The International Journal of Prosthodontics, 01/2009

Purpose: The aim of this study was to compare, prospectively, treatment with implant-retained mandibular overdentures versus conventional complete dentures. Materials and Methods: Part 2 of this paper reports on the outcome after 7 years of denture use, using additional questionnaires. Results: Patients with implant-stabilized overdentures continued to be more satisfied with their mandibular dentures and their diet than those using conventional complete dentures. About 50% of the implant group who completed the questionnaire had had their dentures remade. The other 50% remained satisfied with their original dentures and were still using them at the 7-year review. The average chairside time spent on them was 467 minutes. Conclusions: Mandibular overdentures with two endosseous implants permit better function than conventional complete dentures.

Purpose: This study presents successful maxillofacial prosthetic rehabilitation using telescopic and crowns on zygoma implants as abutments. Materials and Methods: Fifteen patients received 36 zygomatic and 24 dental implants and were followed-up for an average of 65 months (range: 13 to 102 months). Machined zygoma implants were positioned classically in the maxillary molar region. In larger defects, premolar and canine implants were also used. Follow-up included implant and prosthetic success parameters as well as the completion of the Oral Health Impact Profile (OHIP14G). Results: Seventy-three percent of patients during the study period did not encounter notable complications after prosthetic rehabilitation. There was an 89% cumulative 8-year zygoma implant survival rate and a 100% survival rate for the dental implants. Three losses occurred due to overloading and persistent infection; each was immediately replaced. Five successfully osseointegrated implants had to be removed in two patients due to recurrences of disease; one patient died. Peri-implant bleeding and plaque index scores decreased. After prosthetic treatment with electroplated gold or galvanotelescopes, all patients who had participated in the follow-up declared function (ie, retention, speech, and mastication) and esthetics as having improved. Other positive aspects mentioned were good hygiene, comfortable usage, and a decrease in sore spots. OHIP scores were 25 ± 12 on a scale of 0 (no impairment) to 56 (maximum impairment). Conclusion: Within the limitations of this study (a variable evaluation period), it was observed that zygomatic implants are reliable retention for maxillofacial prostheses. Losses were diagnosed as occuring primarily from chronic infection and overloading. A trapezoid prosthesis design support is recommended with a sufficient number of implants.

Materials used for dental impressions are usually safe. This study describes a case of fatal anaphylaxis that appeared immediately after the oral mucosa came into contact with an alginate paste used for dental impressions. The cadaveric examination and the postmortem toxicology report confirmed that the cause of death was anaphylactic shock. The patient was affected by both cardiovascular and lung diseases that worsened the condition and forbade the use of epinephrine. To the authors' knowledge, dental impression materials, and alginate in particular, have not been reported previously as being a cause of anaphylaxis.

Purpose: The aim of this study was to investigate data on the prevalence of tooth wear in adults and assess possible correlations using a systematic review. Materials and Methods: A search of the literature, using PubMed and the Cochrane Library, from January 1980 to July 2007 was made using keywords "tooth + wear"; "dental + attrition + prevalence"; "dental + wear + prevalence"; "erosion + prevalence"; and "abrasion + prevalence." References were independently screened for inclusion and exclusion by two investigators and Cohen Kappa was used as the measure of agreement. Data were collected and converted into the Smith and Knight Tooth Wear Index. Results: One hundred eighty-six references were initially selected and subjected to the systematic review procedure; 13 survived the inclusion procedure. Four articles were suitable for regression analysis at tooth level (R2 = .593) and 3 at subject level (R2 = .736), using "age and age squared" and "age squared" as variables, respectively. Six studies reported males having significantly more tooth wear than females. Conclusion: The predicted percentage of adults presenting with severe tooth wear increases from 3% at the age of 20 years to 17% at the age of 70 years. Increasing levels of tooth wear are significantly associated with age.

Purpose: Bruxism and parafunctions are potential risk factors for implant and prosthodontic treatment failure. However, the etiology of bruxism remains unknown. This study sought to clarify the relationship between bruxism behavior and a salivary stress biomarker level. Materials and Methods: Forty-six volunteers (23 men, 23 women) participated in this study. Bruxism behavior was assessed using a self-administered questionnaire, study casts, and BiteStrip, a miniature electronic screener used to detect sleep bruxism. The questionnaire consisted of six items asking about bruxism, occlusion, jaw functional limitation, and dentition. Occlusal wear was assessed from dental casts and calculated as the sum of the facets in the maxillary arch segment. Participants used BiteStrip at home for one night and the score was evaluated. Two-minute stimulated whole saliva samples were collected from participants to measure daytime levels of chromogranin A (CgA), a major salivary stress biomarker. Nonparametric tests of the relationship between variables were performed using the Spearman R and Kendall t statistical correlation tests. Results: There was a positive correlation between self-reported bruxism and self-reported jaw functional limitation. Occlusal wear did not significantly correlate with occlusion, jaw functional limitation, or dentition, but it did significantly correlate with self-reported bruxism behavior, as well as the BiteStrip score. It was interesting to find that the CgA level was significantly negative in correlation with the BiteStrip score. Conclusion: Sleep bruxism is believed to be a stress-related sleep disorder. The results suggest that daytime psychological stress level is significantly negative in correlation with sleep bruxism behavior.

The purpose of this study was to evaluate the fracture-load values of cantilevered all-ceramic fixed partial dentures (FPDs). Fifty FPDs were manufactured using a zirconia frame to replace a missing molar. The FPDs were divided into five groups, each with a different framework design. After thermocycling and mechanical loading, the load to fracture was measured. The Mann-Whitney U test was used for statistical analysis. The mean fracture-load values for the test groups ranged from 346 to 548 N. Reinforcement of the shoulder on the oral side of the occlusal wall resulted in higher fracture load values, while increasing the wall thickness of the distal abutment did not improve fracture resistance. The results indicate that all-ceramic cantilever FPDs cannot yet be recommended for clinical replacement of a missing molar.

Purpose: This study was conducted to measure, in vitro, the chewing load forces transmitted through crowns made of different prosthetic restorative materials onto dental implants. Materials and Methods: A masticatory robot capable of reproducing the mandibular movements and the forces exerted during chewing was used. The forces transmitted to the simulated peri-implant bone during the robot mastication were analyzed using four different occlusal materials: three resin composites and one glass ceramic crown. Results: The ceramic crowns transmitted significantly greater forces (up to +63.06%, P .0001) than the composite crowns tested. Conclusion: Composite crowns are better able to absorb shock from occlusal forces than crowns made of ceramic material.

Purpose: The aim of this study was to test the hypothesis that viscoelastic finite element analyses can reliably predict the effect of geometry on maximum tensile stresses in bilayer screening tests that are used to determine thermal compatibility. Materials and Methods: Three-dimensional viscoelastic finite element models of a beam, cylinder, disk, sphere, central incisor crown, molar crown, and posterior three-unit fixed partial denture (FPD) were used to calculate residual stresses after simulated bench cooling. Four compatible and four incompatible systems were evaluated. Results: The highest residual tensile stresses for all material combinations were associated with the three-unit FPD. Residual tensile stresses ranged from 5.4 MPa in the disk for a compatible combination to 262 MPa in the three-unit FPD for an incompatible system. Residual tensile stresses in the three-unit FPD ranged from 16.8 MPa to 44.0 MPa for the compatible systems and from 175 MPa to 262 MPa for the incompatible systems. Conclusion: Based on finite element calculations, it is predicted that all-ceramic dental prostheses with an average thermal contraction mismatch (500°C to 25°C) greater than ± 1.0 ppm/K will likely exhibit a relatively high percentage of failures in clinical use compared with systems having smaller thermal contraction mismatch between core and veneering ceramics.

This study investigated whether metals or resins can replace human teeth in in vitro fracture tests of endodontically treated teeth (ETT), as ETT show high heterogeneity and small availability. Eight incisor-shaped roots per group were adhesively restored with fiber-reinforced composite posts, composite core build-ups and Co-Cr-Mo crowns. Specimens were thermally cycled and mechanically loaded (TCML) and fracture strength was determined. The results varied between 0 N and 348 N. Extracted ETT may show comparable strength and survival during TCML to teeth in situ and therefore are the first choice for in vitro testing. Substitutes show comparable fracture patterns but different fracture values.

Purpose: Dental esthetics has increasingly become an important and rewarding discipline in dentistry as patients have begun to request anterior restorations of high esthetic quality. Clinicians must be prepared to meet the esthetic demands and high expectations of their patients. Different variables may influence the esthetic quality of restorations. Quality evaluations may vary with clinical or patient assessments. This study attempted to assess the esthetic quality of maxillary anterior restorations in order to determine the percentage of restorations with satisfactory quality, examine variables affecting esthetic quality, and make comparisons between agreements and disagreements in clinical and patient evaluations. Materials and Methods: Restorations in patients attending different dental clinics in Irbid, Jordan were examined. Clinicians compared the color and shape of the restorations with those of a natural tooth using Ryge criteria, and patients evaluated the same parameters and the surface texture using a Visual Analogue Scale (VAS). Evaluations ranked the quality as good, satisfactory, or poor. Results: The percentage of esthetic complaints was 32.4%, whereas the percentage of satisfactory restorations revealed was 43.8% and 67.6% by clinical and patient assessments, respectively. Restorations yielded significantly better scores on both evaluations when they were prepared by dental students, made in the Dental Teaching Centre (DTC), or were less than one year old. The number of agreements between clinical and patient rankings was significantly less than disagreements. Conclusions: There were statistically significant disagreements on the esthetic quality between clinicians and patients. Age, gender, practice sector, qualification of the operator, type, and longevity of restoration significantly affected the assessments.

It was investigated whether L*a*b* values for teeth as well as shade tabs for one 3D-Master shade were similar to one another. Teeth were measured using Vita Easyshade and L*a*b* values and the closest 3D shade was then recorded. The shade-guide tabs were also measured using the same device. 3D-Master shades yielded different L*a*b* values for the teeth than for the tabs. L* and a* values, especially, were systematically different. Therefore, Easyshade L*a*b* values for teeth and tabs could not be directly compared.

The aim of this study was to investigate color matching under natural daylight and daylight lamp conditions. Twenty-nine preclinical students underwent a training course and then matched randomly chosen shade tabs of Vita 3D-Master Shade Guide under both natural daylight and daylight lamp conditions. Color difference (Delta Eab) between presented and selected shade tabs was calculated. Statistical differences were explored by use of multivariate analyses. Mean Delta Eab was 2.5 (1.0 to 4.3) with daylight lamp and 3.4 (0.9 to 7.4) with natural daylight. The difference was statistically significant (P .001). The use of a daylight lamp helps to standardize light conditions and significantly improve the ability to match colors.

Purpose: Mechanical analyses of idealized crown-cement-tooth systems through finite element analysis (FEA) has provided valuable insight concerning design parameters and materials that favor lower stress patterns. However, little information regarding variation of basic preparation guidelines in stress distribution has been available. The primary objective of this study was to evaluate maximum principal stresses on a molar crown veneer plus core system natural tooth configuration preparation with variations in the ratio of proximal axial length (PAL) to buccal axial length (BAL) as well as loading condition and position. Materials and Methods: Three-dimensional models comprising a crown veneer (porcelain), crown core (zirconia), cement layer, and tooth preparation (4.2 mm BAL with PAL reductions of 0.8 mm, 1.0 mm, and 1.2 mm) yielding BAL:PAL ratios of 1.23, 1.31, and 1.4 were designed by computer software (Pro/Engineering). The models were imported into an FEA software (Pro/Mechanica), with all degrees of freedom constrained at the root surface of the tooth preparation. Each tooth preparation crown configuration was evaluated under a vertical (axial) 200 N load, and under a combined vertical 200 N and horizontal (buccally) 100 N load applied at different positions from the central fossa to the cusp tip. Maximum principal stress (MPS) was determined for the crown core for each crown BAL:PAL ratio, loading condition, and position. Results: Under both vertical and combined loading conditions, the highest MPSs were located at the occlusal region and in the occlusogingival region of the ceramic core. MPS values increased in the proximal region as the BAL:PAL ratio increased. Combined loading resulted in a general increase in MPS compared to vertical loading. Conclusion: Increasing the BAL:PAL ratio (reducing the proximal axial length of the preparation) acted as a stress concentrator at regions near the crown margins, suggesting this area may be vulnerable to damage from fit adjustment as well as during function. Such increases in stress concentration should be considered in clinical scenarios, especially when inherent flaws are present in the material, since extensive high-magnitude tensile stress fields have been noted under all loading conditions.

Purpose: The aim of this study was to evaluate whether there is a need to develop a new questionnaire measuring dental appearance or if this is already covered by the Oral Health Impact Profile (OHIP-49). Materials and Methods: Based on internationally accepted guidelines about dental esthetics, a questionnaire was developed to measure dental appearance (QDA). Eleven items defined a QDA sum score (0 = absolutely satisfied, 44 = absolutely dissatisfied). Furthermore, oral health-related quality of life was evaluated using the German version of the OHIP-49 and the OHIP-esthetic. Thirty patients (14 women, 16 men; mean age 59 ± 10 years) were included in the study. All patients received a complete oral rehabilitation including the anterior teeth of the maxilla. Questionnaires were completed before and after treatment. Results: The median values were 16 and 1.5 for the QDA sum score, 46 and 16 for the OHIP sum score, and 14.5 and 2 for the OHIP-esthetic before and after rehabilitation, respectively. The improvement after treatment was significant for all questionnaires (P £ .0001). Between the QDA sum score and the OHIP sum score or any of the OHIP subscales (the only exception being "psychological discomfort"), no significant correlation could be found (P > .05). Between the QDA sum score and the OHIP-esthetic, a significant correlation could be found before treatment (r = 0.505, P = .004) but not after treatment (P > .05). Conclusions: If the OHIP-49 is used in clinical studies and a profound evaluation of dental appearance is desired, it is reasonable to use an additional esthetic modulus.

Purpose: The aim of this study was to compare the debond/crack initiation strength (D/CIS) of a leucite-based low-fusing ceramic pressed (PC) to metal and feldspathic porcelain (FP) fused to metal. Materials and Methods: Forty rectangular metal specimens, 20 noble alloy (NA; gold-palladium) and 20 base metal alloy (BA; cobalt-chromium) were fabricated per ISO 9693:1999 standards (25.0 mm 3 0.5 mm 3 3.0 mm). Ten samples in each group received FP and the remaining 10 received PC. The samples in the PC group underwent wax pattern build-ups and subsequent investing and casting. The ceramic dimensions in all four groups were 8.0 mm 3 1.0 mm 3 3.0 mm. The final metal-ceramic specimen thickness was 1.5 mm. All specimens were subject to the Schwickerath crack-initiation three-point bending test at a crosshead speed of 1.5 mm/min. Metal-ceramic fracture loads were recorded in Newtons and D/CIS was calculated using the formula: tb = k × Ffail. Results: Mean D/CIS were as follows: BA-FP: 36.11 ± 2.31 MPa, NA-FP: 42.64 ± 1.94 MPa, BA-PC: 37.47 ± 6.02 MPa, and NA-PC: 47.94 ± 3.92 MPa. A 2-way ANOVA revealed no significant difference in D/CIS values between the four groups. A statistically significant difference was noted when comparing the mean D/CIS values obtained between the two metal alloys used (NA: 45.29 MPa and BA: 36.79 MPa). Conclusion: No differences (P > .05) in mean D/CIS were found between the low-fusing ceramic pressed to metal and the FP fused to metal. A higher mean D/CIS (P > .05) was found for the NA compared to the BA, with both ceramics tested.