Friedrich Graef

Strain situation after fixation of three-unit ceramic veneered implant superstructures.

The passive fit of superstructures used in implant prosthodontics is affected by several variables. The objective of this study was to quantify the strain development in various fixed partial dentures (FPDs), both in the condition as cast and after ceramic veneering. Five different types of three-unit FPDs (cementable/repositioning technique impression; cementable/pick-up technique impression; screw-retained/plastic cylinder; screw-retained/gold cylinder; screw-retained/bonded) with 10 samples each, representing commonly used FPD-types, were investigated before and after ceramic veneering. Two ITI implants were anchored in a measurement model simulating a real-life patient situation and strain gauges were mounted close to the implants. The strain development was recorded during cement setting and screw fixation. For statistical analysis, multivariate two-sample tests were performed with the level of significance set at P = 0.1. All FPDs revealed measurable amounts of strain. Neither the impression technique nor the fabrication modes for conventional screw-retained FPDs had a significant influence on strain development. Ceramic veneering caused an increase in strain development for the conventional bridge types. Furthermore, cementing appears to be able to compensate fabrication inaccuracies better than screw retention. The lowest strains were found in FPDs bonded to gold cylinders on the measurement model for metal frames and ceramic-veneered FPDs. Conventional procedures are unable to produce superstructures with an absolute passive fit. The technique of bonding superstructures to prefabricated components in the oral cavity seems to compensate for various shortcomings in superstructure fabrication.

Entropy Optimizing Methods for the Estimation of Tables

A new procedure for the problem of recovering tabular data in case of incomplete or inconsistent information is presented. It generalizes the well kown RAS (or IPF) algorithm by allowing a wider class of constraints concerning the table entries such as equalities and inequalities over arbitrary cross sections. The theoretical background of the procedure is outlined and some examples of applications are reported.

Improvement and long‐term stability of neuromuscular adaptation in implant‐supported overdentures

OBJECTIVES In edentulous patients, implant-supported overdentures can improve chewing efficiency and patient satisfaction, and even a positive impact on bone tissue preservation has been observed. The objective of this long-term study was to investigate whether kinesiographic and electromyographic (EMG) parameters would also benefit from implant placement and whether the status achieved would remain consistent over time. MATERIAL AND METHODS The functional adaptability of the neuromuscular system in edentulous patients has been recorded in four different states of restoration: (1) insufficient old dentures, (2) new complete dentures, (3) implant-supported overdentures, and (4) implant-supported overdentures 10 years in use. In each state of restoration, the neuromuscular adaptation was assessed during masticatory activity on the basis of myodynamic parameters such as vertical opening, frontal extension and closing velocity. EMG parameters, i.e. Musculus masseter and Musculus temporalis activities were recorded simultaneously. RESULTS The results revealed a general increase in the myodynamic and EMG-parameters. All of them clearly approached the values for normal dentate subjects and maintained this level over a period of 10 years. The significant changes between states 2 and 3 indicate that implant stabilization of dentures is accompanied by an immediate increase of the neuromuscular parameters. CONCLUSIONS In elderly edentulous patients, the treatment with two interforaminal implants provides evidence of neuromuscular adaptation towards values of healthy dentate. Thus, the known benefits of implant placement such as tissue perseverance and improved function are complemented by improved neuromuscular adaptation.

Passivity of fit of CAD/CAM and copy-milled frameworks, veneered frameworks, and anatomically contoured, zirconia ceramic, implant-supported fixed prostheses

STATEMENT OF PROBLEM There is less information on the quality of fit of zirconia frameworks with or without ceramic veneer than on anatomically contoured milled zirconia restorations. PURPOSE The purpose of this in vitro study was to evaluate the strain development of CAD/CAM fabricated zirconia ceramic frameworks with and without ceramic veneering, copy-milled zirconia ceramic frameworks, and copy-milled zirconia ceramic anatomic contour restorations. MATERIAL AND METHODS Four groups of 3-unit implant-supported cement-retained restorations were fabricated (n=10) to fit an in vitro model with 2 implants. Strain gauges which recorded the strain development of all restorations during cementation were attached to the model mesially and distally adjacent to the implants. Mean absolute strain values were recorded for statistical analysis (MANOVA with Pillais trace; α=.05). RESULTS Mean absolute strain development at the different strain gauge locations ranged from 83.23 µm/m for copy-milled zirconia ceramic anatomic contour restorations to 301.20 µm/m for veneered CAD/CAM fabricated zirconia ceramic restorations. Significant effects (P<.001) of the fixed factors restoration type and veneering status, as well as of their interaction term (P=.001) were found. Ceramic veneering of CAD/CAM frameworks resulted in higher strain development, whereas the greater volume in copy-milled anatomic contour restorations did not affect accuracy. CONCLUSIONS With the systems used in this study, zirconia ceramic-based anatomic contour restorations show greater passivity of fit than ceramic veneered CAD/CAM fabricated zirconia ceramic frameworks.

In vitro fracture resistance of copy-milled zirconia ceramic posts

STATEMENT OF PROBLEM Current copy-milling systems allow for the fabrication of 1-piece zirconia ceramic posts and cores, which can be used in combination with ceramic crowns to restore endodontically treated teeth in an esthetic manner. However, limited data are available on the fracture resistance of copy-milled zirconia ceramic posts. PURPOSE The purpose of this in vitro study was to compare the fracture resistance of prefabricated posts made from zirconia ceramic and fiber-reinforced composite resin with the fracture resistance of copy-milled zirconia ceramic posts. MATERIAL AND METHODS Three groups of posts and cores were fabricated (n=10): prefabricated zirconia ceramic posts with composite resin cores (ZIR), fiber-reinforced composite resin posts with composite resin cores (FRC), and copy-milled zirconia ceramic posts and cores (CM). Following artificial aging by thermal cycling and masticatory simulation, compressive tests were performed in a universal testing machine with the posts mounted at an angle of 135 degrees to the long axis of the posts. The maximum forces needed to fracture the posts were recorded for statistical analysis (1-way ANOVA, Tukeys Honestly Significant Difference test; alpha=.05). RESULTS The mean maximum forces (SD) needed to fracture the posts and cores were 123.10 (19.38) N for FRC, 139.30 (42.70) N for CM, and 267.10 (59.11) N for ZIR. The prefabricated zirconia ceramic posts required significantly higher fracture loads as compared to FRC (P<.001) and CM (P<.001). CONCLUSIONS The fracture load of copy-milled zirconia ceramic posts is significantly lower than that of prefabricated zirconia ceramic posts of the same size.

The effect of load cycling on metal ceramic screw-retained implant restorations with unrestored and restored screw access holes

STATEMENT OF PROBLEM It has been shown that under cyclic loading, more chipping fractures of the veneer ceramic occur on the occlusal surface of screw-retained implant-supported fixed partial dentures (FPDs) with unrestored screw access holes (SAHs) than in cemented restorations. This lack of stability may result in esthetic and functional problems. PURPOSE The purpose of this study was to investigate whether, under dynamic loading, fewer chipping fractures occur on the occlusal surface of screw-retained ceramic veneered implant FPDs with restored SAHs than in those with unrestored SAHs. MATERIAL AND METHODS Twenty screw-retained ceramic veneered 5-unit FPDs were manufactured for a 3-implant situation and divided into 2 groups of 10 unrestored and 10 SAHs restored with adhesive composite resin restorations (Tetric Evo Ceram). A masticatory simulator was used to load the FPDs occlusal to the implant positions for 20,000 cycles with a force of 100 N applied for 1 second, followed by 1 second of no loading. Three prosthodontists evaluated the FPDs using a light microscope and a dental probe. The number of chipping fractures found were analyzed using a generalized linear model with Poisson response and log link function (alpha =.05). RESULTS Investigators found significantly more chipping fractures in the group of screw-retained FPDs with unrestored SAHs. The rate ratio of unrestored versus restored prostheses was 3.29 (P=.006). CONCLUSIONS Adhesive composite resin restorations can significantly reduce the number of chipping fractures occurring around the SAHs of screw-retained implant-supported restorations.

Osstell Resonance Frequency Measurement Values as a Prognostic Factor in Implant Dentistry

Resonance frequency analysis (RFA) using the Osstell device (Osstell AB, Gothenburg, Sweden) has been advocated for quantifying implant stability on a relative scale of implant stability quotients (ISQ). It was the goal of this prospective clinical study to evaluate whether a certain ISQ level, at the time an implant is placed, correlates with successful osseointegration as some have claimed. Four hundred ninety-five implants (Straumann AG, Basel, Switzerland), varying in length and diameter, were placed in a private practice, strictly adhering to the implant manufacturers surgical protocol. After placement and after healing periods of 42 days in the mandible and 56 days (implant manufacturers protocol) in the maxilla, implant stability was measured using RFA. After healing, implants were torqued forward at 35 Ncm and allowed to heal further if the patients felt discomfort. Statistical analysis of the data obtained was based on Welch tests and Kolmogorov-Smirnow tests (level of significance α = 0.05). Results showed that 432 implants were osseointegrated after the predefined healing periods while 8 implants were lost and, in 55 cases, healing was prolonged. Both at insertion (P = .025) and after healing (P < .001), successful implants showed significantly different ISQ values as compared to implant failures or implants with prolonged healing. However, overlapping ISQ distributions at implant insertion demonstrated that there was no correlation among the data that could be used to predict successful osseointegration. Within the limits of this study, the prognostic value of ISQ values appears to be ambiguous.

Sensitivity of transillumination for detecting microcracks in feldspathic and zirconia ceramic materials

STATEMENT OF PROBLEM Despite good clinical success rates of ceramic restorations, fractures of substructures made from high-strength dental ceramics remain an issue. Transillumination of ceramic restorations has been proposed as a means of quality assurance. PURPOSE The purpose of this study was to compare the sensitivity of transillumination and the fluorescent penetrant method (FPM) in detecting microcracks in zirconia and feldspathic ceramic materials. MATERIAL AND METHODS Two groups (n=20) of standardized plates were fabricated from zirconia ceramic (Cercon) and feldspathic ceramic (VITABLOCS Mark II for CEREC) materials, and central holes were created to induce microcracks. The plates were microscopically analyzed at ×20 magnification by means of transillumination and FPM. Based on whether the criterion crack was recognized or not recognized, contingency tables were developed. Fishers exact test for count data was used to compare frequency distributions (α=.05). RESULTS Minimum crack length as detected by FPM was 18 μm in zirconia ceramic and 17 μm in feldspathic ceramic. For transillumination, minimum detectable crack length was 54 μm in zirconia ceramic and 33 μm in feldspathic ceramic. Thirty-seven percent of cracks in feldspathic ceramic plates and 64% of cracks in zirconia ceramic plates could not be detected by means of transillumination. The conditional probabilities for a crack being detected by transillumination, although it was detected by FPM, were significantly lower than 1 for both materials (P<.001). Although transillumination was less sensitive than FPM on a relative scale, it was not possible to demonstrate a general difference between the 2 analyzing techniques by using statistical methods. CONCLUSIONS Using FPM as a relative reference system, transillumination appears to be less sensitive in detecting microcracks in ceramic components.

Use of Osteotomes for Implant Bed Preparation—Effect on Material Properties of Bone and Primary Implant Stability

The aim of this study was to evaluate the efficacy of osteotomes in enhancing bone quality as compared to conventional implant bed preparation using burrs. Polyurethane foam blocks differing in den...

Determination of Alveolar Bone Quality during Dental Implant Surgery by Means of Compressive Testing

It has been demonstrated that alveolar bone of poor quality is associated with higher failure rates for dental implants. The aim of this investigation was to test a novel device (BoneProbe) for the determination of bone quality during implant surgery based on compressive testing.