Ivo Krejci

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.

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.

Influence of Dentinal Fluid and Stress on Marginal Adaptation of Resin Composites

The influence of dentinal fluid and of a number of stress procedures on the quality of the margins of class V restorations located in both enamel and dentin was quantitatively assessed in vitro with the aid of a scanning electron microscope. The materials tested were GLUMA 2000 experimental, Prisma Universal Bond 3, and Syntac, together with the fine hybrid composites supplied by the respective manufacturers (Pekafill, AP.H, and Tetric). All materials achieved over 95% of continuous margin in enamel before and after stressing. In dentin, the initial values, with as well as without dentinal fluid simulation, were situated between 93.2 and 98.2%. With GLUMA 2000 experimental after stressing, a continuous margin occurred in only 50.2%, but with Prisma Universal Bond 3 and Syntac, the value was 79.0%. The influence of dentinal fluid simulation was dependent on the dentinal adhesive used. The effects of the various stress procedures were not significantly different.

Wear and marginal adaptation of composite resin inlays

MOD inlays were made with conventional, coarse hybrid, fine hybrid, and two microfilled composite resins. They were adhesively luted in six extracted human molars for each group and were subjected to longitudinal, in vitro testing. Final wear ranged from 46.8 +/- 18.6 microns for fine hybrid composite resin to 132.0 +/- 39.3 microns for conventional composite resin for the inlays and from 19.3 +/- 6.6 microns for homogeneous microfilled composite resin to 136.3 +/- 65.1 microns for coarse hybrid composite resin on enamel antagonists. The wear of the luting composite resins ranged from 11.2 +/- 11.2 microns to 20.0 +/- 23.6 microns. Marginal adaptation at the beginning of the test exceeded 88.7% of continuous margin for all groups in enamel. However, marginal gaps were evident in dentin without dentinal adhesives. Marginal adaptation of the microfilled composite resin inlays deteriorated during loads even when a dentinal adhesive and an inlay primer were used. The margins of the other composite resin inlays remained stable during load application.

Effects of Thermocycling and Occlusal Force on Adhesive Composite Crowns

The aim of this in vitro study was to provide first quantitative data on the marginal adaptation and the required load to fracture of adhesive composite crowns with and without adhesive composite cores. Eighteen caries-free extracted human premolars were restored using fine hybrid composite crowns with margins located entirely in dentin. Six crowns were adhesively luted to dentin stubs, six to endodontically treated teeth with adhesive titanium posts and adhesive composite cores, and six to adhesive composite cores without posts. Another ten unprepared teeth served as a control. All restored teeth were subjected to long-term occlusal and thermal stresses. The marginal adaptation was evaluated in the SEM before and after loading. Load to fracture was recorded at the end of the stress. Before stressing, 72.2 to 85.0%, and after stressing, 51.9 to 66.2% of continuous margin were recorded at the dentin-luting composite interface. The best results after stressing were achieved with crowns luted to adhesive composite cores without titanium posts. At the luting composite-composite crown interface, 61.6 to 88.7% of continuous margin before and 57.7 to 75.5% after stressing were recorded. The required load to fracture the restored teeth ranged from 72.0 to 89.2% of the unrestored, unloaded control. Adhesive composite cores without titanium posts yielded the best results.

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.

Effect of Contact Area Size on Enamel and Composite Wear

The effect of contact area dimensions on the wear of composite specimens and their opposing enamel cusps was evaluated in vitro. Thirty-six standardized cylindrical composite specimens were placed into metal cavities (8 mm x 2 mm) and divided randomly into five groups. The composite used was a fine-particle hybrid and was stressed as follows: storage in 75% aqueous ethanol solution for 24 h, toothbrush/toothpaste-abrasion for 30 min, followed by 300 thermal cycles in water ranging from 5° to 55°C and simultaneous 120,000 occlusal chewing loads at a frequency of 1.7 Hz at 53 N maximum force. In group 1 (n = 12), the occlusal chewing loads were applied by palatal cusps of extracted human maxillary molars with natural morphology. In groups 2 to 5 (n = 6), the cusp tips had standardized contact area dimensions of 0.26, 0.38, 1.18, and 4.10 mm2, respectively. Wear of composite specimens and antagonistic enamel cusps (means ± SD) was assessed in μm by means of a 3-D scanner. Additionally, the contact surfaces of the restorations and of the antagonistic enamel cusps were evaluated by SEM. Increases in enamel contact areas after being loaded were measured by means of a digitizer and expressed in percent of the initial size before stress exposure. The wear of the composite specimens varied from 69.8 ± 19.9 to 9.5 ± 3.6 μm, and that of antagonistic enamel cusps from 31.3 ± 3.4 to 8.8 ± 1.5 μm. The increase in contact area varied between 27.8 and 0.1%. Composite and antagonistic enamel wore significantly (p < 0.001, ANOVA, Scheffe) less with increased contact area dimensions. The most severe disintegration of the composite was found in specimens occluding with the smallest enamel contact area. The extent of wear and the wear mechanisms were related to the chewing pressure, which in turn was governed by the contact area dimension.

Time required to remove totally bonded tooth-colored posterior restorations and related tooth substance loss

OBJECTIVESnThe study was conducted to measure the time required to remove large totally bonded tooth-colored posterior restorations and related tooth substance loss. This information was collected to determine if there were differences between bonded restorations and conventional restorations.nnnMETHODSnMolars were restored with the following materials: amalgam, composite, glass ionomer cement or glass ceramic cusp coverages. After submitting them to an in vitro aging process, they were attached to a lower jaw model in a phantom head. Six dentists removed the test restorations under standardized, quasi-clinical conditions.nnnRESULTSnWhile the amalgam was completely removed, some glass ionomer cement vestiges were found. In the glass-ceramic group, the margins were covered with remnants of the composite luting agent in several places. The most restorative material was left in the composite group. The loss of tooth structure after removal of amalgam, glass ionomer cement, composite and glass ceramic was 17.6 mm3, 19.6 mm3, 39.9 mm3 and 41.8 mm3, respectively. When comparing the removal time, the glass ionomer group scored best with an average of 11.9 min followed by the amalgam group with an average of 15.2 min, followed by 24.9 min for the composite group and 30.4 min for the glass ceramic group.nnnSIGNIFICANCEnThe removal of totally bonded posterior restorations made of composite and ceramic is more technically demanding and more time-consuming than the removal of glass ionomer and amalgam restorations.