The International Journal of Prosthodontics, 05/2001

Purpose: The purpose of this study was to evaluate the stress distribution under various loading conditions within posterior metal-free crowns made of new composite materials. Materials and Methods: A three-dimensional finite element model representing a mandibular first molar was constructed. Variations of the model had crowns of two types of composite, a glass ceramic, and porcelain fused to metal. A load of 600 N, simulating the maximum bite force, was applied vertically to the crowns. Loads of 225 N, simulating masticatory force, were applied from three directions (vertically, at a 45-degree angle, and horizontally). Results: The stress distributions in both types of composite crown were similar to that of the glass-ceramic crown. In the test simulating maximum bite force, the maximum tensile stresses on all crowns (17.9 to 18.3 MPa) concentrated around the loading points. In the masticatory force-simulation test, the specimens experienced maximum tensile stresses of 20.3 to 26.6 MPa under a horizontal load and 10.9 to 11.0 MPa under a vertical load. When the load was applied horizontally, the maximum tensile stress was observed around the loading points on the surface in the case of composite and glass-ceramic crowns, and in the cervical area of the metal coping in the porcelainfused- to-metal crowns. Conclusion: It would appear that the strength of occlusal contact points is important to the integrity of posterior metal-free crowns made of new composite materials and that bite forces applied from the horizontal direction are a critical factor determining success and failure.

Purpose: This study evaluated stress distribution in metal frameworks constructed on implants under masticatory forces using computer simulations. Materials and Methods: Three-dimensional finite element analysis was used to study four different veneering materials-metal framework combinations using Calcitek implants. The veneering materials used in the study were porcelain, heat-polymerized poly(methyl methacrylate) resin, microfilled composite resin, and glass-modified composite resin. All computations were conducted for different levels on the buccal and lingual sides. Results: Changing the veneering material on the prosthesis produced significant effects on stress levels and stress distribution on the metal frameworks. Stresses were concentrated along the marginal area of the prosthesis. Acrylic resin showed greater displacement than porcelain, probably because of its lower modulus of elasticity. Conclusion: In comparison to porcelain, more stress is borne by the acrylic resin-veneered metal framework under static loading.

Purpose: The purpose of this study was to determine the marginal discrepancy and retention of silver-palladium crowns cemented with zinc phosphate (Phosphacap) and glass-ionomer cement (Fuji Cap 1) using different seating forces on preparations with various margin designs. Materials and Methods: Crown preparations with three finish lines-chamfer, shoulder, and shoulder with a 45-degree bevel-were sequentially prepared on a dentoform premolar. A metal die for each of the three finish lines was constructed. Complete metal crowns were fabricated for each metal die using a silverpalladium alloy. Three different seating forces-25, 100, and 300 N-were used to load the crowns until initial set of the cement. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using a digimatic indicator. Retention was determined by measuring the tensile strength using the Lloyd universal testing machine. Results: The higher seating forces produced better crown seating but had no significant effect on crown retention. The shoulder and shoulder with bevel finish lines provided better crown retention than the chamfer. Glass-ionomer cement provided greater crown retention than zinc phosphate cement. No significant correlation between marginal seating and crown retention was revealed using a Pearson analysis. Conclusion: Marginal seal was not influenced by either margin design or type of luting cement, but was improved with higher seating force. Crown retention was affected by the margin finish line and the luting agent.

Purpose: The purpose of this article is to draw attention to the need for regular life-long follow-up care of cleft lip and palate patients to maintain adequate masticatory function, speech, and esthetics, thereby supporting psychosocial function. Materials and Methods: Intitial and revisional prosthodontic treatments over a period of 32 years in a patient with a bilateral cleft lip and palate are described. Results: Despite an initial dentition of poor health and prognosis and suboptimal patient cooperation, it was possible to arrive at an improved clinical and radiologic state of oral health by the end of the observation period. Conclusion: Regular life-long prosthodontic follow-up with adequate maintenance and revisional treatments should be regarded as an essential part of the long-term care for subjects with clefts.

Purpose: This article presents the results from a survey of patients' degree of satisfaction with their removable partial dentures (RPD) and the comparison between patient and prosthodontist assessments. Materials and Methods: A total of 165 experienced RPD wearers filled in a questionnaire and graded their RPDs depending on their level of satisfaction. A scale ranging from 1 to 5 was used to assess general satisfaction with RPDs and to assess their esthetics, retention, and hygiene. A specialist in prosthodontics assessed the same prostheses using the same scale, not knowing the patient's opinion. Results: The patients' assessments were high, and more than half of them graded their dentures as excellent. On average, all variables were assessed higher by the patients than by the prosthodontist ( P .001). For the patients who gave the worst grades to their dentures, the grades were lower than the prosthodontist's ( P .001), while the satisfied patients graded their dentures much better than did the prosthodontist ( P .001). Conclusion: On average, patient assessment of the treatment outcomes with RPDs was less critical than prosthodontist assessment. However, the few dissatisfied patients assessed their dentures worse than did the prosthodontist.

Purpose: The purpose of this study was to investigate whether the interchangeability of new Hanau semiadjustable articulators fulfills the manufacturer's criterion (102 µm) in the mediolateral direction and the defined 166-µm criterion three dimensionally and whether the articulators maintain the same interchangeability as new articulators after a period of function. Materials and Methods: The spatial deviations in three dimensions of ten new, ten 18-month-old, and ten 30-month-old Hanau articulators were measured with a fieldinspection gauge and compared to those of a master articulator. Results: Compared to the master articulator, nine of 10 new articulators met the manufacturer's criterion of articulator interchangeability in the mediolateral direction. However, only four of the 10 articulators fulfilled the criterion for three-dimensional interchangeability. The articulators were found to be interchangeable among the groups when the spatial deviations of test articulators from the master articulator at the position of the lingual cusp of the right maxillary first premolar were compared. However, using the geometric mean deviations of test articulators, the 30- month group was not interchangeable with the new and the 18-month articulator groups. Conclusion: This limited study revealed that most of the articulators tested met the manufacturer's criterion of articulator interchangeability, but most did not pass the threedimensional interchangeability test. Clinicians should be aware of the amount of occlusal error in the range of 0.2 mm that may result from interchanging dental casts on the articulator system. The articulator system might be able to maintain the same level of interchangeability for up to 18 months of routine use.

Purpose: The aim of the study was to compare results after 1 and 3 years when single crowns supported by CerAdapt (test) ceramic abutments or CeraOne (control) titanium abutments were loaded. Materials and Methods: The material was divided into two groups: in group A, 69 (34 test, 35 control) abutments/crowns from all involved clinics were followed for 1 year; and in group B, 20 (10 test, 10 control) abutments/crowns from one of the clinics were followed for 3 years. Results: No implant failed, giving a cumulative success rate of 100% for the implants. Two CerAdapt abutments in group A fractured, giving a cumulative success rate of 93% for the CerAdapt and 100% for the CeraOne abutments after 1 year. No abutment failed in group B, giving a cumulative success rate of 100% both for the CerAdapt and the CeraOne abutments between 1 and 3 years. The CerAdapt fractures might have been due to the fact that the abutments were impaired through too-extensive preparation and/or had been exposed to a too-high bending moment. Almost no marginal bone loss was recorded, indicating a stable bone situation both at CerAdapt and CeraOne abutments on single-tooth implants. Healthy conditions, with a relatively stable level of the periimplant mucosa in relation to the abutment/crown, were recorded for soft tissues both at CerAdapt and CeraOne abutments. Both clinicians and patients rated the esthetic result as excellent for practically all cases. Conclusion: The results demonstrate the esthetic possibilities and the safety of single-tooth replacement when accepted treatment concepts are followed and documented components are used. The tested abutments worked well, although the fractured CerAdapt abutments indicate that ceramic abutments are more sensitive to handling procedures than the titanium abutments.

Purpose: The objective of this study was to determine the cytocompatibility of three different extracts of denture base resins and to compare the cytotoxic effect of these materials on a human oral epithelial KB cell line and primary human oral fibroblasts derived from buccal mucosa. Materials and Methods: Set specimens from a heat-cured resin, a self-cured resin, and a light-cured resin were eluted with culture medium for 1, 3, and 5 days. Cytotoxicity was judged using tetrazolium bromide reduction assay. Results: The eluates from self-cured, heat-cured, and light-cured denture base resins were cytotoxic to primary human buccal fibroblast cultures and KB cells. Self-cured resin was the most toxic denture base material among the chemicals tested in all cultures. The cytotoxicity decreased in the order of self-cured resin > heat-cured resin > light-cured resin for KB cells. The rank for buccal fibroblast cells was self-cured resin > heat-cured resin > light-cured resin. Conclusion: The influence of the cytotoxicity depended on the materials tested and the cell culture system used. The use of both permanent and primary cells is recommended for a better screening of the cytotoxic effects of denture base resins.

Purpose: Occlusal overload may contribute to the loss of osseointegration of oral implants, so some clinicians are reluctant to place implants in patients with signs of bruxism. This study evaluated the effect of occlusal wear as a probable sign of bruxism on bone loss and implant stability. Materials and Methods: The study investigated 379 patients who had worn implant-retained or implant-supported restorations for many years. Occlusal wear, patient age and gender, time of prosthetic loading, jaw, location in the dental arch, implant diameter, prosthesis construction, occlusal material, periimplantitis, and loosening of the prosthetic construction were recorded. One implant from each patient was selected for radiographic and Periotest measurements. The implant with the highest bone resorption was chosen. A forward stepwise multiple linear regression analysis was performed to analyze the effect of the explanatory variables on Periotest value and radiographic bone loss. Results: The statistical models could account for part of the variation in bone loss rate and Periotest value. Some influence of time of loading, jaw, and implant diameter on bone loss or Periotest value was formally established. Occlusal wear failed to have any statistical impact on vertical annual bone loss rate or Periotest value. Conclusion: This study gave no indication that implants in patients with occlusal wear have an increased bone loss rate or Periotest value.

Purpose: This study determined (1)the effect of polymerization mode of resin composite core materials and dental adhesives on the bond strength to dentin, and (2)if dental adhesives perform as well to dentin etched with phosphoric acid as to dentin etched with self-etching primer. Materials and Methods: Human third molars were sectioned 2 mm from the highest pulp horn and polished. Three core materials (Fluorocore [dual cured], Core Paste [self-cured], and Clearfil Photo Core [light cured]) and two adhesives (Prime & Bond NT Dual Cure and Clearfil SE Bond [light cured]) were bonded to dentin using two dentin etching conditions. After storage, specimens were debonded in microtension and bond strengths were calculated. Scanning electron micrographs of representative bonding interfaces were analyzed. Results: Analysis showed differences among core materials, adhesives, and etching conditions. Among core materials, dual-cured Fluorocore had the highest bond strengths. There were incompatibilities between self-cured Core Paste and Prime & Bond NT in both etched (0 MPa) and nonetched (3.0 MPa) dentin. Among adhesives, in most cases Clearfil SE Bond had higher bond strengths than Prime & Bond NT and bond strengths were higher to self-etched than to phosphoric acid-etched dentin. Scanning electron micrographs did not show a relationship between resin tags and bond strengths. Conclusion: There were incompatibilities between a self-cured core material and a dual-cured adhesive. All other combinations of core materials and adhesives produced strong in vitro bond strengths both in the self-etched and phosphoric acid-etched conditions.

Purpose: The aim of this in vitro study was to examine the adherence of yeasts to newly polymerized and water-stored denture base polymers using four Candidastrains with different cell surface hydrophobicities. Materials and Methods: Thirty-two autopolymerized denture base polymer specimens were stored in distilled water at 37°C for 7 days and 32 were newly polymerized. Sixteen specimens of each group were pretreated with unstimulated mixed saliva (saliva group), and 16 were pretreated with phosphate-buffered saline ([PBS] PBS group) at 37°C for 1 hour. Hydrophobicity of the newly polymerized and water-stored specimen surfaces was determined by contact angle measurements. C guilliermondii, C albicans, C glabrata,and C tropicaliswere grown on tryptic soy agar. They were pretreated either with saliva or PBS and suspended in PBS. Four parallel test specimens were incubated without agitation in each yeast suspension at 37°C for 1 hour, washed, and allowed to dry in air. Adherent cells were fixed, gram stained, and counted from 10 high-power light-microscopy fields of each specimen. Results: Enhanced adherence of yeasts was observed in water-stored test specimens in comparison to newly polymerized test specimens. Salivary pellicle reduced the hydrophobicity of test specimens and the adherence of yeasts. No differences in contact angles of distilled water between newly polymerized and water-stored polymers were observed. Conclusion: Yeasts seem to adhere less to newly polymerized than waterstored denture base polymer. This may be due to the release of residual monomer from the newly polymerized material.

Purpose: The purpose of this study was to compare the emotional effects of tooth loss in three edentulous populations. Materials and Methods: A questionnaire study involved 142 edentulous subjects undergoing routine prosthodontic care at Guy's, King's and St Thomas's Dental Institute, London; the Dental School, Dundee, Scotland; and the Faculty of Dentistry, University of Hong Kong. Data were analyzed using the chi-squared test. Results: Difficulty in accepting tooth loss was a relatively common experience (44%) in all groups, with almost half feeling that their confidence had been affected. The majority (66%) felt that their choice of food was restricted and that the overall eating experience was less enjoyable, particularly the Hong Kong group. A significant proportion of the participants were concerned about their appearance without dentures, although the trend was less marked in Hong Kong. Forty-three percent felt that they were not adequately prepared for tooth loss, although the Hong Kong group was least concerned. Conclusion: In general, the emotional effect of tooth loss was significant in all groups. The restrictions on daily activities were generally greater in the Hong Kong group. However, this group was much less inhibited by denture wearing. The differences observed in the Hong Kong Chinese are most likely due to different cultural values and expectations associated with these aspects of daily living.

Purpose: The aim of this article is to highlight the strong worldwide trend of enhancing the opportunities for individuals with rare disorders to get adequate information and treatment. Hypohidrotic ectodermal dysplasia is used as an example. Materials and Methods: The development in recent years of databases for rare disorders, the establishment of resource centers in dentistry, and the strong movement of user influence by the formation of patient organizations and exchange of information through the Internet are described. Reference is made to the recent Scandinavian consensus conference on ectodermal dysplasia. Results: Motives for the centralization of treatment planning to resource centers for persons with rare disorders, the compilation of treatment outcomes in databases, and the advocation of a multidisciplinary team approach in dentistry are presented. Conclusion: The prosthodontic profession has a key position in the habilitation and rehabilitation of many different diagnoses of rare disorders.

Purpose: The aim of this article is to describe the oral habilitation, over a period of 20 years, of a young patient with hypohidrotic ectodermal dysplasia and agenesis of 15 permanent teeth. Materials and Methods: Different clinical interventions were adapted to suit the patient's dental and psychologic stage of development. The prosthodontic treatment, which took place at different ages, comprised several treatment modalities: composite-retained onlay fixed partial dentures, a removable partial denture, toothsupported and implant-supported fixed partial dentures, and laminate crown therapy. Results: The different phases of treatment were successful, and the patient is satisfied from a functional as well as a psychosocial point of view. Conclusion: Extensive prosthodontic treatment in growing individuals should preferably be performed with a multidisciplinary team approach. In treatment that is planned and performed over long periods, this approach has the advantages of continuity and shared responsibility for therapy decisions.