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[Prosthetic abutment preparation related to tooth shape and pulp extension].

Using a radiographic measuring technique, the authors determined the pulp-hard tissue ratio in 759 extracted, cariesfree, maxillary and mandibular teeth of exactly indicated ages. On the basis of the results obtained, recommendations are given for the depth of preparation of the various surfaces of the teeth as related to their ages. The suitability of various types of preparation for prosthetic abutments is discussed. For the preparation of the vestibular surface, the authors describe a modification of the grooving technique as yet recommended.

Adult↗

The effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation.

OBJECTIVE: The objective of this study is to evaluate the effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation. METHODS: Strain gages were bonded to maxillary premolars. The rigidity was tested by applying a load to a sequence of sound, prepared and restored teeth as follows: sound tooth, MOD preparation, amalgam restoration, amalgam removed recovering the MOD preparation, bonded amalgam restoration, bonded amalgam removed recovering the MOD preparation, bonded composite restoration. The relative stiffness (RS) and relative deformation (RD) of each condition for each cusp to that of the sound tooth was determined. RESULTS: The premolar cusps were deformed 1.80, 2.14, and 2.32 times more than the cusps of the sound tooth for the three succeeding MOD preparations. For these three preparations, the stiffness of the premolar cusps was 0.58, 0.48, and 0.46 relative to a stiffness of 1.00 for the sound tooth. The deformation was 1.77, 1.27, and 1.16 for the non-bonded amalgam, the bonded amalgam, and the bonded composite, respectively, corresponding to a mean RS of 0.59, 0.80, and 0.88. The calculated mean stiffness parameter C (standard deviation) was 2.6% (6.9) for the amalgam restoration, 62.5% (12.8) for the bonded amalgam restoration, and 77.8% (15.8) for the bonded composite restoration. The stiffness parameter C measured the extent to which the procedure returned the stiffness of the restored tooth to the original stiffness of the intact tooth (100%). SIGNIFICANCE: Cavity preparation reduced the stiffness and weakened the tooth. Restoring the prepared tooth with unbonded amalgam did not restore the lost tooth stiffness. Restoring the prepared tooth with bonded amalgam or with bonded composite recovered a significant portion of the lost tooth stiffness. It was concluded that bonding amalgam to tooth structure could partly restore the strength and rigidity lost by the cavity preparation. This might lead to a reduction in cuspal flexure and the incidence of tooth fracture due to fatigue.

Analysis of Variance↗

Tooth structure removal associated with various preparation designs for posterior teeth.

The amount of tooth structure removed for various innovative and conventional preparation designs for fixed prosthodontics was quantified. Four Typodont resin teeth representing maxillary and mandibular premolars and molars were prepared in various abutment designs: adhesive, box (A2); adhesive, wing and groove (A3); mesioocclusal or distoocclusal inlay; mesio-occlusodistal inlay (13); mesio-occlusodistal onlay; partial crown; half crown (only molars); complete crown, 0.8-mm circumferential tapered chamfer (F1); complete crown, 1.0-mm circumferential rounded shoulder; and complete crown, 1.4-mm axial reduction facial shoulder, 0.7-mm lingual chamfer (F3). After tooth preparation (10 per group), the root was separated from the anatomic crown at the cementoenamel junction. Removal of tooth structure was measured by gravimetric analysis in a high-precision balance. Preparations A3 and F3 were assigned as abutments for metal-supported restorations, whereas all other preparations were used for all-ceramic restorations. When the mean structure removal of all teeth tested was compared, the adhesive and inlay abutments were the least invasive preparation designs, ranging from approximately 5.5% (A2) to 27.2% (13) tooth structure removal. Complete crowns required the most invasive preparations, ranging from 67.5% (F1) to 75.6% (F3) tooth structure removal. The tooth structure removal required for F3 retainers was almost 14 times greater than for an A2 preparation. Tooth structure removal was also influenced by the morphology of the tooth. The first comprehensive tooth preparation design classification system was introduced. The measurement system used in this study provides an accurate method of quantifying tooth structure removal for fixed prosthodontic preparations. The innovative preparation designs studied conserved significant amounts of tooth structure, yielding a better prognosis for the restored tooth.

Bicuspid↗

Different methods of finishing and polishing enamel.

STATEMENT OF PROBLEM: Highly polished enamel surfaces are recommended for axial tooth surfaces that will serve as guiding planes and be contacted by component parts of a removable partial denture. There is little evidence to support the assumption that this tooth modification will provide accurate adaptation of the framework and prevent build-up of plaque. PURPOSE: The aim of this investigation was to evaluate the surface roughness of the tooth enamel, prepared to serve as guiding planes, with different polishing systems. MATERIAL AND METHODS: Four different methods (designated A, B, C, and D) for finishing and polishing the prepared enamel surfaces of 20 freshly extracted third molar teeth were studied. Each method involved 3, 4, or 5 different steps. The roughness of each specimen was measured at the start of each method before recontouring, after recontouring, and after each step of the 4 finishing and polishing procedures. The 4 experimental finishing methods were applied after recontouring the axial surfaces (buccal, lingual, and proximal) of each tooth. Thus the 20 teeth (60 surfaces) were finished and polished by use of 1 of the experimental methods. Surface roughness was measured with a profilometer (microm); the readings of the unpolished enamel surfaces were recorded as control measurements. Results were statistically analyzed with one-way analysis of variance followed by Tukey's test at the 95% level of confidence. RESULTS: The highest roughness mean values (14.41 microm to 16.44 microm) were found when the diamond bur was used at a high speed for tooth preparation. A significant decrease in roughness values was observed with the diamond bur at a low speed (P<.05). Analysis of the roughness values revealed that all polishing methods produced surface roughness similar to that of the corresponding control teeth. CONCLUSION: Within the limitations of this study, all finishing procedures tested effectively promoted an enamel surface similar to the original unpolished enamel.

Analysis of Variance↗