Prosthet Dent Research Articles

Cyclic loading of implant-supported prostheses: Changes in component fit over time

Statement of Problem. Dental literature suggests that an implant-supported prosthesis must exhibit a passive fit to prevent implant fracture, component breakage, and screw loosening. From a practical standpoint, passive fit is impossible to achieve; instead, minimal misfit may be the clinical goal. To date no specific range of misfit (below which problems are minimal and above which catastrophic failure occurs) has been established. Purpose. The purpose of this study was to determine whether the fit of an implant-supported prosthesis changes through cyclic loading and to quantify the amount of change between the gold cylinder and implant abutment over time. Materials and Methods. Fifteen implant-supported frameworks were fabricated with conventional casting techniques and were cyclically loaded under 3 different loading conditions. Five frameworks were loaded on the anterior portion of the framework, 5 were loaded on the left unilateral posterior cantilever, and 5 were loaded bilaterally on the posterior cantilevers with a servohydraulic testing machine. A cyclical load of 200 N was applied to each framework for up to 200,000 cycles. Linear measurements were made in micrometers of the gap between the prosthetic cylinder and the implant-supported abutment at 4 predetermined reference points. These measurements were recorded before the application of the cyclical load, after 50,000 cycles, and after 200,000 cycles. A repeated measures of variance model was fit separately to the data for each load location (P<.05). Results. There was a significant (P=.024) decrease in gap dimensions at individual reference points and a significant (P=.031) decrease in the average gap when the load was applied to the anterior portion of the framework. When the load was applied unilaterally or bilaterally on the posterior cantilever, significant gap closure was not observed (P=.33 and P=.35, respectively). Conclusion. Within the limitations of this study, the fit between the prosthetic superstructure and the implant-supported abutment changed when simulated functional loading of the anterior portion of the prosthesis was performed. Simulated functional loading applied unilaterally or bilaterally to the posterior cantilever portion of the prosthesis did not result in changes in the measured gap sizes. (J Prosthet Dent 2003;89:346-51.)

Contingent electrical lip stimulation for sleep bruxism: A pilot study

Statement of Problem. No effective method has been found to fully control sleep bruxism, although contingent feedback methods show some promise. Purpose. This demonstration-of-concept study evaluated the effect of contingent electrical lip stimulation on sleep bruxism. Material and Methods. Recordings of masseter muscle activity were performed over 5 nights in 7 subjects with acknowledged bruxism and dental attrition (5 men, 2 women). A small electrical switch, activated with light force clenching, was mounted between 2 occlusal orthotics. This switch triggered a stimulator, which delivered slightly noxious electrical pulses to the subject's lip. After a baseline first night recording session, stimulation was delivered in 1-hour blocks for half of each sleep period during nights 2 through 5. Paired t tests (α = 0.05) were conducted on 4 recorded bruxism parameters. Results. With stimulation, the number (±SD) of events/hour reduced from a baseline level of 3.9 ± 2.0 to 2.4 ± 0.8 and the mean amplitude (% maximum voluntary contraction) reduced from 28.7 ± 20.0 to 17.6 ± 4.1. There was a mean decrease in the duration (s/event) from 10.6 ± 1.4 to 9.1 ± 2.5 and the total event time (s/hour) was reduced from 41.7 ± 22.4 to 23.2 ± 11.0. Among these measures, bruxism events with and without stimulation were compared, and only the duration of individual bruxism events (s/event) showed a significant change (P=.038). Finally, no subject reported being awakened from sleep by the stimulation. Conclusion. The reductions in bruxism events were noteworthy, especially considering that stimulation was delivered for only half of the sleeping period. (J Prosthet Dent 2003;89:412-7.)

Adjunctive commissure splint therapy: A revised approach

The management of trauma to the commissures has been an ongoing challenge for the medical and dental professions. Multiple surgical and prosthetic approaches have been used. Commissure splint therapy is often effective in association with surgery in reducing the effects of scar contraction that ultimately results in microstomia and reduced quality of life. This article describes methods of fabrication of the commissure splint appliance, the rationale for its modification, advantages, and disadvantages. (J Prosthet Dent 2003;89:408-11.)

Implant prosthodontic management of partially edentulous patients missing posterior teeth: The Toronto experience

Statement of the Problem. The clinical success of implant-supported fixed partial dentures has been documented. However, few studies have reported long-term results or any association between implant outcomes and host determinants. Purpose. This study reports on implant and prosthesis outcomes in a group of partially edentulous patients treated with Brånemark implants in the posterior zones. It also examines factors described in the medical history that may influence implant survival. Material and Methods. The charts of patients treated with implants from 1983 and followed prospectively through December 2001 at the University of Toronto were reviewed. One hundred thirty partially edentulous patients treated with implant-supported restorations in the posterior zones (area distal to mental foramen) were selected. Implant and prosthesis treatment outcomes were recorded and analyzed through the Kaplan-Meier and Cox regression methods (P<.05). Results. A total of 130 patients received 432 Brånemark dental implants in 174 posterior edentulous spans. The mean age of the patients at the time of insertion of the implants was 50.97 ± 13.27 years. At 15 years, the overall implant and prosthesis survival rates were 91.6% and 89%, respectively. At 5 years, the survival rate of the wide-platform 5-mm-diameter implants was 76.3%. Implant diameter (P=.0001) and a history of a chronic medical condition (P=.01) were correlated with implant survival outcomes. Conclusions. High success of implant-supported prostheses in the posterior zones of both the maxilla and mandible. It corroborated other studies that have shown higher failure rates for wide-platform implants, emphasizing the need for proper establishment of clinical trials prior to marketing of new implant designs. (J Prosthet Dent 2003;89:352-9.)

Production and properties of soft magnetic composites with multi-component dielectrics : I. Chicinas et al. (University of of Cluj-Napoca, Cluj-Napoca, Romania.)

Rare earth magnets have been used in prosthodontics, but their tendency for corrosion in the oral cavity and insufficient attractive forces limit long-term clinical application.The purpose of this study was to evaluate the attractive force of different types of new-generation magnetic attachment systems.The attractive force of the neodymium-iron-boron (Nd-Fe-B) and samarium-cobalt (Sm-Co) magnetic attachment systems, including closed-field (Hilop and Hicorex) and open-field (Dyna and Steco) systems, was measured in a universal testing machine (n=5). The data were statistically evaluated with 1-way ANOVA and post hoc Tukey-Kramer multiple comparison test (α=.05).The closed-field systems exhibited greater (P<.001) attractive force than the open-field systems. Moreover, there was a statistically significant difference in attractive force between Nd-Fe-B and Sm-Co magnets (P<.001). The strongest attractive force was found with the Hilop system (9.2 N), and the lowest force was found with the Steco system (2.3 N).The new generation of Nd-Fe-B closed-field magnets, along with improved technology, provides sufficient denture retention for clinical application. (J Prosthet Dent 2011;105:203-207)

The influence of fiber reinforcement of composites on shear bond strengths to enamel

Statement of Problem. Fiber-reinforced composites (FRC) are used in direct intra-oral applications as periodontal splints and chairside tooth replacement by bonding them to etched enamel with resin adhesives and composites. There is little information regarding the effect of FRC on the shear bond strength of composite to etched enamel. Purpose. The purpose of this study was to examine the effect of resin preimpregnated and non-preimpregnated fiber-reinforced composites on enamel to composite shear bond strength (SBS). Material and Methods. Specimen groups (n = 12) consisted of a control (composite with no fiber reinforcement), Ribbond, Splint-It Unidirectional, Splint-It Woven, and Connect, which were bonded to 37% phosphoric acid etched Prime and Bond NT adhesive-treated bovine enamel surfaces on a bed of Tetric Flow composite. Specimens were thermocycled 1000 times between 5° and 55°C and loaded on a universal testing machine in shear at a linear increasing load until fracture (MPa). The fractured surfaces of the debonded specimens were evaluated to determine the nature of the fracture with a light binocular microscope (×10). Shear bond strength data were subjected to analysis of variance (ANOVA) and Student-Newman-Kuels tests (P <.05). Results. Mean MPa ± SD for the test groups were as follows: Control, 15.6 ± 2.4; Splint-It Unidirectional, 15.3 ± 2.4; Splint-It Woven, 16.5 ± 1.8; Connect, 18.8 ± 1.5; and Ribbond, 15.8 ± 2.2. The Connect FRC group had significantly higher (P <0.05) enamel SBS than all other groups. Fracture analysis showed varying types of failures among the groups, with cohesive fractures within the fiber reinforcement of Splint-It Unidirectional and Connect, cohesive fractures within the bonding resin/flowable composite for Ribbond and the control, and adhesive fracture at the fiber reinforcement interface with Splint-It Woven. Conclusion. Within the limitations of this study, no differences in SBS were observed with the addition of 3 of the 4 FRCs compared to composite without FRC, with the exception of the Connect product which provided significantly higher SBS values. (J Prosthet Dent 2003;89:388-93.)

The effect of design modifications on the torsional and compressive rigidity of U-shaped palatal major connectors

Statement of Problem. Rigidity is a requirement of removable partial denture frameworks. Although commonly used by dentists, the U-shaped (horseshoe) maxillary major connector lacks the rigidity of other maxillary major connector designs. Purpose. The purpose of this study was to determine the effects of changing width, thickness, and shape on the rigidity of U-shaped maxillary major connectors. Material and Methods. Five nickel-chrome alloy frameworks were fabricated from the same master cast for each of 4 different U-shape removable partial denture designs. The designs were an 8-mm wide U-shaped strap with a 6-mm posterior strap (A-P strap), a 13-mm-wide U-shape strap (Wide), an 8-mm-wide U-shape strap that widened to 13 mm at the midline (Notch), and an 8-mm-wide U-shaped strap that was twice the thickness of the other straps (Thick). A fifth group of 5 frameworks was made by removing the posterior strap from the A-P strap frameworks (A strap). Two testing points were marked on each framework corresponding to the first premolar and second molar positions. The frameworks were mounted in a universal testing machine, and vertical (torsional) and horizontal (compressive) loads were applied using a 10-kN load cell at a cross-head speed of 2 mm/min until a deflection of 1 mm occurred. A force-deflection curve was generated for each test, and slope of the curves (N/mm) was compared with analysis of variance and Scheffe's F test (α=0.05). Results. The Thick group was found to be significantly more rigid (P<.05) than the other frameworks when torsional loads were applied to both the premolar (22.42 N/mm) and molar (10.88 N/mm) areas, and when a compressive load was applied to the premolar (232.85 N/mm) area. The A-P strap group was significantly more rigid (P≤.05) than the other designs when a compressive load was applied to the molar (69.56 N/mm) area. Both the Thick and A-P strap groups were significantly more rigid (P<.05) than the Notch and A strap groups in all tests. Conclusion. Doubling the thickness of the anterior strap of a U-shaped maxillary major connector improved the rigidity of the framework to torsional loads. A posterior strap became more effective in maintaining framework rigidity to compressive forces as the length of the arch increased. (J Prosthet Dent 2003;89:400-7.)

Early functional loading of conical Brånemark implants in the edentulous mandible: A 12-month follow-up clinical report

Treatment of patients with implant-supported mandibular fixed prostheses performed according to an early loading concept has shown excellent results in several reports. The outcome of such treatments with 4 implants, in which the posteriors are distally inclined, has not been reported. This clinical report describes a 12-month evaluation of 17 consecutive patients with 68 conical Brånemark implants placed between the mental foramina according to a 1-stage surgical procedure. Fixed mandibular prostheses were connected to the implants an average of 33 days after implant placement. Clinical and radiographic examinations were performed at the time of placement of the fixed prosthesis and at a 12-month examination. Five implants were lost during the observation period, 3 before loading and 2 after prosthesis connection, rendering an implant survival rate of 93%. One patient lost her prosthesis because of a failing implant. The average marginal bone loss was 0.24 mm. (J Prosthet Dent 2003;89:335-40.)

Biaxial flexural strength, elastic moduli, and x-ray diffraction characterization of three pressable all-ceramic materials

Statement of Problem. Before the release of an advanced ceramic material, independent assessment of its strength, elastic modulus, and phase composition is necessary for comparison with peer materials. Purpose. This study compared the biaxial flexural strength, elastic moduli, and crystalline phases of IPS Empress and Empress 2 with a new experimental ceramic. Material and Methods. Twenty standardized disc specimens (14 × 1.1 mm) per material were used to measure the biaxial strength. With a universal testing machine, each specimen was supported on 3 balls and loaded with a piston at a crosshead speed of 0.5 mm/min until fracture. Three standardized bars (30 × 12.75 × 1.1 mm) for each material were prepared and excited with an impulse tool. The resonant frequencies (Hz) of the bars were used to calculate the elastic moduli with the equation suggested by the standard ASTM (C 1259-94). X-ray diffraction with Cu Kα at a diffraction angle from 20 to 40 degrees was used to identify the crystalline phases by means of a diffractometer attached to computer software. The data were analyzed with 1-way analysis of variance followed by pairwise t tests (P<.05). Results. Mean biaxial strengths were 175 ± 32, 407 ± 45, and 440 ± 55 MPa for IPS Empress, Empress 2, and the experimental ceramic, respectively. Elastic modulus results were 65, 103, and 91 GPa for the same materials, respectively. There was no significant difference in strength and elastic modulus between Empress 2 and the experimental ceramic. Both materials demonstrated a significantly higher elastic modulus and strength than IPS Empress. X-ray diffraction revealed leucite as the main crystalline phase for IPS Empress and lithium disilicate for both Empress 2 and the experimental ceramic. Conclusion. Within the limitations of this study, the improved mechanical properties of Empress 2 and experimental ceramic over those of IPS Empress were attributed to the nature and amount of their crystalline content lithium disilicate. (J Prosthet Dent 2003;89:347-80.)

Split-frame implant prosthesis designed to compensate for mandibular flexure: A clinical report

When an edentulous mandible is restored with 4 or more implants connected by a metal bar and retained with screws, mandibular flexure may cause screw loosening and unnecessary stresses and strains on the prosthesis and implants. Separating the prosthesis at the midline can relieve these stresses and strains. This article describes the separation of a hybrid mandibular denture at the midline. (J Prosthet Dent 2003;89:341-3.)

Fracture resistance of endodontically treated teeth restored with composite posts

Statement of Problem. The most recent application of fiber-reinforced composites involves their use as post and core systems to restore endodontically treated teeth. Even though this last application has been advertised and used clinically by many dentists, there is very little information regarding the physical properties of these post systems. Purpose. The purpose of this study was to compare the effect of 3 fiber-reinforced composite post systems on the fracture resistance and mode of failure of endodontically treated teeth. Material and Methods. Ninety maxillary central incisors were divided into 8 experimental groups and 1 stainless steel (ParaPost) control group of 10 specimens each. Eighty teeth were assigned to 2 main experimental groups called “narrow” and “flared” canals. For the narrow canal group, post spaces were prepared with the corresponding reamer to restore the teeth with FibreKor, Luscent anchors, and Ribbond posts of 1.5 mm, 1.6 mm, and 2.0 mm in diameter, respectively. For the flared canals group thin-walled canals were simulated. Teeth for the flared canals were restored with the same posts but were cemented into tapered 2 mm wide canals created with a tapered diamond bur. Prefabricated posts (FibreKor and Luscent anchors) for narrow and flared canals were cemented with an autopolymerized resin cement and a flowable composite, respectively, whereas customized Ribbond posts were luted with a light-polymerized flowable composite for both canal types. An additional set of 20 Ribbond posts with coronal portions of variable size and shape referred to as “Ribbond nonstandardized” were also prepared and evaluated. Specimens were loaded to failure (kg) with a universal testing machine at a crosshead speed of 0.05 cm/min until failure occurred. Data were analyzed with analysis of variance and Student t tests (P<.05). Results. Statistical analysis revealed no significant difference between flared and narrow canals in mean load to failure between the post systems except for the Ribbond posts (P<.01). For the narrow canal, the mean load ranged from a low of 4.55 (±1.49) kg for the Ribbond standard to a high of 12.9 (±1.64) kg for the Luscent anchors. For the flared canal the low mean was 9.04 (±1.76) kg for FibreKor and the high was equal for both Luscent anchors and Ribbond standard, 12.87 (±2.69) and 12.87 (±3.54), respectively. Overall, the ParaPost control group had the highest load value (18.33 ± 3.27 kg) (P<.05). Ribbond nonstandardized had a mean load to failure of 24.91 (±11.53) Kg for the narrow canal group and 31.95 (±11.98) kg for the flared canal. Results from these groups were excluded from the statistical analysis because of the uncontrolled core sizes and high standard deviations. No root fractures occurred in any of the experimental groups. Conclusion. Results from the study show that the load to failure of the stainless steel posts were significantly stronger than all the composite posts studied. However, the mode of failure or deflection of the fiber-reinforced composite posts is protective to the remaining tooth structure. (J Prosthet Dent 2003;89:360-7.)

Effect of different bonding agents on shear bond strengths of composite-bonded porcelain to enamel

Statement of Problem. The use of bonding agents in the luting procedure for porcelain laminate restorations to enamel is not clear. Purpose. This study evaluated the shear bond strength differences between an enamel-luting composite and a heat-pressed ceramic with 6 different bonding systems. Material and Methods. Seventy standardized heat-pressed IPS Empress ceramic discs (4-mm diameter, 3-mm height) were prepared. A vertical planar enamel-bonding surface was prepared on the buccal or lingual enamel of 70 freshly extracted sound human molars and premolars. The teeth were oriented to maintain a parallel relationship between the bonding plane and the shear loading axis of a universal testing machine. Tooth specimens were divided into 7 groups (n=10) comprising equal numbers of molars and premolars. The enamel surfaces of specimens in groups 1 through 6 were prepared with 1 of 6 bonding agents (Scotchbond Multi Purpose Plus, Heliobond, PQ1, SE Bond, Prime&Bond NT, and Prompt L-Pop). Finally, the specimens were luted to the ceramic discs with the composite cement (Opal Luting Composite). Ceramic discs in the seventh group (Control) were luted to the etched enamel with the composite cement without using bonding material. Enamel-ceramic specimens were kept in distilled water at room temperature for 30 days after cementation. All specimens were shear loaded axially in a universal testing machine with a crosshead speed of 0.05 mm/min until fracture. Shear bond strength was measured and recorded for each group in MPa. To determine the statistical significance of the differences between the mean shear bond strength values, a 1-way analysis of variance was used (α=.05). Post-hoc multiple comparisons were made with Duncan's multiple range analysis. Fractured surfaces of each specimen were also inspected with a stereomicroscope to evaluate failure modes. Results. A 1-way analysis of variance revealed significant differences between the test groups (P=.00). Bond strength values (MPa) from the highest to the lowest were as follows: Prompt L-Pop, 25.46 ± 5.6; Prime&Bond NT, 18.99 ± 4.93; Heliobond, 17.28 ± 4.0; SE Bond, 16.21 ± 2.6; PQ1, 15.60 ± 2.8; Scotchbond MPP, 14.82 ± 2.4; and Control, 10.55 ± 1.6. Duncan's multiple range post hoc analysis exhibited significant differences between the control group and the adhesive bonding agent groups (P<.05). There were also significant differences between the bonding agent groups (P<.05). Prompt L-Pop showed the highest bond strength values. Conclusion. Within the limitations of this study, bonding agents appear to have a strengthening effect on the shear bond strengths of the enamel/composite/porcelain interface of the materials tested. Bonding agents used in this study showed similar bond strength values except for Prompt L-Pop, which demonstrated the highest bond strength values. (J Prosthet Dent 2003;89:394-9.)

Dentin bond strengths of two ceramic inlay systems after cementation with three different techniques and one bonding system

Statement of Problem. Cementation of inlay restoration is critical. Because of its high organic content, dentin is a less favorable substrate for bonding than enamel. Therefore it is important to improve dentin adhesion when placing ceramic inlay restorations. Purpose. The purpose of this study was to compare the dentin bond strengths of 2 different ceramic inlay systems after cementation with 3 different techniques and 1 bonding system. Material and Methods. One hundred twenty freshly extracted caries- and restoration-free molar teeth used in this study were stored in saline solution at room temperature. Standardized Class I preparations were made in all teeth. Each preparation had a length of 6 mm, a width of 3 mm, a depth of 2 mm, and 6-degree convergence of the walls. Teeth were randomly assigned to 2 groups of 60 each to evaluate the bonding of 2 ceramic systems, Ceramco II (Group I) and IPS Empress 2 (Group II), to dentin. Each of the 2 groups were further divided into 3 cementation technique groups of 20 each (Group I A, B, and C and Group II A, B, and C). Groups I A and B and Groups II A and B used dentin bonding agent (DBA) Clearfil Liner Bond 2V, and resin cement (Panavia F). Groups I C and II C served as control groups and used Panavia F without the dentin-bonding agent. In Groups I A and II A, the DBA was applied immediately after the completion of the preparations (D-DBA). Impressions were then made, and the ceramic inlays were fabricated according to the manufacturers' guidelines. In Groups I B and II B the DBA was applied just before luting the inlay restorations (I-DBA). In Groups I C and II C, no bonding agent was used before the cementation of the inlay restorations (No DBA). Cementation procedures followed a standard protocol. After cementation, specimens were stored in distilled water at 37° C for 24 hours. The teeth were sectioned both mesial-distally and buccal-lingually along their long axis into three 1.2 × 1.2 mm wide |-shaped sections. The specimens were then subjected to microtensile testing at a crosshead speed of 1 mm/min, and the maximum load at fracture (in kilograms) was recorded. Two-way analysis of variance and Tukey honestly significant difference tests were used to evaluate the results (P<.05). Scanning electron microscopy analysis was used to examine the details of the bonding interface. The fractured surfaces were observed with a stereomicroscope at original magnification ×22 to identify the mode of fracture. Results. Although no significant difference was found among the 2 ceramic systems with regard to dentin bond strengths (P>.05), the difference between the cementation techniques was found to be significant (P<.001). Comparison among techniques showed that the dentin bond strength in the D-DBA technique had a significantly higher mean (40.27 ± 8.55 Kg) than the I-DBA (30.20 ± 6.78 Kg) and No DBA techniques (32.43 ± 8.58 Kg). As a result of scanning electron microscopy analysis, a distinct and thicker hybrid zone with more, and longer resin tags were found in specimens treated with the D-DBA technique than with the other 2 techniques. Most failures (353 of 360) were adhesive in nature at the bonding resin/dentin interface. Only 7 specimens showed cohesive failure within the bonding resin. Conclusion. Within the limitations of this in vitro study, the cementation of the ceramic inlays tested with the D-DBA technique used resulted in higher bond strengths to dentin. (J Prosthet Dent 2003;89:275-81.)

Resin-ceramic bonding: A review of the literature

Current ceramic materials offer preferred optical properties for highly esthetic restorations. The inherent brittleness of some ceramic materials, specific treatment modalities, and certain clinical situations require resin bonding of the completed ceramic restoration to the supporting tooth structures for long-term clinical success. This article presents a literature review on the resin bond to dental ceramics. A PubMed database search was conducted for in vitro studies pertaining to the resin bond to ceramic materials. The search was limited to peer-reviewed articles published in English between 1966 and 2001. Although the resin bond to silica-based ceramics is well researched and documented, few in vitro studies on the resin bond to high-strength ceramic materials were identified. Available data suggest that resin bonding to these materials is less predictable and requires substantially different bonding methods than to silica-based ceramics. Further in vitro studies, as well as controlled clinical trials, are needed. (J Prosthet Dent 2003;89:268-74.)

The magnitude of cutting forces at high speed

Statement of the Problem. Previous research has used a range of cutting forces for preparing teeth, but there are no data available on the forces actually imposed while cutting teeth with high-speed handpieces. Purpose. The purpose of this study was to measure the forces imposed while cutting teeth with tungsten carbide burs used in high-speed handpieces. Material and Methods. Thirty-one dentists each cut 8 conventional class II MO and DO preparations in intact extracted third molars, by use of 2 different air turbine handpieces with different torque-speed characteristics. Two different flat fissure, plain and cross-cut tungsten carbide burs, cutting wet and dry in each handpiece/bur combination. The teeth were mounted in a custom-made transducer unit that displayed the forces imposed by the bur. Data were analysed with a 1-way ANOVA (α =.05) and Spearman correlation test. Results. The results showed that there was no significant difference in the applied force between plain and cross-cut burs, cutting wet or cutting dry, but there was a significant difference between the high and the lower torque handpieces. The higher torque handpiece was used at a mean cutting force of 1.44 N and the lower torque handpiece at 1.20 N (P<.002). The overall general mean force observed was 1.30 N. Conclusion. It was concluded that the forces used in cutting teeth with the tungsten carbide burs tested related both to the type of the handpiece and to the forces chosen by clinical operators. There was no difference between the plain and cross-cut burs, there was no difference between the cutting wet or dry, and the higher torque handpiece required a higher mean cutting force. (J Prosthet Dent 2003;89:286-91.)

M. M. House mental classification revisited: Intersection of particular patient types and particular dentist's needs

Fifty-three years ago, M. M. House devised a classification of patients on the basis of how they behaved in response to the prospect of becoming edentulous and on how they subsequently adapted to wearing complete dentures. Although House's system was an important contribution, it failed to consider the dentist's emotional reaction to a patient's behavior as part of an understanding of how the patient and doctor cope with the dental treatment. This article presents an expansion of the House classification to include the behavior of the dentist as a codeterminer of the patient's behavior. This expanded classification system is based on empiricism and awaits scientific validation or clinical application to determine its ultimate validity, reliability, and effectiveness. (J Prosthet Dent 2003;89:297-302.)

Sound analysis of temporomandibular joint internal derangements with phonographic recordings

Statement of Problem. Temporomandibular joint (TMJ) sound recordings could be analyzed to assess the state of TMJ internal derangements. Purpose. The aim of the study was to assess the value of sound analysis in the diagnosis of the type of the TMJ internal derangements. Material and Methods. After clinical and radiologic examinations, phonographic sound recordings on mandibular excursions were obtained in 52 patients with TMJ internal derangements and 12 control individuals. Sound correlations were made on the basis of opening-closing, protrusive-retrusive, and lateral excursions of the mandible. Results. Clicking was a consistent finding of anterior disc displacement with reduction, whereas crepitation was found in varying degrees in anterior disc displacement and osteodegenerative arthritis. Silent TMJs were the feature of normal TMJs, except for the situations of acute lock. Although in 29 TMJs opening click was followed by a closing click (reciprocal clicking), 46 TMJs with opening click also had clicking on protrusion. On the other hand, 19 TMJs with opening click also had clicking on ipsilateral motion, and 40 TMJs with opening click had clicking on contralateral motion of the mandible. The sound patterns were found to be similar in opening-protrusive clicks and opening-contralateral clicks. The lack of protrusive clicking in the presence of opening click was considered an indication of late disc reduction on opening. Crepitation was observed in advanced cases of TMJ internal derangements. Conclusion. Within the limitations of this study, the results suggest that TMJ sound analysis on mandibular excursions was indicative for diagnosis and establishment of severity of TMJ internal derangements. Clicking and crepitation may be looked on as signs of abnormal joint disorder, clicking indicating anterior disc displacement with reduction, and crepitation, indicating progression from anterior disc displacement without reduction to osteodegenerative arthritis. (J Prosthet Dent 2003;89:311-8.)

The anterior cantilever in the implant-supported screw-retained mandibular prosthesis

Statement of Problem. When implants are placed interforaminally in mandibular implant-supported screw-retained prostheses, the most anterior implant is usually positioned lingual to the incisors of the prosthesis. This creates an anterior cantilever with the entire prosthesis acting as a class I lever and possibly placing the anterior implant under alternating tension and compression during function. Purpose. The purpose of this study was to measure the anterior cantilever of randomly chosen patients with restored mandibular implant-supported fixed prostheses, and to establish the proportions of anterior to posterior cantilever lengths relative to the anteroposterior spread. Material and Methods. Thirteen edentulous patients were recruited from the University of Minnesota's dental implant program. Each patient had been restored with a maxillary complete denture and a mandibular implant-supported screw-retained prosthesis supported by 5 endosseous implants. Each patient had 1 mandibular impression made with irreversible hydrocolloid, which was poured in type III gypsum. A FaroArm precision 3D measuring stylus was used to make multiple-axis (X-Y-Z) measurements (mm) on the casts of the dental implants, of anteroposterior spread, and anterior and posterior cantilevers. Presence or absence of screw loosening was noted using a screwdriver with finger pressure. Data were analyzed using a 1-way analysis of variance to compare prostheses with loose screws to prostheses without loose screws, for each of 3 outcome measures: length of anterior cantilever, length of posterior cantilever, and anteroposterior spread (P<.05). Results. Mandibular anterior cantilever lengths ranged from 5.5 to 14.4 mm with a mean of 8.78 mm. Combined posterior cantilever lengths ranged from 9.2 to 20.9 mm with a mean of 16.2 mm. Anteroposterior spread ranged from 5.2 to 12.3 mm with a mean of 7.9 mm. From a total of 65 retaining screws, 7 were found to be completely loose. No apparent correlation was found between length of mandibular anterior cantilever and screw loosening (P=.45), although the ratio of posterior cantilever to anteroposterior spread (2:4) was significantly associated with screw loosening (P=.006). Conclusion. Within the limitations of this study, anterior cantilevers in mandibular implant-supported screw-retained prostheses were frequent and appeared to depend on implant placement and prosthesis design. The ratio of anterior to posterior cantilever lengths was approximately 1:2. (J Prosthet Dent 2003;89:244-9.)

Effect of thermocycling on tensile bond strength of six silicone-based, resilient denture liners

Statement of Problem. Adhesion failure between silicone resilient denture lining materials and denture base resin is commonly encountered in clinical practice. Adhesion failure results in localized unhygienic conditions at the debonded regions and often causes functional failure of the prosthesis. Purpose. The purpose of this study was to investigate the effect of thermocycling on the tensile bond strength of 6 soft lining materials. Material and Methods. Six commonly used silicone-based resilient denture liners (Ufigel C, Ufigel P, Mollosil, Molloplast B, Permafix, and Permaflex) were chosen for the investigation. The bond strength was determined, in tension, after processing to PMMA. The resilient denture liners for each group (n = 24) were 10 × 10 × 3 mm and were processed between 2 polymethyl methacrylate specimens according to manufacturer's instructions. Two PMMA specimens were prepared by investing brass dies with a 3-mm-thick spacer in a denture flask. Specimens were made by processing the resilient denture liners against the polymerized PMMA block. After polymerization, the brass spacer was removed from the mold, the 2 PMMA resin specimens were trimmed, and the surfaces to be bonded were smoothed. The PMMA block was placed back into the molds and the resilient denture liners were packed into the space made by brass spacer, trial packed, and polymerized according to the manufacturer's instructions. Half of the specimens for each group were stored in water for 24 hours, and the other half were thermocycled (5000 cycles) between baths of 5° and 55°C. All specimens were placed under tension until failure in a universal testing machine at a crosshead speed of 5 mm/min. The maximum tensile stress before failure and mode of failure were recorded. The mode of failure was characterized as cohesive, adhesive, or mixed mode, depending on whether the fracture surface was in the soft liner only, at the denture base-soft liner interface only, or in both. Failure strength was recorded in kg/cm2. Results were tested by multiple analysis of variance (ANOVA) for mode of failure (adhesive, cohesive, and mix), 2-way ANOVA (storage-products), and 1-way ANOVA (storage-products interaction, before and after thermocycling). Duncan's test was used to determine whether significant changes in the tensile bond properties of the materials occurred during thermocycling. Results. Varying degrees of bond strengths were found for soft lining materials and were significantly different (P<.05). Results of this study also indicated that the bond strengths of soft lining materials had significantly decreased after thermocycling except Ufigel C and Mollosil. Conclusions. Because the adequate adhesive value for soft lining materials is given 4.5 kg/cm2, all of the materials were acceptable for clinical use. (J Prosthet Dent 2003;89:303-10.)

Fit of implant frameworks: An in vitro comparison between two fabrication techniques

Statement of Problem. It has been suggested that a precise fit between the implant and the framework cylinder is necessary to ensure a satisfactory long-term clinical outcome. Purpose. The purpose of this study was to compare the precision of fit between implant abutments and framework cylinders in frameworks fabricated by the Procera system and those fabricated from cast gold-alloy. Material and Methods. A total of 19 frameworks, 14 made with the Procera system (type 1) and 5 made of a cast gold-alloy (type 2), were fabricated. A total of 95 implants, 70 type 1 and 25 type 2 frameworks, were evaluated. Three replicas of the space between the implant abutments and the framework cylinders of the master cast were made for each test specimen. The replicas were cut with a scalpel in 2 axial directions: buccal-lingual and right-left. For the purpose of measurement, a microscope with a precision of ± 0.5 μm was used at original magnification ×30. The Student t test was used to determine whether there were significant differences between the framework designs. Results. The buccal-lingual measurements for the type 1 and type 2 frameworks showed mean values of 28.1 μm (SD 9.8) and 42.0 μm (SD 1.8) on the buccal side, respectively, and 25.6 μm (SD 11.2) and 51.6 μm (SD 10.9) on the lingual side, respectively. For the right-left view, the mean measurements were 26.6 μm (SD 8.4) and 49.2 μm (SD 11.4) on the right side, respectively, and 27.4 μm (SD 8.5) and 44.4 μm (SD 6.5) on the left side, respectively. The total mean value for type 1 frameworks was 26.9 μm (SD 9.3); that for type 2 frameworks was 46.8 μm (SD 8.8). Conclusion. Within the limitations of this experiment, it was demonstrated that the fit of frameworks made with the Procera system was significantly better than that of the frameworks made with cast gold-alloy (P<.01). (J Prosthet Dent 2003;89:256-60.)