An Investigation of the Properties of a New Resin Inlay System

Scott, James Alun (1993) An Investigation of the Properties of a New Resin Inlay System. PhD thesis, University of Glasgow.

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This study was a laboratory based investigation of a new tooth coloured inlay system for posterior teeth; the composite resin inlay. These inlays, although made from conventional composite resin materials are, generally, fabricated outside the mouth and subjected either to hydropneumatic curing in a heat/pressure oven or a secondary cure, following light curing, in a heat\light oven. It has been suggested that this method of fabrication and subsequent curing results in a filling with many advantages over conventional composite resin fillings. Through the study of three proprietary composite resin inlay systems (two light\heat cured and one heat\pressure cured) an attempt was made to assess these proposed advantages and, furthermore, to investigate aspects of the composite resin inlay technique which may be of some clinical relevance. The differences in materials and curing regimes were examined. Two materials were light curing hybrid composite resins which were post cured using a heat\light oven. The third material was a microfilled composite which did not light cure; it was cured in a heat\pressure oven. Pressure, temperature, light intensity and curing duration within the "post cure" ovens differed between systems. It was considered that these differences may be important in production of the post curing effect. Investigation of basic physical properties showed that post curing of light cure composite resins could improve certain physical properties in certain materials. These improvements in properties appeared to be material specific for a given post curing regime and could also be influenced by post curing temperature and duration of post cure. Hydropneumatic curing of a microfilled composite resin resulted in superior physical properties to literature values for similar materials cured by light. This was probably due to the reduced porosity of the set material. Although it cannot be excluded, no evidence was observed for annealing as a process important in improving material properties as no change in physical properties was observed during a storage period of two months. The physical properties of the dual curing composite resin luting cements, for use in these inlay systems were assessed. Properties for the two hybrid materials were significantly greater than those of the microfilled material and were similar to the light\cured composite with which they were used. However, the properties were significantly less than those of the post cured inlays, suggesting a potential weakness in the system. If allowed to self cure, as would be the case under a thick inlay values of flexural strength and hardness dropped by over 20% in both hybrid materials and by 50% in the microfilled material, suggesting that these materials are not truly dual curing at all. Curing time was assessed for the composite cements both with direct light exposure and when illuminated through 1.5mm of inlay. The introduction of inlay material resulted in a 3-4x increase in setting time. These findings suggest that very long exposure times would be necessary to cure the inlay cement to its full potential. The proposed mechanism of improvement in physical properties was the increased degree of cure following post curing. Investigation of the materials using Fourier Transfer Infra Red (FTIR) spectroscopy showed this to be the case, with increases of 7% and 12% in methacrylate conversion being observed when light cured and post cured materials were compared. The degree of cure of the heat\pressure cured materials was found to be similar to the light/heat post cured materials with around 65% conversion. None of the materials tested exhibited cure of over 70%. Fracture toughness testing of the composite resin inlay materials was carried out. The hybrid materials had a higher fracture toughness than the microfil, however no advantage was found in KIc following post curing. This was suggestive of the fact that in addition to the increase in methacrylate conversion occurring during post curing, which increased the flexural modulus, other potentially weakening processes were occurring within the material balancing this effect. No effect was observed in KIc following storage for periods of up to two months. The increased methacrylate conversion of post cured materials has been cited as a reason for poor bond between inlay and luting resin. This potential for debonding was investigated and found not to be the case in heat\light post cured materials, but to be true of hydropneumatically cured composite. As the degree of cure was similar in all materials an alternative reason for debonding of this group was required. Through the use of scanning electron microscopy and confocal light microscopy differences in the fitting surface morphology and potential for micromechanical bonding were found between the groups. This suggested that the lack of porosity, caused by the use of pressure during curing of the microfilled materials, resulted in lack of micromechanical bonding sites on the fitting surface in this system leaving it liable to debond.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Ronnie Strang
Keywords: Dentistry
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-75647
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Dec 2019 09:15
Last Modified: 19 Dec 2019 09:15

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