Have you received the telephone number of your laboratory technician and there is a terrible news that you did not reduce enough crown preparation? I would be so bold that all of us who fix teeth will get this message at least once. Some of us get more news than we would like to admit.
More and more all-ceramic restorations are being manufactured, and the preparation design and occlusion are less important for the strength and life of their materials. For bonding, e.max (Ivoclar Vivadent Inc.) restorations have an average bending strength of 500 MPa at a thickness of 1 mm. Some zirconia restorations are robust and have a thickness of 0.5 mm.
What happens if we reduce our preparation? When this happens we have only five options:
Let the patient return to represent the tooth again and leave a new impression on the person. Although this is ideal, for dental clinics this can be time consuming and expensive.
The lab is required to make crowns with the desired thickness and plan to reduce the relative teeth. This option may be effective, but we must ask or inform the patient about removing the tooth structure from the teeth on the opposite dental arch. What happens if the patient is unwilling to do this, or is the tooth sensitive during enamel formation? This choice has some inherent challenges, including potential disruptions in patient trust. If I encounter a patient each time, he says that his or her previous dentist had issued an unsuitable crown and then shaved off other teeth. Then my dental loan will be paid off!
Ask the lab to make a countermeasure. When inserting an appointment, the shrinking response will be placed on your crown preparation and will be used as a guide to reduce any deficiencies in the tooth structure before the crown will fit the teeth. Apart from the first option, this may be the best. It can save additional appointments for patients and offices to represent the teeth, but care must be taken to reduce the amount of tooth structure. If the tooth structure is too narrow, the fit between the crown and the teeth may not be close despite the use of a shrinking response. Depending on where the reduction occurred, this may lead to reduced crown retention or an increased dependence on cement strength.
According to the demand of the proposed repair material, all these problems are eliminated and the appropriate amount of tooth structure is reduced. There are some tools that can be used to ensure that a proper amount of tooth structure is reduced.
Occlusion and cutting edges reduce burrs
Burs (WRC Depth Limiting System, Brassler, USA) can cut the edge at a specific depth, allowing the dentist to reduce the tooth structure to a predetermined depth. These gears limit the possibility of over-reduction. Deep incisions can be placed in the teeth, or the burrs can be used to complete the reduction of the occlusion or cut.
Advantages: These drills are available in a variety of depths and they provide a lot of versatility for a variety of recommended repair materials. The depth limit function prevents over-preparation of tooth structure. These burs can be autoclaved and can be reused.
Disadvantages: They are diamonds, so this practice will increase costs.
The Flex Tabs from Kerr are flexible, disposable labels of various thicknesses (1.0mm, 1.5mm, 2.0mm) that can be placed between the crown preparation and the opposing dentition to determine when the tooth structure is reduced for full coverage. Restoration is enough. They are disposable and disposable.
Advantages: The label can be cut to the desired width. They are relatively low cost. They help determine where the tooth structure is deficient; an articulated piece of paper can be wrapped around the label to mark locations where additional adjustments are needed.
Disadvantages: These labels are flat, and the preparation usually has a built-in main anatomy, so care must be taken to ensure that any resistance on the tabs is caused by a lack of shrinkage, rather than a flexible label catching the sharp corners. Another observation is that these are useless for all partially covered prostheses, some of which are intact.
The PrepSure Crown Preparation Guide (ContacEZ) is a high pressure autoclavable plastic device designed to ensure optimal tooth preparation for crowns and inlays. These dental instruments contain three types: 1 mm, 1.5 mm, and 2.0 mm. One side of the preparation is measured for one half of the medium and the other side is for the preparation of the distal half. The measurement tip can be placed in the reduction groove to ensure proper reduction, or the measurement tip can be placed between the prepared tooth structure and the opposing teeth after the occurrence of reduction in occlusion. The handle of the instrument is curved to facilitate all aspects of measurement preparation. The PrepSure crown preparation guide is used to slide between the prepared tooth and the opposing tooth structure. If the PrepSure guide does not slide passively, more preparation is required. This is a positive feature of the instrument because other methods may need to be explained. Another feature is that the guides can be placed against the axial wall of the formulation to assess axial compression.
Advantages: The PrepSure Crown Preparation Guide is autoclavable and can be easily adapted to crown preparations to ensure a reduction in the proper tooth structure for repair made from a variety of materials. They can be positioned to assess the occlusion reduction that partially covers the restoration. They can evaluate occlusion and axial reduction.
Disadvantages: Although their cost is reasonable, these dental instruments may need to be replaced after about 25 uses.
We have a variety of dental materials for our use to create natural, long-lasting restorations. Various materials require specific thicknesses and preparation designs, and the lifetime of many of these materials depends on the design of the formulation, including reduction in bite. Using tools to ensure that enough teeth are reduced will help us provide patients with beautiful restorations that provide longevity.
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