Evaluation of a collagen scaffold for cell-based bone repair

PURPOSE

To determine whether a collagen scaffold could provide an environment for mesenchymal stem cell (MSC)-related bone repair of critical-size bone defects in rat calvaria.

MATERIALS AND METHODS

Craniotomy defects were created in 28 adult Sprague-Dawley rats. Two additional rats were used as MSC donors by means of femoral bone marrow lavage and culture. The rats were randomly divided into four groups: (1) empty/no graft; (2) collagen scaffold (matrix)+saline; (3) matrix+MSCs; (4) matrix+bone morphogenetic protein. The animals were euthanized 28 days after surgery. Microcomputed tomographic reconstructions were obtained to measure bone fill. The specimens were processed for histologic examination, and the total defect and bone fill areas were measured.

RESULTS

Mean bone fill (± standard deviation) of 9.25%±10.82%, 19.07%±17.38%, 44.21%±3.93%, and 66.06%±15.08%, respectively, was observed for the four groups; the differences were statistically significant. Bone repair was statistically significant for groups 3 and 4. No significant difference was seen for bone repair between groups 1 and 2 or between groups 3 and 4. Bone formation differed significantly across the four groups. Statistically significant changes in radiodensity were observed between groups 1 and 3, groups 1 and 4, and groups 2 and 4. Significant differences were not observed between groups 1 and 2, groups 2 and 3, or groups 3 and 4.

CONCLUSION

After grafting of adult MSCs adherent within a collagen matrix, repair of bone was significant. Expanded three-dimensional collagen represents a radiolucent, resorbable, biocompatible scaffold that is capable of supporting MSC repair of bone.

Molecular assessment of osseointegration in vivo: a review of the current literature

This paper reports on the results of a structured review of the literature concerning in vivo molecular assessment of osseointegrated endosseous dental implants. A search of electronic databases was performed up to and including August 2011. Thirty articles met the inclusion criteria. A descriptive evaluation and analysis of the gene expression data concerning the process of osseointegration were performed. Broad consensus was observed among the study results, perhaps as a result of the similar targeted gene expression events. More recent investigations using gene arrays or gene profiling techniques offer new insights into the fundamental molecular events that support the osseointegration process. Evidence for the influence of surface topography on osteogenesis and osteoinduction has been reported. Additional investigations are required to further solidify the functional associations between individual or orchestrated gene expression events and the clinical result of osseointegration.

Complications and patient-centered outcomes with an implant-supported monolithic zirconia fixed dental prosthesis: 1 year results

PURPOSE

To characterize the number and type of complications that occur with a monolithic zirconia fixed dental prosthesis (MZ-FDP) supported by four endosseous implants in the edentulous mandible over time and to quantify the impact of treatment on oral health quality of life (OHQoL).

METHODS

Seventeen edentulous participants were enrolled. New conventional dentures were fabricated for each participant. Four Astra Tech Osseospeed TX implants (Dentsply) were then placed in the parasymphyseal mandible, and after a period of healing, a full-arch monolithic zirconia prosthesis (Zirkonzahn) was inserted. Complication data were recorded and OHQoL was evaluated using the Oral Health Impact Profile (OHIP-49), administered on four occasions: enrollment; implant surgery; and 6- and 12-month recalls.

RESULTS

Sixty-eight implants were placed in 17 edentulous individuals aged 30 to 78 (mean 57.9 years). Implant survival was 94% from the subject perspective and 99% from the implant perspective. Prosthesis survival was 88%. Twelve complications occurred in ten participants, whereas seven participants remained complication free. Both OHIP-49 severity and extent scores decreased significantly between enrollment and 12-month recall (p < 0.001). The mean OHIP-49 severity score at baseline was 94.8 (95% confidence interval [CI]: 73.9, 115.8) and declined an average of 76.8 (95% CI: -91.3, -62.3) units per participant. The mean OHIP-49 extent score at baseline was 17.2 (95% CI: 10.8, 23.6) and declined 16.3 (95% CI: -20.2, -12.4) units per participant on average.

CONCLUSIONS

Implant survival was high, and few complications related to the MZ-FDP were observed. The most common prosthetic complication was tooth chipping in the opposing maxillary denture, which accounted for 50% of all complication events. Substantial and clinically important improvements in OHQoL were achieved with both conventional dentures and the implant-supported MZ-FDP. The data of this short-term study indicate that the implant-supported MZ-FDP is a therapeutic option with particular advantages in the edentulous mandible that warrants further long-term study.

Prosthodontic management of implant therapy

Implant-supported dental restorations can be screw-retained, cement-retained, or a combination of both, whereby a metal superstructure is screwed to the implants and crowns are individually cemented to the metal frame. Each treatment modality has advantages and disadvantages. The use of computer-aided design/computer-assisted manufacture technologies for the manufacture of implant superstructures has proved to be advantageous in the quality of materials, precision of the milled superstructures, and passive fit. Maintenance and recall evaluations are an essential component of implant therapy. The longevity of implant restorations is limited by their biological and prosthetic maintenance requirements.

Radiographic stents: integrating treatment planning and implant placement

The pivotal point in treatment planning for dental implants occurs when the location of bone is viewed radiographically in the context of the planned prosthesis. Radiographic planning for dental implant therapy should be used only after a review of the patient's systemic health, imaging history, oral health, and local oral conditions. The radiological diagnostic and planning procedure for dental implants can only be fully achieved with the use of a well-designed and -constructed radiographic guide. This article reviews several methods for construction of radiographic guides and how they may be utilized for improving implant surgery planning and performance.

"Rules of Six"--diagnostic and therapeutic guidelines for single-tooth implant success

Replacing a single anterior tooth with an implant requires meeting a number of interdependent challenges, including biologic, functional, and esthetic features of success. The principles of osseointegration, the fundamentals of esthetics, and concerns regarding occlusion and function are elements that need to be addressed to achieve implant-supported crown success. In this report, the "Rules of Six" for effectively placing a single-tooth dental implant are described. These rules represent diagnostic targets and a single therapeutic guideline useful in directing clinical success and preventing common complications.

Comparative molecular assessment of early osseointegration in implant-adherent cells

OBJECTIVE

The objective of our study is to identify the early molecular processes involved in osseointegration associated with a micro roughened and nanosurface superimposed featured implants.

MATERIALS AND METHODS

Thirty-two titanium implants with surface topographies exhibiting a micro roughened (AT-II) and nanosurface superimposed featured implants (AT-I) were placed in the tibiae of 8 rats and subsequently harvested at 2 and 4 days after placement. Total RNA was isolated from cells adherent to retrieved implants. A whole genome microarray using the Affymetrix Rat Gene 1.1 ST Array followed by validation of select genes through qRT-PCR was used to describe the gene expression profiles that were differentially regulated by the implant surfaces.

RESULTS

While significant differences at the gene level were not noted when comparing the two-implant surfaces at each time point, the microarray identified several genes that were differentially regulated at day 4 vs. day 2 for both implant surfaces. A total of 649 genes were differentially regulated at day 4 vs. day 2 in AT-I and 392 genes in AT-II implants. Functionally relevant categories related to ossification, skeletal system development, osteoblast differentiation, bone development, bone mineralization and biomineral tissue development were upregulated and more prominent at AT-I (day 4 vs. day 2) compared to AT-II. Analysis of the downregulated gene lists (day 4 vs. day 2) with average fold change >2 (were not statistically significant) revealed the biological processes involved with the inflammatory/immune response gene expression. The number of genes that were associated with the inflammatory/immune response category was greater for AT-I than AT-II.

CONCLUSIONS

The presence of nanosurface features modulated in vivo bone response. Gene regulation implicating osteogenesis as well as the inflammatory/immune responses that occur as a function of surface topography may affect bone mass shortly after implant placement.

Mammalian two-hybrid assays for studies of interaction of p300 with transcription factors

The two-hybrid system is a powerful genetic assay that allows the interaction between two proteins to be detected in vivo. It was originally described in 1989 and since then it has been one of the main techniques used to identify interactions between proteins from different cellular organisms. Here we describe the methods to study the interaction of p300 with other transcription factors, specifically between p300 and two transcription factors related to hypoxia and inflammation, HIF-1α and NF-κB-p65, respectively.

Osteoblastic and cytokine gene expression of implant-adherent cells in humans

OBJECTIVES

Implant surface topography is a key determinant affecting osteoblastic differentiation and cell-cell signaling of implant-adherent cells.

MATERIALS AND METHODS

To assess the early osteoinductive and cell-cell signaling events in adherent cells, commercially pure titanium implants (2.2 × 5 mm) with nanotopography (HF-treated TiO2 grit-blasted) were compared with micron-scale topography TiO2 grit-blasted (micron-scale, control) implants in vivo. Six implants (n = 3/surface) were placed in 10 systemically healthy subjects and removed by reverse threading at 1, 3, and 7 days. Gene expression profiles of adherent cells were interrogated using low-density RT-PCR arrays.

RESULTS

Osteoinduction was not observed at day 1 on either surface. At 3 days, elevated levels of BMP6, osteopontin, and osterix (OSX) were observed in RNA of cells adherent to both micron-scale and nanotopography surfaces. Both surfaces supported osteoinductive gene expression at 7 days; however, modest elevations of most mRNAs and significantly higher OSX mRNA levels were measured for cells adhered to nanotopography implants. Further, chemokine and cytokine profiles including CXCL10, CXCL14, IL-9, IL-22, and TOLLIP were upregulated on nanotopographic surfaces as compared with microtopographic surfaces.

CONCLUSIONS

Implants with superimposed nanoscale topography generate a greater induction of genes linked to osteogenesis and cell-cell signaling during the early phases of osseointegration.

Evaluation of post-implant buccal bone resorption using cone beam computed tomography: a clinical pilot study

PURPOSE

Buccal bone responses following dental implant placement are considered significant determinants of esthetic outcomes. The aim of this pilot study was to evaluate whether cone beam computed tomography (CBCT) could be used to measure buccal alveolar bone changes following implant placement. The second aim of this investigation was to determine both qualitatively and quantitatively if changes could be determined 1 year postoperatively at the buccal aspect of implants placed in healed ridges or extraction sockets.

MATERIALS AND METHODS

Twenty patients in need of a single tooth in the maxillary anterior or first premolar region were recruited under an institutional review board-approved protocol. Patients were allocated into two groups: those missing a tooth with a healed alveolar ridge and those needing an extraction. Following treatment planning, implants were placed and immediately loaded. Zirconia abutments and all-ceramic crowns were delivered 16 weeks following implant placement. CBCT images of the maxilla were obtained at three different time points; 2 weeks before surgery, immediately after surgery, and 12 months after implant placement. A single examiner measured each implant three times in four different sites. The data between different implants or subjects were compared among groups by the nonparametric sign test.

RESULTS

Evaluation of the CBCT images revealed that it was possible to discern the presence or absence of the buccal bone plate both prior to and 1 year following implant placement in the majority of subjects. The median alteration after 1 year for the vertical distance from the abutment/implant interface to the buccal alveolar bone crest for all subjects was -1.12 mm (P = .018). The horizontal alteration of the buccal bone measured 1 mm apical to the implant/abutment interface was -0.62 mm (P = .004). At the midimplant and apical regions of the implants, the 1-year horizontal bone alteration was -0.57 mm (0.004) and -0.19 mm (P = .059), respectively.

CONCLUSIONS

Buccal bone and alterations following implant placement may be visualized by CBCT in both extraction sockets and healed ridges. When the implant was appropriately displaced from the buccal wall of the socket, bone changes could be qualitatively evaluated by CBCT 1 year following placement.

"Rules of 10"--guidelines for successful planning and treatment of mandibular edentulism using dental implants

The three "Rules of 10" for treatment planning dental implant therapy in the edentulous mandible are designed to improve the success of both the endosseous implants and the prosthesis. These "rules" acknowledge and provide a method to control the mechanical environment, addressing factors affecting implant and prosthesis longevity, including magnitude of forces, resistance of the prosthesis against these forces, and the biology of bone and its ability to respond to loading environments. The rules specify that for any IRO or ISFP, there must be a minimum of 10 mm of alveolar dimension (inferior/superior) and a minimum of 10 mm of interocclusal (restorative) dimension measured from the soft-tissue ridge crest to the occlusal plane. Additionally, for an ISFP, the anterior/posterior distribution of implants must be greater than 10 mm. This article provides support in the literature for these rules and illustrates their application in the treatment of mandibular edentulism.

Full-mouth rehabilitation of a patient with gastroesophageal reflux disease: a clinical report

Gastroesophageal reflux disease (GERD) is a chronic condition caused by stomach acid regurgitating into the esophagus or oral cavity, often causing heartburn. Tooth erosion and wear are common oral manifestations of GERD. This clinical report describes the full-mouth rehabilitation of a patient with over 30 years of GERD, causing wear of maxillary and mandibular anterior teeth, along with complications associated with past restorations. Full-mouth rehabilitation of natural teeth in conjunction with dental implants was selected as the treatment option. Ideal occlusal design and optimal esthetics, along with reinforcement of oral hygiene, ensure a favorable prognosis.

Titanium surface topography affects collagen biosynthesis of adherent cells

Collagen-dependent microstructure and physicochemical properties of newly formed bone around implant surfaces represent key determinants of implant biomechanics. This study investigated the effects of implant surface topography on collagen biosynthesis of adherent human mesenchymal stem cells (hMSCs). hMSCs were grown for 0 to 42 days on titanium disks (20.0 × 1.0 mm) with smooth or rough surfaces. Cell attachment and spreading were evaluated by incubating cells with Texas-Red-conjugated phalloidin antibody. Quantitative real-time PCR was used to measure the mRNA levels of Col1α1 and collagen modifying genes including prolyl hydroxylases (PHs), lysyl oxidases (LOXs) and lysyl hydroxylases (LHs). Osteogenesis was assessed at the level of osteoblast specific gene expression and alizarin red staining for mineralization. Cell layer-associated matrix and collagen content were determined by amino acid analysis. At 4h, 100% cells were flattened on both surfaces, however the cells on smooth surface had a fibroblast-like shape, while cells on rough surface lacked any defined long axis. PH, LH, and most LOX mRNA levels were greater in hMSCs grown on rough surfaces for 3 days. The mineralized area was greater for rough surface at 28 and 42 days. The collagen content (percent total protein) was also greater at rough surface compared to smooth surface at 28 (36% versus 26%) and 42 days (46% versus 29%), respectively (p<.05). In a cell culture model, rough surface topography positively modulates collagen biosynthesis and accumulation and the expression of genes associated with collagen cross-linking in adherent hMSC. The altered biosynthesis of the collagen-rich ECM adjacent to endosseous implants may influence the biomechanical properties of osseointegrated endosseous implants.

Comparison of three-implant-supported fixed dentures and two-implant-retained overdentures in the edentulous mandible: a pilot study of treatment efficacy and patient satisfaction

PURPOSE

The mandibular two-implant overdenture has been shown to be a highly successful treatment. However, overdenture patients who desire a fixed prosthesis may not be satisfied with a removable overdenture. This prospective study sought to compare prosthetic outcomes, patient satisfaction, and survival rates of implants between two-implant-supported overdentures (IODs) and three-implant-supported fixed dentures (ISFDs).

MATERIALS AND METHODS

Twenty completely edentulous patients were randomly and equally assigned to two groups. New conventional complete dentures were made, and the mandibular denture was used as a surgical guide during implant placement. Implants were placed in one stage, followed by a mandibular denture soft reline (provisional loading). Ball attachments were inserted at 8 weeks, and ISFDs were delivered at 16 weeks. IODs were connected to the attachments at 8 weeks, using each patients's existing denture. The definitive ISFDs were fabricated using computer-aided design/computer-assisted manufacture milled titanium frameworks and acrylic resin base and teeth. Patient satisfaction and panoramic radiographs were investigated at 6 and 12 months.

RESULTS

Both treatments had significant and positive effects on patient satisfaction and quality of life. None of the 50 implants placed had failed at 12 months of follow-up; therefore, the implant survival rate was 100%. Prosthetic complications were generally rare and easily manageable.

CONCLUSIONS

Both the treatment modalities-the ISFD supported by three implants and the IOD supported by two implants-significantly and similarly improved patient satisfaction and oral health-related quality of life, and prosthetic complications were relatively rare for both treatments. Three implants can be used to support a mandibular fixed prosthesis; however, a longer observation period is needed to validate this treatment modality.

NF-κB suppresses HIF-1α response by competing for P300 binding

Hypoxia has emerged as a key determinant of osteogenesis. HIF-1α is the transcription factor mediating hypoxia responses that include induction of VEGF and related bone induction. Inflammatory signals antagonize bone repair via the NF-κB pathway. The present investigation explored the functional relationship of hypoxia (HIF-1α function) and inflammatory signaling (NF-κB) in stem like and osteoprogenitor cell lines. The potential interaction between HIF-1α and NF-κB signaling was explored by co-transfection studies in hFOB with p65, HIF-1α and 9x-HRE-luc or HIF-1α target genes reporter plasmids. Nuclear cross-talk was directly tested using the mammalian Gal4/VP16 two-hybrid, and confirmed by co-immunoprecipitation/western blotting assays. The results show that inflammatory stimulation (TNF-α treatment) causes a marked inhibition of HIF-1α function at the HRE in all cell lines studied. Also, co-transfection with p65 expression vector leads to reduced hVEGFp transcription after DFO-induced hypoxia. However, TNF-α treatment had little effect on HIF-1α mRNA levels. The functional interaction of Gal4-HIF-1α and VP16-p300 fusion proteins is effectively blocked by expression of p65 in a dose dependent manner. It was concluded that NF-κB-mediated inflammatory signaling is able to block HIF-1α transactivation at HRE-encoding genes by direct competition for p300 binding at the promoter. Inflammation may influence the stem cell niche and tissue regeneration by influencing cellular responses to hypoxia.

Comparison of radiographic and clinical outcomes following immediate provisionalization of single-tooth dental implants placed in healed alveolar ridges and extraction sockets

PURPOSE

The primary goal of this study was to compare implant survival 12 months after immediate loading of single implants placed in healed ridges versus extraction sockets. Secondary outcomes were to compare marginal bone adaptation and soft tissue changes over time.

MATERIALS AND METHODS

A prospective multicenter clinical investigation was initiated to assess clinical performance of immediately loaded implants in the maxilla. Implant survival was ascertained at the time of impression making (8 to 10 weeks) and after 1 year by clinical stability. Radiographic marginal bone levels, soft tissue levels, and plaque and bleeding scores were compared with baseline values (implant placement and provisionalization).

RESULTS

One hundred thirty-nine patients received 157 implants in the maxilla. Single implants with provisional crowns were placed in extraction sockets of 55 patients (58 implants) and in healed ridges of 60 patients (65 implants). In addition, 19 patients (23 implants) required bone grafting prior to implant placement, and 11 implants in 10 patients among all groups were not immediately loaded because of insufficient initial stability after surgery. Three implants (5.2%) failed in extraction sites and one implant (1.5%) failed in a healed ridge. The mean change in marginal bone level 1 year after implant placement was 1.30 mm (SD 2.52) (gain) in extraction sockets and -0.40 mm (SD 1.43) (loss) in healed ridges. The mucosal zenith was stable or moved incisally following definitive crown placement in 83.7% of immediate implants and 87.0% of implants placed in healed ridges. Plaque and inflammation scores were low and did not differ between groups.

CONCLUSIONS

The responses of local bone and soft tissues at immediately loaded implants placed in extraction sockets or healed ridges were similar. Furthermore, these 1-year results suggest that clinical management of esthetically critical soft tissue may be predictably achieved in both indications.

The combination of micron and nanotopography by H(2)SO(4)/H(2)O(2) treatment and its effects on osteoblast-specific gene expression of hMSCs

H(2)SO(4)/H(2)O(2) treatment of titanium implants imparts nanofeatures to the surface and alters the osteoblast response. The aim of this study was to evaluate the effect of H(2)SO(4)/H(2)O(2) treatment of commercially pure Titanium (cpTi) surfaces on gene expression of human mesenchymal stem cells (hMSCs) differentiated into osteoblasts. Commercially pure grade IV titanium disks (20.0 mm x 1.0 mm) were polished or polished and subsequently treated by grit blasting or grit-blasting/acid etching with an H(2)SO(4)/H(2)O(2) solution. The surfaces were divided into three groups: smooth (S), grit-blasted (Gb), and nanostructured: grit-blasted/acid etched (Nano). Surfaces were examined by scanning electron microscopy and atomic force microscopy. HMSCs were grown on the disks. The data points analyzed were at 3, 7, 14, and 28 days. Real-time PCR was used to measure the mRNA levels of ALP, BSP, Runx2, OCN, OPN, and OSX. The housekeeping gene GAPDH was used as a control. Descriptive statistics were calculated using Microsoft Excel. T-test was performed for comparison of mRNA levels when compared with S surfaces (p < 0.05). All osteoblast-specific genes were regulated in surface-dependent patterns and most of them were upregulated on the Nano surfaces. Runx2 and OSX mRNAs were more than threefold upregulated at days 14 and 28 on Nano. Higher levels for ALP (38-fold), BSP (76-fold), and OCN (3-fold) were also observed on the Nano surfaces. A grit-blasted surface imparted with nanofeatures by H(2)SO(4)/H(2)O(2) treatment affected adherent cell bone-specific gene expression. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.