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JADA Specialty Scan - Prosthodontics
 
Prosthodontics - A Quarterly Newsletter on Dental SpecialtiesJADA Specialty Scan

Single-implant and interproximal contact loss

Biological and mechanical complications may lead to interproximal contact loss (ICL) between fixed implant prostheses and adjacent teeth. A team of researchers investigating the prevalence of such complications discovered that more than one-half of the single-implant restorations it evaluated experienced ICL.

In an article published in the September/October 2016 issue of The International Journal of Oral & Maxillofacial Implants, the authors wrote, “... open contacts create food impaction, which may lead to periodontal defects and recurrent tooth decay. To prevent tooth decay and implant-tooth periodontal sequelae, a new proximal contact may have to be established between the implant prosthesis and adjacent tooth.”

Researchers aimed to provide guidelines, based on the outcomes of their retrospective, cross-sectional study, to prevent ICL.

They chose 128 patients seen at recall appointments at Columbia University College of Dental Medicine (CU CDM), New York, NY, and at a private faculty clinic for the study. The male and female study participants, aged 19 through 91 years, collectively had 174 single-implant restorations inserted in the posterior or anterior region. They received implant crowns at CU CDM's postgraduate prosthodontic program and at the private faculty practice.

Researchers verified interproximal contacts with 0.07-millimeter–thick dental floss and radiographs at the time of insertion. CU CDM prosthodontic residents and faculty evaluated the implant restorations at recall appointments from 3 months through 11 years after insertion.

In their evaluations, researchers considered a contact to be open if floss passed without resistance from adjacent teeth. They also used visual confirmation for ICL identification along with radiographic verification. If 1 implant restoration had both mesial and distal contact openings, they recorded 2 ICLs.

This pilot study included the prevalence of ICL, the presence or absence of food impaction, and patient's awareness of ICL, wrote the authors. They collected data on the implant crown’s location, date of insertion, whether the open contact was mesial, distal, or both (verified via floss, visual confirmation, and radiographs), the patient’s awareness of ICL and food impaction (via clinical examination and patient inquiry).

After observing that 52.8% of the studied implant restorations demonstrated ICL—78.2% mesial versus 21.8% distal—the authors offered clinical suggestions. “Due to the high prevalence of ICL, techniques should incorporate retrievable implant restorations,” they wrote. “Cement-retained implant crowns should use provisional cement and a Whitehead box to facilitate crown removal. The high prevalence of ICL is justification for proper informed consent. It is the clinician’s obligation to inform the patient of ICL as a potential implant complication. Patient awareness may prevent additional complications.”

The authors also suggest the use of an Essix retainer to prevent the ICL between the implant restoration and the adjacent tooth.

Noting that, “The phenomenon of ICL seems to be multifactorial,” the researchers also concluded that further research is needed to identify causative factors, which make ICL very difficult to prevent.

The cited limitations of this pilot study included not examining opposing dentition, angle classification, parafunctional habit, prior orthodontic therapy, mobility of adjacent teeth, type of implant restoration (screw versus cemented), and exact time that open contact was made. “Future studies will investigate these parameters that could play an important role in the contribution of ICL,” the researchers wrote.

Read the original article.

 

Consulting Editor: Donald A. Curtis, DMD, FACP
Diplomate, American Board of Prosthodontics Professor,
University of California San Francisco

Relationship between fixed restoration fractures and bruxism

Implant-borne ceramic veneers are prone to fracture, and a new investigation indicates that this tendency may pose additional risk for bruxers.

German researchers—working in the Department of Prosthetic Dentistry, Dental School, University Hospital Carl Gustav Carus, Dresden University of Technology, Dresden, Germany—conducted a retrospective clinical study based on a hypothetical correlation between bruxism and ceramic veneer fractures. The study was published in the May/June 2016 issue of The International Journal of Prosthodontics.

Osseointegrated implants, ankylosed directly to bone, lack mechanoreceptors and pulp receptors of natural teeth. These mechanisms provide tactile sensitivity and moderate the impact of mastication, protections that are no longer available after the implantation of replacement prostheses. Bruxers are particularly exposed to additional force against their fixed restorations.

To determine the relationship between ceramic veneer fractures and bruxism, if any, the researchers recruited 144 adult patients 18 years or older who received a collective 507 implant-borne porcelain-fused-to-metal (PFM) or veneered zirconium dioxide all-ceramic (AC) fixed dental restorations from January 1995 through August 2011. The researchers subdivided the restorations and units into 2 groups, PFM and AC. Of the 507 restorations, 483 PFM and 24 AC were included in the analysis. “Of these units, 291 represented single crowns (SCs) or splinted crowns (SCCs) (278 PFM, 13 AC), 28 represented implant-borne fixed dental prostheses (FPDs) (28 PFM, 0 AC), 16 were implant-tooth borne FPDs (14 PFM, 2 AC), and 14 were implant-borne cantilevered FPDs (13 PFM, 1 AC).”

Study patients self-reported bruxism by means of a questionnaire that included 12 simple questions to which they answered yes or no about possible parafunctional habits. In addition, these participants submitted to a clinical examination, in which researchers recorded the presence of occlusal wear facets, tongue and/or cheek impressions, and wedge-shaped defects.

The researchers conducted the clinical examination under relatively dry conditions and noted any present ceramic veneer fracture that they classified in 1 of 4 defect type groups, reflecting extent and position. These defect type groups included —

  • group A: no fracture, intact restoration;
  • group B: acceptable fracture/chipping, polishing possible, good function and esthetics;
  • group C: acceptable fracture, fracture reaches framework, intraoral repair possible, poor function and esthetics;
  • group D: unacceptable fracture, new restoration needed, poor function and esthetics.

Ultimately, the researchers diagnosed bruxism in 69 (47.9%) of the participants. “Of the examined patients, 9 used an occlusal splint,” noted the authors. “Bruxism significantly affected (P = .002) the prevalence of ceramic fractures, and bruxers had 3.6 times higher odds than nonbruxers. Nonbruxers demonstrated only minor defects (group B), while in the bruxer group larger defects (group C) were also detectable. No fracture of a unit in group D was detected.”

The small number of AC restorations in this study did not allow for their statistical evaluation, the authors wrote.

The conclusion drawn, respecting the limitations of the retrospective study design, is that bruxism poses a risk for ceramic veneer fractures in implant-borne fixed dental prostheses.

The authors noted that occlusal splints may protect against veneer fractures in bruxers and could be recommended for prevention; however, only 9 patients in this study used splints. They observed “a slightly higher fracture prevalence in nonsplinted compared with splinted SCs in bruxers, without statistical significance. Because of the wide confidence interval, this observation should be carefully interpreted.”

Read the original article.

 
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Intraoral digital scanner maintenance

German researchers’ inability to produce consistent outcomes using comparable settings with identical intraoral digital scanners after 18 months led them to test whether manufacturer maintenance through regular calibration improved accuracy.

In an article published in the January/February 2017 issue of The International Journal of Prosthodontics, researchers from the Department of Prosthodontics, School of Dental Medicine, Justus-Liebig-University, Giessen, Germany, reported how they fabricated a laser-sintered cobalt-chromium master model based on a Frasaco model of the maxilla. They inserted into the model a second molar, a second premolar, and a central incisor that they had separately machine milled with a cone angle of 4 degrees and a shoulder margin. They digitized the final master model using a Nikon LC 15DX laser scanner with an accuracy of ± 3.5 micrometers and saved in the standard tessellation language (STL) file format as a reference data set.

They tested three manufacturers’ scanners, one of which served as a control because they did not see a difference in the results for it after 18 months.

After prescribed calibration of the devices according to the manufacturers’ guidelines, 10 scans per device were obtained. “All scans were exported to STL format and compared to the master scan (GOM Inspect) … ,” wrote the researchers. “Subsets of the entire scan representing the prepared teeth were analyzed separately. The mean deviation (positive and negative) was calculated for the superimposed areas. The data were tested for normal distribution (Kolmogorov-Smirnov). Analysis of variance was used to check for significant differences among all groups. In case of significant differences, Dunnett C test was applied (SPSS 19, IBM).”

Outcomes indicated to the researchers that “There were no significant differences among all systems after calibration, including the [control]. The positive and negative deviations observed were comparable. Results clearly indicate that at least some intraoral scanning systems are prone to decalibration and thus loss of accuracy that the user cannot directly recognize.”

In fact, the authors say they found that after inspection and calibration, both of the scanners tested were significantly more accurate for the single preparation and for the entire arch.

The conclusion drawn is that manufacturers should establish and provide regular maintenance for their intraoral digital scanner systems as some “seem to be sensitive to hardware decalibration that is invisible to the user” even while showing high accuracy.

“From a technical viewpoint, all these systems are high-precision, sensitive optical instruments,” wrote the authors. “Any shock applied to them (eg, concussions and vibrations while moving the system around or even dropping of the camera) may be expected to foster decalibration. The problem is that—at least in the cases reported—this decalibration was not discernible, the system software did not offer any hint in this regard, and the systems worked without visible problem.”

A decalibrated system, said the authors, does not necessarily lead to clinically unacceptable results or completely nonfitting restorations.

Read the original article.

 

Digital workflow compositing and virtual patients for restorations

Merging output from 3-dimensional (3D) digital imaging technologies to create a virtual patient may be useful in noninvasive simulations.

Enhanced virtual patient simulations can improve the modeling of potential dental and medical treatments, outcomes and patient–health care provider communication for more effective restorations, say researchers in a clinical report published online September 22, 2016, in The Journal of Prosthetic Dentistry.

The report compares the benefits and drawbacks of digital imaging technologies—some strong at capturing hard tissue and others strong at capturing soft tissues—and then demonstrates how combining them into composites can yield a more realistic 3D virtual patient.

The authors describe building a digital workflow that incorporates technologies developed for implant dentistry, including cone-beam computed tomography (CBCT) and intraoral and extraoral scanning—3D imaging modalities; digital photographs—2D imaging, virtual implant planning software; and computer-aided design and computer-aided manufacturing (CAD-CAM) surgical templates and prostheses.

“Studies have shown that 3D volumetric data from the CBCT (hard tissue) and extraoral 3D facial surface acquisition (soft tissue) can be merged to create a 3D composite virtual craniofacial model, allowing the concurrent assessment of both hard and soft tissues,” the authors wrote.

To illustrate their merger proposal, the authors describe using a digital workflow combining various technologies to treat a partially edentulous, 48-year-old woman. They composited images from the various technologies to create a 3D virtual patient as illustrated in the article. “The 3D virtual patient was used in the VSD [virtual smile design] and treatment planning process of computer-guided implant surgery and CAD-CAM interim fixed and removable dental prostheses,” they wrote.

The described digital workflow details the handling and integration of file formats used by the various technologies, including the Digital Imaging and Communications in Medicine (DICOM) files of CBCT imaging, the standard tessellation language (STL) files of intraoral optical scans, the Joint Photographic Experts Group (JPEG) file format of digital photographs, and the Polygon File Format (PLY) files of 3D extraoral facial scan.

The authors forwarded the collected digital diagnostic imagery in the various file formats to a dental laboratory over a secure Internet server. According to the authors, “A complete 3D virtual patient with realistic facial soft tissue (data obtained from extraoral scanner and digital camera), craniofacial hard tissue (data obtained from CBCT imaging), and remaining dentition (data obtained from CBCT imaging) was then created at the patient’s exaggerated smile under static conditions.”

Clinicians used the resulting 3D virtual patient to assist the virtual diagnostic tooth arrangement process and provide the patient with a pleasing preoperative virtual smile design harmonized with her facial features. They also used the 3D virtual patient as a communication tool to obtain pretreatment approval from the patient. Ultimately, they designed a prosthetically driven surgical plan for computer-guided implant surgery and fabricated an interim prosthesis.

Aside from yielding a more fully realized 3D virtual patient via merged files, the described digital workflow is cost conscious, say the authors, as is the associated clinical treatment plan.

“The main advantage of this proposed clinical treatment workflow was to eliminate the need for dental clinicians to obtain expensive dental/medical extraoral 3D surface imaging systems and to incorporate a 3D virtual patient with realistic appearance into the preoperative diagnostic and treatment planning process, the VSD in particular,” the authors stated.

Read the original article.

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*According to “Dosimetry of Orthodontic Diagnostic FOVs Using Low Dose CBCT Protocol” by JB Ludlow and J Koivisto. For a copy of this study, visit www.planmecausa.com.

 

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*According to “Dosimetry of Orthodontic Diagnostic FOVs Using Low Dose CBCT Protocol” by JB Ludlow and J Koivisto. For a copy of this study, visit www.planmecausa.com.

 

What is Specialty Scan?

This is one in a series of quarterly newsletters updating dentists on selected specialties in dentistry. Information presented is aggregated and summarized from previously published materials, each item attributed to its publication of origin. This issue of JADA Specialty Scan focuses on prosthodontics, the first in the series on this topic for 2017. Other Specialty Scan issues are devoted to endodontics, orthodontics, oral pathology, oral and maxillofacial radiology, pediatric dentistry and periodontics. The ADA has engaged the specialty organizations in these areas as well as its own Science Institute and Division of Legal Affairs to assist with these newsletters. We welcome your feedback on this and all Specialty Scan issues.

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Any statements of opinion or fact are those of the authors and do not necessarily reflect the views of the American Dental Association. Neither the ADA nor any of its subsidiaries have any financial interest in any products mentioned in this publication. Any reference to a product or service, whether in advertisements or otherwise, is not intended as an endorsement or as approval by the ADA or any of its affiliated organizations unless accompanied by an authorized statement that such approval or endorsement has been granted.

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