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6CCVD Research

Influence of the Operator`s Experience, Working Time, and Working Position on the Quality of the Margin Width - In Vitro Study

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2023-01-27
JournalMedicina
AuthorsKinga MĂĄria JĂĄnosi, Diana Cerghizan, Zsigmond RĂ©tyi, AlpĂĄr KovĂĄcs, Andrea SzĂĄsz
InstitutionsUniversitatea de Medicină, Farmacie, Științe și Tehnologie „George Emil Palade” din TĂąrgu Mureș
Citations3
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study investigated the factors influencing the quality (width) of heavy chamfer finish line preparations, a critical step for fixed ceramic restorations. The research compared results achieved by experienced university lecturers (T1, T2) and inexperienced dental students (t1, t2) across varying working times and patient positions.

  • Core Objective: To determine if operator experience, working time (tiredness), or patient position (sitting/supine) affect the ability to achieve the target 0.5 mm heavy chamfer width.
  • Key Finding on Experience: Operator experience significantly influences the width and stability of the prepared finish line (p < 0.0001). Experienced operators (T1, T2) showed more stable results but often removed excess tissue, exceeding the 0.5 mm target.
  • Key Finding on Students: Student t1 achieved the closest overall mean width (0.45 mm) to the target 0.5 mm, while student t2 and experienced operator T2 had the widest preparations (0.84 mm and 0.79 mm, respectively).
  • Working Conditions: Daytime or weeklong tiredness and patient position (sitting vs. supine) were found not to affect the width quality of the heavy chamfer preparation.
  • Methodology Impact: The preparation depth is influenced by the methodology of instruction and the instructor’s work style, suggesting training standardization is crucial.
  • Clinical Relevance: Achieving the precise 0.5 mm width is mandatory for minimally invasive preparations, ensuring material strength and preventing fracture in modern monolithic zirconia crowns.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Target Heavy Chamfer Width0.5mmIdeal width for minimally invasive ceramic restorations.
Clinically Acceptable Marginal Gap< 120”mStandard for fixed restorations (McLean and Von Fraunhofer).
Diamond Bur TypeRound-end tapered 016N/AUsed for preparation.
Diamond Bur Taper3°Standard taper of the rotary instrument.
Diamond Bur Active End Diameter1.1mmHalf the diameter (0.55 mm) was used to guide the 0.5 mm chamfer.
Total Preparations Analyzed160N/A40 teeth prepared by each of the 4 participants.
T1 Mean Chamfer Width (Overall)0.559125mmExperienced operator (closest to target 0.5 mm).
t1 Mean Chamfer Width (Overall)0.450000mmInexperienced operator (prepared less invasively).
T2 Mean Chamfer Width (Overall)0.79625mmExperienced operator (high tissue removal).
t2 Mean Chamfer Width (Overall)0.840500mmInexperienced operator (highest tissue removal).
Statistical Significance (ANOVA)p < 0.0001N/AExtremely significant variation among column means (experience).

Key Methodologies

Section titled “Key Methodologies”
  1. Material and Setup: Forty artificial left upper-second molars were prepared in Planmeca simulators. Teeth were fixed in standardized positions.
  2. Instrument Control: A new round-end tapered 016 diamond bur (1.1 mm diameter, 3° taper) was used for each individual preparation to eliminate efficiency variables associated with bur reuse.
  3. Preparation Technique: Operators aimed for a minimal taper close to 6° and maintained the diamond bur parallel to the tooth axis to avoid undercuts and achieve the heavy chamfer finish line equigingivally.
  4. Working Conditions Protocol: Preparations were conducted across five days (Monday to Friday) at specific times (morning/evening) to simulate varying levels of tiredness. Operators worked from the 9-11 o’clock area (ISO Standard 11226).
  5. Patient Position Simulation: Preparations were performed under two simulated patient positions: sitting and supine.
  6. Reference and Calibration: An unprepared molar was marked at the prosthetic equator. Prepared teeth were placed in this reference position and photographed using a Canon D5300 camera with a macro lens. A ruler was placed parallel to the finish line for digital calibration.
  7. Digital Measurement: Measurements were performed using Image-Pro Insight software. Chamfer width was measured three times at eight standardized reference points (distance between the chamfer’s outer edge and the axial wall’s inner edge).

Commercial Applications

Section titled “Commercial Applications”

The findings are highly relevant to the standardization and quality control of dental procedures, particularly in the context of advanced ceramic materials.

  • Dental Training Simulators: Validates the efficacy of haptic and traditional simulators for developing fundamental skills, provided they are coupled with objective digital assessment tools (e.g., intraoral scanners or digital analysis software like Image-Pro Insight).
  • Zirconia and All-Ceramic Restorations: Provides engineering data supporting the necessity of precise 0.5 mm preparation depth for monolithic zirconia crowns to ensure biomechanical performance and fracture resistance under maximum mastication forces (up to 850 N).
  • Rotary Instrument Manufacturing: Confirms the utility of specific bur geometries (round-end tapered diamonds) designed to achieve predictable, standardized finish lines, minimizing the risk of hard tissue damage.
  • Ergonomic Equipment Design: Supports the current ISO standards for operator working positions (9-11 o’clock area), confirming that preparation quality is maintained regardless of whether the patient is sitting or supine, simplifying equipment requirements.
  • Digital Dentistry Workflow: Reinforces the need for integrating digital technology (magnification, digital scanning, and software analysis) into clinical practice to objectively evaluate and improve preparation precision, especially among less experienced practitioners.
View Original Abstract

Background and Objectives: Appropriate tooth preparation is mandatory to obtain a perfect marginal fit of fixed restorations. The heavy chamfer is the most commonly used finish line, especially for minimally invasive tooth preparation. The aim of the study was to compare the width of the finish line obtained during tooth preparation performed by experienced (university lecturers) and inexperienced persons (dental students) in different working times and positions. Materials and Methods: Forty left upper-second molars were prepared on the simulator by each participant, totalizing 160 prepared teeth. A new round-end tapered diamond was used to obtain the 0.5 mm width of the heavy chamfer. The prepared teeth were photographed using a Canon D5300 camera with a macro lens attached to a tripod. The measurements were made with the Image-Pro Insight software selecting the same eight reference points. From these points, perpendicular lines were drawn above the finish line to the axial walls and the distance between the chamfer’s outer edge and the axial wall’s inner edge was measured. GraphPad Instat and NCSS Dowson Edition software were used. The statistical significance was set at p < 0.05. The mean (M) and standard deviation (SD) were calculated. The used tests: one sample t-test, ANOVA test, and Tukey-Kramer Multiple Comparisons Test. Results: Statistically significant differences were obtained according to the experience of the participant, preparation time, patient’s position, and the chamfer width on the prepared tooth different surfaces. Conclusions: Daytime or weeklong tiredness and patient position do not affect the width of the heavy chamfer prepared by experienced and inexperienced persons. The experience and the operator’s working position influence the width of the prepared finish line.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2008 - Consistency of labial finish line preparation for metal ceramic crowns: An investigation of a new bur [Crossref]
  2. 2015 - Iatrogenic damage to periodontium by restorative treatment procedures: An overview [Crossref]
  3. 2021 - Influence of manufacturing technique on marginal fit of cobalt chromium restorations: An in-vitro study [Crossref]
  4. 1971 - The estimation of cement film thickness by an in vivo technique [Crossref]
  5. 2003 - A comparison of the depths produced using three different tooth preparation techniques [Crossref]
  6. 2007 - Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM [Crossref]
  7. 2008 - Effect of preparation angles on the precision of zirconia crown copings fabricated by CAD/CAM system [Crossref]
  8. 1980 - Periodontal conditions and carious lesions following the insertion of fixed prostheses: A 10-year follow up study
  9. 1976 - Periodontal conditions in patients 5 years following insertion of fixed prostheses [Crossref]
  10. 2009 - Improving your margins

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