December 15, 2017
Occlusal forces at work in implant therapy
Protecting the implant and surrounding peri-implant bone requires an understanding of how occlusion plays a role in influencing long-term implant stability, according to a literature review published in the December 2016 issue of Implant Dentistry.
The authors conducted the review to describe how occlusal forces impact dental implants and their surrounding bone, to describe occlusal overload on implants and possible resulting complications, and to develop clinical recommendations for implant occlusion.
The authors completed a literature search using the PubMed database and relevant articles from January 1950 to September 20, 2015.
Authors of the review acknowledged that the study of occlusal overload and interpretation of existing literature is difficult. Although occlusal forces can be described in 4 variables (magnitude, duration, distribution, and direction), the authors noted that studies often take into account just 1 variable (magnitude). And although occlusal load can be measured at the prosthesis or abutment level, mechanical measurements cannot be obtained from the bone-implant interface. Confounders and risk of bias make the issue more complicated. Finally, clinical trials applying occlusal overload in humans are unethical.
One study found that dynamic occlusal overload created marginal bone loss, although the extent was determined by the presence of inflammation. Without inflammation, the bone resorption did not occur below the implant neck. The presence of plaque-induced inflammation led to significantly greater bone loss to the level of the implant threads.
Another study found that a deviation of 15 degrees in a buccolingual direction contributed to occlusal overloading. Aiming forces in an axial direction and reducing shear forces protected the supporting peri-implant bone.
Multiple studies concluded that a modified version of the mutually protected occlusal scheme leads to a harmonious implant occlusion. The force distribution should be equal bilaterally and maximized on adjacent teeth. Light to medium occlusal contact in maximum intercusptation is recommended for the adjacent natural teeth, with lighter contact or clearance between the occlusal face and opposing tooth.
If the canine has been replaced with an implant restoration, it should not be subjected to heavy lateral, shear forces. Occlusal forces should be aimed to be compressive, aligned, and axially directed. Periodontally compromised anteriors or an anterior bridge in a Kennedy class IV patient should not be subjected to heavy anterior protrusion. If an implant was placed in a palatal position (owing to limited buccal bone), the implant is likely to undergo shear forces with occlusion. The authors of 1 study advise placing the teeth in crossbite to avoid nonaxial loading.
Another study found that that prosthesis failure was more common in cantilevered restorations greater than 15 millimeters long. A separate systematic review and meta-analysis found that minor complications such as abutment screw loosening were more common with cantilevered restorations than with noncantilevered restorations. Several authors speculated that prosthetic complications of cantilevered restorations are associated with nonaxial forces.
Multiple studies found that choosing a reduced cuspal inclination protects the tooth from shear forces while decreasing force magnitude. A narrow occlusal table ensures that forces will be directed axially, prevents cantilever effects and bending moments, and reduces the magnitude of forces. One study found that narrowing the occlusal table by 30% reduced the magnitude of lateral forces by almost 50%.
Recommendations for single implants or implant-supported fixed partial dentures include a mutually protected occlusion with anterior guidance and evenly distributed contacts with wide freedom in centric relation. Suggestions for reducing occlusal overload include reducing cantilevers, increasing the number of implants and contact points, monitoring for parafunctional habits, narrowing the occlusal table, decreasing cuspal inclines, and using progressive loading in patients with poor bone quality.
“To avoid high occlusion on an implant restoration, occlusal adjustments may be necessary,” the authors concluded. “Maintaining good force distribution and direction will help maintain the longevity of the implant.”
Read the original article here.
Consulting Editor: Clark M. Stanford, DDS, PhD
Distinguished Professor and Dean
University of Illinois at Chicago College of Dentistry
Treasurer, Academy of Osseointegration Board of Directors
Factors affecting interproximal contact loss rates at follow-up visits
Loss of interproximal contact (IC) between fixed implant prostheses and adjacent teeth often occurs at follow-up visits, especially at the mesial aspects of the prostheses. This may cause food impaction and an adverse effect on the peri-implant tissue. The findings are from a study published in the November/December 2010 issue of International Journal of Prosthodontics.
Researchers designed the study to evaluate the IC loss rate between fixed implant prostheses and adjacent teeth and to clarify the factors affecting it.
Researchers recruited 105 patients (38 men, 67 women) from 20 through 78 years old with 353 implants (91 in the maxilla, 262 in the mandible) for the study. A total of 146 screw- or cylinder-type implant prostheses were placed. The period after insertion ranged from 1 through 123 months.
The definitive implant prostheses were single crowns, 2 to 4 splinted crowns supported by 2 to 4 implants, or 3- to 6-unit fixed partial dentures supported by 2 to 4 implants. The prostheses consisted of all-ceramic crowns, porcelain-fused-to-metal crowns, hybrid and resin-faced metal crowns, or full-cast metal crowns.
Adjacent teeth consisted of natural teeth, single crowns, 2- to 6-unit splinted crowns and 3- to 8-unit fixed partial dentures. Opposing and natural teeth were natural teeth, single crowns, splinted crowns, 3- to 14-unit fixed partial dentures, implant prostheses, removable partial dentures, or removable complete dentures.
Researchers used a contact gauge with a 50 micrometer-thick metal strip to measure IC between implant prostheses and adjacent teeth. IC was regarded as “adequate” if the gauge could be inserted into the IC area with moderate resistance and “lost” if the gauge could be inserted without resistance. Researchers calculated the IC loss rate at the mesial and distal aspects and in the maxilla and mandible regions.
Of the 186 IC areas researchers selected as samples, 80 (43%) were regarded as lost. IC loss at the mesial and distal aspects of the prostheses was 51.8% and 15.6%, respectively. The mesial aspect loss was significantly greater than the loss at the distal aspect. The IC loss rate in the mandible was significantly higher than in the maxilla.
Cox regression analysis showed that age, opposing dentition condition, vitality of adjacent teeth, and the splintering of adjacent teeth significantly affected the loss of IC at the mesial aspect of the prostheses, but no factors significantly affected the loss of IC at the distal aspects of the prostheses.
“Close attention should be paid at follow-up visits to IC areas at the mesial aspect after the delivery of an implant-supported prosthesis in the mandible,” the authors concluded. “Additional care should be given to elderly patients and to patients in whom the opposing teeth are natural teeth or implants and the adjacent teeth are non-vital and non-splinted.”
Read the original article here.
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The role of occlusion in dental implant and peri-implant
Existing evidence supports the harmful role of occlusal overload and the theory that occlusion affects dental implant and peri-implant conditions. These conclusions are from a literature review published online November 16, 2016, in Open Dentistry Journal.
The authors cited several animal and human studies in their review. In an older study, 4 monkeys underwent extraction of the mandibular first molars, premolars and incisors. Five implants were placed 8 months later: 2 in both premolar regions and 1 in the incisor region. The implants were uncovered and received abutments 6 months later.
One site received splinted restorations casted in silver-palladium alloy with supraocclusal contacts. The restorations were replaced at least once during the study to rule out wearing down of the prosthesis and to ensure that supraocclusal contacts remained. Implants underwent toothbrushing once a week and subgingival cleaning once a month.
Clinical and radiographic evaluations were made when the prostheses were inserted and at 3, 6, 9, 12, and 18 months. Results showed that 5 of the overloaded implants exhibited mobility and distinct radiolucency around the extent of the implant with none or a small loss of height of marginal bone. The loss of integration and mobility was observed at 4.5 months and 15.5 months after loading.
None of the implants that received plaque accumulation were mobile but they had increasing loss of radiographic bone height. Researchers concluded that the overloading an implant could be the main factor for the loss of osseointegration around a previously integrated dental implant, whereas plaque accumulation could be the main factor for progressive marginal bone loss height.
Another monkey study investigated the effect of different levels of traumatic occlusal force under an inflammation-free state. Prostheses were fabricated at excessively high force: 100 micrometers, 180 μ and 250 μ. Results showed that bone resorption around the implant tended to increase with 180 μ or more excessive height. The 180 μ and 250 μ excess height models showed a tendency to develop greater probing depths compared with the preocclusal loading conditions. In the 180 μ sites, slight bone resorption was observed in almost one-half of the implant. In the final model with 250 μ of excess height, the vertical bone resorption reached the apex of the implant, and epithelial down growth was observed in both the buccal and lingual aspects. This suggests that the threshold of excessive height of the prosthesis at which peri-implant bone breakdown starts to occur is around 180 μ. Bone resorption around dental implants can result owing to excessive occlusal trauma even when there is no inflammatory status around the peri-implant tissue.
A canine study examined 2 greyhounds that underwent unilateral mandibular third premolar and molar extractions. Four implants were placed 6 weeks later. After 12 weeks, nonsplinted, screw-retained crowns that increased the occlusal vertical dimension by 3 millimeters were fabricated and placed. The occlusal design was oblique to ensure functional loading in both axial and nonaxial manners. Researchers used an in vivobite force detection device to measure the in vivoocclusal load as the dogs functioned. Researchers assessed the peri-implant tissue after 8 weeks of function. All implants were successfully integrated and showed no signs of redness, swelling, bleeding on probing, suppuration, or mobility. The authors concluded that in in vivo and in vitroconditions, peri-implant bone was not found to be under pathologic overload after supraocclusal function.
A human study detailed a case report in which peri-implant bone loss was repaired after performing occlusal adjustment only. A 63-year-old woman with a history of bruxism came to a periodontal examination 38 months after an implant crown placement on tooth no. 30. The radiograph showed considerable bone loss. The patient had heavy occlusion on the implant. Limited occlusal adjustment was performed, and 5 months later, the radiograph revealed repair of the peri-implant bone loss. This case of bone loss did not show the characteristic features of bleeding on probing or probing depths greater than 4 mm.
Another case report showed that loss of integration could occur without inflammatory signs on the marginal tissue, thus attributing the loss of osseointegration to other factors such as excessive occlusal loading. A 61-year-old woman received 2 implants in teeth nos. 2 and 3. The implants were restored with single-screw restorations with even occlusal contacts and without contacts in lateral movement and protrusion. A year after delivery of the restorations, the patient unhealthy dental implant complained of implant crown mobility on tooth no. 3. Clinical evaluation revealed no more than 1 mm dislocation of the crown without any signs of peri-implant inflammation or deep pockets. When attempting to unscrew the crown with the wrench, the crown rotated without loosening of the abutment screw, which indicated spinning of the implant in the bone socket. Loss of osseointegration was noted based on the observed rotation. No marginal bone was lost, but researchers observed a radiolucent halo around the implant.
Read the original article here.
Effects of lifelong craniofacial growth on osseointegrated implants
Continued subtle growth can have an unexpected effect on functional and esthetic outcomes of implant restorations in some adults for whom growth was assumed to have stopped. The finding is from a study published in the February 2013 issue of International Journal of Oral and Maxillofacial Implants.
Researchers designed the study to describe complications that may take place when teeth and implants coexist and subtle adult craniofacial growth occurs.
The authors conducted a long-term observation of implant restorations in partially edentulous patients with up to 20 years of follow-up. Follow-up results showed a poor sequence of treatment due to growth that occurred based on the assumption that a stable jaw dimension had been achieved.
The authors found that occlusion changes can stem from continued growth in the arch containing the implants as well as in the opposing arch. The position of the implants and associated restoration are static but the teeth can move in facial and occlusal directions. These movements can negate the effectiveness of posterior free-end implant restorations that support significant occlusal loads over time.
The authors also found that contact points can open between the implant restoration and the natural tooth anterior to the restoration over time. They cited a study that found this in up to 40% of restorations, with loss of the natural tooth contact medial to the implant restoration greatly affected by age, condition of the opposing dentition, vitality of the adjacent tooth, and splinting of the natural anterior teeth. Contact loss was not sex-specific but was more common in the mandible, and the rate increased over time.
The authors noted that subtle growth over time also produced visible esthetic changes in 3 areas: the incisal edge length, gingival margin height, and the facial contour alignment. Extrusion and lingual tipping of the anterior maxilla and teeth can cause all 3 discrepancies.
Thinning of labial soft tissue over the implant or abutment represent other consequences. A discrepancy in facial alignment that makes the implant more labial is correctible but depends on implant axial alignment, available soft-tissue depth, and labial-palatal positioning of the implant in the ridge. A growing discrepancy between the implant restoration’s cervical gingival margin and adjacent natural teeth could be an esthetic problem with no easy solution.
“Early definitions of success based on osseointegration assumed that if osseointegration was maintained steadily then the system was static,” the authors noted. “However, in a mixed reconstruction with both teeth and implants, the system may not be as static as once thought.
“Both the implant and restoration may meet the criteria for short-term success, but the influence of long-term craniofacial growth may still compromise the overall long-term results,” they concluded. “This presents a dilemma; the same implants utilized to stabilize the resorptive process that would occur while wearing a removable appliance also function as a barrier to further local alveolar growth.”
Read the original article here.
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Registration open for AO’s 2018 Annual Meeting
For the first time in its history, the Academy of Osseointegration (AO) will be hosting its 2018 Annual Meeting in Los Angeles.
To be held February 28-March 3, 2018 at the Los Angeles Convention Center, “Inspiring Imagination — Enhancing Health” will include exciting new interactive features to promote maximum audience participation. All sessions will assemble global authorities in research and clinical practice on the cutting edge of scientific discovery in implant dentistry.
For an additional registration fee, scientific content of the Annual Meeting can also include a number of options for hands-on workshops, all of which will take place on February 28, 2018.
On the social side, the 2018 President’s Reception will held in Microsoft Square within the L.A. Live area, just outside the headquarters hotel. This event, complementary to registered attendees, will provide an Oscar-themed evening filled with many surprises and an atmosphere of a miniature Times Square.
Don’t delay in securing your attendance, making your hotel reservations, or taking advantage of early bird rates for this must-attend event. Register here today!
Are your estate planning needs covered?
No matter what stage of your dental career you’re in, it’s important to be organized and prepared for the future when it comes to managing and protecting your assets. Tom Kacirek, vice president, Specialty Insurance Markets for Great-West Financial, discusses the importance of life insurance, disability insurance and effective risk management in his article, Do You Have All Your Estate Planning Needs Covered? The article is featured in the Fall 2017 issue of Dental Practice Success.
This is the third installment in an ongoing series of estate planning articles prepared in cooperation with Great-West Financial, underwriter for ADA Members Insurance Plans. Other articles include Why You Need an Estate Plan and Common Mistakes with Estate Planning and Risk Management.
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