170 Stom Glas S, vol. 54, 2007.

KRATAK SADRŽAJUvod: Najčešće korišćeni gradivni materijali za izra-

du baze totalne ili parcijalne proteze su polimetil-metakri-lati, koji zadovoljavaju sve fizičko-hemijske zahteve. Funk-cionalna vrednost mobilnih zubnih nadoknada zavisi, pored ostalog, i od kvaliteta veze između akrilatnog zuba i baze proteze.

Cilj: Cilj ovog rada je bio da se ispita uticaj različitih postupaka pripreme fabričkih akrilatnih zuba na kvali-tet veze s akrilatnom bazom proteze, da se izmeri veličina pukotine između akrilatnog zuba i protetske baze optičkim ili elektronskim mikroskopom, kao i da se ispita mehanička veza zuba i baze proteze merenjem čvrstoće na pritisak.

Materijal i metod: Kao materijal u ovom in vitro istraživanju korišćeno je 48 akrilatnih modela sa vezom akrilatnog zuba i protetske baze i 12 modela za merenje čvrstoće na pritisak. Akrilatni modeli podeljeni su u četiri grupe (po 12 uzoraka) za mikroskopiranje, odnosno po tri za merenje čvrstoće. U akrilatnu bazu fiksirani su fabrički nepromenjeni zubi, nahrapavljeni zubi, zubi navlaženi monomerom i nahrapavljeni i monomerom navlaženi zubi. Akrilatni modeli su bili istih dimenzija, a površina modela je pripremljena spororotirajućom preciznom teste-rom, abrazivnom dijamantnom pastom i posebnim papir-nim šajbnama. Za merenje čvrstoće napravljen je kalup unutrašnjih dimenzija 20 x 9 mm. Merenje veličine pukoti-ne je obavljeno na svetlosnom mikroskopu (Nikon Epiphot 300), a čvrstoća na pritisak na aparatu Zwick-Roel ZO10.

Rezultati: Rezultati ispitivanja pokazuju da je pro-sečna vrednost pukotine kod mehaničko-hemijski obrađe-

SUMMARYIntroduction: The most commonly used materials

for prosthetic denture base are acrylic resins - polymethyl methacrylate, which has all the important physical and chemical properties. The bond between a denture base and an acrylic tooth has a significant functional value.

Aim: To evaluate the influence of various procedures on bonding quality between the denture base and the artificial tooth, the measurement of gaps when connecting the tooth and the denture base using an optical or electron microscope, and evaluating the mechanical properties by compressive testing.

Materials and methods: Forty eight acrylic models with bonds between acrylic teeth and prosthetic denture-bases, and 12 models for compressive testing were created as the materials in this in vitro study. The acrylic models were allocated to four groups (with 12 samples) for microscopy, and three groups for compressive testing. The samples for microscopy contained denture bases with fixed, unprocessed acrylic teeth, mechanically processed acrylic teeth, chemically processed acrylic teeth, and mechanically and chemically processed acrylic teeth, respectively. The acrylic models had the same dimensions, and the surface of each model was prepared using a slow-speed saw, abrasive diamond paste, and special paper grinders. A special metal cast was created for compressive testing with internal dimensions of 20 x 9 mm. The size of a gap was measured on the light inverse microscope (Nikon Epiphot 300) and pressure testing was performed on a Zwick/Roell Z010 pressure machine.

Evaluacija kvaliteta veze veštačkog zuba i polimerne baze mobilne protezeEvaluation of the artificial tooth and polymer-base bond in removable dentures

COBISS. SR-ID 8417026

Martin Pavlin1, Vjekoslav Jerolimov2, Rebeka Rudolf3, Dragoslav Stamenković4, Ivan Anžel3

1Privatna zubna ordinacija, Martin Pavlin, Maribor, Slovenia, 2Zavod za stomatološku protetiku, Stomatološki fakultet, Sveučilište u Zagrebu, Zagreb, Hrvatska, 3Mašinski fakultet Univerzitet u Mariboru, Maribor, Slovenija, 4Stomatološki fakultet, Univerzitet u Beogradu, Beograd, Srbija1Private dental practice, Martin Pavlin, Maribor, Slovenia, 2Faculty of stomatology, University of Zagreb, Zagreb, Hrvatska, 3Faculty of mechanical engineering, University of Maribor, Maribor, Slovenia, 4Faculty of stomatology, University of Belgrade, Belgrade, Serbia

ORIGINALNI RAD (OR)ORIGINAL ARTICLE

DOI: 10.2298/SGS0703170P

UDC: 616.314-089-77:615.242.03 ISSN 0039-1743

Serbian Dental J, 2007, 54 171

Today, many artificial resins are used in dentistry but acrylic resin is the most commonly used one. They have to satisfy ISO standards regarding usage. The requirements for physical and chemical properties state that the mate-rial has to be insoluble in the mouth, exhibit little water sorption, has neutral taste and smell, and dimensional stability. The mechanical properties required include frac-ture resistance, pressure toughness, modulus of elasticity, fracture modulus and hardness. One of the most impor-tant demands is also the biocompatibility of polyacryl-ics. Until recently, most mobile dentures had been made by conventional polymerization over the last 60 years.1,2,3 This material, however, has some drawbacks. Acrylic res-ins and the process of polymerization have been modi-fied over the past 10 years and resulted in better physical and chemical properties. This has been achieved by add-ing certain chemical substances, and changing the proc-ess of polymerization by adding light and microtalamic energy.4,5

Two important factors for the structuring of acrylic resins are the polymerization procedure and the oral envi-ronment. This is why, in technical aspects, the denture base must be created as efficient as possible. This is where the bond between the tooth and denture-base comes in. Acryl-ic teeth are convenient for chemical bonding to the den-ture-base, but this bonding is the problem in therapy with removable dentures. Significant research work has shown that almost 30% of all repairs are due to mistakes during tooth-denture base bonding.6 The results in this research have forced researchers to do more, towards discovering the cause of de-bonding. This is why the factors that cause de-bonding, and those factors that make the bond better, should be analyzed.

Today acrylic resins are the most frequently used materials in both orthodontics and prosthodontics. Although an acrylic tooth is convenient for chemical bonding to a denture-base, these bonds present a problem because of breakage. Many factors are responsible for

U stomatologiji se danas koriste različite veštačke smole, među kojima su najčešće akrilne smole. Da bi se upotreblja-vale u stomatološkoj protetici, one moraju da zadovolje ISO standarde. Fizičko-hemijska svojstva su netopivost materijala u usnoj duplji, mala apsorpcija vode, neutralan ukus i miris, i dimenziona stabilnost. Mehanička svojstva koja takvi mate-rijali treba da zadovolje su čvrstoća na pritisak, čvrstoća na udar, modul elastičnosti, modul loma i tvrdoća. Osnovni zah-tev je biokompatibilnost poliakrilata. Danas se većina mobil-nih proteza izrađuje konvencionalnim postupkom polimeriza-cije koji je u upotrebi već 60-tak godina1,2,3. Pored njegovog visokog kvaliteta pojavljuje se i određeni broj nedostataka. Akrilatne smole i procesi polimerizacije su tokom poslednjih 10 godina modifikovani, što dovodi do poboljšanja fizičkih i radnih svojstava. To se postiže dodatkom hemijskih supstan-ci i načinom polimerizacije kao što je primena mikrotalasne energije i vidljivog svetla4,5.

Značajan činilac koji određuje svojstva akrilatne smole je njena struktura koja zavisi od postupka polime-rizacije i uslova kojima je smola izložena u usnoj duplji. Da bi zubna nadoknada napravljena od akrilata zadovo-ljila kriterijume mora biti i tehnički dobro izrađena. To se odnosi na vezu veštačkog akrilatnog zuba i baze proteze. Akrilatni zubi pogodni su za hemijsku vezu s proteznom bazom. Baš ta veza danas predstavlja jedan od problema u terapiji moblinim protezama. Istraživanja su pokazala da je od svih zubnih nadoknada vraćenih na korekturu, pri-bližno 30% bilo zbog grešaka veze zuba i baze proteze6. Podaci dobijeni u tim istraživanjima podstakli su istraži-vače na nova istraživanja kako bi se otkrili uzroci pucanja veze zuba i baze proteze. Zbog toga su ispitivani faktori za koje se pretpostavlja da mogu prouzrokovati pucanje veze i faktori koji tu vezu mogu ojačati.

Danas se akrilatne mase najviše od svih materijala upotrebljavaju za izradu protetskih nadoknada i ortodont-skih aparata. Iako akrilatni zubi imaju sposobnost hemij-skog vezivanja s proteznom bazom, te veze predstavljaju problem zbog lomova. Taj problem prouzrokuje više čini-

nih modela iznosila 68,250 μm što je značajno manje nego kod neobrađenog uzorka čija je prosečna vrednost 103,75 μm. Izmerena čvrstoća na pritisak kod neobrađenog uzor-ka je 3200 N/mm2 a kod mehaničko-hemijski obrađenog iznad 6000 N/mm2.

Zaključak: Na osnovu dobijenih rezultata može se zaključiti da površine veštačkog zuba i polimerne baze koje dolaze u kontakt treba mehanički i hemijski obra-diti. Iako se u praksi kos mobilnih proteza veza ostavru-je najčešće mehaničkom retencijom akrilatni zub - pro-tezna baza, ovde se pojavljuje veća pukotina nego kod mehanički i hemijski obrađenih površina.Ključne reči: veza, veštački zub, polimerna baza, mobilna proteza

Results: The average value of the gap on mechanically and chemically treated samples was 68.250 μm, which was significantly lower than the gap on the untreated samples with the average value of 103.75 μm. The compressive strength was 3200 N/mm2 on untreated samples and above 6000 N/mm2 on the mechanically and chemically treated ones.

Conclusions: It can be concluded that surfaces which come into contact must be mechanically and chemically processed. Although in practice prostheses are made using mechanical tooth-base retention, larger gaps occur when compared to mechanically and chemically processed surfaces.Keywords: Bond, acrylic tooth, polymer base, removable denture

172 Stom Glas S, vol. 54, 2007.

breakage but there is still a common belief that the main responsibility lies on technicians. There can also be errors in factory production. Extensive research papers have been written on this topic6-9.

The aim of this study was to evaluate the influence of various treatments on the quality of the bond between the denture-base and the artificial tooth, the measurement of gaps between the acrylic tooth and denture base using an optical or electron microscope, and the evaluation of mechanical properties by compressive testing.

Materials and methods

Forty eight models were created, all representing the bond between an acrylic tooth and a denture-base and 12 models were made for compressive testing.

These acrylic models were allocated to four groups of 12 samples each for microscopic study, and four groups of three samples each for compressive testing. Sample A: untreated teeth fixed in an acrylic base; Sam-ple B: abrased teeth fixed in an acrylic base; Sample C: teeth moisture with monomer fixed in an acrylic base; Sample D: abrased teeth moistened with monomer fixed in an acrylic base.

Pro Base HOT and Gnathostar acrylic teeth by Ivo-clar were used for the production of experimental models. Acrylic resin was prepared and polymerized according to manufacturer’s instructions. A plastic cast was also made to ensure the uniformity of shape.

Models for microscopic analysis were prepared using an ISOMET slow-speed saw (Buehler, Lake Bluff, USA), abrasive diamond paste (3-9 μm), and special paper grinders. Alcohol and ultrasound were then used for cleaning. Prepared models were analyzed using a light inverse NIKON Epiphot 300 microscope (Nikon Instech Co., Ltd., Kawasaki, Japan). The selected models were also analyzed with an Jeol 840 A scanning micro-scope (JEOL, Peabody, Massachusetts, USA) for visuali-sation of the microstructure and the crystals orientation and structure.

The acrylic models were created in a dental labora-tory. A uniformly shaped cast with external dimensions 26.5×26.5×7 mm and internal dimensions 25.5×25.5×6 mm was made of Plexiglass, while models for pressure testing were made with external dimensions 30×12 and internal dimensions 20×9 mm. Mandibular right first molars Gnathostar (Ivoclar-Vivadent, Schaan, Liechten-stein) were used for testing. All models were created using the same procedure.

Sample A: The surface was untreated and cleaned with 70% ethyl alcohol (10 sec), degreased and put above boiling water (10 sec). The cleaned tooth was placed on an elastomer-base.

laca. Najčešće se okrivljuju zubni tehničari zbog nestruč-nosti ili nemara tokom rada. Moguće su i greške u fabrič-koj proizvodnji. Na tu temu sprovedena su brojna ispitiva-nja i istraživanja koja su dala različite rezultate6-9.

Cilj ovog istraživanja je da se ispita uticaj različitih tretmana pripreme fabričkih akrilatnih zuba na kvalitet veze s akrilatnom bazom proteze, da se izmeri veličina pukotine između akrilatnog zuba i protezne baze pomoću optičkog ili elektronskog mikroskopa, kao i da se ispita mehanička veza zuba i baze proteze merenjem čvrstoće na pritisak.

Materijal i metod

Za istraživanje je izrađeno 48 akrilatnih modela koji predstavljaju vezu akrilatnog zuba i protezne baze i 12 modela za merenje čvrstoće na pritisak. Akrilatni modeli podeljeni su u četiri grupe po 12 uzoraka za mikroskopira-nje, odnosno po tri za mehaničko merenje. Uzorak A činili su fabrički nepromenjeni zubi fiksirani u akrilatnu bazu, uzorak B - nahrapavljeni zubi fiksirani u akrilatnu bazu, uzorak C - zubi navlaženi monomerom fiksirani u akrilat-nu bazu i uzorak D - nahrapavljeni i monomerom navlaže-ni zubi fiksirani u akrilatnu bazu.

Za izradu akrilatne baze upotrebljen je toplo polime-rizirajući akrilat ProBase HOT (IVOCLAR, Schaan, Lie-chtenstein) i akrilatni zubi istog proizvođača. Akrilat je bio pripremljen i polimerizovan prema uputstvu proizvođaća, a za izradu modela upotrebljen uniformni kalup.

Postupak pripreme površine modela za istraživanje izve-den je sporo rotirajućom preciznom testerom ISOMET (BUE-HLER, Lake Bluff, USA), abrazivnim dijamantnim pastama granulacije 3-9 μm i posebnim brusnim papirnim šajbnama. Sledilo je čišćenje alkoholom i ultrazvukom. Tako pripremlje-ni uzorci pregledani su svetlosnim inverznim mikroskopom NIKON Epiphot 300 (Nikon Instech Co., Ltd., Kawasaki, Japan). Odabrani modeli su pregledani i scanning elektron-skim mikroskopom (SEM) - Jeol 840 A (JEOL, Peabody, Mas-sachusetts, USA), koji omogućava vizuelizaciju mikro-strukture i analizu orijentacije i strukture kristala.

Akrilatni modeli izrađeni su u zubotehničkoj labora-toriji. Za uniformni oblik modela poslužio je kalup naprav-ljen od pleksiglasa, spoljašnjih dimenzija 26.5×26.5×7 mm i unutrašnjih 25.5×25.5×6 mm sa zidovima od 90º, dok je za merenje čvrstoće kalup napravljen od metala spoljašnjih dimenzija 30×12 mm i unutrašnjih 20×9 mm. Za testiranje su upotrebljeni prvi desni donji molari Gna-thostar (Ivoclar-Vivadent, Schaan, Liechtenstein), naprav-ljeni u istoj seriji. Postupak pripreme modela bio je kod svih uzoraka isti.

Za uzorak A površina zuba je neobrađena i očišćena 70% etil alkoholom (10 sekundi) i sredstvom za razma-šćivanje. Sledilo je držanje zuba iznad pare ključale vode tokom 10 sekundi. Tako očišćen zub stavljan je na elasto-merno postolje.

Serbian Dental J, 2007, 54 173

Sample B: The surface towards the acrylic base was mechanically prepared with a 3M-8691C paper grinder (3M Dental, Pithiviers, France). This paper grinder was pulled over the contact surface twice.

Sample C: The surface was cleaned and moistened using some monomer. The model was then left to dry at room temperature. The procedure was repeated after drying.

Sample D: The surface towards the acrylic base was mechanically prepared, cleaned and moistened using some monomer (20 sec). The model was then left to dry at room temperature. The procedure was repeated after drying.

The models were inserted in a brazen mold filled with gypsum. The mold was closed and placed into boiling water after the gypsum had hardened in order for the wax to melt. Then the mold was opened, the elastomere base removed, and wax remains cleaned. The mixed acrylate mixture was left in a closed container at room tempera-ture (23 °C) for 8–10 min, and then applied in the mold. A mold was exposed to a pressure of 2 × 107 Pa (200 bar). The samples were thermally polymerized (at 65 - 70°C for the first 45 min, and at 100°C for the next 45 min). The mold was left for 30 minutes at room temperature and was completely cooled in cold water after that. The com-pletely cooled mold was opened, the models were extract-ed, cleaned and polished by applying the procedures used when polishing acrylic dentures (figure 1).

Za uzorak B površina zuba, koja dolazi u kontakt sa postoljem, mehanički je nahrapavljena brusnim diskom 3M oznake 8691C (3M Dental, Pithiviers, Francuska). Brusni disk dva puta je povučen po kontaktnoj površini.

Za uzorak C površina zuba je prethodno očišćena i navlažena je monomerom. Model je nakon toga ostavljen na sobnoj temperaturi 10 minuta. Nakon sušenja postupak je ponovljen.

Za uzorak D površina zuba, koja dolazi u kontakt sa postoljem, mehanički je nahrapavljena očišćena i navlaže-na monomerom u trajanju od 20 sekundi. Model je nakon toga ostavljen na sobnoj temperaturi 10 minuta. Nakon sušenja postupak je ponovljen.

Modeli su uloženi u kivetu napunjenu gipsom. Kiveta je zatvorena i nakon vezivanja gipsa, stavljena je u klju-čalu vodu da se vosak istopi. Kiveta je otvorena, izvađeni su elastomerno postolje i ostaci voska. Zamešana akrilatna smesa ostavljena je u zatvorenoj posudi na sobnoj tempera-turi (23 °C) 8–10 minuta, a potom je aplikovana u kivetu.

Tako napunjena kiveta izložena je pritisku od 2 × 107 Pa. Uzorci su toplo polimerizovani (prvih 45 minuta na 65-70°C, a sledećih 45 minuta na 100°C). Nakon polime-rizacije kiveta je ostavljena 30 minuta na vazduhu i zatim je do kraja ohlađena u vodi. Potpuno ohlađena kiveta je otvorena, modeli su izvađeni iz kivete, očišćeni i polira-ni postupcima koji se primjenjuju kod poliranja proteza (slika 1).

Slika 1: Akrilatni model nakon vađenja iz kivete, pripremljen za mikroskopiranjeFigure 1: Acrylic model after its removal from the mold, prepared for microscopy

Akrilatni modeli obrađeni su posebnim postupcima. Modeli su nakon polimerizacije bili izloženi ultrazvučnom čišćenju. Svaki od modela je presečen na dva jednaka dela pomoću precizne sporo rotirajuće testere ISOMET-low speed saw (BUEHLER, Lake Bluff, USA). Rez je naprav-ljen u mezio-distalnom smeru okluzalne površine. Brzina rotacije je bila 22 obrtaja u minuti (proces sečenja jednog modela trajao je 30 minuta), kako bi se sprečilo pregre-vanje akrilata (testera je dodatno hlađena vodom), što bi moglo prouzrokovati deformacije mikrostrukture, koja se nakon toga pripremala za mikroskopiranje i merenje. Sle-deća faza je bila brušenje modela na aparatu Metasinex. Brušenje je izvedeno posebnim vodootpornim papirnim šajbnama 40-10 μm, na 150 obrtaja u minuti uz doliva-nje vode kako bi se sprečilo pregrevanje akrilata. Sledila je faza poliranja na gumenoj rotirajućoj površini Polisher

The acrylic models were treated using special proce-dures. First, they were ultrasonically cleansed after polym-erization. Each of the models was halved into equal pieces using the ISOMET®.. The sectioning was performed in the mesio-distal direction of the occlusal surface. The speed was 22 rpm (the cutting process for each model lasted for 30 min), in order to prevent the overheating of the acrylic resin (the saw was additionally cooled with water from the lower side), that could cause deformation of the microstruc-ture, which was prepared for microscopy and measurements afterwards. The next phase was the grinding of the models on the Metasinex machine. The water-cooled grinding was per-formed using waterproof paper pads of 40–10 μm (Streuers) at 150 rpm. The models were, then, polished using a rubber rotating surface Polisher Ecomet III Grinder (BUEHLER, Lake Bluff, USA) with the addition of an abrasive diamond

174 Stom Glas S, vol. 54, 2007.

paste with 3-9 μm granulation. After polishing, the models were cleaned with alcohol and ultrasonically treated for high-brightness, and then dried with warm air.

Mechanical characteristics were tested using a Zwick/Roell ZO10 machine. Compressive testing was carried out to evaluate the effects of treating the surface on the boundary line between the tooth and the base. The compressive tests showed the influence of the surface preparation procedure and the resulting border surface on the point tooth – denture base regarding pressure of chewing forces, which dental prostheses pass on the jaw segment during their function in the oral cavity. The problem was specific in this case, since molar teeth were chosen for testing which are only subject-ed to direct pressure forces. Special models in molds were created for the testing. Special supports were created so that models could be fixed into the machine, and the supports were placed in such a way to simulate the occlusal rela-tionship between upper and lower teeth in the mouth (fig-ure 2). During compressive testing, the applied force grew to the point where deformation and cracking of the material occurred (either the tooth or the base). The starting force to which the models were exposed was 1N, and the loading speed was 10 mm/min. The force grew from the starting 1 N to a breaking point between 3200 N/mm2 and 6000 N/mm2.

Ecomet III Grinder (BUEHLER, Lake Bluff, USA) uz dodavanje abrazivne dijamantne paste granulacije 3-9 μm. Nakon poliranja, modeli su bili očišćeni alkoholom i pono-vo stavljeni u ultrazvuk. Tako očišćeni dobili su visoki sjaj i izloženi su sušenju toplim vazduhom.

Za određivanje mehaničkih karakteristika merena je čvrstoća na pritisak na aparatu Zwick/Roell ZO10. Merenjem čvrstoće je trebalo ustanoviti uticaj postup-ka pripreme površine i nastale granične površine izme-đu spoja zub - protezna baza na žvačne sile, koje zubne nadoknade prenose na vilični tegment tokom svoje funkcije. U ovom slučaju problem je bio specifičan zato što su za testiranje bili uzeti molarni zubi koji su podvr-gnuti samo direktnim pritisnim silama. Za testiranje su izrađeni posebni modeli u kalupima. Da bi modeli mogli da se fiksiraju u uređaj, napravljeni su posebni nosači koji su postavljeni tako da simuliraju okluzalne odnose gornjih i donjih zuba u ustima (slika 2). Kod merenja čvrstoće na pritisak primenjivana sila rasla je do tačke na kojoj je došlo do deformacija i pucanja materijala (zuba ili postolja). Početna sila kojoj su izloženi modeli iznosila je 1N, a brzina opterećenja 10mm/min. Sila je rasla od početnih 1 N do granice pucanja između 3200 N i 6000 N.

Slika 2: Akrilatni modeli fiksirani i pripremljeni za ispitivanje u kidalici Zwick/Roell Z010Figure 2: Acrylic models prepared and fixed for testing in the Zwick/Roell ZO10 machine

Rezultati

Dobijeni rezultati su prikazani u tabeli 1, slikama 3-7 i grafikonima 7 i 8.

Uzorci su imali poliranu površinu koja nije bila opti-malno glatka, već je imala reljefnu strukturu i različitu orijentaciju strukturnih kristala. Veličina pukotine merena je na optičkom mikroskopu.(slika 3). Rezultati merenja su svrstani u kategorije:

V-rub: debljina pukotine merena na rubu veze - merna tačka 1;

V-200: udaljenost merenja od ruba veze za 200μm - merna tačka 2;

Results

The results are showed in table 1, figures 3-7 and graphs 7 and 8.

The samples had polished surfaces, not optimally smooth, but with a rough structure and different orienta-tions of structural crystals. The size of each gap was meas-ured on an optical microscope, with the resulting complex microstructure in the material (Figure 3). The measure-ment results are classified according to the following cat-egories:

V-margin: gap diameter measured at the margin of a joint-measuring point 1;

Serbian Dental J, 2007, 54 175

V-200: the distance of measurement from the margin joint at 200 micrometers-measuring point 2;

V-curve: measurement at the twisted part of the gap (the location where a horizontal part exceeds to vertical) - measuring point 3;

V-mean (middle): measuring gap at the middle of the horizontal part-measuring point 4;

V-max: maximal measured gap diameter along the whole gap-measuring point 5;

V-min: minimal measured gap diameter along the whole gap-measuring point 6.

Twelve measurements and the average measured results were recorded at every measuring point (Table 1). Statistical analysis included the mean and standard deviation values, and the test for equal variances. Data were statistically proc-essed using the SPSS 8.0 software for Windows.

V-krivina: merenje na zakrivljenom delu pukotine (mesto gde horizontalni deo prelazi u vertikalni) - merna tačka 3;

V-sredina: merenje pukotine u sredini horizontale - merna tačka 4;

V-max: maksimalna izmerena debljina pukotine duž cele pukotine - merna tačka 5;

V-min: minimalna debljina pukotine duž cele pukoti-ne - merna tačka 6.

Dobijeni rezultati merenja uneti su u tabelu 1, pri čemu se na svakom mestu izvedeno po 12 merenja. Sta-tistička obrada izmerenih podataka je uključivala izraču-navanje srednje vrednosti i standardne devijacije i jedno-faktorska analiza varijanse. Podaci su statistički obrađeni pomoću programa SPSS 8.0 for Windows.

Tabela 1: Statistički prikaz mernih tačaka svih uzoraka

Table 1: Statistical analysis - summary

TYPE Measuring point Arithmeticalmiddle value x (μm)

Standard deviation SD

Test of the homogenus variances

F P

Test differencearithm.middle value

F P

Sample A 1 103,750 6,607

1,550 0,215 68,110 0,000

Sample B 1 86,083 4,757

Sample C 1 84,583 3,965

Sample D 1 68,250 8,148

Sample A 2 100,500 6,403

0,044 0,988 64,679 0,000

Sample B 2 88,667 7,303

Sample C 2 83,917 6,735

Sample D 2 62,958 6,690

Sample A 3 88,417 5,501

3,210 0,032 171,085 0,000

Sample B 3 69,833 5,357

Sample C 3 65,250 2,989

Sample D 3 48,250 3,166

Sample A 4 114,167 9,916

2,930 0,044 18,717 0,000

Sample B 4 99,333 4,677

Sample C 4 100,417 5,125

Sample D 4 81,083 11,139

Sample A 5 122,167 10,986

0,563 0,642 28,510 0,000

Sample B 5 122,417 8,691

Sample C 5 112,750 7,581

Sample D 5 89,583 12,139

Sample A 6 84,333 4,793

4,660 0,006 137,086 0,000

Sample B 6 66,000 7,519

Sample C 6 61,750 2,527

Sample D 6 43,833 3,298

176 Stom Glas S, vol. 54, 2007.

Results at measuring point 1 showed that the hypoth-esis on homogeneous variances, which was the basis of the analysis, was justified (α = P=0.215). The results for the universal F-test showed that there was a statistically signifi-cant difference (α = P=0.000) between the included types at the variable V-margin. Sample A had the highest average (x = 103.750 μm), samples B and C had similar mean values and sample D has the smallest average (x = 68.250 μm).

At measuring point 2, the results also showed that the hypothesis on homogeneous variances was justified (α = P=0.988). The results of the universal F-test showed a sta-tistically significant difference (α = P=0.000) between the included types at the variable V-margin. Sample A had the highest average, samples B and C had similar mean values and sample D had the smallest average (x = 62.958 μm).

Analysis at measuring point 3 showed that the hypothesis on homogeneous variances was not justified (α = P=0.032). It was used as an approximate method of variance analysis (Welch’s F-test). This test showed a sta-tistically significant difference between medians. Again, sample A has the highest median value, samples B and C had similar median values and sample D had the smallest average (x = 48.250 μm). At measuring point 3, the values were again reduced at sample D. The measuring point was at a curve, where all models showed lower width than at the flat parts.

At measuring point 4, it was confirmed that the hypothesis on homogeneous variances was not justified (α = P=0.044). The Welch’s F-test showed a statistically significant difference (α = P=0.000) between median val-ues. Sample A had the highest average (x = 114.167 μm),

Rezultati u mernoj tački 1 pokazuju da je pretpo-stavka o homogenosti varijansi na kojoj se temelji analiza varijanse opravdana (α = P=0,215). Rezultat opšteg F-te-sta ukazuje na to da postoji statistički značajna razlika (α = P=0,000) između uključenih tipova kod varijable V-rub. Kod uzorka A je najviši prosek (x = 103,750μm), kod uzo-raka B i C slične su srednje vrednosti, a kod uzorka D je najmanji prosek (x = 68,250 μm).

U mernoj tački 2 takođe važi da je pretpostavka o homogenosti varijansi na kojoj se temelji analiza varijanse opravdana (α = P=0,988). Rezultat opšteg F-testa ukazuje na to da postoji statistički značajna razlika (α = P=0,000) izme-đu uključenih tipova kod varijable V-rub. Kod uzorka A je najviši prosek, kod uzoraka B i C su slične srednje vrednosti, a kod uzorka D najmanji je prosek (x = 62,958 μm).

Analiza u mernoj tački 3 pokazuje da pretpostavka o homogenosti varijansi u ovom slučaju nije opravdana (α = P=0,032). Zato je korišćena aproksimativna metoda anali-ze varijanse (Welch-ov F-test). Taj test pokazuje da posto-ji statistički značajna razlika među aritmetičkim sredina-ma. Ponovno je kod uzorka A maksimalna vrednost, kod uzoraka B i C slične su srednje vrednosti, a kod uzorka D je najmanji prosek (x = 48,250 μm). Na mernoj tački 3 se vidi kako vrednosti ponovo padaju kod uzorka D. Mesto merenja nalazi se u krivini gde se kod svih modela javlja manja širina nego na ravnim delovima.

I u mernoj tački 4 je potvrđeno kako pretpostavka o homogenosti varijansi na kojoj se temelji analiza varijan-se nije opravdana (α = P=0,044), pa rezultat i Welch-ovog F-testa ukazuje na to da postoji statistički značajna razlika (α = P=0,000) između aritmetičkih sredina. Kod uzorka A

Slika 3: Shematski prikaz tačaka merenja pukotine akrilatnog modela na mikro-nivouFigure 3: Schematic survey of measuring points of acrylic model at micro-level

Serbian Dental J, 2007, 54 177

samples B and C had similar medians, and sample D had the smallest value (x = 81.083 μm). The measuring point 4 was placed in the middle of the horizontal part of the gap. Again, sample D had the smallest values compared with other samples, but there were differences between samples B and C. At sample C, the gap increased at some points because of different surfaces.

At measuring point 5, results show that the hypothe-sis on homogeneous variances was justified (α = P=0.642) and is shown in the result of the universal F-test. It con-firmed statistically significant differences between the four samples. The most similar were the mean values at samples A (x = 122.167μm) and B (x = 122.417μm). They were followed by an average at sample C (x = 112.750 μm), and finally at sample D (x = 89.583 μm).

At measuring point 6 the differences between the meadian values is based on Welch’s approximation method for variance analysis because the hypothesis on homogene-ous variances was unjustified (P = 0.006). There was a sta-tistically significant difference between the analyzed medi-ans (P = 0.000). Medians were the highest at sample A (x = 84.333μm), and lowest at sample D (x = 43.833μm).

Detailed research for all samples included inspection and analysis of the border area at the junction of a tooth and the denture base. It is important to emphasize that it was analyzed the lower gap surface with SEM, because of the higher magnification. Because of that, it was not possible to visualize upper and lower gap surface together (Figure 4).

je najveći prosek (x = 114,167μm), kod uzoraka B i C su slične srednje vrednosti, a kod uzorka D je najmanji pro-sek (x = 81,083 μm). Merna tačka 4 nalazila se na sredini horizontalnog dela pukotine. I kod tog merenja je uzorak D imao najmanje vrednosti u odnosu na ostale uzorke, ali su uočljive razlike kod uzoraka B i C. Naime, kod uzorka C došlo je do povećanja pukotine na pojedinim mestima zbog nejednake površine.

U mernoj tački 5 je pretpostavka o homogenosti vari-jansi na kojoj se temelji analiza varijanse opravdana (α = P=0,642). Upravo taj test potvrđuje postojanje statistički značajne razlike između četiri uzorka. Najsličnije su ari-tmetičke sredine kod uzoraka A (x = 122,167μm) i B (x = 122,417μm). Sledi prosek kod uzorka C (x = 112,750μm) i na kraju prosek kod uzorka D (x = 89,583μm).

U mernoj tački 6 razlika između aritmetičkih sredi-na rezultira na Welch-ovoj aproksimativnoj metodi ana-lize varijansi, jer pretpostavka o homogenosti varijansi nije opravdana (P = 0,006). Među analiziranim prosecima postoji statistički značajna razlika (P = 0,000). Najveća aritmetička sredina je kod uzorka A (x = 84,333μm), a naj-manja kod uzorka D (x = 43,833μm).

Detaljna istraživanja za sve uzorke uključivala su pregled i analizu graničnog područja na spoju zuba sa pro-teznom bazom. Važno je naglasiti, da je sa SEM-om bila ispitivana donja granična površina pukotine zbog većeg uveličanja. Zbog toga nije bilo moguće zajedno obuhvatiti gornje i donje granične površine pukotine (Slika 4).

Slika 4. S Shematski prikaz gledanja na elektronskom mikroskopu (donja granična površina pukotine)Figure 4. Schematic survey of SEM photographs (lower margin surface of the fissure)

Na slici 5 prikazan je EM (elektronski-mikroskop-ski) snimak presečenog uzorka A. Analiza je pokazala, da je granična površina dosta ravno oblikovana s ocenjenom debljinom oko 1μm, a da širina nije konstantna. Zbog teš-koća tokom pripreme uzoraka (brušenje, poliranje, nagri-zanje) nije bilo moguće ukloniti ogrebotine koje su vid-ljive kao poprečne i dijagonalne linije. S druge strane na ispitanom uzorku su uočljive pore koje mogu biti posledi-ca nepravilnog tehnološkog postupka.

Figure 5 shows an EM (electron-microscopic) picture of sample A. This analysis shows that the border surface was quite flat, with the thickness of about 1μm, and a non-constant width. Scratches, which can be seen as transver-sal and diagonal lines, could not be removed because of difficulties which arose during sample preparation (grind-ing, polishing, and etching). On the other hand, there are visible pores on the examined sample, which may be due to irregular technological procedure.

178 Stom Glas S, vol. 54, 2007.

The border surface acquired during roughening was completely different and is visible at the cross- section of sample B (Figure 6). The border surface was not flat; it was vertically twisted by 20 μm. At the twisted locations material porosities are visible, of about 5 μm. The border surface was corrugated because of the tooth higher level of surface roughness, which could not be removed during further processing. The border surface had further variable thickness. Also, it is assumed that the scratches on this sample were due to difficult technological process during sample preparation.

Potpuno drugačijeg oblika je granična površina dobi-jena postupkom hrapavljenja koja je vidljiva na popreč-nom preseku uzorka B (slika 6). Granična površina nije ravna, nego je uzduž zakrivljena za 20 μm. Na mestima gde se susreću zakrivljenosti vidljive su poroznosti mate-rijala od 5 μm. To je posledica postupka hrapavljenja gde je nastao veći stepen hrapavosti površine zuba koja nije mogla biti odstranjena tokom dalje obrade, pa je zato gra-nična površina valovita. Granična površina je i dalje pro-menjive debljine. I na tom uzorku su vidljive ogrebotine koje su najverovatnije posledica teškoća koje se javljaju tokom tehnološkog postupka pripreme uzorka.

Slika 5: EM snimak uzorka A (neobrađena površina zuba)Figure 5: EM picture of the sample A (untreated tooth surface)

Slika 6: EM snimak uzorka B (mehanički obrađena površina zuba)Figure 6: EM picture of the sample B (mechanically treated tooth surface)

Granična površina na slici 7 uzorka C jako je uska u poređenju s uzorcima A i B, pa zato nije uočljiva ni poro-znost materijala. Ovaj uzorak ima najmanji stepen zakrivlje-nosti. Kod uzorka C zubi su bili navlaženi monomerom pa je verovatno došlo do hemijskog nagrizanja u jako uskom sloju zuba, a posledica toga je uklanjanje makro-abrazija.

The border surface in Figure 7 of sample C was very narrow compared with samples A and B, so there was no visible material porosity. This sample had the smallest twisted level. On sample C, the teeth were wetted with some monomer, and there was probably chemical etch-ing in the very narrow tooth layer, which resulted in the removal of macro-abrasions.

Serbian Dental J, 2007, 54 179

On sample D, where the tooth was previously rough-ened and wetted with monomer, a corrugated border sur-face without porosities is visible (Figure 8). There was no porosity because of additional etching of the surface with monomer causing high level of removal of so-called microabrasion. It was impossible to remove any macroa-brasion formed during the roughening process, because of the relatively short interval of wetting using monomer (10 sec). The border surface had uniform thickness.

Na uzorku D, gde je zub bio prethodno nahrapav-ljen i navlažen monomerom, uočljiva je valovita granična površina bez poroznosti (slika 8). Do poroznosti nije došlo zbog naknadnog postupka nagrizanja površine monome-rom gde je bio visok stepen uklanjanja tzv. mikroabrazija. Zbog relativno kratkog vremena vlaženja monomerom (10 sekundi) nije bilo moguće odstraniti makroabrazije koje su nastale postupkom hrapavljenja. Granična površina je jed-nake debljine.

Slika 7: EM snimak uzorka C (monomerom navlažena površina zuba)Figure 7: EM picture of the sample C (tooth surface moistened using monomer)

Slika 8: EM snimak uzorka D (mehanički obrađena i monomerom navlažena površina zuba)Figure 8: EM picture of the sample D (tooth surface mechanically treated and moistened using monomer)

Čvrstoća na pritisak uzorka A ocenjena je na oko 3200 N. Oblik krive ima karakteristike krtog materijala. Najveće relativne deformacije javljale su se na površini zubne nadoknade pa je stoga do loma došlo na tom mestu (slika 9).

Čvrstoća na pritisak uzorka B ocenjena je na oko 6000 N. Kriva je valovitog oblika pa se može zaključiti da su vidljivi delovi gde je došlo do tečenja materijala. Posle-dica toga je, bez obzira na sve, krti lom koji je dobro vid-ljiv na lomnoj površini zuba.

The compressive strength of sample A was estimat-ed at about 3200 N/mm2. The shape of the curve has the characteristics of a fragile material. The largest relative deformations were at the surface of the denture, resulting in fractures (Figure 9).

The compressive strength of sample B was estimated at about 6000 N/mm2. The curve has a wavy shape, and it can be concluded that the parts which are visible are those where the material flowed. The consequence was a fragile fracture visible at the surface of the fractured tooth.

180 Stom Glas S, vol. 54, 2007.

The compressive strength of sample C was estimated at about 5800 N/mm2 (figure 10). The shape of the curve has the characteristics of a fragile material without mate-rial flowing. The largest relative deformations were at the surface of the denture, resulted in fracture. Similar shape has curve of sample D, the compressive strength was esti-mated over 6000 N.

Discussion

It can be concluded, based on the acquired results, that the thickness and width of the gap depend on the type and mechanical pre-treatment of the surface of the tooth11,13,14,16,25. In sample A measuring point 1, the aver-age value was 103.75 μm, and at sample D only 68.250 μm. This means that a gap should be narrower with good mechanical pre-treatment, in other words, mechanical bonding will be better11,13,14,16. Based on the results of measurements at point 2, the width of a gap depends on any mechanical pre-treatment. This has an influence on

Čvrstoća na pritisak uzorka C ocenjena je na oko 5800 N (slika 10). Oblik krive ima karakteristike krtog materijla bez tečenja materijla. Najveće relativ-ne deformacije javljale su se na površini nadoknade pa je stoga lom nastao na tom mestu. Sličan oblik ima i kriva kod uzorka D, čvrstoća na pritisak ocenjena je preko 6000 N.

Diskusija

Na osnovu dobijenih rezultata može se zaključiti da su debljina i širina pukotine zavisne od vrste meha-ničke pripreme površine zuba11,13,14,16,25. Kod uzorka A na mernoj tački 1 prosečna vrednost iznosi 103,75μm, a kod uzorka D samo 68,250 μm. To znači da se kod dobre mehaničke pripreme može očekivati da pukotina bude uža, odnosno da se na taj način postiže bolja mehanič-ka veza11,13,14,16. Na osnovu rezultata merenja na tački 2 može se zaključiti da je širina pukotine zavisna od mehaničke pripreme, što utiče na otpornost na pritisak

Slika 9: Grafički prikaz dijagrama σ-ε dobijenog pri merenju čvrstoće na pritisak za uzorak A Figure 9: Graphic survey of the diagram σ-ε acquired from pressure testing for sample A

Slika 10. Grafički prikaz dijagrama σ-ε dobijenog pri merenju čvrstoće na pritisak za uzorak CFigure 10: Graphic survey of the diagram σ-ε acquired from pressure testing for sample C

Serbian Dental J, 2007, 54 181

the pressure characteristics of the denture. At point 2 the width of a gap at sample D was only 63 % of the value for sample A. With mechanical and chemical pre-treatment of the surfaces the width of a gap decreases, which has been confirmed by previous studies11,13,25. In comparison with other measuring points, gap-width results at measur-ing point 5 were considerably higher. Visible defects were present in this area (material porosity). Compressive test-ing confirmed that the compressive strength at sample A was twice as low as at sample D.

At measuring point 6, the gap width was small. When comparing the results of other measuring points, it can be noted that gap widths on all four samples were the lowest due to the highest pressures during model preparation. It was, therefore, possible to bring the acrylic tooth closest to the denture base.

Regarding the type of mechanical and chemical pre-treatment, it was specific because the gap in sample D was 50% smaller than in sample A. Research was based on the use of optical and electron microscopy which gave results about the gap size between the acrylic teeth and the den-ture base in samples prepared in four ways. The prepara-tion procedure for those samples (models) with classical warm polymerization corresponded fully to the procedure for denture manufacturing in a dental laboratory. Measure-ments confirmed, as it was expected, that gaps on untreat-ed models would be the greatest (p=0.642) compared with treated models. In almost all comparisons, Vmax was the highest for untreated models, and Vmin was the lowest for mechanically and chemically treated models11,13,25.

The comparison between mechanically and chemical-ly treated models and untreated ones showed that parame-ters were considerably lower for untreated models17,18,19,25. The smallest gap was measured for mechanically and chemically treated models, where parameters V-margin, V-200 and V-max were statistically significant, in com-parison with the other three samples. The remaining three parameters of gap thickness (V-curve, V-middle and V-min) did not show any statistically significant dif-ference. Different statistical methods were performed to confirm measurement results. They showed differences between samples A, B, C and D indicating it is necessary to treat the surface in different ways19,20,21,25.

In the present study different measurement devices were used compared with previous studies. Onlya few articles showed other experimental techniques, mechani-cal loading (model fracture), and only indirect comparison was possible.

Can and Kansu13 evaluated the bond strength between an acrylic tooth and denture base with applied mechanical retentions. The retention grooves were cut on the cervical part of the tooth. It was followed by an evaluation of the influence of the remaining material during processing on the bond between the acrylic tooth and the denture base. The results indicated that if the processing procedure was correct, a strong bond would be formed. But, if there is was remain-

zubne nadoknade. U tački 2 širina pukotine kod uzorka D doseže samo 63 % vrednosti uzorka A. Širina puko-tine smanjuje se sa stepenom mehaničko-hemijske pri-preme površina, a ovo je potvrđeno i rezultatima drugih istraživača11,13,25. U poređenju sa ostalim mernim tačka-ma, dobijeni rezultati širine pukotine u mernoj tački 5, su veći. U ovom području prisutni su defekti (poroznost materijala). Prisustvo defekata je potvrdilo i merenje čvr-stoće na pritisak pri čemu je čvrstoća kod uzorka A dva puta manja od čvrstoće uzorka D.

Kod merne tačke 6 širina pukotine je mala. Upoređi-vanje rezultata svih mernih tačaka pokazuje da je na toj tački, kod sva četiri uzorka, širina pukotine najmanja. To znači da su za vreme izrade modela u tom području posti-gnuti najveći pritisci. Zbog toga je bilo moguće akrilatni zub najviše približiti proteznoj bazi.

Kad se analizira tip mehaničko-hemijske pripreme, može se zaključiti da je i on specifičan jer je pukotina kod uzorka D za oko 50% manja od one kod uzorka A. Istraži-vanja u ovom radu temelje se na primeni svetlosne i elek-tronske mikroskopije koja daje podatke o veličini pukotine između akrilatnog zuba i protezne baze pripremljene na četiri načina. Postupak izrade modela klasičnom toplom polimerizacijom u potpunosti je odgovarao postupku izra-de proteza u zubotehničkoj laboratoriji. Očekivalo se, što su pokazala i merenja, da će pukotina kod neobrađenih mode-la, biti statistički značajno najveća (p=0,642) u odnosu na one kod obrađenih modela. Gotovo u svim poređenjima Vmax je najveći kod neobrađenih modela, dok je Vmin naj-manji kod mehanički i hemijski obrađenih modela11,13,25.

Kada se pogledaju mehanički i hemijski obrađe-ni modeli, vidi se da su mereni parametri znatno niži od onih kod neobrađenih modela17,18,19,25. Najmanja pukotina izmerena je kod mehanički i hemijski obrađenih modela kada su parametri V-rub, V-200 i V-max statistički zna-čajni u odnosu na ostala tri uzorka. Preostala poređenja tri različita parametara debljine pukotine (V-krivina, V-sre-dina i V-min) nisu pokazala statistički značajnu razliku. Zbog provere rezultata dobijenih merenjem sprovedene su različite statističke metode koje su pokazale razliku između uzoraka A, B, C i D. Zbog toga je zaključeno da je površinu potrebno obraditi na različite načine19,20,21,25.

Pregledom literature nije pronađen identičan ekspe-rimentalni postupak u kome su mereni parametri iz ovog rada i u kome je bio upotrebljen isti merni uređaj. U samo nekoliko radova su primenjene druge tehnike eksperimen-ta, i to mehanička opterećenja (kidanje modela), tako da su moguća jedino indirektna poređenja.

Can i Kansu13 su evaluirali jačinu veze izme-đu akrilatnog zuba i baze proteze pomoću mehaničke retencije. Na cervikalnom delu napravljene su retencije u obliku jamica. Upoređivan je uticaj preostalog mate-rijala pri izradi na vezu između akrilatnog zuba i baze, i dobijeni su sledeći rezultati: ako su u pripremnim postupcima poštovani propisi, ostvarena veza ima čvr-stoću. Međutim, ukoliko se pojavi ostatak voska na cer-

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ing wax at the cervical part of the tooth and if the polymeri-zation was not correct, the bond strength would decrease.

Cunningham and Benington14 found that acrylic tooth surface modification strongly influences bond qual-ity. They used four denture base resins. The models were tested on a universal testing device (model S2000, Lloyds Instruments, Hants., UK) and loaded. Acrylic resin was prepared using the processing guidelines at 23°C. After 9 min, the resin was placed in the mold and left for 12 min. The models were filled immediately after acrylic resin mixing and again 10 min later. The results showed that the acrylic resin filled immediately after mixing formed a less intimate bond with the acrylic tooth surface.18 This study showed the importance of model preparation on denture bond quality. The authors showed the significance of the remaining monomer and mechanical processing of the model surface (acrylic tooth) on bond quality. They concluded that mechanical retentions smaller than 0.5 mm do not influence retention, but retention grooves with widths and depths of 2 mm have a significant influence. When there are also axial retentions with lengths of 5 mm (+/- 0.5 mm), the bond strength increases. Based on these results it can be said that mechanical retention and quanti-ty of residual monomer are the factors which significantly improve denture quality.19

Stronger bond in mechanically processed models could be explained with stronger embedding of the acrylic resin into the retention points. There is better surface hard-ness, and the porosity is similar. According to the present study, the margin between two materials is statistically very different. Some authors claim that retentions are not important for the retention between tooth and denture base20, while others suggest the opposite.21,22,23,25

According to some authors13, the reason for breakage, i.e. low quality of the tooth-base bond, is the residual wax which remains at tooth surface before filling with acrylic resin. Therefore, it is very important to remove all residual wax and to degrease model surfaces.

Some studies have shown a higher breaking-limit of the chemically and mechanically treated models during chewing because of strong chewing forces.24,25 This is a consequence of the intimate contact between two acrylic materials with similar compositions. This research con-firmed that with the wider gap, the bond between the tooth and the base is lower, and the breaking limit decreases.

For sample A, where average width was around 100 μm, pressure hardness was 3200 N/mm2, and for sample D with the width of 70 μm, pressure hardness was 6000 N/mm2. Decreasing the gap for 30% could increase pres-sure hardness twice.

Conclusion

This article shows that gap width depends on the type of mechanical and chemical pre-treatment. The gap in untreated samples were about 100 μm, and the pretreated

vikalnom delu i ako je polimerizacija nepravilno izve-dena, jaćina veze se smanjuje.

Cunningham i Benington14 su ustanovili da način pri-preme površine akrilatnog zuba značajno utiče na kvalitet veze. Za obradu su koristili četiri različite akrilatne mase za izradu proteza. Modeli su bili testirani u univerzalnom apa-ratu za testiranje (model S2000, Lloyds Instruments, Hants., UK) i izloženi opterećenju. Akrilatna masa je mešana prema uputstvima na temperaturi od 23 °C. Nakon devet minuta je bila spremna za punjenje kivete i ostala je u tom stanju 12 minuta. Modeli su punjeni odmah nakon pripreme mase i 10 minuta nakon mešanja. Rezultati su pokazali da masa koja je punjena odmah nakon mešanja, stvara manje intimnu vezu s površinom akrilatnog zuba 18. Ovim radom je doka-zan uticaj pripreme modela na kvalitet veze u protezi. Auto-ri su utvrdili značaj uticaja preostalog monomera, odnosno njegove količine, na vezu i obradu površine modela, u ovom slučaju akrilatnog zuba. Zaključili su da mehaničke retenci-je koje su manje od 0,5 mm nemaju veći uticaj na retenciju, dok preparacije površine širine i dubine 2 mm imaju. Kad im se dodaju i retencije duž aksijalne dužine od 5 mm (+/- 0.5 mm), jačina veze raste. Zbog toga bi se moglo reći da su mehanička retencija i količina preostalog monomera činioci koji značajno utiču na kvalitet zubne nadoknade19.

Jača veza kod obrađenih modela bi se mogla objasni-ti time što se akrilat jače utiskuje u retencijska mesta nego kod neobrađene površine. Tako se dobija poboljšana čvr-stoća, dok je poroznost otprilike ista. Tako se, prema našem istraživanju, granica između dva materijala statistički znat-no razlikuje. Pojedini autori navode da napravljena retencija nema posebnog uticaja na retenciju zuba za bazu proteze20, dok nalazi drugih autora govore suprotno21,22,23,25.

Prema mišljenju nekih autora13, uzrok mnogih lomo-va, odnosno loše veze zuba s bazom, je vosak koji zaostaje nakon kivetiranja i koji nije uklonjen s površine zuba pre ubacivanja akrilatnog testa. Zbog toga je važno eliminisati sve ostatke voska i to mesto razmastiti.

Neke studije su pokazale da je prag loma zbog veli-kih sila koje nastaju tokom žvakanja viši kod hemijski i mehanički obrađenih modela24,25. To je posledica prilju-bljenosti dve površine akrilatnih masa koje su po sastavu jako slične. Povećanjem pukotine veza zub-protezna baza slabi, čime se snižava prag loma.

Sa povećanjem pukotine veza zub-protezna baza slabi, što su potvrdila i ova istraživanja. Kod uzorka A, gdje je prosečna debljina bila oko 100 μm, čvrstoća na pritisak je iznosila 3200 N/mm2, dok je kod uzorka D ta debljina iznosila oko 70 μm, a čvrstoća na pritisak 6000 N/mm2. Smanjenjem debljine pukotine za 30% dva puta se povećava čvrstoća na pritisak veze zub-protezna baza.

Zaključak

Dobijeni rezultati su pokazali da širina pukotine zavi-si od tipa mehaničko-hemijske pripreme. Kod neobrađenih uzoraka širina pukotine je iznosila oko 100 μm, dok je kod

Serbian Dental J, 2007, 54 183

samples had gaps of about 70 μm wide. There was no sta-tistically significant difference between roughened models and monomer-wetted ones, but there was a statistically significant difference between roughened and monomer-wetted models, and untreated models. Models prepared by roughening and wetting with monomer had the most homogeneous structure and the smallest gap.

The thickness of a gap has an influence on the mechan-ical charactreristics of a sample. The pressure hardness of the untreated sample was 3200 N/mm2 while the mechani-cally and chemically treated samples showed pressure hard-ness of 6000 N/mm2. Microscopic examination of border surfaces showed that untreated samples often have flaws, such as porosity, which have a strong influence on the qual-ity of the bond between an artificial tooth and denture base.

obrađenih iznosila oko 70 μm. Nisu uočene statistički zna-čajne razlike između nahrapavljenih modela i onih navla-ženih monomerom, ali postoji statistički značajna razlika između nahrapavljenih i monomerom navlaženih modela i onih neobrađenih. Modeli pripremljeni hrapavljenjem i vlaženjem monomerom su najhomogenije strukture i na njima je bila najmanja pukotina.

Debljina pukotine utiče na mehanička svojstva uzor-ka. Izmerena čvrstoća na pritisak kod neobrađenog uzorka je iznosila 3200 N/mm2, a kod mehaničko-hemijski obra-đenog iznad 6000 N/mm2. Mikroskopska istraživanja gra-ničnih površina su pokazala da se kod neobrađenih uzora-ka često javljaju greške u vidu poroznosti i nesklada gra-ničnih površina, koje mogu bitno uticati na kvalitet veze veštačkog zuba i baze proteze.

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Autor odgovoran za korespondencijuDr.sci. Rebeka Rudolf, univ.dipl.ing. Mašinski fakultet Smetanova ulica 17, 2000 Maribor, Slovenija tel.: +386 2 220 7865 e-mail: Rebeka.Rudolf@uni-mb.si

Address for correspondenceDr.sci. Rebeka Rudolf, univ.dipl.ing. Faculty of mechanical engineering Smetanova ulica 17, 2000 Maribor, Slovenia tel.: +386 2 220 7865 e-mail: Rebeka.Rudolf@uni-mb.si