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The fracture topography of acrylic dentures broken in service
Thefracture topography of acrylic denturesbrokenin service D.J. Limb, Brgan Ellis’ and R. van Noort Department of Restorerive Dentistry 8nd ‘Depsrtment Sheffield, South Yorks, UK (Received 12 June 1984; r8vised 10 September 1984)
The fracture smfacrs born examined usina daducrd and indicate denture tooth/denture dentuns. Keywords:
of Ceramics,
AND
Dent81 materiel.
denture,
acrylic.
fracture,
strength,
Butterworth
1fO
Biometeriels
University
of Sheffield,
topography
varied to obtain fractures which ran labio-lingually and others which ran linguo-labially. Their fracture surfaces were examined by the same methods used for dentures which had failed in service.
RESULTS AND DISCUSSION The site of crack initiation could be located in the laboratoryfractured dentures because the direction of the applied impulsive force was known. Certain characteristic features of the fracture surface were observed. Whether the crack passed from the labial to the lingual or vice versa, a rough zone (Figure 7) characterized the site from which the crack was initiated. Next after passing through a smooth zone devoid of landmarks, the fracture ended at the opposite side in a zone of striations lying parallel to
MATERIALS
The broken acrylic full dentures of 16 patients attending the Charles Clifford Dental Hospital, Sheffield for denture repair were collected. Before repair one of the fractured surfaces was entirely removed with a fretsaw, cleaned in a water spray, mounted and gold coated so that the fracture surface could be examined by SEM. Eight upper and eight lower dentures were studied in this way. For comparison, six lower full dentures made in the Department of Restorative Dentistry, were fractured through the incisor region by a direct blow. The direction of the blow was @ 1965
8nd l%lymers,
of full drnturrs that failed in smricr, and othan broken undar controlled conditions, have scanning electron microscopy. The results allow the direction of crack propagation to be that brittla impact is the predominant moda of fracture. lmprovaments in the strangth of the base bond may be the most effective meens of achieving an increase in the strength offull
The topography of the experimental fracture of poly(methyl methacrylate) (PMMA) has been studied by many workers14. The results have been confusing and the features described have tended to vary with the mode of fracture employed. It has been stated that fatigue is a cause of full denture failure, a claim that has encouraged investigation of the fatigue properties of dental acrylic resins5. However, it has yet to be established that sufficient deformation of a denture can occur during mastication to allow the necessary separation of the crack surfaces, to cause fatigue crack growth. It is the purpose of this communication to present the findings of a scanning electron microscope (SEM) study of the fractography of dentures which have failed in service. By comparing the findings with those of dentures made in the Department of Restorative Dentistry, University of Sheffield and fractured by impact in the laboratory, it has been possible to draw preliminary conclusions on the mode of fracture of dentures in service. If established they may indicate how preventive measures can be taken, with the possibility of financial benefit to the NHS where the cost of repairing full dentures rose recently to f 1.5 million per yea?.
METHODS
Gl8sses
Et Co (Publishers) 7985,
Vol6
Ltd. 0142-9612/65/02011
March
SO3803.00
Figure 1 The fracture ~48~8 of 8n experimentally broken full lower denture. The rough surf8ce (R) is Ch8r8CtenMiC of the site of crack initiation, the surface becoming smoother 8s the creek progresses in direction (DJ.
Dental
Figure 2 The fracture surface of an experimentally broken fufi lower denture. The striated zone (S) is characteristic of the site of crack termination.
fractures:
D.J. Lamb et af.
described by van Noon and Ellis’ as being characteristic of the fracture of PMMA test pieces without an initiator crack. The fracture surface then became smooth and featureless, and ultimately developed undulations (not present in all specimens) before terminating (Figure 4). opposite the site of initiation, in a zone showing striations inning parallel to the direction of crack travel. Upper dentures showed three similar zones (rough, smooth and striated) but in a relationship modified by the shape of the structure involved. Again the crack started in a rough zone (on the lingual surface this time) adjacent to the denture tooth/denture base interface (Figure 5). The fracture then passed, as a smooth zone, anteriorly and posteriorly. Anteriorly the crack passed to the surface in the fraenal notch - a well documented site of weakness in a full upper denture’. The surface in this region (Figure 6) shows the striated zone indicating crack termination. Posteriorly the crack passed through the palate of the denture where it terminated in a mixture of rough and striated zones (Figure 7). This latter observation may indicate that failure can take place by multiple impacts so explaining the presence of plaque on many of the specimens. In this initial study our results resembled those obtained by experimental fracture of PMMA rods in the Charpy mode, and a majority of our dentures breaking in service showed features characteristic of this type of brit-
Figure 3 The fracture surface of a full iower denture broken in sewice. The rough surface (R), which indicates the likely site of crack initiation, lies adjacent to the interface (I) between the missing incisor tooth and the denture base. The fracture s&ace becomes smoother as the crack progresses in a labia-lingual direction ID).
the direction of crack propagation (Figure 2). These characteristics most resemble those described by recent worker@ as typical of the surfaces of rods broken in the Charpy impact test. The crack normally propagated through the body of any associated tooth indicating good adhesion between the teeth and the denture base. While the crack path of the dentures broken in service always passed through the region of the incisorteeth, it never propagated through the body of a tooth. Instead it passed through the interface between a denture tooth and the denture base which appeared to be a site of weakness. Five of the dentures fractured in service showed no characteristic features either because much of the surface remained covered by plaque deposited from the saliva, or because the surface was entirely irregular. However, with minor variations, five lower and six upper dentures revealed features similar to those broken experimentally. By comparison with the experimentally fractured dentures, the site of initiation of the fractures of dentures broken in service could be assigned. At the point of initiation a representative lower denture showed not the mirror zone described by some authors2 but a small rough area adjacent to the denture tooth/denture base interface on the labial surface (Figure 3). This appeared to be equivalent to the initial ‘banded rough and smooth area’
Figure 4 The fracture surface of a full lower denture showing the aree of crack te~~nation on the fingual surface. The s&ace is generally smooth but a zone of striations (S) parallel to the direction of crack travel (D), characterizes the point at which the fracture comes to the surface.
Figure 5 The site of crack initiation on the lingual surface of a full upper denture. The surface is rough and lies adjacent to the interface (1) between the missing incisor tooth and the denture base.
%iomateriafs
?3%5_ Vat 6 March
fll
Dental fractures: D.J. Lamb et al
between the acrylic tooth and the denture base resin contributes to the incidence of denture fracture. Poor bonding between the denture tooth and the denture base may occur easily during the processing of dentures due to contamination of the denture teeth’. Improvement of the adhesion between denture teeth and denture base may provide the simplest means of securing a reduction in the annual cost of denture repair.
ADDENDUM
Figure 6 The site of crack termination in the fraenalnotch on the !8biat surface of a frectured full upper denture. The striated zone (S) marks the site where the crack comes to the surface. In places the striations are obscured by plaque (P} indicating that the fracture has been incomplete in ?he pslataf region allowing the denture to be worn ternpo~~~y.
It has been suggested by the referee that Figure 5 shows features attributable to fatigue crack growth, and some investigators accept that dentures fracture due to fatigue crack propagation. Our view, which coincides with that of Stafford*, is that fatigue is not a major factor in denture failure. However we are only too well aware that the present study is insufficient to settle such a vexed question. Clearly further experimental evidence is needed before an unequivocal answer can be given to the question of denture fracture in use.
We would like to thank Mrs J. Johnson and Mrs B. Hague at the Department of Restorative Dentistry, Sheffield Dental Hospital, for their help in collecting clinical material.
REFERENCES
Figure 7 Two parts of the fractured paletal surfece of a full upper dentum. The rough and striated zones intermingle indicating intermittent creek propagation.
tle impact fracture. This confirms the suggestion that fatigue fracture of dentures is less important than previously thoughts. All dentures fracturing in service showed evidence of weakness of the denture tooth/denture base bond, not apparent in any of the dentures made on the premises and broken in the laboratory. This infers that lack of adhesion
ff2
Biomaterials fSB5, Voi 6 March
Andrews, E.H., Fracture in Polymers, Oliver and Boyd, London, 1968, p 185 Kusy, R.P. and Turner, D.T., Influence of the molecular weight of poly(methyl methacrylete) on fracture morphology in tension, Polymer 1977, 18, 391-402 Doyle, M.J., Striations on the fracture surface of glassy polymers, J. Mater. Sci. 1975, 10, 159-l 54 Doyle. M.J., A mechanism of crack branching in polyfmethyt methaccylate) and the origin of the bands on the surfaces of fracture, J. Mater. Sci. 1983, 18, 687-702 Stafford, G.D.. Lewis, T.T. and Huggett, R., Fatigue testing of denture base polymers, J. &a/ ffehebil. 1982, 9, 134-154 vsn Noort, R. end Ellis, B., The fracture topography of poly(methyl methecrylate), ./. Mater. Sci., Letters, (in press) Hill, R.G., Bates, J.F., Lewis, T.T. end Rees, N., Fracture toughness of acrylic denture base, Biometerials 1983, 4. 112-120 Stafford, G.D., (Personal communication) Schoonover, l.c., Fischer, 1.5, Serio, A.F. and Sweeney, W.T., Bonding of plastic teeth to heat-cured denture base resins, J. Am. Dent. Ass. 1952, 44, 285-287
The fracture smfacrs born examined usina daducrd and indicate denture tooth/denture dentuns. Keywords:
of Ceramics,
AND
Dent81 materiel.
denture,
acrylic.
fracture,
strength,
Butterworth
1fO
Biometeriels
University
of Sheffield,
topography
varied to obtain fractures which ran labio-lingually and others which ran linguo-labially. Their fracture surfaces were examined by the same methods used for dentures which had failed in service.
RESULTS AND DISCUSSION The site of crack initiation could be located in the laboratoryfractured dentures because the direction of the applied impulsive force was known. Certain characteristic features of the fracture surface were observed. Whether the crack passed from the labial to the lingual or vice versa, a rough zone (Figure 7) characterized the site from which the crack was initiated. Next after passing through a smooth zone devoid of landmarks, the fracture ended at the opposite side in a zone of striations lying parallel to
MATERIALS
The broken acrylic full dentures of 16 patients attending the Charles Clifford Dental Hospital, Sheffield for denture repair were collected. Before repair one of the fractured surfaces was entirely removed with a fretsaw, cleaned in a water spray, mounted and gold coated so that the fracture surface could be examined by SEM. Eight upper and eight lower dentures were studied in this way. For comparison, six lower full dentures made in the Department of Restorative Dentistry, were fractured through the incisor region by a direct blow. The direction of the blow was @ 1965
8nd l%lymers,
of full drnturrs that failed in smricr, and othan broken undar controlled conditions, have scanning electron microscopy. The results allow the direction of crack propagation to be that brittla impact is the predominant moda of fracture. lmprovaments in the strangth of the base bond may be the most effective meens of achieving an increase in the strength offull
The topography of the experimental fracture of poly(methyl methacrylate) (PMMA) has been studied by many workers14. The results have been confusing and the features described have tended to vary with the mode of fracture employed. It has been stated that fatigue is a cause of full denture failure, a claim that has encouraged investigation of the fatigue properties of dental acrylic resins5. However, it has yet to be established that sufficient deformation of a denture can occur during mastication to allow the necessary separation of the crack surfaces, to cause fatigue crack growth. It is the purpose of this communication to present the findings of a scanning electron microscope (SEM) study of the fractography of dentures which have failed in service. By comparing the findings with those of dentures made in the Department of Restorative Dentistry, University of Sheffield and fractured by impact in the laboratory, it has been possible to draw preliminary conclusions on the mode of fracture of dentures in service. If established they may indicate how preventive measures can be taken, with the possibility of financial benefit to the NHS where the cost of repairing full dentures rose recently to f 1.5 million per yea?.
METHODS
Gl8sses
Et Co (Publishers) 7985,
Vol6
Ltd. 0142-9612/65/02011
March
SO3803.00
Figure 1 The fracture ~48~8 of 8n experimentally broken full lower denture. The rough surf8ce (R) is Ch8r8CtenMiC of the site of crack initiation, the surface becoming smoother 8s the creek progresses in direction (DJ.
Dental
Figure 2 The fracture surface of an experimentally broken fufi lower denture. The striated zone (S) is characteristic of the site of crack termination.
fractures:
D.J. Lamb et af.
described by van Noon and Ellis’ as being characteristic of the fracture of PMMA test pieces without an initiator crack. The fracture surface then became smooth and featureless, and ultimately developed undulations (not present in all specimens) before terminating (Figure 4). opposite the site of initiation, in a zone showing striations inning parallel to the direction of crack travel. Upper dentures showed three similar zones (rough, smooth and striated) but in a relationship modified by the shape of the structure involved. Again the crack started in a rough zone (on the lingual surface this time) adjacent to the denture tooth/denture base interface (Figure 5). The fracture then passed, as a smooth zone, anteriorly and posteriorly. Anteriorly the crack passed to the surface in the fraenal notch - a well documented site of weakness in a full upper denture’. The surface in this region (Figure 6) shows the striated zone indicating crack termination. Posteriorly the crack passed through the palate of the denture where it terminated in a mixture of rough and striated zones (Figure 7). This latter observation may indicate that failure can take place by multiple impacts so explaining the presence of plaque on many of the specimens. In this initial study our results resembled those obtained by experimental fracture of PMMA rods in the Charpy mode, and a majority of our dentures breaking in service showed features characteristic of this type of brit-
Figure 3 The fracture surface of a full iower denture broken in sewice. The rough surface (R), which indicates the likely site of crack initiation, lies adjacent to the interface (I) between the missing incisor tooth and the denture base. The fracture s&ace becomes smoother as the crack progresses in a labia-lingual direction ID).
the direction of crack propagation (Figure 2). These characteristics most resemble those described by recent worker@ as typical of the surfaces of rods broken in the Charpy impact test. The crack normally propagated through the body of any associated tooth indicating good adhesion between the teeth and the denture base. While the crack path of the dentures broken in service always passed through the region of the incisorteeth, it never propagated through the body of a tooth. Instead it passed through the interface between a denture tooth and the denture base which appeared to be a site of weakness. Five of the dentures fractured in service showed no characteristic features either because much of the surface remained covered by plaque deposited from the saliva, or because the surface was entirely irregular. However, with minor variations, five lower and six upper dentures revealed features similar to those broken experimentally. By comparison with the experimentally fractured dentures, the site of initiation of the fractures of dentures broken in service could be assigned. At the point of initiation a representative lower denture showed not the mirror zone described by some authors2 but a small rough area adjacent to the denture tooth/denture base interface on the labial surface (Figure 3). This appeared to be equivalent to the initial ‘banded rough and smooth area’
Figure 4 The fracture surface of a full lower denture showing the aree of crack te~~nation on the fingual surface. The s&ace is generally smooth but a zone of striations (S) parallel to the direction of crack travel (D), characterizes the point at which the fracture comes to the surface.
Figure 5 The site of crack initiation on the lingual surface of a full upper denture. The surface is rough and lies adjacent to the interface (1) between the missing incisor tooth and the denture base.
%iomateriafs
?3%5_ Vat 6 March
fll
Dental fractures: D.J. Lamb et al
between the acrylic tooth and the denture base resin contributes to the incidence of denture fracture. Poor bonding between the denture tooth and the denture base may occur easily during the processing of dentures due to contamination of the denture teeth’. Improvement of the adhesion between denture teeth and denture base may provide the simplest means of securing a reduction in the annual cost of denture repair.
ADDENDUM
Figure 6 The site of crack termination in the fraenalnotch on the !8biat surface of a frectured full upper denture. The striated zone (S) marks the site where the crack comes to the surface. In places the striations are obscured by plaque (P} indicating that the fracture has been incomplete in ?he pslataf region allowing the denture to be worn ternpo~~~y.
It has been suggested by the referee that Figure 5 shows features attributable to fatigue crack growth, and some investigators accept that dentures fracture due to fatigue crack propagation. Our view, which coincides with that of Stafford*, is that fatigue is not a major factor in denture failure. However we are only too well aware that the present study is insufficient to settle such a vexed question. Clearly further experimental evidence is needed before an unequivocal answer can be given to the question of denture fracture in use.
We would like to thank Mrs J. Johnson and Mrs B. Hague at the Department of Restorative Dentistry, Sheffield Dental Hospital, for their help in collecting clinical material.
REFERENCES
Figure 7 Two parts of the fractured paletal surfece of a full upper dentum. The rough and striated zones intermingle indicating intermittent creek propagation.
tle impact fracture. This confirms the suggestion that fatigue fracture of dentures is less important than previously thoughts. All dentures fracturing in service showed evidence of weakness of the denture tooth/denture base bond, not apparent in any of the dentures made on the premises and broken in the laboratory. This infers that lack of adhesion
ff2
Biomaterials fSB5, Voi 6 March
Andrews, E.H., Fracture in Polymers, Oliver and Boyd, London, 1968, p 185 Kusy, R.P. and Turner, D.T., Influence of the molecular weight of poly(methyl methacrylete) on fracture morphology in tension, Polymer 1977, 18, 391-402 Doyle, M.J., Striations on the fracture surface of glassy polymers, J. Mater. Sci. 1975, 10, 159-l 54 Doyle. M.J., A mechanism of crack branching in polyfmethyt methaccylate) and the origin of the bands on the surfaces of fracture, J. Mater. Sci. 1983, 18, 687-702 Stafford, G.D.. Lewis, T.T. and Huggett, R., Fatigue testing of denture base polymers, J. &a/ ffehebil. 1982, 9, 134-154 vsn Noort, R. end Ellis, B., The fracture topography of poly(methyl methecrylate), ./. Mater. Sci., Letters, (in press) Hill, R.G., Bates, J.F., Lewis, T.T. end Rees, N., Fracture toughness of acrylic denture base, Biometerials 1983, 4. 112-120 Stafford, G.D., (Personal communication) Schoonover, l.c., Fischer, 1.5, Serio, A.F. and Sweeney, W.T., Bonding of plastic teeth to heat-cured denture base resins, J. Am. Dent. Ass. 1952, 44, 285-287