The study of the mucosa under the denture and the mechanical properties under the mucosa is of great significance for the study of the mechanism of the force acting on the mucosa under the denture and the bone tissue under the mucosa after denture restoration. Guide the repair of the shape so that the force is within the allowable range, and evaluate the damage to the supporting tissue when the force exceeds the allowable force. For many years, the determination of this force has been paid attention by researchers in the dental prosthetics field and medical sensors, and most of the existing measurement methods are to paste a patch piezoresistive pressure sensor under the denture base, but the patch piezoresistive The elastic modulus of the pressure sensor is inconsistent with the denture base, and does not coincide with the surface of the detected tissue. It is also difficult to be flush with the surrounding base surface. The error of the measured force is relatively large, and it is difficult to measure the distribution of force.
In response to these problems, the principle of MEMS capacitive pressure sensor is adopted in this paper, a MEMS capacitive pressure sensor with a length x width x height of 2.2 mmx 1.8 mmx 0.6 mm is designed, and then distributed embedded implant denture base is used. The method inside the bracket can accurately test the force and force distribution on the mucosa under the denture and the bone tissue under the mucosa. The sensor has a stable structure, good measurement stability, good linearity, minimum force resolution of 0.1 g, high sensitivity, can work stably in a temperature range of 100 ° C to 200 ° C, and has a wide temperature range. The range can be applied to the measurement of the force in the harsh environment of the oral cavity.
1 The technological process of the sensor
The sensor is realized by MEMS technology [34], the processes used are: oxidation, photolithography, sleeve engraving, diffusion, ICP engraving, coating, silicon-glass bonding and other processes. The processing process mainly includes the processing technology on the silicon wafer, the processing technology on the glass, and the processing technology after the silicon-glass bonding.
The semiconductor silicon wafer is oxidized, photoetched, etched, diffused, reoxidized, over-etched, and etched to complete the process on the front side of the silicon wafer, which mainly includes the formation of grooves and insulating layers. The reverse side is then subjected to reverse side photolithography and etching to form positive and negative electrode lead lines PAD and fill the groove. Among them, the purpose of diffusion is to form a functional borosilicate film (P + film) of about 2 m. Before diffusion, the silicon wafer should be standard cleaned. Because of the diffusion, the silicon surface will interact with oxygen to form a layer of borosilicate glass, so it must be removed. Wet etching is used to remove excess borosilicate glass on the surface. In the processing of glass, the 7740 glass wafer of Xiamen Fuxin Microelectronics Technology Co., Ltd. is used to form a metal layer sputtered on the glass through photolithography and coating, which is the metal electrode of the lower plate. Then through silicon-glass bonding, etching, ICP engraving, and coating, the entire sensor is completed. The device integrated on a piece of silicon is divided into small devices by slicing, so as to facilitate the next packaging and testing.
2 Packaging and testing
In the pressure test under the load of a single sensor, the method adopted by the research group is: using the same material as the denture base resin
As a base, dig a square small hole with a side length of 2 mm on the resin, embed the sensor, and then use the same material for condensation
The resin and the special resin for the denture base are mixed and dropped on the surface of the sensor to make the package flat, so that its plane is consistent with the plane of the base. After it is solidified, you can get a covering surface with the same surface material and denture material.
3 Conclusion
The test results show that the sensor has good performance, has a relatively stable input and output relationship, and can accurately measure the pressure change of the outside world. In addition, because the measured capacitance is relatively small, it is susceptible to interference from external factors such as wires and solder joints during the test, which will produce certain errors. Therefore, in the following work, an ADC can be used to convert the analog voltage signal into a digital signal and use it. This kind of trend line with good fitting degree is used as the corresponding curve between externally applied pressure and output voltage to write a corresponding software system for direct reading of data during clinical testing.