Veerapravati et al.

Int Chin J Dent 2005; 5: 75-79.

Fracture resistance of endodontically treated premolars restoredwith different restorations
Weeraporn Veerapravati, DDS, MS,a Nattaya Vongphan, DDS,bHarnirattisai, DDS, PhD,b and Jaruma Sakdee, DDSa

Cholthacha

aDepartment of Conservative Dentistry and Prosthodontics, Faculty of Dentistry, Srinakharinwirot
bUniversity, and Department of Operative Dentistry, Mahidol University, Bangkok, Thailand
Purpose: To compare in vitro fracture resistance of endodontically treated premolars restored with bondedamalgam or resin composite.
Materials and Methods: Fifty intact and caries-free premolars that had been extracted for orthodontic treatment
were selected. All teeth were subjected to endodontic procedures and MOD cavity preparation. They were thenrandomly divided into the five following groups of ten teeth each: without restoration (control group),
intracoronal bonded resin composite restoration, intracoronal bonded amalgam restoration, cuspal coverage
bonded resin composite restoration, and cuspal coverage bonded amalgam restoration. The teeth were embeddedin poly(vinyl chloride) (PVC) blocks and subjected to compressive fracture tests. The fracture resistance wasstatistically analyzed using ANOVA and multiple comparison; Dunnett T3 test was performed at the 5% level.
Results: The cuspal coverage bonded amalgam group provided significantly highest fracture resistance (1138.94
N). The fracture resistance of intracoronal bonded amalgam restoration (279.68 N) was less than the group ofintracoronal resin composite (383.37 N) and not significantly different from that of the cuspal coverage bonded
resin composite restoration (346.19 N) and the control group (257.90 N).
Conclusion: Cuspal-coverage bonded amalgam restoration provided higher fracture resistance thancuspal-coverage bonded resin composite restoration while intracoronal bonded amalgam restoration provided
lower fracture resistance than intracoronal bonded resin composite restoration.
(Int Chin J Dent 2005; 5: 75-79.)
Key Words: endodontically treated premolar, fracture resistance, restoration.

Introduction
The success of endodontic treatment depends not only on the endodontic procedure but also on appropriate
and timely coronal restoration of the tooth.

One study has reported that failure to restore properly theendodontically treated tooth was a primary cause of endodontic failure.1 Studies showed that an endodonticallytreated tooth was susceptible to fracture.2,3 Reduction in tooth stiffness due to loss of tooth structures from caries
and endodontic or restorative procedures may cause this fracture.4-6
Various restorative procedures have been used to reinforce endodontically treated teeth. Studies showed theadvantages of coronal-coverage indirect restorations especially in posterior teeth.7-9 The importance of cuspal
coverage had been proposed to minimize marginal and cuspal fractures in endodontically treated teeth.7
However, many different issues including patients’ medical and financial status have limited the use of the idealrestoration. Dentists have sought alternatives that address these issues. Recent improvement of restorativetechniques and materials had offered conservative way of restoring endodontically treated posterior teeth.10-12
The purpose of this study was to compare in vitro fracture resistance of endodontically treated teeth restoredwith amalgam or resin composite in conjunction with adhesive materials by using intracoronal or cuspal
coverage technique.

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Materials and Methods
Fifty intact and caries free premolars extracted for orthodontic reason were selected and kept in distilled waterat room temperature. All teeth had undergone endodontic procedures with master apical file number 40 at 1 mmfrom anatomical apex and flared up to number 110 at cemento-enamel junction. The root canals were filled with
gutta percha using lateral condensation technique, and gutta percha was removed to the level of 1 mm fromcemento-enamel junction.

Then the root canal orifices were sealed with zinc phosphate cement to thecemento-enamel junction level. All teeth were divided into five groups of ten teeth each and embedded inplaster stone. An impression was made for the occlusal part in each group with silicone impression material forplaster stone occlusal index making. The teeth that were embedded in plaster stone and the plaster stone
occlusal index in each group were mounted in a plain-line articulator before the teeth were prepared for theMOD cavity. The thickness of buccal and lingual surfaces at cemento-enamel junction was left 3 and 2 mm,respectively. The teeth were subjected to the following materials and procedures.
Group 1: The control group. All teeth were left unrestored.
Group 2: The teeth were intracoronally restored with a resin composite (Z100, 5AG; 3M ESPE, St. Paul, MN,USA) and Scotchbond Multipurpose (Acid Gel, 5JC; Primer, 5HT, Bonding Agent, 5BJ; 3M ESPE) using
incremental technique.
Group 3: The teeth were intracoronally restored with amalgam (Valiant Ph.D, 950915A; Dentsply, Milford,DE, USA), All Bond II (9500009869; Bisco, Schaumburg, IL, USA), and Resinomer (9500007930; Bisco).
Group 4: The buccal and lingual cusps were reduced 2 mm, with a 5-degree wall convergence toward occlusal
plane, and restored with indirect resin composite restoration (Z100). The restorations were fixed with All Bond
II and Resinomer.
Group 5: The buccal and lingual cusps of all teeth were horizontally reduced for 2 mm and were restored
using cuspal coverage bonded amalgam (Valiant Ph.D) with All Bond II and Resinomer.
All restored teeth were removed from plain-line articulators before they were embedded in PVC blocks andsubjected to compressive fracture tests using a universal testing machine (4502, Instron Corp., London, UK)with a crosshead speed of 0.5 mm/minute until fracture occurred. The load required to fracture and the fracture
patterns were recorded.

The fracture resistance was statistically analyzed using ANOVA and multiple

comparisons. Dunnett T3 test was performed test at the 5 % level.

Results
The mean fracture load of each group is shown in Table 1. The results reveal that the group of cuspal
coverage bonded amalgam restoration had the highest fracture resistance. The second highest group was thegroup of intracoronal bonded resin composite restoration, which was not statistically different from the group ofcuspal coverage bonded resin composite restoration (p>0.05).

The group without any restorations; thenegative-control group, provided the least fracture resistance while the group of intracoronal bonded amalgam
restoration and the group of cuspal coverage bonded resin composite restoration showed no difference from thenegative-control group.
The fracture pattern is shown in Table 1 and Fig. 1. Patterns of fracture remained consistent within groups.
All restorations without cuspal coverage experienced vertical fracture that split the teeth at the cemento-enamel
junction, while those restorations with cuspal protection, the fractures occurred within the restorative materials.

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Table 1.

Int Chin J Dent 2005; 5: 75-79.

Fracture load, statistical category, and fracture mode.

Group
1. Unrestored
2. Intracoronal resin composite
3. Intracoronally bonded amalgam
4. Cuspal coverage resin composite
5. Cuspal coverage bonded amalgam

Mean (N) S.D. (N)Category

Fracture mode

257.90383.37279.68346.191138.94aVertical tooth fracture
Vertical tooth fracture
Vertical tooth fracture
Fracture in resin composite
Fracture in amalgam

55.30
48.54
56.95
136.43310.91baa bcS.D.; Standard deviation. Category; Identical letters indicate that the values are not statistically different (p>0.05).

Group 1

Group 2

Group 3Fig. 1.
Fracture pattern.
Each groupcorresponds to thatshown in Table 1.
Group 4

Group 5

Discussion
The previous study had showed no significant difference in fracture resistance between unrestored MOD
preparation and restored with bonded amalgam or resin composite.3 The results of this study confirmed thefinding that the benefit of adhesive materials was not significant for the group of intracoronal bonded amalgam
restorations. Therefore, the force required for fracture in the group of resin composite was higher than in thegroup of amalgam. The reason may be the strength of the amalgam bonded to the tooth structure which was
range from 1-10 MPa13-17 has been lower than resin composite which was in excess of 17 MPa.18-20 The results
clearly indicated that the fracture resistance of endodontically treated posterior teeth could not be improved byusing an intracoronal bonded amalgam restoration since the fracture resistance is not different from theunrestored teeth.
The restorations in this study used simple materials and techniques that are generally used in operativedentistry. We used direct technique in the groups of intracoronal amalgam or resin composite and cuspal
coverage amalgam restoration but indirect technique in the group of cuspal coverage resin composite because itis easier to create the large resin composite restoration with this technique.
The results showed that cuspal coverage restoration provided the highest fracture resistance when amalgam
was used but not with resin composite. The reason is due to the higher compressive strength of amalgam.21,2277

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Int Chin J Dent 2005; 5: 75-79.

The different fracture pattern that each group demonstrated was also interesting. For those with cuspal coverage
restorations, the fractures occurred at the restorative materials while those restorations without cuspal protection
experienced vertical fracture that split the teeth at the cemento-enamel junction. For the intracoronal restorationgroups, the force loads were applied directly to the remaining dentine.

Thus, the teeth split at thecemento-enamel junction, which is the thinnest part.
In this study, after root canal treatment, cuspal coverage restoration with high compressive strength material
such as amalgam provided high fracture resistance that withstood the mean maximal normal bite force in theposterior teeth region, 500-900 N for men and 400-600 N for women.23,24 Moreover, when the cuspal coverage
restoration failed, the fracture was usually within the restorative material itself, which could be easily replaced orrepaired. On the other hand, the restorations without cuspal coverage not only provided low fracture resistancebut also their fracture pattern usually involved tooth structures, which would make the failure difficult to berepaired or eventually cause the tooth loss. Although many previous studies have demonstrated that casting
cuspal coverage restoration is proper treatment for endodontically treated posterior teeth,8,9 the results from thisstudy indicate that direct cuspal coverage restoration with high strength materials such as amalgam are analternative restoration to patients who have questionable prognosis or compromised treatment.
Since this study was conducted in vitro, there might be difference in the results in vivo. Several factors
beyond our control made the situation different from real-life scenarios. The factors that might affect the results
include the size and shape of sample teeth, tooth preparation and biting force from only one direction instead ofthe multiple directions of actual biting force.

Conclusion
1.

Cuspal coverage restoration provided higher fracture resistance than intracoronal restoration when amalgam
was the restorative material. When resin composite was the restorative material, cuspal coverage andintracoronal restoration had no statistically different fracture resistance.

2.

Intracoronally bonded amalgam restoration provided lower fracture resistance than intracoronally bonded
resin composite restoration.

3.

The fractures of cuspal coverage restorations occurred at the restorative materials while those restorations
without cuspal protection experienced tooth fracture.

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Reprint request to:Dr. Weeraporn Veerapravati
Department of Conservative Dentistry and Prosthodontics
Faculty of Dentistry, Srinakharinwirot University
Sukhumvit 23, Sukhumvit Rd., Wattana, Bangkok 10110, Thailand
Fax: +66-2-6641000 E-mail: weerapor@yahoo.com
Received July 14, 2005. Revised September 5, 2005. Accepted September 25, 2005.
Copyright ©2005 by the Editorial Council of the International Chinese Journal of Dentistry.

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