Annual review of selected dental literature: report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

Coronal Microleakage of Teeth Restored with Cast Posts and Cores Cemented with Four Different Luting Agents after Thermocycling

PURPOSE

The apical seal provided by a root canal filling may be breached via coronal leakage. This study aimed to compare the teeth restored with custom-made cast metal posts and cores cemented with different luting agents in terms of coronal microleakage after thermocycling.

MATERIALS AND METHODS

This in vitro study was conducted on 32 extracted single-canal teeth. Root canals were prepared by step-back technique and filled with gutta percha and sealer. The coronal 7 mm of gutta percha was removed, and post space was prepared using peeso reamers #2 and #3 consecutively. After fabricating the acrylic resin patterns of the posts and cores, they were cast using Ni-Cr metal alloy. The specimens were divided into 4 groups in which the castings were cemented using one of the following luting agents: zinc phosphate (ZP), glass ionomer (GI), Panavia F 2.0, and Speed CEM. After cementation, the teeth were immersed in distilled water and incubated for 7 days. Then, the teeth were subjected to thermocycling, immersed in silver nitrate for 6 hours, and finally sectioned. The degree of dye penetration into the coronal part of the specimens was measured using a stereomicroscope. Data were analyzed using Kruskal-Wallis and Mann-Whitey U tests with significance level of 0.05.

RESULTS

The median microleakage in ZP, Speed CEM, GI, and Panavia were 171.89, 114.76, 26.51, and 20.02 μm, respectively. Pairwise comparisons among GI and ZP, GI, and Speed CEM, ZP and Panavia, ZP and Speed CEM, and Panavia and Speed CEM groups yielded significant differences (p < 0.05).

CONCLUSION

Complete coronal seal was not achieved with any of the luting agents. The highest and the lowest degree of microleakage was yielded by ZP and Panavia luting agents, respectively.

The influences of implant angulations in one and two directions on the retentive properties of overdenture attachments: an in vitro study

Implant alignment is an important factor in overdentures retained by solitary abutments. In this study, the effect of implant angulations in two directions, on the amount of retention of attachments was evaluated. Ninety models were divided into nine groups of two blocks each; one for two implants and one for two attachments. The implants were placed either parallel to, at 5°, or at 10° relative to the reference plane. The attachments were related to the implants with a 0, 5, or 10° angulations. The direction of the implant was either labial or distolabial. The initial and the subsequent retention values of each sample were measured after each 500 cycles of insertion and removal. The measurements were repeated for five consecutive 3,000 cycles, and the results were analyzed by means of one-way ANOVA and Tukey HSD tests. Group 9 with a 10° distolabial tilt of the implants and of their attachments showed the highest initial retention, whereas group 1 with a 0° angulations and parallel attachments showed the lowest (6.9 ± 0.28 and 3.88 ± 0.19 N, respectively). The initial retention and the final loss of retention was significantly higher in those groups with the distolabial tilt of the implants (p < 0.05). Within the limitations of this study, it was demonstrated that the more divergent the implants and their retentive components, the higher their initial retention and the lower their final retention may be.

The in vitro effect of different implant angulations and cyclic dislodgement on the retentive properties of an overdenture attachment system

STATEMENT OF PROBLEM

The retentive capacity of ball attachments may be altered by a change in implant angulations.

PURPOSE

The purpose of this in vitro study was to investigate the effect of cyclic dislodgement on the retention of an overdenture attachment system when 2 implants were placed at angulations of 0, 5, 10, 15, and 20 degrees.

MATERIAL AND METHODS

Twelve acrylic resin blocks were fabricated and divided into 6 groups of 2 pairs each. In each of the 6 groups, 1 acrylic resin block was used to house the implants (block A), while the other (block B) was used to house the overdenture attachments. Two implants positioned at 0/0 degrees, with a standard plastic component(white) designed for 0-degree angulations, served as a control (CTRL), while the other 5 pairs of implants were placed in 5 different angulations: 0D: 0/0 degrees, 5D: 5/5 degrees, 10D: 10/10 degrees, 15D: 15/15 degrees, 20D: 20/20degrees (n=5). The extended range (green color) attachment was used for all groups except the control group. Implants(4.3 mm x 13 mm, internally hexed) were placed in blocks B. All angled implants were mesially tilted. Thirty pairs of attachments (Locator) were used. Dislodging cycles were applied to the overdenture attachment system. The initial retentive forces among the groups were not identical. The cycles required for the retentive forces of the attachments to decrease from the initial values to 60 N, and then to 40 N and 20 N, were recorded for standardization purposes.One-way ANOVA and Tukey HSD tests were used to analyze the difference in retention loss among the 6 groups(alpha=.05). A regression analysis (alpha=.05) was also performed to investigate the relationship between the implant angulation,the retentive force, and the logarithm of the number of cycles required for ball attachment retention decrease.

RESULTS

The 1-way ANOVA and the Tukey HSD tests revealed significant differences for the number of cycles required by different implant angulation groups for the initial retentive values to decrease to 60 N, 40 N, and 20 N (P<.001).The 0D and 5D groups required the longest time for retention loss, while 20D and CTRL groups demonstrated the shortest time for retention loss. The results of the regression analysis of the logarithmic number of cycles on retentive force and implant angulation demonstrated a significant effect (P<.001).

CONCLUSIONS

Implant angulations negatively affect attachment retention longevity. (J Prosthet Dent 2009;102:140-147)

Effect of conventional and experimental gingival retraction solutions on the tensile strength and inhibition of polymerization of four types of impression materials

In the present study, two types of tests (tensile strength test and polymerization inhibition test) were performed to evaluate the physical and chemical properties of four impression materials [a polysulfide (Permlastic), a polyether (Impregum), a condensation silicone (Xantopren) and a polyvinylsiloxane (Aquasil)] when polymerized in contact with of one conventional (Hemostop) and two experimental (Vislin and Afrin) gingival retraction solutions. For the tensile strength test, the impression materials were mixed and packed into a steel plate with perforations that had residues of the gingival retraction solutions. After polymerization, the specimens were tested in tensile strength in a universal testing machine. For the polymerization inhibition test, specimens were obtained after taking impressions from a matrix with perforations that contained 1 drop of the gingival retraction solutions. Two independent examiners decided on whether or not impression material remnants remained unpolymerized, indicating interference of the chemical solutions. Based on the analysis of the results of both tests, the following conclusions were reached: 1. The tensile strength of the polysulfide decreased after contact with Hemostop and Afrin. 2. None of the chemical solutions inhibited the polymerization of the polysulfide; 3. The polyether presented lower tensile strength after polymerization in contact with the three gingival retraction agents; 4. The polyether had its polymerization inhibited only by Hemostop; 5. None of the chemical solutions affected the tensile strength of the condensation silicone; 6. Only Hemostop inhibited the polymerization of the condensation silicone; 7. The polyvinylsiloxane specimens polymerized in contact with Hemostop had significantly lower tensile strength; 8. Neither of the chemical solutions (Afrin and Vislin) affected the tensile strength of the polyvinylsiloxane and the condensation silicone; 9. Results of the tensile strength and polymerization inhibition tests suggest that Vislin can be used as substance of gingival retraction without affecting the tested properties of four impression materials.

Attachment Systems for Implant Retained Overdentures: A Literature Review

This article presents a comparison between different attachment systems used to retain and support maxillary and mandibular overdentures in completely edentulous patients. A literature review based on a MEDLINE search limited to English-language articles published from 1988 to the present was performed, and a large number of attachments available in the dental market were reviewed with regard to several factors, including: (1) implant survival rate, (2) marginal bone loss, (3) soft tissue complications, (4) retention, (5) stress distribution, (6) space requirements, (7) maintenance complications, and (8) patient satisfaction. These factors are considered essential for the successful outcome and good long-term prognosis of the prostheses. Selection criteria previously published in the literature are discussed as well. Product names and manufacturers are mentioned only if related to attachment systems, as they are cited in the original articles.

A pilot study of a simple photon migration model for predicting depth of cure in dental composite

OBJECTIVES

The purpose of this study was to build a photo migration model to calculate the radiant exposure (irradiancextime) in dental composite and to relate the radiant exposure with extent of cure using polymer kinetics models.

METHODS

A composite (Z100, Shade A2) cylinder (21 mm diameter by 15 mm deep) was cured with a tungsten-halogen lamp emitting 600 mW/cm2, 1 mm above the composite for 60s. For each of the 2x1 mm grids along the longitudinal cross section (diameter versus depth), the degree of conversion (DC) and hardness (KHN) were measured to construct the curing extent distribution. The inverse adding-doubling method was used to characterize the optical properties of the composite for the Monte Carlo model simulating the photon propagation within the composite cylinder. The calculated radiant exposure (H) distribution along the cross section was related to the curing extent DC/DC(max) distribution and fitted with two polymer curing kinetics models, the exponential model DC=DC(max)[1-exp((ln0.5)H/H(dc)(50%))] and Racz's model [Formula: see text] , where H(dc)(50%) is a fitting parameter representing the threshold for 50% of the maximum curing level.

RESULTS AND SIGNIFICANCE

The absorption and scattering coefficients of uncured composite were higher than that of cured composite at wavelengths between 420 and 520 nm. A roughly hemi-spheric distribution of radiant exposure in the Monte Carlo simulation result was comparable with the curing profiles determined by both DC and KHN. The relationship between DC (or KHN) and H agreed with the Racz model (r2=0.95) and the exponential model (r2=0.93). The H(dc)(50%) was 1.5(0.1), equal for the two models (P<0.05). The estimated radiant exposure threshold for 80% of the maximum curing level was between 3.8 and 8.8 J/cm2. The simulation results verify that the radiant exposure extends to a greater depth and width for composite with lower absorption and scattering coefficients. Given the optical properties and the geometry of the composite, and the spectrum and the geometry of the light source, the Monte Carlo simulation can accurately describe the radiant exposure distribution in a composite material to predict the extent of cure.

Diagnosis and treatment planning are essential prior to commencing endodontic treatment: discuss this statement as it relates to clinical endodontic management

Diagnosis and treatment planning are essential to the practice of endodontics. Diagnosis aims to determine whether pathological involvement of the dental pulp has or is occurring. Treatment planning meanwhile, involves appropriately selecting cases, determining how difficult the treatment may be to perform on a specific individual and sequencing treatment procedures to achieve a healthy and functional dentition. In endodontic management, this may involve establishing whether the tooth is restorable and periodontally sound, the patient is able to tolerate the treatments and the clinician has the skills to perform the required treatment procedures. Careful consideration of these issues must be given prior to commencing treatment.