Effect of package weight on the total amount of die stone used annually in a dental school.

PURPOSE: This study compared the total amount of Type IV dental stone (die stone) used annually by dental students when they were supplied with either 70-g or 140-g preweighed packages of die stone. MATERIALS AND METHODS: In September 1994, all the bulk containers of die stone were removed from the student dental clinic and laboratories and replaced by 70-g preweighed packages of die stone (Silky-Rock; Whip Mix, Louisville, KY). At the end of August 1998, all 70-g packages of die stone were removed from the student dental clinic and laboratories. The average annual number of 70-g packages of preweighed die stone used by the students from 1994 to 1998 was calculated. From September 1998 to the end of August 1999, only 140-g preweighed packages of die stone (Silky-Rock) were supplied to the students. The number of the 140-g packages of preweighed die stone and total weight used by students during this period were calculated and compared with the average annual number of 70-g preweighed packages of die stone used during the 1994-1998 period. RESULTS: From September 1994 to August 1998, the students used an annual average of 4060 +/- SD 250 of the 70-g packages (284.2 +/- 17.5 kg per annum). From September 1998 to August 1999, the students used 3360 of the 140-g packages (470.4 kg). CONCLUSIONS: Although the students used in total 700 fewer of the 140-g die stone packages per annum than the annual average number of 70-g packages, they used 186.2 kg (65.5%) more die stone when supplied with the 140-g packages.

Interchangeability of two semiadjustable articulators.

PURPOSE: Interchangeability between articulators allows mounted casts to be transferred accurately from one articulator to another. The purpose of this study was to evaluate the interchangeability of 109 new, unused interchangeable articulators in the centric position. MATERIALS AND METHODS: The interchangeability of 38 unused Whip Mix model #2240 and 71 unused model #3040 semiadjustable articulators was evaluated using the Whip Mix #2245 check system as the standard. Vertical discrepancies between the check system cylinders were also measured. RESULTS: Within the standard for interchangeability established by the Whip Mix #2245 check system (< 94 microns horizontal discrepancy), 101 (93%) of 109 articulators were interchangeable (34 were model #2240 and 67 were model #3040). Overall, the amount of vertical space between the check system cylinders was < or = 52 microns in 99.4% of the model #2240 articulators and 99.7% of the #3040 articulators. CONCLUSION: New, unused Whip Mix model #2240 and #3040 articulators are potentially interchangeable in the centric position.

Margin adaptation of indirect composite inlays fabricated on flexible dies.

STATEMENT OF PROBLEM: Indirect composite restorations can be made in 1 appointment using a flexible die. Interactions between different impression materials and flexible die materials may affect the accuracy of fit and margin adaptation of the restoration. PURPOSE: This study compared the margin adaptation of composite inlays made using the following 5 impression/flexible die material combinations; condensation silicone/polyvinyl siloxane (CS/PVS), wash viscosity polyvinyl siloxane/medium or heavy viscosity polyvinyl siloxane (PVS/PVS), irreversible hydrocolloid impression/medium viscosity polyvinyl siloxane (IH/PVS), wash viscosity polyvinyl siloxane impression/polyether (PVS/PE), with composite inlays made using a control system of a wash viscosity polyvinyl siloxane impression and a type IV stone die. MATERIAL AND METHODS: For each test and control system, 10 impressions were made of a class II composite inlay preparation in a metal master die. One die was made from each impression and one composite inlay was made and finished on each die (a total of 60 inlays). Inlays were placed on the master die and the margin opening at the buccal, distal, and gingival sites was recorded with a measuring microscope (x40 magnification). RESULTS: The overall mean +/- SD margin openings of inlays made from the systems were as follows: PVS wash/PVS heavy viscosity 149.5 +/- 107. 4 microm; PVS wash/PVS medium viscosity 87.4 +/- 63.0 microm; IH/PVS medium viscosity 76.7 +/- 48.9 microm; CS/PVS 73.3 +/- 48.7 microm, PVS wash viscosity/PE 64.0 +/- 44.3 microm, PVS wash viscosity/stone 53.9 +/- 48.3 microm. Composite inlays made using the PVS wash viscosity/PVS heavy viscosity system had significantly larger distal, gingival, and overall mean margin openings than all other inlays (ANOVA and Fisher PLSD test; P =.05). The separating medium required between some impression and die materials did not work consistently. Composite inlays fabricated on dies made of material different than the impression material had mean buccal, distal, gingival, and overall margin openings < or =100 microm. CONCLUSION: Composite inlays made on the CS/PVS, IH/PVS medium viscosity, PVS wash viscosity/PE flexible dies, and control PVS wash viscosity/stone dies had statistically similar (P =.05) mean buccal, distal, gingival, and overall mean margin openings that were < or =100 microm. Composite inlays made on dies that were made of the same type of material as the impression material (PVS/PVS) had mean gingival margin openings >100 microm that were significantly larger than all other systems tested (P =.05).

Use of discriminant and regression analyses to modify a clinical certification board examination.

The National Dental Examining Board of Canada (NDEB) conducts mandatory, high stakes, pass/fail, certification examinations for dental licensure. One of these examinations was a seven-part, simulated clinical examination in which candidates were required to perform procedures on typodonts. These requirements were two intracoronal and two extracoronal preparations, an amalgam restoration, a provisional crown, and a diagnostic wax-up. Feedback from candidates and examiners indicated that one or more of the requirements may not have been contributing effectively to the overall evaluation of candidates. The NDEB's Clinical Examination Committee therefore requested that an in-depth statistical analysis be performed to identify potential areas of concern and to provide a basis for modifying the examinations. The results of two examination sessions with a total of 168 candidates were subjected to both a discriminant and a logistic regression analysis. Every candidate had results for each of the seven requirements, and no candidate participated in both sessions of the examination. The discriminant analysis revealed that six of the seven requirements could be used to reliably assign examinees according to their true pass/fail classifications. Stepwise discriminant analysis resulted in a 98.81 percent classification success rate with a corresponding 2.50 percent false-positive classification error rate. The logistic regression analysis showed that five components correctly predicted 99.40 percent with a 1.25 percent false-positive rate. The Clinical Examination Committee concluded that one requirement (diagnostic wax-up) should be eliminated and that a second requirement (PFM preparation) be significantly modified and reevaluated. This study demonstrates the usefulness of statistical methods in the analysis and modification of a clinical certification board examination.

Comparison of the surface detail reproduction of flexible die material systems.

STATEMENT OF PROBLEM: Flexible die materials have been introduced to facilitate the fabrication of indirect provisional or definitive restorations in 1 appointment. PURPOSE: This study compared the surface detail reproduction of 7 potential flexible die materials when used in combination with 7 elastomeric impression materials. METHODS: Surface detail reproduction of 17 impression material/flexible die material systems was compared with a control system containing an elastomeric impression material and a Type IV dental stone. Test dies of each system were prepared in a random order with the American Dental Association apparatus for testing detail reproduction, compatibility, and dimensional stability. RESULTS: One flexible die system had better surface detail reproduction than the control stone die, other systems had similar or worse reproduction. Surface detail reproduction was adversely affected when a separator was required between the impression and flexible die material. CONCLUSIONS: Impregum F die material with Extrude Light impression material produced better surface detail reproduction than the control dies. Impregum F impressions were incompatible with Blu-Mousse, Impregum F, or Imprint die materials. Polyvinyl siloxane impressions were incompatible with polyvinyl siloxane dies unless a separator was used. When a separator was used, the surface detail reproduction was not as good as the control die system or the Extrude Light impression material/Impregum F die material combination.

Modifications to the National Dental Examining Board of Canada's certification process.

Following a lengthy and intense consultation with stakeholders, and an analysis of the present certification process, the National Dental Examining Board of Canada (NDEB) and the 10 provincial licensing authorities recently approved major changes to the certification process for dental licensure in Canada. As of January 1997, graduates of dental programs accredited by the American Dental Association's Commission on Dental Accreditation (ADA Commission) must complete successfully the same examinations as graduates of programs accredited by the Commission on Dental Accreditation of Canada (CDAC) to be licensed to practice in Canada. In addition, NDEB's examination system for graduates of dental programs that are not accredited by CDAC or the ADA Commission (i.e. international programs) will be discontinued on December 31, 1999. As of January 1, 2000, graduates of non-accredited programs will be required to complete a CDAC accredited, university-based qualifying program to be eligible to participate in the same certification process as graduates of ADA Commission and CDAC accredited dental programs.

Results of the National Dental Examining Board of Canada written examination and implications for certification.

In 1994, following a request from the ten Provincial Licensing Authorities, the National Dental Examining Board of Canada (NDEB) implemented significant changes to the certification process for dentists seeking a license to practice in Canada. Prior to 1994, graduates of accredited Canadian dental programs were certified without further examination while graduates of United States and other international programs (non-Canadian, non-U.S.) were required to complete successfully a written and three-phase clinical certification examination. Changes implemented in 1994 required graduates of accredited Canadian programs to take both a Written and Objective Structured Clinical Examination (OSCE) Examination. The analysis of the results of the Written Examination for all candidates over the 1994-1996 period supports the following conclusions. There was no meaningful difference in performance of graduates across the ten Canadian dental programs; there was a small difference between the performance of graduates of Canadian and U.S. programs; and Canadian and U.S. graduates performed significantly better than graduates of other international programs. This level of candidate performance and changes to the respective accreditation processes supported the formal agreement providing reciprocal recognition of dental accreditation in Canada and the United States. As of January 1, 1997, graduates of dental programs in Canada and the United States are required to take the same certification examination while international graduates are required to complete a different certification process. These changes to the certification process were ratified by all ten Provincial Licensing Authorities, therefore maintaining a system of national portability for dental licensure in Canada that does not require preclinical or clinical board examinations for graduates of accredited North American dental programs.

Certification of competence: a national standard for dentistry in Canada.

After consulting a large community of interested parties, the National Dental Examining Board of Canada (NDEB) and the provincial licensing authorities recently made significant changes to the certification process for dentists in Canada. This paper provides a chronology of the evolution of national certification and a summary of the present certification processes for graduates of both accredited and non-accredited programs.

Clinical evaluation in prosthodontics: practical methods to improve validity and reliability at the undergraduate level.

The potential causes of reliability and validity problems with traditional methods of evaluating a student's clinical prosthodontic skills are reviewed. Practical methods of evaluating critical skills in a reliable and valid way are presented. These methods include clinical tests using written criteria and anonymous examiners, skills assessment by faculty members, patient-based written examinations, and bell ringer examinations.

The dimensional accuracy of 12 impression material and die stone combinations.

This study determined the dimensional accuracy of dies made using a combination of four impression materials and three Type IV die stones. A metal die was prepared for a molar complete cast crown, and 10 stone replicas were made using 12 different combinations of impression materials and die stones. The distances between reference points on the metal and stone dies were measured in three directions with a traveling microscope. Analysis of variance and Duncan's MR comparisons (P less than or equal to .05) showed that all of the stone dies were larger than the metal die. Although there were significant differences between some of the impression material/die stone combinations, all of the stone dies were measured to be within 9 microns of each other. No one impression material/die stone combination consistently produced the smallest or largest die in the three measured directions.

Use of mouthguards during tooth preparation for patients with extreme tooth hypersensitivity.

During tooth preparation, the air and water from a dental handpiece occasionally cause painful stimulation of hypersensitive teeth. Use of mouthguards may be an alternative for the management of patients with tooth hypersensitivity.

Potential errors when using a computerized pantograph.

This study determined the effect on articulator settings of using an arbitrary hinge axis as compared with the terminal hinge axis in orienting a computerized pantograph on a patient. The effect of an error in measuring the reference plane angle or clutch angle was also determined. Two subjects were pantographed 30 times by using the terminal hinge axis and 30 times by using the arbitrary hinge axis. Statistically the articulator settings obtained by using the arbitrary hinge axis and the terminal hinge axis were different, but the difference was small. One subject was pantographed on 18 occasions by using different reference plane angle and clutch angle settings. Analysis showed that 1-degree change in the reference plane angle setting produced approximately 0.9-degree change in the protrusive and orbiting path articulator settings. A 1-degree change in the clutch angle setting produced approximately 0.9-degree change in the progressive side shift settings. It was concluded that the terminal hinge axis should be used as the posterior reference point and the reference plane angle and clutch angle should be carefully recorded.