Biomechanical evaluation of the interfacial strength of a chemically modified sandblasted and acid-etched titanium surface

The functional capacity of osseointegrated dental implants to bear load is largely dependent on the quality of the interface between the bone and implant. Sandblasted and acid-etched (SLA) surfaces have been previously shown to enhance bone apposition. In this study, the SLA has been compared with a chemically modified SLA (modSLA) surface. The increased wettability of the modSLA surface in a protein solution was verified by dynamic contact angle analysis. Using a well-established animal model with a split-mouth experimental design, implant removal torque testing was performed to determine the biomechanical properties of the bone-implant interface. All implants had an identical cylindrical shape with a standard thread configuration. Removal torque testing was performed after 2, 4, and 8 weeks of bone healing (n = 9 animals per healing period, three implants per surface type per animal) to evaluate the interfacial shear strength of each surface type. Results showed that the modSLA surface was more effective in enhancing the interfacial shear strength of implants in comparison with the conventional SLA surface during early stages of bone healing. Removal torque values of the modSLA-surfaced implants were 8-21% higher than those of the SLA implants (p = 0.003). The mean removal torque values for the modSLA implants were 1.485 N m at 2 weeks, 1.709 N m at 4 weeks, and 1.345 N m at 8 weeks; and correspondingly, 1.231 N m, 1.585 N m, and 1.143 N m for the SLA implants. The bone-implant interfacial stiffness calculated from the torque-rotation curve was on average 9-14% higher for the modSLA implants when compared with the SLA implants (p = 0.038). It can be concluded that the modSLA surface achieves a better bone anchorage during early stages of bone healing than the SLA surface; chemical modification of the standard SLA surface likely enhances bone apposition and this has a beneficial effect on the interfacial shear strength.

Application of periodontal tissue engineering using enamel matrix derivative and a human fibroblast-derived dermal substitute to stimulate periodontal wound healing in Class III furcation defects

BACKGROUND

Enamel matrix derivative (EMD) has been shown to promote several aspects of periodontal regeneration in vitro and in vivo. Recently, a bioengineered tissue (DG) was developed to promote wound healing of chronic skin ulcers. This pilot study sought to assess the effects of EMD and DG, alone or in combination, on periodontal wound healing in surgically created Class III furcation defects.

METHODS

Six female baboons received bilateral ostectomy of approximately 10 mm around the first and second mandibular molars to achieve Class III, subclass C furcation defects. Wire ligatures and cotton pellets were left in place for 2 months to maintain the depth of the defects and promote plaque accumulation. Each furcally involved molar was then assigned to one of four treatments: open flap debridement (OFD), OFD plus EMD, OFD plus DG, or OFD plus DG and EMD. This resulted in six total sites per treatment group. Seven months after defect creation and 5 months after treatment, and after no oral hygiene, tissue blocks of the mandible were taken for blinded histometric analysis to assess parameters of periodontal regeneration adjacent to furcal root surfaces and from the mid-furcal aspect (i.e., new bone, new connective tissue attachment, new epithelial attachment, and new cementum formation).

RESULTS

Histometric analysis demonstrated differential regenerative responses with respect to treatment within each animal. However, statistically significant differences between treatments from all six animals were not observed (P >0.20, mixed-model analysis of variance). EMD-treated sites presented mildly positive regenerative results and no negative responses. Both DG only and combination therapy demonstrated similar or less than positive responses relative to OFD controls.

CONCLUSION

The descriptive analysis may suggest a positive effect of enamel matrix proteins and a negative effect of DG used alone or in combination with enamel matrix proteins on the regeneration of Class III furcation defects in baboons.

Consequences of Implant Design

The use of dental implants to replace missing teeth is becoming a preferred alternative for restorative dentists and their patients. There are two general surgical approaches for the placement and restoration of missing teeth using endosseous dental implants. One approach places the top of the implant at the alveolar crest and the mucosa is sutured over the implant. An alternative approach places the coronal aspect of the implant coronal to the alveolar crest and the mucosa is sutured around the transmucosal aspect of the implant. This article reviews one-piece and two-piece implants as well as biologic implications of submerged and non-submerged surgical techniques for placing implants.

Human Periodontal Fibroblast Response to Enamel Matrix Derivative, Amelogenin, and Platelet-Derived Growth Factor-BB

BACKGROUND

The ideal goal of clinical therapy in periodontal defects is regeneration of all lost structures. For regeneration to occur, cell proliferation, migration, and extracellular matrix synthesis are prerequisites. Attempts at regeneration of periodontal defects by guided tissue regeneration using bone grafts and membranes have not always yielded predictable results. Recently, attempts at engineering the defects using various materials have shown promising results. Two such approaches have been used to regenerate periodontal defects, one using extracellular matrix such as enamel matrix proteins and the other using growth factors. However, to our knowledge, no study has looked at combining these two approaches to achieve potentially even greater regeneration.

METHODS

Primary human periodontal ligament (PDL) fibroblasts were explanted, and alkaline phosphatase (ALK PHOS) activity was determined. Phenotypically different cell lines were incubated for 1, 3, 6, and 10 days in 0.2% fetal bovine serum (FBS) media containing different concentrations of either enamel matrix derivative (EMD), amelogenin, platelet-derived growth factor-BB (PDGF-BB), EMD+PDGF-BB, or amelogenin+PDGF-BB. A culture of 0.2% FBS alone served as a negative control, and a culture of 10% FBS served as a positive control. Cell proliferation was measured using a Coulter counter to determine the cell number. The effects on a wound-fill model were evaluated by scraping a 3-mm wide cell-free zone in PDL monolayers across the diameter of the tissue-culture plate and determining PDL cell migration into the cell-free zone using computer assisted histomorphometry.

RESULTS

Compared to the control, only EMD+PDGF-BB significantly increased PDL cell proliferation in an ALK PHOS (-) cell line (P<0.001), and EMD alone, EMD+PDGF-BB, and amelogenin+PDGF-BB significantly increased PDL cell proliferation in an ALK PHOS (+) cell line (P<0.001) with EMD+PDGF-BB showing a trend for greater proliferation than either PDGF or EMD alone. Individually, EMD and amelogenin had no significant effect on PDL cell proliferation. In the wound-fill experiment, all factors and their combinations except amelogenin significantly enhanced cell migration compared to the control (P<0.05) at the wound edge. In addition, EMD+PDGF-BB had additive effects on the ALK PHOS (-) cell line at the wound edge. At the center of the wound, neither EMD nor amelogenin had a significant wound-fill effect. However, the combination of EMD+PDGF-BB additively increased wound fill for both ALK PHOS (+) and ALK PHOS (-) cells.

CONCLUSIONS

The combination of EMD and PDGF-BB produces greater proliferative and wound-fill effects on PDL cells than each by themselves. If these combined effects can be translated clinically, one may see greater regeneration in periodontal defects with this combination. However, amelogenin does not have significant effects on PDL cell proliferation or migration by itself. This may suggest that either another enamel matrix component in EMD may be responsible for some of its clinical effects, or that amelogenin alone may not trigger the regenerative potential of periodontal tissues and that it requires a combined interaction with other enamel matrix components of EMD to direct the regenerative process.

The Effect of rhBMP-2 Around Endosseous Implants With and Without Membranes in the Canine Model

BACKGROUND

Bone morphogenetic protein (BMP) is a potent differentiating agent for cells of the osteoblastic lineage. It has been used in the oral cavity under a variety of indications and with different carriers. However, the optimal carrier for each indication is not known. This study examined a synthetic bioabsorbable carrier for BMP used in osseous defects around dental implants in the canine mandible.

METHODS

Twelve canines had their mandibular four premolars and first molar teeth extracted bilaterally. After 5 months, four implants were placed with standardized circumferential defects around the coronal 4 mm of each implant. One-half of the defects received a polylactide/glycolide (PLGA) polymer carrier with or without recombinant human BMP-2 (rhBMP-2), and the other half received a collagen carrier with or without rhBMP-2. Additionally, one-half of the implants were covered with a non-resorbable (expanded polytetrafluoroethylene [ePTFE]) membrane to exclude soft tissues. Animals were sacrificed either 4 or 12 weeks later. Histomorphometric analysis included the percentage of new bone contact with the implant, the area of new bone, and the percentage of defect fill. This article describes results with the PLGA carrier.

RESULTS

All implants demonstrated clinical and radiographic success with the amount of new bone formed dependent on the time and presence/absence of rhBMP-2 and presence/absence of a membrane. The percentage of bone-to-implant contact was greater with rhBMP-2, and after 12 weeks of healing, there was approximately one-third of the implant contacting bone in the defect site. After 4 weeks, the presence of a membrane appeared to slow new bone area formation. The percentage of fill in membrane-treated sites with rhBMP-2 rose from 24% fill to 42% after 4 and 12 weeks, respectively. Without rhBMP-2, the percentage of fill was 14% rising to 36% fill, respectively.

CONCLUSIONS

After 4 weeks, the rhBMP-2-treated sites had a significantly higher percentage of contact, more new bone area, and higher percentage of defect fill than the sites without rhBMP-2. After 12 weeks, there was no significant difference in sites with or without rhBMP-2 regarding percentage of contact, new bone area, or percentage of defect fill. In regard to these three outcomes, comparing the results with this carrier to the results reported earlier with a collagen carrier in this study, only the area of new bone was significantly different with the collagen carrier resulting in greater bone than the PLGA carrier. Thus, the PLGA carrier for rhBMP-2 significantly stimulated bone formation around dental implants in this model after 1 month but not after 3 months of healing. The use of this growth factor and carrier combination appears to stimulate early bone healing events around the implants but not quite to the same degree as a collagen carrier.

Effects of Enamel Matrix Derivative on Bone-Related mRNA Expression in Human Periodontal Ligament Cells In Vitro

BACKGROUND

Enamel matrix derivative (EMD) has demonstrated the potential to stimulate periodontal regeneration with mineralized tissue formation. Molecular regulators of bone metabolism include osteoprotegrin (OPG), receptor activator of nuclear factor kappa B ligand (RANKL), cyclooxygenase 2 (COX2), and core binding factor alpha 1 (Cbfa1). The role of these regulatory molecules within the context of EMD stimulation of mineralized tissue formation is unknown. Therefore, the purpose of this investigation was to explore the effects of EMD on these bone-related molecules in human periodontal ligament (PDL) cells.

METHODS

Human PDL-cell cultures were treated with EMD (5 to 100 microg/ml) for 24 hours. Total RNA was isolated using phenolchloroform, and reverse transcription-polymerase chain reaction (RT-PCR) was performed using primers specific for OPG, RANKL, COX2, Cbfa1, and aldolase, with amplification in the exponential range for each molecule studied.

RESULTS

The results of this study show that there is a significant (P <0.05) increase in COX2 mRNA levels with EMD treatment, and no effects were noted on mRNA levels for Cbfa1. RANKL mRNA levels were significantly decreased (P <0.01) up to 50% with EMD treatment > or =25 microg/ml. OPG levels showed minimal effects with EMD treatment. However, the RANKL/OPG ratio showed a 40% to 55% reduction with EMD >or =25 microg/ml.

CONCLUSION

This study supports a role for EMD stimulation of mineralized tissue formation consistent with periodontal regeneration by modulating regulatory molecules critical to bone metabolism at the RNA level.

Integrin beta1 silencing in osteoblasts alters substrate-dependent responses to 1,25-dihydroxy vitamin D3

Surface microroughness increases osteoblast differentiation and enhances responses of osteoblasts to 1,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. The observations that beta1 integrin expression is increased in osteoblasts grown on Ti substrates with rough microarchitecture, and that it is regulated by 1alpha,25(OH)2D3 in a surface-dependent manner, suggest that beta1 may play a role in mediating osteoblast response. To test this hypothesis, we silenced beta1 expression in MG63 human osteoblast-like cells using small interfering RNA (siRNA) and examined the responses of the beta1-silenced osteoblasts to surface microtopography and 1alpha,25(OH)2D3. To better understand the role of beta1, MG63 cells were also treated with two different monoclonal antibodies to human beta1 to block ligand binding. beta1-silenced MG63 cells grown on a tissue culture plastic had reduced alkaline phosphatase activity and levels of osteocalcin, transforming growth factor beta1, prostaglandin E2, and osteoprotegerin in comparison with control cells. Moreover, beta1-silencing inhibited the effects of surface roughness on these parameters and partially inhibited effects of 1alpha,25(OH)2D3. Anti beta1 antibody AIIB2 had no significant effect on cell number and osteocalcin, but decreased alkaline phosphatase; MAB2253Z caused dose-dependent decreases in cell number and alkaline phosphatase and an increase in osteocalcin. Effects of 1alpha,25(OH)2D3 on cell number and alkaline phosphatase were reduced and effects on osteocalcin were increased. These findings indicate that beta1 plays a major and complex role in osteoblastic differentiation modulated by either surface microarchitecture or 1alpha,25(OH)2D3. The results also show that beta1 mediates, in part, the synergistic effects of surface roughness and 1alpha,25(OH)2D3.

Platelet-derived growth factor inhibits demineralized bone matrix-induced intramuscular cartilage and bone formation. A study of immunocompromised mice

BACKGROUND

Platelet-derived growth factor (PDGF) has been proposed as a therapeutic agent to promote bone-healing. The purpose of this study was to examine the effect of PDGF on the ability of human demineralized bone matrix to induce bone formation in a nude-mouse muscle-implantation model. We also examined whether platelet-rich plasma, which contains PDGF, also modulates osteoinduction in this model.

METHODS

Human demineralized bone matrix, previously shown to be osteoinductive in the calf muscles of nude mice, was mixed with PDGF-BB (0, 0.1, 1, and 10 microg/10 mg of demineralized bone matrix) and was implanted bilaterally in the calf muscles of immunocompromised (nu/nu) mice (six mice in each group). Heat-inactivated demineralized bone matrix was used as a control. Tissue was harvested at fourteen, twenty-eight, and fifty-six days after implantation. Platelet-rich plasma was prepared from the blood of a healthy donor with use of the Harvest PRP preparation device, activated with thrombin, and mixed with active and inactive demineralized bone matrix. Fifty-six days post-implantation, tissues were harvested. Osteoinduction was assessed with use of a qualitative scoring system and with quantitative histomorphometry.

RESULTS

Cartilage was present at fourteen days in all tissues that had received an implant, but the amount decreased as the PDGF concentration increased. PDGF reduced bone formation at twenty-eight days in a dose-dependent manner. This inhibitory effect was resolved by fifty-six days, except in tissues in which demineralized bone matrix and 10 microg of PDGF had been implanted. In sites treated with 10 microg of PDGF, the area of new bone was decreased and the area of bone marrow was reduced at twenty-eight and fifty-six days. PDGF also appeared to retard resorption of demineralized bone matrix in a dose-dependent manner. Platelet-rich plasma reduced osteoinduction by human demineralized bone matrix that had high osteoinductive activity and had no effect on osteoinduction by demineralized bone matrix with low activity.

CONCLUSIONS

PDGF inhibits, in a dose-dependent manner, intramuscular osteoinduction and chondrogenesis by demineralized bone matrix in immunocompromised mice. Platelet-rich plasma also reduces the osteoinductivity of active demineralized bone matrix.

The effect of a machined collar on coronal hard tissue around titanium implants: a radiographic study in the canine mandible

PURPOSE

The purpose of this study was to radiographically evaluate the effect of a machined titanium coronal collar on the marginal bone around 1-part endosseous dental implants placed at different heights relative to the bone crest.

MATERIALS AND METHODS

Sixty dental implants were placed in edentulous spaces bilaterally in 5 foxhounds. Thirty test implants had a sandblasted, large-grit, dual acid-etched surface (SLA) over the entire length of the implant. The other 30 implants (control) had a machined collar around the most coronal 1.8 mm of the implant; an SLA surface covered the remainder of the implant. Both control and test implants were placed at 3 distinct levels relative to the bone crest. Six implants (3 control and 3 test) were randomly placed side by side in each hemimandible. Radiographs were taken at placement (baseline) and monthly for 6 months postplacement using a standardized radiographic template.

RESULTS

Fifty-eight of the implants integrated and were analyzed on each proximal surface. Bone loss occurred around all implants over the 6 months of the study. In general, implants placed with the top of the SLA surface above the bone crest had significantly less bone loss than implants with the top of the SLA surface placed flush with the bone level. Apically placed implants had greater bone loss than coronally placed implants. The magnitude of bone loss around paired control and test implants was approximately the same.

DISCUSSION AND CONCLUSION

The least bone loss with each implant type was observed when the top of the implant was placed above the alveolar crest. When there was no machined collar, the least distance from the implant top to the bone crest (not, however, the least bone loss) was observed when the top of the implant was level with the bone crest.

The CO2 laser for excisional biopsies of oral lesions: a case series study

During a period of 12 months, 139 patients with 164 intraoral pathologic lesions were treated with a CO2 laser. Intra- and postoperative complications and the method of pain control during and after surgery were recorded. The diagnostic evaluability of the 133 soft tissue biopsy specimens sent for histopathologic analysis was examined, and the clinical and histopathologic diagnoses were compared. Nine intra- and six postoperative complications occurred. Pain control during CO2 laser surgery could be performed with a topical anesthetic in almost one third of the lesions; in the other 111 lesions, a local anesthetic had to be applied. For pain relief after the operation, 101 patients (72.7%) used only an adhesive wound paste, without any additional oral analgesic. The thermal damage from the CO2 laser on the borders of the biopsy specimens never interfered with the pathologist's establishment of a firm diagnosis. The CO2 laser is an appropriate instrument for excisional biopsies of oral soft tissue lesions. Intra- and postoperative complications were minimal, pain relief during and after surgery could be achieved in many cases through topical anesthetics, and incisional or excisional biospsies caused no diagnostic problems because of collateral thermal damage of the specimen from the laser.

Evaluation of Demineralized Bone Matrix Paste and Putty in Periodontal Intraosseous Defects

BACKGROUND

Demineralized bone matrix (DBX) paste and putty are particulate demineralized bone matrices in a 2% or 4% hyaluronate carrier, respectively. The purpose of this study was to determine the effectiveness of DBX paste and putty compared to demineralized freeze-dried bone allograft (DFDBA) in the treatment of human intraosseous periodontal defects.

METHODS

Sixty systemically healthy individuals between the ages of 31 and 71 years with at least one intraosseous periodontal defect of > or = 3 mm in depth and radiographic evidence of at least 40% to 50% vertical bone loss were accrued. Following initial non-surgical periodontal therapy, sites were randomly selected to receive either DBX paste, DBX putty, or DFDBA (control). Baseline and 6-month reentry soft and hard tissue parameter measurements were made by calibrated examiners. Data were analyzed within and between groups utilizing analysis of variance (ANOVA) and paired and unpaired Student t tests.

RESULTS

Probing depth reductions were significantly improved in all treatment groups with DFDBA, DBX paste, and putty patients demonstrating 2.8 mm, 3.6 mm, and 2.3 mm, respectively. Attachment level gains were significantly improved from baseline for all treatment groups with DFDBA, DBX paste, and putty, respectively, demonstrating 2.4 mm, 2.9 mm, and 1.6 mm. Bone fill was similar between all groups with DBX paste, putty, and DFDBA control groups demonstrating 2.0 mm, 2.4 mm, and 2.2 mm, respectively. All groups yielded significant improvements in percent bone fill with DFDBA, DBX paste and putty, respectively, achieving 37%, 42.1%, and 50% with no significant differences between the groups.

CONCLUSION

In summary, demineralized bone matrix paste, demineralized bone matrix putty, and demineralized freeze-dried bone allograft all demonstrated similar favorable improvements in soft and hard tissue parameters in the treatment of human intraosseous defects.

Crestal Bone Changes Around Titanium Implants. Part I: A Retrospective Radiographic Evaluation in Humans Comparing Two Non-Submerged Implant Designs With Different Machined Collar Lengths

BACKGROUND

Experimental studies demonstrated that peri-implant crestal hard and soft tissues are significantly influenced in their apico-coronal position by the rough/smooth implant border as well as the microgap/ interface between implant and abutment/restoration. The aim of this study was to evaluate radiographically the crestal bone level changes around two types of implants, one with a 2.8 mm smooth machined coronal length and the other with 1.8 mm collar.

METHODS

In 68 patients, a total of 201 non-submerged titanium implants (101 with a 1.8 mm, 100 with a 2.8 mm long smooth coronal collar) were placed with their rough/smooth implant border at the bone crest level. From the day of surgery up until 3 years after implant placement crestal bone levels were analyzed digitally using standardized radiographs.

RESULTS

Bone remodeling was most pronounced during the unloaded, initial healing phase and did not significantly differ between the two types of implants over the entire observation period (P >0.20). Crestal bone loss for implants placed in patients with poor oral hygiene was significantly higher than in patients with adequate or good plaque control (P <0.005). Furthermore, a tendency for additional crestal bone loss was detected in the group of patients who had been diagnosed with aggressive periodontitis prior to implant placement (P = 0.058). In both types of implants, sand-blasted, large grit, acid-etched (SLA) surfaced implants tended to have slightly less crestal bone loss compared to titanium plasma-sprayed (TPS) surfaced implants, but the difference was not significant (P >0.30).

CONCLUSION

The implant design with the shorter smooth coronal collar had no additional bone loss and may help to reduce the risk of an exposed metal implant margin in areas of esthetic concern.

The Use of Guided Tissue Regeneration Principles in Endodontic Surgery for Induced Chronic Periodontic-Endodontic Lesions: A Clinical, Radiographic, and Histologic Evaluation

BACKGROUND

Chronic periodontic-endodontic lesions are not uncommon in clinical practice and their regenerative capacity has long been questioned. However, there are no published studies investigating the application of guided tissue regeneration techniques in combination with endodontic surgery using an induced perio-endo defect model. This study evaluated the clinical, radiographic, and histologic outcomes of three surgical procedures used to treat induced perio-endo lesions.

METHODS

Pulpal necrosis was induced in foxhounds along with surgical removal of radicular buccal bone. After 4 weeks, chronic lesions were clinically and radiographically assessed. Treatment surgery consisted of apicoectomy, root canal instrumentation, and retrofilling with mineral trioxide aggregate. Teeth were then assigned to one of the following treatment groups: open flap debridement only (OFD), OFD with bioabsorbable porcine-derived collagen membrane (BG), or OFD with BG and anorganic bovine bone matrix (BO/BG). Clinical parameters and standardized radiographs were assessed at defect creation; treatment surgery; and at 1, 2, 4, and 6 months. Animals were sacrificed at 6 months and specimens prepared for histometric analysis.

RESULTS

Clinical and radiographic conditions improved during the study period. Mean epithelial attachment was similar between all groups. Mean connective tissue attachment for groups OFD, BG, and BO/BG was 3.79 mm, 2.63 mm, and 1.75 mm, respectively, and mean radicular bone height was 2.16 mm, 3.24 mm, and 3.45 mm, respectively. Statistically significant increases in the amount of new cementum were observed in groups BG and BO/BG when compared with OFD (P <0.05).

CONCLUSIONS

Treatment of combined induced perio-endo lesions using bioabsorbable collagen membranes alone or in combination with anorganic bovine bone matrix resulted in increased amounts of bone, periodontal ligament, and significant increases in the amount of new cementum when compared to open flap debridement in a canine model.

High surface energy enhances cell response to titanium substrate microstructure

Titanium (Ti) is used for implantable devices because of its biocompatible oxide surface layer. TiO2 surfaces that have a complex microtopography increase bone-to-implant contact and removal torque forces in vivo and induce osteoblast differentiation in vitro. Studies examining osteoblast response to controlled surface chemistries indicate that hydrophilic surfaces are osteogenic, but TiO2 surfaces produced until now exhibit low surface energy because of adsorbed hydrocarbons and carbonates from the ambient atmosphere or roughness induced hydrophobicity. Novel hydroxylated/hydrated Ti surfaces were used to retain high surface energy of TiO2. Osteoblasts grown on this modified surface exhibited a more differentiated phenotype characterized by increased alkaline phosphatase activity and osteocalcin and generated an osteogenic microenvironment through higher production of PGE2 and TGF-beta1. Moreover, 1alpha,25OH2D3 increased these effects in a manner that was synergistic with high surface energy. This suggests that increased bone formation observed on modified Ti surfaces in vivo is due in part to stimulatory effects of high surface energy on osteoblasts.

Enhanced bone apposition to a chemically modified SLA titanium surface

Increased surface roughness of dental implants has demonstrated greater bone apposition; however, the effect of modifying surface chemistry remains unknown. In the present study, we evaluated bone apposition to a modified sandblasted/acid-etched (modSLA) titanium surface, as compared with a standard SLA surface, during early stages of bone regeneration. Experimental implants were placed in miniature pigs, creating 2 circular bone defects. Test and control implants had the same topography, but differed in surface chemistry. We created the test surface by submerging the implant in an isotonic NaCl solution following acid-etching to avoid contamination with molecules from the atmosphere. Test implants demonstrated a significantly greater mean percentage of bone-implant contact as compared with controls at 2 (49.30 vs. 29.42%; p = 0.017) and 4 wks (81.91 vs. 66.57%; p = 0.011) of healing. At 8 wks, similar results were observed. It is concluded that the modSLA surface promoted enhanced bone apposition during early stages of bone regeneration.

Microrough implant surface topographies increase osteogenesis by reducing osteoclast formation and activity

Titanium implant surfaces with rough microtopographies exhibit increased pullout strength in vivo suggesting increased bone-to-implant contact. This is supported by in vitro studies showing that as surface microroughness increases, osteoblast proliferation decreases whereas differentiation increases. Differentiation is further enhanced on microrough surfaces by factors stimulating osteogenesis including 1alpha,25(OH)2D3. Levels of PGE2 and TGF-beta1 are increased in cultures grown on rough microtopographies; this surface effect is enhanced synergistically by 1alpha,25(OH)2D3-treatment. PGE2 and TGF-beta1 regulate osteoclasts as well as osteoblasts, suggesting that surface microtopography may modulate release of other factors from osteoblasts that regulate osteoclasts. To test this hypothesis, we examined the effects of substrate microarchitecture on production of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL), which have been identified as a key regulatory system of bone remodeling. We also examined the production of 1alpha,25(OH)2D3, which regulates osteoblast differentiation and osteoclastogenesis. MG63 osteoblast-like cells were grown on either tissue culture plastic or titanium disks of different surface microtopographies: PT (Ra < 0.2 microm), SLA (Ra = 4 microm), and TPS (Ra = 5 microm). At confluence, cultures were treated for 24 h with 0, 10(-8) M or 10(-7) M 1alpha,25(OH)2D3. RANKL and OPG were determined at the transcriptional level by RT-PCR and real time PCR and soluble RANKL, OPG and 1alpha,25(OH)2D3 in the conditioned media were measured using immunoassay kits. Cell number was reduced on SLA and TPS surfaces and 1alpha,25(OH)2D3 caused further decreases. OPG mRNA levels increased on rougher surfaces and 1alpha,25(OH)2D3 treatment caused a further synergistic increase. While the cells expressed RANKL mRNA, levels were low and independent of surface microtopography. OPG protein was greater when cells were grown on SLA and TPS. 1alpha,25(OH)2D3 increased OPG by 50% on the smooth Ti surface but on SLA, 10(-8) M 1alpha,25(OH)2D3 caused a 100% increase and 10(-7) M 1alpha,25(OH)2D3 increased OPG by 200%. On TPS 10(-7) M 1alpha,25(OH)2D3 increased OPG 350%. Soluble RANKL was not detected in the conditioned media of any of the cultures. 1alpha,25(OH)2D3 was produced endogenously and levels were positively correlated with surface roughness. Thus, on surfaces with rough microtopographies, osteoblasts secrete factors that enhance osteoblast differentiation while decreasing osteoclast formation and activity.

Clinical and histologic evaluation of anorganic bovine bone collagen with or without a collagen barrier

This study evaluated an anorganic bovine-derived xenograft (Bio-Oss Collagen) in the treatment of human periodontal defects. Four patients with intrabony defects on teeth that were treatment planned for extraction were enrolled in the study. Presurgical measurements of probing depth, attachment level, and recession were recorded. The surgical procedure consisted of flap reflection, debridement of the osseous defects and root surface, placement of a notch through calculus into the root surface, topical application of a tetracycline paste to the root surface, grafting with Bio-Oss Collagen, and flap closure. Three of the eight defects examined received a resorbable collagen barrier (Bio-Gide) in addition to the bone graft. Patients were seen every 2 weeks for plaque control and review of oral hygiene measures. Six months postsurgery, clinical parameters were rerecorded prior to en bloc resection of teeth and adjacent graft sites. The majority of sites showed a favorable clinical response with respect to probing depth reduction and clinical attachment gain. Histologic analysis demonstrated new bone, cementum, and periodontal ligament coronal to the reference notch in two of the eight specimens. Two sites demonstrated new attachment, and four showed a long junctional epithelium. Periodontal regeneration is possible following a bone-replacement graft of Bio-Oss Collagen.

Initial Implant Position Determines the Magnitude of Crestal Bone Remodeling

BACKGROUND

The ability to predict the amount of bone remodeling around implants is important for a stable and predictable esthetic result. The purpose of this study was to investigate the amount of radiographic bone remodeling that occurs over time using a one-piece implant system.

METHODS

Twenty-seven patients receiving implants in the maxilla and 15 receiving implants in the mandible were included in the study. All implants were placed with a non-submerged surgical technique with varying locations of the rough-smooth border with respect to the alveolar crest. Clinical exams and radiographs were taken on the day of implant placement, at 6 months, and annually up to 5 years. Linear measurements from digitized radiographs were made from the implant shoulder to the first bone-to-implant contact at all time points.

RESULTS

A significant amount of bone remodeling compared to baseline occurred for all implants at the 6-month follow-up visit (1.10 mm), with the remaining time points showing virtually no change (0.1 mm). A relationship was found between the amount of bone remodeling and the location of the rough-smooth border with respect to the alveolar crest. Those implants with the rough-smooth border surgically placed below the crest had, on average, a greater amount of remodeling at 6 months (average 1.72 mm) than implants with the rough-smooth border placed at or near the crest (average 0.68 mm). In both situations, this remodeling: 1) occurred early (within 6 months), 2) reached a similar level, and 3) remained virtually unchanged up through 60 months (0.05 mm).

CONCLUSIONS

A physiologic dimension appears to exist between the bone and the implant-crown interface around one-piece implants that is established early and maintained over time. These results are significant because they demonstrate in patients that the magnitude of initial bone remodeling around these one-piece dental implants is dependent on the positioning of the rough-smooth border of the implant in an apico-coronal dimension. Furthermore, the dimension, from the crown-implant interface to the first bone-to-implant contact, is consistent with the formation of a biologic width similar to that found around the natural dentition.

RGD-containing peptide GCRGYGRGDSPG reduces enhancement of osteoblast differentiation by poly(L-lysine)-graft-poly(ethylene glycol)-coated titanium surfaces

Osteoblasts exhibit a more differentiated morphology on surfaces with rough microtopographies. Surface effects are often mediated through integrins that bind the RGD motif in cell attachment proteins. Here, we tested the hypothesis that modulating access to RGD binding sites can modify the response of osteoblasts to surface microtopography. MG63 immature osteoblast-like cells were cultured on smooth (Ti sputter-coated Si wafers) and rough (grit blasted/acid etched) Ti surfaces that were modified with adsorbed monomolecular layers of a comb-like graft copolymer, poly-(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), to limit nonspecific protein adsorption. PLL-g-PEG coatings were functionalized with varying amounts of an integrin-receptor-binding RGD peptide GCRGYGRGDSPG (PLL-g-PEG/PEG-RGD) or a nonbinding RDG control sequence GCRGYGRDGSPG (PLL-g-PEG/PEG-RDG). Response to PLL-g-PEG alone was compared with response to surfaces on which 2-18% of the polymer sidechains were functionalized with the RGD peptide or the RDG peptide. To examine RGD dose-response, peptide surface concentration was varied between 0 and 6.4 pmol/cm(2). In addition, cells were cultured on uncoated Ti or Ti coated with PLL-g-PEG or PLL-g-PEG/PEG-RGD at an RGD surface concentration of 0.7 pmol/cm(2), and free RGDS was added to the media to block integrin binding. Analyses were performed 24 h after cultures had achieved confluence on the tissue culture plastic surface. Cell number was reduced on smooth Ti compared to plastic or glass and further decreased on surfaces coated with PLL-g-PEG or PLL-g-PEG/PEG-RDG, but was restored to control levels when PLL-g-PEG/PEG-RGD was present. Alkaline phosphatase specific activity and osteocalcin levels were increased on PLL-g-PEG alone or PLL-g-PEG/PEG-RDG, but PLL-g-PEG/PEG-RGD reduced the parameters to control levels. On rough Ti surfaces, cell number was reduced to a greater extent than on smooth Ti. PLL-g-PEG coatings reduced alkaline phosphatase and increased osteocalcin in a manner that was synergistic with surface roughness. The RDG peptide did not alter the PLL-g-PEG effect but the RGD peptide restored these markers to their control levels. PLL-g-PEG coatings also increased TGF-beta1 and PGE(2) in conditioned media of cells cultured on smooth or rough Ti; there was a 20x increase on rough Ti coated with PLL-g-PEG. PLL-g-PEG effects were inhibited dose dependently by addition of the RGD peptide to the surface. Free RGDS did not decrease the effect elicited by PLL-g-PEG surfaces. These unexpected results suggest that PLL-g-PEG may have osteogenic properties, perhaps correlated with effects that alter cell attachment and spreading, and promote a more differentiated morphology.

Osteoblasts generate an osteogenic microenvironment when grown on surfaces with rough microtopographies

Osteoblasts respond to microarchitectural features of their substrate. On smooth surfaces (tissue culture plastic, tissue culture glass, and titanium), the cells attach and proliferate but they exhibit relatively low expression of differentiation markers in monolayer cultures, even when confluent. When grown on microrough Ti surfaces with an average roughness (Ra) of 4-7 mum, proliferation is reduced but differentiation is enhanced and in some cases, is synergistic with the effects of surface microtopography. In addition, cells on microrough Ti substrates form hydroxyapatite in a manner that is more typical of bone than do cells cultured on smooth surfaces. Osteoblasts also respond to growth factors and cytokines in a surface-dependent manner. On rougher surfaces, the effects of regulatory factors like 1alpha,25(OH)2D3 or 17beta-estradiol are enhanced. The response to the surface is mediated by integrins, which signal to the cell through many of the same mechanisms used by growth factors and hormones. Studies using PEG-modified surfaces indicate that increased differentiation may be related to altered attachment to the surface. When osteoblasts are grown on surfaces with chemistries or microarchitectures that reduce cell attachment and proliferation, and enhance differentiation, the cells tend to increase production of factors like TGF-beta1 that promote osteogenesis while decreasing osteoclastic activity. Thus, on microrough Ti surface, osteoblasts create a microenvironment conducive to new bone formation.

Periodontal Regeneration with a Combination of Enamel Matrix Proteins and Autogenous Bone Grafting

BACKGROUND

Attempts to stimulate periodontal regeneration in the past have focused on either filling the defect with some type of material or providing a space for host cells to repopulate the site and elicit new tissue. In some cases, these approaches have been combined with the assumption that the filler material will help maintain the space necessary for the host cells to invade the area. Growth stimulating substances such as growth factors and other proteins have also been used to encourage periodontal tissue regeneration and histological evaluation supports the use of these substances. Thus, the role for and the necessity of a certain amount of space maintenance for periodontal regeneration is not exactly understood. In addition, it is not known if there is some critical size required for space maintenance or for exactly how long the space must be maintained in order for the host cells to stimulate new cementum, periodontal ligament, and bone. The goal of this study was to evaluate periodontal regeneration in intrabony defects of various sizes treated with a combination of enamel matrix proteins and autogenous bone graft.

METHODS

Periodontal defects ranging in size from 1 to 6 mm were randomized and created bilaterally beside three teeth in the mandibles of baboons. Plaque was allowed to accumulate around wire ligatures placed into the defects. After 2 months, the wire ligatures were removed, the teeth and roots scaled and root planed, and a notch was placed with a chisel at the base of the defect. On one side of the mandible, neutral ethylene diamine tetracetic acid and enamel matrix derivative (EMD) were first used to treat the defect. Autogenous bone taken from the same surgical site was treated with enamel matrix derivative in a dampen dish and then added to the EMD-treated defects. The other side of the mandible served as control with neutral ethylene diamine tetracetic acid and scaling and root planing. Flaps were sutured and the animals were allowed to heal without oral hygiene procedures. After 5 months, the animals were sacrificed and the teeth were processed for histological evaluation.

RESULTS

The results revealed new cementum, periodontal ligament with Sharpey's fibers, and new bone tissue similar to native periodontal tissues. Remnants of the autogenous bone chips were still present at this 5-month post-healing period. Thus periodontal regeneration occurred in all sizes of the periodontal defects. In general, EMD plus autogenous graft treatment resulted in greater tissue formation than controls. In fact, in many cases, very dramatic tissue formation occurred far coronal to the base of the defects in the EMD plus autogenous graft-treated lesions. In addition, horizontal bone fill occurred in the defects and was prominent in the 4 or 6 mm wide lesions. When evaluating the combined 1 and 2 mm defects, the height of new cementum with EMD plus graft was 3.88 mm versus 2.03 mm in the controls, a statistically significant (P < 0.005) difference. In the wider (4 and 6 mm) lesions, this difference was not significant and was much less between treated and control lesions with 2.78 and 2.57 mm of new cementum respectively. In the case of new bone height, in the smaller lesions EMD plus graft resulted in 4.00 mm new bone versus 2.22 mm in the controls, again a statistically significant (P < 0.005) difference. In the larger lesions, EMD plus autogenous bone graft had 3.24 mm new bone height compared to 2.71 mm in the controls, a difference that was not statistically significant. Additionally, in the smaller lesions, new cementum width at the level of the notch was twice as great (statistically significant, P < 0.015) in the EMD plus graft sites compared to control. The width of the periodontal ligament at the coronal aspect of the new bone tissue was similar in the smaller lesions between treated and control sites. The results from the wider defects must be interpreted cautiously as the interproximal bone heights were remodeled adjacent to the wider defects and likely limited the potential for regeneration.

CONCLUSIONS

The combination of enamel matrix derivative plus autogenous bone graft stimulated statistically significant periodontal regeneration in the more narrow 1 and 2 mm lesions. No statistically significant difference was observed in the wider 4 and 6 mm lesions. In many cases, dramatic amounts of new cementum, Sharpey's fibers, periodontal ligament, and bone tissue were formed far above the notch placed at the base of the contaminated defects. This was especially significant considering the width of some of the defects and the fact that no oral hygiene was performed over the 5-month healing period. This periodontal regeneration occurred in the absence of exogenous growth factors or barrier membranes. In summary, the combination of enamel matrix derivative and autogenous bone represents a therapeutic combination that can be highly effective in stimulating significant amounts of periodontal regeneration.

Platelet-Derived Growth Factor-BB Stimulated Cell Migration Mediated Through p38 Signal Transduction Pathway in Periodontal Cells

BACKGROUND

Intracellular signaling pathways mediate specific responses to growth factors. The manipulation of these pathways ultimately may be used to control the clinical outcomes of periodontal regenerative therapy. The purpose of this study was to examine the role of the p38 signal transduction pathway in the responses of periodontal cells to platelet-derived growth factor-BB (PDGF).

METHODS

Primary cultures of human periodontal ligament cells (PDLs) and gingival fibroblasts (GFs) were used for all experiments. Cell numbers, 3H-thymidine incorporation, and Boyden chamber assays were used to characterize the effects of SB 203580 (SB), a specific inhibitor of the p38 signaling pathway, on cell proliferation and migration. An in vitro wound model also was used to assess the effects of SB. For the in vitro wound assay, triplicate wells were incubated for 1, 3, 5, and 7 days using 0.1% fetal bovine serum (FBS), 10% FBS +/- 10 microM SB, or 20 ng/ml PDGF +/- 10 microM SB. Digital histomorphometric analysis assessed cellular fill within the wound area.

RESULTS

SB specifically inhibited PDGF-induced migration in the Boyden chamber assays without affecting cell proliferation. The wound model data showed similar levels of wound fill for PDLs and GFs in 10% FBS. Relative to 10% FBS, PDLs stimulated with PDGF showed significantly (P < 0.01, analysis of variance) greater wound fill (74%) than GFs (12%). SB inhibited the PDGF-induced wound fill of PDLs and GFs by 64% and 57%, respectively. This inhibition was significant (P < 0.01, ANOVA) only for PDLs. The addition of SB to 10% FBS did not significantly affect the wound fill response of either cell type compared to 10% FBS alone.

CONCLUSIONS

These results demonstrate that periodontal cells possess distinct responses to PDGF that may be altered at the signal transduction level. The manipulation of these responses through the use of inhibitors to specific signaling pathways may enhance our control of periodontal regeneration in the future.