Cement Layer Thickness Research Articles

Effects of scanning technique on in vitro performance of CAD/CAM-fabricated fiber posts.

This study assessed push-out strength, cement layer thickness, and interfacial nanoleakage of luted fiber posts fabricated with computer-aided design/computer-assisted manufacture (CAD/CAM) technology after use of 1 of 3 scanning techniques, namely, direct scanning of the post space (DS), scanning of a polyether impression of the post space (IS), and scanning of a plaster model of the post space (MS). Thirty premolars were randomly assigned to three groups corresponding to the scanning technique. Posts were computer-designed and milled from experimental fiber-reinforced composite blocks. The mean (±SD) values for push-out strength and cement thickness were 17.1 ± 7.7 MPa and 162 ± 24 μm, respectively, for DS, 10.7 ± 4.6 MPa and 187 ± 50 μm for IS, and 12.0 ± 7.2 MPa and 258 ± 78 μm for MS specimens. Median (interquartile range) interfacial nanoleakage scores were 3 (2-4) for DS, 2.5 (2-4) for IS, and 3 (2-4) for MS. Post retention was better for fiber posts fabricated by DS technique than for those fabricated by IS and MS. Cement thickness did not differ between DS and IS specimens, but the cement layer was significantly thicker in the MS group than in the other two groups. Scanning technique did not affect sealing ability, as the three groups had comparable nanoleakage values.

Influence of Alveolar Bone Loss and Cement Layer Thickness on the Biomechanical Behavior of Endodontically Treated Maxillary Incisors: A 3-dimensional Finite Element Analysis

IntroductionIn order to understand the mechanical behavior of a weakened incisor, this study aimed to evaluate the stress distribution caused by different alveolar bone heights and cement layer thickness. MethodsA finite element analysis was conducted for this investigation. An intact maxillary central incisor was initially modeled, and the bone of the models was modified in order to simulate 4 levels of bone height: BL0 (no bone loss), BL1 (1/3 bone loss), BL2 (1/2 bone loss), and BL3 (2/3 bone loss). These teeth models were remodeled with a fiber post at 2 different cement thicknesses and restored with a ceramic crown; “A” refers to the well-adapted fiber post (0.3 mm) and “B” to the nonadapted fiber post (1 mm), resulting in 12 models. RelyX ARC (3M ESPE, St Paul, MN) cement was simulated for the cementation of the crowns and fiber posts for all groups. Numeric models received a load of 100 N on the lingual surface. All materials and structures were considered linear elastic, homogeneous, and isotropic. Numeric models were plotted and meshed with isoparametric elements, and results were expressed in maximum principal stress. ResultsFor fiberglass posts, cement, and dentin, the highest stress concentration occurred in the groups with increased bone loss. For cortical bone, the highest values were for the groups with 1/3 bone loss. A greater thickness of cement layer concentrates more stress. ConclusionsMore bone loss and greater CLT were the influential factors in concentrating the stress.

The circles of life: age at death estimation in burnt teeth through tooth cementum annulations.

Age at death estimation in burnt human remains is problematic due to the severe heat-induced modifications that may affect the skeleton after a burning event. The objective of this paper was to assess if cementochronology, which focuses on the cementum incremental lines, is a reliable method of age estimation in burnt remains. Besides the classical approach based on the counting of incremental lines, another approach based on the extrapolation of incremental lines taking into account the cement layer thickness and the incremental line thickness was investigated. A comparison of the performance of the two techniques was carried out on a sample of 60 identified monoradicular teeth that were recently extracted at dentist offices and then experimentally burnt at two maximum temperatures (400 and 900°C). Micrographs of cross-sections of the roots were taken via an optical microscope with magnification of ×100, ×200 and ×400. Incremental line counting and measurements were carried out with the ImageJ software. Age estimation based on incremental line counting in burnt teeth had no significant correlation with chronological age (p = 0.244 to 0.914) and led to large absolute mean errors (19 to 21years). In contrast, age estimation based on the extrapolation approach showed a significant correlation with known age (p = 0.449 to 0.484). In addition, the mean absolute error of the latter was much smaller (10 to 14years). The reason behind this discrepancy is the heat-induced dimensional changes of incremental lines that affect their visibility and individualization thus complicating line counting. Our results indicated that incremental lines extrapolation is successful at solving this problem and that the resulting age estimation is much more reliable.

Non-linear growth kinematics of opening-mode fractures

Fracture aperture is commonly assumed to be a linear function of fracture length, stress, and elastic material properties. Under constant stress, fracture opening displacement may change without concurrent length or height growth if the material effectively weakens after initial linear elastic fracture growth by changes in elastic properties or by non-elastic deformation processes. To investigate the kinematics of fracture opening and its dependence on length and height growth, we reconstructed the opening history of three opening-mode fractures that are bridged by crack-seal quartz cement. Similar crack-seal cement bridges had been interpreted to form by repeated incremental fracture opening and subsequent precipitation of quartz cement. Using scanning electron microscope cathodoluminescence imaging, we determined the thickness and number of crack-seal cement layers as a function of position along fracture length and height. Observed trends in crack-seal cement layer thickness and number of fracture opening increments are consistent with non-linear fracture growth kinematics, consisting of an initial stage of fast fracture propagation relative to aperture growth, followed by a stage of slow propagation and pronounced aperture growth. Consistent with earlier fluid inclusion observations indicating fracture opening and propagation occurring over 40–50 m.y., we interpret the second stage of pronounced aperture growth and slow propagation to result from fracture opening strain accommodated by solution-precipitation creep and concurrent slow, possibly subcritical, fracture propagation.

The effect of luting cement type and thickness on stress distribution in upper premolar implant restored with metal ceramic crowns

Objectiveto study the effect of using two cement types, with three different thicknesses, on stress levels and distributions within bone around implant premolar using three-dimensional Finite Element Analysis techniques. Materials & methodsA three 3D Finite Element models were built for this purpose. Threaded titanium dental implant was implemented in simplified geometry for jaw bone. While the crown geometry, was acquired by 3D scanner. Two cement materials (Zinc phosphate, Glass Ionomer), with three values of cement layer thicknesses (20, 40, and 60 μm) were investigated. Twenty-four case studies were reported within this research. Each case was analyzed under vertical and oblique loading at Palatal Cusp Tip and Central Fossa. ResultsLinear static stress analysis was performed. The results of the model showed the superiority of 60 μm thickness cement layer over the other two thicknesses. ConclusionsUsing thicker cement layer increase its lifetime, in addition to reducing the cortical bone Von Mises stress. While, the effect of cement layer thickness and type on spongy bone, is negligible.

Effects of Differing Thickness and Mechanical Properties of Cement on the Stress Levels and Distributions in a Three‐Unit Zirconia Fixed Prosthesis by FEA

This study analyzed the impact of cement layer thickness (CLT) and Young's modulus of the cement on the stress distribution in a three-unit zirconia fixed dental prosthesis (FDP) and in the bonding interfaces by means of finite element method. A 3D finite element model was created from a stylized three-unit FDP-cement-tooth/socket system. The pulp and the periodontal ligament were not modeled. Two CLTs (50 and 150 μm) and two values of Young's modulus of the cement (4.9 for simulation of resin cement, 20.1 GPa for glass ionomer cement) were evaluated. A 500 N static vertical load was applied at the central fossa of the pontic to calculate maximum displacement in the framework and maximum principal stresses in both framework and bonding interfaces. The simulated results showed that the Young's modulus affected stress occurrence only in the cement interface. Lower moduli were associated with less stress. The thickness of the cement layer influenced the maximum principal stress in both the FDP and in the cement layer itself. Thicker cement layers led to higher stresses in the framework but lower stresses in the cement layer. Maximum displacement was less dependent of the investigated variables. During all trials, the location of the maximum principal stress did not change. Maximum stress concentrations were observed at the lower embrasures of the connector areas and in the bonding layer at the cervical margin of the preparation. Choosing cements with a preferably low Young's modulus in combination with a CLT as small as possible might increase the clinical survival rate.

Primary stability of unicompartmental knee arthroplasty under dynamic compression-shear loading in human tibiae

BackgroundThe objective of our study was to evaluate the impact of a single- (“implant only”) versus a double-layer (“implant & bone”) cementing technique on the primary stability of unicompartmental tibial plateaus under dynamic compression-shear loading conditions in human tibiae. MethodsTwelve fresh-frozen human knees of a mean donor age of 72.3years were used to perform medial UKA under a less invasive parapatellar surgical approach. The tibiae were divided into two groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability, a new method based on a combination of dynamic compression-shear testing, kinematic analysis of the tibial plateau migration relative to the bone and evaluation of the cement layer by CT-scans and fragments cut through the implant–cement–bone interface in the frontal plane was introduced. FindingsFor the “implant only” cementation technique the mean load to failure was 2600 (SD 675) N and for “implant & bone” it was 2820 (SD 915) N. Between the final load level at failure and the bone mineral density a significant correlation was found for the groups “implant only” (rs=0.875) and “implant & bone” (rs=0.907). InterpretationFrom our observations, we conclude that there is no significant difference between a single- (“implant only”) and double-layer (“implant & bone”) cementing technique in the effect on the primary stability of unicompartmental tibia plateaus, in terms of failure load, correlation between final load at failure and bone mineral density, migration characteristics, cement layer thickness and penetration depth.

Internal fit of two all-ceramic systems and metal-ceramic crowns

Objectives The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA - In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD), and metal-ceramic (MC - Ni-Cr alloy) crowns. Material and Methods Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS), axial space (AS) and total mean (TM) using two-way ANOVA with Tukey's multiple comparison test (p<0.05). Results No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. Conclusions The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS.

Bond strengths, degree of conversion of the cement and molecular structure of the adhesive–dentine joint in fibre post restorations

ObjectivesBecause fibre post restorations are influenced by multiple factors such as the types of bonding materials, the dentine region and the time under moist exposure, this study sought to determine the bond strength of endodontic restorations and its relation to the degree of conversion of the cement layer and the molecular structure of the dentine-bonded joints. MethodsThe performance of 2 etch-and-rinse (All-Bond 2 and One-Step Plus) and 2 self-etch (Clearfil SE Bond and Xeno III) adhesives at post spaces regions, after 7d or 4m, was evaluated. FRC Postec Plus posts were cemented to the root canal with a dual-cure resin cement (Duo-Link). Transverse sections of the tooth were subjected to push-out testing, to degree-of-conversion measurements and to hybrid layer evaluation through μ-Raman spectroscopy. ResultsCoronal bonding was higher than cervical and middle bonding. The hybrid layer was thicker for the etch-and-rinse systems, with thicknesses decreasing towards the middle region. The degree of conversion measured for the 3-step etch-and-rinse group after 4m was significantly higher than that for the self-etching groups. ConclusionsAlthough not totally stable at the adhesive–dentine interface, the 3-step etch-and-rinse adhesive in the coronal dentine provided the best bond strength, degree of conversion of the cement and hybrid layer thickness in post restorations, in both short- and long-term analyses.

Glass ionomer layer thickness and its influence on zirconia failure

Objectives: To investigate the influence of glass ionomer cement layers with various thickness and cement contamination on the fracture resistance of thin zirconia plates luted onto coplanar human molars. Materials and methods: Zirconia plates measuring 0.7 mm in thickness were luted onto 70 coplanarly trimmed human molars with glass ionomer cement. Cement layers measuring 100, 250, 1000, and 2000 μm in thickness were produced. Contamination of the tooth surface was achieved by applying hand-piece oil, contamination of the cement by mixing glass ionomer with H 2O 2 to produce voids and gas bubbles. Results: Fracture resistance was independent from cement layer thickness (median ranging from 1220 to 1367 N). Oil contamination moderately reduced fracture resistance (1135 N). Fracture resistance was significantly affected by the presence of a considerable amount of voids or gas bubbles in the cement (877 N). Conclusions: The fracture resistance of thin zirconia plates was not affected by different cement layer thickness but by contamination of the tooth surface as well as by high cement porosity due to simulated handling errors.

Marginal Adaptation and Microleakeage of Directly and Indirectly Made Fiber Reinforced Composite Inlays

Aim:This study evaluated in vitro microleakage of inlays made by direct or indirect techique with or without fiber reinforced composite (FRC) substructure. Materials and Methods: Standardized mesio-occlusal cavities were prepared and restored using direct-technique with composite resin only or FRC-composite resin, and indirect technique with laboratory composite only or FRC-laboratory composite resin. After thermocycling, teeth were immersed in basic fuchsin dye, sectioned and examined under a stereo-microscope (x40). Results:No differences of cement thickness and dye penetration were found in gingival area (p>0.05), whereas microleakage revealed statistical differences between groups (p=0.02) in occlusal area, where FRC-groups had lower microleakage than composite restorations. Thickness of cement layer did not show significant difference between groups with indirect technique (p>0.05). Conclusion: The present study suggests that insertion of FRC substructure to the inlay cavity by direct composite filling technique does not increase the marginal leakage compared to that of cementing indirectly made restotorations by composite resin luting cement.Clinical Significance: On the basis of the results of this in vitro study, the use of direct FRC technique might be an effective way to decrease the marginal leakage.

Three-dimensional FEA of Effects of Two Dowel-and-Core Approaches and Effects of Canal Flaring on Stress Distribution in Endodontically Treated Teeth

The aim of this 3D finite element analysis (FEA) was to assess stress distribution and levels in endodontically treated teeth restored with two dowel-and-core systems with differing root canal configurations. Four 3D finite element models of a laser-digitalized maxillary central incisor embedded in alveolar bone were created. Internal morphology data and mechanical properties of the materials were obtained from the literature. Models included a (1) sound tooth (control) versus an endodontically treated maxillary central incisor with a crown ferrule preparation with two restorative approaches of a ceramic crown over a (2) gold alloy dowel-and-core or (3) glass-fiber dowels with composite cores (4) the latter with a flared root canal. A 100 N static load was applied in the center of the palatal surface at a 45° angle, and the stress distribution pattern was analyzed using ANSYS(®) software. In Model 1 (control), maximum stresses occurred at the coronal third of the buccal (2.32 × 10(7) Pa) and palatal aspects of dentin. The stress peak value of the model (2.45 × 10(7) Pa) occurred on the palatal aspect of the enamel at the level of the cementoenamel junction. With the insertion of dowels with thin cement layers (Models 2 and 3), stress concentrations in radicular dentin decreased, while they increased in the dowel/cement/dentin interface. These models exhibited the greatest stress peak values in the incisal margin of the gold alloy core (18.9 × 10(7) Pa) and in the cement layer (4.7 × 10(7) Pa). In Model 4, stress peak value was observed in the porcelain crown (4.62 × 10(7) Pa), and there was no stress concentration inside the cement layer. Within the limits of this study, the results suggest that the use of dowels and cements with mechanical properties similar to those of dentin, and an increased cement layer thickness, results in mechanical behavior similar to the physiological behavior of a sound tooth.

Use of a CAD/CAM-fabricated glass fiber post and core to restore fractured anterior teeth: A clinical report

Prefabricated glass fiber posts are widely used; however, their shape cannot be changed and they can be unsuitable for severely damaged teeth with wide root canals. This clinical report describes a procedure for restoring a severely damaged anterior tooth with a customized 1-piece glass fiber post and core, fabricated using a CAD/CAM system. This 1-piece glass fiber post and core adapts better to the root canal than a prefabricated glass fiber post, and reduces the cement layer thickness. Furthermore, it does not require the use of a composite resin foundation.

Free bone cement fragments after minimally invasive unicompartmental knee arthroplasty: an underappreciated problem

The minimally invasive implantation of unicompartmental knee arthroplasty (UKA) leads to excellent functional results, but due to the reduced intraoperative visibility the removal of excessive cement may be difficult. In a retrospective study we assessed radiologically the incidence of loose and excess bone cement in 120 UKAs and correlated it to the thickness of the tibial cement layer. In 25 cases loose or attached excess cement was seen. Two of these patients with loose cement bodies required revision surgery. An additional 2 patients not operated at our institution required revision because of pain and loss of motion. The average thickness of the tibial cement layer was 3.1 (1.7-5.0) mm in all the patients. But it was significantly higher in the group with excess cement bodies [3.3 (2.3-5.0) mm] compared to the group without excess cement [3.0 (1.7-4.1) mm] (P < 0.05). Symptomatic free cement bodies need to be removed immediately, if necessary arthroscopically, in order to avoid damage to the implants. To avoid this problem in minimally invasive UKA, intraoperative fluoroscopy, a dental mirror or a nerve hook seem to be useful tools to identify and remove loose or excess cement.

906 人工股関節置換術におけるセメントマントル圧力の測定(J04-1 臨床医歯学における非・低侵襲計測技術の展開(1) 歯科・整形外科における計測および生体シミュレーション,ジョイントセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

One of the factors influencing initial fixation of total hip arthroplasty with bone cement is cement pressure° Cement mantle pressure is thought to change with the shape of a stem, the roughness of the stem surface, and the thickness of the bone cement layer. This in vitro study examined cement pressurization during the insertion of femoral stems, namely PERFECTA (PER) and ANCAFIT (AFJ) stems, into seven pairs of human cadaver femorao Cement pressures were measured at proximal and distal stem levels during the insertion of each stemo AFJ with a thin cement layer showed greater cement pressures than PER with a thick cement layer at both proximal and distal stem regions. Distal stem levels appeared to show greater pressures than proximal levels for both AFJ and PER.

Finite-Elemente-Analyse einer zementierten, keramischen Femurkomponente unter Berücksichtigung der Einbausituation bei künstlichem Kniegelenkersatz / Finite element analysis of a cemented ceramic femoral component for the assembly situation in total knee arthroplasty

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.

The Effect of PMMA Thickness on Thermal Bone Necrosis around Acetabular Sockets

One aim of custom acetabular hip replacement sockets is to achieve fixation through a uniform cement layer of selected thickness. In vitro experiments demonstrate that curing temperatures are determined by cement thickness and position relative to the socket rim. A maximum thickness of 7 mm is indicated by interpretation of curing temperature-time relationships in terms of predicted bone necrosis. It is concluded that the results contribute to the establishment of an optimum cement layer thickness, but other factors require investigation to complement this work to gain further understanding of the problem.

Influence of cement layer thickness on the adhesive bond strength of polyalkenoate cements

The fracture toughness and yield stress values of model zinc polycarboxylate and glass polyalkenoate cements have been used to calculate plastic zone sizes. The size of the plastic zone at the crack tip in these materials has been used to predict whether cement layer thickness is likely to influence the adhesive bond strength. In the model zinc polycarboxylate cement studied, the plastic zone size was comparable to the cement layer thickness and had a pronounced influence on the shear bond strengths obtained. In contrast, the plastic zone sizes obtained for the glass polyalkenoate cements were much smaller and the shear bond strengths were found to be much less dependent on cement layer thickness.

カルシア系鋳型材を用いたチタン鋳造冠の基礎的研究

The interest in the application of titanium and its alloys to dental prostheses is increasing since they possess good mechanical properties. However, fabrication of titanium prostheses, especially the casting procedure, has been very difficult because of its chemical reactivity at high temperatures. In our previous study, we could obtain a sound titanium casting using the calcia mold which is very stable for titanium. In this study, we investigated the calcia investments containing metal titanium powder to improve the casting accuracy. Setting and thermal expansion at 1, 000°C of the calcia investment with 8.8wt% titanium powder was 0.5% and 1.2%, respectively. The marginal opening and cement layer thickness between the die and the titanium cast crowns obtained from the calcia mold fired at 1, 000°C were found to be improved when the content titanium powder was 8.6wt% or 8.8wt%. The contamination of oxygen produced a hardened layer with a thickness of about 250μm under surface of titanium casting; nevertheless, it was possible to finish a glazing surface by the conventional polishing procedures.

Nondestructive, three-dimensional internal fit mapping of fixed prostheses

Crown fit may be three-dimensionally mapped by using a nondestructive optical technique. Reflected light transmission through thicknesses of a colored impression material was shown to follow the Beer-Lambert relationship over a range of approximately 10 to 300 μm, a useful range of interest for study of cement layer thickness. Control thicknesses of impression material were first formed between the measuring platens of a micrometer, and light transmission values (relative reflections) were measured through these control thicknesses of impression material held against air-abraded, noncast gold alloy. Relative reflection values were similarly measured from impression material formed inside cast gold crowns seated on their respective dies and these values were plotted against direct thickness measurements by using the Beer-Lambert relationship. It was established that the micrometer-produced control specimens yielded a valid standard curve for use with the cast gold crowns. Precementation space measurements determined photometrically were found to correlate significantly (r = 0.72, p < 0.001) with zinc phosphate cement thickness measured on subsequently cemented and cross-sectioned crowns. A three-dimensional representation of the precementation space inside one crown was developed after mapping of 45 points in less than 5 minutes.