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To assess the amount of excess cement and the retentive strengths of two different cementation techniques (conventional cementation and practice abutment) using copings fabricated with three different cement thicknesses (20 μm, 35 μm, and 50 μm). Thirty zirconia copings were fabricated on screw retained abutments and randomly divided into three equal groups (n = 10) according to the cement thickness (20 μm, 35 μm, and 50 μm). Each group was cemented with tow cementation techniques. Cementation was performed with provisional cement (Temp-Bond). In the conventional cementation technique, cement was applied until each coping was approximately half filled, and the copings were subsequently placed on the implant–abutment assembly. Then, the copings were cleaned and cemented using the practice abutment cementation technique to remove excess cement prior to the process. Each technique was performed using copings with three different cement thicknesses (20 μm, 35 μm, and 50 μm). The specimens with the cemented copings were weighed on a high-precision analytical balance before and after removing the extruded cement, and the differences between the two measurements were calculated. Then, each specimen was subjected to a pullout test using a universal testing machine. The load required to dislodge the coping was recorded. The data were analyzed using two-way and one-way analysis of variance and independent sample t tests at a significance level of 0.05. The highest retention values were obtained for 20 μm cement thickness in the conventional technique and the practice abutment cementation technique. The amount of excess cement was the highest for the 50 μm cement thickness obtained for both cementation techniques, whereas the lowest mean values were recorded for the 20 μm cement thickness. The conventional cementation technique is recommended over the practice abutment technique to increase the retention of crowns cemented with provisional cement. However, care must be taken to remove the extruded cement. A cement thickness of 20 μm is preferable for enhancing the retention of cemented crowns and for reducing the amount of excess cement when applying both conventional and practical abutment cementation approaches. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to perform a preliminary analysis of the fitting of different fiber-reinforced composite (GFRC) posts to tooth root canals and determine the resin cement layer thickness. The following GFRC posts were assessed: bundle posts (Rebilda GTTM, VOCO, Germany), sleeve system (SAPTM, Angelus Ind, Brazil), and accessory posts (ReforpinTM, Angelus, Brazil). Twenty-four freshly extracted mandibular single-rooted pre-molars were endodontically treated and divided into six groups, according to the type of GFRC post and resin cement (self-adhesive or conventional dual-cured). Then, specimens were cross-sectioned and inspected by optical microscopy regarding the cement layer thickness and presence of defects such as pores, voids, or fissures were assessed. Bundle and accessory posts revealed a regular distribution of resin cement with a lower number of voids than found with sleeve systems. The sleeve system posts showed poor fitting at the apical portion of the root canals. The type of resin cement did not affect the thickness of the interface, although both bundle and accessory posts allow a better distribution of resin cement and fibers. The present preliminary study reveals interesting insights on the fitting of bundle and accessory posts to root dentin and resin cement layer thickness in oval-shape root canals. The sleeve system posts showed adequate fitting only at the coronal portion of the canals. [ABSTRACT FROM AUTHOR]

Using a three-dimensional finite element analysis, this study aimed to evaluate the effect of different cements' thicknesses and Poisson's ratios on the stress distribution in enamel, dentin, restoration, and resin cement in a computer-aided design of a class II disto-occlusal cavity. Dental tomography was used to scan the maxillary first molar, creating a three-dimensional tooth model. A cavity was created with a 95 degree cavity edge angle. Resin cement with varying Poisson's ratios (V1: 0.35 and V2: 0.24) was used under the amalgam. The simulated groups' thicknesses ranged from 50 µm to 150 µm. A load of 600 N was applied to the chewing area. The finite element method was used to assess the stress distribution in the enamel, dentin, restorations, and resin cement. The stress in the restoration increased with the use of a 100 µm resin cement thickness and decreased with the use of a 150 µm resin cement thickness. For the V1 and V2 groups, the cement thickness with the maximum stress value for the enamel and dentin was 150 µm, while the cement thickness with the lowest stress value was 50 µm. The greatest stress values for V1 and V2 were obtained at a 150 µm cement thickness, while the lowest stress values were observed at a 100 µm cement thickness. Using resin cement with a low Poisson's ratio under amalgam may reduce stress on enamel and restorations. [ABSTRACT FROM AUTHOR]

Using a three-dimensional finite element analysis, this study aimed to evaluate the effect of different cements’ thicknesses and Poisson’s ratios on the stress distribution in enamel, dentin, restoration, and resin cement in a computer-aided design of a class II disto-occlusal cavity. Dental tomography was used to scan the maxillary first molar, creating a three-dimensional tooth model. A cavity was created with a 95 degree cavity edge angle. Resin cement with varying Poisson’s ratios (V1: 0.35 and V2: 0.24) was used under the amalgam. The simulated groups’ thicknesses ranged from 50 µm to 150 µm. A load of 600 N was applied to the chewing area. The finite element method was used to assess the stress distribution in the enamel, dentin, restorations, and resin cement. The stress in the restoration increased with the use of a 100 µm resin cement thickness and decreased with the use of a 150 µm resin cement thickness. For the V1 and V2 groups, the cement thickness with the maximum stress value for the enamel and dentin was 150 µm, while the cement thickness with the lowest stress value was 50 µm. The greatest stress values for V1 and V2 were obtained at a 150 µm cement thickness, while the lowest stress values were observed at a 100 µm cement thickness. Using resin cement with a low Poisson’s ratio under amalgam may reduce stress on enamel and restorations.

Background: Fiber posts are broadly used due to their good esthetics and elasticity close to that of dentin, which allows for uniform stress distribution within a root and lowers the possibility of nonrestorable root fractures. Aim and Objectives: The study assessed the layer of cement thickness and interfacial nanoleakage of luted fiber posts which were fabricated with CAD/CAM technology following direct scanning of the post space (DS) method, scanning of a polyether impression of the post space (IS), and scanning of a plaster model of the post space (MS). Methodology: Ninety premolars were chosen randomly and were assigned to three groups according to the scanning technique. Posts were computer designed and milled from experimental fiber-reinforced composite blocks. Results: The mean and standard deviation values of cement thickness, respectively, were: DS 172 ± 39 = m; IS 199 ± 55 = m, and MS MPa 272 ± 81 = m. The fiber posts fabricated following DS technique demonstrated superior performance compared to posts fabricated upon IS and MS, in terms of the post retention. The cement thickness did not differ between DS and IS, whereas in MS group, the cement layer was significantly thicker than in the remaining two groups. The scanning technique did not influence the sealing ability, as all groups showed comparable nanoleakage. Conclusion: Fiber posts fabricated following DS technique demonstrated superior performance. Furthermore, scanning technique did not influence the sealing ability, as all groups showed comparable nanoleakage.

The main goal of periodontal therapy is to eliminate the infection and achieve healthy periodontal enviroment by removing bacterial deposits of dental plaque, dental calculus and the presence of subgingival concrements and endotoxins from the root surface. The ultimate goal of all periodontal procedures is to make the treated root surface biologically compatible with the host's periodontal tissues and to enable proper healing of the periodontium. During the initial periodontal treatment, mechanical debridement is performed on the periodontally compromised root surface to eliminate all calcified deposits (supra- and subgingival concrements), as well as bacteria and their cement endotoxins to restore the biological compatibility of the root to the disease. Thorough mechanical debridement of the root surfaces allows fibroblasts to attach to previously pathologically affected or non-affected areas of the tooth roots. This procedure is a significant prerequisite for proper regeneration of lost periodontal tissues. There are two basic therapeutic modalities in periodontology - conventional and laser-assisted therapy. Conventional therapy involves ultrasound instrumentation followed by mechanical debridement. Laser-assisted therapy involves laser treatment preceded by ultrasound instrumentation. Based on these facts, the main goal of this research was to determine the thickness of the remaining cement after performing different types of periodontal therapy procedures (ultrasound instrumentation, conventional therapy or laser-assisted periodontal therapy). For the realization of the main goal, a randomized controlled in vitro study was conducted. The examined sample included a total of 100 teeth that had an indication for extraction. The patients from whom the examined sample originated - extracted teeth - were older than 35 years. All extracted teeth that are part of the sample confirm the diagnosis - stage III and IV of periodontal disease according to the new classification framework of periodontal diseases from 2018. All research samples were divided into five groups of 20 teeth, according to which of the performed therapeutic procedures was applied. The basic division included the following groups: (I) samples treated with ultrasound instruments; (II) samples treated with ultrasound instruments and Gracey's curettes or conventional periodontal therapy; (III) samples treated with laser-assisted treatment using LiteTouch Er: YAG laser; (IV) samples from parodontal diseassed teeth and (V) control group: impacted teeth that have an indication for extraction or teeth that are extracted for non-periodontal cause (occlusal trauma, orthodontic therapy or prosthetic cause). With the SEM analysis of each of the examined surfaces, the thickness of cement was determined. Before the analysis of the samples with the help of SEM, an efficient procedure for dehydration and drying was performed in order to avoid the formation of artifacts that could distort the quality of the obtained microphotographs. After the analysis, it was noticed that the average thickness of the remaining cement after the performed therapy only with ultrasonic instrumentation was 146.0324 ± 13.42917 micrometers. The average thickness of the remaining cement after conventional periodontal therapy was the lowest and was 103.3144 ± 13.52161 micrometers. Finally, the thickness of the remaining cement after laser-assisted periodontal therapy in this study was 123.0332 ± 15.83445 micrometers. The result of SEM evaluation revealed a significant ( P < 0.001) decrease in the thickness of cementum layer on the diseased root surfaces compared to the healthy surfaces. Based on the results of this study, we can conclude that during periodontal disease there is a significant reduction in the thickness of the cement in relation to the healthy tooth. Regarding the therapeutic modalities, it can be concluded that in conventional periodontal therapy there is a greatest loss of tooth cement. Also, it can be noted that the most appropriate therapeutic modality for periodontal disease is laser-assisted therapy in which there is no significant loss of cement. [ABSTRACT FROM AUTHOR]

• Fracture resistance of 5Y-TZP with a taper of 30° decreased compared to 10° and 15°. • Pre-defined cement space did not affect the load at fracture. • Fracture origin for ¾ of the crowns was in the cervical area. • The crowns with pre-defined cement space of 60 μm had closer axial fit than 30 μm. Monolithic zirconia crowns have become a viable alternative to conventional layered restorations. The aim of this study was to evaluate whether the taper, and thus wall thickness, of the abutment or pre-defined cement space affect the fracture resistance or fracture mode of monolithic zirconia crowns. A model tooth was prepared with a taper of 15° and a shallow circumferential chamfer preparation (0.5 mm). Two additional models were made based on the master model with a taper of 10° and 30° using computer-aided design software. Twenty monolithic 3rd generation translucent zirconia crowns were produced for each model with pre-defined cement space set to either 30 μm or 60 μm (n = 60). The estimated cement thickness was assessed by the replica method. The cemented crowns were loaded centrally in the occlusal fossa at 0.5 mm/min until fracture. Fractographic analyses were performed on all fractured crowns. The load at fracture was statistically significant different between the groups (p < 0.05). The crowns with 30° taper fractured at lower loads than those with 10° and 15° taper, regardless of the cement space (p < 0.05). The fracture origin for 47/60 crowns (78%) was in the cervical area, close to the top of the curvature in the mesial or distal crown margin. The remaining fractures started at the internal surface of the occlusal area and propagated cervically. The fracture resistance of the monolithic zirconia crowns was lower for crowns with very large taper compared to 10 and 15° taper even though the crown walls were thicker. [ABSTRACT FROM AUTHOR]

purpose of this study was to compare the fracture resistance of ceramic veneers with digital die spacer settings at 20 μm, 40 μm, and 100 μm. Materials and Methods: Eighteen sound maxillary first premolars were divided into three groups (n=6) according to their digital die spacer settings: group A=20 μm, group B=40 μm, group C=100 μm. Each tooth was prepared to a depth of 0.5 mm to receive lithium disilicate veneers (IPS e.max CAD, Ivoclar Vivadent). All groups were thermocycled (2500 cycles at 5– 55°C) and subjected to fracture resistance test using a universal testing machine until failure. Failure modes were examined using a stereomicroscope. Results: The values (N) for group A=1181.34± 301.33, group B=1014.29± 291.12, and group C=841.89± 244.59. One-way ANOVA showed no statistical difference among the three groups (p=0.145). However, chi-square test showed that a significant difference was present in the modes of failure (p=0.009). Tukey's post hoc test indicated that the failure modes of group A were statistically different from those of group C, showing 83.3% adhesive failure for group A compared to 0% adhesive failures in group C. A p-value of ≤ 0.05 was considered as statistically significant. Conclusion: Digital die spacer thickness did not influence the mean fracture resistance values of CAD/CAM lithium disilicate veneers. However, the way the failure occurred differed significantly at various die spacer thicknesses. [ABSTRACT FROM AUTHOR]

Background: Limited literature exists concerning the femoral cement mantle quality that can be achieved through an anterior approach in total hip arthroplasty (THA). We radiologically evaluated the quality and thickness of the femoral cement mantle in patients undergoing THA utilizing the direct anterior approach (DAA). Methods: Immediate postoperative anteroposterior and lateral radiographs of 116 consecutive patients who underwent hybrid or fully cemented THA using the DAA and cemented Quadra-C stem (Medacta, International, SA, Switzerland) were assessed by 2 arthroplasty surgeons blinded to the study. Surgical indications were hip osteoarthritis or subcapital hip fracture. The cement mantle and stem alignment were evaluated using the Barrack classification and Khalily methods, respectively. After calibration of radiographs, the thinnest part of the cement mantle per Gruen zone was recorded. Parameters were compared between obese and nonobese patients. Results: Agreement between raters was substantial for the cement quality in anteroposterior (k = 0.707, P ≤ .001) and moderate for lateral radiographs (k = 0.574, P ≤ 001). The cement mantle was graded A in 39.25%, B in 53.0%, and C in 7.75% of anteroposterior radiographs and similarly for lateral radiographs (40.1% A, 51.75% B, 9.5% C). 93% of stems had neutral alignment. The mean thinnest cement mantle (P = .237) and incidence of inadequate cement mantle ( .05) and stem alignment (P = .652) were comparable between obese and nonobese patients. Conclusions: DAA enables correct implantation and effective cementation of straight femoral stems. A high-quality cement mantle can be achieved using DAA even in obese patients.

Objective: This study evaluated the effects of different post diameter and oversized post spaces on the push-out bond strength of a fiber post to dentin. Method and Materials: Fifty extracted human maxillary central incisors and canines were divided into five groups and submitted to the push-out test (0.5 mm min-1). Groups 1, 2, and 3 were restored using a fiber post size that was identical to the drill size (sizes 1, 2, and 3, respectively), and groups 4 and 5 were both prepared with drill size 3, and restored using the size 2 and 1 fiber post, respectively. The fiber posts were cemented using self-adhesive dual-polymerized resin cement (RelyX Unicem). The data were analyzed using a one-way analysis of variance (ANOVA) and the Tukey test. Results: There were no significant differences in the mean values for push-out bond strength between groups with different post diameters (P > .05). However, the push-out bond strengths were significantly different between groups with different cement thicknesses, and group 4 yielded the highest bond strength (11.7 ± 0.4 MPa). For all groups, the apical third had the lowest bond strength value (P < .05). Conclusion: The highest push-out bond strength values were obtained when one incremental oversized post space was used. Clinically, fiber post space has to provide an optimum cement thickness (around 120 μm) for adequate cementation. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the fracture resistance and marginal quality of maxillary molars restored using lithium disilicate glass‐ceramic (LDG) occlusal veneers with two preparation designs. Methods: Sixteen extracted maxillary molars were assigned to two groups (n = 8). In group 1 (G1), the teeth received a preparation for a conservative full‐coverage occlusal veneer restoration with a 90° rounded shoulder margin. In group 2 (G2), the teeth underwent a 1‐mm cusp reduction with a marginal chamfer. LDG restorations (IPS e.max CAD) were obtained with the Cerec 3 CAD/CAM system and luted with Variolink II cement. After thermomechanical aging (1 250 000 cycles), the specimens were loaded to fracture. A semiquantitative marginal seal evaluation was performed observing resin replicas of the specimens at the scanning electron microscope. Cement thickness was assessed at the stereomicroscope on sectioned specimens. Collected data were statistically analyzed by parametric and nonparametric tests. Results: The maximum load to fracture was 2395.01 ± 150.96 N in G1 and 2408.39 ± 112.66 N in G2. Most of the observed specimens exhibited restorable fractures and continuous margins. Cement thickness was 132 ± 38 μm in G1 and 150 ± 41 μm in G2. No differences between the groups emerged. Conclusion: This study demonstrated similar satisfactory performance of the two considered preparations designs for occlusal veneer with LDG. Clinical Significance: A new minimally invasive occlusal veneer preparation with marginal chamfer exhibited promising fracture resistance and marginal adaptation that were comparable to those of a standard conservative preparation for the restoration of molars with CAD/CAM lithium disilicate occlusal veneers. [ABSTRACT FROM AUTHOR]

Background: Fiber posts are broadly used due to their good esthetics and elasticity close to that of dentin, which allows for uniform stress distribution within a root and lowers the possibility of nonrestorable root fractures. Aim and Objectives: The study assessed the layer of cement thickness and interfacial nanoleakage of luted fiber posts which were fabricated with CAD/CAM technology following direct scanning of the post space (DS) method, scanning of a polyether impression of the post space (IS), and scanning of a plaster model of the post space (MS). Methodology: Ninety premolars were chosen randomly and were assigned to three groups according to the scanning technique. Posts were computer designed and milled from experimental fiber-reinforced composite blocks. Results: The mean and standard deviation values of cement thickness, respectively, were: DS 172 ± 39 = m; IS 199 ± 55 = m, and MS MPa 272 ± 81 = m. The fiber posts fabricated following DS technique demonstrated superior performance compared to posts fabricated upon IS and MS, in terms of the post retention. The cement thickness did not differ between DS and IS, whereas in MS group, the cement layer was significantly thicker than in the remaining two groups. The scanning technique did not influence the sealing ability, as all groups showed comparable nanoleakage. Conclusion: Fiber posts fabricated following DS technique demonstrated superior performance. Furthermore, scanning technique did not influence the sealing ability, as all groups showed comparable nanoleakage. [ABSTRACT FROM AUTHOR]

Background and Objectives: This in vitro study seeks to evaluate and compare the marginal and internal fit of cobalt-chromium copings fabricated using the conventional and direct metal laser sintering (DMLS) techniques. Methods: A master model of a prepared molar tooth was made using cobalt-chromium alloy. Silicone impression of the master model was made and thirty standardized working models were then produced; twenty working models for conventional lost-wax technique and ten working models for DMLS technique. A total of twenty metal copings were fabricated using two different production techniques: conventional lost-wax method and DMLS; ten samples in each group. The conventional and DMLS copings were cemented to the working models using glass ionomer cement. Marginal gap of the copings were measured at predetermined four points. The die with the cemented copings are standardized-sectioned with a heavy duty lathe. Then, each sectioned samples were analyzed for the internal gap between the die and the metal coping using a metallurgical microscope. Digital photographs were taken at ×50 magnification and analyzed using measurement software. Statistical analysis was done by unpaired t-test and analysis of variance (ANOVA). Results: The results of this study reveal that no significant difference was present in the marginal gap of conventional and DMLS copings (P > 0.05) by means of ANOVA. The mean values of internal gap of DMLS copings were significantly greater than that of conventional copings (P < 0.05). Conclusions: Within the limitations of this in vitro study, it was concluded that the internal fit of conventional copings was superior to that of the DMLS copings. Marginal fit of the copings fabricated by two different techniques had no significant difference.

Introduction: Porcelain laminate veneer has evolved as a dependable treatment option due to their superior optical properties similar to natural tooth and exceptional aesthetic outcome. Among the factors which influence the final shade of laminate veneers, shade and thickness of resin cement used for luting contributes to the ultimate result. Aim: To analyse whether the shade and thickness of resin cement affects the final colour of the veneer restoration. Materials and Methods: Electronic databases Cochrane, MEDLINE and PubMed were searched for articles published in English between 1990 and 2017 based on set inclusion criteria. Data screening and extraction was performed in covidence systematic review software. Pre-clinical studies which assessed the effects of resin cement shade and thickness on the final shade of porcelain laminate veneers were included in the study. The initial search of literature included 22 studies, of which five articles were excluded, a total of 17 articles for full text reading were included after which 14 articles which did not meet the inclusion criteria were eliminated and remaining three articles were accepted as eligible for the review. Results: The search resulted in three studies reporting the effect of resin cement shade on porcelain. The mean colour difference was assessed in terms of clinical acceptability and perceptibility threshold. Various resin cement systems with similar shade showed different colour parameters and changes in final translucency. None of the studies compared the thickness parameter of resin cement on the final colour of restoration. Conclusion: The aesthetic outcome of veneer restorations are reflected by the shade of resin luting cements, considering the mean colour difference within various cement systems. There is a definite need for further research to evaluate the effect of cement thickness on final colour of veneers and a standardised resin cement shade classification.

Introduction: Porcelain laminate veneer has evolved as a dependable treatment option due to their superior optical properties similar to natural tooth and exceptional aesthetic outcome. Among the factors which influence the final shade of laminate veneers, shade and thickness of resin cement used for luting contributes to the ultimate result. Aim: To analyse whether the shade and thickness of resin cement affects the final colour of the veneer restoration. Materials and Methods: Electronic databases Cochrane, MEDLINE and PubMed were searched for articles published in English between 1990 and 2017 based on set inclusion criteria. Data screening and extraction was performed in covidence systematic review software. Pre-clinical studies which assessed the effects of resin cement shade and thickness on the final shade of porcelain laminate veneers were included in the study. The initial search of literature included 22 studies, of which five articles were excluded, a total of 17 articles for full text reading were included after which 14 articles which did not meet the inclusion criteria were eliminated and remaining three articles were accepted as eligible for the review. Results: The search resulted in three studies reporting the effect of resin cement shade on porcelain. The mean colour difference was assessed in terms of clinical acceptability and perceptibility threshold. Various resin cement systems with similar shade showed different colour parameters and changes in final translucency. None of the studies compared the thickness parameter of resin cement on the final colour of restoration. Conclusion: The aesthetic outcome of veneer restorations are reflected by the shade of resin luting cements, considering the mean colour difference within various cement systems. There is a definite need for further research to evaluate the effect of cement thickness on final colour of veneers and a standardised resin cement shade classification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: To evaluate the marginal and internal cement thicknesses of inlay restorations made of various CAD/CAM materials using 3D X‐ray micro‐computed tomography (micro‐CT) technique. Materials and Methods: Caries‐free extracted mandibular molars (N = 30) with similar size were randomly assigned to three groups (N = 10 per group). Mesio‐occlusal‐distal (MOD) cavities were prepared, and inlay restorations were obtained by milling out CAD/CAM materials namely, (a) IPS: monolithic lithium disilicate (control), (b) VE: polymer‐infiltrated ceramic, and (c) CS: nano‐ceramic using a CAM unit. Marginal and internal cement thicknesses were measured using 3D micro‐CT. Data were analyzed using 1‐way ANOVA and Tukey's tests (alpha = 0.05). Results: The mean marginal and internal cement thickness were not significant in all inlay materials (p > 0.05). Mean marginal cement thickness (μm) was the lowest for the IPS group (67.54 ± 10.16) followed by VE (84.09 ± 3.94) and CS (95.18 ± 10.58) (p > 0.05). The internal cement thickness (μm) was the lowest in the CS group (54.85 ± 6.94) followed by IPS (60.58 ± 9.22) and VE (77.53 ± 12.13) (p > 0.05). Conclusion: Marginal and internal cement thicknesses of MOD inlays made of monolithic lithium disilicate, polymer‐infiltrated ceramic, and nano‐ceramic CAD/CAM materials were similar and all less than 100 μm, which could be considered clinically acceptable. Clinical significance: MOD inlays made of different CAD/CAM materials presented similar cement thickness, less than 100 μm. [ABSTRACT FROM AUTHOR]

Purpose. This study evaluated the effects of different dowel space (DS) diameters on pull-out bond strength of a cylindrical post, of threaded steel, to dentin. Materials and methods. Forty-five extracted human teeth were divided in 3 groups with DSs, with the same depth (6 mm), differing for the diameter (i.e. 1.5 mm, Group 1; 1.75 mm, Group 2; 2.00 mm, Group 3). Both the diameter of the post (1.3 mm) and the composite resin cement (Panavia 21) were the same for all the samples. The samples were submitted to pull-out test by means an Universal Testing Machine (Mod. 1193, Instron) (1KN load cell, crosshead speed 0.5 mm/min). Results. The mean values of the bond strength (BS) were: Group 1, 442±128.3N; Group 2, 411.3±111N; Group 3, 448.7±142.29N. While the calculated average shear bond strengths (SBSs) were: Group 1, 14.7±4.27MPa; Group 2, 11.6±3.14MPa; Group 3, 11±3.5MPa. ANOVA test showed not significative differences, among the groups, concerning the BS: Group 1 vs Group 2 (p = 0.490); Group 1 vs Group 3 (p = 0.894); Group 2 vs Group 3 (p = 0.431). Significative differences were observed, among the groups, concerning the SBS for Group 1 vs Group 2 (p = 0.032) and Group 1 vs Group 3 (p = 0.014). While a not significative difference was found, concerning this parameter, for Group 2 vs Group 3 (p = 0.641). Conclusion. The cement thickness can influence the SBS of the adhesively luted posts, in our setting, the best values were obtained with a thickness of 100 µm. [ABSTRACT FROM AUTHOR]

Background and Objectives: This in vitro study seeks to evaluate and compare the marginal and internal fit of cobalt-chromium copings fabricated using the conventional and direct metal laser sintering (DMLS) techniques. Methods: A master model of a prepared molar tooth was made using cobalt-chromium alloy. Silicone impression of the master model was made and thirty standardized working models were then produced; twenty working models for conventional lost-wax technique and ten working models for DMLS technique. A total of twenty metal copings were fabricated using two different production techniques: conventional lost-wax method and DMLS; ten samples in each group. The conventional and DMLS copings were cemented to the working models using glass ionomer cement. Marginal gap of the copings were measured at predetermined four points. The die with the cemented copings are standardized-sectioned with a heavy duty lathe. Then, each sectioned samples were analyzed for the internal gap between the die and the metal coping using a metallurgical microscope. Digital photographs were taken at ×50 magnification and analyzed using measurement software. Statistical analysis was done by unpaired t-test and analysis of variance (ANOVA). Results: The results of this study reveal that no significant difference was present in the marginal gap of conventional and DMLS copings (P > 0.05) by means of ANOVA. The mean values of internal gap of DMLS copings were significantly greater than that of conventional copings (P < 0.05). Conclusions: Within the limitations of this in vitro study, it was concluded that the internal fit of conventional copings was superior to that of the DMLS copings. Marginal fit of the copings fabricated by two different techniques had no significant difference. [ABSTRACT FROM AUTHOR]

BACKGROUND: The use of dental computer-aided design/computer-aided manufacturing (CAD/CAM) restoration is rapidly increasing. OBJECTIVE: This study was performed to evaluate the marginal and internal cement thickness and the adhesive gap of internal cavities comprising CAD/CAM materials using two digital impression acquisition methods and micro-computed tomography. METHODS: Images obtained by a single-image acquisition system (Bluecam Ver. 4.0) and a full-color video acquisition system (Omnicam Ver. 4.2) were divided into the BL and OMgroups, respectively. Silicone impressions were prepared from an ISO-standard metal mold, and CEREC Stone BC and New Fuji Rock IMP were used to create working models (n = 20) in the BL and OMgroups (n = 10 per group), respectively. Individual inlays were designed in a conventional manner using designated software, and all restorations were prepared using CEREC inLab MC XL. These were assembled with the corresponding working models used for measurement, and the level of fit was examined by three-dimensional analysis based on micro-computed tomography. RESULTS: Significant differences in the marginal and internal cement thickness and adhesive gap spacing were found between the OM and BL groups. CONCLUSIONS: The full-color movie capture system appears to be a more optimal restoration system than the single-image capture system. [ABSTRACT FROM AUTHOR]

Objective To evaluate the stress distribution in bi-layered Y-TZP based crowns, according to the occlusal internal spacing between coping and abutment. Methods Twelve premolar shaped Y-TZP copings were made by a CAD/CAM system and seated on an abutment to evaluate the internal fit at the occlusal third using micro-CT images. Considering the fitting range obtained experimentally, two 3D finite element models, consisting on bone tissue, a titanium implant, a zirconia abutment, cement layer and a bi-layered Y-TZP ceramic crown were constructed based on the micro-CT images, one corresponding to the thinnest cement space and other representing the specimen with the thickest cement space obtained experimentally. A 250 N axial load was applied at the center of the occlusal surface of the crown (≅0,8 mm 2 area) and the first principal stress distribution was plotted and analyzed. Results The greatest maximum principal stress occurred within the veneer ceramic right below the site of loading. The thickest cement model showed higher stress concentration at the center of occlusal surface of veneer and the center of occlusal internal surface of coping. Significance Knowledge of stress distribution in ceramic crowns with different cement thicknesses will help clinicians to properly adjust crown fit, in seeking to avoid porcelain fractures. [ABSTRACT FROM AUTHOR]

This study evaluated the fracture resistance and marginal fit of CAD/CAM ceramic and composite inlays. Molars (N = 80) were prepared to receive Mesio-occlusal-distal (MOD) inlays and randomly divided into four groups to be restored depending on the materials: (a) HLD: heat-pressed lithium disilicate ceramic (IPS e.max Press), (b) CLD: CAD/CAM-fabricated lithium disilicate ceramic (IPS e.max CAD), (c) NC: CAD/CAM nano-ceramic resin (Lava Ultimate), (d) RC: Indirect resin composite (Filtek P60). Each group was randomly divided into two subgroups regarding the resin cement: (a) High-viscosity resin cement (Syntac, Variolink II), (b) Self-adhesive low-viscosity cement (RelyX Ultimate). After marginal gap and cement thickness measurements, specimens were loaded to fracture in a Universal Testing Machine (1 mm/min). Intact molars acted as the control group (n = 10). Data were analyzed using one-way and two-way ANOVA, Tukey’s tests (α = 0.05). Before cementation, CLD group showed significantly lower mean marginal gap (65 ± 22.4 μm) and after cementation, cement thickness was again the lowest with CLD (82.6 ± 24.6 μm) and the highest with HLD (108.4 ± 21.3 μm) (p < 0.001). The mean marginal gaps of inlays at the gingival margin were significantly higher than at the occlusal and the axial margins (p < 0.05). While material type significantly affected the mean fracture resistance (p < 0.001), the cement type had no effect on the results (p = 0.083). NC group (2486 ± 40 N) showed significantly higher mean fracture load compared to those of other three groups (1997.5 ± 60–2007 ± 30) (p < 0.05). The mean fracture resistance of control group with the intact teeth was significantly higher than those of all groups (p < 0.05) except for NC (p > 0.05). [ABSTRACT FROM PUBLISHER]

This study evaluated the effect of Er,Cr:YSGG laser on the root canal dentin after luting a fiber post. Twenty-four bovine teeth roots were prepared using NiTi instruments and filled with Sealer 26 and gutta-percha. Post spaces were prepared and roots were distributed according to dentin treatment ( n = 8): 2.5%NaOCl (group control), Er,Cr:YSGG laser (1.5 W, 20 Hz, 20 s) (group test 1) or 2.5%NaOCl + Er,Cr:YSGG laser (group test 2). Fiber posts were luted using adhesive cement (Rely X U200, 3M) and roots were prepared to confocal laser scanning microscopy (CLSM) and scanning electron microscope (SEM). The morphology of interface, thickness of cement, and the gaps and tags were analyzed. Non-parametrical data for thickness of cement were submitted to Friedman and Kruskall-Wallis tests ( α = 0.05) and parametrical data for gaps to ANOVA ( α = 0.05). CLSM of the cement thickness and gaps revealed no significant difference in surface treatment (NaOCl, Er,Cr:YSGG laser and NaOCl + Er,Cr:YSGG laser) ( p > .05) and canal thirds (cervical, middle, and apical) ( p > 0.05). SEM showed tags and a residual layer of cement adhered to dentin, mainly in laser-irradiated specimens. The pretreatment of root canal with Er,Cr:YSGG laser previously to luting the fiber post with a self-adhesive cement did not influence the cement thickness and gaps but affected the dentin interaction. [ABSTRACT FROM AUTHOR]

Objectives to evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50 μm and 500 μm) was tested, in order to better measure the influence of this variable. Methods Feldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50 μm and 500 μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens ( n = 20) were submitted to cyclic loads (500,000 cycles at 20 Hz; initial maximum load = 40% of monotonic load, from previous data) following a staircase sensitivity design (step size = 25 N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol). Results Crowns with an occlusal cement layer of 50 μm were more resistant than those cemented with 500 μm (246.4 ± 22.9 N vs . 158.9 ± 22.9 N), under wet cyclic testing conditions ( p < 0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50 μm; to 53% of monotonic for 500 μm. Significance An occlusal cement thickness of 50 μm was more favorable for the structural performance of feldspathic crowns than was 500 μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading. [ABSTRACT FROM AUTHOR]

Aim: The purpose of this study is to compare and evaluate the influence of two different cement space settings and two different cement types on the stress distribution under occlusal surfaces of tooth restored with two different types of crowns and studied by using three-dimensional (3D) finite element analysis (FEA)., Materials and Methods: Eight 3D finite element models (FEMs) representing a mandibular first molar tooth restored with crowns of, porcelain-fused-to-metal (PFM) and porcelain-fused-to-zirconia (PFZ) crowns with two cement space settings (50 and 80 µm) and with two different types of cement were constructed, using an FEA software (ANSYS, version 10). Each model was subjected to a distributed load simulating normal masticatory bite force of 225 N and was applied axial direction. Also, von Mises stress of each individual part in the system of models was calculated., Results: The PFM crowns undergo less stress distribution than the PFZ crowns. The PFM crowns are more compatible with self-adhesive cements, and the PFZ crowns are more compatible with resin-modified glass ionomer cements., Conclusion: The PFM crowns with G-Cem Link Ace with 50 µm and PFZ crowns with RelyX Luting Plus with 80 µm combinations displayed less amount of stress distribution under normal masticatory bite force., Clinical Significance: Self-adhesive resin cements with PFM crowns and PFZ with resin-modified glass ionomer cements show more benefits in stress distribution under occlusal surfaces under normal masticatory bite force.

Abstract: Metal-on-metal hip resurfacing prostheses were re-introduced during the last 10–15 years. These prostheses have the potential to better restore normal function with limited activity restriction, being an option for younger and more active patients. Resurfacing procedures have demonstrated high failure rates in national registers [1,2]. Multiple factors may affect early and long-term HR performance. The influence of femoral cement mantle thickness and different interface characteristics between the prosthesis components on the long-term performance of resurfacing prostheses is still unknown. In the present work, a model was used to predict bone remodeling with different mantle thicknesses and interface characteristics. A very thin cement mantle (0.25mm) increased bone resorption at the superior femoral head, while greater thickness (1 or 3mm) had a lesser effect. In all cases, bone apposition was predicted around the stem and at the stem tip. Bone formation and resorption were observed clinically in good agreement with the predictions calculated in simulations. Computed results showed that 1-mm cement mantle thickness combined with a bonded bone–cement interface and a debonded implant–cement interface was an appropriate configuration. Bone remodeling results and computed equivalent strains were correlated. In conclusion, we have been able to demonstrate the importance of choosing an adequate cement mantle thickness. Additionally, computational studies should consider realistic interface characteristics between the components in order to perform simulations closer to reality. [Copyright &y& Elsevier]

Objectives: Due to morphological differences along the root canal, serious structural damage, or extensive endodontic preparation, cement thickness of luted fibre-reinforced com- posite (FRC) post systems can largely vary. This study aimed at evaluating the effects of a self-etch (Multilink Automix, MLA) and various self-adhesive resin cements (G-Cem, GCM; Maxcem Elite, MXE; RelyX Unicem, RLX; SmartCem 2, SMC) on the pull-out bond strengths of FRC posts to root canal dentine, and to compare the effects of different cementation thicknesses. Methods: 100 bovine incisor roots were embedded in acrylic resin and randomly assigned to two groups. Root canals of group 1 were prepared with RelyX Fiber Post drill size one (Ø 1.3 mm), whereas in group 2 drill size three (Ø 1.9 mm) was used to attain different cement thicknesses (thicknesses 1 and 2). Each group was then subdivided into five subgroups (n = 10). RelyX Fiber Posts size one (Ø 0.70 mm) were luted with the respective resin cements. All specimens were subjected to pull-out evaluation using a universal testing machine. Post surface areas covered with cement were measured by means of stereomicroscopy. Results: RLX revealed the significantly highest pull-out bond strengths in both groups ( p < 0.05), while MXE exhibited the significantly lowest pull-out bond strengths in group 2 ( p < 0.05). Main failure modes were determined as adhesive at the cement-post surface for all examined groups (except for SMC, group 2). Conclusions: The different resin cements influenced the pull-out bond strengths, whereas the cement thickness itself was not responsible for any differences. Clinical significance: Self-adhesive resin cements can provide an acceptable retention of FRC posts even in case of use with wider post space conditions. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The aim of this study was to analyze the influence of polymerization shrinkage of the cement layer on stresses within feldspathic ceramic crowns, using experimentally validated FEA models for (1) increasing occlusal cement thickness; and, (2) bonded versus non-bonded ceramic-cement interfaces. Methods: 2-D axial symmetric models simulated stylized feldspathic crowns (1.5mm occlusal thickness) cemented with resin-cement layers of 50–500μm on dentin preparations, being loaded (500N) or not. Ceramic–cement interface was either bonded or not. Cement was bonded to the dentin in all models. Maximum axial shrinkage of 0%, 1%, 2%, 3%, 4% and 4.65% were simulated. The first principal stresses developing in the cementation surface at the center and at the occluso-axial line-angle of the crown were registered. Results: Polymerization shrinkage of the cement increased tensile stresses in the ceramic, especially in loaded non-bonded crowns for thicker cement layers. Stresses in loaded non-bonded crowns increased as much as 87% when cement shrinkage increased from 0% to 4.65% (100–187MPa), for a 500μm-thick cement. Increasing polymerization shrinkage strain raised the tensile stresses, especially at the internal occlusal-axial line-angle, for bonded crowns. Significance: Changes in the polymerization shrinkage strain (from 0% to 4.65%) have little effect on the tensile stresses generated at the cementation surface of the ceramic crowns, when the occlusal cement thickness is thin (approx. 50μm for bonded crowns). However, as the cement becomes thicker stresses within the ceramic become significant. [Copyright &y& Elsevier]

Objective. The aim of this study was to evaluate the effect of luting cement thicknesses on the push-out bond strength of the fiber posts. Materials and methods. Sixty human maxillary canine teeth were endodontically treated. Post spaces were prepared and root specimens randomly divided into three groups: Group 1: etch-and-rinse (Variolink II/Exite DSC), Group 2: self-etch (Panavia F2.0/ED primer) and Group 3: self-adhesive (Clearfil SA Cement). Then each group was divided into four sub-groups according to the cement thickness, as follows: Sub-group 1: 0.35 mm, Sub-group 2: 0.25 mm, Sub-group 3: 0.15 mm, and Sub-group 4: 0.05 mm. Three slices of 1 mm thickness were obtained from each root specimen ( n = 15). Push-out tests were performed and data was analyzed with two-way ANOVA and Tukey tests. Results. The etch-and-rinse system (Variolink II) had a significantly higher bond strength compared with the other systems ( p < 0.05). The thickest cement group (0.35 mm) had a significantly lower bond strength compared with the 0.15 and 0.05 mm groups in the etch-and-rinse and self-adhesive groups ( p < 0.05). In the self-etch group, the cement thicknesses did not significantly affect the bond strength ( p > 0.05). Conclusions. The etch-and-rinse system offered better bonding to root dentine than the self-adhesive and self-etch systems. The increases in cement thickness significantly reduced the bond strength of fiber posts to root dentine for both the etch-and-rinse and self-adhesive systems. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Internal three-dimensional (3D) “fit” of prostheses to prepared teeth is likely more important clinically than “fit” judged only at the level of the margin (i.e. marginal “opening”). This work evaluates two techniques for quantitatively defining 3D “fit”, both using pre-cementation space impressions: X-ray microcomputed tomography (micro-CT) and quantitative optical analysis. Both techniques are of interest for comparison of CAD/CAM system capabilities and for documenting “fit” as part of clinical studies. Methods: Pre-cementation space impressions were taken of a single zirconia coping on its die using a low viscosity poly(vinyl siloxane) impression material. Calibration specimens of this material were fabricated between the measuring platens of a micrometre. Both calibration curves and pre-cementation space impression data sets were obtained by examination using micro-CT and quantitative optical analysis. Regression analysis was used to compare calibration curves with calibration sets. Results: Micro-CT calibration data showed tighter 95% confidence intervals and was able to measure over a wider thickness range than for the optical technique. Regions of interest (e.g., lingual, cervical) were more easily analysed with optical image analysis and this technique was more suitable for extremely thin impression walls (<10–15μm). Specimen preparation is easier for micro-CT and segmentation parameters appeared to capture dimensions accurately. Conclusions: Both micro-CT and the optical method can be used to quantify the thickness of pre-cementation space impressions. Each has advantages and limitations but either technique has the potential for use as part of clinical studies or CAD/CAM protocol optimization. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the biomechanical interactions between cuspal preparation designs and cement thickness in a cusp-replacing ceramic premolar restoration. The cavity was designed in a typical MODP (mesial-occlusal-distal- palatal) restoration failure shape when the palatal cusp has been lost. Twelve 3D finite element (FE) models with four cavity preparations (without coverage and with buccal cuspal coverage in 1.0, 1.5 and 2.0 mm reducing in cuspal height) and three cement thicknesses (50, 100 and 150 μm) were constructed to perform the simulations. The results indicated that enamel and cement stresses in designs with no buccal cusp replacement or a 1.0 mm thick buccal cusp replacement were higher than the designs with 1.5 and 2.0 mm thick replacement. No apparent differences were found in the dentin, enamel, and cement stresses based on cement thicknesses of 50, 100, or 150 μm. This study concluded that when cusp replacement is indicated, reduction of the buccal cusp by 1.5 mm at least could reduce stress. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: This study investigates the influence of cement thickness on the macro- and micro-mechanical responses in a ceramic veneer adjacent to an incisal overlapped incisor. Methods: Seven finite element (FE) ceramic veneer macro-models with different cement thicknesses (10–180μm) were generated. A 10N load was applied with an angulation of 60° to the longitudinal tooth axis. Seven FE micro-models corresponding to the macro-models were constructed at an enamel–adhesive interface where the stress concentration was found. Based on an interfacial scanning electron microscope (SEM) micrograph, morphology of resin tags in the micro-models was generated. The micro-model boundary conditions were determined from the macro-model results. The principal stress on each node in the macro- and micro-models was calculated to investigate interfacial mechanics. A tensile test was performed to obtain an ultimate cement tensile strength to determine the material failure parameters. Results: The highest stress concentration within the cement was found at the resin tag base of the enamel–adhesive interface in lingual side. Maximum stress values from 10.6 to 14.7MPa for the micro-models were higher (44–48%) than that from 7.2 to 10.0MPa for the macro-models when the cement layers increased. Based on the ultimate tensile strength (11.8MPa), bonding failure could found when the micro-models with the cement layers presented more than about 50μm. This seems to correspond with data from previous studies. Conclusions: Higher stresses develop in the adhesive as the cement thickness increases. Cement thicknesses less than 50μm might reduce the adhesive bonding failure. [Copyright &y& Elsevier]

Abstract: Objectives: This study investigates the biomechanical interactions among restorative materials, cuspal preparation designs, and cement thickness in a cusp-replacing adhesive premolar restoration. Methods: Twenty-seven, 3D finite element (FE) models designed in a typical MODL restoration with three restorative materials (CAD/CAM ceramic block, indirect resin composite and glass-ceramic), three cavity preparation designs (buccal cuspal reduction of 1.0mm, 1.5mm and 2.0mm in cuspal height) and three cement thicknesses (50μm, 100μm and 150μm) were constructed to perform the simulations. The ANOVA test was performed to determine the relative importance of the investigated factors and main effects for each of the three investigated factor levels (restorative material, preparation design and cement thickness) in terms of the principal stress values. Results: The results indicated that the stress value in the restorative material was influenced primarily by the restorative material itself (95.49%). Preparation design was found as the major factor (>80%) affecting the stress values in the remaining tooth and luting cement. Conclusions: Using a low modulus restorative material presented more favorable biomechanical performance and the cuspal height might be at least 1.5mm to critically reduce the stress values when cuspal-coverage treatment is considered. The investigated cement thickness only slightly affected the mechanical behavior of the cuspal replacement restoration. [Copyright &y& Elsevier]

Abstract: Background: There is no consensus on possible detrimental effects of reduced thickness of the cement mantle surrounding hip stems. This work originated from the suspect that a successful design would yield inferior survival when implanted with a lower cement thickness. The scope was to assess with a reproducible in vitro experiment if a thinner cement mantle could cause a reduction of the long-term implant fatigue resistance. Methods: A comparative in vitro study was designed based on the same commercial stem (Centrament, Aesculap), implanted with the recommended (2–3mm) and reduced (1–2mm) cement thickness. Tests were carried out simulating 24 years of activity of active hip patients. A multifaceted approach was taken: inducible and permanent micromotions were recorded throughout the test; cement micro-cracks were quantified using dye-penetrants and statistically analyzed; crack surface and stem–cement fretting damage was investigate under Scanning Electron Microscopy. Findings: The same stem, when implanted with a thinner cement mantle, tended to migrate significantly more (up to 0.3mm), with a tendency to loosen over time (increasing migration rate over time). After cyclic testing the cement mantle of the thinner specimens showed significantly more and longer cracks than the standard implants, with loose cement chips and signs of stem–cement fretting. Interpretation: All these results confirmed that: (i) the stem under investigation had a good performance (in comparison with similar published work) when implanted with the recommended thickness; (ii) micromotion, cement cracking and fretting damage significantly increased when reduced cement mantle was used. Excessively thin cement mantle can result in critical conditions even for designs, which, in general, show low complications. [Copyright &y& Elsevier]

The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate cement using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0° to 70° and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4·58 ± 1·13 to 73·13 ± 78·32 μm. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4·03 ± 0·61 to 12·12 ± 0·33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0·62), and retention (r = −0·91). Crown retention and marginal discrepancy were influenced by the preparation convergence design. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0° to 70° and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4.58 ± 1.13 to 73.13 ± 78.32 μm. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4.03 ± 0.61 to 12.12 ± 0.33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0.62), and retention (r = −0.91). Complete veneer crown retention and marginal discrepancy were influenced by the preparation convergence design. [ABSTRACT FROM AUTHOR]

The results are reported of a radiographic study of cement mantle thickness in 112 consecutive primary hip replacements. Measurements were made by three observers of the apparent cement thickness medially and laterally using standard anterior-posterior radiographs. The average cement thickness was 3.2 mm, which is 1.2 mm greater than the size difference between the broach and the prosthesis, and was in the range 2-5 mm in 67 per cent of all measurement points. This has significance for the design of instrumentation to prepare the femoral cavity to give a defined cement mantle thickness. There was a greater cement mantle thickness proximally than distally. In 95 cases it was possible to determine the orientation of the stem within the cement mantle, which showed an even distribution between varus and valgus orientation; 49 per cent were within 1 degree of neutral and only one case was more than 5 degrees from neutral. [ABSTRACT FROM AUTHOR]

This study evaluated the influence of occlusal resin cement space on the fatigue performance of bonded-leucite crowns to a dentin-analogue material. Leucite anatomical crowns were adhesively cemented to dentin-like preparations having distinct occlusal cement space (50, 100 and 300 μm) (n = 18), and subjected to step-stress fatigue testing (150 N – 350 N; step-size: 25 N; 20,000 cycles/step; 20 Hz). Fatigue data (load and number of cycles for failure) were analyzed using Kaplan–Meier and Mantel–Cox (log-rank) tests (p <0.05). Fractographic analysis and occlusal internal space measurements were also performed. There was no significant difference for the distinct occlusal cement layer (50 μm: 289 N, 136,111 cycles; 100 μm: 285 N, 132,778 cycles; 300 μm: 246 N, 101,667 cycles). Occlusal internal space analysis showed a mean thickness of 120.4 (50 μm), 174.9 (100 μm) and 337.2 (300 μm). All failures were radial cracks originating at the ceramic-cement interface. Distinct occlusal cement spaces had no effect on the fatigue behavior of anatomical leucite crowns. [ABSTRACT FROM AUTHOR]

• SIF at the interfaces of cemented cup increases as the cement thickness decreases. • Cement thickness plays an important role in interface failure. • Cement-bone interface is weaker than the cement-implant interface. • The anterior location is more prone to failure than other anatomic locations. • Chance of interface failure is more with edge crack as compared to center crack. The goal is to determine the influence of interface crack and non-uniform cement thickness on mixed-mode stress intensity factors (SIF) and the prediction of interface failure of the cemented cup. Nine three-dimensional (3D) finite element (FE) models of implanted pelvic bone were developed having the uniform and non-uniform cement thickness based on computed tomography (CT) dataset. Physiological loading conditions and location-dependent material properties of cancellous bone were considered for the present analysis. In order to understand the influence of crack at cement-bone and implant-cement interfaces, two-dimensional (2D) cracked models were generated and solved using the element free Galerkin method (EFGM). For cracked analysis, a rectangular section was considered at both the interfaces in the superior, inferior, anterior, and posterior anatomic locations to determine the SIF. The average stress values obtained from 3D FE analysis was transferred at the cut boundary of the rectangular section and considered as a mixed-mode loading condition to understand the influence of crack and non-uniform cement thickness on interface failure. The results of the present study indicated that the cement thickness plays an important role in interface failure. SIF increases as the cement thickness decreases. Anterior location is more prone to failure as compared to other anatomic locations. The chance of cement-bone interface failure is more as compared to the implant-cement interface. The present study also indicated that the chance of interface failure is more for the generation of edge crack as compared to center crack. [ABSTRACT FROM AUTHOR]