The flexural strength of 3D-printed provisional restorations fabricated with different resins: a systematic review and meta-analysis.

BACKGROUND: Three-dimensional (3D) printing technology has revolutionized dentistry, particularly in fabricating provisional restorations. This systematic review and meta-analysis aimed to thoroughly evaluate the flexural strength of provisional restorations produced using 3D printing while considering the impact of different resin materials. METHODS: A systematic search was conducted across major databases (ScienceDirect, PubMed, Web of Sciences, Google Scholar, and Scopus) to identify relevant studies published to date. The inclusion criteria included studies evaluating the flexural strength of 3D-printed provisional restorations using different resins. Data extraction and quality assessment were performed using the CONSORT scale, and a meta-analysis was conducted using RevMan 5.4 to pool results. RESULTS: Of the 1914 initially identified research articles, only 13, published between January 2016 and November 2023, were included after screening. Notably, Digital Light Processing (DLP) has emerged as the predominant 3D printing technique, while stereolithography (SLA), Fused Deposition Modeling (FDM), and mono-liquid crystal displays (LCD) have also been recognized. Various printed resins have been utilized in different techniques, including acrylic, composite resins, and methacrylate oligomer-based materials. Regarding flexural strength, polymerization played a pivotal role for resins used in 3D or conventional/milled resins, revealing significant variations in the study. For instance, SLA-3D and DLP Acrylate photopolymers displayed distinct strengths, along with DLP bisacrylic, milled PMMA, and conventional PMMA. The subsequent meta-analysis indicated a significant difference in flexure strength, with a pooled Mean Difference (MD) of - 1.25 (95% CI - 16.98 - 14.47; P < 0.00001) and a high I2 value of 99%, highlighting substantial heterogeneity among the studies. CONCLUSIONS: This study provides a comprehensive overview of the flexural strength of 3D-printed provisional restorations fabricated using different resins. However, further research is recommended to explore additional factors influencing flexural strength and refine the recommendations for enhancing the performance of 3D-printed provisional restorations in clinical applications.

The accuracy of gypsum casts obtained from the disinfected extended-pour alginate impressions through prolonged storage times.

BACKGROUND: Manufacturers of the extended-pour alginates claimed their dimensional stability through prolonged storage. No data confirmed the ability of these materials to maintain their dimensions and the reproduced oral details following their chemical disinfection. Therefore, this study evaluated the dimensional stability and surface detail reproduction of gypsum casts obtained from disinfected extended-pour alginate impressions through different storage time intervals. METHODS: Two hundred and forty three hydrocolloid impressions were made from one conventional (Tropicalgin) and two extended-pour (Hydrogum 5 and Chromaprint premium) alginates. These impressions were subjected to none, spray and immersion disinfection before their storage in 100% humidity for 0, 72 and 120 h. The dimensional stability and the surface detail reproduction were indirectly evaluated under low angle illumination on the resulted gypsum casts. At α = 0.05, the parametric dimensional stability data were analyzed using One-Way ANOVA and Tukey's comparisons, while the nonparametric detail reproduction data were analyzed using KrusKal Wallis and Mann-Whitney's tests. RESULTS: All gypsum casts exhibited a degree of expansion; however, the recorded expansion values did not differ between test categories (P > 0.05). Generally, casts obtained from spray-disinfected impressions showed lower detail accuracy (P < 0.05). Immersion-disinfected extended-pour alginates produced casts with better detail accuracy following 120 h of storage (P < 0.05). CONCLUSION: All alginates materials offer comparable cast dimensions under different testing circumstances. Extended-pour alginates offer casts with superior surface details following their immersion disinfection and 120 h of storage. Spray-disinfection using 5.25% sodium hypochlorite affects the surface details of casts obtained from conventional and extended-pour alginates adversely.

Influences of Successive Exposure to Bleaching and Fluoride Preparations on the Surface Hardness and Roughness of the Aged Resin Composite Restoratives.

Background and Objectives: Surfaces of composite restorations are adversely affected upon bleaching and topical fluoride application. Such a procedure is normally carried out in the presence of restorations already serving in a different oral environment, although previous in vitro studies only considered the freshly-prepared composite specimens for assessment. The current study accordingly aimed to evaluate both the surface hardness and roughness of aged composite restoratives following their successive exposure to bleaching and topical fluoride preparations. Materials and Methods: Disc specimens were prepared from micro-hybrid, nano-filled, flowable and bulk-fill resin composites (groups 1-4, n = 60 each). All specimens were subjected to artificial aging before their intermittent exposure to surface treatment with: none (control), bleach or topical fluoride (subgroups 1-3, n = 20). All surface treatments were interrupted with two periods of 5000 thermal cycles. Specimens' surfaces were then tested for both surface hardness (Vickers hardness number (VHN), n = 10) and roughness (Ra, n = 10). The collected VHNs and Ras were statistically analyzed using two-way ANOVA and Tukey's comparisons at α = 0.05 to confirm the significance of differences between subgroups. Results: None of the tested composites showed differences in surface hardness and roughness between the bleached and the non-treated specimens (p > 0.05), but the bleached flowable composite specimens only were rougher than their control (p < 0.000126). In comparison to the control, fluoride treatment not only reduced the surface hardness of both micro-hybrid (p = 0.000129) and flowable (p = 0.0029) composites, but also increased the surface roughness of all tested composites (p < 0.05). Conclusion: Aged composite restoratives provide minimal surface alterations on successive bleaching and fluoride applications. Flowable resin composite is the most affected by such procedures. Although bleaching seems safe for other types of composites, the successive fluoride application could deteriorate the aged surfaces of the tested resin composites.

Patterns and associated factors of shisha usage among the undergraduate students of Jouf University, Saudi Arabia: A cross-sectional study.

INTRODUCTION: Shisha tobacco use is gaining popularity around the world, especially among young people and college students. Shisha users are exposed to many of the same harmful substances as cigarette smokers but at much higher levels, which could have more serious adverse health impacts. The aims of this study were to: 1) determine the patterns of shisha smoking among university students in the Northern Province of Saudi Arabia; 2) identify the reasons for using shisha tobacco; and 3) ascertain whether usage of shisha smoking differs by their sociodemographic characteristics. METHODS: A cross-sectional survey was conducted among students of seven different colleges at a public university between October and December 2022. A modified version of the Global Youth Tobacco Survey questionnaire was used to collect information specifically on shisha smoking. After adjusting for confounding variables, a logistic regression analysis was used to determine the related factors. RESULTS: A total of 418 participants were included in the study. Of the studied population, shisha smoking was seen in 73.7% (n=308). Out of 308 shisha smokers, 208 (67.5%) had their first session of shisha smoking within the past two years; 34.4% of participants had used it in the past 30 days (current users), of which 27.4% had smoked shisha from 1 to 7 days during the past 30 days. The majority of respondents (63.6%) reported having friends that smoke. The most popular flavor among respondents (24.6%) was apple. For quitting attempts, 46.4% reported a 24-hour quit attempt in the previous year. Stress (23.0%) was reported as the main reason for beginning shisha use. Shisha smoking was significantly associated with age (Ref. 18-20 years; 24-26 years, AOR=0.08; 95% CI: 0.02-0.33, p<0.001; ≥27 years, AOR=0.12; 95% CI: 0.02-0.62, p=0.01), living status (Ref. alone; with family, AOR=0.23; 95% CI: 0.11-0.47, p<0.001; with friends, AOR=0.36; 95% CI: 0.18-0.76, p<0.001), with parents having higher education level (Ref. primary school and lower; Bachelor's, AOR=0.33; 95% CI: 0.14-0.76, p<0.001; diploma, AOR=0.33; 95% CI: 0.15-0.73, p<0.001; PhD, AOR=5.15; 95% CI: 1.00-9.65, p=0.05). CONCLUSIONS: Shisha use was more frequent among Saudi Arabian college students, especially those who were aged 18-20 years, living alone, and having highly educated parents.

Role of Robotics and Artificial Intelligence in Oral Health and Preventive Dentistry - Knowledge, Perception and Attitude of Dentists.

PURPOSE: To assess the knowledge, attitude and perception of dentists (dental students, dental school graduates/interns, postgraduate dentists) of the role of robotics (R) and artificial intelligence (AI) in oral health and preventive dentistry. The null hypothesis was that dentists would not be aware of R and AI use in dentistry and would not be ready to accept them in oral health and preventive dentistry for dental care management and training. MATERIALS AND METHODS: This was an observational cross-sectional study in which data was collected from a representative population in Saudi Arabia. 570 participants answered 26 closed-ended questions. The questionnaire's validity and reliability were evaluated for vetting and remarks. The questionnaire collected demographic data of participants and their knowledge, perception and attitude about R and AI. Questions were to be answered with 'yes', 'no' and 'I don't know'. Descriptive statistical analysis was performed using the control chart technique and the chi-squared test, with statistical significance set at p < 0.05. RESULTS: The majority of the participants (n = 313; 54.6%) were males. Dental students, dentist school graduates/interns, and postgraduate dentists comprised of 58.8%, 18.2%, and 23.0% respectively. Most of the respondents gave affirmative answers for knowledge, attitude and perception of R and AI (58.3%, 67.4%, and 60.3%, respectively). Participants agreed that R and AI is beneficial in dentistry and would provide better results. Most (83.3%) would be willing to be treated using R/AI and would recommend (84.5%) treatment with R/AI, as shown in the control chart by affirmative answers. These were significantly above the overall affirmative answers, as the corresponding point lies above 95% UCL (upper confidence limit). CONCLUSION: Most dentists were unacquainted with R and AI. Dentists had a positive attitude towards R/AI, but due to inadequate knowledge and understanding, its use and applications were very limited. There is significant need in the near future to increase awareness of this concept, as it may increase treatment efficiency and effectiveness.

Debonding characteristics of orthodontic brackets subjected to intraoral stresses under different adhesive regimes: An in-vitro study.

AIM: To evaluate the effect of simulated intraoral hydraulic, thermal, and mechanical stresses on the debonding characteristics of orthodontic brackets under different adhesive regimes. MATERIALS AND METHODS: Groups of pre-coated (G1) and non-coated (G2) orthodontic metal brackets were bonded onto the buccal surfaces of 96 premolars using etch-and-rinse (SG1, n = 24) and self-etch (SG2, n = 24) primers. Twelve specimens (C1) from each subgroup were subjected to early debonding resistance tests, while the other twelve (C2) were used to test delayed debonding resistance after exposure to conditions simulating intraoral hydraulic, thermal, and mechanical stresses. The debonding resistance of the brackets was evaluated using a universal testing machine and the debonding patterns were micro-visualized to determine the adhesive remnant indexes of subgroups of specimens. RESULTS: Within each group, the etch-and-rinse primer (SG1) resulted in higher debonding resistance than self-etch primers (SG2) (p < 0.05), while there was no difference between non-stressed and stressed specimens (p > 0.05). Within each category of test specimens, there was no difference between pre-coated (G1) and non-coated (G2) brackets (p > 0.05). The tested specimens in all categories showed comparable adhesive remnant indexes. However, higher percentages of favorable scores (0 and 1) were obtained for all stressed specimens. CONCLUSIONS: Short-term cumulative intraoral stresses have no adverse effect on the debonding values of either pre-coated or non-coated brackets when either etch-and-rinse or self-etch primer is used for bonding. Exposure of the bonded brackets to different types of stress reflects favorable debonding patterns.

Microleakage of Aesthetic Restorations Following Functional Simulation and Immersion in Saudi-Traditional Mouth Rinses.

AIM: The study is aimed to assess the effect of 3 Saudi-traditional types of mouth rinses (Karadah, Myrrh, salted water) on the microleakage of composite and glass-ionomer restorations subjected to thermal cycling and cyclic loading. MATERIAL AND METHODS: Class V cavities in both buccal and lingual surfaces of eighty extracted premolars were restored with both nano-filled composite and glass-ionomer restoratives. Half the number of restored teeth (group 1, n = 40) were subjected to further thermal cycling and cyclic loading to mimic the in-service functional stresses. The rest of the teeth were left as control with no functional simulation (group 2, n = 40). Teeth of each group were then stored wet for one month in 4 subgroups (n = 10) according to the storage media (distilled water, salted water, Myrrh and Karadah extracts). Following wet ageing, all teeth were immersed in methylene blue solution for 24 hrs, followed by sectioning in Bucco-lingual direction. The microleakage was inspected using stereomicroscope and rated from 0-4 according to its penetration depth. The collected non-parametrical data was then analysed statistically using Kruskal-Wallis One-way ANOVA at α = 0.05. RESULTS: There was no statistically significant difference observed in microleakage between specimens treated with any of the mouthwashes for both glass ionomer and composite restorations in the presence and absence of thermal cycling and cyclic loading (p = 0.889). CONCLUSION: Given the results of the present study, the Saudi-traditional types of mouth rinses are not contributory to microleakage in aesthetic-based composite and glass-ionomer restorations.

Bonding of resin composite to tooth structure of uremic patients receiving hemodialysis: shear bond strength and acid-etch patterns.

PURPOSE: To investigate the influence of uremia on the shear bond strength (SBS) of composite resin to enamel and dentin substrates with assessment of the micromorphological pattern of etched enamel and dentin surfaces using atomic force microscopy (AFM). MATERIALS AND METHODS: A total of 44 natural molars was collected from healthy individuals (n=22 molars) and uremic patients (n=22 molars). Each set of teeth was then divided into 2 equal subsets (n=11 molars) relative to the bonding substrate to be tested. In each subset, the surfaces of 7 molars were flattened and polished up to 2000-grit roughness using wet silicon carbide (SIC) abrasive papers. A three-step adhesive was used to bond Tetric Ceram composite buildups to the prepared tooth surfaces. All specimens were thermocycled before they were stressed in shear using a universal testing machine. Fractured specimens were stereomicroscopically examined to detect the mode of bond failure. In the remaining 4 molars, enamel and dentin specimens were prepared for AFM examination to assess the micromorphological patterns of acid-etched surfaces. RESULTS: The mean bond strength values in MPa to enamel (22.40 +/- 4.30) and dentin (17.97 +/- 4.65) of teeth of healthy individuals were significantly different (p < 0.001) from those to enamel (12.40 +/- 2.81) and dentin (7.83 +/- 2.05) of teeth of uremic patients. Most of the tested enamel specimens showed a mixed type of bond failure, but the adhesive type was predominant with dentin specimens. AFM examinations revealed a shallow etching pattern for uremic enamel and dentin specimens compared to those of healthy individuals. The mean roughness average (Ra) values after etching of healthy enamel (238.0 +/- 4.65) and dentin (267.0 +/- 4.79) were significantly different (p < 0.001) from those to etched uremic enamel (111.0 +/- 5.24) and dentin (143.0 +/- 2.16). CONCLUSION: Uremia adversely affects bonding of composite resin to enamel and dentin and confers an altered micromorphological etching pattern.

Influence of adhesive-composite application modalities on their bonding to tooth structure and resistance of the performed restorations to failure.

BACKGROUND/PURPOSE: The longevity of bonded composite restorations could be affected by the utilized adhesive-composite application techniques. This in vitro study aimed to evaluate the influence of adhesive-composite application modalities on their bonding values to tooth structure and on the failure resistance of the performed restorations on loading. MATERIALS AND METHODS: Resin composite studs, 2 mm in diameter and 4 mm high, were bonded in 2 groups to flattened enamel and dentin surfaces of 80 extracted premolars using pre-cured (PC) and co-cured (CC) self-etch resin adhesive. Studs in each group were built-up in 4 subgroups using either multiple increments of nano-filled composite (IF, control) or single increment of preheated nano-filled (PH), bulk-fill (BF) and sonic-activated bulk-fill composites (SF). Another 80 premolars with standard class II cavities were also restored using the same adhesive-composite application modalities. All specimens were then stressed on a universal testing machine to assess the composite-tooth shear bond strength and the resistance of the performed restorations to failure. The modes of specimens' failure were also assessed following each test. RESULTS: The PC adhesive provided higher bond strength to dentin (p < 0.05) and comparable bond strength to enamel in comparison to the CC one (p>0.05%). Both PH and BF composites showed lower bond strength to dentin in presence of PC adhesive (p < 0.05). Comparable bond strengths were noticed for PH, BF and SF composites to dentin in presence of CC adhesive (p > 0.05). PH and SF restorations presented the highest resistance to failure (p < 0.05). CONCLUSION: Both incrementally and bulky-inserted composites offer clinically acceptable bond strength in presence of pre-cured resin adhesive. Both Preheated and sonic-activated composite restorations offer the highest resistance to failure on loading. The preheating procedure renders regular composite material suitable for bulk-fill applications.

Fracture Resistance of Ceramic Crowns Supported with Indirect Chair-side Composite Cores.

AIMS AND OBJECTIVES: To evaluate the influence of indirect chair-side polymerization of resin composite cores on the fracture resistance of overlaying IPS e.max Press crowns. MATERIALS AND METHODS: Root canals of 60 extracted premolars were prepared to receive #2 fiber posts after the crowns were sectioned 2 mm above the cervical line. In Groups 1-3 (n = 10 each), posts were luted to the prepared dowel spaces using self-adhesive resin cement. Resin composite cores were then bonded and incrementally built-up using Filtek Z250 XT, Filtek P60, and Filtek P90 resin composites. In Groups 4-6 (n = 10 each), the fabricated post-core systems were subjected to post-curing heat and pressure treatment before cementation to their respective teeth using self-adhesive resin cement. Another 10 sound premolars served as control. All teeth in the test and control groups were then subjected to standardized preparation to receive IPS e.max Press crowns before testing their fracture resistance and the mode of restorations' failure. The collected results were statistically analyzed using ANOVA, Kruskal-Wallis, and Tukey's tests on the past software used at α = 0.05 to stand on the significance of the detected differences. RESULTS: Significant differences were detected between the fracture resistance of teeth in different groups (ANOVA, P = 2.857E-35). Crowns in Groups 4-6 provided higher fracture resistance than those in Groups 1-3 (Tukey's test, P < 0.05). Crowns in Groups 4 and 6 provided higher fracture resistance than the control, while those in Groups 2 and 3 provided lower fracture resistance than the control (Tukey's test, P < 0.05). CONCLUSION: Indirect composite cores improved the fracture resistance of IPS e.max Press crowns when compared to directly fabricated post and cores. The directly and indirectly polymerized nanohybrid, methacrylate-based composite (Filtek Z250 XT) cores yielded the highest fracture resistance for the utilized all-ceramic crowns.

Fracture Resistance of Tilted Premolars Restored with Different Post-Core Systems.

AIMS AND OBJECTIVE: To assess the effect of root tilt on the fracture resistance and failure pattern of endodontically-treated premolars restored with different post-core systems. MATERIALS AND METHODS: Ninety endodontically-treated premolars were mounted in acrylic blocks with 0°, 12°, and 24° axial root tilt. Teeth in each group were restored in three subgroups with cast post-core, readymade metal posts and composite cores, and fiber post and composite cores. Crowns of all teeth were prepared coinciding with the long axis of the acrylic blocks to receive all-ceramic crowns. All restored teeth were stressed to record the maximum load at failure and the associated failure pattern. The collected data were statistically analyzed using two-way ANOVA, Tukey's, and Kruskal-Wallis tests at α = 0.05 on past software to detect any differences between subgroups. RESULTS: Analysis of the collected data indicated significant differences between the tested subgroups (ANOVA, P = 3.86). Further analysis showed significant difference between all test subgroups and the control (Tukey's, P < 0.05). In general, teeth with 0° tilt seemed more resistant to fracture than the tilted ones. For all groups, teeth restored with fiber post and composite cores (SG3) were more resistant to fracture compared to other post-core systems (SG1 and SG2) (Tukey's, P < 0.05). The root fracture was the most commonly seen mode of failure. CONCLUSIONS: Root tilting usually affects the fracture resistance of teeth restored with post-core systems. The fiber post and composite cores seemed to be the best choice to restore teeth with different root tilting possibilities.

Bonding of single-component adhesives to dentin following chemomechanical caries removal.

PURPOSE: To determine the effect of chemomechanical caries removal on the bonding quality of contemporary single-component adhesives to dentin. MATERIALS AND METHODS: N-monochloro-DL-2-aminobutyrate solution (NMAB) and Carisolv gel were used to chemomechanically remove dentin caries in 60 extracted human molars. Caries removal with rotating instruments served as the control. Two single-component adhesive systems, Syntac Single Component and Excite, were applied to bond the hybrid composite Tetric Ceram to the treated dentin surfaces. The prepared samples were sectioned for microtensile bond strength testing and SEM examination of the bonding interfaces. The debonding patterns of the fractured samples were also assessed. RESULTS: No statistically significant differences were found between the bond strengths of either adhesive to the conventionally and the NMAB-treated dentin (p > 0.05). However, the Carisolv-treated dentin yielded significantly higher (p > 0.05) bond strength values with both adhesives compared to those on dentin prepared with rotating instruments. No statistical difference could be discerned between the 2 adhesive systems (p > 0.05), nor was the interaction between the 2 variables under investigation (method of caries removal and the type of adhesive) statistically significant (p = 0.7712). SEM images indicated unspecific effects of the tested variables on both the thickness of the hybrid layer and the length of the resin tags. CONCLUSION: Under the conditions of this study, using the Carisolv chemomechanical caries removal system to prepare dentin surfaces enhanced the dentin/adhesive bond strength. In addition, the chemical nature of the adhesive systems seems to have no effect on the values of bond strength.

Influence of resin cements and aging on the fracture resistance of IPS e.max press posterior crowns.

The purpose of this study was to evaluate the effect of different adhesive cements and thermocycling on the fracture resistance of IPS e.max Press posterior single crowns. Thirty-two sound maxillary molars were subjected to standardized preparation and received IPS e.max Press crowns. Another 16 molars were left unprepared to serve as controls (group 1). Panavia F 2.0 and Rely X Unicem luting cements were used to bond the fabricated crowns (n = 16 each) to their respective prepared teeth. Eight specimens from each of the three groups were selected randomly for further thermocycling (5,000 cycles). All specimens were then subjected to fracture resistance testing using anatomical metal attachments fixed to the upper portion of the universal testing machine (1 mm/min). Data were analyzed statistically using two-way analysis of variance and the Student t test (α = .05). Natural teeth presented significantly higher (1,043 and 1,279 N) fracture resistance than that of adhesively cemented ceramic crowns (907 to 986 N) before and after thermocyling, respectively (P < .05). Cement type did not significantly affect fracture resistance results (986 N and 974 N for Panavia F 2.0 and Rely X Unicem, respectively; P > .05). Thermocycled specimens showed lower fracture resistance than that of nonthermocycled ones (P < .05). Neither conventional adhesive cement nor self-etching adhesive cement affected the fracture resistance of IPS e.max crowns. Thermocycling decreased the fracture strength of the crowns in both cement groups. Natural teeth fractured at significantly higher loads than the ceramic crowns.

Bonding quality of contemporary dental cements to sandblasted esthetic crown copings.

AIM: To evaluate the shear bond strength of current luting cements to sandblasted crown-coping substrates. METHODS: Specimens of nickel-chromium, pressable glass ceramic, and zirconia crown-coping substrates were sandblasted in three groups (n = 30 each) with 50 (group 1), 110 (group 2), and 250 µm (group 3) alumina particles at a pressure of 250 kPa. Cylinders of glass ionomer, universal resin, and self-adhesive resin cements were then built up on the sandblasted substrate surfaces of each group (n = 10). All bonded specimens were stressed to evaluate the cement-substrate shear bond strength. Both the mode and incidence of bond failure were also considered. RESULTS: No difference was noticed between all test groups in terms of cement-substrate bond strength. In comparison to self-adhesive type, the universal resin cement provided lower bond strengths to both metal and glass-ceramic substrates in group 1. The self-adhesive resin cement provided the highest bond strengths to the zirconia substrates in groups 2 and 3. The adhesive type of bond failure was common in the metal and zirconia substrates in all groups. CONCLUSIONS: Cement-substrate bonding quality is not affected by the size of sandblasting particles. Resin cements bond better to different coping substrates. Self-adhesive resin cement is the best choice to bond zirconia-based substrates.

Fracture load of composite resin and feldspathic all-ceramic CAD/CAM crowns.

STATEMENT OF PROBLEM: Various machinable materials are currently used with computer-aided design/computer-assisted manufacturing (CAD/CAM) technologies for the chairside fabrication of restorations. However, properties of these new machinable materials, such as fracture load, wear, marginal deterioration, and color stability, should be investigated in vitro under replicated clinical conditions prior to time-consuming clinical studies. PURPOSE: This study investigated the effect of cyclic loading fatigue and different luting agents under wet conditions on the fracture load of CAD/CAM machined composite resin and all-ceramic crowns. MATERIALS AND METHODS: Ninety-six intact human maxillary premolars were prepared for composite resin and all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the cemento-enamel junction, 1.5-mm axial reduction, 2-mm occlusal reduction, and 5-mm occluso-gingival height. Sixteen unprepared premolars served as controls. Forty-eight all-ceramic crowns (Vita Mark II) and 48 millable composite resin crowns (MZ100 Block) were fabricated using a CAD/CAM system (Cerec 3). Three luting agents-RelyX ARC (RX), GC Fuji CEM (FC), and zinc phosphate cement (ZP)-were used for cementation (n = 16). After 1-week storage in water, half of the specimens (n=8) in each subgroup were cyclically loaded and thermal cycled under wet conditions for 600,000 masticatory cycles and 3500 thermal cycles (58 degrees C/4 degrees C; dwell time, 60 seconds) in a masticatory simulator; the other half (n = 8) were fractured without cyclic loading. All specimens were loaded in a universal testing machine with a compressive load (N) applied along the long axis of the specimen at a crosshead speed of 1 mm/min until fracture. Fracture loads (N) were recorded for each specimen. Three-way analysis of variance was used to detect the effects of the experimental factors (crown material, luting agent, and loading conditions) on the fracture load. The comparison with the unprepared natural teeth as controls was done by means of t tests (alpha=.05). RESULTS: Analysis of variance revealed a statistically significant influence of the luting agent and the cyclic loading (P < .001), whereas the crown material had no significant influence. Cyclic loading fatigue significantly decreased the mean fracture load of test groups independent of the 3 luting agents used: MZ100/ZP, 827.1 to 552.5 N; MZ100/FC, 914.7 to 706.2 N; MZ100/RX, 955.9 to 724.4 N; Vita/ZP, 772.3 to 571.5 N; Vita/FC, 923.6 to 721.1 N; and Vita/RX, 929.1 to 752.7 N. However, there was no significant difference in the mean fracture load of control specimens before and after cyclic loading (1140.1 N and 1066.2 N, respectively). Adhesive luting agents RelyX ARC and GC Fuji CEM increased fracture load significantly compared to zinc phosphate cement. CONCLUSIONS: Cyclic loading fatigue significantly reduced the fracture loads of composite resin and all-ceramic crowns, whereas adhesive cementation significantly increased the fracture loads.

The wetting of surface-treated silicone impression materials by gypsum mixes containing disinfectants and modifiers.

PURPOSE: This work evaluated wettability of silicone impression surfaces by gypsum mixes containing disinfectants. MATERIALS AND METHODS: Two types of dental stone were modified by mixing with aqueous solutions of either sodium hypochlorite or povidone iodine. These materials were subjected to further modification by adding a mixture of 1% gum arabic and 0.132% calcium hydroxide to reduce the water requirement of the hemihydrate. Mix consistency tests were carried out to determine the effect of the disinfectants and the modifying additives on the mix fluidity. Contact angles of the mixed materials were measured when they were poured against a polyvinylsiloxane impression material that had undergone the following treatments (1) no treatment (control), (2) surfactant treated, (3) disinfectant treated, and (4) treated with both surfactant and disinfectant. One-way analysis of variance (ANOVA) was carried out using Dunnett's method to determine if experimental groups were significantly different from the control. RESULTS: Gypsum mix consistency was reduced by the presence of combined gum arabic and calcium hydroxide additives. Contact angle data showed that the additives and disinfectants incorporated into the gypsum had, in general, no beneficial effect on the wetting of an untreated silicone surface, or a surface treated with surfactant. In some instances, better wetting was obtained with disinfectant-treated surfaces, and surfaces that had been disinfected and treated with surfactant. CONCLUSIONS: Fluidity of the mixed gypsum was affected by the modifying additives. Chemical disinfectants incorporated in gypsum have little effect on the wetting behavior of dental gypsum. Modifying dental stone powders with gum arabic and calcium hydroxide additives (before mixing at the manufacturers' recommended liquid/powder ratios), improved the wetting behavior of the mixed materials in some cases, but results were not consistent.

The effect of disinfectants on the properties of dental gypsum: 1. Mechanical properties.

PURPOSE: This study was conducted to evaluate the effect of selected disinfectants incorporated in the liquid of dental stones on material strength properties with the aim of developing a material with acceptable mechanical properties. MATERIALS AND METHODS: Two types of dental stone (types III and V) were mixed with aqueous solutions of 0.525% sodium hypochlorite, 0.1% and 10% povidone-iodine, and 2% glutaraldehyde, and with water as a control. The liquid/powder ratios recommended by the manufacturer were used. These materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide to the hemihydrate powders before mixing with the disinfectant solutions at 2 different liquid/powder ratios for each. Both the regular and the modified materials were tested for compressive and diametral tensile strength after 1 hour and 1 week from the start of the mix. The structure of set materials was determined by scanning electron microscopy examination of fracture surfaces. RESULTS: The disinfectants often reduced the strength of both types of dental stone. However, using either 0.1% povidone-iodine or 0.525% sodium hypochlorite resulted in strength values comparable with that of the control. The addition of gum arabic and calcium hydroxide helped reduce the mixing liquid/powder ratios, improving the strength properties of the disinfected materials. CONCLUSIONS: Chemical disinfectants reduce the strength of dental gypsum when used as mixing water substitutes. Gum arabic and calcium hydroxide additives permit a lower liquid/powder ratio and can help offset this weakening.

The effect of disinfectants on the properties of dental gypsum, part 2: surface properties.

PURPOSE: This study is part of an ongoing investigation to evaluate the surface properties of dental stones mixed with disinfection solutions, and to determine the effect of adding gum arabic and calcium hydroxide on the same properties. MATERIALS AND METHODS: Aqueous solutions of 2 chemical disinfectants were used in mixing 2 types of dental stones (type III and type V). These dental stones were modified further by adding 1% gum arabic and 0.132% calcium hydroxide to their hemihydrate powders before mixing. Five specimens prepared from each type of dental stone were classified into 7 groups according to the hemihydrate powder modification and mixing liquid/powder ratio. Surface roughness was tested by 2-dimensional profilometery and scanning electron microscopy (SEM). Knoop hardness testing was carried out, and detail reproduction was assessed using ADA specification 25 in addition to SEM and 3-dimensional profilometer studies. RESULTS: Dental stones mixed with chemical disinfectants showed higher average roughness (R(a)) values than those of the controls. However, adding gum arabic and calcium hydroxide to the hemihydrate powders before mixing restored values to the level of the control. The additives seemed to have a role in the improvement of surface hardness. There was no significant difference between the experimental and the control group in the terms of detail reproduction. CONCLUSIONS: Using SEM, 3-dimensional profilometry, and ADA testing methods, we found that the surface roughness of stone casts was adversely affected by using the disinfectant solutions as mixing water substitutes. Gum arabic and calcium hydroxide additives can yield a harder stone surface without compromising other surface properties.

Evaluation of disinfected casts poured in gypsum with gum arabic and calcium hydroxide additives.

STATEMENT OF PROBLEM: Disinfection of stone casts is an important measure for the control of cross-contamination. Many approaches have been used to disinfect stone casts, but information regarding the accuracy of the resultant casts is limited. PURPOSE: The purpose of this in vitro study was to evaluate the dimensional accuracy, incidence of abutment fracture, and the abutment reproduction of disinfected stone casts made from elastomeric impressions and to determine the effect of gum arabic and calcium hydroxide additives on these properties. MATERIAL AND METHODS: Two aqueous solutions of chemical disinfectants (0.525% sodium hypochlorite and 0.1% povidone iodine) were used as mixing water substitutes for 3 types of dental stone: Types III (Lab Stone), IV (Mile Stone), and V (Die Keen). These stone powders were subjected to further modification by adding 1% gum arabic and 0.132% calcium hydroxide before mixing at the manufacturer-recommended liquid/powder ratios (0.30 for Type III, 0.21 for Types IV and V, respectively). As these additives increased the fluidity of the mix, reduced liquid/powder ratios (0.26 for Type III, 0.19 for Types IV and V, respectively) were also evaluated. Unmodified stone powder mixed with water served as the control. These modifications resulted in 7 test groups for each type of stone. Mixed stones of these groups were poured into 10 putty/wash vinyl polysiloxane impressions made of a customized definitive cast. The percentage of abutments fractured at the time of releasing the resultant casts, as well as the percentages of incompletely reproduced abutments, abutments with air bubbles, and abutments with defective finish lines were compared statistically among the tested groups using the chi-square test (alpha=.05). The average dimensional deviations of the resultant cast from the definitive cast measured in mm were statistically analyzed using 1-way ANOVA (alpha=.05) followed by the Dunnett test to detect any differences among the tested groups. RESULTS: No significant difference was found in abutment fracture or abutment defects for the different formulations of each type of stone used. The resultant casts showed no significant dimensional changes except for Type III and IV stones modified by gum arabic and calcium hydroxide additives and mixed at the recommended liquid/powder ratios. CONCLUSION: Both 0.525% sodium hypochlorite and 0.1% povidone iodine can be used to disinfect dental gypsum with no significant effect on the dimensional accuracy and reproducibility of the resultant casts. Addition of gum arabic and calcium hydroxide to the hemihydrate powders before mixing does not aid in reducing the incidence of defective abutment reproduction.

Reproducibility of sterilized rubber impressions.

Impressions, dentures and other dental appliances may be contaminated with oral micro-flora or other organisms of varying pathogenicity from patient's saliva and blood. Several approaches have been tried to control the transmission of infectious organisms via dental impressions and because disinfection is less effective and has several drawbacks for impression characterization, several sterilization methods have been suggested. This study evaluated the reproducibility of rubber impressions after sterilization by different methods. Dimensional accuracy and wettability of two rubber impression materials (vinyl polysiloxane and polyether) were evaluated after sterilization by each of three well-known methods (immersion in 2% glutaraldehyde for 10 h, autoclaving and microwave radiation). Non-sterilized impressions served as control. The effect of the tray material on impression accuracy and the effect of topical surfactant on the wettability were also evaluated. One-way ANOVA with Dunnett's method was used for statistical analysis. All sterilizing methods reduced the reproducibility of rubber impressions, although not always significantly. Microwave sterilization had a small effect on both accuracy and wettability. The greater effects of the other methods could usually be overcome by using ceramic trays and by spraying impression surfaces with surfactant before pouring the gypsum mix. There was one exception: glutaraldehyde still degraded dimensional accuracy even with ceramic trays and surfactant. We conclude that a) sterilization of rubber impressions made on acrylic trays was usually associated with a degree of dimensional change; b) microwave energy seems to be a suitable technique for sterilizing rubber impressions; c) topical surfactant application helped restore wettability of sterilized impressions.