Analysis of stress on a fixed partial denture with a blade-vent implant abutment.

Using a two-dimensional finite element method, a study was made that compared the behavior of a model mandibular posterior fixed partial denture constructed on the second premolar abutment and a blade-vent implant imbedded at the site of the second molar with the behavior of a fixed partial denture constructed on the second premolar and second molar abutments. The following were the results: 1. Deflections of the implant fixed partial denture were less than those of the natural tooth fixed partial denture in vertical and inclined loads. 2. Stress concentration was markedly found in the pontic and the mesial and distal parts of the premolar retainer in both restorations and the implant neck in the implant fixed partial denture. 3. In the implant fixed partial denture, stresses induced in the surrounding bone became higher around the posterior abutment and became lower around the premolar retainer than the stresses produced with the natural tooth fixed partial denture. 4. Therefore it was suggested that, to relieve stress to the surrounding bone around the implant abutment, occlusal forces loaded to the implant fixed partial denture have to be more concentrated on the premolar abutment than do forces loaded to the natural tooth fixed partial denture.     

Dimensional profile of oral mucosa around combined tooth-implant-supported bridgework in macaque mandible

Purpose: A stable oral mucosa is crucial for long‐term survival and biofunctionality of implants. Most of this evidence is derived from clinical and animal studies based solely on implant‐supported prosthesis. Much less is known about the dimensions and relationships of this soft tissue complex investing tooth‐implant‐supported bridgework (TISB). The aim here was to obtain experimental evidence on the dimensional characteristics of oral mucosa around TISB with two different abutment designs. Methods: Sixteen 3‐unit TISB were constructed bilaterally in the mandible of eight adult Macaca fascicularis. An implant system with a standard progressive thread design was the bone‐anchoring implant in the second mandibular molar region while the second mandibular premolar served as the natural tooth abutment. Eight implants were connected with the tapered abutment, the remaining with butt‐joint abutment, in a split‐mouth design. These were allowed to functional load for 6 months before sacrification for histomorphometry. Six soft tissue indices were scored: coronal gingival mucosa‐to‐implant top distance (DIM); sulcus depth (SD); junctional epithelium (JE); connective tissue contact (CTC); implant top to first bone‐to‐implant contact distance (DIB); and biologic width (BW=SD+JE+CTC); corresponding parameters in the natural tooth abutment were also measured. Results: Mucosal dimensions in tapered implants (^*BW=3.33±0.43; SD=1.03±0.24; JE=1.08±0.13; CTC=1.22±0.23 mm) were comparable with those of natural tooth abutments (BW=3.04±0.18; SD=0.93±0.1; JE=0.78±0.1; Attachment=1.33±0.09 mm), but differed from butt‐joint implants (^*BW=4.88±1.24; SD=1.47±0.38; JE=1.49±0.4; CTC=1.92±0.93 mm) (^*P<0.05). Conclusions: Results suggested that soft tissue dimensions around TISB are influenced by the implant–abutment interface and abutment material used. Mucosa investing tapered abutment tends to recapitulate soft tissue physiologic dimensions of natural tooth. To cite this article:
Siar CH, Toh CG, Ali TBT, Seiz D, Ong ST. Dimensional profile of oral mucosa around combined tooth‐implant‐supported bridgework in macaque mandible.
Clin. Oral Impl. Res. 23 , 2012 438–446.
doi: 10.1111/j.1600‐0501.2010.02145.x     

Changes in abutment tooth mobility by wearing parital denture: a continued report

Follow-up measurements of the abutment tooth mobility were carried out to examine the mobility changes for a long period of 12 to 14 years. The subjects were 6 patients, having 12 abutments and they were wearing mandibular unilateral distal extension partial dentures of the same design. These results were as follows: The tooth mobility of the abutment hadn't increased exclusively by the wearing of the distal extension denture over a 10-year period. Among the 12 abutments, 7 abutments showed nearly the same degree of mobility as the initial level, and the mobility of the other 4 abutments increased slightly. However, one abutment alone was extracted because of severe increased mobility. There was an extremely slight difference in the mobility between both abutments and the mobility of each abutment presented nearly the same amount. Also the tendency in the mobility change indicated a similar pattern. The long-term prognosis of mandibular unilateral distal extension partial denture, of the most common clasp design, presented a favourable state during the 12 to 14 years, judging from the changes in the abutment mobility.     

The mandibular first premolar as an abutment for distal-extension removable partial dentures: a modified clasp assembly design

Sound mandibular first premolars can be used as sole abutments for bilateral distal-extension removable partial dentures, if the denture is designed to minimise the torque applied to the abutment teeth. A simplified modification of the conventional torque-releasing clasp-assembly designs is suggested for these teeth. This modification entails a mesial rest on each abutment tooth connected to the distal proximal plate via a lingual bracing arm. A circumferential clasp arm is optional for buccal retention of the removable partial denture. As with conventional designs, the metal framework is designed to permit some rotational tissueward movement of the distal extension bases, yet not compromise the retention and stability of the prosthesis.     

A modified protocol for restorative implant abutment selection by using computer-aided design and computer-aided manufacturing technology

Statement of problemImplant abutment selection is complex because of the numerous factors involved. Computer-aided design (CAD) technology allows for the virtual selection and placement of abutments after all parameters have been precisely measured. The outcome of this new protocol should be validated.PurposeThe purpose of this in vitro study was to validate a new digital protocol in which abutment selection is made through a CAD software program, the abutments are virtually placed, and the restoration is then designed based on the virtual abutments to fit the actual abutments when delivered to the implants intraorally.Material and methodsA cast with 2 parallel implants was scanned 10 times. Then, 2 abutments were placed and scanned 10 times. Twenty identical superstructures were designed and manufactured to simulate the clinical situation of a 3-unit fixed partial denture, screw-retained to 2 implants. These were divided into 2 groups—A, real abutment and B, virtual abutment—and then compared by means of digital and optical measurements.ResultsNo significant differences were detected for the measurements between the control and test groups in either the x-axis or y-axis; significant differences were found for the median value of the measurements obtained from both groups regarding the z-axis (P=.046). The mean gap in the virtual abutment group was 50 μm and 35 μm in the real abutment group.ConclusionsSuperstructures produced after the virtual selection and placement of intermediate restorative abutments compared favorably with those produced after the digitalization of actual abutments and placement in the implant model, thus validating the proposed digital protocol for virtual abutment selection and placement.     

三种不同连接方式的天然牙—游离端种植体联合支持的 固定义齿集中载荷应力分析

目的 研究三种不同连接方式的天然牙——游离端种植体联合支持的固定义齿在集中载荷下的应力值和应力分布。方法 应用三维有限元应力分析法。结果 ①固定连接式固定义齿的种植体基牙应力峰值高于天然牙;②刚性栓道式固定义齿的种植体基牙应力峰值最高;③缓冲式固定义齿的种植体基牙应力峰值最低。结论 ①固定连接式固定义齿设计可能损伤种植体基牙,需采取适当措施;②刚性栓道式固定义齿设计对种植体基牙损伤最大;③缓冲式固定义齿设计有利于保护种植体基牙。     

Effect of splinting on abutment tooth movement

The effect of splinting on abutment tooth movement was investigated in an in vitro study. An acrylic resin mandibular model with missing molars and a removable partial denture framework were constructed. The roots of the premolars and edentulous ridges were coated with silicone rubber. A modified Ney surveyor was used for load application, and abutment tooth movement measurements were made with a macroperiodontometer. Four conditions were tested by applying unilateral loadings: 1. Single abutments of both sides 2. Load side double abutment 3. Nonload side double abutment 4. Double abutments of both sides The results showed that a significant decrease in the magnitude of movement resulted when the abutment teeth were splinted.     

Correcting a nonparallel implant abutment for a mandibular overdenture retained by two implants: a clinical report

A mandibular overdenture supported by 2 implants is an effective treatment alternative for the maladaptive denture wearer. The implants may be either splinted, using a bar, or nonsplinted and retained by attachments, such as balls or magnets. When the use of a ball attachment is contemplated, the implant abutments should be parallel to one another along the path of insertion. The following report describes the procedure to correct a nonparallel implant abutment to retain a mandibular overdenture.     

Three-dimensional finite element analysis of implant-assisted removable partial dentures

Statement of problem

Whether the implant abutment in implant-assisted removable partial dentures (IARPDs) functions as a natural removable partial denture (RPD) tooth abutment is unknown.

Intrusion Of Teeth In The Combination Implant-to-Natural-Tooth Fixed Partial Denture: A Review of the Theories

This article reviews the literature dealing with the combination implant-to-natural-tooth-supported fixed partial denture. The restoration of masticatory function with a combination implant-to-natural-tooth fixed partial denture is associated with a variety of undesirable clinical sequelae, including the breakage of implant components, damage to the abutment teeth, or intrusion of the abutment teeth. Theories regarding intrusion of abutment teeth combined with implants for fixed partial dentures are only speculative. Several theories are presented to explain the intrusion of natural teeth in association with implant-to-natural-tooth fixed partial dentures. One of the first theories was based on the idea that a lack of normal stimulation of the periodontal ligament produces atrophy of the periodontal ligament and intrusion of the tooth. The remaining theories relate to excessive forces being placed on the natural tooth, resulting in movement of the tooth to a less stressful position. These forces are placed on the tooth by differential energy dissipation, mandibular flexion and torsion, flexion of the fixed partial denture framework, impaired rebound memory, debris impaction or microjamming, or ratchet effect related to the use of precision attachments. Based a review of the literature, a philosophy for treating combination implant-to-natural-tooth restorations is presented.     

Photoelastic stress analysis of implant-tooth connected prostheses with segmented and nonsegmented abutments

STATEMENT OF PROBLEM: There is some question about whether implant abutment selection affects the transfer of load between connected implants and natural teeth. PURPOSE: The purpose of this study was to compare stress transfer patterns with either 1 or 2 posterior implants connected to a single anteriorly located simulated natural tooth with either 1 or 2 segmented and nonsegmented implant abutments under relevant functional loads by use of the photoelastic stress analysis technique. MATERIAL AND METHODS: A model of a human left mandible, edentulous posterior to the first premolar, with two 3.75-mm x 13-mm screw-type implants embedded within the edentulous area, was fabricated from photoelastic materials. The implants were in the first and second molar positions. Two fixed partial denture prosthetic restorations were fabricated with either segmented conical abutments or nonsegmented UCLA abutments. Vertical occlusal loads were applied at fixed locations on the restorations. The photoelastic stress fringes that developed in the supporting mandible were monitored visually and recorded photographically. The stress intensity (number of fringes), stress concentrations (closeness of fringes), and their locations were subjectively compared. RESULTS: Loading on the restoration over the simulated tooth generated apical stresses of similar intensity (fringe order) at the tooth and the first molar implant for both abutment types. Low-level stress was transferred to the second molar implant. Loading directed on the implant-supported region of the restoration demonstrated low transfer of stress to the simulated tooth. Nonvertical stress transfer with slightly higher intensity was observed for the nonsegmented abutment. CONCLUSION: Within the limitations of this simulation study, stress distribution and intensity for the 2 implant conditions was similar for segmented and nonsegmented abutment designs. Magnitude of stresses observed for both abutment designs was similar for the single implant condition. Vertical loading produced more nonaxial stresses away from the force applied for the 1 implant condition with the nonsegmented abutment. Direct loading results were similar for both abutment designs. Specific recommendations for selection of implant abutment and application should be based on clinical criteria.     

The cantilever fixed partial denture--a literature review.

The cantilever fixed partial denture (FPD) is a restoration with one or more abutments at one end and unsupported at the other end. Forces transmitted through the cantilevered pontics can cause tilting and rotational movements of the abutments. In a cross-arch unilateral cantilever FPD, the distal cantilevered unit is subjected to comparatively less force than the contralateral posterior abutment. The unilateral lack of terminal abutments causes lateral bending forces activate peripheral inhibitory feedback reactions from the periodontal and/or temporomandibular mechanoreceptors. The greatest strain in distal cantilevered FPDs is recorded mesial to the most distal retainer because most fractures occur in this location. To improve the prognosis of the FPD cantilever, the number of abutments should be increased and the number of pontics decreased. The abutment teeth need long roots and acceptable alveolar support. Prepared abutments require adequate length and parallel axial walls. An equilibrated and harmonious occlusion is necessary, as well as exemplary oral hygiene. A cantilevered FPD with adequate periodontal support can replace any tooth in the dental arch, but is especially useful as an alternative to a removable partial denture. The cantilevered FPD requires at least two abutment teeth. The only documented exception permitting a single abutment is the replacement of a maxillary lateral incisor with the canine as an abutment. An alternative to the cantilevered FPD is the osseointegrated implant. As osseointegrated implants become more popular, the need for the tooth-supported cantilevered FPD may decline, but it will remain an alternative treatment modality.     

Effects of overdenture attachment systems with different working principles on stress transmission: A three-dimensional finite element study

PURPOSEThe aim of the present study was to compare the stress distributions on the dental implants, abutments, and bone caused by different overdenture attachment types under functional chewing forces.MATERIALS AND METHODSThe 3D finite element models of the mandible, dental implants, attachment types, and prostheses were prepared. In accordance with a conventional dental implant supported overdenture design, the dental implants were positioned at the bone level in the canine teeth region bilaterally. A total of eight models using eight different attachment systems were used in this study. All the models were loaded to simulate chewing forces generated during the centric relationship (450 N), lateral movement (400 N), protrusive movement (400 N), and also in the presence of a food mass unilaterally (200 N). Stress outputs were obtained as the maximum principal stress and the equivalent von-Mises stress.RESULTSIn all attachment types, higher stress values were observed in the abutments, dental implants, and bone in the magnet attachments in different loading conditions. The highest stress values were observed among the magnet systems in the components of the Titanmagnetics model in all loading conditions (stresses were 15.4, 17.7, and 33.1 MPa on abutment, dental implant, and bone, respectively). The lowest stress value was observed in the models of Zest and O-Ring attachments.CONCLUSIONThe results of the present study implied that attachment types permitting rotation and tolerating various angles created lower stresses on the bone, dental implants, and abutments.     

Biomechanical behavior of mandibular overdenture retained by two standard implants or 2 mini implants: A 3-dimensional finite element analysis

Statement of problemMini implants (<3 mm in diameter) are being used as an alternative to standard implants for implant-retained mandibular overdentures; however, they may exhibit higher stresses at the crestal level.PurposeThe purpose of this finite element analysis study was to evaluate the biomechanical behavior (stress distribution pattern) in the mandibular overdenture, mucosa, bone, and implants when retained with 2 standard implants or 2 mini implants under unilateral or bilateral loading conditions.Material and methodsA patient with edentulous mandible and his denture was scanned with cone beam computed tomography (CBCT), and a 3D mandibular model was created in the Mimics software program by using the CBCT digital imaging and communications in medicine (DICOM) images. The model was transferred to the 3Matics software program to form a 2-mm-thick mucosal layer and to assemble the denture DICOM file. A 12-mm-long standard implant (Ø3.5 mm) and a mini dental implant (Ø2.5 mm) along with the LOCATOR male attachments (height 4 mm) were designed by using the SOLIDWORKS software program. Two standard or 2 mini implants in the canine region were embedded separately in the 3D assembled model. The base of the mandible was fixed, and vertical compressive loads of 100 N were applied unilaterally and bilaterally in the first molar region. The material properties for acrylic resin (denture), titanium (implants), mucosa (tissue), and bone (mandible) were allocated. Maximum von Mises stress and strain values were obtained and analyzed.ResultsMaximum stresses of 9.78 MPa (bilaterally) and 11.98 MPa (unilaterally) were observed in 2 mini implants as compared with 3.12 MPa (bilaterally) and 3.81 MPa (unilaterally) in 2 standard implants. The stress values in the mandible were observed to be almost double the mini implants as compared with the standard implants. The stresses in the denture were in the range of 3.21 MPa and 3.83 MPa and in the mucosa of 0.68 MPa and 0.7 MPa for 2 implants under unilateral and bilateral loading conditions. The strain values shown similar trends with both implant types under bilateral and unilateral loading.ConclusionsTwo mini implants generated an average of 68.15% more stress than standard implants. The 2 standard implant–retained overdenture showed less stress concentration in and around implants than mini implant–retained overdentures.     

Posterior implants for distal extension removable prostheses: a retrospective study

Common complaints associated with the Kennedy Class I (bilateral free end) and Class II (unilateral free end) removable partial denture situations are lack of stability, minimal retention, and unesthetic retentive clasping. Some of the same complaints have been reported for implant overdentures with only anterior implants. Starting in 1995, 10 of these patients were treated at the University of Washington with posterior osseointegrated implants to provide stability and/or retention of the removable prostheses, eliminating the need for clasps when possible. This article describes implant alternatives and prosthesis designs and presents a follow-up clinical evaluation of at least 1 year consisting of patient satisfaction, radiographic examination, and soft tissue health. Two groups were evaluated. Group 1 included patients whose implants were used as vertical stops for mandibular distal extension prostheses. Care was taken to ensure that the implants were not loaded laterally by creating a single-point contact at the center of a modified healing abutment. In these cases, sufficient retention was available from the anterior teeth and/or implant abutments. Group 2 included patients whose implants required retention because of lack of adequate tooth abutments. In those cases, a resilient type of attachment was used, which allowed for a small divergence from the path of insertion. Results indicated consistent increased satisfaction in all patients, minimal component wear, no radiographic evidence of excessive bone loss, and stable peri-implant soft tissues.     

Evaluation of a platform-switched Morse taper connection for all-on-four or six treatment in edentulous or terminal dentition treatment: A retrospective study with 1–8 years of follow-up

Background

The survival rate, marginal bone loss and soft tissue health of the Ankylos implants and the balanced base abutments in all-on-four or six implant restoration of edentulous or terminal dentition patients has not been reported in the clinical research.

Purpose

This retrospective study aimed to evaluate the Ankylos implants and the balanced base abutments in all-on-four or six implant restoration of edentulous or terminal dentition patients after 1–8 years of follow-up.

Materials and Methods

A retrospective study was conducted based on the medical records of 33 patients who received all-on-four or six treatments from April 2014 to May 2020. Four radiographic examinations [immediate postoperative (T0), definitive restorations (T1), 1–3 years after prosthetic restorations (T2), and more than 3 years after prosthetic restorations (T3)] were obtained to evaluate vertical bone height (VBH). We also calculated the survival rate and examined the condition of soft tissue with this implant system in edentulous or terminal dentition patients. Three-level linear model analyses were used to explore potential risk factors for VBH changes on the mesial and distal sides. The generalized linear model was used to analyze the influencing factors of BOP and plaque.

Results

A total of 218 implants were included in this study. The cumulative survival rate of the implants was 97.25% before the definitive prosthesis, 96.33% within 3 years of follow-up and 95.32% after more than 3 years of follow-up. The mean ± standard deviation (SD) bone losses of the VBH were 0.27 ± 0.05 mm (T1-T3) on the mesial side and 0.49 ± 0.06 mm (T1-T3) on the distal side. During 1–8 years of follow-up, the height and angle of the abutment (p < 0.001), the mandible implant site (p < 0.001), the length of the implant (p = 0.014 < 0.05) and age (p = 0.029 < 0.05) showed statistically significant effects on vertical mesial bone height (VMBH) and vertical distal bone height (VDBH). The risk of BOP among participants who brushed three times a day was lower than those who brushed less than three times. The plaque risk of short abutment height was higher than the long abutment.

Conclusion

The current study showed that the Ankylos implants with the balanced base abutments in all-on-four or six implants treatment is a viable and predictable option with a high survival rate and low marginal bone loss in edentulous or terminal dentition patients. VBH around the implants was strongly associated with the mandible implant site, abutment height and angle, the length of the implant and age. Moreover, teeth-brushing times and abutment height significantly affect soft tissue health.     

Pre-fabricated zirconium dioxide implant abutments for single-tooth replacement in the posterior region: success and failure after 3 years of function

Objective. Zirconia implant abutments have gained a much broader clinical use over the past few years. The aim of the present study was to assess the clinical performance of a pre-fabricated zirconium dioxide implant abutment for single-tooth replacement in the posterior region. Materials and methods. Forty implants of the XiVE® S plus screw type (DENTSPLY Friadent, Mannheim, Germany) were inserted in the posterior region of 24 patients and provided with zirconium dioxide abutments (FRIADENT® CERCON® Abutment, DENTSPLY Friadent). The following parameters were used to document the state of soft tissue: modified plaque index, modified sulcus bleeding index and pocket depth. Mesial and distal bone levels were determined on radiographs during the prosthetic treatment and at the 36-month recall. Results. Thirty-seven implants could be followed up after 36 months in function. One patient wearing two abutments was lost to follow-up. One abutment exhibited a rotational misfit after 2 years in function. A further abutment showed the same failure at the 36-months recall appointment. In the remaining 36 implants the soft and hard tissue parameters were indicative of a low inflammatory status. Compared to the baseline situation, a partly significant bone apposition could be observed. Chipping of parts of the veneering ceramic was registered in 22% of the remaining implant restorations. Conclusions. The use of zirconia abutments in this study lead to mainly healthy peri-implant hard and soft tissue conditions but, considering the observed failures after 3 years in function, clinical long-term results should be awaited before recommending full zirconia implant abutments in a posterior indication.     

Use of Implant Retained Splint for Vestibuloplasty: Alternative to Conventional Technique

It is generally agreed that firmly attached keratinized mucosa surrounding the implant and abutment is thought to provide additional protection against mechanical trauma. Inflammation of soft tissue can result in peri-implantitis [1] with marginal bone loss or hyperplasia of surrounding mucosa. The purpose of this article is to describe our experience in using the two dental implants placed in the canine region in completely edentulous mandible and implant retained denture as a stent for vestibuloplasty.     

Analysis of abutment tooth movement utilizing mandibular kinesiography (MKG). Part 2. Effects of clasp design in unilateral free-end denture

The three-dimensional dynamic movement of the abutment tooth was successfully analyzed on a simulation model utilizing the mandibular kinesiography. When the unilateral free-end denture retained by the RPA, RPI or Aker's clasp was subjected to various directions of loads, the abutment tooth was inclined mainly by the sliding displacement of the denture over the alveolar ridge and the lever action around the denture. The Aker's clasp assembly induced the largest tooth movement. The RPA clasp generally exhibited similar tendencies to the Aker's clasp, showing a larger tooth inclination in the disto-buccal direction. The RPI clasp seemed to be preferable for protecting the periodontal tissues from damage associated with unfavorable tooth movements since it induced less distal tooth inclination.