Fifteen-year outcome of three-unit fixed dental prostheses made from monolithic lithium disilicate ceramic.

OBJECTIVES: The purpose of this prospective study was to evaluate the clinical long-term outcome over 15 or more years of crown-retained fixed dental prostheses (FDPs) made from a lithium disilicate ceramic (IPS e.max Press, Ivoclar Vivadent AG). METHODS: Thirty-six three-unit FDPs replacing anterior (16%) and posterior (84%) teeth were inserted in 28 patients. Abutment teeth were prepared following a standardized protocol. The size of the proximal connector of the FDPs was 12 mm² (anterior) or 16 mm² (posterior). FDPs were cemented either conventionally with glass-ionomer cement (n = 19) or adhesively with composite resin (n = 17). The following parameters were evaluated at baseline, 6 months after cementation and then annually (at abutment and contralateral teeth): probing pocket depth, plaque index, bleeding on probing, and tooth vitality. RESULTS: Three FDPs were defined as drop-outs. The mean observation period of the remaining 33 FDPs was 167 months (range: 79-225 months). The survival rate (survival being defined as FDPs remaining in place either with or without complications) according to Kaplan-Meier was 48.6% after 15 years. The success rate (success being defined as free of complications and remaining unchanged) was 30.9% after 15 years. CONCLUSIONS: Fatigue and crack propagation caused by clinical aging in monolithic lithium disilicate ceramics seem to take considerable time, as shown by the presented survival and success rates after 15 years. Further long-term studies are necessary to evaluate the reliability of FDPs made from other all-ceramic materials over a period of 15 or more years.

Increased intraosseous temperature caused by ultrasonic devices during bone surgery and the influences of working pressure and cooling irrigation.

PURPOSE: The purpose of this study was to investigate the increases in intraosseous temperature generated by a modern ultrasonic device for bone surgery (UDBS) and the influences of working pressure and cooling irrigation on this temperature. MATERIALS AND METHODS: Twenty human mandibular bone specimens (20x15x5 to 7 mm) were used; three vertical cuts were performed for a duration of 12 seconds per cut. Each bone specimen was machined with a different combination of working pressure (1.5, 2.0, 3.0, 4.0, or 6.0 N) and cooling irrigation (0, 30, 60, or 90 mL/min), and intraosseous temperatures were measured. Harmful temperature development was defined as an increase of more than 10°C for the 75th percentile and/or a maximum increase of more than 15°C. Cutting performance was also measured. RESULTS: Harmless intraosseous temperature development was identified for working pressures of 1.5 N and 2.0 N with cooling irrigations of 30, 60, and 90 mL/min and for 3.0 N at 90 mL/min. The maximum temperature observed was 72°C (6.0 N with 60 mL/min). The mean cutting performance values were 0.21±0.02 mm/s for 6.0 N, 0.21±0.06 mm/s for 3.0 N, 0.20±0.01 mm/s for 4.0 N, 0.11±0.05 mm/s for 1.5 N, and 0.08±0.03 mm/s for 2.0 N. CONCLUSIONS: To prevent tissue damage in dental bone surgery, a minimum coolant amount of 30 mL/min is recommended. The working pressure should be chosen with great care because of its significant influence on intraosseous temperature. Doubling of the working pressure from 1.5 to 3.0 N requires a tripling of the coolant (30 to 90 mL/min) to prevent tissue damage. A working pressure above 3.0 N did not result in improved cutting performance.

Forces charging the orbital floor after orbital trauma.

The objectives of this study were (i) to evaluate different fracture mechanisms for orbital floor fractures and (ii) to measure forces and displacement of intraorbital tissue after orbital traumata to predict the necessity of strength for reconstruction materials. Six fresh frozen human heads were used, and orbital floor defects in the right and left orbit were created by a direct impact of 3.0 J onto the globe and infraorbital rim, respectively. Orbital floor defect sizes and displacement were evaluated after a Le Fort I osteotomy. In addition, after reposition of the intraorbital tissue, forces and displacement were measured. The orbital floor defect sizes were 208.3 (SD, 33.4) mm(2) for globe impact and 221.8 (SD, 53.1) mm(2) for infraorbital impact. The intraorbital tissue displacement after the impact and before reposition was 5.6 (SD, 1.0) mm for globe impact and 2.8 (SD, 0.7) mm for infraorbital impact. After reposition, the displacement was 0.8 (SD, 0.5) mm and 1.1 (SD, 0.7) mm, respectively. The measured applied forces were 0.061 (SD, 0.014) N for globe impact and 0.066 (SD, 0.022) N for infraorbital impact. Different fracture-inductive mechanisms are not reflected by the pattern of the fracture. The forces needed after reposition are minimal (~0.07 N), which may explain the success of PDS foils [poly-(p-dioxanone)] and collagen membranes as reconstruction materials.

Forces charging the orbital floor after fractures.

The objective of this study was first to establish a method to measure forces and displacement of the orbital content in defects of the orbital floor in truncated fresh and unfixed heads and second to characterize reconstruction materials with regard to punctuation strength and compression.Orbital floor defects (10 × 20 mm and 15 × 20 mm; 3 mm behind the orbital rim) were prepared after Le Fort I osteotomy. The values of force and displacement were recorded in 6 freshly frozen human heads. In addition, the punctuation strength of 2 reconstruction materials (polydioxanone [PDS] foil and collagen membrane) was evaluated using a Zwick Z010 TN1 universal testing machine. The forces of the orbital content (28.41 [SD, 1.6] g) applied to the defects of 10 × 20 mm and 15 × 20 mm with an intact periorbita were 0.04 (SD, 0.003) N (0.0002 MPa) and 0.07 (SD, 0.02) N (0.0002 MPa), respectively, and with a split periorbita were 0.06 (SD, 0.03) N (0.0003 MPa) and 0.08 (SD, 0.06) N (0.00026 MPa), respectively. The displacement values without reconstruction materials of the 10 × 20-mm and 15 × 20-mm defects were 0.94 (SD, 0.7) mm and 1.2 (SD, 0.5) mm, respectively. The PDS foil could withstand forces of 118.9 (SD, 14.1) N (0.375 MPa), and the collagen membrane could withstand forces of 44.5 (SD, 5.3) N (0.14 MPa). This is the first study to report forces charging the orbital floor. The presented results support the use of PDS foils and collagen membranes as reconstruction materials for orbital floor defects, at least in smaller and medium-sized fractures.

Changes in human mandibular bone morphology after heat application.

PURPOSE: Intraosseous heat development is always a problem during bone surgery performed using rotary burs and ultrasound devices. However, only few data exist regarding the morphological effects of applied heat on bone surfaces. METHODS: We used 24 human mandibular bone specimens of the mental region from six body donators. Three body donators were fixed in ethanol and the others were stored frozen. Heat application to the bone surfaces at temperatures of 40 degrees C, 50 degrees C, 60 degrees C and 100 degrees C for 1 min respectively, was performed under controlled conditions using an iron heater, and followed by examination using (i) scanning electron microscopy (SEM), (ii) demineralized paraffin sections, and (iii) cryostat sections (both HE staining). RESULTS: There was no difference in the morphology or histology between fixed or unfixed bone specimens. The bone surface was smooth in both groups at 40 degrees C and 50 degrees C of heat application. Applications of 60 degrees C and 100 degrees C induced a rough-textured surface with small cavities visible with SEM and demineralized HE staining. The bone appeared to be unaffected at lower planes. The frozen HE histology could not be evaluated. Although useful in other studies, here the sections were broken and displaced on the glass slide. Therefore, this technique is not recommended by the authors. CONCLUSION: Our findings suggest the applicability of SEM for bone surface morphology and demineralized paraffin sections (HE staining) for frontal plane evaluation. Fixed and non-fixed bone specimens seem to be equal in their morphology and can both be used in these kinds of studies.