Development of an injectable composite as a carrier for growth factor-enhanced periodontal regeneration

AIM

Biomaterials are often applied in periodontal therapy; however, not always well adapted for tissue regeneration. The objective of this study was to evaluate the physico-chemical properties and biocompatibility of an injectable, in situ setting composite for growth factor-enhanced periodontal regeneration.

MATERIAL AND METHODS

The composite constitutes bioresorbable poly(lactic-co-glycolic acid) (PLGA) and additives forming in situ a matrix designed as a carrier for recombinant human growth/differentiation factor-5 (rhGDF-5). In vitro characterization included the porosity, biointeraction, biodegradation, injectability, and biological activity of released rhGDF-5. Biocompatibility was compared with granular beta-tricalcium phosphate and an absorbable collagen sponge using a canine periodontal defect model.

RESULTS

The PLGA composite showed a highly porous (500-1000 mum) space-providing structure. It effectively induced coagulation exhibiting an intimate interaction with the fibrin clot. The biphasic biodegradation was complete within 4 weeks. The composite was conveniently injectable (90.4+/-3.6 N) for ease of use. It exhibited a sustained rhGDF-5 release over 4 weeks (40.8%) after initial burst (3.4%) detected by ALP activity. Sites receiving the composite showed limited, if any, residuals and had no appreciable negative effect on periodontal wound healing. There were no noteworthy inflammatory lesions in sites receiving the PLGA composite.

CONCLUSION

Characteristics of the PLGA composite makes it an attractive matrix to support native wound healing and rhGDF-5-enhanced periodontal regeneration.

The interdental gingiva, a visible guide for placement of mini-implants

OBJECTIVES

To determine whether the tip of the interdental gingiva can serve as a visible guide for placement of mini-implants.

SETTING AND SAMPLE POPULATION

Computer tomography (CT) images from 15 males and 15 females (mean age 27 years, range: 23-35 years) were used to evaluate the distance from the tip of the interdental gingiva to the alveolar crest from the central incisor to the 1st molar. The distance from a reference point to the tip of interdental gingiva was recorded from study models using a caliper. The distance between the reference point and the alveolar crest was recorded using CT and added to the model recordings thus providing the distance from the tip of interdental gingiva to the alveolar crest for the various interdental sites. Two-way anova and Student-Newman-Keuls test for multiple comparisons were used for the statistical analysis.

RESULTS

There was no significant difference in the distance from the tip of interdental gingiva to the alveolar crest between maxilla and mandible. The distance between the tip of interdental gingiva and the alveolar crest at the central/lateral incisors was the shortest compared with that of other sites. There was also a statistically significant difference between the male and female groups except for the maxillary 2nd premolar/1st molar interradicular site.

CONCLUSION

The tip of interdental gingiva appears a reasonable visual guide for the placement of mini-implants for orthodontic anchorage.

Bone healing dynamics at buccal peri-implant sites

BACKGROUND

It is common belief that immediate implant placement into extraction sites may act to preserve the alveolar process. The objective of this study was to evaluate healing dynamics at buccal peri-implant sites in relation to the dimensions of the alveolar ridge.

METHODS

Bilateral, critical-size, supraalveolar, peri-implant defects were created in 12 male Hound Labrador mongrel dogs following surgical horizontal cut-down of the alveolar ridge. Each jaw quadrant received three 10-mm titanium implants placed 5 mm into extraction sites of the third and fourth premolar teeth leaving 5 mm in a supraalveolar position. The mucoperiosteal flaps were advanced, adapted, and sutured for primary intention healing. Bone fluorescent markers were administered at weeks 3 and 4 postsurgery, and pre-euthanasia. Incandescent, polarized, and fluorescent light microscopies were used to assess the width of the buccal wall of the alveolar ridge and local bone remodeling over the 8-week healing interval.

RESULTS

There was a significant association between the width of the buccal alveolar ridge and extent of bone resorption evaluated by incandescent and fluorescent light microscopy. A non-linear association was observed between the buccal ridge width and resorption of the alveolar ridge. A 2-mm threshold was established to account for this non-linearity. The strength of this association was two times greater in specimens with a buccal ridge width <2 mm compared with a wider ridge (beta=1.62 vs. 0.80) observed by fluorescent light microscopy. Accordingly, mean buccal resorption was significantly greater when the ridge width was <2 mm. Fluorescent light microscopy consistently showed greater buccal resorption compared with incandescent light microscopy (P<0.05). Agreement between the examination techniques was low (concordance correlation coefficient=0.49), especially for higher values of buccal resorption.

CONCLUSION

When implants are placed into extraction sites, proximity to the buccal alveolar crest appears a major consideration. The observations herein suggest that the width of the buccal alveolar ridge should be at least 2 mm to maintain the alveolar bone level. These observations likely have general implications for implant placement using most surgical protocols.

Bone formation at rhBMP-2-coated titanium implants in the rat ectopic model

BACKGROUND

The objective of this study was to evaluate local bone formation at titanium porous oxide (TPO) implant surfaces adsorbed with recombinant human bone morphogenetic protein-2 (rhBMP-2).

METHODS

In vitro studies were used to estimate the kinetics of I125-labeled rhBMP-2 released from TPO surfaces with narrow (N) or open (O) pores. Machined/turned titanium (MT) surfaces served as control. The rat ectopic model was used to assess local bone formation. Briefly, TPO-N, TPO-O, and MT disc implants adsorbed with 5, 10, or 20 microg rhBMP-2, respectively, were implanted subcutaneously into the ventral thoracic region in 5-week-old male Long Evans rats. The animals were euthanized at day 14 postsurgery when implants with surrounding tissues were removed, radiographed, and gross observations recorded. The specimens were processed for histologic evaluation using conventional cut-and-grind techniques. TPO implants without rhBMP-2 included in a preliminary evaluation revealed no evidence of bone formation, tissue encapsulation, or vascularity, thus such controls were not further used.

RESULTS

TPO and MT implant surfaces adsorbed with 5 microg rhBMP-2 retained 2.3-5.4% rhBMP-2 following immersion and rinse in buffer, and 1.1-2.2% rhBMP-2 following repeated immersions and rinses over 27 days. TPO implants retained the most rhBMP-2 and MT implants retained the least. Explants revealed increased hard tissue formation, tissue encapsulation, and vascularity at TPO compared with MT implants. Radiographic observations were consistent with the explant observations. The histologic analysis showed greater amounts of bone formation, osteoblastic cells, osteoid, marrow, tissue encapsulation, vascularity, and bone voids for implants adsorbed with 10 and 20 microg rhBMP-2, and for TPO implants at the 5-microg rhBMP-2 dose. The histometric analysis revealed significantly greater bone formation at TPO-O than at MT implants at the 5-microg rhBMP-2 dose. All surfaces showed significant bone formation at the 10- and 20-microg dose.

CONCLUSIONS

rhBMP-2 adsorbed onto TPO implant surfaces executes an osteoinductive effect including bone contacting the implant surface. This effect is surface- and dose-dependent; the TPO-O surface yielding the most bone at the low discriminating rhBMP-2 dose.

Surface-etching enhances titanium implant osseointegration in newly formed (rhBMP-2-induced) and native bone

PURPOSE

The influence of surface modifications on osseointegration in newly formed bone is not well established. The purpose of this study was to compare osseointegration at acid-etched versus turned implants in newly formed and native bone.

METHODS

Supra-alveolar peri-implant defects were created in 8 hound/Labrador mongrel dogs. Titanium implants 10 mm long (2 turned and 1 dual acid-etched) were placed 5 mm into the surgically reduced alveolar crest, creating 5-mm supra-alveolar peri-implant defects. Recombinant human bone morphogenetic protein-2 (rhBMP-2; 0.4 mg) in a collagen carrier was used to induce new bone formation. A macroporous, expanded polytetrafluoroethylene device was used to delineate new bone formation. The animals were euthanized at 8 weeks for histometric analysis of the experimental sites.

RESULTS

There were no significant differences in rhBMP-2-induced bone density (mean +/- SD) at acid-etched versus turned implants (20.6% +/- 5.3% vs 23.8% +/- 4.7%; P = .232). However, there was a significant difference in bone-implant contact in favor of the acid-etched implants (12.3% +/- 6.8% vs 7.9% +/- 3.1%; P = .05). Native bone density averaged 63.9% +/- 7.5% and 64.5% +/- 9.0% for acid-etched and turned implants, respectively (P = .641). Nevertheless, bone-implant contact was significantly enhanced at acid-etched versus turned implants (59.7% +/- 11.3% vs 40.7% +/-21.2%; P =.005).

CONCLUSIONS

Surface dual acid-etching of titanium implants has a positive effect on osseointegration in newly formed and native bone. Significant differences in bone density do not appear to influence this effect.

Transforming Growth Factor-β1Accelerates Resorption of a Calcium Carbonate Biomaterial in Periodontal Defects

BACKGROUND

In a previous study, recombinant human transforming growth factor-beta1 (rhTGF-beta(1)) in a calcium carbonate carrier was implanted into critical-size, supraalveolar periodontal defects under conditions for guided tissue regeneration (GTR) to study whether rhTGF-beta(1) would enhance or accelerate periodontal regeneration. The results showed minimal benefits of rhTGF-beta(1), and a clear account for this could not be offered. One potential cause may be that the rhTGF-beta(1) formulation was biologically inactive. Several growth or differentiation factors have been suggested to accelerate degradation of biomaterials used as carriers. The objective of this study was to evaluate possible activity of rhTGF-beta(1) on biodegradation of the calcium carbonate carrier.

METHODS

rhTGF-beta(1) in a putty-formulated particulate calcium carbonate carrier was implanted into critical-size, supraalveolar periodontal defects under conditions for GTR in five beagle dogs. Contralateral defects received the calcium carbonate carrier combined with GTR without rhTGF-beta(1) (control). The animals were euthanized at week 4 post-surgery and block biopsies of the defect sites were collected for histologic and histometric analysis. Radiographs were obtained at defect creation and weeks 2 and 4 after defect creation.

RESULTS

No statistically significant differences were observed in new bone formation (bone height and area) among the treatments. However, total residual carrier was significantly reduced in sites receiving rhTGF-beta(1) compared to control (P = 0.04). Similarly, carrier density was considerably reduced in sites receiving rhTGF-beta(1) compared to control; the difference was borderline statistically significant (P = 0.06).

CONCLUSION

Within the limitations of the study, it may be concluded that rhTGF-beta(1) accelerates biodegradation of a particulate calcium carbonate biomaterial, indicating a biologic activity of the rhTGF-beta(1) formulation apparently not encompassing enhanced or accelerated periodontal regeneration.

Bone reconstruction following implantation of rhBMP-2 and guided bone regeneration in canine alveolar ridge defects

BACKGROUND

Alveolar ridge aberrations commonly require bone augmentation procedures for optimal placement of endosseous dental implants. The objective of this study was to evaluate local bone formation following implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier with or without provisions for guided bone regeneration (GBR) as potential treatment modalities for alveolar augmentation.

METHODS

Surgically induced, large, mandibular alveolar ridge saddle-type defects (2 defects/jaw quadrant) in seven young adult Hound dogs were assigned to receive rhBMP-2/ACS, rhBMP-2/ACS combined with GBR (rhBMP-2/GBR), GBR, and surgery controls. The animals were euthanized at 12 weeks post-surgery when block sections of the defect sites were collected for histologic analysis.

RESULTS

Clinical complications included swelling for sites receiving rhBMP-2 and wound failure with exposure of the barrier device for sites receiving GBR (4/6) or rhBMP-2/GBR (3/7). The radiographic evaluation showed substantial bone fill for sites receiving rhBMP-2/ACS, rhBMP-2/GBR, and GBR. In particular, sites receiving rhBMP-2/GBR presented with seroma-like radiolucencies. The surgery control exhibited moderate bone fill. To evaluate the biologic potential of the specific protocols, sites exhibiting wound failure were excluded from the histometric analysis. Sites receiving rhBMP-2/ACS or rhBMP-2/GBR exhibited bone fill averaging 101%. Bone fill averaged 92% and 60%, respectively, for sites receiving GBR and surgery controls. Bone density ranged from 50% to 57% for sites receiving rhBMP-2/ACS, GBR, or surgery controls. Bone density for sites receiving rhBMP-2/GBR averaged 34% largely due to seroma formation encompassing 13% to 97% of the sites.

CONCLUSION

rhBMP-2/ACS appears to be an effective alternative to GBR in the reconstruction of advanced alveolar ridge defects. Combining rhBMP-2/ACS with GBR appears to be of limited value due to the potential for wound failure or persistent seromas.

The critical-size supraalveolar peri-implant defect model: characteristics and use

OBJECTIVE

Novel implant technologies and reconstructive therapies for alveolar augmentation require pre-clinical evaluation to estimate their biologic potential, efficacy, and safety before clinical application. The objective of this report is to present characteristics and use of the critical-size, supraalveolar, peri-implant defect model.

METHODS

Bilateral extraction of the mandibular premolars was performed in 12 Hound Labrador mongrel dogs following horizontal surgical cut-down of the alveolar ridge approximating 6 mm. Each jaw quadrant received three custom-produced TiUnite, phi 4.0 x 10 mm threaded implants placed into osteotomies prepared into the extraction sites of the third and fourth premolars. The implants exhibited a reference notch 5 mm from the implant platform to facilitate surgical placement leaving 5 mm of the implant in a supraalveolar position, and to serve as a reference point in the radiographic, histologic and histometric analysis. The implants were submerged under the mucoperiosteal flaps for primary intention healing. Fluorescent bone markers were administered at weeks 3 and 4 post-surgery, and pre-euthanasia. The animals were euthanized following an 8-week healing interval when block biopsies were collected for analysis.

RESULTS

Healing was generally uneventful. The radiographic and histometric evaluations demonstrate the limited osteogenic potential of this defect model. Whereas lingual peri-implant sites exhibited a mean (+/-SE) bone gain of 0.4+/-0.1 mm, resorption of the buccal crestal plate resulted in a mean bone loss of 0.4+/-0.2 mm for an overall osteogenic potential following sham-surgery averaging 0.0+/-0.1 mm. Overall bone density and bone-implant contact in the contiguous resident bone averaged 79.1+/-1.1% and 76.9+/-2.3%, respectively.

CONCLUSION

The results suggest that the critical-size, supraalveolar, peri-implant defect model appears a rigorous tool in the evaluation of candidate technologies for alveolar reconstruction and osseointegration of endosseous oral implants. Limited innate osteogenic potential allows critical evaluation of osteogenic, osteoconductive, or osteoinductive technologies in a challenging clinical setting.

Histologic Evaluation of Implants Following Flapless and Flapped Surgery: A Study in Canines

BACKGROUND

Flapless surgery requires penetration of the alveolar mucosa and bone without reflection of mucoperiosteal flaps. Do these techniques force gingival tissue or foreign materials into osteotomies? If so, do such tissues or materials interfere with osseointegration? A proof-of-principle study using a canine model attempted to answer these questions.

METHODS

Five young adult Hound Labrador mongrel dogs received implants with a moderately roughened surface by anodic oxidation using flapless or conventional one-stage (control) surgery in contralateral jaw quadrants. The implants were placed into the osteotomies, and the international stability quotient (ISQ) was recorded using resonance frequency analysis. These measurements were repeated following a 3-month healing interval when the animals were euthanized, and implants and surrounding tissues were retrieved and processed for histologic analysis.

RESULTS

The implants were stable upon insertion and demonstrated increased stability at 3 months without significant differences between surgical protocols. The histologic evaluation showed high bone-implant contact (flapless surgery: 54.7% +/- 8.4%; control: 52.2% +/- 13.0%; P >0.05) without evidence of gingival tissue or foreign body inclusions. There were no significant differences in marginal bone levels between the surgical protocols. Post-insertion and at 3 months, ISQ values depended on the amount of torque delivered. Immediately post-insertion, for every 1-unit increase in torque value, the ISQ increased by 0.3 (95% confidence interval: 0.1 to 0.4; P = 0.0043). Three months postoperatively, for every one-unit increase in torque the ISQ value decreased 0.2 (95% confidence interval: -0.4 to -0.1; P = 0.0012). The effect of torque on ISQ values was independent of treatment effects and remained significant after adjustment for treatment.

CONCLUSIONS

The results suggest that implants placed without flap reflection remain stable and exhibit clinically relevant osseointegration similar to when implants are placed with flapped procedures. Greater torque at implant placement resulted in less implant stability at 3 months.

Validity of radiographic evaluations of bone formation in a rat calvaria osteotomy defect model

OBJECTIVE

The objective of this study was to evaluate the validity of radiographic evaluations of bone formation in a critical-size rat calvaria osteotomy defect model.

METHODS

Bilateral, critical-size ( [symbol in text] 6 mm) calvaria osteotomy defects in 30 adult Sprague-Dawley rats treated with a rat platelet-rich plasma preparation or control treatments were evaluated by radiographic and histometric measures following a 4- or 8-week healing interval. Standardized radiographic images of the rat calvaria gross specimens were used to assess bone formation within the defect sites by visual evaluation of the grey scale by three masked examiners. The most central portion of each defect site was subject to histometric analysis using a PC-based image analysis system. Kappa statistics and percentage agreement between the radiographic and histometric analysis were estimated.

RESULTS

Radiographic evaluations of bone formation are associated with significant weaknesses poorly representing actual healing events; kappa statistics (0.17) denoting slight agreement beyond chance. Perfect agreement between the histologic and radiographic analysis for defect sites showing complete and partial histologic bone fill was achieved 63% and 50% of the time, respectively. Agreement reached only 20% for sites with no/limited bone fill. When no/limited and partial bone fill occurred, the radiographic analysis tended to overestimate bone fill and underestimate bone fill when complete closure of the defect sites was observed in the histologic analysis.

CONCLUSION

Low accuracy was observed when radiographic evaluations were employed in identifying and characterizing bone fill in the rat calvaria osteotomy defects. Assessment of bone healing in animal models aiming at treatment recommendations for clinical application must not solely be based on radiographic analysis, but should be confirmed using histologic observations.

Observations on healing following endodontic surgery in nonhuman primates (Macaca fascicularis): Effects of rhBMP-2

OBJECTIVES

The potential of recombinant human bone morphogenetic protein-2 (rhBMP-2) to enhance bone healing following endodontic surgery was tested. The pattern and timing of de novo bone formation and cementum regeneration, and the potential for root resorption and ankylosis to accompany bone formation were evaluated.

STUDY DESIGN

Pulpal infections were induced in maxillary and mandibular incisor teeth in young adult Cynomolgus monkeys. The teeth received conventional endodontic treatment immediately followed by surgical root resection. In a randomized split-mouth design, contralateral apical bone defects received rhBMP-2 in absorbable collagen sponge (ACS) carrier or served as sham-surgery controls to provide histological and radiographic evaluations following 1 (mandibular incisors) and 4.5 (maxillary incisors) month(s) postsurgery.

RESULTS

At 1 month postsurgery trabecular bone filled the apical bone defects. The newly formed bone appeared considerably more mature and had assumed characteristics of the contiguous resident bone at 4.5 months postsurgery. The resected root tips were almost completely covered by new cementum with a maturing functionally oriented periodontal ligament. Localized inflammatory infiltrates were associated with the filled root canals and extruded root-filling material. Root resorption and ankylosis were not observed. There were no apparent differences in healing patterns between sites implanted with rhBMP-2/ACS and those serving as sham-surgery controls.

CONCLUSIONS

Under conditions where the influence of infectious elements and irritation caused by root filling material are minimized, bone formation and cementum regeneration appears rapid following endodontic surgery. rhBMP-2/ACS did not offer an obvious benefit above and beyond that of the native osteogenic potential in this animal model.

Bone-implant contact at calcium phosphate-coated and porous titanium oxide (TiUnite)-modified oral implants

BACKGROUND

Calcium phosphate (CP)-coated implants are usually referred to as having osteoconductive properties, whereas titanium implants with a native oxide layer are considered less osteoconductive. Often smooth titanium oxides (TOs) are compared to relatively rough CP structures. The objective of this study was to evaluate osteoconduction by comparing bone-implant contact at a relatively smooth, highly crystalline CP coating with a structured, porous TO (TiUnite)-modified surface.

MATERIAL AND METHODS

Ten adult Hound Labrador mongrel dogs were used. Four titanium implants (Nobel Biocare) with CP-coated (2) or TO-modified (2) surfaces were installed 12 weeks following mandibular premolar and molar teeth extraction. The implants were alternated within and between jaw quadrants in consecutive animals. Mucosal flaps were advanced and sutured leaving the implants in a submerged position. The animals were injected with fluorescent bone labels at 3 and 4 weeks postsurgery, and pre-euthanasia to monitor progress of bone formation. The animals were euthanized at 8 weeks postsurgery and block biopsies were prepared for histologic and histometric analysis.

RESULTS

There were no remarkable differences in bone formation and apparent bone-implant contact comparing the TO-modified and CP-coated surfaces. However, the measured average bone-implant contact was 71% and 57% (P=0.027) for TO-modified and CP-coated implants, respectively.

CONCLUSIONS

We conclude that the TO surface exhibits osteoconductive properties exceeding that of the CP surface. One or several of the chemical and physical properties of the TO surface may result in the remarkable bone formation along its surface. This study indicated that crystallinity and/or chemistry may be important.

Analysis of rat calvaria defects implanted with a platelet-rich plasma preparation: histologic and histometric observations

OBJECTIVES

It has been suggested that degranulating platelet alpha-granules release growth factors having a potential to modulate bone formation. The objective of this study was to evaluate the osteoconductive potential of a platelet-rich plasma (PRP) preparation.

METHODS

Thirty adult male Sprague-Dawley rats were used. The PRP preparation was obtained from 10 ml of whole blood drawn from one age-matched donor rat. The preparation was processed by gradient density centrifugation and stored at -80 degrees C until use. Using aseptic techniques, the PRP preparation soak loaded onto an absorbable collagen sponge (ACS) or ACS alone was surgically implanted into contralateral critical size 6-mm calvaria osteotomies in 18 animals. Twelve animals received ACS versus sham surgery in contralateral defects. Animals were sacrificed at 4 and 8 weeks when biopsies were collected for histologic and histometric analysis.

RESULTS

The animals were maintained without adverse events. Bone formation was highly variable in sites receiving PRP and control treatments. Defect bone fill at 4 weeks averaged (+/-SD) 28.8+/-27.4% (PRP/ACS) versus 39.1+/-24.4% (ACS; p=0.2626) and 62.0+/-20.0% (ACS) versus 71.6+/-32.2% (sham surgery; p=0.1088), and at 8 weeks 81.0+/-12.9% (PRP/ACS) versus 64.5+/-28.1% (ACS; p=0.2626) and 75.6+/-34.1% (ACS) versus 74.1+/-24.2% (sham surgery; p=0.7353). Remnants of the ACS biomaterial were observed at both 4 and 8 weeks in sites implanted with PRP/ACS or ACS.

CONCLUSIONS

The results suggest that the PRP preparation has a limited potential to promote local bone formation.

Prognostic factors for alveolar regeneration: effect of space provision

OBJECTIVES

The role of space provision as an independent prognostic factor for periodontal regeneration remains to be established. The objective of this study was to evaluate the role of space provision on alveolar bone regeneration in periodontal sites.

METHODS

Critical size, supra-alveolar, periodontal defects were created in 11 young adult Beagle dogs. Six animals received a porous ePTFE device to provide for space provision. Five animals received sham surgery. The animals were euthanized at 8 weeks post-surgery. A histometric analysis assessed vertical regeneration of alveolar bone and the width of the alveolar crest at the base of the defect. Because of the correlation of within-dog measurements, a mixed model anova/ancova was used to analyse the data.

RESULTS

A significant relationship between the width of the alveolar crest at the base of the defect and bone regeneration was observed with no significant difference between sites receiving the different treatments (p=0.84). Bone regeneration at sites treated with the space-providing device was significantly greater compared with that at sites treated with sham surgery (p=0.0003), and the difference remained significant after adjusting for bone width (p=0.0001).

CONCLUSIONS

Space provision has a significant effect on alveolar bone regeneration in periodontal sites. The width of the alveolar bone appears to influence space provision effectively supporting bone regeneration.

Analysis of Rat Calvaria Defects Implanted With a Platelet-Rich Plasma Preparation: Radiographic Observations

BACKGROUND

Platelet-rich plasma (PRP) harbors growth factors identified in bone. It has been suggested that these factors enhance osteogenesis. The objective of this study was to conduct a radiographic evaluation on local bone formation following surgical implantation of a PRP preparation using a critical-size rat calvaria defect model.

METHODS

Thirty 22-week-old male Sprague-Dawley rats were used. The PRP preparation was obtained from 10 ml of whole blood drawn from one age-matched donor rat. The preparation was processed by gradient density centrifugation and stored at -80 degrees C until use. Using aseptic techniques, the PRP preparation soak-loaded onto an absorbable collagen sponge (ACS) carrier or ACS alone was surgically implanted into contralateral critical-size 6 mm rat calvaria osteotomies in 18 animals. Twelve animals received ACS alone versus sham surgery in contralateral defects. Animals were sacrificed at 4 and 8 weeks when biopsies were collected and radiographs were obtained using a standardized protocol. Three masked examiners independently evaluated the radiographic images of the defect sites. Examiner reproducibility was examined by repeat evaluation of all defect sites (r=0.6; P <0.0001).

RESULTS

The animals were maintained without adverse events. Defect sites in two animals receiving ACS versus sham surgery (4-week healing interval) were not evaluated due to specimen damage. Seventy-five percent of the sites (PRP/ACS or ACS) exhibited partial closure at 4 weeks; one site (ACS) exhibited full closure without significant differences between protocols (P=0.1797). Fifty percent of the sites receiving PRP/ACS exhibited full closure and 20% partial closure at 8 weeks versus 20% and 80%, respectively, for the ACS control (P=0.7532). There were no noteworthy differences between sites receiving ACS versus sham surgery at 4 or 8 weeks.

CONCLUSION

The results suggest that the PRP preparation does not have a significant effect on osteogenesis.