Occlusal overloading, as reported in the scientific literature, is the primary cause of biomechanical implant complications; this includes fracture and/or loosening of the implant fixture and/or the prosthetic components. The intricate bond between the implant surface and bone may also be disrupted, leading to peri-implant bone loss and, eventually, implant failure.1 This overcharge could be associated with occlusal interferences, nonaxial loading,2 as well as parafunctional habits (eccentric bruxism or grinding and centric bruxism or clenching). It stands to reason, risk factors associated with clenching may well be made more severe due to the fact that this parafunctional condition can occur during daytime as well as during sleep. Additionally, with centric bruxism (clenching), the forces released could be as high as 6 times than those forces produced in normal chewing.3 Literature cites that 20% of the population exhibits some type of bruxism,4 making management of this phenomenon far from trivial.
In patients who do not exhibit parafunction, proper occlusal management is still highly significant. However, in patients who are diagnosed with some kind of bruxism, the adjustment in the occlusion over implants should be done as carefully and accurately as possible. This should be done by following the lineaments of the organic occlusion, keeping function slightly less strong than found in the natural teeth (passive occlusion).5 Some clinicians go as far as to leave these restorations completely out of occlusion, a tactic that is not supported and strongly discouraged by this author.
In addition to being concerned about parafunctional habits, and other factors such as but not limited to implant position, restoration engineering, and occlusal design, thought should be taken in selection of the restorative materials as well. There is great debate as to the effects of harder restorations placed over rigid titanium implants which are inserted into the bone with no periodontal ligament whatsoever, and with very limited capacity to absorb or dissipate the occlusal loads. There are studies that have shown that the degree of hardness of the restoration over an implant does not make any difference.6-9 Yet, if we believe this to be true, it seemingly is contrary to the design of a natural tooth and its supporting structures. A natural tooth is designed, with the hardest tissue in the human body (enamel), layered over and supported by a living tissue (dentin) that is 4.7 times less hard. The natural dentate is designed to dissipate the occlusal forces, dentin supporting the enamel, both working in unison, helping to manage shock, vibration, and occlusal loading to resist fractures. In addition, the periodontal ligament functions as a shock absorber, helping further to dissipate forces from occlusal loads. In short, a tooth is a combination of maximum hardness and natural flexibility so perfectly balanced that, under healthy conditions, it can function without issues for more than 90 years. This natural design is unlike solid one-piece titanium implants embedded in the bone prosthetically, then restored (in most cases) with restorations that are much harder than enamel. All these make an extraordinarily rigid unit with seemingly limited cushioning capacity (Figure 1).
|Figure 1. In nature, a dental crown is comprised of the hardest tissue in the human body (enamel); however, it is supported by a tissue 4.7 times less hard (dentin).|
| Table. Differences Between Tooth and Implant|
|Figure 2. Based on these points of view, it is possible to infer that dental implants with no periodontal ligaments, and no periodontal receptors, are probably more sensitive to the occlusal overload.|
Although the bone has a certain capacity for absorbing occlusal stress (osseoflexion), its ability to do so is dramatically inferior to that of the periodontal ligament.5 In Figure 2, one can see the differences between a natural tooth and an implant. We can first note the importance of counting on a periodontal ligament in the natural teeth, because the physiological movement of the teeth depends on this ligament that provides the capacity of adaptation to any skeletal deformation/torsion. It also works as a mechanoreceptor through which it is possible to transmit vital information to the central nervous system, working as a mechanism of negative feedback nervous regulation to occlusal overload.5 It is plausible to infer, in the absence of both periodontal ligaments and periodontal receptors, there is more sensitivity to occlusal overload being that the capacity of loading support, adaptation to occlusal forces and proprioception, are significantly reduced.
The lack of resiliency in the system may create a great disadvantage which can result in high stress concentrations and damaging results, including restorative failure, high tension on the osseous crest causing issues with screws loosening or breaking, stress on the bone implant interface, bone loss, or even implant failure. In this 2-part series, we will look at 3 implant restored patients over a 10-year period and explore various methods the author has applied to stabilize occlusion, manage and protect occlusal overloading, and encourage stable restorative performance, soft-tissue health, and bone stability.
Internally Reinforced Gold Metal Ceramic Technology
From a restorative perspective, precious metal alloys remain a popular choice for implant superstructures.2 The use of metal-free options available today are extremely helpful in achieving aesthetic outcomes in certain situations, but in the author’s experience, should be used with caution. All 3 cases in this report were restored with internally reinforced gold, or otherwise referred to as metal composite restorations (Captek [Argen]). First introduced to the literature in 1995,10 this material possesses unique physical and biological characteristics that are reported to encourage high aesthetics, high fracture resistance, zero corrosion, and reduction of harmful sulcular bacterial plaque.11 Metal composite is purported to possess potential for shock and vibration protection, resulting in higher porcelain fracture resistance (Figure 3).10 It is theorized that the stress control designed by inventors Shoher and Whiteman to protect porcelain may also help to protect underlying tooth structures from damaging occlusal loads.
|Figure 3. The nanometal composite structure that comprises Captek (Argen) is an internally reinforced structure of hard thermally stable particles of platinum and palladium that support the resilient gold matrix.||Figure 4. Diagram of metal composite coping, absorbing shock and vibration from chewing and clenching.|
The most current iteration of this material12 (Captek Nano [Argen]) incorporates a higher density of hard strengthening particles into the gold matrix in addition to an updated porcelain bonding interface.13 A 97.5% gold, 2.5% silver combination provides a resilient matrix to the internal hard structure of interconnected platinum-palladium particles (Figure 4). The inherent design of the reinforced gold produces a dynamic elastic modulus reported to be similar in range to that of natural tooth structure. The author has chosen this material due to the unique low dynamic modulus, strength factors,14 and aesthetic and health potential.11 The updated materials are currently available in a digital workflow via lab die scans and/or intraoral scanners such as iTero (Align Technology) and Sirona Connect (Sirona Dental).15
The author utilizes a wide array of metal and metal-free materials, yet for all of the factors listed, metal composite is one of the author’s materials of choice in many clinical situations, including for implant restorations.
Diagnosis and Treatment Planning—A 45-year-old female lost her mandibular left first molar (tooth No. 19) years ago. The tooth had been previously restored with a very large occlusal restoration that was designed without good cuspal protection. The restored tooth had also experienced occlusal overload via clenching. It was thought that the extraction must have been done in a very traumatic way, because the entire buccal plate had been lost, and there was a small band of keratinized tissue present.
|Figure 5. The patient had lost her mandibular left first molar (tooth No. 19) due to a previously placed large restoration in combination with repeated occlusal overload via clenching. The tooth had been extracted in traumatic way. She presented with the loss of the entire buccal plate of bone and a large amount of keratinized tissue.|
|Figure 6. Capillary metal technology; coping designed with a metal collar margin.|
|Figure 7. A prefabricated solid abutment (Straumann) was placed; ceramic was added to the Captek coping.|
|Figure 8. After crown cementation, a big gap between the margin of the restoration and the gingival margin was observed (left). A huge osseous defect was also observed on the buccal side (right).|
Clinical Protocol—We suggested a bone grafting procedure, but the patient refused the idea. Therefore, a 10 x 4 mm implant (ITI [Straumann]) was placed in the lingual half of the alveolar process (Figure 5). This was, in this case, perhaps not the ideal implant made to withstand the loads and overloads of a big first molar for the long term. Because of this, we decided to use a Captek coping/crown due to its inherent ability to absorb some of the occlusal load and to transmit less strain on the bone crest, giving the implant a better chance for long-term survival.
During the osseointegration period of the implant, we restored the lower second molar, and the upper first molar with 2 Captek crowns on the same side (Figure 6).
We placed a prefabricated Straumann solid abutment and built up the ceramic over the Captek coping (Figures 7 and 8). After crown cementation, we saw a big gap between the margin of the restoration and the gingival margin, because the margin of the implant was left supragingival. Also evident were huge osseous defects on the buccal side.
A radiograph was taken after the crown was permanently cemented to make sure there were no traces of excess cement remaining. We also used this radiograph to check the final marginal adaptation of the Captek coping, as well as the level of the osseous crest (Figure 9).
|Figure 9. A radiograph was taken after cementation to ensure that there were no traces of excess cement inadvertently left behind.|
(Note: This restoration was one of the 5 that we will review in this 2-part article. All of these restorations were part of the clinical project done 10 years ago in which we opted for the use of Captek copings in clenching patients in order to give them the best long-term prognosis.)
LONG-TERM CASE FOLLOW-UP
After 10 years, our patient came back and we discovered/observed 4 important things:
- We noticed that the tissue had crept up. The tissue filled the gap that had existed between the gingival margin and the margin of the restoration with a thick band of keratinized tissue. This is what we have commonly observed around Captek restorations with metal collars in complicated tissue cases (Figure 10).16
- We observed that the occlusal surfaces, after 10 years of function and clenching, were in very good condition. This was true for both the implant restoration and for the second molar Captek crown (Figure 11).
- The “centered occlusion” (author’s own occlusal technique) was still functioning very well (Figure 12).
- The most important observation comes in the last photo (Figure 13). Note the before and after level of the osseous crest. The bone level appeared as good as the first day, if not better.
Figure 10. After 10 years, we observed that the tissue had crept up, filling out the gap that had existed between the gingival margin and the margin of the restoration with a thick band of keratinized tissue. Figure 11. The occlusal surfaces, after 10 years of function (and clenching) were in good condition. This was true for both the implant restoration and the Captek crown placed on the second molar. Figure 12. The “centered occlusion” (author’s own occlusal technique) was still functioning very well at 10 years postoperatively, and none of the Captek crowns placed had fractured. Figure 13. Here we can observe the before and after levels of the osseous crest. The bone levels, seen here at 10 years, were as good as the first day, if not better.
Nature designs teeth with a periodontal ligament, giving them the capacity of adaptation to the skeletal/torsional bone deformation. It also works as a mechanoreceptor through which it is possible to transmit vital information to the central nervous system, working as a mechanism of negative feedback regulation (via the nerves) for occlusal overloading.5 Dental implants have proven to work quite well without a periodontal ligament. Even though the literature is mixed on the subject of building in less hard or semiresilient mechanism over implants, it behooves clinicians to still take great care to manage occlusal loads whenever possible. And when practical, it could be beneficial to have something in place to dissipate the forces that these loads can produce.
While I cannot say that the resilience of this composite metal technology is solely responsible for the survival and the healthy state of the peri-implant bone (as in the case presented here), it has at least been my clinical experience that it probably at least plays a part in the success observed. It is my opinion that scientific research would be warranted to see how much the compression capacity of this composite metal contributes to the long-term survival in patients with occlusal overload.
Editor’s Note: Two more cases will be followed up and evaluated by the author in part 2 of this article series.
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- Lowe R. A Comparison of Captek Nano EZ versus Porcelain to Zirconia All Ceramic Crowns in the Esthetic Zone: A Case Report. Oral Health Canada. 2012. oralhealthgroup.com/news/a-comparison-of-captek-nano-ez-versus-porcelain-to-zirconia-all-ceramic-crowns-in-the-esthetic-zone/1001035668/?type=Print%20Archives. Accessed March 4, 2013.
- Test of Captek ceramic‐metal composite bond 2010: ENEA research center, Faenza, Italy, Giancarlo Garotti, restorations fabricated by Dentalprotesi srl Laboratory of Mr. Godeas, Conegliano veneto, Italy.
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Disclosure: Dr. Escalante reports no disclosures.