Radiographic identification of threaded endosseous dental implants

STATEMENT OF PROBLEM: The identification of dental implant bodies in patients without available records is a considerable problem due to increased patient mobility and to the large number of implant systems with different designs. PURPOSE: The purpose of this study was to document features that would help dentists identify threaded implant bodies from their radiographic images. MATERIAL AND METHODS: More than 50 implant manufacturers were contacted and asked to provide implants with dimensions as close as possible to 3.75 mm (diameter) x 10 mm (length). Forty-four implants were donated, 28 of which were identified as threaded. Radiographs were made of these implants at 0 degrees, 30 degrees, 60 degrees, and 90 degrees horizontal rotation combined with -20 degrees, -10 degrees, 0 degrees, +10 degrees, and +20 degrees vertical inclination relative to the radiographic beam and film. A total of 20 images per implant were taken and examined to identify consistent, unique features that would aid in implant identification. At a 20 degrees vertical inclination, vital features of implants were distorted enough to be deemed unrecognizable. Therefore, only those observations made from radiographs between -10 degrees and +10 degrees vertical inclination were used for implant identification purposes. RESULTS: All implants could be recognized from radiographs made between -10 degrees and +10 degrees vertical inclination. A series of tables and flowcharts describe the implants according to their identifying features. CONCLUSION: Information from this study should help dentists identify threaded endosseous implants from their radiographic images.     

Macro design morphology of endosseous dental implants

STATEMENT OF PROBLEM: The identification of dental implant bodies in patients without available records is a considerable problem due to increased patient mobility and to the large number of implant systems with different designs. PURPOSE: The purpose of this study was to document the designs of selected implants to help clinicians identify these implants from their radiographic images. MATERIAL AND METHODS: More than 50 implant manufacturers were contacted and asked to provide implants with dimensions as close as possible to 3.75 mm (diameter) x 10 mm (length). Forty-four implants were donated, separated into threaded and non-threaded categories, and further sorted into tapered and non-tapered categories. The implants were examined visually, and features on the entire circumference and length of each implant were recorded and categorized as coronal, midbody, or apical. RESULTS: A series of tables describe the 44 implants according to coronal, midbody, and apical features. CONCLUSION: The results of this project offer dentists basic knowledge of the design of selected dental implants. Such knowledge can aid the radiographic identification of these implants.     

Identification of dental implants on radiographs.

In the future, dentists will more frequently encounter patients who have dental implants. To use radiographs to identify implants that were previously inserted by other dentists, dentists have to be familiar with the detailed morphology of different products and types of fixtures as well as with the principles for formation of their radiographic images. In the present study, radiographic images of ten common dental implants were analyzed. Images varied with viewing angles. The influences of surface structures, such as threads, cuts, holes, perforations, and flutes, are demonstrated.     

Bone level changes at axial- and non-axial-positioned implants supporting fixed partial dentures. A 5-year retrospective longitudinal study

AIM: The aim of this study was to retrospectively analyze the potential influence of implant inclination on marginal bone loss at freestanding, implant-supported, fixed partial dentures (FPDs) over a 5-year period of functional loading. MATERIAL AND METHODS: The material comprised 38 periodontally treated, partially dentate patients with a total of 42 free-standing FPDs supported by implants of the Astra Tech System. Mesio-distal inclination of the implants in relation to a vertical axis perpendicular to the occlusal plane was measured with a protractor on standardized photographs of the master cast. The two tail quartiles of the distribution of the implants with regard to the implant inclination were defined as axial-positioned (mean 2.4 degrees; range 0-4 degrees) and non-axial-positioned implants (mean 17.1 degrees; range 11-30 degrees), respectively. For FPDs supported by two implants, both the mesial-distal and buccal-lingual inter-implant inclination was measured. The primary outcome variable was change in peri-implant bone level from the time of FPD placement to the 5-year follow-up examination. Comparison between axial- and non-axial-positioned implants was performed by the use of a Mann-Whitney U-test. Spearman's correlation analysis was used to analyze relationships between inter-implant inclination (mesial-distal and buccal-lingual) and 5-year bone level change on the FPD level. RESULTS: The 5-year mean bone level change amounted to 0.4 mm (SD 0.97) for the axial and 0.5 mm (0.95) for non-axial-positioned implants (P>0.05). For the FPDs supported by two implants, the mean inter-implant inclination was 9.2 degrees (1-36 degrees) in the mesial-distal direction and 6.7 degrees (0-24 degrees) in the buccal-lingual direction. Correlation analysis revealed lack of statistically significant correlation between inter-implant inclination (mesial-distal and buccal-lingual) and 5-year bone level change (r=-0.19 and r=-0.32, respectively). CONCLUSION: The study failed to support the hypothesis that implant inclination has an effect on peri-implant bone loss.     

Mathematical analysis of projection errors in "paralleling technique" with respect to implant geometry

"Standardized" radiographs acquired in paralleling technique serve for monitoring of marginal bone levels around endosseous implants. Under clinical conditions, parallel adjustment of the film to the implant is beset with great difficulties. A mathematical model matching clinical conditions was developed to evaluate projection geometry within an interval of clinically relevant angulations (+/- 10 degrees from parallel position). Radiographs of two implants (Frialit 2, Friadent AG, Mannheim, Germany; Implant No. 1: 3.8 mm, length 10 mm; Implant No. 2: 6.5 mm, length 13 mm) were separately produced per angulation (2 degrees increments) at one focus-object distance (FO=322.9 mm). Implant images were repeatedly measured along their midline/vertical edge, local magnification (MF) was calculated and the values were compared to the computed ones. Projected dimensions of the implants were calculated for a second distance (232.3 mm). The experimentally acquired data were in agreement with the mathematical calculation. MF calculated for assessment along the vertical edge varied less (+/-1.94% from mean value) than along the midline (+/-2.74%), with a range of 1.037-1.068 (FO=322.9 mm) and 1.061-1.099 (FO=232.3 mm) for implant No.1, and 1.060-1.101 (FO=232.3 mm) and 1.037-1.069 (FO=322.9 mm) for Implant No. 2. Magnification revealed a mean variation of 4%. Radiographic evaluation of periimplant bone level should not exceed a precision of 0.5 mm, when parallelism between film and implant is not guaranteed and FO is less than 380 mm.     

Biomechanical effects of double or wide implants for single molar replacement in the posterior mandibular region

Double implants have been thought to have biomechanical advantages for single molar replacement. To evaluate the effectiveness of double implants versus a wide implant, the vertical forces and torque on each implant were calculated by three-dimensional geometric analysis. Buccal load (100N) perpendicular to cuspal inclination (20 degrees) was applied at the occlusal surface of the superstructure. The three kinds of load points (A, B, C) were 1.5, 3.5, and 5.5 mm from the mesial contact point, respectively. Three implants were compared: mesial and distal double implants (phi 3.3 mm), and a wide implant (phi 5 mm). The wide implant showed torque around the long axis (1.8-15.0 N x cm) whereas double implants had no torque. On the other hand, the vertical forces on the mesial double implant were both smaller (60%: loaded at point C) and larger (140%: loaded at point A) than the wide implant. Given the smaller surface area of the mesial double implant, this large force may generate much higher stress in the peri-implant bone. These results suggest that the biomechanical advantage of double implants for single molar replacement is questionable when the occlusal force is loaded at the occlusal surface near the contact point.     

Clinical outcome and prosthodontic compensation of tilted interforaminal implants for mandibular overdentures

PURPOSE: The aim of this study was to evaluate the sagittal inclination of interforaminal implants, the clinical implant outcome, and the necessary extent of prosthodontic compensation modalities for implant overdentures (IODs). MATERIALS AND METHODS: Lateral cephalometric radiographs of 62 patients, each with a mandibular IOD retained by 2 to 4 implants, were analyzed. The sagittal inclination of the longitudinal implant axis of the most anterior implant was analyzed relative to the mandibular and occlusal planes. The angle needed to compensate for the inclination of the mandibular implant to obtain Angle's class I for the prosthesis (the compensation angle) was measured and compared with respect to skeletal class. Peri-implant structures were measured using the Plaque Index and the Gingival Index. The compensation angle was correlated with the mandibular implant inclination, the degree of mandibular atrophy, and the anterior facial height. RESULTS: The most anterior mandibular implants showed a mean retroinclination of 74.3 +/- 9.3 degrees in relation to the mandibular plane; retroinclination was significantly more pronounced in skeletal class II than skeletal classes I and III (P < .05). The compensation angle (26.9 +/- 10.5 degrees) was more significant for skeletal class II than for skeletal classes I and III (P < .01). Sagittal mandibular implant inclination correlated significantly to the compensation angle (r = -0.46; P < .05), mandibular atrophy (r = 0.32; P < .05) and mandibular facial height (r = -0.45; P < .05). Implant survival rate and peri-implant parameters (bone loss, pocket-depth, Plaque and Gingival Indices) of the interforaminal implants were not shown to be influenced by implant retroinclination. Nine patients (2 skeletal class 1, 7 skeletal class II) reported phonetic problems with the IOD because of narrowing of the lingual space but described significant improvement after a median 4.7 months (range, 3 to 12 months). DISCUSSION AND CONCLUSION: Depending on skeletal class, prosthetic compensatory mechanisms will be operative in the presence of mandibular implant retroinclination for IOD. Knowledge of mandibular inclinations and the compensatory mechanisms may be an essential factor in successful prosthetic rehabilitation and may provide for a homogenous design of the bar construction and easier handling and may also reduce stress on the attachment mechanism.     

Evaluation of postsurgical crestal bone levels adjacent to non‐submerged dental implants

In most of the studies on long-term radiographic evaluations of crestal bone levels adjacent to dental implants, no baseline radiographs taken immediately post-surgically had been obtained.The aim of this study was to test the reproducibility of a simple radiographic method for linear measurements of changes in bone levels and to evaluate changes in crestal bone levels adjacent co non-submerged ITI® implants 1 year following the surgical procedure. From 128 patients enrolled in a clinical and radiographic longitudinal study 40 patients also had radiographs taken immediately postsurgically. They were, however, not obtained as “identical” images. The radiographs were mounted onto slides and projected on a screen. Mesially and distally from 57 implants triplicate linear measurements of the distance implant shoulder to bone crest were taken, using known dimensions of the implants as internal reference distances. The median difference of 213 (out of 228 possible) duplicate measurements was 0.00 mm (ranging from ?1.72 mm to +1.47 mm when comparing the second co the third reading). Some 81% of the double measurements were within ±0.5 mm and the precision was 0.30 mm. In the immediate postoperative radiographs the median mesial bone level was located at 2.07 mm (distally 2.19 mm) from the implant shoulder. A statistically significant amount of bone loss in the first year was observed mesially (median=?0.78 mm) and distally (0.85 mm)(Wilcoxon matched pairs signed rank test ±0.001). No statistically significant influence of the implant location, the implant length, type of the implant (screw; cylinder) was observed (Kruskal-Wallis P>0.05).The age of the patients was not correlated significantly to the amount of bone loss observed. In conclusion, methodological limitations existed when evaluating linear bone changes in non-identical radiographs using reference dimensions of the implants. The amount of postsurgical bone loss estimated in other studies was confirmed when using an immediate postoperative radiograph as a baseline.     

In vitro evaluation of a method for obtaining periapical radiographs for diagnosis of external apical root resorption

This in vitro study was conducted to evaluate a method to obtain reproducible periapical radiographs, using individualized positioning devices, of upper central incisors submitted to simulated orthodontic movement. Linear measurements of tooth length were carried out on 29 extracted human central incisors. The teeth were radiographed in a tissue simulator, at different inclinations in the bucco-lingual direction (0 initial, 0 control, -10, -5, +5, and +10 degrees). The radiographs were digitized and quantitative analysis of tooth length was carried out using an electronic ruler. The linear measurements of tooth length were reproducible (r = 0.99) for repeated measurements as well as in the comparison of the initial and control images at 0 degree, where measurements did not differ significantly (analysis of variance, P = 0.827) in radiographs with different angulations. These results show that the method proposed for obtaining in vitro periapical radiographs results in reproducible images of tooth length, even when orthodontic movement is simulated by inclination of the tooth up to 20 degrees in the bucco-lingual direction.     

Standardized radiographs of the alveolar crest around implants in the mandible.

The techniques currently used for standardized longitudinal radiographic evaluation of the supporting bone around dental implants are not suitable for general application. An aiming device is described for intraoral radiography used to evaluate the crestal bone height around dental implants used as retention for overdentures. This aiming device has been tested on four different implant systems by four dentists. Error analysis of serial radiographs indicates small deviations in reproducibility. It is concluded that this method is suitable for routine evaluation of dental implants.     

下磨牙区种植体尖端与下颌管间安全距离的探讨

目的:探讨下颌磨牙区植入的种植体尖端与下牙槽神经管上缘之间的安全距离。方法:用游标卡尺测量23例患者全景片中的30颗下颌磨牙区种植体长度,除以对应的种植体实际长度,计算全景片中下颌磨牙区垂直放大率(vertical magnification factor,MF);选择种植体尖端至下牙槽神经管上缘间距离小于2mm的8例患者的全景片,测量片中12颗种植体尖端至下牙槽神经管上缘间的距离,除以对应种植体的垂直放大率,计算其实际距离;记录该8例患者有无下唇和(或)颏部感觉异常。结果:①全景片中下颌磨牙区垂直放大率为1.27±0.02;②12颗种植体尖端距下牙槽神经管上缘之间的距离为(1.19±0.33)mm(0.69～1.89mm);③8例接受种植体植入的患者,无一例出现下唇或颏部感觉异常。结论:下颌磨牙区植入种植体的尖端与下颌管上缘之间保存完整的骨壁,是防止损伤下牙槽神经的最关键因素之一。     

Long-term evaluation of hollow screw and hollow cylinder dental implants: clinical and radiographic results after 10 years

BACKGROUND: In 1988, an implant manufacturer offered a new dental implant system, with a wide choice of hollow cylinder (HC) and hollow screw (HS) implants. The purpose of this retrospective study of HS and HC implants was to evaluate clinical and radiographic parameters of peri-implant tissue and to analyze surgical and prosthetic aftercare. METHODS: A total of 89 HS and 26 HC implants in 38 edentulous patients were available for complete evaluation. The patients were treated with overdentures stabilized by two or four implants. The follow-up period was 10 years. RESULTS: The results of the clinical evaluation showed a mean sulcus probing depth of 3.3+/-1.3 mm (range=2 to 10 mm). The mean radiographic bone loss was 2.2+/-2.1 mm (range=0.1 to 12.2 mm). One implant (HS) was removed during the osseointegration period. Three other implants (two HS and one HC) in three patients had to be removed after 10 years. The survival rate of the HS implant (96.6%) was comparable to the HC implant (96.1%). The success rate of the HS implant (93.3%) was slightly more favorable compared to the HC implant (88.5%). The HS and HC implants met the Albrektsson criteria of success. CONCLUSIONS: HS and HC implants provide a stable base for long-term support of a mandibular overdenture. Furthermore, it is important to monitor peri-implant bone level by taking annual radiographs and measuring probing depth, especially after prolonged service.     

A comparison of the diagnostic advantages of panoramic radiography and computed tomography scanning for placement of root form dental implants

This study evaluated the advantages of computed tomography (CT) in comparison to routine panoramic radiography for dental implant treatment planning. An in vitro validation study was performed to assess the accuracy of CT and panoramic radiography film images for measurement of anatomic structures and distances between anatomic structures. After correcting by a standard 25% magnification on the panoramic images, a significant difference in measurements was found between the CT and panoramic radiography images. Ten subjects requiring implants in compromised ridges were treatment planned with either CT and panoramic radiographs or panoramic radiographs alone. The ideal implant length was determined at surgery with direct digital radiography. The dentists were significantly more confident using CT and panoramic images than panoramic radiographs alone. Implant length treatment planned with panoramic radiography alone underestimated length significantly compared with the implant length determined to be ideal during surgery.whereas treatment planning with CT and panoramic radiography demonstrated no significant difference. The data indicate the CT may be of value in treatment planning for dental implants, especially when gaining maximum length is of critical importance.     

Fraudulent use of radiographic images

The aim of this study was to evaluate the ability of trained observers to identify altered radiographic images after modifications using an image-editing software. Based on implantology in 10 radiographs, eight panoramic and one linear tomograph were modified while one tomograph was untouched. Implants were placed or removed and bone levels were altered, and seventy dentists were invited to identify these alterations. The results showed that the percentage of the correct answers was 12.5% or 2 identifications per examiner. The rate of false positives in relation to correct answers was at a level of 6:1. We concluded that the professionals have difficulty in identifying altered radiographs after using an image-editing software and that the seriousness of this situation demands that dentists be warned of the dangers of the use and abuse of this technology.     

Research methods in dentistry 9. Follow-up of permucosal implants in an edentate mandible using panoramic radiography

Panoramic radiographs are frequently used for routine follow-up of mandibular implants. The objective of this study was to determine whether measurement on a panoramic radiograph of the vertical dimension of the mandible near by an implant, using the known implant length as a reference, is a reliable method. In 11 patients, 2 permucosal implants were placed in the anterior part of the edentulous mandible. During the first year after implantation, 2 panoramic radiographs and 2 sets of standardized oblique lateral cephalometric radiographs were made. Oblique lateral cephalometric radiographs are the golden standard for measuring the vertical dimension of an edentulous mandible. The length of the implants and the vertical dimension of the mandible dorsally to the implants were measured on all oblique lateral cephalometric radiographs. The measured and known implant length were used to calculate the image enlargement factor. This factor was used to calculate the real vertical dimension of the mandible. The same measurement procedures were performed on the panoramic radiographs. Using a paired t-test, the calculated values of the vertical dimensions of the mandibles found on panoramic radiographs were compared with the calculated values found on oblique lateral cephalometric radiographs. No statistically significant differences were found. It was concluded that under the described circumstances, panoramic radiographs can be used for reliable measurement of the vertical dimension of the mandible near by permucosal implants.     

Effect of x-ray angulation on radiographic periodontal ligament space width.

The aim of this study was to set up a model for quantitating a change in radiographic PDL width on variation of x-ray angulation within anticipated clinical limits. Four incisor and 4 molar sites of 6 human skulls were radiographed at varying angulation. Horizontal angulation changes were made over a 12 degrees range, in 3 degrees increments. Vertical angulation change was in one 10 degrees increment. Baseline radiographs were taken with the x-ray beam perpendicular to a buccal tooth surface in a horizontal direction and perpendicular or 10 degrees off the perpendicular in a vertical direction. The radiographs were converted to digitized images and PDL width measurements made utilizing a mouse-driven computer program. The mean PDL width differences between all possible horizontal and vertical combinations (n = 45) were compared with the mean of those obtained from differences observed in PDL width measurements on replicate baseline radiographs. Mean PDL width differences for incisor locations were statistically different from the mean baseline PDL width difference; posterior PDL width difference showed no statistical variation from the mean baseline PDL width difference. For radiographs taken within the range expected under clinical conditions, a significant change in PDL width may be observed in incisor locations. Posterior sites may not exhibit this significant change due to the anatomy of the region which may reduce the clarity of the radiographic image.     

Cross-sectional study of the factors that influence radiographic magnification of implant diameter and length

PURPOSE: To study the factors that influence radiographic magnification of implant diameter and length. MATERIALS AND METHODS: The dental records and panoramic radiographs of 80 patients with 210 dental implants treated with implant-supported prostheses at Bundang Jesaeng Hospital in South Korea from January 2000 through February 2003 were reviewed. The panoramic radiographs were developed under standardized conditions. The patient's gender and the anatomic locations of implants were identified from the dental records. To prevent bias, a blinded investigator measured implant diameter and length on a panoramic radiograph. To evaluate intra-examiner variability, the intraclass correlation coefficient (R(I)) was calculated. The Mann-Whitney rank-sum test and the Kruskal-Wallis test were used to determine the statistical significance of the difference between actual length and radiographic length. RESULTS: The intraclass correlation coefficients (R(I)) were 0.83 for diameter and 0.87 for length. There was no statistically significant difference in length in regard to gender (P = .08). Magnification of diameter did differ on the basis of gender (P = .03; 25% magnification in radiographs of women; 20% in men). No difference in diameter was found in regard to anatomic location (P = .51), however, while evidence of difference in length in regard to anatomic location was found (P = .01). DISCUSSION: Radiographic magnification of implant dimensions in diameter and length can have different influencing factors. CONCLUSIONS: This study found that radiographic magnification of implant diameter was influenced by gender, whereas radiographic magnification of implant length was influenced by anatomic location. Each anatomic location had a different amount of radiographic magnification for implant length.     

Photoelastic stress analysis of various retention mechanisms on 3-implant-retained mandibular overdentures

STATEMENT OF PROBLEM: There are various stress transfer studies of 2- or 4-implant-retained mandibular overdenture designs. However, the influence of various types of attachments and implant inclination on stress distribution of 3-implant-retained mandibular overdenture designs has not been sufficiently assessed. PURPOSE: The purpose of this study was to compare the load transfer characteristics of 4 attachment systems for 3-implant-retained mandibular overdenture designs for vertically oriented and inclined implants. MATERIAL AND METHODS: Two photoelastic mandibular models were fabricated having 3 screw-type implants (3.7 x 14 mm with 4.8-mm diameter abutment platform) embedded in the interforaminal region. In the first model, the implants were parallel to each other and vertically oriented. In the second model, 1 implant in the midline was vertically oriented, and the other 2 implants were positioned 20 degrees divergent from the center implant. Four retention mechanisms were studied for each model--the Locator, Swissplus ball, Bredent bar, and Bredent bar-ball. The bar design connected the 3 implants, and the bar-ball design used the bar in a similar fashion but additionally incorporated distally placed ball attachments. A vertical force of 135 N was applied unilaterally to the central fossa of the right first molar. The resultant stresses that developed in the supporting structure were monitored photoelastically and recorded photographically. RESULTS: For the splinted and unsplinted 3-implant-retained overdenture designs evaluated, moderate and low level stresses were observed with different attachment systems. For both the vertically oriented and inclined implants, the bar-ball attachment system produced the lowest stress level. CONCLUSIONS: For vertical and inclined implant designs, lowest stress was transferred to all implants with the bar-ball attachment system, while moderate stresses were observed in implants on the loaded side with unsplinted attachment systems. The highest stress level observed with all attachment systems was moderate. For the vertical implant design, the observed stresses were distributed to all implants except with the ball attachment system, which demonstrated little discernible stresses on the non-loaded side implant.