The effect of fabrication methods (conventional, computer-aided design/computer-aided manufacturing milling, three-dimensional printing) and material type on the fracture strength of provisional restorations.

Background: Fracture is the most common reason for the failure of provisional restorations. This study aimed to assess the effects of the fabrication method (conventional, computer-aided design/computer-aided manufacturing [CAD/CAM] milling, three-dimensional [3D] printing) and material type on the fracture strength of provisional restorations. Materials and Methods: In this in vitro study, 60 provisional restorations were made through the conventional (Tempron and Master Dent), CAD/CAM milling (Ceramill and breCAM.HIPC) and 3D Printing (3D Max Temp) methods based on a scanned master model. The provisional restorations were designed by the CAD unit and fabricated with milling or 3D printing. Then, an index was made based on the CAD/CAM milling specimen and used for fabricating manual provisional restorations. To assess the fracture resistance, a standard force was applied by a universal testing machine until the fracture occurred. One-way ANOVA and Tukey's test were used to compare the groups (α = 0.05). Results: The mean fracture strength was significantly different among the five groups (P < 0.001), being significantly higher in the breCAM.HIPC group (P < 0.001), followed by the Tempron group (P < 0.05). However, the three other groups were not significantly different (P < 0.05). Conclusion: Despite the statistical superiority of some bis-acrylics over methacrylate resins, the results are material specific rather than category specific. Besides, the material type and properties might be more determined than the manufacturing method.

Marginal fit of endocrowns fabricated by three-dimensional printing and the conventional method: An in vitro study.

Background: Marginal fit is a key factor in success of prosthetic restorations. This study aimed to assess and compare the marginal fit of endocrowns fabricated by three-dimensional (3D) printing and the conventional method. Materials and Methods: This in vitro, experimental study evaluated 20 endocrowns, of which 10 were fabricated by 3D printing and 10 were fabricated by the conventional wax-up technique. The marginal gap was measured at 8 points under a stereomicroscope. The results were analyzed using the Shapiro-Wilk test, paired t-test, independent t-test, and one-way analysis of variance (α = 0.05). Results: The mean marginal gap was maximum at the distal point, and minimum at the buccal point for the conventionally fabricated endocrowns with an overall mean marginal gap of 99.67 ± 4.59 µm. The mean marginal gap was maximum at the mesiobuccal and minimum at the buccal point before pressing (overall mean of 103.92 ± 2.19 µm) before pressing, and maximum at the distobuccal and minimum at the mesiobuccal point after pressing (overall mean of 117.67 ± 2.87 µm). According to paired t-test, the mean marginal gap of endocrowns fabricated by 3D printing significantly increased after pressing at all 8 points and also in general, compared with before pressing (P < 0.001). Furthermore, the mean marginal gap at all points was significantly greater in endocrowns fabricated by 3D printing compared with those fabricated by the conventional method (independent t-test, P < 0.001). Conclusion: Within the limitations of this in vitro study, the results showed that endocrowns fabricated by the conventional method had significantly superior marginal fit than those fabricated by 3D printing.

Bond Strength of Porcelain to Milled Sintered and Casting Base Metal Alloys.

STATEMENT OF THE PROBLEM: The success of metal-ceramic restorations depends on the bond strength between porcelain and alloy. These restorations can be fabricated through different casting and computer-aided design/computer-aided manufacturing (CAD/CAM) techniques. PURPOSE: This study aimed to compare the bond strength of porcelain to milled sintered (Sintron) and casting (Co-Cr and Ni-Cr) base metal alloys. MATERIALS AND METHOD: In this in vitro experimental study, 63 rectangular bars (25×3×0.5 mm) were fabricated of three base metal alloys: casting Ni-Cr, casting Co-Cr, and milled sintered Co-Cr alloy. Feldspathic porcelain (3×8 mm) was applied at the center of each bar with 1.5 mm thickness. The specimens were thermally aged. Bond strength was evaluated through three-point flexural test. Failure mode was evaluated by optical and electron microscope. Data were analyzed with one-way ANOVA and Tukey's post hoc test (α=0.05). RESULTS: The mean flexural bond strength of porcelain to milled sintered Co-Cr alloy (24.58±5.16 MPa) was significantly higher than that of casting Ni-Cr (21.13±6.34 MPa) (p= 0.03) and casting Co-Cr (20.98±4.84 MPa) alloys (p= 0.04). However, the two casting alloys were not significantly different in this regard (p= 0.93). The failure mode in all specimens was of cohesive type. CONCLUSION: Bond strength of CAD/CAM milled sintered Co-Cr alloy was better than that of the conventional casting alloys and could serve as a suitable alternative to those alloys.

Effectiveness of buccal pouch grafting in minimizing loss of alveolar dimension: A canine investigation.

BACKGROUND: The study's purpose was to study buccal pouch grafting (BPG) with xenograft, freeze-dried bone allograft (FDBA), or FDBA + decalcified FDBA (DFDBA) on alveolar ridge width preservation and overlying soft tissue thickness at dog premolar extraction sites. MATERIALS AND METHODS: In this animal study, 4 dogs had their mandibular first premolar (P1) and distal roots of P2, P3, and P4 extracted (after endodontic treatment of the mesial roots) bilaterally. A small buccal pouch was created at each extraction socket and four treatments tested: nothing, xenograft, FDBA, or FDBA + DFDBA. Casts made pretreatment and at 1 and 3 months after treatment allowed measurements of buccolingual alveolar ridge width (BLRW), while overlying buccal soft tissue thicknesses were measured clinically. Data were assessed using analysis of variance to compare changes in soft tissue thickness and BLRW between times and treatments. Tukey-Kramer adjustment for multiple comparisons was applied for doing post hoc, pairwise comparisons. Results were considered significant if P < 0.05. RESULTS: Control sites showed significant (P = 0.0067) decreases in soft tissue thickness over time while there was a trend for increased soft tissue thickness at all grafted sites. There were significant losses in BLRW over time for control (P = 0.0032) and FDBA groups (P = 0.015) with a trend for loss with FDBA + DFDBA. Pairwise comparison using Tukey-Kramer adjustment revealed significant increases in BLRW from T1 to T3 for the xenograft group relative to all the others. CONCLUSION: BPG using xenograft is effective in maintaining hard and soft tissue stability following tooth extraction.