Contraction stress of composite resin build-up procedures for pulpless molars.
OBJECTIVE
The purpose of this study was to photoelastically evaluate contraction stresses associated with various resin composite build-up procedures for pulpless molars.


METHODS
Photoelastic models of endodontically treated mandibular molars were fabricated to simulate a preparation for a full-cast crown. The model configuration included three lateral walls, but no post space. The buildups were made with dual-curing resin composite using the following procedures: 1) bulk dual cure, 2) bulk chemical cure, 3) horizontal two increments, dual cure, and 4) indirect. Five specimens were fabricated for each condition. The stresses developed in the models were recorded photographically in the field of a circular polariscope.


RESULTS
The build-up procedures tested generated widely different stress distributions and intensities. The highest stresses were seen with the bulk dual-cure method. The slower polymerization chemical-cure group developed distributions similar to the bulk dual-cure group with a significantly lower fringe order. The two horizontal increments dual-cure techniques developed an individual group of fringes for each layer. Compared with the bulk dual-cure group, stresses around the occlusal margin were reduced by incrementalization, while fringes were more closely spaced at the line angles with a slightly lower fringe order. The indirect method demonstrated the lowest stress which extended over the smallest area.


CONCLUSIONS
Contraction stress in resin composite buildups varied significantly depending upon the procedures of fabrication. The bulk dual-cure method developed the most severe contraction stresses, while the indirect technique resulted in significantly lower contraction stresses than the other techniques tested.
Kuroe
Toshifumi
T
Section of Geriatric Stomatology, Department of Oral Health Science, Hokkaido University, Graduate School of Dental Medicine, Sapporo, Japan. kuroe@den.hokudai.ac.jp
Tachibana
Kana
K
Tanino
Yukinori
Y
Satoh
Noriyuki
N
Ohata
Noboru
N
Sano
Hidehiko
H
Inoue
Nobuo
N
Caputo
Angelo A
AA
D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003442:Crowns; D017220:Dentin-Bonding Agents / Q000737:chemistry; D004853:Epoxy Resins / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008953:Models, Anatomic; D008963:Molar / Q000473:pathology*; D010781:Photography; D011108:Polymers / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D019246:Tooth Preparation; D019553:Tooth, Nonvital / Q000503:physiopathology / Q000628:therapy*
D003188:Composite Resins; D017220:Dentin-Bonding Agents; D004853:Epoxy Resins; D011108:Polymers; D019279:Resin Cements; C074669:Clearfil Photo Bond