Shrinkage vectors in flowable bulk-fill and conventional composites: bulk versus incremental application

OBJECTIVES Sufficient depth of cure allows bulk-fill composites to be placed with a 4-mm thickness. This study investigated bulk versus incremental application methods by visualizing shrinkage vectors in flowable bulk-fill and conventional composites. MATERIALS AND METHODS Cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared in 24 teeth and then etched and bonded with OptiBond FL (Kerr, Italy). The composites were mixed with 2 wt% radiolucent glass beads. In one group, smart dentin replacement (SDR, Dentsply) was applied in bulk "SDR-bulk" (n = 8). In two groups, SDR and Tetric EvoFlow (Ivoclar Vivadent) were applied in two 2-mm-thick increments: "SDR-incrementa" and "EvoFlow-incremental". Each material application was scanned with a micro-CT before and after light-curing (40 s, 1100 mW/cm2), and the shrinkage vectors were computed via image segmentation. Thereafter, linear polymerization shrinkage, shrinkage stress and gelation time were measured (n = 10). RESULTS The greatest shrinkage vectors were found in "SDR-bulk" and "SDR-increment2," and the smallest were found in "SDR-increment1-covered" and "EvoFlow-increment1-covered." Shrinkage away from and toward the cavity floor was greatest in “SDR-bulk“ and “EvoFlow-increment2", respectively. The mean values of the shrinkage vectors were significantly different between groups (one-way ANOVA, Tamhane's T2 test, p < 0.05). The linear polymerization shrinkage and shrinkage stress were greatest in Tetric EvoFlow, and the gelation time was greatest in "SDR-bulk". CONCLUSIONS The bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor. CLINICAL RELEVANCE Incremental application remains the gold standard of composite insertion

Reliability of Bonded MOD Restorations in Maxillary Premolars: Microleakage and Cusp Fracture Resistance

Svrha: Ovo in vitro istraživanje provedeno je na maksilarnim pretkutnjacima kako bi se procijenili mikropropusnost i otpornost kvržica na frakturu. Materijal i metode: Uzorci su se sastojali od adhezivno vezanih direktnih ispuna i keramičkih inlaya (ranije pripremljenih umetaka), a ispitani su nakon umjetno simuliranog starenja s pomoću termičkog i okluzalnog cikličkog opterećenja. Za to je uporabljeno 66 tek izvađenih maksilarnih pretkutnjaka, a bilo ih je po šest u svakoj skupini. Zatim su izrađeni standardizirani MOD - kaviteti i podijeljeni u dvije glavne skupine, ovisno o smještaju gingivne stijenke i to jedan milimetar iznad (A1) ili jedan milimetar (A2) ispod cementno-caklinskog spoja (CCS-a). Nakon toga uzorci su podijeljeni u dvije podskupine: Z 250 kompozit za direktno postavljanje i IPS Empress – staklokeramički ispun zatvoren kompozitnim cementom Variolink II. Skupina intaktnih zuba te dvije skupine s prepariranim kavitetima A1 i A2 služile su kao kontrola. Restaurirani zubi uloženi su zatim u blokove od akrilatne smole i stavljeni u stroj za cikličko-termičko i mehaničko opterećenje. Mikropropusnost je procijenjena metodom ocjenjivanja prodora boje pod Zeissovim stereomikroskopom. Rezultati: Otpornost kvržica na frakturu ispitana je vertikalnim opterećenjem do pucanja. Srednje vrijednosti testa frakturnog opterećenja i mikropropusnosti analizirane su statistički. Proučavani ispuni nisu pokazali veću razliku u adaptaciji ispuna na caklinskim rubovima. Keramički ispuni bolje su brtvili te snažnije ojačali strukturu zuba nego kompozitni, posebice na necaklinskim rubovima. Priprema kaviteta dosta je oslabila strukturu. Zaključak: Ispuni su samo djelomice nadoknadili učinak slabljenja zbog njegove preparacije. Poboljšanje adhezivnih ispuna, tj. adaptacija i pojačanje strukture zuba, stalan su izazov u restaurativnoj dentalnoj medicini.Purpose: This in vitro investigation was performed to assess microleakage and cusp fracture resistance of maxillary premolars specimens involving composite resin direct restorations and ceramic inlay restorations. Material and methods: Specimens were tested after artificial aging provoked by thermal and occlusal load cycling. For that purpose, 66 extracted maxillary premolars were used with six premolars in each study group. Standardized MOD cavities were prepared and classified into two main groups according to gingival-margins location either 1mm above (A1) or 1 mm below (A2) the CEJ. Specimens were subdivided into two subgroups: Z250 composite resin direct restorations and IPS Empress glass ceramic restorations cemented with Variolink II resincement. Group of intact teeth specimens and two groups of A1 and A2 type prepared but not restored teeth served as control groups. Restored teeth were mounted in acrylic-resin blocks before loading and thermocycling. Microleakage was assessed by examining dye penetration scores under Zeiss-stereomicroscope. Cusp fracture resistance was performed using vertical static loading until failure. The fracture-load test mean values and microleakage results were statistically analyzed. Results: Investigated restorations showed insignificant difference in adaptation at enamel margins. Ceramic restorations showed better sealability and tooth structure reinforcing effects than composite restorations, especially at non-enamel margins. Conclusions: Cavity preparation produced significant weakening effect. Restorations just partly compensated weakening effect of cavity preparation. Upgrading the performance of adhesive restorations in terms of adaptation and tooth structure reinforcement poses a continuing challenge to restorative dentistry