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PubMed2003

Structural transitions and elasticity from torque measurements on DNA.

Knowledge of the elastic properties of DNA is required to understand the structural dynamics of cellular processes such as replication and transcription. Measurements of force and extension on single molecules of DNA have allowed direct determination of the molecule's mechanical properties, provided rigorous tests of theories of polymer elasticity, revealed unforeseen structural transitions induced by mechanical stresses, and established an experimental and conceptual framework for mechanical assays of enzymes that act on DNA. However, a complete description of DNA mechanics must also consider the effects of torque, a quantity that has hitherto not been directly measured in micromanipulation experiments. We have measured torque as a function of twist for stretched DNA--torsional strain in over- or underwound molecules was used to power the rotation of submicrometre beads serving as calibrated loads. Here we report tests of the linearity of DNA's twist elasticity, direct measurements of the torsional modulus (finding a value approximately 40% higher than generally accepted), characterization of torque-induced structural transitions, and the establishment of a framework for future assays of torque and twist generation by DNA-dependent enzymes. We also show that cooperative structural transitions in DNA can be exploited to construct constant-torque wind-up motors and force-torque converters.

DNA↗
PubMed2001

Force and torque effects of a 1.5-Tesla MRI scanner on cardiac pacemakers and ICDs.

Magnetic resonance imaging (MRI) is a widely accepted tool for the diagnosis of a variety of disease states. However, the presence of an implanted pacemaker is considered to be a strict contraindication to MRI in a vast majority of centers due to safety concerns. In phantom studies, the authors investigated the force and torque effects of the static magnetic field of MRI on pacemakers and ICDs. Thirty-one pacemakers (15 dual chamber and 16 single chamber units) from eight manufacturers and 13 ICDs from four manufacturers were exposed to the static magnetic field of a 1.5-Tesla MRI scanner. Magnetic force and acceleration measurements were obtained quantitatively, and torque measurements were made qualitatively. For pacemakers, the measured magnetic force was in the range of 0.05-3.60 N. Pacemakers released after 1995 had low magnetic force values as compared to the older devices. For these devices, the measured acceleration was even lower than the gravity of the earth (< 9.81 N/kg). Likewise, the torque levels were significantly reduced in newer generation pacemakers (< or = 2 from a scale of 6). ICD devices, except for one recent model, showed higher force (1.03-5.85 N), acceleration 9.5-34.2 N/kg), and torque (5-6 out of 6) levels. In conclusion, modern pacemakers present no safety risk with respect to magnetic force and torque induced by the static magnetic field of a 1.5-Tesla MRI scanner. However, ICD devices, despite considerable reduction in size and weight, may still pose problems due to strong magnetic force and torque.

Contraindications↗
PubMed2000

Knee joint torques: a comparison between women and men during barefoot walking.

OBJECTIVE: To determine if knee joint torques, which are likely relevant to the development and, possibly, progression of knee osteoarthritis, are equivalent between genders during natural, barefoot walking. DESIGN: Collected stereophotogrammetric and force platform data during comfortable, barefoot walking. Knee joint torques were plotted and statistically compared between genders using both an unpaired t test (p < .05) and an equivalence test (20% delta). SETTING: A gait laboratory. PARTICIPANTS: One hundred ten healthy, nondisabled young women and men. MAIN OUTCOME MEASURES: Four knee joint torque parameters normalized for height and weight: (1) peak and (2) duration of sagittal flexor joint torque from early to midstance, and (3) first and (4) second peak coronal (frontal) varus torque values during the stance period. RESULTS: No statistically significant differences between genders were found, and the values were equivalent between genders for each of the 4 knee joint torque parameters. CONCLUSION: These findings support the hypothesis that under similar barefoot conditions women and men have a similar intrinsic biomechanic risk for knee osteoarthritis. Future research to assess the effects of other potential biomechanic factors, such as shoe-wear and activity type, may assist not only in preventing knee joint osteoarthritis, but also in developing new rehabilitative strategies to treat osteoarthritis of the knee.

Adult↗
PubMed2003

Effect of fatigue on torque output and electromyographic measures of trunk muscles during isometric axial rotation.

OBJECTIVES: To examine the changes in torque output resulting from fatigue, as well as changes in electromyographic measures of trunk muscles during isometric axial rotation and to compare these changes between directions of axial rotation. DESIGN: Subjects performed fatiguing right and left isometric axial rotation of the trunk at 80% of maximum voluntary contraction while standing upright. SETTING: A rehabilitation center. PARTICIPANTS: Twenty-three men with no history of back pain. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Surface electromyographic signals were recorded from 6 trunk muscles bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were also measured. RESULTS: During the fatiguing axial rotation contraction, coupling torques of both sagittal and coronal planes were slightly decreased and no difference was found between directions of axial rotation. Decreasing median frequency and an increase in electromyographic amplitude were also found in trunk muscles with different degrees of changes in individual muscles. There were significant differences (P<.05) between right and left axial rotation exertions in median frequency slope of external oblique, internal oblique, latissimus dorsi, and iliocostalis lumborum muscles, but no such difference was found in median frequency slope of rectus abdominis and multifidus muscles. This could be attributed to different functional roles among the muscles. Similar differences (P<.05) between right and left axial rotation in median frequency slope were also detected in the electromyographic amplitude slope of the trunk muscles. Coefficient of variation of the torque output and electromyographic activation in most of the trunk muscles increased during the fatigue process. CONCLUSION: The changing coupling torque, different fatigue rate, and activation changes of trunk muscles, as well as the increase in variability during fatiguing axial rotation exertion, could affect the internal loading and stability of the spine; this needs to be further quantified in future studies.

Abdominal Muscles↗
PubMed2003

Maximal voluntary eccentric, isometric and concentric torque recovery following a concentric isokinetic exercise.

To examine neuromuscular fatigue and recovery following an isokinetic fatiguing exercise, nine active females performed a fatiguing exercise comprising of ten sets of ten maximal concentric knee extensions. Before (pre-test), five minutes (post-test), 24 h and 48 h after the fatiguing exercise, maximal voluntary eccentric (-1.05 rad x s(-1); -2.09 rad x s(-1)), isometric (0 rad x s(-1)) and concentric (1.05 rad x s(-1); 2.09 rad x s(-1)) torque were measured. In order to distinguish central from peripheral factors involved in torque decrement, activation level (twitch interpolation technique) and twitch contractile properties were recorded. During the course of the fatiguing exercise, concentric torque was significantly lower during the 3rd set than pre-test (-5.6 +/- 12.3 %) and further decreased to the 10th (-10.3 +/- 9.5 %). Eccentric and isometric torques were significantly lower during post-test than pre-test (-16.8 +/- 8.8 % at -2.09 rad x s(-1), -15.1 +/- 7.4 % at -1.05 rad x s(-1), and -10.4 +/- 5.9 % at 0 rad x s(-1); p < 0.05), while concentric torque was not significantly modified. Voluntary activation, peak twitch torque, twitch maximal rates of force development and relaxation were also significantly declined (p < 0.05) at post-test. Twenty-four hours later, all the measured parameters were close to their pre-fatigue values. The present results reveal that the best way to test concentric-induced alteration of neuromuscular function was to use stressful testing conditions, such as eccentric contractions.

Adult↗
PubMed2000

Effect of repeated closures on opening torque values in seven abutment-implant systems.

STATEMENT OF PROBLEM: Implant abutment screw joints tend to loosen under clinical conditions. During impression and prosthesis fabrication, repeated clinical closing and opening of abutment screws may cause component wear and decrease frictional fit of the mating parts, resulting in altered resistance to opening and potential for loss of preload in function. PURPOSE: This study recorded changes in opening torque values due to multiple consecutive closures at a constant torque within and between different abutment/implant (A/I) systems. MATERIAL AND METHODS: Repeated opening-closing cycles were used to simulate in vitro embedment relaxation and component wear of 7 A/I systems from 5 manufacturers. Screw opening torque values were recorded up to 200 consecutive closures at 20 N/cm. RESULTS: A progressive decrease in opening torque values was measured in all implant systems. Significant differences were found between A/I systems. Systems with morse tapered and spline connections consistently maintained a higher resistance to opening force. Percentage torque loss ranged from 3% to 20% on immediate opening, and from 4.5% to 36% for average of first 30 opening/closing cycles. CONCLUSION: Repeated opening and closing of implant abutment screws caused progressive loss of torque retention with variations between systems. This was probably due to a decrease in the coefficient of friction between the mating components.

Analysis of Variance↗
PubMed2002

The effect of repeated torque on the ultimate tensile strength of slotted gold prosthetic screws.

STATEMENT OF PROBLEM: Repeated torque may alter the mechanical properties and fracture resistance of certain prosthetic retaining screws. PURPOSE: This study evaluated the effect of repeated torque and salivary contamination on the ultimate tensile strength of one type of slotted gold prosthetic retaining screw. MATERIAL AND METHODS: Forty-five slotted gold prosthetic screws from the same manufacturer (Implant Innovations) were divided randomly into 9 groups of 5 screws each, with group 0X being an unused control. Groups 1XL, 5XL, 10XL, and 20XL were lubricated with human saliva, tightened to 10 Ncm, and removed 1, 5, 10, and 20 times, respectively. This procedure was performed in an unused stack of implant components consisting of an implant, an abutment cylinder and screw, and a gold cylinder. Groups 1XN, 5XN, 10XN, and 20XN were not lubricated. A custom load cell, load frame, and strain gauge torque wrench with associated electronics were used to apply torque; ultimate tensile strength was measured on a universal testing machine. Fracture load values were analyzed against torque cycles with 1-way analysis of variance and a Tukey test (P<.05). Differences between the 2 conditions (lubricated and nonlubricated) were characterized with Student's t test (P<.05). RESULTS: Mean fracture load values ranged from 97.6 +/- 2.2 kg (group 0X) to 102.0 +/- 2.1 kg (group 5XN). Analysis of variance and Tukey's test revealed no significant differences between the lubricated and nonlubricated conditions for all groups and no significant reduction of tensile strength. For 2 of the nonlubricated groups, 5XN and 20XN, a significant increase in fracture load values was recorded (P=.02 and P=.03, respectively). CONCLUSION: Within the limitations of this study, the results suggest that the slotted gold prosthetic screw tested can be tightened and removed up to 20 times without any effect on its ultimate tensile strength. The use of human saliva as a lubricant during torquing also had no apparent effect on ultimate tensile strength.

Analysis of Variance↗
PubMed2005

Forearm torque strengths and discomfort profiles in pronation and supination.

This experiment investigated maximum forearm pronation and supination torques and forearm discomfort, for intermittent torque exertions in supine and prone forearm angles for the right arm. Twenty-two subjects participated in the study that comprised two parts, the first of which involved measurement of maximum forearm torque in both twisting directions at five forearm angles including neutral. This was followed by endurance tests at 50% maximum voluntary contraction (MVC) in both directions. The second part of the study involved subjects performing 5-min duration of intermittent isometric torque exercises at 20% MVC in both directions at 11 forearm angles. Regression equations were developed that accurately predict torques as a function of forearm angle expressed as a percentage of maximum motion. Analysis of the discomfort data for the intermittent isometric torque exertions indicated that both forearm angle and twisting direction significantly affected forearm discomfort (p < 0.001). A significant two-way interaction (p < 0.01) was identified between forearm angle and direction for supine forearm angles only. The results provide important strength and discomfort models for the design of tasks involving static or repetitive forearm twisting. Such tasks have a strong association with forearm injuries including lateral and medial epicondylitis. These results provide needed data on the risk factors associated with these injuries so they can be prevented.

Adult↗
PubMed1996

Muscle tenderness and peak torque changes after downhill running following a prior bout of isokinetic eccentric exercise.

Unaccustomed exercise (usually of an eccentric nature) is often followed by delayed onset muscle soreness (DOMS). Previous studies have found that prior eccentric activity produces a training effect which reduces DOMS and morphological changes. The aim of this study was to examine the effects of a prior bout of maximal isokinetic eccentric exercise on DOMS, strength loss and plasma creatine kinase (CK) changes following a downhill run. Ten male subjects with a mean (+/- S.D.) age of 22.5 +/- 2.8 years, body mass of 62.67 +/- 0.05 kg and height of 176 +/- 3 cm were allocated to either a treatment group or a control group. The treatment group performed 100 maximal eccentric activations of the knee extensors in the dominant leg at 0.52 rad s-1. Two weeks later, the downhill run was performed on a motor-driven treadmill. This consisted of five bouts of 8 min at a gradient of -10% at a speed corresponding to 80% of the predicted maximal heart rate. The untrained group performed the downhill run as above but without the prior isokinetic session. Tenderness measurements, plasma CK activity and concentric and eccentric isokinetic peak torque measurements of the knee extensors at 0.52 and 2.83 rad s-1 were recorded prior to, immediately following and 2, 4 and 7 days after each protocol. The isokinetic protocol caused an increase (P < 0.01) in CK and tenderness and a decrease (P < 0.05) in concentric and eccentric torque at both speeds in the treatment group. Following the downhill run, a reduction in peak torque (P < 0.01) was observed in the eccentric and concentric modes at both isokinetic speeds in the control group. For the treatment group, the decrease in peak torque occurred only at the faster eccentric speed. With the exception of the faster eccentric speed, the decrement in peak torque was greater in the control group in all post-exercise isokinetic strength tests. There was less tenderness (P < 0.01) in the trained knee extensor muscle group. Peak torque also returned to pre-downhill values earlier for the trained group. Although plasma CK activity increased in both groups after downhill running, it was much lower (P < 0.01) in the trained group. The results suggest that a prior bout of isokinetic eccentric training reduces muscle damage, reduces the amount of strength loss and decreases the sensation of DOMS after downhill running.

Adult↗
PubMed2005

Acute changes in knee-extensors torque, fiber pennation, and tendon characteristics.

The aim of the current study was to examine the relationships between quadriceps torque, vastus lateralis pennation angle (theta), and patella tendon stiffness (K) at 07:45 and 17:45 h. Using short-duration static contractions, simultaneous recordings were made of vastus lateralis (VL) electromyograph (EMG), theta and patella tendon K. Peak isometric extension torque (Peak torque Ext(corr)) increased by 29.4+/-6.5% at a knee angle of 70 degrees (p=0.03) in the evening compared to the morning. In the contracted muscle, a 35.0+/-11.0% (p=0.02) time-of-day (TOD)-related change in theta (to a greater evening compared to morning theta) was observed. Morning and evening measures of theta were also made, both at rest and at a standardized force level (250 N), to separate architecture change effects from increased torque capacity effects. Significant increments in theta in both the resting muscle (13.0+/-5.1%, p=0.046) and during the standardized exertions (8.0+/-3.1%, p=0.04) were observed in the evening versus the morning. Increases in theta with TOD were significantly correlated with the 40% (p=0.018) decrease in K both during the standardized contractions (r=0.788, p<0.001) and at rest (r=0.77, p=0.026). These data show that TOD affects K and theta and that these two important factors involved in in-vivo muscle torque generation capacity are associated. The data also show that despite the potentially deleterious effects of the direction of the changes in both K and theta with TOD, peak torque Ext(corr) still shows a significant upward shift in the evening relative to the morning.

Adult↗
PubMed2000

Effects of isokinetic strength training on concentric and eccentric torque development in the ankle dorsiflexors of older adults.

This study quantifies concentric and eccentric dorsiflexor muscle torque at various movement velocities and determines the neuromuscular effects from short-term practice of repeated maximal voluntary contractions using an isokinetic resisted exercise program in older adults. Twenty-eight subjects (76.3+/-4.6 years) trained concentric and eccentric dorsiflexion 3 days per week for 2 weeks at 30 degrees, 90 degrees, and 180 degrees/s through 40 degrees of dorsiflexion range of motion. Peak torque, rate of torque development, surface electromyography, and strength curves at each velocity were compared before and after training. Increases were found for concentric (27%) and eccentric (20%) dorsiflexor peak torque and concentric rate of torque production (20%-53%) across all movement velocities (p < .01). Training also significantly increased dorsiflexor concentric (64%) and eccentric (55%) surface electromyography; taken together, this is evidence of apparent adaptation of neural factors in older adults with short-term training. These findings support that eccentric and concentric strength training enhances the control and production of ankle muscle dorsiflexor torque in older adults, with implications for improving functional mobility of the ankle joint.

Aged↗
PubMedDate not supplied

Electrical cortical activity associated with joint torque direction in the human arm.

The objective of this study is to determine whether electrical brain activity differs for static joint torques generated in the elbow flexion/extension and shoulder abduction/adduction directions in humans. Electrical brain activity was quantified using a technique that incorporates a realistic, subject-specific electromagnetic head model to create a three-dimensional spatial resultant vector representation of the cortical region of activation. The findings demonstrate that generation of torque in each of the four directions produced significantly different locations of centers of cortical activation. These differences in location were maintained from preparatory to the early execution phases of the task. The organization of the centers of cortical activity during the generation of elbow/shoulder torques resulted in centers associated with the generation of elbow torques that were more lateral than centers accompanying shoulder torques in all five subjects tested. The authors conclude that electrical brain activity is spatially organized during the generation of joint torques in opposing directions at the elbow and shoulder joints. In addition, the results indicate that the center of the electrical brain activity associated with these static tasks is localized over the primary motor cortex as opposed to secondary sensorimotor cortices.

Adult↗
PubMed2005

Analysis of torque and force with differently tapered rotary endodontic instruments in vitro.

The aim of this study was to compare torques and forces developed by two sequences of nickel-titanium rotary instruments, using only .04 taper instruments or a combination of .04 and .06 tapers, respectively. Curved canals in plastic blocks were shaped in a torque-testing device; torque, force, contact areas and numbers of working rotations were determined. Analysis of variance and Pearson correlation coefficients were used to compare the two sequences. Mean torque ranged from 0.2 +/- 0.03 to 3.19 +/- 0.28 Ncm and was higher for instrument sizes 25 to 45 in group A. Mean vertical forces ranged from 1.49 +/- 0.54 to 12.0 +/- 3.5 N; there were significant correlations between torque and force as well as between torque and contact areas. Numbers of rotations were lower in the combined .04 and .06 sequence. An instrumentation sequence encompassing various tapers seems to be safer regarding torsional and fatigue failure compared to a sequence that used one single taper. However, the former sequence requires the use of more instruments.

Analysis of Variance↗
PubMed2005

Influence of professional dance training on peak torque and proprioception at the ankle.

OBJECTIVE: To investigate the influence of professional dance training on the peak torque ratio of plantar flexion to dorsiflexion (PF/DF), angle replication ability, and balance in comparison to age-matched and gender-matched controls. The effects of injuries sustained before and during the study time period were also assessed. DESIGN: Prospective age-matched and gender-matched nonrandomized intervention study. SETTING: Premises of the Orthopedic University Hospital, Heidelberg, where measuring apparatus belonging to the hospital was used for the tests. PARTICIPANTS: One group of 42 dancers (31 female, 11 male) in professional training (State Academy) and 40 age-matched and gender-matched controls with no prior dance or specific sport training. MAIN OUTCOME MEASUREMENTS: Isokinetic tests for peak torque at 30 degrees /s and 120 degrees /s, a passive angle-replication test (Biodex system 3), and a test of 1-legged standing were each carried out on 2 measurement dates (M1, M2): at the beginning of a season of professional dance training (M1) and after 5 months of such training (M2). Symptoms and/or injuries sustained during this period were ascertained continuously by means of questionnaires and interviews. RESULTS: A significant increase in peak torque in PF was observed in both dancer groups and male controls between M1 and M2. A significant increase in PF/DF peak torque ratio at 30 degrees /s was observed in both male groups between M1 and M2. At M2, no significant differences in PF/DF peak torque ratio could be found between male dancers and controls, but at 30 degrees /s between the female groups. However, in both female groups, the PF/DF ratio was not found to increase significantly between M1 and M2. In the angle-replication and 1-legged standing test, no consistent improvement was observed between M1 and M2 in either dancers or controls. In the angle-replication test, there were no significant differences between dancers and controls at M2. In the 1-legged standing test, the dancers did significantly better than controls. A total of 7 ankle injuries were recorded, but no difference was found between injured and uninjured subjects in the proprioceptive tests either at M1, as the predicator, or at M2 as the residual. CONCLUSIONS: Dance training did not increase the peak torque ratio of PF/DF within 5 months, but a group difference was found between the women groups. Ballet training alone without concurrent additional coordinative training does not lead to improvements in ankle joint position sense or improved measures of balance within this period of observation.

Adolescent↗
PubMed2006

Percentile values of isokinetic peak torque in children six through thirteen years old.

PURPOSE: The purpose of this study was to standardize an isokinetic testing protocol for quadriceps and hamstrings in children who are typically developing and are six through 13 years of age, to establish percentile charts of isokinetic peak torque strength for quadriceps and hamstrings by gender and age, and to determine the best predictors of strength for each of three testing speeds. METHODS: A total of 3587 children were tested for isokinetic knee strength according to our protocol on Biodex System II and III isokinetic dynamometers. Therapists participating in the study were trained on the protocol and inter-rater reliability was established. Both dominant and nondominant legs were tested at three speeds. Data were collected on peak torque, time to peak torque, and agonist/antagonist ratio. Data were also gathered on maturation level, gender, height, weight, leg length, laterality, and activity level to allow for investigation of correlations with peak torque. All data were entered in an Excel spreadsheet. RESULTS: Percentile charts of normal isokinetic muscle strength were generated using SPSS 12.0 for each age and gender at three speeds (60, 120, and 180 degrees per second). Stepwise regression analysis determined height to be the best predictor of peak torque for both quadriceps and hamstrings at all speeds. CONCLUSIONS: This study is the first to report normative peak torque values for quadriceps and hamstrings in children. By using a standardized testing protocol and normative data, clinicians will be able to assess the degree of muscle weakness as well as the effectiveness of intervention strategies.

Adolescent↗
PubMed2005

Stripping torque as a predictor of successful internal fracture fixation.

BACKGROUND: Internal fixation of fractures using plates and screws is a common method of treatment. Occasionally the internal fixation fails prior to fracture healing. This often requires revision surgery. Determining the force that internal fixation needs to withstand postoperatively would enable this force to be applied intraoperatively as a test to predict successful fixation. The purpose of the present paper was to determine the minimum stripping torque needed to predict successful internal fixation strength. METHODS: The pull-out strength and stripping torque relationships of 4.5-mm cortical bone screws in Sawbones polyurethane foam were determined. Screw forces were directly measured using an LCM load cell washer on a model intertrochanteric neck of femur fracture fixed with 135 degrees 4-hole pin and plate loaded to single leg stance conditions. Additionally a 135 degrees 4-hole pin and plate was mounted on foam blocks and loaded until failure of the shaft screws from the foam occurred. Predicted stripping torque/yield load was determined. RESULTS: Pull-out strength and stripping torque of 4.5-mm cortical bone screws in polyurethane foam have a high degree of linear correlation R(2) = 0.95. Direct measurement of shaft screw forces at single leg stance conditions were 585-686 N. This correlated with a stripping torque of 0.9 Nm. Load to yield testing at single leg stance conditions corresponded to a stripping torque of 1.8 Nm. CONCLUSION: Withstanding 0.9-1.8 Nm of torque during insertion of the femoral shaft screws of a 135 degrees 4-hole pin and plate predicts that the construct will successfully withstand single leg stance.

Bone Nails↗
PubMed1999

Effects of age on the reciprocal peak torque ratios during knee muscle contractions in elite soccer players.

To investigate the effects of age on the reciprocal peak torque ratios during knee muscle contractions, 25 elite male soccer players, aged 22.3 +/- 3.8 yr (18-28), volunteered for the present study. The players were grouped as adult (> 21 years, n = 13) and young players (< or = 21 years, n = 12). Maximal concentric (CON) and eccentric (ECC) isokinetic thigh muscle strength was measured at angular velocities of 30 degrees, 180 degrees, 240 degrees and 300 degrees/s. ECC and CON peak torques of knee flexors (hamstring, HAM) and CON peak torques of knee extensors (quadriceps, QUA) in the dominant knee were greater (P < 0.05) in adult players than in young players at 180, 240 and 300 degrees/s. ECC HAM/CON QUA peak torque ratio at 300 degrees/s was greater (P < 0.05) for adult players compared to young players in the dominant knee but not in the nondominant knee. Furthermore, conventional HAM/QUA peak torque ratios of the dominant knee at all angular velocities for ECC contraction were higher (P < 0.05) in adult players than in young players. In conclusion, the findings of the present study indicate that the reciprocal torque ratio is influenced by age in the dominant knee of elite soccer players. Because there was no effect of age for the nondominant leg, the findings of the present study are more likely to be the result of the training background of the players than their age.

Adolescent↗
PubMed2004

Cutting torque measurements in conjunction with implant placement in grafted and nongrafted maxillas as an objective evaluation of bone density: a possible method for identifying early implant failures?

BACKGROUND: Bone grafts are frequently used to enable the placement of dental implants in atrophied jaws. The biomechanical properties of bone grafts used in one- or two-stage implant procedures (in comparison with the use of nongrafted bone) are not well known. PURPOSE: The purpose of this study was (1) to measure cutting torques during the placement of self-tapping dental implants in nongrafted bone and in bone grafts, either as blocks or in a milled particulate form, in patients undergoing implant treatment in an edentulous maxilla and (2) to identify implants with reduced initial stability and to correlate these findings with a clinical classification of jawbone quality. MATERIALS AND METHODS: The study included 40 consecutive patients with edentulous maxillas, 27 of whom were subjected to bone grafting prior to or in conjunction with implant placement (grafting group) and 13 of whom received implants without grafting (nongrafted group). Grafted bone from the iliac crest bone was used (1) as onlay blocks, (2) as maxillary sinus inlay blocks, or (3) in particulate form in the maxillary sinus. Implants were placed after 6 to 7 months of healing, except in the maxillary sinus inlay blocks, where implants were placed simultaneously. Cutting torque values were obtained from 113 grafted implant sites and from 109 nongrafted implant sites. RESULTS: Significantly lower cutting torque values were assessed in grafted regions than in nongrafted regions, irrespective of grafting technique. Lower values were also seen for implants placed in block grafts after 6 months when compared to other grafting techniques used. The cutting torque values revealed an inverse linear relation to the Lekholm and Zarb bone quality index. CONCLUSION: The cutting torque values correlated well with the Lekholm and Zarb index of bone quality. Significantly lower cutting torque values were seen in grafted bone than in nongrafted bone.

Alveolar Bone Loss↗