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Statement of problem. There are no studies that analyze the long-term durability of minimally invasive fixed partial dentures (FPDs) by comparing different methods of adhesive bonding. Purpose. This in vitro study examined the influence of cavity design and operative technique on the marginal adaptation of resin-bonded composite FPDs. Material and methods. Slot-inlay tooth preparations with cavity margins located in enamel were prepared in 18 maxillary canines and 18 maxillary first molars designated as abutments. The specimens were divided equally into 3 experimental groups. In all groups, butt joint tooth preparations were created in canines and molars. In group 2, canines were prepared additionally with a 1.5-mm wide palatal bevel in enamel. After pretests with modification spaces of 11 and 17 mm (length), 2 missing premolars were replaced by the ceromer Targis and reinforced with the glass-fiber material Vectris. The prostheses were inserted with Tetric Ceram with use of an ultrasonic-supported, high-viscosity technique. Restorations were selectively bonded to cavity finish lines in groups 1 and 2 ("selective bonding"). In group 3, restorations were bonded totally to the whole cavity surface ("total bonding"). The restorations were stressed in a computer-controlled masticator. Marginal quality was examined with an SEM at ×200. Results. The percent area of optimal margins after thermomechanical loading between composite and enamel in each group was as follows: group 1, 86.2% ± 12.3% for canines and 95.5% ± 3.5% for molars; group 2, 95.3% ± 2.1% for canines and 96.2% ± 2.7% for molars; and group 3, 95% ± 0.9% for canines and 86.4% ± 3.2% for molars. The marginal quality for molars inserted with total bonding was significantly lower ( P ≤.05). Conclusion. Within the limitations of this study, the selective bonding technique for slot inlay-retained fixed partial dentures resulted in a negligible loss of marginal quality after extensive mechanical and thermal stress. The selective bonding technique is recommended for box-shaped cavity preparations. (J Prosthet Dent 2001;86:81-92.)

This study measured in vitro the displacement of natural canal centres in 18 human teeth before and after shaping by the step-back or Lightspeed techniques. Experimental roots (n = 9 per group), embedded in clear plastic, were cross-sectioned using a 0.1-mm-thick band saw at distances 1.25 mm, 3.25 mm and 5.25 mm from the apices. A stereo microscope was used to take 35 mm slides of the cut surfaces of the sectioned roots and canals. The slides of the uninstrumented canals were scanned into a computer and saved. Each sectioned root was then reassembled and the canals shaped by the step-back or Lightspeed technique. File size 40 and instrument size 50 were selected as the master apical file and master apical rotary for the step-back and Lightspeed groups, respectively. The 18 prepared canals were photographed, and the 35 mm slides scanned and computer stored as previously. This allowed the positions of the pre- and postinstrumented roots to be electronically superimposed for subsequent analyses. Displacements of the root canal centres before and after preparation were assessed in relation to the cross-sectional diameter of the files or instruments used. In addition, increases in cross-sectional area of the root canals after preparation were evaluated in relation to the cross-sectional area of the files or instruments used. Engine-driven nickel-titanium Lightspeed instruments caused significantly less (P < 0.001) displacement of the canal centres, so roots in the Lightspeed group remained better centred than those in the step-back group. The mean cross-sectional area after preparation in the Lightspeed group was significantly less (P < 0.001) than that recorded in the step-back group. Clinically, this implies less apical transportation and less dentine destruction with the Lightspeed technique than with the step-back technique.

In an attempt to compare the morphology of the resin-dentin interface in areas where the dentinal tubules run perpendicularly or at an angle to the cavity surface with that of areas where they run parallel to it, we studied a dentin adhesive system using transmission electron microscopy and fluorescence confocal laser scanning microscopy. The design of the study included the simulation of the normal hydrostatic pressure within the pulp and the dentinal tubules. Following acid etching of the dentinal surface with maleic acid/HEMA, the smear layer was removed, and a superficial zone was demineralized in such a way that the exposed collagenous dentin matrix retained its integrity. Confocal laser scanning microscopal investigations using primer labeled with rhodamine B showed that the penetration of the primer occurred not only vertically via surface porosities, but mainly laterally, via the dentinal tubules. The adhesive resin labeled with fluorescein completely infiltrated the demineralized layer, thereby forming a hybrid layer. The orientation of the dentinal tubules had a profound effect on the formation of the hybrid layer. In areas with perpendicular tubule orientation, the layer was 3.2 +/- 0.8 microns thick, showing solid 27.2 +/- 0.8 microns long resin tags in the dentinal tubules, and a network of tiny tags in their side-branches. In areas with parallel tubule orientation the layer was significantly thinner (1.3 +/- 0.6 microns) and resin tags were absent.

The effectiveness of 5 different brands of dentifrices on caries and plaque were tested in rats in 2 experiments. 10 litters of rats each were infected with Streptococcus sobrinus OMZ-176 and Actinomyces viscosus Ny1. The rats were offered the diet 2000a containing either 40% of sucrose (study I) or 10% of sucrose (study II). The following products were tested topically: (1) H2O, (negative control); (2) chlorhexidine diacetate, (positive control); (3) Parodontax NF; (4) Meridol; (5) Colgate Total; (6) Mentadent C; (7) Dent Xpress. Comparisons with the water control in study I showed that plaque extent was decreased by chlorhexidine diacetate, Dent Xpress and by Mentadent C only. All fluoride-containing dentifrices tested reduced caries. In study II, comparisons with the water control showed that plaque extent was reduced by chlorhexidine diacetate, Parodontax, Meridol, Dent Xpress and by Mentadent C. All dentifrices reduced caries, however, the incidence was low. These 2 studies confirm that fluorides incorporated in dentifrices decrease dental caries in the rat. Differences in the effectiveness of caries inhibition between the 5 dentifrices could not be explained either by the form of fluoride utilized or by the antimicrobials added. Rather, the performance of a given dentifrice depended upon the concerted action of the particular ingredients. It appears that the effect of antiplaque agents should be evaluated in the rat model using a diet containing sucrose at a low level.

Two electronic apex locators based on the gradient (Apit) and absolute (Odontometer) impedance principles were evaluated. Distances of file tips to apical foramina were determined in vivo with the electronic apex locators and subsequently verified after extraction. Mean differences between file tips and apical foramina were +0.14 +/- 0.27 mm and -0.36 +/- 0.71 mm for the Apit and Odontometer, respectively. These differences were statistically significant (p0.001). the Apit's and Odontometer's results ranged from +0.85 to -0.65 mm and from +0.35 to 2.45 mm from the apical foramen, respectively. Ninety-three and 73% of the findings for the Apit and the Odontometer, respectively, were within the +/- 0.5 mm range, whereas 100% and 86%, respectively, were within the +/- 1.0 mm range. Thirty-three and 43% of the results for the Apit and the Odontometer, respectively, were 1.0 mm or less coronal to the apical foramen. The Apit tended to yield the more reliable results because of the narrower range.

Objectives. The 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. Methods. Molars 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 phantom head. Six dentists removed the test restorations under standardized, quasi-clinical conditions. Results. While 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. Significance. The 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.

To determine the loss of enamel after a single 20-secondsapplication of a microabrasion slurry and to evaluate structural changes by means of laser fluorescence, and microscopic and optical measurements.Defined buccal areas with a diameter of 2 mm from 16 extracted human molars were demineralized for 12 weeks using a demineralization gel (pH 4.8). The created artificial white-spot lesions were divided corono-apically in control and test sites, using a rubber cement that prospectively covered the untreated control site. Teeth were divided into two groups of eight teeth each. One group was treated with an abrasive cleaning paste (Pell-ex) and the other group with a commercially available microabrasion slurry (Opalustre) for 20 seconds, applying a load of 200 g. Before and after treatment, standardized photographs were taken for the determination of luminescence and profilometric tracings of the surface, and these were recorded for the determination of enamel loss. The grade of demineralization was quantified using a laser fluorescence method (Diagnodent). Statistical differences were checked using a Mann Whitney and student t-test. Replicas of the treated areas were made for scanning electron microscopy (SEM) analysis, and teeth were histologically investigated by polarized light microscopy.Loss of tooth substance was significantly higher (Por = 0.001) for the microabrasion group (134.8 +/- 35.5 microm) compared with the abrasive cleaning paste group (4.5 +/- 1.2 microm). After treatment, statistically significant differences in fluorescence and luminescence measurements could only be detected for microabraded teeth. No significant changes were noted for teeth treated with an abrasive cleaning paste. Histological findings confirmed removal of the demineralized surface zone when microabrading the enamel, whereas no changes were observed in the test group treated with an abrasive cleaning paste. Polarized light microscopy did not indicate any changes in the mineralization pattern, for example compaction, in the treated subsurface zone.

This in vitro study evaluated: (1) marginal adaptation and (2) attritional wear of composite resin materials with simplified bonding systems.36 standardized Class II MOD cavities were prepared in human mandibulary first molars and divided randomly in six equal groups. Restorations were placed with combinations of resin composites and simplified bonding systems: A = Arabesk and Solobond, B = Z 100 and Scotchbond 1, C = Prodigy and OptiBond, D = FHC Merz light and Resulcin Aqua Prime/Monobond as well as E = Sculpt-It and Bond 1. F = Amelogen Universal in combination with the classical 3 part adhesive system Permaquick served as control for marginal adaptation. For wear rates, enamel versus human enamel served as control. All specimens were subjected to long-term thermomechanical stress in a computer-controlled masticator. Human enamel cusps served as antagonists. Marginal adaptation was evaluated by SEM quantitatively before and after stress. Attritional wear in occlusal contact areas was measured on specimens and antagonists with a surface analyzer. Results were tested for statistical significance with ANOVA.SEM marginal analysis exhibited variations from 45.1 +/- 19.9% (D) to 7.9 +/- 5.4% (E) continuous margin after thermomechanical loading in test groups. All groups achieved statistically significant lower scores (P0.05) for marginal adaptation than the control (F: 87.4 +/- 15.5%). Total attritional wear (specimen + antagonist) varied from 153.2 +/- 32.3 microm (D) to 272.3 +/- 132.7 microm (A). Wear of A and F was statistically significantly higher (P0.05) than enamel versus enamel (162.2 +/- 111.2 microm).

This study evaluated the cleaning and polishing effect of a prophylaxis paste (Cleanic), two differently shaped abrasive-bristle brushes (Occlubrush normal cup and Occlubrush minipoint), and a nylon-bristle brush (Prophy brush) on a fine (Tetric Ceram) and a coarse hybrid resin composite (Tetric Condense) under standardized conditions.A total of 48 round specimens with a diameter of 17.2 mm (232.32 mm2) of a fine and a coarse hybrid resin composite were readied and fixed on scanning electron microscopic mounts. After a standardized polishing procedure, the mean surface roughness values were evaluated using five horizontal and five vertical measurements over an area of 1 x 3 mm. The gloss of each specimen was assessed with a spectrophotometer. Both hybrid resin composite groups were treated with one of the following instruments: a nylon-bristle brush (n = 8), a normal-cup abrasive-bristle brush, or a minipoint abrasive-bristle brush. The medium used was either water (control) or a prophylaxis paste. Surface roughness and gloss were measured after instrumentation times of 15, 30, 60, 90, and 120 seconds. For the evaluation of cleaning ability, another 48 total round specimens of fine and coarse hybrid resin composite were covered with a thin layer of black dispersion color and air dried for 24 hours. Specimens were treated with a nylon-bristle brush or an abrasive-bristle brush in combination with water or prophylaxis paste for 15, 30, 60, 90, and 120 seconds. At the beginning and after every treatment interval, the specimens were scanned, the images were digitized, and the percentage of cleaned surface was measured planimetrically.The abrasive-bristle brush, used in combination with water, produced the best outcomes for cleaning ability, surface roughness, and gloss on resin composite restorations.There is no positive cumulative effect when an abrasive-bristle brush, with its cleaning and polishing effect, is used in conjunction with a prophylaxis paste. Abrasive-bristle brushes used with plain water are highly suitable for cleaning and polishing resin composite surfaces.

To evaluate the "Materials and Methods" of long-term clinical studies in relation to documentation, reproducibility and comparability with and without employing the systematic methods of evidence-based medicine.The "Materials and Methods" sections in 45 clinical long-term published studies of direct posterior resin-based composite restorations were evaluated for their use of systematic methods of evidence-based medicine. The search was limited to the years 1988-1997, using the key words "clinical study/evaluation/results/report, long-term, in vivo, posterior, Class I/II, composite, restoration". Special attention was directed to comparisons of the underlying documentation, descriptions of the operative techniques used, and their reproducibility. In addition, an evidence-based search was carried out using the Internet PubMed interface for MEDLINE, using identical synonyms, to identify studies with high levels of quality of evidence. Documentation, reproducibility, and comparability of "Materials and Methods" were also evaluated.Results revealed how difficult it is to interpret results based on tenuous premises, subjective standards, and inadequate study designs. Only one article could be identified when the search was limited to "humans" and "randomized clinical trials". None of the articles, even when fulfilling the highest quality of evidence, showed sufficient or satisfactory quality of reproducibility in their descriptions in Materials and Methods.

To clinically evaluate conservative fiber-reinforced composite inlay fixed partial dentures (IFPDs) bonded to inlay abutments.Forty fiber-reinforced composite IFPDs were made for 29 patients. Restorations were manufactured with the composite Targis reinforced by Vectris prefabricated glass-fiber elements and were inserted with a high viscosity insertion technique. Forty bonded IFPDs were examined clinically after 1 year, and 25 after 2 years, using modified USPHS criteria. Twenty-five abutment inlays and 12 pontics were analyzed quantitatively by scanning electron microscopy SEM. Results were tested for statistical significance with ANOVA.Although most clinical criteria were rated "alpha", four IFPDs had to be replaced: two retainers debonded and two presented total delamination of veneering material from fiber framework. Two partial delaminations were repaired intraorally. No fractures of framework were observed. SEM marginal analysis of tooth-composite interface exhibited 96.5 +/- 3.0% continuous margin at baseline, 91.0 +/- 5.7% at the 1-year and 89.6 +/- 5.2% at the 2-year recall. Decrease of marginal quality was statistically significant between baseline and 1 year (P= 0.001), but not between 1- and 2-year recalls.

A newly developed prophylaxis paste that contains perlite as an abrasive medium was compared to conventional prophylaxis pastes with regard to relative dentin and enamel abrasion, cleaning ability, and polishing power. Rubber cups and nylon brushes were used as paste carriers. Water, flour of pumice, and a dentin polishing paste served as controls. The Prophylaxis Paste Index was created to assess the clinical potential of the various prophylaxis pastes more accurately. The index was computed for dentin as cleaning ability divided by relative dentin abrasion x surface roughness (in Ra) x 10, and for enamel as cleaning ability divided by relative enamel abrasion x surface abrasion (in Ra). On dentin and enamel, the perlite-based prophylaxis paste consistently yielded low relative dentin and enamel abrasion values, a good cleaning ability, and low surface roughness scores with both rubber cups and nylon brushes. Of all tested prophylaxis pastes, the perlite-based prophylaxis paste excelled in the Prophylaxis Paste Index on dentin and enamel and with both rubber cup and nylon brush applications. Therefore, a perlite-containing prophylaxis paste may have broad professional therapeutic indications and may be used universally as a single paste to clean and polish both dentin and enamel.

Eugenol is claimed to interfere with the polymerization of composite resins and to affect shear bond strengths of dentine-bonded composite restorations. Eugenol-based sealers are used during root canal treatment in teeth that may require build-ups or extensive restorations. Unfortunately, the adverse effect of eugenol has mostly been assessed in shear bond tests and this variable may be clinically inappropriate. The current study evaluate the effect of eugenol in a eugenol-based endodontic sealer on marginal adaptation of composite resin restorations with and without thermo-mechanical stress.Thirty Class V cavities with half of the cavity margins in dentine and half of the cavity margins in enamel were prepared in extracted human premolars and then divided into 5 groups. Teeth in group 1 were not contaminated with eugenol. Cavities in groups 2-4 were contaminated with a eugenol-based sealer (Tubli-Seal, Kerr) and cleaned with: (i) sandblasting, (ii) bur finishing alone or (iii) bur finishing combined with swabbing with alcohol. These 4 groups were temporized for 6 weeks (Ketac, ESPE), whilst group 5 received no eugenol, was not temporized and acted as the control. Cavities were restored with Tetric Ceram using Syntac Classic (Vivadent) as a dentine-bonding agent. The specimens were then thermo-mechanically stressed. The percentages of marginal adaptation in dentinal and enamel margins were assessed in a SEM at x200 magnification before and after stress using a replica method. Mean percentages of marginal adaptation were calculated and compared using a two way-ANOVA (influence of eugenol and cleaning procedure) and non-parametric tests.Marginal adaptation in enamel exceeded 95% and 92% in all specimens before and after thermo-mechanical stress, respectively. Before stress, marginal adaptation in dentine ranged from 92.3 +/- 7.9% to 95.7 +/- 6.2% in groups 1-5. After stress, the percentage of marginal adaptation in dentine decreased significantly overall (P0.05, range 39.8 +/- 21.1% to 82.9 +/- 13.7%). The effect of contamination with eugenol was not significant (P0.05): in contrast, there was a significantly beneficial effect when the entire cavity was finished with burs (P0.01).Under the conditions of this study, the eugenol containing sealer did not significantly impair marginal adaptation in dentinal margins of mixed Class V restorations when bur finishing was employed before placement. However, no other cleaning method was sufficient to produce acceptable figures of marginal adaptation.

Statement of Problem: An in vitro study revealed that a celluloid strip–finished composite surface discolored more than the polished composite surface. Thus, the celluloid strip–finished composite surface may not cure enough compared with the polished composite surface. Purpose: This study tested the hypothesis that the celluloid strip–finished composite surface did not cure enough compared with the polished composite surface. Methods and Material: The composite was placed in a 1.5-mm thick aluminum mold and the upper surface was covered with a celluloid strip. Composite was light cured for 60 seconds, then a layer of approximately 200 μm thick was ground away from the lower surface and polished. The hardness of the upper composite surface that was polymerized under a celluloid strip and the polished lower surface were measured with Vickers hardness measuring instrument 15 minutes, 6 hours, and 6 days after light curing. The hardnesses of polished and celluloid strip–finished surfaces were compared using a paired t test. One-way ANOVA and Tukey was used for tests for the significant differences in hardnesses between 15 minutes, 6 hours, and 6 days after light curing for a given surface. Results: Microhardness of the celluloid strip–finished composite surface was 380.6 N/mm 2 at 15 minutes, 442.5 N/mm 2 at 6 hours, and 519.2 N/mm 2 at 6 days after light curing. Microhardnesses of the polished composite surface was 476.6 N/mm 2 at 15 minutes, 511.7 N/mm 2 at 6 hours, and 535.0 N/mm 2 at 6 days after light curing. The hardness of the celluloid strip–opposed composite surface was significantly lower than that of the polished surface 15 minutes and 6 hours after light curing ( P Conclusion: The hardness of the celluloid strip–opposed composite surface was lower than that of the polished surface at 15 minutes and at 6 hours after light curing. However, there was no difference in microhardness in 6 days. (J Prosthet Dent 2000;83:660-3.)

Quality standards for restorations recently have been defined in Switzerland. Amalgam substitutes must meet restoration Grade 2 requirements (i.e., pulp and dental hard substance must be preserved, and both form and function of the tooth have to be reconstituted). The pertinent operative technique has to be simple and amalgam-like. A minimum service life of 8 years is required. This in vitro study investigated the clinical potential of several amalgam substitutes, taking into account the operative requirements, the defined restorative guidelines, and the required service life.Potential amalgam substitutes evaluated in this study included compomers (Compoglass, Dyract, Dyract AP, Elan, F 2000) and resin-based composites (Alert, Ariston, Definite, Nulite, Solitaire, Surefil). The composites Adaptic and Tetric Cream, using a simplified placement technique, were tested as negative and positive controls, respectively. Marginal adaptation and wear properties were measured in vitro in mixed Class II cavities. Relative radiopacity was measured in terms of millimeters of equivalent aluminum.All compomers showed a radiopacity of 2.5 mm or more aluminum. Only Dyract AP and Elan were more wear resistant than amalgam. After stressing, the percentage of continuous margin was at best 31% overall and 17% in dentin only. Among resin-based composites, the minimum requirements of radiopacity were fulfilled only by Alert, Surefil, and Tetric. Only Definite, Surefil, Solitaire, and Tetric exhibited wear resistance greater than amalgam. After stressing, the best marginal qualities were 41% continuous margin overall, and 8% in dentin only.

Statement Of Problem. Restorative dentistry searches for nonmetal reinforcement of esthetic fixed partial dentures (FPDs). Purpose. This clinical study evaluated conservative fiber-reinforced composite FPDs bonded to inlay abutments. Material And Methods. Twenty fiber-reinforced composite inlay FPDs were made for 15 patients. Restorations were manufactured with the Targis Vectris glass–fiber-reinforced composite system and a simplified laboratory technique. The 20 bonded inlay FPDs were examined clinically and by SEM after 1 year. Results. All 20 FPDs were intact at the 1-year examination. There were no signs of fracture, surface defects, or excessive wear with SEM. SEM marginal analysis exhibited 91.6% ± 5% excellent margins at the tooth-luting composite interface and 86.1% ± 8% excellent margins at luting composite/restoration interface. Conclusion. On the basis of the results of this descriptive study, bonded glass–fiber-reinforced composite inlay FPDs were considered clinically successful at the 1-year examination. (J Prosthet Dent 1999;82:662-8.)

This survey evaluated acceptance of the Lightspeed canal preparation (LS) technique by Swiss practitioners. The technique was introduced to Switzerland in June 1994 and 10 other continuing education (CE) courses were held at the Zurich Dental School by July 1995. Acceptance was assessed by posting questionnaires to the CE course attendees. Of the 305 questionnaires posted, 177 (58%) were returned. Of the CE participants 80% had used the technique with 60% finding the method easier and 43% finding it quicker than their usual preparation techniques. Of the respondents 58% used the technique on all tooth types and 76% of the LS users had fractured an instrument at least once. Amongst others, fractures were caused by too much pressure (25%), incorrect insertion angles (17%) and by a complicated root morphology (15%). Fractures occurred high up on the instrument shaft (74%) and near the tip (7%). Working lengths were claimed by 62% to be easier to maintain by LS than their usual preparation techniques. Among the respondents 52% obturated LS prepared canals more easily and quickly compared with their usual preparation techniques. Only 10% of LS users would not recommend the technique, but those who would suggested that proper tuition was necessary to minimize the risk of instrument fracture. The LS technique was positively assessed by clinicians who attended the CE courses in Switzerland where endodontics is not accepted as a specialty.

Objectives. This study compared the efficacy of three dentinal adhesives using the “all etch” technique (All-Bond 2, Bisco; Scotchbond MP, 3M Dental Products Co.; OptiBond, Kerr) with a dentinal adhesive which still uses phosphoric acid to condition enamel and a self-etching primer for dentin (A.R.T.-Bondm, Coltene/Whaledent). Methods. Eight V-shaped mixed Class V restorations were placed per group in extracted human premolars. The restorations were subjected to 1,200,000 mechanical occlusal cycles (max. force 49 N; frequency 1.7 Hz) and 3,000 simultaneous thermal cycles (5-50-5°C). Dentinal fluid was simulated using 1:3 diluted horse serum and fed into the pulp chamber both during restoration and loading. Percentages of “continuous margin” were assessed on SEM replicas of enamel and dentinal margins at 200x magnification immediately before and after stressing, respectively. Results. No significant differences were observed before stress between the materials either in enamel or in dentin. After stress, however, OptiBond and A.R.T.-Bond performed significantly better in dentin than the two other adhesives (Kruskal-Wallis, Mann-Whitney; p < 0.05). Although high initial values were observed, All-Bond 2 and Scotchbond MP were not stress-resistant under simulated physiological conditions. Significance. The predicted clinical potential of All-Bond 2 and Scotchbond MP is inferior to that of OptiBond and A.R.T.-Bond.

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.

Encouraging results achieved when using composite resins for anterior dental restorations have resulted in increased indications for use of these materials. Composite resins are widely used in conventionaliy prepared Class I cavities in molars and premolars, despite the disadvantages of their low wear-resistance.1 A tendency to adapt cavity design to the specific physical properties of composite materials has become evident, z-' Some of Black's cavity preparation principles are being questioned because of the practicability of mechanical bonding of resinous materials to acid-etched enamel. Therefore, the principles of preparing macroscopic dentinal retention, resistance form, and extension for prevention have lost some of their validity and significance. In a recent investigation under in vitro conditions, Class II composite resin restorations showed no microleakage at the tooth-restoration interface and had perfect marginal adaptation. Their use resulted in a smaller loss of sound tooth substance when compared to conventional cavity preparation. 5' 6 These Class II restorations were prepared according to the procedures described for adhesive restorations (AR).3. 5 They consisted of a special cavity design, enamel etching, and the combined use of a lowviscosity sealant and a composite resin restoration. Although long-term assessments are not yet available, the preliminary clinical results of the AR are highly encouraging. 7 It was the aim of the present in

The histopathology of human root caries was examined in extracted teeth by different optical methods. The present part of the study details the sequential stages of initial caries in both cementum and peripheral dentin. Significant differences are shown between the mechanisms operating on the various dental hard tissues during development of caries. Histologically distinguishable reaction patterns depended on both the degree of the cariogenic challenge and the respective structural features of cementum and peripheral dentin. Earliest lesions, histologically visible as small clefts traversing cementum and extending into peripheral dentin, were clinically not detectable. Cementum was stepwise destroyed until peripheral dentin became exposed. The exposed peripheral dentin was sclerosed and tubule-free. Demineralization of dentin preceded the degradation of the organic matrix. Frequently, a hypermineralized layer occurred in both cementum and exposed dentin. Its localization was not identical with the anatomical surface. Initial penetration of bacteria into peripheral dentin occurred along small clefts. Breakdown of the organic matrix was the final step in the destructive phase of the carious process.

A comparison using various composite resins and placement techniques is made of the margin quality and isotope microleakage of Class II composite resin restorations placed in extracted molars. Margin quality and isotope microleakage analyses of Class II restorations placed in extracted human molars were compared using various composite resins and placement techniques. At occlusal margins, the traditional (experimental) composite resin restoration placed by the incremental technique showed less microleakage than did the experimental (commercial) composite resin restoration placed by the bulk technique. In each group, the occlusal and proximal adaptations had significantly higher “excellent margin” than did the cervical adaptation. Thus, the marginal adaptation at the cervical aspect of conventional Class II composite resin restorations may present a problem with respect to microleakage.