Journal of Dental Medicine

Background and Aim: Because of stable aesthetic and minimum destructive technique, Porcelain laminate veneer has an important role in aesthetic dentistry. But main reason of failure in this treatment is restoration fracture. Therefore tooth preparation have an important role in fracture resistance of porcelain laminate veneer. The aim of this in vitro study was to evaluate the fracture resistance of porcelain laminate veneer dependent on tooth preparation after exposure to dynamic loading.

Materials and Methods: In this study, 30 caries free mandibular incisors were devided into 3 groups. First group (Control group) remained unprepared. In second group (Window preparation) facial surface was prepared with 0.3, 0.5, 0.7 mm in cervical, middle and incisal, respectively. In third group (Incisal lap preparation) the preparation was like second group and included 2 mm of incisal edge. 20 feldespatic ceramic veneer were bonded adhesively with dual-cure luting cement (Rely X). All specimens were subjected to cyclic mechanical loading (720000 cycles, 1.3Hz, 30N) and thermal cycling (5-55 C, dwell time 60seconds, 500 cycles). The specimens were exposed to Universal testing machine until failure occurred with a constant crosshead speed of 1mm/min.

Results: Five specimens of first group, one specimen of second group and two specimens of third group fractured during cyclic loading. The mean failure loads(MPa) after exposure to continues load were as follows: First group: 168/96 (561.01-1115.08), second group: 394.10 (248.92- 641.33) and third group: 273.47 (135.45 - 479.80). Data analysis was performed by ANOVA, LSD and chi Square test.

Conclusion: Significant difference between 3 groups were found. Fracture resistance of control group was significantly higher than other groups and window group preparation was significantly higher than incisal lap group. The samples were under the cyclic loads before they put under the continuous pressures of universal testing machine. It was clear that incisal lap preparation is more resistance against fatigue failure compared to window preparation.

  Background and Aims: Tooth crowning often leads to changes in periodontal index through changes in emergence profile zone. The purpose of this study was to compare the effect of metal-ceramic with that of
All-Ceramic restorations on the plaque a accumulation.

  Materials and Methods: In this clinical trial, we used 102 teeth covered with metal-ceramic and all-ceramic restorations. Before and after crowning, plaque index (PI) and gingival indexes (MGl) were measured. Data were analyzed using covariance (ANCOVA) test.

  Results: Measured PI and MGI (Mean±SD) in PFM Group prior to crowning were (1.96±0.38) and (1.45±0.48), respectively. In metal-ceramic restorations group, six months after crowning, measured PI and MGI (Mean±SD) were (1.22±0.49) and (1.82±0.61), respectively. Measured PI and MGI (Mean±SD) in All-Ceramic Group prior to crowning were (1.22±0.52) and (1.25±0.29), respectively. In All-Ceramic, six months after crowning, measured PI and MGI (Mean±SD) were (0.88±0.51) and (1.43±0.50), respectively. ANOVA test showed statistical significance difference between metal-ceramic and All-Ceramic Groups in Indexes (P<0.001).

  Conclusion: Metal-ceramic and All-Ceramic crowns were associated with inflammatory changes in gingival. Metal-ceramic restorations were associated with higher inflammatory indexes compared with All-Ceramic crowns.