Assessment of Retention and Resistance Form of Tooth Preparations for All Ceramic Restorations using Digital Imaging Technique

Abstract

Aim: This in vitro study evaluated the resistance form of die preparations for all ceramic restorations and, thereby, explored the concept of effective taper and its correlation between the ideal in theory and actual in the clinical situation by analyzing the digital images of the die preparations. Materials and methods:Scanned digital images of 114 die preparations for all ceramic restorations (n = 114) were collected from a dental laboratory. All the images were also analyzed digitally using Adobe Photoshop ® software to analyze the degree of taper (angle of convergence) of each preparation and then applied the Zuckerman's circle, and the Lewis perpendicular methods were used to measure the resistance form.Results: For the current study, the overall average degree of taper was found to be 20.9° (range, 2-80°), which is more than what is recommended by most previous studies and also sharply greater than the textbook ideal of 3 to 6°. Mean degree of taper for maxillary was 17.56° (anterior-10.50°, posterior-23.7°), and for mandibular teeth, it was 25.22° (anterior-15°, posterior-28.45°). Out of the 64 analyzed images of maxillary teeth, 61 presented resistance form, while 3 were without it. Out of the 50 mandibular teeth analyzed, 38 possessed resistance form, whereas 12 were without. All the anterior teeth showed resistance form irrespective of the arch. Conclusion:The degree of taper showed a significant relationship with resistance and retention form, which was inversely Thodupuzha, Kerala India, e-mail: abhinavjoyce@gmail.com proportional to each other. The recommended "degree of taper" is not always the clinically achievable as advocated in textbooks, as it is modified by various factors in the actual clinical situation. Assessment of Retention and Resistance Form of Tooth Preparations for All Ceramic Restorations using Digital Clinical significance:The study provides scientific background regarding the relationship between the degree of taper with resistance and retention form, and the relationship was found to be inversely proportional to each other. The recommended "degree of taper" is not always the clinically achievable as advocated in textbooks, and it is modified by various modifying or limiting factors in the actual clinical situation.

Volumetric analyses of restorative crown preparations in simulated-premolar and -molar teeth

“…Thus, 12 & 16⁰ volume loss in both two forms would be expected to follow this detrimental rotational stress pattern in function, i.e., differential An additional factor to be considered in the mix is the average clinician's ability to accomplish "ideal" convergence angles in the preparation of a natural tooth. Amongst a large number of studies too numerous to be cited in this manuscript, these two citations demonstrate that both dental students 41 and experienced clinicians 42 do not have the skills to accomplish the ideal standards in everyday tooth preparation. Most can be assumed to attain 12 to 16⁰ axial wall taper in their clinical preparations on patients.…”

The Effect of the Digital Manufacturing Technique, Preparation Taper, and Cement Type on the Retention of Aged Anterior Provisional Crowns: An In Vitro Study

“…Retention and resistance forms are the features of a preparation that prevent prostheses from becoming uncemented, debonded, or cement failures [29]. Occlusal convergence may be described as the converging angle of two opposite axial walls in a given plane.…”

Effect of two Blocking Reverse Taper Preparation Methods on the Internal Fit of CAD/CAM Monolithic Zirconia Crowns (An In-vitro study)

“…12 o TOC provides the final restorations with optimal resistance and retention forms. 13,14,16,17 On the other hand, reverse taper preparation presents multiple complications, such as distortion of the final impression, uneasy seating of the final restoration. It requires overpreparation of the tooth in order to eliminate it.…”