Polymerisation shrinkage of luting agents for crown and bridge cementation

The volumetric contraction of a variety of luting agents, including Panavia 21, All-Bond C&B Cement, Superbond., Variolink and zinc phosphate cement, was assessed and compared using a minimal transducer The contraction among the materials tested was determined from the post-gel linear displacement of a deflecting coverslip resting on 4 silicone rubber spacers between which a mixed material was centrally located. Finally, the rate and duration of shrinkage over a period of 60 minutes from the moment of rigid contraction for all materials were investigated, and the final shrinkage values among the materials tested were compared. The analysis of variance showed that there were highly significant differences (P< 0.001) between the materials and the mean of each group was significantly different from that of any of the other groups (Tukey's test). Superbond produced the highest values of the final polymerisation shrinkage, followed by All bond C&B, Variolink, Panavia 21 and zinc phosphate cement respectively. Also, there was a marked variation in the overall magnitude of shrinkage (from 1.34% to 4.62%) among the materials tested. The method used to measure the polymerisation shrinkage in the present study was shown to be a precise measure in that it produced consistent and reproducible results. It can also offer the ability to observe the development of polymerisation shrinkage against time, during the post-gelation phase, for a range of chemically-cured resin materials.     

Film thickness of new adhesive luting agents.

This study determined and compared the film thicknesses of new adhesive luting agents. The method was in compliance with American National Standards Institution/American Dental Association (ADA) Specification No. 8 for zinc phosphate cement. Each of the 20 materials tested was manipulated exactly as described in the manufacturers' instructions. An electronic gauge with an accuracy of 0.5 micron was recalibrated after each recording, and each luting agent was measured 10 times. The mean film thickness and standard deviation were calculated for each luting agent; an analysis of variance and a multiple comparison test were also performed. Nine materials satisfied the ADA type I specification for film thicknesses less than 25 microns, and these included a hydroxyapatite cement, glass ionomer cements, zinc phosphate cements, and polycarboxylate cements. Five other materials met the ADA type II specification for film thicknesses of less than 40 microns, and these included a glass ionomer cement, a resinous cement, a zinc phosphate cement, and glass ionomer-resinous hybrids. Six resinous cements recorded film thicknesses greater than 40 microns, and suggestions were made regarding future development and research.     

Microleakage of new crown and fixed partial denture luting agents.

This study measured the in vitro microleakage of conventional and new FPD luting agents. Standardized preparations were made on 42 freshly extracted premolars. Facial and lingual chamfer margins were placed in enamel, mesial and distal in dentin and cementum, and castings were made in Rexillium III alloy and were then cemented with a standardized technique. Six groups of seven samples were tested, (1) polycarboxylate, (2) zinc phosphate, (3) glass ionomer, (4) Den-Mat Thin Film cement, (5) Panavia Ex, and (6) Den-Mat Thin Film cement with Tenure. The ranking of groups for stain ingress was from the greatest (1) to the least (6). A one-way analysis of variance and Tukey-Student range analysis revealed significantly similar groups, p less than 0.05:(1,2,3,4) (5,6).     

Influence of ceramic thickness on mechanical properties and polymer structure of dual-cured resin luting agents.

OBJECTIVE: To investigate the influence of ceramic thickness on the mechanical properties and polymer structure (degree conversion and cross-linking density) of three dual-cured resin luting agents. METHODS: Three dual-cured resin luting agents [Linkmax HV (GC), Nexus 2 (Kerr), and Variolink IIHV (Ivoclar-Vivadent)] were polymerized with or without 800 mW/cm2 irradiation through 0-3-mm-thick GN-I (GC) machinable ceramic. Bar-shape specimens were subjected to three-point bending to determine flexural strength (FS) and elastic modulus (EM) after dry storage at 37 degrees C for 24 h. Knoop hardness was measured on the irradiated surface of disk-shaped specimens before (KHN1) and after (KHN2) storage of 100% ethanol solution at 37 degrees C for 24 h. KHN1 and KHN2 were estimated as indirect indicators of degree of conversion (DC) and cross-linking density, respectively. Data were analyzed by one-way ANOVA and Student-Newman-Keuls test for each luting agent, and four mechanical properties were subjected to regression analysis. RESULTS: For three resin luting agents with dual-cured mode, FS, EM, KHN1, and KHN2 decreased with the increase of ceramic thickness. FS except for Nexus 2 and EM for three resin luting agents had a positive linear relationship with both KHN1 and KHN2. SIGNIFICANCE: The variables tested behaved differently. When the ceramic thickness increased, the chemical cured components of dual-cured resin luting agents did not produce significant compensation for all variables. Mechanical properties and polymer structure of dual-cured resin luting agents was dependent on the intensity of light irradiation.     

Experimental study on the influence of various dental luting cements on the crown elevation during cementation

Cementing manipulation is an important final step in adapting crown prosthesis to various oral environments. Preventing elevation of full cast crowns during cementation and improving adaptability of the margin after cementation are especially critical. The purpose of this article is twofold: 1) To clarify the relationship between the viscosity of dental cement and the extent of crown elevation, with special attention to viscosity changes occurring in various cement materials during the hardening process. 2) To study the effects on cemented-crown elevation of the space created between the abutment tooth and the crown, which may be partly related to dental cement behavior during cementation. A total of 4 cement materials was used: Elite Cement 100 as a zinc-phosphate cement, Super Bond C & B and Chemiace as MMA-resin cements containing 4-META, and Panavia EX as a phosphoricester cement. Viscosity was measured by means of MR-3 Soliquidmeter with a cone and plate system (Reheology Engineering). A brass material was processed to experimental crowns cemented to abutment teeth of brass. Crown elevation was measured by comparator (Measurescope Model II, Nikon). In addition, effects of the resistance of dental cement during cementation on crown elevation were studied for the sake of a comprehensive understanding of the elevation phenomenon. 1. Changes in dental-cement viscosity during the hardening process 1) Elite Cement 100 demonstrated the highest initial steady flow coefficient of viscosity. It was followed by Super Bond C & B, Chemiace, and Panavia EX, in that order. The t-test revealed significant differences among these cement materials (significance taken to be 1%). 2) As experimental temperature increased, the viscosity of all tested cement materials increased with progressive hardening. 3) With the passing of time, changes in torque, which represents a change pattern in viscosity, indicated that the tested cement materials have different viscosity-change patterns during the initial setting period. 4) From a clinical viewpoint, Super Bond C & B and Elite Cement 100 had very limited working time, whereas Chemiace and Panavia EX had relatively long working time. 2. Elevation after cementation of experimental crowns 1) For Elite Cement 100, mean elevation was 334microns, for Super Bond C & B 281 microns, for Chemiace 164microns, and for Panavia EX 130microns. The t-test revealed significant differences among these cement materials (significance taken to be 1%). 2) In all the cement materials tested, with a reliability of 99%, sequential correlation was observed between crown elevation and steady flow coefficient of viscosity.(ABSTRACT TRUNCATED AT 400 WORDS)     

An evaluation of the film thickness of resin luting agents

Acid-etched cast metal resin-bonded retainers require resin luting agents with film thicknesses similar to dental cements to allow complete seating of frameworks without the need for post-bonding adjustments. Conventional cements, restorative resins, and resin cements were compared in terms of film thickness by using the American Dental Association Specification No. 8 for zinc phosphate cement. Most of the resin luting agents had film thicknesses of 20 to 40 microns. Working time was seen to affect film thickness. The particle size of one resin was also examined under scanning electron micrograph.     

Cement failure loads of 4 provisional luting agents used for the cementation of implant-supported fixed partial dentures

The major disadvantage of cement-retained implant-supported fixed partial dentures (FPDs) is difficulty in retrievability. The retentive strengths of the provisional luting agents usually employed in these cases are therefore an important consideration. This study evaluated the cement failure loads of 4 provisional luting agents used for the cementation of FPDs supported by 2 implants or 4 implants. Nogenol luting agent exhibited the lowest retentive values in both types of FPD. ImProv proved to be the most retentive cement of all tested. Temp Bond NE and Temp Bond presented significantly different values (P < .05) for the 2-implant FPD, but not for the 4-implant model. On the basis of the study results, it may be concluded that Nogenol appears to be more appropriate for cementation of both 2- and 4-implant-supported FPDs when removal of the provisionally cemented superstructure is anticipated.     

Mechanical and physical properties of contemporary dental luting agents

STATEMENT OF PROBLEM: New luting agents, particularly with adhesive capability, are being introduced in an attempt to improve clinical success. Independent studies of basic comparative data are necessary to characterize these materials in relation to mechanical and physical properties. PURPOSE: The purpose of this study was to compare the flexural strength, modulus of elasticity, and radiopacity and pH of representatives of 5 types (categories) of luting agents. MATERIAL AND METHODS: The luting agents included a zinc phosphate, a conventional and a resin-modified glass ionomer, 2 dual-polymerizing resins ("photopolymerized" after mixing and "unphotopolymerized" conditions), and an auto-polymerizing resin. The specimens were prepared and the testing was conducted by 1 person to maximize standardization. Flexural strength (MPa) and modulus of elasticity (GPa) were determined on bar-shaped specimens (2 x 2 x 20 mm) at 24 hours and 3 months (n = 8). Radiopacity (mm Al) was measured by exposing 1 mm thick specimens along with an aluminum step wedge (n = 4). pH was measured using a pH electrode immediately after mixing; at 1, 5, 15, 30 minutes; and at 1, 2, 4, 6, and 24 hours (n = 4). The data were subjected to statistical analyses with analysis of variance and Duncan's multiple range test (P<.05). RESULTS: The resin luting agents (64 to 97 MPa) showed higher flexural strength than all other materials tested (7 to 27 MPa), with the "photopolymerized" (83 to 97 MPa) conditions higher than "unphotopolymerized" (64 to 81 MPa) (P<.0005). Zinc phosphate was the most radiopaque (6.4 mm Al) (P<.0001) and provided the highest rigidity (9.2 GPa) (P<.05). The autopolymerization resin cement was the most radiolucent (1.1 mm Al) (P<.0001). Zinc phosphate and conventional glass ionomer cements were the most acidic immediately after mixing (pH 1.5 to 2.2) but were the least acidic after 24 hours (pH 6.4 to 6.8) (P<.0001). CONCLUSIONS: Within the limitations of this study the data showed a wide variation of material properties. The dual-polymerization resin luting agents tested showed the best combination of mechanical and physical properties combined with the highest setting pH. Photopolymerization of these resin-based materials was necessary to maximize strength and rigidity.     

Investigation of stress distribution in roots restored with different crown materials and luting agents

The purpose of this study was to identify crown materials and luting agents that would decrease the stress concentrated at the roots of endodontically treated teeth. To this end, natural tooth model (NT), full cast crown model (gold-silver-palladium alloy; MC), polymer-based restorative material crown model (HCC), and all-ceramic crown model (ACC) were constructed. In each model, methyl methacrylate-based resin cement (MMA) and composite cement (CC) were used as luting agents. The magnitudes of von Mises stress of the roots during function were compared. When the luting agent was changed from MMA to CC, von Mises stress in the cervical area decreased by 37.8% for MC, 27.1% for HCC, and 37.0% for ACC. Within the limitations of this study, the combination of HCC and CC gave rise to the lowest stress concentration at the cervical area.     

Film thickness of die coating agents.

Die coating agents are often used during the fabrication of porcelain margins for crowns and fixed partial dentures. These agents seal microscopic irregularities within the stone die and resist abrasion. This investigation measured the film thickness of several die coating agents. A specific reference point was used during the measurement process. The results indicate that there is no significant difference between the die coating agents examined under the conditions of the study. The film thickness measurements ranged between 0.367 microns for Duro Super Glue Material and 2.3 microns for Zap CA material.     

Film thickness of various dentine bonding agents

summary Curing dentine bonding agents create a film thickness on the surface of teeth which are prepared for all-ceramic crowns. The aim of this study was to investigate if the film thickness of dentine bonding agents (DBAs) is acceptable with the fit of definitive restorations of 50–100 μ. AllBond 2®, Syntac®, ART Bond®, P-Bond® (an experimental DBA), and the Primer of AllBond 2 were applied onto teeth which were prepared with standardized all-ceramic crown preparations. The DBAs were applied onto the prepared tooth surfaces according to manufacturers'instructions and under a standardized simulation of intrapulpal pressure. After curing the DBAs, the teeth were cut mesiodistally and orolingually and the film thickness was measured under a light microscope. Only the film thicknesses of AllBond 2 and P-Bond were low enough and, therefore, would enable curing to take place immediately after their application.     

Solving the frustrations of crown cementation

Restoration cementation is a routine procedure, but it commonly is accomplished improperly. In this article, I have discussed several of the most frequently occurring problems with restoration cementation and have made suggestions about how to prevent them.     

Effect of seating force on film thickness of new adhesive luting agents.

This study examined the effect of seating force on the film thickness of new adhesive luting agents. The method was in compliance with American National Standards/American Dental Association Specification No. 8 for zinc phosphate cement. The materials tested were zinc phosphate cement, glass ionomer cement, polycarboxylate cement, and a resinous cement with a dentinal bonding agent. All materials were manipulated exactly as described in the manufacturer's instructions, and an electronic gauge with an accuracy of 0.5 micron was used. Each class of material was measured 10 times at six different seating forces. Analysis of variance and multiple comparisons testing disclosed that the seating force and class of material strongly influenced the film thicknesses of luting agents. A mathematical model describing the response of zinc phosphate cement within the range tested was reported.     

Influence of cyclic loading and luting agents on the fracture load of two all-ceramic crown systems

STATEMENT OF PROBLEM: Inherent mechanical properties, fabrication techniques, luting agents, and intraoral conditions are primary factors attributing to longevity of all-ceramic crowns. Before doing time-consuming and costly clinical studies, preclinical in vitro studies should be conducted to evaluate the durability of these crowns. Purpose This study investigated the influence of different luting agents and cyclic loading under wet conditions on the fracture load of CAD-CAM and pressable all-ceramic crowns. MATERIAL AND METHODS: Ninety-six human premolars were prepared for all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the CEJ, 2-mm occlusal reduction, and occluso-gingival height of 5 mm. Sixteen unprepared premolars served as controls. Forty-eight crowns were laboratory fabricated from a lithium disilicate glass-ceramic (IPS-Empress 2), while 48 CAD-CAM crowns were directly fabricated using a leucite-reinforced glass-ceramic (ProCAD) and the Cerec 3 CAD-CAM system. Three luting agents (Panavia F, Superbond C&B and ProTec CEM) were used for cementation (n = 16). After 1 week storage in water, half of the specimens of each subgroup (n = 8) were cyclically loaded and thermal cycled under wet conditions for 600,000 masticatory cycles and 3500 thermal cycles (58 degrees C/4 degrees C; dwell time 60 seconds) in a masticatory simulator. All specimens were loaded in a universal testing machine with the compressive load (N) applied along the long axis of the specimen at a crosshead speed of 1 mm/min until fracture. Fracture load was recorded for each specimen. The Kruskal-Wallis test was used first to detect overall significance, followed by Mann-Whitney U tests to identify which pairs of groups had significant differences (P =.05). RESULTS: Cyclic loading significantly decreased the median fracture load of ProCAD crowns luted using Superbond from 987.2 to 786.0 N (P =.014) and those luted using ProTec CEM from 914.4 to 630.7 N (P =.007). Also, the median fracture load of Empress 2 crowns luted using ProTec CEM decreased significantly from 977.3 to 622.9 N (P =.013). However, cyclic loading did not decrease the median fracture load of crowns luted using Panavia F, Empress 2 (P =.431) and ProCAD (P =.128). With the same loading conditions and luting agents, there were no significant differences in the fracture loads of ProCAD and Empress 2 crowns (P >.05). CONCLUSIONS: Cyclic loading reduced the fracture load of ProCAD crowns luted with Superbond C&B and ProTec CEM and of Empress 2 crowns luted with ProTec CEM.     

The influence of temporary cements on dental adhesive systems for luting cementation

Objective

This study tested the hypothesis that bond strength of total- and self-etching adhesive systems to dentine is not affected by the presence of remnants from either eugenol-containing (EC) or eugenol-free (EF) temporary cements after standardized cleaning procedures.

Methods

Thirty non-carious human third molars were polished flat to expose dentine surfaces. Provisional acrylic plates were fabricated and cemented either with EC, EF or no temporary cements. All specimens were incubated for 7 days in water at 37 °C. The restorations were then taken out and the remnants of temporary cements were mechanically removed with a dental instrument. The dentine surfaces were cleaned with pumice and treated with either total-etching (TE) or self-etching (SE) dental adhesive systems. Atomic force microscopy was used to examine the presence of remnants of temporary cements before and after dentine cleaning procedures. Composite resin build-ups were fabricated and cemented to the bonded dentine surfaces with a resin luting cement. The specimens were then sectioned to obtain 0.9 mm² beams for microtensile bond strength testing. Fractographic analysis was performed by optical and scanning electron microscopy.

Results

ANOVA showed lower mean microtensile bond strength in groups of specimens treated with EC temporary cement than in groups treated with either no cement or an EF cement (p < 0.05). Mean microtensile bond strength was lower in groups employing the SE rather than the TE adhesive system (p < 0.001). SE samples were also more likely to fail during initial processing of the samples. There was no evidence of interaction between cement and adhesive system effects on tensile strength. Fractographic analysis indicated different primary failure modes for SE and TE bonding systems, at the dentine-adhesive interface and at the resin cement-resin composite interface, respectively.

Conclusion

The use of eugenol-containing temporary cements prior to indirect bonding restorations reduce, to a statistically similar extent, the bond strength of both total- and self-etching adhesive systems to dentine.     

Comparison of luting cements for minimally retentive crown preparations.

OBJECTIVE: The purpose of this study was to compare the retentive strengths of resin, glass-ionomer, and zinc phosphate cements under adverse conditions. METHOD AND MATERIALS: Thirty extracted teeth were mounted and prepared in their long axis. The axial wall height was 3 mm and the convergence angle was 28 degrees. These conditions increased the role of the cement and decreased the role of the preparation in providing retention of the casting. The axial surface area was determined. Copings were fabricated with a ring aligned in the long axis to facilitate removal of the crown. They were cemented with a resin cement, a glass-ionomer cement, or a zinc phosphate cement. A block randomization scheme was used to assign cements so that the mean surface areas of the teeth were equivalent in all groups. The copings were loaded in tension, and the amount of force required to remove the coping was recorded. The stress required to remove the coping was calculated. RESULTS: The mean stress required to remove the copings was 9.4, 5.0, and 3.1 MPa for the resin, glass-ionomer, and zinc phosphate cements, respectively. CONCLUSION: The resin cement group was significantly stronger than both the glass-ionomer cement and the zinc phosphate cement groups. The glass-ionomer cement was significantly stronger than the zinc phosphate cement.