Comparison of the Fit of Lithium Disilicate Crowns made from Conventional, Digital, or Conventional/Digital Techniques.

PURPOSE: To evaluate the fit of single crowns fabricated using conventional, digital, or cast digitization methods. MATERIALS AND METHODS: One subject with a peg-shaped maxillary lateral incisor was selected in this study. Tooth preparation for an all-ceramic crown was performed and 10 conventional poly(vinyl siloxane) impressions, and 10 digital impressions using an intraoral scanner were made. Each working cast was scanned using a laboratory scanner and an intraoral scanner. Four groups were tested Group 1: conventional impressions. Group 2: cast laboratory scans. Group 3: cast scans using intraoral scanner. Group 4: direct intraoral scans. For group 1, heat-pressed glass ceramic crowns (IPS e.max Press) were fabricated using casts produced from the conventional impressions. For groups 2-4, crowns were milled using ceramic blocks (IPS e.max CAD). Ten crowns were fabricated for each group. Marginal and internal gaps were measured using a replica technique. Replicas were sectioned mesiodistally and buccolingually and were observed under a stereomicroscope. Three measurements were selected for each cut: occlusal, axial, and marginal. Statistical analysis was performed using two-way ANOVA and Tukey HSD tests. RESULTS: For each replica, 6 measurements were made for the mesiodistal and the same for the buccolingual cuts, producing 12 measurement points per crown (4 measurements for marginal, 4 for axial, 4 for occlusal), 120 measurements for each group (40 measurements for marginal, 40 for axial, 40 for occlusal), and 480 measurements in total. Two-way ANOVA revealed location to be a significant factor (p = 0.001). No significant differences among groups (p = 0.456), and no interactions between groups and locations (p = 0.221) were found. Means for the occlusal site were significantly larger than other sites in most group combinations, while the difference between the marginal and axial sites was not significant. No significant differences among groups were found for each measurement. The marginal gaps ranged from 125.46 ± 25.39 µm for group 3 to 135.59 ± 24.07 µm for group 4. The smallest axial mean was in group 1 (98.10 ± 18.77 µm), and the largest was 127.25 ± 19.79 µm in group 4. The smallest occlusal mean was in group 2 (166.53 ± 36.51 µm), and the largest occlusal mean was in group 3 (203.32 ± 80.24 µm). CONCLUSIONS: Ceramic crowns, which were made using all-digital approach or cast digitization by a laboratory or intraoral scanner had comparable fit to those produced by conventional approach.

The effect of Nd:YAG and Er,Cr:YSGG lasers on the microhardness of human dentin.

The current investigation determined the microhardness of dentin tissue irradiated with erbium, chromium-doped yttrium scandium gallium garnet (Er,Cr:YSGG) and neodymium-doped yttrium-aluminum garnet (Nd:YAG) lasers. Thirty non-carious human molars were used in this study. Dentin disks were prepared by horizontal sectioning of one third of the occlusal surface. Halves of dentin specimens were irradiated with 3.5- and 4.5-W Er,Cr:YSGG lasers and with a 2-W Nd:YAG laser. The remaining halves served as controls. The microhardness measurements were recorded with a Vickers surface microhardness tester. The results were statistically evaluated by paired t test and one-way ANOVA (p = 0.05). Laser irradiation has significantly reduced the microhardness of dentin within each group compared to its control. Moreover, statistically significant differences were observed among the different groups (p < 0.05). The 3.5-W Er,Cr:YSGG laser produced the greatest reduction in microhardness of dentin followed by 4.5 W and Nd:YAG laser. The differences between all the groups were statistically significant. It was concluded that both laser devices used in this study have resulted in significant thermal damage and subsequent reduction in dentin microhardness values.

Effect of Er,Cr:YSGG laser on human dentin fluid flow.

The aim of the current investigation was to assess the rate and magnitude of dentin fluid flow of dentinal surfaces irradiated with Er,Cr:YSGG laser. Twenty extracted third molars were sectioned, mounted, and irradiated with Er,Cr:YSGG laser at 3.5 and 4.5 W power settings. Specimens were connected to an automated fluid flow measurement apparatus (Flodec). The rate, magnitude, and direction of dentin fluid flow were recorded at baseline and after irradiation. Nonparametric Wilcoxon signed ranks repeated measure t test revealed a statistically significant reduction in fluid flow for all the power settings. The 4.5-W power output reduced the flow significantly more than the 3.5 W. The samples showed a baseline outward flow followed by inward flow due to irradiation then followed by decreased outward flow. It was concluded that Er,Cr:YSGG laser irradiation at 3.5 and 4.5 W significantly reduced dentinal fluid flow rate. The reduction was directly proportional to power output.

Reaction of rat connective tissue to Mineral Trioxide Aggregate and Diaket.

BACKGROUND: The aim of this study was to compare the reaction of rat connective tissue to two root-end filling materials: white Mineral Trioxide Aggregate (WMTA) and Diaket. METHODS: Each of the materials was placed in dentine tubes and implanted subcutaneously in the dorsal connective tissue of 21 Wistar albino rats. Tissue biopsies were collected 7, 30, and 60 days after the implantation procedure. The specimens were processed and stained with hematoxylin and eosin and examined microscopically. After determining inflammatory cell numbers in sections from each specimen, inflammatory reaction scores were defined as follows: 0; no or few inflammatory cells (no reaction), 1; less than 25 cells (mild reaction), 2; 25 to 125 cells, (moderate reaction), and 3; 125 or more cells (severe reaction). Statistical analysis was performed using the Kruskal-Wallis and Mann-Whitney tests. RESULTS: There were statistically significant differences in the median inflammatory cell numbers throughout the three test periods, with the most severe degree of inflammation observed at the one-week period. Few cases of necrosis were observed with WMTA. Diaket exhibited the most severe degree of inflammation and necrosis. After 30 days, both materials provoked moderate inflammatory reaction. The eight-week period showed the least severe degree of inflammation in all groups. CONCLUSIONS: It was concluded that WMTA exhibits a more favourable tissue response compared with Diaket which induced more severe inflammatory reaction than WMTA and the control.

Effect of an occlusal screw-access hole on the fracture resistance of permanently cemented implant crowns: a laboratory study.

This study aimed to evaluate the fracture resistance of cement-retained metal-ceramic implant-supported posterior crowns. Three groups of 10 restorations each were tested: group A (cement-retained using zinc phosphate), group B (cement-retained using zinc oxide-eugenol), and group C (cement-retained using zinc phosphate but with an occlusal screw-access hole). All specimens were thermocycled and vertically loaded in a universal testing machine. Mean values of fracture loads were calculated and analyzed statistically. The cement-retained restorations without an occlusal screw-access hole showed significantly higher mean fracture loads than those having one. The type of cement did not affect the porcelain fracture resistance significantly.

Histological evaluation of rat tissue response to GMTA, Retroplast, and Geristore retrograde filling materials.

The aim of the study was to compare the short-term biocompatibility of grey mineral trioxide aggregate (GMTA), Retroplast and Geristore. Silicon tubes filled with the materials and empty control tubes were implanted in the dorsal connective tissue of 30 Wistar albino rats. The tubes and surrounding tissues were excised and prepared for histological examination at 1 week, 1 month and 2 months after implantation. Inflammatory cell counts and the presence or absence of necrosis adjacent to the materials and control tubes were recorded. Data were statistically analysed using one-way anova and Tukey's multiple comparisons tests. The empty control tubes were well tolerated. All tested materials showed a more severe initial reaction than the control group. With time, the reaction became chronic, with variable increase in the numbers of inflammatory cells. Retroplast recorded the most statistically significant increase in the sum of inflammatory cells. Although the increase in the sum of inflammatory cells was statistically significant for Geristore but not for GMTA, the inflammatory cell counts for both were comparable. It was concluded that the three materials continued to irritate tissues throughout the evaluation period. Retroplast was the least biocompatible of the three tested materials at 2 months, followed by Geristore then GMTA.

Porcelain fracture resistance of screw-retained, cement-retained, and screw-cement-retained implant-supported metal ceramic posterior crowns.

PURPOSE: The purpose of this in vitro study was to compare the porcelain fracture resistance between screw-retained, cement-retained, and combined screw- and cement-retained metal-ceramic (MC) implant-supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw-access opening on porcelain fracture resistance of screw-retained and cement-retained MC implant-supported posterior single crowns. MATERIALS AND METHODS: Forty standardized MC molar-shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw-retained, screw-access hole placed in the center of the occlusal surface; Group SRO: screw-retained, screw access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement-retained, zinc phosphate cement was used; Group CSC: cement-retained with a screw-access hole in the center of the occlusal surface. The screw-retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one-way ANOVA and Tukey's Studentized test (alpha= 0.05). RESULTS: Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 +/- 593; Group SRO: 1885 +/- 491; Group CRP: 3707 +/- 1086; Group CSC: 1700 +/- 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05). CONCLUSION: The cement-retained restorations showed significantly higher mean fracture loads than the restorations having screw-access openings in their occlusal surface. The position of the screw-access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.

The retention of cast metal dowels fabricated by direct and indirect techniques.

PURPOSE: To explore the effect of fabrication technique, cement type, and cementation procedure on retention of cast metal dowels. METHODS AND MATERIALS: Eighty intact single-rooted teeth were selected. The clinical crown was removed at the cementoenamel junction level. Each root was prepared to receive a cast metal dowel of 10-mm length and 1.45 mm in diameter. The 80 specimens were divided into two major groups of 40 based on fabrication technique (direct and indirect). Each group was further divided into four subgroups of ten based on the cement type (zinc phosphate and glass ionomer), and cementation procedure (with and without lentulo spiral). The dowels were subjected to a constantly increasing tensile force, in a universal Instron testing machine, at crosshead speed of 5 mm/min until failure. RESULTS: The most significant factor to affect retention was the cementation procedure, as cementation with lentulo spiral produced greater retention than cementation without the use of lentulo spiral (p < 0.05); however, there seems to be a close interaction between fabrication technique, cement type, and cementation procedure (p= 0.051). The least retentive group was the one fabricated by direct technique, cemented with zinc phosphate without the use of lentulo spiral. CONCLUSION: Fabrication technique does not affect retention of cast dowels, except when zinc phosphate was the luting agent and placed in the canal space without using a lentulo spiral. The cementation procedure had a significant effect on retention; thus, it is recommended that cementation should be done using the lentulo spiral.

Parallelism of abutment teeth on fixed partial dentures.

A total of 100 working dies for fixed partial denture (FPD) abutments were prepared to fit 50 three-unit fixed-fixed conventional FPDs. For each FPD, the axial convergence angles between the mesial and distal axial walls of the abutment teeth were measured. For all FPDs, there were no statistically significant differences between the mesial and distal convergence angles of abutment teeth measured, regardless of their location within the oral cavity. The distal convergence angle of posterior FPD abutments was the highest angle, while the lowest was recorded for the mesial convergence angle of the anterior FPD abutments.

Factors associated with postoperative sensitivity of amalgam restorations.

UNLABELLED: Postoperative sensitivity is a common clinical problem with restorative treatments. STUDY AIMS: To identify factors that may be predictive of reported postoperative sensitivity to cold following placement of class I and II amalgam restorations in primary carious lesions. MATERIALS AND METHODS: One hundred and twenty patients were recruited. Patients were telephoned on days two and seven postoperatively and asked about sensitivity to cold and its intensity. If sensitivity remained up to day seven, patients were also contacted on days 30 and 90. RESULTS: Of the 51 teeth that had sensitivity at day two, 17 experienced mild pain, 26 were moderately painful and eight had severe pain. The percentage of females experiencing postoperative sensitivity was higher than that of males at days two, seven and 30 (P=0.000, 0.016 and 0.028, respectively). Younger patients reported significantly more postoperative sensitivity than older ones at day two (P=0.010) but not at days seven and 30 (P=0.157 and 0.877). Postoperative sensitivity did not differ among the different tooth types at days two, seven and 30 (P=0.219, 0.236 and 0.338, respectively), nor with respect to class I and class II cavities at days two, seven and 30 (P=0.219, 0.769 and 0.259, respectively). Patients who had some pre-operative pain had significantly more postoperative sensitivity (P=0.000, 0.000, and 0.004 at days two, seven and 30, respectively). CONCLUSIONS: Regression analysis suggested that younger patients, females, and pre-operative sensitivity to cold might be predictive of postoperative sensitivity following placement of amalgam restorations.

Effect of cavity disinfection on postoperative sensitivity associated with amalgam restorations.

This clinical study assessed the postoperative cold sensitivity reported by patients following the Class I and Class II amalgam restoration of primary carious lesions after different cavity treatments. One hundred and twenty patients, each with a previously untreated tooth requiring an amalgam restoration due to the presence of a carious lesion, were included. Sixty teeth had lesions that were radiographically judged to be located in the middle third of dentin, and another 60 were located in the inner third of dentin. Six different cavity treatment regimens were used: Group 1--no treatment; Group 2--calcium hydroxide liner (Life); Group 3--cavity varnish (Copalite); Group 4--resin modified glass ionomer liner (Vitrebond); Group 5--dentin adhesive resin liner (Single Bond); Group 6--chlorhexidine disinfectant (Consepsis). Patients were telephoned on days 2 and 7 postoperatively and asked whether they experienced sensitivity to cold, and if so, its duration and intensity. If sensitivity remained up to day 7, patients were also contacted on days 30 and 90. The Kruskal-Wallis test showed postoperative sensitivity to be significantly different among cavity treatments at days 2, 7 and 30 (p = 0.026, 0.044, 0.015, respectively). Lesion depth also affected postoperative sensitivity at day 2, with 27% of teeth with middle-third lesions producing pain, and 58% of those with lesions extending to the inner third producing pain (p = 0.000). This difference showed up at 7 and 30 days (p = 0.001, 0.015, respectively). Of the 51 teeth with sensitivity at day 2, 17 had mild pain, 26 were moderately painful and 8 had severe pain; each category reduced in degree of sensitivity and number with time. It would seem that medium-term (beyond 30 days) postoperative sensitivity is affected neither by the method of cavity treatment nor the depth of lesion, although, in the shorter-term, these factors do influence the postoperative sensitivity reported.

Survey of attitudes, materials and methods employed in endodontic treatment by general dental practitioners in North Jordan.

BACKGROUND: General dental practitioners provide the majority of endodontic treatment in Jordan. The aim of this study was to gather information on the methods, materials and attitudes employed in root canal treatment by dentists in North Jordan, in order to evaluate and improve the quality of current practice. METHODS: A questionnaire was posted to all registered general dental practitioners working in private practice in Irbid Governate in North Jordan (n = 181). The questionnaire included information on methods, materials and techniques used in endodontic treatment. RESULTS: Reply rate was 72% (n = 131). The results demonstrated that only five dentists used rubber dam occasionally and not routinely. The majority used cotton rolls for isolation solely or in combination with a high volume saliva ejector (n = 116). The most widely used irrigants were sodium hypochlorite and hydrogen peroxide, which were used by 32.9% (n = 43) and 33.6% (n = 44) of the respondents, respectively. Forty eight percent of the respondents (n = 61) used the cold lateral condensation technique for canal obturation, 31.3% (n = 41) used single cone, 9.9% (n = 13) used vertical condensation and 12.2% (n = 16) used paste or cement only for the obturation. The majority used zinc oxide eugenol as a sealer (72.5%). All, but one, respondents used hand instruments for canal preparation and the technique of choice was step back (52.7%). More than 50% (n = 70) of the dentists took one radiograph for determining the working length, whilst 22.9% (n = 30) did not take any radiograph at all. Most practitioners performed treatment in three visits for teeth with two or more root canals, and in two visits for teeth with a single root canal. CONCLUSIONS: This study indicates that dentists practicing in North Jordan do not comply with international quality standards and do not use recently introduced techniques. Many clinicians never take a radiograph for determining the working length and never used rubber dam or intra-canal medicaments.

Convergence angle, occlusal reduction, and finish line depth of full-crown preparations made by dental students.

OBJECTIVE: To measure the convergence angle, incisal/occlusal clearance, and finish line depth, which indicate the amount of axial reduction of full metal-ceramic crown preparations made by final-year dental students. METHOD AND MATERIALS: A total of 157 preparations were assessed. Convergence angle and finish line depths were measured by Tool Maker Microscope, while crown height was measured using a digital caliber. RESULTS: The mean convergence angle, faciolingually and mesiodistally, was 22.4 and 25.3 degrees, respectively. The mean for molars was statistically significantly greater than that for other teeth. The incisal/occlusal reduction ranged from 1.8 to 2.2 mm and averaged 2 mm. Buccal shoulder finish line depth averaged 0.86 mm, and mean chamfer finish line depth was 0.74 mm lingually, 0.7 mm mesially, and 0.66 mm distally. The buccal shoulder for mandibular anterior teeth was significantly smaller than for other teeth and averaged only 0.45 mm. CONCLUSION: The mean convergence angle was clinically acceptable. However, shoulder depth was less than the recommended depth of 1.0 to 1.5 mm for metal ceramic crowns. Incisal/occlusal reduction was clinically adequate to provide enough structural durability and color matching.