The International Journal of Prosthodontics, 02/2001

Purpose: Metal-ceramic inlay designs were developed to determine if the esthetic qualities of all-ceramic inlays could be duplicated and at the same time improve their strength and stability. The objectives of this study were to: (1) compare the fracture resistance of metal-ceramic inlays with that of all-ceramic inlays; (2) determine the correlation between the degree of preparation taper and fracture resistance; and (3) determine the correlation between marginal gap width and fracture resistance. Materials and Methods: Inlay preparations were made on 60 Dentoform teeth, with 30 teeth allocated for metal-ceramic inlays and 30 teeth for all-ceramic inlays. Each group was further subdivided into 5-, 10-, and 20-degree taper preparations. Metal-ceramic inlays were fabricated using Goldtech Bio 2000 metal and Ceramco porcelain extending to the margin, while all-ceramic inlays were made from Empress II ceramic. Marginal gap widths were measured at six critical areas after fabrication. The load at failure was measured using an Instron Universal Testing Machine. Results: The mean fracture load for all-ceramic inlays and metal-ceramic inlays at 5, 10, and 20 degrees was 70 ± 40 N, 48 ± 37 N, 33 ± 7 N, and 40 ± 23 N, 29 ± 22 N, and 14 ± 4 N, respectively. The mean gap width was 105 ìm and 126 ìm for all-ceramic and metal-ceramic inlays, respectively. Conclusion: The mean fracture load for Empress inlays was significantly higher than that for metal-ceramic inlays. Inlays with a 5-degree taper were significantly more fracture resistant than those with a 20-degree taper. There was no relation between marginal gap width and fracture resistance.

Purpose: The aim of this work was a simulation of the onset of osseointegration of the transmandibular implant system in the mandible. This was achieved by imposing joint elements at the implant-bone interface. Materials and Methods: The geometric model was derived from the anatomic measurement of several mandibles by tomographic scanning. The spring constants of the joint elements interposed at the implant-bone interface were varied between 1 N/mm and 109 N/mm to represent the conditions leading to osseointegration. Results: Increasing the value of the spring constant at the joint elements gradually increases the effective stress in an increasing volume of crestal cortical bone. Additionally, a larger volume of crestal cortical bone assumes a higher stress value as the simulation proceeds. Conclusion: This work indicates that considerable changes in stress magnitude and distribution occur in the crestal cortical bone margins as osseointegration is simulated, which may be the necessary stimulus for bone remodeling.

Purpose: This study had a twofold aim: first, to gather knowledge about the prevalence of radiologic signs of temporomandibular joint osteoarthritis (TMJ-OA) and possible risk factors in patients who had worn an implant prosthesis for between 2.5 and 10 years; and second, to investigate the diagnostic value of radiologic TMJ-OA signs for orofacial pain in a non-temporomandibular disorders group. Materials and Methods: Two hundred thirty patients (134 women, 96 men) answered a questionnaire regarding orofacial pain. In mean, they were 64 years old and wore 98 fixed and 132 removable implant dentures. The effect of age, gender, state of the dentition, time span after prosthesis placement, parafunction, and TMJ sounds on radiologic TMJ-OA signs was estimated through multiple logistic regression. The predictive values were calculated to assess the diagnostic value of severe TMJ-OA signs to predict orofacial pain. Results: Prevalence of TMJ-OA signs was 70% for flattening, 23% for osteophytes, and 24% for erosion. Some effect on radiologic TMJ-OA signs of gender and state of the dentition was found. The predictive values for orofacial pain from radiologic TMJ-OA ranged from 0.22 to 0.81. Conclusion: Radiologic signs of TMJ-OA were common findings. The study gave no indication that long-term wearing of an implant prosthesis has a negative effect on TMJ-OA. It was not possible to predict orofacial pain from radiologic TMJ-OA signs.

Purpose: The objective of the current study was to investigate the surface morphologic characteristics of prosthodontic composite materials treated with an acidulated phosphate fluoride (APF) agent. Materials and Methods: Seven composite materials (Artglass, Axis, Belleglass, Cesead II, Dentacolor, Solidex, and Targis) were examined. Each material was packed into a split plastic mold and was polymerized with a laboratory photo-curing unit. Half of each composite disk surface was coated with a varnish, and the entire surface of the sample was treated with an APF agent. After removal of the varnish, surface roughness values (Ra) for the treated and untreated (ie, previously varnish coated) sides of all specimens were recorded with a surface analyzer and observed with a scanning electron microscope. Results: Ra values for Cesead II, Solidex, and Targis showed a significant increase as a result of treatment with the APF solution. Microphotographs demonstrated that the macroinorganic fillers in the Cesead II and Solidex materials showed substantial dissolution caused by the APF agent. There were no significant statistical differences in the Ra values between the treated and untreated halves for any of the materials containing inorganic fillers composed entirely of diameters up to 1.0 µm. In particular, microphotographs of prepolymerized silica composite (classified as microfilled materials in Axis and Dentacolor) did not reveal any change of the specimen surfaces. Conclusion: The APF agent attacked inorganic fillers in the composite materials. Microfilled material surfaces were insensitive to the agent in comparison with macroinorganic filled material surfaces.

Purpose: The aim of this study was to evaluate the prosthetic complications with implant-supported overdentures in the maxilla. Materials and Methods: Forty-one patients (mean age 61 years) were consecutively admitted for treatment from 1991 to 1998. A total of 173 ITI implants were placed. Four to six implants either connected with a bar (34 overdentures) or with single anchors (seven overdentures) supported the denture, and only a few parties had fewer than four implants. The overdentures had a horseshoe design and were reinforced by a cast-metal framework. The mean observation time was 3.2 years. Oral hygiene and periimplant parameters were regularly assessed, and records were kept of prosthetic maintenance service. All prosthetic complications encountered were classified related to (1) implant components and anchorage devices, (2) mechanical and structural failures of dentures, or (3) denture-related adjustments. Results: Three implants did not osseointegrate, and five implants were lost after loading. Thus, the overall survival rate of the implants was 95.5%. Altogether, 85 prosthetic complications were encountered. The most frequent finding was retightening of the bar screw and adjustments of the bar retainers. Repair of dentures was not frequent and was mostly related to broken teeth. No fracture of dentures was observed. Renewal of dentures occurred twice, once after loss of all implants in one patient. Thirty-nine overdentures had been continuously worn; thus, the overall denture stability was 95%. Mucosal irritation and need for occlusal adjustment were the most frequent findings in the first year. Over time, a decrease of complications was observed. Conclusion: Planned maxillary overdentures supported by implants are a successful treatment modality on a short-term basis.

Purpose: This study was undertaken to characterize the fracture resistance and mode of fracture of endodontically treated incisors restored with cast post-and-core, prefabricated stainless steel post, or carbon fiber-reinforced composite post systems. Materials and Methods: Ten endodontically treated teeth restored with each technique were subjected to a compressive load delivered at a 130-degree angle to the long axis until the first sign of failure was noted. The fracture load and the mode of fracture were recorded. Results: The failure loads registered in the three groups were not significantly different. Between 70% and 80% of teeth from any of the three groups displayed fractures that were located above the simulated bone level. Conclusion: The use of carbon fiber-reinforced composite posts did not change the fracture resistance or the failure mode of endodontically treated central incisors compared to the use of metallic posts.

Purpose: Most research on the accuracy of dental computer-aided design/manufacturing (CAD/CAM) systems focuses on the marginal gap. A detailed analysis of the various components of CAD/CAM systems (digitizer, software, and milling machine) using this approach is nearly impossible. The purpose of this study was to determine the accuracy of the manual mechanical digitizer of the Precident-DCS system. Materials and Methods: Gauge blocks were aligned to the coordinate planes of the digitizer to determine the point and length measurement uncertainty. The values for each measuring point were compared for statistical differences concerning first versus second operator, pressure, and mode of sensing using analysis of variance. The measurement uncertainty was given by 95th percentiles. Results: The mean one-dimensional point measurement uncertainty in the Y direction was 11 µm for the first, 8 µm for the second, and 37 µm for both operators. The three-dimensional point measurement uncertainty in the Y direction was 10 µm for the first, 33 µm for the second, and 60 µm for both operators. The point measurement uncertainty was significantly influenced by the pressure during sensing and by the operator as well. There were significant differences between the first and second recordings. The length measurement uncertainty in the Y direction for a gauge block of 20 mm was 52 µm for both operators. Conclusion: The reliability of the manually guided Precident-DCS digitizer is limited because of the significant influence of the operator and the mode of sensing (one or three dimensional). Compared with an automatic digitizing system, the measurement uncertainty of the manually guided digitizer exceeds the values published in the literature.

Purpose: This laboratory study investigated the accuracy of four implant impression procedures using two impression techniques and two different materials. Materials and Methods: A master model was used to produce 40 different stone casts incorporating laboratory implant or abutment analogues from the different combinations of two impression techniques (the repositioning impression coping technique at the implant level and the pickup impression technique at the abutment level) and materials (President polyvinyl siloxane and Impregum F polyether). Variations in the resulting working casts were measured using the Reflex Microscope to derive distances and angles from the three-dimensional coordinates of optical targets that were attached to a test coping placed on the implant analogue and on a reference device positioned on the occlusal surfaces of the casts. Results: The results showed greater variations in analogue position with the repositioning impression technique than with the pickup technique. The rotational errors were large enough to be of clinical concern. No significant differences were found between polyvinyl siloxane and polyether impression materials for the two tested types of impression techniques. Conclusion: The repositioning impression technique at the implant level can produce less predictable results than the pickup technique at the abutment level. The choice of impression material made no significant difference.

Purpose: Solid one-piece standard and conical abutments, which do not involve the external implant hex when seated, have been designed. The present clinical study represents a 1-year follow-up of the use of these abutments for anchorage of implant-supported fixed prostheses for oral rehabilitation of 36 completely and eight partially edentulous patients. Materials and Methods: After 1 year of loading, the implant-supported dentures were removed, and the seating of the 214 one-piece abutments was inspected clinically and radiographically. Results: After 1 year of loading, no loose abutments were observed. One complication was reported; it involved fracture of two abutment screws within the same fixed denture. Prosthesis mobility and gold screw loosening accompanied this complication. Ninety-one percent of the patients exhibited healthy gingiva, and 9% showed erythema/edema. No periimplantitis was identified. Conclusion: The results of this study--healthy marginal tissue, a mean bone loss of 0.3 ± 0.6 mm, and no abutment retightening 1 year after loading--support the use of the one-piece abutment design in implant-supported screw-retained restorations.

Purpose: A critical review of the literature on the periodontal considerations in removable partial denture (RPD) treatment is presented. Materials and Methods: A MEDLINE search was conducted for studies pertaining to the effects of RPDs on the periodontal tissues during the various phases of prosthetic treatment. The review included both in vivo and in vitro studies. Results: The use of RPDs leads to detrimental qualitative and quantitative changes in plaque. There seems to be a lack of information regarding the effects of RPDs on the status of periodontally compromised abutments. A number of studies, mainly in vitro, have failed to agree on the ideal RPD design. Clinical trials have shown that if basic principles of RPD design are followed (rigid major connectors, simple design, proper base adaptation), periodontal health of the remaining dentition can be maintained. Conclusion: Removable partial dentures do not cause any adverse periodontal reactions, provided that preprosthetic periodontal health has been established and maintained with meticulous oral hygiene. Frequent hygiene recalls and prosthetic maintenance are essential tools to achieve a good long-term prognosis. More prospective clinical trials are needed on the effect of RPDs on the condition of periodontally involved abutment teeth.

Purpose: The aim was to examine a method described by Wehner et al for calculating the width of a missing central incisor using preextraction photographs. Materials and Methods: Three photographic views were obtained for each of 30 dentate subjects: full face, oblique, and reduced-size full face. The width of the maxillary right central incisor (MR1) was calculated using a formula. The difference between the actual width and calculated width of MR1 was determined for each subject. The median difference and interquartile range were determined because the data were skewed. Results: The width of MR1 calculated using the larger full-face view was typically smaller than the actual width, with a median difference of -0.18 mm. The interquartile range of the difference was from -0.42 to 0.05 mm. For both the oblique and reduced-size views, the calculated width was typically larger, with a median difference of 1.19 mm with an interquartile range from 0.82 to 1.76 mm and a median difference of 0.84 mm with an interquartile range from 0.59 to 1.41 mm, respectively. Conclusion: The technique described by Wehner et al is of proven value in calculating the width of a central incisor when the only available evidence is a preextraction photograph. However, it is of value only when the photograph is a full-face portrait of sufficient size.

Purpose: The risks of radiotherapy to normal tissues are well known. In many cases, a tumor patient suffering a relapse cannot undergo radiotherapy a second time. One exception may be the local application of brachytherapy. Afterloading devices allow the position of radiating materials near the site for treatment exactly according to three-dimensional treatment planning. This report shows the technical procedure for the fabrication of an intracavitary afterloading radiation device. Materials and Methods: A 48-year-old woman who had received neutron radiotherapy and tumor surgery for adenoid cystic carcinoma had to be treated for relapse. The mouth opening was limited to 15 mm. The mixing tip of a silicone impression system was used as an axis for a pivoting appliance. Results: Two years after reradiation, the patient was free of relapse symptoms, although an increased limitation of mouth opening was recorded. Conclusion: Even if the mouth opening is severely limited after tumor surgery and/or radiation, intracavitary brachytherapy still can be performed in edentulous patients using a pivoting device.

Purpose: The objective of this 3-year prospective study was to evaluate a new titanium dental implant system and to identify any mechanical concerns or deficiencies in its design. Materials and Methods: One periodontist placed 78 single-tooth implants in 59 subjects. One restorative dentist using one dental laboratory fabricated all of the crowns. Each patient then was seen eight times by the authors for clinical, radiographic, and laboratory testing. Results: One of the 78 implants failed to integrate and was removed. There were no structural failures per se, although six of the cemented crowns and six of the restorative posts and cores (abutments) became loose. On a few occasions, the emergence profile was esthetically or functionally unsatisfactory. The manufacturer introduced changes in design and created an adjustable torque wrench, a torque-adjusting beam scale, and die replicas of the abutment posts in response to the identified concerns. Conclusion: The clinical trial helped in the development of an implant system that is user friendly, cost effective, and able to withstand parafunctional forces in the absence of antirotational features.