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Biomedical subjects

A A Caputo

Publications and source records attributed to A A Caputo.

At least 19 recordsLinked to original sources
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↗
PubMed1992

Adhesion of resin to casting alloys.

The bond strength of a composite resin bonded to various dental casting alloys with three adhesive systems--Silicoater, Panavia, and Superbond C&B--was investigated. The metal surfaces were treated solely with aluminum oxide blasting before application of the adhesive. Thermal cycling caused a reduction in bond strength for all combinations of the adhesive systems and alloys, but the Silicoater system recorded the greatest bond strength. The 4-META system was equivalent to Panavia system in bond strengths to most metals and exhibited greater strength with others.

Adhesives↗
PubMed1992

Load transfer by a maxillary distal-extension removable partial denture with cap and ring extracoronal attachments.

This study photoelastically compared the stress distribution characteristics of maxillary, bilateral, distal-extension removable partial dentures retained by light and heavy ERA extracoronal attachments. One prosthesis included supporting rests and the other had no rests. Both designs were tested with and without abutment splinting. The most favorable stress distributions were obtained with light retention elements, supporting rests, and splinting of the abutments. In this configuration the attachment prosthesis compared favorably in stress distribution with the maxillary I-bar retained removable partial denture in a previous study that used a comparable maxillae model.

Dental Prosthesis Retention↗
PubMed1992

The retentive and stress distributing properties of split threaded endodontic dowels.

A threaded, parallel-sided endodontic dowel that has a longitudinal split was tested to determine its retention and stress distribution properties. Photoelastic stress analysis revealed high installation stresses unless the dowels were counterrotated. Axial loading created stresses at the threads, with elevated coronal and apical stresses. Even higher coronal stresses were recorded with inclined loads, and shorter dowels generated greater stresses than longer dowels. The retentive values were generally lower than those in comparable studies.

Analysis of Variance↗
PubMed1992

Comparison of load transfer by maxillary distal extension removable partial dentures with a spring-loaded plunger attachment and I-bar retainer.

This study photoelastically compared the stress distribution characteristics of two maxillary bilateral distal-extension removable partial denture designs, one using I-bar retention and the other using a semiprecision spring-loaded plunger attachment. Each prosthesis was subjected to vertical and horizontal extension-base loads. Comparisons were made from photographic recordings of isochromatic fringe distributions. The two retention designs produced comparable stresses with splinting of abutments for the plunger attachment. The attachment-retained prosthesis proved less stable with some loadings. Stress patterns followed three trajectories in the maxilla. A basis for stress distribution comparisons to other maxillary removable partial denture attachments is established.

Analysis of Variance↗
PubMed1992

Microleakage of new crown and fixed partial denture luting agents.

This study measured the in vitro microleakage of conventional and new FPD luting agents. Standardized preparations were made on 42 freshly extracted premolars. Facial and lingual chamfer margins were placed in enamel, mesial and distal in dentin and cementum, and castings were made in Rexillium III alloy and were then cemented with a standardized technique. Six groups of seven samples were tested, (1) polycarboxylate, (2) zinc phosphate, (3) glass ionomer, (4) Den-Mat Thin Film cement, (5) Panavia Ex, and (6) Den-Mat Thin Film cement with Tenure. The ranking of groups for stain ingress was from the greatest (1) to the least (6). A one-way analysis of variance and Tukey-Student range analysis revealed significantly similar groups, p less than 0.05:(1,2,3,4) (5,6).

Adhesives↗
PubMed1992

Endodontic dowel retention with resinous cements.

This study compared the capability of three composite resin cements to sustain a standard endodontic dowel. All of the systems incorporated some form of smear layer removal on the dentin of the endodontic channel. One system that used a methyl ethyl ketone drying agent provided inadequate clinical resistance to dislodgment of 5.4 DaN. A second cementing system that used only smear layer removal resisted loads at 54.7 DaN. The third cementing regimen that included a surface-initiated dentinal adhesive and smear layer removal recorded retention of 77.4 DaN. This study supported the concept that passively cemented dowels with composite resin can be as effective as actively seated dowels.

Acrylic Resins↗
PubMed1991

A new endodontic stabilizer implant device.

A new endodontic stabilizer implant device is presented that can be used immediately after enucleation of large periapical cysts. The force transmission characteristics of this implant were evaluated by means of photoelasticity. The implant served to distribute incisal forces within the supporting structure. Improved stress conditions resulted at the tooth apex and between the apex and the superior border of the implant when the tooth was subjected to apicoectomy.

Apicoectomy↗