IntroductionZirconia provides adequate mechanical strength to be used as a framework for all ceramic prostheses. Such prostheses must be covered with suitable porcelain to obtain good aesthetic results. The aimTo study the effect of the firing cycle numbers of veneering ceramics (one cycle, two cycles, and three cycles) on the marginal fit of computer-aided design (CAD) and computer-aided manufacturing (CAM) zirconia bridges. Materials and methodsThe sample consisted of 30 full ceramic zirconia bridges, designed by CAD/CAM on a metal bridge model that was designed for this purpose. The sample was divided into three groups (N = 10); group A underwent a single firing cycle, group B underwent two cycles, and group C underwent three cycles. The copper model of the bridge was prepared to be a three-unit bridge, and the impressions of the metal models were taken to make zirconia cores. After that, the veneering ceramic layer and the micro-marginal gap were measured (in microns) on both the buccal and lingual surfaces of each bridge in the sample using the replica technique. A one-way ANOVA test was used to detect statistically significant differences between the groups. ResultsThere were no significant differences between the studied groups in binary comparison; however, the arithmetic mean values of the marginal gap in group C were greater than all the studied groups. ConclusionWithin the limitations of the current work, we found that increasing the number of firing cycles of zirconia cores affects the marginal fit; thus, it is recommended to follow the two firing cycle protocol for better adaptation of the CAD/CAM zirconia bridges.

The current gold standard is a conventional impression made with various impression materials and trays and results in a gypsum cast. With the development of milling and printing materials in dentistry, especially zirconia, a digital model has become increasingly important. ObjectivesTo compare the accuracy of the conventional impression scan (CIS), gypsum cast scan (GCS), and digital impression scan (DIS) to obtain a full-arch digital model. Materials and methodsA resin reference cast was fabricated. It was scanned by an extra-oral scanner to measure its accuracy as a reference scanner. Eight conventional impressions of the reference cast were taken by polyvinyl siloxane and scanned. After that, they were poured with type IV dental stones and scanned too. The reference cast was scanned by an intraoral scanner eight separate times. Digital models within each group were superimposed individually to measure precision. In addition, each model from each group was superimposed on one model from the reference scanner precision group to measure trueness. ResultsThe reference scanner showed the highest accuracy among groups with a precision of 1.5±0.8 µm and a trueness of 5.5±1.9 µm (P<0.006), while precision values of gypsum cast were 8.1±1.7 µm and trueness values were 9.3±2.6 µm (P<0.012). Conventional impressions showed a precision of 14.06±2.01 µm and a trueness of 16.15±2.07 µm (P<0.012). Digital impressions were the least accurate among the groups, as precision values were 38.22±15.23 μm and trueness values were 35.19±8.7 μm (P<0.006). ConclusionThe gypsum cast scans showed the highest accuracy, followed by the conventional impression scans, and finally the digital impression scans, with no clinical significance.

BackgroundImplant-supported prostheses are widely used to replace extracted teeth. Therefore, studies on abutments' designs, shapes, and benefits had increased in recent years, as the design of the standard abutment still poses many problems in periodontal and cosmetic aspects. So, could the hybrid abutment solve some of these problems? AimWe aim to conduct a clinical comparison between standard and hybrid abutments in terms of the state of peri-implant gingival tissues and patients' aesthetic and functional satisfaction after the cementation of the final prostheses. Material and methodsThe study sample consisted of 10 patients, with 20 dental implants. Each patient received two implants as a standard abutment was placed over one implant and a hybrid abutment was placed over the other. Clinical assessment of the peri-implant gingival tissue and patients' aesthetic and functional satisfaction was performed (immediately, three months, six months, and one year) after the cementation of the final prostheses. The Mann-Whitney U test was used to detect statistically significant differences between groups. ResultsThe percentage of the thick gingival biotype was 80%, and the percentage of the thin gingival biotype was 20% in each group during the follow-up periods. In addition, all papilla fill the whole interdental space in all samples of the two groups after six months and one year. Finally, there were no significant differences in patients' aesthetic satisfaction between groups during one year of follow-up (P = 0.631), and there were no significant differences in patients' functional satisfaction between groups during one year of follow-up (P = 0.684). ConclusionWithin the limitations of the current work, there are no differences between standard and hybrid abutments in terms of affecting the peri-implant gingival tissue and patients' aesthetic and functional satisfaction.