Zinc Phosphate Cement Research Articles

The Effect of Variability in the Powder/Liquid Ratio on the Strength of Zinc Phosphate Cement

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Student's t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturer's recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturer's instructions. The maximum and minimum powder/liquid ratios, together with the manufacturer's recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (P = 0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (P < 0.001) and from the mean value obtained from the recommended ratio (P < 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material.

Analysis of the Properties of Dental Cements after Exposure to Incubation Media containing Streptococcus mutans

Indirect restorations are increasingly used in dentistry, and the cementation interface is possibly the most critical region of the work. The objective of the present work was to evaluate the influence of exposure to a culture medium containing S. mutans on the hardness and solubility of four different cementing agents (zinc phosphate, glass ionomer, glass ionomer modified with resin and resin cement). Test specimens composed of these cements were exposed for 30 days in a culture medium containing S. mutans. After leaching, the test materials were assessed in terms of their solubility (loss of mass) and Knoop (KHN) microhardness. Changes in surface morphology were identified using scanning electron microscopy (SEM). The resin cement showed no significant solubility and its hardness increased following exposure and leaching, while the zinc phosphate cement was the most soluble and its hardness decreased after exposure to the culture medium. SEM analyses identified morphological alterations on the surfaces of the test materials that were compatible with the solubility results. It is concluded that resinous cements perform better than water-based cements when exposed to acidic conditions. The effects of acids from Streptococcus mutans can interfere with the efficiency and properties of some cements used for fixation of indirect restorations, exposed to the buccal environment.

The effect of tooth and foundation restoration heights on the load fatigue performance of cast crowns

In badly damaged teeth and teeth with short clinical crown heights, the placement of foundation restorations has been advocated to permit the development of retention and resistance form. However, there is little information on the effect of these foundation restorations on the clinical performance of the definitive restoration. The purpose of this study was to evaluate the load fatigue performance of teeth restored with posts and cores, with varying tooth heights, and to compare them with similar groups having no posts and cores. A secondary purpose was to determine whether a critical tooth height existed at which the placement of a foundation restoration resulted in no significant difference in the load fatigue performance. Three test groups (n=10) with prepared tooth heights of 2, 3, and 4 mm were tested. These were compared with another 3 groups with similar tooth heights that were restored with prefabricated titanium posts and core heights of 4, 3, and 2 mm, respectively. Cast complete crowns were then fabricated and cemented with zinc phosphate cement. A fatigue load of 58.8 N was applied at an angle of 135 degrees to the long axis of each crown-tooth specimen. The number of cycles to preliminary failure was determined. Significant differences in cycles to preliminary failure were assessed with 1-way ANOVA, followed by Tukey HSD tests (α=.05). The group with the greatest preparation height (4 mm) and a 2-mm post-retained foundation had the highest number of cycles to preliminary failure (437,701), while the group with the shortest preparation height and no foundation had the lowest number of cycles (53,806). The Tukey HSD multiple comparison tests showed that for all 3 tooth heights, groups with foundation restorations had a significantly higher number of cycles to preliminary failure than those without foundation restorations. For a given tooth height, teeth restored with foundation restorations had a significantly better load fatigue performance than those with no foundation restoration.

Optimisation of hardness and setting time of dental zinc phosphate cement using a design of experiments

The main objective of this study is to demonstrate the application of strategy of an experiment design to optimize the compressive strength and setting time of zinc phosphate cement used in the dental application. For this work, the extreme vertices design was chosen. Its factors are components of the mixture forming a ternary system: zinc oxide, aluminum phosphate and orthophosphoric acid (ZnO–AlPO4–H3PO4). The local region of dental cement – in simplex space- explored and limited by upper and lower limits of the three components of the mixture. The optimization of each response and then all together by graphical methods allowed us to obtain the adequate cement.

Prospective Observation of CAD/CAM Titanium‐Ceramic‐Fixed Partial Dentures: 3‐Year Follow‐Up

There is lack of knowledge about the clinical performance of computer-aided design/computer-aided manufacturing (CAD/CAM) titanium-ceramic-fixed partial dentures (FPDs). The purpose of this study was to evaluate CAD/CAM titanium-ceramic FPDs after 3 years in function. Thirty-one FPDs were fabricated for 23 patients. The Ti frameworks were completely fabricated using CAD/CAM technology, and the low-fusing porcelain was veneered. After confirming there were no mechanical or biological complications, the FPDs were cemented using zinc phosphate cement. The patients were recalled at 12, 24, and 36 months after cementation to examine for the presence of any mechanical complications, such as fractures of the veneering porcelain or the supportive framework, or biological complications, including caries, gingivitis, or periodontitis. The periodontal condition was measured using probing depth (PD), bleeding on probing (BOP), and plaque index (PI). Success and survival rates were estimated using the Kaplan-Meier analysis. There were four cohesive and three adhesive porcelain fractures, but no framework fractured. The Kaplan-Meier cumulative success rate of the CAD/CAM titanium-ceramic crown with regard to mechanical complications was 76.4%, and the cumulative survival rate was 96.8% after 3 years of use. One patient developed caries, but the condition was not associated with marginal discrepancy. No other biological complications were reported. The periodontal parameters demonstrated a tendency that slightly increased up to 24 months and was maintained by 36 months. At the end of the follow-up, PD was 2.86 mm, percentile of surface with BOP was 23.5, and PI was 0.45. The CAD/CAM titanium-ceramic FPDs survived in the mouths of patients without major complications for 3 years, although the risk of porcelain fracture appeared to be relatively high.

Influence of corrosion on the interface between zinc phosphate steel fiber and cement

AbstractThe interface bond between steel fibers and concrete matrix is a key factor influencing bearing capacity of steel fiber reinforced concrete (SFRC). In order to improve the interface bond strength and corrosion resistance, a kind of method was put forward by depositing zinc phosphate (ZnPh) coating on steel fiber surface in this paper. The corrosion behavior was investigated in 5% NaCl solution by using linear polarization measurement. Microstructure analysis (SEM and EDX) and fiber pull‐out test in combination with linear polarization measurement were carried out. The results prove that ZnPh coatings fabricated on the carbon steel surface can not only protect steel fiber against corrosion, but also enhance the mechanical interlocking bonds between fibers and matrix.

Influence of core materials in the microleakage of cast crowns

Endodontically treated teeth can be restored with prosthetic crowns over cast metal cores or prefabricated posts with composite resin cores. Prosthetic failure is frequently observed possibly due to microleakage. To verify the influence of the core materials in the microleakage of cast crowns, this research studied three experimental conditions: (a) teeth with partial dental remaining core with prefabricated post and partial composite resin cores, (b) teeth with cast metal posts/cores, and (c) teeth with prefabricated posts and composite resin cores. Teeth preparations were standardized, duplicated and the crowns were made in NiCr alloy, which were cemented with zinc phosphate cement. The specimens were submitted to thermocycling and mechanical stresses. They were immerged in a 0,05% aqueous solution of basic fuchsin for 8 hours during 3 days. The crowns were sliced buccal-lingually, and their microleakage was evaluated by glass magnification, according to a score scale. There was no statistical difference between conditions (a) and (c). Microleakage at cervical region of axial wall was observed in both cases. Condition (b) showed higher microleakage, which reached medium third of axial wall.

Effect of air-abrasion on the retention of zirconia ceramic crowns luted with different cements before and after artificial aging

Objectives The purpose of this in vitro study was to evaluate the effect of intaglio surface air-abrasion on the retention of CAD/CAM produced zirconia ceramic crowns cemented with three different types of cement. In addition the influence of artificial aging in masticatory simulator and thermocycling was tested. Methods Extracted human premolars were prepared for all-ceramic crowns (12° taper, 3 mm axial length). CAD/CAM zirconia crowns were manufactured. Half of the crowns were air-abraded with 50 μm alumina particles at 0.25 MPa, the rest was left as machined. The crowns were luted with zinc phosphate cement (Hoffmann), glass ionomer cement (Ketac Cem), or composite resin (Panavia 21), subgroups were either stored for 3 days in 37° water bath or stored for 150 days in 37° water bath, with additional 37,500 thermal cycles (5–55°) and 300,000 cycles dynamic loading with 5 kg in a masticatory simulator. Then crown retention was measured in tension at a crosshead speed of 2 mm/min using a universal testing machine. Statistical analysis was performed with three-way ANOVA. Results Mean retention values were ranged from 2.8 to 7.1 MPa after 3 days and from 1.6 to 6.1 MPa after artificial aging. Air-abrasion significantly increased crown retention ( p < 0.001), while artificial aging decreased retention ( p = 0.017). In addition, the luting material had a significant influence on retention ( p < 0.001) with the adhesive luting resin providing the highest retention. Significance The use of phosphate monomer containing composite resin on air-abraded zirconia ceramic can be recommended as most retentive luting method.

An in vitro study to evaluate the retention of complete crowns prepared with five different tapers and luted with two different cements.

This study includes comparatively evaluating and drawing general conclusion about the best advisable taper and cement for maximal retention. Eighty extracted human maxillary premolar teeth with sound surfaces were selected using dial vernier caliper. Selected teeth were randomly divided into five different taper groups (0°, 3°, 6°, 9° and 12°). The crown preparations with different tapers respectively were achieved by graduated customized device. Preparations were verified with special set up. Crowns were cast with Co-Cr alloy; metal copings were luted with glass ionomer and zinc phosphate cement. Retention was measured (MPa) by separating the metal crowns from the teeth under tension on a universal testing machine, data was recorded and statistically analyzed. Glass ionomer cemented 0° and 12° taper group showed increase in retentive strength (p=0.003 hs), when compared to zinc phosphate cement. 9° and 12° group showed decreased retentive strength (p=0.001 vhs) when compared with 0° taper group. No significant difference found between 0° and 3° and 6° group. The choice of cement for crowns prepared within this ideal range (0°-6° taper) might be of limited clinical significance. 3° and 6° taper with zinc phosphate or glass ionomer cement shown to be ideal for maximum retention.

Porcelain Fracture Resistance of Screw‐Retained, Cement‐Retained, and Screw‐Cement‐Retained Implant‐Supported Metal Ceramic Posterior Crowns

The purpose of this in vitro study was to compare the porcelain fracture resistance between screw-retained, cement-retained, and combined screw- and cement-retained metal-ceramic (MC) implant-supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw-access opening on porcelain fracture resistance of screw-retained and cement-retained MC implant-supported posterior single crowns. Forty standardized MC molar-shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw-retained, screw-access hole placed in the center of the occlusal surface; Group SRO: screw-retained, screw access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement-retained, zinc phosphate cement was used; Group CSC: cement-retained with a screw-access hole in the center of the occlusal surface. The screw-retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one-way ANOVA and Tukey's Studentized test (alpha= 0.05). Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 +/- 593; Group SRO: 1885 +/- 491; Group CRP: 3707 +/- 1086; Group CSC: 1700 +/- 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05). The cement-retained restorations showed significantly higher mean fracture loads than the restorations having screw-access openings in their occlusal surface. The position of the screw-access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.

Comparison of the marginal fit of different all-ceramic and metal-ceramic crown systems: an in vitro study

STATEMENT OF PROBLEM: High levels of fracture resistance offered by today's ceramic crown systems might eliminate the need for adhesive cementation. However, high accuracy of fit involving gap widths <75 µm is also required for conventional cementation. PURPOSE: This in vitro study was performed to evaluate six ceramic crown systems for their accuracy of fit. MATERIAL AND METHODS: A total of 60 experimental crowns were fabricated from four all-ceramic systems (Vita Mark II/Cerec 2, IPS Empress/staining, Vita In-Ceram Alumina/Cerec 2, and Procera All-Ceram) and two metal-ceramic systems (electroformed or conventional copings). All restorations were delivered to prefabricated stone dies with conventional zinc-phosphate cement. Gap widths were measured by light microscopy (magnification ×200). Intergroup differences were analyzed by one-way ANOVA. Kolmogorov–Smirnov test was used to evaluate normal distribution plots and box plots of different measurements within each group. RESULTS: Marginal gaps averaged 142.3 µm for Vita Mark II, 109.3 µm for IPS Empress, 98.1 µm for Vita In-Ceram Alumina, and 47.3 µm for Procera All-Ceram. Galvano-ceramic and metal-ceramic restorations yielded 68.5 and 77.5 µm. Differences reached statistical significance for Vita Mark II versus all other systems except IPS Empress; for galvanic restorations versus Vita Mark II and IPS Empress; and for Procera All-Ceram versus all other all-ceramic systems. CONCLUSIONS: The incorporation of all ceramic crowns requires different ways of cementation, depending on the marginal gap. This in vitro study showed that Procera All-Ceram crowns can be conventionally cemented with zinc-phosphate cement. CLINICAL IMPLICATIONS: Procera All-Ceram crowns offer marginal gap widths well below 75 µm. Therefore they can be cemented with conventional zinc-phosphate cement. Different cementation techniques are strongly recommended for all other all-ceramic systems tested.

Assessment of crown and bridge work quality among Sudanese dental practitioners

The aim of the present study is to investigate the quality of crown and bridge work among dentists in Khartoum state by mean of a questionnaire. Questionnaire was distributed to all dentists (about 230) who work in private clinics and primary health centers in Khartoum state. A total of 152 usable questionnaires were collected, giving a response rate 66.09%. High-speed hand pieces were the instrument of choice (80.54%) and according to number of spray ports single port was found to be the most common type (80.43%). Alginate was the material of choice as a final impression material (68.24%) followed by condensation-cured silicone (24.32%). Impression trays used by dentists were metal tray 23.53%, rigid plastic tray 12.5% and both 63.97%. Results in concern of the use of the retracting cord indicated that 53.69% never use it. Results also indicated that 36.05% never used temporary crown and bridge. Traditional glass ionomer cements and zinc phosphate cements (56%) were equally selected as best choice for final luting cement of crown and bridge work. Both verbal and written prescriptions (81.73%) were the most common used way of communication between dentists and dental technicians. It is concluded that the majority of the surveyed dentists mainly used alginate as a final impression material for crown and bridge work. It was also observed, the absence of application of retraction cord and temporary restoration in their practice for crown and bridge work.

Eficácia do ultrassom na remoção de retentores intr-radiculares metálicos fundidos

This study aimed at comparing the efficacy of 3 ultrasonic vibration devices in cast post-and-cores removal. Forty-five upper central human incisors received endodontic therapy and cast post-and-cores (NiCr) fixed with zinc-phosphate cement. The specimens were divided into 3 groups (n=15), according to the ultrasonic device (G1 = Enac OE3; G2 = JET Sonic Total; G3 = Profi III Bios) and the time of removal (s) was measured. Tukey‘s test (5%) revealed that G3 (797s) > G1 (67.73s) = G2 (151.60s). In G3, only 3 post-and-cores were removed. It can be concluded that G1 and G2 were similarly well succeed in cast post-and-cores removal.

The three‐dimension finite element analysis of stress in posterior tooth residual root restored with postcore crown

Teeth that have been endodontically treated and restored with postcore crown may experience fracture sometimes. Some researchers have analyzed the stress of the anterior teeth after postcore crown restoration, but the stress of the posterior teeth after such restoration has not been reported. We used three-dimension finite element methods to analyze the stress magnitude and distribution of remaining dentin in posterior tooth residual root restored with postcore crown. The binding material, loading direction, number, length and material of posts were studied. The models of residual root of maxillary first molar restored with postcore crown were created by CT scanning, mimics software and abaqus software. Different number, length and material of posts were used in the modeling. The posts were cemented with zinc-phosphate cement or composited resin. A load of 240 N was applied to the occlusal surface in four directions and tensile, shear, and von Mises stresses were calculated. (i) The maximum stress on remaining dentin changed irregularly as the number and length of posts changed. (ii) The maximum stress on remaining dentin decreased slightly as elastic modulus of the material of posts increased. (iii) The maximum stress on bonding layer and remaining dentin was lower when bonded with resin luting agent than with zinc-phosphate cement. (iv) The maximum stress on remaining dentin increased markedly as loading angle increased. The number, length, material of posts, bonding material and loading angle all have influence on the magnitude and distribution of stress. The influence of loading angle is most apparent.

Fracture resistance of endodontically treated teeth restored with custom cast post core using non uniform and uniform ferrule length luted with two different cements: In vitro study

Post and core are a commonly accepted time honored method for restoring endodontically treated teeth. The present consensus regarding post is to provide retention of the core rather than reinforcement of the tooth. The purpose of the study was to evaluate & compare in vitro the fracture resistance of endodontically treated teeth restored with custom cast post core using non uniform and uniform ferrule length luted using zinc phosphate & resin cement. A total of 60 human single rooted maxillary central incisors were endodontically treated and restored with custom cast gold post core and were randomly assigned to 6 groups of 10 teeth each having the following features. Uniform ferrule (2 mm buccal, lingual & 2 mm proximal) were placed in group 1 and 3, non uniform ferrule ( 2 mm buccal, lingual and 0.5 mm proximal) were placed in group 2and 4,no ferrule were given for group 5 and 6. Post and cores for group 1,2 and 5 were luted with zinc phosphate cement and group 3,4and 6 were luted with Resin cement. Fracture resistance of the entire specimen group was measured using INSTRON testing machine and the data obtained was statistically analyzed. The gold cast post core using 2mm uniform ferrule luted with Resin cement showed highest fracture resistance compared to all the groups.

A comparative study of retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements with stainless steel crowns - An in vitro study

An in vitro study was conducted to compare the retentive strengths of zinc phosphate, polycarboxylate and glass ionomer cements using Instron universal testing machine. Thirty preformed and pretrimmed stainless steel crowns were used for cementation on 30 extracted human primary molars which were divided into three groups of 10 teeth in each group. Then the teeth were stored in artificial saliva and incubated at 37°C for 24 h. A load was applied on to the crown and was gradually increased till the crown showed dislodgement, and then the readings were recorded using Instron recorder and analyzed for statistical significance. The surface area of crown was measured by graphical method. The retentive strength was expressed in terms of kg/cm 2 , which was calculated by the equation load divided by area. Retentive strengths of zinc phosphate (ranged from a minimum of 16.93 to amaximum of 28.13 kg/cm 2 with mean of 21.28 kg/cm 2 ) and glass ionomer cement (minimum of 13.69 - 28.15 kg/cm 2 with mean of 20.69 kg/cm 2 ) were greater than that of polycarboxylate cement (minimum of 13.26 - 22.69 kg/cm 2 with mean of 16.79 kg/cm 2 ). Negligible difference (0.59 kg/cm 2 ) of retentive strength was observed between zinc phosphate (21.28 kg/cm 2 ) and glass ionomer cements (20.69 kg/cm 2 ). Glass ionomer cements can be recommended for cementation of stainless steel crowns because of its advantages and the retentive strength was almost similar to that of zinc phosphate cement.

Post cementation sensitivity evaluation of glass Ionomer, zinc phosphate and resin modified glass Ionomer luting cements under class II inlays: Anin vivocomparative study

Objective:This study aims to compare the patient-perceived post-cementation sensitivity of class II metal restorations preoperatively, immediately after cementation, one week after cementation and one month after cementation with (1) Glass Ionomer luting cement (2) Zinc Phosphate cement and (3) Resin-modified Glass Ionomer luting cement.Materials and Methods:A total of 60 patients, irrespective of sex, in the age group of 15-50 years were selected and the teeth were randomly divided into three groups of 20 each. Twenty inlay cast restorations were cemented with three different luting cements. The criteria adapted to measure tooth sensitivity in the present study were objective examination for sensitivity. (1) Cold water test (2) Compressed air test and (3) Biting pressure test.Results:The patients with restorations cemented with Resin-modified Glass ionomer demonstrated the least postoperative sensitivity when compared with Glass Ionomer and zinc phosphate cement at all different intervals of time evaluated by different tests.Conclusion:The patients with restorations cemented with resin-modified Glass ionomer demonstrated the least postoperative sensitivity.

Crown cementing strategy for naval divers

Background: A large number of personnel working in hyperbaric environment such as divers and submariners during escape drills report to the out patient department with split teeth, displacement of restoration and pain during ascent after diving. These symptoms are probably attributable to dental barotraumas. Therefore, a need was felt to undertake a study in this area, with a specific interest for treating these patients. Methods: Sixty extracted single rooted premolar teeth were prepared and full cast crowns were cemented. Out of these, 20 were prepared with zinc phosphate, 20 with glassionomer and 20 with resin cement. After seven days of storage, each of the teeth in experimental group was pressure cycled 15 times to 3 atmospheres after which the force required to dislodge the crowns was tested on an Instron testing machine. Result: A significant difference was found (student's t test p value<0.01) between the force required to dislodge the crowns with zinc phosphate cemented control group (141.70 ± 38.62) and experimental group (16.92 ± 10.13). Similarly a significant difference was observed in the glassionomer cemented control group (184.33 ± 25.33) and experimental group (90.50 ± 34.07). On the other hand, no difference was found between the resin cemented control group (289.15 ± 81.48 ) and experimental (279.43±87.48) group. Conclusion: Within the limitations of this study and based on the results, it was concluded that environmental pressure cycling affected the retention of crowns cemented with zinc phosphate and glassionomer cement. Panavia resin cement used in this study appeared to be unaffected by environmental pressure cycling. On the basis of the results of this study, dental surgeons should consider cementing fixed prosthesis with resin cements for patients who are exposed to marked variations in environmental pressure, such as divers and submariners during escape drills.

In vitro evaluation of microleakage of various types of dental cements

Microleakage is defined as the clinically undetectable seepage of oral fluids containing bacteria and debris between cement layer and tooth restoration. This in vitro study investigated the effect of different dental cements (zinc-phosphate, polycarboxylate, glass-ionomer and resin cement) on microleakage in different ceramic crown systems (metal ceramic crown, metal ceramic crown with a porcelain margin, Empress 2 and in Ceram all-ceramic crowns) fixed on extracted human teeth. One hundred and sixty intact human premolars were randomized to four groups of forty teeth each, according to the different ceramic crown systems. They were prepared in a standardized manner for metal-ceramic and all-ceramic crowns. Crowns were made following a standard laboratory technique, and each group of crowns were divided into four groups according to the different cement agents and cemented on their respective abutments. The specimens were subjected to thermocycling, placed in methylene blue solutions, embedded in resin blocks and vertically cut in the bucco-oral and meso-distal direction. The microleakage in the area of tooth-cement interface was defined as linear penetration of methylene blue and was determined with a microscope to assign microleakage scores using a five-point scale. A significant association was found between a cement type and degree of microleakage (p = 0.001). No statistically significant differences were found among the different ceramic crown systems luted with the same dental cement. The smallest degree of microleakage was observed in specimens luted with resin cement (X = 1.73), followed by glass-ionomer cement (X=2.45) and polycarboxylate cement (X = 3.20). The greatest degree of microleakage was detected in the crowns fixed with zincphosphate cement (X = 3.33). The investigated dental cements revealed different sealing abilities. The use of resin cement resulted in the percentage of 0 microleakage scores. Due to this feature, the resin cement is to be recommended in everyday clinical practice.

Effect of Different Cements on the Biomechanical Behavior of Teeth Restored with Cast Dowel-and-Cores-In Vitro and FEA Analysis

To test the hypothesis that the type of cement used for fixation of cast dowel-and-cores might influence fracture resistance, fracture mode, and stress distribution of single-rooted teeth restored with this class of metallic dowels. The coronal portion was removed from 40 bovine incisors, leaving a 15 mm root. After endodontic treatment and standardized root canal relief at 10 mm, specimens were embedded in polystyrene resin, and the periodontal ligament was simulated with polyether impression material. The specimens were randomly divided into four groups (n = 10), and restored with Cu-Al cast dowel-and-cores cemented with one of four options: conventional glass ionomer cement (GI); resin-modified glass ionomer cement (GR); dual-cure resin cement (RC); or zinc-phosphate cement (ZP). Sequentially, fracture resistance of the specimens was tested with a tangential load at a 135 degrees angle with a 0.5 mm/min crosshead speed. Data were analyzed using one-way analysis of variance (ANOVA) and the Fisher test. Two-dimensional finite element analysis (2D-FEA) was then performed with representative models of each group simulating a 100 microm cement layer. Results were analyzed based on von Mises stress distribution criteria. The mean fracture resistance values were (in N): RC, 838.2 +/- 135.9; GI, 772.4 +/- 169.8; GR, 613.4 +/- 157.5; ZP, 643.6 +/- 106.7. FEA revealed that RC and GR presented lower stress values than ZP and GI. The higher stress concentration was coincident with more catastrophic failures, and consequently, with lower fracture resistance values. The type of cement influenced fracture resistance, failure mode, and stress distribution on teeth restored with cast dowel-and-cores.