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An intraoral surveyor.

A device is described for checking tooth preparations of abutment teeth for fixed or removable partial dentures. The device quickly and accurately indicates the planned path of insertion of the prosthesis intraorally, serves as a visual guide during the preparation of teeth, and aids the dentist in evaluating tooth preparations before making a final impression. This intraoral surveyor provides an inexpensive, practical, and readily available method for producing optimal tooth preparations for fixed and removable partial dentures.

Dental Abutments↗

Ability of various impression materials to produce duplicate dies from successive impressions.

This in vitro study evaluated the ability of five different impression techniques to make duplicate dies of two different types of tooth preparation. One mandibular second premolar Ivorine tooth was prepared for a complete crown and one for an onlay. A master impression was made of each tooth preparation with the use of five impression techniques for a total of 10 master impressions, and a master die was made from each of these impressions. Castings were made on these master dies, and the fit of each casting was verified on the respective Ivorine tooth. Marginal openings of the castings on the master dies were recorded under magnification at four predetermined points. Five successive impressions, with the use of each impression material, were then made of each tooth preparation for a total of 50 test impressions, and 50 test dies were made from these impressions. The fit of the respective casting was evaluated under magnification for each test die at the four predetermined points, and marginal openings were recorded. Differences between the marginal discrepancies of the casting on the master die and on the test die were tabulated and the results were statistically analyzed. Results indicated that none of the impression materials was capable of producing exact replicas. Polysulfide rubber performed significantly better than two materials for the production of duplicate dies with the complete crown preparation; and polyvinyl siloxane used with a putty-light body, single-stage technique produced mean marginal discrepancies that were significantly greater than the other four techniques when used for the onlay preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Bicuspid↗

When to use fillers, build-ups or posts and cores.

After preliminary tooth preparation for crowns, all previously placed tooth restorative material should be removed from teeth before making final tooth preparations. Small areas of missing teeth should be replaced with fillers (compomer); larger pieces of missing teeth should be replaced with build-ups (bonded composite resin or bonded amalgam); and endodontically treated teeth with half or more of the coronal tooth structure missing should receive a titanium or titanium alloy post and core and a bonded composite resin or bonded amalgam build-up.

Compomers↗

Marginal seal of sealant and compomer materials with and without enameloplasty.

OBJECTIVES: This in vitro study evaluated the quality of marginal seal and fissure penetration of a resin-sealant (Concise) and a compomer restorative material (F2000) with and without enameloplasty. SAMPLE AND DESIGN: Thirty extracted sound human permanent third molar teeth were divided into six groups of five and used in this in vitro study. METHODS: Occlusal surfaces of the teeth in different groups were either left intact or prepared using a #582 S diamond bur. Teeth were then restored with Concise and F2000 restorative materials using combinations of different surface treatments. Teeth were prepared for microleakage, then immersed in 5% methylene blue for 4 h, and subsequently sectioned into four bucco-lingual sections. Sections (20 per group) were examined using a stereomicroscope. The following parameters were evaluated: marginal leakage, marginal gap, voids and filling defects, as well as enamel fissure penetration. RESULTS: Kruskal-Wallis one-way ANOVA showed statistically significant differences between the groups for marginal leakage (P < 0.0001), marginal gap (P < 0.001), and enamel fissure penetration (P < 0.001). No statistically significant differences between the groups for voids and filling defects were detected. Non-parametric Tukey's multiple range test showed that microleakage of sealant with acid etch and tooth preparation and compomer with acid etch, bonding agent and tooth preparation were statistically significantly less than that of compomer with bonding agent and no tooth preparation (P < 0.0001) and compomer with bonding agent and tooth preparation (P < 0.01). CONCLUSIONS: Microleakage is similar when sealant with acid etching, and compomer with acid etching and bonding agent, are used with and without enameloplasty. Marginal gap is more evident in the compomer group with bonding agent and without enameloplasty. Enamel fissure penetration is better when enameloplasty and acid etching are used.

Acid Etching, Dental↗

A comparison of student performance in a simulation clinic and a traditional laboratory environment: three-year results.

With simulation clinics, dental schools have improved their preclinical laboratories to provide a more realistic clinical teaching environment. However, there is very little data to support the assumption that these facilities actually improve student performance of technical skills. This study compared the scores of two fixed preparations for full cast crowns by third-year dental students. One of the preparations was made in the simulation clinic manikin, and the other was prepared on the bench top. Three prosthodontic faculty members scored the preparations in the areas of occlusal reduction, axial reduction, resistance and retention, and margination. The study also compared the performance of three classes of dental students: one class with no experience in the simulation clinic, one with one year of experience, and one with two years of experience. The amount of time since completing the fixed prosthodontics course among the students was also evaluated. This was done because the third-year students at the University of Iowa rotate through a series often-week clerkships rather than a comprehensive care model. (Therefore, not all students start clinical prosthodontics at the same time.) In addition, all student participants completed a questionnaire that addressed their perception of their clinical readiness prior to treating their first fixed prosthodontic patient. When we compared the classes of years 1, 2, and 3 by average preparation score, we found a significant difference among the scores for teeth prepared on the bench top (p = 0.0001) but not for the teeth prepared in the mannequin (p = 0.1176). For Year 1 (no simulation clinic experience), the amount of elapsed time following completion of the fixed prosthodontic course was not significant for the tooth prepared on the bench top or in the manikin (p = 0.57113 and 0.0661). For Year 2 (one year of simulation clinic experience), the elapsed time following completion of the fixed prosthodontic course was significant for the tooth prepared on the bench top (p = 0.0482), but it was not significant for the tooth prepared in the manikin (p = 0.2968). For Year 3 (two years of simulation clinic experience), the amount of elapsed time following completion of the fixed prosthodontic course was not significant for the tooth prepared on the bench top or in the manikin (p = 0.7275 and 0.6007). The questionnaire revealed that, in general, the majority of the students perceived their clinical readiness as more than adequate. These results are mixed in that students with more bench top experience scored better on the bench top, and students with more manikin experience scored equally in both environments.

Analysis of Variance↗

Novel porcelain laminate preparation approach driven by a diagnostic mock-up.

UNLABELLED: One critical step in the porcelain laminate technique is the achievement of sufficient ceramic thickness. At least two different strategies for tooth preparation can be found in the literature: (1) earlier simplified techniques included the use of depth cutters guided by the existing tooth surface-however, that approach did not take into consideration alterations of the tooth owing to aging, wear, or loss of enamel and thus led to greater risks for dentin exposures; (2) more recent and sophisticated methods have integrated an additive diagnostic procedure (ie, wax-up or mock-up) to compensate for tooth aging or severe existing loss of tooth substance. This approach allows for more enamel preservation and, as a consequence, more predictable bonding, biomechanics, and esthetics. The present article illustrates in detail the latest development in tooth preparation for porcelain laminates. This technique combines the time efficiency of earliest methods with the rationale and diagnostic foundations of the more recent techniques. CLINICAL SIGNIFICANCE: Using this new laminate porcelain preparation approach, clinicians should be able to produce not only more accurate preparations, but also higher-quality tooth preparations in a time-efficient fashion.

Composite Resins↗

Direct composites in a contemporary restorative practice.

Composite resins can restore teeth to natural appearance and function while conserving tooth structure. Adhesive technology has revolutionized tooth preparation, allowing minimum tooth removal without large retentive undercuts. Today's dental adhesives have strong bond strengths, bonding to both dentin and enamel. Many are available with fewer components, simplifying application. Composites are available in a large variety of shades in both microhybrids and microfills. Microhybrids are used in areas that need strength, whereas microfills are used in regions that require high surface gloss or decreased stiffness. Composites should be placed to natural form and shades before curing; finishing primarily involves polishing using silicone abrasives. Composites can be used to restore incisal edges, close diastemas, veneer facial surfaces, and repair defects, making teeth appear natural.

Compliance↗

Improving the fit of crowns with die spacers.

This investigation studied the dependence of seating crowns on the thickness of layers of spacers applied to dies. Extracted molars were prepared to designated taper angles. Artificial stone dies were prepared in polyether impressions of tooth preparations and covered with one to five layers of new or old spacer material in a predetermined manner. Wax patterns were invested to obtain a uniform and low expansion. Crowns were cast, luted to the teeth, invested in acrylic resin, ground parallel to the axes of the teeth, and inspected microscopically. The average thickness of layers of new and old spacer material was determined. The application of spacers up to the shoulder margins of dies decreased the elevation of the casting above the margin of the tooth preparation until an average minimum elevation above the shoulder of the preparation was obtained. A further increase in the spacer thickness did not affect the elevation, but increased the cement thickness at the axial walls. The average minimum elevation results mainly from individual protrusions on the casting surface. The optimum thickness of the spacer results in the minimum elevation at the margin together with a low cement thickness at the axial walls. Leaving the cervical part of the axial walls near the margin uncovered with spacer negates the effect of a thick spacer on the remaining die surface almost completely and is therefore contraindicated.

Cementation↗

Ensuring retention for crowns and fixed prostheses.

Crowns and fixed prostheses are well-proven, accepted and routinely used restorations. However, they occasionally come loose from tooth preparations. Many things can cause these failures. In this article, I have discussed the following reasons for lack of adequate retention of crowns and fixed prostheses: inadequate tooth preparation; too much trust in dentin bonding agents and lack of adequate tooth buildup; tooth preparations that lack irregularities; improper selection of cements; and lack of postoperative occlusal adjustment.

Crowns↗

Effect of convergence angle on retention of resin-bonded retainers cemented with resinous cements.

STATEMENT OF PROBLEM: Poor retention is a common cause of failure for resin-bonded restorations. PURPOSE: This study evaluated the effect of the convergence angle of tooth preparations on retention of resin-bonded restorations, luted with adhesive and conventional resinous cements. MATERIAL AND METHODS: A total of 80 posterior retainers with four different tooth preparation angles were cemented with two different resinous cements, and retentive strength was measured. RESULTS: The results indicated that (1) increased tapering of tooth preparations resulted in loss of retention and this variable was statistically significant for both cements used when convergence angles exceeded 10 degrees and (2) sandblasted nickel-chromium retainers, combined with adhesive resins, should provide sufficient retention for posterior resin-bonded fixed partial dentures.

Adhesives↗

Potassium nitrate-zinc oxide eugenol temporary cement for provisional crowns to diminish postpreparation tooth pain.

Pulpal injury commonly occurs with tooth preparation for complete fixed partial dentures. This can be documented by the substantial incidence of pain after tooth preparation. In this study, a 4% potassium nitrate-zinc oxide eugenol temporary cement was used to secure provisional crowns over recently prepared teeth and it significantly reduced the incidence and severity of pain after tooth preparation and impression taking.

Adult↗

Accuracy of intraoral data acquisition in comparison to the conventional impression.

The achievable accuracy is a decisive parameter for the comparison of direct intraoral digitization with the conventional impression. The objective of the study was therefore to compare the accuracy of the reproduction of a model situation by intraoral digitization vs. the conventional procedure consisting of impression taking, model production, and extraoral digitization. Proceeding from a die model with a prepared tooth 16, the reference data set of the teeth 15, 16 and 17 was produced with an established procedure by means ofextraoral digitization. For the simulated intraoral data acquisition of the master model (Cerec 3D camera, Sirona, Bensheim), the camera was fastened on a stand for the measurement and the teeth digitized seven times each in defined views (occlusal, and in each case inclined by 20 degrees, from the mesio-proximal, disto-proximal, vestibular and oral aspect). Matching was automated (comparative data sets B1-B5). A clinically perfect one-step putty-and-wash impression was taken from the starting model. The model produced under defined conditions was digitized extraorally five times (digi-SCAN, comparative data sets C1-C5). The data sets B1-B5 and C1-C5 were assigned to the reference data set by means of best-fit matching and the root of the mean quadratic deviation (RMS; root mean square) calculated. The deviations were visualized, and mean positive, negative and absolute deviations calculated. The mean RMS was 27.9 microm (B1-B5) or 18.8 microm (C1-C5). The mean deviations for the prepared tooth were 18 microm/-17 microm (B1-B5) and 9 microm /-9 microm (C1-C5). For tooth 15, the mean deviations were 22 microm/-19 microm (B1-B5) and 15 microm/-16 microm (C1-C5). The intraoral method showed good results with deviations from the CAD starting model of approx. 17 microm, related to the prepared tooth 16. On the whole, in this in-vitro study, extraoral digitization with impression taking and model production showed higher accuracy than intraoral digitization. Since the inaccuracies in the conventional impression under real clinical conditions may be higher than the values determined above, a comparison under clinical conditions should be performed subsequently.

Bicuspid↗

A new technique for generating a computer-aided design and computer-integrated machining crown: case report.

A new technique for producing a Computer-Aided Design and Computer-Integrated Machining Ceramic Reconstruction crown is presented. After completion of the tooth preparation, an "optical" impression of the tooth was made with a charged couple device camera, and the electronic image was transferred to a computer screen. The "proposed" crown was electronically designed on the screen by the operator, and a proper prefabricated ceramic block was selected and used as milling material. A miniature milling machine then fabricated the crown from the ceramic block. The marginal adaptation and the contour of the crown were verified, and an external shading technique was utilized to improve the esthetics. The prepared tooth and crown were acid-etched, and the crown was cemented with a dual-curing composite luting agent. Once bonded in place, the occlusion was adjusted and the crown polished and finished. The advantage of this technique is that it eliminates the traditional laboratory casting procedure and corresponding laboratory fee while utilizing materials with superior physical properties for maximum strength and esthetics.

Adult↗

Titanium dental copings prepared by a powder metallurgy method: a preliminary report.

PURPOSE: The purpose of this study was to determine if the Procera pressed-powder method can be used to fabricate titanium copings. MATERIALS AND METHODS: Commercially pure titanium powder was used to prepare the copings. The powder was pressed onto an enlarged tooth preparation die of aluminum using cold isostatic pressing. The outer shape of the coping was formed using a Procera milling machine, and the copings were vacuum sintered. RESULTS: Titanium copings could be prepared using this method. The density of the sintered copings reached 97% to 99%+ of theoretic density, and the copings showed ductile behavior after sintering. Enlarging the tooth preparation die to compensate for the sintering shrinkage could optimize the final size of the copings. CONCLUSION: Ductile and dense titanium dental copings can be produced with powder-metal processing using cold isostatic pressing, followed by milling and sintering to final shape. The forming technique has, if properly optimized, a potential of becoming a more cost-efficient production method than spark erosion.

Cold Temperature↗

Restoring tetracycline-stained teeth with a conservative preparation for porcelain veneers: case presentation.

Tetracycline exposure in utero and in early childhood often results in intrinsic tooth staining that varies in severity based upon timing, duration, and form of tetracycline administered. Traditionally, dental aesthetics compromised by tetracycline staining have been restored with modalities requiring aggressive tooth preparation. In this case involving a patient with extremely severe staining of healthy and aesthetically shaped dentition, a conservative tooth preparation strategy and porcelain veneers were utilized to preserve tooth shape and arch form while restoring natural color.

Adult↗

Pulpal evaluation of teeth restored with fixed prostheses.

The literature demonstrates that each of the elements of crown fabrication involves possible and probable insult to the pulpal tissues of the tooth. Preparation of the tooth can result in pulpal inflammation or even burn lesions. The impression technique can result in reduction of the odontoblastic layer caused by drying of the dentin. Temporary coverage of the preparation involves the use of self-curing resins and temporary cements, both of which can irritate the pulp. The final restoration is attached with cements that are often implicated in pulpal irritation. Dental caries and the procedures necessary to remove it and restore the tooth before preparation for a fixed prosthesis can injure the pulp. This study was done to evaluate the effects of complete coverage fixed prosthetic restorations on the dental pulp. A recall letter was mailed to 1221 patients who had received a fixed partial denture or single crown during the years 1984-1988. One hundred thirty patients were examined. Each tooth was evaluated for pulpal health, periodontal integrity, and clinical acceptability of the restoration. Of the 603 teeth examined, 166 had undergone root canal therapy before placement of the restoration, leaving 437 that were crowned while vital. Of these, 25 (5.7%) were in need of root canal therapy or had undergone root canal therapy after cementation of the fixed prosthesis.

Crowns↗

Accuracy of casts generated from dual-arch impressions.

STATEMENT OF PROBLEM: Dual-arch trays are often used to make simultaneous impressions of a prepared tooth and the opposing teeth. Many dentists are concerned with the accuracy of the casts generated from this type of impression. PURPOSE: The purpose of this investigation was to compare the accuracy of stone casts of a prepared tooth generated using 2 types of dual-arch impression tray/impression material combinations. MATERIAL AND METHODS: The maxillary left first molar on a dentoform mounted on an articulator was prepared for a full-coverage gold crown. Ten impressions were made with either a plastic (P) or metal (M) tray and a polyether (PE) or vinyl polysiloxane (VPS) impression material. Each impression was cast in improved dental stone, and the buccolingual dimension of the die was measured at the midpoint of the buccal and lingual gingival margins. The prepared tooth (T) served as the control. The data were analyzed using a 2-factor analysis of variance (ANOVA) alpha=.05. RESULTS: The P/VPS combination (10.673 mm) produced the largest die, followed by P/PE (10.602), T (10.508), M/PE (10.484), and M/VPS (10.472). The 2-factor ANOVA showed a significant difference between the tray types but not between the impression materials. CONCLUSION: The metal trays produced dies smaller than the tooth, and the plastic trays produced dies that were larger.

Dental Impression Materials↗