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Crystal growth on the outer enamel surface—An alternative to acid etching
American Journal of ORTHODONTICS i
i
Founded in 1915
Volume 89 Number 3
March, 1986
Copyright © 1986 by The C. V. Mosby Company
ORIGINAL ARTICLES
Crystal growth on the outer enamel surface An alternative to acid etching R. Mailer* and D. C. Smith** Toronto, Ontario, Canada
Over the past 2 years an increasing concern has developed about the possible iatrogenic effects of phosphoric acid-etch bonding techniques on the enamel surfacel There is an evident need to develop a mechanical or chemical retention system that would not alter (or would minimallY alter) the outer enamel surface. An alternative tO the conventional phosphoric acid etch technique has been developed. A preliminary clinical trial showed promising performance under normal clinical conditions. These results were achieved with a minimal loss of surface enamel as evidenced by scanning electron microscopy. Debonding and cleanup were greatly facilitated. Creating a micromechanical retentive surface by the formation of a crystalline interface is a potential alternative to phosphoric acid etching. (AM J ORTHOO89: 183-193, 1986.) Key words: Adhesion, bracket debonding, debonding, acid etching
T h e use of an acid etch technique to attach orthodontic appliances to the tooth enamel has now been widely accepted as an alternative tO full banded orthodontics. Although information is available in the literature on the possible difficulties andwide effects of bonding and debonding ~'2 brackets, many orthodontists appear to overlook these iatrogenic effects. ~-4Some believe, on the basis of earlier work, that after acid etching and once brackets and bonding resins are removed the enamel surface rapidly retums to norreal.5-7'~°'HOthers suggest that once the attachment is removed and the gross excess bonding material is eliminated by means of rotary instruments, this surface is smoothed out by means of toothbrush abrasion. ~2zs Is there a real basis for concern regarding damag e to the outer enamel surface and, if so, what are those c o n c e r n s q.1-4,8,9~10-12,18,49 J From 'the Department of Biomaterials, Faculty of Dentistry, University of Toronto. This work was supported in part by the Ontario Provincial Health Research GrantPR 851. *Research Associate, Department of Biomaterials. **Professor of Biomaterials.
The iatrogenic factors involved in acid etching may be listed as follows: 1. Loss of enamel caused by etching 4'~3 2. Retention of resin tags that can lead to possible discoloration of enamel 5"6'~3'~4 3. Leakage at the bracket interface leading to bracket corrosion and staining ~82° 4. Enamel loss caused by fracturing of enamel at time of debonding 4'8'9'15'22'49 5. A rougher surface with enamel cracks if deb°nding is carried out improperly, resulting in increased plaque retention 5'6,8,9,~7'2~,29'49 6. A softer enamel surface with lower fluoride content, morepredisposed to decalcification ~5 In view of the greater awareness and concern for the aftereffects Of direct bonding that is developing among dentists': 2 and the public at large, let us review some of these points in greater detail. 1. Enamel loss on etching and finishing has been well documented by a number of workers, z2-29Approximately 10 to 20 txm of outer enamel is lost due to acid etching *,5'3° and another 6 to 50 ~m on debonding, depending on the technique and the operator. ~528 A1-
183
184 Maijer and Smith
Am. J. Orthod. March 1986
Fig. 1. Enamel staining associated with corrosion of stainless steel bracket. A, Black corrosion deposit Visible after bracket removal. B, Residual enamel stain after finishing.
though this amount is accepted by many clinicians, frequent rebonding could lead to excessive loss of outer enamel and result in a rougher surface after finishing. 4,9,18This variable loss occurs in all cases using acid etch technique. 2. Resin tags penetrate the enamel to a depth Of 80 ixm or more. 4 Discoloration of resin tags in the enamel has been noted by clinicians, 9'17'36 especially when the ultraviolet (UV) Cured resins were in use. For obvious reasons UV cured resins did not contain UV absorbers and consequently the resin tags that remained in the enamel gradually discolored when exposed to sunlight. Little discussion of this is available in the literature. 3. Acid etching results in production of fine pores into the enamel. 4'32 These pores serve as a mechanical interlock for the resins that flow over and into these pores. If the pores are not cOmpletely filled or covered, this may create pathways by which stains and bacteria can penetrate the enamel. Problems with staining have been reported by Ceen and GwinnetP ° and by Maijer and Smith.19 These stains result from biodegradation of the metals Used in fixed orthodontic appliances. 19.20The corrosion of stainless steel bases has been found to giv e rise to deposition of chromium salts. Small voids in the resin at the interface allow saliva to carry these colored salts into the resin or the enamel. This is illustrated in Fig. 1, A and B. 4. Loss of enamel caused by fracturing has been demonstrated by a number of workers. 4'8'9 Retief37 and Retief and Denys 38 have shown that during resin removal from the enamel, small enamel fragments can
be broken Off from the existing enamel Surface. This would then lead to greater difficulty in obtaining a smooth outer surface on the enamel. Increased plaque retention has been illustrated by Gwinnett and Ceen 21 and Bennett, Schoen, and Going. 8 Ceen and Gwinnetd ° pointed out that increased plaque retention was observed on acid etched enamel as well as at the junction of the bracket base and resin periphery during bonding. Bennett, Schoen, and Going 8 showed an increased plaque accumulation following debonding. No longterm clinical study on this question has been published. 5. Debonding and cleanup is accomplished in a variety of ways. Several workers have discussed the problem of achieving a smooth surface with minimal damage to the enamel. 1.2.9.22.25.29It is generally accepted that a two-step procedure should be used. In the first step coarse resin removal is achieved by means of debonding pliers, hand instrumentS, rotary instruments, or ultrasonic scalers. Some clinicians even employ hand chisels and mallets to separate resin from enamel. Final removal is by means of abrasive cups Or discs, together with a suitable polishing medium. Discs in particular can produce facetting. Little attention has been paid to the heat production in these debonding techniques, which may contribute to enamel cracks. 9'24'51'59An increased incidence of enamel cracks as a result of traumatic debonding techniques has been observed by Zachrisson, Skogan, and H6ymyhr, 57 sandison, 9 and Diedrich. 4 Unfortunately there is presently no data to indicate the relation between specific techniques and crack frequency. Recently consideration has been given
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Crystal growth on outer enamel surface
Number 3
185
Fig. 2. Crystal growth on enamel surface after 30-second application of crystal bonding liquid. A, Original magnification x 1500. B, Individual spherulite, original magnification x 2200.
to the porosity of the enamel surface after debonding. The final enamel surface appears to be more predisposed to decalcification and absorption of stains following acid etching. 9'4° 6. An important consequence of enamel Surface removal is the loss of most of the acquired fluoride that resides mainly in the outer 10 p~m of the surface. 3°'34 These considerations make evident a need to develop a mechanical or chemical retention system that would not alter (or would minimally alter) the outer enamel surface. 4°'4i After completion of treatment, removal of this retention mechanism without any clinically deleterious side effects to the outer enamel
should be possible. This article reports on one such system. CRYSTAL GROWTH INTERLOCKING The authors have previously described 41 a new method of bonding that involves crystal growth on the enamel surface. This system consists of a polyacrylic acid treatment liquid containing a sulfate component that reacts with the calcium in the enamel surface to form a dense growth of small, needle-shaped crystals. These crystals grow in so-called spherulitic habit (Fig. 2). The crystal buildup on the enamel serves as an additional retentive mechanism for the resin that bonds
186 Maijer and Smith
Am. J. Orthod, March 1986
Fig. 3. Resin fracture surface after bond strength test showing resin penetration around crystals. (Original magnification × 3000.)
Fig. 4. Fractured and disturbed crystal growth after brushing surface. (Original magnification x 2000.)
the orthodontic attachment to the teeth (Fig. 3). In this procedure the bond does not rely on extensive penetration into the enamel. Micromechanical interlocking is created at the enamel surface; hence most of the problems mentioned in the previous section are eliminated. To evaluate this system, let us look at the basic principles, some laboratory results, and finally the preliminary clinical experience with this technique.
Principles of the technique A full drop of the viscous treatment liquid is placed on the cleaned (pumiced) tooth surface to be bonded.
It is left undisturbed for at least 30 seconds, usually 45 seconds. It is important to note that if a brush or cotton swab is used to agitate the gel, as is done in the acid etch technique, this may affect the crystal-enamel in. terface and consequently may reduce the bond strength. Fig. 4 shows a crystal site that has been disturbed by agitation. In comparison to Fig. 2, the effect on crystal integrity can be readily observed. After the prescribed number of seconds, the material is washed off thoroughly with clean tap water. After washing for at least 20 seconds as in acid etching, the tooth is dried with cool, dry, moisture-free clean air. A dense crystal
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Crystal growth on outer enamel surface
Table I. Tensile bond strengths of orthodontic
Table II. Comparison of acid etch and crystal
brackets to bovine enamel
growth
Time of storage (days)
Enamel treatment
Tensile bond strength* (MPa)
Tensile bond* strength (mPa)
Acid etch 1 28 90
Acid etch Crystal Acid etch Crystal Acid etch Crystal
1.11 1.24 1.05 0.99 1.00 0.99
-+ ± ± -+ ± -+
0.36 0.45 0.21 0.27 0.10 0.14
*Dynabond, Unitek Inc., Monrovia, Calif
growth can be seen in the scanning electron microscope (SEM) (Fig. 2). Too forceful a water spray may fracture some of the superficial crystals. However, this has only a minor effect on bond strength since the layer of crystals on the surface, which is primarily responsible for bonding, is still present. A dull whitish deposit is seen with the naked eye in the area that was exposed to the material. The fluid resin bonding agent is then allowed to flow onto the treated area. Penetration of the unset material around the crystals and into the reacted readilywettable enamel surface results in an efficient, micromechanical interlocking 4~ after either chemical or light activated polymerization. The bracket is then bonded to the sealant in the usual way. In vitro characterization
In vitro data that have been published elsewhere 41-45 using several orthodontic bonding agents show that tensile bond strength with the crystal interface is comparable to the acid etch technique using the same bonding resin. Further, the tensile bond strength has remained comparable after water exposure for 6 months at 37 C. 41'42Table I shows summary data for tensile bond strength for two orthodontic bonding resins to human enamel after storage in water for various periods. These data were obtained by a technique similar to that previously described, 4~ namely, by bonding a mesh-based orthodontic bracket to the cleaned and treated enamel surface. Table II shows further data obtained after storage in water compared to storage in 0.1N lactic acid. 43 These data confirm that a stable bond is obtained comparable to one obtained by means of a phosphoric acid etch. Shear strength of the crystal bonds are 65% to 80% of the shear strength for acid etch technique using the same resin. 43-45However, the strength in this mode appears satisfactory for clinical practice (see later) and results in a much more easily debondable system. 41,45 Chemical analysis of calcium release indicate that the surface loss with the polyacrylic acid solution is only
187
Storage days Water Lactic acid
7 --
30 1.03 + 0.19 1.12 4- 0.22
Crystal growth 7 0.96 ± 0.08 0.99 +- 0.09
30 1.11 ± 0.16 1.01 ± 0.13
*Dynabond, Unitek Inc,, Monrovia, Calif.
about one sixth of that with 50% phosphoric acid. 43 SEM studies show that minimal penetration of the resin into the surface enamel occurs after polyacrylic acid treatment. 43-45 Thus the advantages of crystal bonding technique are predicted to be as follows: 1. There is minimal effect on the outer (fluoride rich) enamel layer. 42 2. The enamel surface is not significantly damaged.43-46,58
3. Few, if any, resin tags are left behind the enamel.43-~6
4. Adequate bond strength for clinical practice is achieved. 41-z5 5. Debonding and cleanup are much easier with minimal iatrogenic damage. 4~'44'45'58 6. The crystal interface offers the possibility of the incorporation of fluoride or other antiplaque agents in the future to provide an anticariogenic action. 43'46 These in vitro studies showed that for normal enamel a contact time of 30 to 60 seconds was adequate for copious crystal growth and that complete washing away of the reactive liquid was as important as in the acid etch technique. A bonding resin able to wet and penetrate the crystalline surface was also necessary. Encouraged by these in vitro investigations, a preliminary clinical trial was initiated. Clinical trial
Materials and methods. A clinical trial was undertaken on a randomly selected group of 20 patients from the private practice of one of the authors (R.M.). The patients' ages ranged from 10 to 32 years. Patients' teeth were bonded directly with 0.022 inch straight wire brackets.* A half mouth technique was employed. Usually at least six upper and six lower anterior teeth were bonded directly. One arch at a time was bonded. The positions of the crystals and acid treatment were reversed in the opposing arch. To avoid cross contamination, a matrix stript was placed between the central incisors. *"A" Company, San Diego, Calif. "~KerrManufacturing Co., Romulus, Mich.
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Maijer and Smith
Am. J. Orthod, March 1986
Minimal
Slight
Moderate
Severe
Fig. 6. Diagrammatic representation of the scoring system to evaluate dye penetration.
Fig. 5. A, Decalcification with acid-etched bonded case after 20 months. B, Crystal bonded tooth immediately after debonding following 18 months of treatment.
A sulfated polyacrylic acid solution was prepared by aqueous polymerization of acrylic acid. 4~ Teeth were treated with this liquid for 30 to 90 seconds as described previously. The phosphoric acid used was 37% phosphoric acid that was left on the tooth with slight agitation for 60 seconds. Care was taken not to cross contaminate the other side. The opposing arch was bonded on a separate appointment. Attachments were plated using accepted orthodontic techniques with a bracket placement tweezer* and a Boone gauge.t Acid etch brackets were bonded with a widely used orthodontic bonding agent.$ The crystal bonded brackets were attached with a selected sealant-paste system. § Silicone impressions were made of the labial surface before treatment of the enamel with the polyacrylic acid liquid or acid etching, and following debonding and finishing for subsequent SEM studies. Five of the 20 patients were treated with crystal forming solution and phosphoric acid etching as previously described, but the
*ETM #2222, Monrovia, Calif. tUnitek #807-022, Monrovia, Calif. SUnite, Unitek, Monrovia, Calif. §Dynabond, Unitek, Monrovia, Calif.
enamel was dried with a hair dryer held 12 cm from the mouth. The temperature of the warm air was approximately 108 ° F. Brackets were debonded with a Winegart or a Howe plier using gentle squeezing. Cleanup for the crystal bonded teeth was completed with a sickle scaler; the enamel was polished with a polishing medium* and a rubber cup. Cleanup for acid etched teeth was achieved by means of a 12 fluted burr followed by a rubber cup as described elsewhere in the literature. 24 Leakage at the bracket resin interface has been considered a major problem and a cause for bond failure and white spot initiation. 4952Before debonding the teeth were treated with disclosing solution.:~ Following removal of the brackets, the teeth were examined and scored according to the degree of dye penetration beneath the bracket (Fig. 6). The scores were as follows: 1. Minimal--A red outline present at the resin periphery 2. Slight--A slightly wider band of dye penetration near the edge of the resin indicating slight seepage underneath the bracket base 3. Moderate--One third of the resin underneath the bracket base with dye penetration 4( Severe--More than one third of the bracket base with dye penetration Bracket loss and other data were obtained from the patient records at the completion of treatment. To provide data for comparison, the records of a *Zircate, L.D. Caulk, Milford, Del. tJet #7903, Beaver's Dental Products, Morrisburg, Ontario, Canada. ~:Dis-Plaque, Pacemaker Corporation, Portland, Ore.
Volume89 Number 3
large group of patients undergoing routine treatment after acid etch bonding (using the same materials and techniques in the same office [rural location]) were tabulated for a 1-month period. Similar cross-sectional data were obtained from another office of i_he author (R.M.) in an urban location. RESULTS In the first group of 5 patients, 38 brackets were crystal bonded Using a warm air drying technique; 17 were lost within 3 days of placement. It appeared the hot air may have adversely affected the crystals. Thus this group of patients was dropped from th e experiment and room temperature air was used for drying in the subsequent cases. Table III shows the overall bracket losses for crystal bonding and acid etching in the remaining 15 patients over an average treatment time of 22 months. The losses were similar but were affected by patient trauma as indicated in the footnotes to Table III. Patient R.W. was very Uncooperative and thus was dropped from the trial. Table IV shows the distribution of the bracket losses with respect to upper and lower teeth over the total treatment period. Table V sets out an average monthly incidence and distribution of bracket loss for the patients undergoing routine treatment with the acid etch technique in the rural and urban locations. There were 220 patients in the rural area involving 4,400 brackets; in the urban area, there were 315 patients involving 6,300 brackets. Table VI summarizes the incidence of leakage as measured by dye penetration around the bonded brackets in the clinical trial. It can be seen that there was a similar resistance to leakage for both the acid-etched and crystal bonded groups with a tendency toward slight staining in the former. After debonding there was no evidence of decalcification or white spot formation with the crystal bonded group, whereas four white spot lesions were observed in the acid-etched bonded group. As found in our previous study 4~ debonding and cleanup were easily accomplished with the crystal bonded brackets, detachment occurring at the enamel surface; whereas debonding in the acid etch group generally took place at the bracket-resin interface necessitating removal of the resin layer. DISCUSSION It can be seen from Table III that 24 of the 116 crystal bonded brackets experienced failure and 18 of the 99 acid-etched bonded brackets failed over the 22month period of the trial. When the uncooperative patient R.W. is not included, the losses become 18/106 (17.0%) and 14/89 (15.7%). These losses show no sig-
Crystal growth on outer enamel surface
189
Table III. Overall bracket loss in clinical trial Of crystal bonding and acid etching Brackets crystal
Placed acid
Brackets crystal
Lost acid
A.N. D.S. D.p. L.L.***** M.G.**** ~'.M. T:F.*** M.H.** L.H. M.D. C.S. W.K. R.W.* J.P. I.P.
18 6 6 6 8 5 6 9 8 6 8 8 10 7 5 116
-6 6 6 9 6 6 10 8 6 8 8 10 6 4 99
0 0 0 1 0 0 1 2 2 1 4 2 6 4 1 24
-1 0 1 0 0 1 3 1 0 3 0 4 2 1 18
Results minus R.W.
106
89
i8
14
Patients' initials
*Patient R.W. was somewhat neglectful of his appliances and did not watch his dietary intake. Six brackets were lost over a period of 18 months. A loss of 4 to 6 brackets Over an 18-month period is not uncommon in patients with careless dietary habits. **Patient M.H.--Bracket loss due to trauma--thrown and kicked by a horse. ***Patient T.F.--Brackets ioosened and teeth partially avulsed due to accident--hit by baseball bat. ****Patient M.A.--Patient has been in intermaxillary fixation following maxillofacial surgery with no brackets lost during intermaxillary fixation. *****Patient L.L.--Attachment (upper first molar) lost while eating steak.
nificant differences for the tWO techniques (X 2 = 0.11; P > 0.05). As indicated in the footnotes to Table III, this random group of patients in a rural location experienced some unusual traumas that undoubtedly increased the incidence of failure. These loss figures are higher for both techniques than others reported in the literature. 39'47,48'54-s6 Mizrahi 39 has reviewed the recent literature and cites overall failure rates of directly bonded brackets in the acid etch technique ranging from 4% to 30% with highest rates on maxillary and mandibular molar and premolar teeth, and lower failure rates on maxillary Central and lateral incisor teeth. The rates of loss on anterior t e e t h 39'54-56 a r e c i t e d 39 to be 3.6% to 7.9% in the maxilla and 4.9% to 12.9% in the mandible. It is difficult to compare these data, however, since the time periods over which the various authors reported bracket losses varied from 6 to 12 months and 14 to 32 months. Total numbers of brackets lost cannot be described as 'rates' unless they are related to a specific time pe-
190
Am. J. Orthod. March 1986
Maqer and Smith
Table IV. Distribution of bracket losses in clinical trial of crystal bonding Number of failures Bond type
Tooth
1
Crystal--106 brackets
Upper Lower
3 0
Acid-etch--89 brackets
Upper Lower
I
]
2
I
2 0
0 1
3 2
Total
3
4
5
6
No.
3
2
1
2
3
1
t4
1
0
4
~
~
~
Tg
[
% 26.4 7.5
17.--6
1
0
0
0
4
2
3
l
1
10
9.1 22.2
5
5
i
i
1-2
15.7
Table V. Incidence of bond failure with acid etching in rural and urban settings in an average month Number of failures
3
4
5
No.
%
3 2 5
2 0 2
0 3 ~
4 8 1--2
11 16 2-7
0.50 0.72 0.61
7 1 -8 13
1 3 4 6
0 5 5 8
12 8 2--0 32
2i 20 4-i68
0.67 0.63 0.6--~ 0.64
Location
Tooth
1
2
Rural--220 patients, 4,400 brackets
Upper Lower
2 3
Urban--315 patients, 6,300 brackets
Upper Lower
1 3 9
TOTAL
Table VI. Incidence of leakage and dye staining around bonded brackets Leakage rating* Acid
Crystals
1 Total %
84 94
3 3
2 3
E --
1
2
100 94
6 6
---
---
*See Fig. 6.
riod. While it may be a presumption that many bonding failures occur early, there appear to be no time-related statistics to show loss rate. Newman's data 56 appear to show a trend tO higher losses over the longer time periods. Continuing loss over a 2-year treatment period may be expected because of bond deterioration and fatigue; Such losses may be influenced by the brackets used, the bonding material, the orthodontic technique, the specific teeth bonded, and the nature of the patient population. Newman's study, which involved 2,218 brackets with an average treatment time of 22 months, indicated that higher forces increased bracket loss. This suggests that higher losses should be seen in edgewise techniques as opposed to lower force techniques. This is borne out by the lower failure rate of 4.6% over a similar treatment period experienced by MizrahP 3 using
I
Total
a Begg light wire technique and an exothermic tweezer for bracket placement as compared to the corresponding figure of 15.6% from Newman's data. There appear to be few studies that document cumulative bracket loss over a 24-month period under the normal routine conditions found in a busy orthodontic practice. To put the present data into a local perspective, Table V shows 1-month cross-sectional bracket loss data for the practices of the clinical author in (1) the same rural area as the test patients and (2) in an urban location. These losses over a 1-month period relate to patients undergoing treatment for an average time period of 22 months similar to that of the present clinical total. As is evident from Table V, the 10ss rates were very similar for both the rural and urban locations. There was a slight tendency for higher losses in the lower teeth (as noted by others) in the rural area, but not in the urban area. These monthly rates of about 0.64% give overall losses of approximately 7.7% annually and 15.4% over 24 months. For the incisors and canines considered as a group, the corresponding figures are 5.2% and 10.4% loss incidence. Considering the differences in the procedures, ttiese data agree well with those reported by Gorelick54 and Zachrisson s5 for treatment periods of 6 to 12 months, and those of Newman 56 for treatment periods of 14 to 32 months. Thus the average treatment time in the latter study 56was 22 months and the weighted average percent
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losses for the anterior teeth were 15.3% and for the incisors and canines as a group, 8.4%. For the present study (from Table V), the corresponding figures are calculated to be 15.4% and 10.5%, respectively, from the total of 10,700 brackets and 535 patientS. This close correspondence suggests that a steady rate of bracket loss does occur on average in a routine practice as presumed from the cross-sectional data of Table V. As a check on this point, the charts for 59 randomly selected completed cases from the urban location were examined. For an average treatment time of 23.5 months, 152 failures from a total of 1,062 brackets were observed, that is, total overall cumulative failure rate of 14.7%--a very good agreement with the previous figures. Against this background it is evident that the acid etch rate of 15.7% observed in the clinical trial (and presented in Table IV) is in close agreement with the foregoing data for both the routine clinical data of this study and that of Newman, 56 using similar materials and techniques. The mandibular failure rate was considerably higher than that for the maxilla (found also by Newman) although this finding may be influenced by the small numbers and patient histories. As noted earlier, the crystal bond failure rate was slightly higher, although Statistically similar, to the acid etch rate. Table IV shows the maxillary rate to be abnormally high and again this may be a consequence of the small numbers and individual traumas. As c a n b e seen in Table VI, slight or moderate dye penetration was observed in the acid-etch bonded teeth and slight dye penetration noted in the crystal bonded cases. The two cases employing acid etch technique in which moderate leakage was seen each had a related white spot lesion. This suggests that acid-etched bonded brackets can remain partially bonded to the enamel and in this way allow plaque buildup in a void under the bracket base.19,4° After debonding these cases, there was no incidence of decalcification or white sport formation with the crystal bonded group, whereas four white spot lesions were associated with the acid-etched bonded brackets. The incidence of white spot lesions is increased by orthodontic treatment as repotted by Mizrahi 5°'52 and Gorelick, Geiger, and Gwinnett. 5~ The incidence of four white spots seemed tO agree w!th those of previous authors in that three of the four white spots were on lateral incisors. In all cases where white Spot formation was seen, poor to fair oral hygiene was encountered. White spot lesion formation may be facilitated in phosphoric acid etch techniques because of the loss of the outer fluoride rich layer of the enameP 5 and thus a lowered resistance to decalcification. Newman 5~ noted a reduced incidence of decalcification in acid-
Crystal growth on outer enamel surface
191
etched bonding when a sealant was used on the etched surface prior to bonding. In the polyacrylic acid-based crystal system used in this study, enamel loss and porosity were much less than with phosphoric acid etching. Hence decalcification is less likely to occur. Further crystal bonded brackets are unlikely to remain partially bonded to the enamel, but rather become detached, thus avoiding cavitation and white spo t formation. Poorer in vitro bond strength results using experimental sulfated polyacrylic acid were found by Farquahar s8 and unsatisfactory in vivo bonding by McPhee, Way, and Gali159 using a now withdrawn commercial material. Differences in techniques and materials may account for these results. More recently, with improved understanding of the technique, in vitro and in vivo findings similar to those reported here have been obtained by Burkey 44 and by Beech and Russell. 45 In a clinical trial using a commercial material, the latter authors experienced a 13% failure rate with crystal bonding as compared to a 4% loss with acid etching. Our experience as outlined here does not agree with that reported recently by Artun and Bergland 6~ for another experimental crystal-forming solution. However, their material is based on other development and does not correspond with our material, which is based on our previously reported data. 4~43 Although the present crystal-forming solution can yield satisfactory clinical results with significant advantages following an appropriate technique, it is clear that further potential for development of improved bonding exists through a study of the formation of a crystalline layer attached to the enamel surface. Further investigation of these possibilities is proceeding. SUMMARY AND CONCLUSION
A preliminary report on a clinical study of a material that produces crystal growth on the outer surface of the enamel has been presented. Creating a mechanical retention system by means of surface interaction and CryStal growth appears to be a convenient method of bonding orthodontic attachments to tooth enamel. Exposure of cleaned enamel to the crystal bonding solution for 30 to 60 seconds produced a dense crystal growth on normal enamel. The operator sensitive areas were application and washingi Inadequate Washing did not remove the polyacrylic acid treatment solution, it was therefore important for maximum bond strength that a careful technique be strictly adhered to as in the case of acid etching. If attention is paid to the proper steps, crystal bonding could be used in most instances where acid etching is currently used. The results of these studies using this crystal bond-
199
Maijer and Smith
ing t e c h n i q u e i n d i c a t e t h a t , in a d d i t i o n to r e m o v i n g less er/amel f r o m the t o o t h d u r i n g d e b o n d i n g , a s i g n i f i c a n t t i m e s a v i n g is e x p e r i e n c e d b y f a s t e r c l e a n u p f o l l o w i n g d e b o n d i n g w i t h less l i k e l i h o o d o f e n a m e l t r a u m a a n d damage. Also, the minimal reaction with the underlying enamel reduces the incidence and possibility of enamel staining. N o s i n g l e c a s e o f w h i t e spot f o r m a t i o n o r s t a i n i n g h a s b e e n n o t e d in a s s o c i a t i o n w i t h a n y o f the crystal b o n d i n g c a s e s t r e a t e d o v e r t h e last 2 years o f clinical use. A l t h o u g h the p r i n c i p l e s o f the p r o c e d u r e s h a v e b e e n d e s c r i b e d at l e n g t h , t h e b a s i c t e c h n i q u e is s i m i l a r to t h a t o f acid e t c h i n g . T h e a d v a n t a g e s are s u c h t h a t i t c o u l d b e c o m e a n a l t e r n a t i v e to the p r e s e n t l y u s e d p r o c e d u r e s , e s p e c i a l l y in the a n t e r i o r r e g i o n s . F u r t h e r i n v e s t i g a t i o n s o f t h e p r i n c i p l e is i n d i c a t e d .
Am. J. Orthod. March 1986
17. 18. 19. 20. 21. 22. 23.
24.
25. REFERENCES
1, Fields HW: Bonded resins in orthodontics. Pediatr Dent 4: 5160, 1982. 2. Council on dental materials, instruments and equipment: State of the art and science of bonding in orthodontic treatment. J Am Dent Assoc 105: 844-850, 1982. 3~ Garberoglio R, Cozzani G: In vivo effect of oral environment on etched enamel: A scanning electron microscopic study. J Dent Res 58: 1859-1865, 1979. 4. Diedrich P: Enamel alterations from bracket bonding and debonding: A study with the scanning electron microscope. AM J ORTHOD 79: 500-522, 1981. 5. Gwinnett AL: HistologiC changes in human enamel following treatment with acidic adhesive conditioning agents. Arch Oral Biol 16: 731-738, 1971. 6. Lee H et al: Application of scanning electron microscopy to in vivo remineralization studies of human enamel. Lee Pharmaceuticals, Research Report, pp 70-147, 197.0. 7. Arana ME: Clinical observations of enamel after acid-etch procedure. J Am Dent Assoc 89: 1102-1106, 1974. 8. Bennett CG, Schoen FJ, Going RE: Alterations of the enamel surface following direct-bonded bracket therapy. J Pedod 3: 99li3, 1979. 9. Sandison RM: Tooth surface appearance after debonding. Br J Orthod 8: 199-201, 1981. 10. Albert M, Grenoble DE; An in vivo study of enamel remineralization after acid etching. J South Calif State Dent Assoc 39: 747-755, 1971. 11. Gwinnett AJ, Buonocore MG: Adhesives and caries prevention. Br Dent J 119: 77-80, 1965. 12. Miura F, Nakagawa K, Masuhara E: New direct bonding system for plastic brackets. AM J ORTHOD59: 350-361, 1971. 13. Silverstone LM: Fissure sealants, the susceptibility to dissolution of acid etched and subsequently abraded enamel in vitro. Caries Res 11: 46-51, 1977. 14. Davidson DL, Bekke-Hoekstra IS: Chemical and wear resistance of superficially sealed enamel. J Oral Rehabil 7: 299-305, 1980. 15. Lehman R, Davidson DL: Loss of surface enamel after acid etching procedures and its relation to fluoride content. AM J ORTHOD 80: 73-82, 1981. 16. Silverstone LM: The acid etch technique: In vitro studies with special reference to the enamel surface and the enamel-resin interface. In Silverstone LM, Dogon IL (editors): The acid etch
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36. 37. 38.
39. 40.
technique. St. Paul, 1975, North Central Publishing Company, p13. Badner M: Personal communication. Maijer R, Smith DC: Variables influencing the bond strength of metal orthodontic bracket bases. AM J ORTHOD79: 20-34, 1981. Maijer R, Smith DC: Corrosion of orthodontic bracket bases. AM J ORTHOD81: 43-48, 1982. Gwinnett AJ: Corrosion of resin-bonded orthodontic brackets. AM J ORTHOD82"- 441-446, 1982. Gwinnett AJ, Ceen RF: Plaque distribution on bonded brackets: A scanning microscoPe study. AM J ORTHOD75:667-677, 1979. Zachrisson BU, Arthun J: Enamel surface appearance after various debonding techniques. AM J ORTHOD75: 121-137, 1979. Brobakken GO, Zachrisson BU: Abrasive wear of bonding adhesives: Studies during treatment and after bracket removal. AM J ORTHOD79" 134-147, 1981. Maijer R, Smith DC: Enamel finishing procedures after debonding orthodontic attachments. J Dent Res (Special Issue A): 173, Abstract 396, 1978. Fitzpatrick DA, Way DC: The effects of wear, acid etching, and bond removal on human enamel. AM J ORTHOD 72: 671-681, 1977. Brown L, Way DC: Enamel loss during orthodontic bonding and subsequent loss during removal of filled and unfilled adhesives. AM J ORTHOD74: 663-671, 1978. Pus MD, Way DC: Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques. AM J ORa~OD 77: 269-283, 1980. Thompson RE, Way DC: Enamel loss due to prophylaxis and multiple bonding/debonding or orthodontic attachments. AM J ORTHOD 79: 651-665, 1977. Gwinnett AJ, Gorelick L: Microscopic evaluatio n of enamel after debonding: Clinica! application. AM J ORTHOD 71: 651-665, 1977. Clarkson BH, Wei SHY: Topical fluoride therapy. In Stewart RE, Barber TK, Troutman KC, Wei SHY (editors): Pediatric dentistry. St. Louis, 1982, The C. V. Mosby Company, p 752. Uchtmann H, Duschner H: Electron spectroscopic studies on interaction between superficially applied fluorides and surface enamel. J Dent Res 61: 423-428, 1982. Silverstone L: The structure and characteristics of human dental enamel. In Smith DC, Williams DF (editors): Biocompatibility of dental materials. Boca Raton, Fla., 1983, CRC Press, p 39. Wefel JS: Mechanisms of action of fluoride. In Stewart RE, Barber TK, Troutman KC, Wei SHY (editors): Pediatric dentistry. St. Louis, 1982, The C. V. Mosby Company, p 772. Smith DC, Peltoniemi A: Release and enamel retention of fluoride from tooth coatings and other dental materials. In Smith DC, Williams DF (editors): Biocompatibility of dental materials. Boca Raton, F!a-, 1982, CRC Press, p 189. Groeneveld A, Arends J: Influence of pH and demineralizati0n time on mineral content, thickness of surface layer, and depth of artificial lesions. Caries Res 9: 36-44, 1975. Woodside DG: Personal communication. Retief DH: Failure of the dental adhesive-etched enamel interface. J Oral Rehabil 1: 265-284, 1974. Retief DH, Denys RF: Finishing of enamel surfaces after debonding of orthodontic attachments. Angle Orthod 49: 1-10, 1979. Mizrahi E: Orthodontic bands and directly bonded brackets: A review of clinical failure rate. J Dent 11:231-236, 1982. Ceen RF, Gwinnett AJ: Indelible iatrogenic staining of enamel following debonding. J Clin Orthod 14: 713-715, 1980.
Volume 89 Number 3 41. Maijer R, Smith DC: A new surface treatment for bonding. J Biomed Mater Res 13: 975-985, 1979. 42. Smith DC, Bennett A, Peltoniemi R, Maijer R: Further studies of bonding through crystal growth. J Dent Res 59(Special Issue B): 995, Abstract 435, 1980. 43. Smith DC, Lux J, Maijer R: Crystal bonding to enamel. J Dent Res 60(Special Issue A): 368, Abstract 231, 1981. 44. Burkey PS: Enamel conditioning with acid etch and ceystal bonding techniques: Tensile and shear bond strength comparisons and a scanning electron microscopic observations. M.Sc. Thesis, University of Iowa, 1985. 45. Beech DR, Russell ML: Bond strength, SEM and clinical studies of crystal bonding. Australia-New Zealand Divisional IADR Meeting Proceedings. Abstract 55, 1985. 46. Smith DC, Maijer R: In vitro comparison of etched and crystal grown enamel surfaces. To be published. 47. Beech DR, Jalaly T: Clinical and laboratory evaluation of some orthodontic direct bonding systems. J Dent Res 60: 972-978, 1981. 48. Cohl ME, Green LJ, Eick JD: Bonding of clear plastic orthodontic brackets using an ultra-violet sensitive adhesive. AM J ORTHOD 621 400-411, 1972. 49. Daft DS, Lugassy AA: A preliminary study of orthodontic treatment with the use of directly bonded brackets. AM J ORTHOD 65: 407-418, 1974. 50. Mizrahi E: Enamel demineralization following orthodontic treatment. AM J ORTHOD82: 62-67, 1982. 51. Gorelick L, Geiger AM, Gwinnett AJ: Incidence of white spot formation after bonding and banding. AM J ORTHOD8I: 93-98, 1982. 52. Mizrahi E: Surface distribution of enamel opacities following orthodontic treatment. AM J ORTHOD 84-" 323-331, 1983.
Crystal growth on outer enamel surface
193
53. Mizrahi E: Success and failure of banding and bonding: A clinical study. Angle Orthod 52: 113-117, 1982. 54. Gorelick L: Bonding metal brackets with a self-polymerizing sealant-composte. A 12-month assessment. AM J ORTHOD 71: 542-553, 1977. 55. Zachrisson BV: A post-treatment evaluation of direct bonding in orthodontics. AM J ORTHOD 71: 173-189, 1977. 56. Newman GV: A post-treatment survey of direct bonding of orthodontic attachments to teeth by means of an epoxy resin adhesive. AM J ORTHOD 74: 197-206, 1978. 57, Zachrisson B, Skogan 0, Hrymyhr S: Enamel cracks in debonded, debanded and orthodontically treated teeth. AM J ORTHOD 77: 307-319, 1980. 58. Farquahar RB: A study of orthodontic direct bonding comparing a polyacrylic acid and phosphoric acid technique. M Clin Dent Thesis. University of Western Ontario, 1983. 59. MacPhee CA, Way DC, Galil KA: Experimental and clinical evaluation of crystal bonding. J Dent Res 64(Special Issue): 277, Abstract 918, 1985. 60. Hibberd G: A comparison of different bonding techniques, adhesive resins and debondiug procedures used in orthodontics. Dip Orth Thesis, University of Toronto, 1984. 61. Artun J, Bergland S: Clinical trials with crystal growth conditioning as an alternative to acid etch enamel pretreatment. AM J ORTHOD 55: 333-340, 1984. Reprint requests to: Dr. D. C. Smith Department of Biomaterials Faculty of Dentistry, University of Toronto 124 Edward Street Toronto, Ontario, Canada, M5G 1G6
i
Founded in 1915
Volume 89 Number 3
March, 1986
Copyright © 1986 by The C. V. Mosby Company
ORIGINAL ARTICLES
Crystal growth on the outer enamel surface An alternative to acid etching R. Mailer* and D. C. Smith** Toronto, Ontario, Canada
Over the past 2 years an increasing concern has developed about the possible iatrogenic effects of phosphoric acid-etch bonding techniques on the enamel surfacel There is an evident need to develop a mechanical or chemical retention system that would not alter (or would minimallY alter) the outer enamel surface. An alternative tO the conventional phosphoric acid etch technique has been developed. A preliminary clinical trial showed promising performance under normal clinical conditions. These results were achieved with a minimal loss of surface enamel as evidenced by scanning electron microscopy. Debonding and cleanup were greatly facilitated. Creating a micromechanical retentive surface by the formation of a crystalline interface is a potential alternative to phosphoric acid etching. (AM J ORTHOO89: 183-193, 1986.) Key words: Adhesion, bracket debonding, debonding, acid etching
T h e use of an acid etch technique to attach orthodontic appliances to the tooth enamel has now been widely accepted as an alternative tO full banded orthodontics. Although information is available in the literature on the possible difficulties andwide effects of bonding and debonding ~'2 brackets, many orthodontists appear to overlook these iatrogenic effects. ~-4Some believe, on the basis of earlier work, that after acid etching and once brackets and bonding resins are removed the enamel surface rapidly retums to norreal.5-7'~°'HOthers suggest that once the attachment is removed and the gross excess bonding material is eliminated by means of rotary instruments, this surface is smoothed out by means of toothbrush abrasion. ~2zs Is there a real basis for concern regarding damag e to the outer enamel surface and, if so, what are those c o n c e r n s q.1-4,8,9~10-12,18,49 J From 'the Department of Biomaterials, Faculty of Dentistry, University of Toronto. This work was supported in part by the Ontario Provincial Health Research GrantPR 851. *Research Associate, Department of Biomaterials. **Professor of Biomaterials.
The iatrogenic factors involved in acid etching may be listed as follows: 1. Loss of enamel caused by etching 4'~3 2. Retention of resin tags that can lead to possible discoloration of enamel 5"6'~3'~4 3. Leakage at the bracket interface leading to bracket corrosion and staining ~82° 4. Enamel loss caused by fracturing of enamel at time of debonding 4'8'9'15'22'49 5. A rougher surface with enamel cracks if deb°nding is carried out improperly, resulting in increased plaque retention 5'6,8,9,~7'2~,29'49 6. A softer enamel surface with lower fluoride content, morepredisposed to decalcification ~5 In view of the greater awareness and concern for the aftereffects Of direct bonding that is developing among dentists': 2 and the public at large, let us review some of these points in greater detail. 1. Enamel loss on etching and finishing has been well documented by a number of workers, z2-29Approximately 10 to 20 txm of outer enamel is lost due to acid etching *,5'3° and another 6 to 50 ~m on debonding, depending on the technique and the operator. ~528 A1-
183
184 Maijer and Smith
Am. J. Orthod. March 1986
Fig. 1. Enamel staining associated with corrosion of stainless steel bracket. A, Black corrosion deposit Visible after bracket removal. B, Residual enamel stain after finishing.
though this amount is accepted by many clinicians, frequent rebonding could lead to excessive loss of outer enamel and result in a rougher surface after finishing. 4,9,18This variable loss occurs in all cases using acid etch technique. 2. Resin tags penetrate the enamel to a depth Of 80 ixm or more. 4 Discoloration of resin tags in the enamel has been noted by clinicians, 9'17'36 especially when the ultraviolet (UV) Cured resins were in use. For obvious reasons UV cured resins did not contain UV absorbers and consequently the resin tags that remained in the enamel gradually discolored when exposed to sunlight. Little discussion of this is available in the literature. 3. Acid etching results in production of fine pores into the enamel. 4'32 These pores serve as a mechanical interlock for the resins that flow over and into these pores. If the pores are not cOmpletely filled or covered, this may create pathways by which stains and bacteria can penetrate the enamel. Problems with staining have been reported by Ceen and GwinnetP ° and by Maijer and Smith.19 These stains result from biodegradation of the metals Used in fixed orthodontic appliances. 19.20The corrosion of stainless steel bases has been found to giv e rise to deposition of chromium salts. Small voids in the resin at the interface allow saliva to carry these colored salts into the resin or the enamel. This is illustrated in Fig. 1, A and B. 4. Loss of enamel caused by fracturing has been demonstrated by a number of workers. 4'8'9 Retief37 and Retief and Denys 38 have shown that during resin removal from the enamel, small enamel fragments can
be broken Off from the existing enamel Surface. This would then lead to greater difficulty in obtaining a smooth outer surface on the enamel. Increased plaque retention has been illustrated by Gwinnett and Ceen 21 and Bennett, Schoen, and Going. 8 Ceen and Gwinnetd ° pointed out that increased plaque retention was observed on acid etched enamel as well as at the junction of the bracket base and resin periphery during bonding. Bennett, Schoen, and Going 8 showed an increased plaque accumulation following debonding. No longterm clinical study on this question has been published. 5. Debonding and cleanup is accomplished in a variety of ways. Several workers have discussed the problem of achieving a smooth surface with minimal damage to the enamel. 1.2.9.22.25.29It is generally accepted that a two-step procedure should be used. In the first step coarse resin removal is achieved by means of debonding pliers, hand instrumentS, rotary instruments, or ultrasonic scalers. Some clinicians even employ hand chisels and mallets to separate resin from enamel. Final removal is by means of abrasive cups Or discs, together with a suitable polishing medium. Discs in particular can produce facetting. Little attention has been paid to the heat production in these debonding techniques, which may contribute to enamel cracks. 9'24'51'59An increased incidence of enamel cracks as a result of traumatic debonding techniques has been observed by Zachrisson, Skogan, and H6ymyhr, 57 sandison, 9 and Diedrich. 4 Unfortunately there is presently no data to indicate the relation between specific techniques and crack frequency. Recently consideration has been given
Volume89
Crystal growth on outer enamel surface
Number 3
185
Fig. 2. Crystal growth on enamel surface after 30-second application of crystal bonding liquid. A, Original magnification x 1500. B, Individual spherulite, original magnification x 2200.
to the porosity of the enamel surface after debonding. The final enamel surface appears to be more predisposed to decalcification and absorption of stains following acid etching. 9'4° 6. An important consequence of enamel Surface removal is the loss of most of the acquired fluoride that resides mainly in the outer 10 p~m of the surface. 3°'34 These considerations make evident a need to develop a mechanical or chemical retention system that would not alter (or would minimally alter) the outer enamel surface. 4°'4i After completion of treatment, removal of this retention mechanism without any clinically deleterious side effects to the outer enamel
should be possible. This article reports on one such system. CRYSTAL GROWTH INTERLOCKING The authors have previously described 41 a new method of bonding that involves crystal growth on the enamel surface. This system consists of a polyacrylic acid treatment liquid containing a sulfate component that reacts with the calcium in the enamel surface to form a dense growth of small, needle-shaped crystals. These crystals grow in so-called spherulitic habit (Fig. 2). The crystal buildup on the enamel serves as an additional retentive mechanism for the resin that bonds
186 Maijer and Smith
Am. J. Orthod, March 1986
Fig. 3. Resin fracture surface after bond strength test showing resin penetration around crystals. (Original magnification × 3000.)
Fig. 4. Fractured and disturbed crystal growth after brushing surface. (Original magnification x 2000.)
the orthodontic attachment to the teeth (Fig. 3). In this procedure the bond does not rely on extensive penetration into the enamel. Micromechanical interlocking is created at the enamel surface; hence most of the problems mentioned in the previous section are eliminated. To evaluate this system, let us look at the basic principles, some laboratory results, and finally the preliminary clinical experience with this technique.
Principles of the technique A full drop of the viscous treatment liquid is placed on the cleaned (pumiced) tooth surface to be bonded.
It is left undisturbed for at least 30 seconds, usually 45 seconds. It is important to note that if a brush or cotton swab is used to agitate the gel, as is done in the acid etch technique, this may affect the crystal-enamel in. terface and consequently may reduce the bond strength. Fig. 4 shows a crystal site that has been disturbed by agitation. In comparison to Fig. 2, the effect on crystal integrity can be readily observed. After the prescribed number of seconds, the material is washed off thoroughly with clean tap water. After washing for at least 20 seconds as in acid etching, the tooth is dried with cool, dry, moisture-free clean air. A dense crystal
Volume89 Number3
Crystal growth on outer enamel surface
Table I. Tensile bond strengths of orthodontic
Table II. Comparison of acid etch and crystal
brackets to bovine enamel
growth
Time of storage (days)
Enamel treatment
Tensile bond strength* (MPa)
Tensile bond* strength (mPa)
Acid etch 1 28 90
Acid etch Crystal Acid etch Crystal Acid etch Crystal
1.11 1.24 1.05 0.99 1.00 0.99
-+ ± ± -+ ± -+
0.36 0.45 0.21 0.27 0.10 0.14
*Dynabond, Unitek Inc., Monrovia, Calif
growth can be seen in the scanning electron microscope (SEM) (Fig. 2). Too forceful a water spray may fracture some of the superficial crystals. However, this has only a minor effect on bond strength since the layer of crystals on the surface, which is primarily responsible for bonding, is still present. A dull whitish deposit is seen with the naked eye in the area that was exposed to the material. The fluid resin bonding agent is then allowed to flow onto the treated area. Penetration of the unset material around the crystals and into the reacted readilywettable enamel surface results in an efficient, micromechanical interlocking 4~ after either chemical or light activated polymerization. The bracket is then bonded to the sealant in the usual way. In vitro characterization
In vitro data that have been published elsewhere 41-45 using several orthodontic bonding agents show that tensile bond strength with the crystal interface is comparable to the acid etch technique using the same bonding resin. Further, the tensile bond strength has remained comparable after water exposure for 6 months at 37 C. 41'42Table I shows summary data for tensile bond strength for two orthodontic bonding resins to human enamel after storage in water for various periods. These data were obtained by a technique similar to that previously described, 4~ namely, by bonding a mesh-based orthodontic bracket to the cleaned and treated enamel surface. Table II shows further data obtained after storage in water compared to storage in 0.1N lactic acid. 43 These data confirm that a stable bond is obtained comparable to one obtained by means of a phosphoric acid etch. Shear strength of the crystal bonds are 65% to 80% of the shear strength for acid etch technique using the same resin. 43-45However, the strength in this mode appears satisfactory for clinical practice (see later) and results in a much more easily debondable system. 41,45 Chemical analysis of calcium release indicate that the surface loss with the polyacrylic acid solution is only
187
Storage days Water Lactic acid
7 --
30 1.03 + 0.19 1.12 4- 0.22
Crystal growth 7 0.96 ± 0.08 0.99 +- 0.09
30 1.11 ± 0.16 1.01 ± 0.13
*Dynabond, Unitek Inc,, Monrovia, Calif.
about one sixth of that with 50% phosphoric acid. 43 SEM studies show that minimal penetration of the resin into the surface enamel occurs after polyacrylic acid treatment. 43-45 Thus the advantages of crystal bonding technique are predicted to be as follows: 1. There is minimal effect on the outer (fluoride rich) enamel layer. 42 2. The enamel surface is not significantly damaged.43-46,58
3. Few, if any, resin tags are left behind the enamel.43-~6
4. Adequate bond strength for clinical practice is achieved. 41-z5 5. Debonding and cleanup are much easier with minimal iatrogenic damage. 4~'44'45'58 6. The crystal interface offers the possibility of the incorporation of fluoride or other antiplaque agents in the future to provide an anticariogenic action. 43'46 These in vitro studies showed that for normal enamel a contact time of 30 to 60 seconds was adequate for copious crystal growth and that complete washing away of the reactive liquid was as important as in the acid etch technique. A bonding resin able to wet and penetrate the crystalline surface was also necessary. Encouraged by these in vitro investigations, a preliminary clinical trial was initiated. Clinical trial
Materials and methods. A clinical trial was undertaken on a randomly selected group of 20 patients from the private practice of one of the authors (R.M.). The patients' ages ranged from 10 to 32 years. Patients' teeth were bonded directly with 0.022 inch straight wire brackets.* A half mouth technique was employed. Usually at least six upper and six lower anterior teeth were bonded directly. One arch at a time was bonded. The positions of the crystals and acid treatment were reversed in the opposing arch. To avoid cross contamination, a matrix stript was placed between the central incisors. *"A" Company, San Diego, Calif. "~KerrManufacturing Co., Romulus, Mich.
188
Maijer and Smith
Am. J. Orthod, March 1986
Minimal
Slight
Moderate
Severe
Fig. 6. Diagrammatic representation of the scoring system to evaluate dye penetration.
Fig. 5. A, Decalcification with acid-etched bonded case after 20 months. B, Crystal bonded tooth immediately after debonding following 18 months of treatment.
A sulfated polyacrylic acid solution was prepared by aqueous polymerization of acrylic acid. 4~ Teeth were treated with this liquid for 30 to 90 seconds as described previously. The phosphoric acid used was 37% phosphoric acid that was left on the tooth with slight agitation for 60 seconds. Care was taken not to cross contaminate the other side. The opposing arch was bonded on a separate appointment. Attachments were plated using accepted orthodontic techniques with a bracket placement tweezer* and a Boone gauge.t Acid etch brackets were bonded with a widely used orthodontic bonding agent.$ The crystal bonded brackets were attached with a selected sealant-paste system. § Silicone impressions were made of the labial surface before treatment of the enamel with the polyacrylic acid liquid or acid etching, and following debonding and finishing for subsequent SEM studies. Five of the 20 patients were treated with crystal forming solution and phosphoric acid etching as previously described, but the
*ETM #2222, Monrovia, Calif. tUnitek #807-022, Monrovia, Calif. SUnite, Unitek, Monrovia, Calif. §Dynabond, Unitek, Monrovia, Calif.
enamel was dried with a hair dryer held 12 cm from the mouth. The temperature of the warm air was approximately 108 ° F. Brackets were debonded with a Winegart or a Howe plier using gentle squeezing. Cleanup for the crystal bonded teeth was completed with a sickle scaler; the enamel was polished with a polishing medium* and a rubber cup. Cleanup for acid etched teeth was achieved by means of a 12 fluted burr followed by a rubber cup as described elsewhere in the literature. 24 Leakage at the bracket resin interface has been considered a major problem and a cause for bond failure and white spot initiation. 4952Before debonding the teeth were treated with disclosing solution.:~ Following removal of the brackets, the teeth were examined and scored according to the degree of dye penetration beneath the bracket (Fig. 6). The scores were as follows: 1. Minimal--A red outline present at the resin periphery 2. Slight--A slightly wider band of dye penetration near the edge of the resin indicating slight seepage underneath the bracket base 3. Moderate--One third of the resin underneath the bracket base with dye penetration 4( Severe--More than one third of the bracket base with dye penetration Bracket loss and other data were obtained from the patient records at the completion of treatment. To provide data for comparison, the records of a *Zircate, L.D. Caulk, Milford, Del. tJet #7903, Beaver's Dental Products, Morrisburg, Ontario, Canada. ~:Dis-Plaque, Pacemaker Corporation, Portland, Ore.
Volume89 Number 3
large group of patients undergoing routine treatment after acid etch bonding (using the same materials and techniques in the same office [rural location]) were tabulated for a 1-month period. Similar cross-sectional data were obtained from another office of i_he author (R.M.) in an urban location. RESULTS In the first group of 5 patients, 38 brackets were crystal bonded Using a warm air drying technique; 17 were lost within 3 days of placement. It appeared the hot air may have adversely affected the crystals. Thus this group of patients was dropped from th e experiment and room temperature air was used for drying in the subsequent cases. Table III shows the overall bracket losses for crystal bonding and acid etching in the remaining 15 patients over an average treatment time of 22 months. The losses were similar but were affected by patient trauma as indicated in the footnotes to Table III. Patient R.W. was very Uncooperative and thus was dropped from the trial. Table IV shows the distribution of the bracket losses with respect to upper and lower teeth over the total treatment period. Table V sets out an average monthly incidence and distribution of bracket loss for the patients undergoing routine treatment with the acid etch technique in the rural and urban locations. There were 220 patients in the rural area involving 4,400 brackets; in the urban area, there were 315 patients involving 6,300 brackets. Table VI summarizes the incidence of leakage as measured by dye penetration around the bonded brackets in the clinical trial. It can be seen that there was a similar resistance to leakage for both the acid-etched and crystal bonded groups with a tendency toward slight staining in the former. After debonding there was no evidence of decalcification or white spot formation with the crystal bonded group, whereas four white spot lesions were observed in the acid-etched bonded group. As found in our previous study 4~ debonding and cleanup were easily accomplished with the crystal bonded brackets, detachment occurring at the enamel surface; whereas debonding in the acid etch group generally took place at the bracket-resin interface necessitating removal of the resin layer. DISCUSSION It can be seen from Table III that 24 of the 116 crystal bonded brackets experienced failure and 18 of the 99 acid-etched bonded brackets failed over the 22month period of the trial. When the uncooperative patient R.W. is not included, the losses become 18/106 (17.0%) and 14/89 (15.7%). These losses show no sig-
Crystal growth on outer enamel surface
189
Table III. Overall bracket loss in clinical trial Of crystal bonding and acid etching Brackets crystal
Placed acid
Brackets crystal
Lost acid
A.N. D.S. D.p. L.L.***** M.G.**** ~'.M. T:F.*** M.H.** L.H. M.D. C.S. W.K. R.W.* J.P. I.P.
18 6 6 6 8 5 6 9 8 6 8 8 10 7 5 116
-6 6 6 9 6 6 10 8 6 8 8 10 6 4 99
0 0 0 1 0 0 1 2 2 1 4 2 6 4 1 24
-1 0 1 0 0 1 3 1 0 3 0 4 2 1 18
Results minus R.W.
106
89
i8
14
Patients' initials
*Patient R.W. was somewhat neglectful of his appliances and did not watch his dietary intake. Six brackets were lost over a period of 18 months. A loss of 4 to 6 brackets Over an 18-month period is not uncommon in patients with careless dietary habits. **Patient M.H.--Bracket loss due to trauma--thrown and kicked by a horse. ***Patient T.F.--Brackets ioosened and teeth partially avulsed due to accident--hit by baseball bat. ****Patient M.A.--Patient has been in intermaxillary fixation following maxillofacial surgery with no brackets lost during intermaxillary fixation. *****Patient L.L.--Attachment (upper first molar) lost while eating steak.
nificant differences for the tWO techniques (X 2 = 0.11; P > 0.05). As indicated in the footnotes to Table III, this random group of patients in a rural location experienced some unusual traumas that undoubtedly increased the incidence of failure. These loss figures are higher for both techniques than others reported in the literature. 39'47,48'54-s6 Mizrahi 39 has reviewed the recent literature and cites overall failure rates of directly bonded brackets in the acid etch technique ranging from 4% to 30% with highest rates on maxillary and mandibular molar and premolar teeth, and lower failure rates on maxillary Central and lateral incisor teeth. The rates of loss on anterior t e e t h 39'54-56 a r e c i t e d 39 to be 3.6% to 7.9% in the maxilla and 4.9% to 12.9% in the mandible. It is difficult to compare these data, however, since the time periods over which the various authors reported bracket losses varied from 6 to 12 months and 14 to 32 months. Total numbers of brackets lost cannot be described as 'rates' unless they are related to a specific time pe-
190
Am. J. Orthod. March 1986
Maqer and Smith
Table IV. Distribution of bracket losses in clinical trial of crystal bonding Number of failures Bond type
Tooth
1
Crystal--106 brackets
Upper Lower
3 0
Acid-etch--89 brackets
Upper Lower
I
]
2
I
2 0
0 1
3 2
Total
3
4
5
6
No.
3
2
1
2
3
1
t4
1
0
4
~
~
~
Tg
[
% 26.4 7.5
17.--6
1
0
0
0
4
2
3
l
1
10
9.1 22.2
5
5
i
i
1-2
15.7
Table V. Incidence of bond failure with acid etching in rural and urban settings in an average month Number of failures
3
4
5
No.
%
3 2 5
2 0 2
0 3 ~
4 8 1--2
11 16 2-7
0.50 0.72 0.61
7 1 -8 13
1 3 4 6
0 5 5 8
12 8 2--0 32
2i 20 4-i68
0.67 0.63 0.6--~ 0.64
Location
Tooth
1
2
Rural--220 patients, 4,400 brackets
Upper Lower
2 3
Urban--315 patients, 6,300 brackets
Upper Lower
1 3 9
TOTAL
Table VI. Incidence of leakage and dye staining around bonded brackets Leakage rating* Acid
Crystals
1 Total %
84 94
3 3
2 3
E --
1
2
100 94
6 6
---
---
*See Fig. 6.
riod. While it may be a presumption that many bonding failures occur early, there appear to be no time-related statistics to show loss rate. Newman's data 56 appear to show a trend tO higher losses over the longer time periods. Continuing loss over a 2-year treatment period may be expected because of bond deterioration and fatigue; Such losses may be influenced by the brackets used, the bonding material, the orthodontic technique, the specific teeth bonded, and the nature of the patient population. Newman's study, which involved 2,218 brackets with an average treatment time of 22 months, indicated that higher forces increased bracket loss. This suggests that higher losses should be seen in edgewise techniques as opposed to lower force techniques. This is borne out by the lower failure rate of 4.6% over a similar treatment period experienced by MizrahP 3 using
I
Total
a Begg light wire technique and an exothermic tweezer for bracket placement as compared to the corresponding figure of 15.6% from Newman's data. There appear to be few studies that document cumulative bracket loss over a 24-month period under the normal routine conditions found in a busy orthodontic practice. To put the present data into a local perspective, Table V shows 1-month cross-sectional bracket loss data for the practices of the clinical author in (1) the same rural area as the test patients and (2) in an urban location. These losses over a 1-month period relate to patients undergoing treatment for an average time period of 22 months similar to that of the present clinical total. As is evident from Table V, the 10ss rates were very similar for both the rural and urban locations. There was a slight tendency for higher losses in the lower teeth (as noted by others) in the rural area, but not in the urban area. These monthly rates of about 0.64% give overall losses of approximately 7.7% annually and 15.4% over 24 months. For the incisors and canines considered as a group, the corresponding figures are 5.2% and 10.4% loss incidence. Considering the differences in the procedures, ttiese data agree well with those reported by Gorelick54 and Zachrisson s5 for treatment periods of 6 to 12 months, and those of Newman 56 for treatment periods of 14 to 32 months. Thus the average treatment time in the latter study 56was 22 months and the weighted average percent
Volume89
Number 3
losses for the anterior teeth were 15.3% and for the incisors and canines as a group, 8.4%. For the present study (from Table V), the corresponding figures are calculated to be 15.4% and 10.5%, respectively, from the total of 10,700 brackets and 535 patientS. This close correspondence suggests that a steady rate of bracket loss does occur on average in a routine practice as presumed from the cross-sectional data of Table V. As a check on this point, the charts for 59 randomly selected completed cases from the urban location were examined. For an average treatment time of 23.5 months, 152 failures from a total of 1,062 brackets were observed, that is, total overall cumulative failure rate of 14.7%--a very good agreement with the previous figures. Against this background it is evident that the acid etch rate of 15.7% observed in the clinical trial (and presented in Table IV) is in close agreement with the foregoing data for both the routine clinical data of this study and that of Newman, 56 using similar materials and techniques. The mandibular failure rate was considerably higher than that for the maxilla (found also by Newman) although this finding may be influenced by the small numbers and patient histories. As noted earlier, the crystal bond failure rate was slightly higher, although Statistically similar, to the acid etch rate. Table IV shows the maxillary rate to be abnormally high and again this may be a consequence of the small numbers and individual traumas. As c a n b e seen in Table VI, slight or moderate dye penetration was observed in the acid-etch bonded teeth and slight dye penetration noted in the crystal bonded cases. The two cases employing acid etch technique in which moderate leakage was seen each had a related white spot lesion. This suggests that acid-etched bonded brackets can remain partially bonded to the enamel and in this way allow plaque buildup in a void under the bracket base.19,4° After debonding these cases, there was no incidence of decalcification or white sport formation with the crystal bonded group, whereas four white spot lesions were associated with the acid-etched bonded brackets. The incidence of white spot lesions is increased by orthodontic treatment as repotted by Mizrahi 5°'52 and Gorelick, Geiger, and Gwinnett. 5~ The incidence of four white spots seemed tO agree w!th those of previous authors in that three of the four white spots were on lateral incisors. In all cases where white Spot formation was seen, poor to fair oral hygiene was encountered. White spot lesion formation may be facilitated in phosphoric acid etch techniques because of the loss of the outer fluoride rich layer of the enameP 5 and thus a lowered resistance to decalcification. Newman 5~ noted a reduced incidence of decalcification in acid-
Crystal growth on outer enamel surface
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etched bonding when a sealant was used on the etched surface prior to bonding. In the polyacrylic acid-based crystal system used in this study, enamel loss and porosity were much less than with phosphoric acid etching. Hence decalcification is less likely to occur. Further crystal bonded brackets are unlikely to remain partially bonded to the enamel, but rather become detached, thus avoiding cavitation and white spo t formation. Poorer in vitro bond strength results using experimental sulfated polyacrylic acid were found by Farquahar s8 and unsatisfactory in vivo bonding by McPhee, Way, and Gali159 using a now withdrawn commercial material. Differences in techniques and materials may account for these results. More recently, with improved understanding of the technique, in vitro and in vivo findings similar to those reported here have been obtained by Burkey 44 and by Beech and Russell. 45 In a clinical trial using a commercial material, the latter authors experienced a 13% failure rate with crystal bonding as compared to a 4% loss with acid etching. Our experience as outlined here does not agree with that reported recently by Artun and Bergland 6~ for another experimental crystal-forming solution. However, their material is based on other development and does not correspond with our material, which is based on our previously reported data. 4~43 Although the present crystal-forming solution can yield satisfactory clinical results with significant advantages following an appropriate technique, it is clear that further potential for development of improved bonding exists through a study of the formation of a crystalline layer attached to the enamel surface. Further investigation of these possibilities is proceeding. SUMMARY AND CONCLUSION
A preliminary report on a clinical study of a material that produces crystal growth on the outer surface of the enamel has been presented. Creating a mechanical retention system by means of surface interaction and CryStal growth appears to be a convenient method of bonding orthodontic attachments to tooth enamel. Exposure of cleaned enamel to the crystal bonding solution for 30 to 60 seconds produced a dense crystal growth on normal enamel. The operator sensitive areas were application and washingi Inadequate Washing did not remove the polyacrylic acid treatment solution, it was therefore important for maximum bond strength that a careful technique be strictly adhered to as in the case of acid etching. If attention is paid to the proper steps, crystal bonding could be used in most instances where acid etching is currently used. The results of these studies using this crystal bond-
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ing t e c h n i q u e i n d i c a t e t h a t , in a d d i t i o n to r e m o v i n g less er/amel f r o m the t o o t h d u r i n g d e b o n d i n g , a s i g n i f i c a n t t i m e s a v i n g is e x p e r i e n c e d b y f a s t e r c l e a n u p f o l l o w i n g d e b o n d i n g w i t h less l i k e l i h o o d o f e n a m e l t r a u m a a n d damage. Also, the minimal reaction with the underlying enamel reduces the incidence and possibility of enamel staining. N o s i n g l e c a s e o f w h i t e spot f o r m a t i o n o r s t a i n i n g h a s b e e n n o t e d in a s s o c i a t i o n w i t h a n y o f the crystal b o n d i n g c a s e s t r e a t e d o v e r t h e last 2 years o f clinical use. A l t h o u g h the p r i n c i p l e s o f the p r o c e d u r e s h a v e b e e n d e s c r i b e d at l e n g t h , t h e b a s i c t e c h n i q u e is s i m i l a r to t h a t o f acid e t c h i n g . T h e a d v a n t a g e s are s u c h t h a t i t c o u l d b e c o m e a n a l t e r n a t i v e to the p r e s e n t l y u s e d p r o c e d u r e s , e s p e c i a l l y in the a n t e r i o r r e g i o n s . F u r t h e r i n v e s t i g a t i o n s o f t h e p r i n c i p l e is i n d i c a t e d .
Am. J. Orthod. March 1986
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Volume 89 Number 3 41. Maijer R, Smith DC: A new surface treatment for bonding. J Biomed Mater Res 13: 975-985, 1979. 42. Smith DC, Bennett A, Peltoniemi R, Maijer R: Further studies of bonding through crystal growth. J Dent Res 59(Special Issue B): 995, Abstract 435, 1980. 43. Smith DC, Lux J, Maijer R: Crystal bonding to enamel. J Dent Res 60(Special Issue A): 368, Abstract 231, 1981. 44. Burkey PS: Enamel conditioning with acid etch and ceystal bonding techniques: Tensile and shear bond strength comparisons and a scanning electron microscopic observations. M.Sc. Thesis, University of Iowa, 1985. 45. Beech DR, Russell ML: Bond strength, SEM and clinical studies of crystal bonding. Australia-New Zealand Divisional IADR Meeting Proceedings. Abstract 55, 1985. 46. Smith DC, Maijer R: In vitro comparison of etched and crystal grown enamel surfaces. To be published. 47. Beech DR, Jalaly T: Clinical and laboratory evaluation of some orthodontic direct bonding systems. J Dent Res 60: 972-978, 1981. 48. Cohl ME, Green LJ, Eick JD: Bonding of clear plastic orthodontic brackets using an ultra-violet sensitive adhesive. AM J ORTHOD 621 400-411, 1972. 49. Daft DS, Lugassy AA: A preliminary study of orthodontic treatment with the use of directly bonded brackets. AM J ORTHOD 65: 407-418, 1974. 50. Mizrahi E: Enamel demineralization following orthodontic treatment. AM J ORTHOD82: 62-67, 1982. 51. Gorelick L, Geiger AM, Gwinnett AJ: Incidence of white spot formation after bonding and banding. AM J ORTHOD8I: 93-98, 1982. 52. Mizrahi E: Surface distribution of enamel opacities following orthodontic treatment. AM J ORTHOD 84-" 323-331, 1983.
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53. Mizrahi E: Success and failure of banding and bonding: A clinical study. Angle Orthod 52: 113-117, 1982. 54. Gorelick L: Bonding metal brackets with a self-polymerizing sealant-composte. A 12-month assessment. AM J ORTHOD 71: 542-553, 1977. 55. Zachrisson BV: A post-treatment evaluation of direct bonding in orthodontics. AM J ORTHOD 71: 173-189, 1977. 56. Newman GV: A post-treatment survey of direct bonding of orthodontic attachments to teeth by means of an epoxy resin adhesive. AM J ORTHOD 74: 197-206, 1978. 57, Zachrisson B, Skogan 0, Hrymyhr S: Enamel cracks in debonded, debanded and orthodontically treated teeth. AM J ORTHOD 77: 307-319, 1980. 58. Farquahar RB: A study of orthodontic direct bonding comparing a polyacrylic acid and phosphoric acid technique. M Clin Dent Thesis. University of Western Ontario, 1983. 59. MacPhee CA, Way DC, Galil KA: Experimental and clinical evaluation of crystal bonding. J Dent Res 64(Special Issue): 277, Abstract 918, 1985. 60. Hibberd G: A comparison of different bonding techniques, adhesive resins and debondiug procedures used in orthodontics. Dip Orth Thesis, University of Toronto, 1984. 61. Artun J, Bergland S: Clinical trials with crystal growth conditioning as an alternative to acid etch enamel pretreatment. AM J ORTHOD 55: 333-340, 1984. Reprint requests to: Dr. D. C. Smith Department of Biomaterials Faculty of Dentistry, University of Toronto 124 Edward Street Toronto, Ontario, Canada, M5G 1G6