Adhesive restorations replacing cusps

Contains fulltext : 49219.pdf (publisher's version ) (Open Access)This study addressed a clinical problem in dentistry. The problem concerns the occurrence of complete fracture of a cusp of premolars with an existing Class II restoration, and the required treatment after this cusp fracture. The traditional treatment in these cases is the making of a crown. Crown preparation requires the removal of (sound) tooth tissue. Adhesive restorations, which require less tissue removal, may offer a tissue saving alternative. The general objective was to develop clinical procedures for adhesive cusp-replacing restorations and to investigate their clinical performance. The main questions were: (1) can we rely solely on the adhesion to the remaining tooth surfaces that are exposed after cusp fracture or do we have to alter the cavity configuration and (2) which are the optimal restorative procedures for successful adhesive cusp-replacing restorations? To find answers to the research questions, in vitro load tests, finite element analyses and a clinical study were performed. After fracture of a cusp in a restored premolar and removal of the existing restoration, a large cavity remains that involves the major part of the clinical crown. The point of departure of the treatment in this study was to restore those fractured premolars by a tissue saving technique. This minimal invasive restorative procedure is characterized by the removal of carious tooth tissue and grinding of a bevel; further preparation is omitted. The results suggest that the remaining cavity does not need adaptation. Consequently, the tooth tissue saving approach should be considered in case of cusp fracture in premolars. From the laboratory studies, no essential differences were shown regarding several restoration procedures. Since there are no indications that the clinical behavior of direct and indirect restorative procedures show differences, the preferences of the dentist and the patient dictate the restorative technique of choice.RU Radboud Universiteit Nijmegen, 27 april 2005198 p

Adhesive restorations replacing cusps.

This study addressed a clinical problem in dentistry. The problem concerns the occurrence of complete fracture of a cusp of premolars with an existing Class II restoration, and the required treatment after this cusp fracture. The traditional treatment in these cases is the making of a crown. Crown preparation requires the removal of (sound) tooth tissue. Adhesive restorations, which require less tissue removal, may offer a tissue saving alternative. The general objective was to develop clinical procedures for adhesive cusp-replacing restorations and to investigate their clinical performance. The main questions were: (1) can we rely solely on the adhesion to the remaining tooth surfaces that are exposed after cusp fracture or do we have to alter the cavity configuration and (2) which are the optimal restorative procedures for successful adhesive cusp-replacing restorations? To find answers to the research questions, in vitro load tests, finite element analyses and a clinical study were performed. After fracture of a cusp in a restored premolar and removal of the existing restoration, a large cavity remains that involves the major part of the clinical crown. The point of departure of the treatment in this study was to restore those fractured premolars by a tissue saving technique. This minimal invasive restorative procedure is characterized by the removal of carious tooth tissue and grinding of a bevel; further preparation is omitted. The results suggest that the remaining cavity does not need adaptation. Consequently, the tooth tissue saving approach should be considered in case of cusp fracture in premolars. From the laboratory studies, no essential differences were shown regarding several restoration procedures. Since there are no indications that the clinical behavior of direct and indirect restorative procedures show differences, the preferences of the dentist and the patient dictate the restorative technique of choice

[Research methods in dentistry 5. The finite element method]

Contains fulltext : 58892.pdf (publisher's version ) (Open Access)The finite element method is a commonly applied experimental research technique. The method comprises computer simulation of constructions under load and of internal mechanical processes, which enables the study of effects of geometrical and material variations. The analysis shows internal stresses and, consequently, predictions can be made of possible failure. In dentistry, the method is applied in disciplines, such as orthodontics, oral and maxillofacial surgery, implantology en restorative dentistry

Microhardness of resin composite materials light-cured through fiber reinforced composite.

Contains fulltext : 79595.pdf (publisher's version ) (Closed access)OBJECTIVES: To compare polymerization efficiency of resin composite basing materials when light-cured through resin composite and fiber reinforced composite (FRC) by testing microhardness. METHODS: Simulated indirect restorations were prepared by application of resin composite (Clearfil AP-X) or FRC (EverStick) to nylon rings with 1.5mm thickness and 8mm diameter, followed by light-curing. Resin composite basing material (Clearfil Majesty Flow or Clearfil AP-X) was applied to identical rings and light-cured through the simulated indirect restorations with exposure times of 20, 40, or 60s. Light-curing though a ring without resin material (=no indirect restoration) served as control. For each combination of basing material and indirect restoration 10 specimens were prepared for each exposure time. Top and bottom surface Vickers microhardness numbers (VHNs) of basing materials were recorded after 24h. RESULTS: After 60s exposure time, VHNs with indirect FRC were not different from control VHNs, while VHNs with indirect resin composite were significantly lower (p<0.001). Linear regression analysis revealed that resin composite basing material used had the greatest effect on top and bottom VHNs (p<0.001). The presence of an indirect restoration resulted in decreased VHNs (p<0.001), with resin composite resulting in lower VHNs when compared to FRC. Moreover, a longer exposure time resulted in increased VHNs (p<0.001). SIGNIFICANCE: Results suggest that polymerization of resin composite basing materials is more effective when light-curing through an FRC than through a resin composite indirect restoration. Prolonging of exposure time, however, is necessary when compared to light-curing without presence of indirect restoration material

Fracture strength of cusp replacing resin composite restorations.

Item does not contain fulltextPURPOSE: To assess the influence of an additional shoulder preparation on the fracture strength of a cusp-replacing direct resin composite restoration in a premolar that previously had an amalgam MOD restoration followed by fracture of a cusp. MATERIALS AND METHODS: Two preparation designs were tested. In extracted sound premolars an MOD amalgam cavity was simulated followed by fracture of a cusp (Group A). Group B was the same as Group A but a shoulder was added along the cervical outline of the preparation. As a control group, cusp fracture was simulated but no MOD amalgam cavities were prepared. For each group, 14 preparations were made using a copy milling technique. All 42 preparations were restored using a direct resin composite restoration technique. Restorations were loaded until fracture. RESULTS: The fracture strength of the preparation with shoulder was not significantly different from the preparation without the shoulder. The fracture strength of the preparations in the reference group, which had no resistance form, was significantly less than in Groups A and B (ANOVA, P<0.05)

Fatigue resistance of teeth restored with cuspal-coverage composite restorations.

Item does not contain fulltextPURPOSE: This study assessed the influence of palatal cuspal coverage on the in vitro fatigue resistance and failure mode of Class II resin composite restorations including replacement of the buccal cusp in premolars. MATERIALS AND METHODS: A master model was made of a maxillary premolar with an MOD amalgam cavity and a simulated fracture of the buccal cusp from the isthmus floor to the CEJ. Using a copy-milling machine, this preparation was copied to 20 extracted human maxillary premolars (group A). Subsequently, the palatal cusp was reduced by 1.5 mm; this modified preparation was copied to 20 additional maxillary premolars (group B). Direct resin composite restorations were made in all teeth. Cyclic load (5 Hz) was applied, starting with a load of 200 N (10,000 cycles), followed by stages of 400, 600, 800, and 1,000 N at a maximum of 50,000 cycles each. Samples were loaded until fracture or to a maximum of 210,000 cycles. RESULTS: Of the restored premolars of group A, 20% withstood all 210,000 loading cycles; in group B, this figure was 55%. In group A, 19% of the fractures ended below the CEJ; in group B, 78% did. CONCLUSION: Palatal cuspal coverage increased the fatigue resistance of Class II resin composite restorations with replacement of the buccal cusp in premolars. However, fractures of restorations with cuspal coverage led to more dramatic failures that made restoration virtually impossible. This suggests caution in lowering remaining cusps for these adhesive restorations in the clinical situation

Shear resistance of fiber-reinforced composite and metal dentin pins

Item does not contain fulltextPURPOSE: To assess whether dentin pins increase shear resistance of extensive composite restorations and to compare performance of mini fiber-reinforced composite (FRC) anchors with metal dentin pins in the laboratory. METHODS: 30 extracted sound molars were randomly divided into three groups. Occlusal surfaces were ground flat with a standard surface area and resin composite restorations were made in Group A. In Groups B and C similar restorations were made, with additionally four metal pins placed in Group B and four FRC pins in Group C. Specimens were statically loaded until failure occurred. Failure modes were characterized as intact remaining tooth substrate (adhesive or cohesive failure of restoration) or fractured remaining tooth substrate. RESULTS: Mean failure stresses were 6.5 MPa (SD 3.2 MPa) for Group A, 9.7 MPa (SD 2.6 MPa) for Group B and 9.2 MPa (SD 2.6 MPa) for Group C. Difference in mean failure stresses between Group A and Groups B and C was statistically significant (P = 0.01), while the difference between Groups B and C was not (P = 0.63). Failures of the restoration without fracture of tooth substrate were seen for 80% of specimens in Group A and 20% in Groups B and C (P = 0.04)

Does layering minimize shrinkage stresses in composite restorations?

Item does not contain fulltextPolymerization shrinkage of resin composites may impair restoration longevity. It is hypothesized that layering, rather than bulk, techniques result in less stress in the tooth-restoration complex. The aim of this study was to compare shrinkage stresses for different restorative techniques used for cusp-replacing restorations with direct resin composite. In a 3-D FE model, the dynamic process of shrinkage during polymerization was simulated. Time-dependent parameters (shrinkage, apparent viscosity, Young's modulus, Poisson ratio, and resulting creep), which change during the polymerization process, were implemented. Six different restorative procedures were simulated: a chemically cured bulk technique, a light-cured bulk technique, and 4 light-cured layering techniques. When polymerization shrinkage is considered, a chemically cured composite shows the least resulting stress. The differences seen among various layering build-up techniques were smaller than expected. The results indicate that the stress-bearing locations are the interface and the cervical part of the remaining cusp

A comparison of fatigue resistance of three materials for cusp-replacing adhesive restorations.

Contains fulltext : 49805.pdf (publisher's version ) (Closed access)OBJECTIVES: To investigate the fatigue resistance and failure behaviour of cusp-replacing restorations in premolars using different types of adhesive restorative materials. METHODS: A class 2 cavity was prepared and the buccal cusp was removed in an extracted sound human upper premolar. By using a copy-milling machine this preparation was copied to 60 human upper premolars. In groups of 20 premolars each, direct resin composite restorations, indirect resin composite restorations and ceramic restorations were made. All restorations were cusp replacements made in standardized shape and with adhesive techniques. Cyclic load (5 Hz) was applied starting with a load of 200 N (10,000 cycles) followed by stages of 400, 600, 800 and 1000 N at a maximum of 50,000 cycles each. Samples were loaded until fracture or to 2,10,000 cycles maximum. In case of fracture, the failure mode was recorded. RESULTS: No differences were seen in fracture strength between the three groups (Wilcoxon P = 0.16). No differences were observed with regard to failure mode above or below the cemento enamel junctions (chi2 P = 0.63). The indirect resin composite and ceramic restorations showed significantly more combined cohesive and adhesive fractures than the direct resin composite restorations, which showed more adhesive fractures (chi2 P = 0.03 and 0.002). CONCLUSIONS: The results of this study suggest that ceramic, indirect resin composite and direct resin composite restorations provide comparable fatigue resistance and exhibit comparable failure modes in case of fracture, although the indirect restorations tend to fracture more cohesively than the direct restorations