The effects of crown venting or pre‐cementing of CAD/CAM‐constructed all‐ceramic crowns luted on YTZ implants on marginal cement excess

Objectives

The purpose of this study was to analyze the cement excess produced when cementing CAD/CAM‐fabricated lithium disilicate (L) or zirconium dioxide (Z) crowns using adhesive cement (A) or resin‐modified glass ionomer cement (B). Three different cementation techniques were applied: palatal venting (PV), pre‐cementation with custom analogs (CA), and conventional standard procedure (SP).

Materials and Methods

Seventy‐two crowns (36 each material) were assigned to 12 experimental groups depending on the restoration material (L, Z), type of cement (A, B), and cementation technique (PV, CA, SP). Weight measurements were taken during cementation, and the amounts of excess cement, cement retained in crown, and relative excess cement were calculated and statistically analyzed.

Results

A significant direct relation between the amounts of cement applied and excess cement was observed in groups CA and SP. Vented crowns showed least amounts of marginal excess cement (0.8 ± 0.3 μl) followed by CA (4.2 ± 1.1 μl) and SP (8.8 ± 2.5 μl; p < .001). In CA, 32.1% less excess cement (95%CI: 28.4, 35.7) was produced than in the SP group (p < .001), but 27.4% more than in the PV group (95%CI: 23.8,31.0; p < .001). Overall, slightly smaller amounts of adhesive cement (A) than of glass ionomer cement (B) were retained in crowns.

Conclusions

Using crown venting was the most effective measure to reduce the amount of marginal excess cement, followed using a pre‐cementation device. To keep the marginal excess cement of one‐piece zirconia implants to a minimum, both techniques should be considered for clinical application.     

Internal fit of three‐unit fixed dental prostheses produced by computer‐aided design/computer‐aided manufacturing and the lost‐wax metal casting technique assessed using the triple‐scan protocol

Suboptimal adaptation of fixed dental prostheses (FDPs) can lead to technical and biological complications. It is unclear if the computer‐aided design/computer‐aided manufacturing (CAD/CAM) technique improves adaptation of FDPs compared with FDPs made using the lost‐wax and metal casting technique. Three‐unit FDPs were manufactured by CAD/CAM based on digital impression of a typodont model. The FDPs were made from one of five materials: pre‐sintered zirconium dioxide; hot isostatic pressed zirconium dioxide; lithium disilicate glass‐ceramic; milled cobalt‐chromium; and laser‐sintered cobalt‐chromium. The FDPs made using the lost‐wax and metal casting technique were used as reference. The fit of the FDPs was analysed using the triple‐scan method. The fit was evaluated for both single abutments and three‐unit FDPs. The average cement space varied between 50 μm and 300 μm. Insignificant differences in internal fit were observed between the CAD/CAM‐manufactured FDPs, and none of the FPDs had cement spaces that were statistically significantly different from those of the reference FDP. For all FDPs, the cement space at a marginal band 0.5–1.0 mm from the preparation margin was less than 100 μm. The milled cobalt‐chromium FDP had the closest fit. The cement space of FDPs produced using the CAD/CAM technique was similar to that of FDPs produced using the conventional lost‐wax and metal casting technique.     

Platform switching and marginal bone‐level alterations: the results of a randomized‐controlled trial

Objectives: This randomized‐controlled trial aimed to evaluate marginal bone level alterations at implants restored according to the platform‐switching concept, using different implant/abutment mismatching. Material and methods: Eighty implants were divided according to the platform diameter in four groups: 3.8 mm (control), 4.3 mm (test group₁), 4.8 mm (test group₂) and 5.5 mm (test group₃), and randomly placed in the posterior maxilla of 31 patients. After 3 months, implants were connected to a 3.8‐mm‐diameter abutment and final restorations were performed. Radiographic bone height was measured by two independent examiners at the time of implant placement (baseline), and after 9, 15, 21 and 33 months. Results: After 21 months, all 80 implants were clinically osseointegrated in the 31 patients treated. A total of 69 implants were available for analysis, as 11 implants had to be excluded from the study due to early unintentional cover screw exposure. Radiographic evaluation showed a mean bone loss of 0.99 mm (SD=0.42 mm) for test group₁, 0.82 mm (SD=0.36 mm) for test group₂ and 0.56 mm (SD=0.31 mm) for test group₃. These values were statistically significantly lower (P<0.005) compared with control (1.49 mm, SD=0.54 mm). After 33 months, five patients were lost to follow‐up. Evaluation of the remaining 60 implants showed no difference compared with 21 months data except for test group₂ (0.87 mm) and test group₃ (0.64 mm). There was an inverse correlation between the extent of mismatching and the amount of bone loss. Conclusions: This study suggested that marginal bone level alterations could be related to the extent of implant/abutment mismatching. Marginal bone levels were better maintained at implants restored according to the platform‐switching concept. To cite this article:
Canullo L, Fedele GR, Iannello G, Jepsen S. Platform switching and marginal bone‐level alterations: the results of a randomized‐controlled trial.
Clin. Oral Impl. Res. 21 , 2010; 115–121.     

Long‐term,retrospective evaluation (implant and patient‐centred outcome) of the two‐implant‐supported overdenture in the mandible. Part 2: marginal bone loss

Objective: In part 2 of this long‐term, retrospective study on the two‐implant‐supported overdenture in the mandible, the annual marginal bone loss was evaluated in detail and parameters, with a significant effect on the annual bone loss, were verified. Material and methods: For all 495 patients with an overdenture in the mandible at least 5 years in function, data up to their last follow‐up visit had been collected, including long‐cone radiographs (taken at the abutment connection and after years 1, 3, 5, 8, 12 and 16 of loading) and probing data at their last evaluation. General information (medical history, implant data, report on surgery) was retrieved from the patient's file. Two hundred and forty‐eight patients had been clinically examined recently. For the others, information on bone level and probing depths were retrieved from the patient's files, as all patients had been enrolled in our annual follow‐up schedule. Results: The mean annual bone loss on a site level (without considering the first year of bone remodelling) after 3 years of loading was 0.08 mm/year (SD=0.22, n=1105), after 5 years of loading 0.07 mm/year (SD=0.14, n=892), after 8 years of loading 0.06 mm/year (SD=0.12, n=598), after 12 years 0.04 mm/year (SD=0.07, n=370) and 0.05 mm/year (SD=0.05, n=154) after 16 years of loading. Ongoing bone loss was seen in a number of implants (n=26) with the annual bone loss exceeding 0.2 mm. Some factors clearly showed a significant impact on bone loss: smoking (≥10 cigarettes/day), GBR, the presence of dehiscence and bone quantity(the latter only during the first year). The probing data showed a favourable condition, with <1.2% of the approximal pockets being ≥6 mm, and 4.1%=5 mm. Conclusions: The mean annual bone loss over the study period was <0.1 mm/year after the first year of loading. However, a small number (2.5%) of the implants showed continuing bone loss. To cite this article :
Vercruyssen M, Quirynen M. Long‐term, retrospective evaluation (implant and patient‐centred outcome) of the two‐implants‐supported overdenture in the mandible. Part 2: marginal bone loss.
Clin. Oral Impl. Res. 21 , 2010; 466–472.
doi: 10.1111/j.1600‐0501.2009.01902.x