An open CAM system for dentistry on the basis of China-made 5-axis simultaneous contouring CNC machine tool and industrial CAM software
China-made 5-axis simultaneous contouring CNC machine tool and domestically developed industrial computer-aided manufacture (CAM) technology were used for full crown fabrication and measurement of crown accuracy, with an attempt to establish an open CAM system for dental processing and to promote the introduction of domestic dental computer-aided design (CAD)/CAM system. Commercially available scanning equipment was used to make a basic digital tooth model after preparation of crown, and CAD software that comes with the scanning device was employed to design the crown by using domestic industrial CAM software to process the crown data in order to generate a solid model for machining purpose, and then China-made 5-axis simultaneous contouring CNC machine tool was used to complete machining of the whole crown and the internal accuracy of the crown internal was measured by using 3D-MicroCT. The results showed that China-made 5-axis simultaneous contouring CNC machine tool in combination with domestic industrial CAM technology can be used for crown making and the crown was well positioned in die. The internal accuracy was successfully measured by using 3D-MicroCT. It is concluded that an open CAM system for dentistry on the basis of China-made 5-axis simultaneous contouring CNC machine tool and domestic industrial CAM software has been established, and development of the system will promote the introduction of domestically-produced dental CAD/CAM system.
The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns.
OBJECTIVES
The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (microCT).


METHODS
Cerec3 PCCs of three different preparation designs (n=20) were fabricated according to the following: Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the microCT scanning was performed. For obtaining the average internal gap (AIG), the microCT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) microCT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the microCT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test.


RESULTS
For the 3D reconstruction technique, the AIGs were as followed: Group I 197.3+/-48.2microm, Group II 171.2+/-45.1microm, and Group III 152.7+/-27.1microm. For the 2D microCT views, the gaps of each group were the smallest on the margins ranging from 35.4+/-32.2 to 128.4+/-69.5microm, and the largest on the horizontal or angle walls ranging from 184.5+/-41.2 to 406.5+/-176.1microm. According to the results, Group I showed larger marginal and internal gaps compared with the other groups.


CONCLUSIONS
For the PCCs, the simplified designs (Groups II and III) demonstrated superior results compared to the traditional cusp capping design (Group I). The marginal gaps were smaller than the internal gaps in all groups.
Influence of pressure and fluidization velocity on the hydrodynamics of a fluidized bed containing horizontal tubes
Abstract An experimental investigation of the influence of horizontal tubes on the bubble behaviour and through-flow velocity of gas inside bubbles was carried out and the influence of pressure and fluidization velocity was studied. The visible bubble flow rate and the gas velocity through the bubbles were measured simultaneously in a pressurized fluidized bed, using capacitance and Pitot-static pressures probes respectively. Silica sand with a mean particle diameter of 0.7 mm was fluidized at pressures between 01. and 1.6 MPa, in a bed of 0.2 × 0.3 m cross-section. Six different horizontal tube configurations were used and comparisons were made with results obtained in the same bed operated without tubes. The results from the bed with tubes show that the influence of pressure and fluidization velocity is basically the same as in the bed without tubes; an increase in pressure and fluidization velocity increases the bubble activity. At low excess gas velocities, the influence of immersed tubes on the bubble behaviour is less pronounced than at high excess gas velocities. Measurements and visual observations show that a small tube pitch gives a more uniform distribution of the visible bubble flow over the bed cross-section. At a combination of high pressure, high excess gas velocity and a large tube pitch, a preferred bubble path was observed in the centre of the bed cross-section. The pressure probe measurements show that the through-flow velocity of gas inside the bubbles is in most cases higher when tubes are present in the bed. The through-flow velocity consistently decreases with increasing pressure in the bed without tubes. The tendency is largely the same at a low excess gas velocity when tubes are present, but at a high excess gas velocity the through-flow velocity first decreases and then increases as the pressure is increased.