Photoelastic occlusions Stephen Lopuck, Sepulveda
comparison
D.D.S.,*
James Smith,
Veterans Administration
Hospital.
of posterior D.D.S.,**
and Angelo
Sepulveda,
Calif.
ndentures
distribute stresses to the residual alveolar ridge which contribute to the degeneration of the supporting bone.‘.’ The mandible seems especially susceptible to such degeneration.“-“’ In long-term longitudinal studies of denture patients Atwood” and Tallgren” substantiated the fact that under complete denture function approximately four times more bone reduction occurs in the mandible than in the maxillae. The edentulous mandible is not structurally capable of withstanding forces that the dentoalveolar attachment apparatus had once dissipated effectively.‘. ‘I-I4 Dentists have been aware of this problem and have developed numerous philosophies about tooth form, tooth materials, and placement of teeth.‘:-‘” The objective of this investigation was to evaluate the stresses that complete mandibular dentures transmit to the residual alveolar ridge when various tooth forms and materials are used. METHOD
AND MATERIALS
Photoelastic stressanalysis is useful in dentistry for evaluating stresscharacteristics of some systems.J”-‘S This type of analysis consistsof replicating an object in photoelastic plastic, loading the photoelastic model, and viewing the resultant stress patterns developed in the model through special polarizing filters. In this study a representative edentulous mandibular arch of medium ridge height and form was replicated in a photoelastic materialt (Figs. I and 2). *Senior Resident in Removable Prosthodontics, Veterans Administration Hospital, Sepulveda. Calif. **Formerly Staff Prosthodontist, Sepulveda Veterans Administration Hospital; Presently in private practice in Omaha. Neb. ***Formerly Bio-Dental Engineer, Sepulveda Veterans Administration Hospital; Presently Professor and Chairman of Riomaterial Science, UCLA School of Dentistry, Los Angeles, Calif. iPI. 2. Photolastic Inc.. &Ialvrrn. Pa.
18
JULY
1976
VOLUME
40
NUMBER
1
denture Caputo, Ph.D.***
Four stone casts of the photoelastic model were mounted on a Hanau H articulator* using a special jig to maintain centric and vertical positions. The photoelastic model also was mounted on the same articulator with the samejig. Four identical sets of dentures were fabricated. Plastic teeth with two posterior forms, one Hat and the other at a 33 degree cusp angulation, were used on two sets. Porcelain teetht with the same two forms of flat and 33 degree cusps were used on the other two sets. All maxillary anterior teeth were set with a special placement device. Then the mandibular anterior teeth were set with the sameamount of horizontal and vertical overlap in the four dentures. There was no contact between the anterior teeth in centric occlusion. The posterior teeth bvere set directly on the crest of the ridge. The occlusal plane was located on an imaginary line between the distal of the lower canine and the middle of the retromolar pad. A standard heat-cure processing technique was usedfor the dentures, and adjustments were made to eliminate processing changes and restore the prescribed vertical dimension of occlusion. The denture-bearing surface of the mandibular dentures was uniformly relieved to a depth of 2 mm to create space for a resilient layer of mercaptan light-bodied impression materialt to simulate the mucosa (Fig. 3). The simulated mucosa was made the samethickness in each denture by mounting the photoelastic model in the articulator and repeating vertical closuresin the four dentures (Fig. 3). The photoelastic model was set on a table in the center of a straining frame that could rotate 360 degrees(Fig. 4). A fixed fiber optic light source was placed in the center of the model through an opening in the table. The model could be rotated around the ‘Hanau Engineering, Buffalo, N. Y. tTrubytr. Dcntsply International. Inc.. York. Pa $Coe-Flex. Coe I.aboratorirs, Inc.. Chicago. III.
PHOTOELASTIC
Fig.
1.
COMPARISON
OF OCCLUSIONS
Photoelastic mandibular analogue, front view.
light source without interference. The entire lateral surface of the model was visible while under a load in the straining frame (Fig. 5). The dentures, still sealed in centric occlusion, were affixed to the photoelastic model. The maxillary cast was mounted to the load cell of the straining frame with plaster. This procedure was repeated for all four sets of dentures. After the mounting the occlusion of all dentures was equilibrated to ensure equal and bilateral contacts in the posterior occlusions. The positions selected for observation of stress distribution were the anterior portion of the arch, centric occlusion, and the right and left working positions. The mounted dentures were loaded in a pure vertical direction with 11, 22, 33. and 44 pounds, respectively, to represent realistic clinical values.‘“-” A 35 mm camera was placed in a fixed position with appropriate polarizing filters and quarter-wave plates in the proper locations. White light with color film was used to photograph the stress patterns of each set of dentures at all load values.
RESULTS The stress developed was observed within the model for four sets of dentures tested and varied directly with the intensity of the applied load. The specific characteristics of the resulting stress patterns varied with type of posterior tooth. However, stress was generated in the anterior region of every denture irrespective of the type of tooth that was used. The stress patterns observed within the model with each type of posterior occlusion showed unique variation as well as some similarities. The flat occlusal schemes had stress patterns that extended anteroposteriorly in a more uniform manner (Fig. 6). The cusp teeth had stress patterns that were localized more anteriorly within the range of the flat stress pattern (Fig. 7). In overall effect the flat occlusal scheme transmitted slightly less force to the ridge than the cuspal forms did. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 2. Photoelastic mandibular analague, side view.
Fig. 3. Mercaptan soft tissue simulant on the underside of the mandibular denture. Comparison of the magnitude and depth of the stress by tooth material indicated that the porcelain teeth generated more stress within the ridge than did the plastic teeth (Figs. 6 and 7). Porcelain cusp teeth generated the most stress, while the plastic Hat teeth showed the least stress within the photoelastic model. Minor differences between porcelain flat teeth and the plastic cusp teeth were noted. Probably these differences were related to the combination of form and material.
DISCUSSION This study indicated that denture-related stress could affect the residual alveolar ridge and that minor alterations in tooth form, material, and technique could readily modify the effects. Other investigators have tested the specific effects of such modifications on physical changes in the denture during function. Kydd’” found that the mandibular denture became deformed during chewing and that the deformation was worse with cusp teeth than with flat teeth. Regli and Kydd”’ reported that adding a metal base allowed less deformation than using a denture made solely of plastic. Swoope and Kydd’“’ showed that the amount and type of deformation were related to the type of tooth in function, with consid19
LOPUCK,
Fig. 5. The mandibular elastic mandible.
Fig. 4. Loading frame with the load cell attached maxillary denture.
to the
erably less compression and extension occurring in the denture with the flat posterior occlusal scheme than in the one with 33 degree posterior teeth. Other investigators have compared anatomic (cusp) and nonanatomic flat teeth; their results seem to agree with the findings of this study. !’ Stress generated in the model was significantly less in magnitude with flat teeth than with cusp teeth. Cusp teeth, having numerous contacts on inclined planes. apparently generated erratic torquing forces within the denture. a*m QillE-zm-3 Fig. 6. Diagrammatic representation of stresses developed with flat occlusal schemes. The stresses are indicated by r values graded in increasing intensity from u, to ra.
Fig. 7. Diagrammatic representation of stresses deveioped with cusp occlusal schemes. The stresses are indicated by d values graded in increasing intensity from IT, to 04.
Whatever this effect, strong empirical evidence seems to indicate that this torquing action in the symphysis region is closely related to bone resorption. Both Tallgren’ and Atwood’ found the mandibular anterior region extremely susceptible to denture-related trauma and eventual resorption in comparison with other regions. Frost and Epker,“” studying bone resorption in long bones, found a strong resorptive effect? associated with bending. Their findings indicated that long bones under a bending torque showed resorption in convex regions and bone formation in concave regions. Numerous theories have been advanced about the bone deformation-resorption. Bassett and Becker.” independently found that bones, when stressed, exhibited an electrical potential that was proportional to the stress up to the elastic limit of the bone. This is the piezoelectric phenomena. Many investigators subsequently confirmed the stress/deformation-generated electric potentials..“. I!’ This mechanically induced bioelectric response in bone might be one aspect of the resorption process in the mandible. The mandible in the dentulous state may not be a long bone in the true sense of the word, but rather a triarticulated bone with teeth and condyles representing articulating interfaces. After extraction of the teeth and healing, the mandible more accurately may be considered a long bone and may be subjected to the same morphologic responses as long bones, i.e., resorption and bone formation.
SUMMARY
THE JOURNAL
OF PROSTHETIC
DENTISTRY
AND CONCLUSION
The development of stress patterns was observed within a photoelastic model under complete mandibular dentures. Characteristic stress patterns were teeth related to type of tooth material. Plastic transmitted less force than porcelain teeth. Cusp teeth induced concentrated regions of force within the model that contrasted with the uniform distribution of force observed with flat teeth. ‘The dentist should be aware of the biomechanicat problems associated with any posterior denturr occlusion in relation to the residual alveolar ridge.
REFERENCES 1.
Kelsey,
C. C.:
Alveolar
bone
resorption
under
complete
dentures. J PROSTHET DENT 25: 152, 197 I. 2. (7ampbel1, R. L.: A comparative study of the resorption of the alveolar ridges in denture-wearers and nondemur+ wearers. J Am Dent Assoc 60:143, 1960. 3. Jozefowicz. W.: The influence of wearing dentures on residual ridges-A comparative study ,J PKOSTHET DENT 4. 5.
6.
7.
24:654, 1970. Atwood, D. ‘4.: Reduction of residual ridges: A major dkease entity. J PROSTHET DENT 26:266, 1971. Atwood, D. A.: Clinical, cephalometric. and densito-metric study of the reduction of residual ridges. ,J PRUSTHET DENT 26~280, 1971. Tallgren, A.: The continuing reduction of the residual alveolar ridges in complete denture wearers: A mixed longitudinal study covering 25 years. ,J PROSTHET DEN.~ 27:120, 1972. Tallgren, A.: The reduction in face height of edrntulous and
21
LOPUCK,
8.
9.
10.
11. 12.
13.
14.
15.
16. 17. 18.
19. 20.
21.
22.
23.
22
partially edentulous subjects during long-term denture war. Acta Odontol Stand 24:195. 1966. Tallgren, A.: The effect of denture wearing on facial morphology-A seven year longitudinal study. Acta Odontol Stand 25:563, 1967. Tallgren, A.: Positional changes of complete dentures A seven year longitudal study. Acta Odontol Sand 27:539, 1969. Tallgren, A.: Alveolar bone loss in denture wearrrs as relatrd to facial morphology. Acta Odontol Stand 28:251, 1970. Edwards, I..: The edentulous mandible. J PROSI.HF.I. DFXI 4:222, 1954. Neufeld, J. 0.: Changes in the trabecular pattern of the mandible following the loss of teeth. ,J PK~~~HBT DENT 8~685. 1958. Ortman, H.: ‘I‘he role of occlusion in preservation and prevention in complete prosthodonticr. J PROSTIIU DEW 25:121, 1971. Atwood, I). A.: Postextraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and serial cephalometric roentgenograms. J PROSTHET DENT 13:810, 1963. Wright, C.: Evaluation of the factors necessary to develop stability in mandibular dentures. J PaosTrtvr DF.KT 16:414. 1964. Sears. v.: Thirty years of non-anatomic teeth. J PROSTHFT DENT 3:596. 1953. Payne, H.: A posterior set-up to meet individual requircments. Dent Dig 47:20, 1941. Myerson. R. L.: Use of porcelain and plastic teeth in opposmg complete dentures. J PROSTHEI DEW 7:625. 1957. Tropozzano, V. R.: Tests of balanced and nonbalanced occlusions. J PROSTHET DENT 10:476, 1960. Brodsky, J., Caputo. A., and Furstman, L.: Root tipping: A photoelastic-histopathologic correlation. Am J Orthod 67: I. 19i5. Warren, A., and Caputo, A.: A load transfer to alveolar bone as influenced by abutment designs for tooth-supported dentures. J PROSTHET DEST 33: 137. 1975. Craig, R.. Farah. J., and El-Tahaivi. H.: Three dimensional photoelastic stress analysis of maxillary complete dentures. J PROSTHET DF.ST 31:122. 1974. Fisher, D.. Caputo, A.. Shillingburg, H., and Duncansun. M.: Photoelastic analysis of inlay and onlay preparations. J PROWHET DFNT 33:47. 1975.
24.
25. 26.
27. 28. 29.
30.
31.
32. 33. 34. 35.
36.
37.
38.
39.
SMITH,
ANI)
C .API’TO
Cutriqht. I).. Brudvik, .J.. Gay. I\‘.. and Scltinq. \\. I ISSU< pressure under complete maxillarv tirnturrt ,J I’K~,,III~ 1 DEYI. 35:160. 1976. Boos. R. H.: Intermaxillary relation5 establishctl tv blrinq powers .J Am Dent .4ssor 27:I 192. 1940. Knowlton. ,J, P: Masticator) perforrnarwr cxrrtv~l x ith implant dentures as comparrd with raft rirvwlwrncdentures. .J PROSI.IWI. DEM 3:721. 1!1.‘>3 Thompson. J. (:.. The load factor ill wrnplvt?. rlcntur-e intolerance. .J PROSTHFT DEW 25:4. 1971. Kydd. CV.: Complete denture base deformation with varwd occlusal tooth forms. J Pwswt~~ D~NI ti:i Ii. I!%. Regli. C.. and Kydd. W.: A preliminary study of th
comparison
D.D.S.,*
James Smith,
Veterans Administration
Hospital.
of posterior D.D.S.,**
and Angelo
Sepulveda,
Calif.
ndentures
distribute stresses to the residual alveolar ridge which contribute to the degeneration of the supporting bone.‘.’ The mandible seems especially susceptible to such degeneration.“-“’ In long-term longitudinal studies of denture patients Atwood” and Tallgren” substantiated the fact that under complete denture function approximately four times more bone reduction occurs in the mandible than in the maxillae. The edentulous mandible is not structurally capable of withstanding forces that the dentoalveolar attachment apparatus had once dissipated effectively.‘. ‘I-I4 Dentists have been aware of this problem and have developed numerous philosophies about tooth form, tooth materials, and placement of teeth.‘:-‘” The objective of this investigation was to evaluate the stresses that complete mandibular dentures transmit to the residual alveolar ridge when various tooth forms and materials are used. METHOD
AND MATERIALS
Photoelastic stressanalysis is useful in dentistry for evaluating stresscharacteristics of some systems.J”-‘S This type of analysis consistsof replicating an object in photoelastic plastic, loading the photoelastic model, and viewing the resultant stress patterns developed in the model through special polarizing filters. In this study a representative edentulous mandibular arch of medium ridge height and form was replicated in a photoelastic materialt (Figs. I and 2). *Senior Resident in Removable Prosthodontics, Veterans Administration Hospital, Sepulveda. Calif. **Formerly Staff Prosthodontist, Sepulveda Veterans Administration Hospital; Presently in private practice in Omaha. Neb. ***Formerly Bio-Dental Engineer, Sepulveda Veterans Administration Hospital; Presently Professor and Chairman of Riomaterial Science, UCLA School of Dentistry, Los Angeles, Calif. iPI. 2. Photolastic Inc.. &Ialvrrn. Pa.
18
JULY
1976
VOLUME
40
NUMBER
1
denture Caputo, Ph.D.***
Four stone casts of the photoelastic model were mounted on a Hanau H articulator* using a special jig to maintain centric and vertical positions. The photoelastic model also was mounted on the same articulator with the samejig. Four identical sets of dentures were fabricated. Plastic teeth with two posterior forms, one Hat and the other at a 33 degree cusp angulation, were used on two sets. Porcelain teetht with the same two forms of flat and 33 degree cusps were used on the other two sets. All maxillary anterior teeth were set with a special placement device. Then the mandibular anterior teeth were set with the sameamount of horizontal and vertical overlap in the four dentures. There was no contact between the anterior teeth in centric occlusion. The posterior teeth bvere set directly on the crest of the ridge. The occlusal plane was located on an imaginary line between the distal of the lower canine and the middle of the retromolar pad. A standard heat-cure processing technique was usedfor the dentures, and adjustments were made to eliminate processing changes and restore the prescribed vertical dimension of occlusion. The denture-bearing surface of the mandibular dentures was uniformly relieved to a depth of 2 mm to create space for a resilient layer of mercaptan light-bodied impression materialt to simulate the mucosa (Fig. 3). The simulated mucosa was made the samethickness in each denture by mounting the photoelastic model in the articulator and repeating vertical closuresin the four dentures (Fig. 3). The photoelastic model was set on a table in the center of a straining frame that could rotate 360 degrees(Fig. 4). A fixed fiber optic light source was placed in the center of the model through an opening in the table. The model could be rotated around the ‘Hanau Engineering, Buffalo, N. Y. tTrubytr. Dcntsply International. Inc.. York. Pa $Coe-Flex. Coe I.aboratorirs, Inc.. Chicago. III.
PHOTOELASTIC
Fig.
1.
COMPARISON
OF OCCLUSIONS
Photoelastic mandibular analogue, front view.
light source without interference. The entire lateral surface of the model was visible while under a load in the straining frame (Fig. 5). The dentures, still sealed in centric occlusion, were affixed to the photoelastic model. The maxillary cast was mounted to the load cell of the straining frame with plaster. This procedure was repeated for all four sets of dentures. After the mounting the occlusion of all dentures was equilibrated to ensure equal and bilateral contacts in the posterior occlusions. The positions selected for observation of stress distribution were the anterior portion of the arch, centric occlusion, and the right and left working positions. The mounted dentures were loaded in a pure vertical direction with 11, 22, 33. and 44 pounds, respectively, to represent realistic clinical values.‘“-” A 35 mm camera was placed in a fixed position with appropriate polarizing filters and quarter-wave plates in the proper locations. White light with color film was used to photograph the stress patterns of each set of dentures at all load values.
RESULTS The stress developed was observed within the model for four sets of dentures tested and varied directly with the intensity of the applied load. The specific characteristics of the resulting stress patterns varied with type of posterior tooth. However, stress was generated in the anterior region of every denture irrespective of the type of tooth that was used. The stress patterns observed within the model with each type of posterior occlusion showed unique variation as well as some similarities. The flat occlusal schemes had stress patterns that extended anteroposteriorly in a more uniform manner (Fig. 6). The cusp teeth had stress patterns that were localized more anteriorly within the range of the flat stress pattern (Fig. 7). In overall effect the flat occlusal scheme transmitted slightly less force to the ridge than the cuspal forms did. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 2. Photoelastic mandibular analague, side view.
Fig. 3. Mercaptan soft tissue simulant on the underside of the mandibular denture. Comparison of the magnitude and depth of the stress by tooth material indicated that the porcelain teeth generated more stress within the ridge than did the plastic teeth (Figs. 6 and 7). Porcelain cusp teeth generated the most stress, while the plastic Hat teeth showed the least stress within the photoelastic model. Minor differences between porcelain flat teeth and the plastic cusp teeth were noted. Probably these differences were related to the combination of form and material.
DISCUSSION This study indicated that denture-related stress could affect the residual alveolar ridge and that minor alterations in tooth form, material, and technique could readily modify the effects. Other investigators have tested the specific effects of such modifications on physical changes in the denture during function. Kydd’” found that the mandibular denture became deformed during chewing and that the deformation was worse with cusp teeth than with flat teeth. Regli and Kydd”’ reported that adding a metal base allowed less deformation than using a denture made solely of plastic. Swoope and Kydd’“’ showed that the amount and type of deformation were related to the type of tooth in function, with consid19
LOPUCK,
Fig. 5. The mandibular elastic mandible.
Fig. 4. Loading frame with the load cell attached maxillary denture.
to the
erably less compression and extension occurring in the denture with the flat posterior occlusal scheme than in the one with 33 degree posterior teeth. Other investigators have compared anatomic (cusp) and nonanatomic flat teeth; their results seem to agree with the findings of this study. !’ Stress generated in the model was significantly less in magnitude with flat teeth than with cusp teeth. Cusp teeth, having numerous contacts on inclined planes. apparently generated erratic torquing forces within the denture. a*m QillE-zm-3 Fig. 6. Diagrammatic representation of stresses developed with flat occlusal schemes. The stresses are indicated by r values graded in increasing intensity from u, to ra.
Fig. 7. Diagrammatic representation of stresses deveioped with cusp occlusal schemes. The stresses are indicated by d values graded in increasing intensity from IT, to 04.
Whatever this effect, strong empirical evidence seems to indicate that this torquing action in the symphysis region is closely related to bone resorption. Both Tallgren’ and Atwood’ found the mandibular anterior region extremely susceptible to denture-related trauma and eventual resorption in comparison with other regions. Frost and Epker,“” studying bone resorption in long bones, found a strong resorptive effect? associated with bending. Their findings indicated that long bones under a bending torque showed resorption in convex regions and bone formation in concave regions. Numerous theories have been advanced about the bone deformation-resorption. Bassett and Becker.” independently found that bones, when stressed, exhibited an electrical potential that was proportional to the stress up to the elastic limit of the bone. This is the piezoelectric phenomena. Many investigators subsequently confirmed the stress/deformation-generated electric potentials..“. I!’ This mechanically induced bioelectric response in bone might be one aspect of the resorption process in the mandible. The mandible in the dentulous state may not be a long bone in the true sense of the word, but rather a triarticulated bone with teeth and condyles representing articulating interfaces. After extraction of the teeth and healing, the mandible more accurately may be considered a long bone and may be subjected to the same morphologic responses as long bones, i.e., resorption and bone formation.
SUMMARY
THE JOURNAL
OF PROSTHETIC
DENTISTRY
AND CONCLUSION
The development of stress patterns was observed within a photoelastic model under complete mandibular dentures. Characteristic stress patterns were teeth related to type of tooth material. Plastic transmitted less force than porcelain teeth. Cusp teeth induced concentrated regions of force within the model that contrasted with the uniform distribution of force observed with flat teeth. ‘The dentist should be aware of the biomechanicat problems associated with any posterior denturr occlusion in relation to the residual alveolar ridge.
REFERENCES 1.
Kelsey,
C. C.:
Alveolar
bone
resorption
under
complete
dentures. J PROSTHET DENT 25: 152, 197 I. 2. (7ampbel1, R. L.: A comparative study of the resorption of the alveolar ridges in denture-wearers and nondemur+ wearers. J Am Dent Assoc 60:143, 1960. 3. Jozefowicz. W.: The influence of wearing dentures on residual ridges-A comparative study ,J PKOSTHET DENT 4. 5.
6.
7.
24:654, 1970. Atwood, D. ‘4.: Reduction of residual ridges: A major dkease entity. J PROSTHET DENT 26:266, 1971. Atwood, D. A.: Clinical, cephalometric. and densito-metric study of the reduction of residual ridges. ,J PRUSTHET DENT 26~280, 1971. Tallgren, A.: The continuing reduction of the residual alveolar ridges in complete denture wearers: A mixed longitudinal study covering 25 years. ,J PROSTHET DEN.~ 27:120, 1972. Tallgren, A.: The reduction in face height of edrntulous and
21
LOPUCK,
8.
9.
10.
11. 12.
13.
14.
15.
16. 17. 18.
19. 20.
21.
22.
23.
22
partially edentulous subjects during long-term denture war. Acta Odontol Stand 24:195. 1966. Tallgren, A.: The effect of denture wearing on facial morphology-A seven year longitudinal study. Acta Odontol Stand 25:563, 1967. Tallgren, A.: Positional changes of complete dentures A seven year longitudal study. Acta Odontol Sand 27:539, 1969. Tallgren, A.: Alveolar bone loss in denture wearrrs as relatrd to facial morphology. Acta Odontol Stand 28:251, 1970. Edwards, I..: The edentulous mandible. J PROSI.HF.I. DFXI 4:222, 1954. Neufeld, J. 0.: Changes in the trabecular pattern of the mandible following the loss of teeth. ,J PK~~~HBT DENT 8~685. 1958. Ortman, H.: ‘I‘he role of occlusion in preservation and prevention in complete prosthodonticr. J PROSTIIU DEW 25:121, 1971. Atwood, I). A.: Postextraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and serial cephalometric roentgenograms. J PROSTHET DENT 13:810, 1963. Wright, C.: Evaluation of the factors necessary to develop stability in mandibular dentures. J PaosTrtvr DF.KT 16:414. 1964. Sears. v.: Thirty years of non-anatomic teeth. J PROSTHFT DENT 3:596. 1953. Payne, H.: A posterior set-up to meet individual requircments. Dent Dig 47:20, 1941. Myerson. R. L.: Use of porcelain and plastic teeth in opposmg complete dentures. J PROSTHEI DEW 7:625. 1957. Tropozzano, V. R.: Tests of balanced and nonbalanced occlusions. J PROSTHET DENT 10:476, 1960. Brodsky, J., Caputo. A., and Furstman, L.: Root tipping: A photoelastic-histopathologic correlation. Am J Orthod 67: I. 19i5. Warren, A., and Caputo, A.: A load transfer to alveolar bone as influenced by abutment designs for tooth-supported dentures. J PROSTHET DEST 33: 137. 1975. Craig, R.. Farah. J., and El-Tahaivi. H.: Three dimensional photoelastic stress analysis of maxillary complete dentures. J PROSTHET DF.ST 31:122. 1974. Fisher, D.. Caputo, A.. Shillingburg, H., and Duncansun. M.: Photoelastic analysis of inlay and onlay preparations. J PROWHET DFNT 33:47. 1975.
24.
25. 26.
27. 28. 29.
30.
31.
32. 33. 34. 35.
36.
37.
38.
39.
SMITH,
ANI)
C .API’TO
Cutriqht. I).. Brudvik, .J.. Gay. I\‘.. and Scltinq. \\. I ISSU< pressure under complete maxillarv tirnturrt ,J I’K~,,III~ 1 DEYI. 35:160. 1976. Boos. R. H.: Intermaxillary relation5 establishctl tv blrinq powers .J Am Dent .4ssor 27:I 192. 1940. Knowlton. ,J, P: Masticator) perforrnarwr cxrrtv~l x ith implant dentures as comparrd with raft rirvwlwrncdentures. .J PROSI.IWI. DEM 3:721. 1!1.‘>3 Thompson. J. (:.. The load factor ill wrnplvt?. rlcntur-e intolerance. .J PROSTHFT DEW 25:4. 1971. Kydd. CV.: Complete denture base deformation with varwd occlusal tooth forms. J Pwswt~~ D~NI ti:i Ii. I!%. Regli. C.. and Kydd. W.: A preliminary study of th
