The International Journal of Prosthodontics, 01/1999

Purpose: This article reviews recent research on the esthetics of the smile, covering the attractiveness of the smile, the effect of aging on the smile, oral condition and the smile, personality and smile, and smile exercises. Material and Methods: The subjects were Koreans with normal occlusion. Photographs of a full smile were taken and the esthetic quality of the subjects' smiles was estimated. Smile scores were correlated with oral condition, personality, the practice of smile exercises, and elements of the smile, such as the position of the lip in a smile. The personality of the subjects was assessed by means of a Sixteen Personality Factor Questionnaire. Gibson's smile exercises were used to investigate the effect of smile exercise. Results: In an attractive smile, the full shape of the maxillary anterior teeth was shown between the upper and lower lip, the upper lip curved upward or was straight, the maxillary anterior incisal curve was parallel to the lower lip, and teeth were displayed to the first molar. The amount of maxillary incisal exposure gradually decreased with age, accompanied by a gradual increase in mandibular incisal exposure. Personality traits such as warmth, calmness, extroversion, and low anxiety were closely related to an attractive smile. Smile exercises were an effective means of improving the esthetic level of the smile if patients exercises continuously. Conclusion: An attractive smile is important for esthetic treatment. The lip position, oral condition, personality traits, and smile exercise affect the esthetics of the smile

Purpose: The purpose of this article is to describe an automated technique that creates a mirror-image wax model of the contralateral ear using a rapid prototyping technique, which allows precise positioning and adaptation to the deficient side of the face. Materials and Methods: Magnetic resonance images (MRI) are taken of the face and then digitized and reformatted into a 3-dimensional image. The image of the normal ear is extracted, mirrored, and positioned onto the image of the deformed side of the face. The digitized data, when used in conjunction with stereolithorgraphy, produces a photopolymerized resin model ear. A model wax ear is created by pouring molten wax into a silicone mold of the resin model ear. Results: A model wax ear of identical dimensions, shape, and internal contouring as the contralateral normal ear is created. The technique allows the undersurface of the model wax ear to be precisely positioned against the surface contours of the deformed side of the face in 1 patient. Conclusion: The use of stereolithography from MRI scan data is a suitable technique for producing a model wax ear that fits the deformed side of the face. The 3-dimensional computer image of the face may also be used to plan the position (level and protrusion) of the ear.

Purpose: To investigate the effects of fatigue on the strength of materials used in all-ceramic crowns, the biaxial flexural strength of all-ceramic restorative materials was measured with precracked and laminated specimens after cyclic loading. Materials and Methods: Two types of all-ceramic systems were used to prepare specimens: a glass-infiltrated alumina core system (In-Ceram) and a leucite-reinforced feldspathic porcelain system (IPS-Empress). Monolayer and laminated disks with a diameter of about 11.75 mm and a thickness of 1.20 ± 0.05 mm were prepared. The biaxial flexural strength of the specimens that were polished and/or created with a precrack was measured. Their strength was also measured following cyclic loading. A cyclic load that was 60% of the mean breaking load of the specimens (before cyclic loading) was applied to specimens for 10 to the fifth power cycles in 37 degrees C water. Results: Although 20% to 30% of the polished specimen samples fractured during cyclic loading, the biaxial flexural strength of specimens that survived the cyclic loading was nearly the same as that of specimens not subjected to the cyclic loading. The strength of the alumina system decreased with the introduction of precracks, and nearly all specimens fractured during cyclic loading. The strength of the leucite system, however, did not decrease with the presence of precracks, and no fractures were observed on these specimens during cyclic loading. Conclusion: These results suggest that although the alumina system has high flexural strength, it is more sensitive to flaws and susceptible to fatigue fracture. The effect of fatigue on the leucite system appears to be lo

Purpose: This study determined the fracture strength of magnesia-core porcelain after using a glass infiltration firing technique. Materials and Methods: Eighty refractory dies were replicated from a stainless steel master die milled to the dimensions of a maxillary premolar that had been prepared for a porcelain crown. The core porcelain was applied to the refractory dies using traditional condensation methods, and then formed into standardized copings using a centrifugal sculpturing device. The copings were vacuum-fired from 593 degrees C to 1 of 8 high temperatures. Five copings per temperature were then coated with a glass-infiltrate and ground back to a standard t hickness. The finished copings were bonded to a duplicate die with an adhesive resin luting system and placed in an Instron testing machine and loaded to fracture. Results: Analysis of variance and Student-Newman-Keuls tests demonstrated significant differences among treatments and temperatures (P 0.05). A significant increase in fracture strength was observed after glass infiltration of the magnesia-core porcelain. Sintering the copings to 871 degrees C or 899 degrees C prior to glass infiltration gave the highest fracture load values. Conclusion: Glass infiltration significantly increased the fracture strength of the magnesia-core porcelain.

Purpose: The aim of this study was to investigate attitudes among general dentists in Sweden in relation to gender, age, prosthodontic activity, and dental delivery system (private or public). Materials and Methods: Questionnaires were sent to a random sample of 2,059 dentists, and a response rate of 76% (1,567 dentists) was achieved. Among those who responded, 50% were private practitioners, and 50% were publicly employed practitioners; 42% were female and 58% were male. The questionnaire contained 10 statements aimed at measuring attitudes. Their dimensionality was analyzed using principal components analysis. The resulting factors were related to delivery system (public or private), gender, age, job satisfaction, and weekly working hours used for prosthodontics in multiple regression models. Results: There was a wide variation in the answers to the statements, indicating great individual differences in opinions among dentists. Several distributions differed with respect to gender and delivery system, but the mean diffe rences between various groups of dentists were small. The most affirmative attitude was shown for delegation of impression taking to auxiliaries (mean 6.7; SD 1.8), and the most negative attitude was shown for close cooperation between dentists (mean 1.8; SD 1.4). The factor analysis gave 3 factors, with a variance explanation of 57%. Regression models for the 3 attitude dimensions ( patient influence, delegation, and patient information ) showed that female dentists felt more positive about delegation and information than male dentists. The explained variance was very low for all 3 models and varied from 0.01 to 0.05. Conclusion: Although the differences in attitudes between various groups of dentists were statistically significant, these differences were small in relation to the large variation in attitudes among individual dentists.

Purpose: Selecting artificial teeth for a denture is complex when there are no remaining natural teeth and no pre-extraction records. The aim of this paper is to review the methods used to select artificial anterior teeth for the edentulous individual. Materials and Methods: The review takes account of the majority of papers published during the last 100 years and is organized according to the methods used for determining artificial tooth form. Results: Several factors have been proposed as aids for artificial tooth selection, and numerous methods have been devised for the evaluation of reliable esthetic factors in determining artificial tooth form. Conclusion: To date, no universally reliable method of determining tooth form has been found. The Williams classification (1914) is the most universally accepted method of determining anterior tooth form.

Purpose: Bonding techniques are commonly used today to ensure the durability of porcelain laminate veneers and ceramic inlay-onlays, which are esthetically pleasing solutions to the problem of dental restoration. Acid etching and silanization of porcelain have been widely used to enhance the retention between bonding resins and ceramic restorations. The purpose of this study was to evaluate the effect of surface modifications with 10% hydrofluoric acid gel and a coupling agent (a dual component silane) on the bond strength of 2 dental feldspathic ceramics (GC and PVS) bonded with an unfilled resin (Super-Bond). Material and Methods: Eighty samples of GC and eighty samples of PVS were built for a mechanical study. Mechanical tests were conducted using a Lloyd T 6000 R tensile machine, which determined the bond strengths of the 2 ceramics after different surface treatments (etching or silanization). In the next part of the study, 10 surfaces of GC and 10 surfaces of PVS were studied with a scanning mechanical microscope to evaluate the action of hydrofluoric acid gel on the roughness of the 2 ceramics. Results: Etching ceramic with hydrofluoric acid gel increased the developed surface of feldspathic ceramics, especially for PVS, but this treatment was not sufficient to obtain the highest shear bond strength. The highly positive influence of silanization was shown, particularly for GC ceramic bonded with an unfilled resin. Conclusion: Silane combined with the action of hydrofluoric acid gel is the most effective surface treatment for ceramic.

Purpose: The purpose of this study was to report the 5-year clinical performance of implant-supported prostheses with laser-welded titanium frameworks and to compare their performance with that of prostheses provided with conventional cast frameworks. Materials and Methods: On a routine basis, a consecutive group of 824 edentulous patients were provided with fixed prostheses supported by implants in the edentulous mandible. In addition to conventional gold-alloy castings, patients were at random provided with 2 kinds of laswer-welded titanium frameworks. In all, 155 patients were included in the 2 titanium framework groups. A control group of 53 randomly selected patients with conventional gold-alloy castings was used for comparison. Clinical and radiographic 5-year data was collected for the 3 groups. Results: All followed patients still had fixed prostheses in the mandible after 5 years. The overall cumulative success rates were 95.9% and 99.7% for titanium-framework prostheses and implants, respectively. The corresponding success rates for the control group were 100% and 99.6%, respe ctively. Bone loss was 0.5 mm on average during the 5-year follow-up period. The most common complications for titanium frameworks were resin or tooth fractures, gingival inflammation, and fractures of the metal frames (10%). One of the cast frameworks fractured and was resoldered. Loose and fractured implant screw components were few ( 1%). Conclusion: Even though the cast frameworks had a higher success rate, the overall titanium framework treatment result was well in accordance with the result of the control group. The test groups performed better after clinicians had gained some experience with the technique, and laser-welded titanium frameworks seem to be a viable alternative to conventional castings in the edentulous mandible.

Purpose: Denture-induced fibrous inflammatory hyperplasia (FIH) occurs around the borders of an ill-fitting denture. There has been no report in the literature concerning epithelial proliferative activity in FIH. The purpose of this study was to observe the labeling of proliferating cell nuclear antigen (PCNA) and evaluate its clinicopathologic results. Materials and Methods: The labeling index (LI) was assessed by using the PCNA, a nuclear protein synthesized main ly in the G1-S stages of the cell cycle that could be det ected immunohistochemically by the monoclonal antibody PC10. The PCNA LI was assessed in FIH specimens, in clinically normal specimens 1 cm from the FIH margin (adjacent group), and in clinically normal specimens located at least 2 cm from the adjacent group; the last were considered the control group. Results: The mean PCNA LI values in the basal, parabasal, and overall epithelial layers were similar in FIH and in the adjacent group and were significantly higher than in the control group. Conclusion: These data support the importance of the surgical treatment of FIH with wide excision (about 1 cm) since the clinically normal tissue around the lesion could be histologically altered.

Purpose: The purpose of this in vitro study was to evaluate th e influence of post and ferrule length on the resistance to cyclic (fatigue) loading of teeth with prefabricated titanium posts (ParaPost) and crowns. Materials and Methods: Ninety bovine teeth with similar dimensions were mounted in acrylic blocks with artificial silicone periodontal ligaments. Combinations of post lengths of 5 mm, 7.5 mm, and 10 mm, and ferrule lengths (ie, the vertical dentinal overlap of the crown) of 1 mm, 1.25 mm, and 2.5 mm made up 9 different groups consisting of 10 teeth each. The posts were cemented with zinc phosphate cement. Composite-resin cores were made and crowns were cemented. Each test specimen underwent cyclic loading of 400 N with a frequency of 1 load per second at an angulation of 45 degrees to the long axis of teh tooth. Results: All but 2 specimens failed with a root fracture; in the remaining 2 specimens the core lost retention. A large variation in the results between the various groups was observed. A nonparametric 2-way analysis for groups with a natural order revealed that the fracture resistance to cyclic loading increased statistically significantly with increasing ferrule length (P 0.01), whereas increasing post length did not increase fracture resistance (P = 0.44). Conclusions: Ferrule length was more important than post length in increasing fracture resistance to cyclic loading of crowned teeth.

Purpose: The use of reinforcing fibers in dentures has raised concerns about possible increased adherence of yeasts t o the surface. The aim of this in vitro study was to compare the adherence of Candida albicans to the surface of denture-base polymer and to E-glass fibers. Materials and Methods: Test specimens were made from an autopolymerized denture-base resin (Palapress) reinforced with preimpregnated unidirectional E-glass fibers, which were exposed at the surface. The test specimens were pretreated with parotid saliva and incubated without agitation in standardized yeast suspensions (10 to the eighth power colony-forming units per mL) in phosphate-buffered saline at 37 degrees C for 1 hour. The test specimens were then washed to remove nonadherent cells. After being air dried, they were sputter coated with gold-palladium for scanning electron microscopy (SEM). To compare the adherence to different surfaces, the num ber of yeast cells found either on the polymer matrix or on the glass fibers was counted from SEM fields (170 um x 120 um, 600x) of randomly selected areas. Results: The mean density of yeast cells found on the surface of the polymer matrix was significantly higher (P 0.001) than that on the surface of glass fibers. The number of adherent yeast cells found at the interface between the fibers and polymer matrix was high. Conclusion: The adherence of C albicans to E-glass fibers was lower than to polymer matrix in the denture composite. If fibers are exposed only during polishing of the composite, the reinforcing material appears not to increase the adherence of this common oral yeast. However, areas with permanently exposed fibers may provide mechanical retention for yeast cells at the interface of the components.