The effect of different extraction upon incisor retYactfion Raleigh Williams, B.S., D.D.S., M.S.D.,* Fred J. Hosila, D.D.S., M.S.D.**
sites
and
La Grange and Chicago, Ill.
T
his is a study of the relation between root surface area and extraction site selection upon anterior (incisor) retraction. Over the years there has been a series of reports in the literature on just how to reduce the amount of incisor retraction when extractions are necessary.‘-5 The euphemism for this is “borderline extraction cases.” They all have one solution in common, extraction of second instead of first premolars. Scanning the orthodontic literature of the last few years brings to light that a large number of clinical articles have as their theme the merits of second premolar extraction. The principal virtue ascribed to this procedure by the authors thereof is that such extraction avoids the pitfall of overretraction of incisors in “borderline extraction” cases that otherwise would be unstable if treated by expansion. The number of recent articles along this theme is a growing testimony to ever-increasing effectiveness of modern fixed appliances to conserve (not preserve) anchorage. The relatively large number of reports on this topic in the last few years would suggest that current mechanotherapy has become so efficient in conserving anchorage that overretraction of incisors is a common clinical problem. Unfortunately, none of these reports gives a qualitative analysis of how much less incisor retraction is produced when second premolars are extracted than when first premolars are extracted. This article will attempt to do so. It will also report on a quantitative analysis of the amount of incisor retraction which occurs when exPresented before the Northeastern Society of Orthodontists on Nov. 8, 1974, and based on a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry (Orthodontics), Department of Orthodontics, Northwestern University Dental School, March, 1975. *Source of data and faculty director of this **Graduate student, Orthodontic Department,
388
thesis. Northwestern
University
Dental
School.
Different
Fig. 1. The
position of the incisal edge “diagnostic line” is important to facial should be on or slightly in front of the
extraction
sites and i?lcisor retraction
of the lower incisor esthetics and the A-P line.
relative stability
to the A-P line of the dentition.
389
or It
traction sites other than premolars are selected or when no extraction sites are used. This study will deal solely with cases treated by Begg light-wire mechanics in which no headgear was used to override tooth movements. Thus, a pure measurement of incisor retraction versus posterior anchorage consumption is possible. The absence of headgear in pure Begg treatment also makes it possible to compare the results of treatment with Storey’s theory that tooth movements arc directly related to root surface areas when they occur under optimal pressure conditions (force per unit area). The light-wire technique, as developed by Begg, is based primarily on the use of light continuous forces. Begg believed that, with this technique of light forces, he could take advantage of the principle of using the large posterior root surface areas available for controlling the movement of the anterior teeth that have smaller root surface areas. As Begg” claims, “Failure to move anterior teeth back and inability to prevent posterior teeth from moving forward . . is not due to the use of insufficient anchorage . . . but to the use of excessive force.” In May, 1969, an article entitled “The Diagnostic Line” referred to a hypothesis of Williams7 that the amount of anterior retraction was directly related to the ratio of root surface areas existing between anterior and posterior teeth in extraction casts and between upper and lower teeth in nonextraction cases. It contended that as the extraction site moved posteriorly, less incisor retraction occurred.
390
IlJilliams
and Hosila
It was important to know whether or not this was true, as it would affect the clinician’s ability to place the tip of the lower incisor on or slightly in front of the A-P line, a necessary goal if the clinician is to achieve the optimum in facial esthetics and denture stability (Fig. 1). Clinical results with the Begg technique through the years seemed to confirm this hypothesis that altering the location of the extraction site or not extracting at all did make a difference in the amount of anterior (incisor) retraction. In time it became obvious that this impression should be tested under clinical conditions, exposure to trial by fire as it were. The hypothesis was based on the principle that as the amount of posterior root surface areas decreased along with a corresponding increase in anterior root surface areas, there would be a decrease in incisor retraction. Originally, a limited number of case reports were used to support this contention. Now, to test this contention more thoroughly, careful measurements and statistical analysis of a large number of cases treated with Begg mechanics, some without extraction and some with extraction at different sites, have been undertaken to support or negate Williams’ hypothesis of 1969 which states that, by a change in the location of the extraction site, there will be a change in the relative root surface areas between the anterior and posterior segments, enough to influence the potential for incisor retractions Materials
and
methods
The data for this study were secured from 260 cases treated by the Begg light-wire method. Five categories of treatment were chosen, four extraction and one nonextraction category. The subjects within each category were chosen at random. No subject in any category was selected for potential growth or nongrowth characteristics. Nor was any subject selected for response or nonresponse to orthodontic treatment or for posttreatment response. No selection in any category was based on age, sex, or dental classification. No initial elastic force greater than 3155 ounces was ever used in any case. The elastic force used predominantly was 3 ounces when the elastics were initially placed, and this value rapidly decayed to 21/e ounces within the first hour of wear and was found to decay very slowly down to 2 ounces by the end of the next 47 hours, 48 hours being the usual wearing interval before the patient was to replace the elastics with new ones. The material consisted of three lateral cephalometric films of each subject, one taken at the start of treatment, one taken the day the appliances were removed, and a final one taken from 1 to 10 years after treatment. Measurements were obtained directly from these head films. Of the 260 cases, 40 were treated on a. nonextraction basis, 101 were treated by extraction of maxillary and mandibular first premolars, 24 by extraction of maxillary first premolars and mandibular second premolars, 79 by extraction of maxillary and mandibular first molars, and 16 by extraction of maxillary and mandibular first premolars plus first molars. Retraction and advancement, elevation and depression of molars and incisors were measured. Anterior (incisor) retraction results were determined for non-
Different
extraction
Fig. 2. In all lower incisors
the different types of extraction were retracted to some degree.
was combined between the on this basis.
to produce the different categories
net
sites awl incisor
treatment in this article, The amount by which
anterior retraction. of extraction and
Comparisons nonextraction
Fig. 3. If the incisal edge of the lower incisor should move treatment, the forward movement was given a negative value distal movement of the incisal edge of the upper incisor. This net retraction in nonextraction treatment and was the basis retraction potentials in extraction cases.
retraction
both each
391
the upper and was retracted
of retraction treatment
were
potential made
forward in nonextraction and subtracted from the constituted the combined for comparison with the
extraction and for the four different types of extraction cases. Anchorage consumption or molar advancement for the various types of treatment, such as nonextraction or extraction at various sites, were also analyzed to see what differences mere to be expected and whether they could bc relied upon to recur. Root surface areas were used to calculate resistance values of the teeth. Since anterior tooth movement was pitted against posterior tooth movement in extraction cases (Fig. 2), and upper teeth were pitted against lower teeth in nonextraction cases (Fig. 3), it was natural to use Storey’s suggested tool of root surface areas to see if the actual tooth movement tha.t was found in any way correlated with the anticipated tooth movement calculated from root surface areas. Freeman’s* values for root surface areas, when compared with Jepsen’s,” were found to have less than 0.5 per cent difference, and so they were used (Fig. 4). Mandibular superimposition was done as described by Bjiirk.lO Maxillary superimposition was done by aligning the superior and inferior borders of the palate posteriorly and the anterior configuration at the anterior nasal spine’l (Fig. 5). The subject’s records and posttreatment x-ray films were also examined to determine the success rate of lower third molar eruption after the five different
392
Williams
and Hosila
Fig. 4. Freeman’s values tional to the resistance surface area, the greater
Fig. and
for root surface values of the the resistance
5. Method of superimpositioning Bjijrk, respectively.
areas. These various teeth. to movement.
of
maxillas
areas are considered Theoretically, the
and
mandibles
to be proporlarger the root
according
to
Downs
types of treatment (one nonextraction and four extraction). This was to determine whether changing the location of the extraction site would influence the success rate of lower third molar eruption. Changes in the mandibular plane were also measured by treatment groups to observe the effects of treatment and the posttreatment responses. Results
In all categories of treatment the actual mean incisor retraction was at least as great as, if not greater than, the anticipated retraction based on a calculation of root surface areas. Incisor retraction was greater than anticipated in nonex-
Volume Wumber
Differed
69 4
extraction
sites and incisor retraction
&il
sites
and
La Grange and Chicago, Ill.
T
his is a study of the relation between root surface area and extraction site selection upon anterior (incisor) retraction. Over the years there has been a series of reports in the literature on just how to reduce the amount of incisor retraction when extractions are necessary.‘-5 The euphemism for this is “borderline extraction cases.” They all have one solution in common, extraction of second instead of first premolars. Scanning the orthodontic literature of the last few years brings to light that a large number of clinical articles have as their theme the merits of second premolar extraction. The principal virtue ascribed to this procedure by the authors thereof is that such extraction avoids the pitfall of overretraction of incisors in “borderline extraction” cases that otherwise would be unstable if treated by expansion. The number of recent articles along this theme is a growing testimony to ever-increasing effectiveness of modern fixed appliances to conserve (not preserve) anchorage. The relatively large number of reports on this topic in the last few years would suggest that current mechanotherapy has become so efficient in conserving anchorage that overretraction of incisors is a common clinical problem. Unfortunately, none of these reports gives a qualitative analysis of how much less incisor retraction is produced when second premolars are extracted than when first premolars are extracted. This article will attempt to do so. It will also report on a quantitative analysis of the amount of incisor retraction which occurs when exPresented before the Northeastern Society of Orthodontists on Nov. 8, 1974, and based on a thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry (Orthodontics), Department of Orthodontics, Northwestern University Dental School, March, 1975. *Source of data and faculty director of this **Graduate student, Orthodontic Department,
388
thesis. Northwestern
University
Dental
School.
Different
Fig. 1. The
position of the incisal edge “diagnostic line” is important to facial should be on or slightly in front of the
extraction
sites and i?lcisor retraction
of the lower incisor esthetics and the A-P line.
relative stability
to the A-P line of the dentition.
389
or It
traction sites other than premolars are selected or when no extraction sites are used. This study will deal solely with cases treated by Begg light-wire mechanics in which no headgear was used to override tooth movements. Thus, a pure measurement of incisor retraction versus posterior anchorage consumption is possible. The absence of headgear in pure Begg treatment also makes it possible to compare the results of treatment with Storey’s theory that tooth movements arc directly related to root surface areas when they occur under optimal pressure conditions (force per unit area). The light-wire technique, as developed by Begg, is based primarily on the use of light continuous forces. Begg believed that, with this technique of light forces, he could take advantage of the principle of using the large posterior root surface areas available for controlling the movement of the anterior teeth that have smaller root surface areas. As Begg” claims, “Failure to move anterior teeth back and inability to prevent posterior teeth from moving forward . . is not due to the use of insufficient anchorage . . . but to the use of excessive force.” In May, 1969, an article entitled “The Diagnostic Line” referred to a hypothesis of Williams7 that the amount of anterior retraction was directly related to the ratio of root surface areas existing between anterior and posterior teeth in extraction casts and between upper and lower teeth in nonextraction cases. It contended that as the extraction site moved posteriorly, less incisor retraction occurred.
390
IlJilliams
and Hosila
It was important to know whether or not this was true, as it would affect the clinician’s ability to place the tip of the lower incisor on or slightly in front of the A-P line, a necessary goal if the clinician is to achieve the optimum in facial esthetics and denture stability (Fig. 1). Clinical results with the Begg technique through the years seemed to confirm this hypothesis that altering the location of the extraction site or not extracting at all did make a difference in the amount of anterior (incisor) retraction. In time it became obvious that this impression should be tested under clinical conditions, exposure to trial by fire as it were. The hypothesis was based on the principle that as the amount of posterior root surface areas decreased along with a corresponding increase in anterior root surface areas, there would be a decrease in incisor retraction. Originally, a limited number of case reports were used to support this contention. Now, to test this contention more thoroughly, careful measurements and statistical analysis of a large number of cases treated with Begg mechanics, some without extraction and some with extraction at different sites, have been undertaken to support or negate Williams’ hypothesis of 1969 which states that, by a change in the location of the extraction site, there will be a change in the relative root surface areas between the anterior and posterior segments, enough to influence the potential for incisor retractions Materials
and
methods
The data for this study were secured from 260 cases treated by the Begg light-wire method. Five categories of treatment were chosen, four extraction and one nonextraction category. The subjects within each category were chosen at random. No subject in any category was selected for potential growth or nongrowth characteristics. Nor was any subject selected for response or nonresponse to orthodontic treatment or for posttreatment response. No selection in any category was based on age, sex, or dental classification. No initial elastic force greater than 3155 ounces was ever used in any case. The elastic force used predominantly was 3 ounces when the elastics were initially placed, and this value rapidly decayed to 21/e ounces within the first hour of wear and was found to decay very slowly down to 2 ounces by the end of the next 47 hours, 48 hours being the usual wearing interval before the patient was to replace the elastics with new ones. The material consisted of three lateral cephalometric films of each subject, one taken at the start of treatment, one taken the day the appliances were removed, and a final one taken from 1 to 10 years after treatment. Measurements were obtained directly from these head films. Of the 260 cases, 40 were treated on a. nonextraction basis, 101 were treated by extraction of maxillary and mandibular first premolars, 24 by extraction of maxillary first premolars and mandibular second premolars, 79 by extraction of maxillary and mandibular first molars, and 16 by extraction of maxillary and mandibular first premolars plus first molars. Retraction and advancement, elevation and depression of molars and incisors were measured. Anterior (incisor) retraction results were determined for non-
Different
extraction
Fig. 2. In all lower incisors
the different types of extraction were retracted to some degree.
was combined between the on this basis.
to produce the different categories
net
sites awl incisor
treatment in this article, The amount by which
anterior retraction. of extraction and
Comparisons nonextraction
Fig. 3. If the incisal edge of the lower incisor should move treatment, the forward movement was given a negative value distal movement of the incisal edge of the upper incisor. This net retraction in nonextraction treatment and was the basis retraction potentials in extraction cases.
retraction
both each
391
the upper and was retracted
of retraction treatment
were
potential made
forward in nonextraction and subtracted from the constituted the combined for comparison with the
extraction and for the four different types of extraction cases. Anchorage consumption or molar advancement for the various types of treatment, such as nonextraction or extraction at various sites, were also analyzed to see what differences mere to be expected and whether they could bc relied upon to recur. Root surface areas were used to calculate resistance values of the teeth. Since anterior tooth movement was pitted against posterior tooth movement in extraction cases (Fig. 2), and upper teeth were pitted against lower teeth in nonextraction cases (Fig. 3), it was natural to use Storey’s suggested tool of root surface areas to see if the actual tooth movement tha.t was found in any way correlated with the anticipated tooth movement calculated from root surface areas. Freeman’s* values for root surface areas, when compared with Jepsen’s,” were found to have less than 0.5 per cent difference, and so they were used (Fig. 4). Mandibular superimposition was done as described by Bjiirk.lO Maxillary superimposition was done by aligning the superior and inferior borders of the palate posteriorly and the anterior configuration at the anterior nasal spine’l (Fig. 5). The subject’s records and posttreatment x-ray films were also examined to determine the success rate of lower third molar eruption after the five different
392
Williams
and Hosila
Fig. 4. Freeman’s values tional to the resistance surface area, the greater
Fig. and
for root surface values of the the resistance
5. Method of superimpositioning Bjijrk, respectively.
areas. These various teeth. to movement.
of
maxillas
areas are considered Theoretically, the
and
mandibles
to be proporlarger the root
according
to
Downs
types of treatment (one nonextraction and four extraction). This was to determine whether changing the location of the extraction site would influence the success rate of lower third molar eruption. Changes in the mandibular plane were also measured by treatment groups to observe the effects of treatment and the posttreatment responses. Results
In all categories of treatment the actual mean incisor retraction was at least as great as, if not greater than, the anticipated retraction based on a calculation of root surface areas. Incisor retraction was greater than anticipated in nonex-
Volume Wumber
Differed
69 4
extraction
sites and incisor retraction
&il
