Vladimir Golubovic

Biodegradation of different synthetic hydrogels made of polyethylene glycol hydrogel/RGD-peptide modifications: an immunohistochemical study in rats

AIM The aim of the present study was to investigate the pattern of biodegradation of different polyethylene glycol (PEG) hydrogel/RGD-peptide modifications in rats. MATERIAL AND METHODS Two different hydrogels were employed: (i) a combination of four-arm PEG-thiol, M(n)=2.3 kDa, and eight-arm PEG-acrylate, M(n)=2.3 kDa (PEG1); and (ii) a combination of four-arm PEG-thiol, M(n)=2.3 kDa, and four-arm PEG-acrylate, M(n)=15 kDa (PEG2). Both PEG1 and PEG2 were either used alone or combined with a nine amino acid cys-RGD peptide (RGD). A non-cross-linked porcine type I and III collagen membrane [BioGide (BG)] served as control. Specimens were randomly allocated in unconnected subcutaneous pouches separated surgically on the back of 60 wistar rats, which were divided into six groups (1, 2, 4, 8, 16, and 24 weeks). Specimens were prepared for histological (tissue integration, foreign body reactions, biodegradation) and immunohistochemical (angiogenesis) analysis. RESULTS All materials investigated revealed unimpeded and comparable tissue integration without any signs of foreign body reactions. While BG exhibited transmembraneous blood vessel formation at 1 week, all PEG specimens were just surrounded by a well-vascularized connective tissue. The hydrolytic disruption of PEG1 and PEG1/RGD specimens was associated with an ingrowth of blood vessels at 4 weeks. Biodegradation times were highest for PEG1 (24 weeks)>PEG1/RGD (16 weeks)>BG (4 weeks)>PEG2=PEG2/RGD (2 weeks). CONCLUSION Within the limits of the present study, it was concluded that (i) all materials investigated revealed a high biocompatibility and tissue integration, and (ii) hydrogel biodegradation was dependent on PEG composition.

Surgical therapy of advanced ligature‐induced peri‐implantitis defects: cone‐beam computed tomographic and histological analysis

OBJECTIVES To evaluate radiological bone level (RBL) (i.e. cone-beam computed tomography) and histological bone levels (HBL) as well as re-osseointegration [bone-to-implant contact (BIC)] after surgical resective (i.e. implantoplasty) and/or regenerative therapy of advanced ligature-induced peri-implantitis in dogs. MATERIAL AND METHODS At all defect sites (n=6 dogs, n=48 implants), the intrabony component was filled with a particulate bovine-derived natural bone mineral (NBM). The supracrestal component was treated by either the application of an equine bone block (EB) or implantoplasty. In a split-mouth design, NBM and EB were soak-loaded with recombinant human bone morphogenetic protein (rhBMP)-2 or sterile saline. All sites were covered by a native collagen membrane and left to heal in a submerged position for 12 weeks. RESULTS A premature wound exposure was observed at nine defect sites. Mean RBL and HBL values were lowest in the P+rhBMP-2 group, reaching statistical significance when compared with the EB group. Mean BIC values were comparable in all groups. Within-group comparisons commonly revealed a close correlation between RBL and HBL values. CONCLUSIONS It was concluded that (i) in all groups the investigations failed to predictably obtain complete defect resolution, (ii) the surgical procedure was associated with high exposure rates, and (iii) RBL was closely correlated with HBL.

Impact of abutment material and dis‐/re‐connection on soft and hard tissue changes at implants with platform‐switching

OBJECTIVES To assess the impact of abutment material and dis-/re-connection on soft and hard tissue changes at implants with platform-switching. MATERIAL & METHODS Titanium implants (n = 12), placed epicrestally in the upper jaws of three dogs, were connected with titanium (Ti) and zirconium dioxide (ZrO(2) ) abutments (horizontal mismatch of 0.4 mm) and randomly allocated in a split-mouth design either to repeated (2x) dis-/re-connection at 4 and 6 weeks (test), respectively, or left undisturbed (control). At 8 weeks, histomorphometrical measurements were made between the mucosal margin (PM), implant shoulder (IS) and the apical extension of the long junctional epithelium (aJE),-the most coronal level of bone in contact with the implant (CBI). RESULTS Repeated abutment manipulation was associated with increased mean PM-aJE and IS-CBI values at both Ti (1.82 ± 0.37-1.99 ± 0.40 mm and 0.72 ± 0.18-1.12 ± 0.60 mm) and ZrO(2) (1.90 ± 0.28-2.67 ± 0.67 mm and 0.22 ± 0.10-2.15 ± 0.77 mm) abutments at 8 weeks. These vertical dimensions were comparable at both vestibular and oral aspects. Between group comparisons, however, failed to reveal a significant difference between test and control sites. CONCLUSIONS Repeated manipulation may be associated with dimensional changes of peri-implant soft and hard tissues formed at both non-matching Ti and ZrO(2) abutments.

Influence of two barrier membranes on staged guided bone regeneration and osseointegration of titanium implants in dogs: part 1. Augmentation using bone graft substitutes and autogenous bone

OBJECTIVES To assess the influence of two barrier membranes and two bone graft substitutes mixed with autogenous bone (AB) on staged guided bone regeneration and osseointegration of titanium implants in dogs. MATERIALS AND METHODS Four saddle-type defects each were prepared in the upper jaw of six fox hounds and randomly filled with a natural bone mineral (NBM)+AB and a biphasic calcium phosphate (SBC)+AB and allocated to either an in situ gelling polyethylene glycol (PEG) or a collagen membrane (CM). At 8 weeks, modSLA titanium implants were inserted and left to heal in a submerged position. At 8+2 weeks, dissected blocks were processed for histomorphometrical analysis (e.g., treated area [TA], bone-to-implant contact [BIC]). RESULTS The mean TA values (mm(2) ) and BIC values (%) tended to be higher in the PEG groups(TA: NBM+AB [10.4 ± 2.5]; SBC+AB [10.4 ± 5.8]/BIC: NBM+AB [86.4 ± 20.1]; SBC+AB [80.1 ± 21.5]) when compared with the corresponding CM groups (TA: NBM+AB [9.7 ± 4.8]; SBC+AB [7.8 ± 4.3]/BIC: NBM+AB [71.3 ± 20.8]; SBC+AB [72.4 ± 20.3]). A significant difference was observed for the mean TA values in the SBC+AB groups. CONCLUSION It was concluded that all augmentation procedures investigated supported bone regeneration and staged osseointegration of modSLA titanium implants. However, the application of PEG may be associated with increased TA values.

Measurement of mini-implant stability using resonance frequency analysis.

OBJECTIVE To investigate whether resonance frequency analysis (RFA) is suitable to measure orthodontic mini-implant stability. Implant size significantly affects the level of resonance frequency. Regarding the operating mode of RFA, it has to be proven whether the resonance frequency of mini-implants in bone fits the range of frequency emitted by the Osstell ISQ device. MATERIAL AND METHODS For this purpose the SmartPegs in the Osstell ISQ device were modified to fit with the inner screw thread of orthodontic mini-implants, and 110 mini-implants were inserted into porcine pelvic bone. RFA was performed parallel and perpendicular to the run of superficial bone fibers. A suitability test, Periotest, was also performed in the same directions. Compacta thickness was measured using cone-beam computed tomography. Correlation tests and linear regression analysis were carried out between the three methods. RESULTS The RFA showed a mean Implant Stability Quotient value of 36.36 ± 2.67, and the Periotest mean value was -2.10 ± 1.17. The differences between the two directions of measurement were statistically significant (P > .001) for RFA and the Periotest. There was a high correlation between RFA and the Periotest (r  =  -0.90) and between RFA and compacta thickness (r  =  0.71). The comparison between the Periotest and compacta thickness showed a correlation coefficient of r  =  -0.64. CONCLUSION The present results suggest that RFA is feasible as a measurement method for orthodontic mini-implant stability. As a consequence, it could be used for clinical evaluation of current stability and allow stability-related loading of mini-implants to reduce the failure rate.

Influence of two barrier membranes on staged guided bone regeneration and osseointegration of titanium implants in dogs. Part 2: augmentation using bone graft substitutes

OBJECTIVES To assess the influence of two barrier membranes and two bone graft substitutes on staged guided bone regeneration and osseointegration of titanium implants in dogs. MATERIALS AND METHODS Saddle-type defects were prepared in the lower jaws of 6 fox hounds and randomly filled with a natural bone mineral (NBM) and a biphasic calcium phosphate (SBC) and allocated to either an in situ gelling polyethylene glycol (PEG) or a collagen membrane (CM). At 8 weeks, modSLA titanium implants were inserted and left to heal in a submerged position. At 8+2 weeks, respectively, dissected blocks were processed for histomorphometrical analysis (e.g., mineralized tissue [MT], bone-to-implant contact [BIC]). RESULTS The mean MT values (mm2) and BIC values (%) tended to be higher in the PEG groups (MT: NBM [3.4±1.7]; SBC [4.2±2]/BIC: NBM [67.7±16.9]; SBC [66.9±17.8]) when compared with the corresponding CM groups (MT: NBM [2.5±0.8]; SBC [2.3±1.6]/BIC: NBM [54.1±22.6]; SBC [61±8.7]). These differences, however, did not reach statistical significance. CONCLUSION It was concluded that all augmentation procedures investigated supported bone regeneration and staged osseointegration of modSLA titanium implants.

Impact of plaque accumulation on the osseointegration of titanium–zirconium alloy and titanium implants. A histological and immunohistochemical analysis

OBJECTIVES To evaluate the impact of plaque accumulation on osseointegration at surface enhanced modified hydrophilic titanium-zirconium (TiZr) alloy and titanium (Ti) implants. MATERIALS AND METHODS TiZr and Ti implants with a sand-blasted, acid etched, and chemically modified endosseous and a machined (M) transmucosal portion were bilaterally (i.e., one implant type on each side) inserted in the maxilla of six foxhounds. In a split-mouth design, experimental mucositis was induced at one randomly assigned side (NPC), while the contralateral side received mechanical plaque removal three times per week (PC). After 16 weeks, tissue biopsies were processed for histological (primary outcome: bone-to-implant contact [BIC]) and immunohistochemical (CD68) analysis. RESULTS Mean BIC values varied between 81.96% (TiZrM) and 88.72% (TiM) in the NPC group, and between 87.88% (TiM) and 92.69% (TiZrM) in the PC group. Even though BIC values tended to be lower within the endosseous coronal compartment at NPC sites, within group (NPC vs. PC) comparisons failed to reach statistical significance at both types of implants. These non-BIC areas were not associated with any CD68 positive cells. CONCLUSIONS Osseointegration of both TiZrM and TiM implants was not influenced by plaque accumulation in this experimental model.