The effect of adhesive luting agent-dentinal surface interactions on film thickness

The effect of luting media on the fracture resistance of a flame sprayed all-ceramic crown

OBJECTIVES

This in vitro study investigated the effect of selected luting media on the fracture resistance of a flame-sprayed all-ceramic crown.

METHODS

Three groups of 10 human upper premolar teeth were prepared for crowning using a standardised technique. Flame sprayed crowns were fabricated and cemented onto the preparations using zinc phosphate (ZPC), glass polyalkenoate (GPC) or composite luting cement (CLC). During crown seating, a pressure perfusion system simulated pulpal fluid outflow equivalent to 300mm of H2O. Compressive fracture resistance was determined for each group using a Universal Testing Machine with a crosshead speed of 1mm min(-1). A group of unrestored teeth acted as a control.

RESULTS

The fracture resistance of the groups ranked as follows: ZPC>CLC>>GPC=unrestored teeth. The difference between the fracture resistance of ZPC and CLC groups and the control group was statistically significant. The mode of fracture between the luted crowns and natural crowns was markedly different.

CONCLUSIONS

When tested in compression, a new, flame-sprayed all-ceramic crown, when luted in place using ZPC, GPC or CLC, could produce strengths comparable to or greater than natural unrestored teeth. The luting agent used significantly affected the recorded fracture loads.

Effect of tooth surface roughness on marginal seating and retention of complete metal crowns

STATEMENT OF PROBLEM

Retention and marginal adaptation factors have major influence on the failure of cemented complete veneer crowns.

PURPOSE

This study investigated the effect of axial surface roughness on the marginal seating and retention of silver-palladium crowns luted with zinc phosphate, glass ionomer, and resin cements.

MATERIAL AND METHODS

Coarse and fine diamond stones were used to create various surface roughnesses of premolars. A milling machine was used to control the height and angle of the axial walls of tooth preparations. Ten cast metal crowns in 6 subgroups were luted with 3 cements (Phosphacap, Fuji Cap I, and Panavia 21). Marginal seating was recorded with a Digimatic indicator. Retention was determined by measuring the tensile force required to remove a metal crown with a Lloyd testing machine.

RESULTS

Two-way analysis of variance revealed statistically significant differences (P <.001) in retention for both luting cements and surface roughness. No significant difference was recorded for marginal seating relative to roughness (P =.860) and interaction effects (P =.204). Tukey-HSD tests revealed substantial differences in retention among Phosphacap, Fuji Cap I, and Panavia 21 cements. Significant differences were not confirmed in marginal seating between Fuji Cap I and Phosphacap cements with coarse diamonds, and Phosphacap and Panavia 21 cements with fine diamonds.

CONCLUSIONS

The best retention for complete metal crown was demonstrated for tooth preparations ground with coarse diamonds and cemented with Panavia 21 cement. Differences in axial surface roughness had no effect on the marginal seating of the complete metal crowns.

In vivo marginal adaptation of cast crowns luted with different cements

Large marginal crown discrepancies are deleterious. Although previous studies have examined casting seating in vitro, few have evaluated the effects of different luting cements on in vivo seating. Hence this in vivo study compared marginal discrepancies created by different cements on cast crowns. Tooth preparations were completed according to acceptable procedures on previously intact human molars that were severely periodontally compromised and scheduled for extraction. Castings were made by conventional techniques. The castings were randomly assigned to the following luting agents: zinc phosphate cement, resin-modified glass-ionomer cement, and the same resin-modified glass-ionomer cement with a dentinal bonding agent. After 6 months the teeth were carefully extracted, embedded, and sectioned, and vertical and horizontal discrepancies were measured. Analysis of variance revealed that all cements resulted in similar discrepancies. Vertical discrepancies were considerably greater than horizontal discrepancies, and the distributions of marginal discrepancies were skewed towards upper ranges.

An investigation into the pressure transmitted to the pulp chamber on crown cementation: a laboratory study

Pressure changes in the pulp chamber resulting from crown cementation have not been previously quantified. An experiment was designed to investigate the effect of smear layer removal on the peak pressure transmitted to the pulp chamber with crown cementation. Ten matched pairs of single-rooted premolar teeth were collected from adolescents and prepared for full-coverage crowns. The pulp tissue from each tooth was removed. One tooth from each pair had the smear layer removed with the application of 37% phosphoric acid for 30 s. The null hypothesis states that the removal of the dentinal smear layer will not change pressure in the pulp chamber resulting from the cementation. Before cementation, a hydrostatic head of pressure was used to perfuse the tooth, and the perfusion rate was recorded. Crowns were cemented with zinc phosphate cement with a seating force of 100 N. The mean peak pressures recorded were 85 Pa (SE 12 Pa) with the smear layer intact, and 194 Pa (SE 49 Pa) when the dentin was etched. The difference in the peak pressures transmitted to the pulp chamber with the two groups was significant (p < or = 0.05). A significant negative correlation was found between dentin thickness and the peak pressure transmitted to the pulp chamber (r = -0.5531, p < or = 0.01). We have shown that the pressure transmission to the pulp chamber during crown cementation can be measured. Since smear layer removal significantly influences the peak pressure, it is concluded that the pressure detected is at least partially dependent on the fluid flow through the dentin.

Luting cement-metal surface physicochemical interactions on film thickness

Low film thickness is critical to the clinical success of cemented castings. This study investigated the effect of luting agent-metal physico-chemical surface interactions on film thicknesses of representative luting agents. Control group luting agents were placed between two glass plates, as described by American Dental Association specifications 8, 61, and 66, and test group luting agents were positioned between glass and metal plates. The materials selected were zinc phosphate cement, polycarboxylate cement, glass ionomer cement, glass ionomer-composite resin hybrid cement and a resinous cement, with a type III gold alloy, a noble metal ceramic alloy, and a base metal ceramic alloy. A two-way analysis of variance and follow-up tests were done. The effects of the type of metal surface, type of cement, and their statistical interaction significantly affected film thickness (p < 0.0001). The type of cement had a greater affect on film thickness than the type of metal. A glass ionomer cement produced lower overall film thicknesses than other cement types, and a noble metal ceramic alloy created lower overall film thicknesses than other types of metal. American Dental Association specifications for cement film thickness did not accurately reflect normal cement use.

Fracture strength of full-contoured ceramic crowns and porcelain-veneered crowns of ceramic copings

This is vitro study compared the fracture strength of Dicor ceramic crowns with a 1 mm axial wall thickness and a 2 mm occlusal thickness with Dicor copings veneered with Vitadur-N or Dicor-Plus porcelain to create similar contours. Tooth preparations for complete crowns were made on human molars with a 10-degree total convergence and a 1 mm shoulder. The artificial crowns were internally etched, given an application of silane, and cemented with a dual-cured resinous cement. After thermocycling, each sample was loaded to failure with a vertical load on the occlusal surface. There were no significant differences in fracture strength between full-contour Dicor crowns and crowns of copings veneered with either Vitadur-N or Dicor-Plus porcelain.

Effect of adhesive luting agents on the marginal seating of cast restorations

This study determined the effect of new adhesive luting agents on the marginal seating of cast restorations. Standardized preparations were completed on freshly extracted premolars, impressions were made, and complete metal veneer crowns were cast with a base metal alloy. The castings were placed on their respective teeth and the extent of marginal opening was recorded. They were then assigned to a luting agent group: glass ionomer cement (GI), polycarboxylate cement (PC), microfilled BIS-GMA composite resin with NPG-GMA/PMDM dentinal bonding agent (GMA + NPG), microfilled BIS-GMA/phosphate ester composite resin (GMA/PE), or zinc phosphate cement (ZP). The castings were cemented and marginal openings remeasured. ANOVA revealed that the cement groups were similar before cementation (p 0.35) but were different after cementation (p < 0.0001). Tukey's multiple comparisons test identified statistically similar groups that were different from other groups and ranked them from lesser to greater marginal opening: (GI, ZP, PC) (GMA/PE, GMA + NPG).