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Prosthodontics - A Quarterly Newsletter on Dental Specialties
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Placing dental implants — a matter of experience

Dental implants can't be considered successful unless they're esthetic as well as functional. Without accurate placement, meeting these objectives is impossible.

New technologies, such as stereolithographic* (SLA) models created from cone-beam computed tomography (CBCT) data combined with software-driven treatment planning, allow for the planning of surgical templates that guide implants into the right position

How to transfer the virtual implant plan to the patient is a major consideration. Despite the fact that the technology is being used to plan and place implants, little information about the effect of operator experience on the process is available.

So just how precise is dental implant placement with a bone supported stereolithographic surgical template that was created from a virtual implant plan? And, moreover, what is the effect of operator experience on implant placement accuracy?

Answering these questions was central to a study published in the April 2013 issue of The Journal of Prosthetic Dentistry by researchers at the U. S. Air Force Wilford Hall Medical Center, Lackland Air Force Base, and the University of Texas Health Science Center.

The purpose of their investigation was to compare errors of implants placed with a bone-level SLA surgical template produced from a virtual implant plan with that of the original plan under in vitro conditions. Also, the investigation aimed to assess the effect of operator experience on implant placement error when using this technique.

Four operators who had volunteered placed implants. Two had a lot of experience (each had placed more than 100 implants) and two had little (less than 10 implants placed). Each operator placed 25 implants — five implants into five lower jawbones.

Researchers calculated the amount of angular, horizontal and vertical deviation of the placed implants from the virtually planned implants at the apex and platform. They analyzed differences between the operator groups with more experience and those with less.

Among the study's primary findings was that even in vitro, a certain amount of inaccuracy exists when using guided surgery and virtual planning techniques to place implants.

"There is inherent inaccuracy when accomplishing virtual surgical plans, and error can arise from the acquisition of the CBCT scans, the interpolation by software programs used for planning, the processes used to create the surgical templates, the fit and placement of the template on the patient and operator error," authors noted. "A critical step is the virtual planning of the surgery and the transfer of that plan to the patient."

The researchers concluded that the experience level of the operator placing the implants contributes to the accuracy of implant placement, with more experienced operators placing more implants accurately.

Supporting this study were grants from the U. S. Air Force Wilford Hall Medical Center Clinical Research Division, San Antonio, Texas, and from the Academy of Prosthodontics Foundation in 2010.

*(Stereolithography is a computer-guided laser-dependent, rapid prototyping polymerization process that can duplicate the exact shape of the patient's skeletal anatomical landmarks in a sequential layer of polymer to produce a three-dimensional transparent resin model, which fits intimately with the hard and/or soft tissue surface.)

http://www.sciencedirect.com/science/article/pii/S0022391313600530



Consulting Editor Lars O. Bouma, DDS
Diplomate, American Board of Prosthodontics
 

 
Controlling excess cement around implant restorations

Clinicians often prefer cement over screws for attaching restorations to implants. Advantages of cement include ease of use and better esthetics.

A disadvantage of using cement is that residual excess is linked to inflammation and disease around the implant. Different techniques have been reported in the literature to locate and remove excess cement.

Researchers publishing in the April 2013 issue of The Journal of Prosthetic Dentistry investigated and compared excess cement accumulation with four methods of application and two types of cement — an interim or a definitive luting agent.

Forty specimens were divided into four groups of 10 as follows:

  • IM — cement applied on internal marginal area of crown;
  • AH — cement applied on apical half of axial walls of crown;
  • AA — cement applied to all axial walls of interior surface of crown, excluding the occlusal surface;
  • PI — crown filled with cement then seated on putty index formed to internal configuration of restoration.

After seating the crowns, researchers subjected them to constant load with laboratory clamps for 10 minutes and then weighed the excess cement from each specimen.

The amount of excess cement for specimens in the PI group was significantly lower than for those in the other groups. Group AA showed the most excess, but was not significantly different than the other two remaining groups. Researchers found no difference in the amounts of excess cement between the two different cement types.

"Within the limitations of this in vitro study, it was shown that the least amount of excess cement was present when a cementation device was used to displace excess before seating a crown on an abutment," researchers concluded. "In this technique, a uniform luting agent was distributed over the interior surface of the crown, and a reduced volume of excess cement was found after the restoration was seated."

Managing natural teeth that border missing teeth

How do the teeth next to edentulous spaces and dentures fare?

Much of the literature suggests that their long-term health is dependent on the type of treatment provided for the missing teeth. Those next to fixed partial dentures (FPDs) seem to fare better than those next to spaces left untreated or next to removable partial dentures.

More recently it has been speculated that implant-supported dentures may protect the teeth adjacent to edentulous space. But a study published in the May/June 2013 issue of the International Journal of Prosthodontics found that treatment type may not be the primary risk factor for problems in adjacent teeth after all.

Scientists at the Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences in Japan set out to compare complications in natural teeth bordering implant supported dentures (IFDs) with those serving as abutments for fixed partial dentures (FPDs). They also sought to assess other risk factors for problems in these teeth.

To explore the topic, they conducted a retrospective eight-year study of patients seeking treatment for no more than two missing adjoining teeth. The study group of 127 was split according to those who were treated with IFDs (61) and FPDs (66). The patients matched in terms of age, sex and the number of missing teeth. The only significant baseline difference between the IDF and the FDP groups was condition of tooth pulp.

A total of 24 complications emerged — six in the IDF group and 18 in the FDP group – as follows:

  • fracture or loss of prosthesis (IFD — 4; FDP — 9)
  • periodontal lesion (IFD — 2: FDP — 4)
  • periapical lesion (IFD — 0: FDP — 5)

In this study, the eight-year cumulative survival rate of the IFD group was significantly higher (92.1 percent) than that of the FPD group (59.3 percent). However, because a significant difference was noted between the two groups regarding dental pulp vitality, the researchers probed further by comparing vital and nonvital teeth adjacent to the edentulous spaces.

They found that four of the vital teeth endured complications (6 percent), while 20 of the nonvital teeth did (45.9 percent). A subsequent analysis demonstrated that tooth complications were significantly related to nonvitality of dental pulp and not to the type of treatment.

"These results indicated that the main risk factor for complications in the tooth adjacent to edentulous space not exceeding two missing teeth was the vitality of dental pulp, not whether an IFD or FPD was the treatment provided," authors said in discussion. "These reported observations support the notion that a nonvital tooth is an important risk factor for eventual complications with the tooth itself or when used as an abutment tooth to support a prosthesis."

Authors noted positive aspects of IFD treatment. It avoids tooth preparation, as well as excessive bending overload on the adjacent teeth—of particular importance when adjacent teeth are nonvital, according to their findings.

Complication rates for teeth adjacent to bounded edentulous spaces were significantly lower in the IFD-treated group than in the group where teeth served as abutments for FPDs. In addition, conservation of vitality in teeth adjacent to edentulous spaces was the key finding to limit further tooth loss, researchers concluded.

Product Spotlight
Managing implants in bruxing patients with occlusal guards
image: Doctor Abai

For patients who have undergone implant therapy, the potential for parafunctional developments due to bruxism is a cause for concern, observes Dr. Siamak Abai of Glidewell Laboratories.

Consequences, he notes, can range from excessive wear on the restoration and surrounding dentition, to a lack of osseointegration, to loosening or facture of the implant restoration.

"Use of an occlusal guard is strongly recommended to mitigate these consequences," says Dr. Abai, who earned his dental degree from Columbia University, a certificate in prosthodontics from Harvard University and is currently director of Research and Development for Glidewell's Implant Division.

He explained that the Comfort H/S Hard Soft Bite Splint is made of two layers: a 1-millimeter soft, comfortable polyurethane inner layer and a 3-millimeter hard, durable copolyster outer layer (Fig. 1).

"Achieving mutually protected occlusion within the design of the guard ensures that the implant prosthesis is not subject to the negative phenomena exhibited by bruxing patients, and that the exerted pressures are spread over the entire arch and lessened," says Dr. Abai, editor of Inclusive magazine.

Prescription of a hard occlusal splint begins with the clinician taking maxillary and mandibular polyvinyl siloxane impressions. A bite registration also is taken at the minimum opening needed for splint material fabrication with the patient's temporomandibular joints in the centric occlusion position.

Bite registration material is injected into the posterior openings of both quadrants with the patient in this open centric relation (Fig. 2). An additional interocclusal record is taken to capture the anterior opening in centric relation (Fig. 3).

Fabrication of the occlusal splint begins when the laboratory receives these impressions and makes a stone cast. Upper and lower models are mounted onto a thermoforming jig and articulated to build mutually protected occlusion.

The splint material is then heated and vacuum formed over the maxillary arch, while the mandibular arch is pressed into the material to create occlusal relief. The vacuum-formed splint is then cut free of the model, smoothed, polished and delivered to the clinician.

During the delivery appointment, the clinician checks the orthotic in the mouth to ensure proper fit and makes any necessary adjustments (Fig. 4).

Protrusive and laterotrusive movements are confirmed, and the appliance is adjusted to achieve clinically acceptable, mutually protected occlusion. A one-week recall appointment is required to re-evaluate and adjust the occlusion of the splint.

"The Comfort H/S Bite Splint can negate the excessive forces exhibited by patients with bruxism, greatly improving the chances of optimal restorative outcomes," notes Dr. Abai. "With high value cases, such as those utilizing implants, occlusal guards are strongly recommended in order to protect the patients' investment along with their health.

For more information, go to http://www.glidewelldent#766F1B

News You Can Use
Office design is focus of next 'JADA Live' seminar

image: Dr. Tholen image: JADA logo

"JADA Live," a series of continuing education seminars that debut last year, will continue in 2013, starting with Dr. Mark Tholen's presentation "Advancing Your Practice Through Office Design" set for July 19 at The Westin San Francisco Market Street.

Dr. Tholen, a renowned author and lecturer on dental office design, will break down the office design process while teaching techniques for boosting office efficiency during a full-day session in the City by the Bay

JADA Live seminars are presented by the publishers of The Journal of the American Dental Association. Each seminar offers six hours of CE credit provided though the ADA's Continuing Education Recognition Program. For more information and to register for Dr. Tholen's presentation, visit www.JADALive.com/SanFrancisco

Other upcoming JADA Live topics and venues include:

  • "Dentistry in the Digital Age: Unlock Your Practice Potential"
        Aug. 9, 2013 — Nashville, Tenn.
        Sept. 27, 2013 — Houston, Texas
  • "Modern-day Treatment Planning — The Role of 3D Imaging"
        Sept. 13, Seattle, Wash.
JADA Live CE seminars are supported in part by DEXIS, Gendex and Henry Schien Dental.

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