The main differences between them are: • The slow-speed handpiece uses a latch grip bur (Figure 19.14) instead of the friction grip bur used in the speed-increasing handpiece. This phenomenon can be further reduced by using a reciprocating prophylaxis handpiece (Figure 19.17). According to this, due to formation of fluoroapatite, strength of linkage between organic and inorganic phases of enamel is increased which helps in reducing their destruction. This will damage the chuck and the bur. • Fluoride content is lesser in carious enamel and dentin as compared to a sound tooth. There may be significant fluctuations in air pressure due to the various demands on the compressor due to demand from other clinics in a multi-clinic practice. • The specific plaque hypothesis says that only a few organisms out of the diverse collection in the plaque flora are actively involved in the disease. It is important that the knurling is not too deep or close together to avoid compromising cleaning and sterilizing of the instrument (Figure 19.8). This pecking motion causes a rippling effect on the material, leading to the formation of microcracks (Figure 19.12). 4.3), Fig. LOCAL FACTORS AFFECTING THE INCIDENCE OF CARIES (FIG. The internal components of a high-speed handpiece are shown in Figures 19.4 and 19.5. Enamel hatchet (4x). Functions and feature. • High-speed handpiece, also known as an air rotor or air turbine (Figure 19.1). This drop in pH can demineralize tooth structure depending on the absolute pH decrease, as well as the length of time that the pH is below the “critical pH” level. • According to this theory, organic portion of the tooth plays an important role in the development of dental caries. This will result in irregular removal of the tissue being prepared so more tissue is removed than is necessary. 4.5: Physical nature of diet affects the incidence of dental caries. Table 19.1 Comparison of the features of high-speed and speed-increasing handpieces. Colonization with Streptococcus mutans at an early age is an important factor for early caries initiation. The materials used to manufacture the instrument influence the weight of the instrument. Each hand instrument is composed of three parts: the handle, the shank, and the blade. DEFINITION . Smaller heads overcome these disadvantages but as a consequence, torque of the instrument was reduced in the early designs. [Article in Modern Greek (1453-)] Author K X Gkobedaros. Our dental instruments are designed for providing dental treatment such as examining, manipulating, treating, restoring and removing teeth and surrounding oral structures. It is remarkable that it is possible to remove tooth tissue (enamel and dentine) and all restorative materials (including ceramics, metals and plastics) using the same implement, the dental handpiece. Table 19.3 Ring colour and internal gearing of dental handpieces. Note the long smooth cylindrical portion of the bur, which is held in the jaws of the chuck by friction. In addition, ISO 7711-2:2011 selects five specific shapes with their specific dimensions. This cutting instrument group used in operative dentistry includes : Excavators Chisels Hatchets Hoes Gingival margin trimmers. By Dr.Eslam Mahdy (DDS, BUC). 19.14 A latch grip bur used in a slow-speed handpiece. 4.4), Fig. • Any salivary dysfunction, effect of medication or radiotherapy can result in decreased quantity and quality of saliva which further promotes caries. Frequent sugar intake encourages the growth of acidogenic and aciduric species, thus predisposing to caries. 4.6: Stephan curve graph showing plaque pH before and after glucose rinse. Less control for the dentist due to the irregular cutting. The free running speed of a 1:5 speed-increasing handpiece is the same as its cutting speed at approximately 200 000 rpm, i.e. the relationship of speed of rotation of the bur to power. Example of chelation reaction is hemoglobin in which 4 pyrrole nuclei are linked to iron by a similar bond. The resulting light is whiter, more intense and the working life is much longer. Dental probe: It’s used to detect the depth of caries or the depth of caries. • Pathogenic Properties of Cariogenic Bacteria and Pathogenesis of Dental Caries, • Hypothesis Concerning Relation between Plaque and Caries, • “Caries Balance Concept” (Proposed by Featherstone), LOCAL FACTORS AFFECTING THE INCIDENCE OF CARIES, • Environment of the Tooth: Saliva and Diet, • According to Whether it is a New Lesion or Recurrent Carious Lesion, • According to the Activity of Carious Lesion, • According to Speed of Caries Progression, • Based on Treatment and Restoration Design, • Based on Number of Tooth Surfaces Involved, • Classification According to the Severity, • Methods to Reduce Demineralizing Factors, • Genetic Modalities in Caries Prevention. This results in initiation of the caries. Tel: 319-335-7414. As we know, dental caries is a multifactorial disease of tooth which has been explained by many theories. Praxis . G.V. 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