ABSTRACT
This study evaluated the influence of the type of restoration and the amount of interdental spacing on the stress distribution in maxillary central incisors restored by means of porcelain laminate veneers and direct composite resin restorations. Three-dimensional finite element models were fabricated to represent different types of restorations. Four clinical situations were considered. Type I, closing diastema using composite resin. Labial border of composite resin was extended just enough to cover the interdental space; Type II, closing diastema using composite resin without reduction of labial surface. Labial border of composite resin was extended distally to cover the half of the total labial surface; Type III, closing diastema using composite resin with reduction of labial surface. Labial border of the preparation and restored composite resin was extended distally two-thirds of the total labial surface; Type IV, closing diastema using porcelain laminate veneer with a feathered-edge preparation technique. Four different interdental spaces (1.0, 2.0, 3.0, 4.0 mm) were applied for each type of restorations. For all types of restoration, adding the width of free extension of the porcelain laminate veneer and composite resin increased the stress occurred at the bonding layer. The maximum stress values observed at the bonding layer of Type IV were higher than that of Type I, II and III. However, the increasing rate of maximum stress value of Type IV was lower than that of Type I, II and III.
Subject(s)
Dental Porcelain , Diastema , IncisorABSTRACT
Objective: To intimately assess the internal stress distribution in ceramic veneer bonding layer. Methods:Six buccolingual cross section models of the incisor restored with IPS-Empress ceramic veneer were built with the MSC/NASTRAN software. 2D-finite element method was used to analyze the stress distribution regularity of the bonding layer on the models under different functional load. Results: Stress concentration areas of ceramic veneer bonding layer were regularly located on the incisal margin and cervical margin. Under the same condition, incisal load caused highest stresse on the adhesive layer. Following the load shift from incisal to gingival area, the stress was gradually decreased.When the functional load acted on the palate margin of the restoration, the compressive stress on the bonding layer was significantly increased. Different load angle generated stress change in the bonding layer. The shear stress on adhesive layer increased following the horizontal load angle increasing close to the debonding level. Among the different incisal reduction designs there was no significant Von Mises stress variation under the same load condition. However, when the incisal edge was reduced by more than 4 mm, the tensile stresses in the bonding layer greatly increased. Conclusion: Restoration margin should be kept away from the tooth contact area, be exposed to minimal occlusion contact. The functional load should be induced to follow the tooth long axis. Edge to edge occlusion should be avoided. When incisal areas need to be altered, the incisal overlap or butt margin design will not cause any stress problem in the bonding layer. When restoring the incisal defect for more than 4 mm, the bonding agents must be selected carefully.