Keith M. Phillips

Fracture load and mode of failure of ceramic veneers with different preparations.

STATEMENT OF PROBLEM Fracture is a clinical failure modality for ceramic veneers. Whether design of tooth preparation can affect the strength of ceramic veneers remains controversial. PURPOSE This in vitro study evaluated fracture load and mode of failure of ceramic veneers, with 4 tooth preparation designs, that were bonded on extracted human maxillary central incisors. Identical parameters were also measured on unrestored intact teeth for comparison. MATERIAL AND METHODS Fifty maxillary central incisors were randomly divided into 5 equal groups. Each group was assigned a different tooth preparation design: (1) no incisal reduction, (2) 2 mm incisal reduction without palatal chamfer (butt joint), (3) 1 mm incisal reduction and 1 mm height palatal chamfer, (4) 4 mm incisal reduction and 1 mm height palatal chamfer, and (5) unrestored (control). Forty teeth were prepared to accommodate ceramic veneers of equal thickness and incisocervical length. Stone dies were fabricated and veneers made from IPS Empress ceramic. Ceramic veneers were bonded and all teeth mounted in phenolic rings with epoxy resin. Fracture loads were recorded with a mechanical testing machine. RESULTS Mean fracture loads (SD) in kgf were as follows: group 1, 23.7 (6.11); group 2, 27.4 (9.63); group 3, 16.4 (3.44); group 4, 19.2 (6.18); and group 5, 31.0 (10.38). Modes of failure were also analyzed for both ceramic veneers and teeth. One-way ANOVA with multiple comparisons revealed 3 significant subsets: groups 1-2-5, groups 4-1, and groups 3-4 (P <.05). Groups 1 and 2 had no ceramic veneer fractures; group 3 had 3 ceramic veneer fractures, and group 4 had 6 ceramic veneer fractures. CONCLUSION Groups 1 and 2 recorded the greatest fracture loads that were comparable to an unrestored control.

The effect of hydrofluoric acid surface treatment and bond strength of a zirconia veneering ceramic

STATEMENT OF PROBLEM Clinicians are frequently faced with a challenge in selecting materials for adjacent restorations, particularly when one tooth requires a zirconia-based restoration and the next requires a veneer. While it may be desirable to use the same veneering ceramic on adjacent teeth, little information is available about the use of veneering ceramics over a zirconia-based material. PURPOSE The purpose of this study was threefold: (1) to study the influence of hydrofluoric acid-etched treatment on the surface topography of the zirconia veneering ceramic, (2) to test the bond strength of zirconia veneering ceramic to enamel, and (3) to evaluate the flexural strength and the elemental composition of ceramic veneers. MATERIAL AND METHODS Three zirconia veneering ceramics (Cerabien CZR (CZ), Lava Ceram (L), and Zirox (Z)) and 4 conventional veneering ceramics (Creation (C), IPS d.Sign (D), Noritake EX-3 (E), and Reflex (R)) were evaluated. Twenty ceramic bars of each material were fabricated and surface treated with hydrofluoric acid according to the manufacturers recommendations. Ten specimens from each group of materials were examined with a profilometer, and a sample of this group was selected for quantitative evaluation using a scanning electron microscope (SEM). Another 10 acid-etched specimens from each group of materials were treated with silane prior to cementing with resin cement (Variolink II) on enamel surfaces. These luted specimens were loaded to failure in a universal testing machine in the shear mode with a crosshead speed of 0.05 mm/min. The data were analyzed with a 1-way ANOVA, followed by Tukeys HSD test (alpha=.05). An additional 10 ceramic bars from each material group were fabricated to evaluate flexural strength and elemental composition. The flexural strength (MPa) of each specimen was determined by using a 4-point-1/4-point flexure test. A Weibull statistic tested the reliability of the strength data; pairwise differences among the 7 groups were evaluated at confidence intervals of 95%. The chemical composition of each bar was determined by energy dispersive spectroscopy (EDS). RESULTS There was a significant difference in the surface roughness in all testing groups. Conventional veneering ceramics (groups C and R) had a mean surface roughness higher than the groups of zirconia veneering ceramics (P<.001). Group D showed no difference in surface roughness compared with the groups of zirconia veneering ceramics. The SEM micrographs revealed differences in the acid-etched surfaces of ceramics. Zirconia veneering ceramics were smooth, with some groove formations, while conventional veneering ceramics had an amorphous, spongy-like structure with numerous microporosites. The mean bond strength (SD) of zirconia veneering ceramics to enamel revealed a significant difference. Group R (25.16 (3.40) MPa) followed by group C (22.51 (2.82) MPa) had significantly higher mean bond strength than the groups of zirconia veneering ceramics (P<.001, P=.009 respectively). Groups D (16.54 (2.73) MPa) and E (17.92 (3.39) MPa) showed no differences. Only group L (9.45 (1.62) MPa) exhibited significantly lower mean bond strength when compared with conventional veneering ceramics (P<.001). For flexural strength, only 1 group, group CZ, had a significantly lower flexural strength than all other groups (P<.001). CONCLUSIONS Effective ceramic interface management, such as acid etching and enamel bonding, is essential for successful ceramic laminate veneer restorations. Not all zirconia veneering ceramics display the same quality of surface roughness after hydrofluoric acid etching and the same bond strength to enamel when used as laminate veneer materials.

A clinical study comparing the three-dimensional accuracy of a working die generated from two dual-arch trays and a complete-arch custom tray

STATEMENT OF PROBLEM Dual-arch trays are often used by the dentists to make crown impressions of opposing quadrants simultaneously. Metal and plastic trays are available, but little is known about the accuracy of the impressions and resultant working dies. PURPOSE The purpose of this study was to conduct a clinical trial to compare the accuracy of gypsum working dies made from impressions with metal dual-arch, plastic dual-arch, and complete-arch custom trays. MATERIAL AND METHODS Eight patients requiring a posterior single tooth implant restoration were selected on the basis of inclusion and exclusion criteria. A customized abutment was measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) by use of a measuring microscope. Three polyvinyl siloxane impressions were made of the abutment with a complete-arch custom tray, a plastic, and a metal dual-arch tray. Each impression was poured with type IV improved dental die stone. The diameter (buccolingual and mesiodistal), from gingivoaxial to gingivoaxial point angle, and height (occlusogingival), gingivoaxial to occlusoaxial point angle of the abutment standard was determined by measuring each dimension several times to obtain a mean. These 3 mean values served as the controls and were compared with the same measurements of the gypsum dies generated by the 3 different impression techniques. The patient was asked to rank the 3 impressions in order of overall comfort. A multivariate repeated measures single factor ANOVA was used in the statistical analysis (alpha=.05). When main effects were significant, a pairwise comparison of mean values was conducted with Bonferonni adjustment for multiple comparisons. RESULTS There were no significant differences in die accuracy among the 3 trays for the mesiodistal (3.507 mm) and occlusogingival (3.584 mm) dimensions of the implant abutment. Dies were smaller than the standard for these 2 dimensions and larger in the buccolingual dimension. There was a significant difference in accuracy between the metal and plastic dual-arch trays. The dies produced from the metal dual-arch tray were 20 microm larger than the abutment standard compared with 3 microm larger for the plastic tray. The occlusogingival dimension of the working dies was 30 to 40 microm shorter than the implant abutment. Seven of the 8 patients ranked the plastic dual-arch impression as the most comfortable and the complete-arch custom tray as the least comfortable. CONCLUSIONS Within the limitations of this study, the dimensions of working dies from a custom tray impression did not differ significantly from those created with dual arch trays. However, working dies from a plastic dual-arch tray were more accurate buccolingually than those from metal dual-arch trays.

Load fatigue of teeth with different ferrule lengths, restored with fiber posts, composite resin cores, and all-ceramic crowns

STATEMENT OF PROBLEM There is no evidence to suggest that the ferrule length needed for an all-ceramic crown is different from that needed for a cast metal or metal ceramic crown. PURPOSE The purpose of this study was to relate different ferrule lengths with the number of fatigue cycles needed for failure of the crown cement for an all-ceramic crown cemented with a resin cement. MATERIAL AND METHODS Fifteen maxillary central incisors were divided into 3 groups (n=5), with ferrules of 0.0 mm (no-ferrule group), 0.5 mm (0.5-mm ferrule group), and 1.0 mm (1.0-mm ferrule group), respectively. Each tooth was restored with a 0.050-inch glass-filled composite post (ParaPost FiberWhite) and a composite resin core (ParaCore). The posts were cemented with resin cement (ParaPost Cement), and the composite resin cores were bonded to dentin using a dentin bonding agent (ParaPost Cement, Conditioner A & B). Each specimen was prepared with a 7-mm total preparation height, a 1.5-mm lingual axial wall, and a 1.0-mm shoulder around the tooth. The crowns for all specimens were pressed with a pressable ceramic material (IPS Empress 2) and cemented with resin cement (Variolink II). A 6-kg cyclic test load was applied to each specimen at 135 degrees to the long axis of the tooth. The independent variable measured was the number of load fatigue cycles required for failure of the crown cement. The data were subjected to the Kruskal-Wallis test to detect overall significance and the Mann-Whitney U test for pairwise comparisons with Bonferroni correction (alpha=.017). RESULTS The mean (SD) number of cycles to failure for each group was: no-ferrule group, 213 (317); 0.5-mm ferrule group, 155,137 (68,991); and 1.0-mm ferrule group, 262,872 (21,432). None of the specimens in the 1.0-mm ferrule group failed. Significant differences were found between the no-ferrule group and the 0.5-mm ferrule group, and the no-ferrule group and the 1.0-mm ferrule group (P<.017), but not between the 0.5-mm ferrule group and the 1.0-mm ferrule group (P>.017). CONCLUSIONS Specimens with a 0.0-mm ferrule survived few fatigue cycles despite the fact that both the post and crown were bonded with resin cement. Teeth with a 0.5-mm ferrule showed a significant increase in the number of fatigue cycles over the 0.0-mm group, whereas teeth with the 1.0-mm ferrule exhibited a significantly higher fatigue cycle count over the 0.0-mm but not the 0.5-mm group.

Influence of preparation design and existing condition of tooth structure on load to failure of ceramic laminate veneers

STATEMENT OF PROBLEM Although investigators have evaluated the effect of ceramic veneer preparation design, limited information is available regarding preparation design in association with the condition of existing tooth structure. PURPOSE The purpose of this in vitro study was to evaluate the effect of preparation design and the amount of existing tooth structure on the fracture resistance of pressable ceramic laminate veneers. MATERIAL AND METHODS Thirty-two extracted human maxillary central incisors were allocated into 4 groups (n=8) to test for 2 variables: (1) the preparation design (a 2 mm incisal reduction shoulder finish line with or without palatal chamfer) and (2) the existing amount of tooth structure (non-worn tooth or worn tooth). Measurement of the remaining enamel thickness on the inciso-occlusal surface was made after the tooth was prepared. All prepared teeth were restored with pressable ceramic (IPS Empress) veneers, and the veneers were luted with resin cement (Rely-X Veneer). These luted specimens were loaded to failure in a universal testing machine, in the compression mode, with a crosshead speed of 0.05 mm/min. The data were analyzed using a 2-way ANOVA and Tukeys HSD multiple comparison test (α=.05) RESULTS Preparation design and the amount of existing tooth structure had a significant effect on the load to failure value (P<.001); however, the interaction between preparation design and existing amount of tooth structure was not significant (P=.702). Mean (SD) load to failure values were as follows: a preparation design with a palatal chamfer margin with a non-worn tooth (166.67 N (28.89)) revealed a significantly higher failure load than the group with a shoulder finish line alone (131.84 N (18.88)) (P<.01). The preparation design with a palatal chamfer margin for worn teeth (119.56 N (23.88)) revealed a significantly higher failure load than a shoulder finish line design alone (90.56 N (9.32)) (P<.05). The preparation design with a shoulder finish line for worn teeth had a significantly lower failure load than those on non-worn teeth (P<.003). CONCLUSIONS Preparation design and the amount of existing tooth structure had a significant effect on load to failure for ceramic veneers. This study revealed that using a palatal chamfer margin design significantly increased the load to failure compared to a shoulder finish line.

Early loading of surface modified implants in the posterior mandible – 5 year results of an open prospective non-controlled study

AIM The aim of the present study was to evaluate an early loading protocol for surface modified implants placed in the posterior mandible. MATERIAL AND METHODS A total of 134 implants with a TiO(2) blasted, fluoride modified surface were inserted into the posterior mandibles of 44 patients. The implants were functionally loaded after 7 weeks of healing. Implant stability quotient (ISQ) values (during the first year), bleeding on probing (BOP), plaque accumulation and marginal bone level (MBL) were assessed until the end of the observation period of 5 years. A total of 41 patients with 123 implants completed the study. RESULTS No implants were lost. ISQ values decreased significantly from the time of insertion to 2 weeks and increased significantly until the 1-year follow up. BOP varied until the end of the observation period between 7.9% and 13.0%. Plaque accumulation decreased from the time of early loading to the end of the study. MBL changed from 0.59 mm at the time of implant placement to 0.80 mm at the time of early loading. Thereafter, only slight variations in MBL occurred until the end of the observation period. CONCLUSIONS The results confirm that early loading is a promising option also in posterior edentulism of the mandible.

Interdisciplinary Planning, Development, and Treatment

Interdisciplinary treatment planning in dentistry has become both more complicated and facilitated with the advent of dental implants. The use of dental implants allows the practitioner to make their therapies more predictable by removing biomechanical issues, minimizing the need for tooth preparation, minimizing the use of compromised teeth, and allowing for more simplified planning. This, along with the use of digital workflows, allows for more efficient therapies for our patients. This digital world can help in the proper planning for implant placement to be in harmony with all components of the stomatognathic system. Combining the tools available from both the analog and digital worlds is key to contemporary interdisciplinary treatment planning from the initial visit through the actual fabrication of the definitive prostheses.

COMMENTARY. A Novel Method for Creating an Optimal Emergence Profile Adjacent to Dental Implants1

As stated by the authors, there have been numerous descriptions in the literature describing techniques to achieve esthetic emergence profiles for dental implant restorations.The aim is to do this in an efficient and cost-effective manner.The technique described may fit this bill. It is prefabricated and begins the esthetic emergence at the time of implant placement which allows the tissues to heal against a form that is similar to the recently extracted tooth.They compare this with a lab-fabricated provisional in which the contour is carved into the soft tissue model which they describe as an “arbitrary” form. My contention is that this may be less “arbitrary” than the preformed healing abutments because the contours are designed according to the patient’s presenting anatomy, and not from an average number taken from a textbook on dental anatomy.