Implant restorations in patients who are fully or partially edentulous have proven to be very successful in the last 15 years, with success rates in the 90+ percent range.
This remarkable success rate has encouraged more dental practitioners to include implants as part of their restorative protocol for their patients. When clinicians first began treating patients with a combination of restoring natural teeth and implants, there was some reluctance to extract teeth with questionable prognoses.
With experience, dentists began extracting more and more teeth for “Prosthetic Convenience”; that is, teeth that would compromise or complicate the periodontal, restorative, or esthetic result. Unfortunately, the trend seems to be that more and more teeth are extracted and replaced with implants, that would otherwise have been salvageable with comprehensive traditional treatment, such as periodontal, endodontic, orthodontic, occlusal, and prosthodontic therapies.
Today the clinician is faced with a dilemma: should the patient be subjected to complex, time-consuming and sometimes costly therapy to preserve some “questionable teeth”; or should these questionable teeth be extracted and replaced with implant-supported prostheses. The driving philosophy seems to be the mistaken belief that implants have a better long-term prognosis than natural teeth.
The purpose of this article is to stimulate discussion and consideration of one particular aspect of treatment planning that is often missing from patient treatment; and that is the qualitative experience when the patient functions with the new restoration. To help decide how best to treatment plan some of the more challenging cases, this article attempts to compare teeth and implants from a proprioceptive and occlusal trauma perspective.
WHY KEEP TEETH?
The natural dentition is designed to function in physiologic harmony in the individual for the entire lifespan of the person, not withstanding disease entities such as periodontal disease, occlusal trauma, and enamel and root caries. Dentistry, over the last century, has provided effective techniques to prevent and control dental disease for a very large segment of the population in both Europe and North America. Advanced techniques such as are practiced in Periodontal-Prosthesis, has demonstrated the ability to preserve dentitions that were judged to have poor or hopeless prognoses. Dr. Morton Amsterdam, who formalized this “sub-specialty” of Periodontics, published convincing data to show periodontal healing and long-term tooth retention when pathologic processes were brought under control.1
Teeth provide lip support, phonetic support, aesthetic and masticatory function, proprioceptive input, thermal input, and protective reflex actions through the periodontal ligament and its related innervation that sheathes the root inside the bony socket. When teeth are removed, the supportive and sensory functions of the subject teeth are also removed from the patient. These sensory nerves modulate neuromuscular protective functions in the patient.
WHY PLACE IMPLANTS?
Implants provide independent support for replaced teeth. They are a root analog and when correctly restored, provide masticatory, phonetic and aesthetic functions much like teeth. They are resistant to caries and periodontal disease. Given the success rates of implants in recent years, they can provide long-term benefits for the patient.
However, in edentulous cases where implants are the only restoration supporting structures, there is a deficiency in proprioceptive input. The patient’s ability to control occlusal forces developed by the masticatory muscles often results in occulsal trauma that manifests itself as fractured retaining screws, loose screws, broken solder joints, fractured porcelain and occasionally fractured implants.
Jacobs and van Steenberghe evaluated the oral tactile function in patients with teeth or implant- supported prosthesis. Different thicknesses of steel foil were placed between the incisal edges of natural teeth; implant-crowns opposing natural teeth; and complete dentures opposing implant-supported overdentures. The ability to detect something between the incisal edges of the opposing teeth or implants varied from 20 microns to 108 microns of foil thickness for teeth versus dentures. Similarly, a discrimination task between different thickness of foil yielded results with teeth being 2 to 5 times more sensitive than the implant/overdenture/ denture combination. The authors concluded that the tactile sensitivity is reduced in implants compared to natural teeth but the peri-implant tissues might play a compensatory role in a reduced proprioceptive function as compared to natural teeth.2
The same authors, in a later study, demonstrated a temperature as well as a tactile interocclusal sensibility of natural teeth which implants lack.3
Hammerle, et al, measured the threshold of tactile sensitivity perceived with dental implants and natural teeth. Their results indicated that a greater than 8-fold threshold value exists for implants compared with teeth; i.e. implants are 8 times less sensitive in detecting something between the opposing occluding surfaces.4 It is apparent that the periodontal ligament of natural teeth plays a role in providing important sensory information to the patient.
Mericske-Stern, et al, measured maximal occlusal force, minimal perceived thickness (of foils) and minimal detection pressure in patients with implant supported crowns, and patients with healthy natural dentition. Their results indicated that the maximum occlusal force a subject could exert averaged 50% higher on teeth than on the implant-supported crowns in the same area of the dentition, suggesting a force modulation function for the periodontal ligament. As in previous studies, the minimal perceived thickness of foil and the minimal detection pressure threshold were significantly higher with implants than natural teeth.5
In practical terms, during normal eating, the individual has to hold the food and manipulate it inter-occlusally in the anterior of the dentition before incising and masticating the food bolus. A very elegant study by Trulsson, et al, compared the food holding and biting behaviour in human subjects lacking periodontal receptors. Twenty-four subjects were divided into 3 groups: 8 subjects with natural teeth; 8 subjects with complete U/L dentures; 8 subjects with implant-supported fixed prostheses opposing each other. The task for the subjects was to hold half of a peanut between incisor teeth for 3 seconds, then split the peanut with the front teeth. The subjects’ performance was measured with respect to how often the peanut was dropped in the “hold phase”, the “hold forces” developed , and the “split forces” developed during the trials. The results showed that subjects with dentures or implants dropped the peanut 8 times more often than the subjects with natural teeth. The denture and implant group produced 3 to 4 times more force to hold the peanut than the natural teeth group, but the “split forces” among all 3 groups were about the same. The authors concluded that periodontal receptors play a significant role in modulating “the level, direction, and point of attack on forces used to hold and manipulate food between the anterior teeth. Moreover, other types of mechano-receptors cannot fully compensate for the loss of periodontal receptors.”6
Gartner, et al, demonstrated that habitual chewing in subjects with natural teeth compared to those with implant-supported prostheses had similar co-ordination of masticatory muscles during habitual chewing; but in maximal occluding force the implant group activated working and non-working side muscles simultaneously. They concluded that “during a non-habitual function such as maximal occluding force, our pilot data revealed a less coordinated masticatory muscle activity in the implant patients.”7
It is apparent from the foregoing studies, that implant-supported prostheses do not fully restore all the functionality of natural teeth. There are significant differences in the patient’s perception of the thickness, hardness, and temperature of substances placed inter-occlusally; and the lack of sensory input from the periodontal ligament affects the masticatory muscles’ ability to modulate forces when manipulating food. This lack of sensation is a significant qualitative change when patients eat; and may reduce the enjoyment of eating, in some cases.
When deciding on a treatment plan where questionable teeth might be sacrificed in favour of implant-supported replacements, consider the consequences to the patient’s dental awareness, chewing ability and “natural feel” before a tooth is extracted. Obviously, if the pathology is so advanced that the tooth cannot be preserved, the dental implant is an excellent treatment modality for tooth replacement.
The following few clinical cases illustrate ways to maintain periodontal ligament input in implant supported prostheses by preserving some seemingly hopeless teeth as part of the overall restoration. The author’s experience has been that, in cases where mobile teeth were retained for proprioceptive purposes, the mobility of those teeth were reduced to physiologic levels, when the occlusion was supported by the implant-supported prostheses.
The patient is a 75-year old male with extensive root caries and failed maxillary fixed partial dentures. There is also advanced bone loss due to periodontal and periapical lesions on several teeth. (Fig. 1) The patient does not want implants; and requested an interim treatment to provide function; and time for evaluation of many questionable remaining teeth. A full maxillary fixed acrylic provisional partial denture, utilizing festooned metal band margins inside the supporting crowns, was fabricated for this purpose. (Figs. 2-6) Subsequent follow-up examinations indicated a stable and well-functioning maxillary dentition. The patient elected to maintain the provisional restorations as long as possible (Figs. 7 & 8).
The patient is a 70-year old female in excellent physical health, who has an ill-fitting complete upper denture and a poorly fitting mandibular cast RPD. The remaining mandibular teeth, except for #3.1 and #3.2, have hopeless prognoses (Fig. 9). The treatment plan included a new complete upper denture and an implant/ Hader-bar supported cast partial overdenture; and the retention and restoration of teeth #3.1 and #3.2 to provide proprioceptive and qualitative sensory input for the patient. (Figs. 10 & 11) The patient elected to restore the maxillary arch 2 years later, with an implant-supported Hader-bar/complete overdenture.
The patient is a 65-year old female in good physical health who presented with an ill-fitting CUD and a poorly retained cast mandibular partial denture. Three of the five remaining mandibular anterior teeth had hopeless prognoses (Fig. 12). Teeth #3.1 and #3.2, with a 2 degree mobility had guarded prognoses. (Fig. 13) The treatment plan included implant-supported fixed partial dentures in the mandibular arch and retaining #3.1 and #3.2 for tactile sensory input. The maxillary arch was to be restored with an implant-supported Hader-bar and complete overdenture (Fig. 14). Two years after completion of the initial treatment, the patient elected to convert the maxillary overdenture case to a fixed, implant-supported partial denture, with the addition of 4 more implants. (Fig. 15)
An article appeared in the journal COMPENDIUM in December, 1996 by Doctors Rose and Weisgold8 that presented a case report of one patient treated periodontally and restored with fixed partial dentures that were maintained for 16 years, even though the initial prognosis for the remaining teeth of this patient was considered poor to hopeless. After 16 years, the case was converted from a maxillary tooth-supported fixed partial denture to a complete implant supported fixed partial denture in the maxillary arch. For the next 10 years, to 1996, the implant-supported case has been functioning problem free. The authors ponder the question, whether the patient was well served for 16 years with the tooth-supported restoration, or would an implant-supported fixed partial denture have been a better choice initially. The article concludes that there is insufficient data on the prognosis of implant-supported maxillary fixed partial dentures at 15 plus years in function; whereas tooth-supported restorations have longer historical data. They suggest that dentists re-examine their treatment philosophies and focus on preserving the natural dentition in a state of health for as long as possible.
Although implants have shown remarkable success in the last several years of application, it behooves the dentist to consider all the implications of a particular treatment plan that includes the use of dental implants. We, as practitioners, need to have a broad perspective when planning treatment for our patients, since any alteration of the patient’s natural dentition has positive and negative biologic, and quality of life consequences.
Dr. Alex F. Koranyi has taught restorative dentistry, oral diagnosis and treatment planning, and pathology, at the University of Toronto, and prosthodontics to senior students at the University of Pennsylvania. He teaches clinical periodontics, part time, at the University of Toronto.
He provides periodontal services, implant-supported reconstruction and advanced restorative dentistry to his patients at his office in North York, ON.
Oral Health welcomes this original article.
1.Amsterdam MA: Periodontal prosthesis: 25 years in retrospect. Alpha Omegan 67(3):8-52, 1974.
2.Jacobs R., van Steenberghe D., Clinical Oral Implants Research 2:75-80, 1991 April-June.
3.Jacobs R., Schotte A., van Steenberghe D., J. Periodontal Research 27(6):581-7, 1992 November.
4.Hammerle CH., Wagner D., Bragger U., Lussi A., Karayiannis A., Joss A., Lang NP., Clinical Oral Implants Research 6(2):83-90, 1995 June.
5.Mericske-Stern R., Assal P., Merricske E., Burgin W., Int. J. Oral & Maxillofacial Implants 10(3):345-53, 1995 May-June.
6.Trulsson M., Gunne HSJ., J. Dental Research 77(4):574-82, 1998 April.
7.Gartner JL., Mushimoto K., Weber HP., Nishimura I., J. Prosthetic Dentistry 84(2):185-93, 2000 August.
8.Rose LF., Weisgold AS., Compendium 17(12):1151-57, 1996 December.