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.

Il danno dentale in protesi fissa: aspetti valutativi medico-legali

Objectives

Through a critical review of the most recent literature about fixed prosthesis on natural pillars, the authors discuss the quantification of permanent biological damage of the teeth used as prosthetic abutments.

Materials and methods

In cases of traditional fixed prosthetic rehabilitation, preparation of the natural elements that serve as a pillar inevitably shapes an irreversible injury of the coronal hard tissues, recognized by the customary forensic evaluation even if in the absence of specific tabular values. However, what is not taken into account usually is the share of permanent biological damage resulting from the reprocessing of stumps needed for a new prosthetic rehabilitation, whether it is a future renewal in civil liability cases or a remake of structure considered incongruous in professional liability cases. The physiological changes of the periodontal tissues of the tooth, resulting in a progressive exposure of the prosthetic margin and of the root tissue, or the design of a prosthetic device with overhanging margins and incongruous emergency profiles require the clinician to re-prepare the abutment before the implementation of the new manufacture.

Results

The loss of dental hard tissue caused by multiple prosthetic filings correlates with a progressive reduction in the size of the abutment, with its consequent weakening and exposure to an increased risk of fracture. This condition inevitably affects the degree of survival of the corresponding prosthetic device, which must be replaced by a prosthesis longer than the previous one, or even another type of prosthesis, if not more repeatable with the same characteristics.

Conclusions

The irreversible loss of dental tissue resulting after prosthetic reprocessing makes necessary an adequate medicolegal evaluation of the damage, which aims to identify the clinical expression of the injury and resulting impairment in its fullness.     

Clinical performance of cantilevered fixed dental prostheses abutments in the shortened dental arch

Objectives

This article is part of a randomized clinical trial on different treatments in the shortened dental arch (SDA). It focused on the abutment tooth prognosis with cantilevered fixed dental prostheses (CFDPs).

Methods

Sixty-two patients with a bilaterally SDA up to the first or second premolar in the mandible or maxilla were evaluated. In 57 of 124 quadrants, second premolars were replaced by a CFDP (cantilever group). In the remaining 67 quadrants, a natural second premolar was present and thus no need for a CFDP was given (non-cantilever group). Patients were recalled annually up to 5 years.

Results

The mean observation period was 56.3 months (min. 3.0, max. 76.2, SD 16.1). Kaplan–Meier survival rates concerning tooth loss and tooth fracture were 93.9%/94.0% in the cantilever group and 91.9%/92.8% in the non-cantilever group. Differences between both groups were not significant. The survival rate concerning loss of retention of CFDP retainers was 92.1% in the cantilever group.

Conclusion

After 5 years of clinical service, CFDPs for the replacement of the second premolar showed no negative impact on the abutment tooth prognosis.

Clinical significance

Cantilevered fixed dental prostheses present a viable treatment option in the shortened dental arch without compromising the medium-term abutment tooth prognosis.     

Usage of removable partial dentures in Saudi male patients after 1 year telephone interview

Objective

The success of removable partial dentures (RPDs) is partly dependent on patients’ acceptance and compliance in using them. The purpose of this study was to describe the usage of removable partial dentures (RPDs) by patients 1 year after insertion and to evaluate the factors that influence their denture usage.

Methods

Forty-seven patients who received 75 new RPDs at the undergraduate clinic of College of Dentistry, King Saud University, were contacted by telephone 1 year later for an interview. The questions covered denture usage, patient’s satisfaction and reasons for non-use.

Results

Results showed that 36% of patients discarded or occasionally used their RPDs. There was no significant association between denture usage and RPD experience, location or Kennedy classification. A significantly more RPD rejection was found when it was opposed by natural teeth or complete denture. The most quoted reason for RPD rejection was pain and discomfort.

Conclusion

Despite the short follow-up period, RPDs were poorly accepted by patients treated by undergraduate students.     

A novel dental implant abutment with micro-motion capability—Development and biomechanical evaluations

Objective

The aim of this study was to develop a novel dental implant abutment with a micro-motion mechanism that imitates the biomechanical behavior of the periodontal ligament, with the goal of increasing the long-term survival rate of dental implants.

Methods

Computer-aided design software was used to design a novel dental implant abutment with an internal resilient component with a micro-motion capability. The feasibility of the novel system was investigated via finite element analysis. Then, a prototype of the novel dental implant abutment was fabricated, and the mechanical behavior was evaluated.

Results

The results of the mechanical tests and finite element analysis confirmed that the novel dental implant abutment possessed the anticipated micro-motion capability. Furthermore, the nonlinear force–displacement behavior apparent in this micro-motion mechanism imitated the movement of a human tooth. The slope of the force–displacement curve of the novel abutment was approximately 38.5 N/mm before the 0.02-mm displacement and approximately 430 N/mm after the 0.03-mm displacement.

Significance

The novel dental implant abutment with a micro-motion mechanism actually imitated the biomechanical behavior of a natural tooth and provided resilient function, sealing, a non-separation mechanism, and ease-of-use.     

Survival of anterior cantilevered all-ceramic resin-bonded fixed dental prostheses made from zirconia ceramic

Objectives

This study evaluated the clinical outcome of all-ceramic resin-bonded fixed dental prostheses (RBFDPs) with a cantilevered single-retainer design made from zirconia ceramic.

Methods

Forty-two anterior RBFDPs with a cantilevered single-retainer design were made from yttrium oxide-stabilized zirconium oxide ceramic. RBFDPs were inserted using Panavia 21 TC as luting agent after air-abrasion of the ceramic bonding surface.

Results

During a mean observation time of 61.8 months two debondings occurred. Both RBFDPs were rebonded using Panavia 21 TC and are still in function. A caries lesion was detected at one abutment tooth during recall and was treated with a composite filling. Therefore, the overall six-year failure-free rate according to Kaplan–Meier was 91.1%. If only debonding was defined as failure the survival rate increased to 95.2%. Since all RBFDPs are still in function the overall survival rate was 100% after six years.

Conclusions

Cantilevered zirconia ceramic RBFDPs showed promising results within the observation period.

Clinical Significance

Single-retainer resin-bonded fixed dental prostheses made from zirconia ceramic show very good mid-term clinical survival rates. They should therefore be considered as a viable treatment alternative for the replacement of single missing anterior teeth especially as compared to an implant therapy.     

Survival rate of endodontically treated teeth with posts after prosthetic restoration

The purpose of this retrospective clinical study was to evaluate the survival rate of teeth that were endodontically treated and restored with endodontic posts and prosthodontic restorations. A total of 864 teeth in 360 patients were included in the study. Dental records and radiographs of the patients were evaluated and four parameters were documented. The parameters were type of post, type of prosthodontic restoration, observation time, and, in cases of failure, failure mode. Statistical survival analyses were performed according to Kaplan-Meier. The mean observation time was 22.5 +/- 14.9 months. The calculated survival rates of the abutments were statistically significant different for fixed partial dentures (FPDs) and for removable partial dentures (RPDs) with survival rates of 92.7% and 51.0% after 60 months, respectively. Most of the presumed factors influencing the survival rate of endodontically treated abutment teeth only affected the outcome in the RPD group. Teeth restored with post and cores present a high risk for failure when used as abutments for conical-double-crown-retained RPDs.     

A 3-year retrospective and clinical follow-up study of zirconia single crowns performed in a private practice

Objectives

All-ceramic crowns have become increasingly used also in the posterior regions, but there are only few studies documenting the clinical outcome of these restorations. The aim was therefore to present the 3-year outcome of zirconia (NobelProcera™) single crowns.

Methods

All patients treated with porcelain-veneered zirconia single crowns in a private practice during the period October 2004 to November 2005 were included. The patient records were scrutinized for data on the restorations and the supporting teeth. Information was available for 161 patients and 204 crowns. At the 3-year recall appointments, a sample of 18 patients with 25 crowns was clinically examined and interviewed regarding patient satisfaction.

Results

Most crowns (78%) were placed on premolars and molars. The clinical outcome of the crowns was favourable. No zirconia core fractured and no caries was observed on the abutment teeth. Some types of complication were recorded for 32 (16%) crowns or abutment teeth. The most severe complications, in total 12 restorations (6%), were recorded as failures: abutment tooth was extracted (5), remake of crown due to lost retention (4), veneer fracture (2) and persistent pain (1). The CDA criteria for 25 crowns were rated favourably, and patient satisfaction with the zirconia crowns was in general high.

Conclusions

The porcelain-veneered zirconia crowns (NobelProcera™) showed good clinical results, were well accepted by the patients, and only few complications were reported over the 3-year follow-up period.     

Accuracy of CAD-CAM-fabricated removable partial dentures

Statement of problem

The conventional fabrication of removable partial dentures (RPDs) is a complex, error-prone, time-consuming, and expensive process. The use of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques, especially rapid prototyping, promises a more effective method for fabricating RPD frameworks.

Long-term survival of endodontically treated,maxillary anterior teeth restored with either tapered or parallel-sided glass-fiber posts and full-ceramic crown coverage

Objectives

This retrospective study investigated the clinical effectiveness over up to 8 years of parallel-sided and of tapered glass-fiber posts, in combination with either hybrid composite or dual-cure composite resin core material, in endodontically treated, maxillary anterior teeth covered with full-ceramic crowns.

Methods

The study population comprised 192 patients and 526 endodontically treated teeth, with various degrees of hard-tissue loss, restored by the post-and-core technique. Four groups were defined based on post shape and core build-up materials, and within each group post-and-core restorations were assigned randomly with respect to root morphology. Inclusion criteria were symptom-free endodontic therapy, root-canal treatment with a minimum apical seal of 4 mm, application of rubber dam, need for post-and-core complex because of coronal tooth loss, and tooth with at least one residual coronal wall. Survival rate of the post-and-core restorations was determined using Kaplan–Meier statistical analysis.

Results

The restorations were examined clinically and radiologically; mean observation period was 5.3 years. The overall survival rate of glass-fiber post-and-core restorations was 98.5%. The survival rate for parallel-sided posts was 98.6% and for tapered posts was 96.8%. Survival rates for core build-up materials were 100% for dual-cure composite and 96.8% for hybrid light-cure composite.

Conclusions

For both glass-fiber post designs and for both core build-up materials, clinical performance was satisfactory. Survival was higher for teeth retaining four and three coronal walls.     

Quantification of residual dentine thickness following crown preparation

Objectives

Pulpal response to tooth preparation is a major concern in fixed prosthodontics. Research has suggested that 2 mm or more of remaining dentine is critical in protecting the pulp following tooth preparation. However, clinicians have no means of knowing dentine thickness either before or after preparation and therefore lack feedback about this important aspect of preparation quality. The aim of this project was to develop a method for measuring local dentine thickness following tooth preparation for metal ceramic crowns, in vitro, which could be used as a tool to evaluate preparation technique and instrumentation.

Methods

Microtomography (XMT or micro-CT) scans were taken of extracted teeth before and after crown preparation. Local dentine thickness was defined for every voxel within the 3D tooth image as the sum of distances from that voxel to the pulp and to the anatomical surface. The method also allows the thickness of material removed to be quantified. Three-dimensional colour-coded maps of dentine thickness were generated, and the distributions of dentine thickness throughout the teeth were analysed. This was tested by a single operator on sixteen extracted upper central incisors.

Results

This method enabled clear visualisation and analysis of residual dentine thickness. In the trial, it revealed consistent over-prepared regions along the labial proximal line angles which, in a clinical case, could affect subsequent tooth and restoration longevity. All but one of the prepared teeth had regions with a residual dentine thickness of less than 1.5 mm, in 6 it was less than 1.0 mm and in 3 of these it was less than 0.5 mm.

Conclusion

Although ex vivo, this method can be used as a research tool to look for patterns of over- or under-preparation, leading to possible modification of technique, instrumentation and, or crown design.

Clinical significance

It is not currently possible for clinicians to know the thickness of residual dentine following crown preparation, a key factor in long term outcome. The described method of quantifying and visualising this thickness allows preparation techniques and instrumentation to be evaluated in vitro, leading to prospective improvements in clinical procedures.     

The Effect of Rubber Dam Usage on the Survival Rate of Teeth Receiving Initial Root Canal Treatment: A Nationwide Population-based Study

Introduction

It is well-known that the usage of rubber dams during root canal treatment (RCT) improves infection control and treatment efficacy and protects patients. However, the effect of rubber dam usage on endodontic outcomes remain uncertain. The aim of the present study was to investigate whether rubber dam usage affects the survival rate of initial RCT using a nationwide population-based database.

Methods

A total of 517,234 teeth that received initial RCT between 2005 and 2011 met the inclusion criteria and were followed until the end of 2011. Univariate and multivariate Cox proportional hazards models were used to estimate the effects of rubber dam usage on the risk of tooth extraction after initial RCT.

Results

Of the 517,234 teeth, 29,219 were extracted, yielding a survival rate of 94.4%. The survival probability of initial RCT using rubber dams after 3.43 years (the mean observed time) was 90.3%, which was significantly greater than the 88.8% observed without the use of rubber dams (P < .0001). After adjusting for age, sex, tooth type, hospital level, tooth scaling frequency per year after RCT, and systemic diseases, including diabetes and hypertension, the tooth extraction hazard ratio for the RCT with rubber dams was significantly lower than that observed for RCT without rubber dams (hazard ratio = 0.81; 95% confidence interval, 0.79-0.84).

Conclusions

The use of a rubber dam during RCT could provide a significantly higher survival rate after initial RCT. This result supports that rubber dam usage improves the outcomes of endodontic treatments.     

Experimental research on the relationship between fit accuracy and fracture resistance of zirconia abutments

Objectives

The purpose of the study was to investigate the correlation between fit accuracy and fracture resistance of zirconia abutments, as well as its feasibility for clinical applications.

Methods

Twenty self-made zirconia abutments were tested with 30 Osstem GSII implants. First, 10 Osstem GSII implants were cut into two parts along the long axis and assembled with the zirconia abutments. The microgaps between the implants and the zirconia abutments were measured under a scanning electron microscope. Second, the zirconia abutments were assembled with 20 un-cut implants and photographed before and after being fixed with a central screw of 30-N cm torque. The dental films were measured by Digora for Windows 2.6 software. Then the fracture resistance of zirconia abutments was measured using the universal testing machine at 90°. All results were analyzed using SPSS13.0 software.

Results

The average internal-hexagon microgaps between the implants and zirconia abutments were 19.38 ± 1.34 μm. The average Morse taper microgap in the implant–abutment interface was 17.55 ± 1.68 μm. The dental film showed that the Morse taper gap in the implant–abutment interface disappeared after being fixed with a central screw of 30-N cm torque, and the average moving distance of the zirconia abutments to the implants was 0.19 ± 0.02 mm. The average fracture resistance of zirconia abutments was 282.93 ± 17.28 N. The internal-hexagon microgap between the implants and zirconia abutments was negatively related to the fracture resistance of the abutments (r₁ = −0.97, p < 0.01). The Morse taper microgap in the implant–abutment interface was negatively related to the fracture resistance of the abutments (r₂ = −0.84, p < 0.01).

Conclusions

The microgap between implant and abutment was negatively related to the fracture resistance of the abutment, while the internal-hexagon microgap has better correlation than the Morse taper microgap. The closure of microgap is helpful to improve the fracture resistance of zirconia abutments. The fracture resistance of zirconia abutments can satisfy the clinical application.     

Microbiological risk for periodontitis of abutment teeth in patients with removable partial dentures

Summary  Tannerella forsythia , Porphyromonas gingivalis and Treponema denticola are identified as the red complex which exists in high proportions in periodontally diseased patients. The aim of this study was to assess the microbiological risk for periodontitis of abutment teeth in subjects wearing removable partial dentures (RPDs) by measuring the red complex using BANA-ZymeTM test. Thirty-eight subjects (mean age: 62·2 years) with Kennedy Class II partially edentulous arch participated in this study. The red complex and clinical parameters, such as plaque index, gingival index, probing depth and tooth mobility were recorded at abutment teeth in contact with the direct retainer of unilaterally designed RPDs and the corresponding non-abutment teeth on the opposite side. Mean scores for the red complex, plaque index, gingival index and tooth mobility of the abutment teeth were significantly greater than those of the non-abutment teeth ( P  < 0·01). No significant mean difference in pocket depth was found between the abutment and non-abutment teeth. Logistic regression analysis revealed that abutment teeth, high scores of plaque index and a maintenance interval longer than 6 months were significant predictors for positive red complex scores ( P  < 0·05). These results suggest that the microbiological risk for periodontitis of abutment teeth is greater than that for non-abutment teeth in RPD wearers.     

Long-term clinical evaluation of 211 two-unit cantilevered resin-bonded fixed partial dentures

Objectives

This retrospective study aims to evaluate the long term clinical performance of two-unit cantilevered resin-bonded fixed partial dentures (RBFPDs) relating to their retention, success and survival rate.

Materials and methods

Prostheses that were placed at least four years previously were clinically reviewed to evaluate retention, success and survival rate. Additional information was also collected, including patient's gender, age and satisfaction on their prosthesis, operator's experience, prosthesis service life, root canal therapy if performed, abutment mobility, bone support, the presence of shim-stock contacts on the abutment or pontic in intercuspal position, and the presence of proximal axial contacts adjacent to the prosthesis. The date of any debonding with subsequent treatment was also recorded.

Results

A total of 211 two-unit RBFPDs were placed in 153 patients, with a mean service life of 113.2 ± 33.5 months. Twenty-eight prostheses debonded, resulting in a retention rate of 86.7 percent, and another five teeth were extracted with the prostheses, resulting in a success rate of 84.4 percent. 90.0 percent prostheses were functioning (survival rate) by means of rebonding at the time of review. The location of the replaced tooth had a significant effect on the retention of RBFPDs with posterior RBFPDs lower than anterior (p = 0.020). Kaplan–Meier analysis revealed 5-, 10- and 15-year cumulative probability of surviving was 0.97, 0.91 and 0.84, respectively.

Conclusions

211 two-unit RBFPDs were observed to have a success, retention and survival rate of 84.4, 86.7 and 90.0 percent, respectively, with a mean service life of 9.4 years.

Clinical Significance

Based on the clinical results, two-unit RBFPD are shown to be a durable prosthesis over the long term with high patient satisfaction. The posterior prostheses, particularly in the lower arch appeared to have a higher failure rate, and improved design features should be considered.     

Effect of direct retainer and major connector designs on RPD and abutment tooth movement dynamics

Designs of removable partial dentures are suggested to affect the mobility of abutment teeth and removable partial denture (RPD) during oral functions. This study aimed to examine the effect of direct retainer and major connector designs on RPD dynamics under simulated loading. Six different Kennedy class II maxillary RPDs were fabricated on a maxillary model. These dentures involved 3 different direct retainers (wrought-wire clasp, RPA clasp, and conical crown telescopic retainer) and 2 different major connectors (Co-Cr major connector and heat-cured acrylic resin with a metal strengthener). Using an experimental model with simulated periodontal ligaments and mucosa that were fabricated using silicone impression material, three-dimensional displacements of the RPDs were measured under a simulated 30-N loading with a displacement transducer type M-3. Significant effects of "direct retainer design" on bucco-palatal displacements and "major connector" on mesio-distal displacements were revealed by 2 x 3 two-way analysis of variance of abutment teeth movements (P < 0.001 and P = 0.002, respectively). Additionally, analysis of variance of RPD displacements revealed significant effects of "direct retainer design" on corono-apical displacements and "major connector" on mesio-distal displacements (P = 0.001 and P = 0.028, respectively). Rigid direct retainers and rigid major connectors decrease the movements of both abutment tooth and RPD.     

A possible risk of CAD/CAM-produced composite resin premolar crowns on a removable partial denture abutment tooth: a 3-year retrospective cohort study

Purpose

To evaluate the early performance of computer-aided design/computer-aided manufacturing (CAD/CAM)-produced composite resin crown (CAD/CAM composite crown) treatment on premolars, specifically, placement on a removable partial denture (RPD) abutment tooth, and the distalmost tooth in the dental arch, as possible clinical risk factors.

Impact of diabetes mellitus, hypertension, and coronary artery disease on tooth extraction after nonsurgical endodontic treatment

Introduction

Limited prospective data are available on the long-term prognosis of teeth receiving nonsurgical root canal treatment (NSRCT) in patients with systemic diseases including diabetes mellitus (DM), hypertension (HT), and coronary artery disease (CAD). This prospective study aimed to elucidate the impact of systemic diseases on the risk of tooth extraction after NSRCT.

Methods

A total of 49,334 NSRCT teeth were randomly selected from databank in October 2003 and were followed for 2 years for tooth extraction after NSRCT. Cox proportional hazards model was used to estimate the risk of tooth extraction after NSRCT.

Results

Of the 49,334 teeth, 1592 (3.2%) were extracted during the 2-year follow-up period, yielding a 2-year tooth retention rate of 96.8%. We found that DM (hazard ratio [HR], 1.79), HT (HR, 1.75), and CAD (HR, 1.70) were significant risk factors for tooth extraction after NSRCT (all P values <.0001) in univariate Cox proportional analyses. After adjustment for age, gender, and tooth type in multivariate analyses, DM (HR, 1.29) and HT (HR, 1.18) remained as independent risk factors (both P values <.05). Simultaneous possession of 2 diseases of DM, HT, and CAD was a significant and robust predictor for an increased long-term risk of tooth extraction after NSRCT (P for trend <.001).

Conclusions

An increased risk of tooth extraction after NSRCT is significantly associated with DM, HT, and CAD individually. Moreover, the constellation of systemic disease burden also manifests the importance in addition to other potential confounders.     

Fracture analysis of randomized implant-supported fixed dental prostheses

Objective

Fractures of posterior fixed dental all-ceramic prostheses can be caused by one or more factors including prosthesis design, flaw distribution, direction and magnitude of occlusal loading, nature of supporting infrastructure (tooth root/implant), and presence of adjacent teeth. This clinical study of implant-supported, all-ceramic fixed dental prostheses, determined the effects of (1) presence of a tooth distal to the most distal retainer; (2) prosthesis loading either along the non-load bearing or load bearing areas; (3) presence of excursive contacts or maximum intercuspation contacts in the prosthesis; and (4) magnitude of bite force on the occurrence of veneer ceramic fracture.

Methods

89 implant-supported FDPs were randomized as either a three-unit posterior metal–ceramic (Au–Pd–Ag alloy and InLine POM, Ivoclar, Vivadent) FDP or a ceramic–ceramic (ZirCAD and ZirPress, Ivoclar, Vivadent) FDP. Two implants (Osseospeed, Dentsply) and custom abutments (Atlantis, Dentsply) supported these FDPs, which were cemented with resin cement (RelyX Universal Cement). Baseline photographs were made with markings of teeth from maximum intercuspation (MI) and excursive function. Patients were recalled at 6 months and 1–3 years. Fractures were observed, their locations recorded, and images compared with baseline photographs of occlusal contacts.

Conclusion

No significant relationship existed between the occurrence of fracture and: (1) the magnitude of bite force; (2) a tooth distal to the most distal retainer; and (3) contacts in load-bearing or non-load-bearing areas. However, there was a significantly higher likelihood of fracture in areas with MI contacts only.

Clinical significance

Because of the absence of a periodontal ligament, this clinical study demonstrates that there is a need to evaluate occlusion differently with implant-supported prostheses than with natural tooth supported prostheses. Implant supported prostheses should have minimal occlusion and lighter contacts than those supported by natural dentition.

Clinical Trials.gov No

K23 D2007-46.     

The restoration of permanent immature anterior teeth,root filled using MTA: A review

Objectives

Immature anterior teeth are at high risk of root fracture following root canal treatment. The literature was explored to determine the current status for post-endodontic restorative management of these teeth.

Data and sources

The authors explored multiple search engine databases to November 2008. Experiments included in the review involved simulated human or animal immature teeth with mineral trioxide aggregate as an apical plug. The experiments were designed to assess and compare the fracture strength of teeth restored with various materials. Studies that did not fulfil inclusion criteria were omitted from the review.

Study selection

Four in vitro studies fulfilled selection criteria and were systematically reviewed. All studies differed in sources of teeth, their simulated immature tooth model and mode of force application.

Clinical Implications

Current evidence, mostly from laboratory studies, suggests the use of composite resin materials placed deep into the coronal aspect of the root canal to impart superior fracture resistance. Further clinical research is needed to assess other reinforcing materials, which include a variety of post systems and luting agents.