The role of the American Prosthodontic Society in founding The Journal of Prosthetic Dentistry.
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History, 20th Century↗
Biomedical subjects
B R Lang
Publications and source records attributed to B R Lang.
Examination of the implant-abutment interface after fatigue testing.
PURPOSE: This study examined potential differences in detorque values of abutment screws after fatigue testing when the dimensions between external implant hexagon and internal abutment hexagon were altered or the implant external hexagonal shape was eliminated. MATERIAL AND METHODS: Three subsets (N = 10) of NobelBiocare implants were assessed: (1) standard external hexagon (R), (2) modified hexagon (M), and (3) circular (C) platform geometry. Thirty Procera machined abutments with 25-degree angulated loading platforms were manufactured. Abutments were retained with gold Unigrip abutment screws tightened to 32 N/cm with an electronic torque controller. Vertical scribes across the implant-abutment interface allowed longitudinal displacement evaluation. A carousel-type fatigue testing device delivered dynamic loading forces between 20 and 200 N for 5,000,000 cycles, or the approximate equivalent of 5 years in vivo mastication, through a piston to the abutment platform. Macroscopic and radiographic examination of the implant/abutment specimens was performed. The abutment screws were removed and the detorque values recorded. Bearing surfaces were examined microscopically. RESULTS: No abutment looseness or longitudinal displacements at the implant-abutment interface were noted. Radiographic examination demonstrated no indication of screw bending or displacement. The mean detorque values for R, M, and C were 14.40 +/- 1.84 N/cm, 14.70 +/- 1.89 N/cm, and 16.40 +/- 2.17 N/cm, respectively. The analysis of variance demonstrated significant differences between only designs R and C (P=.031). CONCLUSION: Increasing the vertical height, or degree of fit tolerance, between the implant external hexagon and the abutment internal hexagon or completely eliminating the implant external hexagon did not produce a significant effect on the detorque values of the abutment screws after 5,000,000 cycles in fatigue testing, or the equivalent of 5 years' of mastication for the implant/abutment specimens evaluated.
Analysis of Variance↗
A tribute to leadership, dedication, and performance in publishing.
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History, 20th Century↗
The overview: an article that interrogates the literature.
Although the question on the efficacy of chlorhexidine therapy for the clinician's adult patient may not have been totally answered, a greater perspective on this treatment modality was gained by the reader because of the quality of the overview cited, and the evidence-based approach used by the authors in performing the overview.
Dental Research↗
Clinical methods for evaluating implant framework fit.
STATEMENT OF PROBLEM: Passive fit of implant-supported-prosthesis frameworks has been suggested as a prerequisite for successful long-term osseointegration. However, there are no scientific guidelines as to what is passive fit and how to achieve and measure it. PURPOSE: The purpose of this article is to discuss passive fit and to review the various clinical methods that have been suggested for evaluating implant framework fit.Methods. The dental literature was reviewed to identify the clinical methods that have been used to evaluate implant framework fit. CONCLUSIONS: The suggested levels of passive fit are empirical. Numerous techniques have been advocated to evaluate the prosthesis-implant interface, but none individually provides objective results. It is suggested that clinicians use a combination of the available methods to minimize misfits.
Dental Alloys↗
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↗
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↗
Resistance to fracture of three all-ceramic systems.
All-ceramic restorations have become an attractive alternative to porcelain-fused-to-metal crowns, but their strength is still an important issue. The purpose of this study was to compare the in vitro fracture resistance of three all-ceramic systems: IPS Empress, In-Ceram, and Procera AllCeram. Thirty dies were replicated from a master die using high filler resin with a modulus of elasticity similar to dentin. Ten cores each of In-Ceram and Procera were fabricated to a thickness of 0.5 mm. The remaining porcelain was applied using a sculpting device to produce a crown with a final thickness of 1.0 mm axially and 2.5 mm occlusally. Ten IPS Empress crowns were mixed to the same dimensions and were pressed by the manufacturer. The internal surfaces of all the crowns were etched and silanated prior to cementation with a resin cement (Panavia 21). The cemented samples were loaded in an Instron machine until fracture. The mean fracture loads were: IPS Empress, 222.45 (+/- 49) kg; In-Ceram, 218.8 (+/- 36) kg; Procera AllCeram, 194.20 (+/- 37) kg. Tukey's test showed no statistically significant differences among the three all-ceramic systems at p < .05.
Aluminum Oxide↗
Procera: a new way to achieve an all-ceramic crown.
The Procera System embraces the concept of computer-assisted design and computer-assisted machining to fabricate an all-ceramic crown composed of a densely sintered, high-purity aluminum oxide coping combined with a compatible veneering porcelain. Strength, precision of fit, color stability, cementation, and wear characteristics are among the many factors that concern clinicians when fabricating all-ceramic restorations with this new crown system. This article presents, in summary form, the data from the many studies on Procera AllCeram crowns that have been conducted at clinical and laboratory centers around the world. The evidence reported in these studies clearly demonstrates that the Procera AllCeram crown represents a combination of computer technology and creativity for which a positive prognosis can be made. Today its application is restricted to single crowns; however, with continued development, multiple unit all-ceramic anterior and posterior fixed partial dentures are clearly in the future.
Cementation↗
Critical evaluation of patient responses to dental implant therapy.
STATEMENT OF PROBLEM: Successful rehabilitation of the edentulous condition requires functional and psychosocial adaptation by the patient. Quality of life is markedly affected by the amount of satisfaction or dissatisfaction with their dental therapy. Patient concerns are primarily related to comfort, function, and esthetics. When these do not meet the patients expectations, anxiety, insecurity, diminished self-esteem, and introversion are typical psychosocial responses. PURPOSE: The objectives of the study were to assess the patient's subjective feelings about: (a) comfort, (b) function, (c) esthetics, (d) speech, (e) self-image, and (f) overall dental health with their existing complete dentures, and after implant therapy and prosthodontic rehabilitation. MATERIAL AND METHODS: Two health-related quality of life (HRQL) questionnaires were developed to evaluate the effectiveness of dental implant therapy; one dealing with their feelings about their conventional complete dentures, and the second dealing with implant therapy. The first questionnaire was administered with supervision before receiving implant treatment. The second questionnaire was administered within 1 year after completion of prosthetic rehabilitation. Twenty-six patients who received implants to support a mandibular prosthesis and a new maxillary denture formed the experimental population. RESULTS: Discriminative and evaluative analysis of subjective patient responses provided reliable, accurate, and reproducible results. Assessment of subject feelings before and after implant therapy and prosthodontic rehabilitation demonstrated significant differences when before treatment responses were compared with the responses after therapy. CONCLUSIONS: Significant differences for comfort, function, speech, esthetics, self-image, and dental health were demonstrated when conventional complete dentures and dental implant therapy were compared. HRQL data provided scientific evidence of an improved quality of life after dental implant therapy (p < 0.000).
Adaptation, Physiological↗
Fit of implant frameworks fabricated by different techniques.
PURPOSE: This study evaluated the precision of fit between an implant framework and a patient simulation model that consisted of five implant abutments located in the mandibular symphysis area. One-piece cast frameworks were compared with Procera machined and laser-welded frameworks with laser videography. MATERIAL AND METHODS: Five frameworks of each type were measured with a laser digitizer and a graphics computer program to determine a single point represented as the "Centroid" for each framework component and each implant abutment. Differences between the paired centroids for each framework/abutment interface are reported as x- and y-axis displacements, and z-axis gaps. The direction of the x- and y-axis displacements was determined. RESULTS: There were significant differences (p < 0.05) in the precision of fit between both the one-piece cast frameworks and the Procera frameworks, when compared with the abutments in the patient simulation model. The laser-welded framework exhibited a more precise fit than the one-piece casting, with significant differences at four of the five prosthodontic interfaces, when evaluated by the mean z-axis gap at the centroid points.
Computer Graphics↗
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↗
A regression analysis of filler particle content to predict composite wear.
STATEMENT OF PROBLEM: It has been hypothesized that composite wear is correlated to filler particle content. There is a paucity of research to substantiate this theory despite numerous projects evaluating the correlation. PURPOSE OF STUDY: The purpose of this study was to determine whether a linear relationship existed between composite wear and filler particle content of 12 composites. MATERIAL AND METHODS: In vivo wear data had been previously collected for the 12 composites and served as basis for this study. Scanning electron microscopy and backscatter electron imaging were combined with digital imaging analysis to develop "profile maps" of the filler particle composition of the composites. These profile maps included eight parameters: (1) total number of filler particles/28742.6 microns2, (2) percent of area occupied by all of the filler particles, (3) mean filler particle size, (4) percent of area occupied by the matrix, (5) percent of area occupied by filler particles, r (radius) 1.0 < or = micron, (6) percent of area occupied by filler particles, r = 1.0 < or = 4.5 microns, (7) percent of area occupied by filler particles, r = 4.5 < or = 10 microns, and (8) percent of area occupied by filler particles, r > 10 microns. Forward stepwise regression analyses were used with composite wear as the dependent variable and the eight parameters as independent variables. RESULTS: The results revealed a linear relationship between composite wear and the filler particle content. CONCLUSION: A mathematical formula was developed to predict composite wear.
Analysis of Variance↗
Examining patients' responses about the effectiveness of five denture adhesive pastes.
In this clinical trial, the authors evaluated the responses of 25 experienced denture wearers in regard to the effectiveness of five denture adhesive pastes. The patients responded to questions about the effect of the pastes on quality and duration of retention as well as on mastication. Subjects were also asked which product they considered to be best. Eighteen (72 percent) of the 25 subjects rated Secure (John O. Butler Co.) denture adhesive paste best overall.
Adhesives↗
Analysis of strain at selected bone sites of a cantilevered implant-supported prosthesis.
Cantilever length of the superstructure of an implant-supported prosthesis can be affected by the location, number, and dimensions of the implants, arch form, opposing dentition, and functionally generated forces. In this study, the effects of cantilever length on load distribution to implants was analyzed. A fresh bovine rib was used to create a clinical simulation in which three implants were used to support an implant prosthesis. The implants were connected by means of a cantilevered superstructure. Six linear strain gauges were placed in strategic locations where it has been reported that stress is concentrated. The model was loaded with an Instron machine and the load was applied at 0, 5, 10, 15, 20 and 25 mm along the cantilever length. Each loading test was repeated five times, and loads of 10 and 20 pounds were applied. Dynamic registration of the strain was recorded at each gauge. Significant differences in the magnitude of strain between the six strain gauge locations were recorded with the 10 and 20 lb loads and at all cantilevered lengths. The results revealed that the greatest maximum strain occurred at the strain gauge positioned on cortical bone over the apex of the most distal implant under both loading conditions.
Analysis of Variance↗
The influence of occlusal design on simulated masticatory forces transferred to implant-retained prostheses and supporting bone.
The influence of occlusal surface design on the longitudinal success of implant treatment is believed to be significant, but it is not well understood. It has been suggested that limiting lateral forces by reducing cuspal inclination is beneficial in the maintenance and preservation of osseointegration. This study used a method to apply quantified vertical forces to a food substance and record the forces and strain transmitted through cusped 33-degree and cuspless 0-degree occlusal design specimens to a simulated implant-retained prosthesis and the supporting bone. A series of five masticatory cycles were applied to each of the specimens with a universal testing machine. The data were analyzed to compare (1) forces required to cause initial breakage of the food, (2) maximum breakage forces applied before cycle termination, and (3) maximum strain registered by strain gauges at the bone level. Initial breakage forces for the cuspless specimen were 50% less than for the cusped specimen (p = 0.006). No significant differences were found between maximum breakage forces and maximum strain (p values 0.744 and 0.315, respectively). The results of this pilot study indicated that the occlusal configuration and cusp angulation of implant-retained prostheses play a significant role in force transmission and the stress-strain relationship in bone.
Animals↗
Measuring fit at the implant prosthodontic interface.
Four centers in the United States and Sweden have been working for 2 years to develop systems and methods for measuring fit at the prosthodontic interface. Two systems are based on stylus contact techniques, one system uses a laser as its reader source, and one system is photogrammetric. All the systems are capable of providing data as three-dimensional x, y, and z axes coordinate values that can be transformed into linear and angular data that characterize the bearing surfaces of abutments or abutment replicas and their mating components in the prosthesis framework. The centroid, a single point computed from the collected data, was the measurement unit, derived for these bearing surfaces, that was used to compare the systems. All four methods can most likely detect misfits that are relevant in the clinical setting; however, only one system can be used intraorally. When any measurement system is assessed, the data should always be examined for repeatability to establish the reliability of the system. This investigation made comparisons among the measurement methods used at the four centers. It was apparent from this study that comparisons of data from measurement systems should be rounded to the nearest 10 microns. The SDs determined in the comparisons were larger than 5 microns and therefore misfits should be calculated in terms smaller than 10 microns. This final point is important to the clinician who relies on research reports about precision of fit when selecting treatment approaches in caring for the implant prosthodontic needs of their patients.
Calibration↗
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↗