Written by Rodrigo Escalante Vasquez, DDS Thursday, 18 July 2013 08:31
This is part 2 of a 2-part article series. Part 1 of Dr. Escalante’s article was published in the April 2013 issue of Dentistry Today and can be found in our archived articles at the Web site dentistrytoday.com.
According to scientific literature, the primary cause of biomechanical implant complications is occlusal overloading; this includes fracture and/or loosening of the implant fixture and/or prosthetic components. The intricate bond between the implant surface and bone may also be disrupted, leading to peri-implant bone loss and eventual implant failure.1-3 When a tooth suffers occlusal overload, the problems that this generates can revert when the overload is gone. This does not happen with the implants because these do not show clinical or radiographic evidence generally until it is too late (osseous crest loss, or peri-implantitis); once the osseointegration is lost, it will not regenerate.
The lack of soft-tissue interface between the bone and the implant produces a concentration of forces on the implant bone union. If the initial load of a premature contact is equally applied to an implant and a natural tooth, the implant supports a greater proportion of load that is not dissipated on the surrounding structures (such as in the teeth).3
According to the free online dictionary, dissipate means: to attenuate to, or almost to the point of disappearing. According to this definition, we can deduct that the harder a material is, the less dissipation capacity there is, and, the softer a material is, the bigger the dissipation capacity. For these reasons, the wings of airplanes are not completely rigid, the wheels of a car are made of rubber with suspensions that have shocks, and the larger structural components of automobiles are even softer to absorb energy when any impact occurs. There are many technological examples of this phenomenon inside of as well as outside of dentistry. One very visual and radical example is the innovative new Michelin air-free metallic prototype wheels and their new shock absorbing mechanism. Since 1995, one material that has reported to dissipate stress in crown and bridge application is the internally-reinforced gold metal-ceramic technology (Captek [Argen]) (Figures 1 and 2).
|Figure 1. A cross section of the internally reinforced gold metal ceramic technology (Captek [Argen]). The inner and outer gold layers have the ability to be compressed, potentially dissipating certain occlusal loads.||Figure 2. The newly introduced Lava Ultimate Restorative (3M ESPE) is reportedly made of a tough and yet shock-absorbing material, showing that companies remain concerned about producing new restorative products with these characteristics.|
This dissipation capacity is also found in nature—teeth are clear evidence to that. The wear facets, the enlargement of the periodontal ligament, and the loss of vertical dimension all support this concept. This is unlike the implant-supported prosthesis, where the wear is minimal while tension generally occurs, screw loosening, and fracture of the abutments. It is hard for me to think that restorations over implants are an exception.4,5 Bruxism has no cure; it is a multifactorial disease, it can be cyclical, and it reaches people of any age. When a person suffers from this, we must be very careful when performing any kind of restorative treatment, especially with implant-supported prostheses.6 For these reasons, 10 years ago, the author chose to restore the implants for 3 patients who were diagnosed with centric bruxism with Captek restorations. These restorations have shock-absorbing characteristics, as pointed out in the first part of this article.7 It is interesting that some very contemporary restorative materials (such as Lava Ultimate Restorative [3M ESPE]) are still being developed and introduced that seek to reduce occlusal overloads via a higher modulus of resiliency (Figure 2).
CASE REPORTS (Continued from Part 1) Case 2
In a 32-year-old patient who had lost her mandibular right first molar, a Microlock implant was placed alone with a prefabricated abutment. A Captek coping was fabricated over the abutment and designed with a mesial extension to support the interproximal porcelain (Figure 3). In all of these cases, 360° bevel margins were placed to have gold (Captek) in contact with the surrounding tissue, due to its ability to retain the least amount of bacteria and ensure healthier gingival tissues.8 In Figure 3, it is also shown why stone is the best material to detect worn areas on teeth; on the occlusal surface of the second molar, the signs of wear due to centric bruxism (clenching) are highly visible.
The final anatomy of the ceramic crown was designed slightly to the lingual (the bone buccally was a little resorbed) (Figure 4, left).
After cementing the crown, it was noted that the buccal gingival margin receded slightly from the finish line of the restoration and this area would be watched closely over time (Figure 4, right).
|Figure 3. Internall reinforced gold metal ceramic technology coping with the metal collar margin and the finger in the mesial area.|
|Figure 4. A lingualized crown built up by the author, with an occlusal anatomy made to have contact with the opposite tooth in small dots.|
Considering the differences between natural teeth and dental implants (as described in this 2-part article), a specific occlusal scheme protocol was developed for implant restorations with the following guidelines: The restoration must have a reduced occlusal plane buccal-lingually with good occlusal anatomy. It must possess a passive occlusion where only the working opposite cusp (natural or restored) (oriented axially to the position of the implant) makes contact with the crown at 3 or 4 small points; only when the natural teeth are in an active contact in maximum occlusion, with immediate disclusion on any eccentric movements (Figure 5).
|Figure 5. Occlusal arrangement guidelines (as developed and outlined by Dr. Escalante) are aimed at directing the occlusal load axially to the implant longitudinal axis through very small dots/points.|
In the final x-ray, the author observed several things:
- Make sure that there isn’t cement trapped under the restoration
- The height of the osseous crest in relation to the first thread of the implant
- The marginal adjustment of the restoration
- The interface bone-implant.
Everything was found to be in order, as planned, although a little bit of periodontal ligament enlargement in the premolars was noticed, likely provoked by the clenching (Figure 6).
|Figure 6. Radiograph taken after the crown was cemented with no traces of cement trapped around the crown. Note also the enlargement of the periodontal ligament at the first and second bicuspids.|
Long-Term Case Follow-Up
Ten years later, the patient presented with a great amount of dental plaque and tartar all over his teeth, except around the restoration of the implant. In addition, in the slight gingival to restoration gap that was observed at the time the crown was cemented had closed (typical of the gingival behavior in contact with the metallic margin of the Captek copings).9 The occlusion of the crown looked great after 10 years; better than the adjacent natural teeth (Figure 7).
|Figure 7. After 10 years, despite poor oral hygiene, the gingival tissue around the implant is better than the day of the cementation.|
|Figure 8. The occlusal surface at 10 years is still intact despite the continued clenching habit. In addition, the gingival margin at the lingual that has been in contact with the Captek metal collar margin is healthy, now covering the entire metal margin.|
The occlusal surfaces did not show any sign of wear/fracture after 10 years, and, therefore, the occlusal scheme that we utilized, including using Captek with its shock-absorbing characteristic, had fulfilled its purpose so far in this case (Figure 8).
The good clinical results at 10 years were confirmed by the excellent radiographic findings. Note that the level of the osseous crest had grown in height, filling the mesial bone defect and further improving the level of osseointegration (Figure 9).
|Figure 9. Before and after radiographs. Note that we can see how the mesial osseous defect has filled with bone (right). Note also the enlargement of the periodontal ligament at the bicuspids, indicating that the clenching continues after 10 years.|
In order to recover lost teeth in a 55-year-old female patient who was partially edentulous on her mandibular right side, 3 implants ([BIOMET 3i]) were placed with 3 prefabricated abutments (GingiHue Abutment [BIOMET 3i]) and covered with 3 Captek copings. It was decided to splint them due to the strong centric bruxism that this patient suffers from, the small space between the implants, and the width of the implants (not too wide) (Figure 10).
|Figure 10. Three prefabricated (BIOMET 3i) abutments were placed; because of the width of the implants (3.5 mm) they were splinted.|
|Figure 11. Due to limited space between the implants and the width of the same, we could only make 2 bicuspids and one small molar (left). Our occlusal scheme (right) is clearly visible in the last molar; only the mesial-lingual cusp of the opposite tooth is occluding because it is the most vertical to the axial position of the implant.|
To replace the first bicuspid and the first and second molars, the laboratory team was asked to fabricate 2 bicuspids and a small molar (with reduced occlusal surface) (Figure 11). This was done with the same occlusal scheme as in prior cases, directing the occlusal forces axially toward and across the axis of the implants by making contact just with the closest opposing working cusp in a vertical direction to the axial position of the implant. The occlusal contact in this case was made to be in 3 small points (not areas), creating mesial-distal and buccal-lingual occlusal stability. Note: A few months after the restorations over the 3 implants were cemented, the patient decided to replace a previously placed crown on his natural first bicuspid with a Captek restoration.
Ten years later, we can see that, in spite of the strong and continued clenching, only a very small part of the distal-lingual cusp on the second molar chipped. The small, keratinized tissue band surrounding the implants was in healthy and stable condition as is expected surrounding Captek restorations (Figure 12).
|Figure 12. After 10 years of heavy clenching, only a very little part of the distal-lingual cusp tip had chipped off. Note: The old crown of the natural second bicuspid was replaced with a new crown (Captek) months after the cementation of the implant restorations.|
|Figure 13. As in the last 2 cases, the before and after radiograph is most significant because, after 10 years, the osseous crest around these 3 implants is as good as before, if not slightly better.|
As in prior cases, the best thing is the bone behavior; the osseous crest, at 10 years postoperatively, was found at the same or even slightly better level than before (Figure 13).
In this 2-part article we have looked at the implants/restorations of 3 patients at 10 years postoperatively. All of these middle-age patients, partially edentulous and suffering from centric bruxism (clenching), were rehabilitated with internally-reinforced metal-ceramic technology (Captek) restorations over medium-diameter Straumann 3i and Microlog implants (3.5 to 4.5 mm average). All had relatively thin but good quality posterior mandibular bone. All cases were designed and based on the fundamental principles of organic occlusion.
After observing these results, the author has arrived at the following clinically based conclusions:
1. The implant-supported restorations are an excellent option for long-term treatment in partially edentulous patients with centric bruxism (clenching).
2. Due to the lack of mechanisms to dissipate occlusal overload in cases such as these, occlusal design plays a vital role for proper long-term function.
3. Especially important in cases like these is the selection of restorative materials that have the ability to dissipate occlusal loads; such as the one used in these 3 cases that possesses the ability for shock absorption, resulting in higher porcelain fracture resistance.9
It is important to note that these conclusions are based upon purely clinical observations and thus have no scientific validity. However, from the clinical observations, theories lead to scientific research. It is the author’s opinion that scientific research would be warranted to see how much the compression capacity of this internally reinforced gold metal ceramic technology contributes to the long-term survival of these restorations in patients who exhibit conditions for chronic occlusal overload.
- Fu JH, Hsu YT, Wang HL. Identifying occlusal overload and how to deal with it to avoid marginal bone loss around implants. Eur J Oral Implantol. 2012;(suppl 5):S91-S103.
- Miyata T, Kobayashi Y, Araki H, Ohto T, Shin K. The influence of controlled occlusal overload on peri-implant tissue. Part 3; a histologic study in monkeys. Int J Oral Maxillofac Implants. 2000;15:425-431.
- The “ABC” of occlusion in prosthetic rehabilitation over dental implants. In: Manns Freese AE, Biotti Picand JL. Practical Handbook Of Dental Occlusion. 2nd ed. Caracas, Venezuela: Amolca; 2006:229-238.
- Antonio CC, Claudia Angela MV. The importance of occlusion in implantology. In: Dinato JC, Polido WD. Osseointegrates Implants: Surgery and Prosthesis. São Paulo, Brazil: Artes Médicas; 2003:95-100.
- Desai SR, Singh R, Karthikeyan I, Jyothilaxmi, R. Three-dimensional finite element analysis of effect of prosthetic materials and short implant biomechanics on D4 bone under immediate loading. Journal of Dental Implants. 2012;2:2-8.
- Bassit R, Lindström H, Rangert B. In vivo registration of force development with ceramic and acrylic resin occlusal materials on implant-supported prostheses. Int J Oral Maxillofac Implants. 2002;17:17-23.
- Escalante R. Management of occlusion over implants, part 1: three 10-year case follow-ups and evaluations. Dent Today. 2013;32:106-111.
- Shoher I, Whiteman A. Captek—A new capillary casting technology for ceramometal restorations. Quintessence Dent Technol. 1995;18:9-20.
- Escalante R. Combining radiosurgery and Captek restorations in complicated tissue cases: Part 2. Dent Today. 2007;26:98-101.
Disclosure: Dr. Escalante reports no disclosures.
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