Peak Removal Torque Research Articles

Expandable Screws Can Increase Fixation Strength But Can They Be Removed? An in-vivo Sheep Study Demonstrating Removal Of A Novel Expandable Screw

Screw fixation failures remain clinically challenging especially hip fracture fixation in osteoporotic bone. Prior studies have shown that expandable orthopaedic screw devices can improve biomechanical fixation in bone, but concerns over their removability remains. A novel expandable screw implant has been developed that optimizes both implant fixation and removability. The present study investigated the implant removability in an animal model. A specially manufactured expandable screw implant was surgically implanted in 5 sheep for 4 months. The distal femur were extracted with the implants in-situ after euthanasia. The bone samples were scanned using micro-CT and the retraction torque of the expandable screw wings were measured to assess ease of removability. Analysis of the micro-CT images verified that bone had not grown inside the expandable screw mechanism and all expandable screw samples were removed without complication. The mean peak torque to fully retract the screws ready for removal was 0.86 Nm (0.59-1.30 Nm) and the mean peak removal torque for the retracted screws was 7.98 Nm (1.70-15.40 Nm). This large animal study result shows the feasibility of an expandable screw concept with a novel gapless design, to improve screw fixation strength mechanically, without compromising on the implant removability.

Effect of Implant Macro-Design and Magnetodynamic Surgical Preparation on Primary Implant Stability: An In Vitro Investigation.

Macro-geometry and surgical implant site preparation are two of the main factors influencing implant stability and potentially determining loading protocol. The purpose of this study was to assess the initial stability of various implant macro-designs using both magnetodynamic and traditional osteotomy techniques in low-density bone. The parameters examined included peak insertion torque (PIT), implant stability quotient (ISQ), and peak removal torque (PRT). Four groups of 34 implants each were identified in accordance with the surgery and implant shape: T5 group (Five implant and osteotomy using drills); M5 group (Five implant and magnetodynamic osteotomy using Magnetic Mallet); TT group (TiSmart implant and osteotomy with drills); and MT group (TiSmart implant and magnetodynamic osteotomy). Every implant was placed into a low-density bone animal model and scanned using CBCT. The PIT and PRT were digitally measured in Newton-centimeters (Ncm) using a torque gauge device. The ISQ was analyzed by conducting resonance frequency analysis. The PIT values were 25.04 ± 4.4 Ncm for T5, 30.62 ± 3.81 Ncm for M5, 30 ± 3.74 Ncm for TT, and 32.05 ± 3.55 Ncm for MT. The average ISQ values were 68.11 ± 3.86 for T5, 71.41 ± 3.69 for M5, 70.88 ± 3.08 for TT, and 73 ± 3.5 for MT. The PRT values were 16.47 ± 4.56 Ncm for T5, 26.02 ± 4.03 Ncm for M5, 23.91 ± 3.28 Ncm for TT, and 26.93 ± 3.96 Ncm for MT. Based on our data analysis using a t-test with α = 0.05, significant differences in PIT were observed between TT and T5 (p < 0.0001), M5 and T5 (p < 0.0001), and MT and TT (p = 0.02). Significant differences in the ISQ were found between TT and T5 (p = 0.001), M5 and T5 (p < 0.001), and MT and TT (p = 0.01). The PRT also exhibited significant differences between TT and T5, M5 and T5, and MT and TT (p < 0.0001). Our data showed favorable primary implant stability (PS) values for both implant macro-geometries. Furthermore, the magnetodynamic preparation technique appears to be more effective in achieving higher PS values in low-density bone.

Can Bone Compaction Improve Primary Implant Stability? An In Vitro Comparative Study with Osseodensification Technique

Background: This study aims to analyze bone compaction and osseodensification techniques and to investigate how cancellous bone compaction could influence primary implant stability (PS). Methods: Two different surgical protocols (bone compactors—BC; osseodensification drills—OD) were compared by placing 20 implants into 20 fresh pig ribs for each procedure. Peak insertion torque (PIT) and peak removal torque (PRT) were investigated using an MGT-12 digital torque gauge, and implant stability quotient (ISQ) was analyzed using an Osstell® Beacon device. Results: Analysis of our data (T-test p &lt; 0.05) evidenced no statistically significant difference between BC and OD in terms of PIT (p = 0.33) or ISQ (p = 0.97). The comparison of PRT values showed a statistically significant difference between BC and OD protocols (p = 0.009). Conclusions: Cancellous bone compaction seems to improve PS, preserving a significant amount of bone and evenly spreading trabeculae on the entire implant site. While the PIT and ISQ values obtained are similar, the PRT values suggest different physical responses from the surrounding bone tissue. Nevertheless, a larger sample and further in vivo studies are necessary to validate the usefulness of BC protocol in several clinical settings.

Primary Stability of Three Different Osteotomy Techniques in Medullary Bone: An in Vitro Study.

Background: The aim of this in vitro study was to analyse the primary stability of 20 implants placed with Twist drills (TD) versus 20 implants placed with Summers osteotomes (SO) and 20 implants placed with B&B bone compactors (BC) in medullary bone (quality type III and type IV). Methods: The implants were placed in 10 fresh pig ribs fixed on a bench vice in order to avoid micro-movements during surgical procedures and measure recording. Peak insertion torque (PIT) and Peak removal torque (PRT) were recorded with MGT-12 digital torque gauge and ISQ was recorded through OSSTELL ISQ™ device by an independent operator. Results: Comparing our data (Tukey test p = 0.05), it was evidenced a statistically significant difference in the PIT between TD and BC groups (p = 0.01). Analysing ISQ data, there was a statistically significant difference between the TD and BC groups (p = 0.0001) and between the SO and BC groups (p = 0.014). The analysis of PRT evidenced a statistically significant difference between the TD and BC groups (p = 0.038). Conclusions: This study evidenced that bone compactor preparation can positively influence primary implant stability (PS), however further in vivo studies and a larger sample are necessary to assess the usefulness in several clinical settings.

Comparison of implant stability measurements between a resonance frequency analysis device and a modified damping capacity analysis device: an in vitro study.

PurposeA stability-measuring device that utilizes damping capacity analysis (DCA) has recently been introduced in the field of dental implantology. This study aimed to evaluate the sensitivity and reliability of this device by measuring the implant stability of ex vivo samples in comparison with a resonance frequency analysis (RFA) device.MethodsSix implant beds were prepared in porcine ribs using 3 different drilling protocols to simulate various implant stability conditions. Thirty-six pork ribs and 216 bone-level implants measuring 10 mm in height were used. The implant beds were prepared using 1 of the following 3 drilling protocols: 10-mm drilling depth with a 3.5-mm-diameter twist drill, 5-mm drilling depth with a 4.0-mm-diameter twist drill, and 10-mm drilling depth with a 4.0-mm-diameter twist drill. The first 108 implants were external-connection implants 4.0 mm in diameter, while the other 108 implants were internal-connection implants 4.3 mm in diameter. The peak insertion torque (PIT) during implant placement, the stability values obtained with DCA and RFA devices after implant placement, and the peak removal torque (PRT) during implant removal were measured.ResultsThe intraclass correlation coefficients (ICCs) of the implant stability quotient (ISQ) results obtained using the RFA device at the medial, distal, ventral, and dorsal points were 0.997, 0.994, 0.994, and 0.998, respectively. The ICCs of the implant stability test (IST) results obtained using the DCA device at the corresponding locations were 0.972, 0.975, 0.974, and 0.976, respectively. Logarithmic relationships between PIT and IST, PIT and ISQ, PRT and IST, and PRT and ISQ were observed. The mean absolute difference between the ISQ and IST values on a Bland-Altman plot was −6.76 (−25.05 to 11.53, P<0.05).ConclusionsWithin the limits of ex vivo studies, measurements made using the RFA and DCA devices were found to be correlated under a variety of stability conditions.

Biomechanical evaluation of peak reverse torque (PRT) in a dynamic compression plate-screw construct used in a goat tibia segmental defect model

BackgroundPeak reverse torque (PRT) is a valid method to evaluate implants’ secondary stability in the healing bone. The secondary stability is achieved by the implant over time and it has been positively correlated with the implants’ osseointegration level. In other words, peak reverse torque is the force required to break the bone-implant interface. The purpose of this study was to compare the peak reverse torque for the self-tapping and non-self-tapping screws used in a dynamic compression plate–screw–bone construct after 60 days of loading when used to stabilize 2.5-cm defects in the tibia of goats. The second objective was to compare the peak removal torque of the screws placed in the different positions to evaluate the impact of construct biomechanics on implants osseointegration.ResultsIn total, 176 non-self-tapping screws and 66 self-tapping screws were used to fix the 8-holes dynamic compression plates to the bones. The screws were placed in the tibiae from proximal (position sites 1,2, 3) to distal (position sites 4,5,6) and were removed 60 days post-implantation. The animals remained weight-bearing throughout the study period. The screws placed in the proximal diaphysis had significantly less peak reverse torque than screws placed in the distal diaphysis in both groups (p < 0.05). The peak reverse torque resistance was also significantly less for the non-self-tapping screws as compared with the self-tapping screws (p < 0.05). The intracortical fractures in the trans-cortex occurred significantly more frequently during the placement of non-self-tapping screws (p < 0.05) as compared with self-tapping screws (p < 0.05).ConclusionsBased on these results, we concluded that self-tapping screws may be expected to maintain a more stable bone-implant interface during the first 60 days of loading as compared with non-self-tapping screws. This should be a consideration for orthopedic surgeons and scientists using bone plates to stabilize non-load sharing fractures when a stable plate-screw-bone interface is needed to ensure prolonged stability.

Effects of Biomineralization on Osseointegration of Pure Titanium Implants in the Mandible of Beagles

The purpose of this study was to investigate the effect of a biologically active dental implant surface (treated with sandblasting and acid etching [SLA] followed by immersion in simulated body fluid [SBF]) on osseointegration. We randomly divided 9 healthy adult male beagles (aged 8months; body weight, 12kg) into 3 groups: machined, SLA, and SLA-biomineralization (SLA-Bio). Six pure titanium implants (diameter of 3.5mm and length of 8mm) were used in the mandible of each dog after observation of the surface morphology, as well as analysis of the composition of the surface elements by scanning electron microscopy-energy dispersive x-ray spectroscopy. At 4, 8, and 12weeks after implantation, animals were euthanized to collect the mandibles so that we could perform the removal torque test to evaluate the implant stability in bone and histomorphometry to analyze the implant-bone osseointegration. Scanning electron microscopy results showed that uniformly distributed sponge-like structures were found on the SLA-treated surface and an apatite layer was observed on the SLA-SBF-treated surface (SLA-Bio group). In the energy dispersive x-ray spectroscopy analysis, the elements titanium, oxygen, carbon, calcium, and phosphorus were found on the surfaces of the SLA-Bio group, whereas titanium was the only element found in the other groups.The removal torque test showed that the peak removal torque values of the 3 groups increased gradually with the passage of time, and the peak removal torque values of the SLA-Bio group were significantly higher than those of the other groups (P<.01) at 4, 8, and 12weeks after implantation. Histomorphometric analysis showed that osseointegration was being enabled more rapidly in the SLA-Bio group, as well as that the mineral apposition rate and percentage of bone-to-implant contact of the SLA-Bio group were higher than those of the remaining groups at 4, 8, and 12weeks after implantation (P<.01). Treating titanium implants with SLA-SBF can improve osseointegration as well as increase the interfacial shear strength.

The Performance of Titanium‐Zirconium Implants in the Elderly: A Biomechanical Comparative Study in the Minipig

The aim of this study was to test the following hypothesis: (1) Aging would adversely affect bone integration of implants; (2) Titanium-zirconium-SLActive (TiZr-SLActive) implant might perform better in osseointegration than Ti-SLA implant in aged group. Thirteen miniature pigs (six of them were young adult minipigs, with other seven being aged ones.) were enrolled in this study. The right mandibular premolars (P1, P2, P3) and the first molar (M1) were extracted in all animals. Three months later, one TiZr-SLActive and one Ti-SLA implants were inserted into the endentulous area in mandible of each animal. The animals were sacrificed 8 weeks after placement of implants. Implants in the mandibles were used for removal torque (RT) tests, while vertebra and femur being retrieved for bone mineral density (BMD) tests. Implant success rate in the young group was significantly higher than that in the aged group. Higher survival rate of implants was also observed in younger group than that in the aged group but without significant difference. Within the young group, mean value for peak RT of Ti-SLA implants was higher than that of TiZr-SLActive implants without significant difference. In the aged group, the TiZr-SLActive implants showed a higher mean value for peak RT than Ti-SLA implants. No significant difference was found in the mean BMD in both vertebra and femur between different age groups. Within the limits of this study, aging could negatively affect osseointegration of dental implants. TiZr-SLActive implants might to some degree compensate for the compromise in osseointegration brought by aging.

Removal torque analysis of chemically modified hydrophilic and anodically oxidized titanium implants with constant angular velocity for early bone response in rabbit tibia

Implant geometry and surface properties are important factors for successful osseointegration. The purpose of this study was to compare hydrophilic and hydrophobic implants with different geometries via the continuous measurement of removal torque (RT) and calculation of angular momentum for each implant. Five New Zealand white rabbits were used in the study. Each rabbit received 2 implants. A chemically modified hydrophilic implant with buttress thread was inserted into one tibia, and an anodically oxidized hydrophobic implant with V-shape threads was inserted into the other. After 1 week of healing, RT values were measured continuously in real-time. Using the time-torque curve resulting from the measurements, the maximum values were determined and angular momentums were calculated. The chemically modified hydrophilic implant exhibited significantly higher peak RT and mean torque values before the peak torque (MTBP) than the anodically oxidized hydrophobic implant (p < 0.05). The chemically modified hydrophilic implants exhibited superior early bone response compared to the anodically oxidized implants.

Evaluation of Early Bone Response to Fluoride-Modified and Anodically Oxidized Titanium Implants Through Continuous Removal Torque Analysis

To compare between a bioactive and a bioinert implant with different geometries by continuous measurement of the removal torque and calculation of the angular momentum of each surfaced implant. Six New Zealand white rabbits were used in the study. Each rabbit received 2 implants. A bioactive fluoride-modified implant with a conical connection and microthread design was inserted into one tibia, and a bioinert anodically oxidized implant with an external connection design was inserted into the other. After 2 weeks of implant insertion, the removal torque values were continuously measured according to time. Using the time-torque curve resulting from the measurements, the maximum values were determined, and the angular momenta were calculated. The anodically oxidized implant had significantly higher peak removal torque and angular momentum values than the fluoride-modified implant (P < 0.05). The impact of the fluoride-modified bioactive implant on early bone response remains unclear. Considering the angular momentum of dental implants may assist in the elucidation of the effect of implant geometry on bone response.

Effect of surface anodization on stability of orthodontic microimplant

ObjectiveTo determine the effect of surface anodization on the interfacial strength between an orthodontic microimplant (MI) and the rabbit tibial bone, particularly in the initial phase after placement.MethodsA total of 36 MIs were driven into the tibias of 3 mature rabbits by using the self-drilling method and then removed after 6 weeks. Half the MIs were as-machined (n = 18; machined group), while the remaining had anodized surfaces (n = 18; anodized group). The peak insertion torque (PIT) and the peak removal torque (PRT) values were measured for the 2 groups of MIs. These values were then used to calculate the interfacial shear strength between the MI and cortical bone.ResultsThere were no statistical differences in terms of PIT between the 2 groups. However, mean PRT was significantly greater for the anodized implants (3.79 ± 1.39 Ncm) than for the machined ones (2.05 ± 1.07 Ncm) (p < 0.01). The interfacial strengths, converted from PRT, were calculated at 10.6 MPa and 5.74 MPa for the anodized and machined group implants, respectively.ConclusionsAnodization of orthodontic MIs may enhance their early-phase retention capability, thereby ensuring a more reliable source of absolute anchorage.

The effect of calcium ion concentration on the bone response to oxidized titanium implants

To investigate the effect of calcium concentration on the bone tissue response to Ca-incorporated titanium implants. Two titanium surfaces containing 4.2% and 6.6% calcium were prepared using the micro-arc oxidation process. The implants were inserted in the tibia of nine New Zealand White rabbits. After 6 weeks of healing, the bone response to the implants was quantitatively compared by biomechanical and histomorphometrical measurements. Ca 4.2% and Ca 6.6% containing implants revealed no distinctive differences in their qualitative surface chemistry; chemical bonding state of Ca in titanium oxide was mainly calcium titanates. No significant differences were observed between two implants in peak removal torque and shear strength comparisons (P>0.05). Histomorphometrical analyses presented no significant differences in bone-metal contact, bone area and newly formed bone measurements between two implants (P>0.05). From biomechanical and histomorphometrical measurements, the two calcium concentrations in this study did not differ significantly with respect to their influence on the bone tissue response. This similar bone response in rabbit tibiae may be explained by the similarity of the qualitative Ca chemistry in titanium surfaces.

Enhanced bone regeneration around dental implant with bone morphogenetic protein 2 gene and vascular endothelial growth factor protein delivery

To evaluate the synergistic effect of bone morphogenetic protein 2 (BMP-2) and vascular endothelial growth factor (VEGF) on the repair of bone defects around dental implants. Five groups of scaffold were fabricated by a freeze-drying method, including pure chitosan/collagen scaffold; scaffold loaded with adenoviruses expressing BMP-2, adenoviruses expressing VEGF, both adenoviruses expressing BMP-2 and VEGF, VEGF protein and adenovirus expressing BMP-2. In vitro studies examined whether bone marrow stromal cells were responsive to these scaffolds over time. Bone formation capacity, bone-to-implant contact, as well as removal torque values were investigated in vivo. Differences between the various groups were statistically analyzed using the one-way analysis of variance test. The in vitro study revealed a burst and rapid release of VEGF with a sustained high-level expression of BMP-2 in scaffold combined with VEGF protein and adenoviruses expressing BMP-2. Histomorphometry demonstrated that scaffolds expressing BMP-2 enhanced more bone formation compared with other groups; VEGF alone is insufficient to promote bone formation. New bone formation in the bone defects around dental implants, bone-to-implant contact and mean peak removal torque showed statistically significant difference for the adenoviral vector encoding human bone morphogenetic protein 2 (Ad-BMP-2) and VEGF protein and adenovirus expressing BMP-2 groups. Furthermore, scaffold combined with VEGF protein and Ad-BMP-2 represented the best outcomes in this model. A combination of BMP-2 gene and VEGF protein could have a synergistic effect in promoting bone healing.

Mechanical properties of self-drilling orthodontic micro-implants with different diameters

The hypothesis to be tested is that peak-insertion torque of self-drilling micro-implants of an appropriate diameter correlates with peak-removal torque mechanically. A total of 360 self-drilling micro-implants composed of five different types were used. They (24 of each group) were inserted in three types of artificial bone with the use of a driving torque tester at a speed of 15 rpm. Insertion torque was measured during the placement, while the removal torque was measured within 3 days after insertion. Most of the micro-implants in type A sheared before they were completely inserted in 40-pounds per cubic foot bone. The implants in other types were successfully inserted without implant breakage and bone fracture in all bone densities. There was a statistically significant correlation between insertion torque and removal torque (r > or = 0.43543, P = .0001). There were significant differences in insertion and removal torque among the diameters of implants and bone densities with an increasing tendency. The torque loss rates reduced as the diameter of the implant and bone density increased. Micro-implants with a diameter of less than 1.3 mm are unsuitable for insertion into a bone with a density greater than 40 pounds per cubic foot mechanically when one is using a self-drilling technique.

Reliability and validity of the instrumental assessment of implant stability in dry human mandibles

The aim of this study was to determine the intra- and interobserver reliability and validity of the instrumental assessment of primary dental implant stability, using resonance frequency analysis (RFA). Sixteen tapered implants and 16 cylindrical implants were installed in eight unfixed dry human mandibles (Cawood classification IV/V). Implant stability quotients (ISQ; the outcome variable of RFA) and peak removal torque were determined. Both the intra-observer reliability and the interobserver reliability of the RFA measurements were fair-to-good, while no significant correlations between the ISQ values and removal torque were found. The removal torque of the cylindrical implants was higher than that of the tapered implants. The smallest detectable difference was almost nine ISQ units. Within the limitations of the present dry cadaver study, it was concluded that (i) primary dental implant stability can be assessed reliably with RFA measurements, (ii) the concurrent validity between RFA measurements and removal torque is poor, (iii) cylindrical implants may be more stable than tapered ones and (iv) two subsequent readings of RFA measurements need to differ at least nine ISQ units before the difference between the two measurements can be considered statistically significant. More research is needed to see whether these conclusions can be extrapolated to the clinical situation, including the assessment of implants during function (secondary stability).

Effects of orthopedic implants with a polycaprolactone polymer coating containing bone morphogenetic protein-2 on osseointegration in bones of sheep

To determine elution characteristics of bone morphogenetic protein (BMP)-2 from a polycaprolactone coating applied to orthopedic implants and determine effects of this coating on osseointegration. 6 sheep. An in vitro study was conducted to determine BMP-2 elution from polycaprolactone-coated implants. An in vivo study was conducted to determine the effects on osseointegration when the polycaprolactone with BMP-2 coating was applied to bone screws. Osseointegration was assessed via radiography, measurement of peak removal torque and bone mineral density, and histomorphometric analysis. Physiologic response was assessed by measuring serum bone-specific alkaline phosphatase activity and uptake of bone markers. Mean +/- SD elution on day 1 of the in vitro study was 263 +/- 152 pg/d, which then maintained a plateau at 59.8 +/- 29.1 pg/d. Mean peak removal torque for screws coated with polycalprolactone and BMP-2 (0.91 +/- 0.65 dN x m) and screws coated with polycaprolactone alone (0.97 +/- 1.30 dN.m) did not differ significantly from that for the control screws (2.34 +/- 1.62 dN x m). Mean bone mineral densities were 0.535 +/- 0.060 g/cm(2), 0.596 +/- 0.093 g/cm(2), and 0.524 +/- 0.142 g/cm(2) for the polycaprolactone-BMP-2-coated, polycaprolactone-coated, and control screws, respectively, and did not differ significantly among groups. Histologically, bone was in closer apposition to the implant with the control screws than with either of the coated screws. BMP-2 within the polycaprolactone coating did not stimulate osteogenesis. The polycaprolactone coating appeared to cause a barrier effect that prevented formation of new bone. A longer period or use of another carrier polymer may result in increased osseointegration.

An in vivo evaluation of the biocompatibility of anodic plasma chemical (APC) treatment of titanium with calcium phosphate

Implant loosening is an unresolved complication associated with prosthetics. Previous studies report improved osseointegration with hydroxyapatite (HA) or tri-calcium phosphate coatings. Unfortunately, the brittleness and low strength of these coatings in adhesion to the implant or internal cohesion is problematic, restricting their use. Anodic plasma-chemical (APC) treatment, an advanced anodisation method, allows for porous oxide layer formation with incorporation of calcium and phosphate directly into the oxide. This produces superior adhesive strength than a conventional coating of calcium phosphate offering potential for long-term osseointegration. Although the cytocompatibility of several APC treatments have been previously shown, this study was the first to investigate the biocompatibility and osteoconductivity of APC surfaces in vivo when compared with standard HA coated and noncoated commercially pure titanium implant cortical screws. Sample screws were implanted in female Swiss alpine sheep for 12 weeks. Bone remodelling in situ, differences in bone apposition resulting in cortical thickening as well as peak removal torque measurements were assessed. We found no significant differences between the tested coatings and no delamination was observed with any of the APC-treated surfaces. The results suggest that APC-treated samples have similar biological performance to HA-coated screws. In our opinion, APC treatment, which also has superior binding strength to the base metal compared with standard HA coatings as well as similar biocompatibility as shown here, holds great potential for biomedical applications. Now that the in vivo biocompatibility has been proven, the work is being extended to more challenging in vivo models.

Biomechanical and histological comparison of self-drilling and self-tapping orthodontic microimplants in dogs

The purpose of this study was to compare the influences of different implant modalities on orthodontic microimplants and surrounding tissues biomechanically and histologically. Fifty-six titanium alloy microimplants placed on the buccal side of the maxillae and the mandibles in 2 dogs were divided into 2 groups of 28; one group of microimplants was self-drilling, and the other was self-tapping. Approximately 200 g of continuous and constant forces were applied immediately between 2 microimplants by stretching closed nickel-titanium coil springs for 9 weeks. Peak insertion torque and removal torque were recorded immediately after the implants were placed and when the dogs were killed, respectively. Undecalcified sections of the microimplants and the surrounding tissues were studied with light microscope and fluorescent microscope. Success rates were higher in the self-drilling group (93%) than in self-tapping group (86%). Higher peak insertion torque and peak removal torque values were seen in the self-drilling group in both the maxilla and the mandible. A tendency to fracture was found in self-drilling group. The percentage of bone-to-implant contact values was greater in the self-drilling group. Self-drilling microimplants can provide better anchorage and can be recommended for use in the maxilla and in thin cortical bone areas of the mandible.

Biomechanical comparison of self-drilling and self-tapping orthodontic micro-implants

To evaluate the biomechanical influences of self-drilling and self-tapping methods on orthodontic micro-implants under immediate loading. Fifty-six micro-implants placed at the interradicular areas of buccal side of upper and lower jaws in two dogs were divided into self-drilling and self-tapping groups. A horizontal load of 1.96 N was immediately given for 9 weeks. Peak insertion torque and peak removal torque were tested immediately after implantation and after the dogs were killed, respectively. Both in the upper and lower jaws peak insertion torque was significantly higher in self-drilling group [(5.6 +/- 1.1) N.cm and (8.7 +/- 2.3) N.cm] than in self-tapping group [(3.5 +/- 2.1) N.cm and (7.4 +/- 1.1) N.cm] (P < 0.05). Both in the upper and lower jaws peak removal torque was higher in self-drilling group [(-6.5 +/- 2.2) N.cm and (-7.1 +/- 2.0) N.cm] than in self-tapping group [(-5.7 +/- 2.3) N.cm and (-6.1 +/- 0.5) N.cm]. No significant difference was found (P > 0.05). The tendency of fracture was found in self-drilling group. Self-drilling micro-implants have high initial stability and can be used in the maxilla and at thin cortical bone area of mandible.

Stimulation of Directed Bone Growth at Oxidized Titanium Implants by Macroscopic Grooves: An In Vivo Study

The influence of thread design at the millimeter level and surface topography at the micrometer level on bone integration and the stability of dental implants have been studied extensively. However, less is known about the influence of implant structures in the range of 50 to 200 microm. The present in vivo investigation was undertaken to study if bone formation and implant stability were influenced by 110 (S1) and 200 (S3) microm-wide and 70 microm-deep grooves positioned at a thread flank of oxidized titanium implants. Eighteen rabbits and oxidized titanium implants (3.75 mm in diameter and 7 mm long) were used in the study. Nine rabbits received three control implants and three test implants with a 110 microm-wide groove added to one thread flank. The remaining nine rabbits received three control implants and three test implants with a 200 microm-wide groove. The animals were followed for 6 weeks. Removal torque (RTQ) tests were applied to two of the implants in each leg. The remaining implant per leg was retrieved for histology. The degree of bone fill within the grooves and corresponding bone formation at the opposing surfaces, the bone area within the threads, and the degree of bone-implant contact were calculated for each implant. The histologic analyses revealed an affinity for bone formation within the grooves. The RTQ tests showed that the peak RTQ was approximately 30% higher for the S1 implants compared with control implants without a groove. The difference was statistically significant (p < .05) for tibial and pooled implants. A similar but smaller and not statistically significant effect, approximately 8%, was measured for the S3 implants. The histomorphometric measurements confirmed the observed affinity of bone for the grooves. For S1 implants, 78.7 +/- 15.8% of the grooves were filled with bone, whereas only 46.2 +/- 27% of the corresponding flank surface showed the presence of bone (p < .05). The corresponding figures for S3 and control implants were 72.7 +/- 25.1% and 48.5 +/- 13.6%, respectively (p < .05). The degrees of bone-implant contact and bone area within the threads were similar for test and control implants. It is concluded that 110 and 200 microm-wide and 70 microm-deep grooves at oxidized implant surfaces stimulated bone to preferentially form within and along the groove in the rabbit model. The 110 microm-wide groove was shown to increase the resistance to shear forces significantly. It is suggested that implants with such a groove may be one way to optimize implant stability in suboptimal clinical conditions.