F. Lutz

Quality and durability of marginal adaptation in bonded composite restorations

Excellent marginal adaptation extends the longevity of restorations. Unfortunately, polymerization shrinkage of composite restorations adversely affects this quality requirement. The residual stress within the cured resin compromises the materials properties, causes marginal openings, and flexes cavity walls. In this study, the wall-to-wall contraction in MOD cavities was measured for different placement techniques. In addition, the restoration margins were quantitated before and after thermo-cycling and mechanical stressing. Factors which enhanced adaptation also optimized marginal quality and reduced the amount of residual stress. The latter was expressed by intercuspal narrowing after the restoration was completed. Both quality and stress resistance of the marginal adaptation were inversely correlated to the intercuspal narrowing caused by the polymerization contraction of bonded and excellently adapted resin restorations. The most effective factors which optimized marginal quality included: guidance of the shrinkage vectors; reducing the ratio of bonded to free, unbonded restoration surfaces; and minimizing the mass of in situ-cured composite. The latter principle was followed best in the adhesive inlay technique. In medium-sized adhesive MOD composite inlays, the volume loss induced by the polymerization contraction of the composite cement was non-destructively compensated for by an inward flexing of each cavity wall of approximately 10 microM.

Wear of ceramic inlays, their enamel antagonists, and luting cements

The wear of ceramic inlay materials and antagonist enamel cups was measured in vitro. Per group, six MOD inlays were adhesively cemented in extracted molars. Castable glass ceramic, pressed glass ceramic, and feldspathic porcelain were used as inlay materials. A microfilled and a fine hybrid composite served as luting agents. The restorations were exposed to an in vitro wear test that corresponds to approximately 5 years of clinical service. The wear in the occlusal contact area was quantified during and at the end of the test with a three-dimensional scanner. Final wear measurements on the inlays (mean +/- SD) ranged from 21.8 +/- 8.8 microns for pressed glass ceramic to 59.0 +/- 37.9 microns for castable glass ceramic. The mean wear of the enamel antagonists ranged from 74.6 +/- 32.9 microns for pressed glass ceramic to 153.2 +/- 61.5 microns for feldspathic porcelain. The wear of the luting composites at the end of the test ranged from 4.9 +/- 5.1 microns for microfilled to 12.3 +/- 6.3 microns for fine hybrid.

The Influence of Antagonist Standardization on Wear

For differences among materials to be easily detected, low variation in in vitro wear tests is desirable. The working hypothesis of this paper was that antagonists standardized for shape and size and according to materials would show mean values similar to those found in natural, non-standardized cusps, and that standardization would lead to a reduction in mean variation. First, the shapes and sizes of palatal cusps of non-erupted human upper third molars were measured. The cusp cupola was best described by the formula y = 0.001 x2 and was symmetrical around the axis of rotation. Up to 200 μm of the y-axis, this parabola corresponded best to a ball radius of 0.6 mm. Based on this information, standardized antagonists were fabricated from both human enamel and steatite. Wear in the occlusal contact area and the wear of opposing conventional ceramic and fine hybrid composite, respectively, were quantified in a computerized chewing simulator. As a control, natural human enamel cusps were used. Standardization of enamel cusps did not reduce the variation of the resulting wear compared with that of non-standardized enamel antagonists. Furthermore, standardization led to significantly different results both in the antagonists and in the opposing restorative materials. Thus, natural enamel antagonists are preferable for the simulation of wear in the occlusal contact area.

Marginal adaptation of class V restorations using different restorative techniques

This in vitro study compares the marginal adaptation of Class V restorations with margins located half in enamel and half in dentine, which were placed using different restorative techniques. Five operative procedures were evaluated both in saucer-shaped erosion lesions and in box-shaped cavities with bevels in enamel. The five procedures included a composite inlay technique using both the chemically and the light curing versions of a resin based composite cement, a bulk placement technique using a chemically curing composite resin, an incremental technique and an incremental technique combined with a built-up base, using a light curing composite resin. A combination of Gluma/Clearfil served as the dentinal adhesive. The micromorphology of the tooth/restoration interface was analysed before and after thermal cycling; the marginal seal was analysed after thermal cycling only. In the conventional cavities, the restorations showed less leakage, and micromorphologically a better, but statistically insignificant superior marginal adaptation. The inlay technique rendered the best marginal quality in both enamel and dentine before and after thermal cycling. Due to the unique curing characteristics of the chemically cured composite resin and cement resulting in a significantly reduced rigid contraction, the inlays cemented with the chemically curing cement and the restorations placed with the chemically curing composite resin were superior to their light cured counterparts. The built-up base yielding a reduction of the composite mass did not enhance marginal adaptation because of the partial replacement of the strong adhesion to dentine mediated by the Gluma/Clearfil combination by the weaker bond promoted by the etched glass ionomer cement.

Marginal adaptation and fit of adhesive ceramic inlays

This in vitro study compared the marginal adaptation of CAD/CAM and laboratory-made ceramic inlays before, during and after loading. Six MOD inlay preparations of standardized design with one cervical margin in dentine and the other in enamel were prepared for each inlay type: CAD/CAM fabricated MGC-glass ceramic inlays, CAD/CAM fabricated feldspathic porcelain inlays, laboratory-made glass ceramic inlays and laboratory-made feldspathic porcelain inlays. Appropriate luting composite materials were used. The restored teeth were subjected to occlusal loading, thermal cycling, toothbrush-toothpaste abrasion and chemical degradation in vitro. Marginal adaptation was quantitated along the entire length of the cavosurface margin and along selected sections of the margin using SEM, following in vitro testing corresponding to 0, 0.5, 1.0, 2.7 and 5.0 years of clinical service. In addition, marginal fit of the cemented inlays was evaluated in the SEM. The initial marginal adaptation in enamel was excellent in all groups. After in vitro testing, significant marginal discrepancies were found in all groups. A high percentage of marginal openings was recorded, notably in the cervical portions of the margins in both enamel and dentine.

Chewing Pressure us. Wear of Composites and Opposing Enamel Cusps

The effects of various chewing pressures on the wear of composites and enamel were assessed in vitro. Standardized composite discs (8 mm in diameter, 2 mm in height) were made of a fine-particle hybrid (FPH), a coarse-particle hybrid (CPH), and ahomogeneous microfilled composite (HMC). The composite specimens were chemically degraded by immersion in 75% ethanol for 24 h, brushed for 30 min, and then thermocycled 300 times (5-55-5°C) while being occlusally loaded 120,000 times at 1.7 Hz, with chewing forces of 25, 50, 75, and 100 N. Standardized human enamel cusps with a uniform contact area of 0.384 mm2 served as antagonists in the chewing machine. Wear of the composites and enamel cusps, their combined wear, and the increase of the enamel contact surfaces were quantified. An increase in chewing pressure significantly enhanced the wear of both composite and enamel in all groups except for the antagonists opposing a HMC. The FPH was most wear-resistant to in vitro chewing pressures in the range of 6.58 to 19.74 MN/m2, the CPH at 26.32 MN/m2, while the HMC was the most enamel-friendly of the three composites tested. The FPH composite had the least disintegration in the occlusal contact area. The ranking of the composites generally varied at the different chewing pressures with respect to the three types of quantified wear-that is, composite wear, enamel wear, and total wear.

Histopathology of Root Surface Caries

The histopathology of active and arrested human root caries was examined in extracted teeth by different optical methods. Significant differences were observed between the mechanisms operating on the various dental structures. Three different patterns of initial cementum and dentin lesions could be distinguished, depending on the severity of the cariogenic attack, the degree of sclerosis of the peripheral dentin, and the presence of calculus. Advanced lesions were characterized by various patterns of demineralization. In particular, a massive lateral spread of bacteria into intertubular dentin was observed. Consequently, unaffected dentinal areas became continuously undermined. In arrested lesions, either a partial or complete mineralization of the intertubular dentin was apparent. Dentinal tubules were sclerosed passively by re- or precipitation of Ca and P04 ions. In contrast, tubules filled with ghosts of bacteria appeared mineralized by fine-granular crystals. Our observations indicate that both the arrestment and the remineralization of active lesions depend on (1) the degree of active sclerosis of dentinal tubules in areas underlying the lesion, (2) the degree of the bacterial infection of the dentin, (3) the degree of progression of the lesions, and (4) the location of the lesions at the various root surfaces. It is suggested that remineralization of active lesions can occur. This supports the concept of non-invasive treatment of root caries lesions without cavitation.

Consistency in the amount of linear polymerization shrinkage in syringe-type composites

OBJECTIVES The purpose of this study was to investigate whether the composite resin in a syringe showed a consistent shrinkage through its content. Additionally, the amount of linear shrinkage was compared between materials. METHODS Five brands of syringe-type and one brand of carpule-type composite resins were used in this study. To each brand, two to three syringes were assigned. In the carpule-type composite, 15 carpules were used. The linear polymerization shrinkage was measured using a custom-made linometer. In this linometer, the amount of displacement of an aluminum disk, which was caused by the linear shrinkage of composite resin, was recorded by a computer every second for 90 s. RESULTS The syringe-type composites showed similar consistencies in the amount of linear shrinkage except one. The linear shrinkage of the carpule-type Tetric Ceram showed more consistency compared with syringe-type composites. The amount of linear polymerization shrinkage varied between materials. SIGNIFICANCE This investigation demonstrates that the use of carpule-type composites is recommended instead of syringe-types, because of the consistency in its linear shrinkage. The custom-made linometer provides an effective way to study polymerization shrinkage.

Mixed class V restorations: the potential of a dentine bonding agent

The marginal micromorphology and seal of mixed Class V restorations (i.e. restorations with margins located 50 per cent in dentine and 50 per cent in enamel) using Scotchbond VLC or Scotchbond 2 bonded to dentine in conventional and saucer-shaped cavities were evaluated. The four operative systems tested included a two-step incremental filling technique using the light-curing composite Silux, two direct inlay techniques using Silar or Silux as a luting cement and an inlay technique utilizing a Ca(OH)2 liner. All restoration types showed poor marginal adaptation in dentine irrespective of cavity design and bonding agent used. The inlay technique, tested in seven different variations, did not optimize marginal adaptation. Cavity lining with the Ca(OH)2 base material adversely affected dentine bonding. In mixed Class V restorations, marginal adaptation at the dentinal cavosurface line angle continues to pose a problem.

P-10 — Its potential as a posterior composite

Abstract P-10, a hybrid composite resin marketed as a genuine resin-based amalgam substitute, has been evaluated for its effectiveness in stress-bearing posterior restorations. Radiopacity and marginal adaptation were assessed in vitro in MOD-restorations; wear data were derived from 8 MODs after 2.5 years in vivo . The insufficient radiopacity, the poor marginal adaptation and the high wear rate preclude P-10 as an amalgam substitute.