Torque-fitting and resonance frequency analyses of implants in conventional sockets versus controlled bone defects in vitro.

The primary stability of implants should be high on insertion into fresh extraction sockets. Torque-fitting and resonance frequency analyses (RFA) are used to assess primary implant anchorage and stability. The torque-fitting and RFA of implants placed in conventional surgical sockets and sockets with controlled coronal bone defects was compared. The possible relation between torque-fitting and RFA was explored. Ø 3.3 mm x 12 mm implants were placed in 16 sockets finalized with Ø 2.8mm surgical pilot drills in the right iliac crests of two fresh cadavers (control). In the test group, implants were placed into sockets prepared by Ø 2.8mm drill followed by Ø 4.2mm twist drills to a depth of 6mm to create circumferential controlled coronal bone defects (50% bone loss). Primary implant stability was assessed using insertion torque values (ITV) followed by RFA. Mean ITV and RFA measurements for test groups (7.83+/-0.91 N cm and 40.88+/-3.57) were significantly lower than controls (14.80+/-1 N cm and 66.31+/-0.9) (P<0.05). Reductions of ITV and RFA measurements in relation to bone defect were 47% and 38%. The existence of controlled bone defects eliminating contact coronally leads to decrease in torque-fitting and primary stability of implants. No relationship was observed between torque-fitting and RFA.

Comparison of microleakage properties of three different filling materials. An autoradiographic study.

The aim of this study was to compare the microleakage behaviour of three restorative materials using the autoradiographic method. The study was accomplished in vitro using freshly extracted human molars and a Ca45 radioisotope and autoradiography. Twenty-seven molar teeth were divided into three experimental groups of seven specimens each. Class II cavities were prepared at the mesio-occlusal aspect and restored with amalgam and two different composite resins. The restorations were finished, thermocycled and tested for microleakage, using the Ca45 radioisotope. The results were analysed using the Kruskal-Wallis analysis test. Amalgam exhibited more leakage compared with composite resins. However the differences among the leakage behaviours of three filling materials were not statistically significant (P=0.064).

Finite element stress analysis of the effect of short implant usage in place of cantilever extensions in mandibular posterior edentulism.

Although the destructive effect of cantilevered implant supported fixed partial prosthesis is well known, in some cases usage of cantilever extension seems to be inevitable for many clinicians. The purpose of this study was to evaluate the effect of additional placement of a shorter implant in place of a cantilever extension on stress distribution compared with cantilevered fixed prosthesis in mandibular posterior edentulism. A mandibular Kennedy II finite element model was constructed. Six different implant supported fixed partial prosthesis were designed according to two main configurations; anterior and posterior cantilever extensions compared with the placement of additional shorter implant configurations. An oblique occlusal load of 400 N was applied. Tensile and compressive stress values in the cortical bone surrounding the cervical regions of implants and Von Misses stress values in the implants were evaluated. Significant lower stress values were recorded at the shorter implant placement configurations compared with the cantilevered prosthesis. Posterior cantilever extension performed higher stress values than the anterior counterpart. In clinical applications where cantilevered fixed partial prosthesis seems to be inevitable because of anatomical restrictions and/or complications such as loss of implant, an additional placement of a shorter implant should be considered.

Evaluation of the effect of the residual bone angulation on implant-supported fixed prostheses in mandibular posterior edentulism. Part I: Spiral computed tomography study.

Dental implants are usually angulated buccolingually because of the anatomy of the residual bone in mandibular posterior edentulous cases. Although angulated dental implants compromise the construction of implant-supported prostheses, the effect of buccolingual angulation of the residual bone has not been clearly stated. This study is performed to determine the biomechanical effect of buccolingual angulation. The goal was to reveal the actual buccolingual angulation values of the residual bone in which implants were to be placed. Thirty mandibular Kennedy I and II cases comprised of forty edentulous posterior regions with missing second premolars and first, second, and third molars were included. Buccolingual angulation values along the 28 mm of residual bone were measured on 1-mm spacing cross-sectional images of spiral computed tomography. Paired sample t test was used for the statistical analysis. The minimum angulation values at the second premolar, first molar, and second molar region were 0 degrees, 3 degrees, and 9 degrees, respectively. The average angulation values were 4 degrees, 10 degrees, and 15 degrees, respectively, and the maximum angulation values were 11 degrees, 18 degrees, and 22 degrees, respectively. The ability to measure the buccolingual angulation of mandibular posterior residual bone before dental implantation may help the clinician at the implant treatment-planning phase.

Finite element stress analysis of the influence of staggered versus straight placement of dental implants.

Bending moments resulting from non-axial overloading of dental implants may cause stress concentrations exceeding the physiologic supporting capacity of cortical bone, leading to various kinds of failures. The aim of this study was to evaluate the effect of staggered (offset, tripodization) implant placement configuration and placement of wider-diameter implants in a straight-line configuration in mandibular posterior edentulism. A mandibular Kennedy Class II partially edentulous finite element model was constructed. Seven different partial fixed prostheses supported by 3 implants were designed according to 2 main configurations: straight-line or staggered implant placement. In 5 of the designs, implants with various diameters and length were placed along a straight line. In the other 2 models, offset placement of the middle implant buccally and lingually was simulated. A 400 N static load was applied perpendicular to the buccal inclination of the buccal cusps on each unit. Tensile and compressive stress values on cortical bone in the cervical region of the implants were evaluated. Lower stress values were recorded for the configuration with wider implants placed in a straight line. Other configurations, including staggered implant placement, produced similar stress values. Despite the offset implant placement, the stresses were not decreased; however, straight placement of wider implants may decrease bending moments.

Tensile bond strength of ceramic orthodontic brackets bonded to porcelain surfaces.

The aim of this study was to compare various surface treatment methods to define the procedure that produces adequate bond strength between ceramic brackets and porcelain. The specimens used in this study, 60 porcelain tabs, were produced by duplication of the labial surface of a maxillary first premolar. The 6 different preparation procedures tested were: (1) sandblasting with 50 microm aluminum oxide in a sandblasting device, (2) application of silane to the porcelain and the bracket base, (3) sandblasting followed by application of silane, (4) acid etching with 9.6% hydrofluoric acid, (5) acid etching with 9.6% hydrofluoric acid followed by application of silane, and (6) sandblasting followed by application of 4-Meta adhesive. The ceramic brackets were bonded with no-mix orthodontic bonding material. A bonding force testing machine was used to determine tensile bond strengths at a crosshead speed of 0.5 mm per second. The results of the study showed that porcelain surface preparation with acid etching followed by silane application resulted in a statistically significant higher tensile bond strength (P < .05). Sandblasting the porcelain surface before silane treatment provided similar bond strengths, but sandblasting or acid etching alone were less effective. Silane application was recommended to bond a ceramic bracket to the porcelain surface to achieve bond strengths that are clinically acceptable.

Evaluation of the effect of the residual bone angulation on implant-supported fixed prosthesis in mandibular posterior edentulism. Part II: 3-D finite element stress analysis.

Buccolingual angulation of the mandibular posterior edentulous region may affect the prosthetic load conditions, so as to cause high stress concentrated areas that may easily lead to failure. The aim of this study was to evaluate the effect of various predetermined buccolingual angulation values on stress distribution in the mandibular posterior edentulous region restored with implant-supported fixed partial dentures, using three-dimensional finite element analysis. Stress analyses were performed applying 400N oblique force to implant-supported fixed prosthesis. Stress analyses indicated tensile stress values on the buccal surface and compressive stress values on the lingual surface of cortical bone were increased as the angulation of the edentulous bone increased (especially corresponding to the cervical region of the implants). Compressive stress values, observed where two implants were placed at the second premolar and second molar regions (5-7 design) and first and second molar regions (6-7 design), respectively, were very close to or even exceeded the ultimate compressive strength of bone. It is concluded that when a definite buccolingual angulation is added to other existing risk factors such as bruxism, placing an implant for every missing tooth might reduce the high stress concentration areas.

A multidisciplinary approach to single-tooth, implant-supported prostheses: a report of three cases.

Dental implants and their successful long-term results have begun a new era in dentistry. In recent years, the increasing trend of using dental implants at single-tooth edentulous cases has been taken into consideration. Although treatment goals and objectives are similar for both prosthodontists and orthodontists, they rarely cooperate. Usually prosthodontists are in need of preprosthodontic orthodontic preparations for younger patients. In this paper, different preprosthodontic orthodontic procedures that may be required before the placement of implants at single-tooth edentulous cases are presented. In the first and second cases, decreased mesio-distal space was regained by different orthodontic treatment methods, whereas the occlusal relationship was corrected for better function in the third case.

Comparision of diametral tensile strength of microwave and oven-dried investment materials.

STATEMENT OF PROBLEM: Microwave drying technique for investment materials is believed to be timesaving by accelerating the elimination of free water content. PURPOSE: This study compared the diametral tensile strength of 4 investment materials used in removable partial denture framework fabrication. The investment materials were subjected to microwave and conventional oven drying at different time intervals. MATERIAL AND METHODS: Type III partial denture casting investments (Wirovest, Wiroplus, Biosint, PH2) were tested. A total of 160 specimens were prepared in cylindrical form at a height of 40 mm and a diameter of 20 mm, in accordance with the manufacturers' recommendations. Forty specimens were prepared from each product; 20 specimens were dried at 230 degrees C for 1 hour in an electric furnace, the other 20 were dried in a microwave oven for 10 minutes at 600 W. The dried specimens were tested at 2- and 4-hour intervals in diametral compression at a crosshead speed of 0. 5 cm/min. RESULTS: The microwave drying technique resulted in greater diametral tensile strength values for all investment materials. CONCLUSION: Within the limitations of this study, microwave drying of type III dental investment materials at 600 W for 10 minutes was, apart from strengthening the material, timesaving for the dental laboratory.

The effect of weight loss of liquid on the diametral tensile strengths of various kinds of luting cements.

The role of water evaporation from the liquids of the cements were tested, and the effect of this loss on their strength was evaluated for 0, 10, 20 and 30 minute, intervals. After 30 minutes the evaporation of liquid from the cements was so high that they lost their luting consistency. The data suggests that the highest weight loss was with polycarboxylate cement liquids, with glass-ionomer and zinc phosphate cement liquids following respectively. However, when diametral tensile strength test values were evaluated it was determined that glass-ionomer exhibited the highest resistance to fracturing and zinc phosphate the lowest. Upon examination of samples which were fractured, while polycarboxylate and glass-ionomer cracked and split into large fragments, zinc phosphate cements fractured into a multitude of small pieces. On the basis of this study, it appears that the manufacturers' recommendations about the powder-to-liquid ratio and the mixing procedures is confirmed particularly and should be adhered to for optimal results.