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Biomedical subjects

A A Caputo

Publications and source records attributed to A A Caputo.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effects of periodontal support and fixed splinting on load transfer by removable partial dentures.

STATEMENT OF PROBLEM: Periodontally compromised abutment teeth complicate the design of bilateral distal extension removable partial dentures. PURPOSE: This study investigated the stress induced in the remaining oral structures by a bilateral distal extension I-bar-retained RPD with periodontally involved abutments in a photoelastic simulation model. MATERIAL AND METHODS: Composite photoelastic models were used as a simulation model in determining the stress generating characteristics of I-bar RPDs with varying degrees of periodontal involvement of the distal abutments. Effects of fixed splinting were considered. RESULTS AND CONCLUSIONS: Under the same load conditions, the highest stresses developed in the model with the largest osseous defect. Increasing the number of splinted teeth did not provide a proportional decrease in maximum stress levels. The more severe the osseous defect, the greater assistance was provided by splinting to periodontally sound teeth. This simulation study suggests that routine cross-arch splinting may not be appropriate.

Acrylic Resins↗
PubMed1998

Characteristics of headgear release mechanisms: safety implications.

The risk of serious eye injury caused by a headgear appliance is a significant concern. Various safety release mechanisms have been developed in order to help prevent this type of injury, but little testing has been done. The purpose of this study was to test 18 headgear release mechanisms. Four characteristics were evaluated: force at release, extension at release, consistency of release, and performance at different rates of pull. At the point of release, mean force values ranged from 5.33 pounds to 32.83 pounds, and mean extension values ranged from 0.84 inches to 2.93 inches. Consistency was based on the percent standard deviation, and the appliances were ranked relative to each other. Nine of the 18 appliances had statistically significant differences in the two pull rates for either variable or both, but the clinical significance is uncertain. The results show a wide range of performance among the 18 appliances tested and indicate that some perform better than others.

Analysis of Variance↗
PubMed1997

Torsion-axial force characteristics of SR-PLLA screws.

The torsion axial-force characteristics of biodegradable screws are central to their ability to generate interfragmentary compression when used as lag screws. The purpose of this investigation was to compare the torsion-axial force characteristics of prototype self-reinforced poly-L-lactide (SR-PLLA) screws with conventional titanium screws. Axial forces developed by incremental increases in the torque applied to the individual screws were measured in a test apparatus incorporating an Instron machine. For the SR-PLLA screws, the relationship between applied torque and axial force development was non-linear with a marked relaxation throughout the test range. The axial forces reached a maximum with increasing torque, after which failure of the screws occurred. The response curve for titanium screws of the same length demonstrated a steeper slope. No failures or force relaxation were observed with the titanium screws. The results of this investigation suggest that, at this time, the use of SR-PLLA screws for lag screw fixation should be restricted to low stress bearing areas.

Biodegradation, Environmental↗
PubMed1996

Strength of porcelain fused to titanium beams.

The purposes of this study were to measure strengths of layered porcelain fused to titanium beams, determine failure modes, and investigate the porcelain-titanium interface. A three-point flexural test and formulas derived especially for this purpose were used. The strength of layered porcelain-ceramic beams was limited by the cohesive tensile or compressive strengths of the porcelain, not by the porcelain-titanium interfacial bond, namely, the porcelain failure occurred at lower loads than did failure of the porcelain-titanium interface. The porcelain-titanium bond strength was at least 26 MPa. Scanning electron microscopy and energy-dispersive x-ray spectroscopy demonstrated that the bond was limited by delamination of a thin titanium-titanium oxide interface. Theoretic curves that describe effects of relative layer and total thickness on the force-bearing capacity of model beams were plotted. These curves indicated that porcelain-titanium prostheses should be made as thick as is practical, but the relative thickness of the porcelain and titanium layers would be less important.

Analysis of Variance↗
PubMed1996

Effects of overdenture retention designs and implant orientations on load transfer characteristics.

Various approaches have been used for the retention and stabilization of implant-supported overdentures. This study examined photoelastically the simulated load transfer characteristics of a resilient cap attachment with moderately atrophied mandibular plastic models with two implant orientations. Comparison was made with overdentures supported by a splinting bar and a bar with distal resilient cap attachments. Stress patterns developed by simulated occlusal loading demonstrated little cross-arch load sharing and more uniform stress distribution with noninclined implants for all retention designs. The most equitable simulated occlusal force transfer was provided by the resilient cap attachments direct to the implants.

Biomechanical Phenomena↗
PubMed1996

Experimental analysis of functional stability of sagittal split ramus osteotomies secured by miniplates and position screws.

PURPOSE: This study determined the relative functional stabilities of various miniplate systems and configurations used to stabilize sagittal split ramus osteotomies (SSROs) and compared them with conventional internal screw fixation. MATERIALS AND METHODS: The biomechanical model was a reproducible prototype of a mandible sagittal osteotomy with consistent material and geometric properties. After advancing the distal segment by 7 mm, each set of mandible analogs (1 set = 3 analogs) was fixed bilaterally by one of three miniplate systems applied in various configurations, and tested with and without a supplemental 2.4-mm bicortical screw applied in the retromolar region. Reduced analogs were placed in a straining frame, and simulated masticatory loads were applied alternatively to the mandibular first molars. Ensuing osteotomy site displacements were measured by transducers attached to a computer-based data acquisition program. A coordinate transformation procedure was used to convert the component displacements captured by the individual transducers into a common "instability factor" to reflect fixation stability for each construct and loading condition. Instability factors for the individual constructs were compared with each other and with those obtained from analogs reduced exclusively with 2.4-mm position screws. RESULTS: Osteotomies stabilized with a combination of miniplates and position screws were more stable than those stabilized exclusively with miniplates (P < .0001). Post-hoc comparisons of mean instability factors (Dunnet's method) showed the miniplate-position screw combinations to be more stable than the 2.4-mm position screw system used as standard (P < .05). Miniplate systems alone were the least stable of the test constructs, with differential rates of failure between the individual miniplate systems. CONCLUSIONS: Exclusive use of miniplate fixation may not provide the consistent stability necessary for early functional restoration after SSROs. The addition of a position screw in the retromolar region substantially enhances the fixation stability of miniplate systems. The use of miniplates with retromolar position screws offers both technical and stability advantages over conventional miniplate or internal screw fixation. The fixation stability of the miniplate-position screw combination is independent of the type of miniplate system used.

Analysis of Variance↗
PubMed1996

Functional stability of sagittal split ramus osteotomies: effects of positional screw size and placement configuration.

PURPOSE: This study examined the effects of positional screw size and placement configuration on osteotomy site stability in a sagittal split ramal osteotomy model. MATERIALS AND METHODS: A reproducible analog of a sagittal split ramus osteotomy was developed to facilitate equitable comparisons of fixation stability. The distal segment of each analog was advanced by 7 mm and fixed bilaterally with 2.0-mm or 2.4-mm cortical screws applied in either a linear or a triangular configuration. Reduced analogs were placed in a straining frame, and simulated masticatory loads wee applied alternatively to the mandibular first molars. Ensuring osteotomy site displacements were acquired and registered by displacement transducers attached to a computer-based data acquisition program. A coordinate transformation procedure was used to convert the component displacements captured by the individual transducers into a common "instability factor" to reflect fixation stability for each construct and loading condition. RESULTS: Between configurations, the magnitude of interfragmentary displacement was less when the screws were applied in a triangular than in a linear configuration (P < or = .0001). Within configurations, 2.4-mm cortical screws provided greater stability than 2.0-mm screws. The stability profiles of the 2.0-mm screws, applied in a linear configuration at the superior border, were very similar regardless of whether two or three screws were used. The loads at which the linear systems became unstable were significantly higher (P < or = .0001) than for the triangular systems. Despite the twofold or higher difference in the mean instability factor of the individual test constructs, the SDs for each construct were only one tenth to one fifth of the corresponding means. CONCLUSIONS: None of the internal screw systems were grossly unstable when used to stabilize ramal osteotomies. Other conditions, including quality and strength of investing bone, being equal, cortical screws placed in a triangular configuration provide greater stability than screws placed in a linear configuration. Osteotomy sites stabilized by 2.4-mm screws are more stable than those stabilized by 2.0-mm screws. It does not matter whether two or three screws are applied at the superior border in a linear configuration, provided that the outer screws are an inch apart. The model system has a very good measurement precision and has important implications in optimizing fixation device design and placement configuration.

Bite Force↗
PubMed1995

Fracture line stability as a function of the internal fixation system: an in vitro comparison using a mandibular angle fracture model.

PURPOSE: This study was conducted to determine and compare the initial mechanical stability and functional capability of six contemporary internal fixation systems used to fix mandibular angle fractures. MATERIALS AND METHODS: An iterative analog of a mandibular angle fracture was developed to ensure replicability of material properties and fracture configuration across the test constructs. Each of six sets of mandible analog (1 set = 3 mandibles) was reduced according to prescribed technique by a variety of compressive and adaptive fixation systems. The compressive systems included the 1) eccentric dynamic compression plate, 2) Würzburg plate, 3) Luhr plate, and 4) solitary lag screw technique. The Champy miniplate and the Mennen clamp plate represented the adaptive fixation systems. The reduced analogs were placed in a straining frame, and simulated masticatory loads were applied to predetermined occlusal sites. Fracture line displacements were acquired and registered by displacement transducers attached to a computer-based data acquisition program. A coordinate transformation procedure was used to convert the generalized displacements at the fracture line into the individual rotations of the segments. An "instability factor" computed from the force-displacement data recorded at various loading conditions for each test construct was used to characterize a particular system's ability to restrain relative motion at the fracture surfaces. RESULTS: There were minimal variations in the stability profiles of the individual compressive fixation systems. However, the fixation stability provided by the compressive and adaptive systems differed significantly (P < or = .0001). A large initial setting and a susceptibility to variations in loading patterns characterized the functional stability provided by the adaptive systems. Even at low masticatory loads (2 DaN), the adaptive systems had an instability that was two to three times as much as that of the compressive systems. Post-hoc comparisons between pairs of devices showed that angle fractures fixed by compressive systems provided significantly greater stability (P < or = .05) than those fixed by the Champy and Mennen systems. Between the adaptive systems tested, fracture fixation with Mennen plates was more stable than reduction by Champy miniplates (P < or = .05) when averaged over loads. CONCLUSIONS: Compressive fixation systems are biomechanically superior to adaptive systems and provide good immediate functional stability to reduced mandibular angle fractures. The Champy and Mennen systems permit significantly higher motion at the fracture site, even at the attenuated masticatory forces encountered in the early postoperative period. Because the functional stability afforded by these adaptive systems is influenced by variations in the biting patterns, the risk of infection and complicated healing is correspondingly increased. Also, the low displacement resistance of the adaptive systems may not protect the alignment of the mandibular segments through the healing period and may manifest as occlusal discrepancies in the dentate patient. The biomechanical test system developed for this study allows an equitable comparison of fixation stability and appears to be a promising tool for investigating a variety of fixation systems and optimizing device design on a rational basis.

Analysis of Variance↗
PubMed1994

Effects of thermocycling, load-cycling, and blood contamination on cemented implant abutments.

This study compared the effects of thermocycling, load-cycling, and human blood contamination on the retentive strength of five different cements for luting posts to root-form implants. For each cement, 10 specimens (controls) were stored in an incubator, 10 specimens were thermocycled, 10 specimens were subjected to cyclic compressive loading, 10 specimens were subjected to a combination of thermocycling and cyclic compressive loading, and 10 specimens were contaminated with blood before cementation, then exposed to a combination of thermocycling and compressive loading. After 70 hours, retentive tests were performed on the Instron machine, and data were recorded in kilograms. Significant retentive differences were identified among the cements and with load-cycling, but minimal effect on the retentive strength was demonstrated from thermocycling. Blood contamination in combination with thermocycling and load-cycling adversely affected the retentive strengths of all of the cements and could be a major cause of abutment failure in dental implants.

Analysis of Variance↗
PubMed1994

Effect of cantilever length on stress transfer by implant-supported prostheses.

Cantilever lengths for fixed implant supported prostheses have been based largely on empirical judgment. This study determined the effects of cantilever length on load transfer to the mandible. A photoelastic model of a moderately resorbed edentulous human mandible with five 13 mm Bränemark implants was constructed. Simulated occlusal loads at varying cantilever lengths were applied to the occlusal surface of a routinely fabricated fixed prosthesis. The highest stresses were located at the ridge crest on the distal surface of the distal implant for all cantilever lengths. Apical stresses at this implant developed in reciprocation to the effect of the distal tipping force on the cantilever. Curves describing the effect of cantilever length on maximal stress are presented. Little load transfer to adjacent implants was found. Disproportionate increases in maximum stress with increasing cantilever length occurred. Minor variations in implant angulation had a distinct effect on stress magnitude.

Dental Implantation, Endosseous↗
PubMed1994

Moduli of rupture of layered dental ceramics.

OBJECTIVE: The purpose of this study was to determine the moduli of rupture of layered beams made of strong core materials veneered with weaker conventional feldspathic porcelain. METHODS: A three-point flexural test, and formulae derived especially for this purpose were used. Two systems were investigated. The first consisted of Vitadur N (Vita Zahnfabrik), a conventional feldspathic porcelain; and Dicor MGC (L.D. Caulk), a machinable glass ceramic. The second consisted of Vitadur N and In-Ceram (Vita Zahnfabrik), a strong reinforced aluminous porcelain. RESULTS: Two-way ANOVA and Tukey tests were used to evaluate the effect of numerous factors on the modulus of rupture. The results indicated that the material forming the tensile surface, the material forming the compressive surface and their interaction had a highly significant effect on modulus of rupture (p < 0.05). The effect of the material forming the tensile surface on modulus of rupture was of much greater magnitude than that of the compressive surface. Theoretical curves describing effects of the layers' elastic moduli and thickness on the force-bearing capacity of model beams were plotted. These indicated that for a wide range of thickness ratios and for a wide variety of elastic modulus ratios, the tensile material dominates the force-bearing capacity of layered beams except when a very much lower modulus material forms the compressive layer. SIGNIFICANCE: Layered prostheses made of strong cores veneered with weaker feldspathic porcelain may be prone to failure when the feldspathic surfaces are subjected to tensile force.

Aluminum Oxide↗
PubMed1994

Biomechanical rationale for surgical-orthodontic expansion of the adult maxilla.

OBJECTIVE: To develop a biomechanical rationale for surgical-orthodontic correction of transverse maxillary deficiencies in adults by clarifying the internal stress responses to rapid palatal expansion in a photoelastic model. MATERIALS AND METHODS: A three-dimensional photoelastic analog of an adult human skull was constructed by fabricating the individual facial bones from a photoelastic material and fixing them along their anatomic sutural areas. After determining the force-activation characteristics of a Hyrax expansion appliance in a straining frame, the appliance was applied to the analog and incrementally activated. The stresses developing at the different craniofacial areas were visualized and photographed in the field of a circular polariscope. Sequential cuts were performed to simulate midpalatal, zygomatic buttress, and pterygomaxillary osteotomies, and the alterations in the internal stress responses were recorded after each individual cut. RESULTS: The force-activation characteristics of the Hyrax appliance are in the orthopedic range (500 g). The magnitude and distribution of the stresses induced by appliance activation differed notably between the simulated osteotomies. Analysis of fringe patterns showed that the midpalatal and pterygomaxillary articulations were the primary anatomic sites of resistance to expansion forces. The patterns of distribution and the increase in the magnitude of the stresses at superior sutural location were particularly pronounced after the pterygomaxillary cuts. The forces produced by the Hyrax appliance had deep anatomic effects, with internal stresses also manifesting at regions distant from the site of force application. CONCLUSIONS: Based on photoelastic observation, it may be concluded that complete midpalatal and pterygomaxillary osteotomies are essential for predictable skeletal expansion in adults. Exclusive use of bilateral zygomatic buttress osteotomies appears to be inadequate. The expansion forces exerted by the Hyrax appliance are orthopedic in nature and produce deep anatomic effects. Clinicians should be aware that the craniofacial stresses produced by appliance activation may be experienced by the patient as pain or discomfort.

Adult↗
PubMed1994

Evaluation of ultrasonic and sonic instruments for intraradicular post removal.

Ultrasonic instruments are a valuable asset for removing intraradicular posts from root canals before nonsurgical endodontic therapy. The purpose of this study was to evaluate the relative efficacy of post removal by ultrasonic and sonic devices. Fifty extracted teeth were instrumented and obturated. The canals were prepared and Parapost #5 posts were cemented with zinc phosphate cement. The teeth were divided into five groups, subjected to ultrasonic or sonic instrumentation and the time measured until post removal. Median values in minutes for the post extractions in each group were: Cavitron = 6.0, Enac = 8.3, and Neosonic = 41.2. Sonic instruments were generally unable to remove the posts. The results of this experiment indicate that the Cavitron and Enac ultrasonic units are significantly more efficient for removing posts than the Neosonic. Sonic instruments were not useful for post removal.

Cementation↗
PubMed1994

Critical analysis of the balanced force technique in endodontics.

The "balanced force" technique was introduced in 1985 and it was reported that the resistance of the dentin, as it circumferentially contacted the flutes of a file in a curved root canal, would be sufficient to override and mask any tendency of the file to straighten during rotational instrumentation. An alternative mechanism based on compressive force and file flexure is presented in this article. In a laboratory study, the apical force necessary to cause files of sizes #10 to #70 to bend and conform to an average canal curvature was determined. These measurements were then related to the apical forces applied to teeth when utilizing the Balanced Force technique in a simulated clinical setting. It was then proposed that the apically directed force necessary to prevent coronal movement of the file and to effect dentinal shearing during counterclockwise rotation placed the file in compression, flexing it to conform to the curvature of the canal. This explanation was consistent with the experimental data for the files used in this study up to size #60 for an average canal curvature and for average instrumentation forces.

Analysis of Variance↗
PubMed1993

Maxillary distal-extension removable partial denture abutments with reduced periodontal support.

An in vitro study that used photoelastic models compared stress distribution characteristics of three maxillary, bilateral, distal-extension removable partial denture designs when the abutments were subjected to a progressive loss of periodontal support. One design used I-bar retention, a second design used a semiprecision, spring-loaded plunger attachment, and a third design used the ERA attachment. Both attachment designs were tested with and without splinted abutments. The ERA design was also tested with and without supporting rests and included light and heavy retention elements. Periodontal support loss up to 35%, a 60/40 crown-to-root ratio, resulted in increased stress concentrations. The ERA design with supporting rests, light retention elements, and splinted abutments compared very favorably with the I-bar retained design on nonsplinted abutments.

Alveolar Bone Loss↗
PubMed1993

Effect of surface design on retention of dowels cemented with a resin.

This study compared the retentive ability of endodontic dowels cemented with a resin when the surfaces of the dowels were varied. Dowels of standardized material, shape, length, and diameter were cemented with an unfilled Bis-GMA resin. Four dowel surface configurations were tested: transverse serrated, crosshatched, threaded, and longitudinal spirals. The results indicated that the dowel surface design can significantly influence the retention of a resin-cemented dowel. Dowels with transverse serrations or crosshatching were retained better than dowels with longitudinal spirals or threads.

Analysis of Variance↗