The Ability of Dental Practitioners to Light-Cure Simulated Restorations.

OBJECTIVES: To determine the ability of dental professionals to deliver a radiant exposure of at least six J/cm2 in 10 seconds to simulated restorations. METHODS AND MATERIALS: The study initially examined 113 light-emitting-diode (LED) light polymerization units (LPUs) used in dental offices to determine if they could deliver at least 6 J/cm2 radiant exposure (RE) in 10s. This assessment was completed by using a laboratory-grade light measuring device (checkMARC, BlueLight Analytics, Halifax, NS, Canada). The participating dental professionals whose LPUs could deliver 6 J/cm2 then used their own LPU to light-cure simulated anterior and posterior restorations in the MARC Patient Simulator (BlueLight Analytics). They then received specific instructions and were retested using the same LPUs. Data were statistically analyzed with a series of one-way analysis of variance (ANOVA), two-way ANOVA, paired-samples t-tests, Fisher post hoc multiple comparison tests, and McNemar tests with a preset alpha of 0.05 (SPSS Inc). RESULTS: Ten (8.8%) LPUs could not deliver the required RE to the checkMARC in 10s and were eliminated from the study. For the anterior restoration, most dental practitioners (87.3%) could deliver at least 6 J/cm2 before instructions. After receiving additional light-curing instructions, only two (1.9%) participants were unable to deliver 6 J/cm2 to the anterior location. At the posterior location, only 55.3% (57) participants could deliver at least 6 J/cm2 before the instructions. After receiving these instructions, an additional 32 participants delivered at least 6 J/cm2. Overall, after receiving instructions on how to use the LPU correctly, the participants improved the amount of RE they delivered to anterior and posterior restorations by 22.5% and 30%, respectively. CONCLUSION: This study revealed that at the baseline, 44.7% of participating dental professionals failed to deliver 6 J/cm2 in 10s to the posterior simulated restoration when using their own LPU.

Effect of light curing method on volumetric polymerization shrinkage of resin composites.

Volumetric polymerization shrinkage of three resin composites (Suprafil, Z100 and Filtek P60) was determined using four light curing methods: method 1: continuous output with conventional intensity light; method 2: continuous output with higher intensity light; method 3: ramp output and method 4: pulse-delay output. Five disc-shaped specimens were prepared from each material for each curing method. Specimen weight was determined with an analytical electronic hydrostatic balance in air and in water before and after curing. Specific gravity values were then determined. Volumetric polymerization shrinkage was calculated using mathematical formulas. Mean volumetric polymerization shrinkage ranged from 1.882 (.015)% to 2.169 (.028)%. ANOVA indicated significant differences among the materials (p<.05). Light curing methods had no effect on volumetric polymerization shrinkage except for Z-100, where method 2 resulted in significantly higher shrinkage than methods 1 and 4. Suprafil shrunk significantly less than the other two materials in all curing methods.

The use of resin cements in restorative dentistry to overcome retention problems.

The use of resin cements in combination with dentin bonding agents can result in superior attachment of prostheses to tooth structure. This paper describes four clinical cases in which dentin-bonded resin cements were used to overcome retention problems. In the first case, a detached fixed partial denture, which was in good condition when separated, was recemented to abutment teeth prepared with less-than-ideal angle of convergence. In the second case, a detached all-porcelain crown was recemented with a dentin-bonded resin cement after appropriate surface treatment. In the third case, a porcelain-fused-to-metal crown made for a molar tooth was cemented to a short clinical crown, avoiding crown-lengthening surgery. In the fourth case, a 3-unit fixed partial denture was recemented to abutments with less-than-ideal supporting features. Dentin-bonded resin cements can help to extend the life of detached prostheses until the patient is financially prepared for replacement or it can help to avoid crown-lengthening surgery.

Management of extensive carious lesions in permanent molars of a child with nonmetallic bonded restorations--a case report.

The badly decayed molar teeth of a 12-year-old were restored using resin composite and ceramic restorations. The maxillary first left permanent molar, which had an extensive carious lesion that had destroyed most of the coronal hard tissues of the tooth, was restored to shape and function with a heat-treated resin composite onlay restoration. The restoration was followed up for two years. The mandibular right first molar had a failing large amalgam restoration with extensive recurrent caries. After a three-month period of pulp-capping, the tooth was restored with a bonded ceramic onlay restoration. A nine-month follow-up of this restoration is provided. The maxillary right first molar, which also had a failing large amalgam/resin composite restoration, was restored with a direct resin composite restoration. Under traditional treatment regimens, these extensive cavities would have been treated using more invasive procedures such as pin-retained restorations or elective root canal therapy, post placement, core build-up and crowning. Bonded non-metallic restorations avoid the trauma, time and cost that accompany such extensive procedures and offer a more conservative approach.

Influence of composite inlay/onlay thickness on hardening of dual-cured resin cements.

This investigation evaluated the effect of resin composite inlay/onlay thickness on the hardness of a group of eight dual-cure resin-based cements. Fourteen disc specimens measuring 6 mm in diameter and 2.5 mm thick were prepared from each of eight dual-cure cements: Adherence, Choice, Duolink, Enforce, Lute-It, Nexus, Resinomer and Variolink. Two specimens from each material were directly light-cured while the remainder of the specimens were light-cured through resin composite spacers varying in thickness from 1 mm to 6 mm. Curing through the spacers always resulted in a decrease in the Knoop hardness number. For some cements, hardness values were reduced by 50% or more when the resin composite spacer thickness was 4 mm or greater even when measurements were made one week after dual-curing. Low hardness values indicate the presence of a weak chemical-curing mechanism that may compromise cement quality in areas of the cavity not readily accessible to the curing light.

Retention of a posterior resin-bonded fixed partial denture with a modified design: an in vitro study.

PURPOSE: The aim of this study was to test in vitro the resistance of a modified resin-bonded fixed partial denture (RBFPD) to detachment using a laboratory setup simulating load fatigue of mastication forces. The effect of varying the cement type was also investigated. MATERIALS AND METHODS: Extracted teeth were used to prepare specimens each consisting of a premolar and a molar with a space equivalent to a molar in between. Five test groups were prepared (n = 7). Specimens in group 1 were prepared to receive conventional RBFPDs with proximal grooves, occlusal rests, and lingual wings. Specimens in groups 2 and 3 were prepared to receive modified RBFPDs with retentive-slot restorations. Specimens in group 4 were prepared to receive RBFPDs with retentive-slot restorations only, whereas specimens in group 5 were prepared similarly to the ones in groups 2 and 3 but with inlay preparations instead of the retentive slots. Castings were made and their fit surfaces microetched. In groups 1, 2, 4, and 5 castings were cemented with Cement-It, whereas castings of group 3 were cemented with Panavia 21. Slot cavities of groups 2, 3, and 4 were restored with a resin composite. Specimens were subjected to compressive load cycling for 230,000 cycles at 4 Hz under water. Castings were then separated from the abutments under tensile loading. RESULTS: Mean separation forces were: group 1 = 361 N, group 2 = 525 N, group 3 = 562 N, group 4 = 449 N, and group 5 = 417 N. Groups 2 and 3 had significantly higher mean separation forces than groups 1 and 5. Separation of castings in groups 2 and 3 was associated with a higher frequency of cohesive fracture of the abutments than in group 1. Adhesive failure was uncommon among specimens of groups 2, 3, and 4. CONCLUSION: The modified RBFPDs of groups 2 and 3 had better potential for retention. Increased resistance to dislodgment of the modified RBFPDs was not directly related to the surface area of the castings, nor was it related to the type of resin cement, but rather to mechanical interlocking of the castings with the retentive-slot resin composite restorations.

Resin-bonded fixed partial dentures--a literature review with presentation of a novel approach.

PURPOSE: Resin-bonded fixed partial dentures (RBFPD) have been in our profession for over 20 years. The aim of this work was to provide some background about their development and the factors that influence their clinical longevity. MATERIALS AND METHODS: A recent literature search conducted using MEDLINE along with analysis of bibliographies of published papers revealed a considerable number of publications of RBFPDs since their first introduction in the mid-1970s. Critical analysis of these publications revealed some important and interesting key facts. These were divided into sections about developments in the treatment of the fit surface of the casting, bonding systems, and prosthesis design. A separate section about factors that affect the longevity of RBFPDs is included, along with a detailed description of preparation designs of an anterior and a posterior RBFPD. RESULTS: The typical design of RBFPDs is characterized by a high degree of conservation of tooth structure of abutments compared with designs of conventional fixed prostheses. While the early RBFPDs were associated with a high frequency of premature failure--mostly because of debonding--developments in preparation design and bonding techniques as well as better understanding of the appropriate type of metal alloy to be used and the best preparation method for enhanced bonding have led to significant improvements in their long-term survival. CONCLUSION: RBFPDs should be considered viable treatment options for those clinical situations that are best suited for their use. Preparation design, cement type, and casting alloy type as well as surface treatment are among the most important factors that influence longevity of RBFPDs.

Hardening of new resin cements cured through a ceramic inlay.

This study investigated the degree of hardening achieved through self-curing only and through dual-curing a group of eight new resin-based cements. In addition, the effect of ceramic inlay thickness on cement hardness was determined. Disk specimens measuring 6 mm in diameter and 2.5 mm thick were prepared from eight cements: Adherence, Choice, Duolink, Enforce, Lute-It, Nexus, Resinomer, and Variolink. Eight specimens were prepared from each material; half were self-cured, while the remainder were dual-cured. Knoop hardness measurements were then made at 1-hour, 1-day, and 1-week intervals. In addition 12 specimens of the same dimensions were prepared from each cement and were dual-cured through ceramic spacers of varying thickness (1-6 mm). Hardness measurements were made as above. ANOVA showed significant differences in hardness of self-cured versus dual-cured specimens for all cements (P < 0.0001). Significant differences were also found in the hardness of specimens dual-cured through ceramic spacers 2-3 mm in thickness or more compared with those that were dual-cured without spacer. It is concluded that for some materials self-curing alone was not adequate to achieve sufficient hardening; cement hardness was significantly reduced when ceramic inlay thickness was 2-3 mm or more.

Posterior resin-bonded fixed partial denture with a modified retentive design: a clinical report.

A uncomplicated clinical procedure to enhance the retention of posterior resin-bonded fixed partial dentures was described. This method involves some modifications to the preparation and casting design and requires slightly more time and attention at the cementation stage of the prosthetic treatment.

Radiopacity of dual-cured and chemical-cured resin-based cements.

PURPOSE: The objective of this study was to determine radiopacity values of a group of resin-based cements and to compare them to those of enamel and dentin. MATERIALS AND METHODS: Three specimens 2.5 mm thick were prepared from each of 18 cements (nine chemical-cured and nine dual-cured). Three tooth sections 2.5 mm thick were cut from extracted molars. Specimens and tooth sections were divided into three matching groups. Following standard radiographic techniques, images of each group of specimens, along with an aluminum step wedge were obtained. Optical density readings for each material were determined with a transmission densitometer. Radiopacity values were subsequently calculated as equivalents of aluminum thickness. RESULTS: Analysis of variance indicated significant differences in radiopacity values among the materials (P < 0.0001). Four dual-cured cements (Variolink, Geristore, Enforce, and Nexus) had radiopacity values significantly greater than that of enamel, while two (Choice and Adherence) had radiopacity values similar to enamel. For the remaining three dual-cured cements, Duolink had a radiopacity value significantly lower than that of enamel but higher than that of dentin, while both Lute-It and Resinomer had values similar to dentin. For the chemical-cured cements, five materials had radiopacity values significantly higher than enamel (Sealbond, Advance, Scotchbond, Cement-It, and Dyract-Cem), while two had values significantly lower than enamel but higher than dentin (Biomer and Panavia 21). The remaining two cements had radiopacity values significantly lower than dentin. CONCLUSION: For a group of 18 resin-based cements, some had radiopacity values similar to or significantly lower than that of dentin.

Restorative certainty and varying perceptions of dental caries depth among dentists.

OBJECTIVE: The question of whether dentists who most frequently identify tooth surfaces for definite restoration perceive dental caries as significantly deeper than other dentists is assessed. METHODS: One group of 20 dentists independently examined 145 unrestored approximal tooth surfaces on 16 bitewing radiographs and recorded their restorative and depth decisions. Another group of 15 dentists similarly scored 304 unrestored surfaces on 30 bitewing radiographs. Each group of dentists was later divided into four subgroups according to the number of surfaces designated for definite restoration by each dentist. RESULTS: As the number of tooth surfaces designated for definite restoration increased, mean caries depth (P < .05 for the high vs low subgroups) and the percent of dentinally carious surfaces increased, while the percent of surfaces assessed as sound decreased. Dentists with the lower numbers of surfaces designated for definite restoration came closest to the true histologic mean caries depth of the examined tooth surfaces. CONCLUSIONS: Dentists who designated high numbers of approximal tooth surfaces for definite restoration assessed caries as deeper than other dentists, and deeper than was proven histologically.

Retention of metal ceramic crowns cemented with resin cements: effects of preparation taper and height.

This study investigated the effect of varying crown preparation taper and height on the retention of metal ceramic crowns cemented with resin cements. In part 1, 32 extracted molars were divided into four groups. All groups received complete-veneer crown preparations, two with a 12-degree wall angle and two with a 35-degree wall angle. Crowns were cemented with zinc phosphate and dentin-bonded resin cements. After 24 hour water storage at 37 degrees C, the crowns were separated in tension. Crowns cemented with zinc phosphate were cleaned and recemented with another dentin-bonded resin cement and after similar storage, the crowns were separated. Mean separation forces of resin-cemented crowns were higher than those of crowns cemented with zinc phosphate cement. Mean separation force of 35-degree crowns cemented with one dentin-bonded resin cement was found to be significantly higher than for the 12-degree crowns cemented with zinc phosphate cement. In part II, 32 extracted molars were divided into two groups of complete-veneer crown preparations (group I preparations were 3 mm high and group II were 5 mm high). Crowns for all teeth were cast and cemented with zinc phosphate. After 48 hours' water storage at 37 degrees C, the crowns were separated in tension. Crowns and teeth were then cleaned and each group was subdivided into 2 equal subgroups. In one subgroup of teeth with 3 mm and in one with 5 mm high preparations, the crowns were recemented with one of the two resin cement systems and the other two subgroups were recemented with the other resin cement. After 48-hour water storage, the crowns were separated. Mean separation forces of the resin-cemented crowns were greater than those of crowns cemented with zinc phosphate. Also, mean separation force of 3 mm crowns cemented with one resin cement was significantly greater than the 5 mm crowns cemented with zinc phosphate. Cohesive dentin fracture on separation was observed with some resin-cemented crowns but never with crowns cemented with zinc phosphate.

Posterior acid-etch bridge--a modified retentive design.

This article reviews the recent literature on clinical trial studies of acid-etch bridges. Due to long-term retention problems, acid-etch bridges are not as yet considered among the permanent types of bridge prosthesis. When failure of acid-etch bridges occurs, the weak link seems to be the enamel-resin junction rather than the metal-resin junction. A modified posterior acid-etch bridge design is described in detail. This design, which incorporates a major retention-promoting component, is meant to improve long-term retention of posterior acid-etch bridges. Cast projections are added to the bridge design. These fit loosely into slot cavities made in the abutment teeth. Following bridge cementation, the slot cavities are restored with posterior composite. As a result, the cast metal projections are locked into the abutment teeth. This added retention device will maximize the long-term retention of posterior acid-etch bridges.

Chemical versus dual curing of resin inlay cements.

Dual-cure inlay resin cements polymerize both chemically and through light activation; however, clinically some aspects of the cement are not readily accessible to the light source. This study investigated the degree of cement hardening achieved through chemical curing only versus dual curing and the effect of inlay thickness on cement hardness. Disks 6 x 2.5 mm were prepared from seven commercially available cements. Eight specimens were prepared from each material; half of the specimens were cured chemically only, and the remainder were dual-cured. Knoop hardness measurements were then recorded at 1-hour, 1-day, and 1-week intervals. In addition, 24 specimens of the same dimensions were prepared from each cement. Twelve specimens were dual-cured through resin composite spacers of varying thicknesses (1 to 6 mm), and the others were cured through similar ceramic spacers, and hardness measurements were recorded. Multivariate analysis of variance revealed significant differences in hardness of chemically cured versus dual-cured specimens at the 5% level of significance for all examined cements. Significant differences were also found in the hardness of specimens dual cured through ceramic or resin composite spacers 2 to 3 mm in thickness or more versus those that were dual cured without spacer regardless of the spacer material. It is concluded that chemical curing alone was not sufficient to achieve maximum hardening of the examined cements. Cement hardness was significantly reduced when inlay thickness was 2 to 3 mm or more.

Retention of paraposts cemented with dentin-bonded resin cements.

The main purpose of this study was to assess the retention of Paraposts cemented with dentin-bonded resin cements in single-rooted teeth with elliptical canals. Forty-two mandibular premolars and canines were used in this study. The crowns of these teeth were removed 1 mm above the cementoenamel junction and the root canals instrumented to a depth of 8 mm to receive size 5 Paraposts. Prepared teeth were divided into six equal groups. Each group was assigned to a different cementation system at random. The six cementation systems used were: Fleck's Cement, Universal Post Cementation Kit, Prisma Universal Bond 3/Biomer, Scotchbond 2/Resiment, All-Bond 2/All-Bond C & B Cement, and Scotchbond Multi-Purpose/Resiment. Following post cementation, the teeth were stored in water at 37 degrees C for 24 hours, after which the posts were subjected to uniaxial tensile force on a testing machine until post separation occurred. Paraposts cemented with Prisma Universal Bone 3/Biomer or with Scotchbond Multi-Purpose/Resiment had significantly greater separation forces than posts cemented with any of the other cementation systems. Adhesive failure of the posts occurred in all of the specimens of the resin cement groups, whereas cohesive failure of the cement occurred in the majority of the specimens of the zinc phosphate cement group. The effects of thermocycling and post length (5 mm versus 8 mm) on the retention of Paraposts cemented with dentin-bonded resin cements were also investigated. Neither thermocycling nor post length had a significant effect on post separation force.

Restorative decision making by Ontario dentists.

One-half of the dentists in general practice in Ontario were randomly selected for a survey in June 1992 to determine their practices and decision-making regarding some aspects of restorative dentistry. Using patient scenarios to describe clinical situations, respondents stated the threshold at which a restoration should be placed in various tooth surfaces of persons of different ages, according to the severity of the carious lesion and the usual restorative procedure for different case situations. A total of 1,276 (52 per cent) dentists responded to a detailed mail questionnaire. Data were entered into a personal computer (PC) and analyzed using frequencies and chi-square with the SPSS/PC+ statistical package. Multivariate analyses were undertaken to examine what characteristics of dentists independently explained variations in their usual restorative procedures for approximal and occlusal caries. With approximal lesions, as seen on bitewing radiographs, 60 per cent of the dentists indicated that they would place a restoration in a 12 year old with an enamel lesion that had not reached the dentino-enamel junction, whereas with 30- and 55-year-old patients, 28 and 20 per cent, respectively, would do so. At each patient age, there was a tendency for significantly younger dentists to restore enamel-only lesions more often than other dentists (p < .01). Variations in proposed treatment for an adult patient with above average oral hygiene, but with a small (1-1.5 mm diameter) occlusal cavity that had penetrated through the dentino-enamel junction, were also observed. In this case, 23 per cent of the dentists would prepare a conventional cavity extending to include all fissures, and restore the tooth with amalgam or composite; 45 per cent would prepare a cavity just larger than the outline of the lesion and restore it in the same way; 32 per cent would prepare a small cavity and place a preventive resin restoration. Significant differences in cavity design were also observed between graduates of the University of Toronto and the University of Western Ontario with respect to restoring approximal carious lesions. A number of the dentists' characteristics were significantly associated (p < .01) with these variations in procedures. These included the dentists' gender, year and university education and type of practice. The documentation and explanation of these large variations in restorative practices have important implications for continuing dental education.

Meta-analysis on long-term clinical performance of posterior composite restorations.

Meta-analysis is a formalized method of combining results of different studies to provide conclusions about the effectiveness of a treatment modality. The aims of this study were to use meta-analysis to determine the clinical performance of posterior composite restorations using the assessment criteria of the USPHS guidelines by combining data from selected multiple studies and to estimate the overall survival rates of posterior composite restorations over time. A computer-aided search of the literature revealed 97 publications on clinical trials of posterior composites in the last 10 years. Following specific selection criteria, which included the year and language of publication, duration of study, class of cavities restored and type of resin composite material used and clinical characteristics assessed; 16 studies were found to be suitable for, and included in a meta-analysis. These involved eight different resin composite materials. Assessment criteria data were extracted from each selected study and tabulated on the basis of years of follow-up and materials. The criteria were coded as binary variables. Homogeneity amongst studies was assessed using Woolf's statistic prior to combining the data. Weighted average proportions and standard errors were determined for each of the assessment criteria. Using Kaplan-Meier estimates, survival analyses of individual assessment criteria (outcomes) for two posterior composite materials were conducted and the resultant survival curves for these outcomes for the two materials are presented. Considering the limited number of studies of variable length available for meta-analysis, the results indicate generally high clinical performance of the various posterior composites for the number of outcomes analysed.

Radiopacity of resin-based inlay luting cements.

The radiopacity of a group of seven resin-based inlay luting cements in addition to two porcelain veneer cements was determined. Four inlay cements (Indirect Porcelain System Dentist Bonding Kit, Dicor MGC, Duo, and Twinlook) were found to have radiopacity values significantly greater than the radiopacity of enamel. Two other inlay cements (Dual and Porcelite Dual Cure) were found to have radiopacity values not significantly different from that of enamel, while All-Bond Crown and Bridge cement had a radiopacity value significantly lower than the radiopacity of dentin. For the two porcelain veneer cements examined, one material (Mirage Bond) had a radiopacity value significantly greater than that of enamel, while the other (G-Cera Porcelain Veneer Bonding System) had a radiopacity value significantly lower than that of dentin. It was concluded that only the materials that have radiopacity values greater than or equivalent to the radiopacity of enamel are suitable for use as inlay cements. For porcelain veneers, a relatively high radiopacity value of the cement is advantageous.

Fracture strength and fracture patterns of maxillary premolars with approximal slot cavities.

The fracture strength and fracture patterns of maxillary premolar teeth prepared with two different cavity designs and tested with and without amalgam restorations were determined. No significant difference in the fracture strength of intact premolars and premolars prepared with conventional MOD cavities or slot MO/DO cavities was found whether or not the teeth were restored with amalgam. However, fracture pattern analysis revealed significant differences among the groups of teeth. Premolars with MO/DO slot cavities or slot amalgam restorations exhibited minimal fractures that involved enamel only in the majority of the cases. This behavior was similar to what was observed with intact premolars. In contrast, premolars with conventional MOD cavities or MOD amalgam restorations exhibited severe fractures that involved enamel, dentin, and the root in the majority of the cases. These severe fractures were statistically significantly different from those of premolars with slot cavities or slot restorations as well as from those of intact premolars. It is concluded that when maxillary premolars require restoration of carious lesions on both approximal sides without occlusal involvement, MO/DO slot amalgam restorations will be expected to result in teeth that are unlikely to undergo severe cuspal fracture compared to conventional MOD amalgam restorations.