significant difference in the proportion of positive cells expressed by Cbfa1/Runx2, OSN/SPARC and OC between the grafted and non-grafted socket. Furthermore, the cell density did not correlate to the quantity of stained cells independent of the used proteins.nnnDISCUSSIONnAfter a 6-week healing period, the provisional matrix was demonstrated to have a high proportion of cells displaying a maturation of mature osteoprogenitor cells to osteoblasts. The grafting procedure did not influence the quantity of osteogenic cells in the extraction socket.

Sudden death in miniature pigs.

Fluorescent dyes or fluorochromes can be useful tools for analyzing changes in bone morphology. Their presence in bone sections indicates site, time and amount of bone deposition, which cannot be determined using conventional histological techniques1. Fluorescent dyes were originally used for metal titration because they chelate with metals but are now also used to stain calcified tissues. Yellow tetracyclines, xylenol orange, alizarin red derivatives and green fluorescein derivatives such as calcein can be easily distinguished in bone by the color of their fluorescence. They all share a common iminodiacetic acid group, which chelates with calcium hydroxyapatite, the principal mineral in bone and teeth. Fluorochromes are administered systemically and incorporated into bone during the mineralization phase of ossification. When treated bone is examined under fluorescence microscopy, these fluorochrome dyes exhibit photoluminescence that allows identification of the mineralized tissue. Filter sets for fluorescence microscopy can be chosen for selective excitation of single fluorochromes, or broad band filters may be used for simultaneous visualization of several fluorochromes1. The administration of several fluorochromes, distinguishable by color, offers distinct advantages over single labels. For example, evaluating the distance between different fluorochromes administered at different times shows both the deposition of bone during a specific time period and the direction of ossification1. We used eight 2-year-old female Göttingen miniature pigs (Ellegaard Göttingen Minipigs ApS, Dalmose, Denmark) that weighed on average 45 kg in our study. We created cavities in the premolar and molar regions of the upper and lower jaws that measured 30 mm × 10 mm by surgically removing the teeth in these locations. The pigs were anesthetized during the procedure, and postoperative analgesia consisted of buprenorphine (Temgesic, Essex Pharma, Grünenthal, Germany) administered every 8 h for 3 d and carprofen (Rimadyl, Pfizer GmbH, Karlsruhe, Germany) given once a day for an additional 7 d. In the first four weeks after surgery we also gave the antibiotic enrofloxacin (Baytril-10%, Bayer AG, Leverkusen, Germany) daily to the pigs. After a healing period of 8 weeks, we then added autologous bone collected from the pig’s iliac crest or fibula to the cavities. To evaluate the dynamics of ossification and bone remodeling, we used polychrome sequential labeling that entailed administering different fluorochromes to the miniature pigs 2, 5 and 8 weeks after adding autologous bone to the jaw defects. We gave xylenol orange (Sigma-Aldrich Chemie GmbH, Munich, Germany, 90 mg per kg body weight) at 2 weeks, calcein (Sigma-Aldrich Chemie GmbH, Munich, Germany, 20 mg/kg) at 5 weeks and the alizarin red derivative alizarine complexone (VWR International GmbH, Darmstadt, Germany, 30 mg/kg) at 8 weeks. All fluorochromes were administered intravenously while the pigs were heavily sedated. Our anesthetic protocol consisted of ketamine (Ketamin-10%, WDT, Garbsen, Germany, 10 ml i.m.), xylazine (Rompun, Bayer AG, Leverkusen, Germany, 6 ml i.m.), azaperone (Stresnil, Janssen Cilag GmbH, Neuss, Germany, 3 ml i.m.) and atropine sulfate (1 ml i.m.). All eight of the miniature pigs showed mild skin discoloration after administration of both xylenol orange and calcein. Sudden death in miniature pigs Baerbel Ruehe, DVM1, Olivia Kershaw, DVM2, Stefan Niehues, DMD3 & Katja Nelson, DDS1