الفهرس 
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Abstract
The efficiency of zirconia restorations is influenced by the sintering technique used. Also, different surface treatment techniques were proposed to increase bond strength of zirconia to resin cement. The aim of this study was to evaluate the effect of different sintering techniques (microwave assisted sintering, speed sintering and conventional sintering) and different surface treatment techniques (laser irradiation and tribochemical silica coating) on monolithic zirconia fixed partial dentures both in-vitro and in-vivo.
For the in-vitro study: a) Thirty four-unit full contour monolithic zirconia fixed partial dentures (FPDs) were constructed on epoxy resin dies and divided into 3 groups (n=10) according to the sintering technique (group II: microwave sintering, group II: speed sintering, and group III: conventional sintering). Each group was divided into two subgroups according to the surface treatment applied to the retainers’ intaglio surface (subgroup A: Er, Cr: YSGG laser treatment, and subgroup B: tribochemical silica coating). Marginal adaptation was evaluated using stereomicroscope. The FPDs were then cemented and subjected to cyclic loading and finally loaded until fracture in universal testing machine. b) Eighteen 10x10x4 mm zirconia block specimens were fabricated and divided into to the same groups as in the previous study (n=6). The zirconia surface was investigated by x-ray diffraction. Afterwards, the zirconia specimens were bonded to composite blocks using resin cement, and cut into microbars of 1mm2(n=30). The microbars were subjected to microtensile bond strength test. For the clinical study: Thirty patients with missing mandibular second premolar and first molar received a four-unit full contour zirconia FPD and were assigned randomly into the same groups as in the previous studies. The clinical performance of the FPDs was followed up at baseline, 6 months and 1 year using the USPHS criteria for evaluation.
Concerning marginal fit, there was no statistical difference between group I (microwave sintering) and group III (conventional sintering). There was a significant difference between group II (speed sintering) and group III with group II showing higher marginal gap values.
Concerning fracture resistance, there was no statistical difference between group I and group III. There was a significant difference when group II was compared with both groups I and III. group II showed the lowest failure load values.
Concerning microtensile bond strength, there was a significant difference upon comparing the two surface treatment techniques in each group and in total. Subgroups B (tribochemical silica coating) showed higher bond strength values than subgroups A (Er, Cr: YSGG laser irradiation).
In the clinical study, the 1-year survival rate was 100% in all groups. No fractures or cracks were observed in any of the FPDs. No clinical change between the base line, 6 months and one year scores of marginal integrity, shade match, anatomic form, secondary caries, wear and presence of cracks/fractures parameters was observed, and all have shown satisfactory results.