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| 2010-22 |
| 22-1 |
ISSN (Print) 1013-9052
EISSN 1658-3558
P.O. Box 52500,
Riyadh 11563,
Kingdom of Saudi Arabia
| Tel. |
966-1-467-7328 |
| Fax. |
933-1-467-7308 / 966-1-467-7534 |
| Email |
saudidj@ksu.edu.sa |
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Causes of denture fracture : A
survey
Ali M. El-Sheikh, BDS, MSD, MSc, PhD Saied B. Al-Zahrani, BDS, MS Department of Prosthetic Dentistry Dammam Central Hospital, Dammam Dental Cente
Fracture of acrylic resin removable dentures occurs frequently during service through heavy occlusal force or accidental damage. OBJECTIVES: The purpose of this survey was to determine the number and type of damaged removable dentures at Dammam Dental Center, Dammam, Saudi Arabia and to ascertain the statistical relationship between certain variables and damage to dentures. MATERIALS and METHODS: Three operators were instructed to complete the questionnaires for each denture received for repairs at the center over a period of 6 months. Eleven variables were examined for each damaged denture. RESULTS: Results obtained showed that the type of dentures most commonly needing repair was the lower partial denture (46.4%). Results also showed that 53.6% of the damaged dentures had been in use more than 1 year and less than 3 years. Impact failure (80.4%) was the most common cause of damage. The most frequent type of damage was breakdown of the acrylic base (71.4%). The Chi-square test showed a statistical dependence (P<0.05) between damaged dentures and some of tested variables namely, Kennedy classification of partial denture, age of the denture, causes of fracture, type of fracture, retention of the denture, type of antagonist and strengthener of the denture. CONCLUSIONS: It could be concluded that damage to removable dentures is quite frequent and provides much distress and cost for patients. These difficulties can best be prevented by regular examinations of the mouth and dentures. A new, more suitable method of reinforcing the base of dentures during preparation is also needed.
The
material most commonly used for the fabrication of dentures is the acrylic
resin, poly methyl methacrylate (PMMA). This material is not ideal in every
respect and it is the combination of properties rather than one single
desirable property that accounts for its popularity and usage. Despite its popularity
in satisfying aesthetic demands whereby, with an appropriate degree of clinical
expertise and with the careful selection and arrangement of artificial acrylic
teeth, it is possible to produce a prosthesis which defies detection, it is
still far from ideal in fulfilling the mechanical requirements of a prosthesis.1
This is reflected in the unresolved problem of denture fracture and the
accompanying costs to
effect repair.2
Types of damaged removable dentures, complete and
partial acrylic resin dentures were studied. Three operators were instructed to
complete the questionnaires (Table 1) for each damaged denture received for
repairs at Dammam
Dental Center
over a period of 6 months. One hundred and twelve questionnaires were
completed. The questionnaire consisted of eleven variables, and the damaged
dentures were evaluated on a nominal scale. The denture types were classified
into four categories: upper complete dentures, lower complete dentures, upper
partial dentures and lower partial
To fulfill the purpose of this study, the analysis was primarily descriptive in nature, and involved calculating frequency tabulations, and cross-classifications for categorical data. Chi-square test was carried out to establish the statistical independence between the selected variables and damaged dentures. Significance level was set at 5%.
The commonest type of damage was that of lower partial
dentures (46.4%). As illustrated in Table 2, 84.6% of the damaged lower partial
denture was Class I Kennedy classification. As illustrated in Table 1, 53.6% of
the damaged dentures had been in use more than 1 year and less than 3 years.
The Chi-square test showed a statistical dependence between damaged dentures and
age of the denture (P< 0.05). The frequency of male wearers of
damaged dentures (65.2%) was higher than female wearers (34.8%). There was no
statistically significant difference between damaged dentures and gender of
denture wearer (P = 0.842). Impact failure was the most common cause of
damage (80.4%). The most frequent type of damage was breakdown of the acrylic
base (71.4%). There was a statistical significant relationship between damaged
dentures and type of fracture (P = 0.004). More than half the dentures
repaired (56.3%) had broken for the first time. There was no statistically
significant relationship (P = 0.777) between damaged dentures and number
of previous fracture. On the other hand, there was statistical significance (P
= 0.005) between damaged dentures and retention of the denture, type of
antagonist and strengthener of the denture.
Several studies have investigated the incidence and types of fracture of dentures. Darbar et al.2 in a survey distributed a questionnaire to three laboratories, and reported that 33% of the repairs carried out were due to debonded/ detached teeth and 29% were repairs to midline fractures more commonly seen in upper complete dentures. The remaining 38% were other types of fractures, the majority of which were repair to upper partial dentures, e.g. detachment of acrylic resin saddles from metal-based dentures and fracture of connectors in all acrylic resin partial dentures. The present study reported that 53.6% of the damaged dentures had been in use more than 1 year and less than 3 years and 46.4% of damaged dentures were lower partial dentures. These results agree with that of Hargreaves9 who in a survey, reported that 63% of dentures had broken within 3 years of their provision, there being a greater proportion of partial than complete denture. Lower partial dentures represented the majority of repairs in the present study. This would be explained by the fewer upper dentures worn and possibly fewer produced by dentists. Such dentures are easily damaged because the structures of partial dentures are quite complex. Hargreaves9 and Smith10 have both indicated that midline fractures in dentures are most likely to occur after 2 to 3 years of use. The present study confirmed that most upper complete dentures (29.4%) were damaged after 3 years of use. The damages after a few years' use may indicate that fatigue of the denture material is somehow linked to denture damage, but dimensional failures in laboratory technique of denture bases also predispose to damage. Chemical degradation of polymer in the oral environment weakens the denture, and this also predisposes it to damage. Impact failure (80.4%) was the most common cause of damage of the dentures in the present study. This agrees with that of Lambrecht and Kydd6, and Hargreaves.9 This could be explained by the lack of attention being paid by the patients towards the care of their dentures. The most frequent type of damage seen in this study was the breakage in the acrylic base. The problem of acrylic resin fracture can be reduced by the use of the improved high impact resins. There is also need for a new and more suitable method of reinforcing the denture base during preparation. This could be achieved by using continuous electrical-glass (E-glass) partial fiber reinforcement. Reinforcement with glass fibers enhances the mechanical strength characteristics of denture bases such as the transverse strength, ultimate tensile strength, and impact strength.11 This type of reinforcement is superior to metal-wire reinforcement in terms of esthetics and bonding to the resin matrix. Continuous, unidirectional E-glass partial fiber reinforcement has been shown to considerably improve the mechanical properties of removable complete and partial dentures in vitro.12-14 The failure of artificial teeth included fractures and detachments. The type of artificial teeth used influenced the incidence of artificial teeth failure regardless of the type of denture. As plastic teeth have a strong bond to the denture base, the incidence of plastic artificial teeth failure in the present study was low. It has been reported that the insertion of metal wire or metal mesh as ‘strengtheners' into acrylic resin dentures is not very satisfactory. This could explain why fewer number of dentures (4.5%) in the present study used the metal wire as a strengthener. It is probable that the acrylic resin shrinks away from the ‘strengthening' material leaving a material with a network of voids which weakens the structure by creating new points of stress concentration. Matthews and Wain15 have shown that under load the maximum tensile stresses are on the palatal aspect of the denture. Factors that contribute to stress concentrations will enable the initiation and propagation of cracks thereby influencing the rate of failure. Both the presence of notches and diastema act as stress concentrators thereby influencing the risk of failure. A majority of the midline fractures can be avoided by the application of established prosthodontic principles during denture construction. The principles include even and adequate bulk of denture base material cured to achieve optimum polymerization and free of porosity; relief of incompressible tissue in the center of the hard palate; addition of labial flange to increase rigidity of denture base as well as even and balanced occlusion to reduce wedging effect and locking of occlusion. Improvements in denture base resin and the reduction of stress concentrators such as notches and diastema to minimum would also help prevent these fractures.
Within the limitations of this study, the following conclusions were drawn:
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