Effects of polycarboxylate and glass ionomer cements on stainless steel crown retention.

Retentive properties of three dental cements were tested using stainless steel crowns Fitted to extracted third molar teeth. No significant difference was Found between the overall mean retentive Forces of the polycarboxylate cement and the two glass ionomer cements. Mechanical retention of the crowns was not a Factor in the overall retentive value. Few studies have investigated the retention of stainless steel crowns. Savide et al. 1 studied five types of preparations encountered in dental practice and their effects on the retention of stainless steel crowns, while Mathewson2 compared cementing agents for stainless steel crowns. Both studies compared the retention of stainless steel crowns with and without cementation (i.e., mechanical retention from the crown alone and retention due to cementation), and both found the retention due to cementation to be far greater than that gained from mechanical retention alone. Mathewson2 found the highest retentive strengths using copper phosphate cement. He attributed this strength to the low pH of the cement during the setting reaction and a possible acid-etching effect on the tooth creating a better bond between the cement and the tooth. He also speculated that the acidity of the cement potentially was harmful to pulp tissues in vital teeth. The next most retentive cements found by Mathewson were zinc phosphate and polycarboxylate. They are currently the most widely used luting agents today. The zinc phosphate cements rely on a mechanical interlocking between the cement and tooth structure and therefore have a lower adhesive strength, although they do have a rather high compressive strength. 3 Zinc phosphate cements are also a potentially caustic substance to vital pulp tissue due to their low pH.4 The polycarboxylates form an ionic bond with enamel and dentin 3’ ~ and have a higher adhesive strength than zinc phosphate. They also have a somewhat lower compressive strength 3, 6 than zinc phosphate cements. One advantage of polycarboxylate over zinc phosphate cements is that they are relatively nontoxic to vital tissue. 7’ 8, 0 Recently, glass ionomer cement has been made available commercially in North America. It forms a strong ionic bond to enamel, dentin, and nickel-chrome alloys giving it a high adhesive strength. 1°-1s The unique composition and structure of A1+3 and Ca+2 ions and polyacrylic acid solution give it a high compressive strength.S, 10. 12 It also has been found to be relatively nontoxic to vital pulp tissue. 17 The purpose of this investigation was to compare the retentive properties of two glass ionomer cements and one polycarboxylate cement. Methods and Materials Materials utilized were two glass ionomer cements, referred to as glass ionomer cement Aa and glass ionomer cement Bb, and a polycarboxylate cement, c All luting cements were mixed at the respective manufacturers’ recommendations. A total of 18 extracted noncarious human third molars were embedded in acrylic blocks and stainless steel crownsa were cemented with the three different cements. All three cements were used on each preparation with all possible preparation-cementation sequences being tested. The specific cementing sequence was assigned to each preparation utilizing a table of random numbers to minimize any bias due to the order of the cements or any preparation variance. Each tooth was subjected to a 30-second toothbrush prophylaxis with fine pumice followed by a distilled water wash and 15 seconds of drying with compressed, oil-free air. a Chembond, L.D. Caulk Co., Milford, Del. b Fuji Type I, G-C Industrial Corp., Tokyo. c Durelon, Premier Dental Products, Norristown, Pa. a Unitek Corp., Monrovia, Calif. 68 IONOMER CEMENTS/STAINLESS STEEL CROWN RETENTION: Noffsinger et al. The crown preparation was similar to the type recommended by Mink and Bennett in 1968. TM The occlusal surface of the third molar was reduced uniformly 2 mm. The proximal surfaces were prepared so that the contact areas were broken and all mesial and distal undercuts were removed. First permanent molar stainless steel crowns, d were fitted for proper size and were uniformly contoured and crimped. A #114a pliers was used to contour the buccal and lingual surfaces as described by Savide. 1 This method was used to place a continuous crimp along the buccal and lingual crown margins so that all margins were in contact with the prepared tooth surface. The proximal margins were left uncontoured and uncrimped. The stainless steel crowns were altered by placing a hole through the central part of the occlusal surface with a #6 round bur. A one-inch nail was inserted through the hole from the undersurface of the crown for subsequent gripping by the test machine. A separate stainless steel crown was fitted for each trial of crown retention, i.e., a new crown was fitted for each cement used and for the no-cement trials on the individual preparations. All crowns were seated to a predetermined reference position on the preparations approximately 1 mm above the cementoenamel junction. After setting times had elapsed the specimens were placed in 100% humidity at 37°C for 24 hours before testing. All excess cement was removed from crown margins before mounting in the test apparatus (Figure 1). The experimental data consisted of two types: retentive forces and failure patterns. The retentive force was defined as the force required to separate the crowns from the tooth preparations. It was applied with an Instron e testing machine at a crosshead speed of 0.05 in / min. The loads required for separation were recorded ~ Stainless Steel Crown