Biomedical subjects

Murat C Cehreli

Publications and source records attributed to Murat C Cehreli.

At least 19 recordsLinked to original sources

PubMed2006

Impression techniques and misfit-induced strains on implant-supported superstructures: an in vitro study.

The purpose of this study was to compare misfit-induced strains on implant-supported superstructures fabricated by two impression techniques and two different elastomeric impression materials. A master cast hosting four Straumann implants was constructed. On this cast, a total of 21 implant-level impressions were made by the direct technique using a polyether impression material and synOcta screwed aluminum impression caps (PE-D), and by the indirect technique using polyether (PE-IN) or polyvinylsiloxane impression material (VPS-IN) with snap-on impression caps and synOcta plastic positioning cylinders. Two casts were randomly selected from each group of seven, and a total of four screw-retained superstructures, supported by either two or four implants (one of each type on both casts), were cast in a gold alloy for each group. Linear strain gauges were bonded on the superstructures, and misfit-induced strains were recorded during superstructure connection on each of the working casts and on the master cast using a data acquisition system and corresponding software at a sample rate of 10 kHz. Connection on the implants in the master cast increased strains considerably on most of the superstructures, in comparison with strain gradients measured when the superstructures were connected on the casts from which they were fabricated (P <.05). The differences in strain amplitude between connection on the cast from which the superstructure was fabricated and on the master cast were higher for superstructures fabricated by PE-D than for those fabricated by PE-IN and VPS-IN. The snap-on indirect impression technique for Straumann implants leads to acceptable superstructures, regardless of the impression material used.

Aluminum↗

PubMed2005

Fracture resistances of cast metal and ceramic dowel and core restorations: a pilot study.

PURPOSE: The purpose of this study was to compare fracture strengths of teeth restored with cast metal and ceramic dowel and cores supporting all-ceramic crowns. MATERIALS AND METHODS: Eighteen recently extracted teeth were randomly divided into 3 equal groups. Metal dowel and cores (MDC) were fabricated for 1 group using a base metal alloy, and served as the control. The other groups received In-Ceram Spinell (ICS) and IPS Empress 2 (IPS) dowel and cores. IPS Empress 1 crowns were fabricated for all samples. Each tooth was subjected to a shear force at a crosshead speed of 2 mm/min on a universal testing machine until failure occurred. RESULTS: The mean fracture strengths and standard deviations of MDC, ICS, and IPS restorations were 1101 N (361), 832 N (288), and 1137 N (367), respectively. The differences between groups were insignificant (p < 0.05). Fractures of the all-ceramic crowns were observed in the MDC group, whereas the failure of ceramic dowel and core restorations was associated with root fracture at the cervical region. CONCLUSIONS: Due to improved mechanical properties, In-Ceram Spinell and IPS Empress 2 ceramic dowel and cores may be candidates for the restoration of endodontically treated anterior teeth.

Aluminum Oxide↗

PubMed2005

Mechanobiology of bone and mechanocoupling of endosseous titanium oral implants.

OBJECTIVE: To provide an evidence-based overview and critical evaluation of the mechanobiology of bone and mechanocoupling of osseointegrated oral implants and the consequences of varying clinical and potential artificial loading regimens on bone tissue differentiation around implants. METHODS: The literature was searched, using medline and manual tracing of references cited in key papers as well as submitted fundamental studies otherwise not elicited, for original research articles and review articles relating to the mechanobiology of bone and load-bearing endosseous implants and the time-dependent biological and biomechanical outcome of conventional-, early-, immediate-, and artificial-loading regimens on initial and long-term effectiveness of oral implants. CONCLUSIONS: Implant design, particularly implant surface, has a decisive role on interface force transmission but not on the long-term clinical effectiveness of oral implants. Overloading and stress shielding have often been cited as the primary biomechanical factors leading to marginal bone loss around implants, although there is no consensus on these factors. Low-magnitude, high-frequency mechanical signals may be future candidates for promoting osseointegration and increasing bone density and bone mass around load-bearing osseointegrated implants. Computational technologies and (bio)sensors used for mechanobiological/biomechanical evaluation of bone and oral implants are still at their early stages of application, which results in a little pool of evidence on mechanocoupling of oral implants and biomechanical evaluation of various clinical loadings.

Animals↗

PubMed2004

Analysis of strain around endosseous dental implants opposing natural teeth or implants.

STATEMENT OF PROBLEM: Natural teeth and implants have different force transmission characteristics to bone. PURPOSE: The purpose of this study was to compare strains induced around a natural tooth opposing an implant with strains around occluding implants under static and dynamic loads. MATERIAL AND METHODS: Occlusion was created between a natural molar tooth and an implant in 1 side, and 2 implants in the contralateral side of acrylic resin models of both jaws. Strain-gauges were bonded around the neck of the natural tooth and implants, and strains were measured under 75 N and 100 N static axial and lateral dynamic loads in separate load situations using a data acquisition system at sample rate of 1000 Hz. The strain data of the natural tooth and implants were compared for each load by Kruskal-Wallis testing followed by the multiple comparison test (alpha=.05). RESULTS: Compressive strains were induced around natural tooth and implants as a result of static axial loading, whereas combinations of compressive and tensile strains were observed during lateral dynamic loading. Strains around the natural tooth were significantly lower than the opposing implant and occluding implants in the contralateral side for most regions under all loading conditions ( P <.05). There was a general tendency for increased strains around the implant opposing natural tooth under higher loads and particularly under lateral dynamic loading ( P <.05). CONCLUSION: Under static and dynamic loads, strain magnitudes around a natural tooth were significantly lower than that of an opposing implant and occluding implants in the contralateral side.

Bite Force↗

PubMed2004

Narrow-diameter implants as terminal support for occlusal three-unit FPDs: a biomechanical analysis.

The purpose of this study was to examine force transmissions of narrow-diameter ITI implants when used as a terminal support for freestanding three-unit fixed partial dentures (FPD). Photoelastic and strain-gauged models of two 4.1-mm-diameter solid-screw implants; a 3.3-mm reduced-diameter implant and a 4.1-mm-diameter solid-screw implant; and a 3.3-mm-diameter narrow-neck implant and a 4.1-mm-diameter solid-screw implant supporting fixed prostheses were fabricated. A static force of 100 N was applied on both implants and on the pontic of the prostheses in separate load cases, and the generation of isochromatic fringes was observed and photographed in the field of a circular polariscope. The strain-gauge signals were digitized by a data-acquisition system and displayed in a computer by corresponding software at a sample rate of 10,000 Hz, and the principal strains were calculated. The use of narrow-neck and reduced-diameter implants resulted in an overall increase in stress and strain magnitudes around supporting implants in comparison with support from two standard solid-screw implants. Narrow-diameter ITI implants may be used to support FPDs for patients with low bite forces. In other clinical situations involving narrow-diameter implants, increasing the implant support is crucial to improve the biomechanical outcome of the treatment.

Biomechanical Phenomena↗

PubMed2003

The effect of current bleaching agents on the color of light-polymerized composites in vitro.

STATEMENT OF PROBLEM: Bleaching agents may affect the color of existing composite restorations. PURPOSE: The purpose of this study was to compare the effect of 10% carbamide peroxide and 10% hydrogen peroxide on the color of light-polymerized hybrid, macrofilled, and polyacid-modified composites. MATERIAL AND METHODS: Two light-polymerized hybrid composites (3M Valux and Spectrum TPH), 1 macrofilled condensable composite (Solitaire), and 2 polyacid-modified composites (Dyract AP and Compoglass) were used. The hybrid composites served as controls. The color of 8 specimens of each material was analyzed by use of a spectrophotometer before bleaching. The specimens were then divided randomly into 2 subgroups (n=4). One group was immersed in 10% carbamide peroxide solution and the other in 10% hydrogen peroxide, for 8 hours each for 14 consecutive days. After bleaching, color changes (Delta E) were determined for each material and compared by use of the Kruskal-Wallis test, followed by the Mann-Whitney U test (P<.05). RESULTS: After bleaching with carbamide peroxide, the color changes (Delta E) for Dyract AP (2.18; SD = 1.41), Compoglass (1.14; SD = 0.26) and Solitaire (1.56; SD = 0.89) were higher than the color changes recorded for 3M Valux (0.63; SD = 3.60), and Spectrum TPH (0.66; SD = 1.24). The differences between materials bleached with carbamide peroxide were not statistically significant. After bleaching with hydrogen peroxide, the color changes for Dyract AP (9.39; SD = 0.53) and Compoglass (5.15; SD = 0.52) were higher than the changes recorded for Spectrum TPH (4.53; SD = 1.53) and 3M Valux (3.41; SD = 4.40), whereas the color change of Solitaire (3.69; SD = 0.57) was significantly higher than that of 3M Valux (P=.01). The color changes for all restorative materials tested were clinically detectable after the application of 10% hydrogen peroxide. However, clinically noticeable discoloration was observed only for Dyract AP treated with 10% carbamide peroxide. CONCLUSION: In comparison to 10% carbamide peroxide, 10% hydrogen peroxide caused more color changes in the composites tested.

Carbamide Peroxide↗

PubMed2003

Effects of hydroxyapatite-coated and commercially pure titanium oral implant surfaces on compound nerve action potentials.

The aim of this study was to investigate the effects of hydroxyapatite-coated and commercially pure titanium oral implants on nerve conduction. Isolated rat sciatic nerves were placed between two suction electrodes in a bath containing a tyrode solution. The implants were brought into intimate contact with the nerves and evoked compound action potentials (cAPs) were recorded before and after contact with the implants. The commercially pure titanium implants did not cause any change in cAPs. A gradual reduction in cAPs was observed for hydroxyapatite-coated implants. However, this reduction was < 50% after an application time of 120 min. Recovery of the cAPs in this group was recorded after approximately 60 min. We conclude that, although intimate contact with hydroxyapatite-coated implants leads to a reduction in cAPs in nerves in vitro, neither this surface nor a commercially pure titanium surface leads to irreversible neurotoxic effects.

Action Potentials↗

PubMed2002

In vitro evaluation of the effect of a current bleaching agent on the electrochemical corrosion of dental alloys.

The nightguard bleaching of discoloured teeth is currently performed by using % 10 carbamide peroxide. While the material is effective on the bleaching of natural teeth, it may deteriorate crowns, bridges and amalgam restorations placed in the mouth. The purpose of the present study was to investigate the effect of 10% carbamide peroxide on the electrochemical corrosion of various dental casting alloys used for fixed partial dentures and dental amalgam. Tafel extrapolation curves were obtained by the corrosion cell that facilitated simulation of the oral environment and comparison of the corrosion rates of alloys and amalgam was accomplished. The results revealed that unpolished amalgam and nickel-chromium alloy samples had the most and noble alloys had the least corrosion rate.

Carbamide Peroxide↗

PubMed2002

A surgical guide for accurate mesiodistal paralleling of implants in the posterior edentulous mandible.

Malaligned implants often complicate the clinical and laboratory procedures employed for the fabrication of superstructures. Due to improper load distribution, an overall increase in stress concentrations on supporting implants may occur; in the long run, this may compromise the maintenance of the bone-implant interface. The utilization of surgical stents is imperative for optimum implant installation. This article describes a modified surgical stent that serves as a guide to proper mesiodistal paralleling of dental implants.

Bicuspid↗

PubMed2002

Comparison of post-gel shrinkage strains in light-polymerized composite resins.

STATEMENT OF PROBLEM: Polymerization shrinkage is associated with light-polymerized and polyacid-modified composites. PURPOSE: This in vitro study compared the polymerization shrinkage of a light-polymerized hybrid composite, a posterior composite, and a polyacid-modified composite. MATERIAL AND METHODS: Five disk-shaped specimens (1 cm in diameter and 2 mm in thickness) were prepared in a mold from each of the following test materials: a light-polymerized hybrid composite (3M Valux Plus), a posterior composite (Filtek P60), and a polyacid-modified composite (Dyract AP). The hybrid composite served as the control material. A linear strain gauge was placed at the center of each specimen. After the specimens were light-polymerized for 60 seconds under 400-mW/cm(2) light intensity, microstrains were recorded with the strain indicator continuously every 4 seconds for 120 seconds. The data were evaluated with 1-way analysis of variance (P<.05) followed by a post hoc least significant difference test. RESULTS: During the first 20 seconds of light polymerization, all materials exhibited tensile strains between 6 and 55 mu epsilon that quickly converted into compressive strains and continued rising after the light source was removed. The strains for all materials increased at a declining rate until they reached a constant level between 148 and 180 seconds. The polymerization shrinkage recorded for Filtek P60 was the lowest (-190.56 mu epsilon), followed by 3M Valux Plus (-303.94 mu epsilon) and Dyract AP (-345.64 mu epsilon) (P<.05). The dimensional change between Filtek P60 and Dyract AP and between Filtek P60 and 3M Valux Plus was significant (P=.001). However, the difference between Dyract AP and 3M Valux Plus specimens was not significant (P=.208). CONCLUSION: Within the limitations of this study, the light-polymerized posterior composite tested demonstrated less polymerization shrinkage than the polyacid-modified and hybrid composites tested. Polymerization shrinkage velocity significantly affected the magnitude of strains.

Analysis of Variance↗

PubMed2002

A dual-purpose guide for optimum placement of dental implants.

Correct placement of implants is a requirement for implant treatment. The use of computed tomography and precise surgical guides is required when inadequate bone support is anticipated. This article describes the fabrication and use of an acrylic resin dual-purpose guide for radiographic evaluation of recipient sites and implant placement, which uses internally stacked stainless steel surgical guide channels. The drill guides are machined to allow consecutive surgical drills to be used without changing the implant angulation during surgery.

Acrylic Resins↗

PubMed2002

The use of computerized tomography for diagnosis and treatment planning in implant dentistry.

Preoperative radiographic imaging of recipient sites for implant placement is imperative to obtain a functional and aesthetic implant-supported prosthesis. Although conventional radiographic techniques have inherent problems that restrict accurate imaging, the main drawback of panoramic and periapical radiography is the two-dimensional image. Computerized tomography provides cross-sectional radiographic images that facilitate proper assessment of potential recipient sites for implant placement. This paper reviews the role of computerized tomography in implant dentistry.

Anatomy, Cross-Sectional↗

PubMed2002

In vitro strain gauge analysis of axial and off-axial loading on implant supported fixed partial dentures.

The purpose of this study was to compare the in vitro strains on dental implants supporting cement-retained fixed partial dentures under axial and off-axial loading conditions. Ten implants incorporating strain gauges were placed in a certain configuration to simulate different clinical situations and were embedded in an experimental model. Two implant supported three-unit fixed partial dentures were fabricated on four groups of implants, and each group consisted of seven restorations. The prostheses were cemented with a temporary cement. Fifty N vertical load was applied on predetermined axial and off-axial loading locations on the prostheses. Strain indicator readings were recorded at a standardized time following each loading sequence. The point of load transfer affected strains on implants. For all prosthetic designs, off-axial loading generated more strain than axial loading on implants (P < 0.05). In comparison with axial loading, off-axial loading causes bending of the implants that may affect bone loss around the implant collar. Axial loading of implants should be provided by using wide diameter implants, narrow occlusal tables, and proper occlusal contacts on implant restorations.

Analysis of Variance↗

PubMedDate not supplied

The influence of functional forces on the biomechanics of implant-supported prostheses--a review.

OBJECTIVES: To evaluate published evidence related to the influence of functional forces on the biomechanics of implant-supported prostheses. DATA AND SOURCES: The literature was searched for original research articles relating control of loads on dental implants, effects of early and late occlusal loads, the influence of bone quality, prosthesis type, prosthesis material, number of supporting implants, and engineering techniques employed for evaluating mechanical and biomechanical behavior of implants using MEDLINE and manual tracing of references cited in key papers otherwise not elicited. STUDY SELECTION: Current literature on implant biomechanics as main focus and pertinent to key aspects of the review. CONCLUSIONS: The outcome of implant treatment is often maximized when implants are placed in dense bone, number of supporting implants are increased, implant placement configuration reduces the effects of bending moments, and when a fixed prosthesis is delivered to the patient.

Animals↗

PubMedDate not supplied

A comparison of three-dimensional finite element stress analysis with in vitro strain gauge measurements on dental implants.

PURPOSE: The purpose of this study was to evaluate the compatibility of three-dimensional finite element stress analysis and in vitro strain gauge analysis in the measurement of strains on a dental implant. MATERIALS AND METHODS: Two vertically placed implants embedded in a poly(methyl methacrylate) model were used. Strain gauges were bonded to the cervical parts of the implants, and seven cement-retained fixed partial dentures were fabricated. A three-dimensional model of the strain gauge analysis model was constructed, and an additional model in which human bone simulation was provided was also constructed. A static vertical load of 50 N was applied at certain locations to simulate centrally positioned axial and laterally positioned axial loading for strain gauge analysis and three-dimensional finite element stress analysis. RESULTS: Statistically significant increases in strain levels were recorded between loading types in the strain gauge analysis (P < .05). Strains obtained from strain gauge analysis were higher than for three-dimensional finite element stress analysis. There was a remarkable difference between the two finite element models under the conditions of laterally positioned axial loading. CONCLUSION: There are differences regarding the quantification of strains between strain gauge analysis and three-dimensional finite element stress analysis. However, there is a mutual agreement and compatibility between three-dimensional finite element stress analysis and in vitro strain gauge analysis on the determination of the quality of induced strains under applied load.

Analysis of Variance↗

PubMedDate not supplied

Comparison of uniaxial resistance forces of cements used with implant-supported crowns.

PURPOSE: Provisional cements are commonly used to facilitate retrievability of cement-retained fixed implant restorations. While the functional life spans of these cements are unpredictable, the relative retentiveness of various permanent and provisional cements between dental alloys and titanium abutments is not well documented. The aim of this study was to compare the uniaxial resistance forces of permanent and provisional luting cements used for implant-supported crowns. MATERIALS AND METHODS: Seven samples on 4 different abutments (a total of 28 crowns) were cast using a gold-platinum-palladium alloy. The crowns were cemented with 3 different provisional, polycarboxylate, and glass-ionomer cements and 1 zinc phosphate cement. After storage of samples in artificial saliva for 24 hours, tensile tests were performed. RESULTS: While the highest uniaxial resistance forces were recorded for polycarboxylate cements, provisional cements exhibited significantly lower failure strengths (P < .05). The uniaxial resistance force of cements on different abutments exhibited notably different trends; however, more force was required to remove crowns cemented to long abutments (P < .05). DISCUSSION: Glass-ionomer and zinc phosphate cements may be used to increase the maintenance of implant-supported crowns. Temporary cementation of such restorations may necessitate frequent recementation, particularly for restorations on short abutments. CONCLUSIONS: Temporary cementation may be more suitable for restorations supported by multiple implants.

Analysis of Variance↗

PubMedDate not supplied

Comparison of non-linear finite element stress analysis with in vitro strain gauge measurements on a Morse taper implant.

PURPOSE: To understand the mechanical and biomechanical behavior of dental Implants, validation of stress and strain measurements is required. The objective of this study was to compare a non-linear finite element stress analysis with in vitro strain gauge measurements on strains in an implant-abutment complex. MATERIALS AND METHODS: Strain gauges were bonded to an Implant-abutment complex and embedded in polymethylmethacrylate resin. A force of 75 N was applied vertically and laterally in separate load cases, and strains were recorded with a strain indicator. Then, a finite element model of the strain gauge model was constructed. Contact analysis with normal contact detection and separation behavior was performed between the Implant and the abutment. The same loading protocol was followed, and strains were recorded at regions where gauges were bonded. RESULTS: Under vertical loading, the qualification and quantification of strains were similar in both methods. Under lateral loading, the measurement of strains on the abutment and in the resin were similar in both methods. However, strains on the implant collar as measured by non-linear finite element analysis were higher. DISCUSSION AND CONCLUSION: There is a compatibility between non-linear finite element stress analysis and in vitro strain gauge analysis on the measurement of strains under vertical loading. However, there are differences between the methods in the quantification of strains on the collar of Implants under lateral loading.

Acrylic Resins↗

PubMedDate not supplied

Accuracy of 2 impression techniques for ITI implants.

PURPOSE: The aim of this study was to compare the accuracy of casts produced by 2 impression techniques and elastomeric impression materials commonly used for the fabrication of implant-supported fixed prostheses. MATERIALS AND METHODS: A master model with 4 synOcta ITI implants placed unilaterally in place of the mandibular right central incisor, canine, first premolar, and first molar was constructed. Implant-level impressions were made by direct and indirect techniques. In the direct technique, synOcta impression caps with integral guide screws were used to transfer the implants using a custom-made acrylic resin tray and a polyether impression material (the PE direct technique). In the indirect technique, synOcta plastic positioning cylinders with impression caps were used to transfer the implants with either a custom-made acrylic resin tray and polyether impression material (the PE indirect technique) or with a stock tray with a vinylpolysiloxane impression material (the VPS indirect technique). After impression making, all casts (n = 21) were poured in type IV dental stone. Linear changes in -x or -y direction and numeric and descriptive angular changes between the implants were quantified using a coordinate measuring machine. RESULTS: Seven of 12 distance measurements (6 for -x direction, 6 for -y direction) showed differences between groups (P < .05). Of these, 5 were associated with the PE direct versus PE indirect and PE indirect versus VPS indirect, and 3 were associated with PE direct versus VPS indirect. Two implants also showed angular changes but only for the PE indirect technique versus the VPS indirect technique (P < .05). CONCLUSION: The snap-on VPS indirect impression technique using a stock tray, which has the advantages of being clinically convenient and eliminating repositioning after removal of the impression, resulted in dimensional accuracy similar to that achieved with the PE direct technique.

Dental Implants↗