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PubMed2002

The effect of repeated torque on the ultimate tensile strength of slotted gold prosthetic screws.

STATEMENT OF PROBLEM: Repeated torque may alter the mechanical properties and fracture resistance of certain prosthetic retaining screws. PURPOSE: This study evaluated the effect of repeated torque and salivary contamination on the ultimate tensile strength of one type of slotted gold prosthetic retaining screw. MATERIAL AND METHODS: Forty-five slotted gold prosthetic screws from the same manufacturer (Implant Innovations) were divided randomly into 9 groups of 5 screws each, with group 0X being an unused control. Groups 1XL, 5XL, 10XL, and 20XL were lubricated with human saliva, tightened to 10 Ncm, and removed 1, 5, 10, and 20 times, respectively. This procedure was performed in an unused stack of implant components consisting of an implant, an abutment cylinder and screw, and a gold cylinder. Groups 1XN, 5XN, 10XN, and 20XN were not lubricated. A custom load cell, load frame, and strain gauge torque wrench with associated electronics were used to apply torque; ultimate tensile strength was measured on a universal testing machine. Fracture load values were analyzed against torque cycles with 1-way analysis of variance and a Tukey test (P<.05). Differences between the 2 conditions (lubricated and nonlubricated) were characterized with Student's t test (P<.05). RESULTS: Mean fracture load values ranged from 97.6 +/- 2.2 kg (group 0X) to 102.0 +/- 2.1 kg (group 5XN). Analysis of variance and Tukey's test revealed no significant differences between the lubricated and nonlubricated conditions for all groups and no significant reduction of tensile strength. For 2 of the nonlubricated groups, 5XN and 20XN, a significant increase in fracture load values was recorded (P=.02 and P=.03, respectively). CONCLUSION: Within the limitations of this study, the results suggest that the slotted gold prosthetic screw tested can be tightened and removed up to 20 times without any effect on its ultimate tensile strength. The use of human saliva as a lubricant during torquing also had no apparent effect on ultimate tensile strength.

Analysis of Variance↗
PubMed2002

Tensile bond strength of acrylic resin denture teeth to a microwave- or heat-processed denture base.

STATEMENT OF PROBLEM: Fracture of acrylic resin prosthetic teeth from acrylic resin denture bases can be a problem for some patients. The optimal combination of acrylic resin denture tooth, denture base material, and processing method is not known. Purpose. The objective of this study was to compare the tensile bond strengths of heat- and microwave-polymerized acrylic resins among 4 types of acrylic resin denture teeth. MATERIAL AND METHODS: Heat-polymerized (Lucitone 199) and microwave-polymerized (Acron MC) acrylic resins were used. Four types of acrylic resin denture teeth (IPN, SLM, Vitapan, and SR-Orthotyp-PE) were milled to a fixed diameter according to ADA specification no. 15. Ten specimens of each tooth type were processed to each of the denture base materials according to the manufacturers' instructions. Ten additional resin control specimens without teeth also were fabricated. Specimens were thermocycled and tested for strength until fracture with a custom alignment device. Data were analyzed with analysis of variance and Duncan's multiple range test. A scanning electron microscope was used to identify adhesive and cohesive failures within debonded specimens. RESULTS: The mean force required to fracture the specimens ranged from 5.3 +/- 3.01 to 21.6 +/- 5.2 MPa for the microwave-polymerized base and 11.2 +/- 3.0 to 39.1 +/- 5.1 MPa for the heat-polymerized base. The most common failure was cohesive within the denture tooth. With each base material, Orthotyp and IPN teeth exhibited the highest bond strengths; SLM and Orthotyp bond strengths were similar. In general, heat-polymerized groups failed cohesively within the denture base resin or the tooth, and microwave-polymerized groups failed adhesively at either the ridge lap or occlusal surface of the denture tooth. CONCLUSION: Within the limitations of this study, the results suggest that the type of denture base material and denture tooth selected for use may influence the tensile bond strength of the tooth to the base. Selection of more compatible combinations of base and resin teeth may reduce the number of prosthesis fractures and resultant repairs.

Acrylic Resins↗
PubMed2006

Optimizing resin cement removal around esthetic crown margins.

OBJECTIVE: To quantify luting cement at the crown-tooth interface of esthetic crowns fabricated using four different techniques and two methods of excess cement removal. MATERIAL AND METHODS: Four methods of crown fabrication were used: the feldspathic porcelain and platinum foil technique, the feldspathic porcelain and refractory die technique, the resin composite crown and CAD/CAM technique, and the feldspathic porcelain crown and CAD/CAM technique. Half of the cemented crowns were allocated to Group A: removal of excess cement by flicking-off with a plastic instrument 3 min after initial polymerization, or Group B: removal of excess cement using a wiping action with cotton pellets. Morphologic measurements, using non-destructive digital profilometry, were made of the volume of excess cement (mm(3)), mean maximum and mean depth of excess cement (microm), and surface area of excess cement (mm(2)). RESULTS: ANOVA and Duncan post-hoc tests revealed no statistical differences (p<0.05) between the four types of crown fabrication with respect to volume and mean depth of retained luting cement. There was a significantly greater volume, mean depth, and mean maximum depth of luting cement retained using the "flick off" method compared to the cotton pellet "wiping" method for excess cement removal, but no statistical differences in mean surface area between the two methods. CONCLUSIONS: Following removal of excess luting cement, as judged clinically, using two methods, subclinical amounts of cement remained adherent to the tooth surface of all specimens at the crown-tooth interface.

Analysis of Variance↗
PubMed1999

The durability of parylene coatings on neodymium-iron-boron magnets.

A parylene coating is frequently used to prevent corrosion of neodymium-iron-boron magnets when they are used intra-orally. This in vitro study was designed to test the durability of parylene coating in a simulated oral environment. Single and double parylene-coated magnets were subjected to grinding and crushing forces in an industrial ball mill. The results demonstrate that abrasion and wear was visible around the edges after 1 hour of testing, with a breach of the coating noted under high magnification scanning electron microscopy (SEM). The conclusion of the study is that parylene coating is unlikely to withstand intra-oral forces. The shape of the magnets, the manufacturing process involved in their production, and the thickness of the parylene coating are important factors to consider with respect to the durability of magnets used in the mouth.

Boron↗
PubMed2003

Effect of fatigue testing on core integrity and post microleakage of teeth restored with different post systems.

The purpose of this study was to evaluate a new nondestructive test system, which could test concurrently fatigue and microleakage. Fifty, single-rooted teeth were restored with one of the following posts systems and a composite core: titanium ParaPost cemented with zinc phosphate cement; CosmoPost; C-Post; Esthetic C-Post; and FibreKor post, all cemented with resin cement. Samples were embedded and placed in a positioning jig. They were impacted at 45 degrees to the long axis of the tooth with a force of 55 N at a frequency of 3 Hz for a total of 100,000 impacts. After 60,000 impacts, samples were thermocycled. Core integrity and post microleakage were evaluated periodically throughout the 100,000 impacts. Samples showed no detectable displacement of any of the cores, but the metallic group showed a statistically significant increase in microleakage (p < 0.05) at the conclusion of the study compared with the nonmetallic groups.

Analysis of Variance↗
PubMed2004

Post placement and restoration of endodontically treated teeth: a literature review.

The restoration of endodontically treated teeth is a topic that is extensively studied and yet remains controversial from many perspectives. This article reviews the major pertinent literature on this topic, with an emphasis on major decision-making elements in post placement and restoration of endodontically treated teeth. Recommendations are made for treatment planning, materials, and clinical practices from restorative and endodontic perspectives.

Cementation↗
PubMed1992

An evaluation of the Periotest system. Part II: Reliability and repeatability of instruments. Dental Implant Clinical Research Group (Planning Committee).

Investigators involved in a clinical study on dental implants being conducted by the Dental Implant Clinical Research Group participated in a two-part in vitro evaluation of the Periotest system. The first part involved each of 35 investigators taking three readings for each of 16 models designed to simulate an implant in place in the oral cavity and to cover most of the effective measuring range of the instrument. The second part, with which this article is concerned, was conducted by three study investigators to determine the level of agreement in readings for six different Periotest instruments. Readings were taken according to the manufacturer's instructions until two coincident readings were obtained. The readings were compared to evaluate inter- and intrainstrument reliability. Instrument repeatability was evaluated by examining the number of attempts required to obtain the two coincident readings. The Periotest system generally demonstrated a high degree of repeatability and reliability, with higher variability associated with specific model samples.

Dental Implants↗
PubMed1993

Providing optimum torque to implant prostheses: a pilot study.

Ten N/cm torque has been proposed as the optimum level for the tightening of implant retaining gold screws in order to preload the implant components to limit loosening and fracture. The purpose of this study was to determine the influence of instrumentation and operator experience on the torque generated during manual tightening of slotted gold screws. Sixteen subjects, divided into four groups based on experience, were instructed to tighten five screws into implant analogs with 20-mm and 37-mm slotted screwdrivers. The screws were then removed with a torque gauge. All of the groups of subjects were able to generate significantly greater torque with the 37-mm screwdriver. Dentists with no implant treatment experience generated significantly less torque than the other three groups. Of the 12 dentist subjects, only 3 generated the optimal amount of torque when using the 20-mm screwdriver. Operators who had little experience dealing with implant prostheses were not able to provide the recommended torque and experienced operators tended to generate more than the recommended amount. None of the subjects were able to generate consistent torque values.

Analysis of Variance↗
PubMedDate not supplied

Root intrusion in tooth-implant combination cases.

The various proposed etiologies for root intrusion in tooth-implant combination cases are discussed. Clinical examples of root intrusion are illustrated. Advantages and disadvantages of nonrigid connector and coping/suprastructure techniques are presented.

Dental Abutments↗
PubMed1993

Finite element analysis of four-abutment Hader bar designs.

Three-dimensional finite element analyses were conducted on the four-abutment Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three stiffener heights (1, 2, and 3 mm) were analyzed representing a clinical range of usage. Three material types were studied which represent a selection of alloys commonly used clinically. The model consisted of a representative Hader bar of 1.8-mm diameter with a 1-mm inferior stiffener. The ends of the bar were fixed to a 5-mm diameter coping which was attached to a 3.8-mm root form-type implant fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200 Newton occlusal force was imposed on the mesial bar and a 450 Newton force on the distal bar for the three stiffener heights. The results of these analyses predicted yielding and fracture (failure) for all 1-mm stiffener height and type IV gold alloy cases studied. Stiffener height was found to play a strong role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. Factors of safety with respect to static yield strength ranged from 1.44 to 2.12 on the distal portion.

Chromium Alloys↗
PubMed1994

The influence of implant type, material, coating, diameter, and length on periotest values at second-stage surgery: DICRG interim report no. 4. Dental Implant Clinical Research Group.

Many of the presently used methods of evaluating osseointegration at second-stage surgery are highly subjective. The Periotest is claimed to offer a more objective means to assess osseointegration by means of microcomputer-controlled percussion. In 1991 the Dental Implant Clinical Research Group initiated a long-term clinical study in cooperation with the Department of Veterans Affairs to investigate the influence of implant design, application, and site of placement on clinical performance and crestal bone height. As part of this investigation, the Periotest values for 1,565 root form implants were determined at second-stage surgery and correlated with type, material, coating, diameter, and length. Hydroxyapatite-coated implants and increased implant diameter and length produced Periotest values that indicated a greater extent of stability as compared with noncoated implants with shorter diameters and lengths. Hydroxyapatite-coated cylinder-type implants yielded the most favorable Periotest readings. Not only does the Periotest have the potential of being a valuable instrument for assessing implant mobility at second-stage surgery, but it also appears to have the capability of determining slight differences in the implant-bone complex.

Dental Alloys↗
PubMed1994

Bar patterns in implant prosthodontics.

An extensive discussion of bar patterns is presented, including historical background, current bar designs, and precision milling concepts. Research that has been done on different bar configurations is discussed along with technical and clinical considerations for various bar pattern designs.

Dental Clasps↗
PubMed1996

Testing progressive loading of endosteal implants with the Periotest: a pilot study.

The progressive loading of implants was first suggested by Misch in 1980. A major indicator of successful osseointegration is lack of implant mobility. In a pilot study, 26 implants were placed in eight patients. Fifteen of the implants were progressively loaded before placement of the final restorations. The remaining 11 implants were allowed to heal with healing abutments only and were not loaded until placement of the final restorations. Three measurements were taken for each of the implants at the time of uncovering and at the final restoration appointment using the Periotest. The mean change in Periotest values was -0.27 for the non-loaded group as compared with -1.51 for the progressively loaded group. There was a significantly larger increase (P < 0.001) in implant rigidity for the progressively loaded group. Progressive loading appears to enhance implant rigidity. The Periotest has the potential of being a valuable instrument for the determination of osseointegration.

Alveolar Process↗
PubMed1997

Repair of a transmandibular implant: clinical report.

The use of many currently available implant systems may be limited in patients with severe mandibular atrophy because of the lack of available bone in the symphyseal region. The transmandibular implant is a rigid box-frame structure that can distribute masticatory forces along a severely atrophied mandible with as little as 4 mm of vertical bone with an implant-borne prosthesis. Although the success rate of the transmandibular implant is favorable as compared with other systems, complications can occur after placement, including infection, partial extrusion, and fracture of a post. A case report of fractures of two posts at the necks and the bar approximately 18 months after placement is presented.

Aged↗
PubMed1997

Long-term efficacy of hydroxyapatite-coated cylindrical implants.

A two-site clinical study of hydroxyapatite-coated cylindrical titanium alloy implants was undertaken to evaluate their efficacy. Observations were recorded before surgery, at first-stage surgery, at second-stage surgery, at loading, and at quarterly postrestoration prophylactic examinations and annual comprehensive patient visits. Implant failure criteria included mobility, peri-implant radiolucency, fracture, exfoliation, removal for any reason, and patient reported pain on palpation. Soft tissue indices were monitored as part of the study. Postrestoration implant performance was analyzed using life table methodology. From the 316 implants restored in 154 patients, 11 implants in 8 patients failed before prosthetic attachment, for a surgical success rate of 96.4 percent. Four implants failed during an observation period extending up to 85 months after completion of prosthetic treatment. The Cutler-Ederer life table success rate after 6 years was 97.8 percent. No significant adverse events were reported during the observation period. Results of this investigation suggest that hydroxyapatite-coated cylindrical titanium alloy implants are an effective treatment modality.

Adolescent↗