Biomechanical analysis of the press-fit effect in a conical Morse taper implant system by using an in vitro experimental test and finite element analysis.

STATEMENT OF PROBLEM: The press-fit (Morse taper) implant system is commonly used to restore edentulous areas. However, abutment screws in this system may be damaged because of the 2- or 3-piece design, consequently causing complications. How these damaging situations occur is unclear. PURPOSE: The purpose of this in vitro and finite element analysis (FEA) study was to elucidate the mechanisms of the press-fit implant system underlying abutment screw damage. MATERIAL AND METHODS: The ANKYLOS implant system was used as a simulation model and for experimental test specimens. The experimental test was performed by using a material test system, and the obtained data were used to validate the FEA outcome. In the FEA simulation, the bilinear material property and nonlinear contact conditions were applied to simulate the process of tightening the abutment screw between the abutment and implant. A force of 300 N was then applied to the abutment to investigate the stress distribution and deformation of the implant system. RESULTS: In the experimental test, the fracture site of all specimens was observed at the abutment-screw thread. All implants and abutments exhibited permanent bending deformation. The results of the FEA simulation generally concurred with the experimental outcomes. CONCLUSIONS: The abutment torque used to generate the press-fit contact interface between the abutment and implant induced stresses within the implant components, substantially increasing the failure probability of the conical implant system during function.

Mechanical analysis of a dental implant system under 3 contact conditions and with 2 mechanical factors.

STATEMENT OF PROBLEM: A unidiameter abutment attached to a large-diameter implant has been reported to result in an unexpectedly high failure rate, inconsistent with the general understanding of dental implant mechanics. PURPOSE: The purpose of this finite element analysis study was to investigate the mechanical mechanism underlying these unexpected failures with the hypothesis that the cold welding or interference fit interface between abutment and implant increases the failure probability of a large-diameter implant system with a unidiameter abutment. MATERIAL AND METHODS: A conical implant system with different abutment gingival heights and implant diameters was analyzed for 3 contact conditions of the abutment-implant interface (bond and frictional coefficients of 0.3 and 0.7). A computer model was created using computed tomography images, and an oblique load of 100 N was applied to the abutment to determine the mechanical effect of the implant diameter and gingival height under the 3 contact conditions. RESULTS: When the abutment-implant interface was bonded, the peak stress of the abutment increased and that of the bone decreased with increasing implant diameter. When friction was applied to the abutment-implant interface, the peak stress of the implant, screw, and bone decreased with increasing implant diameter. Furthermore, the peak stress of the implant system and bone increased when the abutment gingival height increased under all contact conditions. CONCLUSIONS: Cold wielding or interference fit at the abutment-implant interface can prevent a screw fracture; however, it puts high stress on the unidiameter abutment neck when the implant diameter is increased. Screw loosening may lead to a slide between the abutment and implant, considerably increasing the stress of the screw. A system with a narrow diameter implant may cause an implant fracture rather than an abutment fracture when friction is applied to the abutment-implant interface.

Predicting the holistic force-displacement relation of the periodontal ligament: in-vitro experiments and finite element analysis.

BACKGROUND: The biomechanical property of the periodontal ligament (PDL) is important in orthodontics and prosthodontics. The objective of this study was to evaluate the feasibility of measuring the biomechanical behavior of the periodontal ligament using micro-computed tomography (micro-CT). METHODS: A custom-made apparatus measured the force and displacement of a porcine PDL specimen within the micro-CT environment. Synchronized computed tomography (CT) images were used to obtain the deformation and displacement of the entire specimen and to reconstruct the three-dimensional mesh model. To match the experimental results, finite element analysis was then applied to simulate the biomechanical response of the PDL. The mechanical model of the PDL was assumed as the hyperelastic material in this study. RESULTS: The volume variations of the tooth and the alveolar bone were less than 1%, which implies that tooth displacement was caused mostly by displacement of the PDL. Only translational displacement was observed with each load step because the transformation matrix acquired from the CT image registration was identical. The force-displacement curve revealed the nonlinear behavior of the PDL. There was a high correlation between the experimental displacement results and the simulation displacement results. The numerical results (based on the assumption that the PDL is the hyperelastic material) showed good agreement with the experimental results. CONCLUSIONS: Nondestructive measurements by micro-CT obtained the biomechanical behavior of the PDL. Using the hyperelastic characteristic as the constitutive model can properly predict the force-displacement relation of the PDL after loading. This study provided a feasible approach for measuring the biomechanical behavior of the PDL for further dental application.

Assessments of polymerization shrinkage by optical coherence tomography-based digital image correlation analysis-Part II: Effects of restorative composites.

OBJECTIVES: To examine the polymerization shrinkage of different resin-based composite (RBC) restorations using optical coherence tomography (OCT) image-based digital image correlation (DIC) analysis. METHODS: The refractive index (RI) of three RBCs, Filtek Z350XT (Z350), Z350Flowable (Z350F), and BulkFill Posterior (Bulkfill), was measured before and after polymerization to calibrate their axial dimensions under OCT. Class I cavities were prepared in bovine incisors and individually filled with these RBCs under nonbonded and bonded conditions. A series of OCT images of these restorations were captured during 20-s light polymerization and then input into DIC software to analyze their shrinkage behaviors. The interfacial adaptation was also examined using these OCT images. RESULTS: The RI of the three composites ranged from 1.52 to 1.53, and photopolymerization caused neglectable increases in the RI values. For nonbonded restorations, Z350F showed maximal vertical displacements on the top surfaces (-16.75 µm), followed by Bulkfill (-8.81 µm) and Z350 (-5.97 µm). In their bonded conditions, all showed increased displacements. High variations were observed in displacement measurements on the bottom surfaces. In the temporal analysis, the shrinkage of nonbonded Z350F and Bulkfill decelerated after 6-10 s. However, Z350 showed a rebounding upward displacement after 8.2 s. Significant interfacial gaps were found in nonbonded Z350 and Z350F restorations. SIGNIFICANCE: The novel OCT image-based DIC analysis provided a comprehensive examination of the shrinkage behaviors and debonding of the composite restorations throughout the polymerization process. The flowable composite showed the highest shrinkage displacements. Changes in the shrinkage direction may occur in nonbonded conventional composite restorations.

Three-dimensional bone structure and bone mineral density evaluations of autogenous bone graft after sinus augmentation: a microcomputed tomography analysis.

OBJECTIVE: The purpose of this study was to determine the relationships and differences in three-dimensional (3D) bone mineral density (BMD) and microtrabecular structures between autogenous bone grafts and their adjacent native bone after a healing period following maxillary sinus augmentation. MATERIALS AND METHODS: Nine rod-shaped human bone biopsy samples were taken from patients receiving two-stage sinus augmentation therapy in implantation areas and analyzed using microcomputed tomography (micro-CT). Before micro-CT scanning, two BMD phantoms were placed near to the bone biopsy samples for executing BMD calculations of the grafted and native bone samples. In addition, 3D structural parameters of the trabeculae were analyzed for both the grafted and native bone, including percentage of bone volume [bone volume (BV)/tissue volume (TV)], bone-specific surface [bone surface (BS)/BV], trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), trabecular pattern factor (Tb.Pf), and structure model index (SMI). RESULTS: No significant correlations with regard to BMD and trabecular-structure parameters were found between native bone and grafted bone; however, BS/BV and Tb.Pf were higher and Tb.Th and Tb.Sp were 37.35% and 12.74% lower in grafted bone than in native bone. For grafted bone, there were significant correlations (P < 0.05) between BMD and BV/TV, and Tb.N. CONCLUSIONS: When using autogenous bone as a graft material, BMD and micromorphological conditions of grafted bone were not influenced by the condition of the native bone in the maxilla. Differences were found in surface complexity, trabecular thickness, trabecular separation, and the connectivity of trabeculae between grafted and native bone. The BMD in grafted bone was affected by the quantity of the trabeculae.

Relation between insertion torque and bone-implant contact percentage: an artificial bone study.

OBJECTIVES: The purpose of this study was to determine the correlation between the peak insertion torque value (ITV) of a dental implant and the bone-implant contact percentage (BIC%). MATERIAL AND METHODS: Dental implants were inserted into specimens comprising a 2-mm-thick artificial cortical shell representing cortical bone and artificial foam bone representing cancellous bone with four densities (groups 1 to 4--0.32, 0.20, 0.16, and 0.12 g/cm(3)). Each specimen with an inserted implant was subjected to micro-computed tomography (micro-CT) scanning, from which the 3D BIC% values were calculated. Pearson's correlation coefficients (r) between the ITV and BIC% were calculated. RESULTS: The ITVs in groups 1 to 4 were 56.2 ± 4.6 (mean±standard deviation), 45.6 ± 0.9, 43.3 ± 4.3, and 38.5 ± 3.4 N cm, respectively, and the corresponding BIC% values were 41.5 ± 0.5%, 39.0 ± 1.0%, 30.8 ± 1.1%, and 26.2 ± 1.6%. Pearson's correlation coefficient between the ITV and BIC% was r = 0.797 (P < 0.0001). CONCLUSION: The initial implant stability, quantified as the ITV, was strongly positively correlated with the 3D BIC% obtained from micro-CT images. CLINICAL RELEVANCE: The ITV of a dental implant can be used to predict the initial BIC%; this information may provide the clinician with important information on the optimal loading time.

Bone stress when miniplates are used for orthodontic anchorage: finite element analysis.

INTRODUCTION: The success rate of miniplates is superior to that of other temporary anchorage devices; nevertheless, the biomechanical behavior of miniplates during orthodontic use is not totally understood. The aim of this study was to investigate bone stress by finite element analysis when miniplates are used for orthodontic anchorage. METHODS: A 3-dimensional model consisting of a bone block integrated with a miniplate and fixation screw system was constructed to simulate various types of miniplates, screw numbers, screw lengths, cortex thicknesses, and force magnitudes and directions. RESULTS: The peak von Mises cortex stress values were highest with the I-type plates followed by the L-type, Y-type, and T-type plates. Bone stress decreased as the screw numbers increased but was not related to screw length. Bone stress increased as the cortex thickness decreased. Bone stress was linearly proportional to the force magnitude, and the highest values were produced when the force was in the forward direction. CONCLUSIONS: When a T- or Y-type plate is used, or when the force direction is in the tensile mode, bone stress decreases. Bone stress also decreases as the screw numbers increase and as the cortex thickness increases. Furthermore, it decreases as the force magnitude becomes less.

Finite element analysis of miniscrew implants used for orthodontic anchorage.

INTRODUCTION: The miniscrew has been developed and effectively used as orthodontic anchorage, but current studies of its usage are insufficient to provide information about the underlying mechanical mechanisms. The aim of this study was to investigate the roles of bone quality, loading conditions, screw effects, and implanted depth on the biomechanics of an orthodontic miniscrew system by using finite element analysis. METHODS: A 3-dimensional model with a bone block integrated with a miniscrew was constructed to simulate various cortex thicknesses, cancellous bone densities, force magnitudes and directions, screw diameters and lengths, and implanted depths of miniscrews. RESULTS: Both stress and displacement increased with decreasing cortex thickness, whereas cancellous bone density played a minor role in the mechanical response. These 2 indexes were linearly proportional to the force magnitude and produced the highest values when the force was perpendicular to the long axis of the miniscrew. A wider screw provided superior mechanical advantages. The exposed length of the miniscrew was the real factor affecting mechanical performance. CONCLUSIONS: The screw diameter was the dominant factor for minscrew mechanical responses. Both bone stress and screw displacement decreased with increasing screw diameter and cortex thickness, and decreasing exposed length of the screw, force magnitude, and oblique loading direction.

Influence of post material and length on endodontically treated incisors: an in vitro and finite element study.

STATEMENT OF PROBLEM: Cast posts require sufficient length for prosthesis retention and root strength. For prefabricated metal and fiber posts, the effects of different post lengths on the strength and internal stress of the surrounding root need evaluation. PURPOSE: The purpose of this study was to examine, using both experimental and finite element (FE) approaches, the influence of post material and length on the mechanical response of endodontically treated teeth. MATERIAL AND METHODS: Sixty extracted incisors were endodontically treated and then restored with 1 of 3 prefabricated posts: stainless steel (SS), carbon fiber (CF), and glass fiber (GF), with intraradicular lengths of either 5 or 10 mm (n=10). After composite resin core and crown restorations, these teeth were thermal cycled and then loaded to fracture in an oblique direction. Statistical analysis was performed for the effects of post material and length on failure loads using 2-way ANOVA (α=.05). In addition, corresponding FE models of an incisor restored with a post were developed to examine mechanical responses. The simulated tooth was loaded with a 100-N oblique force to analyze the stress in the root dentin. RESULTS: The SS/5 mm and all fiber post groups presented no statistical differences, with mean (SD) fracture loads of 1247 to 1339 (53 to 121) N. The SS/10 mm group exhibited a lower fracture load, 973 (115) N, and a higher incidence of unfavorable root fracture (P<.05). The FE analysis showed high stress around the apical end of the long SS post, while stress was concentrated around the crown margins in the fiber post groups. CONCLUSIONS: Both long and short fiber posts provided root fracture resistance comparable to that of SS posts. For metal posts, extending the post length does not effectively prevent root fracture in restored teeth.

The effect of microrough surface treatment on miniscrews used as orthodontic anchors.

OBJECTIVES: The aim of this study was to investigate the effects of two different microrough surface treatments on miniscrews with loading over different time periods in vivo. MATERIAL AND METHODS: Twenty-four New Zealand white rabbits were selected. One hundred and forty-four miniscrews with a machined (MA), sandblasted and acid-etched (SLA) or sandblasted and alkaline-etched (SL/NaOH) surface were implanted into the tibia of the rabbits. Then, orthodontic forces with Ni-Ti coils were applied immediately to two of the three miniscrews in each tibia, with the center one serving as the control. After 2, 4, 8 and 12 weeks, the rabbits were sacrificed. The removal torque value (RTV) was tested and bone-to-implant contact (BIC) was examined. RESULTS: In most groups, there were no differences between the RTV in the unloaded and loaded conditions at different time periods. In the loaded condition, the RTV of the SLA groups increased significantly after 4 weeks of healing. The RTV in the SL/NaOH groups increased after 8 weeks, and reached a significant difference with the SLA groups after 12 weeks. After 12 weeks, the BIC in the SLA and SL/NaOH groups was higher than in the MA groups. A regression test revealed a moderate correlation between the BIC and the RTV. CONCLUSIONS: There were no differences between the loaded and unloaded conditions in most groups. The RTV and BIC increased with time. In the loaded condition, the RTV of the SLA surface increased earlier, at 4 weeks, while the SL/NAOH group showed the highest RTV after 8 weeks.

Effect of fluoridated carbamide peroxide gels on enamel microtensile bond strength.

The aim of this study was to examine the resin bond strength on enamel treated with different fluoridated bleaching agents. Forty-eight bovine incisors were divided into four groups to receive bleaching treatments, over a 14-d period, as follows: no treatment; 10% carbamide peroxide (CP) bleaching; 10% CP containing 0.11% fluoride; and 10% CP containing 0.37% fluoride. Immediately, and 7 and 14 d after bleaching, the enamel surfaces were respectively bonded with composite and sectioned to create resin-enamel beams. These beams were subjected to the microtensile bond strength (microTBS) test, then assessed for failure mode under scanning electron microscopy. The results showed that the 0.37% fluoridated group demonstrated a microTBS equivalent to that of the unbleached group at all stages. Non-fluoridated and 0.11% fluoridated groups showed a weaker microTBS after bleaching but regained the bond strength after 14 or 7 d of storage, respectively. In the non-fluoridated group, adhesive failure was the predominant fracture pattern that comprised the enamel prism demineralization change and widely dispersed voids on the resin-enamel interfaces. No evident enamel erosion and fewer microporosities were found in the 0.37% fluoridated group. Accordingly, treatment with 0.37% fluoridated CP maintained the microTBS as effectively as the unbleached enamel. Additional fluoride in the bleaching agents may facilitate subsequent restorative treatment by inhibiting enamel demineralization.

Effect of fluoride containing bleaching agents on enamel surface properties.

OBJECTIVES: To evaluate the effects of fluoridated bleaching agents and post-bleaching fluoridation treatment on the whitening efficiency and microhardness of bovine enamel. METHODS: Twenty five freshly extracted bovine incisors were cut into halves, embedded and then divided into the following five groups: Group 1, untreated controls; Group 2, treatment with 10% carbamide peroxide (CP) bleaching agent; Group 3, treatment with 10% CP followed by a 0.9% sodium fluoride gel application, Group 4, treatment with 10% CP containing 0.11% fluoride; Group 5, treatment with an experimental bleaching agent consisting of 10% CP and 0.37% fluoride. Groups 2-5 were treated 8h per day for 14 days then immersed in saliva for 2 weeks. Enamel morphology changes were evaluated under SEM on Day 14. Changes in enamel color and microhardness were evaluated on Days 7 and 14, and compared with the baseline data. Additionally, microhardness was determined on post-bleaching Days 21 and 28. RESULTS: After 2 weeks, an erosion pattern was noted on the specimens in Groups 2 and 3. Groups 4 and 5 showed a milder demineralized pattern. All the bleached enamel specimens revealed increased whiteness and overall color value. Groups 2 and 3 showed significantly decreased enamel microhardness compared to their baseline data. The specimens treated with fluoridated bleaching agents showed relatively less reduction in enamel microhardness than those treated with nonfluoridated agents during the bleaching treatment. CONCLUSIONS: The fluoridated bleaching agents produced less demineralization of surface morphology and microhardness. The addition of fluoride did not impede the whitening effect.

The number of screws, bone quality, and friction coefficient affect acetabular cup stability.

One of the major causes of loosening of cementless acetabular cup implants is insufficient initial stability. This study used three-dimensional finite element models of the pelvis and acetabular components to investigate the effects of the number of screws, bone quality, and friction coefficient of the acetabular cup on the initial stability under normal walking. A commercially available hemispherical acetabular cup with five screw holes was used as the default model. The stiffness of the pelvis and the friction coefficient of the cup were systematically varied, within a realistic range, to assess the initial stability of the acetabular cup. The simulations showed that the inserted screws provide only a localized reduction in the relative micromotion between the cup and pelvis therefore inserting several screw closed together might not be useful. Changes in the pelvic stiffness have a non-linear effect on the initial stability of acetabular cup and the subchondral bone provides good support for fixation of the cementless cup. The friction coefficient of the acetabular cup plays a limited role, comparing with the factor of bone quality, in resisting relative micromotion in the cup-pelvis interface.

A novel conversion method for radiographic guide into surgical guide.

BACKGROUND: The study proposed a novel method for converting a radiographic guide into a surgical guide and evaluated its accuracy. MATERIALS AND METHODS: Radiographic guide was reformed with the addition of index rods for geometric conversion method (GCM). Planning implants were projected on geometric projection planes, and the implant positions were measured. The radiographic guide was converted into surgical guide using a generic bench drill machine with GCM data. Two experiments were designed to validate the GCM. (1) In vitro test: Twenty implants were placed on five edentulous dental models by using the GCM (group 1) and Stereolithography (SLA) method (group 2), respectively. The deviations of planned and placed implant were calculated, and the precision error (PE) value was calculated to evaluate the stability of the GCM and SLA. (2) In vivo test: Nine edentulous subjects were selected for clinical implant surgery with the GCM guide. Two level of the index rods of radiographic guides were prepared for surgical guides forming. The differences between the planned and actual implants were calculated in implant head, apex, and angulation. RESULTS: The in vitro test revealed no significant differences in the planned and placed angulations between groups 1 and 2 (P > .05). The PE was not significantly different between groups 1 and 2 (P > .05). The in vivo test revealed a successful treatment of the subjects, and 16 implant sites were evaluated. The results indicated that GCM guide could achieve the three-dimensional (3D) offset deviations of 1.03 ± 0.27 mm and 1.17 ± 0.24 mm at the implant head and apex, respectively, and 1.37° ± 0.21° for the 3D angulation. CONCLUSION: The novel method for converting a radiographic guide into a surgical guide appears accurate and stable compared with SLA.

Influence of enamel wetness on resin composite restorations using various dentine bonding agents: part I-effects on marginal quality and enamel microcrack formation.

OBJECTIVES: To investigate the influence of enamel wetness on marginal quality and enamel microcrack formation using various dentine bonding adhesives; and to determine the changes of marginal quality and enamel microcracks over time. METHODS: Forty extracted molars were each prepared with a cylindrical cavity and divided into five groups. Groups 1-4 were acid-etched and treated separately with either an ethanol-based adhesive (Single Bond) or an acetone-based adhesive (Prime&Bond NT) on either dry or wet enamel. Teeth in Group 5 were treated with a self-etching adhesive (Clearfil SE Bond). Epoxy replicas of different stages were taken after cavity preparation, after restoration, after 24 h storage, and after thermocycling test. These replicas were examined under a scanning electron microscope for their restorative marginal quality and enamel microcrack. Quantitative measurement was performed to measure the length ratio of different margin patterns, and enamel microcracks. RESULTS: There was no difference in the marginal quality when ethanol-base adhesive was applied on dry or wet dentin. The group using acetone-based adhesive on the dry enamel presented higher intact margin ratio than the group on wet enamel did only after restoration. Using self-etching primer led to higher open margin ratio at all stages. Enamel microcracks were found in all five groups and were higher in groups using acetone-based adhesives. CONCLUSION: Enamel wetness did not show a significantly adverse effect on the marginal quality of the restorations using either acetone- or ethanol-based adhesive. Using self-etching adhesive may lead to high incidence of margin deterioration.

Influence of enamel wetness on composite restorations using various dentine bonding agents: part II-effects on shear bond strength.

OBJECTIVES: To investigate the bond strength and fracture characteristics of various dentine bonding agents (DBAs) on wet or dry enamel. METHODS: Forty molar halves with enamel flattened were divided into 5 groups. Groups 1-4, teeth were acid-etched and treated separately with either an ethanol-based adhesive (Single Bond) or an acetone-based adhesive (Prime & Bond NT) on dry or wet enamel. Group 5 was treated with a self-etching adhesive (Clearfil SE Bond). The treated enamel surfaces were bonded with Z 250 composite with metal rings. The composite-ring assemblies were subjected to shear bond test until failure. Failure patterns on the debonded surfaces were inspected under a scanning electron microscope. The bonded enamel thickness was measured on sectioned specimens to investigate their statistical evidence. Results of open margin and enamel microcrack ratios from Part I of this study were compared with these fracture characteristics. Data was analyzed statistically. RESULTS: There was no difference in the bond strength between paired groups using the same DBA on wet or dry enamel. The teeth restored with self-etching adhesive exhibited lower bond strength and higher adhesive-enamel failure rate than the other groups. No correlation between enamel thickness, microcrack, bond strength, and failure patterns was revealed. CONCLUSION: The self-etching adhesive had a lower enamel bond strength than the other bonding systems. The difference in the failure patterns of groups with ethanol- and acetone-based DBAs on wet or dry enamel was indistinct. The frequently observed enamel microcrack cannot be directly correlated with the bond strength of bonding systems.

Thin-plate spline analysis of the effects of face mask treatment in children with maxillary retrognathism.

BACKGROUND: Face mask therapy is indicated for growing patients who suffer from maxillary retrognathia. Most previous studies used conventional cephalometric analysis to evaluate the effects of face mask treatment. Cephalometric analysis has been shown to be insufficient for complex craniofacial configurations. The purpose of this study was to investigate changes in the craniofacial structure of children with maxillary retrognathism following face mask treatment by means of thin-plate spline analysis. METHODS: Thirty children with skeletal Class III malocclusions who had been treated with face masks were compared with a group of 30 untreated gender-matched, age-matched, observation period-matched, and craniofacial configuration-matched subjects. Average geometries, scaled to an equivalent size, were generated by means of Procrustes analysis. Thin-plate spline analysis was then performed for localization of the shape changes. RESULTS: Face mask treatment induced a forward displacement of the maxilla, a counterclockwise rotation of the palatal plane, a horizontal compression of the anterior border of the symphysis and the condylar region, and a downward deformation of the menton. The cranial base exhibited a counterclockwise deformation as a whole. CONCLUSION: We conclude that thin-plate spline analysis is a valuable supplement to conventional cephalometric analysis.

Morphometric analysis of mandibular growth in skeletal Class III malocclusion.

BACKGROUND: The craniofacial growth patterns of untreated individuals with skeletal Class III malocclusion have rarely been systemically investigated. This study used morphometric techniques to investigate the growth characteristics of the mandible in individuals with skeletal Class III malocclusion. METHODS: Lateral cephalometric head films of 294 individuals with untreated skeletal Class III malocclusion (134 males, 160 females) were selected and divided into five triennial age groups (T1-T5) and by gender to identify the morphologic characteristics and sexual dimorphism in changes of mandibular growth. Procrustes, thin-plate spline, and finite element analyses were performed for localization of differences in shape and size changes. Maximum and minimum principal axes were drawn to express the directions of shape changes. RESULTS: From T1 (age 6-8 years) to T4 (age 15-17 years), the distribution of localized size and shape changes of the mandible was very similar between the two genders. From T1 to T2 (age 9-11 years), significant lengthening of the condylar region was noted (23.4-39.7%). From T2 to T3 (age 12-14 years), the greatest size and shape change occurred at the condylar head (27.4-34.9%). From T3 to T4, the greatest size and shape changes occurred in the symphyseal region (23.6-42.1%). From T4 to T5 (age>or=18 years), significant sexual dimorphism was found in the distribution and amount of localized size and shape changes. Females displayed little growth increments during T4. Despite differences in the remodeling process, the whole mandibular configurations of both genders exhibited similarly significant upward and forward deformation from T4 to T5. CONCLUSION: We conclude that thin-plate spline analysis and the finite element morphometric method are efficient for the localization and quantification of size and shape changes that occur during mandibular growth. Plots of maximum and minimum principal directions can provide useful information about the trends of growth changes.

An intra-oral hydraulic system for controlled loading of dental implants.

This study reports a method for controlling loads on an in vivo dental implant and its application for the investigation of early loading versus delayed loading of dental implants. The method was developed for the purpose of studying an ongoing hypothesis that amounts to bone loss around dental implants are related to mechanical-mediated adaptation of the alveolar bone. Using a customized intra-oral hydraulic system, the daily loading over a dental implant has been completed and recorded for six Sinclair swine. Each pig had a 5-month duration implant loading. During the experiments (loading), no analgesic treatment was supplied. The mean of the in vivo daily loadings was confirmed through an in vitro bench test after each animal was euthanized. Variations of the averaged loading input among the six animals were smaller than 10%. Preliminary data produced by the model suggests that cervical bone loss is less for early loading than for delayed loading. The current system is expected to provide a useful load control model for the study of alveolar bone adaptation around dental implants in relation to various loadings.

Effects of liner stiffness for trans-tibial prosthesis: a finite element contact model.

The socket liner plays a crucial role in redistribution of the interface stresses between the stump and the socket, so that the peak interface stress could be reduced. However, how the peak stress is affected by various liner stiffnesses is still unknown, especially when the phenomenon of the stump slide within the socket is considered. This study employed nonlinear contact finite element analyses to study the biomechanical reaction of the stump sliding with particular attention to the liner stiffness effects of the trans-tibial prosthesis. To validate the finite element outcomes, experimental measurements of the interface stresses and sliding distance were further executed. The results showed that the biomechanical response of the stump sliding are highly nonlinear. With a less stiff liner, the slide distance of the stump would increase with a larger contact area. However, this increase in the contact area would not ensure a reduction in the peak interface stress and this is due to the combined effects of the non-uniform shape of the socket and the various sliding distances generated by the different liner stiffnesses.