Associations of Resonance Frequency Analysis with Dynamic Mechanical Analysis of Dental Implant Systems.

BACKGROUND: Resonance frequency analysis (RFA) has been introduced as a noninvasive method to clinically estimate the stability of dental implant systems. PURPOSE: The objective of this study was to examine whether implant stability quotient (ISQ) values of RFA can account for mechanical stability of the dental implant system, which is assessed using dynamic mechanical analysis (DMA). MATERIALS AND METHODS: Fifty-seven screw-type titanium dental implants were placed in artificial polyurethane foams with seven different thicknesses (3.5 to 12 mm) and eight edentulous mandibles of human cadavers (four men and four women, 79.11 ± 13.48 years). After the ISQ values, insertion torque, and static stiffness of each implant system were measured, the DMA was performed to assess dynamic stiffness and viscoelastic tan δ. RESULTS: The ISQ value had strong positive correlations with thickness, insertion torque, static and dynamic stiffness, and a negative correlation with tan δ of implant systems in artificial bone blocks (r = 0.769 to 0.992, p < .043). However, the ISQ value was correlated with only the insertion torque of implant systems in human mandibles (p < .049). CONCLUSION: The ISQ values could reflect mechanical stability of the dental implant system under the controlled condition of homogeneous density in simple dimensions.

Evaluation of Different Implant Designs in a Ligature-Induced Peri-implantitis Model: A Canine Study.

PURPOSE: Peri-implantitis is a challenging situation that leads to tissue destruction and eventual implant failure. The purpose of this study was to evaluate and compare, clinically and histologically, the influence of ligature-induced peri-implantitis on two implant designs in a canine extraction socket model. MATERIALS AND METHODS: Sixty-four implants (4.1 × 13 mm) were placed bilaterally in eight dogs immediately after extraction of the mandibular premolars (P3, P4) and molars (M1, M2). Thirty-two conventional threaded implants (group A) and 32 tantalum-based porous implants (group B) were placed. After 12 weeks of normal healing, experimental peri-implantitis was induced in four dogs via the placement of ligatures subgingivally around the implant necks in the treatment group; the control group remained ligature-free. Two dogs in each group were euthanized after 12 or 26 weeks of plaque accumulation (control group dogs received regular cleanings). Clinical evaluations were conducted during the observation period and histologic sections were obtained for histologic and histomorphometric assessments. RESULTS: All the implants exhibited clinical and histologic osseointegration. The treatment group showed significant loss of peri-implant tissue from the induced peri-implantitis. Pocket probing depths for the treatment groups were significantly greater than those of the control groups. Mean bone-to-implant-contact values were not statistically different for control vs treatment groups or for group A vs group B. In the treatment group, group B implants exhibited mean bone ingrowth of 28.4% to 36.3% and achieved more bone formation along the length of the implant than group A implants in the treatment group. CONCLUSION: Implant design did not influence the tissue response or histomorphometric findings under induced peri-implantitis in the canine extraction socket.

Outcome after placement of tantalum porous engineered dental implants in fresh extraction sockets: a canine study.

PURPOSE: This study evaluated the stability and histologic proof of osseoincorporation of Trabecular Metal (TM) dental implants, which feature a tantalum-based porous midsection. MATERIALS AND METHODS: A total of 48 TM implants (test group) and Tapered Screw-Vent implants (control group) were immediately placed bilaterally into mandibular extraction sockets in dogs. Resonance frequency analysis was performed at weeks 0, 2, 4, and 12 after implant placement. Histologic and histomorphometric evaluations of the implant interface were performed. RESULTS: Changes in mean implant stability quotients (ISQ) revealed no statistical differences between the test and control groups. Histologic analysis showed bone ingrowth into the porous tantalum structure of all test group implants. Histomorphometric analysis revealed an increased percentage of bone-to-implant contact between 4 and 8 weeks in both test and control groups. The porous sections of the test group exhibited significantly more new bone inside the pores at week 12 in comparison to weeks 2 and 4. No correlation was observed between ISQ and histomorphometric parameters. CONCLUSION: In a canine immediate extraction socket model, both test and control implants demonstrated comparable implant stability and bone-to-implant contact. Bone ingrowth was evident within the tantalum porous section of the test implants during the early healing.

Recovery and purification of rapamycin from the culture broth of Mtcc 5681.

In this study of the recovery and purification of rapamycin from the culture broth of an actinomycetes strain MTCC 5681, we investigated various factors such as biomass separation, suitable solvents for extraction, normal phase and flash chromatographic conditions and selective precipitation to obtain rapamycin in substantially pure form of the product. Adsorption chromatography particularly with normal phase and flash chromatography, in combination with centrifugal decantation is found to be the most suitable for separation as well as purification of rapamycin. Centrifugal decantation technique is likely to emerge as an efficient, industrially scalable, high yielding and economical process for biomass separation. The purity of rapamycin obtained through the method described was 99.4% which has not been reported so far.

Improvement of microbial strain and fermentation process of rapamycin biosynthesis.

The purpose of this investigation is to enhance the production of the immunosuppressant drug rapamycin by subjecting the strain CBS 773.23 to ultraviolet (UV) and N-methyl-N'-nitro-N-nitroso guanidine (NTG) mutations. Among all the mutants tested, MTCC 5681 (NRC-CM03/SH) obtained by NTG mutagenesis of strain CBS 773.72 showed the highest activity, 210 mg/L. The effect of different factors including medium composition, pH, temperature, and intensity of mixing on rapamycin production was studied. Based on the study, the optimal concentrations of soluble starch and dry yeast granules were found to be 50 g/L and 1.5 g/L, respectively. Furthermore, optimal values for pH, temperature, and shaking speed were found to be 6.0, 28°C, and 220 rpm, respectively. The production of rapamycin increased 1.6-fold, to 360 mg/L, in shake-flask culture using the optimal combination of factors observed compared with basal cultivation medium using MTCC 5681 mutant strain.

Distal femoral fixation: a biomechanical comparison of retrograde nail, retrograde intramedullary nail, and prototype locking retrograde nail.

BACKGROUND: Distal femur fractures continue to be a complex surgical problem for which the incidence is increasing. Presently, there is a need for different constructs to address these complex fractures. This study attempts to define the biomechanical properties of several implants. METHODS: A novel, prototype locking retrograde intramedullary nail and the Russell-Taylor femoral retrograde nail were tested at non-destructive, physiological, axial mode load strength using a young, synthetic bone model for a medial segmental shaft defect in the supracondylar region of the distal femur (medial gap of 10mm, 65mm proximal to the distal joint and parallel to the knee axis). Each specimen was compressively loaded and unloaded to the peak load for 80,000cycles at a 0.5Hz frequency. These were compared to the results from the same lab of the retrograde Trigen intramedullary nail. Motion and peak displacement were measured across the fracture site as a reflection of construct stability. FINDINGS: Previous testing demonstrated that Trigen intramedullary nail had significantly less motion across the gap and increased overall stiffness of the construct (P<0.05) compared to both Russell-Taylor and prototype nails. INTERPRETATION: Locking technology used in a nail biomechanically appears to lead to more micro-motion across the fracture gap and to less stiffness in this construct. Further research needs to be invested into intramedullary, locking technology before introducing it into clinical practice.

Impact magnitudes applied by surgeons and their importance when applying the femoral head onto the Morse taper for total hip arthroplasty.

INTRODUCTION: This study was designed to test whether the number of impacts, the experience of the surgeon or impact force made significant difference in pull off forces. MATERIALS AND METHODS: The forces applied by 10 orthopaedic surgeons (five residents and five attending staff) to impact the femoral head onto the trunnion of a femoral component were recorded. The resultant forces were then divided into four energy levels and compared to determine if the number of impacts would make a difference in pull off strength. RESULTS: No significant differences existed between the resident versus attending groups in magnitude of force applied. Through ANOVA testing, it was found that at each of the energy levels, multiple blows demonstrated a significant pull off strength difference compared to a single blow. Increased pull off force was also noted when the magnitude of force of the applied blows was increased. CONCLUSION: We recommend at least two firm, axially aligned blows to impact the femoral head onto the trunnion intra-operatively.

Pullout strength variance among self-tapping screws inserted to different depths.

The cortical self-tapping screw (STS) has replaced the non-STS as an aid in fracture fixation. In a recent biomechanical investigation, Berkowitz and colleagues found that STS pullout strength increased with insertion depth up to 1 mm past the far cortex only. In the present study, we wanted to apply a standardized protocol of assessing pullout strength to STSs of different compositions and manufacturers while eliminating the sample-size and block-variance issues that affected the previous investigation. Ninety STSs were randomly divided into 5 groups, each representing a different insertion depth. Peak force was determined with trials ending in screw pullout or failure. A statistically significant difference in pullout strength was identified with insertion depths up to 1 mm past the far cortex. No block variance was detected. These results support the recommendation that STSs be inserted only 1 mm past the far cortex in healthy cortical bone.

Pullout strength and load to failure properties of self-tapping cortical screws in synthetic and cadaveric environments representative of healthy and osteoporotic bone.

BACKGROUND: The parameters of self-tapping screw (STS) performance in normal and osteoporotic bone have been defined in representative environments, but the question remains as to the clinical application of such findings. The goal of this study was to analyze the biomechanical performance of STSs in cadaveric and synthetic environments representative of healthy and osteoporotic bone. METHODS: Ninety-six Synthes STSs were inserted into cadaveric and synthetic models representative of osteoporotic and healthy bone. Screws were inserted to depths of 1 mm short of the far cortex, flush and 1 mm and 2 mm beyond the far cortex. Screws were tested with an Instron 8511 material testing system utilizing axial pullout forces. A SAS procedure was used to conduct analysis of variance for unbalanced datasets. RESULTS: Substantial differences were appreciated with respect to screw performance between osteoporotic and healthy bone specimens. Although a similar pattern of increased pullout strength and loading energy with increasing depth of insertion was demonstrated, absolute values were lower in osteoporotic specimens. Although performance trends were similar in cadaveric and synthetic testing models for both osteoporotic and healthy bone, values obtained during testing were different. Incomplete insertion of STSs resulted in a 21.5% and 37% reduction of biomechanical properties in osteoporotic and normal bone, respectively. CONCLUSIONS: These results indicate that previously published findings on the performance of STSs in synthetic models cannot reasonably be applied to the clinical realm. Although trends may be similar, screw performance in synthetic, as compared with cadaveric, models is markedly different.

The effect of pilot hole size on the insertion torque and pullout strength of self-tapping cortical bone screws in osteoporotic bone.

BACKGROUND: All surgical screws can experience failure if the torsional, tensile, and flexion loads exerted on the screws are excessively high. The use of self-tapping screws (STS) results in higher insertion torques (IT) as these screws cut their own threads in the pilot hole drilled in the bone. In this study, the torque for inserting the STS into an osteoporotic bone block for different pilot hole sizes (PHS) was measured and the pullout strength (PS) for extraction of the screws was determined for different depths of insertion, 0 mm, 1 mm, and 2 mm beyond the far cortex. METHODS: Seventy-two Synthes stainless steel STS (40 mm length and 3.5 mm diameter) were inserted into pilot holes of sizes 2.55 (A: 73% OD), 2.50 (B: 71.5%), 2.45 (C: 70%), and 2.8 mm (D: 80%). Using a digital torque screwdriver, screws were inserted to 0 mm, 1 mm or 2 mm past the far cortex. Pullout tests were conducted with an Instron materials testing system. Analysis of variance and Student-Neuman-Keuls tests were performed to determine the effect of DOI and PHS on the loading energy, PS, and IT. RESULTS: Results demonstrated that IT of the screws inserted into pilot holes A, B, and C were higher than those in D. It was also observed that PS and loading energy for 1 mm and 2 mm penetration past the far cortex were higher than those for 0 mm regardless of PHS. This study also found that an increase in PHS to 2.8 mm will reduce IT but will also reduce the PS relative to a PHS of 2.5 mm, the current standard for 3.5 mm screws. CONCLUSIONS: The results of previously published studies regarding the effect of pilot hole size on PS in healthy cortical bone cannot be applied to the osteoporotic environment. The findings presented in this research support using PHS no larger than 71.5% of the screw outer diameter (i.e., pilot hole size of 2.5 mm for 3.5 mm screws) and inserting screws at least 2 mm beyond the far cortex to maximize PS and minimize iatrogenic damage in osteoporotic bone.

Experimental evaluation of the holding power/stiffness of the self-tapping bone screws in normal and osteoporotic bone material.

OBJECTIVE: The goal of this study is to compare the holding power of the self-tapping bone screws in normal and osteoporotic bone materials. BACKGROUND: Self-tapping screws are increasingly being used in orthopaedic surgery due to their advantages over the other bone screws. METHODS: Screws were divided into five groups (six screws per group) based on the depth of insertion in the bone coupons that represented normal and osteoporotic bones. Screws were randomly inserted into the bone coupons with tips of the screws being -1 mm, 0 mm, 1 mm, 2 mm and 3 mm relative to the far cortex. Biomechanical testing was performed using an Instron 8,511 in accordance with the American Society for Testing and Materials standards for bone screws. Two-factor analysis of variance (ANOVA) was used to determine if the holding power of the screws were different with respect to insertion depths and bone materials. FINDINGS: The bone materials had a significant difference (P < 0.05) in the holding power and depths of insertion past the far cortex were significantly different from one another in holding power. The affect of the screw material on the holding power of the self-tapping screws in different bone materials was also examined. The performance of stainless steel screws was superior to that of titanium screws in the osteoporotic material. INTERPRETATION: Based on the results it can be concluded that the depth of insertion of the tip of the screw for adequate fracture fixation in normal bone is 1mm or more past the far cortex and in osteoporotic bone it is at least 2mm past the far cortex.