انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة
الكلية كلية طب الاسنان
القسم ترميم ومعالجة الاسنان
المرحلة 3
أستاذ المادة احمد غانم مهدي الهلال
4/27/2011 2:49:39 PM
Tooth preparation:
Teeth do not possess the regenerative ability found in most other tissues. Therefore, once enamel or dentin is lost as a result of caries, trauma, or wear, restorative materials must be used to establish form and function. Teeth require preparation to receive restorations, and these reparations must be based on fundamental principles from which basic criteria can be developed to help predict the success of prosthodontic treatment. The principles of tooth preparation may be divided into three broad categories:
1. Biologic considerations, which affect the health of the oral tissues.
2. Mechanical considerations, which affect the integrity and durability of the restoration.
3. Esthetic considerations, which affect the appearance of the patient.
Biological consideration:
1. Prevention of damage during tooth preparation:
a. Adjacent Teeth.
Damage to an adjacent tooth is a common error in dentistry. Even if a damaged proximal contact area is carefully reshaped and polished, it will be more susceptible to dental caries than the original undamaged tooth surface. This is presumably because the original surface enamel contains higher fluoride concentrations and the interrupted layer is more prone to plaque retention. The technique of tooth preparation must avoid and prevent damage to the adjacent tooth surfaces. A metal matrix band around the adjacent tooth for protection may be helpful; however, the thin band can still be perforated and the underlying enamel damaged. The preferred method is to use the proximal enamel of the tooth being prepared for protection of the adjacent structures.
b. Soft Tissues.
Damage to the soft tissues of the tongue and cheeks can be prevented by careful retraction with an aspirator tip, mouth mirror or flanged saliva ejector. Great care is needed to protect the tongue when the lingual surfaces of mandibular molars are being prepared.
c. Pulp.
Extreme temperatures, chemical irritation, or microorganisms can cause an irreversible pulpitis, particularly when they occur on freshly sectioned dentinal tubules. Prevention of pulpal damage necessitates selection of techniques and materials that will reduce the risk of damage while preparing tooth structure. Tooth preparations must take into consideration the morphology of the dental pulp chamber. Pulp size, which can be evaluated on a radiograph, decreases with age.
2. Conservation of tooth structure:
One of the basic tenets of restorative dentistry is to conserve as much tooth structure as possible consistent with the mechanical and esthetic principles of tooth preparation. This will reduce the harmful pulpal effects of the various procedures and materials used. The thickness of remaining dentin has been shown" to be inversely proportional to the pulpal response, and tooth preparations extending deeply toward the pulp should be avoided. Tooth structure is conserved by using the following guidelines:
1. Use of partial-coverage rather than complete coverage restorations.
2. Preparation of teeth with the minimum practical convergence angle (taper) between axial walls.
3. Preparation of the occlusal surface so reduction follows the anatomic planes to give uniform thickness in the restoration.
4. Preparation of the axial surfaces so tooth structure is removed evenly; if necessary, teeth should be orthodontically repositioned.
5. Selection of a conservative margin compatible with the other principles of tooth preparation.
6. Avoidance of unnecessary apical extension of the preparation.
MECHANICAL CONSIDERATIONS:
Retention: is the ability of the preparation to prevent dislodgement of the restoration by forces directed along its path of insertion.
Resistance: is the ability of the preparation to prevent dislodgement of the restoration by forces directed in apical, oblique or horizontal directions.
Path of insertion: its imaginary line along which the restoration is inserted, the restoration should have a single path of insertion to be retentive. The design of tooth preparations for fixed prosthodontics must adhere to certain mechanical principles; otherwise, the restoration may become dislodged or may distort or fracture during service. These principles have evolved from theoretical and clinical observations and are supported by experimental studies.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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