See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/6294547

Fracture strength of restored premolars

Article in American Journal of Dentistry · May 2007

Source: PubMed

CITATIONS READS
22 445

4 authors, including:

Guilherme Camacho
Federal University of Pelotas
32 PUBLICATIONS 974 CITATIONS

SEE PROFILE

All content following this page was uploaded by Guilherme Camacho on 15 October 2015.

The user has requested enhancement of the downloaded file.

_______________________________________________________________________________________________________________________________________________________________

Research Article
_______________________________________________________________________________________________________________________________________________________________

Fracture strength of restored premolars

GUILHERME BRIÃO CAMACHO, MS, DDS, PHD, MARIANE GONÇALVES, MS, DDS, PHD, TOMIO NONAKA, MS, DDS, PHD
& ANGELA BRYS OSÓRIO, MS

ABSTRACT: Purpose: To evaluate the fracture resistance (axial compressive strength) of premolars restored with
different dental materials under two axial loads. Methods: Fracture strength was performed using two metal spheres
with 3 mm and 9 mm diameter. Five restorative techniques were chosen for MOD cavity preparations (n=10): (1) direct
resin composite restorations (Z-250); (2) indirect resin composite restorations (Z-250 and RelyX); (3) ceramic inlays
(Vitadur Alpha); (4) conventional amalgam restorations (GS-80); (5) bonded amalgam restorations. The restored teeth
were compared to human caries-free premolars (Group 6/control). Enforce resin cement was used for ceramic and
amalgam adhesive restorative techniques, according to the manufacturers’ instructions. Whenever required, the teeth
were conditioned by the total etch technique. Results: The ANOVA analysis pointed out a significant difference among
the groups (P< 0.01) and the “site” factor (P< 0.1). The ceramic restorations presented the highest values for fracture
strength and were similar to the control group. The statistical results of direct and indirect resin composite restorations
were similar but inferior to the control group. The amalgam restorations (conventional and bonded) presented the lowest
values, with no difference between them. All amalgam groups displayed lower strengths when the load was applied on
the central fossa (3 mm Ø sphere) compared to load applied on cusps (9 mm Ø sphere). (Am J Dent 2007;20:121-124).

CLINICAL SIGNIFICANCE: The loads similar to chewing of solid food is relevant to fracture strength, which occurs at
the central fossa where the risk of fracture is higher. The fracture strength of the different restorative techniques was
product-related.

: Prof. Dr. Mariane Gonçalves, Faculty of Dentistry, Department of Dental Materials and Prosthesis, University of
Ribeirão Preto, Avenida do Café, s/n, Ribeirão Preto – SP, CEP 14040-904, Brazil. E- : ane.gon@netsite.com.br

Introduction in PVCb cylinders (20 mm Ø). Immediately, the cylinders were

immersed in cold water to control the resin’s exothermal effect.
Along with materials such as amalgam and resin-based The teeth were randomly assigned to six groups of 20
composites, ceramics have been widely employed as a specimens each. One group was the control; the other five
restorative dental material, for instance in the ceramic inlay received MOD cavities and five different restorative
and onlay restorations. Those restorations present superior techniques:
esthetic, such as color stability, translucency and natural
appearance.1,2 Group 1: ceramic inlays;
These new techniques and ceramic systems such as inlays, Group 2: (conventional) direct resin composite;
onlays and veneers, are also used for esthetic restorations, due Group 3: indirect resin composite (or resin composite inlay);
to their excellent esthetics, function and wear resistance. Group 4: conventional amalgam;
The use of these materials became possible by the advent Group 5: bonded amalgam; and,
of better adhesive techniques and developments in ceramics Group 6 (control): no treatment, caries-free premolars.
such as the increase in structural strength by introducing fused
ceramics reinforced with leucite and alumina. Nevertheless, After performing the restorations, each group was divided
other restorative materials, used either directly or indirectly, in two subgroups of 10 specimens each, and then each
are still common in dental practice.3,4 subgroup, was subjected to one of two types of axial
Several studies2,5-7 reported the results of clinical evalu- compression test (along the tooth’s greater axis) to record the
ations of adhesive restorations and their physical properties. fracture resistance of the restored premolar.
However, there is not enough information about the best In the first test of fracture resistance, the load was exerted
actual restorative technique that increases the fracture on the lingual and facial cusps of each specimen using a 9 mm
resistance of teeth with MOD cavities. Ø metallic sphere, until the premolar fractured. During the
This study compared the performance of different second type, the load was applied on the center of the
restorative techniques through the application of two types of restorations using a 3 mm Ø metallic sphere, corresponding to
occlusal loads. the central fossa of the occlusal surface, until the fracture
occurred (Fig. 1).
Materials and Methods
The preparation of MOD cavities was performed using
One hundred and twenty freshly extracted, sound upper diamond burs (No. 4138c) at high speed under a constant flow
human premolars were selected after being carefully examined of cool water to prepare a standardized size at the proximal
under a stereoscopic microscope, rejecting any with existing and occlusal boxes. These cavities measured 50% of the
enamel fissure caries or defects. intercuspal width in the buccal-lingual direction. The same
The roots of the teeth were embedded in a self-curing distance was utilized for the height of the occlusal boxes. In
acrylic resina up to 1 mm below the cementum-enamel junction the proximal cavities, the cervical wall was kept just below
 American Journal of Dentistry, Vol. 20, No. 2, April, 2007
122 Camacho et al

Table 1. Means and standard deviations (SD) of rupture load values (Kgf) and
standard deviation for all experimental and control groups subjected to two
types of axial compressive loads.
____________________________________________________________________________________________________

Axial Groups
compressive
load I II III IV V VI
____________________________________________________________________________________________________

Type 1(cusps) 159.5 136.6 139.8 75.61 79.66 178

SD 27.25 28.85 20.87 19.94 31.25 38.25
Type 2
(central fossa) 127.62 93.36 75.52 92.59 88.44 157.41
SD 33.18 30.02 26.03 34.77 33.91 40.27
____________________________________________________________________________________________________

Table 2. Statistical analysis (ANOVA 2) test results.

____________________________________________________________________________________________________

Variation Sum of Mean Probability

source squares G.L. squares (F) (H0)
____________________________________________________________________________________________________

Among columns
Fig. 1. Spheres of different diameters (3 mm and 9 mm) used on the two tests (groups) 110678.2266 5 22135.6445 21.70 0.000 (0.01%)
(original drawing). Between lines (loads) 15024.0918 1 15024.0918 14.73 0.044 (0.1%)
Interaction C X L 24005.7070 5 4801.1416 4.71 0.089 (0.1%)
the cementum-enamel junction and with 1 mm thickness. For
Residue 110174.4766 108 1020.1340
the premolars that were treated by indirect techniques, all
Total variation 259882.5000 119
walls were non-retentively conformed to the occlusal-cervical ____________________________________________________________________________________________________

axis. The other cavities were performed parallel to the facial

and lingual walls. Table 3. Statistical analysis (Scheffé test).
____________________________________________________________________________________________________

All composite restorations (direct and indirect) were filled Critical Difference of Statistical
with Filtek Z-250d composite, using the incremental Comparison of groupings value mean values significance
____________________________________________________________________________________________________

technique; the indirect restorations were fixed with the Grouping (1) x Grouping (2) 44.3125 24.2509 1%
RelyXd resin cement and the corresponding Single-Bondd Grouping (1) x Grouping (3) 71.5425 24.2509 1%
adhesive, following the manufacturer’s instructions. All Grouping (2) x Grouping (3) 27.2300 24.2509 1%
____________________________________________________________________________________________________
indirect restorations were manufactured on individual casting
dies made from Type IV stone gypsum (Duronee) molded by the experimental factors. After the statistical study, the
polyether (Impregum Ff). For amalgam restorations the GS- Scheffé’s test was applied to three groupings: (1) control +
80g regular amalgam alloy was used. The ceramic inlays were ceramic; (2) direct resin composite + indirect resin composite,
manufactured with Vitadur Alphah ceramic employing and (3) conventional amalgam + bonded amalgam (Table 3).
refractive dies for two-step baking at 930ºC and self-glazing
The results demonstrated that ceramic inlays provided
at 940ºC during 1 minute.
resistance values similar to non-restored control premolars
Cementation of ceramic inlay restorations and adhesive and showed the higher mean value of axial fracture resistance
amalgam restorations were prepared using Enforcee resin when compared to the other restored premolars. The control
cement, according to the manufacturer’s instructions. and ceramic groups (control + ceramic) presented the highest
After finishing the restorations, all specimens of the values of fracture resistance of all groups, followed by the
experimental and control groups were stored for 7 days in a composite restorations with an intermediate performance
physiological saline solution at 37ºC. Fracture strength tests (similar for direct and indirect types). The lowest mean values
were performed with two kinds of percussive tips: 9 mm Ø were for the third group (amalgam), which presented no
for tests on cusps and 3 mm Ø for tests on central fossa, statistical difference between the conventional and bonded
adapted to a universal testing machine (EMEM 2000i) with a amalgam techniques.
cell load of 200 Kg, with a crosshead speed of 0.5 mm/minute The influence of the load site showed a statistically
until fracture. The results (Kgf) were statistically analyzed. significant difference (P< 0.044). The premolars presented
The specimens were stored for later analysis of the failure lower resistance when the load was applied on the central
modes. fossa compared to the load applied on the cuspal plane.
Results The analysis of the failure modes is summarized in Fig. 2.
Basically, four different types of fractures were observed:
Table 1 shows the results of fracture strength tests (Kgf), Type 1: vertical fractures of the tooth; type 2: fracture of the
with both types of load and five restorative techniques. cusp; type 3: fracture of the restoration; type 4: both fractures,
The statistical analysis presented normal distribution and a of the tooth and restoration. The results were submitted to the
parametric test was applied. The results of the 2-factor Chi-square test and showed a significant difference (P< 0.01).
ANOVA are shown in Table 2. Comparing the loads on the sound teeth, the 3 mm Ø sphere
The results displayed a statistically significant difference created equal numbers of type 1 and 2 fractures, while the 9
(P< 0.001) among the groups. This means that there were mm Ø spheres created a larger degree of type 2 failures
different behaviors among the restored premolars and the (80%). Analyzing the amalgam restorations, the 3 mm Ø
control group. Further statistical analysis was obtained using sphere produced a larger number of type 4 failures (50%),
Tukey’s test, which revealed a tendency to grouping among while the 9 mm Ø created more type 2 failures (80%). The
American Journal of Dentistry, Vol. 20, No. 2, April, 2007
Polymerization kinetics 123

Fig. 3. Gravity levels of the failures (recoverable and catastrophic/

unrecoverable). At the left side, test with the 3 mm Ø sphere and to the right,
the 9 mm Ø sphere.
Fig. 2. Failure modes presented by the experimental groups. At the left side,
test with the 3 mm Ø sphere and to the right, with the 9 mm Ø sphere . constriction. Performance of MOD cavities on those teeth can
bonded amalgam restorations, with the loads of 3 mm Ø, had a certainly cause stress on the cusps, which is transferred to the cer-
uniform distribution of the four failure types while with the 9 vical area. Vertical fractures with collapsed facial and lingual
mm Ø sphere there was a larger number of type 1 (50%) and cusps result from such restorative procedures. The cavities that
type 2 (40%) fractures. The direct resin composite restorations remove marginal ridges and increase the real height of cusps ex-
had, with the 3 mm Ø sphere, more type 1 (50%) failures and, tremely decrease the structural resistance of posterior teeth.14-16
with the 9 mm sphere, failures of type 2 (50%) and type 4 Therefore, the most advisable treatment is the one that
(40%). As for the indirect resin composite restorations, with the restores the lost dental strength after a carious process or a
3 mm Ø sphere, there was a larger number of type 3 (40%) cavity preparation. This is possible only by a restoration that
and 4 (30%) failures, and under the 9 mm sphere, failures of adheres to the remaining dental structure17 and that also
type 1 (40%), 2 (30%) and 4 (30%). The ceramic inlays had reestablishes the shape and function of the tooth.
different behaviors with the loads. While with the 3 mm Ø This study revealed that amalgam restorations that only
sphere there was a larger number of type 3 (60%) and 4 reconstructed shape and function were not effective in restoring
(40%), with the 9 mm sphere there was a larger number of structural resistance to the teeth. The bonded amalgam showed
type 2 (30 %) and 4 (70%) failures. no ability to reinforce the tested specimens, presenting a be-
havior similar to the conventional amalgam restorations, which
The analysis of the failure type in the interface tooth x
disagrees with others. 18,19 The aim of the bonded amalgam
restoration, pointed that indirect composite restorations and
technique is to decrease the marginal leakage, reduce post-op-
bonded amalgam presented a larger incidence of fractures in the
erative sensitivity, protect the pulpal complex and reinforce the
interface cement-restoration (67%) and cohesive failures of the
dental structure, which was not corroborated by the values ob-
restorative material (22%). In the direct composite restorations,
tained.20,21 The same cannot be said about the resin composite
there was a larger number of failures in the interface adhesive
restorations, that promoted a strength increase to the restored
system x restoration (53%) and cohesive fractures (43%).
premolars, but not to the same levels of caries-free premolars
In Fig. 3, the recovery potential of tooth fracture resistance (control group). This could be an effect of cusps bonding by
is observed when new restorations were constructed, showing a resin composite, cavity preparation and effectiveness of the
significant difference in the results of the Chi-squared test (P< employed adhesive system on the tooth-restoration interfaces.22
0.01). The 3 mm Ø sphere was more favorable to thetooth frac- The indirect composite restorations generally attain higher
ture resistance recuperation of the tooth than with the 9 mm Ø. resistance due to improved polymerization presented by this
Except for the amalgam restorations performed by the technique, adhesion and to superior surface polishing of the
conventional method (60% of catastrophic fractures), the other finished restoration.7,23 Nevertheless, the use of the indirect
groups had only 30% serious cracks. However, the sphere of 9 method did not result in a real advantage in reinforcing premo-
mm produced, on average, 70% of catastrophic fractures in all lars when compared to the direct technique. Both restorative
of five types of restorations. The control group presented singu- techniques were statistically similar.
lar failure behavior. There was a larger incidence of catastro- The ceramic inlays were the restorations that provided the
phic fractures with the 3 mm Ø sphere (70%) while the other highest fracture strength. The resistance values were similar to
sphere produced a lower index (50%). those of the caries-free premolars (control group). The results
Discussion confirmed the highest resistance of this material associated to
adhesion to dental structure by the adhesive fixation. The con-
The concern about the relationship of dental structure ditioning of the inner surface of the ceramic restoration using
removal versus fracture resistance is not recent.8,9 Occlusal hydrofluoric acid, associated to silane coating, a procedure
wear with the fracture of the marginal crests creates an increase advised for resin systems, makes possible the bonding of two
of the height of the cusps of posterior teeth with the consequent different materials (tooth and restoration), allowing for
decrease of the resistance to fracture.10-13 It is a well-known fact effective adhesion.16,24
that the upper premolars are fragile due to their cervical con- Furthermore, apart from function and shape, the restorative
 American Journal of Dentistry, Vol. 20, No. 2, April, 2007
124 Camacho et al

material chosen for indirect technique, resin composite or Pelotas, Rio Grande do Sul, Brazil. Dr. Gonçalves is Assistant Professor,
ceramic, should be adhesively bonded. It is known that Department of Dental Materials and Prosthesis and Dr. Nonaka is Assistant
Professor, Department of Restorative Dentistry, Faculty of Dentistry, University
adhesive restorations tend to increase fracture resistance or, at of Ribeirão Preto, Ribeirão Preto, São Paulo, Brazil.
least, some reestablish the original strength due to higher sup-
port of the occlusal forces by the restored teeth, avoiding References
flexures or even micro crack propagation and stress transfer- 1. Phillips RW. Skinner dental materials, 9th ed. Rio de Janeiro: Guanabara
ence to nearby dental structures by the adhesive layer which Koogan, 1991, Chap. 26. (In Portuguese).
2. Tidehag P, Gunne J. A 2-year clinical follow-up study of IPS Empress
acts as a shock absorber or cushion.25,26.In spite of the absolute ceramic inlays. Int J Prosthodont 1995;8:456-460.
necessity of an adhesive system, problems regarding the dura- 3. Giordano RA, Pelletier L, Campbell S, Pober R. Flexural strength of an
bility of the obtained adhesion, due to marginal infiltration, still infused ceramic, glass ceramic, and feldspathic porcelain. J Prosthet Dent
1995; 73: 411-418.
persist as has been observed during long-term evaluations.27-29 4. Seghi RR, Denry IL, Rosenstiel SF. Relative fracture toughness and
As observed, the lowest resistance of the restored premolars hardness of new dental ceramics. J Prosthet Dent 1995; 74:145-150.
was presented when load was applied by the 3 mm diameter 5. Mc Lean JW. New dental ceramics and esthetics. J Esthet Dent 1995;7:
sphere. That may have happened due to the greatest concen- 141-149.
6. Sehgi RR, Sorensen JA. Relative flexural strength of six new ceramic
tration of load on a smaller diameter. The relevance of this is materials. Int J Prosthodont 1995; 8: 239-246.
that the 3 mm diameter sphere is related to the chewing of solid 7. Brunton PA, Cattell P, Burke, FJ, Wilson NH. Fracture resistance of teeth
food, which occurs on the central fossa. According to the restored with onlays of three contemporary tooth-colored resin bonded
restorative materials. J Prosthet Dent 1999; 82: 167-171.
results, the risk of fracture is higher. 8. Vale WA. Cavity preparation. Irish Dent. Rev 1956; 15: 33-41.
On the other hand, it was observed that depending on the 9. Vale WA. High speed cutting in dentistry. Med World 1958; 89: 429-432.
technique and restorative material used, different types of frac- 10. Mondelli J, Vieira DF. The strength of Class II amalgam restorations with
tures can occur. The most interesting point is still regarding the and without pins. J Prosthet Dent 1972; 28: 179-188.
11. Mondelli J, Steagall L, Ishikiriama A, Navarro MF, Soares FB. Fracture
vector type of the applied load on the tooth and its influence on strength of human teeth with cavity preparations. J Prosthet Dent 1980; 43:
reinforcing the teeth with a new restoration. The loads applied 419-422.
on the cusps produced more serious fractures (catastrophic or 12. Larsen TD, Douglas WH, Geistfeld RE. Effect of prepared cavities on the
unrecoverable) than the loads applied on the central fossa. strength of teeth. Oper Dent 1981; 6: 2-5.
13. Re GJ, Norling BK. Fracturing molars with axial forces. J Dent Res 1981;
Thermocycling of specimens is frequently done before frac- 60: 805-808.
ture resistance tests, however, this study did not use thermocy- 14. Steinberg R, Matsson L. Clinical evaluation of glass ceramic inlays (Dicor).
cling to avoid possible interfering variables and focused on the Acta Odontol Scand 1993; 51: 91-97.
15. Vieira GF, Ferreira AM, Garófalo JC, Agra CM. Indirect esthetic
different restorative techniques and loads (3 mm Ø and 9 mm Ø restorations in posterior teeth - Inlays/onlays. São Paulo: Editora Santos,
spheres). The aging process represented by thermocycling 1995; Chap. 4. (In Portuguese).
certainly would influence the resistance to fracture of the 16. De Rijk WG. The fracture resistance of all-ceramic crowns on supporting
premolars, but not the storage time. Therefore, within the structures with different elastic moduli. Int J Prosthodont 1993; 6: 462-467.
17. Lopes LM, Leitão JG, Douglas WH. Effect of a new inlay/onlay restorative
limitations of the methodology used in the present study and material on cuspal reinforcement. Quintessence Int 1991; 22:641-645.
according to the results, it may be concluded that ceramic 18. Eakle WS, Staninec M, Lacy AM. Effect of bonded amalgam on the
restorations presented the highest values of fracture resistance fracture resistance of teeth. J Prosthet Dent 1992; 68: 257-260.
and did not differ statistically from caries-free premolars 19. Dias de Souza GM, Pereira GD, Dias CT, Paulillo LA. Fracture resistance
of premolars with bonded class II amalgam. Oper Dent 2002; 27: 349-353.
(control group). The teeth restored with resin composite, either 20. Staninec M, Holt M. Tensile adhesion and microleakage of resin bonded
by direct or indirect method, showed an intermediate behavior amalgam restoration. J Prosthet Dent 1988; 59: 397-402.
and were statistically similar between them but not to the other 21. Teixeira LC, Gonçalves M. Large amalgam restorations. In: Mooney B.
groups. The specimens restored with conventional and bonded Operative dentistry. 3rd ed. Buenos Aires: Ed. Panamericana, 1999; 1091
(In Spanish).
amalgam presented similar behavior, but exhibited the lowest
22. Freitas CR, Miranda MI, De Andrade MF, Flores VH, Vaz LG, Guimarães
values of fracture resistance and were different from the other C. Resistance to maxillary premolar fractures after restorations of Class II
groups. Furthermore, all premolars presented less fracture resis- preparations with resin composite or ceromer. Quintessence Int 2002; 33:
tance to loads applied on central fossa by a 3 mm Ø sphere as 589-594.
23. Garone Netto N, Burger RC. Metallic and esthetic inlays and onlays. São
when compared to that applied on cusps by a 9 mm Ø sphere. Paulo: Livraria Editora Santos, 1998 (In Portuguese).
a. Clássico, São Paulo, Brazil. 24. Nasedkin NJ. Ceramic inlays and onlays: Update. J Can DentAssoc 1995;
b. Tigre S.A., Joinville, Brazil. 61: 676-682.
c. KG Sorensen, São Paulo, Brazil. 25. Garber DA, Goldstein RE. Esthetic porcelain and composite resin inlays
d. 3M ESPE, St. Paul, MN, USA. and onlays in posterior teeth. Chicago: Quintessence, 1996 (In Portuguese).
e. Dentsply Ind. & Co., Rio de Janeiro, Brazil. 26. Trope M, Langer I, Tronstad L. Resistance to fracture or restored
f. ESPE Dental, Medizin Gmbh & Co, Seefeld, Germany. endodontically treated premolars. Dent Traumatol 1986; 2:35-38.
g. Southern Dental Industries Ltd., Bayswater, Victoria, Australia. 27. Fialho ES, Silva EV, Graff CS, Loguercio AD, Camacho GB, Busato ALS.
h. VITA Zahnfabrik, Bad Säckingen, Germany. Evaluation of marginal leakage of amalgam restorations: Mercury versus
i. EMIC, São Jose dos Pinhais, Brazil. gallium. Braz Oral Res 2000; 14: 5-63.
28. Alavi AA, Kianimanesh N. Microleakage of direct and indirect composite
Acknowledgements: To FAPERGS, Brazil for financial support.
restorations with three dentin bonding agents. Oper Dent 2002; 27: 19-24.
Dr. CamachoҘ is Assistant Professor, Department of Dental Prosthesis Unit III 29. Mota CS, Demarco FF, Camacho GB, Powers JM. Microleakage in cera-
and Dr. Osório is a Masters Student of Dentistry, Pelotas Federal University, mic inlays luted with different resin cements. J Adhes Dent 2003; 5:63-70.

View publication stats