Maxillary interim obturator prosthesis fabrication for a patient with limited mouth opening with a digital approach: A clinical report

Squamous cell carcinoma is a common malignant condition affecting the oral cavity and may involve the surrounding maxillofacial regions. Treatment commonly involves resection of the tumor, followed by prosthetic rehabilitation of the resection defect. This clinical report presents a 62-year-old Asian male patient who had previously undergone surgical resection, resulting in a post-surgical Aramany Class II maxillary defect. The patient's medical history included severe trismus, characterized by restricted mouth opening, as well as a diagnosis of maxillary sinus verrucous squamous cell carcinoma. This report provides a comprehensive account of the rapid fabrication of an interim obturator using digitally assisted dentistry techniques.

Mechanical properties of simulated dentin caries treated with metal cations and L-ascorbic acid 2-phosphate

This pH cycling study aimed to investigate the effects of L-Ascorbic acid 2-phosphate (AA2P) salts of Mg, Zn, Mn, Sr, and Ba on the surface microhardness, compressive strength, diametral tensile strength (DTS), and solubility of root canal dentin. 186 cylindrical dentin specimens from 93 teeth were fortified with optimal concentrations of AA2P salts of Mg (0.18 mM), Zn (5.3 µM), Mn (2.2 × 10-8 M), Sr (1.8 µM), and Ba (1.9 µM). Saline was used as the control group. These dentin specimens underwent a 3-day cycling process simulating dentin caries formation through repeated sequences of demineralization and remineralization. Surface microhardness at 100 and 500 µm depths (n = 10/subgroup), scanning electron microscopy (n = 3/group), compressive strength (n = 10/group), DTS (n = 6/group), and solubility (n = 5/group) tests were performed to analyze the dentin specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, and Post Hoc Tukey tests (p < 0.05). The control group had significantly lower microhardness at both depths (p < 0.001), reduced DTS (p = 0.001), decreased compressive strength (p < 0.001), and higher weight loss (p < 0.001) than all other groups. The Sr group had the highest compressive strength and microhardness among all the groups. The microhardness was significantly higher for the 500 µm depth than the 100 µm depth (p < 0.001), but the difference in microhardness between depths across groups was not significant (p = 0.211). All fortifying solutions provided some protection against artificial caries lesions. Therefore, these elements might have penetrated and reinforced the demineralized dentin against acid dissolution.

Effects of Diabetes on Elemental Levels and Nanostructure of Root Canal Dentin

INTRODUCTION

This study evaluated the effects of diabetes mellitus (DM) on the nanostructure of root canal dentin using high-resolution transmission electron microscopy (HRTEM) and inductively coupled plasma mass spectrometry (ICP-MS).

METHODS

Twenty extracted human premolars from diabetic and nondiabetic patients (n = 10 in each group) were decoronated and sectioned horizontally into 40 2-mm-thick dentin discs, with each disc designated for a specific test. ICP-MS was used to determine the different elemental levels of copper, lithium, zinc, selenium, strontium, manganese, and magnesium in diabetic and nondiabetic specimens. HRTEM was used to analyze the shape and quantity of the apatite crystals in diabetic and nondiabetic dentin at the nanostructural level. Statistical analysis was performed using Kolmogorov-Smirnov and Student t test (P < .05).

RESULTS

ICP-MS revealed significant differences in trace element concentrations between the diabetic and nondiabetic specimens (P < .05), with lower levels of magnesium, zinc, strontium, lithium, manganese, and selenium (P < .05), and higher levels of copper in diabetic specimens (P < .05). HRTEM revealed that diabetic dentin exhibited a less compact structure with smaller crystallites and significantly more crystals in the 2500 nm2 area (P < .05).

CONCLUSION

Diabetic dentin exhibited smaller crystallites and altered elemental levels more than nondiabetic dentin, which could explain the higher root canal treatment failure rate in diabetic patients.

Neural network approach to evaluate the physical properties of dentin

This study intended to evaluate the effects of inorganic trace elements such as magnesium (Mg), strontium (Sr), and zinc (Zn) on root canal dentin using an Artificial Neural Network (ANN). The authors obtained three hundred extracted human premolars from type II diabetic individuals and divided them into three groups according to the solutions used (Mg, Sr, or Zn). The authors subdivided the specimens for each experimental group into five subgroups according to the duration for which the authors soaked the teeth in the solution: 0 (control group), 1, 2, 5, and 10 min (n = 20). The authors then tested the specimens for root fracture resistance (RFR), surface microhardness (SμH), and tubular density (TD). The authors used the data obtained from half of the specimens in each subgroup (10 specimens) for the training of ANN. The authors then used the trained ANN to evaluate the remaining data. The authors analyzed the data by Kolmogorov-Smirnov, one-way ANOVA, post hoc Tukey, and linear regression analysis (P < 0.05). Treatment with Mg, Sr, and Zn significantly increased the values of RFR and SμH (P < 0.05), and decreased the values of TD in dentin specimens (P < 0.05). The authors did not notice any significant differences between evaluations by manual or ANN methods (P > 0.05). The authors concluded that Mg, Sr, and Zn may improve the RFR and SμH, and decrease the TD of root canal dentin in diabetic individuals. ANN may be used as a reliable method to evaluate the physical properties of dentin.

Functional role of inorganic trace elements in dentin apatite tissue-part III: Se, F, Ag, and B

Dentin hydroxyapatite possesses a unique versatile structure which allows it to undergo ionic substitutions. Trace elements play pivotal roles within the oral cavity, especially in dentin apatite tissue. Therefore, it is critical to explore the role of these elements in dentin apatite structure. The roles of other inorganic elements in dentin apatite were discussed in part I (Mg, Sr, Zn, and Fe) and part II (Cu, Mn, Si, and Li) of these series. In the last part of the review series, the role of selenium, fluorine, silver, and boron in the regulation of dentin apatite structure and function was discussed. We evaluated how these elements affect the overall size, morphology, and crystallinity of dentin apatite crystals. Moreover, we investigated the importance of these elements in regulating the solubility of dentin apatite. An electronic search was performed on the role of these trace elements in dentin apatite from January 2010 to January 2022. The concentration of selenium in teeth has been explored only recently, particularly its incorporation into dentin apatite. Silver nanomaterials inhibit the growth of cariogenic microorganisms as well as arrest the degradation of collagen. Fluorine was found to have important roles in dentin remineralization and dentinal tubule occlusion, making it widely used for hydroxyapatite doping. Boron is critical for mineralized tissues like bone, dentin, and enamel, but its exact role in dentin apatite is unknown. Therefore, understanding the impact of these elements on dentin apatite is potentially transformative, as it may help to fill a significant knowledge gap in teeth mechanics.

Functional role of inorganic trace elements in dentin apatite tissue-Part 1: Mg, Sr, Zn, and Fe

Many essential elements exist in nature with significant influence on dentin and bone apatite tissue. Hydroxyapatite (HAp) is the major inorganic crystalline structure of dentin that provides a site for various physiological functions such as surface layer ion exchange. Decades of apatite research have shown that enamel is a high-substituted crystalline apatite, but recent findings suggest that dentin apatite may play a more important role in regulating ion exchange as well as mineral crystallinity. This article is the first part of a review series on the functional role of inorganic trace elements including magnesium, strontium, zinc, and iron in dentin hydroxyapatite. The morphology, physiology, crystallinity, and solubility of these elements as they get substituted into the HAp lattice are extensively discussed. An electronic search was performed on the role of these elements in dentin apatite from January 2007 to September 2021. The relationship between different elements and their role in the mineral upkeep of dentin apatite was evaluated. Several studies recognized the role of these elements in dentinal apatite composition and its subsequent effects on morphology, crystallinity, and solubility. These elements are of great importance in physiological processes and an essential part of living organisms. Magnesium and strontium stimulate osteoblast activity, while zinc can improve overall bone quality with its antibacterial properties. Iron nanoparticles are also vital in promoting bone tissue growth as they donate or accept electrons in redox reactions. Thus, understanding how these elements impact dentin apatite structure is of great clinical significance.

The effect of diabetes on the tensile bond strength of a restorative dental composite to dentin

This study was performed to evaluate the effect of diabetes mellitus (DM) on the tensile bond strength (TBS) of dental composite resin bonding to enamel and dentin of extracted human teeth. Thirty caries-free human premolar teeth (10 from type 1 DM (D1), 10 from type 2 DM (D2), and 10 from non-diabetic individuals (control)) were wet ground and polished to obtain flat surfaces of dentin (n = 10). 37% phosphoric acid was used to etch dentin specimens for 15 s. After the application of the adhesive system, the composite resins were applied and cured for 20 s. Then, specimens were subjected to TBS testing by Universal Testing Machine (1 mm/min). One specimen from each group was prepared and observed under a scanning electron microscope (SEM) and a dot map was generated. Data were analyzed by ANOVA and post hoc Tukey tests (α = 0.05). The TBS values were significantly higher in the control group compared to the D1 and D2 groups (P < 0.05). Between DM groups, D2 values were significantly higher than those in the D1 group. Unlike DM groups, the zigzag fracture pattern was only noticed in the control group. DM adversely affected the TBS of dental composite resins to dentin; this negative effect is more exaggerated by type 1 DM than type 2 DM.

Tissue reaction to novel customized calcium silicate cement based dental implants. A pilot study in the dog

OBJECTIVES

The purpose of this study was to determine the level of periodontal tissue regeneration in a canine model following post-extraction placement of an implant molded from a composite material made from extracted tooth dentin and a calcium silicate cement (CSC) material. The investigation used autologous dentin in conjunction with a CSC material to form a composite implant designed for immediate tooth replacement.

METHODS

Two (2) beagles had a periodontal and radiographic examination performed to rule out any pre-treatment inflammation, significant periodontal disease, or mobility. Then, ination eleven (11) teeth were extracted and polyvinyl siloxane molds were made to fabricate three different types of implants: Particulate Implant (Test Group 1, n = 4), Shell Implant Alone (Test Group 2, n = 2), Shell Implant with Emdogain® (Test Group 3, n = 3). Teeth in the control group were extracted, scaled (n = 2), and then re-implanted into their respective fresh extraction sockets. At 4 weeks, a clinical, radiographic, and histologic assessment was performed.

RESULTS

Clinical evaluation revealed no mobility in any of the test or control implants and no radiographic evidence of significant bone loss or active disease. Based on the MicroCT analysis, direct bone to implant contact was observed in some areas with an apparent periodontal ligament space. Implant-related inflammation, on average, was similar among all groups, with low numbers of infiltrates. Implant-related inflammatory reaction was generally minimal and not interpreted to be adverse.

CONCLUSION

The proposed novel composite materials revealed that not only do these materials demonstrate high biocompatibility, but also their successful integration in the alveolus is likely secondary to a partial ligamentous attachment. The current investigation may lead to the use of calcium silicate-based materials as custom dental implants. Further research on this novel composite's biomechanical properties is necessary to develop the optimal material composition for use as a load-bearing dental implant.

The pH and Bismuth Oxide Particle Size can Affect Diametral Tensile Strength of Mineral Trioxide Aggregate

OBJECTIVE

The aim of the present study was to evaluate the effect of different pHs (4.4, 5.4, 6.4, 7.4, 8.4, and 9.4) and three different particle sizes of bismuth oxide on diametral tensile strength (DTS) of white Mineral Trioxide Aggregate (WMTA).

METHODS

Thirty cylindrical moulds were divided into six groups of five; WMTA was mixed, placed inside the moulds, and wrapped in pieces of gauze soaked in synthetic tissue fluid (STF) with pH values of either 4.4, 5.4, 6.4, 7.4, 8.4, 9.4. For bismuth oxide, eighteen similar molds were divided into three groups of six (n=6). Then bismuth oxide with three particle sizes, including fine (120 nm), medium (200 nm), and coarse (10 μm), were provided and added to the Portland cement, which did not have any bismuth oxide to create WMTA. Then WMTA was mixed, placed inside cylindrical molds. After incubation at 95% humidity for 48 hours, samples were subjected to DTS testing by an Instron Universal testing machine with a crosshead speed of 1 mm/min. Then, one sample from each group was subjected to scanning electron microscope (SEM) analysis. Data were analysed by ANOVA and Tukey tests (α=0.05).

RESULTS

The comparison of DTS in pH groups were: 8.4>7.4>9.4>6.4>5.4>4.4 (P<0.05); and in bismuth oxide groups were: fine particles > medium particles > coarse particles (P<0.05). Acidic pH, negatively affected the distribution of Ca2+ and Si4+ ions, while bismuth oxide with fine particles enhanced it.

CONCLUSION

Acidic pH can decline the DTS of MTA significantly. However, reducing the particle size of bismuth oxide can increase the DTS of MTA significantly.

Effect of Diabetes on Tubular Density and Push-out Bond Strength of Mineral Trioxide Aggregate to Dentin

INTRODUCTION

This study compared the tubular density and push-out bond strength of mineral trioxide aggregate (MTA) to dentin in diabetic and nondiabetic patients.

METHODS

Ten extracted single-rooted human teeth from diabetic and nondiabetic patients (n = 5 in each group) were decoronated, prepared up to a #5 Gates-Glidden drill, and sectioned horizontally at the midroot area to prepare 3 dentin slices, each measuring 2 mm in thickness (1 slice for the push-out test and 2 slices for the tubular density test). MTA was prepared and packed into the root canal space followed by incubation for 3 days. The push-out bond strength values were determined using a universal testing machine. Specimens were viewed under a stereomicroscope and a scanning electron microscope to determine the failure types at the cement-dentin interface. Ten slice specimens in each group were evaluated under SEM at 3 different sites to determine the tubular density. Comparisons were performed using the Mann-Whitney U test (P < .05).

RESULTS

Diabetic patients exhibited significantly lower push-out bond strength of MTA to root canal dentin (P < .05). The pattern of failure at the MTA-dentin interface was different between the 2 groups. The tubular density was significantly higher in diabetic patients (P < .05).

CONCLUSIONS

The dentin in diabetic patients exhibited different physicochemical properties. The failure patterns and modes in diabetic patients might be explained by the changes in the push-out bond strength, the calcification mechanism of the dentin-pulp complex, a higher dentinal tubule density, and less peritubular dentin. These differences could explain the higher failure rate of root canal treatment in these patients.

Moderately Acidic pH Promotes Angiogenesis: An In Vitro and In Vivo Study

INTRODUCTION

This study evaluated the effect of different pH values of 4.4, 5.4, 6.4, 7.4, 8.4, and 9.4 on angiogenesis.

METHODS

Endothelial cells were isolated from the mice molar teeth and placed in 42 Matrigel (Corning, NY)-coated wells, which were prepared and divided into 6 groups (n = 7). Synthetic tissue fluid was prepared and divided into 6 parts, and their pH values were adjusted to 4.4, 5.4, 6.4, 7.4, 8.4, and 9.4. A 2-mL volume from each group was diluted in the growth medium at a ratio of 1:3 and used for tubulogenesis assay. Forty-two 6-week-old mice in 6 groups (n = 7) were used for choroidal neovascularization (CNV). A 2-μL volume from each group or saline (control) was delivered by intravitreal injection on the day of laser application and 1 week later. Data on the number of nodes, the total length of the branches, and CNV areas (μm²) were determined using ImageJ software (National Institutes of Health, Bethesda, MD) and analyzed with 1-way analysis of variance and post hoc Tukey tests. The correlation was assessed between the tested variables.

RESULTS

The number of nodes decreased with changes in pH values as follows: 6.4 > 5.4 > 7.4 > 8.4 > 9.4 > 4.4. The total branch length decreased with pH value changes as follows: 6.4 > 4.4 > 6.4 > 7.4 > 8.4 > 9.4, and the CNV areas decreased with pH value changes as follows: 6.4 > 5.4 > 4.4 > 7.4 > 8.4 > 9.4.

CONCLUSIONS

Moderately acidic pH values (5.4 and 6.4) enhanced angiogenesis, whereas moderately alkaline pH values (8.4 and 9.4) suppressed angiogenesis.

Effect of thermocycling on the surface texture and release of titanium particles from titanium alloy (Ti6Al4V) plates and dental implants: An in vitro study

STATEMENT OF PROBLEM

The release of titanium (Ti) particles from the surface of endosseous dental implants is not well understood.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of thermocycling on the surface texture and release of Ti particles from the surface of dental implants.

MATERIAL AND METHODS

Three MSI dental implants and 3 Ti alloy (Ti₆Al₄V) plates were divided into 6 subgroups (n=3). Specimens in each group were subjected to 0 (control group), 100, 200, 500, 1000, and 2000 thermocycles. After each cycling process, artificial saliva was collected, and the concentrations of released Ti particles were quantified by inductively coupled plasma-mass spectrophotometry (ICP-MS). The surfaces of the dental implants and Ti plates were evaluated before and after thermocycling by scanning electron microscopy (SEM), and SEM images were analyzed by using the ImageJ software program. Data were analyzed by mixed-model ANOVA and post hoc Tukey tests (α=.05).

RESULTS

The greatest Ti release was seen after 2000 thermocycles. After increasing the number of cycles, additional Ti particles were released. SEM images of the surfaces of the dental implants and Ti plates displayed significant changes in surface texture.

CONCLUSIONS

Thermocycling continuously removed the protective TiO₂ layer on the surface of dental implants, resulting in the release of Ti particles. The surface treatment and texture did not affect the release of Ti particles.

Radiodensity of Various Dental Biomaterials for Endodontics: The Role of Particle Size

Introduction: The thickness threshold for detecting endodontic biomaterials depends on many factors, such as the nature of the radiopacifier and the particle size. Aim: The aim of this study was to determine the effect of thickness on radiodensity of various endodontic biomaterials; and evaluate the impact of radiopacifier particle size on radiodensity. Materials and Methods: This in-vitro study was conducted between August 2018 to December 2019. The study was divided in two parts, in first part, Six endodontic biomaterials (AH26, EndoSequence, Endoseal Mineral Trioxide Aggregate (MTA), Nano-MTA, Endocem Zr, and MTA without radiopacifier) were selected and evaluated in different thicknesses, in second part, MTA mixed with Bismuth oxide 10 μm, 200 μm, 120 nm (Groups 1-3), and Zirconium oxide 5 μm, 1 μm and 20 nm (Groups 4-6) were placed in frames with 1 mm, 0.5 mm, 0.2 mm, 0.1 mm thicknesses to evaluate the radiopacity. Results: The mean radiodensity was significantly different among various thickness (p<0.001) and materials (p<0.001). The changes of the radiodensity in various thickness from one material to the other were not uniform (interaction p-value <0.001). A 1 mm thickness had highest radiodensity (206.6±83.99), followed by 0.5 mm (68.9±24.6), 0.2 mm (17.9±4.9), and 0.1 mm thick material had least radiodensity (11.97±4.37). Materials of AH26 (99.1±103.2), Nano MTA (97.4±104.9), Endoseal MTA (87.86±101.4), Endosequence BC sealer (85.5±93.87) and Endocem Zr (71.88±77.67) were significantly different from the control group (16.38±10.85). The size of particles played important role in radiodensity (p<0.001). The radiodensity of Fine GIII (100 nm) material (112.68±108.47) was significantly higher than other materials: Thin GII (200 nm) (100.9±102.4), Fine GVI (20-40 nm) (99.7±95.1), Coarse GI (10 μm) (76.66±74.75), Thin GV (1~3 μm) (63.19±67.3), Coarse GIV (5 μm) (49.66±51.59) and MTA without Radiopaque Agent GVII (100%) (23.67±19.68). The effect of the thickness on radiodensity was different for each biomaterial, with significant differences from the control group. Conclusion: One of the readily available methods for increasing radiodensity is to increase the amount of radiopacifier, which might compromise the physical properties of the material. Fine particle radiopacifier (120 nm) with 1 mm thickness has significantly higher radiodensity than any other biomaterials in this study. Within the limitations of the current study, it can be concluded that the radiopacifier particle size has a significant impact on the level of radiodensity of dental biomaterials. Finding the optimum distribution, size, and geometry of radiopacifier particles within the same fraction rate can enhance the radiodensity.

Effect of length of LOCATOR abutment and cement type on retention to intraradicular dentin in overdentures

STATEMENT OF PROBLEM

Limited information is available on the effect of LOCATOR abutment length and luting cement type on retention to intraradicular dentin in overdentures.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the length of a commercially available LOCATOR abutment and cement type on retention in the root canal.

MATERIAL AND METHODS

Eighty LOCATOR abutments with a standard length of 6 mm were obtained. Half of them were shortened to 3 mm. Eighty recently extracted single-rooted teeth were divided into 2 groups. The post space was prepared to 6 mm in the first group and 3 mm in the second. After preparation, the LOCATOR abutments were luted with one of the following cements: dual-polymerized glass-reinforced resin cement (Parapost Paracore), dual-polymerized resin cement (Variolink II), self-adhesive resin cement (RelyX Unicem), and conventional cement (zinc phosphate). The tensile force required for the removal of the LOCATOR abutments from their corresponding roots was recorded. Data were statistically analyzed with 2-way ANOVA and the Tukey multiple comparison test.

RESULTS

Both the cement type (P<.001) and the length of the LOCATOR abutment (P<.001) significantly affected the mean tensile forces. Dual-polymerized glass-reinforced resin cement (Parapost Paracore) presented significantly higher mean tensile forces for the LOCATOR abutment retention among all cements (P<.05).

CONCLUSIONS

Regardless of the length, LOCATOR abutments luted with Parapost Paracore resin cement presented higher mean resistance to tensile forces compared with those luted with the other cements. LOCATOR abutments of 6 mm in length were more resistant to tensile forces than those of 3 mm in length in combination with all cements.

Retentive strength and marginal discrepancies of a ceramic-reinforced calcium phosphate luting agent: An in vitro pilot study

STATEMENT OF PROBLEM

Information on the properties of a relatively new luting agent with a unique formulation (ceramic-reinforced calcium phosphate) is limited.

PURPOSE

The purpose of this in vitro study was to compare the retentive strengths and marginal discrepancies of a ceramic-reinforced calcium phosphate luting agent (CM) with a self-adhesive resin luting agent (RX) and to determine and compare the mode of failure of dislodged cemented copings.

MATERIAL AND METHODS

Forty extracted human molar teeth were prepared to receive zirconia copings. After cementation, the specimens were divided into 4 subgroups (n=10): CM A (axial loading), CM OA (off-axis loading), RX A (axial loading), and RX OA (off-axis loading). For each subgroup, 9 of the specimens received experimental treatment (thermocycling and dynamic loading), and the tenth received no experimental treatment. Eight copings were pulled off in a universal testing machine (MTS Insight; MTS). The ninth specimen was treated experimentally but was not pull tested. The marginal discrepancy and the dentin interface of the specimens that were not pull tested were analyzed with scanning electron microscopy and energy dispersion spectroscopy. The mode of failure of the dislodged copings was also subjectively evaluated.

RESULTS

The mean retentive strengths were 5.92 MPa for CM A, 5.81 MPa for CM OA, 5.75 MPa for RX A, and 5.69 MPa for RX OA. The marginal discrepancy recorded for both CM and RX ranged from 30 to 45 μm, (mean, 36 ±4.6 μm). Energy dispersion spectroscopy analysis showed the presence of calcium, phosphorus, silicon, and aluminum for the CM marginal discrepancy and the presence of aluminum in the dentinal tubules adjacent to the CM. Calcium and phosphorus were detected in lesser amounts adjacent to the RX marginal discrepancy. The mode of failure for CM was primarily adhesive to the tooth preparation, and, for RX, the failure mode was predominantly adhesive to the coping.

CONCLUSIONS

CM had statistically significantly higher mean retentive strength compared with RX. Subgroups loaded axially had statistically significantly higher retentive strengths compared with those loaded off axis.

Pull-out retentive strength of fiber posts cemented at different times in canals obturated with a eugenol-based sealer

STATEMENT OF PROBLEM

Currently, no standard luting protocol exists for fiber posts. In addition, no agreement has been reached on the time interval between canal obturation and post space preparation and cementation.

PURPOSE

The purpose of this in vitro study was to evaluate the retention of fiber posts cemented with 3 different types of cement: Paracore, Variolink II, and RelyX Unicem cement after 24 hours or 2 weeks in root canals obturated with gutta percha and a eugenol-based sealer.

MATERIAL AND METHODS

Seventy-two caries-free, freshly extracted, single-rooted human mandibular first premolar teeth with straight root canals were prepared and obturated with gutta percha and Endofil sealer. Specimens were divided into 2 groups (n=36): post spaces prepared 24 hours after obturation and post spaces prepared 2 weeks after obturation. Posts in both groups were luted with 1 of 3 different luting agents (n=12), ParaCore, Variolink II, or RelyX Unicem cement. Each tooth specimen was vertically secured in a universal testing machine, and a constant pull-out loading rate of 0.5 mm/min was applied until cement failure occurred. Data were statistically analyzed with 2-way and 1-way ANOVAs and t tests.

RESULTS

Two-way ANOVA indicated statistically significant differences in mean post retention among the 3 cement types (P<.001) and among the means of the different time intervals investigated (P<.001). Significant differences were noted among all cement types tested between the 24-hour and 2-week time intervals (P<.05).

CONCLUSIONS

Time elapsed between canal obturation and post cementation significantly influenced fiber post retention, regardless of the type of resin cement. Fiber posts showed significantly higher retention if cemented after 24 hours of obturation than if cementation occurred after 2 weeks.

Fracture resistance of porcelain veneered zirconia crowns with exposed lingual zirconia for anterior teeth after thermal cycling: An in vitro study

Statement of problem

In some clinical conditions minimally invasive complete crown tooth preparations are indicated. This is especially true when gross removal of tooth structure would weaken the remaining tooth or violate the vitality of the dental pulp.

Objective

The purpose of this study was to investigate the influence of (1) exposed lingual zirconia with veneered zirconia crowns, and (2) reduced lingual thickness of monolithic lithium disilicate crowns on the fracture resistance of the crowns after cyclic loading. Metal-ceramic crowns with exposed lingual metal served as controls.

Materials and methods

Twenty-four maxillary central incisor crowns were fabricated in identical shape on metal testing dies in 3 groups: metal-ceramic crowns (MC, n = 8), veneered zirconia crowns (VZ, n = 8), and monolithic lithium disilicate crowns (MO, n = 8). A conservative preparation design with 0.75 mm lingual clearance was used for each crown system. All crowns were cemented to their corresponding crown preparations with self-adhesive resin cement (Multilink Automix). The crowns were subjected to 1000 cycles of thermal cycling, then cyclic loading of 111 N by means of a stainless steel ball, and 50,000 cycles of loading were applied for the fatigue test. Fatigue loading was followed by a continuously increasing compressive load, at a crosshead speed of 1 mm/min until failure. The compressive load (N) required to cause failure was recorded. Means were calculated and analyzed with one-way ANOVA and the Tukey HSD test (α = .05).

Results

There was a significant difference between MO vs. MC (P = .0001), MO vs. VZ (P = .0001), and VZ vs. MC (P = .012).

Conclusions

There was a significant difference in the mean fracture resistance of MC, VZ, and MO crowns in this in vitro study. The MC group recorded the highest mean fracture strength.

Improving oral health in the Middle East - recommendations from the first Middle East Oral Hygiene Advisory Board meeting

Chronic periodontitis may be a sequela of chronic gingivitis, usually because of accumulation of plaque and calculus. Consistent good dental hygiene can help prevent gingivitis and periodontitis. Mechanical removal of plaque through frequent and efficacious brushing and flossing is the principal means of preventing periodontal diseases and diminishing the risk of caries. According to the American Dental Association (ADA), antimicrobial mouth-washes may provide additional oral health benefits, in addition to brushing and flossing, for preventing and reducing gingivitis and plaque. There is a multitude of mouthwashes available for these purposes. The consensus panel of the Middle East Oral Hygiene Advisory Board has recommended that an antiseptic mouthwash should be used as a daily adjunct to mechanical cleaning for prevention of oral disease. Recommending particular mouthwashes should take into consideration the patient's ability to perform good oral hygiene practices (tooth brushing and dental flossing), the condition of the patient's teeth, gingivae and oral mucosa, and the proven efficacy of the mouthwash along with its potential adverse effects. Of the many mouth rinses available, only a few contain chemical agents that have some ability to penetrate biofilm and to kill plaque biofilm bacteria. Currently, only chlorhexidine mouthrinse and Listerine (an essential oil-containing mouth rinse) products, with the claim of plaque and gingivitis reduction, have been accepted for that purpose by the ADA and have a proven record of safety and efficacy. Essential oil-containing mouthrinses have been clinically proven as effective in reducing plaque and gingivitis. Dental care professionals should spend time discussing biofilm control with their patients, and be an information source for the best oral care products. Therefore, it is essential that dental care professionals should continue to monitor published research and work with their colleagues to make evidence-based decisions. In this way, patients will be directed to dental hygiene aids, including antiseptic mouthwashes that can be most effective for improving their oral health.

Obtaining maxillomandibular records and definitive impressions in a single visit for a completely edentulous patient with a history of combination syndrome

Any attempt to reduce the number of dental visits for the fabrication of complete dentures is appreciated by both the dentist and the patient. This article illustrates clinical and laboratory procedures for making a 2-stage definitive impression combined with the recording of maxillomandibular relations in the same visit for a completely edentulous patient with maxillary anterior mobile soft tissues.

An expedited technique for remaking a single complete denture for an edentulous patient

Traditional techniques for fabricating complete dentures commonly require 5 visits. Reduction of the number of visits and chair time for complete denture fabrication would be welcomed by dentists and patients. This article describes and illustrates clinical and laboratory procedures for fabricating a new denture for a patient with an existing complete denture. The procedure can be completed in 3 to 4 visits.

Treatment history of teeth in relation to the longevity of the teeth and their restorations: Outcomes of teeth treated and maintained for 15 years

STATEMENT OF PROBLEM

Limited clinical data exist on the survival of teeth relative to their treatment history.

PURPOSE

This study evaluated failure of teeth relative to their treatment history.

MATERIAL AND METHODS

Longitudinal data were collected for 3071 teeth from 148 fully compliant patients from 1 private practice in Yamagata, Japan. Follow-up times ranged from 15 to 23 years, with a mean of 19.2 years (SD 2.4). In this study, every tooth and its restoration were evaluated by one of the authors at the time of each maintenance visit. Treatment history of the teeth was categorized at baseline as follows: (1) sound, unrestored tooth (SUT); (2) 1-surface restoration (RT1); (3) 2-surface restoration (RT2); (4) 3-surface restoration (RT3); (5) 4+-surface restoration (RT4); (6) complete crown (CCT); (7) abutment for fixed partial dental prosthesis (AFT); (8) abutment for removable partial dental prosthesis (APDT); and (9) root canal treatment (RCT). Three types of failure modes were evaluated in this study: (1) restorative failure (secondary caries and/or fracture), (2) extraction, and (3) any failure (restorative failure or extraction). Multivariate survival analysis was used to determine the impact of the treatment history on failure (alpha=.05).

RESULTS

Teeth with multi-surface restorations experienced the highest incidence of any failure (P<.001). For secondary caries, similar risks were noted for the different treatment histories. For failures resulting in extraction, the only teeth with an increased risk were abutments for removable partial dental prostheses (relative risk=5.5) (P=.008).

CONCLUSIONS

The data demonstrated that restored teeth experienced a higher incidence of failure compared with unrestored teeth. Complete crowns and abutments for fixed partial dental prostheses had fewer restorative failures when compared with teeth with complex multisurface restorations. Removable partial denture abutments experienced the highest failure rate.

In vitro evaluation of low-temperature aging effects and finishing procedures on the flexural strength and structural stability of Y-TZP dental ceramics

STATEMENT OF PROBLEM

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic material has been reported to possess exceptionally high flexural strength; however, the strength of Y-TZP ceramics can be affected by surface treatments performed by dental laboratory technicians and by intraoral conditions.

PURPOSE

This study investigated the influence of low-temperature-degradation (LTD) treatment, airborne-particle abrasion, and polishing on the flexural strength and structural stability of a Y-TZP ceramic material.

MATERIAL AND METHODS

By sectioning zirconia ceramic blocks (Vita In-Ceram YZ blocks) into 25 x 4 x 2-mm bars, 310 specimens were fabricated and divided into 9 groups: Group C, as-sintered (control); group B24h, boiled in water for 24 hours; group B7d, boiled in water for 7 days; group H6h, stored in humidified air at 250 degrees C for 6 hours; group H24h, stored in humidified air at 250 degrees C for 24 hours; group H7d, stored in humidified air at 250 degrees C for 7 days; group P, polished; group A, airborne-particle abraded; and group AB, airborne-particle abraded and boiled for 7 days. The flexural strengths (MPa) of all specimens were determined by using a 3-point bending test. The variability was analyzed by using Weibull statistics. Pairwise differences among the 9 groups were evaluated by using confidence intervals (95%) for scale and shape parameters. From every block used, 8 specimens were obtained and every specimen was marked according to the location of its origin from the original block. Surfaces of the specimens were evaluated by using scanning electron microscopy (SEM) at various magnifications. X-ray diffraction analysis was performed to identify possible tetragonal-to-monoclinic phase transformations. Energy dispersive spectroscopy (EDS) was used to obtain information on the chemical composition.

RESULTS

Aging or "finishing" treatments had no significant negative effects on flexural strengths. Mean flexural strengths ranged from 796.7 to 950.2 MPa. Group A exhibited the highest mean flexural strength (950.2 MPa). Weibull modulus values ranged between 5.6 and 9.3. Tetragonal-to-monoclinic phase transformation was detected for a specimen boiled for 24 hours. More tetragonal-to-monoclinic phase transformation was detected for specimens boiled for 7 days and stored in humidified air at 250 degrees C for 7 days. The SEM examination of fractured surfaces revealed sintering defects, and EDS analysis showed less yttria concentration on Y-TZP specimens that were boiled for 7 days.

CONCLUSION

Within the limitations of this study, the results suggested that the LTD procedures and the polishing treatment used did not reduce the flexural strengths of zirconia bars. Airborne-particle abrasion increased the flexural strength of specimens.

CLINICAL IMPLICATIONS

Although polishing, airborne-particle abrasion, and various low-temperature degradation (LTD) treatments did not significantly degrade the strength of the Y-TZP ceramic material, LTD resulted in loss of yttria. Over time, gradual dissolution of yttria could decrease the tetragonal-phase stability and long-term clinical serviceability of this dental ceramic material.

An evaluation of the effects of handpiece speed, abrasive characteristics, and polishing load on the flexural strength of polished ceramics

STATEMENT OF PROBLEM

Many studies on the strengthening effects of grinding and polishing, as well as heat treatment on ceramics, are not well standardized or use commercially available industrial polishing systems. The reported effectiveness of these strengthening mechanisms on ceramics may not be applicable to clinical dentistry.

PURPOSE

The purpose of this study was to evaluate the effects of controlled polishing on the flexural strength of dental ceramics by using a custom-made machine that applied standardized loads and speeds that coincided with the mean loads and speeds used by experienced prosthodontists.

MATERIAL AND METHODS

A total of 140 aluminous dental ceramic bar-shaped specimens (Vitadur Alpha Enamel) measuring 1.5 x 2.0 x 25 mm were fabricated and divided into 12 groups (for most groups, n=10). Specimens were untreated, polished with different polishing systems, polished at different speeds, ground and autoglazed, polished and autoglazed, autoglazed and polished, polished with loose (paste) and bonded abrasives, or overglazed. Simulated clinical polishing was performed on the ceramic specimens by using a customized polishing apparatus that allowed independent control over the relevant polishing parameters (abrasive hardness, applied load, linear speed, rotational velocity, and wheel stiffness). Flexural strength (MPa) was measured with a 4-point bending test, and subjective surface roughness was assessed with scanning electron microscopy. Autoglazing was performed at various stages of the polishing sequence to determine the effects of polishing on surface stresses. Mean values, standard deviations, independent-sample t tests, 1-way and 2-way analyses of variance, Dunnett t tests and Kruskal-Wallis tests were applied to the data (alpha=.05).

RESULTS

Under a clinical load of 0.6 N for a coarse polishing wheel, 1.0 N for a medium polishing wheel, and 1.3 N for a fine polishing wheel, a linear speed of 499 mm/min, and a rotational velocity of 10,000 rpm, the use of clinical polishing instruments did not affect the flexural strength of the aluminous ceramics studied (P=.274). At higher rotational velocity (20,000 rpm), specimens polished with the diamond polishing system produced statistically weaker specimens compared with those that had been polished at 10,000 rpm (P=.019). Autoglazing treatment of the diamond-polished specimens did not reverse the strength degradation (P=.125). Conversely, diamond polishing of the autoglazed specimens resulted in significant flexural strength reduction (P=.029). Fine-diamond-bonded abrasive significantly reduced flexural strength (P=.025).

CONCLUSIONS

Simulated clinical polishing at 10,000 rpm did not appear to substantially strengthen or weaken the ceramic specimens. Polishing at 20,000 rpm reduced flexural strength of the ceramic bars.

Finite element analysis of three designs of an implant-supported molar crown

STATEMENT OF PROBLEM

The optimal method of implant support for a single mandibular molar crown is controversial because commonly used, threaded, root-form implants developed by Branemark were not originally designed to support individual crowns.

PURPOSE

The purpose of this study was to develop a finite element model of a single mandibular first molar crown supported by (1) a standard 3.75-mm-diameter implant, (2) a 5-mm, wide-diameter implant, and (3) double standard-diameter implants, and to compare the induced displacements as a result of various loading conditions.

MATERIAL AND METHODS

Three-dimensional finite element models were made to simulate the 3 single-molar implant designs. Each model was analyzed with 2 force magnitudes (35 N and 70 N) and with 2 force directions (vertical and 15 degrees to the vertical axis). Displacements in 3-dimensional space as a result of the simulated loading conditions were evaluated along 3 primary axes, mesiodistal, faciolingual, and superior-inferior.

RESULTS

Mesiodistal and buccolingual displacements for the crown supported by the 5-mm-diameter implant were reduced by approximately 50% compared with the crown supported by the 3.75-mm implant when the crowns were loaded at the distobuccal cusp tip or the distal marginal ridge. The double-implant design recorded the least mesiodistal displacement with off-center loading of the crown.

CONCLUSION

When the crown was loaded off-center, the double-implant design produced substantially less displacement when compared with either of the single-implant designs.

Restoration of endodontically treated teeth

Endodontically treated teeth have lost substantial tooth structure as a result of previous restorations, dental caries, and the access preparation for the endodontic therapy. The topic of restoring these teeth is complex and controversial, and their long-term prognosis is directly connected to the quality of the final restoration. This article describes contemporary knowledge of the biomechanical principles related to the restoration of pulpless teeth and provides a critical review of currently available materials and methods.

Restoration of unfavorably positioned implants for a partially endentulous patient by using an overdenture retained with a milled bar and attachments: A clinical report

The restorative dentist may encounter patients with previously placed misaligned implants that are well integrated. Often, these patients have deficient alveolar ridge contour further complicating treatment options. This clinical report describes a treatment approach for a partially edentulous patient with unfavorably positioned implants that incorporated: (1) an implant-supported milled bar with a removable, metal-acrylic resin, partial overdenture, (2) implant-supported single crowns, and (3) crowns retained by natural teeth.

Laboratory-processed acrylic resin provisional restoration with cast metal substructure for immediately loaded implants

Most methods of immediate loading of implants reported in the literature involve retrofitting a pre-existing denture to the implants. This article describes and illustrates clinical and laboratory procedures for immediate loading of implants in the edentulous mandible with the use of a laboratory-processed, provisional, screw-retained, implant-supported fixed complete denture that incorporates a cast metal reinforcement.

Effects of acid hydrolysis and mechanical polishing on surface residual stresses of low-fusing dental ceramics

STATEMENT OF PROBLEM

Cracks may arise in a ceramic restorative material over time, resulting in sudden fractures at stresses well below the yield stress.

PURPOSE

This study evaluated by means of indentation technique the effects of acid hydrolysis and mechanical polishing on the surface residual stresses of low-fusing ceramic materials.

MATERIAL AND METHODS

A total of 64 ceramic bars were formed to produce 4 groups of 16 bars each for 4 ceramic materials (Duceram-LFC Dentin, Duceram-LFC Enamel, Finesse Dentin, and Finesse Enamel). Four surface-treatment groups (n=4) were then formed for each of the 4 materials. The 4 surface treatments were control (autoglaze), hydrolysis, glaze/polish, and polish/glaze. A Vickers indenter contacted the Duceram-LFC specimens with a 5-N load and the Finesse specimens with a 3-N load for 10 seconds. Scanning electron microscope (SEM) was used to study surface texture before and after hydrolysis and polishing. Differences in mean crack lengths were analyzed with 1-way analysis of variance and least significant difference test (alpha=.05.)

RESULTS

SEM showed obvious surface flaws as a result of hydrolysis on Duceram-LFC Enamel and Dentin specimens. However, statistical analysis of the resulting crack lengths revealed no significant differences between values for the control groups (58.16 +/- 3.88) (53.53 +/- 2.67) and hydrolysis groups (57.11 +/- 4.09) (54.54 +/- 3.15) for Enamel (P=.081) and Dentin (P=.093) respectively. When comparing polished groups and nonpolished groups, the mean crack lengths were significantly shorter for polished specimens of Duceram-LFC Enamel (53.76 +/- 3.17), Finesse Enamel (40.56 +/- 3.31), and Finesse Dentin (39.76 +/- 3.81) porcelains compared with their control groups (58.16 +/- 3.88) (43.54 +/- 4.12) (41.19 +/- 3.47), respectively (P<.0001). The mean crack lengths were significantly longer for polished specimens of Duceram-LFC Dentin (59.16 +/- 3.52) porcelain compared with the control group (53.53 +/- 2.67) (P<.0001).

CONCLUSION

Within the limitations of this study, hydrolysis did not improve surface residual stresses of Duceram-LFC and Finesse ceramic materials. Mechanical polishing improved surface residual stresses of all materials tested, except Duceram-LFC Dentin porcelain.

The effect of thermocycling on microleakage of several commercially available composite Class V restorations in vitro

STATEMENT OF THE PROBLEM

Microleakage is a major factor contributing to the occurrence of secondary carious lesions around composite restorations.

PURPOSE OF STUDY

This in vitro study investigated the effect of thermocycling on microleakage of several composite Class V restorations.

MATERIAL AND METHODS

One hundred twenty molars were randomly distributed into 6 groups of 20 teeth. Class V preparations were made in the buccal and lingual surfaces of each tooth and restored in bulk by use of 6 composites (Arabesk, Silux-Plus, Solitaire 2, Durafill VS, Charisma, and Renew) according to the manufacturers' recommendations. The teeth were stored in distilled water at room temperature for 24 hours. The teeth in each group were divided randomly into 2 subgroups: (a) thermocycled for 500 cycles between 5 degrees and 55 degrees C with a dwell time of 30 seconds, (b) no thermocycling treatment. All restored teeth were immersed in 1% methylene blue dye for 4 hours and sectioned buccolingually with a diamond wheel. Dye penetration was scored by use of a stereomicroscope at original magnification x4. The generalized linear models statistical analysis was used (alpha=.05).

RESULTS

The preparation margins (enamel/dentin) and thermocycling had a significant effect on microleakage (P=.0351, P<.0001, respectively); the type of material had no significant effect (P=.1689).

CONCLUSIONS

Thermocycling significantly increased the microleakage (P<.0001). The overall microleakage at the enamel margins was significantly less than at the dentinal margins (P=.0351).

Occlusal plane discrepancies generated by transverse horizontal axis deviations

STATEMENT OF PROBLEM

Any deviation from the patient's rotational axis of the mandible during closure and the arc of closure on an articulator has been reported to produce occlusal discrepancies. These discrepancies can affect diagnostic planning procedures and the occlusal relationships of restorations.

PURPOSE

This study investigated the magnitude and types of occlusal errors produced by deviations between the patient's transverse horizontal axis and the axle on the articulator.

MATERIAL AND METHODS

A simplified monoplane model was diagrammatically analyzed for deviations from the model's true transverse horizontal axis. Axis deviations of 5 mm were used in 8 different directions from the true transverse horizontal axis of the model. Changes in the orientation of the mandibular plane to the maxillary plane were illustrated diagrammatically. These changes were quantified by geometric and trigonometric assessments.

RESULTS

All axis deviations produced mandibular plane orientation errors with angular plane malalignment to the maxillary plane on complete closure. These axis deviations also produced anterior-posterior shifting of the mandibular plane relative to the maxillary plane.

CONCLUSION

Several different types of planar shifting and angular discrepancies were demonstrated from deviations away from the true transverse horizontal axis.

New abutment for a screw-retained, implant-supported crown

The 1-piece, implant-supported abutment and crown, colloquially described as the UCLA abutment, commonly is used to fabricate single, screw-retained crowns. This abutment was designed to allow attachment of the crown directly to the implant and requires a waxing and casting procedure by a laboratory technician. A new prefabricated abutment has been developed that uses a similar approach but does not require the waxing and casting process. The PDQ abutment is made from a metal-ceramic alloy that is custom contoured by grinding to support a porcelain veneer. Porcelain then is fired to the contoured abutment to develop the 1-piece artificial crown. This article describes the use of the PDQ abutment.

Foundation restorations in fixed prosthodontics: current knowledge and future needs

PURPOSE

The Ad Hoc Committee on Research in Fixed Prosthodontics established by the Academy of Fixed Prosthodontics publishes a yearly comprehensive literature review on a selected topic. The subject for this year is foundation restorations.

METHODS

Literature of various in vitro and in vivo investigations that included technical and clinical articles was reviewed to provide clinical guidelines for the dentist when selecting methods and materials for restoration of structurally compromised teeth. Topics discussed and critically reviewed include: (1) desirable features of foundation restorations, (2) foundations for pulpless teeth, (3) historic perspectives, (4) cast posts and cores, (5) role of the ferrule effect, (6) prefabricated posts, (7) direct cores, (8) foundation restorations for severely compromised teeth, (9) problems and limitations, (10) future needs, and (11) directions for future research.

CONCLUSION

This comprehensive review brings together literature from a variety of in vitro and in vivo studies, along with technique articles and clinical reports to provide meaningful guidelines for the dentist when selecting methods and materials for the restoration of structurally compromised teeth.