Biomedical subjects

K B May

Publications and source records attributed to K B May.

15 recordsLinked to original sources

PubMed1999

The effect of the use of a counter-torque device on the abutment-implant complex.

STATEMENT OF PROBLEM: Little is known about the condition of the abutment-screw joint before loading, after the development of the preload. PURPOSE: This study examined the tightening force transmitted to the implant with and without the use of a counter-torque device during the tightening of the abutment screw. MATERIALS AND METHODS: Forty Brânemark implants and 10 CeraOne, Estheticone, Procera, and AurAdapt abutments formed the experimental populations. Samples in each group were further divided into 2 groups, 1 group was tightened with a torque controller without the use of a counter-torque device, whereas the other used the counter-torque device. Samples were positioned in a special holder within the grips of a Tohnichi BTG-6 torque gauge for measuring transmitted forces. RESULTS: There were significant differences (P =. 0001) in the tightening forces transmitted to the implant with and without the use of a counter-torque device when tightening the abutment screws. CONCLUSION: An average of 91% of the recommended preload tightening torque was transmitted to the implant-bone interface in the absence of a counter-torque device. In all abutment systems, less than 10% of the recommended preload tightening torque was transmitted to the implant when the counter-torque device was used.

Dental Abutments↗

PubMed1999

Evaluation of the implant master cast by means of the Periotest method.

Accurate master casts are essential for the construction of implant-supported prostheses with a precision of fit. The stability of the abutment replicas in the master cast is critical in the accurate reproduction of the patient's oral presentation. The Periotest method is an objective method of quantifying mobility in a tooth and implant. Eighteen gypsum implant master casts containing two brass abutment replicas per cast were evaluated. The abutment replicas were measured three times each for a total of 108 measurements. The mean periotest values and standard deviations were calculated for the master casts and the abutment replicas. The abutment replicas displayed mean periotest values that ranged from +1.3 to -8.0. The study shows that there are significant differences between stable and unstable implant master casts (P = 0.0001, ANOVA-Fisher's protected least significant difference) and abutment replicas (P = 0.0001, Contrast test). The Periotest method will quantify differences in gypsum stone implant master casts as well as the prosthesis supporting brass abutment replicas that are an integral part of the master cast.

Analysis of Variance↗

PubMed1998

Precision of fit: the Procera AllCeram crown.

STATEMENT OF PROBLEM: Strength, color stability, and precision of fit are requirements for all-ceramic restorations. The Procera AllCeram crown system, composed of a densely sintered high-purity alumina core combined with a low fusing surface porcelain, appears to satisfy most of these requirements. However, evaluation of marginal fit has not been reported. PURPOSE: This study measured the precision of fit of the Procera AllCeram crown fabricated with Procera CAD/CAM technology for the premolar and molar teeth fit to a die. MATERIAL AND METHODS: Five ivorine maxillary first premolars and first molars were prepared for full-coverage crowns. Preparations were standardized with a convergence angle of 10 degrees, chamfer margins of 1.3 to 1.5 mm circumferentially, and occlusal reduction of 2.0 mm. AllCeram crowns were fabricated for the dies, and the fit of the crown to the die was determined by using a standardized procedure with a silicone impression material that served a dual role: (1) as a retrievable luting agent, and (2) to replicate the internal aspects of the crown. Laser videography was used to measure the gap dimension between the crowns and the dies at the marginal opening, the axial wall, the cusp tip, and the occlusal adaptation measurement locations. Mean gap dimensions and standard deviations (SDs) were calculated for marginal opening, internal adaptation, and precision of fit. RESULTS: Mean gap dimensions and standard deviations at the marginal opening for the premolar and molar crowns were 56.0 microns SD +/- 21 and 63.0 microns SD +/- 13 microns, respectively. The mean gap dimensions and SDs of the internal adaptation were 69.0 microns SD +/- 17 microns for axial wall, 48.0 microns SD +/- 12 microns for cusp tip, and 36.0 microns SD +/- 7 microns for occlusal adaptation for the premolar crowns; and 49.0 microns SD +/- 3 microns axial wall, 67.0 microns SD +/- 21 microns cusp tip, and 74.0 microns SD +/- 29 microns occlusal adaptation for molar crowns. Precision of fit and SDs for premolar and molar crowns were 52.0 microns SD +/- 19 microns and 63.0 microns SD +/- 20 microns, respectively. Mean marginal openings and precision of fit gap dimensions for the crown groups were not significantly different at the .05 level. However, gap dimensions that defined the internal adaptation at the measurement locations were different (P < or = .05). CONCLUSION: Mean gap dimensions for marginal openings, internal adaptation, and precision of fit for the crown groups were below 70 microns. These findings show that the crowns studied can be prescribed with confidence knowing that the precision of fit will consistently be less than 70 microns.

Aluminum Oxide↗

PubMed1998

Periotest method: implant-supported framework fit evaluation in vivo.

STATEMENT OF PROBLEM: In implant prosthodontics an accurate fit of the framework to the supporting implants is paramount. However, microgaps occur, unknown to the clinician until complications arise that implicate errors in fit. Therefore prosthodontics would welcome a tool or instrument that provides an objective evaluation of the fit at the implant prosthodontic interface. PURPOSE: This clinical investigation determined whether a correlation existed between the laboratory laser measurement of the abutment analog-framework fit and the intraoral abutment-framework fit as measured by the Periotest method. MATERIAL AND METHODS: Fifteen subjects received implant-supported remote fixed partial denture supported by five (11 subjects) or six (4 subjects) implants in the mandibular jaw opposed by a complete maxillary denture. Laser videography was used to quantify the fit of the framework to its respective master cast with six measurements, while the fit of the framework in the mouth was quantified with the Periotest method. Data were statistically analyzed with correlation analyses and multiple regression. RESULTS: The overall correlation coefficient between the two methods was r = 0.51. Regression analysis of variance revealed that the intercept of the laser videography measurement was significant (p < or = 0.05). The mean Periotest values and standard deviation for the abutment-framework interface were negative (-7.3 +/- 1.2). The variance in part for the Periotest values was explained by the misfits in the vertical axis (delta Z, +0.471) and in the misfit direction of the centroids in the x-y plane (X-YVD, -0.244). CONCLUSION: There was no single variable among the six measurement variables that strongly correlated with the periotest method in the identification of mistfit at the bearing surface as indicated by the Periotest value measurements. The misfit laser variables that were weakly correlated to the Periotest values should be observable clinically with greater scrutiny.

Aged↗

PubMed1998

In vitro wear of resin denture teeth.

STATEMENT OF PROBLEM: One of the most important physical properties of artificial teeth used in the restoration of the edentulous patient is wear resistance, and the ability of these teeth to maintain a stable occlusal relationship over time. PURPOSE: This study compared the in vitro wear of four different resin denture teeth against human enamel. MATERIAL AND METHODS: Five denture tooth samples opposing five enamel abraders were positioned in a mechanical wear testing device for two 5,000 cycle wear periods (total of 10,000 cycles) under a 13.4 N load. All tests were conducted in human saliva, and the wear was measured at the end of each test period. RESULTS: The wear of the Classic and Kenson acrylic resin denture teeth was much greater than the DB Plus and MLI composite teeth after 10,000 cycles. The wear of the KENSON denture tooth was also greater than the Classic tooth. No wear differences were found between the two composite teeth. CONCLUSIONS: The wear of DB Plus and MLI resin denture teeth was approximately 50% less than the wear of Classic and Kenson teeth when opposed by human enamel.

Acrylic Resins↗

PubMed1998

Implant and provisional crown placement: a one stage protocol.

Most endosseous implant systems are placed using a two-stage surgical procedure. The surgical stages are separated by a period of 4 to 6 months to allow osseointegration. At Stage-I surgery, the implant is fixed in bone and submerged under mucosa, while at Stage-II surgery, the implant is exposed and the transmucosal abutment is connected to the implant. The one-stage nonsubmerged surgical procedure with immediate transmucosal extension using traditional two-stage implant systems is being used to treat partial and complete edentulism. This is a case report of 10 patients treated with endosseous implants in the maxillary anterior region with immediate provisionalization using a one-stage surgical procedure. The investigators found that all patients experienced minimal discomfort from complications after the one-stage surgery and immediate placement of the provisional restoration. No signs of inflammation or mobility were observed during the first 6 months. The partially edentulous anterior maxilla can be restored to an esthetic form in a single clinic visit.

Adult↗

PubMed1997

The precision of fit at the implant prosthodontic interface.

STATEMENT OF PROBLEM: Percussion, visual observation, and conventional periapical radiographs are the methods most frequently used clinically to evaluate the accuracy of implant component assemblies, whereas methods to measure the precision of fit are limited. PURPOSE: In this study the Periotest instrument was used to evaluate the stability of the interfaces between the implant and the abutment, along with the abutment and the gold cylinder under a series of assembly conditions. The hypothesis tested is that a more negative Periotest value (PTV) would indicate an accurate fit and a more positive value PTV would correlate with an inaccurate fit. MATERIAL AND METHODS: To investigate this hypothesis in vitro, two bovine ribs were used as patient simulation models. Each model contained three self-tapping Brånemark implants placed approximately 7 to 10 mm apart and arranged in a reasonable curvature. A series of component assembly conditions were created as accurate and inaccurate with thickness gauges of 25.4 microns, 50.8 microns, and 101.6 microns. RESULTS: The mean Periotest values and SDs for accurately assembled abutments and gold cylinders were -6.0 +/- 0.32 and -3.4 +/- 0.68, respectively. Periotest value data of the assembly conditions were statistically analyzed with multiple regression analysis. The misfit in the implant to abutment interface resulted in a more negative Periotest value trend (r = 0.54) with increases in gauge thickness. However, the same magnitudes of misfit at the abutment to gold cylinder interface produced a more positive Periotest value trend (r = 0.72). CONCLUSION: The PTV trends were consistent with increased stability at the abutment to implant interface from the increasing magnitude of misfit created with the thickness gauges. In contrast, the measurement trends observed for the abutment to gold cylinder interface were consistent with decreased stability with each increase in gauge thickness inserted at the interface.

Acceleration↗

PubMed1996

Color stability: denture base resins processed with the microwave method.

Several quick heat-cured denture base resin systems and microwave processing resins have been introduced to provide easier and faster processing. The microwave processing method is the fastest of the heat-cured processing methods. Conventional acrylic resins processed with the microwave method seem to possess adequate physical properties, and one study indicated that a microwave acrylic resin was reasonably color stable under conditions of accelerated aging, although manufacturers do not recommend using them for microwave processing. The purpose of this study was to evaluate the color stability of seven conventional and one microwave heat-cured denture base materials processed with the microwave method. The samples were subjected to conditions of accelerated aging to test for color stability. The color stability was quantitatively measured and color measurements were made before weathering and at 300, 600, and 900 hours. The mean color change for each sample group was statistically analyzed with polynomial regression to determine the pattern of color change over time. The differences in color change for the acrylic resins were significant for all materials, but the color change for Lucitone Hy-pro was not noticeable on visual examination. The results of this study revealed that color changes occurred after accelerated aging in heat-cured denture base resins and Acron GC microwave acrylic resins processed with the microwave method. Hy-pro and TruTone materials exhibited the least color change; Hy-pro material was the most color stable material.

Acrylic Resins↗

PubMed1996

The Periotest method: implant-supported framework precision of fit evaluation.

PURPOSE: In this study, the Periotest instrument was used to measure the precision of fit between cast high noble-metal frameworks and the supporting implants in a patient-simulation model. Three framework conditions and three implant-location variables were used to evaluate the rigidity of the assembly as measured by the Periotest method. The framework variables were (1) one-piece castings (OPC); (2) sectioned-soldered inaccurate castings (SSIC); and (3) sectioned-soldered accurate castings (SSAC). The implant-location variables were right anterior (RA), center (C), and left anterior (LA). MATERIALS AND METHODS: The patient simulation model used consisted of three self-tapping Branemark implants in a reasonable arch curvature in bovine bone. Three working casts were fabricated from the patient-simulation model using polyvinyl siloxane and tapered impression copings. From the working casts, three sets of three frameworks were fabricated as OPCs, SSICs, and SSACs using type 3 high noble alloy. The SSICs were fabricated with a quantitative misfit of 101.6 microns at the facial surface, between the abutment-to-gold cylinder interface at the C implant location. Periotest value (PTV) measurements were made at the midfacial surface of the frameworks directly above each abutment-to-gold cylinder interface. Three measurements were made for each test condition. The data were analyzed to compare framework condition(s) and implant location(s) using ANOVA and Fisher's Protected Least Significant Difference Comparison Test. RESULTS: The ANOVA showed that significant differences exist between the mean PTV data for framework condition and for implant location (p < .01). Significant differences were shown between the mean PTV data for the SSAC assemblies and the OPC and SSIC assemblies. The SSICs displayed a more positive (+) mean PTV than the OPCs. The OPC assemblies had a more positive mean PTV than the SSAC assemblies. The mean PTV data for the SSAC assemblies had a significantly different PTV (p < .01) than the other two framework condition assemblies. The OPC and the SSIC assemblies had PTVs that were not significantly different. The C implant location was significantly different from the RA and the LA implant locations (p < .01). The RA and the LA implant locations were not significantly different from each other. The C implant location always demonstrated the most positive mean PTV regardless of the framework condition being tested. CONCLUSIONS: The Periotest instrument quantified differences in the precision of fit between three framework conditions. The SSAC assemblies were significantly more rigid than the OPC and SSIC assemblies. The OPC and SSIC assemblies' mean PTVs were not significantly different. The mean PTVs for the C implant location and the RA and LA implant locations were significantly different (p < .01). The mean PTVs of the RA and LA implant locations were not significantly different. The implant-location PTVs followed the same rank order for all three framework conditions. The procedures used to fabricate a more precise fit between the framework and the supporting implants is influenced by the skill of the clinician and technician.

Analysis of Variance↗

PubMed1995

Silane to enhance the bond between polymethyl methacrylate and titanium.

The machined surface of wrought titanium frameworks used in implant-supported, fixed prostheses does not bond well with acrylic resin. Surface pretreatment has been suggested to enhance the retention of polymethyl methacrylate to machined titanium surfaces. This study evaluated a new bonding material (Rocatec) to determine its effect on the bond strength between titanium and polymethyl methacrylate. Twenty rod-shaped specimens of grade 2 titanium (7.6 x 0.3 cm in diameter) were divided into two groups of 10 samples. Group A received no pretreatment and group B was pretreated with 110 microns alumina air abrasive and the Rocatec material. Heat-cured denture base resin was processed around each titanium sample in a cylindrical shape approximately 0.9 x 1.5 cm. A Shell-Nielsen shear test was performed with a universal testing machine at a crosshead speed of 0.5 mm/minute to determine the bond strength in megapascals (MPa). Group B specimens (23.8 +/- 1.78 MPa) had a shear strength 68% greater than group A (16.1 +/- 1.61 MPa) (p 0.0001). The results of this study indicated that surface pretreatment of grade 2 titanium with 110 microns alumina air abrasive plus Rocatec bonding material significantly enhances the shear bond strength to PMMA.

Air Pressure↗

PubMed1994

A comparison of the color stability of conventional and titanium dental porcelain.

Simulation of naturally appearing enamel in fixed prosthodontics is best achieved with porcelain. This study investigated the color stability of two different dental porcelains, Ceramco and Procera, after they were exposed to 900 hours of accelerated aging. Twenty titanium plates provided the substrate to which the Procera porcelain samples in shades A3, A3.5, C3, and D3 were fired, five in each shade. An equal number of metal-ceramic alloy (Olympia) plates were cast to the same dimensions to form the 20 substrates to which Ceramco porcelain was fired. The four shades of porcelain were again added to each of the samples. Commission International de l'Eclairage L a b readings were recorded with a Minolta Chroma Meter II before and after exposure to 900 hours of accelerated aging simulation. After the aging process the color differences between the pretest and posttest condition were calculated. Although statistical comparisons demonstrated a difference in color change (p < or = 0.05) between Ceramco and Procera porcelain in three of the shades tested, critical remarks of color refer to both types having "slight" color change. In terms of color stability, neither porcelain had "noticeable" changes after 900 hours of accelerated aging.

Color↗

PubMed1993

The shear strength of polymethyl methacrylate bonded to titanium partial denture framework material.

Premachined titanium frameworks are used in implant-supported fixed complete-arch prostheses. Traditionally, retentive mechanisms are incorporated in the wax patterns to provide retention between polymethyl methacrylate and the cast framework. Nontraditional forms of retention are needed with machined frameworks. This study determined whether three different surface characteristics of titanium improve the bond shear strength of polymethyl methacrylate. Thirty rod shaped specimens of titanium were divided into three equal groups: group 1 received no pretreatment; group 2 was pretreated with 110 microns alumina air abrasive; and group 3 was pretreated with 110 microns alumina air abrasive plus silane (clear). Denture resin was processed around each specimen. A Shell-Nielsen shear test was then performed at a crosshead speed of 0.5 mm/minute to determine the bond shear strength in kilograms per square centimeter. The bond shear strength of group 3 was 63% greater than group 1 (significant, p < 0.01; ANOVA-Scheffé interval 63 kg/cm2). The results of this study indicated that surface pretreatment of titanium with 110 microns alumina air abrasive plus silane coating significantly enhances the bond shear strength of polymethyl methacrylate.

Aluminum Oxide↗

PubMed1992

Denture base resins: comparison study of color stability.

Several denture base resins have been recently introduced that provide easier or faster processing. Although these materials have adequate strength properties, the color stability is also of interest. This study evaluated the color stability of five denture base acrylic resins and one denture base repair resin. The samples were subjected to conditions of accelerated aging to test color stability. Five samples of each material were processed and aged for 100 and 300 hours. The color stability was quantitatively measured using the Minolta Chroma Meter II. Color measurements were made before weathering and at 100 and 300 hours the color difference delta E was calculated for all samples. At 300 hours the color change of the materials was significantly different at p less than 0.01. It was found that: (1) the color of Lucitone Hy-pro and Acron was least affected by conditions of accelerated aging; (2) Triad, Accelar 20, and Perm demonstrated noticeable color changes; and (3) Compak-20 had an appreciable color change and was the least color-stable of the materials tested.

Acrylic Resins↗

PubMedDate not supplied

Polishing sequence for titanium using dental armamentarium: a pilot study.

With the increasing use of titanium in dentistry, the methods for maintenance, particularly the polishing sequence, have become especially important. Thirty test samples of commercially pure grade 2 titanium were sandblasted with 110 microns aluminum oxide at 60 psi to establish a baseline surface roughness. Two samples were exposed to each of 15 different polishing sequences. Scanning electron photomicrographs of the polished samples were taken at x100 and randomly assigned identification numbers. The photomicrographs were evaluated and ranked by six dentists for surface smoothness. The best surface polish was obtained with the following sequence: aluminum oxide stone, green Flexie rubber abrasive wheel, white Flexie rubber abrasive wheel, flour of pumice on a wet rag wheel, buffing bar compound on a felt wheel, rouge on a felt wheel, and rouge on a chamois wheel.

Dental Polishing↗

PubMedDate not supplied

4-META polymethyl methacrylate shear bond strength to titanium.

Machined titanium substructures for fixed, complete arch prostheses have been used with various surface pretreatments to enhance acrylic bonding. Since traditional mechanical methods for denture base material retention cannot be used, silane and surface abrasives have been used to enhance retention. The purpose of this study was to determine if a metal bonding denture base material provided a favorable bond strength to machined titanium. Fifteen rod-shaped samples of commercially pure Grade 2 titanium were divided into two groups, five samples representing the control group and 10 samples for the experimental group. The rod samples for the control received no pretreatment, while the experimental samples were pretreated with 110 microns alumina abrasive. Meta-Dent heat-cured polymethyl methacrylate was processed around each sample in a secondary cylindrical shape approximately 0.9 x 1.0 centimeters with the titanium rods extending from each end. A Shell-Nielsen shear test was then performed at a crosshead speed of 0.5 millimeters/minute to determine the bond strength. The experimental group demonstrated a mean bond strength 3.7 times greater than the control group (significant, P = 0.0001, ANOVA). Pretreatment with 110 microns alumina air abrasive significantly enhanced the bond strength of heat-cured metal bonding polymethyl methacrylate to titanium.

Acrylic Resins↗