Prostate motion during standard radiotherapy as assessed by fiducial markers

From November 1993 to August 1994, 55 patients with localized prostate carcinoma had three gold seeds placed in the prostate under transrectal ultrasound guidance prior to the start of radiotherapy in order to track prostate motion. Patients had a planning CT scan before initial simulation and again at about 40 Gy, just prior to simulation of a field reduction. Seed position relative to fixed bony landmarks (pubic symphysis and both ischial tuberosities) was digitized from each pair of orthogonal films from the initial and boost simulation using the Nucletron brachytherapy planning system. Vector analysis was performed to rule out the possibility of independent seed migration within the prostate between the time of initial and boost simulation. Prostate motion was seen in the posterior (mean: 0.56 cm; SD: 0.41 cm) and inferior directions (mean: 0.59 cm; SD: 0.45 cm). The base of the prostate was displaced more than 1 cm posteriorly in 30% of patients and in 11% in the inferior direction. Prostate position is related to rectal and bladder filling. Distension of these organs displaces the prostate in an anterosuperior direction, with lesser degrees of filling allowing the prostate to move posteriorly and inferiorly. Conformal therapy planning must take this motion into consideration. Changes in prostate position of this magnitude preclude the use of standard margins.

Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins

The close association between restorations with overhanging margins and chronic destructive periodontitis has been known for many years. However, the mechanisms by which overhanging restorations will interact in the pathogenesis of periodontal disease are still unknown. Generally it is accepted that overhanging restorations contribute to the promotion of the disease process by virtue of their capacity to retain bacterial plaque. The purpose of the present study was to determine if the placement of subgingival restorations with overhanging margins results in changes in the subgingival microflora. 9 dental students with clean teeth and clinically healthy gingivae (GI less than 0.1) gave their consent to participate in the study. 5 MOD cast gold onlays with 1 mm proximal overhanging margins were placed in mandibular molars for 19-27 weeks. They were replaced in a cross-over design by 5 similar onlays with clinically perfect margins which served as controls. Another 5 onlays were placed in reverse order in the remaining patients. Prior to and every 2-3 weeks after insertion, subgingival microbiological samples were obtained by inserting a fine sterile paper point for 30 sec into the gingival sulcus subjacent to the restoration. The predominant cultivable flora was determined using continuous anaerobic culturing techniques. Following the placement of restorations with overhanging margins, a subgingival flora was detected which closely resembled that of chronic periodontitis. Increased proportions of Gram-negative anaerobic bacteria, black-pigmented Bacteroides and an increased anaerobe: facultative ratio were noted. Following the placement of the restorations with clinically perfect margins, a microflora characteristic for gingival health or initial gingivitis was observed. Black-pigmented Bacteroides were detected in very low proportions (1.6-3.8%). These changes in the subgingival microflora were obvious irrespective of whether the restorations with the overhanging margins were placed in the first period of the experiment or following the cross-over. Clinically, increasing gingival indices were detected at the sites where overhanging margins were placed. Bleeding on gentle probing always preceded the peak level of black-pigmented Bacteroides. Loss of attachment was not detected in any site. Changes in the subgingival microflora after the placement of restorations with overhanging margins document a potential mechanism for the initiation of periodontal disease associated with iatrogenic factors.

Clinical methods for evaluating implant framework fit

STATEMENT OF PROBLEM

Passive fit of implant-supported-prosthesis frameworks has been suggested as a prerequisite for successful long-term osseointegration. However, there are no scientific guidelines as to what is passive fit and how to achieve and measure it.

PURPOSE

The purpose of this article is to discuss passive fit and to review the various clinical methods that have been suggested for evaluating implant framework fit.Methods. The dental literature was reviewed to identify the clinical methods that have been used to evaluate implant framework fit.

CONCLUSIONS

The suggested levels of passive fit are empirical. Numerous techniques have been advocated to evaluate the prosthesis-implant interface, but none individually provides objective results. It is suggested that clinicians use a combination of the available methods to minimize misfits.

Tightening characteristics for screwed joints in osseointegrated dental implants

The significance of tightening abutment screws and gold cylinders to osseointegrated fixtures with the correct torque is demonstrated, and a simple relationship between applied torque and screw preload is derived by use of mechanical engineering principles. The principles of a number of tightening methods are outlined and assessments made of their accuracy. The difference between optimum and design torque is highlighted. The necessity and means of achieving optimum torque to ensure a reliable joint in clinical practice is discussed.

Beta titanium: a new orthodontic alloy

Historically, few alloys have been used in the fabrication of orthodontic appliances. This article reviews the gold-based, stainless steel, chrome-cobalt-nickel, and nitinol alloys, as well as beta titanium, a new material for orthodontics. Mechanical properties and manipulative characteristics are summarized to develop a basis for the selection of the proper alloy for a given clinical situation. The beta titanium wire has a unique balance of low stiffness, high springback, formability, and weldability which indicates its use in a wide range of clinical applications. A number of such applications are described.

Comparison of the fracture resistances of pulpless teeth restored with a cast post and core or carbon-fiber post with a composite core

STATEMENT OF PROBLEM

The survival of pulpless teeth restored with a post and core system is a controversial issue.

PURPOSE

This study compared the fracture resistance of 2 types of restorations: teeth restored with prefabricated carbon-fiber posts and composite cores to cast dowel-core restored teeth.

MATERIAL AND METHODS

A total of 44 recently extracted sound premolars were randomly distributed into 2 equal groups: group I, restored with prefabricated carbon-fiber post and a composite core; and group II, with custom-cast type III gold alloy post and cores. The size and shape of the posts were identical in the 2 groups. All teeth were fully covered with a nonprecious cast crown. Fracture resistance was measured by applying a point force at 45 degrees to the long angle of the tooth.

RESULTS

Mean fracture threshold was 103.7 +/- 53.1 kg for group I versus 202.7 +/- 125.0 kg for group II (differences significant with P = .003). In group II, however, fracture nearly always affected the tooth itself, whereas in group I, the post-core nearly always failed first.

CONCLUSIONS

Significantly higher fracture thresholds were recorded for the cast post and core group. Teeth restored with cast posts typically showed fracture of the tooth, although at loads rarely occurring clinically.

Registration accuracy and possible migration of internal fiducial gold marker implanted in prostate and liver treated with real-time tumor-tracking radiation therapy (RTRT)

BACKGROUND AND PURPOSE

We have developed a linear accelerator synchronized with a fluoroscopic real-time tumor-tracking system to reduce errors due to setup and organ motion. In the real-time tumor-tracking radiation therapy (RTRT) system, the accuracy of tumor tracking depends on the registration of the marker's coordinates. The registration accuracy and possible migration of the internal fiducial gold marker implanted into prostate and liver was investigated.

MATERIALS AND METHODS

Internal fiducial gold markers were implanted in 14 patients with prostate cancer and four patients with liver tumors. Computed tomography (CT) was carried out as a part of treatment planning in the 18 patients. A total of 72 follow-up CT scans were taken. We calculated the relative relationship between the coordinates of the center of mass (CM) of the organs and those of the marker. The discrepancy in the CM coordinates during a follow-up CT compared to those recorded during the planning CT was used to study possible marker migration.

RESULTS

The standard deviation (SD) of interobserver variations in the CM coordinates was within 2.0 and 0.4 mm for the organ and the marker, respectively, in seven observers. Assuming that organs do not shrink, grow, or rotate, the maximum SD of migration error in each direction was estimated to be less than 2.5 and 2.0 mm for liver and prostate, respectively. There was no correlation between the marker position and the time after implantation.

CONCLUSION

The degree of possible migration of the internal fiducial marker was within the limits of accuracy of the CT measurement. Most of the marker movement can be attributed to the measurement uncertainty, which also influences registration in actual treatment planning. Thus, even with the gold marker and RTRT system, a planning target volume margin should be used to account for registration uncertainty.

The congenitally missing upper lateral incisor. A retrospective study of orthodontic space closure versus restorative treatment

Orthodontic treatment for patients with uni- or bilateral congenitally missing lateral incisors is a challenge to effective treatment planning. The two major alternatives, orthodontic space closure or space opening for prosthetic replacements, can both compromise aesthetics, periodontal health, and function. The aim of this retrospective study was to examine treated patients who had congenitally missing lateral incisors and to compare their opinion of the aesthetic result with the dentists' opinions of occlusal function and periodontal health. In this sample, 50 patients were identified. Thirty had been treated with orthodontic space closure, and 20 by space opening and a prosthesis (porcelain bonded to gold and resin bonded bridges). The patient's opinion of the aesthetic result was evaluated using the Eastman Esthetic Index questionnaire and during a structured interview. The functional status, dental contact patterns, periodontal condition, and quality of the prosthetic replacement was evaluated. In general, subjects treated with orthodontic space closure were more satisfied with the appearance of their teeth than those who had a prosthesis. No significant differences in the prevalence of signs and symptoms of temporomandibular dysfunction (TMD) were found. However, patients with prosthetic replacements had impaired periodontal health with accumulation of plaque and gingivitis. The conclusion of this study is that orthodontic space closure produces results that are well accepted by patients, does not impair temporomandibular joint (TMJ) function, and encourages periodontal health in comparison with prosthetic replacements.

Micromotion and dynamic fatigue properties of the dental implant-abutment interface

STATEMENT OF PROBLEM

Clinical loading may result in micromotion and metal fatigue in apparently stable implant screw joints. This micromotion may contribute to tissue inflammation and prosthesis failure.

PURPOSE

This study investigated dental implant screw joint micromotion and dynamic fatigue as a function of varied preload torque applied to abutment screws when tested under simulated clinical loading.

MATERIAL AND METHODS

Fifteen noble alloy single-tooth implant restorations, each containing a hexed UCLA-style gold cylinder, were randomly assigned to 3 preload groups (16, 32, and 48 N.cm). Each group consisted of 5 implants (each 3.75 x 15 mm) and 5 square gold alloy abutment screws. A mechanical testing machine applied a compressive cyclic sine wave load between 20 and 130 N at 6 Hz to a contact point on each implant crown. A liquid metal strain gauge recorded the micromotion of the screw joint interface after 100, 500, 1,000, 5,000, 10,000, 50,000, and 100,000 cycles. Baseline data at 0 N.cm were collected before the application of the specified preload torque.

RESULTS

The 16 N.cm group exhibited greater micromotion (P<.001) than both the 32 and 48 N.cm groups at all cycle intervals (2-way ANOVA, Tukey HSD). Micromotion of the implant-abutment interface remained constant (P=.99) for each of the preload groups through 105 cycles.

CONCLUSION

Under the loading parameters of this study, no measurable fatigue of the implant-abutment interface occurred. However, dental implant screw joints tightened to lower preload values exhibited significantly greater micromotion at the implant-abutment interface.

Comparative evaluation of ceramic-metal bond tests using finite element stress analysis

Eleven porcelain-fused-to-metal bond tests were analyzed for interfacial shear stress distribution using finite-element stress analysis. Stress concentration effects are significant in ten of the 11 tests. A high probability of tensile failure within porcelain or the interfacial region was found in eight of the 11 tests analyzed.

Replacement of maxillary and mandibular molars with single endosseous implant restorations: a retrospective study

This retrospective report presents findings on 22 patients with 24 implants replacing single molars with implant-supported restorations. Patients with known bruxism habits were not considered for single-molar implant replacement. The patients underwent follow-up for an average of 24 months. The cumulative success rate was 95%, which reflects the loss of one 5 x 6 mm wide implant. Eleven implants were placed in edentulous ridges, and 13 were placed in extraction sockets. Most of the implants were placed in type B and C bone quantity and type 2 and 3 bone quality. All implants were restored on abutments with nonrotating gold cylinders. The occlusion for all restorations was developed to minimize centric contacts and lateral interferences. The frequency of gold retaining-screw loosening was obtained for 21 patients. The gold retaining screws loosened in eight implants between one and three times (38%). No incidence of crown or implant fracture occurred. Within the limits of this study, replacement of single-tooth molars by implant-supported restorations was predictable; however, a high incidence of gold screw loosening was seen.

Effects of posts on dentin stress distribution in pulpless teeth

A finite element analysis was carried out to study the roles of posts in reducing dentin stress in pulpless teeth. Two-dimensional plane strain models of the midlabiolingual section of a human maxillary central incisor were first analyzed. The results showed that the gold alloy post reduced maximal dentin stress by as much as 30%. However, the integrity of the dentin was compromised and the effects of the post were likely to be exaggerated in such models. In an effort to correct for these problems, plane stress models with side plates and axisymmetric models were analyzed. Posts were found to reduce maximal dentin stress by only 3% to 8% when the teeth were subjected to masticatory and traumatic loadings in these latter models. Although posts reduced maximal dentin stress by as much as 20% when the teeth were loaded vertically, teeth such as incisors and canines normally are not subjected to vertical loadings. Thus the reinforcement effects of posts seem to be doubtful in these teeth.

Finite element stress analysis of the crowns of normal and restored teeth

Stress distributions are presented for a normal and a restored mandibular second premolar under masticatory-type forces. These were obtained using the finite element method of stress analysis applied to two-dimensional models. The effect of the relative stiffness of the materials is examined in each instance.

Assessment of the periapical and clinical status of crowned teeth over 25 years

OBJECTIVES

The purpose of this study was to examine radiographically changes in the periapical status and compare the clinical status of teeth with a vital pulp and root-filled teeth restored with crowns and bridge retainers during 25 years.

METHODS

During 1967/68, 114 patients received prosthodontic treatment by senior dental students at the Oslo Dental Faculty. In all, 291 teeth with a vital pulp and 106 root-filled teeth were restored with 158 prostheses. All root-filled teeth were restored with a cast dowel and core. The casts were made in a type-3 gold alloy, and cemented with zinc phosphate cement. Forty-six teeth were restored with crowns and 351 teeth with bridge retainers. Radiographs were taken preoperatively, immediately after cementation, and every fifth year. Two independent observers assessed the periapical status on the radiographs according to the PAI-index. At the 25 years examination, 32 patients (28%) with 101 restored teeth (24%) remained in the study. Survival rates of the prostheses and of the restored teeth were estimated using Kaplan-Meyer non-parametric statistics.

RESULTS

The PAI-score of the periapical status deteriorated in 13 vital and four root-filled teeth. The survival rates of the fixed prostheses were not influenced by the pulp vitality of the restored tooth at the baseline. The survival rates of the restored teeth with a vital pulp and of the root-filled teeth were similar. Clinical failures were recorded on approximately one-third of the restored teeth. The main reason for tooth failure was caries (12%), and for the teeth with a vital pulp also pulpal deterioration (10%). Estimates of the proportions of crowned teeth with a vital pulp that will remain free from signs and symptoms of pulpal deterioration were 98% after five years, 92% after 10 years, 87% after 20 years and 83% after 25 years.

CONCLUSIONS

The incidence of periapical lesions on radiographs of crowned teeth was low during 25 years observation. Crowned, root-filled teeth with a high quality endodontic treatment and an optimal morphology of the dowel and core have a similar survival rate as crowned teeth with a vital pulp. A high proportion of crowned teeth with a vital pulp will remain free from signs and symptoms of pulpal deterioration over 25 years.

Fracture strength after dynamic loading of endodontically treated teeth restored with different post-and-core systems

STATEMENT OF PROBLEM

Prefabricated metal and ceramic posts can be used with direct or indirect cores as an alternative to the conventional cast post and core. It is unclear how the fracture strength of zirconia posts with composite or ceramic cores and titanium posts with composite cores compares to the fracture strength of gold posts and cores after dynamic loading.

PURPOSE

This study compared the fracture strength of endodontically treated, crowned maxillary incisors with limited ferrule length and different post-and-core systems after fatigue loading.

MATERIAL AND METHODS

Sixty-four caries-free, human maxillary central incisors were divided into 4 groups. After root canal treatment, Group 1 was restored with titanium posts and composite cores, Group 2 with zirconia posts and composite cores, and Group 3 with zirconia posts and heat-pressed ceramic cores. Teeth restored with cast-on gold posts and cores served as the controls (Group 4). Teeth were prepared with a circumferential shoulder including a 1 to 2 mm ferrule; all posts were cemented with an adhesive resin cement, restored with complete-coverage crowns, and exposed to 1.2 million load cycles (30 N) in a computer-controlled chewing simulator. Simultaneous thermocycling between 5 degrees C and 55 degrees C was applied for 60 seconds with an intermediate pause of 12 seconds. All specimens that did not fracture during dynamic loading were loaded until fracture in a universal testing machine at a crosshead speed of 1.5 mm/min; loads were applied at an angle of 130 degrees at the incisal edge. Fracture loads (N) and modes (repairable or catastrophic) were recorded. The Kruskal-Wallis test was used to compare fracture loads among the 4 test groups. Analyses were conducted both with and without the specimens that failed during the chewing simulation. A Fisher exact test was performed to detect group differences in fracture modes. A significance level of P<.05 was used for all comparisons.

RESULTS

The following survival rates were recorded after the chewing simulation: 93.8% (Group 1), 93.8% (Group 2), 100% (Group 3), and 87.5% (Group 4). The median fracture strengths for Groups 1 to 4 were 450 N, 503 N, 521 N, and 408 N, respectively. No significant differences were detected among the groups. The use of zirconia posts resulted in a nonsignificant lower number of catastrophic root fractures.

CONCLUSION

Within the limitations of this study, the results suggest that zirconia posts with ceramic cores can be recommended as an alternative to cast posts and cores. If a chairside procedure is preferred, zirconia or titanium posts with composite cores can be used. Clinical trials are required to verify these in vitro results.

Reasons for restorative therapy and the longevity of restorations in adults

The aim of this study was to obtain information on the restorative dental care of adults in Finland. A random sample of private dentists was drawn from the register, and in spring 2000 they were sent a questionnaire requesting them to record information for each restoration placed during one ordinary working day. A total of 800 dentists were contacted and 548 responded. The dentists reported placement of 3,455 restorations. Of these, 5% were Class I, 36% were Class II, 13% were Class III, 9% were Class IV, 21% were Class V, and 16% were extensive restorations including 4 or more surfaces. Overall, composite resin was the most common restorative material, and it was used in 79% of the restorations, whereas amalgam was used in 50%, compomers in 4%, and glass ionomers (either conventional or resin-modified) in 7% of cases. In 5%, of the cases, the tooth was restored with indirect restorative methods, using either gold or ceramic materials. Of the treatments, 65% were replacements of previous restorations. Secondary caries was the most common reason for replacement (36%, 52%, and 41% for composite, glass ionomer, and amalgam, respectively). Other common reasons were fractures of the tooth or restoration (23%, 11%, and 22% for composite, glass ionomer, and amalgam, respectively) and lost composite restorations (16%). The median age of failed restorations was 15 years for amalgam, 6 years for composite, and 7 years for conventional glass ionomer. Although the longevity of tooth coloured restorations was shorter than that of amalgam, comparisons with our previous studies indicate improved survival periods for tooth coloured materials.

The effect of various finish line preparations on the marginal seal and occlusal seat of full crown preparations

The influences of the marginal design of a full crown on the occlusal seat and marginal seal of a cemented full crown restoration was examined. Under the conditions of the study, the featheredge and parallel bevel preparations demonstrated the best marginal seal, followed in order by the full shoulder, 45-degree shoulder, and finally the 90-degree shoulders with 30-degree and 45-degree bevels. With regard to seating of the restoration, the 90-degree full shoulder demonstrated the best seat, followed in order by the 45-degree shoulder, 90-degree shoulder with 45-degree bevel, featheredge, 90-degree shoulder with 30-degree bevel, chamfer with parallel bevel, and finally 90-degree shoulder with parallel bevel.

The fit of gold inlays and three ceramic inlay systems. A clinical and in vitro study

Four inlay systems--gold, Cerec, Mirage, and Empress inlays--were evaluated for their adaptation to stone die and clinically to the tooth by means of a replica technique. Twenty inlays of each system were placed on premolars and molars in the lower jaw. A microscope was used to measure the adaptation at the approximal margin, at the inner axial wall, and at the occlusal cavosurface area. An overall better fit was observed for the gold inlays than for the ceramic inlays. When the different measuring locations were compared, a better fit was found for the occlusal area. The greatest discrepancies were recorded for the Cerec inlays, whereas the Mirage and Empress inlays were comparable.