Biomedical subjects

A A Caputo

Publications and source records attributed to A A Caputo.

At least 19 recordsLinked to original sources

PubMed2005

Flexural strength of a layered zirconia and porcelain dental all-ceramic system.

STATEMENT OF PROBLEM: New processing techniques have facilitated the use of zirconia core materials in all-ceramic dental prostheses. Zirconia has many potential advantages compared to existing core materials; however, its performance when layered with porcelain has not been evaluated. PURPOSE: This study investigated the strength of a wide variety of layered zirconia and porcelain beams to determine whether the inclusion of zirconia cores results in improved strength. MATERIAL AND METHODS: Eight types of layered or simple zirconia and porcelain beams (n = 10), approximately fixed partial denture-size, were made of a tetragonal polycrystalline zirconium dioxide partially stabilized with yttria core (Lava System Frame) and a feldspathic dental porcelain (Lava Ceram veneer ceramic). Elastic moduli of the materials were measured using an acoustic method. Maximum force and modulus of rupture were determined using 3-point flexural testing and a universal testing machine. Descriptive statistical methods were used. RESULTS: Beams with porcelain tensile surfaces recorded mean tensile strengths or moduli of rupture from 77 to 85 MPa, whereas beams with zirconia tensile surfaces recorded moduli of rupture almost an order of magnitude higher, 636 to 786 MPa. The elastic moduli of the porcelain and zirconia materials were 71 and 224 GPa, respectively. Crack propagation following initial tensile cracking often involved the porcelain-zirconia interface, as well as bulk porcelain and zirconia. CONCLUSION: The layered zirconia-porcelain system tested recorded substantially higher moduli of rupture than have been previously reported for other layered all-ceramic systems.

Dental Porcelain↗

PubMed2005

Abutment load transfer by removable partial denture obturator frameworks in different acquired maxillary defects.

STATEMENT OF PROBLEM: Excessive stress on abutment teeth adjacent to a maxillary resection defect during loading of partial denture obturator frameworks may shorten the life of the teeth. PURPOSE: The aim of this study was to photoelastically compare the forces exerted on the supporting structures of abutment teeth in 3 differently sized surgical resections with removable partial denture designs used to restore such maxillectomy defects. MATERIAL AND METHODS: Composite photoelastic models were constructed of a human maxilla that had undergone each of 3 maxillectomies: partial, radical, and radical involving the contralateral premaxilla. The abutment teeth included all remaining anterior teeth, the first premolar, and second molar, except the radical maxillectomy, which included the contralateral premaxilla where all remaining teeth were used as abutment teeth. All abutment teeth were restored with complete metal crowns, and removable partial denture frameworks were fabricated. Loading zones were selected according to the resection, and a 10-lb load was applied at each load point. The resulting stresses were observed and recorded photographically in a circular polariscope. The 2 teeth adjacent to the resection were then splinted, and the loading regimens were repeated. RESULTS: Without splinting, loads closer to the defect produced lingual tipping of the teeth adjacent to the resection and a mesial tipping tendency of the second molar. The tipping effects were greatest in the model with the largest resection. Splinting reduced tipping of the teeth adjacent to the resection and produced more uniform stress around these 2 abutment tooth roots for all of the models. CONCLUSION: The results of this in vitro study suggest that splinting the 2 teeth adjacent to a resection defect improves stress distribution around the roots during loading. This could increase the clinical life of the abutment teeth.

Birefringence↗

PubMed2005

Controlled failure mechanisms toughen the dentino-enamel junction zone.

STATEMENT OF PROBLEM: The dentino-enamel junction (DEJ) durably unites dissimilar hard brittle enamel and tough flexible dentin. In contrast to artificial bonds between restorations and dentin, the DEJ rarely fails except when it is affected by inherited disorders. Knowledge of DEJ toughening mechanisms is important in understanding inherited disorders, in biomimetic engineering of junctions between artificial restorations and teeth, and in tissue-engineering a DEJ. PURPOSE: The purpose of this study was to identify specific DEJ-zone failure mechanisms and to survey the fracture toughness of the human DEJ zone. MATERIAL AND METHODS: Fracture toughness indentations were made at 3 sites across the DEJ zone of 10 human incisor teeth. Failure modes identified using optical microscopy and fracture toughness (MPa.m(1/2)) were calculated following Vickers microindentation. Site mean values were then calculated and compared using 1-way analysis of variance (alpha=.05). RESULTS: The DEJ did not undergo catastrophic interfacial delamination; instead, damage was distributed over a broad zone. The primary damage mode involved cracking and damage dispersion in the specialized first-formed enamel close to the DEJ. Multiple, somewhat convoluted and sometimes branching, cracks spread and diffused damage over a wide area of adjacent enamel rather than producing catastrophic interfacial failure. Other secondary mechanisms included short microcracks in the DEJ adjacent dentin with possible cracked bridging, as well as plastic deformation of the DEJ without delamination. A DEJ-zone fracture toughness of approximately 0.8 to 0.9 MPa.m(1/2) was calculated. CONCLUSION: DEJ-zone damage occurred primarily within the adjacent layer of specialized first-formed enamel, and the optical DEJ interface resisted delamination.

Biomechanical Phenomena↗

PubMed2001

Retention of maxillary implant overdenture bars of different designs.

STATEMENT OF PROBLEM: The specific degree of retention for overdenture attachments is unknown in relation to design, location, and alignment to supporting dental implants. PURPOSE: The purpose of this study was to evaluate the initial retention characteristics of 5 implant maxillary overdenture designs under in vitro dislodging forces. MATERIAL AND METHODS: A simulated edentulous maxilla was fabricated with 4 screw-type 3.75 x 13-mm implants anteriorly. Five overdenture designs with the following attachments were evaluated: 4 plastic Hader clips with an EDS bar; 2 plastic anterior Hader clips with an identical EDS bar; 2 Hader clips with 2 posterior ERA attachments; 3 Zaag attachments on a bar; and 4 Zaag attachments with no bar. Overdentures were fabricated with full palatal coverage. Each design was subjected to 10 consecutive retention pulls on a universal testing machine. Data were subjected to analysis of variance and t tests to determine differences. RESULTS: The highest average value after 10 pulls was 19.8 lb for the combination ERA and Hader clip design. The lowest retentive values were recorded for the 2 and 4 Hader clip designs (5.08 +/- 0.89 lb and 5.06 +/- 0.67 lb, respectively). Retention decreased over the course of consecutive pulls for all designs, especially for the most retentive designs. The smallest retention decrease occurred with the least retentive designs. CONCLUSION: The results of this in vitro study suggest that the precise selection and placement of attachments may affect the clinical success of maxillary implant-retained overdentures.

Dental Clasps↗

PubMed2001

Fracture toughness of posterior resin composites.

OBJECTIVES: The purpose of this study was to evaluate and compare the resistance to crack propagation, as measured by the fracture toughness, of some packable posterior resin composites with other posterior resin composite materials. METHOD AND MATERIALS: Fracture toughness determinations were made for the 5 packable and the other posterior resin composites using 3-point flexure of beams with a standardized central single-edge notch. Ten beams of each material were tested on an Instron test machine. The maximum loads were determined, from which the fracture toughness values (KIC) were calculated. The data were analyzed statistically using ANOVA and t tests. RESULTS: The resin composites tested demonstrated a range of KIC values. The materials were separated according to the mean KIC values into 5 groups that were statistically different. While 2 packable resin composites had KIC values that were among the highest, the other packables were substantially lower than nonpackables. The intermediate value group consisted of 3 of the conventional posterior resin composites. CONCLUSION: There was a very weak correlation between fracture toughness and reported volume concentration of particulate reinforcing elements. The posterior resin composites tested exhibited a spectrum of KIC values. The packable resin composites were distributed along this spectrum, with 2 products exhibiting high potential for resistance to crack propagation.

Acrylic Resins↗

PubMed2001

Biomechanical effects of cervical lesions and restoration on periodontally compromised teeth.

OBJECTIVE: The purpose of this study was to photoelastically evaluate the effects of cervical root lesions and their restoration on stress distribution in periodontally compromised teeth. METHOD AND MATERIALS: Three-dimensional composite photoelastic models of a maxillary first premolar with buccal cervical root lesions were fabricated. Two different lesion configurations, wedge- and shallow saucer-shaped, at 20% alveolar bone height reduction were tested. A 35% reduction model was given a wedge-shaped lesion. The lesions were restored with microfine resin composite. Vertical loads of 7.5 lbs were applied to the unrestored and restored models at the tip of the buccal cusp and the tip of the lingual cusp. The resulting stresses within the tooth models were monitored and recorded photographically in the field of a circular polariscope arrangement. RESULTS: For buccal cusp loading of the unrestored models, stress concentrated at the apex of the lesion regardless of the lesion shape or periodontal support conditions. The highest stress concentration was observed around the apex of the wedge-shaped lesion on the 35% reduction model. Restoring the lesions changed stress distribution. Restoration of the lesions resulted in a marked stress reduction at the lesion apex. Stress along the gingival restoration-model interface was characteristic for the restored situation. The interfacial stress followed the contour of the restoration most closely for the wedge-shaped lesion on the 20% support reduction model. CONCLUSION: The shape and dimension of the lesion as well as periodontal support status has considerable influence on stress distribution, especially around the lesion, restored or not restored.

Alveolar Bone Loss↗

PubMed2000

Bonding of light-cured glass ionomer cement to polycarbonate resin treated with experimental primers.

The effect of experimental primers on the shear bond strength of polycarbonate composite resin with light-cured glass ionomer cements was investigated. Mixtures of methylmethacrylate (MMA) with the comonomers 2-hydroxyethyl methacrylate (HEMA), triethyleneglycol methacrylate (TEGDMA), and bisphenol-A-glycidymethacrylate (bisGMA) were used as primers. Polycarbonate composite resin rods of circular cross section and plates were bonded, with and without precured and nonprecured primers, using 2 light-cured glass ionomer cements (commercially available [LC] and experimental [EX]). In addition, commercial polycarbonate composite resin brackets with precured 50% TEGDMA/MMA primer were bonded to etched human enamel with both cements. Shear bond strengths were measured. Results were compared by ANOVA and Scheffe's tests at P = .05. The 30% HEMA/MMA, 50% TEGDMA/ MMA, 10% bisGMA/MMA, and 30% bisGMA/MMA primers produced the higher shear bond strengths (9.5 to 20.8 MPa) with LC and EX to polycarbonate composite resin. The 50% TEGDMA/MMA primer was most effective in improving the shear bond strengths of both LC and EX. Precured 50% TEGDMA/ MMA primer on a commercial resin bracket was effective in providing good shear bond strength to enamel.

Acrylic Resins↗

PubMed2000

Response of headgear release mechanisms to nonaxial force application.

Safety products have been developed to help reduce the incidence of trauma caused by headgear. Previous studies have reported the characteristics of breakaway-type headgear release mechanisms with axial force application. Not all accidental releases are triggered by an axial force and it is necessary to understand the characteristics of these mechanisms with nonaxial force application. Thirteen headgear release mechanisms were tested as part of a complete headgear system. With the system attached to a plaster head and neck model a tensile force was applied to the system at 30 degrees to the sagittal plane at 2 rates. The force of activation at release and the distance traveled were determined and analyzed statistically. Force values ranged from 4.6 to 36.7 pounds and face bow travel before release ranged from 0.97 to 3.42 inches. No consistent pattern of rate dependence was observed. Several devices demonstrated the desirable combination of low force and face bow travel at release.

Analysis of Variance↗

PubMed2000

Center of resistance of anterior arch segment.

It is important to know the location of the center of resistance (CR) to control tooth movement. In this study, photoelastic techniques were used to determine the center of resistance. The photoelastic model included the anterior 4 maxillary teeth, which were interconnected firmly with 6 mm of space between lateral incisors and canines. Determination of the CR for the anterior arch segment was based on considerations of a wide variety of load conditions that generated the more uniform stresses in the supporting alveolar bone simulant. For the arch having the anterior 4 teeth connected, the CR was located within the mid-sagittal plane, 6-mm apical and 4-mm posterior to a line perpendicular to the occlusal plane from the labial alveolar crest of the central incisor.

Birefringence↗

PubMed2000

Effect of anchorage systems and extension base contact on load transfer with mandibular implant-retained overdentures.

STATEMENT OF PROBLEM: Controversy exists regarding the effect of anchorage systems and extension base contact on stress transfer to multiple implants by mandibular overdentures. PURPOSE: This simulation study measured photoelastically the biologic behavior of 4 implants retaining a mandibular overdenture. The purpose of the investigation was to compare the load transfer characteristics of different mandibular-retained overdenture designs, with and without edentulous ridge contact. MATERIAL AND METHODS: A photoelastic model of a human edentulous mandible was fabricated having 4 screw-type implants (3.75 x 10 mm) embedded in the parasymphyseal area. Substructure designs utilizing a cantilevered bar, spark erosion framework, noncantilevered bar, and solitary anchors were fabricated. A vertical load of 30 lb was applied to the first molar unilaterally on each of the 4 standardized overdenture prostheses, with and without a silicone tissue spacer, for a total of 8 tested conditions. Stresses that developed in the supporting structure were monitored photoelastically and recorded photographically. RESULTS: Without the simulated tissue contact on the posterior edentulous ridge, the cantilevered bar framework caused the highest stresses to the terminal implant, followed by spark erosion framework, non-cantilevered bar, and solitary anchor design. With simulated tissue contact under the extension base, stress transfer to the distal implant was uniformly reduced to a low level. CONCLUSION: Without intimate extension base contact with the posterior edentulous ridge, the cantilevered anchorage systems generated the highest stresses, under load, to the ipsilateral terminal implant and the solitary anchor design transferred the least. With simulated intimate extension base contact, all anchorage systems transferred low stress to the distal implant region. For all conditions and designs, low stress was transferred to the contralateral side of the arch.

Alveolar Process↗

PubMed2000

Understandings and experiences of cruelty: an exploratory report.

The authors investigated popular understandings of cruelty among 103 undergraduates who identified the cruelest acts that they had experienced vicariously and personally. The authors also examined the reasons that the cited acts were defined as cruel. Results indicated that most of the vicarious cruel acts involved intense aggression or sexual imposition, whereas personally experienced cruelty was milder, frequently consisting of teasing or gossip. Offense, victim, and perpetrator characteristics were all cited as reasons that acts were considered cruel. The authors also investigated gender differences in reported acts and reasons. Future researchers should address the discrepancies between vicarious and personally experienced cruelty. Findings with regard to personal acts also call for links to the literature on callousness and victimization.

Adolescent↗

PubMed2000

Fracture toughness of various core build-up materials.

PURPOSE: The purpose of this investigation was to compare the fracture toughness of several core materials. MATERIALS AND METHODS: Five core build-up materials were tested: (1) glass ionomer, (2) resin-modified glass ionomer, (3) titanium-reinforced composite, (4) composite resin with fluoride, and (5) amalgam. Fracture toughness determinations were made using 3-point flexure of beams with a central single-edge notch. The notch was standardized by the use of a special mold into which each of the materials was condensed. Ten beams of each material were tested on an Instron test machine (Instron Corp, Canton, MA) at a crosshead speed of 1.25 mm/min. The maximum loads were determined from which the fracture toughness values (KIC) were calculated. The data were analyzed statistically using analysis of variance and t tests. RESULTS: The mean fracture toughness value in MN.m-3/2 for each of them is as follows: (1) glass ionomer, 0.717 +/- 0.071; (2) resin-modified glass ionomer, 0.747 +/- 0.061; (3) titanium-reinforced composite, 1.409 +/- 0.051; (4) composite resin with fluoride, 1.660 +/- 0.086; and (5) amalgam, 1.521 +/- 0.081. There was no significant difference in the KIC values for the glass ionomer-based materials, and both of these were significantly lower than amalgam, titanium-reinforced composite resin, and composite resin with fluoride (p < .001). CONCLUSION: The titanium-reinforced composite resin, the composite resin with fluoride, and amalgam materials showed fracture toughness most likely to withstand the stresses generated during mastication.

Analysis of Variance↗

PubMed2000

Biomechanics of cervical tooth structure lesions and their restoration.

OBJECTIVE: The purpose of this study was to evaluate photoelastically the effects of a cervical tooth structure lesion and its restoration on stress distribution within a tooth. METHOD AND MATERIALS: Three-dimensional composite models of a maxillary first premolar with a buccal cervical lesion were fabricated. Two types of cervical lesion were tested: one was wedge shaped and had a sharp line angle at the apex of the lesion, and the other was more rounded and saucer shaped. Vertical loads of 10 lb were applied to the unrestored and restored models at the tip of the buccal cusp, the tip of the lingual cusp, and the center of the occlusal surface. The resulting stresses within the tooth model were monitored and recorded photographically in the field of a circular polariscope arrangement. RESULTS: In the unrestored situation, stress concentrated at the apex of the lesion, regardless of the lesion configuration. However, the sharper, wedge-shaped lesion demonstrated a more severe stress concentration. In the restored situation, stress around the lesion apex and the lingual cervical lesion decreased, while stresses at the gingival and occlusal margins of the lesion increased, compared with the unrestored situation. These tendencies were most obvious when the buccal cusp was loaded. CONCLUSION: The presence of a cervical lesion changed occlusal load-induced stress distribution and concentrated stress at the apex of the lesion. The shape and dimension of the lesion governed the severity of stress concentration. Restoration of the cervical lesion relieved concentrated stress at the apex of the lesion.

Bicuspid↗

PubMed1999

Topographical characteristics and shear bond strength of tooth surfaces cut with a laser-powered hydrokinetic system.

STATEMENT OF PROBLEM: Erbium lasers, specifically Er;YAG and Er, Cr;YSGG that emit in the near red wavelengths, cut both enamel and dentine. Bonding to these cut surfaces with composites has not been assessed for all laser systems. PURPOSE: This investigation assessed the shear bond strength of composite bonded to tooth structure treated with an Er,Cr;YSGG-powered hydrokinetic system (HKS, Millennium system) and then was compared with surfaces treated with a carbide bur. MATERIAL AND METHODS: Extracted human molars were cut into enamel and dentin with both systems. Nonetched and acid-etched subgroups were evaluated. Shear bond strength was measured with an Instron test machine with a knife-edge loading head. In addition, SEMs were evaluated. RESULTS: There were no significant differences in shear bond strength between etched bur cut (23.3 +/- 2.5 MPa), etched laser-cut enamel (23.7 +/- 4.5 MPa), and nonetched laser-cut enamel (20.5 +/- 2.8 MPa). For nonetched enamel, bond strength values for laser-cut surfaces were significantly higher than the bur-cut surfaces (8.7 +/- 4.3 MPa). Bond strength differences for dentin between bur (14.3 +/- 1.7 MPa) and laser cuts (11.5 +/- 4.3 MPa) were not significant (P =.03). SEM revealed that laser cutting of enamel did not cause formation of a smear layer. CONCLUSION: There were no significant differences in shear bond strength between etched bur-cut, etched laser-cut, and nonetched laser-cut enamel. With nonetched enamel, bond strength values for nonetched laser-cut surfaces were significantly higher than for the bur-cut surfaces. No bond strength differences between bur and laser cutting existed for dentin. Similar topography was observed for bur and laser prepared surfaces of etched enamel and nonetched dentin.

Acid Etching, Dental↗

PubMed1999

Effect of carbamide peroxide bleaching on the shear bond strength of composite to dental bonding agent enhanced enamel.

STATEMENT OF PROBLEM: Carbamide peroxide bleaching has been implicated in adversely affecting the bond strength of composite to enamel. PURPOSE: This in vitro study evaluated the effect of 3 dental bonding agents (OptiBond, All-Bond 2, One-Step) on the shear bond strength of a hybrid composite to enamel which was treated by a 10% carbamide peroxide bleaching system. MATERIAL AND METHODS: Cylinders of composite were bonded to carbamide peroxide-treated enamel on extracted human teeth using 3 dental bonding agents. After thermocycling, shear bond strengths were determined with a universal testing machine. RESULTS: OptiBond aided bond strengths were 23.7 +/- 5.6 MPa to bleached and 19.6 +/- 2.9 MPa to unbleached enamel. For All-Bond 2, bleached enamel exhibited bond strengths of 14.9 +/- 4.0 MPa and unbleached enamel exhibited a bond strength value of 20. 4 +/- 2.3 MPa. The composite bond strength for One-Step was 13.6 +/- 5.9 MPa to bleached and 23.0 +/- 3.9 MPa to unbleached enamel. There was no statistical difference between OptiBond (alcohol base) aided bond strengths for bleached and unbleached enamel; however, the bond strength of composite to bleached enamel with All-Bond 2 or One-Step (acetone base) was significantly lower than unbleached controls. CONCLUSION: The effect of bonding agent usage on composite bond strength to enamel bleached with a particular carbamide peroxide was dependent on the bonding agent used.

Analysis of Variance↗

PubMed1999

Photoelastic stress analysis of load transfer to implants and natural teeth comparing rigid and semirigid connectors.

STATEMENT OF PROBLEM: Controversy exists regarding the connection of implants to natural teeth. PURPOSE: This simulation study measured photoelastically the biologic behavior of implants. Stress transfer patterns with variable implant support and simulated natural teeth through rigid and nonrigid connection were examined under simulated functional loads. MATERIAL AND METHODS: A photoelastic model of a human left mandible edentulous distal to first premolar was fabricated having 2 screw type implants (3.75x13 mm) embedded within the edentulous area. Two fixed prosthetic restorations were fabricated with either a nonsplinted proximal contact or a soldered proximal contact, and cast precision dowel attachment between implant areas and simulated tooth. Simulated vertical occlusal loads were applied at fixed locations on the restorations. Stresses, which developed in the supporting structure, were monitored photoelastically and recorded photographically. RESULTS: The rigid connector in the 1 implant situation caused only slightly higher stresses in the supporting structure than the nonrigid connector. The distally loaded 1 and 2 implant-supported restoration produced the highest apical stresses, which occurred at the distal implant. The rigid connector demonstrated the greatest stress transfer in the 2 implant-supported restoration. CONCLUSIONS: Lower stresses apical to the tooth or implant occurred with forces applied further from the supporting abutment. Although the least stress was observed when using a nonrigid connector, the rigid connector in particular situations caused only slightly higher stresses in the supporting structure. The rigid connector demonstrated more widespread stress transfer in the 2 implant-supported restoration. Recommendations for selection of connector design should be based on sound clinical periodontal health of a tooth and the support provided by implants.

Adult↗

PubMed1999

Effect of contamination and etching on enamel bond strength of new light-cured glass ionomer cements.

The effect of water and saliva contamination on the bond strength of metal orthodontic brackets cemented to etched (10% polyacrylic acid) and unetched human premolar enamel was investigated. Two bonding agents were used: one commercially available product (LC) and one experimental (EX) light-cured glass ionomer. Shear bond strength was measured after aging for 5 minutes, 15 minutes, and 24 hours. The results were compared by ANOVA and Scheffe's tests at p = 0.05. For LC, the bond strength of brackets bonded to etched enamel, with and without contamination, was statistically higher than that of brackets bonded to unetched enamel for all aging times. An exception was the bond strength to unetched enamel with saliva contamination after 24 hours; for EX, this value was statistically higher than that measured on unetched enamel with water contamination. Contamination by saliva did not reduce bond strength to unetched enamel. For both etched and unetched enamel, there was no significant difference between LC and EX after 24 hours for all contamination conditions.

Acid Etching, Dental↗

PubMed1999

Potential for load-induced cervical stress concentration as a function of periodontal support.

PURPOSE: The purpose was to determine, photoelastically, the locations of occlusal load-induced stress concentrations within a maxillary premolar as a function of degree of periodontal support. MATERIALS AND METHODS: Composite three-dimensional models of a maxillary first premolar were fabricated for quasi-three-dimensional photoelastic stress analysis. Individual materials were used to model enamel, dentin, periodontal ligament, and alveolar bone. Three levels of periodontal support reduction (0%, 20%, 25%) were simulated by varying the socket depth. Vertical loads of 10 lb were applied to: (1) tip of buccal cusp, (2) tip of lingual cusp, and (3) center of occlusal surface. The resulting stresses were monitored and recorded photographically in the field of a circular polariscope arrangement. RESULTS: Cuspal loading concentrated stress around the cervical region below the loaded cusp, being highest under buccal cusp loading. The location of the stress concentration shifted apically as periodontal support diminished. CLINICAL SIGNIFICANCE: Observed cervical stress concentration corresponded well to the common location of abfractions seen in clinical situations. Since the location of cervical stress concentration varied with occlusal conditions, occurrence of abfractions must be highly dependent upon each patient's occlusion. Periodontal support reduction shifted the location of highest stress away from the cementoenamel junction. Therefore, abfractions are less likely to occur on periodontally compromised teeth compared to stable teeth.

Alveolar Process↗