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Soft tissue displacement beneath removable partial and complete dentures
SOFT TISSUE DISPLACEMENT AND COMPLETE DENTURES ROBERT B. LYTLE, CAPTAIN Camp Lejeune, N. C.
BENEATH
REMOVABLE
PARTIAL
(DC) USN
in the construction of removable dentures are based V on theories relative toused the characteristics and behavior of the soft tissues of the ARIOUS
TECHNIQUES
denture foundation. The fact that these theories vary widely accounts for much of the confusion in the field of removable denture prosthetics. While few would advocate a universal technique for all patients who require dentures, it would seem logical that a more complete understanding of the behavior of tissues beneath dentures would justify some techniques, condemn others, and result in a more clearly defined approach to each individual situation that confronts those who render denture service. The role the subjacent soft tissues play in the successor failure of removable dentures is unique and interesting. In order to understand this role, one must recognize that the soft tissuesbeneath denture baseshave both a mechanical and a physiologic function. Mechanically, they act as a buffer or cushion through which stresses on the denture are transferred to the supporting bone. Physiologically, the blood vesselsof the soft tissuesprovide nourishment to the supporting bone of the denture foundation. A denture that mechanically abuses the subjacent soft tissues hinders the physiologic functions of these tissues. On the other hand, any systemic condition that affects unfavorably the physiologic function also affects the mechanical capabilities of the tissues. Removable partial dentures that are not entirely tooth supported, as well as all complete dentures, displace and affect the form of the underlying soft tissues. An understanding of this displacement and the relationship that exists between the denture base and the underlying contacting soft tissues is necessary in treatment of patients who require dentures. Close examination reveals that soft tissue displacement may exist for some time after a denture is removed from the mouth. Thus, the soft tissues beneath illfitting dentures are actually deformed. The purpose of this study is to determine the magnitude of soft tissue displacement beneath dentures. The opinions or assertions contained herein are the private ones of the not to be construed as official or reflecting the views of the Navy Department service at large. Read before the Academy of Denture Prosthetics in Minneapolis, Minn. 34
author and are or the Naval
Volume 12 Number 1 DISPLACEMENT
SOFT TISSUE BENEATH
DISPLACEMENT
REMOVABLE
PARTIAL
BENEATH
DENTURES
DENTURE
BASES
35
Pwcedure.-In order to determine the nxqnitude of soft tissue displacement beneath partial denture bases,the following procedures were carried out. Casts were made from hydrocolloid impressions of twenty-five partially edentulous ridges that had been supporting partial dentures. The partial dentures then were removed for a period of time. Casts were made from hydrocolloid impressions of the same ridges after the
Fig.
7
Fig.
2
Fig. 1 .-A platform with guides and pins to aid in comparative measurements of casts oriented to a cast of an impression made after the soft tissues have recovered their normal form. Note that the pins touch the cast and are secured to the guide tubes with wax. Fig. 2.-The platform assembly with the pins secured has been transferred to a cast from an impression made immediately after the removal of the partial denture. Note that the comparative measurements between the casts seen in Figs. 1 and 2 are made with feeler gauges of known thicknesses. The gauge beneath the second pin is 0.018 inch thick and indicates the magnitude of soft tissue displacement in this area.
36
J. Pros. Den. Jan..Feb., 1962
LYTLE
soft tissues had recovered their normal form. (This tendency for soft tissues to return to their normal form will be referred to as tissue recovery.) A plastic platform was constructed that conformed to the occlusal surfaces and incisal edges of the remaining natural teeth (Figs. 1 and 2). This platform extended over the edentulous area. Orthodontic tubes placed vertically in the platform over the edentulous areas served as guides for pins that contacted the ridge at various points. The magnitude of the variations in casts made before and after the soft tissues recovered their normal form was determined by using the points of the pins as reference points. The platform was transferred to different casts of the same arch for comparative measurements. The measurements were made with feeler gauges of known thicknesses. Results.-Underextended partial denture bases caused gross soft tissue displacement. The measurements on one pair of casts revealed soft tissue displacement of more than 3 mm. existed where a mandibular free end partial denture did not cover the retromolar pad. The greatest magnitude of soft tissue displacement occurred in the area farthest from the rest support in the free end extension partial denture.
Fig.
3
Fig.
4
Fig. 3.-Projections on the impression surface of a denture caused the bicuspid and molar regions to be deformed. Fig. 4.-The soft tissues seen in Fig. 3 have recovered to a more nearly offending denture had been removed for 72 hours.
soft
tissues
normal
form.
in
the The
SOFT TISSUE
Fig.
5.- The
comparator,
DISPLACEMENT
BENEATH
37
DENTURES
an instrument for measuring the mucosal sions, casts, and dentures.
surface
contours
of impres-
Partial denture bases with projections that originally extended into unhealed sockets caused gross soft tissue displacement (Figs. 3 and 4). Measurements of several casts revealed these projections caused displacement of more than 1 mm. There was a greater magnitude of soft tissue displacement beneath ill-fitting partial denture bases in younger patients (age 18 to 25) than in older ones. There was gross soft tissue displacement beneath partial denture bases with teeth that contact prematurely. A premature contact of approximately 0.5 mm. caused the soft tissues beneath the denture base to be displaced an equal amount. Generally, only minimal soft tissue displacement occurred when the partial denture was tooth borne. Partial dentures with inadequate occlusal rest support may cause gross soft tissue displacement. Measurements of one pair of casts indicated that a partial denture without occlusal rests caused the soft tissues to be displaced more than 1.5 mm. Some areas displayed clinical evidence of inflammation with comparatively little soft tissue displacement. However, inflammation is nearly always present where there is gross soft tissue displacement. DISPLACEMENT
BENEATH
COMPLETE
DENTURES
Procedure.--In order to determine the magnitude of soft tissue displacement beneath complete dentures the following procedures were carried out. Casts were made from impressions of fifty-five edentulous ridges that showed evidence of soft tissue displacement caused by ill-fitting dentures. The impression material used was a free-flowing type. The ill-fitting dentures causing the displacement were removed for approximately 60 hours. This permitted tissue recovery, return of the tissues to a more normal form.
38
J. Pros. Den. Jan.-Feb., 1962
LYTLE Fig.
6
Fig.
7
Fig. B.-Comparative measurements of casts from impressions made before and after soft tissue recovery in a 24-year-old patient (measurements are indicated in 0.001 inch increments): the contour of the ridge crest before tissue recovery from the right hamular notch ( -) around to the incisive papilla and continuing to the h,amular notch on the left; (- - -) the contour of a cast from an impression made after tissue recovery. Compare the magnitude of soft tissue displacement with that shown in Fig. 7. Fig. 7.-Tissue displacement in a patient 75 years of age: () the contour of the cast made before tissue recovery; ( - - -) the contour of the cast made after tissue recovery. Compare the magnitude of soft tissue displacement with that shown in Fig. 6.
Casts from impressions of the ridges made afterward were compared with the casts made before soft tissue recovery. The comparison was made by using a dental comparator made available to me by the National Bureau of Standards (Fig. 5).* lies&s.-In general, the magnitude of change in form of soft tissues after approximately 60 hours of recovery time was greater in patients less than 30 years of age than in patients older than 30, up to 70 years (Figs. 6 and 7). The soft tissues were usually displaced more on the mandibular arch than on the maxillary arch (Fig. 8). In most instances, the soft tissue displacement allowed the denture to be placed nearer the bony residual ridge ; too, the interocclusal distance was less when the denture was placed again on the ridge after the tissues recovered to a more nearly normal form (Fig. 8). The greatest amount of displacement in the maxillary arch occurred on the crest of the ridge in the anterior region (Fig. 9). Soft tissue displacement measured as much as 0.095 inch on 1 patient (Fig. 9). However, the average displacement in areas of extreme abuse was more often found to be from 0.050 to 0.070 inch. Projections of the denture base that extended into unhealed sockets caused gross soft tissue displacement (Fig. IO). The soft tissues were grossly displaced where there were premature interceptive occlusal contacts (Fig. S) . The contour of the displaced soft tissues was higher than normal, i.e., elevated from the ridge, only where there had been a space between the denture and the *The basic instrument is known as the Dentograph, designed and manufactured by G. R. Kern, with modifications, for the purpose of comparative measurements, made at the National Jr., and W. T. Sweeney. An Bureau of Standards by N. W. Rupp, G. Dickson, M. E. Lawson, article describing this instrument has been pub1ished.l
Volume 12 Number 1
SOFT TISSUE
DISPLACEMENT
BENEATH
DENTURES
39
soft tissues in the area adjacent to an area where the denture caused excessive pressure. The underlying soft tissues tended to conform to the contour of the impression surface of the denture (Fig. 11) . A study of several patients revealed displacement of the soft tissues beneath new dentures that had been properly constructed from impressions of recovered tissues, but this displacement was much less than that caused by ill-fitting dentures (Figs. 12 and 13). Improved tissue color was noted clinically when the soft tissues recovered a more normal form. The soft tissues became more firm when the condition of abuse subsided upon removal of the ill-fitting denture. ADDITIONAL
METHODS
OF STUDY
The magnitude and location of soft tissue displacement may be observed and studied in other ways.2 If impressions are made with a free-flowing material before and after tissue recovery, cross sections of casts from these impressions can be compared to show the magnitude of the change in contour.
Fig. %-Tissue displacement in the first molar region. The soft tissues are displaced as much as 0.045 to 0.055 inch on the crest of the mandibular ridge as compared to 0.028 to 0.030 inch on the crest of the maxillary ridge: ( -) the contour of the cast made before tissue recovery; ( - - - ) the contour of the cast made after tissue recovery,
Fig. Q.-Comparative measurements were made through the midline of maxillary casts. Note the excessive soft tissue displacement of 0.095 inch in the anterior region. Occlusal disharmony with gross intercepthe occlusal contacts in the anterior region was present in the denture: ) the contour of the cast made before tissue recovery; (- - -) the contour of the cast fmade after tissue recovery.
40
LYTLE
J. Pros. Den. Jan.-Feb., 1962
Roentgenograms made before and after tissue recovery offer other evidence of change. A thin strip of metal foil placed on the mucosa of the ridge crest makes it hossible to compare the contour and thickness of the soft tissues.* Cephalometric roentgenograms made with the dentures in place help show the position of the dentures in relation to the bony landmarks of the mandible and skull. Metal markers placed in the impression surface of the denture base in the bicuspid and molar regions make this method of study more precise. Ill-fitting dentures that have displaced the soft tissues of the denture-supporting area may show gross changes in their position, in relation to bony landmarks, when they are replaced on tissues that have recovered normal form. These changes are accompanied by loss of retention, lack of stability, and changes in the occlusal relationship of the dentures. A study of these changes reveals an important fact:
Fig. lO.-The soft tissue was displaced 0.052, 0.048, 0.033, 0.037, 0.030, and 0.036 inch in the areas where projections of the denture base had originally extended into unhealed tooth sockets. This patient had worn the denture 1 year: f) the contour of the cast made before tissue recovery; ( - - - ) the contour of the cast made after tissue recovery.
the soft tissues of the denture-supporting area may accommodate ill-fitting dentures ; because of their ability to make this accommodation, gross occlusal discrepancies may be concealed, and the retention and stability manifested may be at the expense of the health of the soft tissues. When a disclosing material is placed on an impression surface of a denture base that has been out of the mouth for tissue recovery and the denture is reseated, the areas of the base that cause soft tissue displacement will be revealed. SUMMARY
OF RESULTS
The form of the soft tissues beneath complete dentures is affected by (1) pressures on the teeth or denture base opposite the impression surfaces, (2) the contour of the denture impression surface, and (3) the size of the area covered by the denture. The form of the soft tissues beneath removable partial denture bases is affected supporting rests and bracing elements influby the same three factors. However, ence the location and magnitude of displacement. DISCUSSION
Where there is extreme abuse from an ill-fitting denture, the tissues may remain in a displaced state for hours or even days. Considering the time factor, it is *C. 0. Boucher:
Personal
communication.
Volume 12 Number 1
SOFT
TISSUE
DISPLACEMENT
BENEATH
DENTURES
41
difficult to draw a line between normal physiologic displacement and pathologic deformation of the soft tissues. In general, one can say normal physiologic displacement ceases to exist where there is evidence of inflammation caused by mechanical factors. Histologic examination of abused soft tissues of the denture foundation invariably reveals that the blood vessels are dilated and that there is an infiltration of inflammatory cells in the connective tissue. Soft tissues that do not return readily to normal form may have reached a point of fatigue and tend to remain in a displaced form for some time after the offending stress is removed. Some partial denture techniques are based on the ability of the soft tissues to return an appliance to a predetermined position upon the removal of stress. The refractoriness of tissues to return immediately to normal form makes the employment of such a method questionable. Good results from such techniques are more likely attained because of other reasons. Evidence of gross soft tissue displacement or deformation indicates excessive pressures may be damaging the structures that support dentures.3 Often, the first sign of the destruction of the residual ridges under ill-fitting dentures is the deformed and traumatized condition of the soft tissues where there has been excessive pressure. Slight intermittent displacement of the tissues beneath dentures may be beneficial to the supporting structures; however, excessive and prolonged displacement of soft tissues may affect unfavorably the health of the underlying bone.
Fig. Il.-Excessive pressure and the contour of the impression surface of the denture on the left side caused the soft tissues to be depressed 0.060 inch, and adjacent to this area, the soft tissues conformed to the contour of the denture base. Medial to the pressure area, they were 0.030 higher on the cast from an impression made before soft tissue recovery than on the cast from an impression made after soft tissue recovery.
ILL-
FITTING
NEW
DENTURE
OENTURE
Fig. 12.-Soft tissue displacement caused by an ill-fitting maxill,ary denture is compared soft tissue displacement caused by a new denture: ( -) the contour of the cast made tissue recovery; ( - - - ) the contour of the cast made after tissue recovery.
with before
42
J. Pros. Den.
LYTLE
ILL-
FITTING
NEW
Jan.-Feb.,
1962
DENTURE
DENTURE.
Fig. M.-Comparative measurements of contours of mandibular casts. These represent cross sections through the first molar region. Note that the ill-fitting denture caused a greater magnitude of soft tissue displacement than did the new denture: ( -) the contour of the cast made before tissue recovery; ( - - -) the contour of the cast made after tissue recovery.
The importance of conditioning soft tissue abused and deformed by ill-fitting dentures before impressions are made for new dentures can be easily justified when the magnitude of soft tissue displacement, as shown in this study, is recognized. Many dentists have complete denture patients remove their dentures for a period of time before impressions are made for new dentures. Others place temporary relining materials in the ill-fitting dentures in order to condition the tissues. Because of the advantages of each method, a combination of the two procedures is often indicated. Unfortunately, many impressions are made for new partial dentures and immediate dentures when the soft tissues surrounding the remaining teeth and covering the edentulous areas are in a displaced, deformed condition because of an ill-fitting partial denture. This perpetuates deformities and may result in further destruction of the remaining teeth and supporting structures. This faulty practice may be due to the reluctance of patients to be without their dentures or to the difficulty of placing a treatment relining material in their partial dentures. A temporary treatment partial denture with adequate occlusal rest support constructed so the base material does not contact areas of displaced soft tissues may be used to correct this condition before a new denture is constructed. Retention of natural teeth is indicated when satisfactory complete denture service would be hindered by excessive soft tissues that are easily displaced or when the normal physiologic state of the tissues is altered by systemic disturbances. A differential diagnosis that determines whether a patient receives partial or complete denture service should include an evaluation of the estimated soft tissue displacement. The estimated displaceability of the soft tissues may indicate a specific approach to a subsequent phase of the denture service which follows the diagnosis, or it may indicate surgical intervention before the construction of a removable prosthesis is started.
Volume Number
12 1
SOFT
TISSUE
DISPLACEMENT
BENEATH
DENTURES
43
SUMMARY
The soft tissue displacement that occurs beneath denture bases of removable partial and complete dentures was studied. The magnitude of displacement was determined by making comparative measurements of casts from impressions made before and after soft tissue recovery. CONCLUSIONS
1. Dentures that cause only minimal displacement of the subjacent soft tissues are more ideal than those that cause excessive displacement. 2. In order to minimize the displacement of the soft tissues beneath denture bases, the following procedures should be used : (1) Denture bases should be extended to cover the maximum area of the denture foundation compatible with the movement of the border tissues. (2) Denture bases should not extend into unhealed sockets. (3) Interceptive occlusal contacts should be eliminated prior to the time the patient wears a new denture. 3. Removable partial dentures should be designed with strategically placed rests on the remaining natural teeth. 4. Soft tissues that have been displaced by an ill-fitting denture should be returned to normal form before impressions are made for new dentures. 5. Future scientific advancements in removable denture service must include a more complete knowledge and understanding of the physiologic condition of the soft tissues of the denture foundation. REFERENCES
1. Rupp, N. W., Dickson, G., Lawson, M. E., Jr., and Measuring the Mucosal Surface Contours of J.A.D.A. 54:24-32,1957. 2. Lytle, R. B.: The Management of Abused Oral Tissues J. PROS. DEN. 7:27-42, 1957. 3. Lytle, R. B.: Complete Denture Construction Based on Underlying Soft Tissues, J. PROS. DEN. 9:539-S%, M.O.Q. 2301 CAMP
LEJEUXE.
N.
C.
Sweeney, W. T.: A Method for Impressions, Casts, and Dentures, in Complete Denture Construction, a Study of the Deformation 1959.
of the
BENEATH
REMOVABLE
PARTIAL
(DC) USN
in the construction of removable dentures are based V on theories relative toused the characteristics and behavior of the soft tissues of the ARIOUS
TECHNIQUES
denture foundation. The fact that these theories vary widely accounts for much of the confusion in the field of removable denture prosthetics. While few would advocate a universal technique for all patients who require dentures, it would seem logical that a more complete understanding of the behavior of tissues beneath dentures would justify some techniques, condemn others, and result in a more clearly defined approach to each individual situation that confronts those who render denture service. The role the subjacent soft tissues play in the successor failure of removable dentures is unique and interesting. In order to understand this role, one must recognize that the soft tissuesbeneath denture baseshave both a mechanical and a physiologic function. Mechanically, they act as a buffer or cushion through which stresses on the denture are transferred to the supporting bone. Physiologically, the blood vesselsof the soft tissuesprovide nourishment to the supporting bone of the denture foundation. A denture that mechanically abuses the subjacent soft tissues hinders the physiologic functions of these tissues. On the other hand, any systemic condition that affects unfavorably the physiologic function also affects the mechanical capabilities of the tissues. Removable partial dentures that are not entirely tooth supported, as well as all complete dentures, displace and affect the form of the underlying soft tissues. An understanding of this displacement and the relationship that exists between the denture base and the underlying contacting soft tissues is necessary in treatment of patients who require dentures. Close examination reveals that soft tissue displacement may exist for some time after a denture is removed from the mouth. Thus, the soft tissues beneath illfitting dentures are actually deformed. The purpose of this study is to determine the magnitude of soft tissue displacement beneath dentures. The opinions or assertions contained herein are the private ones of the not to be construed as official or reflecting the views of the Navy Department service at large. Read before the Academy of Denture Prosthetics in Minneapolis, Minn. 34
author and are or the Naval
Volume 12 Number 1 DISPLACEMENT
SOFT TISSUE BENEATH
DISPLACEMENT
REMOVABLE
PARTIAL
BENEATH
DENTURES
DENTURE
BASES
35
Pwcedure.-In order to determine the nxqnitude of soft tissue displacement beneath partial denture bases,the following procedures were carried out. Casts were made from hydrocolloid impressions of twenty-five partially edentulous ridges that had been supporting partial dentures. The partial dentures then were removed for a period of time. Casts were made from hydrocolloid impressions of the same ridges after the
Fig.
7
Fig.
2
Fig. 1 .-A platform with guides and pins to aid in comparative measurements of casts oriented to a cast of an impression made after the soft tissues have recovered their normal form. Note that the pins touch the cast and are secured to the guide tubes with wax. Fig. 2.-The platform assembly with the pins secured has been transferred to a cast from an impression made immediately after the removal of the partial denture. Note that the comparative measurements between the casts seen in Figs. 1 and 2 are made with feeler gauges of known thicknesses. The gauge beneath the second pin is 0.018 inch thick and indicates the magnitude of soft tissue displacement in this area.
36
J. Pros. Den. Jan..Feb., 1962
LYTLE
soft tissues had recovered their normal form. (This tendency for soft tissues to return to their normal form will be referred to as tissue recovery.) A plastic platform was constructed that conformed to the occlusal surfaces and incisal edges of the remaining natural teeth (Figs. 1 and 2). This platform extended over the edentulous area. Orthodontic tubes placed vertically in the platform over the edentulous areas served as guides for pins that contacted the ridge at various points. The magnitude of the variations in casts made before and after the soft tissues recovered their normal form was determined by using the points of the pins as reference points. The platform was transferred to different casts of the same arch for comparative measurements. The measurements were made with feeler gauges of known thicknesses. Results.-Underextended partial denture bases caused gross soft tissue displacement. The measurements on one pair of casts revealed soft tissue displacement of more than 3 mm. existed where a mandibular free end partial denture did not cover the retromolar pad. The greatest magnitude of soft tissue displacement occurred in the area farthest from the rest support in the free end extension partial denture.
Fig.
3
Fig.
4
Fig. 3.-Projections on the impression surface of a denture caused the bicuspid and molar regions to be deformed. Fig. 4.-The soft tissues seen in Fig. 3 have recovered to a more nearly offending denture had been removed for 72 hours.
soft
tissues
normal
form.
in
the The
SOFT TISSUE
Fig.
5.- The
comparator,
DISPLACEMENT
BENEATH
37
DENTURES
an instrument for measuring the mucosal sions, casts, and dentures.
surface
contours
of impres-
Partial denture bases with projections that originally extended into unhealed sockets caused gross soft tissue displacement (Figs. 3 and 4). Measurements of several casts revealed these projections caused displacement of more than 1 mm. There was a greater magnitude of soft tissue displacement beneath ill-fitting partial denture bases in younger patients (age 18 to 25) than in older ones. There was gross soft tissue displacement beneath partial denture bases with teeth that contact prematurely. A premature contact of approximately 0.5 mm. caused the soft tissues beneath the denture base to be displaced an equal amount. Generally, only minimal soft tissue displacement occurred when the partial denture was tooth borne. Partial dentures with inadequate occlusal rest support may cause gross soft tissue displacement. Measurements of one pair of casts indicated that a partial denture without occlusal rests caused the soft tissues to be displaced more than 1.5 mm. Some areas displayed clinical evidence of inflammation with comparatively little soft tissue displacement. However, inflammation is nearly always present where there is gross soft tissue displacement. DISPLACEMENT
BENEATH
COMPLETE
DENTURES
Procedure.--In order to determine the magnitude of soft tissue displacement beneath complete dentures the following procedures were carried out. Casts were made from impressions of fifty-five edentulous ridges that showed evidence of soft tissue displacement caused by ill-fitting dentures. The impression material used was a free-flowing type. The ill-fitting dentures causing the displacement were removed for approximately 60 hours. This permitted tissue recovery, return of the tissues to a more normal form.
38
J. Pros. Den. Jan.-Feb., 1962
LYTLE Fig.
6
Fig.
7
Fig. B.-Comparative measurements of casts from impressions made before and after soft tissue recovery in a 24-year-old patient (measurements are indicated in 0.001 inch increments): the contour of the ridge crest before tissue recovery from the right hamular notch ( -) around to the incisive papilla and continuing to the h,amular notch on the left; (- - -) the contour of a cast from an impression made after tissue recovery. Compare the magnitude of soft tissue displacement with that shown in Fig. 7. Fig. 7.-Tissue displacement in a patient 75 years of age: () the contour of the cast made before tissue recovery; ( - - -) the contour of the cast made after tissue recovery. Compare the magnitude of soft tissue displacement with that shown in Fig. 6.
Casts from impressions of the ridges made afterward were compared with the casts made before soft tissue recovery. The comparison was made by using a dental comparator made available to me by the National Bureau of Standards (Fig. 5).* lies&s.-In general, the magnitude of change in form of soft tissues after approximately 60 hours of recovery time was greater in patients less than 30 years of age than in patients older than 30, up to 70 years (Figs. 6 and 7). The soft tissues were usually displaced more on the mandibular arch than on the maxillary arch (Fig. 8). In most instances, the soft tissue displacement allowed the denture to be placed nearer the bony residual ridge ; too, the interocclusal distance was less when the denture was placed again on the ridge after the tissues recovered to a more nearly normal form (Fig. 8). The greatest amount of displacement in the maxillary arch occurred on the crest of the ridge in the anterior region (Fig. 9). Soft tissue displacement measured as much as 0.095 inch on 1 patient (Fig. 9). However, the average displacement in areas of extreme abuse was more often found to be from 0.050 to 0.070 inch. Projections of the denture base that extended into unhealed sockets caused gross soft tissue displacement (Fig. IO). The soft tissues were grossly displaced where there were premature interceptive occlusal contacts (Fig. S) . The contour of the displaced soft tissues was higher than normal, i.e., elevated from the ridge, only where there had been a space between the denture and the *The basic instrument is known as the Dentograph, designed and manufactured by G. R. Kern, with modifications, for the purpose of comparative measurements, made at the National Jr., and W. T. Sweeney. An Bureau of Standards by N. W. Rupp, G. Dickson, M. E. Lawson, article describing this instrument has been pub1ished.l
Volume 12 Number 1
SOFT TISSUE
DISPLACEMENT
BENEATH
DENTURES
39
soft tissues in the area adjacent to an area where the denture caused excessive pressure. The underlying soft tissues tended to conform to the contour of the impression surface of the denture (Fig. 11) . A study of several patients revealed displacement of the soft tissues beneath new dentures that had been properly constructed from impressions of recovered tissues, but this displacement was much less than that caused by ill-fitting dentures (Figs. 12 and 13). Improved tissue color was noted clinically when the soft tissues recovered a more normal form. The soft tissues became more firm when the condition of abuse subsided upon removal of the ill-fitting denture. ADDITIONAL
METHODS
OF STUDY
The magnitude and location of soft tissue displacement may be observed and studied in other ways.2 If impressions are made with a free-flowing material before and after tissue recovery, cross sections of casts from these impressions can be compared to show the magnitude of the change in contour.
Fig. %-Tissue displacement in the first molar region. The soft tissues are displaced as much as 0.045 to 0.055 inch on the crest of the mandibular ridge as compared to 0.028 to 0.030 inch on the crest of the maxillary ridge: ( -) the contour of the cast made before tissue recovery; ( - - - ) the contour of the cast made after tissue recovery,
Fig. Q.-Comparative measurements were made through the midline of maxillary casts. Note the excessive soft tissue displacement of 0.095 inch in the anterior region. Occlusal disharmony with gross intercepthe occlusal contacts in the anterior region was present in the denture: ) the contour of the cast made before tissue recovery; (- - -) the contour of the cast fmade after tissue recovery.
40
LYTLE
J. Pros. Den. Jan.-Feb., 1962
Roentgenograms made before and after tissue recovery offer other evidence of change. A thin strip of metal foil placed on the mucosa of the ridge crest makes it hossible to compare the contour and thickness of the soft tissues.* Cephalometric roentgenograms made with the dentures in place help show the position of the dentures in relation to the bony landmarks of the mandible and skull. Metal markers placed in the impression surface of the denture base in the bicuspid and molar regions make this method of study more precise. Ill-fitting dentures that have displaced the soft tissues of the denture-supporting area may show gross changes in their position, in relation to bony landmarks, when they are replaced on tissues that have recovered normal form. These changes are accompanied by loss of retention, lack of stability, and changes in the occlusal relationship of the dentures. A study of these changes reveals an important fact:
Fig. lO.-The soft tissue was displaced 0.052, 0.048, 0.033, 0.037, 0.030, and 0.036 inch in the areas where projections of the denture base had originally extended into unhealed tooth sockets. This patient had worn the denture 1 year: f) the contour of the cast made before tissue recovery; ( - - - ) the contour of the cast made after tissue recovery.
the soft tissues of the denture-supporting area may accommodate ill-fitting dentures ; because of their ability to make this accommodation, gross occlusal discrepancies may be concealed, and the retention and stability manifested may be at the expense of the health of the soft tissues. When a disclosing material is placed on an impression surface of a denture base that has been out of the mouth for tissue recovery and the denture is reseated, the areas of the base that cause soft tissue displacement will be revealed. SUMMARY
OF RESULTS
The form of the soft tissues beneath complete dentures is affected by (1) pressures on the teeth or denture base opposite the impression surfaces, (2) the contour of the denture impression surface, and (3) the size of the area covered by the denture. The form of the soft tissues beneath removable partial denture bases is affected supporting rests and bracing elements influby the same three factors. However, ence the location and magnitude of displacement. DISCUSSION
Where there is extreme abuse from an ill-fitting denture, the tissues may remain in a displaced state for hours or even days. Considering the time factor, it is *C. 0. Boucher:
Personal
communication.
Volume 12 Number 1
SOFT
TISSUE
DISPLACEMENT
BENEATH
DENTURES
41
difficult to draw a line between normal physiologic displacement and pathologic deformation of the soft tissues. In general, one can say normal physiologic displacement ceases to exist where there is evidence of inflammation caused by mechanical factors. Histologic examination of abused soft tissues of the denture foundation invariably reveals that the blood vessels are dilated and that there is an infiltration of inflammatory cells in the connective tissue. Soft tissues that do not return readily to normal form may have reached a point of fatigue and tend to remain in a displaced form for some time after the offending stress is removed. Some partial denture techniques are based on the ability of the soft tissues to return an appliance to a predetermined position upon the removal of stress. The refractoriness of tissues to return immediately to normal form makes the employment of such a method questionable. Good results from such techniques are more likely attained because of other reasons. Evidence of gross soft tissue displacement or deformation indicates excessive pressures may be damaging the structures that support dentures.3 Often, the first sign of the destruction of the residual ridges under ill-fitting dentures is the deformed and traumatized condition of the soft tissues where there has been excessive pressure. Slight intermittent displacement of the tissues beneath dentures may be beneficial to the supporting structures; however, excessive and prolonged displacement of soft tissues may affect unfavorably the health of the underlying bone.
Fig. Il.-Excessive pressure and the contour of the impression surface of the denture on the left side caused the soft tissues to be depressed 0.060 inch, and adjacent to this area, the soft tissues conformed to the contour of the denture base. Medial to the pressure area, they were 0.030 higher on the cast from an impression made before soft tissue recovery than on the cast from an impression made after soft tissue recovery.
ILL-
FITTING
NEW
DENTURE
OENTURE
Fig. 12.-Soft tissue displacement caused by an ill-fitting maxill,ary denture is compared soft tissue displacement caused by a new denture: ( -) the contour of the cast made tissue recovery; ( - - - ) the contour of the cast made after tissue recovery.
with before
42
J. Pros. Den.
LYTLE
ILL-
FITTING
NEW
Jan.-Feb.,
1962
DENTURE
DENTURE.
Fig. M.-Comparative measurements of contours of mandibular casts. These represent cross sections through the first molar region. Note that the ill-fitting denture caused a greater magnitude of soft tissue displacement than did the new denture: ( -) the contour of the cast made before tissue recovery; ( - - -) the contour of the cast made after tissue recovery.
The importance of conditioning soft tissue abused and deformed by ill-fitting dentures before impressions are made for new dentures can be easily justified when the magnitude of soft tissue displacement, as shown in this study, is recognized. Many dentists have complete denture patients remove their dentures for a period of time before impressions are made for new dentures. Others place temporary relining materials in the ill-fitting dentures in order to condition the tissues. Because of the advantages of each method, a combination of the two procedures is often indicated. Unfortunately, many impressions are made for new partial dentures and immediate dentures when the soft tissues surrounding the remaining teeth and covering the edentulous areas are in a displaced, deformed condition because of an ill-fitting partial denture. This perpetuates deformities and may result in further destruction of the remaining teeth and supporting structures. This faulty practice may be due to the reluctance of patients to be without their dentures or to the difficulty of placing a treatment relining material in their partial dentures. A temporary treatment partial denture with adequate occlusal rest support constructed so the base material does not contact areas of displaced soft tissues may be used to correct this condition before a new denture is constructed. Retention of natural teeth is indicated when satisfactory complete denture service would be hindered by excessive soft tissues that are easily displaced or when the normal physiologic state of the tissues is altered by systemic disturbances. A differential diagnosis that determines whether a patient receives partial or complete denture service should include an evaluation of the estimated soft tissue displacement. The estimated displaceability of the soft tissues may indicate a specific approach to a subsequent phase of the denture service which follows the diagnosis, or it may indicate surgical intervention before the construction of a removable prosthesis is started.
Volume Number
12 1
SOFT
TISSUE
DISPLACEMENT
BENEATH
DENTURES
43
SUMMARY
The soft tissue displacement that occurs beneath denture bases of removable partial and complete dentures was studied. The magnitude of displacement was determined by making comparative measurements of casts from impressions made before and after soft tissue recovery. CONCLUSIONS
1. Dentures that cause only minimal displacement of the subjacent soft tissues are more ideal than those that cause excessive displacement. 2. In order to minimize the displacement of the soft tissues beneath denture bases, the following procedures should be used : (1) Denture bases should be extended to cover the maximum area of the denture foundation compatible with the movement of the border tissues. (2) Denture bases should not extend into unhealed sockets. (3) Interceptive occlusal contacts should be eliminated prior to the time the patient wears a new denture. 3. Removable partial dentures should be designed with strategically placed rests on the remaining natural teeth. 4. Soft tissues that have been displaced by an ill-fitting denture should be returned to normal form before impressions are made for new dentures. 5. Future scientific advancements in removable denture service must include a more complete knowledge and understanding of the physiologic condition of the soft tissues of the denture foundation. REFERENCES
1. Rupp, N. W., Dickson, G., Lawson, M. E., Jr., and Measuring the Mucosal Surface Contours of J.A.D.A. 54:24-32,1957. 2. Lytle, R. B.: The Management of Abused Oral Tissues J. PROS. DEN. 7:27-42, 1957. 3. Lytle, R. B.: Complete Denture Construction Based on Underlying Soft Tissues, J. PROS. DEN. 9:539-S%, M.O.Q. 2301 CAMP
LEJEUXE.
N.
C.
Sweeney, W. T.: A Method for Impressions, Casts, and Dentures, in Complete Denture Construction, a Study of the Deformation 1959.
of the