Removable Partial Denture and its Effects on Periodontal Health
by Dinh X. Bui, D.D.S., M.S.

Removable Partial Denture and its Effects on Periodontal Health
A partial denture, when properly designed, carefully made, and serviced when needed, can be an entirely satisfactory restoration and serve as a means of preserving the remaining oral structures as well as restoring missing dentition. A partial denture should be constructed with adequate abutment support, good periodontal health to the remaining structures, optimal base support, with harmonious and functional occlusion. The occlusion on the partial denture should be made to harmonize with the existing adjusted natural occlusion, and that this can be accomplished by the registration of functional occlusal path. Periodic recall of the patient to evaluate the oral tissues, their response to the restoration, and the restorations themselves is a part of total treatment responsibility. Changes in oral structures or the dentures must be ascertained rather soon to avoid compromised oral health. This can be accomplished by periodic recall. This paper is dealing with several issues concerning the practice of removable prosthetics dentistry, mainly the design and construction of removable partial denture, and its effect on the periodontal health, specifically the oral hygiene, the mobility of the remaining dentition, the gingival index, plaque index, occlusal stability, and pocket depth.
Glickman in 1948 reported that from the periodontal viewpoint, fixed prostheses are the restorations of choice for replacement of missing teeth, but there are some clinical situations in which removable partial prostheses are the only possible way to restore the lost function of the dentition. One of the most common situation is the Kenedy class I and class II of which there is a bilateral or unilateral edentulous areas located posterior to the remaining natural teeth. Patient may not be able to afford implant therapy as the mean of restorative effort. Several issues must be considered when constructing a removable prosthesis. One of the most important is patient oral hygiene. McCracken suggested that the oral hygiene of the patient must be assessed as an important step in diagnosis and treatment planing. Seeman in 1963 emphasized the need for establishment of a satisfactory level of oral hygiene during the treatment planing stage. The presence of a partial denture may increase plaque formation around the remaining teeth, so oral hygiene must receive great emphasis in these patients. It is reasonably fair to assume that the patient will do little better in the long term future than he has done in the past. Therefore, before and after constructing a partial removable prosthesis, patient must be motivated and maintained his remaining dentition with good oral hygiene to preserve the integrity of the periodontal health.
Bergman et al in 1977 published a six year follow up study on 28 patients with removable partial dentures to evaluate the effect of removable denture and oral hygiene. All patients were given Oral Hygiene Instructions and periodontal treatment as needed. The dentures were carefully treated planned and designed according the case. The follow up period included yearly visits to clean and adjust the prosthesis. The results showed that there was little reduction of the periodontal health, and there were small number of carious lesions reported. There was a small deterioration of the occlusion, articulation, stability and clasp retention. These findings are very normal and seems to be related to the inherent fact of using an artificial appliance for mastication and function. These are the main reason for frequent follow up visits for dentures adjustments. In short the authors state that there is little evidence to support the idea that partial dentures will cause various lesions or even periodontal diseases, if with good prosthetic design and plaque control is achieved.
Stipho et al. investigated the relationship between plaque accumulation and removable partial denture design. 14 dental students were included in the study with the prosthesis design of an acrylic palatal base partial denture which covered the palatal gingiva on one side and was relieved on the other side. The plaque from both surfaces was taken. The results showed both sides collected plaque with a higher accumulation on the covered palatal side. In short, the authors suggest that people with less than adequate plaque control should not have partial dentures. However, if a prosthesis must be made, the marginal gingiva should be relieved.
Addy and Bates in 1977 investigated the effect of partial denture and chlorhexidine gluconate gel on plaque accumulation in the absence of oral hygiene on a group of 24 partial denture wearers. Oral hygiene procedures were withdrawn. The modifying effect of a 1% chlorhexidine gluconate gel on this plaque accumulation was measured. Plaque accumulation was measured at the end of four different denture-wearing regimens each 3 days in length. The wearing of a partial denture either day only or day and night, significantly increased plaque accumulation over not wearing a denture. There was no significant difference between plaque accumulation with day wear and day and night wear. The increase in plaque accumulation with day and night wear resulted from an equal and significant increase in both buccal and lingual plaque accumulation. Chlorhexidine gluconate in the form of a gel significantly reduced plaque accumulation during daytime wear. These results tend to confirm that plaque control is a major factor in determining the long-term effects of partial dentures upon the periodontal structures and emphasize the importance of oral hygiene in partial denture wearers.
Bergman, Hugoson, and Olsson investigated the periodontal and prosthetic conditions in patients treated with removable partial dentures and artificial crowns in a longitudinal study of 30 patients over two years. All patients were motivated regarding oral hygiene and received periodontal therapy to achieve good periodontal and dental health prior to receive the partial denture. Clinical parameters are the Loe and Silness’ gingival index, Silness and Loe’s plaque index, pocket depth, and mobility. Caries also were documented and prosthetic factors were examined regarding the occlusion, articulation, and location of crown margin. Finally, resilience of alveolar process and the mucosal changes also were documented. Ten other patients with an average of 9.5 residual teeth per jaw served as the controls, which receive the same kind of treatment but did not receive the partial denture. The results were reported for one and two years after delivery of the RPD. The result indicated that there is no significant change regarding the gingival index, depth of periodontal pockets, and plaque index during the two years observation period. A decrease of mobility of the abutment teeth was noted between 0 and 2 years. The mobility of the teeth had not increased during the two years use of partial denture as suggested in other study. Radiographic assessment of bone loss revealed a reduction in marginal bone level averaging 1.01 per cent of the bone distal to the abutments; however, there was no reduction recorded mesially to the abutments. Reduction was attributed to the direct pressure on the underlying bone. This support the concept of teeth support prosthesis is more favorable in term preserving periodontium compare to tissue supported prosthesis. Location of crown margin also affects the gingival health. The more subgingival the margin was placed, the higher the gingival index was noted. Patient wearing prosthesis did not have an increase in frequency of caries. Some deteriorations regarding the prosthesis occlusion, articulation, stability and clasp retention were noted, which supported the recommendations that patient with RPD should be regularly followed up. The study concluded that with a careful planning of the prosthetic treatment and with an adequate oral and denture hygiene, checked up at every clinical visit, little, if any, damage will be caused to the remaining teeth.
Another study by Schweizer investigated the biological effects regarding mobility of the abutment teeth in splinting teeth with removable bridges. Fifteen abutment teeth with pathologic mobility were splinted with removable telescoped bridges. Mobility was measured at the time the splints were placed and at 1 and 12 month intervals. The result showed that daily removal and insertion of splints did not injure tooth supporting structures and that average tooth mobility did not increase or decrease during the one year test period.
The design of the partial denture is very critical in maintaining periodontal health and preserving the stability of the remaining dentition. To provide maximal stability for removable partial prostheses, every effort should be made to retain posterior teeth for the distal support of the edentulous areas. When posterior teeth cannot be retained to support edentulous areas, the design for the removable partial prostheses becomes challenging and the relationship of the framework to the distal surface of abutment teeth, especially in the case of bilateral distal extension partial dentures (Kenedy class I), becomes an area of controversy.
Carlson, et al in 1965 studied the oral and prosthetic conditions in the use of dentogingivally supported partial dentures. A longitudinal study of 99 patients was performed. The results were interesting because they represent the follow-up of previous studies in which they concluded that indications of partial dentures should be narrowed considerably due to the high frequency of local pathologic alterations. Altogether 36% of the follow up patients did not have their original prosthesis at the time of the five year reevaluation. For the remaining patients, at follow up there was a high percentage of loose abutment teeth. 37 patients were assessed as having acceptable prosthesis based on no clinical or radiographic signs of pathology. There was a higher occurrence for damage to tissues to the tissues of the lower prosthesis than the upper prosthesis. This has to be taken with care because the design and the areas for support are different, so this seems to be observational in nature. Most of the denture users were happy except for trapping food under the denture. This is to understand but if the patient was trapping food underneath the denture, then there is high probability that the denture design was not appropriate In short, the success for a partial denture depends on both the oral as well as the design of the partial. This is a classical study, and very well done. Some of the short comings are that a lot of patients were not seen at recall due to not having the baseline prosthesis, and no designs were stated, as well no standardized radiographs.
Isidor et al evaluated the long term periodontal changes in 52 patients with moderate to advanced bone loss with distally extending cantilever bridges or removable partial dentures. All patients were treated for their periodontal needs, and 27 patients received distally extended cantilever bridges, and 25 received distally extending removable partial in the mandible. PI, GI, PD, and bone level were recorded. The results demonstrated that at reevaluation visit there was no difference in the treatment modalities and that patients can be treated with fixed or removable prostheses. There was a higher PI with patients who had RPD. The last and important statement made by the author is that regular visits and oral hygiene instructions are imperative to success. This seems to be a very well controlled study, and gives a more realistic view of some patients in which removable partial dentures is the only feasible way to restore function.
Benson in 1979 has shown that the I-bar type of removable partial denture can be utilized by many patients with little or no detrimental effect on periodontal health. This particular design utilizes an I-bar infrabulge clasp, mesially positioned occlusal rests, and metal guide planes. The technique emphasizes the need for intraoral adjustment of the denture framework to minimize undue torque on the abutment teeth. This particular design of removable prostheses has also been shown to provide more favorable loading of abutment teeth than that seen with a circumferential clasp design.
Clasp design is very critical since the clasps should be passive and exert no force on the teeth when the partial denture is at rest. Improper clasp design will introduce occlusla trauma to the abutment tooth which the clasp was provided. Research done by Clayton shows that the use of an improperly designed suprabulge or circumferential clasp exerts a great deal of force on the abutment tooth.
Cecconi investigated the effect of four different type of partial denture clasp design on abutment tooth movement. The four designs are: 1) a cast bar retentive clasp arm, cast lingual bracing arm, and distal occlusal rest; 2) a cast circumferential retentive clasp arm, cast lingual bracing arm, and a distal occlusal rest; 3) a cast I bar retentive clasp arm, a distal guide plane, and a mesial occlusal rest; and 4) an 18 gauge wrought wire retentive clasp arm, cast lingual bracing clasp arm, and a distal occlusal rest. Movement of abutment tooth can be observed in four directions: mesial, buccal, distal, and lingual. The test apparatus consists of a gauge mounted to the plywood base of which the test model (with the RPD) was fixed to. Twenty pounds load was applied in five different directions: vertical, anterior, posterior, buccal, and lingual. The result indicated that in regarding to the direction of the movements, the dominant direction of the movement for the abutment tooth was mesial-buccal when it was the load side abutment; and mesial-lingual when the abutment tooth was the non-load side abutment. The direction of abutment tooth movement was not altered significantly by clasp design. In regarding to the magnitude of the abutment movement, casting with I bar as retentive clasp arm exhibit greater abutment tooth movement than did other clasp assemblies. The other three designs did not significantly differ as to their effect on abutment tooth movement.
Bissada et al. investigated the gingival responses to various types of removable partial dentures. The purpose of this investigation was to seek a solution to weather the partial dentures should cover the gingival margin, with or without relief, or should the free gingival margin be uncovered. Sixty eight patients were selected on the basis of having 2 or 3 maxillary teeth missing. During the study, 28 metallic and 40 nonmetallic partial dentures were constructed. There were three dentogingival relationships as described above. Clinical and histologic evidence was taken at 1, 6, and 12 months. The results were that the denture made with no gingival relief had the most associated pathology. In addition the metallic partial caused less inflammation than the resin dentures. There were no radiographic changes noted. This was a very well done study. Most of the basic removable partial denture concepts are based on the relationship between the gingival margin and the denture, and this article added or dictated some of these concepts of denture design. It had every thing except for a control. The take home message is that partial must be away from the tissues. The fact that metallic removable partial dentures elicited less gingival inflammatory changes needs to be related to the type of acrylic used and how fast it became porous and trapped plaque.
Other area of partial designes are the occlusal rest and the use of stress breaker. Occlusal rests should be designed to direct the forces along the vertical axis of the tooth. To accomplish this, the rest is seated in a spoon-shaped preparation in the abutment tooth with the preparation floor inclined so that the deepest point is toward the vertical axis of the tooth. This purpose is also accomplished if occlusal rests are extended beyond the central zone of the occlusal surface of premolars or if the occlusal surface overlying one of the roots of the molars is covered. Removable partial prostheses should always be constructed with occlusal rests. Rests are sometimes omitted for the ostensible purpose of reducing axial load on teeth with weakened periodontal support. Such dentures jeopardize the teeth, because they settle and cause gingival and periodontal disturbances. Stress breakers, which connect the retainer and saddle areas with flexible and movable joints, are sometimes used to prevent excessive occlusal forces on abutment teeth. However, comparisons have revealed no advantage of stress breakers over rigid connectors in this respect. With rigid connectors between clasps and saddle areas, the resilience of the mucosa acts as a stress breaker. It permits controlled movement of the prosthesis so that the tissue-borne sections take the initial occlusal stress and prevent sudden impact on the periodontium of the natural teeth.
Rissin et al published an investigation which purpose was to longitudinally study the response of the periodontal health related to fixed and removable partial denture abutment teeth. This study was performed at a VA facility with 1221 subjects that were recalled at three year intervals to access the purpose of this investigation. The results showed that there was no difference between the periodontal health of fixed and removable partial denture abutment teeth. However, regardless of treatment good home care, and professional care must be taken. The interesting finding was that replacing missing teeth reduced mobility in either the fixed or removable situations. The intentions of this study are good; however, the designs of either prosthetic devices were not considered a factor. But we may take from this that even though we do not know what type of device was used, we can assume that oral hygiene instructions is a must.
Another issue of partial design is to determine the number of abutment teeth to be used. Increase periodontal support can be achieve with higher number of abutment teeth. Multiple abutments reduce injurious lateral and torsional stresses on abutment teeth, and their use should be standard procedure in patients with reduced periodontal support and those who are to receive removable partial dentures. The clinician can make multiple abutments by connecting inlays or crowns or by clasping abutment and adjacent teeth in sequence. When the terminal tooth is periodontally weak, more than one adjacent tooth should be used for added support. Joining a weakened tooth to a strong one is as likely to weaken the strong tooth as to strengthen the weak one. It is always advisable to consider whether the long-term interest of the patient would be better served by extracting the prospective weak abutment tooth and making a multiple abutment of two adjacent teeth that are relatively well supported.
One of the concern regarding removable therapy is the loss of underlying bone height due to direct pressure from the partial. Hedegard in 1962, Carlsson et al. in 1969 reported of reduction of height of the mandible in edentulous segments under removable partial dentures. Preserving the canine and fabricating an over denture can retard progressive residual ridge reduction. This procedure has three obvious advantages for the patient: First, there is increased retention and stability of the denture base. Second, there is evidence that the proprioceptive capacity of a patient with a full denture utilizing some teeth as abutments is dramatically improved over that seen with a conventional full denture design. Third, the presence of teeth under a full denture provides a reduced amount of stress on the edentulous ridges, resulting in less bone resorption over time.
Caranza and Newman outlined essentials factors concerning treatment planing for overdenture:
1. The presence of an adequate zone of attached (keratinized) gingiva around these abutment teeth is of critical importance.
2. Any remaining residual periodontal defects must be treated in the same way as they would be around any periodontally involved tooth prior to the final restoration.
Another advantage in the use of overdenture regarding periodontally involved teeth is that it is possible to improve the crown-to-root ratio dramatically. This results in a great diminution in the forces that are applied to the remaining root.
Davis et al. reported the result of a two year longitudinal study of the periodontal health status of overdenture patients. Roots were prepared endodontically and capped with amalgam, low viscosity composite resin sealant, or gold coping. Overdenture prostheses were constructed with a bilateral balanced occlusal scheme. Periodontal health status of each of abutment root were evaluated using color photograph, visual assessment of tissue tone, color, consistency, and pocket depth measurement were performed using periodontal probe. Amount of attached gingiva were also documented. Tooth mobility and bleeding upon probing were recorded. The results indicated that the overall pocket depth did not change significantly. The mandibular teeth, however, showed greater risk of increased pocket depth than are maxillary teeth when covered with an overdenture. There was no significant decrease in the width of attached gingiva in the maxillary teeth but there was such a decrease in mandibular teeth, which coincided with the increase in pocket depth of the mandibular teeth. Bleeding upon probing also increased with 20% of caries incidence found. Nevertheless, the study concluded that with regular recall of patients, overdentures appear to be a successful method of treatment.
Renner et al. reported a four-year longitudinal study of the periodontal health status of overdenture patients. There were seven patients involved in this study with a total of 12 roots that were treated with overdentures in both the maxillary and mandibular arches. The patients were recalled every six months for a period of 4 years. The findings were that the gingival tissues around the abutment teeth were inflamed and bleed on probing. There was no changes in PD and width of attached gingiva in the same arch, but when comparing maxillary with mandibular there was a difference. Half the roots were immobile at the 4 year mark. Lastly there was a little problem with root caries in 5 of the teeth. In short, good recall program for oral hygiene instructions and adjustment is needed.
Budtz-Jorgensen investigated the effect of denture-wearing habits in 31 overdenture wearers (17 day-and-night wearers, 14 day wearers) during a period of 5 years with controlled oral hygiene. Prior to prosthetic treatment, intensive instruction and motivation in oral hygiene were carried out and the patients were recalled 2-4 x yearly during the study period. Before treatment, mean plaque index (PlI) and gingival index (GI) were 1.5 and 1.6, respectively, in both groups of patients. During the study period, mean PlI and GI were 0.3-0.6 and 0.6-0.8, respectively, in the group of day wearers and 0.5-1.0 and 1.0-1.2, respectively, in the group of day-and-night wearers. With regard to the GI, this difference was statistically significant. Furthermore, during the study period, 20% of the abutment tooth surfaces showed attachment loss (1-4 mm) in the group of day-and-night wearers against 8% of the tooth surfaces in the group of day wearers. This difference was statistically significant. During the 5 years, 40 carious lesions developed in the group of day-and-night wearers against 3 in the group of day wearers. The results of this study have shown that day-and-night wearing of dentures is a major periodontitis and caries risk factor in complete overdenture wearers with controlled oral hygiene.
Today the best option for treating edentulism distal to the remaining teeth is dental implants. Many patients who formerly were treated with removable prosthodontic appliances (e.g., those with bilateral edentulous areas) can now be treated with fixed appliances using dental implants as distal abutments.
Quirynen et al reported on the use of osseointegrated titanium fixtures (Branemark) in partially edentulous patients. The tissue reactions around 509 implants in 97 upper and 71 lower jaws of 146 consecutive patients, rehabilitated by means of partial bridges--supported by implants only (60%) or by the combination of teeth and implants (40%)--were observed longitudinally. The mean number of implants per bridge was 2.40 (range 1-5) for the upper jaw and 2.06 (range 1-5) for the lower jaw respectively. Before loading, a total of 23 fixtures were lost, 15 in the upper and 8 in the lower jaw. This loss could partially be correlated to per- and post-operative complications and to fixture characteristics (length, self-tapping or not). After a loading time of 30 months (range 2 to 77 months), 6 implants, 2 in the upper and 4 in the lower jaw, showed symptoms of non-integration. The cumulative failure rate for the individual fixtures after a 6-year period reached 5.7 and 6.5% for the upper and lower jaw, respectively. The mean annual marginal bone loss, scored on standardized radiographs, was 0.9 mm during the 1st year and 0.1 mm the following years. This loss in marginal bone height was equal in the upper and lower jaws and not related to the type of occlusal material of the bridges. The present data showed that the cumulative failure rate for Branemark implants supporting partial bridges can be limited to 6% after a 6-year period, and that the radiographic bone loss is comparable with that found around fixtures supporting full bridges.
In summary, removable partial denture is an invaluable restorative option to the patient providing the careful diagnosis and treatment planing concerning establishing periodontal health, achieving and maintaining excellent oral hygiene, optimal design and construction of the prosthesis regarding various components and occlusal scheme. The success of the therapy lies in the hands of the clinician who must be totally competent to render a comprehensive diagnosis of the partially edentulous mouth and must plan every detail of treatment. With careful preparation of the patient and accurate design and construction of the prosthesis, the dentist can preserve the longevity of the remaining dentition and restoring the functional and comfort of the patient.

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References

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