Comparative Investigation of the Fracture Strengths of Crowns of Three Different Non-metal Materials

Zahtjevi pacijenata za visokom estetikom tijekom rekonstruktivnih protetskih zahvata pospješili su razvoj novih materijala i tehnologija. Sile koje djeluju u postkaninom dijelu zubnoga niza iznose ≥ 500 N, pa i materijali koji se upotrebljavaju za izradbu nadomjestaka moraju izdržavati te sile. Svrha je istraživanja bila istražiti otpornost na lom triju nekovinskih materijala: 1. ceromer (Targis, Ivoclar-Vivadent), 2. ceromer ojačan vlaknasto ojačanim kompozitom (Targis/Vectris, Ivoclar-Vivadent), 3. nekovinski keramički sustav (IPS Empress 2, Ivoclar-Vivadent). Iz svake vrste materijala izrađeno je po 18 istovjetnih krunica na gipsanome modelu izbrušenog prirodnog drugoga donjeg pretkutnjaka, prema uputama proizvođača. Isti je brušeni zub upotrijebljen za izradbu kovinskoga modela na kojemu su umetane krunice u univerzalnu kidalicu ZWICK. Tlačna je ploča modificirana s trnom dijametra 7 mm koji je djelovao silom na okluzijsku plohu pod kutom od 180°. Sila je aplicirana do prvoga znaka loma, a iznos je zabilježen. Polovina je uzoraka prije ispitivanja termociklirana 1000 puta po 20 sekunda na temperaturi od 2°C i 55°C s razmakom od 40 sekunda između urona za temperiranje uzoraka. Izmjerena srednja vrijednost iznosa sile do loma za netermociklirane uzorke iznosile su za krunice iz ceromera 577,8 ± 113,4 N, za krunice iz ceromera i vlaknasto ojačanoga kompozita 923,3 ± 229 N, a za krunice iz nekovinske keramike 1208,9 ± 161,8 N. Mann-Whitney U testom utvrđena je znatna razlika između svih triju materijala (p<0,05) u iznosima opterećenja do loma uzorka. Termocikliranje nije znatno smanjilo iznos sile do loma uzorka. Istraživanjem je utvrđeno da su sva tri materijala pogodna za izradbu trajnih nadomjestaka u području žvačnoga središta, jer svi mogu izdržati silu veću od 500 N.The demands of patients for high aesthetics during reconstructive prosthetic procedures accelerated the development of new materials and technology. Forces acting in the post-canine part of the dental arch amount to ≥ 500 N, and thus the material used for fabrication of the restoration must withstand such forces. The aim of this investigation was to study the resistance to fracture of three non-metal materials: 1. ceromer (Targis, Ivoclar-Vivadent), 2. ceromer reinforced with fibre reinforced composite (Targis/Vectris, Ivoclar-Vivadent), and 3. non-metal ceramic system (IPS Empress 2, Ivoclar-Vivadent). Eighteen identical crowns were fabricated from each type of material on a plaster model of a polished natural second lower premolar, according to the manufacturer’s instructions. The same tooth was used for fabrication of a metal model on which crowns were placed in the universal testing device ZWICK. The compressive plate was modified with a pin 7mm in diameter, which acted with force on the occlusal surface at an angle of 180˚. Force was applied up to the first sign of fracture, and the amount recorded. Half of the samples prior to the examination were thermocycled 1000x for 20 seconds at temperatures of 2˚C and 55˚C with 40 second intervals between immersion of the tempered sample. The mean value measured of the amount of force up to fracture for non-thermocycled samples amounted to 577.8 +/- 113.4 N for crowns of ceromer, 923.3+/- 229 N for crowns of ceromer and fibre reinforced composite, and 1208.9 +/- 161.8 N. for crowns of non-metal ceramic. Significant difference was determined by Mann-Whitney U test between all three materials (p < 0.05) for the amounts of loading up to fracture of the samples. Thermocycling did not significantly reduce the amount of force up to fracture of the sample. The investigation determined that all three materials are satisfactory for fabrication of permanent restorations in the area of the masticatory centre, as all withstand force greater than 500 N