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Wear of Acrylic Resin Teeth (Progress Report)
252
T h e J o u r n a l o f t h e A m e r ic a n D e n t a l A s s o c ia t io n
one 3.85 grain tablet is m oistened and p laced in the socket. I t read ily m ixes w ith the blood and a slight hem ostatic action results. A sponge is placed over the socket an d a clot o f su lfathiazole and blood forms. T h e patien t is advised not to use a m outhw ash fo r a t least tw o days. In im pacted third m olar cases, tw o or three tablets are placed in the socket. In three days, the socket is irrigated and m ore o f the d ru g is p laced in the socket. T w o applications are u sually sufficient to assure speedy recovery w ith ou t the usual postoperative com plications. CONTRAINDICATIONS
T h e use o f the d ru g is contraindicated w h en there is m arked renal insufficiency, since the d rug is elim inated b y the k id
neys. Since the d ru g m ay cause red u c tion in the w h ite cells and also destroy some o f the red cells, in patients showing abn orm ality o f the blood a blood count should be m ade daily, esp ecially w hen there is to x icity and w h en larger doses of the d ru g are b ein g adm inistered. T h e toxicity o f sulfathiazole is less than th a t of sulfanilam ide or sulfapyridine. T h e toxic reactions are the s a m e ; nam ely, dizziness, nausea, skin eruptions and, in some cases, a m arked chan ge in th e blood itself. S u lfath iazole is still u n der experim entation. T h e literatu re is still m eager. T h e d ru g is not a cureall, b u t promises to w in recognition and de m an d the respect o f the dental as w ell as the m edical profession. 206 East North Street.
WEAR OF ACRYLIC RESIN TEETH (P R O G R E S S R E P O R T )*
By J
ohn
R . B e a l l , -j- B .S., W ashington, D . C .
N T E R E S T in the use o f acrylic resin fo r inlays, bridges and jackets and for the teeth in fu ll and p artial dentures is increasing. A rticles1 h ave appeared in the d en tal literature describing some o f the properties o f the resin as used for teeth and listing advantages to be ob tained through its use. A m o n g the advantages claim ed fo r the m aterial a r e : 1. A m ore n atural a p p earan ce th an th a t of porcelain. 2. Less fria b ility th an porcelain. 3. A m ore n atural “ feel” to the patien t on con tact in g opposing teeth. 4. In dentures, a better bond betw een the teeth and the base m aterial.
I
* A report to the Research Commission of the American Dental Association. fResearch Associate of the American Dental Association at the National Bureau of Stand ards.
Jour. A.D.A., Vol. 30, February 1, 1943
D isadvan tages m entioned in clu d e (1) low surface hardness as m easured by the B rinell or sim ilar tests, (2) insufficient strength in thin sections, (3) a ch an ge in dim ension w ith chan ge in w a ter content, (4) loosening o f cem ented crow ns and inlays and (5) the possibility o f excessive w ear. W h ile there has been m u ch discussion as to the possibility o f excessive w ear, no lab oratory d ata h a ve been m ad e a va il able on w h ich to base a satisfactory con clusion. E arly in 1942, the A m erican D e n tal Association R esearch F ellow sh ip at the N atio n al B u reau o f Standards decided to attem p t to evalu ate the w ea r o f these acrylic resin teeth through a study of such teeth in actu al service in the m outh. CONSTRUCTION OF CASES
Patients w h o w ou ld b e read ily avail-
B e a l l — A c r y l ic R e s in T e e t h
able fo r recall a t desired intervals w ere selected by the dental research laboratory at the N atio n al B ureau of Standards. F ull upp er and low er dentures w ere m ade fo r these patients. T h e base m aterial and the acrylic .resin teeth (a com m ercial brand, on the m arket) w ere supplied by the A m erican D en tal Association R e search Fellow ship. In the tw o cases reported here, one patien t (C ase 19) chew s tobacco regu larly, w h ile the other (C ase 17) smokes
253
obtain records of the condition of the teeth at various times during the test, and in th e hope th a t m easurem ents could be m ade of changes as they o c curred. 1. A fte r the cases had been con structed and all the necessary ad ju st m ents m ade to the satisfaction o f both the dentist and the patients, dental “ stone” m odels w ere prepared by pou rin g the stone d irectly into the base o f the denture. T h e m odels w ere so prepared
Fig. 1.— Replicas of upper denture, showing wear of acrylic resin teeth. A , at beginning of service period. B, after seven months.
cigarets, b u t does not chew tobacco. T hus, the form er m ay represent severe service and the latter norm al service. In both o f these cases and a num ber o f a d d i tional ones to be reported later, L u zern e G . Jordan, o f W ashington, D . C ., coop erated. E X PE R IM E N TAL D A TA
T h e fo llo w in g program w as planned to
that a record o f the entire periphery o f the base w as included. T h e base of the m odel in each instance was m ade parallel to the occlusal plane of the teeth by p la c in g the denture occlusal surface dow n w ard on a plate o f glass. T h e base of the m odel was finished by pressing down another plate o f glass on the unset stone, the second plate o f glass being kept parallel to the first b y a form o f uniform
254
T h e J o u r n a l o f t h e A m e r ic a n D e n t a l A s s o c ia t io n
depth used to shape the sides o f the m odel. 2. W h en these m odels h ad hardened, they w ere rem oved from the form and the denture was rem oved from the m odel. R e lie f o f the m odel w as necessary in the case o f undercuts. T h e m odels, prep ared by pourin g d irectly in to the dentures, obviously, fitted a ccu rately a t the be gin nin g of the test. 3. E ach denture w as replaced on its m odel and the denture and m odel to
5. O n recall o f the patien t, the denture in each instance was replaced on its m odel, the fit noted and a second replica m ade, as in p a rag ra p h 3, above. 6. T h ese second replicas were stored in the contain er fo r from tw enty-four to forty-eight hours p rior to m easure m ent. 7. A ll m odels and replicas w ere m ade from “ albastone,” w hite, from the same can and w ith the same w a te r : pow der ratio, in order to elim inate as nearly as
Fig. 2.— Replicas of lower denture showing wear of acrylic resin teeth. of service period. B, after seven months.
A, at beginning
gether w ere d uplicated in stone, w ith possible any effect o f expansion o f the hydrocolloid al impression m aterial. T h u s, stone. T h e first replicas o f C ase 17 w ere m ade a stone rep lica of each denture on its m odel, w ith the occlusal plane parallel A p ril 16, 1942, th e second set A u gu st 12, 1942, representing a period o f use to the base, was obtained a t the start o f the test period. (Figs. 1 and 2.) R ep ro o f a pproxim ately fo u r months. C ase 19 duction o f d etail w as qu ite satisfactory. was in service approxim ately seven 4. T h e m odels and replicas w ere m onths, the origin al replicas h avin g been stored in a closed container m aintained m ade Jan u ary 20, 1942, and the second set A u g u st 13, 1942. a t 32 per cent relative hum idity.
B e a l l — A c r y l ic : R e s in T e e t h
MEASUREMENTS ON OCCLUSAL SURFACES
W ea r o f the tooth surfaces was d e term ined by differen tial m easurem ents on the replicas m ade on the dates m en tioned a b o v e ; th a t is, a po in t on the replica n ear the tooth surface to be m easured w as selected, in a n area n orm ally expected to b e free from w ear, and the ve rtica l distance betw een this point and the tooth surface w as de term ined on both the “ before” and the “ after” replicas. I f this distance
255
60 degrees and a diam eter o f abou t 0.015 inch a t the sm all end. T h is w as used since a sharp point w ou ld h a ve d u g into the stone. T h e results o f these m easurem ents are presented in the a ccom p an yin g table. I t is b elieved th a t th e m ethod em ployed yields results accu rate to ± 0 .0 0 5 inch o r better. T h u s the values w ith a $ in the table (w here the tooth h a d increased in vertical dim ension) should b e taken to m ean th a t no w ear h a d taken place. A n y
W e a r * o f A c r y l ic R e s i n T e e t h
Case
Tooth
Loss of Vertical Dimensionf in Thousandths Inch on Cusps as Indicated Mesial-Buccal Mesial-Lingual Distal-Buccal
No. 17 upper 4 months service
No. 17 lower
No. 19 upper 7 months service
No. 19 lower
Right 2nd molar Right 1st molar Left 2nd molar Left 1st molar Left 1st bicuspid
0
7
n 6 It Lingual 2
10 13 7 Buccal 0
6 0
Right 1st molar Left 2nd molar Right 2nd bicuspid
5 4 Buccal 0
2
5
4
6
Right 2nd molar Right 1st molar Left 2nd molar Left 1st molar Right 2nd bicuspid Left 1st bicuspid
8 6 6 12
8 18
5 5 7 IS
Left 2nd molar
21
Lingual 10 Lingual 19
28 Buccal 10 Buccal 16
12
4
It It
17
Distal-Lingual 9 5 3 4
6 7
8
4
*As represented by loss of vertical dimension. fFrom differential measurement on stone replicas (reference point to high point of each cusp). {Vertical dimension greater after service. The probable accuracy of determinations is ±0.005 inch. w as less (w here the referen ce point was b elow the occlusal surface) in the case o f the stone replica m ade a t the end o f the period, the occlusal surface had w orn. M easurem ents w ere m ade in this w ay, w ith a surface plate an d d ep th ga g e to the arm o f w h ich w as a ttach ed a dial in d icator w ith th e plu n ger vertical. A special fo o t w as m ade fo r the plunger, term inatin g in a n inverted truncated cone w ith an included angle o f approxim ately
va lu e in the table over 0.005 inch, h o w ever, w ou ld in d icate th a t the tooth had chan ged a t th a t point. V a lu es reported are based on m easurem ents from a selected referen ce po in t to the h igh point o f each cusp as ind icated by the table headings. In some instances, the h igh point h a d w orn aw ay and con tact had shifted laterally as n ew facets w ere w orn on the teeth. N o allow an ce fo r this la t eral shift w as m ade, alth ou gh it is b e lieved th a t the w ea r ind icated in the
256
T h e J o u r n a l o f t h e A m e r ic a n D e n t a l A s s o c ia t io n
table is less than the actu al w ear, in cer tain instances, as a result of this shift. F igures 1 and 2 show the result o f service on the dentures o f C ase 19. In each instance, the letter A indicates the origin al replica and the letter B the later one. A careful study o f these ph oto graphs w ill reveal the chan ge in angle an d size o f facets, as w ell as the develop m en t o f n ew facets on the later replicas. F igu re 1 shows tw o view s o f the replicas o f the upp er denture o f C ase 19, in d icat in g the chan ge in inclination o f the w ork in g surfaces an d th e relative shallowness at B, shown in th e areas m arked 1 and 2 o f the low er view s. T h is is also indicated b y the changed shadow p attern in the sam e area o f the u p p er view s (3 and 4 ). T h e profile o f the m olar and bicuspid area, 5 and 6 in the low er view , appears to be flattened in the case o f B (6 ). T h e up p er view o f the sam e teeth reveals that the pitted areas h ave increased an d that some o f the facets noted on A (7) are distinctly larger on B (8 ). Close exam ination o f the first and second bicuspid and first m olar (3 and 4) reveals the a l m ost com plete loss o f anatom ic detail in these teeth. T h e facets on the anterior teeth a p pear larger in general in B. T h e chip (9) in the lateral incisor occu rred in p re p arin g the replica and was not on the denture. Sim ilarly, in F igu re 2, 1 and 2, and 3 and 4, show th e flatten ing of th e cusps, w h ile en largem ent an d chan ge of the facets m a y be noted on other teeth (5 and
8 ). T h e effect in C ase 17 is n ot so p ro nounced, and w ould n ot show in halfton e reproduction, although one m ay readily detect it w h en studying the replicas. c o n c l u sio n
It is believed that the amount of wear
shown in the illustrations and m easured and reported in the table is o f sufficient m agn itude to w arran t reportin g to the profession even thou gh com parable fig ures and inform ation on porcelain teeth or n atural teeth are n ot availab le a t this tim e. E xposed occlusal inlays and crowns o f acrylic resin, also, m a y be expected to w ear. T h ese experim ents do indicate that w ea r takes place a t an appreciable rate. A rou gh calcu lation shows that, if w ear on a certain m olar area in the case o f the p atien t w ho is ad dicted to chew ing tobacco w ere to continue a t the present rate, the tooth w ou ld be w orn to the level o f the base m aterial in approxim ately three years. A sim ilar study o f the w ear o f porce lain teeth w ill be undertaken. O n ly w hen com parable values are availab le fo r po r celain w ill one be able to m ake an in telligent direct com parison, and to decide w hether the b alan ce o f advantages and disadvantages w arrants unrestricted use o f acrylic resin teeth. U n til such time as reliable d ata are available, as a basis fo r ju d gm en t, it is suggested that the practitioner continue to w arn his patients th at acrylic resin teeth are “ experim ental” rath er th an p er m anent. BIBLIOGRAPHY
L. W .: Use of Acrylic Resin for Jacket Restoration. D. Digest, 4 6 : 198 , June H a rris ,
1940. W i l s o n , W. E .: Casting of Plastic Inlays and Crowns. D. Digest, 46:202, June 1940 . K e l l y , E. B .: All-Plastic Im m ediate D en ture Service. J.A.D.A., 2 9 : 375 , M arch 1942 . T y l m a n , S. D .: W here and How Acrylics M ay Be Used in Restorative Dentistry. J.A.D.A., 2 9 :640 , April 1942 . W i n k l e r , N. D .: Posterior Acrylic Inlays and Crowns. D. Digest, 4 8 : 170 , April 1942 . H a r r i s , L. W .: A nterior Inlays in Acrylic Resin. D. Digest, 4 8 : 274 , June 1942 .
T h e J o u r n a l o f t h e A m e r ic a n D e n t a l A s s o c ia t io n
one 3.85 grain tablet is m oistened and p laced in the socket. I t read ily m ixes w ith the blood and a slight hem ostatic action results. A sponge is placed over the socket an d a clot o f su lfathiazole and blood forms. T h e patien t is advised not to use a m outhw ash fo r a t least tw o days. In im pacted third m olar cases, tw o or three tablets are placed in the socket. In three days, the socket is irrigated and m ore o f the d ru g is p laced in the socket. T w o applications are u sually sufficient to assure speedy recovery w ith ou t the usual postoperative com plications. CONTRAINDICATIONS
T h e use o f the d ru g is contraindicated w h en there is m arked renal insufficiency, since the d rug is elim inated b y the k id
neys. Since the d ru g m ay cause red u c tion in the w h ite cells and also destroy some o f the red cells, in patients showing abn orm ality o f the blood a blood count should be m ade daily, esp ecially w hen there is to x icity and w h en larger doses of the d ru g are b ein g adm inistered. T h e toxicity o f sulfathiazole is less than th a t of sulfanilam ide or sulfapyridine. T h e toxic reactions are the s a m e ; nam ely, dizziness, nausea, skin eruptions and, in some cases, a m arked chan ge in th e blood itself. S u lfath iazole is still u n der experim entation. T h e literatu re is still m eager. T h e d ru g is not a cureall, b u t promises to w in recognition and de m an d the respect o f the dental as w ell as the m edical profession. 206 East North Street.
WEAR OF ACRYLIC RESIN TEETH (P R O G R E S S R E P O R T )*
By J
ohn
R . B e a l l , -j- B .S., W ashington, D . C .
N T E R E S T in the use o f acrylic resin fo r inlays, bridges and jackets and for the teeth in fu ll and p artial dentures is increasing. A rticles1 h ave appeared in the d en tal literature describing some o f the properties o f the resin as used for teeth and listing advantages to be ob tained through its use. A m o n g the advantages claim ed fo r the m aterial a r e : 1. A m ore n atural a p p earan ce th an th a t of porcelain. 2. Less fria b ility th an porcelain. 3. A m ore n atural “ feel” to the patien t on con tact in g opposing teeth. 4. In dentures, a better bond betw een the teeth and the base m aterial.
I
* A report to the Research Commission of the American Dental Association. fResearch Associate of the American Dental Association at the National Bureau of Stand ards.
Jour. A.D.A., Vol. 30, February 1, 1943
D isadvan tages m entioned in clu d e (1) low surface hardness as m easured by the B rinell or sim ilar tests, (2) insufficient strength in thin sections, (3) a ch an ge in dim ension w ith chan ge in w a ter content, (4) loosening o f cem ented crow ns and inlays and (5) the possibility o f excessive w ear. W h ile there has been m u ch discussion as to the possibility o f excessive w ear, no lab oratory d ata h a ve been m ad e a va il able on w h ich to base a satisfactory con clusion. E arly in 1942, the A m erican D e n tal Association R esearch F ellow sh ip at the N atio n al B u reau o f Standards decided to attem p t to evalu ate the w ea r o f these acrylic resin teeth through a study of such teeth in actu al service in the m outh. CONSTRUCTION OF CASES
Patients w h o w ou ld b e read ily avail-
B e a l l — A c r y l ic R e s in T e e t h
able fo r recall a t desired intervals w ere selected by the dental research laboratory at the N atio n al B ureau of Standards. F ull upp er and low er dentures w ere m ade fo r these patients. T h e base m aterial and the acrylic .resin teeth (a com m ercial brand, on the m arket) w ere supplied by the A m erican D en tal Association R e search Fellow ship. In the tw o cases reported here, one patien t (C ase 19) chew s tobacco regu larly, w h ile the other (C ase 17) smokes
253
obtain records of the condition of the teeth at various times during the test, and in th e hope th a t m easurem ents could be m ade of changes as they o c curred. 1. A fte r the cases had been con structed and all the necessary ad ju st m ents m ade to the satisfaction o f both the dentist and the patients, dental “ stone” m odels w ere prepared by pou rin g the stone d irectly into the base o f the denture. T h e m odels w ere so prepared
Fig. 1.— Replicas of upper denture, showing wear of acrylic resin teeth. A , at beginning of service period. B, after seven months.
cigarets, b u t does not chew tobacco. T hus, the form er m ay represent severe service and the latter norm al service. In both o f these cases and a num ber o f a d d i tional ones to be reported later, L u zern e G . Jordan, o f W ashington, D . C ., coop erated. E X PE R IM E N TAL D A TA
T h e fo llo w in g program w as planned to
that a record o f the entire periphery o f the base w as included. T h e base of the m odel in each instance was m ade parallel to the occlusal plane of the teeth by p la c in g the denture occlusal surface dow n w ard on a plate o f glass. T h e base of the m odel was finished by pressing down another plate o f glass on the unset stone, the second plate o f glass being kept parallel to the first b y a form o f uniform
254
T h e J o u r n a l o f t h e A m e r ic a n D e n t a l A s s o c ia t io n
depth used to shape the sides o f the m odel. 2. W h en these m odels h ad hardened, they w ere rem oved from the form and the denture was rem oved from the m odel. R e lie f o f the m odel w as necessary in the case o f undercuts. T h e m odels, prep ared by pourin g d irectly in to the dentures, obviously, fitted a ccu rately a t the be gin nin g of the test. 3. E ach denture w as replaced on its m odel and the denture and m odel to
5. O n recall o f the patien t, the denture in each instance was replaced on its m odel, the fit noted and a second replica m ade, as in p a rag ra p h 3, above. 6. T h ese second replicas were stored in the contain er fo r from tw enty-four to forty-eight hours p rior to m easure m ent. 7. A ll m odels and replicas w ere m ade from “ albastone,” w hite, from the same can and w ith the same w a te r : pow der ratio, in order to elim inate as nearly as
Fig. 2.— Replicas of lower denture showing wear of acrylic resin teeth. of service period. B, after seven months.
A, at beginning
gether w ere d uplicated in stone, w ith possible any effect o f expansion o f the hydrocolloid al impression m aterial. T h u s, stone. T h e first replicas o f C ase 17 w ere m ade a stone rep lica of each denture on its m odel, w ith the occlusal plane parallel A p ril 16, 1942, th e second set A u gu st 12, 1942, representing a period o f use to the base, was obtained a t the start o f the test period. (Figs. 1 and 2.) R ep ro o f a pproxim ately fo u r months. C ase 19 duction o f d etail w as qu ite satisfactory. was in service approxim ately seven 4. T h e m odels and replicas w ere m onths, the origin al replicas h avin g been stored in a closed container m aintained m ade Jan u ary 20, 1942, and the second set A u g u st 13, 1942. a t 32 per cent relative hum idity.
B e a l l — A c r y l ic : R e s in T e e t h
MEASUREMENTS ON OCCLUSAL SURFACES
W ea r o f the tooth surfaces was d e term ined by differen tial m easurem ents on the replicas m ade on the dates m en tioned a b o v e ; th a t is, a po in t on the replica n ear the tooth surface to be m easured w as selected, in a n area n orm ally expected to b e free from w ear, and the ve rtica l distance betw een this point and the tooth surface w as de term ined on both the “ before” and the “ after” replicas. I f this distance
255
60 degrees and a diam eter o f abou t 0.015 inch a t the sm all end. T h is w as used since a sharp point w ou ld h a ve d u g into the stone. T h e results o f these m easurem ents are presented in the a ccom p an yin g table. I t is b elieved th a t th e m ethod em ployed yields results accu rate to ± 0 .0 0 5 inch o r better. T h u s the values w ith a $ in the table (w here the tooth h a d increased in vertical dim ension) should b e taken to m ean th a t no w ear h a d taken place. A n y
W e a r * o f A c r y l ic R e s i n T e e t h
Case
Tooth
Loss of Vertical Dimensionf in Thousandths Inch on Cusps as Indicated Mesial-Buccal Mesial-Lingual Distal-Buccal
No. 17 upper 4 months service
No. 17 lower
No. 19 upper 7 months service
No. 19 lower
Right 2nd molar Right 1st molar Left 2nd molar Left 1st molar Left 1st bicuspid
0
7
n 6 It Lingual 2
10 13 7 Buccal 0
6 0
Right 1st molar Left 2nd molar Right 2nd bicuspid
5 4 Buccal 0
2
5
4
6
Right 2nd molar Right 1st molar Left 2nd molar Left 1st molar Right 2nd bicuspid Left 1st bicuspid
8 6 6 12
8 18
5 5 7 IS
Left 2nd molar
21
Lingual 10 Lingual 19
28 Buccal 10 Buccal 16
12
4
It It
17
Distal-Lingual 9 5 3 4
6 7
8
4
*As represented by loss of vertical dimension. fFrom differential measurement on stone replicas (reference point to high point of each cusp). {Vertical dimension greater after service. The probable accuracy of determinations is ±0.005 inch. w as less (w here the referen ce point was b elow the occlusal surface) in the case o f the stone replica m ade a t the end o f the period, the occlusal surface had w orn. M easurem ents w ere m ade in this w ay, w ith a surface plate an d d ep th ga g e to the arm o f w h ich w as a ttach ed a dial in d icator w ith th e plu n ger vertical. A special fo o t w as m ade fo r the plunger, term inatin g in a n inverted truncated cone w ith an included angle o f approxim ately
va lu e in the table over 0.005 inch, h o w ever, w ou ld in d icate th a t the tooth had chan ged a t th a t point. V a lu es reported are based on m easurem ents from a selected referen ce po in t to the h igh point o f each cusp as ind icated by the table headings. In some instances, the h igh point h a d w orn aw ay and con tact had shifted laterally as n ew facets w ere w orn on the teeth. N o allow an ce fo r this la t eral shift w as m ade, alth ou gh it is b e lieved th a t the w ea r ind icated in the
256
T h e J o u r n a l o f t h e A m e r ic a n D e n t a l A s s o c ia t io n
table is less than the actu al w ear, in cer tain instances, as a result of this shift. F igures 1 and 2 show the result o f service on the dentures o f C ase 19. In each instance, the letter A indicates the origin al replica and the letter B the later one. A careful study o f these ph oto graphs w ill reveal the chan ge in angle an d size o f facets, as w ell as the develop m en t o f n ew facets on the later replicas. F igu re 1 shows tw o view s o f the replicas o f the upp er denture o f C ase 19, in d icat in g the chan ge in inclination o f the w ork in g surfaces an d th e relative shallowness at B, shown in th e areas m arked 1 and 2 o f the low er view s. T h is is also indicated b y the changed shadow p attern in the sam e area o f the u p p er view s (3 and 4 ). T h e profile o f the m olar and bicuspid area, 5 and 6 in the low er view , appears to be flattened in the case o f B (6 ). T h e up p er view o f the sam e teeth reveals that the pitted areas h ave increased an d that some o f the facets noted on A (7) are distinctly larger on B (8 ). Close exam ination o f the first and second bicuspid and first m olar (3 and 4) reveals the a l m ost com plete loss o f anatom ic detail in these teeth. T h e facets on the anterior teeth a p pear larger in general in B. T h e chip (9) in the lateral incisor occu rred in p re p arin g the replica and was not on the denture. Sim ilarly, in F igu re 2, 1 and 2, and 3 and 4, show th e flatten ing of th e cusps, w h ile en largem ent an d chan ge of the facets m a y be noted on other teeth (5 and
8 ). T h e effect in C ase 17 is n ot so p ro nounced, and w ould n ot show in halfton e reproduction, although one m ay readily detect it w h en studying the replicas. c o n c l u sio n
It is believed that the amount of wear
shown in the illustrations and m easured and reported in the table is o f sufficient m agn itude to w arran t reportin g to the profession even thou gh com parable fig ures and inform ation on porcelain teeth or n atural teeth are n ot availab le a t this tim e. E xposed occlusal inlays and crowns o f acrylic resin, also, m a y be expected to w ear. T h ese experim ents do indicate that w ea r takes place a t an appreciable rate. A rou gh calcu lation shows that, if w ear on a certain m olar area in the case o f the p atien t w ho is ad dicted to chew ing tobacco w ere to continue a t the present rate, the tooth w ou ld be w orn to the level o f the base m aterial in approxim ately three years. A sim ilar study o f the w ear o f porce lain teeth w ill be undertaken. O n ly w hen com parable values are availab le fo r po r celain w ill one be able to m ake an in telligent direct com parison, and to decide w hether the b alan ce o f advantages and disadvantages w arrants unrestricted use o f acrylic resin teeth. U n til such time as reliable d ata are available, as a basis fo r ju d gm en t, it is suggested that the practitioner continue to w arn his patients th at acrylic resin teeth are “ experim ental” rath er th an p er m anent. BIBLIOGRAPHY
L. W .: Use of Acrylic Resin for Jacket Restoration. D. Digest, 4 6 : 198 , June H a rris ,
1940. W i l s o n , W. E .: Casting of Plastic Inlays and Crowns. D. Digest, 46:202, June 1940 . K e l l y , E. B .: All-Plastic Im m ediate D en ture Service. J.A.D.A., 2 9 : 375 , M arch 1942 . T y l m a n , S. D .: W here and How Acrylics M ay Be Used in Restorative Dentistry. J.A.D.A., 2 9 :640 , April 1942 . W i n k l e r , N. D .: Posterior Acrylic Inlays and Crowns. D. Digest, 4 8 : 170 , April 1942 . H a r r i s , L. W .: A nterior Inlays in Acrylic Resin. D. Digest, 4 8 : 274 , June 1942 .