Immunohistochemical analysis of cortical and cancellous bone after radiation and the effect of platelet-rich plasma on autogenous bone grafting.

PURPOSE: The collection of autologous platelet-rich plasma (PRP) has demonstrated favorable affects on wound healing in compromised patients. The purpose of this study was to evaluate the expression of PDGF, bFGF, and TGF-beta in irradiated and nonirradiated bone in a rabbit tibia model and the ability of PRP to increase growth factor expression when added to autogenous bone graft in a rabbit cranial defect model. MATERIALS AND METHODS: Ten New Zealand White rabbit tibiae and calvariae were utilized for this study. Tibiae were irradiated at 60 to 70 cGy and evaluated for expression of PDGF, bFGF, and TGF-beta. Rabbit calvariae were also analyzed after grafting with autogenous bone and PRP for determination of growth factor expression. RESULTS: Decreased expression of PDGF, bFGF, and TGF-beta was seen in cortical and cancellous bone samples when irradiated bone was compared to nonirradiated rabbit tibiae. An increase in PDGF, bFGF, and TGF-beta expression was detected in cortical autogenous bone grafts with PRP at 1 and 2 months compared to autogenous bone alone. DISCUSSION: In this study, growth factors, which were decreased in irradiated cortical and cancellous bone, showed increased expression at 1 and 2 months when PRP was added to autogenous bone grafts. Thus, PRP may have potential therapeutic applications when bone grafting is required in patients with reduced bone vascularity, including patients with previous head and neck irradiation, diabetes, and smoking habits. CONCLUSIONS: Decreased expression of PDGF, bFGF, and TGF-beta was seen in radiated rabbit tibia as compared to nonirradiated controls, and increased expression of these growth factors was seen in PRP-containing autogenous bone grafts.

Photoelastic analysis of the effect of palatal support on various implant-supported overdenture designs.

STATEMENT OF PROBLEM: The effect of palatal support on various types of implant-supported maxillary overdenture designs has not been sufficiently assessed. PURPOSE: The purpose of this study was to photoelastically evaluate the palatal support of 3 designs of maxillary implant-supported overdentures. MATERIAL AND METHODS: A photoelastic model of an edentulous maxilla was fabricated with four 3.75 x 13-mm 3i implants. Three maxillary overdenture designs were fabricated: a splinted Hader bar incorporating 2 distal ERA attachments with anterior clips; non-splinted Zaag 4-mm direct abutments and attachments; and nonsplinted Locator 2-mm direct abutments and attachments. All restorative components and attachments were fitted and observed for passivity of fit and alignment. The overdentures were first tested with complete palatal coverage. Unilateral 25-lb loads were applied at the left and right first molars and the incisive papilla area. The photoelastic effects were monitored and recorded photographically. The palatal area was removed from the 3 overdentures and the loading regimens were repeated. RESULTS: The highest stresses under central loading were seen with the splinted Hader bar and complete palatal coverage, followed by similar levels of stress with either Zaag or Locator attachments. After removal of the palate, the center load demonstrated greater differences between designs. The highest stresses were observed with the Hader bar, followed by the Zaag and then Locator attachments. Lack of palatal coverage demonstrated higher levels of stress around implants and visible supporting tissues. The unilateral load produced the highest stress for the splinted Hader bar, followed by Locator, and then Zaag. CONCLUSIONS: Removal of the palatal support produced a greater effect and more concentrated stress difference for maxillary overdentures than differences between the attachment designs tested.

Load transfer by an implant in a sinus-grafted maxillary model.

PURPOSE: This in vitro study determined the stress distribution around an implant placed in a posterior edentulous maxillary model with simulated sinus grafts that had different degrees of stiffness. MATERIALS AND METHODS: The composite photoelastic model with a standard threaded implant consisted of simulated crestal cortical, cancellous, sinus cortical, and grafted bone. The graft maturation process and inherent graft quality were represented in the model by varying the stiffness of the graft. Prior to placement of the simulated graft, axial and inclined loads were applied to the implant The stresses that developed in the supporting structures were analyzed photoelastically. The graft was then placed and the testing procedure was repeated over 4 consecutive days, during which time the simulated graft stiffened. RESULTS: The stress analysis indicated that before placement of the simulated graft, loading on the implant transferred the highest stresses to cortical bone. The presence of the simulated graft transferred stress from the native bone simulants to the simulated grafted bone. DISCUSSION: As the stiffness of the graft increased, a more equitable stress distribution was observed in the multilayer bone surrounding the implant. CONCLUSION: Loading of an implant in a less stiff grafted sinus could lead to overloading of the native bone as well as the maturing grafted bone.

Photoelastic stress analysis of implant-tooth connected prostheses with segmented and nonsegmented abutments.

STATEMENT OF PROBLEM: There is some question about whether implant abutment selection affects the transfer of load between connected implants and natural teeth. PURPOSE: The purpose of this study was to compare stress transfer patterns with either 1 or 2 posterior implants connected to a single anteriorly located simulated natural tooth with either 1 or 2 segmented and nonsegmented implant abutments under relevant functional loads by use of the photoelastic stress analysis technique. MATERIAL AND METHODS: A model of a human left mandible, edentulous posterior to the first premolar, with two 3.75-mm x 13-mm screw-type implants embedded within the edentulous area, was fabricated from photoelastic materials. The implants were in the first and second molar positions. Two fixed partial denture prosthetic restorations were fabricated with either segmented conical abutments or nonsegmented UCLA abutments. Vertical occlusal loads were applied at fixed locations on the restorations. The photoelastic stress fringes that developed in the supporting mandible were monitored visually and recorded photographically. The stress intensity (number of fringes), stress concentrations (closeness of fringes), and their locations were subjectively compared. RESULTS: Loading on the restoration over the simulated tooth generated apical stresses of similar intensity (fringe order) at the tooth and the first molar implant for both abutment types. Low-level stress was transferred to the second molar implant. Loading directed on the implant-supported region of the restoration demonstrated low transfer of stress to the simulated tooth. Nonvertical stress transfer with slightly higher intensity was observed for the nonsegmented abutment. CONCLUSION: Within the limitations of this simulation study, stress distribution and intensity for the 2 implant conditions was similar for segmented and nonsegmented abutment designs. Magnitude of stresses observed for both abutment designs was similar for the single implant condition. Vertical loading produced more nonaxial stresses away from the force applied for the 1 implant condition with the nonsegmented abutment. Direct loading results were similar for both abutment designs. Specific recommendations for selection of implant abutment and application should be based on clinical criteria.

Long-term functional loading of dental implants in rhBMP-2 induced bone. A histologic study in the canine ridge augmentation model.

Osseointegration [direct bone-implant contact (BIC)] is a primary goal following installation of endosseous dental implants. Such bone contact provides stability for the dental implant over time. The objective of this study was to evaluate bone formation and BIC at long-term, functionally loaded, endosseous dental implants placed into bone induced by recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier. Mandibular, saddle-type, alveolar ridge defects (approximately 15 x 10 x 10 mm), two per jaw quadrant, were surgically induced in each of six young adult American fox hounds. The defects were immediately implanted with rhBMP-2/ACS. Two defects per animal additionally received a nonresorbable expanded polytetrafluoroethylene (ePTFE) membrane or a bioresorbable polyglycolide fiber membrane. Healing was allowed to progress for 3 months, when the ePTFE membrane was removed, and machined, threaded, titanium dental implants were installed into the rhBMP-2/ACS induced bone and into the adjacent resident bone. At 4 months of osseointegration, the implants were exposed to receive abutments and prosthetic treatment (two- or three-unit bridges). Some implants were removed for histologic analysis. The remainder of implants were exposed to functional loading for 12 months at which time the animals were killed for histometric analysis. One animal died prematurely due to kidney failure unrelated to the experimental protocol and was not included in the analysis. The 12-month block sections from a second animal were lost in the histological processing. Four sites receiving rhBMP-2/ACS and ePTFE or resorbable membranes experienced wound failure and membrane exposure, and subsequently exhibited limited bone formation. Defects without wound failure filled to contour with the adjacent alveolar bone. The newly formed bone exhibited features of the resident bone with a re-established cortex; however, it commonly included radiolucent areas that resolved over time. Dental implants block biopsied at 4 months exhibited limited, if any, crestal resorption, whereas those exposed to functional loading for 12 months exhibited some crestal resorption. Implants biopsied at 4 months exhibited a mean (+/- SD) BIC of 40.6 +/- 8.2% in rhBMP-2/ACS induced bone vs. 52.7 +/- 11.4% in resident bone. Dental implants exposed to 12 months of functional loading exhibited a mean BIC of 51.7 +/- 7.1% in rhBMP-2/ACS induced bone vs. 74.7 +/- 7.0% in resident bone. There were no significant differences between dental implants placed into rhBMP-2/ACS induced bone and resident bone for any parameter at any observation interval. In conclusion, rhBMP-2/ACS-induced bone allows installation, osseointegration, and long-term functional loading of machined, threaded, titanium dental implants in dogs.