Model observation -2020 medical and health stomatology

The concept and composition of 1. model observation

Model observation (1) is to observe the surface of the gypsum model of dentition defect by model observers, so as to determine the parallel relationship between the axial plane of the remaining natural teeth and the surface of alveolar ridge. Model observation is divided into two processes: diagnosis model observation and working model observation.

(2) The model observer is mainly composed of three parts: observation frame, observation platform and analysis and measurement tools.

1) observation frame: includes a base platform, a vertical support arm fixed on the base, a horizontal arm fixedly connected to the vertical arm or capable of rotating horizontally, a vertical measuring arm that can move up and down, and a chuck located at the end of the vertical measuring arm for fixing analytical tools.

2) Observation platform: place and fix the model on the upper part, and set the steering joint ball on the bottom of the base, so that the model can be adjusted and fixed to tilt in different directions, that is, change the relative angle between the model and the vertical measuring rod.

3) Analysis tool: fixed at the lower end of the vertical measuring arm, with the same direction, used to measure the undercut of natural tooth axial surface and alveolar ridge tissue on the model. Comprises an analysis rod, a tracing line, an inverted concave ruler (the end of which is provided with a circle of lateral protrusions with widths of 0.25mm, 0.5mm and 0.75mm) and a wax shaping knife.

2. Use of model observation

(1) Divide inverted concave area and non-inverted concave area.

The observation line, also known as the guide line, is the connecting line drawn by the lead core of the model observer along the axial surface of the crown and the most prominent points of the soft and hard tissues. The observation line (occlusion) is a non-inverted concave area, and the gingival area of the observation line is an inverted concave area.

Inverted concave can be divided into tooth inverted concave and tissue inverted concave. Tooth inversion refers to the area between the observation line and the gum on the crown, and tissue inversion refers to the area below the tissue protrusion.

(2) When the analytical rod is in contact with the observation line, the vertical distance from a point in the inverted concave area to the analytical rod is called the inverted concave depth of that point, and the inverted concave depths at different positions in the inverted concave area are different.

(3) Inverted concave can be divided into available inverted concave and unfavorable inverted concave. Available undercut means that the retention device of removable partial denture is abutment undercut to obtain denture retention. Adverse undercut means that no part of the denture can enter, otherwise it will affect the dentures or tissues put in and taken out.

Does the vertical measuring arm represent the insertion direction of removable partial denture? In position. In other words, the position of the observation line, that is, the position and depth of the undercut, is related to the direction of the denture. By changing the direction of denture, the position and depth of dentures and tissues can be changed.

3. Application of model observation

(1) Select and determine the position of the denture.

The following two methods are commonly used to determine the position trajectory:

① Average undercut (even undercut method): In the case of large gap of missing teeth and large undercut, the vertical abutment with average undercut of each abutment should be adopted. The orientation of denture is basically the bisector direction of the included angle between abutment teeth at the front and rear ends of the gap and abutment teeth at both sides of the dental arch. If the long axes of abutments are parallel to each other, the direction of abutments is consistent with the direction of the long axes of abutments.

② Adjustment of undercut (undercut adjustment method): that is, the undercut of abutments at both ends of the gap is properly concentrated on one abutment, resulting in favorable undercut. When the denture is tilted in place, the retention force of the denture can be enhanced by the locking effect.

Most of the missing anterior teeth are inclined backward, and the dentures are positioned obliquely from front to back, which can not only eliminate the undercut of labial tissue of alveolar ridge and narrow the gap between artificial anterior teeth and distal adjacent teeth to achieve aesthetics, but also concentrate the undercut of retention on distal abutment teeth, which is beneficial to the placement of retention clasp.

Generally, the model of patients with missing posterior teeth inclines forward, and the denture inclines from back to front.

(2) Determine the position of the guide plane of the remaining teeth.

(3) Determine the inverted concave of soft and hard tissues. Including the position and depth of available retention undercut on abutment and unfavorable undercut that should be adjusted, avoided or eliminated.

(4) to assist in the formulation of repair and treatment programs. Denture design, tissue modification in preparation before restoration, polishing and restoration of remaining teeth, abutment preparation, etc. Should be based on model observation.

The above contents are the knowledge points I want to bring to you today, and I hope it will help you review. We have been trying to review the materials of the entrance examination!