October 2007 - Volume 1, Issue 5

DENTURE FRACTURE - A SURVEY

Ayesh Al-Dweiri. BDS, MSc* From the Department of Dentistry, King Hussein Medical Center (KHMC), Amman-Jordan. Correspondence to: Dr. Ayesh Al-Dweiri P.O. Box 2908 Amman-Jordan. E-maldrdweiri@yahoo.com Mobile: +962 7777409735

ABSTRACT Objective: To determine the prevalence of type of denture fracture in three Military Hospitals in Jordan. Method: Questionnaires distributed to three different prosthetic laboratories in three dental departments in the Royal Medical Services Results: Results obtained showed that 45 % of repairs carried out were due to detached or debonded teeth. 30 % were repairs to midline fracture. The remaining 25 % were other types of fractures. Conclusion: The commonest type of fractures encountered were debonding / fracture of denture teeth in both complete and partial dentures followed by midline fracture of complete dentures. More upper complete and partial dentures were repaired than the lowers.

Key words: denture fracture, military, repair, acrylic resin, (polymethyl methacrylate).

INTRODUCTION

The loss of teeth is a matter of great concern to the majority of people and their replacement by artificial substitutes, such as dentures is vital to the continuance of normal life.
One of the problems encountered in the provision of such prostheses is whether limitations of strength and design meet the functional demands of the oral cavity.
The fracture of acrylic resin dentures is an unresolved problem in removable prosthodontics (1-3). Attempts to analyze and determine the cause of such fractures have received considerable attention in recent years (2-4). A multiplicity of factors may be responsible for the ultimate failure of a denture and failure is not necessarily due to the intrinsic properties of the denture base material (5).

Fractures in dentures result from two different types of forces, namely flexural fatigue and impact. Flexural fatigue occurs after repeated flexing of a material and is a mode of fracture whereby a structure eventually fails after being repeatedly subjected to loads that are so small that one application apparently does nothing detrimental to the component. Impact failures normally occur out of the mouth as a result of a sudden blow to the denture or accidental dropping due to cleaning, coughing or sneezing (2, 6-7).

Fractures are more common in the midline of maxillary complete dentures(2,3) , furthermore, fractures of repaired dentures often occur at the junction of old and new material rather than through the centre of the repair(8).

The material most commonly employed in the construction of dentures is the acrylic resin (poly methyl methacrylate). This material is not ideal in every respect but it is the combination of virtues 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 (9).

Despite this significant problem, there are no published data in Jordan on the prevalence or type of fractures.

The purpose of this survey was to analyze the type of failure encountered by distributing questionnaires to three different prosthetic laboratories in three dental departments in the Royal Medical Services.

The three prosthetic laboratories chosen for the study were in different hospitals of the (RMS): Out-patient clinics-King Hussien Medical Centre, from October 2001 to April 2002, Prince Rashid Bin Al-Hassan Hospital, from April to October 2002 and Prince Hashim Bin Al-Hussien Hospital from February to August 2002.

The laboratories were instructed to complete the questionnaire for each repair received over a period of 6 months and they were under direct supervision of the authors.
However, there was considerable uncertainty and vagueness in the response from many patients and the reliability was suspect and therefore this data was not used in the analysis.
The data collected related to:

A. The appliance
type (complete or partial denture), material of denture base (acrylic resin or metal), presence of diastema and / or notch and incorporation of strengtheners and / or soft lining material.

B. The fracture
number of times fracture had occurred, location (same or different place), cause (chewing or accidental) or notch / diastema included in the fracture line.

C. The teeth
debonded or detached addition of teeth or fractured teeth.

D. Previous attempts of repair.
The results were analysed to identify the types of repair encountered and possible ways of overcoming the problems were considered.

Questionnaires were distributed to the three laboratories, of which 669 were completed and returned (Table I). Of those returned, 84 involved new additions and have been excluded.
A total of 585 repairs is therefore included in this survey. Table II gives details of the types of appliances repaired. 201 upper complete dentures were repaired and approximately twice as many lower complete dentures were repaired as lower partials. 266 upper partial dentures were repaired. Nearly all the dentures repaired had fractured in the mouth whilst chewing with 3 lower dentures having been dropped accidentally. Three dentures showed evidence of previous attempt of repair. Almost half the dentures repaired had broken for the first time; the remainder had broken either twice or more in different places.

The majority of dentures, both complete and partial were made of acrylic resin (Table III). Only 23 had some form of "strengthener" incorporated and 9 had soft linings.

From Table IV, out of 585 repairs, 262 were due to replacement of teeth that had either debonded or fractured. These were more commonly seen in the upper complete dentures and upper partial dentures. 178 were associated with midline fractures, the majority of which were seen in upper complete dentures (117). Where either a notch or diastema, or both, were present in upper complete dentures, these were involved in the fracture line. From a total of 117 fractures: 48 involved a notch, 6 involved a diastema and 39 involved both notch and diastema. Slightly more than half the lower complete dentures repaired were midline fractures of which 27 involved a notch.

Of the 266 repairs to upper partial dentures 13 were midline fractures. The remainder was associated with fracture of the connector horizontally in the anterior region (nearly all upper partial dentures replaced at least one anterior tooth)

Where the prosthesis was made of metal, the fracture invariably involved detachment of an acrylic resin saddle with lower partial dentures; the commonest site of fracture was either in the anterior region or in the premolar region.

The results of this survey show that out of 585 repairs carried out over a period of 6 months, approximately 45 % were due to debonding / fracture of teeth from the denture base resin.
Despite advances in technology, it can be seen that the detachment of denture teeth remains a significant problem and the number of debonding has not decreased.

The strength of the bond achieved at the tooth / denture base interface may be related to the degree of cross-linking and extent of copolymerisation of the acrylic resin tooth and denture base. However, poor laboratory technique involving faulty boil out procedures and indiscriminate use of separating medium have been stated as the more common causes preventing optimum bonding from being achieved between the denture base resin and tooth.
It has been shown that in dentures subjected to bending deformation, tensile stresses are encountered with the area lingual to the incisors being the most heavily stressed. Eventual failure at the tooth / denture base interface will occur when cracks originating from the highly stressed areas propagate(10).

When the bond with the denture base has already been compromised the increase in stress concentration during function (in area of inadequate bonding) enhances crack propagation and eventually detachment of the teeth is seen. The problem of tooth debonding may be exacerbated by heavy or uneven masticatory loads (e.g. clenching or tooth grinding), unbalanced occlusion and patient-related habits such as pipe smoking.

In this study, a higher proportion of teeth were found to be debonded from partial dentures. This can probably be attributed to the higher masticatory loads encountered when natural teeth oppose artificial teeth.

Midline fractures represented 30 % of the total denture repairs carried out. Of these, 66 % were seen in upper complete dentures and 27 % were seen in lower complete dentures. These findings are consistent with other studies, (3, 11) which have shown the midline fracture to be a common and persistent problem in upper complete dentures. This type of fracture has been shown to be a flexural fatigue failure due to acrylic deformation of the base whilst in function where flexure of denture base occurs along the midline.

Both the presence of notches and diastema act as stress concentrators, thereby influencing the risk to fracture. This is confirmed from the findings of this survey, which reveal that where notches or diastema are present they are involved in the fracture.

Other factors affect the deformation of the denture base thereby facilitating fracture such as: (1) Variation in denture base contour. (2) Changes in the supporting tissues. (3) Tooth wear.
A majority of midline fractures can be avoided by the application of established prosthetic principles during denture construction (i.e. even and adequate bulk of denture base material cured, relief of incompressible tissues in the centre of the hard palate, addition of the labial flange to increase rigidity of denture base and even and balanced occlusion to reduce wedging effect and locking the occlusion) and the improvements in denture base resin and the reduction of stress concentration such as notches and diastema to a minimum would also help prevent these fractures.

In partial dentures, 40 % of repairs were related to fracture of the connector in the all acrylic resin dentures and detachment of an acrylic resin saddle in the metal denture.

Upper partial dentures represented the majority (45 %) of repairs. This would be explained by the fewer lower dentures worn and possibly fewer produced by the dentist.

The problem of acrylic resin fracture can be reduced by the careful designing of dentures and the use of the improved high impact resins.

The value of incorporating "strengtheners" which were largely seen in upper partial dentures remains questionable. It has been reported that the insertion of metal wire or metal mesh as strengtheners into acrylic resin dentures is not very satisfactory (12).

In cases of repeated fractures, which are more likely encountered where a complete upper denture opposes a lower natural dentition, the use of a high impact (Rubber graft co-polymer) or fibre reinforcement should be considered (13).

CONCLUSION

It is concluded that the commonest type of fractures encountered are debonding / fracture of denture teeth in both complete and partial dentures followed by the midline fracture of complete dentures.

More upper complete and partial dentures are repaired than lowers; this could be accounted for by the fact that more upper dentures are worn than lowers.

In partial dentures, detachment of the acrylic resin saddle from the metal framework or fracture of the acrylic resin saddle in the anterior region continues to pose problems.
Repeated fractures can be reduced by careful attention to the design and construction of dentures particularly during the laboratory stages.

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