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PubMed1982

Photoelastic stress analysis of cast-gold endodontic posts.

Two-dimensional photoelasticity was used to compare stresses generated upon loading of cast gold endodontic posts of two different diameters. Ten models were used, five for each diameter size tested. The models were constructed to simulate maxillary central incisors. Drill bits were used to prepare the root canal, and after root canal preparation was completed the post preparations were constructed using the Parapost system. The gold posts, made of type III gold, were cast using the Beauty Cast technique. A composite core was then placed on each of the posts to be tested. These models were positioned in a circular polariscope and vertical loads of 30 and 60 pounds were applied to each of the models, with the fringe patterns photographed immediately after each load was applied. The stresses were evaluated by determining the maximum fringe order in the simulated root and periodontium of the model. The results of this study suggest that (1) the diameter of a post with a core affects the magnitude of stress, (2) stress generally increases as post diameter increases, and (3) stress increases as the vertical load increases. It seems advisable to restrict the diameter of the post used in providing support for restorations, particularly when large occlusal for forces are exerted by the patient. The use of smaller diameter posts reduces the stresses exerted upon the dentin of the tooth and the tooth supporting structures, limits the amount of tooth material removed during preparation and, possibly, aids operative procedures by limiting the amount of tooth preparation.

Crowns↗
PubMed2003

A technique to determine a desired preparation axial inclination.

The guidelines recommended in the literature for the convergence angle of a crown preparation vary from 3 to 24 degrees. There is a lack of guidelines on techniques to achieve a specific axial inclination. The purpose of this article was to present a practical technique, with a diamond rotary cutting instrument of known axial inclination, to determine the diamond rotary cutting instrument angulations required to achieve the desired axial inclination of a preparation.

Crowns↗
PubMed1999

Ceramic restorations for posterior teeth: guidelines for the clinician.

UNLABELLED: Metal-free ceramic restorations are increasingly popular for restoring posterior teeth. These restorations are generated through a variety of techniques (e.g., CAD-CAM, copy-milling, heat-pressing, and firing). When appropriately indicated and made, ceramic inlays or onlays can be reliable and provide a highly serviceable restoration. The aim of this article is to review and present updated information regarding indications, restorative technique, and maintenance for this class of restorations, with emphasis to fired ceramic inlays or onlays. The information presented is based on 15 years of controlled clinical experience with this category of restorations. Clinical cases that represent some applications also are presented. CLINICAL SIGNIFICANCE: The fired ceramic inlay/onlay technique is presented as a viable option for the esthetic and adhesive restoration of posterior teeth.

Bicuspid↗
PubMedDate not supplied

Core restoration for crown preparation.

This article will review the relevant literature fom 1991-2003, a period of time when adhesive resin luting materials became available and luting crowns with zinc phosphate cements decreased. The review wtill look at the principles suggesting when a core should be placed, what core materials function best, preparation design with a core, luting material choice with a core, and results of clinical trials. Amalgam cores are regarded as the strongest material, best able to withstand adverse stress and restore teeth having the greatest loss of tooth structure. Composite resins, whether chemically cured or light cured, reinforced or not, appear best capable of core restorationfor moderately broken down teeth. Glass ionomer materials are considered too weak to withstand stress as a core material, but are recommended as a base material tofill in undercuts and improve the accuracy of impression and fit of a crown.

Composite Resins↗
PubMed2004

Effect of preparation convergence on retention and seating discrepancy of complete veneer crowns.

The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0 degrees to 70 degrees and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4.58 +/- 1.13 to 73.13 +/- 78.32 microm. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4.03 +/- 0.61 to 12.12 +/- 0.33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0.62), and retention (r = -0.91). Complete veneer crown retention and marginal discrepancy were influenced by the preparation convergence design.

Cementation↗
PubMed2003

Crowns revisited.

This paper overviews recent changes to making crowns. For the most part it presents clinically relevant information using examples where necessary. The paper will act as a useful reminder for the techniques involved with crown preparations and the choices of materials available.

Cementation↗
PubMed1999

Assessing the quality of shoulder preparations for metal ceramic crowns.

Previous work by the authors indicates a tendency for academic clinicians to under prepare and over angle shoulder preparations for metal ceramic crowns. This has implications for the final restoration in terms of contour, appearance and strength. This study analysed ninety six preparations, forty eight in vitro and forty eight in vivo, performed by six clinicians. The results show a mean shoulder width of 0.804 +/- 0.274 mm and a mean shoulder angle of 116 +/- 18 degrees for preparations performed in vitro; and 0.892 +/- 0.337 mm and 121 +/- 24 degrees for preparations performed in vivo. Thus, despite recommendations that such crowns should have 1-1.5 mm, 90 degrees shoulders, many of the preparations studied here fell short of this, indicating a lack of consistency in preparation geometry and adherence to the perceived 'ideal' preparation for a metal ceramic crown.

Crowns↗
PubMed2006

The efficacy of posterior three-unit zirconium-oxide-based ceramic fixed partial dental prostheses: a prospective clinical pilot study.

STATEMENT OF PROBLEM: Although zirconium-oxide-based restorations for fixed partial denture prostheses (FPDPs) are available for use, clinical studies evaluating their longevity and related complications have not been published. PURPOSE: The aim of this pilot clinical study was to assess the efficacy of zirconia-based posterior 3-unit FPDPs. MATERIAL AND METHODS: Twenty 3-unit posterior FPDPs (Lava) were placed in 16 subjects who were missing a second premolar or a first molar, met specific inclusion and exclusion criteria, and provided informed consent. All teeth were prepared in a standardized manner: occlusal reduction of 1.5 to 2 mm; axial reduction of 1 to 1.5 mm; a 1.0-mm, 360-degree rounded shoulder placed 0.5 mm subgingivally on the facial aspect and supragingivally on the lingual aspect on sound tooth structure; and rounded internal line angles. Impressions were made with vinyl polysiloxane (Express) impression material. Frameworks were fabricated using a computer-aided design/computer-assisted manufacturing technique with a retainer thickness of 0.6 mm, and a minimal connector surface area of 9 mm(2). Restorations were luted with resin-modified glass-ionomer cement (Rely X luting). Recall appointments were made after 2 weeks and 6, 12, 18, 24, and 36 months. Clinical fracture resistance, marginal discoloration, marginal adaptation, radiographic proximal recurrent decay, and periapical pathoses were assessed over time using modified Ryge criteria. The probability distributions of these variables were calculated for the baseline data as well as for recall data. RESULTS: Mean follow-up was 31.2 months. Fifteen restorations were rated Alpha in all measured parameters. Minor chipping of veneering porcelain was detected in 5 restorations rated Bravo for clinical fracture resistance and Alpha for all other assessed parameters. One restoration was rated Bravo in terms of marginal integrity at 36 months. CONCLUSIONS: Zirconia-based posterior 3-unit FPDPs performed well after short-term service.

Adult↗
PubMed1998

Combining treatment modalities for tetracycline-discolored teeth.

Tetracycline-discolored teeth that are to be restored by porcelain laminate veneers present a clinical challenge. Successfully bleaching such teeth prior to veneering will permit the clinician and technician to overcome the technical difficulties associated with masking dark teeth. This article describes a combined treatment modality in which the teeth are bleached after the preparation for porcelain laminate veneers.

Carbamide Peroxide↗
PubMedDate not supplied

A comparative, qualitative and quantitative antimicrobial efficacies of mouthrinses containing chlorhexidine gluconate and essential oils.

A project was launched to evaluate and compare antimicrobial efficacy of Hexidine and Listerine over placebo in 10 day human experimental gingivitis study. A rigid study schedule for subject compliance spanning well over 3 months was sorted out and volunteers recruited for study rinsed all the 3 assigned mouthrinses containing (a) chlorhexidine gluconate, (b) "essential oils" and (c) flavoured distilled water one after the other at certain prefixed intervals. After 10 days of assigned mouthrinse regimen, where the assigned mouthrinse was the only method practiced by the volunteers for oral hygiene, Supragingival Plaque was quantitatively and qualitatively assayed. Qualitatively supragingival plaque was assayed by Gram staining (Direct smear and Thioglycollate Broth) and growth characteristics i.e; Aerobic, Microaerophilic and Anaerobic growth was noted. Quantitatively plaque was assayed by calculating total microbial load per tooth by preparing Mafarland Nephelometer standard and Spectrophotometric analysis. It is concluded that Hexidine and Listerine exert similar antimicrobial efficacy in 10 days experimental gingivitis study. Hexidine and Listerine exert their antimicrobial influence through reduction of total Aerobes and Anaerobes reducing total microbial load per tooth by 58% and 53% respectively as compared to placebo.

Adult↗
PubMed1999

Preparing teeth to receive a removable partial denture.

The success or failure of a removable partial denture is dependent on many factors. To achieve success, the practitioner must develop and sequence a sound treatment plan based on clinical and radiographic evidence. These findings must be carefully considered in prosthesis design and mouth preparation. Particular attention must be given to the proper placement of guiding planes and well-made rest seats and the use of surveyed crowns on abutment teeth. This article describes the rationale, importance, and clinical procedures for abutment preparation for removable partial dentures.

Crowns↗
PubMed1989

Effects of the porcelain firing sequence on the bond strengths of cements.

Bond strengths for the retention of ceramic bonded to metal alloys to the tooth structure involve cavity preparation variables, cement variables and ceramic bonded to metal alloy variables. The aim of this work was to evaluate the retentive strength differences between alloy surfaces, unfired and fired, for porcelain alloys retained with different dental cement compositions. The clinical situation was stimulated by using standardized tooth preparations, extracted teeth and castings cemented with zinc phosphate and polycarboxylate cements, which were debonded on an Instron. Jelenko O, Cameo, Jelstar and Genesis II alloys were compared unfired and fired to simulate porcelain application. Fired Jelenko O casting alloy cemented with polycarboxylate cement produced the greatest bond strengths (6.0 +/- 1.0 MPa). Polycarboxylate cemented castings had greater bond strengths for all alloys whether fired or not. The only effect of firing was an improvement with Jelenko O alloys produced with both cements. All of these differences were statistically significant at the P less than 0.01 level using Tukey's post hoc evaluation. The improvements observed were related to the oxide formation on the internal surfaces of the casting and the ability of polycarboxylate cement to adhere chemically to those layers.

Chromium Alloys↗
PubMed2002

Retrieval of a foreign object from the palatal root canal of a permanent maxillary first molar: A case report.

A 12-year-old boy presented with a fractured sewing needle within the palatal root canal of a nonvital permanent maxillary first molar. The patient admitted that he had often placed a sewing needle in the tooth to relieve discomfort associated with it. A minimal amount of tooth structure was removed around the foreign object to facilitate access for K-type files. Under copious irrigation, the files were worked around the object to loosen it. The fractured needle was removed with a tweezers that had long, narrow beaks. Use of this simple technique allowed the object to be removed from the root canal with minimal damage to internal tooth structure.

Child↗